Interdigitated Electrode Array Research Articles

Laser-induced noble metal nanoparticle-graphene composites enabled flexible biosensor for pathogen detection

Noble metal nanoparticle-3D graphene hybrid nanocomposites possess the advantage of nanoparticles and graphene, which have attracted extensive interest. Here we developed a one-step laser induction method to prepare various noble metal nanoparticle-3D graphene nanocomposites. The nanocomposites were converted from polyimide film coated with the corresponding metal precursor-chitosan hydrogel ink. These nanoparticles including gold nanoparticles (AuNPs), silver nanoparticles (AgNPs), and platinum nanoparticles (PtNPs), were evenly distributed on the surface of porous 3D graphene. Furthermore, we prepared an AuNPs-3D graphene interdigitated array electrode using the one-step laser induction method, which was used to fabricate a flexible impedimetric immunosensor for the detection of Escherichia coli O157:H7. The immunosensor shows excellent performance including low detection limit, high selectivity, and great flexibility.

Redox cycling-based electrochemical CMOS imaging sensor for real time and selective imaging of redox analytes

In this study, we have developed a novel electrochemical device (IDEA-Bio-LSI) incorporating interdigitated electrodes array (IDEA) and a LSI-based amperometric device (Bio-LSI) for high speed (4–200 ms) and selective imaging of an analyte diffusion and cellar activities such as dopamine release. The amplification factor (ηamp) and capture efficiency (CE) of IDEA of the device were 2.17 and 0.767, respectively. Compared with previously reported IDE based imaging sensor, the acquisition speed of the present device to acquire one image was improved up to 50–250 times. In addition, the dopamine release from PC12 spheroids in the presence of ascorbic acid was successfully obtained by using the IDEA-Bio-LSI. Therefore, IDEA-Bio-LSI can apply to rapid analyte diffusion biological events such as release of dopamine release.

In-Situ Characterization of Electrolyte Degradation Products with Lithographically Patterned Electrode Arrays

he successful operation of many beyond-lithium-ion battery chemistries depends on efficient formation of the solid electrolyte interphase (SEI). During the first charge cycles, electrolyte is reduced at the anode surface and insoluble degradation products form a passivating layer, allowing ion transport while preventing additional electrolyte degradation. The solubility of degradation products affects the efficiency of SEI formation. In particular, electrolyte degradation products are more soluble in sodium-ion systems compared to lithium. As a result, sodium-ion batteries are subject to lower columbic efficiency, faster capacity fade, and higher resistance growth than lithium-ion. Addressing this limitation requires improved understanding of degradation product solubility, including methods to measure the relative concentration of dissolved electrolyte products. While differences in solubility have been studied through ex-situ spectroscopic techniques, in-situ detection of soluble degradation products can allow increased understanding of SEI dynamics and enable real time evaluation of the efficiency of SEI formation. 2 Interdigitated electrode arrays are frequently used for sensitive detection of electroactive species. Interdigitated electrode arrays (IDAs) make use of small diffusion lengths between electrodes to allow for a collector-generator arrangement, yielding similar behavior to rotating ring-disk electrodes without the noise of rotation, risk of SEI shearing or need for bulky equipment.3 IDAs are subject to increased feedback current, also known as redox cycling, due to diffusion of products from the collector back to the generator.4 This is useful in the detection of products in very low concentrations but is not desirable for accurate prediction of SEI formation efficiency. Here, we fabricate customized designs of IDAs with a high aspect ratio of Wgen­ to Wcol (10-40:1) using photolithographic techniques. We are able to achieve a low feedback (1-1.1 X) while maintaining relatively high collection efficiency (25-40%). Through this work we demonstrate electrochemical monitoring of soluble products by chronoamperometric detection at the collector during SEI formation at the generator. Utilizing this technique, it is possible to observe the proportion of electroactive soluble degradation products formed as a function of potential and monitor changes in the system with time. (1) Dahbi, M.; Yabuuchi, N.; Kubota, K.; Tokiwa, K.; Komaba, S. Negative Electrodes for Na-Ion Batteries. Phys. Chem. Chem. Phys. 2014, 16 (29), 15007. https://doi.org/10.1039/c4cp00826j. (2) Iermakova, D. I.; Dugas, R.; Palacín, M. R.; Ponrouch, A. On the Comparative Stability of Li and Na Metal Anode Interfaces in Conventional Alkyl Carbonate Electrolytes. J. Electrochem. Soc. 2015, 162 (13), A7060–A7066. https://doi.org/10.1149/2.0091513jes. (3) Aoki, K.; Morita, M.; Niwa, O.; Tabei, H. Quantitative Analysis of Reversible Diffusion-Controlled Currents of Redox Soluble Species at Interdigitated Array Electrodes under Steady-State Conditions. J. Electroanal. Chem. 1988, 256 (2), 269–282. https://doi.org/10.1016/0022-0728(88)87003-7. (4) Odijk, M.; Olthuis, W.; Dam, V. A. T.; Van Den Berg, A. Simulation of Redox-Cycling Phenomena at Interdigitated Array (IDA) Electrodes: Amplification and Selectivity. Electroanalysis 2008, 20 (5), 463–468. https://doi.org/10.1002/elan.200704105. Figure. SEI formation current at generator (blue) and amperometric detection at collector (orange) as a function of time Figure 1

