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Micromachines
Volume 7
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Micromachines, Volume 7, Issue 5 (May 2016) – 20 articles

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13471 KiB  
Article
Characterizing the Deformation of the Polydimethylsiloxane (PDMS) Membrane for Microfluidic System through Image Processing
by Xiang Qian, Wenhui Zhang, Cheng Peng, Xingyang Liu, Quan Yu, Kai Ni and Xiaohao Wang
Micromachines 2016, 7(5), 92; https://doi.org/10.3390/mi7050092 - 16 May 2016
Cited by 11 | Viewed by 6916
Abstract
Polydimethylsiloxane (PDMS) membranes have been widely used in the microfluidic community to achieve various functions such as control, sensing, filter, etc. In this paper, an experimental process was proposed to directly characterize the deformation of the on-chip PDMS membrane at large deformation based [...] Read more.
Polydimethylsiloxane (PDMS) membranes have been widely used in the microfluidic community to achieve various functions such as control, sensing, filter, etc. In this paper, an experimental process was proposed to directly characterize the deformation of the on-chip PDMS membrane at large deformation based on the image processing method. High precision pressures were applied on the surface of the PDMS membrane with fixed edges and a series deformation of the PDMS membrane were captured by the imaging system. The Chan and Vese (CV) level set method was applied to segment the images of the deformed membrane. The volumes wrapped by the deformed membranes were obtained, and pressure-volumes relationships of the PDMS membranes with different geometry parameters were also calculated. Then the membrane capacitance can be derived by differentiating the curve of pressure-volumes. In addition, the theoretical estimation of the capacitance of the PDMS membrane at large deformation was also obtained through finite element simulation (FEM), which was in good agreement with the experimental results. These results are expected to be significant for designing and on-chip measuring of such PDMS membrane based microfluidic components in our future work. Full article
(This article belongs to the Special Issue Polymeric Microsystems)
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Graphical abstract
Full article ">Figure 1
<p>The cross section of a membrane-based microfluidic capacitor: (<b>a</b>) an uncharged capacitor and (<b>b</b>) a charged capacitor.</p> Full article ">Figure 2
<p>The pressure-volumes relationship of a deformed membrane based on the large deformation model and the small deformation model, (<b>a</b>) the magnifying view for the small deformation region; (<b>b</b>) the total view for the large deformation model; (<b>c</b>) the logarithmic view for the large deformation model. The uniform gas pressure was applied on the membrane, and the volume change was defined as the space wrapped by the outer boundary of the deformed membrane. The blue dot is the result of finite element simulation (FEM) based on the large deformation model, the green square is the result of FEM based on the small deformation model and the red circle is the result of small deformation based on the Equation (3).</p> Full article ">Figure 3
<p>(<b>Left</b>) Flow charts of the fabrication process for the polydimethylsiloxane (PDMS) membrane testing chamber: (<b>a</b>) Fabricate the PDMS pie with parallel surfaces; (<b>b</b>) Punch a round hole in the PDMS pie; (<b>c</b>) Cut the PDMS pie into a small block with a round hole; (<b>d</b>) Punch a side hole in small PDMS block used as the uniform pressure channel; (<b>e</b>) Bond the PDMS block and microscope slide together by plasma treatment to ensure the seal; (<b>f</b>) Bond the PDMS membrane and PDMS block together, covering the round hole and obtaining a circular membrane, or acts as an unfinished micro-chip; (<b>Right</b>) Picture of the final experimental device.</p> Full article ">Figure 4
<p>The experimental setup for PDMS membrane testing. The nitrogen bottle acted as a source of the gas pressure, the pressure controller accepted orders from the computer to control its output pressure and connected with the testing device in <a href="#micromachines-07-00092-f003" class="html-fig">Figure 3</a> by gas channel, the testing device was fixed on the reference block to keep vertical to the stage, the digital camera captured the images of the deflected membrane through the objective lens.</p> Full article ">Figure 5
<p>Flow chart for the proposed image processing method to obtain the outer boundary of the deformed membrane: (<b>a</b>) the original image with an image rotation angle <span class="html-italic">α</span>; (<b>b</b>) the result of rotating and cutting the image using a region of interest (ROI) box; (<b>c</b>) the result of cutting; (<b>d</b>) the result of segmentation by thresholding method (red line) and the level set method (blue line).</p> Full article ">Figure 6
<p>The pressure-volumes relationships of the PDMS membrane with different radius <math display="inline"> <semantics> <mi>R</mi> </semantics> </math> and different thickness <span class="html-italic">h</span> derived from the FEM analysis. Subplot (<b>a</b>–<b>f</b>) represent the thickness of the PDMS membrane from 50 to 100 μm with 10 μm a step.</p> Full article ">Figure 7
<p>The pressure-capacitance relationships of the PDMS membrane with different radius <math display="inline"> <semantics> <mi>R</mi> </semantics> </math> and different thickness <span class="html-italic">h</span> derived from the FEM analysis and Equation (8). Subplot (<b>a</b>–<b>f</b>) represent the thickness of the PDMS membrane from 50 to 100 μm with 10 μm a step.</p> Full article ">Figure 8
<p>2D surface plot of (<b>a</b>) the [<span class="html-italic">R</span>, <span class="html-italic">h</span>] → <span class="html-italic">N</span> relationship; (<b>b</b>) the [<span class="html-italic">R</span>, <span class="html-italic">h</span>] → <span class="html-italic">m</span> relationship in logarithmic scale and (<b>c</b>) [<span class="html-italic">R</span>, <span class="html-italic">h</span>] → <span class="html-italic">m</span> relationship. The dot in each plot represents one certain FEM calculated point in <a href="#micromachines-07-00092-t001" class="html-table">Table 1</a>, and the surface in each plot represents the fitting function.</p> Full article ">Figure 9
<p>Profiles of deformed membrane in experiments, the exerted pressures are from 0 to 25 mbar with the step of 0.5 mbar.</p> Full article ">Figure 10
<p>The experimental pressure-volume relationships of the PDMS membrane with different radius <span class="html-italic">R</span> and different thickness <span class="html-italic">h</span>. The “Re” dot plot indicate the results of the experiments and the “Rf” solid lines indicate the results of fitting the experimental data. The “Rs” solid line indicate the theoretical estimation using the same geometry parameters and Equations (13)–(15). Subplot (<b>a</b>–<b>e</b>) represent the measured thickness of the PDMS membrane from 35 to 90 μm.</p> Full article ">Figure 11
<p>The experimental pressure-capacitance relationship of the PDMS membrane. “Ce” and “Cs” are the hydraulic capacitances obtained by experiments and theoretical estimation respectively. Subplot (<b>a</b>–<b>e</b>) represent the thickness of the PDMS membrane from 35 to 90 μm.</p> Full article ">
1672 KiB  
Article
Low-Cost BD/MEMS Tightly-Coupled Pedestrian Navigation Algorithm
by Tianyu Lin, Zhenyuan Zhang, Zengshan Tian and Mu Zhou
Micromachines 2016, 7(5), 91; https://doi.org/10.3390/mi7050091 - 16 May 2016
Cited by 8 | Viewed by 4951
Abstract
Pedestrian Dead Reckoning (PDR) by combining the Inertial Measurement Unit (IMU) and magnetometer is an independent navigation approach based on multiple sensors. Since the inertial component error is significantly determined by the parameters of navigation equations, the navigation precision may deteriorate with time, [...] Read more.
Pedestrian Dead Reckoning (PDR) by combining the Inertial Measurement Unit (IMU) and magnetometer is an independent navigation approach based on multiple sensors. Since the inertial component error is significantly determined by the parameters of navigation equations, the navigation precision may deteriorate with time, which is inappropriate for long-time navigation. Although the BeiDou (BD) navigation system can provide high navigation precision in most scenarios, the signal from satellites is easily degraded because of buildings or thick foliage. To solve this problem, a tightly-coupled BD/MEMS (Micro-Electro-Mechanical Systems) integration algorithm is proposed in this paper, and a prototype was built for implementing the integrated system. The extensive experiments prove that the BD/MEMS system performs well in different environments, such as an open sky environment and a playground surrounded by trees and thick foliage. The proposed algorithm is able to provide continuous and reliable positioning service for pedestrian outdoors and thereby has wide practical application. Full article
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Full article ">Figure 1
<p>Architecture of the proposed system.</p> Full article ">Figure 2
<p>Flow chart of PDR.</p> Full article ">Figure 3
<p>Acceleration data before and after filtering.</p> Full article ">Figure 4
<p>Acceleration modulus of different walking speeds.</p> Full article ">Figure 5
<p>Topological structure of the BP neural network.</p> Full article ">Figure 6
<p>Flow chart of the attitude estimation algorithm.</p> Full article ">Figure 7
<p>Process of time synchronization of the BD and MEMS. PPS: Pulse Per Second.</p> Full article ">Figure 8
<p>Hardware platform.</p> Full article ">Figure 9
<p>The way to hold the prototype device.</p> Full article ">Figure 10
<p>Playground surrounded by trees.</p> Full article ">Figure 11
<p>Comparison of the trajectories.</p> Full article ">Figure 12
<p>Thick foliage environment.</p> Full article ">Figure 13
<p>Comparison of trajectories.</p> Full article ">Figure 14
<p>Open sky environment.</p> Full article ">Figure 15
<p>Comparison of trajectories.</p> Full article ">
31937 KiB  
Review
A Comprehensive Review of Optical Stretcher for Cell Mechanical Characterization at Single-Cell Level
by Tie Yang, Francesca Bragheri and Paolo Minzioni
Micromachines 2016, 7(5), 90; https://doi.org/10.3390/mi7050090 - 13 May 2016
Cited by 50 | Viewed by 12517
Abstract
This paper presents a comprehensive review of the development of the optical stretcher, a powerful optofluidic device for single cell mechanical study by using optical force induced cell stretching. The different techniques and the different materials for the fabrication of the optical stretcher [...] Read more.
