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Sensors, Volume 13, Issue 10 (October 2013) – 85 articles , Pages 12744-14247

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3007 KiB  
Review
Towards a Chemiresistive Sensor-Integrated Electronic Nose: A Review
by Shih-Wen Chiu and Kea-Tiong Tang
Sensors 2013, 13(10), 14214-14247; https://doi.org/10.3390/s131014214 - 22 Oct 2013
Cited by 194 | Viewed by 21385
Abstract
Electronic noses have potential applications in daily life, but are restricted by their bulky size and high price. This review focuses on the use of chemiresistive gas sensors, metal-oxide semiconductor gas sensors and conductive polymer gas sensors in an electronic nose for system [...] Read more.
Electronic noses have potential applications in daily life, but are restricted by their bulky size and high price. This review focuses on the use of chemiresistive gas sensors, metal-oxide semiconductor gas sensors and conductive polymer gas sensors in an electronic nose for system integration to reduce size and cost. The review covers the system design considerations and the complementary metal-oxide-semiconductor integrated technology for a chemiresistive gas sensor electronic nose, including the integrated sensor array, its readout interface, and pattern recognition hardware. In addition, the state-of-the-art technology integrated in the electronic nose is also presented, such as the sensing front-end chip, electronic nose signal processing chip, and the electronic nose system-on-chip. Full article
(This article belongs to the Special Issue Sensing of Scent, Fragrance, Smell, and Odor Emissions from Biota Sources)
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<p>The basic gas identification system blocks: an electronic nose and a mammal olfactory.</p> Full article ">
<p>The portable electronic nose system consists of the hand-held sensing module and the personal digital apparatus: (<b>a</b>) laptop computer, and (<b>b</b>) PDA; (<b>c</b>) the block diagram of the system. Reprinted with permission from [<a href="#b81-sensors-13-14214" class="html-bibr">81</a>].</p> Full article ">
<p>The SEM picture of the integrated tin oxide gas sensor array of (<b>a</b>) the single sensor element, and (<b>b</b>) the 4 × 4 gas sensor array. Reprinted with permission from [<a href="#b100-sensors-13-14214" class="html-bibr">100</a>].</p> Full article ">
<p>(<b>a</b>) The well-defined region for depositing sensing material, occupying an area of 100 × 100 μm<sup>2</sup>. The photograph shows the sensors before and after deposition. (<b>b</b>) The gas sensor array had been integrated into one chip. Reprinted with permission from [<a href="#b139-sensors-13-14214" class="html-bibr">139</a>].</p> Full article ">
<p>(<b>a</b>) The photo shows one corner of the sensor array. The element has the dimension of 220 × 220 μm<sup>2</sup> with 20 μm gap between the electrodes. (<b>b</b>) Single transducer element, the sensing material would be deposited to cover A–C. Reprint the photo in [<a href="#b151-sensors-13-14214" class="html-bibr">151</a>].</p> Full article ">
<p>(<b>a</b>) Block diagram of the wide-dynamic-range resistive interface ASIC, and (<b>b</b>) the die photo of the 4-channel interface circuit ASIC. Reprinted with permission from [<a href="#b159-sensors-13-14214" class="html-bibr">159</a>].</p> Full article ">
<p>The PWM-based interface circuit: (<b>a</b>) schematic, and (<b>b</b>) photograph of silicon prototype. Reprinted with permission from [<a href="#b164-sensors-13-14214" class="html-bibr">164</a>].</p> Full article ">
<p>The row–column interface integrated with 128 SnO<sub>2</sub>-CNT gas sensors, (<b>a</b>) block diagram, and (<b>b</b>) chip photograph. Reprinted with permission from [<a href="#b175-sensors-13-14214" class="html-bibr">175</a>].</p> Full article ">
<p>(<b>a</b>) The differential sensor conditioning circuitry of the read-out circuit and (<b>b</b>) the photo of the integration of SnO2 gas sensors and its differential preprocessing circuits in one chip. Reprinted with permission from [<a href="#b183-sensors-13-14214" class="html-bibr">183</a>].</p> Full article ">
1344 KiB  
Article
A Highly Sensitive Fiber Optic Sensor Based on Two-Core Fiber for Refractive Index Measurement
by José Rafael Guzmán-Sepúlveda, Rafael Guzmán-Cabrera, Miguel Torres-Cisneros, José Javier Sánchez-Mondragón and Daniel Alberto May-Arrioja
Sensors 2013, 13(10), 14200-14213; https://doi.org/10.3390/s131014200 - 22 Oct 2013
Cited by 33 | Viewed by 8320
Abstract
A simple and compact fiber optic sensor based on a two-core fiber is demonstrated for high-performance measurements of refractive indices (RI) of liquids. In order to demonstrate the suitability of the proposed sensor to perform high-sensitivity sensing in a variety of applications, the [...] Read more.
A simple and compact fiber optic sensor based on a two-core fiber is demonstrated for high-performance measurements of refractive indices (RI) of liquids. In order to demonstrate the suitability of the proposed sensor to perform high-sensitivity sensing in a variety of applications, the sensor has been used to measure the RI of binary liquid mixtures. Such measurements can accurately determine the salinity of salt water solutions, and detect the water content of adulterated alcoholic beverages. The largest sensitivity of the RI sensor that has been experimentally demonstrated is 3,119 nm per Refractive Index Units (RIU) for the RI range from 1.3160 to 1.3943. On the other hand, our results suggest that the sensitivity can be enhanced up to 3485.67 nm/RIU approximately for the same RI range. Full article
(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)
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<p>(<b>a</b>) Cross section of the TCF; (<b>b</b>) Spectral response of the TCF.</p> Full article ">
<p>(<b>a</b>) Schematic of the TCF after the etching process; (<b>b</b>) ERI of the central and external core for TCF diameter of 41 μm, 42 μm, and 43 μm.</p> Full article ">
<p>(<b>a</b>) ERI of the even and odd coupled modes; (<b>b</b>) Coupling coefficient as a function of the refractive index of the surrounding media for TCF diameter of 41, 42, and 43 μm.</p> Full article ">
<p>Analytical spectral response of the TCF for different surrounding media.</p> Full article ">
<p>Schematic of the experimental setup for RI measurement.</p> Full article ">
<p>Spectral response of the RI sensor for etching times (<b>a</b>) 267 min; (<b>b</b>) 280 min.</p> Full article ">
<p>(<b>a</b>) Absolute wavelength shift of the sensor response for external media ranging from water to ethylene glycol; (<b>b</b>) Sensitivity of the RI sensor as a function of the thickness of the cladding around the off-axis core.</p> Full article ">
<p>Salinity, high-concentration regime: (<b>a</b>) Absolute wavelength shift of the sensor response; (<b>b</b>) Sensitivity of the TCF sensor as a function of the remaining cladding.</p> Full article ">
<p>Salinity, low-concentration regime: (<b>a</b>) Absolute wavelength shift of the sensor response; (<b>b</b>) Sensitivity of the TCF sensor as a function of the remaining cladding.</p> Full article ">
323 KiB  
Article
Quorum Sensing Activity of Enterobacter asburiae Isolated from Lettuce Leaves
by Yin Yin Lau, Joanita Sulaiman, Jian Woon Chen, Wai-Fong Yin and Kok-Gan Chan
Sensors 2013, 13(10), 14189-14199; https://doi.org/10.3390/s131014189 - 22 Oct 2013
Cited by 44 | Viewed by 10407
Abstract
Bacterial communication or quorum sensing (QS) is achieved via sensing of QS signaling molecules consisting of oligopeptides in Gram-positive bacteria and N-acyl homoserine lactones (AHL) in most Gram-negative bacteria. In this study, Enterobacteriaceae isolates from Batavia lettuce were screened for AHL production. Enterobacter [...] Read more.
Bacterial communication or quorum sensing (QS) is achieved via sensing of QS signaling molecules consisting of oligopeptides in Gram-positive bacteria and N-acyl homoserine lactones (AHL) in most Gram-negative bacteria. In this study, Enterobacteriaceae isolates from Batavia lettuce were screened for AHL production. Enterobacter asburiae, identified by matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) was found to produce short chain AHLs. High resolution triple quadrupole liquid chromatography mass spectrometry (LC/MS) analysis of the E. asburiae spent supernatant confirmed the production of N-butanoyl homoserine lactone (C4-HSL) and N–hexanoyl homoserine lactone (C6-HSL). To the best of our knowledge, this is the first report of AHL production by E. asburiae. Full article
(This article belongs to the Section Biosensors)
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<p>Phylogenetic positions of (<b>a</b>) L1, (<b>b</b>) L2, (<b>c</b>) L3 and (<b>d</b>) L4 isolates, visualized using the standard MALDI Biotyper MSP. The different colors of the branches represent distinct clusters among the organisms in the database.</p> Full article ">
<p>Phylogenetic positions of (<b>a</b>) L1, (<b>b</b>) L2, (<b>c</b>) L3 and (<b>d</b>) L4 isolates, visualized using the standard MALDI Biotyper MSP. The different colors of the branches represent distinct clusters among the organisms in the database.</p> Full article ">
<p>Screening for violacein production using <span class="html-italic">C. violaceum</span> CV026 cross streaking. <span class="html-italic">E. carotovora</span> GS101 and <span class="html-italic">E. carotovora</span> PNP22 were used as positive and negative controls, respectively. (<b>a</b>) Observation of purple pigment formation on the biosensor streak line indicates the production of exogenous short chained AHL molecules by the <span class="html-italic">E. asburiae</span> (L1) isolate; negative purple pigmentation for L2 isolate and (<b>b</b>) both L3 and L4 isolates indicate no AHL production from these isolates.</p> Full article ">
<p>Detection of AHL production by <span class="html-italic">E. asburiae</span>. Bioluminescence measurement was done for 24 h, 37 °C growth in the presence of AHL extracted from spent culture supernatant of <span class="html-italic">E. asburiae</span>, synthetic 3-oxo-C6-HSL and acetonitrile as positive control and negative controls, respectively. Biosensor <span class="html-italic">E. coli</span> [pSB401] served as the biosensor. Data are presented as means of ± SEM values of triplicate experiments.</p> Full article ">
<p>Mass spectra of the extracted AHLs from the spent supernatant of <span class="html-italic">E. asburiae</span>. (<b>a</b>) C4-HSL (<span class="html-italic">m</span>/<span class="html-italic">z</span> 172.0000) and (<b>b</b>) C6-HSL (<span class="html-italic">m</span>/<span class="html-italic">z</span> 200.4000) (boxed).</p> Full article ">
415 KiB  
Article
Remote Driven and Read MEMS Sensors for Harsh Environments
by Aaron J. Knobloch, Faisal R. Ahmad, Dan W. Sexton and David W. Vernooy
Sensors 2013, 13(10), 14175-14188; https://doi.org/10.3390/s131014175 - 21 Oct 2013
Cited by 7 | Viewed by 6600
Abstract
The utilization of high accuracy sensors in harsh environments has been limited by the temperature constraints of the control electronics that must be co-located with the sensor. Several methods of remote interrogation for resonant sensors are presented in this paper which would allow [...] Read more.