Interdigitated electrode arrays made by capillary filling and spin coating for UV-sensor fabrication

In this paper the fabrication of UV-sensors based on an interdigitated electrode array with a 70 nm sputtered ZnO coating is demonstrated. The electrodes were fabricated using polymer substrates prepatterned with nanoimprint lithography, imprinted with μm-sized grooves and reservoirs at two sides. The V-shaped capillaries were filled with nanoparticle based silver ink either by capillary action in an open-fluidics approach or with spin coating. This enables the use of low-resolution additive methods to fabricate high precision wires for low cost flexible electronics. The 1 × 1 mm2 sensor area contained 100 wires in alternating directions that were electrically insulated from each other, and were attached to contact pads. Characterization of UV sensor devices was carried out experimentally by performing electrical measurements under 355 and 385 nm UV light illumination.

An interesting route using electron-beam lithography and photolithography to pattern submicron interdigitated electrodes array for sensing applications

Increasing the interest in the silicon-based devices resulted in developing new methods and techniques to achieve advanced and more reliable designs and devices. In this study, we have developed a combination method of photolithography and electron-beam lithography (EBL) in order to maximize the efficiency and reducing time and costs. Nanometric and micrometric patterns were created using EBL and photolithography methods, respectively. In order to prove the sensing applications, the EBL-based fabricated electrodes were successfully designed and tested as a hydrogen peroxide (H2O2) biosensor using horseradish peroxidase (HRP) enzyme on a graphene oxide substrate. Photoresist provided a passive layer which reduced the passivation steps in the fabrication. The interdigitated electrodes were used to maximize the connections with the graphene oxide substrate. The result was an ohmic biosensor that exhibits a linear relationship with the logarithm of H2O2 concentration in the range between 0.1 µM and 100 mM. The limit of detection (LOD) was about 51 nM.

Diffusion impedance modeling for interdigitated array electrodes by conformal mapping and cylindrical finite length approximation

Impedimetric sensing using interdigitated array (IDA) electrodes usually encounters an analytical problem. Finite diffusion of redox species dominates at low frequencies and confuses researchers, making incorrect understanding of underlying phenomena possible. In this work, an integral equation for calculating the diffusion impedance of IDA electrodes is derived using conformal mapping and cylindrical finite length approximation. Electrodes of different bandwidths and gap widths are fabricated, and their heights and symmetric electrochemical characteristics are verified. Simulations are performed to verify the predicted constant concentration contours. The calculated zero-frequency impedance showed high correlation with the reciprocal of limiting current calculated from literature study (R2 = 0.992) and from chronoamperometry experiments (R2 = 0.970). Further evidence for the correctness of theory is established due to the fact that experimental EIS data and calculated impedances are highly consistent (R2 ≥ 0.948 for real and imaginary part). This sheds some light on explaining the diffusion phenomenon of impedance using IDA electrodes in the low frequency spectrum. An equivalent circuit fitting program is further designed for fitting several elements including the IDA electrode diffusion impedance derived in the theory. The program succeeded to accurately fit the EIS data (average MSE = 0.611), which using the Warburg element failed (average MSE = 54.86). Parameters such as the ratio of electrode bandwidth to gap width and diffusion coefficient can also be determined by fitting the data from a single EIS experiment. Another impedance calculation program is also given, which can aid researchers in relevant fields to model their systems more accurately.

Direct Measurement of Enhanced Ion Conductivity at an Ionic Liquid Electrolyte (ILE)/SiO2 Interface with Interdigitated Electrode Array