This paper presents a comprehensive review of the development of the optical stretcher, a powerful optofluidic device for single cell mechanical study by using optical force induced cell stretching. The different techniques and the different materials for the fabrication of the optical stretcher are first summarized. A short description of the optical-stretching mechanism is then given, highlighting the optical force calculation and the cell optical deformability characterization. Subsequently, the implementations of the optical stretcher in various cell-mechanics studies are shown on different types of cells. Afterwards, two new advancements on optical stretcher applications are also introduced: the active cell sorting based on cell mechanical characterization and the temperature effect on cell stretching measurement from laser-induced heating. Two examples of new functionalities developed with the optical stretcher are also included. Finally, the current major limitation and the future development possibilities are discussed. Full article
(This article belongs to the Special Issue Optofluidics 2015)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Schematic structure of an optical stretcher. (<b>a</b>) Top view of the central fluidic channel with flowing cells and a single cell trapped in the middle of the two opposing laser beams; (<b>b</b>) Cross section of the trapping area as indicated by the dash line in (<b>a</b>). The two opposite laser beams are positioned close to the channel floor.</p> Full article ">Figure 2
<p>The structure of the discrete-element optical stretcher. (<b>a</b>) 3D rendering of the constituent components and their positions; (<b>b</b>) The finished system is mounted on a microscope plate. Figure reproduced from Reference [<a href="#B29-micromachines-07-00090" class="html-bibr">29</a>] with permission from Optical Society of America.</p> Full article ">Figure 3
<p>The chip geometry of the double glass layer assembled optical stretcher. The two glass layer are etched asymmetrically, the top one for large part of the fiber and the entire fluidic channel, the bottom one with shallow grooves for fiber alignment. The misalignment between these two layers show the robustness of this new etching layout. Figure reproduced from Reference [<a href="#B25-micromachines-07-00090" class="html-bibr">25</a>] under CC-BY 3.0 license.</p> Full article ">Figure 4
<p>The polymeric assembled optical stretcher. (<b>a</b>) SEM image of the Ni shim at the area where the fiber grooves meet the channel. Higher position of the fiber grooves with respect to the central channel will lead to the lower position of the fibers after insertion; (<b>b</b>) Bright filed microscope image of the chip at the same area with a photonic crystal fiber (left) and single mode fiber (right) inserted; (<b>c</b>) The finished chip ready for use. The three inlets are for hydrodynamic focusing purpose. Figure reproduced from Reference [<a href="#B30-micromachines-07-00090" class="html-bibr">30</a>] under CC-BY 4.0 license.</p> Full article ">Figure 5
<p>(<b>a</b>) Schematic representation of the three-layer technology for the monolithic optical stretcher fabrication. The central fused silica glass is machined by Femtosecond Laser Irradiation followed by Chemical Etching (FLICE) technique for the central channel and then sealed on both sides with two polished glass slides; (<b>b</b>) Microscope image of the straight microfluidic channel with pairs of waveguides beside it; (<b>c</b>) The finished chip is pigtailed with optical fibers and connected with external tubing through Luer connectors. Figure reproduced from Reference [<a href="#B29-micromachines-07-00090" class="html-bibr">29</a>] with permission from Optical Society of America.</p> Full article ">Figure 6
<p>Scheme of the optical field determination from a Gaussian laser beam with the paraxial ray optics approach. (<b>a</b>) The power carried by each ray, is calculated as the integral of the beam intensity, as a function of the radial coordinate within the area of the annulus associated to the ray; (<b>b</b>) The amplitude <span class="html-italic">A</span>(<span class="html-italic">ρ</span>, <span class="html-italic">z</span>) and the (<b>c</b>) curvature radius <span class="html-italic">R</span>(<span class="html-italic">ρ</span>, <span class="html-italic">z</span>) along the axis <span class="html-italic">z</span> are calculated, which will be exploited respectively for the evaluation of the power and the propagation direction of each ray.</p> Full article ">Figure 7
<p>Coordinate system for a single ray interacting with a particle. (<b>a</b>) A single rays from a Gaussian laser beams hits on the surface of a particle. The locations of the laser beam and particle can be random. The incident plane is defined by the ray and the normal direction of the particle at the hitting point and is indicated by the gray area; (<b>b</b>) the single ray undergoes multiple reflections and refractions on the boundary of the particle.</p> Full article ">Figure 8
<p>Polar plots of the calculated optical stress distribution on the surface of the particle. The Gaussian laser beam has beam waist of 3.1 µm and wavelength of 1.07 µm and carries optical power of 10 mW. The refractive index of the particle is 1.37 and medium 1.33. The distance between the particle center and the beam waist (either one laser or two lasers) is indicated in each panel together with the diameter of the particle. (<b>a</b>–<b>c</b>) show the optical stress from left side laser radiation, right side laser radiation and both side laser radiation respectively; From (<b>d</b>) to (<b>i</b>), the two-side laser irradiation is considered; (<b>d</b>–<b>f</b>) show the optical stress distribution change with particle size increase; (<b>g</b>–<b>i</b>) show the optical stress distribution change with distance increase.</p> Full article ">Figure 9
<p>Flow chart of continuous cell stretching procedure.</p> Full article ">Figure 10
<p>Illustration of the image analysis steps. (<b>a</b>) Phase contrast microscope image of a single cell. The center point (red color) of the cell is manually selected and the circular border (light blue color) for the polar transformation is determined by the original rectangular image border; (<b>b</b>) The polar-transformed image; (<b>c</b>) shows a plot of the gray-scale intensity along the green vertical line appearing in (<b>b</b>). The raw data (red line) is smoothed by Fourier filtering (blue line); (<b>d</b>) shows the first derivative of the blue-line (intensity) and the red circle shows the point identified as minimum, identified as belonging to cell border; (<b>e</b>) by repeating the same procedure for all the polar angles, the cell border is reconstructed on the polar image and (<b>f</b>) then transformed back to original image.</p> Full article ">Figure 11
<p>Single cell optical stretching. (<b>a</b>) Cell dimension variation during optical stretching together with the laser power profile (<b>b</b>): P<math display="inline"> <semantics> <msub> <mrow/> <mi>T</mi> </msub> </semantics> </math> is trapping laser power of 25 mW per side and P<math display="inline"> <semantics> <msub> <mrow/> <mi>S</mi> </msub> </semantics> </math> is stretching power of 1.5 W per side. <span class="html-italic">X</span>-axis is along the laser beam and <span class="html-italic">Y</span>-axis along the cell flowing direction; (<b>c</b>,<b>d</b>) show the phase contrast microscope images of the same cell trapped and stretched respectively. Green contours are cell borders identified by the recognition algorithm. Scale bars in both (<b>b</b>,<b>c</b>) are 10 µm. The cell sample is human breast cancer cell MCF7.</p> Full article ">Figure 12
<p>Optical stretching of single red blood cell (RBC). (<b>a</b>) Microscope images of RBCs stretched at increasing optical powers; (<b>b</b>) Optical deformation of RBCs in terms of elongation along laser axis and contraction in the perpendicular direction at different stretching power. The laser power is the total power for both laser beams. Experimental data is fitted with theoretical prediction from the linear elastic membrane theory. Figure reproduced from Reference [<a href="#B45-micromachines-07-00090" class="html-bibr">45</a>] with permission from Optical Society of America.</p> Full article ">Figure 13
<p>Optical stretching of vesicles. Microscope image of a vesicle trapped at low power (<b>a</b>) and deformed at high power (<b>b</b>); (<b>c</b>) The major axis strain of vesicles under 4 s stretching at various total powers. Figure reproduced from Reference [<a href="#B62-micromachines-07-00090" class="html-bibr">62</a>] with permission from Royal Society of Chemistry.</p> Full article ">Figure 14
<p>Optical stretching of a single MCF7 cell. The laser power is for each side and the cell contour is recognized by the edge detection algorithm in <a href="#micromachines-07-00090-f010" class="html-fig">Figure 10</a>.</p> Full article ">Figure 15
<p>Optical deformability of normal, cancerous, and metastatic breast epithelial cells. (<b>a</b>) The three populations of the MCF cell and (<b>b</b>) the two populations of the MDA-MB-231 cell are clearly distinguishable. Curves represent the fitting of normal distribution. Figure reproduced with permission from Reference [<a href="#B23-micromachines-07-00090" class="html-bibr">23</a>] with permission from Prof. Guck.</p> Full article ">Figure 16
<p>Active cell sorting chip design. (<b>a</b>) Microscope image of the internal structure of the cell sorting microchip. Scale bar: 100 µm; (<b>b</b>) The finished chip with fibers pigtailed and tubing connected is very compact. Scale bar: 1 cm; (<b>c</b>) Schematic of the experimental setup. Figure reproduced from Reference [<a href="#B24-micromachines-07-00090" class="html-bibr">24</a>] with permission from Royal Society of Chemistry.</p> Full article ">Figure 17
<p>Laser writing geometry optimization for internal channel surface roughness control. Figure reproduced from Reference [<a href="#B24-micromachines-07-00090" class="html-bibr">24</a>] with permission from Royal Society of Chemistry.</p> Full article ">Figure 18
<p>Cell sorting efficiency check. Characterization of the cellular size (<b>a</b>) and optical deformability (<b>b</b>) of two cell lines, A375MC2 and A375P; (<b>c</b>) Normalized cellular distributions as a function of their optical deformations from experiment data in (<b>b</b>). The whole area under each cell curve is set equal representing the same concentration. By defining a deformation threshold, a sub-population of A375MC2 can be enriched by collecting cells with higher deformability; (<b>d</b>) The ratio of A375MC2 in the collected cell sample and the ratio of cells in the initial sample that are expected to exhibit deformability higher than the threshold (acceptance rate) versus the defined threshold value. Figure reproduced from Reference [<a href="#B24-micromachines-07-00090" class="html-bibr">24</a>] with permission from Royal Society of Chemistry.</p> Full article ">Figure 19
<p>Spatial temperature profile in an optical stretcher. (<b>a</b>) Color image of the temperature increase from the two opposing laser beams in the optical stretcher. The imaging plane is the channel cross section through the center of the trap and the power of each laser beam is 1 W; (<b>b</b>) Line scan of the temperature along the dashed line in (<b>a</b>). Figure reproduced from Reference [<a href="#B71-micromachines-07-00090" class="html-bibr">71</a>] with permission from Optical Society of America.</p> Full article ">Figure 20
<p>Temporal revolution of the temperature from the laser radiation in the optical stretcher. The laser is turned on at <span class="html-italic">t</span> = 2 s and has a total power of 2 W. Figure reproduced from Reference [<a href="#B71-micromachines-07-00090" class="html-bibr">71</a>] with permission from Optical Society of America.</p> Full article ">Figure 21
<p>Heat shock impact on cell viability with different laser power (temperature) and time duration. The figure was realized exploiting the data reported in Reference [<a href="#B72-micromachines-07-00090" class="html-bibr">72</a>].</p> Full article ">Figure 22
<p>Active temperature control for optical stretcher. (<b>a</b>) Two additional fibers are added and positioned near the two opposing stretching fibers for temperature control; (<b>b</b>) Another laser is coupled into one of the two stretching fibers for temperature control. Figure reproduced from Reference [<a href="#B76-micromachines-07-00090" class="html-bibr">76</a>,<a href="#B79-micromachines-07-00090" class="html-bibr">79</a>] under CC-BY 3.0 license.</p> Full article ">Figure 23
<p>Temperature effect on cell optical deformation. Temperature is changed during the stretching measurement by using the two additional heating fibers (<span class="html-italic">P</span><math display="inline"> <semantics> <msub> <mrow/> <mrow> <mi>h</mi> <mi>e</mi> <mi>a</mi> <mi>t</mi> </mrow> </msub> </semantics> </math>), see <a href="#micromachines-07-00090-f022" class="html-fig">Figure 22</a>a, while keeping the stretcher power (<span class="html-italic">P</span><math display="inline"> <semantics> <msub> <mrow/> <mrow> <mi>s</mi> <mi>t</mi> <mi>r</mi> <mi>e</mi> <mi>t</mi> <mi>c</mi> <mi>h</mi> </mrow> </msub> </semantics> </math>) constant. Figure reproduced from Reference [<a href="#B76-micromachines-07-00090" class="html-bibr">76</a>] under CC-BY 3.0 license.</p> Full article ">Figure 24
<p>Acoustic prefocusing for optical stretcher. (<b>a</b>) Schematic illustration of the all glass microchip with both acoustic actuation (the black dash lines) driven by the underneath piezo ceramic and optical radiation (the red shaded area) emanating from the integrated waveguides. The microfluidic channel has a square cross section, 150 µm × 150 µm; (<b>b</b>) Microscope image of polystyrene beads trapped by acoustic wave in the middle of the microfluidic channel both horizontally and vertically (all beads are in the same focus); (<b>c</b>) Microscope image of red blood cells prefocused with acoustic wave for continuous optical stretching. Two opposing lasers from the waveguides are visible because of the light scattering.</p> Full article ">Figure 25
<p>Optical cell rotator. (<b>a</b>) Illustration of the cell rotator realized in the two opposing laser radiation with an optical stretcher; (<b>b</b>) Microscope image sequences showing precise control of the cell orientation with red blood cell and HL60 cell. Figure reproduced from Reference [<a href="#B83-micromachines-07-00090" class="html-bibr">83</a>] under CC-BY 4.0 license.</p> Full article ">
5408 KiB  
Review
Hybrid Integration of Magnetoresistive Sensors with MEMS as a Strategy to Detect Ultra-Low Magnetic Fields
by João Valadeiro, Susana Cardoso, Rita Macedo, Andre Guedes, João Gaspar and Paulo P. Freitas
Micromachines 2016, 7(5), 88; https://doi.org/10.3390/mi7050088 - 11 May 2016
Cited by 37 | Viewed by 9194
Abstract
In this paper, we describe how magnetoresistive sensors can be integrated with microelectromechanical systems (MEMS) devices enabling the mechanical modulation of DC or low frequency external magnetic fields to high frequencies using MEMS structures incorporating magnetic flux guides. In such a hybrid architecture, [...] Read more.