The utilization of high accuracy sensors in harsh environments has been limited by the temperature constraints of the control electronics that must be co-located with the sensor. Several methods of remote interrogation for resonant sensors are presented in this paper which would allow these sensors to be extended to harsh environments. This work in particular demonstrates for the first time the ability to acoustically drive a silicon comb drive resonator into resonance and electromagnetically couple to the resonator to read its frequency. The performance of this system was studied as a function of standoff distance demonstrating the ability to excite and read the device from 22 cm when limited to drive powers of 30 mW. A feedback architecture was implemented that allowed the resonator to be driven into resonance from broadband noise and a standoff distance of 15 cm was demonstrated. It is emphasized that no junction-based electronic device was required to be co-located with the resonator, opening the door for the use of silicon-based, high accuracy MEMS devices in high temperature wireless applications. Full article
(This article belongs to the Special Issue Sensors for Harsh-Environment Applications)
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<p>Comb drive resonators used for these experiments had a center frequency of 27.2 kHz, linewidth of 4 Hz, and therefore, a Q of 6800 (reproduced from [<a href="#b22-sensors-13-14175" class="html-bibr">22</a>] with permission).</p> Full article ">
<p>Schematic of the setup used to drive the comb drive at its resonance of 27.224 kHz. The picture on the left shows a top view of the die with electrical representation of the comb drive. The right images show examples of the acoustic transducers used to drive the resonator.</p> Full article ">
<p>Demonstration of the ability of each of the transducers to drive the MEMS comb drive into resonance as measured by the piezoresistors on the die.</p> Full article ">
<p>Signal response levels as a function of standoff distance for acoustic drive and wired (piezoresistive) read.</p> Full article ">
<p>A packaged MEMS comb drive is shown in the center with die coupled inductive loop. The 4 cm square board is used simply as wirebond landings and a mechanical substrate to hold the coil. Ultimately, the coil would be printed directly on the board itself for highest reproducibility and lowest cost [<a href="#b22-sensors-13-14175" class="html-bibr">22</a>].</p> Full article ">
<p>A more sophisticated and efficient receiver used a portion of the driving signal as a local oscillator to downconvert the reflected signal to “baseband” at 30 kHz in order to recover the modulation. Furthermore, a circulator was used to eliminate splitting losses between the transmitted and reflected RF signals.</p> Full article ">
<p>One step beyond the architecture of <a href="#f5-sensors-13-14175" class="html-fig">Figure 5</a> is the I/Q architecture where the relative phase between local oscillator and reflected signal is accounted for. This receiver will allow for time varying displacement between the “reader” coil and the “sensor” coil that would be found, for example, in a handheld interrogation approach. Signal processing of the I and Q legs allows the receiver to track the maximum signal amplitude, assuming the variations in relative phase are “slow” relative to the signal bandwidth.</p> Full article ">
<p>A photograph of the experimental setup for the wireless architecture shown in <a href="#f9-sensors-13-14175" class="html-fig">Figure 9</a>.</p> Full article ">
<p>Schematic showing how the acoustic drive and inductive read techniques were combined.</p> Full article ">
614 KiB  
Article
Development of Anodic Titania Nanotubes for Application in High Sensitivity Amperometric Glucose and Uric Acid Biosensors
by Hsiang-Ching Lee, Li-Fan Zhang, Jyh-Ling Lin, Yuan-Lung Chin and Tai-Ping Sun
Sensors 2013, 13(10), 14161-14174; https://doi.org/10.3390/s131014161 - 21 Oct 2013
Cited by 15 | Viewed by 8073
Abstract
The purpose of this study was to develop novel nanoscale biosensors using titania nanotubes (TNTs) made by anodization. Titania nanotubes were produced on pure titanium sheets by anodization at room temperature. In this research, the electrolyte composition ethylene glycol 250 mL/NH4F [...] Read more.
The purpose of this study was to develop novel nanoscale biosensors using titania nanotubes (TNTs) made by anodization. Titania nanotubes were produced on pure titanium sheets by anodization at room temperature. In this research, the electrolyte composition ethylene glycol 250 mL/NH4F 1.5 g/DI water 20 mL was found to produce the best titania nanotubes array films for application in amperometric biosensors. The amperometric results exhibit an excellent linearity for uric acid (UA) concentrations in the range between 2 and 14 mg/dL, with 23.3 (µA·cm−2)·(mg/dL)−1 UA sensitivity, and a correlation coefficient of 0.993. The glucose biosensor presented a good linear relationship in the lower glucose concentration range between 50 and 125 mg/dL, and the corresponding sensitivity was approximately 249.6 (µA·cm−2)·(100 mg/dL)−1 glucose, with a correlation coefficient of 0.973. Full article
(This article belongs to the Special Issue Nanotube and Nanowire Sensors)
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<p>Planar view and cross section of the anodic titania nanotube array film electrode structure.</p> Full article ">
<p>The amperometry measurement system.</p> Full article ">
<p>The variation of current density in anodization process for different electrolytes.</p> Full article ">
<p>FE-SEM images of titania nanotubes grown by electrochemical anodization in (<b>a</b>) Type A electrolyte, and (<b>b</b>) Type B electrolyte.</p> Full article ">
<p>A FE-SEM cross-sectional image of titania nanotubes made by anodization grown at 60 V in an ethylene glycol solution for 1 h.</p> Full article ">
<p>The CV measurement results of the uric acid biosensor.</p> Full article ">
<p>Uric acid concentration response of the uric acid biosensor with amperometric readout circuit.</p> Full article ">
<p>The life time of the uric acid biosensors on TNTs films.</p> Full article ">
<p>The CV measurement results of the glucose biosensor.</p> Full article ">
11829 KiB  
Article
Multi Sensor Fusion Framework for Indoor-Outdoor Localization of Limited Resource Mobile Robots
by Leonardo Marín, Marina Vallés, Ángel Soriano, Ángel Valera and Pedro Albertos
Sensors 2013, 13(10), 14133-14160; https://doi.org/10.3390/s131014133 - 21 Oct 2013
Cited by 38 | Viewed by 11710
Abstract
This paper presents a sensor fusion framework that improves the localization of mobile robots with limited computational resources. It employs an event based Kalman Filter to combine the measurements of a global sensor and an inertial measurement unit (IMU) on an event based [...] Read more.
This paper presents a sensor fusion framework that improves the localization of mobile robots with limited computational resources. It employs an event based Kalman Filter to combine the measurements of a global sensor and an inertial measurement unit (IMU) on an event based schedule, using fewer resources (execution time and bandwidth) but with similar performance when compared to the traditional methods. The event is defined to reflect the necessity of the global information, when the estimation error covariance exceeds a predefined limit. The proposed experimental platforms are based on the LEGO Mindstorm NXT, and consist of a differential wheel mobile robot navigating indoors with a zenithal camera as global sensor, and an Ackermann steering mobile robot navigating outdoors with a SBG Systems GPS accessed through an IGEP board that also serves as datalogger. The IMU in both robots is built using the NXT motor encoders along with one gyroscope, one compass and two accelerometers from Hitecnic, placed according to a particle based dynamic model of the robots. The tests performed reflect the correct performance and low execution time of the proposed framework. The robustness and stability is observed during a long walk test in both indoors and outdoors environments. Full article
(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Spain 2013)
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<p>Differentially driven wheeled robot. (<b>a</b>) Kinematics; (<b>b</b>) Dynamics.</p> Full article ">
<p>Ackermann steering mobile robot. (<b>a</b>) Kinematics; (<b>b</b>) Dynamics.</p> Full article ">
<p>Differential LEGO NXT mobile robot with indoor zenithal camera sensor. (<b>a</b>) Differential Platform; (<b>b</b>) Indoor Global Sensor Setup.</p> Full article ">
<p>Ackermann LEGO NXT mobile robot with outdoor GPS sensor.</p> Full article ">
<p>Algorithms performance in the differential platform, simulation test. (<b>a</b>) Square; (<b>b</b>) Circle.</p> Full article ">
<p>Implemented test, KF onboard the differential LEGO NXT. (<b>a</b>) Square; (<b>b</b>) Circle; (<b>c</b>) Lemniscate; (<b>d</b>) Polar Rose.</p> Full article ">
<p>Relation between <span class="html-italic">R<sub>A,lim</sub></span>, IAE performance, mean percentage error and camera queries for a 3 min square trajectory test, differential robot.</p> Full article ">
<p>Reference error evolution in the PID control of the Left and Right wheels velocities <span class="html-italic">e<sub>L,R</sub></span> and threshold definition.</p> Full article ">
<p>30 min run, methods comparison, differential robot. (<b>a</b>) Odometry from encoders; (<b>b</b>) Algorithm 2 without <span class="html-italic">L<sub>GM</sub></span>; (<b>c</b>) Algorithm 2 with <span class="html-italic">L<sub>GM</sub></span> and EBGC, <span class="html-italic">R<sub>A,lim</sub></span> = 0.5; (<b>d</b>) <span class="html-italic">R<sub>A</sub></span> evolution.</p> Full article ">
214 KiB  
Article
Pandoraea sp. RB-44, A Novel Quorum Sensing Soil Bacterium
by Robson Ee Han-Jen, Yin Wai-Fong and Chan Kok-Gan
Sensors 2013, 13(10), 14121-14132; https://doi.org/10.3390/s131014121 - 18 Oct 2013
Cited by 25 | Viewed by 7434
Abstract
Proteobacteria are known to communicate via signaling molecules and this process is known as quorum sensing. The most commonly studied quorum sensing molecules are N-acylhomoserine lactones (AHLs) that consists of a homoserine lactone moiety and an N-acyl side chain with various [...] Read more.
Proteobacteria are known to communicate via signaling molecules and this process is known as quorum sensing. The most commonly studied quorum sensing molecules are N-acylhomoserine lactones (AHLs) that consists of a homoserine lactone moiety and an N-acyl side chain with various chain lengths and degrees of saturation at the C-3 position. We have isolated a bacterium, RB-44, from a site which was formally a landfill dumping ground. Using matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry analysis, this isolate was identified as a Pandoraea sp.which was then screened for AHL production using biosensors which indicated its quorum sensing properties. To identify the AHL profile of Pandoraea sp. RB-44, we used high resolution tandem mass spectrometry confirming that this isolate produced N-octanoylhomoserine lactone (C8-HSL). To the best of our knowledge, this is the first report that showed quorum sensing activity exhibited by Pandoraea sp. Our data add Pandoraea sp. to the growing number of bacteria that possess QS systems. Full article
(This article belongs to the Section Biosensors)
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<p>AHL screening of strain RB-44 with <span class="html-italic">C. violaeum</span> CV026. <span class="html-italic">E. carotovora</span> GS101 and <span class="html-italic">E. carotovora</span> PNP22 refer to the postive and negative controls, respectively.</p> Full article ">
<p>Bioluminescence assay using <span class="html-italic">E. coli</span> [pSB401] biosensor. Graph was plotted as RLU/OD<sub>495nm</sub> against time. AHL production by strain RB-44 (circle) is confirmed the increased value of RLU/OD<sub>495nm</sub> and observed over 24 h. Negative control (square) was included with extracted AHL in blank LB. Each point represents the mean and error of results from independent triplicate cultures.</p> Full article ">
<p>Score-orientated dendrogram that shows classification of <span class="html-italic">Pandoraea</span> sp. RB-44. Bacterial strain RB-44 is clustered hierarchically based on the protein mass spectra patterns.</p> Full article ">
<p>The evolutionary history was inferred using the Neighbor-Joining method [<a href="#b36-sensors-13-14121" class="html-bibr">36</a>]. The optimal tree with the sum of branch length = 0.08118917 is shown. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (1,000 replicates) are shown next to the branches [<a href="#b37-sensors-13-14121" class="html-bibr">37</a>]. The tree is drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The evolutionary distances were computed using the Maximum Composite Likelihood method [<a href="#b38-sensors-13-14121" class="html-bibr">38</a>] and are in the units of the number of base substitutions per site. The analysis involved 13 nucleotide sequences. Codon positions included were 1st+2nd+3rd+Noncoding. All positions containing gaps and missing data were eliminated. There were a total of 1388 positions in the final dataset. Evolutionary analyses were conducted in MEGA 5.0 [<a href="#b27-sensors-13-14121" class="html-bibr">27</a>].</p> Full article ">
<p>Mass spectrometry analysis of C8-HSL from an AHL standard (<b>a</b>) showed the <span class="html-italic">m/z</span> value 228.100; retention time: 4.633 min; abundance: 115,382.02 and abundance %: 100, while C8-HSL produced by <span class="html-italic">Pandoraea</span> sp. RB-44 (<b>b</b>) showed <span class="html-italic">m/z</span> value: 228.200; retention time: 4.633 min; abundance: 2,459.14 and abundance %: 100.</p> Full article ">
414 KiB  
Review
Optical Fiber-Based MR-Compatible Sensors for Medical Applications: An Overview
by Fabrizio Taffoni, Domenico Formica, Paola Saccomandi, Giovanni Di Pino and Emiliano Schena
Sensors 2013, 13(10), 14105-14120; https://doi.org/10.3390/s131014105 - 18 Oct 2013
Cited by 187 | Viewed by 15009
Abstract
During last decades, Magnetic Resonance (MR)—compatible sensors based on different techniques have been developed due to growing demand for application in medicine. There are several technological solutions to design MR-compatible sensors, among them, the one based on optical fibers presents several attractive features. [...] Read more.
