JP2009269008A - Continuous separation method and device for nanoparticle by ac dielectrophoresis - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To continuously separate and extract metal nanoparticles present in a waste liquid or the like at high efficiency in a flow by a simple method. <P>SOLUTION: Ununiform electric field strength is generated by a flow passage obtained by combining a tapered trapezoidal structure 10 and a branched structure (such as a cross structure 12 and a T-shaped structure 18) arranged at the chip part thereof, and, with dielectrophoretic force in branching as the maximum, substances (gold nanoparticles 6) generating positive dielectrophoresis to a circumferential fluid are separated into a flow passage outlet 3 in a rectilinear propagation direction and substances (polystyrene particles 8) generating negative dielectrophoresis are separated into flow passage outlets 1, 2 in directions other than the rectilinear propagation direction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nanoparticle continuous separation method and apparatus using alternating current dielectrophoresis, and particularly suitable for use in recovering metal nanoparticles such as gold for use in wastewater treatment and the like, and nanoparticles using alternating current dielectrophoresis. The present invention relates to a continuous separation method and apparatus.

  On the basis of micro electro mechanical systems (MEMS), which has been developing rapidly in recent years, a microchannel, called a microchannel, is installed on a palm-sized chip, and a trace liquid sample is installed. In addition, research on micro thermo-fluid devices such as Lab-on-a-chip and μTAS (Micro Total Analysis Systems), which integrates the transport, mixing, reaction, separation, and extraction functions of reagents, has been actively conducted.

  In general, in a micro thermal fluid device, two or more kinds of samples and reagents are mixed to perform reaction and analysis. Conventionally, biological materials such as DNA, proteins, and cells have been mainly manipulated in devices, but catalytic effects, cancer cell staining, fluorescence enhancement (Non-Patent Document 1), and microelectrode preparation (Non-Patent Document 2). 3) There is a growing need for the development of a technique for manipulating metal nanoparticles, especially precious metal nanoparticles, for which research has been conducted. The operation of these samples forms the basis of the device, and for further development, it is indispensable to establish technologies for transporting the sample to an arbitrary reaction point and separating / extracting generated substances and unnecessary substances. In order to realize a practical material manipulation technique, it is necessary to manipulate the material arbitrarily in the flow based on the difference in physical properties, and many studies have been made so far. A technique (Non-Patent Document 4) that generates an asymmetric electric field in the flow field using two types of solutions having greatly different electrical conductivity and separates by electrophoresis based on the difference in the charge amount of the particles, or acoustic radiation pressure is used. Separation technology based on the difference in particle diameter (Non-patent Document 5), separation technology based on the difference in magnetism (Non-Patent Documents 6 and 7), and difference in refractive index using laser radiation pressure. Techniques (Non-Patent Documents 8 and 9) to be operated are also proposed.

  The above method is an effective sample manipulation method in a minute space, but it is difficult to manipulate multiple types of samples freely with only one method, and several separation methods must be used in combination. Don't be. Therefore, it is necessary to develop a further method for performing operation, separation, and extraction based on the difference in physical properties. In recent years, attention has been focused on a sample manipulation technique using dielectrophoresis, which is a phenomenon based on the dielectric constant, focusing on the dielectric constant as a physical property.

  Dielectrophoresis is a phenomenon in which force is applied to a substance by the interaction between the polarization of the substance and a non-uniform electric field. The great advantage is that the direction in which the force acts can be changed by the difference in the dielectric constant of the substance, and that a strong dielectrophoretic force is generated even at a low voltage in a microdevice having a very small distance between electrodes. As a general study of particle separation using dielectrophoresis, there is a method (Non-Patent Documents 10 and 11) in which electrodes are arranged in the middle of a flow path and particles are separated by applying a non-uniform electric field.

  On the other hand, research on a method for separating particles by applying an electric field in a channel in which an obstacle is arranged to generate a spatially non-uniform electric field (Non-patent Document 12) has also been made.

  Material manipulation in the device using dielectrophoresis includes separation of latex particles using a wall-shaped electrode or quadruple electrode (Non-patent Documents 10 and 11), and life and death separation of Escherichia coli using a wall-shaped electrode (Non-Patent Document 13). ), A method of forming a gold nanoparticle crosslinked structure between electrodes (Non-patent Document 2) has been studied.