In this paper, we describe how magnetoresistive sensors can be integrated with microelectromechanical systems (MEMS) devices enabling the mechanical modulation of DC or low frequency external magnetic fields to high frequencies using MEMS structures incorporating magnetic flux guides. In such a hybrid architecture, lower detectivities are expected when compared with those obtained for individual sensors. This particularity results from the change of sensor’s operating point to frequencies above the 1/f noise knee. Full article
(This article belongs to the Special Issue Magnetic MEMS)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) Schematic view of a typical multilayer for spin-valves (SV) and magnetic tunnel junction (MTJ) sensors. SV: antiferromagnet (AFM), pinned layer (FM1), conductive spacer (Cu), sensing layer (FM2 and FM3). MTJ: antiferromagnet (AFM), pinned layer (FM1), insulator spacer (MgO), sensing layer (FM3 and FM4); a synthetic antiferromagnet (SAF) is obtained with the tri-layer FM1/Ru/FM2. The pinned layer magnetization is set in a fixed direction due to exchange-bias at AFM/FM interface; (<b>b</b>) Representative magnetotransport curve obtained for a patterned SV sensor (active area: 40 × 2 µm<sup>2</sup>) exhibiting a linear, centered and hysteresis free response. Red arrows illustrate the relative orientation of the in-plane magnetization in both pinned and sensing layers. <span class="html-italic">S</span> stands for the sensor sensitivity.</p> Full article ">Figure 2
<p>Typical noise spectrum of a MR device (SV array), reaching the thermal level for frequencies around 400 Hz. In the low frequency regime the 1/<span class="html-italic">f</span> noise is dominant, while in the high frequency regime the spectrum is reduced to its thermal level. Both electronic and magnetic noise components are present since the spectrum was recorded with the sensor operating on its linear range.</p> Full article ">Figure 3
<p>Schematic of a MR-MEMS hybrid device used for high frequency modulation of (quasi-)DC magnetic fields, where a MEMS cantilever with incorporated MFCs oscillates at high frequency to modulate the signal of interest. (Courtesy of Guedes A.).</p> Full article ">Figure 4
<p>(<b>a</b>) Schematic view of MFCs with funnel shape geometry and respective integration with a patterned MTJ sensor (before the top contact deposition). Reprinted with kind permission of The European Physical Journal (EPJ); (<b>b</b>) Illustration of steep profile MFCs close to a SV single sensor. Reprinted with permission from Leitao D.C. <span class="html-italic">et al.</span>, <span class="html-italic">Sensors</span> 2015, <span class="html-italic">15</span>, 30311–30318. Copyright 2015 MDPI.</p> Full article ">Figure 5
<p>(<b>a</b>) Schematic cross section of the double layer MFC with a 3D tapered profile, showing a pole angle of 45° in the NiFe film and a steep profile in the CoZrNb pole, integrated with a SV sensor; (<b>b</b>) Effect of the 3D tapered profile MFC integration on the magnetotransport curve of a single SV sensor, showing a sensitivity enhancement of 74 times.</p> Full article ">Figure 6
<p>(<b>a</b>) Schematic view and (<b>b</b>) SEM image of the proposed MEMS flux concentrator device. Reprinted with permission from Edelstein A.S. <span class="html-italic">et al.</span>, <span class="html-italic">J. Appl. Phys.</span> 2006, <span class="html-italic">99</span>, 08B317. Copyright 2006 AIP Publishing LLC.</p> Full article ">Figure 7
<p>(<b>a</b>) SEM image of the hybrid device showing the integration of a SV sensor with static MFCs and a single MEMS cantilever resonator (with an additional MFC on top); (<b>b</b>) Schematic view of the device cross section; (<b>c</b>) SV voltage output exhibiting both electric (capacitive coupling) and magnetic components when the cantilever resonates at a frequency of 200 kHz. Reprinted with permission from Guedes A. <span class="html-italic">et al.</span>, <span class="html-italic">J. Appl. Phys</span>. 2008, <span class="html-italic">103</span>, 07B924. Copyright 2008 AIP Publishing LLC.</p> Full article ">Figure 8
<p>(<b>a</b>) SEM image of the device exhibiting the MEMS torsional structure integrated with a MTJ sensor and both static/dynamic MFCs; (<b>b</b>) Schematic view of the device cross section; (<b>c</b>) MTJ voltage output corresponding to the detection of a DC magnetic field of 0.36 mT when the torsional structure is actuated at a frequency of 230 kHz. Both magnetic and electric (capacitive coupling) components are presented. Reproduced with permission from Guedes A. <span class="html-italic">et al.</span>, <span class="html-italic">IEEE Trans. Magn.</span> 2008, <span class="html-italic">44</span>, 2554; published by IEEE, 2008.</p> Full article ">Figure 9
<p>(<b>a</b>) SEM image of the developed device, showing the SV sensing element between two resonator cantilevers with integrated MFCs; (<b>b</b>) Acquired data resulting from the modulation of a low-frequency AC field (0.3 mT with a frequency of 30 Hz), exhibiting the respective sidebands when the cantilevers are actuated at the resonance frequency (<span class="html-italic">f</span><sub>0</sub> = 17.7 kHz). Reproduced with permission from Guedes A. <span class="html-italic">et al.</span>, <span class="html-italic">IEEE Trans. Magn.</span> 2012, <span class="html-italic">48</span>, 4115; published by IEEE, 2012.</p> Full article ">Figure 10
<p>Schematic operating view of the VMFM based device: (<b>a</b>) cantilever gets close the sensing elements, reducing the magnetic flux through them; (<b>b</b>) cantilever moves upwards, restoring the magnetic flux in the sensing elements; (<b>c</b>) Acquired device output resulting from the modulation of a low-frequency AC field (1.2 μT with a frequency of 1 Hz), exhibiting the respective sidebands when the cantilevers are actuated at the resonance frequency (<span class="html-italic">f</span><sub>0</sub> = 3.57 kHz). The residual signal at <span class="html-italic">f</span><sub>0</sub> arises from the remanence of the Ni<sub>79</sub>Fe<sub>21</sub> flux modulation field and/or from an electric coupling between then sensing elements and the MEMS piezoelectric structure. Reprinted with permission from Hu J. <span class="html-italic">et al.</span>, <span class="html-italic">Appl. Phys. Lett.</span> 2012, <span class="html-italic">100</span>, 244102. Copyright 2012 AIP Publishing LLC.</p> Full article ">Figure 11
<p>(<b>a</b>) Optical and (<b>b</b>) SEM image of modulator combining in-plane electrostatic microactuators with interdigitated fingers comb drive, SV sensors and MFCs; (<b>c</b>) Modulated sensor output as a function of magnetic field amplitude at low frequency (7 Hz); (<b>d</b>) Finite element simulation which illustrates the concentrated magnetic flux in the sensing element for the two positions: off-minimum concentration; on-maximum concentration.</p> Full article ">
4517 KiB  
Article
A Rapid Micromixer for Centrifugal Microfluidic Platforms
by Ziliang Cai, Jiwen Xiang, Hualing Chen and Wanjun Wang
Micromachines 2016, 7(5), 89; https://doi.org/10.3390/mi7050089 - 10 May 2016
Cited by 13 | Viewed by 6559
Abstract
This paper presents an innovative mixing technology for centrifugal microfluidic platforms actuated using a specially designed flyball governor. The multilayer microfluidic disc was fabricated using a polydimethylsiloxane (PDMS) replica molding process with a soft lithography technique. The operational principle is based on the [...] Read more.
This paper presents an innovative mixing technology for centrifugal microfluidic platforms actuated using a specially designed flyball governor. The multilayer microfluidic disc was fabricated using a polydimethylsiloxane (PDMS) replica molding process with a soft lithography technique. The operational principle is based on the interaction between the elastic covering membrane and an actuator pin installed on the flyball governor system. The flyball governor was used as the transducer to convert the rotary motion into a reciprocating linear motion of the pin pressing against the covering membrane of the mixer chamber. When the rotation speed of the microfluidic disc was periodically altered, the mixing chamber was compressed and released accordingly. In this way, enhanced active mixing can be achieved with much better efficiency in comparison with diffusive mixing. Full article
(This article belongs to the Special Issue Centrifugal (Compact-Disc) Microfluidics for Extreme POC)
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<p>(<b>a</b>) Schematic diagrams of the mixing system. It consists of three parts from top to bottom: the microfluidic disc, actuation disc, and the flyball governor system. The mixing chamber is in the compressed state initially. (<b>b</b>) The actuation disc was pulled down by the flyball governor as the spinning rate of the disc increases. At the same time, the pin loses contact with the covering membrane of the mixer chamber. (<b>c</b>) Close-in view of the mixer, the PDMS layer consists of three identical patterns. The microchannel is 300 μm high and 300 μm in width. (<b>d</b>) Schematic design of a single microfluidic system used for testing the performance of the mixer.</p> Full article ">Figure 2
<p>Operational principles of the chaotic mixing system. The two different colors represent two fluid samples that are introduced into the mixing chamber first. The dark circle in the 3rd figure indicates the pin pressing against the covering membrane of the mixing chamber.</p> Full article ">Figure 3
<p>The fabrication process for the microfluidic disc. (<b>a</b>) SU-8 photolithography and development; (<b>b</b>) Pouring of PDMS and curing; (<b>c</b>) Demolding of PDMS replica and punching holes; (<b>d</b>) Bonding PDMS to PMMA disc.</p> Full article ">Figure 4
<p>Photo images showing one complete cycle of mixing operation on the centrifugal microfluidic platform: (<b>a</b>) the samples were introduced into the loading chambers; (<b>b</b>) the samples were delivered to the mixing chamber; (<b>c</b>) the mixing chamber was compressed by the pin connected to the flyball governor at low mixing frequency; and (<b>d</b>) the pin was released at higher spinning speed.</p> Full article ">Figure 5
<p>The spinning speed profile followed in the experiments of the mixer. The compressing-releasing times are controlled to be equal.</p> Full article ">Figure 6
<p>Images of the liquids after (<b>a</b>) one mixing cycle, (<b>b</b>) two mixing cycles, (<b>c</b>) three mixing cycles, and (<b>d</b>) four mixing cycles, respectively.</p> Full article ">Figure 7
<p>Histograms and standard deviations obtained from the gray intensities of the photo images of the mixing chamber after (<b>a</b>) one mixing cycle, (<b>b</b>) two mixing cycles, (<b>c</b>) three mixing cycles, and (<b>d</b>) four mixing cycles, respectively.</p> Full article ">Figure 8
<p>Image of the mixing chamber after the disc was spun after 15 s without using the compression-releasing mechanism. The standard derivation was calculated to be 0.25.</p> Full article ">Figure 9
<p>Comparison of the standard deviation of the mixing performance with and without the holding phase.</p> Full article ">Figure 10
<p>The standard deviation of the mixing performance with two different pin sizes.</p> Full article ">
2883 KiB  
Article
Design and Manufacturing of a Passive Pressure Sensor Based on LC Resonance
by Cheng Zheng, Wei Li, An-Lin Li, Zhan Zhan, Ling-Yun Wang and Dao-Heng Sun
Micromachines 2016, 7(5), 87; https://doi.org/10.3390/mi7050087 - 10 May 2016
Cited by 18 | Viewed by 6013
Abstract
The LC resonator-based passive pressure sensor attracts much attention because it does not need a power source or lead wires between the sensing element and the readout system. This paper presents the design and manufacturing of a passive pressure sensor that contains a [...] Read more.
The LC resonator-based passive pressure sensor attracts much attention because it does not need a power source or lead wires between the sensing element and the readout system. This paper presents the design and manufacturing of a passive pressure sensor that contains a variable capacitor and a copper-electroplated planar inductor. The sensor is fabricated using silicon bulk micro-machining, electroplating, and anodic bonding technology. The finite element method is used to model the deflection of the silicon diaphragm and extract the capacitance change corresponding to the applied pressure. Within the measurement range from 5 to 100 kPa, the sensitivity of the sensor is 0.052 MHz/kPa, the linearity is 2.79%, and the hysteresis error is 0.2%. Compared with the sensitivity at 27 °C, the drop of output performance is 3.53% at 140 °C. Full article
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<p>Structure of the passive pressure sensor.</p> Full article ">Figure 2
<p>Equivalent circuit of the passive pressure sensor.</p> Full article ">Figure 3
<p>ANSYS simulation of diaphragm when <span class="html-italic">p</span> = 0.1 MPa. (<b>a</b>) Deflection; (<b>b</b>) Von Mises stress.</p> Full article ">Figure 4
<p>(<b>a</b>) Capacitance <span class="html-italic">vs</span>. pressure; (<b>b</b>) <span class="html-italic">f</span><sub>0</sub> <span class="html-italic">vs</span>. pressure in simulation.</p> Full article ">Figure 5
<p>Fabrication process of the pressure sensor. (<b>a</b>) Silicon; (<b>b</b>) TMAH etch; (<b>c</b>) Upper plate sputter and pattern; (<b>d</b>) 7740 glass; (<b>e</b>) Lower plate sputter and pattern; (<b>f</b>) Planar coil electroplating; (<b>g</b>) Anodic bonding.</p> Full article ">Figure 6
<p>(<b>a</b>) SEM photograph of part of the coil and plate; (<b>b</b>) SEM photograph of a sensor showing the cross-sectional view.</p> Full article ">Figure 7
<p>Frequency-pressure measurement system.</p> Full article ">Figure 8
<p>(<b>a</b>) Measured <span class="html-italic">f</span><sub>0</sub> <span class="html-italic">vs.</span> frequency; (<b>b</b>) measured <span class="html-italic">f</span><sub>0</sub> <span class="html-italic">vs.</span> frequency under different temperatures.</p> Full article ">
2366 KiB  
Review
Advances in Microfluidic Paper-Based Analytical Devices for Food and Water Analysis
by Lori Shayne Alamo Busa, Saeed Mohammadi, Masatoshi Maeki, Akihiko Ishida, Hirofumi Tani and Manabu Tokeshi
Micromachines 2016, 7(5), 86; https://doi.org/10.3390/mi7050086 - 9 May 2016
Cited by 166 | Viewed by 17796
Abstract
Food and water contamination cause safety and health concerns to both animals and humans. Conventional methods for monitoring food and water contamination are often laborious and require highly skilled technicians to perform the measurements, making the quest for developing simpler and cost-effective techniques [...] Read more.