During last decades, Magnetic Resonance (MR)—compatible sensors based on different techniques have been developed due to growing demand for application in medicine. There are several technological solutions to design MR-compatible sensors, among them, the one based on optical fibers presents several attractive features. The high elasticity and small size allow designing miniaturized fiber optic sensors (FOS) with metrological characteristics (e.g., accuracy, sensitivity, zero drift, and frequency response) adequate for most common medical applications; the immunity from electromagnetic interference and the absence of electrical connection to the patient make FOS suitable to be used in high electromagnetic field and intrinsically safer than conventional technologies. These two features further heightened the potential role of FOS in medicine making them especially attractive for application in MRI. This paper provides an overview of MR-compatible FOS, focusing on the sensors employed for measuring physical parameters in medicine (i.e., temperature, force, torque, strain, and position). The working principles of the most promising FOS are reviewed in terms of their relevant advantages and disadvantages, together with their applications in medicine. Full article
(This article belongs to the Special Issue Magnetic Resonance Sensors)
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<p>(<b>A</b>) FBG used to monitor temperature increase during hyperthermia. Both sensors and mask used to introduce them within the tissue are MR-compatible [<a href="#b23-sensors-13-14105" class="html-bibr">23</a>]; (<b>B</b>) Picture of the prototype used in [<a href="#b32-sensors-13-14105" class="html-bibr">32</a>] for respiratory and heart rate recording; (<b>C</b>) Prototype design with three embedded fiber Bragg grating sensors to measure needle deflection during MRI-guided interventions [<a href="#b37-sensors-13-14105" class="html-bibr">37</a>].</p> Full article ">
<p>(<b>A</b>) FBG used to monitor temperature increase during hyperthermia. Both sensors and mask used to introduce them within the tissue are MR-compatible [<a href="#b23-sensors-13-14105" class="html-bibr">23</a>]; (<b>B</b>) Picture of the prototype used in [<a href="#b32-sensors-13-14105" class="html-bibr">32</a>] for respiratory and heart rate recording; (<b>C</b>) Prototype design with three embedded fiber Bragg grating sensors to measure needle deflection during MRI-guided interventions [<a href="#b37-sensors-13-14105" class="html-bibr">37</a>].</p> Full article ">
<p>Sensing element of FOS based on intensity reflective principle: the output light is modulated by pressure or other physical parameters which cause a mirror displacement [<a href="#b4-sensors-13-14105" class="html-bibr">4</a>].</p> Full article ">
<p>Design of an intensity-modulated FOS manufactured with two fibers. The intensity of the coupled radiation between the two fibers decreases with their distance d [<a href="#b4-sensors-13-14105" class="html-bibr">4</a>].</p> Full article ">
<p>Fiber optic displacement sensors based on macrobending. The radiation intensity is modulated by the displacement of a moving part: when it does not bend the fiber (<b>a</b>); the light intensity is max0imum; on the contrary, the light intensity decreases with the bending (<b>b</b>) [<a href="#b4-sensors-13-14105" class="html-bibr">4</a>].</p> Full article ">
<p>(<b>A</b>,<b>B</b>) Different configurations of intensity-based FOS tested for medical applications [<a href="#b46-sensors-13-14105" class="html-bibr">46</a>,<a href="#b47-sensors-13-14105" class="html-bibr">47</a>]; (<b>C</b>) FOS based on macrobending for respiratory monitoring [<a href="#b27-sensors-13-14105" class="html-bibr">27</a>,<a href="#b31-sensors-13-14105" class="html-bibr">31</a>]; (<b>D</b>) FOS for monitoring needle insertion force using Fabry Perot interferometry [<a href="#b54-sensors-13-14105" class="html-bibr">54</a>].</p> Full article ">
464 KiB  
Article
A Wearable Inertial Measurement Unit for Long-Term Monitoring in the Dependency Care Area
by Daniel Rodríguez-Martín, Carlos Pérez-López, Albert Samà, Joan Cabestany and Andreu Català
Sensors 2013, 13(10), 14079-14104; https://doi.org/10.3390/s131014079 - 18 Oct 2013
Cited by 64 | Viewed by 15748
Abstract
Human movement analysis is a field of wide interest since it enables the assessment of a large variety of variables related to quality of life. Human movement can be accurately evaluated through Inertial Measurement Units (IMU), which are wearable and comfortable devices with [...] Read more.
Human movement analysis is a field of wide interest since it enables the assessment of a large variety of variables related to quality of life. Human movement can be accurately evaluated through Inertial Measurement Units (IMU), which are wearable and comfortable devices with long battery life. The IMU’s movement signals might be, on the one hand, stored in a digital support, in which an analysis is performed a posteriori. On the other hand, the signal analysis might take place in the same IMU at the same time as the signal acquisition through online classifiers. The new sensor system presented in this paper is designed for both collecting movement signals and analyzing them in real-time. This system is a flexible platform useful for collecting data via a triaxial accelerometer, a gyroscope and a magnetometer, with the possibility to incorporate other information sources in real-time. A µSD card can store all inertial data and a Bluetooth module is able to send information to other external devices and receive data from other sources. The system presented is being used in the real-time detection and analysis of Parkinson’s disease symptoms, in gait analysis, and in a fall detection system. Full article
(This article belongs to the Collection Sensors for Globalized Healthy Living and Wellbeing)
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<p><span class="html-italic">9</span> × <span class="html-italic">2</span> sensor and its specially design neoprene belt.</p> Full article ">
<p>General block diagram.</p> Full article ">
<p>Accelerometer calibration positions.</p> Full article ">
<p>Power management block diagram.</p> Full article ">
<p>Firmware's processes interaction.</p> Full article ">
<p>Firmware sequence.</p> Full article ">
<p>Classical classification method.</p> Full article ">
544 KiB  
Article
An Electronic Tongue Designed to Detect Ammonium Nitrate in Aqueous Solutions
by Inmaculada Campos, Lluis Pascual, Juan Soto, Luis Gil-Sánchez and Ramón Martínez-Máez
Sensors 2013, 13(10), 14064-14078; https://doi.org/10.3390/s131014064 - 18 Oct 2013
Cited by 15 | Viewed by 6410
Abstract
An electronic tongue has been developed to monitor the presence of ammonium nitrate in water. It is based on pulse voltammetry and consists of an array of eight working electrodes (Au; Pt; Rh; Ir; Cu; Co; Ag and Ni) encapsulated in a stainless [...] Read more.
An electronic tongue has been developed to monitor the presence of ammonium nitrate in water. It is based on pulse voltammetry and consists of an array of eight working electrodes (Au; Pt; Rh; Ir; Cu; Co; Ag and Ni) encapsulated in a stainless steel cylinder. In a first step the electrochemical response of the different electrodes was studied in the presence of ammonium nitrate in water in order to further design the wave form used in the voltammetric tongue. The response of the electronic tongue was then tested in the presence of a set of 15 common inorganic salts; i.e.; NH4NO3; MgSO4; NH4Cl; NaCl; Na2CO3; (NH4)2SO4; MgCl2; Na3PO4; K2SO4; K2CO3; CaCl2; NaH2PO4; KCl; NaNO3; K2HPO4. A PCA plot showed a fairly good discrimination between ammonium nitrate and the remaining salts studied. In addition Fuzzy Art map analyses determined that the best classification was obtained using the Pt; Co; Cu and Ni electrodes. Moreover; PLS regression allowed the creation of a model to correlate the voltammetric response of the electrodes with concentrations of ammonium nitrate in the presence of potential interferents such as ammonium chloride and sodium nitrate. Full article
(This article belongs to the Section Chemical Sensors)
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<p>The electronic tongue formed by non-noble electrodes.</p> Full article ">
<p>Cyclic voltammograms of the solvent (pH 7 buffered with 0.01 mol·L<sup>−1</sup> phosphate buffer (solid line) and of 0.001 mol·L<sup>−1</sup> NH<sub>4</sub>NO<sub>3</sub> solutions (dashed line) measured at 100 mV·s<sup>−1</sup> using silver (<b>a</b>), copper (<b>b</b>), platinum (<b>c</b>), cobalt (<b>d</b>) and nickel (<b>e</b>).</p> Full article ">
<p>Cyclic voltammograms of the solvent (pH 7 buffered with 0.01 mol·L<sup>−1</sup> phosphate buffer (solid line) and of 0.001 mol·L<sup>−1</sup> NH<sub>4</sub>NO<sub>3</sub> solutions (dashed line) measured at 100 mV·s<sup>−1</sup> using silver (<b>a</b>), copper (<b>b</b>), platinum (<b>c</b>), cobalt (<b>d</b>) and nickel (<b>e</b>).</p> Full article ">
<p>(<b>a</b>) The applied potentials, and (<b>b</b>) the current response of waveform applied to a sample that contains NH<sub>4</sub>NO<sub>3</sub> (C = 1 × 10<sup>−2</sup> mol·L<sup>−1</sup>) when a Ni electrode is used.</p> Full article ">
<p>3 PCA score plot of NH<sub>4</sub>NO<sub>3</sub> (dots) and the remaining 14 salts (triangles) using all the electrodes.</p> Full article ">
<p>Classification of measures by Artificial Neural Networks accord the fifteen salts.</p> Full article ">
<p>Plot score of prediction model of NH<sub>4</sub>NO<sub>3</sub> (predicted <span class="html-italic">versus</span> real concentration) and linear fitting in water (pH 7, phosphate buffer 10<sup>−2</sup> mol·L<sup>−1</sup>) employing the response observed from the Pt, Cu, Co and Ni electrodes using a set of different mixtures containing NH<sub>4</sub>NO<sub>3</sub>, NaCl and NH<sub>4</sub>Cl salts.</p> Full article ">
409 KiB  
Communication
Highly Sensitive Refractive Index Sensor Based on Adiabatically Tapered Microfiber Long Period Gratings
by Wen Bin Ji, Swee Chuan Tjin, Bo Lin and Choong Leng Ng
Sensors 2013, 13(10), 14055-14063; https://doi.org/10.3390/s131014055 - 17 Oct 2013
Cited by 33 | Viewed by 7628
Abstract
We demonstrate a refractive index sensor based on a long period grating (LPG) inscribed in a special photosensitive microfiber with double-clad profile. The fiber is tapered gradually enough to ensure the adiabaticity of the fiber taper. In other words, the resulting insertion loss [...] Read more.
We demonstrate a refractive index sensor based on a long period grating (LPG) inscribed in a special photosensitive microfiber with double-clad profile. The fiber is tapered gradually enough to ensure the adiabaticity of the fiber taper. In other words, the resulting insertion loss is sufficiently small. The boron and germanium co-doped inner cladding makes it suitable for inscribing gratings into its tapered form. The manner of wavelength shift for refractive indices (RIs) differs from conventional LPG, and the refractive index detection limit is 1.67 × 10−5. Full article
(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)
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<p>Schematic view of taper profile.</p> Full article ">
<p>Transmission spectra of adiabatically tapered fiber (taper diameter: 60 μm).</p> Full article ">
<p>Schematic diagram of the experimental set-up.</p> Full article ">
<p>Refractive index profile of the W type double-clad fiber.</p> Full article ">
<p>Wavelength response for different external refractive index (D = 60 μm).</p> Full article ">
<p>A broader spectrum for different external refractive index (D = 55 μm).</p> Full article ">
<p>RI sensitivity characterization for both sensors (D = 60 μm and D = 55 μm).</p> Full article ">
1285 KiB  
Article
Acoustic Emission Source Location Using a Distributed Feedback Fiber Laser Rosette
by Wenzhu Huang, Wentao Zhang and Fang Li
Sensors 2013, 13(10), 14041-14054; https://doi.org/10.3390/s131014041 - 17 Oct 2013
Cited by 36 | Viewed by 7176
Abstract
This paper proposes an approach for acoustic emission (AE) source localization in a large marble stone using distributed feedback (DFB) fiber lasers. The aim of this study is to detect damage in structures such as those found in civil applications. The directional sensitivity [...] Read more.