  The force due to dielectrophoresis acts on the particles in the direction of strong electric field strength (positive dielectrophoresis) or weak direction (negative dielectrophoresis) depending on the dielectric constant of the particles and liquid. When an AC electric field is applied, since the dielectric constant is a function of the AC frequency, the direction in which force is applied can be changed according to the frequency.

  As a technique for generating dielectrophoresis in a micro thermofluidic device, there are many methods (Patent Documents 1 and 2) in which a non-uniform electric field is generated in a flow path by installing an electrode directly in the flow path. There are also methods for generating a non-uniform electric field using the shape of the flow path (Patent Documents 3 to 6). Actual application examples include a technique for concentrating conductors and dielectrics at different locations in the flow path, a life-and-death separation technique for Escherichia coli, and a technique for continuous separation according to the particle size (Patent Document 7).

JP 2003-200081 A JP 2000-61472 A JP 2006-205092 A JP 2003-287519 A JP 2003-107099 A Japanese Patent Laying-Open No. 2005-205408 JP 2007-21465 A K. H. Bhatt, O .; D. Velev, “Control and Modulating of the Dielectrophoretic Assembly of On-Chip Nanoparticles,” Langmuir, 20, 467-476, 2004. G.R.Souza, D.R.Christianson, FI Staquicini, M.G.Ozawa, E.Y.Snyder, R.L.Sidman, J.H. Miller, W.Arap, R. Pasqualini, “Networks of gold nanoparticles and bacteriophage as biological sensors and cell-targeting agents”, Proceedings of the National Academy of Sciences, 103, 1215-1220, 2006. S. H. Ko, I. Park, H. Pan, C. P. Grigoropoulos, A. P. Pisano, C.K. Nano letters, 7, No. 7, 1869-1877, 2007. Takahiro Yamamoto, S. Devasenathipathy, Yohei Sato, Koichi Hishida, “Submicron Particle Separation Technology by Electrokinetic Phenomenon”, Transactions of the Japan Society of Mechanical Engineers (B), 70-697, 2378-2385, 2004. F. Petersson, “Separation of liquids from blood utilizing ultrasonic standing waves in microfluidic channels”, Analyst, 129, 938-943, 2004. O. Hansen, H. Bruus, M. F. Hansen, “Magnetic separation in microfluidic systems using microfabricated electromagnets-experiments and simulations”, Journal of Magnetism and Magnetic Materials, 293, 597-604, 2005. K. Smistrup, PT. Tang, O. Hansen, MF Hansen, “Microelectromagnet for magnetic manipulation in lab-on-a-chip systems”, Journal of Magnetism and Magnetic Materials, 300, 418-426, 2006. A. Ashkin, J. M. Dziedzic, J. E. Bjorkholm, S. Chu, “Observation of single-beam gradient force optical trap for dielectric particles”, Optical letters, 1,288-290, 1986. T. Moriya, Y. Sato, “Micro optical stirrer for mixing in microchannel flow”, Eleventh International Conference on Miniaturized Systems for Chemistry and Life Sciences, 1, 1507-1509, 2007. A. Ramos, H.C. Morgan, N.M. G. Green, A.M. Castellanos, “Ac electrokinetics: a review of forces in microelectrode structures”, J. Am. Phys. D: Appl. Phys. , 31, 2338-2353, 1998. N. G. Green, A.M. Ramos, H.C. Morgan, “Ac electrokinetics: a survey of sub-micrometer particle dynamics”, J. Am. Phys. D: Appl. Phys. 33, 632-641, 2000. K. H. Kang, Y .; Kang, X .; Xuan, D.C. Li, “Continuous separation of microparticles by size with Dielectric current-dielectrophoresis”, Electrophorphoresis, 27, 694-702, 2006. Masato Suzuki, Tomoyuki Yasukawa, Jin Jin, and Tomokazu Suenaga, “Life-and-death separation of Escherichia coli using dielectrophoresis”, Analytical Chemistry, 54, No. 12, 1189-1195, 2005.

  Waste water containing metal (plating waste water, etc.) is very harmful and needs to be removed. Conventionally, the method of precipitating metal by adding chemical treatment and discarding it or reusing it as sludge has been mainly adopted. However, in order to effectively use metal resources, it is necessary to reuse the metal as it is. There is.

  However, although the dielectrophoresis research described above can keep a substance at a specific location in the flow path, there are many researches that are not from the viewpoint of taking it out. Importantly, it was not considered to continuously separate and extract in the flow.