Recently, our group reported a novel solid-state electrolyte material which is constituted of a nano-porous SiO2 monolith and an ionic liquid electrolyte (ILE) which occupies the pores. The unique feature of this solid nano-composite electrolyte (nano-SCE) is its ion conductivity which is higher than that of the ILE itself [1]. Here, we report a direct measurement of this enhanced ion conductivity by measuring the ion conductivity of a thin-film ILE on a planar SiO2 substrate. The enhanced ion conductivity is directly measured with interdigitated electrode arrays deposited on a planar SiO2 substrate, as shown in Figure 1. By depositing a thin-film ILE film on these electrodes, the impedance response of the ILE/SiO2 interface could be measured by impedance spectroscopy (IS). The ion conductivity on the ILE/SiO2 interface could subsequently be quantified by analysis of the equivalent circuit model and by measuring the ILE film thickness. The ILE film thickness is scaled down to the nanometer regime. This is the first time that such thin ILE films could be deposited using liquid processing techniques. The enhanced ion conductivity is revealed when the ILE film thickness is reduced to 20 nm thicknesses and below. The ion conductivity of the ILE films with a thickness around 80 nm have a similar conductivity compared to the bulk ILE. Enhanced ion conductivity along interfaces has been observed before and is typically referred to as heterogenous doping [2]. The mechanism that governs the enhanced conductivity in the nano-SCE are similar to those described by heterogenous doping. However, the ion conductivities measured in this work are many times higher compared to those reported before. In conclusion, for the first time ILE thin-films with thicknesses in the nanometer regime are deposited with liquid processing. Moreover, the ion conductivity at the ILE/SiO2 interface could be quantified and showed an increased conductivity compared to the bulk ILE value.

Towards CMOS Integrated Microfluidics Using Dielectrophoretic Immobilization.

Dielectrophoresis (DEP) is a nondestructive and noninvasive method which is favorable for point-of-care medical diagnostic tests. This technique exhibits prominent relevance in a wide range of medical applications wherein the miniaturized platform for manipulation (immobilization, separation or rotation), and detection of biological particles (cells or molecules) can be conducted. DEP can be performed using advanced planar technologies, such as complementary metal-oxide-semiconductor (CMOS) through interdigitated capacitive biosensors. The dielectrophoretically immobilization of micron and submicron size particles using interdigitated electrode (IDE) arrays is studied by finite element simulations. The CMOS compatible IDEs have been placed into the silicon microfluidic channel. A rigorous study of the DEP force actuation, the IDE’s geometrical structure, and the fluid dynamics are crucial for enabling the complete platform for CMOS integrated microfluidics and detection of micron and submicron-sized particle ranges. The design of the IDEs is performed by robust finite element analyses to avoid time-consuming and costly fabrication processes. To analyze the preliminary microfluidic test vehicle, simulations were first performed with non-biological particles. To produce DEP force, an AC field in the range of 1 to 5 V (peak-to-peak) is applied to the IDE. The impact of the effective external and internal properties, such as actuating DEP frequency and voltage, fluid flow velocity, and IDE’s geometrical parameters are investigated. The IDE based system will be used to immobilize and sense particles simultaneously while flowing through the microfluidic channel. The sensed particles will be detected using the capacitive sensing feature of the biosensor. The sensing and detecting of the particles are not in the scope of this paper and will be described in details elsewhere. However, to provide a complete overview of this system, the working principles of the sensor, the readout detection circuit, and the integration process of the silicon microfluidic channel are briefly discussed.

A microfluidic based biosensor for rapid detection of Salmonella in food products.

An impedance based microfluidic biosensor for simultaneous and rapid detection of Salmonella serotypes B and D in ready-to-eat (RTE) Turkey matrix has been presented. Detection of Salmonella at a concentration as low as 300 cells/ml with a total detection time of 1 hour has been achieved. The sensor has two sensing regions, with each formed from one interdigitated electrode array (IDE array) consisting of 50 finger pairs. First, Salmonella antibody type B and D were prepared and delivered to the sensor to functionalize each sensing region without causing any cross contamination. Then the RTE Turkey samples spiked with Salmonella types B and D were introduced into the biosensor via the antigen inlet. The response signal resulted from the binding between Salmonella and its specific antibody demonstrated the sensor’s ability to detect a single type of pathogen, and multiple pathogens simultaneously. In addition, the biosensor’s selectivity was tested using non-specific binding of E. coli O157 and E. coli DH5 Alpha while the IDE array was coated with the Salmonella antibody. The results also showed the sensor is capable to differentiate low concentration of live Salmonella cells from high concentration of dead Salmonella cells, and high concentration of E. coli cells. A detailed study on antibody immobilization that includes antibody concentration, antibody coating time (0.5–3 hours) and use of cross-linker has been performed. The study showed that Salmonella antibody to Salmonella antigen is not a factor of antibody concentration after electrodes were saturated with antibody, while the optimal coating time was found to be 1.5 hours, and the use of cross-linker has improved the signal response by 45–60%.