This paper proposes an approach for acoustic emission (AE) source localization in a large marble stone using distributed feedback (DFB) fiber lasers. The aim of this study is to detect damage in structures such as those found in civil applications. The directional sensitivity of DFB fiber laser is investigated by calculating location coefficient using a method of digital signal analysis. In this, autocorrelation is used to extract the location coefficient from the periodic AE signal and wavelet packet energy is calculated to get the location coefficient of a burst AE source. Normalization is processed to eliminate the influence of distance and intensity of AE source. Then a new location algorithm based on the location coefficient is presented and tested to determine the location of AE source using a Delta (Δ) DFB fiber laser rosette configuration. The advantage of the proposed algorithm over the traditional methods based on fiber Bragg Grating (FBG) include the capability of: having higher strain resolution for AE detection and taking into account two different types of AE source for location. Full article
(This article belongs to the Section Physical Sensors)
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<p>The demodulation diagram of DFB fiber lasers.</p> Full article ">
<p>Noise level of DFB fiber laser sensing system.</p> Full article ">
<p>Investigation of the AE directivity of DFB fiber laser.</p> Full article ">
<p>An autocorrelation approach is used to extract the periodic AE signal. (<b>a</b>) The amplitude of the signal detected by the DFB fiber laser and (<b>b</b>) the sine AE signal got by the autocorrelation method.</p> Full article ">
<p>The relationship between wavelength drift and the angle of a periodic AE source.</p> Full article ">
<p>The relationship between percentage of wavelet packet energy of the response of DFB fiber laser and the angle of an impact response.0°(a), 30°(a), 45°(a), 60°(a) and 90°(a) represent the time-domain response of DFB fiber laser respectively. 0°(b), 30°(b), 45°(b), 60°(b) and 90°(b) represent the frequency-domain response of DFB fiber laser respectively.</p> Full article ">
<p>The wavelet packet energy percentage at different angle.</p> Full article ">
<p>The relationship between percentage of wavelet packet energy and the angle of a burst AE source.</p> Full article ">
<p>DFB fiber laser rosette.</p> Full article ">
727 KiB  
Article
Simultaneous Determination of Dopamine, Serotonin and Ascorbic Acid at a Glassy Carbon Electrode Modified with Carbon-Spheres
by Jianqing Zhou, Meili Sheng, Xueyue Jiang, Guozhi Wu and Feng Gao
Sensors 2013, 13(10), 14029-14040; https://doi.org/10.3390/s131014029 - 16 Oct 2013
Cited by 62 | Viewed by 7901
Abstract
A novel glassy carbon electrode (GCE) modified with carbon-spheres has been fabricated through a simple casting procedure. The modified GCE displays high selectivity and excellent electrochemical catalytic activities towards dopamine (DA), serotonin (5-HT), and ascorbic acid (AA). In the co-existence system, the peak [...] Read more.
A novel glassy carbon electrode (GCE) modified with carbon-spheres has been fabricated through a simple casting procedure. The modified GCE displays high selectivity and excellent electrochemical catalytic activities towards dopamine (DA), serotonin (5-HT), and ascorbic acid (AA). In the co-existence system, the peak separations between AA and DA, DA and 5-HT, and AA and 5-HT are large up to 230, 180, and 410 mV, respectively. Differential pulse voltammetry (DPV) has been employed to simultaneously detect DA, 5-HT, and AA, and the linear calibration curves for DA, 5-HT, and AA are obtained in the range of 20.0–150.0 μM, 40.0–750.0 μM and 300.0–2,000.0 μM with detection limits (S/N = 3) of 2.0 μM, 0.7 μM and 0.6 μM, respectively. The proposed electrode has been applied to detect DA, 5-HT, and AA in real samples using standard addition method with satisfactory results. Full article
(This article belongs to the Section Chemical Sensors)
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Full article ">
Full article ">
Full article ">
<p>SEM image of the synthesized carbon spheres.</p> Full article ">
<p>Cyclic voltammograms obtained at CS/GCE (<b>A</b>), and bare GCE (<b>B</b>) in the presence(solid line, curve b) or absence(dotted line, curve a) of 1 mM of AA in the phosphate buffer solution (pH 7.0) with a scan rate of 100 mV·s<sup>−1</sup>.</p> Full article ">
<p>(<b>A</b>) CVs obtained at CS/GCE of 1 mM of AA in the phosphate buffer solution (pH 7.0) at different scan rates (from inner to outer): 10, 20, 50, 100, 200, 300, 400 mV·s<sup>−1</sup>; (<b>B</b>) The plot of currents against the square roots of scan rates.</p> Full article ">
<p>CVs obtained at CS/GCE (<b>A</b>), and bare GCE (<b>B</b>) in the presence (solid line) or absence (dotted line) of 1 mM of DA in the phosphate buffer solution (pH 7.0) with a scan rate of 100 m·Vs<sup>−1</sup>.</p> Full article ">
<p>CVs obtained at CS/GCE (<b>A</b>), and bare GCE (<b>B</b>) electrode in the presence(solid line) or absence(dotted line) of 1.5 mM of 5-HT in the phosphate buffer solution (pH 7.0) with a scan rate of 100 m·Vs<sup>−1</sup>.</p> Full article ">
<p>Cyclic voltammetry recordings of 2 mM AA, 0.5 mM DA and 0.5 mM HT at CS/GCE (<b>A</b>) and bare GCE (<b>B</b>) in 0.1 M phosphate buffer solution (pH 7.0) in the presence (solid line) and absence (dotted line) of AA, DA and HT with a scan rate of 100 mV·s<sup>−1</sup>; (<b>C</b>) Differential pulse voltammograms of the same mixture at CS/GCE.</p> Full article ">
<p>(<b>A</b>) DPVs of various concentrations of DA in 1 mM AA and 40 μM 5-HT solution (from a to g: 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.15 mM); (<b>B</b>) DPVs of various concentrations of HT in 1 mM AA and 12 μM DA solution (from a to h: 0, 0.04, 0.35, 0.5, 0.58, 0.6, 0.7, 0.75 mM); (<b>C</b>) DPVs of various concentrations of AA in 12 μM DA and 40 μM 5-HT solution (from a to h: 0, 0.3, 0.5, 0.7, 1.0, 1.3,1.5, 2.0 mM); (<b>D</b>)–(<b>F</b>) are the linear plots of currents against concentrations of DA, 5-HT, and AA, respectively.</p> Full article ">
763 KiB  
Article
Dynamic Task Allocation in Multi-Hop Multimedia Wireless Sensor Networks with Low Mobility
by Yichao Jin, Serdar Vural, Alexander Gluhak and Klaus Moessner
Sensors 2013, 13(10), 13998-14028; https://doi.org/10.3390/s131013998 - 16 Oct 2013
Cited by 16 | Viewed by 6745
Abstract
This paper presents a task allocation-oriented framework to enable efficient in-network processing and cost-effective multi-hop resource sharing for dynamic multi-hop multimedia wireless sensor networks with low node mobility, e.g., pedestrian speeds. The proposed system incorporates a fast task reallocation algorithm to quickly recover [...] Read more.
This paper presents a task allocation-oriented framework to enable efficient in-network processing and cost-effective multi-hop resource sharing for dynamic multi-hop multimedia wireless sensor networks with low node mobility, e.g., pedestrian speeds. The proposed system incorporates a fast task reallocation algorithm to quickly recover from possible network service disruptions, such as node or link failures. An evolutional self-learning mechanism based on a genetic algorithm continuously adapts the system parameters in order to meet the desired application delay requirements, while also achieving a sufficiently long network lifetime. Since the algorithm runtime incurs considerable time delay while updating task assignments, we introduce an adaptive window size to limit the delay periods and ensure an up-to-date solution based on node mobility patterns and device processing capabilities. To the best of our knowledge, this is the first study that yields multi-objective task allocation in a mobile multi-hop wireless environment under dynamic conditions. Simulations are performed in various settings, and the results show considerable performance improvement in extending network lifetime compared to heuristic mechanisms. Furthermore, the proposed framework provides noticeable reduction in the frequency of missing application deadlines. Full article
(This article belongs to the Section Sensor Networks)
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<p>Design objectives.</p> Full article ">
<p>An example of the multi-hop extension process.</p> Full article ">
<p>The dynamic task allocation framework.</p> Full article ">
<p>Minimum Hop Count candidate selection.</p> Full article ">
<p>The self-learning process (SLP).</p> Full article ">
<p>Task Reallocation Decision Maker (TRDM) function flowchart.</p> Full article ">
<p>The SLP genetic algorithm (GA).</p> Full article ">
<p>Example of crossover.</p> Full article ">
<p>Impact of <span class="html-italic">p<sub>move</sub></span> and <span class="html-italic">ν<sub>move</sub></span>. (<b>a</b>) Network link-change events; (<b>b</b>) Deadline miss ratio.</p> Full article ">
1419 KiB  
Article
Accelerometer-Based Event Detector for Low-Power Applications
by József Smidla and Gyula Simon
Sensors 2013, 13(10), 13978-13997; https://doi.org/10.3390/s131013978 - 16 Oct 2013
Cited by 7 | Viewed by 6911
Abstract
In this paper, an adaptive, autocovariance-based event detection algorithm is proposed, which can be used with micro-electro-mechanical systems (MEMS) accelerometer sensors to build inexpensive and power efficient event detectors. The algorithm works well with low signal-to-noise ratio input signals, and its computational complexity [...] Read more.
In this paper, an adaptive, autocovariance-based event detection algorithm is proposed, which can be used with micro-electro-mechanical systems (MEMS) accelerometer sensors to build inexpensive and power efficient event detectors. The algorithm works well with low signal-to-noise ratio input signals, and its computational complexity is very low, allowing its utilization on inexpensive low-end embedded sensor devices. The proposed algorithm decreases its energy consumption by lowering its duty cycle, as much as the event to be detected allows it. The performance of the algorithm is tested and compared to the conventional filter-based approach. The comparison was performed in an application where illegal entering of vehicles into restricted areas was detected. Full article
(This article belongs to the Special Issue Modeling, Testing and Reliability Issues in MEMS Engineering 2013)
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<p>Flow chart of the algorithm in [<a href="#b6-sensors-13-13978" class="html-bibr">6</a>].</p> Full article ">
<p>Operation of the Block-wise Autocovariance-based Algorithm (BAC) algorithm. Arrows represent acceleration data. Rectangles show segments where sampling and processing is performed; red and green rectangles represent segments where the computed autocovariance is higher and lower than the threshold, respectively.</p> Full article ">
<p>Operation of the Block-wise Autocovariance-based Algorithm With Validation (BACV). Narrow rectangles of width <span class="html-italic">τ</span><sub>1</sub> represent segments where preliminary sampling and processing is performed; yellow and green rectangles represent segments where the computed autocovariance is higher and lower than the preliminary threshold <span class="html-italic">ϑ</span>, respectively Wider rectangles of width <span class="html-italic">τ</span><sub>2</sub> represent validation phases, the output of which is compared to threshold Θ to produce the detection signal.</p> Full article ">
<p>The operation of the Adaptive BACV Algorithm (ABACV). Thresholds <span class="html-italic">ϑ</span> and Θ are changed to follow changes over noise properties.</p> Full article ">
<p>The sensor node.</p> Full article ">
<p>The derivation of the robustness parameter, <span class="html-italic">r</span>. The sensor is switched on with period <span class="html-italic">T</span> for time <span class="html-italic">τ</span><sub>1</sub></p> Full article ">
<p>Robustness test of (<b>a</b>) BAC, (<b>b</b>) BACV, (<b>c</b>) ABACV algorithms, (<b>d</b>) a bandpass FIR-based algorithm (<b>e</b>) and an IIR-based algorithm.</p> Full article ">
<p>Error rates of BAC, for (<b>a</b>) different <span class="html-italic">n</span><sub>1</sub> and (<b>b</b>) <span class="html-italic">N</span> values. Thin line: false negative; thick line: false positive.</p> Full article ">
<p>Error rates of BACV, for different (<b>a</b>) <span class="html-italic">n</span><sub>1</sub> and (<b>b</b>) <span class="html-italic">N</span> values.</p> Full article ">
314 KiB  
Article
Identification of Volatiles Produced by Cladosporium cladosporioides CL-1, a Fungal Biocontrol Agent That Promotes Plant Growth
by Diby Paul and Kyung Seok Park
Sensors 2013, 13(10), 13969-13977; https://doi.org/10.3390/s131013969 - 16 Oct 2013
Cited by 66 | Viewed by 10710
Abstract
Certain microbial Volatile Organic Compounds (VOCs) have been reported to enhance the growth and development of plants. The biocontrol fungi, Cladosporium cladosporioides CL-1 significantly improved the growth of tobacco seedlings in vitro when they were co-cultivated without physical contact. SPME Quadrupole GC/MS/MS revealed [...] Read more.