  In addition, as a continuous dielectrophoretic separation based on the shape of the flow path, there is a separation method using the size of the particle size using DC dielectrophoresis, but under direct current, the fluid water is a particle due to a phenomenon called electroosmotic flow. Since each is driven in the direction of an electric field by a phenomenon called electrophoresis, it is necessary to combine voltages in a complicated manner.

  In addition, biochemical substances such as cells and proteins are the main substances handled in micro thermofluid devices, and there are studies using latex particles coated with carbon or conductive substances as conductors. There has been no research to separate them in devices.

  The present invention has been made to solve the above-mentioned conventional problems. Metal nanoparticles such as gold contained in a liquid after use such as a waste liquid can be efficiently and continuously produced in a flow by a simple method. It is an object to separate and extract them.

  The inventors tried a method of separating metal nanoparticles having various characteristics such as surface plasmon, catalytic effect, creation of microelectrodes, cell staining effect, particularly noble metal nanoparticles, using a micro thermofluidic device. Since the dielectric constant of a metal is considered infinite, it is considered that separation based on a dielectric constant difference from other substances is preferable.

  Moreover, in order to separate in the flow, dielectrophoresis by a flow path having a shape in which the electric field intensity distribution becomes non-uniform when an electric field is applied was selected. The majority of research on dielectrophoresis involves applying an electric field between electrodes at intervals of several tens of nanometers to several micrometers installed in the middle of a flow path to generate a non-uniform electric field. Further efficiency can be achieved by using both the method based on the flow path shape and the separation based on the electrodes.

  Glass, PDMS (polydimethylsiloxane), which is the main material of the micro thermofluidic device, is a non-conductor, and when an electric field is applied to the flow path, all the electric field is distributed in the flow path. FIG. 1 shows an example of a trapezoidal flow path 10. In the figure, 6 is a gold nanoparticle, 8 is a polystyrene particle as an impurity, 14 and 16 are electrodes, and 20 is an AC power source.

  When a non-uniform electric field is formed depending on the shape of the flow path, a non-uniform electric field is formed over the entire flow path, while in the technique using electrodes with a distance of several tens of micrometers to several micrometers, the electric field near the electrodes, particularly at the end points The intensity becomes a maximum value, and a local difference occurs in the dielectrophoretic force in the flow path. Therefore, the non-uniform electric field due to the channel shape has an advantage that the dielectrophoretic force can be applied to the entire channel. In the trapezoidal shape, the electric field strength increases as the width becomes narrower.

  On the other hand, if an electric field is applied only in the left-right direction of the cross-shaped branch flow path 12 as shown in FIG. 2, the electric field spreads in the vertical direction at the branch, resulting in non-uniform electric field distribution. This phenomenon is a phenomenon that is generated only by the flow path shape. From the branch portion, the electric field strength is strong in the left-right direction as shown in the figure, and weak in the up-down direction.

  The present invention has been made paying attention to such points, and as illustrated in FIG. 3, the flow is a combination of a tapered trapezoidal structure and, for example, a cruciform branching structure disposed at the tip thereof. Depending on the path, non-uniform electric field strength is generated, and the dielectrophoretic force at the branch is maximized, and the substance that generates positive dielectrophoresis with respect to the surrounding fluid is generated in the straight channel outlet and negative dielectrophoresis occurs. The substance is separated at the channel outlet in a direction other than straight travel.

  Here, when the surrounding fluid is water, the substance that generates the positive dielectrophoresis at an alternating electric field frequency of 1 to 2000 Hz is a metal nanoparticle (for example, gold nanoparticle), and the substance that generates the negative dielectrophoresis is Insulator particles (for example, polystyrene particles) can be used.

  The present invention also provides a flow path combining a tapered trapezoidal structure and a branch structure disposed at the tip thereof, and an electric field is applied to the flow path to generate a non-uniform electric field strength, thereby branching. Means to separate the substance that generates positive dielectrophoresis with respect to the surrounding fluid into the channel outlet in the straight direction and the substance that generates negative dielectrophoresis into the channel outlet in a direction other than the straight direction. And a nanoparticle continuous separation apparatus using alternating current dielectrophoresis, characterized in that