Food and water contamination cause safety and health concerns to both animals and humans. Conventional methods for monitoring food and water contamination are often laborious and require highly skilled technicians to perform the measurements, making the quest for developing simpler and cost-effective techniques for rapid monitoring incessant. Since the pioneering works of Whitesides’ group from 2007, interest has been strong in the development and application of microfluidic paper-based analytical devices (μPADs) for food and water analysis, which allow easy, rapid and cost-effective point-of-need screening of the targets. This paper reviews recently reported μPADs that incorporate different detection methods such as colorimetric, electrochemical, fluorescence, chemiluminescence, and electrochemiluminescence techniques for food and water analysis. Full article
(This article belongs to the Special Issue Micro/Nano Devices for Chemical Analysis)
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<p>Examples of μPADs fabricated using different methods and paper substrates: (<b>a</b>) Wax patterning, WCP1. Reprinted with permission from reference [<a href="#B28-micromachines-07-00086" class="html-bibr">28</a>]. Copyright 2015 American Chemical Society. (<b>b</b>) Wax printing, WP1. Reprinted with permission from reference [<a href="#B31-micromachines-07-00086" class="html-bibr">31</a>]. Copyright 2011 American Chemical Society. (<b>c</b>) Wax printing, AP319. Reprinted with permission from reference [<a href="#B39-micromachines-07-00086" class="html-bibr">39</a>]. Copyright 2015 American Chemical Society. (<b>d</b>) Alkylsilane self-assembling and UV/O<sub>3</sub>-patterning, WFP1. Reprinted with permission from reference [<a href="#B52-micromachines-07-00086" class="html-bibr">52</a>]. Copyright 2013 American Chemical Society. (<b>e</b>) Wax printing with screen-printed electrodes, WCP1. Reprinted with permission from reference [<a href="#B38-micromachines-07-00086" class="html-bibr">38</a>]. Copyright 2010 The Royal Society of Chemistry. (<b>f</b>) Polymer screen printing, WFP4. Reprinted with permission from reference [<a href="#B42-micromachines-07-00086" class="html-bibr">42</a>]. Copyright 2016 The Royal Society of Chemistry. (<b>g</b>) Contact stamping, JPFP40. Reprinted with permission from reference [<a href="#B44-micromachines-07-00086" class="html-bibr">44</a>]. Copyright 2015 The Royal Society of Chemistry. (<b>h</b>) Contact stamping, WFP1. Reprinted with permission from reference [<a href="#B45-micromachines-07-00086" class="html-bibr">45</a>]. Copyright 2014 American Chemical Society. (<b>i</b>) Photolithography, CP. Reprinted with permission from reference [<a href="#B46-micromachines-07-00086" class="html-bibr">46</a>]. Copyright 2013 The Royal Society of Chemistry. WFP1, Whatman No. 1 filter paper; WCP1, Whatman No. chromatography paper; WP1, Whatman No. 1 paper; AP310, Ahlstrom 319 paper; WFP4, Whatman No. 4 filter paper; JPFP40, JProLab JP 40 filter paper; CP, chromatography paper.</p> Full article ">Figure 2
<p>Detection methods for pathogens. (<b>a</b>) An image of a single-channel μPAD and (<b>b</b>) the smartphone application for <span class="html-italic">Salmonella</span> detection on a multi-channel μPAD. Reprinted with permission from reference [<a href="#B46-micromachines-07-00086" class="html-bibr">46</a>]. Copyright 2013 The Royal Society of Chemistry. (<b>c</b>) Schematic layout of the PDMS/paper hybrid μPAD system and illustration of the one-step multiplexed FL detection principle on the μPAD during aptamer adsorption (Step 1) and liberation (Step 2) from the GO surface and the restoration of the FL for detection in the presence of the target pathogen. Reprinted with permission from reference [<a href="#B60-micromachines-07-00086" class="html-bibr">60</a>]. Copyright 2013 The Royal Society of Chemistry.</p> Full article ">Figure 3
<p>Colorimetric detection of pesticides based on the enzyme inhibition properties of the pesticide on nanoceria substrate. Reprinted with permission from reference [<a href="#B42-micromachines-07-00086" class="html-bibr">42</a>]. Copyright 2016 The Royal Society of Chemistry.</p> Full article ">Figure 4
<p>(<b>a</b>) Griess-color reaction assay-based detection methods for nitrite using a smartphone for image processing. Reprinted with permission from reference [<a href="#B45-micromachines-07-00086" class="html-bibr">45</a>]. Copyright 2014 American Chemical Society. (<b>b</b>) Griess-color reaction assay-based detection methods for nitrite and nitrate using 2D (<span class="html-italic">i</span>) and 3D (<span class="html-italic">ii–iv</span>) μPADs. Reprinted with permission from reference [<a href="#B53-micromachines-07-00086" class="html-bibr">53</a>]. Copyright 2014 American Chemical Society.</p> Full article ">Figure 5
<p>Detection methods for metals. (<b>a</b>) Electrochemical device for SWASV analysis of lead in water with screen-printed carbon working and counter electrodes and Ag/AgCl pseudo-reference electrode. Reprinted with permission from reference [<a href="#B47-micromachines-07-00086" class="html-bibr">47</a>]. Copyright 2009 The Royal Society of Chemistry. (<b>b</b>) Multiplexed colorimetric detection of metals based on B-GAL and CPRG interaction in the presence of Hg<sup>2+</sup>, Cu<sup>2+</sup>, Cr<sup>6+</sup> and Ni<sup>2+</sup> mixture. Reprinted with permission from reference [<a href="#B31-micromachines-07-00086" class="html-bibr">31</a>]. Copyright 2011 American Chemical Society.</p> Full article ">Figure 6
<p>Detection methods for other food and water contaminants. (<b>a</b>) Components of the electrochemical detection system for ethanol using a glucometer as a readout device. Reprinted with permission from reference [<a href="#B38-micromachines-07-00086" class="html-bibr">38</a>]. Copyright 2010 The Royal Society of Chemistry. (<b>b</b>) The configuration of the electrochemical cell for the analysis of halides utilizing silver components as electrodes on paper-assisted electrochemical detection. Reprinted with permission from reference [<a href="#B56-micromachines-07-00086" class="html-bibr">56</a>]. Copyright 2015 American Chemical Society. (<b>c</b>) A representative paper-based colorimetric bioassay of BSA based on the enzymatically generated quinone from tyrosinase and chitosan interaction in the presence of the phenolic compound. Reprinted with permission from ref [<a href="#B59-micromachines-07-00086" class="html-bibr">59</a>]. Copyright 2012 American Chemical Society.</p> Full article ">
5058 KiB  
Article
Robust Design of an Optical Micromachine for an Ophthalmic Application
by Ingo Sieber, Thomas Martin and Ulrich Gengenbach
Micromachines 2016, 7(5), 85; https://doi.org/10.3390/mi7050085 - 6 May 2016
Cited by 11 | Viewed by 6512
Abstract
This article describes an approach to the robust design of an optical micromachine consisting of a freeform optics, an amplification linkage, and an actuator. The robust design approach consists of monolithic integration principles to minimize assembly efforts and of an optimization of the [...] Read more.
This article describes an approach to the robust design of an optical micromachine consisting of a freeform optics, an amplification linkage, and an actuator. The robust design approach consists of monolithic integration principles to minimize assembly efforts and of an optimization of the functional components with respect to robustness against remaining assembly and manufacturing tolerances. The design approach presented involves the determination of the relevant tolerances arising from the domains manufacturing, assembly, and operation of the micromachine followed by a sensitivity analysis with the objective of identifying the worst offender. Subsequent to the above-described steps, an optimization of the functional design of the freeform optics with respect to a compensation of the effects of the tolerances is performed. The result leads to a robust design of the freeform optics and hence ensures a defined and optimal minimum performance of the micromachine in the presence of tolerances caused by the manufacturing processes and the operation of the micromachine. The micromachine under discussion is the tunable optics of an ophthalmic implant, an artificial accommodation system recently realized as a demonstration model at a scale of 2:1. The artificial accommodation system will be developed to replace the human crystalline lens in the case of a cataract. Full article
(This article belongs to the Special Issue Micro/Nano Photonic Devices and Systems)
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<p>Schematic representation of the AAS and its position within the capsular bag of the human eye (inset on the right).</p> Full article ">Figure 2
<p>Alvarez-Humphrey optics. Variation of the refraction power by means of a shift of the Alvarez-Humphrey surfaces perpendicular to the optical axis (<span class="html-italic">z</span>-axis in the figure).</p> Full article ">Figure 3
<p>Computer Aided Design (CAD) model of one of both identical lens parts of the AH optics with alignment structures indicated [<a href="#B1-micromachines-07-00085" class="html-bibr">1</a>].</p> Full article ">Figure 4
<p>Design of the amplification linkage (<b>a</b>) and realized silicon linkages manufactured by DRIE (<b>b</b>).</p> Full article ">Figure 5
<p>Optical micromachine and its components: Tunable freeform optics, silicon linkage, and piezoelectric stack actuator [<a href="#B1-micromachines-07-00085" class="html-bibr">1</a>]. <b>Left</b>: contracted actuator and accommodated state, <b>right</b>: expanded actuator and disaccommodated state of the optics.</p> Full article ">Figure 6
<p>Optical model of the AAS.</p> Full article ">Figure 7
<p>Precision-molded rear window of the demonstrator with its integrated optics (optical aperture of 6 mm) [<a href="#B1-micromachines-07-00085" class="html-bibr">1</a>].</p> Full article ">Figure 8
<p>Optical micromachine assembled to the rear half shell of the glass housing.</p> Full article ">Figure 9
<p>Model of the demonstrator optics of the AAS: Cornea lens, sketch of the housing with the integrated optics, the optical micromachine, and the image plane [<a href="#B29-micromachines-07-00085" class="html-bibr">29</a>].</p> Full article ">Figure 10
<p>Different types of position errors identified for the AH optics.</p> Full article ">Figure 11
<p>MTF of the nominal configuration and three different refraction power adjustments: −0.8 dpt (red), 1.5 dpt (blue), and 3.0 dpt (green).</p> Full article ">Figure 12
<p>MTFs for the different types of position tolerances identified (blue) in comparison to the reference (red). (<b>a</b>) Decentration in <span class="html-italic">x</span>; (<b>b</b>) Decentration in <span class="html-italic">y</span>; (<b>c</b>) Decentration in <span class="html-italic">z</span>; (<b>d</b>) Lateral position error; (<b>e</b>) Wedge error; (<b>f</b>) Orientation error.</p> Full article ">Figure 13
<p>MTF for the different types of position tolerances identified and the robust design for three different adjustments of refraction power: −0.8 dpt (red), 1.5 dpt (blue), and 3.0 dpt (green). (<b>a</b>) Decentration in <span class="html-italic">x</span>; (<b>b</b>) Decentration in <span class="html-italic">y</span>; (<b>c</b>) Decentration in <span class="html-italic">z</span>; (<b>d</b>) Lateral position error; (<b>e</b>) Wedge error; (<b>f</b>) Orientation error.</p> Full article ">Figure 13 Cont.
<p>MTF for the different types of position tolerances identified and the robust design for three different adjustments of refraction power: −0.8 dpt (red), 1.5 dpt (blue), and 3.0 dpt (green). (<b>a</b>) Decentration in <span class="html-italic">x</span>; (<b>b</b>) Decentration in <span class="html-italic">y</span>; (<b>c</b>) Decentration in <span class="html-italic">z</span>; (<b>d</b>) Lateral position error; (<b>e</b>) Wedge error; (<b>f</b>) Orientation error.</p> Full article ">Figure 14
<p>MTF for the different types of position tolerances identified and the robust design (green) in comparison with that of the original design as shown in <a href="#micromachines-07-00085-f012" class="html-fig">Figure 12</a> (blue), and the MTF of the error-free configuration (red). (<b>a</b>) Decentration in <span class="html-italic">x</span>; (<b>b</b>) Decentration in <span class="html-italic">y</span>; (<b>c</b>) Decentration in <span class="html-italic">z</span>; (<b>d</b>) Lateral position error; (<b>e</b>) Wedge error; (<b>f</b>) Orientation error.</p> Full article ">Figure 15
<p>Chief ray positions for the individual position errors of the freeform optics for three different adjustments of refraction power: −0.8 dpt (red), 1.5 dpt (blue), and 3.0 dpt (green).</p> Full article ">
5470 KiB  
Article
Large-Scale Integration of All-Glass Valves on a Microfluidic Device
by Yaxiaer Yalikun and Yo Tanaka
Micromachines 2016, 7(5), 83; https://doi.org/10.3390/mi7050083 - 6 May 2016
Cited by 38 | Viewed by 6885
Abstract
In this study, we developed a method for fabricating a microfluidic device with integrated large-scale all-glass valves and constructed an actuator system to control each of the valves on the device. Such a microfluidic device has advantages that allow its use in various [...] Read more.