Certain microbial Volatile Organic Compounds (VOCs) have been reported to enhance the growth and development of plants. The biocontrol fungi, Cladosporium cladosporioides CL-1 significantly improved the growth of tobacco seedlings in vitro when they were co-cultivated without physical contact. SPME Quadrupole GC/MS/MS revealed that CL-1 emited the volatiles α-pinene, (−)-trans-caryophyllene, tetrahydro-2,2,5,5-tetramethylfuran, dehydroaromadendrene, and (+)-sativene. Potential roles of these volatiles in plant growth and development are discussed. Even though there were several fungal VOCs reported in the past that could influence plant growth, their exact mechanisms of action are not fully known. Fungal VOC-mediated plant growth promotion requires in-depth study in order for this technology to be used in large scale for crops, especially those grown under greenhouse conditions. Full article
(This article belongs to the Special Issue Sensing of Scent, Fragrance, Smell, and Odor Emissions from Biota Sources)
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<p>Tobacco growth promotion by volatiles produced by <span class="html-italic">Cladosporium cladosporioides</span> CL-1. (<b>A</b>) The I plate was used to co-culture tobacco seedlings and <span class="html-italic">C. cladosporioides</span> culture without physical contact; (<b>B</b>) 24-well culture plates were used to test the growth promoting effect of volatiles of <span class="html-italic">C. cladosporioides</span>.</p> Full article ">
<p>Tobacco seedling growth promotion by volatiles of CL-1. Volatiles of CL-1 significantly enhanced growth of tobacco seedlings in terms of fresh weight.</p> Full article ">
<p>SPME GC-MS spectrum of volatiles of CL-1. (Volatiles present at undetectable levels/low quantities were not considered in this study).</p> Full article ">
<p>Volatiles from CL-1 by SPME/Quadrupole GC/MS/MS.</p> Full article ">
486 KiB  
Article
Real-Time Label-Free Surface Plasmon Resonance Biosensing with Gold Nanohole Arrays Fabricated by Nanoimprint Lithography
by Josu Martinez-Perdiguero, Aritz Retolaza, Deitze Otaduy, Aritz Juarros and Santos Merino
Sensors 2013, 13(10), 13960-13968; https://doi.org/10.3390/s131013960 - 16 Oct 2013
Cited by 28 | Viewed by 8354
Abstract
In this work we present a surface plasmon resonance sensor based on enhanced optical transmission through sub-wavelength nanohole arrays. This technique is extremely sensitive to changes in the refractive index of the surrounding medium which result in a modulation of the transmitted light. [...] Read more.
In this work we present a surface plasmon resonance sensor based on enhanced optical transmission through sub-wavelength nanohole arrays. This technique is extremely sensitive to changes in the refractive index of the surrounding medium which result in a modulation of the transmitted light. The periodic gold nanohole array sensors were fabricated by high-throughput thermal nanoimprint lithography. Square periodic arrays with sub-wavelength hole diameters were obtained and characterized. Using solutions with known refractive index, the array sensitivities were obtained. Finally, protein absorption was monitored in real-time demonstrating the label-free biosensing capabilities of the fabricated devices. Full article
(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Spain 2013)
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<p>Schematic cross-section of the gold nanohole array fabrication process with thermal-NIL.</p> Full article ">
<p>(<b>a</b>) and (<b>b</b>) SEM images of a master mold with nanohole square arrays (hole diameter 250 nm, periodicity 450 nm, depth 130 nm).</p> Full article ">
<p>(<b>a</b>) and (<b>b</b>) SEM images of a gold nanohole array fabricated with NIL (hole diameter 185 nm, periodicity 450 nm, Ti/Au layer thickness 5/50 nm).</p> Full article ">
<p>Scheme of the optical setup to measure the transmission spectra through the fabricated nanohole arrays.</p> Full article ">
<p>Modulated optical transmission through a gold nanohole array (that of <a href="#f3-sensors-13-13960" class="html-fig">Figure 3</a>.) in air. The resonance peaks are the result of plasmon mediated transmission.</p> Full article ">
<p>(<b>a</b>) Transmission spectra obtained for four sucrose solutions at different concentrations (see inset). A clear red shift with increasing concentration (or refractive index) can be observed; (<b>b</b>) Linear change of the peak wavelength position <span class="html-italic">vs.</span> solution refractive index. From this plot, a 126 nm/RIU sensitivity was obtained.</p> Full article ">
<p>(<b>a</b>) Transmission spectra through a gold nanohole array (that of <a href="#f3-sensors-13-13960" class="html-fig">Figure 3</a>) in contact with PBS buffer (crosses) and after 1 h incubation of a solution of 50 μg/mL BSA solution in PBS buffer (circles). The peak wavelengths <span class="html-italic">λ<sub>SP</sub></span> are 673.1 nm and 675.9 nm respectively (<b>b</b>) Real-time label-free monitoring of the BSA absorption on the gold surface. The transmission intensity was monitored at a wavelength situated in the high-slope region of the peak (<span class="html-italic">λ</span> = 645 nm, see vertical line in (a)) for maximum sensitivity and linearity. The injection of BSA protein (arrow at <span class="html-italic">t</span> = 150 s) results in a change of the transmitted spectra which can be measured as an intensity change at a given wavelength. It can be observed that at after 800 s the surface was saturated with BSA and no further absorption took place. At t = 950 (see arrow) the buffer was switched back to PBS and no signal decrease was appreciable, proving the stability of the formed BSA layer.</p> Full article ">
216 KiB  
Article
Biodiversity Assessment Using Hierarchical Agglomerative Clustering and Spectral Unmixing over Hyperspectral Images
by Ollantay Medina, Vidya Manian and J. Danilo Chinea
Sensors 2013, 13(10), 13949-13959; https://doi.org/10.3390/s131013949 - 15 Oct 2013
Cited by 15 | Viewed by 5573
Abstract
Hyperspectral images represent an important source of information to assess ecosystem biodiversity. In particular, plant species richness is a primary indicator of biodiversity. This paper uses spectral variance to predict vegetation richness, known as Spectral Variation Hypothesis. Hierarchical agglomerative clustering is our primary [...] Read more.
Hyperspectral images represent an important source of information to assess ecosystem biodiversity. In particular, plant species richness is a primary indicator of biodiversity. This paper uses spectral variance to predict vegetation richness, known as Spectral Variation Hypothesis. Hierarchical agglomerative clustering is our primary tool to retrieve clusters whose Shannon entropy should reflect species richness on a given zone. However, in a high spectral mixing scenario, an additional unmixing step, just before entropy computation, is required; cluster centroids are enough for the unmixing process. Entropies computed using the proposed method correlate well with the ones calculated directly from synthetic and field data. Full article
(This article belongs to the Section Remote Sensors)
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<p>Determining number of clusters using critical point “<span class="html-italic">c</span>*”.</p> Full article ">
<p>(<b>Left</b>) A portion of the Guanica forest, size 200 × 200 pixels; (<b>Right</b>) Computed Shannon entropies using the proposed method, zone size 10 × 10 pixels. Higher entropy means more proportional spectral heterogeneity.</p> Full article ">
<p>Three instances of “elbow” curves produced during HAC process using real hyperspectral data. Corresponding critical points <span class="html-italic">c</span>* in: “o” = (272, 2883) produced 16 clusters, “+” = (300, 2970) produced 14 clusters and “×” = (306, 2079) produced 14 clusters.</p> Full article ">
<p>(<b>Left</b>) A set of points with low spectral mixing, most of the points are close to the endmembers; (<b>Right</b>) A set of points with high spectral mixing, most of the points are not close to the endmembers. In both cases, colors represent how the clustering process group the points.</p> Full article ">
315 KiB  
Review
Recent Advances in Optical Biosensors for Environmental Monitoring and Early Warning
by Feng Long, Anna Zhu and Hanchang Shi
Sensors 2013, 13(10), 13928-13948; https://doi.org/10.3390/s131013928 - 15 Oct 2013
Cited by 262 | Viewed by 23587
Abstract
The growing number of pollutants requires the development of innovative analytical devices that are precise, sensitive, specific, rapid, and easy-to-use to meet the increasing demand for legislative actions on environmental pollution control and early warning. Optical biosensors, as a powerful alternative to conventional [...] Read more.
The growing number of pollutants requires the development of innovative analytical devices that are precise, sensitive, specific, rapid, and easy-to-use to meet the increasing demand for legislative actions on environmental pollution control and early warning. Optical biosensors, as a powerful alternative to conventional analytical techniques, enable the highly sensitive, real-time, and high-frequency monitoring of pollutants without extensive sample preparation. This article reviews important advances in functional biorecognition materials (e.g., enzymes, aptamers, DNAzymes, antibodies and whole cells) that facilitate the increasing application of optical biosensors. This work further examines the significant improvements in optical biosensor instrumentation and their environmental applications. Innovative developments of optical biosensors for environmental pollution control and early warning are also discussed. Full article
(This article belongs to the Section Biosensors)
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<p>Schematic of an optical biosensor.</p> Full article ">
<p>Schematic set-up of the portable evanescent wave optical fiber biosensor (EWAB): (<b>a</b>) principle scheme of the portable optical fiber biosensor and (<b>b</b>) the portable platform. Reprinted with permission from [<a href="#b82-sensors-13-13928" class="html-bibr">82</a>].</p> Full article ">
493 KiB  
Article
An InN/InGaN Quantum Dot Electrochemical Biosensor for Clinical Diagnosis
by Naveed Ul Hassan Alvi, Victor J. Gómez, Paul E.D. Soto Rodriguez, Praveen Kumar, Saima Zaman, Magnus Willander and Richard Nötzel
Sensors 2013, 13(10), 13917-13927; https://doi.org/10.3390/s131013917 - 15 Oct 2013
Cited by 28 | Viewed by 8422
Abstract
Low-dimensional InN/InGaN quantum dots (QDs) are demonstrated for realizing highly sensitive and efficient potentiometric biosensors owing to their unique electronic properties. The InN QDs are biochemically functionalized. The fabricated biosensor exhibits high sensitivity of 97 mV/decade with fast output response within two seconds [...] Read more.