  Here, the branch structure may be a cross shape.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to isolate | separate and collect | recover efficiently a metal nanoparticle, especially a noble metal nanoparticle from used liquids, such as a waste liquid. In particular, in the case of metal, no chemical treatment or the like is added, so that it can be reused as it is. Further, since complicated electrodes and voltage operations are not required, it can be easily added to a conventional apparatus and is very useful. Industrial practical application is also expected to play an active role in wastewater treatment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 3, the first embodiment of the present invention has a non-uniform intensity distribution by a flow path having a shape in which a tapered trapezoidal structure 10 and a cross-shaped branch structure (hereinafter referred to as a cross structure) 12 are combined. Is generated. The dielectrophoretic force at the branch is maximized by designing the thinnest part of the trapezoidal tip, that is, the part where the electric field strength is maximum, to come to the flow path branch. In the trapezoidal structure 10, a substance that generates positive dielectrophoresis receives a dielectrophoretic force in the direction of the exit 3 in the straight direction, and a substance that generates negative dielectrophoresis receives a dielectrophoretic force in a direction that avoids the outlet 3. Further, in the cross structure 12, the positive dielectrophoretic material is subjected to dielectrophoretic force in the direction of the exit 3 in the straight direction from the branch portion, and the negative dielectrophoretic material is subjected to the exit 1 or 2 direction in the side. At this time, by increasing the width of the left one of the four cross structures 12, the electric field strength increases only from the branch to the exit 3 direction.

  FIG. 4 shows the distribution of electric lines of force in the flow path branch when an AC voltage of 700 V is applied to the inlet and outlet 3.

  The present invention was actually applied to an actual flow field using an experimental apparatus as shown in FIG.

  In FIG. 5, the experimental flow path 30 on the stage 32 was manufactured from PDMS and glass by a soft lithography method, and was measured by an apparatus using an inverted microscope. Using mercury lamp 40 as an excitation light source, scattered light of gold nanoparticles (diameter 350 to 400 nm, relative permittivity: infinite) in water (relative permittivity 78) and polystyrene fluorescent particles (diameter 1 μm, relative permittivity 2.5) ) Was imaged by a CCD camera 48. In this experiment, a gold nanoparticle obtained by reducing a volume of 0.05% polystyrene particle suspension (particle size: 1 micrometer) and a 0.01% aqueous solution of chloroauric acid with 1% trisodium citrate aqueous solution. A suspension (particle size 350-400 nanometers) was used. The particle suspension is fed by pressure driving, and 300 images are taken at 37 ms intervals before and after applying an electric field of 700 V (24 Hz), the particle velocity is extracted from the image, and individual particles are extracted from the image. It measured by the particle | grain tracking method (PTV: Particle Tracking Velocimetry) which calculates the movement amount. In the figure, 22 is a function generator, 42 is a filter, 44 is an objective lens, 46 is a mirror, and 50 is a personal computer (PC).

  When an electric field of 700 V 24 Hz is applied using the experimental apparatus shown in FIG. 5, the gold nanoparticles are in the direction of the outlet 3 as shown in FIG. 6 and Table 1, and the polystyrene particles are in the outlet 1 or as shown in FIGS. The effect of being separated in two directions was confirmed.

  The above data was obtained by flowing gold nanoparticles and polystyrene particles separately. However, even when flowing simultaneously, as shown in FIG. 8 and Table 3, by applying an electric field of 800 V 24 Hz to the outlet 3, It was confirmed that the gold nanoparticles heading increased by about 20%.

  In this experiment, 2.5 ml of a 0.1% volume concentration polystyrene particle suspension (particle size 0.5 micrometer) and 2.5 ml of gold nanoparticle suspension same as FIG. A 5 ml mixed suspension in which 50 ml of a chloroauric acid aqueous solution was reduced with 0.21 ml of a 1% trisodium citrate aqueous solution was used.

  In the above embodiment, the flow path length is about 1 cm because of the restriction due to the size of the liquid reservoir (because the inner diameter of the liquid reservoir is 1.2 cm, about 1 cm is necessary even in the closest state when mounting them side by side). Thus, a high voltage of 700 V is required, but the same effect can be obtained even at a low voltage by shortening the flow path length. For example, if the flow path length is halved, the required voltage is 350V.

  In the embodiment, since observation with an optical microscope is easy, the gold nanoparticles 6 and the polystyrene fluorescent particles 8 are separated and water is used as the surrounding fluid, but the dielectric constant and AC frequency of the substance are appropriately determined. In this case, the polarity of the dielectrophoresis can be adjusted arbitrarily, so that it can be applied to other substances. Specifically, the direction in which the dielectrophoretic force acts is determined by the sign of the real part of the Clausius-Mossotti term expressed by the equation (1) that determines the dielectrophoretic force.