In this study, we developed a method for fabricating a microfluidic device with integrated large-scale all-glass valves and constructed an actuator system to control each of the valves on the device. Such a microfluidic device has advantages that allow its use in various fields, including physical, chemical, and biochemical analyses and syntheses. However, it is inefficient and difficult to integrate the large-scale all-glass valves in a microfluidic device using conventional glass fabrication methods, especially for the through-hole fabrication step. Therefore, we have developed a fabrication method for the large-scale integration of all-glass valves in a microfluidic device that contains 110 individually controllable diaphragm valve units on a 30 mm × 70 mm glass slide. This prototype device was fabricated by first sandwiching a 0.4-mm-thick glass slide that contained 110 1.5-mm-diameter shallow chambers, each with two 50-μm-diameter through-holes, between an ultra-thin glass sheet (4 μm thick) and another 0.7-mm-thick glass slide that contained etched channels. After the fusion bonding of these three layers, the large-scale microfluidic device was obtained with integrated all-glass valves consisting of 110 individual diaphragm valve units. We demonstrated its use as a pump capable of generating a flow rate of approximately 0.06–5.33 μL/min. The maximum frequency of flow switching was approximately 12 Hz. Full article
(This article belongs to the Special Issue Micro/Nano Devices for Chemical Analysis)
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<p>Conceptual illustration of a large-scale integrated device with all-glass monolithic membrane valves. The many valves have numerous possible functions, such as pumping, flow switching, flow rate regulation, and particle or cell sorting.</p> Full article ">Figure 2
<p>Schematic illustrations of fundamental design and principle of large-scale integrated microfluidic device with all-glass valves. (<b>a</b>) Schematic illustration of the layer structure of the device; (<b>b</b>) Details of layer 1 and layer 2; (<b>c</b>) Four-layer-bonded image of the device; (<b>d</b>) Cut-away and assembled illustrations of a single all-glass valve. The ultra-thin glass sheet seals the chambers on the valve layer, and the chamber gap is 50 μm when the valve is open. (<b>e</b>) On: Initial state of the valve. Off: Applying pressure to the ultra-thin glass sheet pulls the sheet to the valve layer and closes the valve.</p> Full article ">Figure 3
<p>Piezoelectric actuator system for individual control of the all-glass valve. (<b>a</b>) The actuator system consists of three parts: a PC (with an installed graphic user interface (GUI)), a customized circuit board-based controller (with power and control signals), and a piezoelectric head; (<b>b</b>) Graphical pattern of activated valve locations; (<b>c</b>) Time-sequence-editing by the GUI; (<b>d</b>) Piezoelectric head with 110 piezoelectric units in an 11 × 10 array; (<b>e</b>) Fully assembled image of piezoelectric head, microfluidic device, and acrylic mounting jig; (<b>f</b>) Captured image from the demonstration of a word pattern displayed by the piezoelectric units.</p> Full article ">Figure 4
<p>Photographs and valve profile images of prototype. (<b>a</b>) Photograph of a large-scale integrated microfluidic device with 110 all-glass monolithic membrane valves; (<b>b</b>) Image of valves with colored medium loaded; (<b>c</b>) Image of chip after the ultra-thin glass sheets were bonded and cut in half for observation. The black scale bar is 5 mm; (<b>d</b>) Image of single valve unit from top side. The white scale bar is 0.2 mm; (<b>e</b>) SEM image of valve unit before ultra-thin glass sheet bonding; (<b>f</b>) Cross-sectional view showing the details of the valve after glass sheet bonding. The white scale bar is 0.2 mm. The location of the cross-sectional view is shown in (<b>d</b>) with the red dotted line; (<b>g</b>) Enlarged cross-sectional view of single through-hole structure. The white scale bar is 0.05 mm.</p> Full article ">Figure 5
<p>Confirmation of valve action by observing motion of flow containing 1-μm-diameter particles. (<b>a</b>) Valves in different positions were selected to demonstrate the on and off functions of the valves; (<b>b</b>) The motion of the flow containing 1-μm-diameter particles shows that the flow moved through the valve when it was open, and stopped when the valve was closed. The white scale bar is 0.2 mm.</p> Full article ">Figure 6
<p>Pump demonstration experiment using different numbers of valves. (<b>a</b>) The fabricated prototype of the all-glass microfluidic device containing 110 valves; (<b>b</b>) Experimental set-up of the microfluidic device with the piezoelectric head containing 110 piezoelectric units; (<b>c</b>) The numbers of valves used to demonstrate the pump function; (<b>d</b>,<b>e</b>) Plots showing the dependence of the flow velocity in the channel or the flow rate, and the number of valve lines.</p> Full article ">Figure 7
<p>Relationship between valve operation time interval and on-chip flow rate. (<b>a</b>) The valve operation time interval indicates the time to start the action of the next line of valves; (<b>b</b>) The relation between the velocity and valve operation time interval; (<b>c</b>) The relation between the flow rate and valve operation time interval.</p> Full article ">Figure 8
<p>Demonstration experiment of channel selection using valves. (<b>a</b>) Photo of the microfluidic device prototype; (<b>b</b>) The location of the observed area and valve units used; (<b>c</b>) Results of the channel selection demonstration. B ≤ C before: initial state of valve A, off; B, off; C, on; positions of bubbles 1, 2, and 3 in the flow. B ≤ C after: B was turned on, and A and C were turned off; the flow containing bubbles flowed to B. A ≥ C before: initial state of valve A, on; B: off, C, off; the positions of bubbles 1, 2, and 3 in the flow. A ≥ C after: C was turned on, and A and B were turned off; the flow containing bubbles flowed to C. A ≤ B before: initial state of valve A, off; B, on; C, off; the positions of bubbles 1, 2, and 3 in the flow. A ≤ B after: A was turned on, and B and C were turned off; the flow containing bubbles flowed to A. The white scale bar is 1.5 mm.</p> Full article ">Figure 9
<p>Dependency on frequency of flow switching. (<b>a</b>) Switching sequence of the valve units employed in this experiment, and estimated switching sequence of flow direction; (<b>b</b>) The employed valve units and direction measurement location in the channel between these employed valve units; (<b>c</b>) The motion of numerous 1-μm-diameter particles was observed in this location; (<b>d</b>) The delay between the two switching actions was observed and plotted. A maximum frequency of flow switching of 12 Hz was observed for a valve switching frequency of 25 Hz.</p> Full article ">Figure 10
<p>Comparison and confirmation of the thin version all-glass valve chip. (<b>a</b>) Thin version of the all-glass valve chip; (<b>b</b>) Photos of a conventional all-glass valve chip (<b>left</b>), thin version of the all-glass valve chip (<b>middle</b>), and a cover glass (<b>right</b>); (<b>c</b>) Valve actions of the thin version of the all-glass valve chip were confirmed. The off/on action of the valve in the red dotted circle of (<b>a</b>) was captured from <a href="#app1-micromachines-07-00083" class="html-app">Video S9</a>. The white scale bar is 0.1 mm.</p> Full article ">
2322 KiB  
Communication
High Throughput Studies of Cell Migration in 3D Microtissues Fabricated by a Droplet Microfluidic Chip
by Xiangchen Che, Jacob Nuhn, Ian Schneider and Long Que
Micromachines 2016, 7(5), 84; https://doi.org/10.3390/mi7050084 - 5 May 2016
Cited by 13 | Viewed by 5779
Abstract
Arrayed three-dimensional (3D) micro-sized tissues with encapsulated cells (microtissues) have been fabricated by a droplet microfluidic chip. The extracellular matrix (ECM) is a polymerized collagen network. One or multiple breast cancer cells were embedded within the microtissues, which were stored in arrayed microchambers [...] Read more.
Arrayed three-dimensional (3D) micro-sized tissues with encapsulated cells (microtissues) have been fabricated by a droplet microfluidic chip. The extracellular matrix (ECM) is a polymerized collagen network. One or multiple breast cancer cells were embedded within the microtissues, which were stored in arrayed microchambers on the same chip without ECM droplet shrinkage over 48 h. The migration trajectory of the cells was recorded by optical microscopy. The migration speed was calculated in the range of 3–6 µm/h. Interestingly, cells in devices filled with a continuous collagen network migrated faster than those where only droplets were arrayed in the chambers. This is likely due to differences in the length scales of the ECM network, as cells embedded in thin collagen slabs also migrate slower than those in thick collagen slabs. In addition to migration, this technical platform can be potentially used to study cancer cell-stromal cell interactions and ECM remodeling in 3D tumor-mimicking environments. Full article
(This article belongs to the Special Issue Micro/Nano Devices for Chemical Analysis)
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<p>(<b>a</b>) Sketch of the droplet microfluidic chip for generating 3D microtissues (<span class="html-italic">not to scale</span>): Each storage chamber (a cylinder with a radius of 60 µm and height of 50 µm) has one 3D microtissue containing single or multiple cells; (<b>b</b>) Photo of a fabricated chip with 75 storage chambers.</p> Full article ">Figure 2
<p>(<b>a</b>) Photo of arrayed microtissues stored in storage chambers; (<b>b</b>) close-up of one microtissue containing one cell; (<b>c</b>) confocal image of one cell inside polymerized collagen fiber, forming a microtissue.</p> Full article ">Figure 3
<p>Confocal images showing one cell inside a 3D microtissue in a storage chamber: (<b>a</b>) topside view; (<b>b</b>) cross-section view; (<b>c</b>) stacked confocal images of a microtissue showing one cell inside a 3D microtissue.</p> Full article ">Figure 4
<p>Representative optical images showing (<b>a</b>,<b>b</b>) the migration of three cells inside 3D microtissue during a 7 h period at 37 °C; (<b>c</b>,<b>d</b>) the migration of one cell inside 3D microtissue during a 7 h period at 37 °C.</p> Full article ">Figure 5
<p>Representative trajectories of cells embedded in collagen (2 mg/mL) in the chip (<b>a</b>) and embedded in a collagen (2 mg/mL) slab between two coverslips (thick: grey, thin: black); (<b>b</b>) The chip is either filled with a continuous polymerized collagen network (grey) or droplets of collagen within the chambers (black); (<b>c</b>) Average cell speed under the different conditions as well as the length scales associated with each condition. Error bars are 95% confidence intervals.</p> Full article ">
2926 KiB  
Article
Three-Dimensional Fabrication for Microfluidics by Conventional Techniques and Equipment Used in Mass Production
by Toyohiro Naito, Makoto Nakamura, Noritada Kaji, Takuya Kubo, Yoshinobu Baba and Koji Otsuka
Micromachines 2016, 7(5), 82; https://doi.org/10.3390/mi7050082 - 4 May 2016
Cited by 13 | Viewed by 6575
Abstract
This paper presents a simple three-dimensional (3D) fabrication method based on soft lithography techniques and laminated object manufacturing. The method can create 3D structures that have undercuts with general machines for mass production and laboratory scale prototyping. The minimum layer thickness of the [...] Read more.
This paper presents a simple three-dimensional (3D) fabrication method based on soft lithography techniques and laminated object manufacturing. The method can create 3D structures that have undercuts with general machines for mass production and laboratory scale prototyping. The minimum layer thickness of the method is at least 4 µm and bonding strength between layers is over 330 kPa. The performance reaches conventional fabrication techniques used for two-dimensionally (2D)-designed microfluidic devices. We fabricated some 3D structures, i.e., fractal structures, spiral structures, and a channel-in-channel structure, in microfluidic channels and demonstrated 3D microfluidics. The fabrication method can be achieved with a simple black light for bio-molecule detection; thus, it is useful for not only lab-scale rapid prototyping, but also for commercial manufacturing. Full article
(This article belongs to the Special Issue Micro/Nano Devices for Chemical Analysis)
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<p>Schematic cross-sectional illustrations of the 3D fabrication process by conventional photolithography with NOA 81. (<b>a</b>) Fabricated PDMS molds by soft lithography. The numbers indicate layer order and #0 is a mold for a lid. (<b>b</b>) Injection of uncured NOA 81 to the spaces between PDMS molds by capillary force. (<b>c</b>) UV irradiation for partially curing NOA 81. (<b>d</b>) Lamination of NOA 81 sheets. NOA sheets are aligned after one side of PDMS molds are peeled off. The sheets are bonded by UV irradiation. The alignment and UV bonding processes are repeated.</p> Full article ">Figure 2
<p>Structures for characterization. (<b>a</b>) A schematic illustration of a structure for layer thickness characterization. A red dotted box shows a region for close-up views in (<b>b</b>,<b>c</b>). (<b>b</b>) An SEM image of a membrane made by a PDMS mold with a thickness of 50 µm and (<b>c</b>) a membrane made by a PDMS mold with a thickness of 4 µm. (<b>d</b>) 90-µm level-1 Menger sponges; (<b>e</b>) A close up image of the level-1 Menger sponge. (<b>f</b>) 810-µm level-2 Menger sponges from oblique view points.</p> Full article ">Figure 3
<p>Diagrams of a spiral structure. (<b>a</b>) A conceptual image of the structure. (<b>b</b>) A SEM image of the structure from top-down view. (<b>c</b>) Confocal images of vertical cross sections at every 200 µm in the flow direction of the microchannel filled with fluorescein solution. White dotted lines represent cross-sectional shapes of a five-layer structure. Scale bar is 100 µm.</p> Full article ">Figure 4
<p>Confocal microscope images of a flow in the spiral structure channel. (<b>a</b>) Overhead view of the Y-shaped channel with the 5 spiral structures; (<b>b</b>) Confocal microscope images of vertical cross sections of the microchannel at every 200 µm in the flow direction and (<b>c</b>) at blanks. The channel was filled with a fluorescein solution (green) and water (dark). Scale bars are 100 µm.</p> Full article ">Figure 5
<p>Confocal microscope images of a ten-layer spiral structure at every 200 µm in the flow direction of the microchannel. Scale bar is 100 µm.</p> Full article ">Figure 6
<p>Cross-sectional images of a 3D sheath device. (<b>a</b>) Conceptual image of the 3D sheath device. (<b>b</b>) A SEM image of a cross section of the device at position (i) in <a href="#micromachines-07-00082-f006" class="html-fig">Figure 6</a>a, and (<b>c</b>) at position (ii) in <a href="#micromachines-07-00082-f006" class="html-fig">Figure 6</a>c. (<b>d</b>) A confocal microscope image of the 3D sheath at position (iii) with the flow rate of fluorescein as 90 µL/min and rhodamine as 450 µL/min. (<b>e</b>) Fluorescein as 40 µL/min and rhodamine as 210 µL/min. Scale bars are 100 µm.</p> Full article ">
979 KiB  
Review
Unconventional Electrochemistry in Micro-/Nanofluidic Systems
by Sahana Sarkar, Stanley C. S. Lai and Serge G. Lemay
Micromachines 2016, 7(5), 81; https://doi.org/10.3390/mi7050081 - 3 May 2016
Cited by 17 | Viewed by 16178
Abstract
Electrochemistry is ideally suited to serve as a detection mechanism in miniaturized analysis systems. A significant hurdle can, however, be the implementation of reliable micrometer-scale reference electrodes. In this tutorial review, we introduce the principal challenges and discuss the approaches that have been [...] Read more.