Low-dimensional InN/InGaN quantum dots (QDs) are demonstrated for realizing highly sensitive and efficient potentiometric biosensors owing to their unique electronic properties. The InN QDs are biochemically functionalized. The fabricated biosensor exhibits high sensitivity of 97 mV/decade with fast output response within two seconds for the detection of cholesterol in the logarithmic concentration range of 1 × 10−6 M to 1 × 10−3 M. The selectivity and reusability of the biosensor are excellent and it shows negligible response to common interferents such as uric acid and ascorbic acid. We also compare the biosensing properties of the InN QDs with those of an InN thin film having the same surface properties, i.e., high density of surface donor states, but different morphology and electronic properties. The sensitivity of the InN QDs-based biosensor is twice that of the InN thin film-based biosensor, the EMF is three times larger, and the response time is five times shorter. A bare InGaN layer does not produce a stable response. Hence, the superior biosensing properties of the InN QDs are governed by their unique surface properties together with the zero-dimensional electronic properties. Altogether, the InN QDs-based biosensor reveals great potential for clinical diagnosis applications. Full article
(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Spain 2013)
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<p>(<b>a</b>) AFM image of the InN QDs grown on an InGaN layer. Inset: AFM image with enlarged magnification. Some InN QDs are encircled for clarification; (<b>b</b>) AFM image of the InN thin film grown on an InGaN layer; (<b>c</b>) AFM image of the bare InGaN layer; (<b>d</b>–<b>f</b>) I-V curves measured with two Al ohmic contacts deposited on the InN QDs, InN thin film, and InGaN layer, respectively.</p> Full article ">
<p>(<b>a</b>) Schematic diagram of the fabrication process of the biosensor; (<b>b</b>) Schematic illustration of the sensing setup using the working electrode comprised of the InN QDs coated with ChOx and a Ag/AgCl reference electrode; (<b>c</b>) Schematic illustration of the working electrode comprised of the InN QDs coated with ChOx along with the possible electrochemical reaction near the electrode.</p> Full article ">
<p>(<b>a</b>,<b>b</b>) EMF as a function of the logarithmic cholesterol concentration of the InN QDs and InN thin film based biosensors, respectively. Exp # 1–3 denote three different experiments.</p> Full article ">
<p>(<b>a</b>) EMF as a function of time of the InN QDs based biosensor for 500 μM cholesterol concentration; (<b>b</b>) EMF as a function of time of the InN thin film based biosensor for 500 μM cholesterol concentration; (<b>c</b>) EMF as a function of time of the InGaN layer based biosensor for 500 μM cholesterol concentration; (<b>d</b>) EMF as a function of time when adding 50 μM uric acid (UA) and ascorbic acid (AA) to the 500 μM cholesterol solution.</p> Full article ">
<p>(<b>a</b>) Repeated experiments for ten consecutive days for 500 μM cholesterol concentration using same InN QDs-based biosensor; (<b>b</b>) EMF as a function of temperature of the InN QDs-based biosensor for 500 μM cholesterol concentration.</p> Full article ">
3922 KiB  
Article
Omnidirectional Structured Light in a Flexible Configuration
by Carmen Paniagua, Luis Puig and José J. Guerrero
Sensors 2013, 13(10), 13903-13916; https://doi.org/10.3390/s131013903 - 14 Oct 2013
Cited by 15 | Viewed by 6360
Abstract
Structured light is a perception method that allows us to obtain 3D information from images of the scene by projecting synthetic features with a light emitter. Traditionally, this method considers a rigid configuration, where the position and orientation of the light emitter with [...] Read more.
Structured light is a perception method that allows us to obtain 3D information from images of the scene by projecting synthetic features with a light emitter. Traditionally, this method considers a rigid configuration, where the position and orientation of the light emitter with respect to the camera are known and calibrated beforehand. In this paper we propose a new omnidirectional structured light system in flexible configuration, which overcomes the rigidness of the traditional structured light systems. We propose the use of an omnidirectional camera combined with a conic pattern light emitter. Since the light emitter is visible in the omnidirectional image, the computation of its location is possible. With this information and the projected conic in the omnidirectional image, we are able to compute the conic reconstruction, i.e., the 3D information of the conic in the space. This reconstruction considers the recovery of the depth and orientation of the scene surface where the conic pattern is projected. One application of our proposed structured light system in flexible configuration consists of a wearable omnicamera with a low-cost laser in hand for visual impaired personal assistance. Full article
(This article belongs to the Section Physical Sensors)
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<p>Flexible structured light system. (<b>a</b>) Wearable omnidirectional camera; (<b>b</b>) Configuration of the system.</p> Full article ">
<p>Projection of a 3D point to two image points in the sphere camera model.</p> Full article ">
<p>Laser model. (<b>a</b>) Calibration process; (<b>b</b>) Deformation of the conic shape depending on the laser orientation.</p> Full article ">
<p>Depth information from conic correspondence using virtual images.</p> Full article ">
<p>Methods to compute the orientation of the light emitter. (<b>a</b>) Method based on the plane defined by the laser and one endpoint; (<b>b</b>) Method based on the extraction of the laser endpoint and known length.</p> Full article ">
<p>Different configurations of the proposed structured light system. (<b>a</b>) Single conic with azimuth 20°; (<b>b</b>) Single conic with azimuth 30°; (<b>c</b>) Multiple conics varying the azimuth.</p> Full article ">
<p>Simulation results using One-endpoint method with one conic projection. (<b>a</b>) Error in depth; (<b>b</b>) Error in the surface orientation.</p> Full article ">
<p>Simulation results using Two-endpoint method with one conic projection. (<b>a</b>) Error in depth; (<b>b</b>) Error in the surface orientation.</p> Full article ">
<p>Estimation of a plane located 1<span class="html-italic">m</span> from the camera. Real plane in red and estimated plane in blue. (<b>a</b>) Plane computed using One-endpoint method; (<b>b</b>) Plane computed using Two-endpoint method.</p> Full article ">
892 KiB  
Article
Multi-Channel Hyperspectral Fluorescence Detection Excited by Coupled Plasmon-Waveguide Resonance
by Chan Du, Le Liu, Lin Zhang, Jun Guo, Jihua Guo, Hui Ma and Yonghong He
Sensors 2013, 13(10), 13892-13902; https://doi.org/10.3390/s131013892 - 14 Oct 2013
Cited by 6 | Viewed by 5879
Abstract
We propose in this paper a biosensor scheme based on coupled plasmon-waveguide resonance (CPWR) excited fluorescence spectroscopy. A symmetrical structure that offers higher surface electric field strengths, longer surface propagation lengths and depths is developed to support guided waveguide modes for the efficient [...] Read more.
We propose in this paper a biosensor scheme based on coupled plasmon-waveguide resonance (CPWR) excited fluorescence spectroscopy. A symmetrical structure that offers higher surface electric field strengths, longer surface propagation lengths and depths is developed to support guided waveguide modes for the efficient excitation of fluorescence. The optimal parameters for the sensor films are theoretically and experimentally investigated, leading to a detection limit of 0.1 nM (for a Cy5 solution). Multiplex analysis possible with the fluorescence detection is further advanced by employing the hyperspectral fluorescence technique to record the full spectra for every pixel on the sample plane. We demonstrate experimentally that highly overlapping fluorescence (Cy5 and Dylight680) can be distinguished and ratios of different emission sources can be determined accurately. This biosensor shows great potential for multiplex detections of fluorescence analytes. Full article
(This article belongs to the Section Biosensors)
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<p>(<b>a</b>) 1D implementation of a symmetrical optical waveguide structure based on Kretschmann configuration for CPWR excitation. Theoretically calculated angular reflectivity curves (<b>b</b>) and electric field distributions (<b>c</b>) for the architecture given in (<b>a</b>) at the excitation wavelength of 632.8 nm, n(Au) = 0.3123 + 3.146i. Propagation length in this figure refers to the electric field decay distance away from the sensor surface into the analyte.</p> Full article ">
<p>Schematic of the hyperspectral fluorescence detections based on a symmetrical CPWR structure.</p> Full article ">
<p>Demonstration of the data processing. (<b>a</b>) Structure of the two flow channels and the focused laser line; (<b>b</b>) An image captured by CCD, corresponding to the irradiated line region; (<b>c</b>) Fluorescence spectra correspond to channel one and channel two separately. Thicknesses for the three successive layers of MgF<sub>2</sub>-Au- MgF<sub>2</sub> are 500 nm, 40 nm, 600 nm individually.</p> Full article ">
<p>Resonance curves (<b>a</b>) and electric field distribution (<b>b</b>) beyond the sensor films directly into sensed medium simulated with various thicknesses of second layer of magnesium fluoride 600 nm (red), 650 nm (blue), 700 nm (black), 750 nm (cyanine) generated by symmetrical CPWR. Thicknesses of the first layer of magnesium fluoride and Au metal film are 500 nm and 40 nm, respectively. Wavelength of the incident light is 632.8 nm, n(BK<sub>7</sub>) = 1.515, n(MgF<sub>2</sub>) = 1.38, n(Au) = 0.3123 + 3.146i; (<b>c</b>) Fluorescence intensities against to different concentrations responding to sensor films with different thicknesses of second MgF<sub>2</sub> layer ranging from 550 nm to 700 nm.</p> Full article ">
<p>(<b>a</b>) Fluorescence spectra for each concentration; (<b>b</b>) Plot of normalized fluorescence intensities against solution concentrations.</p> Full article ">
<p>Multivariate analysis of mixed solution containing two spectrally overlapping fluorophores.</p> Full article ">
769 KiB  
Article
A Fast Smoothing Algorithm for Post-Processing of Surface Reflectance Spectra Retrieved from Airborne Imaging Spectrometer Data
by Bo-Cai Gao and Ming Liu
Sensors 2013, 13(10), 13879-13891; https://doi.org/10.3390/s131013879 - 14 Oct 2013
Cited by 11 | Viewed by 7275
Abstract
Surface reflectance spectra retrieved from remotely sensed hyperspectral imaging data using radiative transfer models often contain residual atmospheric absorption and scattering effects. The reflectance spectra may also contain minor artifacts due to errors in radiometric and spectral calibrations. We have developed a fast [...] Read more.
Surface reflectance spectra retrieved from remotely sensed hyperspectral imaging data using radiative transfer models often contain residual atmospheric absorption and scattering effects. The reflectance spectra may also contain minor artifacts due to errors in radiometric and spectral calibrations. We have developed a fast smoothing technique for post-processing of retrieved surface reflectance spectra. In the present spectral smoothing technique, model-derived reflectance spectra are first fit using moving filters derived with a cubic spline smoothing algorithm. A common gain curve, which contains minor artifacts in the model-derived reflectance spectra, is then derived. This gain curve is finally applied to all of the reflectance spectra in a scene to obtain the spectrally smoothed surface reflectance spectra. Results from analysis of hyperspectral imaging data collected with the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data are given. Comparisons between the smoothed spectra and those derived with the empirical line method are also presented. Full article
(This article belongs to the Special Issue Spectral Imaging at the Microscale and Beyond)
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<p>An example of a reflectance spectrum derived with ATREM from AVIRIS data acquired in June, 1995 over Cuprite, Nevada, USA.</p> Full article ">
<p>An illustration of the interpolating function <span class="html-italic">h(x)</span>.</p> Full article ">
<p>A sample gain spectrum.</p> Full article ">
<p>An ATREM reflectance spectrum (lower line), a smoothed spectrum (middle line), and a reflectance spectrum obtained with the empirical line method (upper line). For clarity, the three spectra are vertically offset.</p> Full article ">
<p>(<b>A</b>): Six reflectance spectra (displaced vertically for clarity) derived with ATREM from AVIRIS data acquired over Cuprite, Nevada in June, 1995; (<b>B</b>): six smoothed reflectance spectra corresponding to those in (A); and (<b>C</b>): six reflectance spectra derived with the empirical line method and corresponding to those in (A).</p> Full article ">
<p>(<b>A</b>): a false color image (Red: 0.63 μm; Green: 0.86 μm; Blue: 0.47 μm) for an AVIRIS scene over Ivanpah in California, and (<b>B</b>): an ATREM-derived surface reflectance spectrum over a soil pixel (dotted line) and the corresponding smoothed spectrum (solid line). See text for more detailed descriptions.</p> Full article ">
<p>(<b>A</b>): a false color image (Red: 0.63 μm; Green: 0.86 μm; Blue: 0.47 μm) for an AVIRIS scene over Ivanpah in California, and (<b>B</b>): an ATREM-derived surface reflectance spectrum over a green vegetation pixel (dotted line) and the corresponding smoothed spectrum (solid line). See text for more detailed descriptions.</p> Full article ">
<p>(<b>A</b>): a false color image (Red: 0.63 μm; Green: 0.86 μm; Blue: 0.47 μm) for an AVIRIS scene over Ivanpah in California, and (<b>B</b>): an ATREM-derived surface reflectance spectrum over an Ivanpah playa pixel (dotted line), the corresponding smoothed spectrum (solid line), and a field-measured spectrum (dash-dotted line). See text for more detailed descriptions.</p> Full article ">
519 KiB  
Article
Development of a Real Time Sparse Non-Negative Matrix Factorization Module for Cochlear Implants by Using xPC Target
by Hongmei Hu, Agamemnon Krasoulis, Mark Lutman and Stefan Bleeck
Sensors 2013, 13(10), 13861-13878; https://doi.org/10.3390/s131013861 - 14 Oct 2013
Cited by 6 | Viewed by 7532
Abstract
Cochlear implants (CIs) require efficient speech processing to maximize information transmission to the brain, especially in noise. A novel CI processing strategy was proposed in our previous studies, in which sparsity-constrained non-negative matrix factorization (NMF) was applied to the envelope matrix in order [...] Read more.