K = (ε _p −ε _m ) / (ε _p + 2ε _m ) (1)
Here, ε _p is the dielectric constant of the particle, and ε _m is the dielectric constant of the surrounding fluid.

  In an alternating electric field, the dielectric constant is a function of the alternating frequency ω and is expressed by equation (2).

ε ^* = ε− (σ / ω) · j (2)
Here, σ is conductivity.

  According to the present embodiment, it is possible to continuously separate metal particles and polystyrene particles in a flow in a micro thermofluidic device. The experiment was performed with gold nanoparticles and polystyrene fluorescent particles, which can be easily observed with a microscope. However, if the dielectric constant and AC frequency of the substance are appropriately determined, the experiment can be extended to a substance not used in this experiment. The material of the flow path is not limited to the combination of PDMS and glass.

  Further, it is possible to cause dielectrophoresis by simply applying an alternating electric field between two points in the flow path without installing a complicated electrode structure in the flow path, and it can be easily added to the prior art.

  Further, in positive dielectrophoresis, the force increases at an AC frequency of 1000 Hz or less (in this experiment, it was 10 to 100 times). Therefore, separation by positive dielectrophoresis can be performed at a voltage lower than the voltage value required in theory.

  In the above-described embodiment, the flow path structure of the present invention is a single stage. However, as shown in the second embodiment shown in FIG. 9, the flow path structure has two stages, or in series as in the third embodiment shown in FIG. / Separation efficiency can be improved by applying multiple stages in parallel. Here, as shown in detail in FIG. 9, the dielectrophoretic force in the reverse direction of the flow in the connection section can be suppressed by changing the width of the connection section more gently than the separation section.

  In the above embodiment, the cross shape is used as the branch structure. However, as in the fourth embodiment illustrated in FIG. good. In the cross structure 12, the electric field can be made clearer and the particles can be easily removed. Also, the intersection / branch angle is not limited to 90 °.

The figure which shows the electric force line distribution at the time of an electric field application to the trapezoid structure flow path used by this invention Similarly, a diagram showing the distribution of lines of electric force when an electric field is applied to the cross-shaped channel The top view which shows the flow-path shape of 1st Embodiment of this invention. Distribution of electric lines of force at the branch of the flow path when an AC electric field of 700 V is applied to the inlet and outlet 3 in the embodiment. Diagram showing the configuration of the experimental apparatus Diagram showing separation results of gold nanoparticles Diagram showing the separation results of polystyrene particles Diagram showing gold nanoparticle separation results when gold nanoparticles and polystyrene particles flow simultaneously The figure which shows the structure of 2nd Embodiment of this invention. The figure which similarly shows the structure of 3rd Embodiment The figure which similarly shows the structure of 4th Embodiment

Explanation of symbols

6 ... Gold nanoparticles 8 ... Polystyrene particles 10 ... Trapezoidal structure channel 12 ... Cross (shape branch) structure channel 14, 16 ... Electrode 18 ... T-shaped (shape branch) structure channel 20 ... AC power supply

Claims (5)

With a flow path that combines a tapered trapezoidal structure and a branched structure arranged at the tip,
A non-uniform electric field strength is generated and the dielectrophoretic force at the branch is maximized. A substance that generates positive dielectrophoresis with respect to the surrounding fluid is a straight channel outlet, and a substance that generates negative dielectrophoresis is straight. A method for continuously separating nanoparticles by alternating current dielectrophoresis, wherein the separation is performed at the outlet of the flow path in a direction other than the above.   2. The AC dielectrophoresis according to claim 1, wherein the surrounding fluid is water, the substance generating the positive dielectrophoresis is a metal nanoparticle, and the substance generating the negative dielectrophoresis is an insulator particle. Nanoparticle continuous separation method.   The method for continuously separating nanoparticles according to claim 2, wherein the metal nanoparticles are gold nanoparticles, and the insulator particles are polystyrene particles. A flow path that combines a tapered trapezoidal structure and a branched structure disposed at the tip portion thereof, and
Applying an electric field to the flow path to generate a non-uniform electric field strength, maximizing the dielectrophoretic force at the branch, the substance that generates positive dielectrophoresis with respect to the surrounding fluid is Means for separating the substance in which dielectrophoresis occurs in a channel outlet in a direction other than straight travel;
An apparatus for continuous separation of nanoparticles by alternating current dielectrophoresis, comprising:   The apparatus for continuously separating nanoparticles according to claim 4, wherein the branched structure has a cross shape.