Electrochemistry is ideally suited to serve as a detection mechanism in miniaturized analysis systems. A significant hurdle can, however, be the implementation of reliable micrometer-scale reference electrodes. In this tutorial review, we introduce the principal challenges and discuss the approaches that have been employed to build suitable references. We then discuss several alternative strategies aimed at eliminating the reference electrode altogether, in particular two-electrode electrochemical cells, bipolar electrodes and chronopotentiometry. Full article
(This article belongs to the Special Issue Micro/Nano Devices for Chemical Analysis)
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<p>Equivalent circuits for (<b>a</b>) a polarizable and (<b>b</b>) a non-polarizable interface.</p> Full article ">Figure 2
<p>(<b>a</b>) Schematic of a conventional electrochemical cell for voltammetric measurement. The cell consists of three electrodes, termed the working (WE), reference (RE), and counter electrode (CE), immersed in the electrolyte solution. A potential, <span class="html-italic">E</span>, is applied to the WE with respect to the RE. If the current through the RE would be high enough to cause a potential shift, a CE is introduced to minimize the current through the RE. At low currents, it is instead possible to operate with a two-electrode configuration and eliminate the CE altogether (highlighted in green), simplifying the detection circuitry. (<b>b</b>) Equivalent circuit diagram of a two-electrode setup. <span class="html-italic">R<sub>s</sub></span>: solution resistance; <span class="html-italic">R<sub>ct</sub></span>: charge-transfer resistance at the WE; <span class="html-italic">C:</span> electrical double layer capacitance at the WE. This circuit treats the RE as ideally non-polarizable.</p> Full article ">Figure 3
<p>(<b>a</b>) Reference-less two-electrode system where <span class="html-italic">E</span> is the applied potential between the two WEs. (<b>b</b>) Corresponding equivalent-circuit diagram. <span class="html-italic">R<sub>s</sub></span>: solution resistance; <span class="html-italic">R<sub>ct</sub></span><sub>1,2</sub>: (charge transfer) resistance at the WE<sub>1,2</sub>.</p> Full article ">Figure 4
<p>(<b>a</b>) Schematic diagram of a bipolar electrode (brown) in contact with two separate reservoirs. (<b>b</b>) Alternative concept of a bipolar electrode in which a uniform electric field is applied along a channel filled with electrolytic solution. A band electrode exposed to this solution exhibits bipolarity at its opposing ends (cathodic at left and anodic on right). (<b>c</b>) Equivalent circuit for panel (b). <span class="html-italic">E</span> is the potential applied across the solution, <span class="html-italic">R<sub>s</sub></span> is the resistance of the solution, and <span class="html-italic">R<sub>ct</sub></span> is the charge transfer resistance across the anodic/cathodic ends of the bipolar electrode (BPE).</p> Full article ">Figure 5
<p>(<b>a</b>) Schematic diagram of a two-electrode nanogap system in contact with a solution containing reversible redox species. The bottom (unbiased) electrode accumulates charge over time, and the resulting potential shift is used as readout signal. (<b>b</b>) Chronopotentiometric signal <span class="html-italic">versus</span> concentration of redox species (100 µM, 10 µM, and 1 nM Fc(MeOH)<sub>2</sub> in 0.1 M KCl) in response to a triangular potential wave applied to the top electrode (black line).</p> Full article ">
6868 KiB  
Article
High-Resolution Microfluidic Paper-Based Analytical Devices for Sub-Microliter Sample Analysis
by Keisuke Tenda, Riki Ota, Kentaro Yamada, Terence G. Henares, Koji Suzuki and Daniel Citterio
Micromachines 2016, 7(5), 80; https://doi.org/10.3390/mi7050080 - 2 May 2016
Cited by 63 | Viewed by 11968
Abstract
This work demonstrates the fabrication of microfluidic paper-based analytical devices (µPADs) suitable for the analysis of sub-microliter sample volumes. The wax-printing approach widely used for the patterning of paper substrates has been adapted to obtain high-resolution microfluidic structures patterned in filter paper. This [...] Read more.
This work demonstrates the fabrication of microfluidic paper-based analytical devices (µPADs) suitable for the analysis of sub-microliter sample volumes. The wax-printing approach widely used for the patterning of paper substrates has been adapted to obtain high-resolution microfluidic structures patterned in filter paper. This has been achieved by replacing the hot plate heating method conventionally used to melt printed wax features into paper by simple hot lamination. This patterning technique, in combination with the consideration of device geometry and the influence of cellulose fiber direction in filter paper, led to a model µPAD design with four microfluidic channels that can be filled with as low as 0.5 µL of liquid. Finally, the application to a colorimetric model assay targeting total protein concentrations is shown. Calibration curves for human serum albumin (HSA) were recorded from sub-microliter samples (0.8 µL), with tolerance against ±0.1 µL variations in the applied liquid volume. Full article
(This article belongs to the Special Issue Micro/Nano Devices for Chemical Analysis)
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<p>Comparison of resolution achieved for melting of printed wax into paper substrates by hot plate or hot lamination. (<b>a</b>) Wax line widths observed directly after printing and after heating with hot plate (red circles), hot laminator without top side lamination (blue diamonds), and hot laminator with full lamination (green squares) (mean value ± 1σ); (<b>b</b>) Microfluidic channel widths after heating by hot plate (red circles) or hot laminator with full lamination (green squares) (mean value ± 1σ); (<b>c</b>) Dimensions and photographs of 10 parallel microfluidic channels after lamination or hot plate (150 °C for 15 s) treatment. Channels visualized by application of colored aqueous solution.</p> Full article ">Figure 2
<p>(<b>a</b>) Schematic representation of the evaluation of the influence of cellulose fiber direction on sample wicking in patterned filter paper (channel width: 553 ± 31 µm (<span class="html-italic">n</span> = 20) after lamination). The flow distances are measured as indicated by the arrow; (<b>b</b>) Quantitative results averaged for 5 independently fabricated devices (mean value ± 1σ). Circled numbers indicate the respective flow direction.</p> Full article ">Figure 3
<p>Schematic of the experimental method used to evaluate the minimally required wax barrier width. The indicated dimensions (<span class="html-italic">x</span> = 200–350 µm) refer to the values set for wax printing and do not represent the actual dimensions obtained after hot lamination.</p> Full article ">Figure 4
<p>Schematic of the experimental method used to evaluate the minimally required width of microfluidic channels aligned to the cellulose fiber direction in the filter paper. The indicated dimensions refer to the values set for wax printing and do not represent the actual dimensions obtained after hot lamination.</p> Full article ">Figure 5
<p>Micrographs of a wax-printed microfluidic paper-based analytical device (µPAD): (<b>a</b>) before and (<b>b</b>) after hot lamination. The scale bars correspond to a length of 1 mm. Dimensions are indicated before and after hot lamination (values in parentheses). (<b>c</b>) Corresponding photograph.</p> Full article ">Figure 6
<p>Colorimetric human serum albumin (HSA) analysis through the application of 0.8 µL of sample liquid to an optimized µPAD. (<b>a</b>) Calibration curve with data plots and error bars representing mean red intensities and corresponding standard deviations extracted from the four detection zones (parameters of regression line shown in <a href="#micromachines-07-00080-t004" class="html-table">Table 4</a>); (<b>b</b>) Micrographs of µPADs after application of 0, 2, 4, 6, 7, 8, 9, and 10 mg/mL HSA (from upper left to lower right). The scale bars correspond to a length of 1 mm (brightness and contrast adjusted for improved visibility).</p> Full article ">Figure 7
<p>Calibration curves for HSA obtained with variable sample volumes: 0.7 µL (red circles), 0.8 µL (green squares), and 0.9 µL (blue diamonds). Data plots and error bars represent mean red intensities and corresponding standard deviations extracted from four detection zones (parameters of regression lines shown in <a href="#micromachines-07-00080-t004" class="html-table">Table 4</a>).</p> Full article ">
2106 KiB  
Article
Delay Kalman Filter to Estimate the Attitude of a Mobile Object with Indoor Magnetic Field Gradients
by Christophe Combettes and Valérie Renaudin
Micromachines 2016, 7(5), 79; https://doi.org/10.3390/mi7050079 - 2 May 2016
Cited by 10 | Viewed by 6288
Abstract
More and more services are based on knowing the location of pedestrians equipped with connected objects (smartphones, smartwatches, etc.). One part of the location estimation process is attitude estimation. Many algorithms have been proposed but they principally target open space areas where [...] Read more.
More and more services are based on knowing the location of pedestrians equipped with connected objects (smartphones, smartwatches, etc.). One part of the location estimation process is attitude estimation. Many algorithms have been proposed but they principally target open space areas where the local magnetic field equals the Earth’s field. Unfortunately, this approach is impossible indoors, where the use of magnetometer arrays or magnetic field gradients has been proposed. However, current approaches omit the impact of past state estimates on the current orientation estimate, especially when a reference field is computed over a sliding window. A novel Delay Kalman filter is proposed in this paper to integrate this time correlation: the Delay MAGYQ. Experimental assessment, conducted in a motion lab with a handheld inertial and magnetic mobile unit, shows that the novel filter better estimates the Euler angles of the handheld device with an 11.7° mean error on the yaw angle as compared to 16.4° with a common Additive Extended Kalman filter. Full article
(This article belongs to the Special Issue Magnetic MEMS)
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<p>Estimation of the azimuth angle using the Earth’s magnetic field measurement <math display="inline"> <semantics> <mrow> <msub> <mstyle mathvariant="bold" mathsize="normal"> <mi>y</mi> </mstyle> <mi>m</mi> </msub> </mrow> </semantics> </math> and the declination angle between the True North and the horizontal component.</p> Full article ">Figure 2
<p>(<b>a</b>) Motion capture room equipped with the ART IR tracking system, the treadmill and the test subject holding the MIMU in hand. (<b>b</b>) An ART MoCap targets tree is rigidly fixed to the handheld MIMU.</p> Full article ">Figure 3
<p>Norm of the MIMU’s acceleration vector (blue) and the Earth gravity field (red).</p> Full article ">Figure 4
<p>Norm of the local magnetic field and the reference Earth magnetic field.</p> Full article ">Figure 5
<p>Illustration of the accelerometer’s norm for subject S1 in the texting scenario.</p> Full article ">Figure 6
<p>Difference between two magnetic field vectors, <span class="html-italic">i.e.</span>, the Earth field and the MIMU’s local field, for the subject S1 in the texting scenario.</p> Full article ">Figure 7
<p>Norm of the accelerations for subject S1 in the texting (red) and swinging (blue) scenarios.</p> Full article ">Figure 8
<p>Difference between two magnetic field vectors, <span class="html-italic">i.e.</span>, the Earth field and the MIMU’s field, for subject S4 in the swinging scenario.</p> Full article ">Figure 9
<p>Error on the yaw angle estimates for the three attitude estimation filters: AEKF (bleu), MAGYQ (red) and Delay MAGYQ (green).</p> Full article ">Figure 10
<p>Norm of the residual errors (<math display="inline"> <semantics> <mrow> <mstyle mathvariant="bold" mathsize="normal"> <mi>K</mi> </mstyle> <mi mathvariant="sans-serif">δ</mi> <mstyle mathvariant="bold" mathsize="normal"> <mi>z</mi> </mstyle> </mrow> </semantics> </math>) on the quaternion orientation estimated with MAGYQ (red) and Delay-MAGYQ (green).</p> Full article ">
14610 KiB  
Article
Assembly of a 3D Cellular Computer Using Folded E-Blocks
by Shivendra Pandey, Nicholas J. Macias, Carmen Ciobanu, ChangKyu Yoon, Christof Teuscher and David H. Gracias
Micromachines 2016, 7(5), 78; https://doi.org/10.3390/mi7050078 - 28 Apr 2016
Cited by 8 | Viewed by 5792
Abstract
The assembly of integrated circuits in three dimensions (3D) provides a possible solution to address the ever-increasing demands of modern day electronic devices. It has been suggested that by using the third dimension, devices with high density, defect tolerance, short interconnects and small [...] Read more.