Cochlear implants (CIs) require efficient speech processing to maximize information transmission to the brain, especially in noise. A novel CI processing strategy was proposed in our previous studies, in which sparsity-constrained non-negative matrix factorization (NMF) was applied to the envelope matrix in order to improve the CI performance in noisy environments. It showed that the algorithm needs to be adaptive, rather than fixed, in order to adjust to acoustical conditions and individual characteristics. Here, we explore the benefit of a system that allows the user to adjust the signal processing in real time according to their individual listening needs and their individual hearing capabilities. In this system, which is based on MATLABR , SIMULINKR and the xPC TargetTM environment, the input/outupt (I/O) boards are interfaced between the SIMULINK blocks and the CI stimulation system, such that the output can be controlled successfully in the manner of a hardware-in-the-loop (HIL) simulation, hence offering a convenient way to implement a real time signal processing module that does not require any low level language. The sparsity constrained parameter of the algorithm was adapted online subjectively during an experiment with normal-hearing subjects and noise vocoded speech simulation. Results show that subjects chose different parameter values according to their own intelligibility preferences, indicating that adaptive real time algorithms are beneficial to fully explore subjective preferences. We conclude that the adaptive real time systems are beneficial for the experimental design, and such systems allow one to conduct psychophysical experiments with high ecological validity. Full article
(This article belongs to the Special Issue State-of-the-Art Sensors Technology in the UK 2013)
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<p>Advanced combination encoder (ACE) strategy and the proposed sparse constrained non-negative matrix factorization (NMF) strategy.</p> Full article ">
<p>An example of the NMF reconstruction <span class="html-italic">envelopegram</span> with different components of the word ‘Din’ (see [<a href="#b39-sensors-13-13861" class="html-bibr">39</a>] for more detail). The top left panel is the component matrix, <b>W</b>, which determines the activation of different basis vectors over time. The top middle panel is the original <span class="html-italic">envelopegram</span>, <b>Z</b>, of the word ‘Din’, and the other panels are the reconstruction results with different component(s).</p> Full article ">
<p>The experimental setup, including the overall architecture of the host-target HIL real-time cochlear implant (CI<b>)</b> stimulation system. The left and right parts of the figure correspond to the the sound proof room and testing room, respectively.</p> Full article ">
<p>Plot of the optimum lambda values as a function of the signal-to-noise ratio (SNR) value. The blue dashed line shows the optimum values obtained by calculating the NCM of vocoded speech samples after being processed according to the sparse NMF strategy, using the Bamford-Kowal-Bench (BKB) database. The red solid curve corresponds to the fitted optimum λ values based on an exponential decay function.</p> Full article ">
<p>Graph of the exponential fitting of average λ values for babble noise across different SNRs.</p> Full article ">
1407 KiB  
Article
G3 Assisted Rational Design of Chemical Sensor Array Using Carbonitrile Neutral Receptors
by Ahmad Nazmi Rosli, Maizathul Akmam Abu Bakar, Ninie Suhana Abdul Manan, Pei Meng Woi, Vannajan Sanghiran Lee, Sharifuddin Md Zain, Mohd Rais Ahmad and Yatimah Alias
Sensors 2013, 13(10), 13835-13860; https://doi.org/10.3390/s131013835 - 14 Oct 2013
Cited by 4 | Viewed by 8753
Abstract
Combined computational and experimental strategies for the systematic design of chemical sensor arrays using carbonitrile neutral receptors are presented. Binding energies of acetonitrile, n-pentylcarbonitrile and malononitrile with Ca(II), Mg(II), Be(II) and H+ have been investigated with the B3LYP, G3, CBS-QB3, G4 [...] Read more.
Combined computational and experimental strategies for the systematic design of chemical sensor arrays using carbonitrile neutral receptors are presented. Binding energies of acetonitrile, n-pentylcarbonitrile and malononitrile with Ca(II), Mg(II), Be(II) and H+ have been investigated with the B3LYP, G3, CBS-QB3, G4 and MQZVP methods, showing a general trend H+ > Be(II) > Mg(II) > Ca(II). Hydrogen bonding, donor-acceptor and cation-lone pair electron simple models were employed in evaluating the performance of computational methods. Mg(II) is bound to acetonitrile in water by 12.5 kcal/mol, and in the gas phase the receptor is more strongly bound by 33.3 kcal/mol to Mg(II) compared to Ca(II). Interaction of bound cations with carbonitrile reduces the energies of the MOs involved in the proposed σ-p conjugated network. The planar malononitrile-Be(II) complex possibly involves a π-network with a cationic methylene carbon. Fabricated potentiometric chemical sensors show distinct signal patterns that can be exploited in sensor array applications. Full article
(This article belongs to the Section Chemical Sensors)
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<p>G3 optimized geometries of acetonitrile and its complexes with Be(II), Mg(II) and H<sup>+</sup>. (<b>i</b>) CH<sub>3</sub>CN; (<b>ii</b>) CH<sub>3</sub>CN-Mg(II); (<b>iii</b>) CH<sub>3</sub>CN-Be(II); (<b>iv</b>) CH<sub>3</sub>CN-H<sup>+</sup>.</p> Full article ">
<p>Selected G3 molecular orbitals of acetonitrile and its complexes with Mg(II). (<b>i</b>) HOMO-2 of CH<sub>3</sub>CN; (<b>ii</b>) HOMO-3 of CH<sub>3</sub>CN; (<b>iv</b>) HOMO-3 of CH<sub>3</sub>CN-Mg(II); (<b>v</b>) HOMO-4 of CH<sub>3</sub>CN-Mg(II).</p> Full article ">
<p>G4 Dissociation energy <span class="html-italic">versus</span> N-M vibrational frequency (in vacuum).</p> Full article ">
<p>H6 <sup>1</sup>H-NMR shift <span class="html-italic">versus</span> H6 charge (G3, vacuum).</p> Full article ">
<p>N3-Cation bond distance <span class="html-italic">versus</span> acetonitrile binding energy (G4, vacuum).</p> Full article ">
<p>Optimized geometries of <span class="html-italic">n</span>-pentane carbonitrile and its complex with Mg(II).</p> Full article ">
<p>Optimized geometry of Mg(II) complex with two equivalents of acetonitrile.</p> Full article ">
<p>Optimized geometries of malononitrile and its complex with Be(II).</p> Full article ">
<p>(<b>a</b>) Planar optimized structure of Be(II) complex with malononitrile; (<b>b</b>) conjugated <span class="html-italic">π</span>-network in malononitrile-Be(II).</p> Full article ">
421 KiB  
Article
Potential of Visible and Near Infrared Spectroscopy and Pattern Recognition for Rapid Quantification of Notoginseng Powder with Adulterants
by Pengcheng Nie, Di Wu, Da-Wen Sun, Fang Cao, Yidan Bao and Yong He
Sensors 2013, 13(10), 13820-13834; https://doi.org/10.3390/s131013820 - 14 Oct 2013
Cited by 38 | Viewed by 7620
Abstract
Notoginseng is a classical traditional Chinese medical herb, which is of high economic and medical value. Notoginseng powder (NP) could be easily adulterated with Sophora flavescens powder (SFP) or corn flour (CF), because of their similar tastes and appearances and much lower cost [...] Read more.
Notoginseng is a classical traditional Chinese medical herb, which is of high economic and medical value. Notoginseng powder (NP) could be easily adulterated with Sophora flavescens powder (SFP) or corn flour (CF), because of their similar tastes and appearances and much lower cost for these adulterants. The objective of this study is to quantify the NP content in adulterated NP by using a rapid and non-destructive visible and near infrared (Vis-NIR) spectroscopy method. Three wavelength ranges of visible spectra, short-wave near infrared spectra (SNIR) and long-wave near infrared spectra (LNIR) were separately used to establish the model based on two calibration methods of partial least square regression (PLSR) and least-squares support vector machines (LS-SVM), respectively. Competitive adaptive reweighted sampling (CARS) was conducted to identify the most important wavelengths/variables that had the greatest influence on the adulterant quantification throughout the whole wavelength range. The CARS-PLSR models based on LNIR were determined as the best models for the quantification of NP adulterated with SFP, CF, and their mixtures, in which the rP values were 0.940, 0.939, and 0.867 for the three models respectively. The research demonstrated the potential of the Vis-NIR spectroscopy technique for the rapid and non-destructive quantification of NP containing adulterants. Full article
(This article belongs to the Section Chemical Sensors)
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<p>Spectral patterns of the tested notoginseng powder (NP) adulterated by different concentrations of sophora flavescens powder (SFP) and/or corn flour (CF) in 360–1,040 nm (<b>a</b>) and 937–2,500 nm (<b>b</b>). Percentages are shown by mass (g/g).</p> Full article ">
<p>Changing trends of the number of sampled variables in the competitive adaptive reweighted sampling (CARS) calculation. (<b>a</b>) 5-fold the root mean square error of cross-validation (RMSECV) values; (<b>b</b>) and regression coefficients of each variable; (<b>c</b>) with the increasing of sampling runs. The line (marked by asterisk) denotes the optimal point where 5-fold RMSECV values achieve the lowest.</p> Full article ">
1466 KiB  
Article
A Coded Structured Light System Based on Primary Color Stripe Projection and Monochrome Imaging
by Sandro Barone, Alessandro Paoli and Armando Viviano Razionale
Sensors 2013, 13(10), 13802-13819; https://doi.org/10.3390/s131013802 - 14 Oct 2013
Cited by 20 | Viewed by 9725
Abstract
Coded Structured Light techniques represent one of the most attractive research areas within the field of optical metrology. The coding procedures are typically based on projecting either a single pattern or a temporal sequence of patterns to provide 3D surface data. In this [...] Read more.
Coded Structured Light techniques represent one of the most attractive research areas within the field of optical metrology. The coding procedures are typically based on projecting either a single pattern or a temporal sequence of patterns to provide 3D surface data. In this context, multi-slit or stripe colored patterns may be used with the aim of reducing the number of projected images. However, color imaging sensors require the use of calibration procedures to address crosstalk effects between different channels and to reduce the chromatic aberrations. In this paper, a Coded Structured Light system has been developed by integrating a color stripe projector and a monochrome camera. A discrete coding method, which combines spatial and temporal information, is generated by sequentially projecting and acquiring a small set of fringe patterns. The method allows the concurrent measurement of geometrical and chromatic data by exploiting the benefits of using a monochrome camera. The proposed methodology has been validated by measuring nominal primitive geometries and free-form shapes. The experimental results have been compared with those obtained by using a time-multiplexing gray code strategy. Full article
(This article belongs to the Section Physical Sensors)
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<p>Optical set-up of the measurement system based on multi-slit pattern projection.</p> Full article ">
<p>Flowchart representation of the proposed 3D measurement technique.</p> Full article ">
<p>Original color-encoded De Bruijn sequence.</p> Full article ">
<p>Multi-slit binary patterns used for the De Bruijn pattern reconstruction.</p> Full article ">
<p>(<b>a</b>) The 7 different codeword generation, (<b>b</b>) Reconstruction detail of the original color-encoded De Bruijn sequence.</p> Full article ">
<p>(<b>a</b>–<b>c</b>) Projected multi-slit intensity patterns relative to relation <a href="#FD1" class="html-disp-formula">(1)</a> along with their negative versions (<b>d</b>–<b>f</b>).</p> Full article ">
<p>Gray intensity levels along a horizontal scan-line together with the segmented horizontal scan-line.</p> Full article ">
<p>Example of reconstructed color encoded pattern for the Macbeth Color Checker acquisition.</p> Full article ">
<p>Virtual color reconstruction of a Macbeth Color Checker. (<b>a</b>–<b>c</b>) Monochromatic camera acquisition of positive projected patterns, (<b>d</b>–<b>f</b>) Monochromatic camera acquisition of negative projected patterns, (<b>g</b>–<b>i</b>) CMY channels obtained by applying <a href="#FD3" class="html-disp-formula">Equation (3)</a>, (<b>l</b>–<b>n</b>) Effects of the removal of saturated pixels and stretching process.</p> Full article ">
2173 KiB  
Article
A Buoy for Continuous Monitoring of Suspended Sediment Dynamics
by Philip Mueller, Heiko Thoss, Lucas Kaempf and Andreas Güntner
Sensors 2013, 13(10), 13779-13801; https://doi.org/10.3390/s131013779 - 14 Oct 2013
Cited by 8 | Viewed by 8013
Abstract
Knowledge of Suspended Sediments Dynamics (SSD) across spatial scales is relevant for several fields of hydrology, such as eco-hydrological processes, the operation of hydrotechnical facilities and research on varved lake sediments as geoarchives. Understanding the connectivity of sediment flux between source areas in [...] Read more.