The assembly of integrated circuits in three dimensions (3D) provides a possible solution to address the ever-increasing demands of modern day electronic devices. It has been suggested that by using the third dimension, devices with high density, defect tolerance, short interconnects and small overall form factors could be created. However, apart from pseudo 3D architecture, such as monolithic integration, die, or wafer stacking, the creation of paradigms to integrate electronic low-complexity cellular building blocks in architecture that has tile space in all three dimensions has remained elusive. Here, we present software and hardware foundations for a truly 3D cellular computational devices that could be realized in practice. The computing architecture relies on the scalable, self-configurable and defect-tolerant cell matrix. The hardware is based on a scalable and manufacturable approach for 3D assembly using folded polyhedral electronic blocks (E-blocks). We created monomers, dimers and 2 × 2 × 2 assemblies of polyhedral E-blocks and verified the computational capabilities by implementing simple logic functions. We further show that 63.2% more compact 3D circuits can be obtained with our design automation tools compared to a 2D architecture. Our results provide a proof-of-concept for a scalable and manufacture-ready process for constructing massive-scale 3D computational devices. Full article
(This article belongs to the Special Issue Building by Self-Assembly)
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<p>Layout for folded E-blocks. (<b>a</b>) Schematic and experimental photograph illustrating the two dimensional (2D) mapping of circuit layers designed for a three dimensional (3D) cubic E-block; (<b>b</b>) Schematic and photograph of an experimentally realized 3D folded E-block monomer. Scale bar is 5 mm.</p> Full article ">Figure 2
<p>Simulation results for comparison of performance for 2D <span class="html-italic">vs.</span> 3D integration of gates. (<b>a</b>) 2D <span class="html-italic">vs.</span> 3D cell matrix compilers and PAR Tool (Perl Archive Toolkit) performance comparison; (<b>b</b>) comparison of the number of cells required for the same performance when the gates are integrated in 2D and 3D. Both 2D and 3D compilers were programmed to perform routing with A* algorithm, where shortest distance between two nodes are computed to determine the lowest cost of a function [<a href="#B24-micromachines-07-00078" class="html-bibr">24</a>]. Placement of cells was computed using neural and force directed methods where a 2D cell matrix utilized square cell matrix topology, and, in 3D, the compiler was configured to work on a six-sided cell matrix topology.</p> Full article ">Figure 3
<p>Architecture of a self-configurable and scalable 2D cell matrix. (<b>a</b>) Design of a single unit cell with input and output on each side. The cell receives information from neighbor cells, processes it and then feeds its output back to neighboring cells to configure the circuit, (<b>b</b>) a cell matrix is perfectly scalable. Adding a 4 × 1 matrix to a 4 × 4 matrix results into a 4 × 5 cell matrix. Red arrows show that each cell can interact with other cells independently and thus provide self-configurability to the matrix.</p> Full article ">Figure 4
<p>Fabrications of milli-E blocks. (<b>a</b>) Flexible 2D maps of circuits layers were cutout, folded, and mounted on the cube with a commercial microchip on top and interconnected Cu wires on each face using PCB (Printed Circuit Board) photolithography; (<b>b</b>) potentially mass-producible E-blocks were prepared with interconnecting wires to establish connections to the chip and circuit layers. All scales are 5 mm.</p> Full article ">Figure 5
<p>Higher order assembly of E-blocks to create 3D cellular computer. (<b>a</b>) Schematic and experimental illustration of a tetramer (2 × 2 assembly) and (<b>b</b>) an octamer (2 × 2 × 2 assembly) 3D computer. All scales are 5 mm.</p> Full article ">Figure 6
<p>Verification of functionality of a monomer E-block. (<b>a</b>) Schematic and optical images of a wired E-block monomer. The scale bar indicates 5 mm; (<b>b</b>,<b>c</b>) experimentally recorded oscilloscope readings show the output of the monomer configured as (<b>b</b>) OR gate and (<b>c</b>) AND gate. 1 and 2 represent inputs and 3 is the output.</p> Full article ">Figure 7
<p>Verification of functionality of dimer E-blocks. (<b>a</b>) Schematic and optical images of dimer E-blocks. The scale bar indicates 5 mm; (<b>b</b>,<b>c</b>) experimentally recorded oscilloscope readings show the output of the dimer configured as D-latches, where 1 and 2 are LOAD and D inputs respectively, and 3 is the output. LOAD input is the enable line that provides ability to store the previous input value or load the new input value. When LOAD = 1, D-input is passed to output, when LOAD = 0, the D-input remains latched inside. Here, Both (<b>b</b>) and (<b>c</b>) are same circuit configuration but two different tests as D-latch.</p> Full article ">
6946 KiB  
Article
Magnetic Particle Plug-Based Assays for Biomarker Analysis
by Chayakom Phurimsak, Mark D. Tarn and Nicole Pamme
Micromachines 2016, 7(5), 77; https://doi.org/10.3390/mi7050077 - 26 Apr 2016
Cited by 9 | Viewed by 7839
Abstract
Conventional immunoassays offer selective and quantitative detection of a number of biomarkers, but are laborious and time-consuming. Magnetic particle-based assays allow easy and rapid selection of analytes, but still suffer from the requirement of tedious multiple reaction and washing steps. Here, we demonstrate [...] Read more.
Conventional immunoassays offer selective and quantitative detection of a number of biomarkers, but are laborious and time-consuming. Magnetic particle-based assays allow easy and rapid selection of analytes, but still suffer from the requirement of tedious multiple reaction and washing steps. Here, we demonstrate the trapping of functionalised magnetic particles within a microchannel for performing rapid immunoassays by flushing consecutive reagent and washing solutions over the trapped particle plug. Three main studies were performed to investigate the potential of the platform for quantitative analysis of biomarkers: (i) a streptavidin-biotin binding assay; (ii) a sandwich assay of the inflammation biomarker, C-reactive protein (CRP); and (iii) detection of the steroid hormone, progesterone (P4), towards a competitive assay. Quantitative analysis with low limits of detection was demonstrated with streptavidin-biotin, while the CRP and P4 assays exhibited the ability to detect clinically relevant analytes, and all assays were completed in only 15 min. These preliminary results show the great potential of the platform for performing rapid, low volume magnetic particle plug-based assays of a range of clinical biomarkers via an exceedingly simple technique. Full article
(This article belongs to the Special Issue Micro/Nano Devices for Chemical Analysis)
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<p>Principle of magnetic particle plug-based assays: (<b>a</b>) functionalised magnetic particles are introduced into a microchannel and trapped between two magnets, forming a plug; (<b>b</b>) a fluorescently labelled reagent or sample solution is flushed over the particle plug, with the reagent or target analyte binding to the particles; and (<b>c</b>) the microchannel is washed with buffer solution, allowing fluorescence detection of the trapped particle plug.</p> Full article ">Figure 2
<p>Setup of the microfluidic device: (<b>a</b>) photograph of a fused silica capillary located in the 1 mm gap between two 4 × 4 × 6 mm<sup>3</sup> NdFeB magnets that were fixed to a glass microscope slide; and (<b>b</b>) photograph of the glass microscope slide, holding the capillary and magnets, on the sample stage of an inverted fluorescence microscope. Samples, reagents and buffer solutions were introduced into the capillary from reservoirs via a syringe pump in withdrawal mode.</p> Full article ">Figure 3
<p>(<b>a</b>) Photograph of a plug of magnetic particles trapped between two NdFeB magnets in a capillary. (<b>b</b>) Simulation of the magnetic flux density (<b>B</b>) across the microfluidic channel, modelled using FEMM software. (<b>c</b>) Plot of the magnetic flux density along the length of the capillary (<span class="html-italic">x</span>-direction) between the two magnets.</p> Full article ">Figure 4
<p>The effect of flow rate on magnetic particle plug formation. (<b>a</b>–<b>c</b>) Photographs of plug formation at time points of 1, 5 and 10 min for flow rates of: (<b>a</b>) 180 µL·h<sup>−1</sup>; (<b>b</b>) 240 µL·h<sup>−1</sup>; and (<b>c</b>) 300 µL·h<sup>−1</sup>. (<b>d</b>) Plot of measured plug sizes over time at the three different flow rates. Each pixel was approximately equivalent to an area of 5.6 µm<sup>2</sup>.</p> Full article ">Figure 5
<p>The effect of particle concentration on plug formation. (<b>a</b>–<b>c</b>) Photographs of plug formation at time points of 1, 5 and 10 min for particle concentrations of: (<b>a</b>) 5 × 10<sup>6</sup> particles·mL<sup>−1</sup>; (<b>b</b>) 1 × 10<sup>7</sup> particles·mL<sup>−1</sup>; and (<b>c</b>) 2 × 10<sup>7</sup> particles·mL<sup>−1</sup>. (<b>d</b>) Plot of measured plug sizes over time at the three different particle concentrations. Each pixel was approximately equivalent to an area of 5.6 µm<sup>2</sup>.</p> Full article ">Figure 6
<p>Streptavidin-biotin assays performed by flushing a solution of fluorescently labelled biotin over a trapped plug of streptavidin functionalised magnetic particles. (<b>a</b>) Bright-field image of the trapped particle plug. (<b>b</b>–<b>e</b>) Fluorescence images of streptavidin particle plugs exposed to varying concentrations of biotin: (<b>b</b>) 0.1 µg·mL<sup>−1</sup>; (<b>c</b>) 0.5 µg·mL<sup>−1</sup>; (<b>d</b>) 1 µg·mL<sup>−1</sup>; and (<b>e</b>) 5 µg·mL<sup>−1</sup>. (<b>f</b>) Calibration graph of particle plug fluorescence intensities exposed to a range of fluorescently labelled biotin concentrations.</p> Full article ">Figure 7
<p>Results obtained via a magnetic particle plug-based sandwich assay for C-reactive protein (CRP). (<b>a</b>) Fluorescence image of a particle plug prior to the CRP assay, demonstrating the auto-fluorescence of the polystyrene-based particles. Magnetic particles were functionalised with primary CRP antibodies (1° anti-CRP). (<b>b</b>) Fluorescence exhibited by a particle plug after exposure to 1 µg·mL<sup>−1</sup> CRP and subsequent labelling with fluorescently tagged secondary CRP antibody (2° anti-CRP-FITC; 100 µg·mL<sup>−1</sup>); and (<b>c</b>) after exposure to 10 µg·mL<sup>−1</sup> CRP and labelling with 2° anti-CRP-FITC (100 µg·mL<sup>−1</sup>). (<b>d</b>) Plot of fluorescence intensities of the particle plugs at varying concentrations of CRP.</p> Full article ">Figure 8
<p>Results obtained for a progesterone (P4) assay, achieved by flushing P4-FITC over a trapped plug of anti-P4 functionalised magnetic particles. (<b>a</b>–<b>e</b>). Fluorescence images of particle plugs with increasing P4-FITC concentrations. (<b>f</b>) Plot of background-corrected particle plug fluorescence intensities at different concentrations (shown on a logarithmic scale) of P4-FITC.</p> Full article ">
3602 KiB  
Article
A CMOS MEMS Humidity Sensor Enhanced by a Capacitive Coupling Structure
by Jian-Qiu Huang, Baoye Li and Wenhao Chen
Micromachines 2016, 7(5), 74; https://doi.org/10.3390/mi7050074 - 26 Apr 2016
Cited by 16 | Viewed by 7437
Abstract
A capacitive coupling structure is developed to improve the performances of a capacitive complementary metal oxide semiconductor (CMOS) microelectromechanical system (MEMS) humidity sensor. The humidity sensor was fabricated by a post-CMOS process. Silver nanowires were dispersed onto the top of a conventional interdigitated [...] Read more.
A capacitive coupling structure is developed to improve the performances of a capacitive complementary metal oxide semiconductor (CMOS) microelectromechanical system (MEMS) humidity sensor. The humidity sensor was fabricated by a post-CMOS process. Silver nanowires were dispersed onto the top of a conventional interdigitated capacitive structure to form a coupling electrode. Unlike a conventional structure, a thinner sensitive layer was employed to increase the coupling capacitance which dominated the sensitive capacitance of the humidity sensor. Not only static properties but also dynamic properties were found to be better with the aid of coupling capacitance. At 25 °C, the sensitive capacitance was 11.3 pF, the sensitivity of the sensor was measured to be 32.8 fF/%RH and the hysteresis was measured to be 1.0 %RH. Both a low temperature coefficient and a fast response (10 s)/recovery time (17 s) were obtained. Full article
(This article belongs to the Special Issue CMOS-MEMS Sensors and Devices)
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Full article ">Figure 1
<p>Sketch of an interdigitated capacitive humidity sensor: (<b>a</b>) conventional structure; (<b>b</b>) capacitive coupling structure.</p> Full article ">Figure 2
<p>Equivalent circuit of an interdigitated capacitive humidity sensor with a nanowire coupling electrode.</p> Full article ">Figure 3
<p>Fabrication process of the humidity sensor: (<b>a</b>) interdigitated structure fabricated by a complementary metal oxide semiconductor (CMOS) process; (<b>b</b>) structure after deposition of a polyimide film (<b>c</b>) structure after deposition of a silver nanowire electrode.</p> Full article ">Figure 4
<p>Scanning electron microscope (SEM) image of the fabricated structure before and after post-microelectromechanical system (MEMS) process: (<b>a</b>) interdigitated electrodes fabricated by a typical CMOS process; (<b>b</b>) silver nanowires deposited on the top of the structure.</p> Full article ">Figure 5
<p>Test system of the humidity sensor for static measurements.</p> Full article ">Figure 6
<p>Output of the humidity sensor as a function of relative humidity at different temperatures.</p> Full article ">Figure 7
<p>Test system of the humidity sensor for dynamic measurements. (<b>a</b>) The first step of the measurement; (<b>b</b>) The second step of the measurement; (<b>c</b>) The third step of the measurement.</p> Full article ">Figure 8
<p>Dynamic test results of the sensor at 25 °C.</p> Full article ">Figure 9
<p>Relationship between relative change of capacitance and relative humidity at 25 °C.</p> Full article ">
2207 KiB  
Article
Fabrication of Vacuum-Sealed Capacitive Micromachined Ultrasonic Transducer Arrays Using Glass Reflow Process
by Nguyen Van Toan, Shim Hahng, Yunheub Song and Takahito Ono
Micromachines 2016, 7(5), 76; https://doi.org/10.3390/mi7050076 - 25 Apr 2016
Cited by 21 | Viewed by 5770
Abstract
This paper presents a process for the fabrication of vacuum-sealed capacitive micromachined ultrasonic transducer (CMUT) arrays using glass reflow and anodic bonding techniques. Silicon through-wafer interconnects have been investigated by the glass reflow process. Then, the patterned silicon-glass reflow wafer is anodically bonded [...] Read more.
This paper presents a process for the fabrication of vacuum-sealed capacitive micromachined ultrasonic transducer (CMUT) arrays using glass reflow and anodic bonding techniques. Silicon through-wafer interconnects have been investigated by the glass reflow process. Then, the patterned silicon-glass reflow wafer is anodically bonded to an SOI (silicon-on-insulator) wafer for the fabrication of CMUT devices. The CMUT 5 × 5 array has been successfully fabricated. The resonant frequency of the CMUT array with a one-cell radius of 100 µm and sensing gap of 3.2 µm (distance between top and bottom electrodes) is observed at 2.84 MHz. The Q factor is approximately 1300 at pressure of 0.01 Pa. Full article
(This article belongs to the Special Issue Glass Micromachining)
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Full article ">Figure 1
<p>Device structure.</p> Full article ">Figure 2
<p>Electrical equivalent circuit model of CMUT.</p> Full article ">Figure 3
<p>Fabrication process. (<b>a</b>) Silicon wafer; (<b>b</b>) Photolithography and deep RIE; (<b>c</b>) Anodic bonding in vacuum chamber; (<b>d</b>) Glass reflow process; (<b>e</b>) Lapping and polishing; (<b>f</b>) Photolithography and deep RIE; (<b>g</b>) Anodic bonding in vacuum chamber; (<b>h</b>) Silicon and SiO<sub>2</sub> removal, electrical connection and contact pads.</p> Full article ">Figure 4
<p>(<b>a</b>) View of 2 × 2 cm<sup>2</sup> silicon-in-glass wafer; (<b>b</b>) Top view; (<b>c</b>) Cross-sectional view.</p> Full article ">Figure 5
<p>(<b>a</b>) Vacuum cavity; (<b>b</b>) Close-up image.</p> Full article ">Figure 6
<p>Measurement setup.</p> Full article ">Figure 7
<p>Simulation and measurement results. (<b>a</b>) Frequency response at <span class="html-italic">V</span><sub>DC</sub> of 100 V with wide-range observation and FEM simulation; (<b>b</b>) Frequency response at <span class="html-italic">V</span><sub>DC</sub> of 120 V with narrow-range observation.</p> Full article ">
5887 KiB  
Article
Quasi-Optical Terahertz Microfluidic Devices for Chemical Sensing and Imaging
by Lei Liu, Zhenguo Jiang, Syed Rahman, Md. Itrat Bin Shams, Benxin Jing, Akash Kannegulla and Li-Jing Cheng
Micromachines 2016, 7(5), 75; https://doi.org/10.3390/mi7050075 - 25 Apr 2016
Cited by 13 | Viewed by 7247
Abstract
We first review the development of a frequency domain quasi-optical terahertz (THz) chemical sensing and imaging platform consisting of a quartz-based microfluidic subsystem in our previous work. We then report the application of this platform to sensing and characterizing of several selected liquid [...] Read more.
We first review the development of a frequency domain quasi-optical terahertz (THz) chemical sensing and imaging platform consisting of a quartz-based microfluidic subsystem in our previous work. We then report the application of this platform to sensing and characterizing of several selected liquid chemical samples from 570–630 GHz. THz sensing of chemical mixtures including isopropylalcohol-water (IPA-H2O) mixtures and acetonitrile-water (ACN-H2O) mixtures have been successfully demonstrated and the results have shown completely different hydrogen bond dynamics detected in different mixture systems. In addition, the developed platform has been applied to study molecule diffusion at the interface between adjacent liquids in the multi-stream laminar flow inside the microfluidic subsystem. The reported THz microfluidic platform promises real-time and label-free chemical/biological sensing and imaging with extremely broad bandwidth, high spectral resolution, and high spatial resolution. Full article
(This article belongs to the Special Issue Micro/Nano Devices for Chemical Analysis)
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<p>The THz microfluidic chemical sensing and imaging platform: (<b>a</b>) a schematic of the system comprising a quasi-optical THz-FDS spectroscopy and a four-channel microfluidic subsystem; (<b>b</b>) a photo showing the actual experimental setup. Liquid samples are delivered to the microfluidic chip through the four syringes A–D [<a href="#B26-micromachines-07-00075" class="html-bibr">26</a>].</p> Full article ">Figure 2
<p>(<b>a</b>) The fabrication of the quartz-based microfluidic device using wafer bonding; (<b>b</b>) A two-stream laminar flow (with red and blue dyes at an injection rate of 100 μL/min) formed inside the device main channel demonstrating that the design and fabrication of the device were successful.</p> Full article ">Figure 3
<p>(<b>a</b>) Measured system dynamic range showing an average of 50 dB over the frequency range of 570–630 GHz; (<b>b</b>) measured transmission spectrum of Mylar thin films [<a href="#B27-micromachines-07-00075" class="html-bibr">27</a>].</p> Full article ">Figure 4
<p>Measured THz responses (raw data without normalization) for background (ambient), empty microfluidic device and water-filled microfluidic device, respectively [<a href="#B26-micromachines-07-00075" class="html-bibr">26</a>].</p> Full article ">Figure 5
<p>(<b>a</b>) Raw data of the THz spectra responses for isopropylalcohol (IPA), Methanol and water; (<b>b</b>) Comparison of normalized (to water) THz spectra responses for a variety of chemicals (Benzyl alcohol (BEZ ALCH), isopropylalcohol (IPA), methanol (Meth) and acetonitrile (ACN)), demonstrating the system’s capability for discriminating different chemicals.</p> Full article ">Figure 6
<p>THz microfluidic sensing and analysis of IPA-H<sub>2</sub>O and ACN-H<sub>2</sub>O mixtures: (<b>a</b>) normalized (to water) THz transmission spectra of the IPA-H<sub>2</sub>O mixtures with IPA concentration ranging from 10% to 91%; (<b>b</b>) output THz signal responses at three selected frequencies showing strong linear relationship of the signal as a function of IPA concentration; (<b>c</b>) normalized (to water) THz transmission spectra of the ACN-H<sub>2</sub>O mixtures with different ACN concentrations; (<b>d</b>) output THz signal responses at three selected frequencies functions of IPA concentration. Nonlinear relationships observed showing completely different hydrogen dynamics and THz absorption mechanisms (as compared to IPA-H<sub>2</sub>O mixtures).</p> Full article ">Figure 7
<p>THz chemical sensing and imaging (580 GHz) for studying molecular diffusion at liquid-liquid interfaces of two-stream laminar flows: (<b>a</b>) schematic showing the THz imaging of two-stream laminar flow inside the device (lower left inset shows an optical image of a two-stream laminar flow with red and blue dyes at an injection rate of 100 μL/min; upper right inset shows a THz 2-D scanning image of a laminar flow formed by water and IPA; (<b>b</b>) 1-D THz scanning results for two-stream laminar flows formed by water and IPA-H<sub>2</sub>O mixtures [<a href="#B26-micromachines-07-00075" class="html-bibr">26</a>]; (<b>c</b>) 1-D THz scanning across the device at <span class="html-italic">X</span> = 30 mm for laminar flows formed by water and IPA at different injection rate from 40 to 0.5 μL/min. The transition region at the interface is nearly doubled; (<b>d</b>) 1-D THz scanning at different positions of the device (<span class="html-italic">X</span> = 10–25 mm) for a laminar flow by water and IPA at a rate of 0.5 μL/min. The transition at the liquid-liquid interface changes from 5.8 to 6.2 mm when <span class="html-italic">X</span> changes from 10 to 25 mm, showing stronger diffusion at the outlets side of the microfluidic device.</p> Full article ">
2744 KiB  
Article
Influence of Geometry and Surrounding Conditions on Fluid Flow in Paper-Based Devices
by Noosheen Walji and Brendan D. MacDonald
Micromachines 2016, 7(5), 73; https://doi.org/10.3390/mi7050073 - 25 Apr 2016
Cited by 52 | Viewed by 7357
Abstract
Fluid flow behaviour in paper is of increasing interest due to the advantages and expanding use of microfluidic paper-based analytical devices (known as µPADs). Applications are expanding from those which often have low sample fluid volumes, such as diagnostic testing, to those with [...] Read more.
Fluid flow behaviour in paper is of increasing interest due to the advantages and expanding use of microfluidic paper-based analytical devices (known as µPADs). Applications are expanding from those which often have low sample fluid volumes, such as diagnostic testing, to those with an abundance of sample fluid, such as water quality testing. The rapid development of enhanced features in μPADs, along with a need for increased sensitivity and specificity in the embedded chemistry requires understanding the passively-driven fluid motion in paper to enable precise control and consistency of the devices. It is particularly important to understand the influence of parameters associated with larger fluid volumes and to quantify their impact. Here, we experimentally investigate the impacts of several properties during imbibition in paper, including geometry (larger width and length) and the surrounding conditions (humidity and temperature) using abundant fluid reservoirs. Fluid flow velocity in paper was found to vary with temperature and width, but not with length of the paper strip and humidity for the conditions we tested. We observed substantial post-wetting flow for paper strips in contact with a large fluid reservoir. Full article
(This article belongs to the Special Issue Paper-Based Microfluidic Devices for Point-of-Care Diagnostics)
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<p>(<b>a</b>) Schematic of experimental setup to examine wicking behaviour in µPADs using paper strips dipped in a reservoir; (<b>b</b>) paper strip wicking from reservoir during experimentation.</p> Full article ">Figure 2
<p>Experimental results for wicking in 1 CHR strips 10 mm in width and 45 mm in length at ambient (<span class="html-italic">T<sub>a</sub></span>) and fluid (<span class="html-italic">T<sub>f</sub></span>) temperature conditions varying from 15 to 45 °C.</p> Full article ">Figure 3
<p>Comparison of the inverse root of viscosity (from the Washburn equation) to experimental data for wicking distance at 2, 4, and 6 min in 1 CHR, 10 mm width strips at varying temperature conditions.</p> Full article ">Figure 4
<p>Experimental results for wicking in 1 CHR strips 10 mm in width and 45 mm in length, for humidity (<span class="html-italic">H</span>) conditions varying from 30% to 85%.</p> Full article ">Figure 5
<p>Experimental observations for wicking in a 10 mm wide 17 CHR paper strip, in the machine direction (MD) and cross machine direction (CMD).</p> Full article ">Figure 6
<p>Experimental results for wicking in 1 CHR strips of lengths (<span class="html-italic">L</span>) varying from 25 to 65 mm, and a width of 10 mm.</p> Full article ">Figure 7
<p>Experimental results for wicking in 1 CHR strips of widths (<span class="html-italic">w</span>) varying from 5 to 40 mm, and a length of 45 mm.</p> Full article ">Figure 8
<p>Experimental results for wicking in 17 CHR strips of widths (<span class="html-italic">w</span>) varying from 5 to 30 mm, and a length of 45 mm.</p> Full article ">Figure 9
<p>Comparison of colour profiles of the red tone in 1 CHR paper strips (<b>a</b>) upon wetting for the full length of the strip, and (<b>b</b>) 17 min after wetting to detect flow after wetting.</p> Full article ">Figure 10
<p>Colour intensity of a 1 CHR paper strip after wetting.</p> Full article ">Figure 11
<p>Scanning electron micrographs of cellulose fibre networks in (<b>a</b>) 1 CHR at 100× magnification, (<b>b</b>) 1 CHR at 10,000×, (<b>c</b>) 17 CHR at 100×, and (<b>d</b>) 17 CHR at 10,000×.</p> Full article ">
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