Knowledge of Suspended Sediments Dynamics (SSD) across spatial scales is relevant for several fields of hydrology, such as eco-hydrological processes, the operation of hydrotechnical facilities and research on varved lake sediments as geoarchives. Understanding the connectivity of sediment flux between source areas in a catchment and sink areas in lakes or reservoirs is of primary importance to these fields. Lacustrine sediments may serve as a valuable expansion of instrumental hydrological records for flood frequencies and magnitudes, but depositional processes and detrital layer formation in lakes are not yet fully understood. This study presents a novel buoy system designed to continuously measure suspended sediment concentration and relevant boundary conditions at a high spatial and temporal resolution in surface water bodies. The buoy sensors continuously record turbidity as an indirect measure of suspended sediment concentrations, water temperature and electrical conductivity at up to nine different water depths. Acoustic Doppler current meters and profilers measure current velocities along a vertical profile from the water surface to the lake bottom. Meteorological sensors capture the atmospheric boundary conditions as main drivers of lake dynamics. It is the high spatial resolution of multi-point turbidity measurements, the dual-sensor velocity measurements and the temporally synchronous recording of all sensors along the water column that sets the system apart from existing buoy systems. Buoy data collected during a 4-month field campaign in Lake Mondsee demonstrate the potential and effectiveness of the system in monitoring suspended sediment dynamics. Observations were related to stratification and mixing processes in the lake and increased turbidity close to a catchment outlet during flood events. The rugged buoy design assures continuous operation in terms of stability, energy management and sensor logging throughout the study period. We conclude that the buoy is a suitable tool for continuous monitoring of suspended sediment concentrations and general dynamics in fresh water bodies. Full article
(This article belongs to the Section Remote Sensors)
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<p>Technical drawing of the buoy. (<b>a</b>) The side view, (<b>b,c</b>) The top view of the main body and the entire buoy. The measurement chain is not illustrated. It is attached to the center of the bottom side of the main body.</p> Full article ">
<p>Buoy in operation and plate anchor as used for the mooring.</p> Full article ">
<p>Map of Lake Mondsee and buoy position for test deployment. (C) Meteorological gauge operated by the ZAMG (Austrian Meteorological Survey). (G) Hydro-sedimentological gauge at the catchment outlet. (S) Position of the sequential sediment trap. The big black dot on the bathymetric lake map stands for position of the buoy during test deployment. The small black dot in the upper left corner shows the study site relative to the map of Austria.</p> Full article ">
<p>Measured air temperature and relative humidity (<b>left</b>) as well as wind speed in relation to wind direction (<b>right</b>).</p> Full article ">
<p>Measured water temperature by depth as a contour plot recorded by two different sensors. The FTS DTS-12 on the left and the CS547A-L on the right. Sensor allocation by water depth is illustrated by the red squares.</p> Full article ">
<p>Electrical conductivity (CS547A-L, <b>left plot</b>) and turbidity (FTS DTS-12, <b>right plot</b>) displayed in contour plots at the buoy location. Sensor allocation by water depth is illustrated by the red squares. Turbidity is presented with a logarithmic scale.</p> Full article ">
<p>Comparison of turbidity in the Fuschler Ache river at the most downstream gauge (tcg) and of turbidity at the buoy location (tb) at 1 m water depth (<b>upper graph</b>). The position of the catchment gauge is represented by label C in <a href="#f3-sensors-13-13779" class="html-fig">Figure 3</a>. River runoff, flow direction and surface flow speed at the buoy location (<b>lower graph</b>). I and II represent the two reference runoff events. Graphs shown in the upper plot are scaled with one y-axis. In the lower plot, each graph corresponds to the y-axis of the same color.</p> Full article ">
<p>Sedimentation rates from a Technicap PPS4/3 sediment trap working sequentially with a temporal resolution of three days. Sedimentation rates are shown from April to November 2012. The red frame highlights the sedimentation rated during the flood event.</p> Full article ">
<p>Interpolated flow speed (fs) from ADCP and current meter data at the buoy location.</p> Full article ">
1896 KiB  
Review
Development of an Amorphous Selenium-Based Photodetector Driven by a Diamond Cold Cathode
by Tomoaki Masuzawa, Ichitaro Saito, Takatoshi Yamada, Masanori Onishi, Hisato Yamaguchi, Yu Suzuki, Kousuke Oonuki, Nanako Kato, Shuichi Ogawa, Yuji Takakuwa, Angel T. T. Koh, Daniel H. C. Chua, Yusuke Mori, Tatsuo Shimosawa and Ken Okano
Sensors 2013, 13(10), 13744-13778; https://doi.org/10.3390/s131013744 - 11 Oct 2013
Cited by 48 | Viewed by 12269
Abstract
Amorphous-selenium (a-Se) based photodetectors are promising candidates for imaging devices, due to their high spatial resolution and response speed, as well as extremely high sensitivity enhanced by an internal carrier multiplication. In addition, a-Se is reported to show sensitivity against wide variety of [...] Read more.
Amorphous-selenium (a-Se) based photodetectors are promising candidates for imaging devices, due to their high spatial resolution and response speed, as well as extremely high sensitivity enhanced by an internal carrier multiplication. In addition, a-Se is reported to show sensitivity against wide variety of wavelengths, including visible, UV and X-ray, where a-Se based flat-panel X-ray detector was proposed. In order to develop an ultra high-sensitivity photodetector with a wide detectable wavelength range, a photodetector was fabricated using a-Se photoconductor and a nitrogen-doped diamond cold cathode. In the study, a prototype photodetector has been developed, and its response to visible and ultraviolet light are characterized. Full article
(This article belongs to the Special Issue Photodetectors)
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<p>Spectrometric sensitivity chart of a-Se based photodetector after Kubota <span class="html-italic">et al.</span> [<a href="#b17-sensors-13-13744" class="html-bibr">17</a>] (labels translated into English). This photodetector used a CdSe layer to improve quantum efficiency at wavelength larger than 600 nm. The lower edge at around 350 nm should correspond to the absorption by glass substrate.</p> Full article ">
<p>Attenuation coefficient of different X-ray photoconductors plotted in terms of photon energy [<a href="#b4-sensors-13-13744" class="html-bibr">4</a>].</p> Full article ">
<p>Schematic structure of a typical vidicon device [<a href="#b20-sensors-13-13744" class="html-bibr">20</a>].</p> Full article ">
<p>Schematic devise structure of FEA-HARP [<a href="#b21-sensors-13-13744" class="html-bibr">21</a>].</p> Full article ">
<p>Schematic device structure of X-ray FPD by Kasap <span class="html-italic">et al.</span> [<a href="#b4-sensors-13-13744" class="html-bibr">4</a>].</p> Full article ">
<p>Hot filament chemical vapor deposition (HFCVD) system.</p> Full article ">
<p>Comparison between the electron emission characteristics of nitrogen (N), phosphorus (P)-doped and boron (B)-doped diamond [<a href="#b30-sensors-13-13744" class="html-bibr">30</a>].</p> Full article ">
<p>(<b>a</b>) Emission site map and (<b>b</b>) XPS intensity map (O1s) of N-doped diamond [<a href="#b31-sensors-13-13744" class="html-bibr">31</a>].</p> Full article ">
<p>Schematic diagram of Metal-Insulator-Vacuum (MIV) type emission [<a href="#b32-sensors-13-13744" class="html-bibr">32</a>]: (<b>a</b>) experimental setup; (<b>b</b>) band diagram, where electron injection into diamond and electron emission from NEA are schematically drawn.</p> Full article ">
509 KiB  
Article
Sensing Lanthanide Metal Content in Biological Tissues with Magnetic Resonance Spectroscopy
by Dina V. Hingorani, Sandra I. Gonzalez, Jessica F. Li and Mark D. Pagel
Sensors 2013, 13(10), 13732-13743; https://doi.org/10.3390/s131013732 - 11 Oct 2013
Cited by 3 | Viewed by 6186
Abstract
The development and validation of MRI contrast agents consisting of a lanthanide chelate often requires a determination of the concentration of the agent in ex vivo tissue. We have developed a protocol that uses 70% nitric acid to completely digest tissue samples that [...] Read more.
The development and validation of MRI contrast agents consisting of a lanthanide chelate often requires a determination of the concentration of the agent in ex vivo tissue. We have developed a protocol that uses 70% nitric acid to completely digest tissue samples that contain Gd(III), Dy(III), Tm(III), Eu(III), or Yb(III) ions, or the MRI contrast agent gadodiamide. NMR spectroscopy of coaxial tubes containing a digested sample and a separate control solution of nitric acid was used to rapidly and easily measure the bulk magnetic susceptibility (BMS) shift caused by each lanthanide ion and gadodiamide. Each BMS shift was shown to be linearly correlated with the concentration of each lanthanide ion and gadodiamide in the 70% nitric acid solution and in digested rat kidney and liver tissues. These concentration measurements had outstanding precision, and also had good accuracy for concentrations ³10 mM for Tm(III) Eu(III), and Yb(III), and ³3 mM for Gd(III), gadodiamide, and Dy(III). Improved sample handling methods are needed to improve measurement accuracy for samples with lower concentrations. Full article
(This article belongs to the Special Issue Magnetic Resonance Sensors)
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<p>NMR spectra of coaxial samples of Tm(III) ion in nitric acid (left peak) and nitric acid without Tm(III) (right peak) were rapidly acquired and easily analyzed to measure the BMS shift of each sample.</p> Full article ">
<p>Correlation of BMS shift and lanthanide ion concentration. (<b>a</b>,<b>b</b>) The correlation of BMS shift and concentration for each lanthanide ion or gadodiamide at 7 T magnetic field strength showed outstanding linearity with R<sup>2</sup> &gt; 0.98. (<b>c</b>,<b>d</b>) The concentration dependence of BMS shift at 7 T (filled symbols) and 14 T (open symbols) for Tm(III) and Gd(III) showed that the calibration was independent of magnetic field strength.</p> Full article ">
<p>Effect of sample conditions on the concentration-BMS shift calibration. The calibrations of (<b>a</b>) Tm(III) and (<b>b</b>) Gd(III) without (filled symbols) and with 300 mOsm/L NaCl (open symbols) showed that salt had a neglible effect on the concentration-dependent BMS shift. The calibrations of (<b>c</b>) Tm(III) and (<b>d</b>) Gd(III) without (filled symbols) and with 90 μM albumin (open symbols) showed that proteins had a neglible effect on the concentration-dependent BMS shift.</p> Full article ">
<p>Effect of temperature on the concentration-BMS shift calibration. (<b>a</b>) The greatest BMS shifts were observed at lowest temperatures. (<b>b</b>) The BMS shift, Δ<sub>χ</sub>, had a linear dependence on lanthanide ion concentration and inverse temperature, as predicted by theory (<a href="#FD3" class="html-disp-formula">Equation (3)</a>). Each line is labeled with is concentration in mM, with labels for data with solid symbols on the left and labels for data with open symbols on the right.</p> Full article ">
<p>Correlation of BMS shift and concentration of lanthanide ion or gadodiamide in (<b>a</b>,<b>b</b>) rat kidney tissues and (<b>c</b>,<b>d</b>) rat liver tissues showed outstanding linearity with R<sup>2</sup> &gt; 0.97.</p> Full article ">
<p>The recovery of lanthanide ions from (<b>a</b>,<b>b</b>) rat kidney tissues and (<b>c</b>,<b>d</b>) rat liver tissues. (a,c) At least 80% recovery was obtained for samples with ≥ 25 mM Tm(III), Yb(III), and Eu(III). (b,d) At in 85% recovery was obtained for samples with ≥ 3 mM Gd(III), gadodiamide, and Dy(III).</p> Full article ">
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