RF Coupling of Interdigitated Electrode Array on Aerogels for in vivo Nerve Guidance Applications

AbstractAerogels are light-weight porous materials that can tolerate the processing steps required for designing and creating an electric circuit such that the aerogel can be utilized as a substrate for device fabrication. Previous studies have shown the biostability and biocompatibility of polyurea crosslinked silica aerogels both in vivo and in vitro and have demonstrated the potential use of aerogels in biomedical applications. In vitro studies have shown that in the presence of an applied electric field neurites regeneration rate was greater on crosslinked silica aerogels than on tissue culture petridish used as a positive control. Currently, epineural suturing and nerve grafting are the gold standards for surgical reconstruction of injured nerves. However, because they rely on passive mechanisms for reapproximating the distal and proximal terminals they often lead to partial or no recovery leaving room for improvement. The present study investigates the feasibility of a wireless aerogel–based electrically-stimulating implant intended for nerve repair applications. Here the authors report on RF coupling between a secondary coil and a primary coil to wirelessly energize an interdigitated electrode array consisting of eleven interlocking fingers, created on a silica aerogel substrate. The coupling strength was tested both in air and in an animal model, as a function of distance and will be reported. This study focuses on in vivo evaluation and feasibility assessment of a novel active 3-D aerogel-based peripheral nerve repair device. The device utilizes induced EMF to establish a current (hence electrical stimulation) in predetermined pathways where nerve stumps will be confined to. Fundamental differences between in vitro and in vivo models necessitate the in vivo approach. The novel inductively-powered electrical stimulation aerogel-based device utilizes previously established 3-D confinement method for immobilization of nerve stumps, taking advantage of the mesoscopic surface roughness, unique to aerogels. The technique is tested on a mechanically strong, lightweight, porous, and biostable aerogel. Lithographic techniques, gold (Au) thin film metallization, and Faraday induction is used for circuit design, development, and activation.

The growth of ZnO nanorods based on hydrothermal and measurement of conductivity

Zinc Oxide (ZnO) nanorods have been attracted interests as a gas molecule-catcher material in gas sensor applications. In this research, ZnO nanorods was grown on the surface of interdigitated electrode arrays substrate by using a hydrothermal method. The hydrothermal process consists of two steps, i.e., the seeding process and the growth of ZnO nanorods. The precursor material used in seeding process was Zinc Acetate Dihydrate (Zn(CH3COO)2.2H2O), while Zinc Nitrate Tetrahydrate (Zn(NO3)2.6H2O) was used as a precursor in the growth of ZnO nanorods. The sample was characterized by using scanning electron microscopy (SEM) and I-V Curve testing to determine the conductivity properties. SEM results show that ZnO nanorods has an average diameter of <100 nm. The result from the I-V curve with applied voltage in the range of 1–30 volt shows that the greater value of the applied voltage produces a decrease of the resistance value. The resistance value obtained at a given voltage of 1 volt is 7.8 kohm, while at a voltage of 30 volts is 0.5 kohm. The I-V curve profile indicates that interface between ZnO nanorods and Au-electrode shows a Schottky barrier characteristics. The gas effect with various parameters of CO gas concentrations, applied voltages and temperatures is under study.

Sustainable Human-Machine Interactive Triboelectric Nanogenerator toward a Smart Computer Mouse

A rapid increase in day-to-day consumer electronics and maximum usage of it builds multiple possibilities in human–machine interaction (HMI). By considering the use of electronic components, such as smartphones, tablet computers, keyboards, etc., a large amount of biomechanical energy would be generated. To harvest the waste mechanical energy, the authors have fabricated a smart computer mouse-triboelectric nanogenerator (SCM-TENG) with an interdigitated array (IDA) electrode made of aluminum (Al) and nylon, paper, cotton, polyethylene, and fluorinated ethylene propylene (FEP) as sliding layers. The SCM-TENG has a high energy output with FEP/Al as a triboelectric material and shows a maximum output of VOC ≈ 210 V and JSC (peak–peak) ≈ 3 μA/m2. We have also carried out stability tests, load resistance analysis, charging commercial capacitors, and a lithium ion (Li-ion) battery. These types of TENG-based electronic devices pave the way for battery-free electronics and commercialization.

Impedance characterization of wheat starch at various water contents

Wheat starch is used extensively in the food, entertainment, and papermaking industries. It is classified as a non-hazard material and an electrical insulator, but recent events manipulating dispersed grains found that electrical properties can vary in different environmental conditions. In order to make advancements in the safety of processes involving these materials, it is necessary to understand their electrical properties. Here, we study wheat starch grains in terms of the aggregation, dielectric resonant frequency, and moisture level. Samples are characterized by Scanning Electron Microscopy (SEM) and Impedance Spectroscopy (IS) using an interdigital planar electrode array. Results showed that the capacitance measurements increase with an increase in the water content (>27.4 Wt%) and therefore it enhances the ability to store an electric field in the polarization of the starch sample. Nyquist plots showed that the internal resistance of the medium decreases for larger grains at low and intermediate stimulus frequencies and at high moisture contents (21–27 Wt%). At high frequencies, the materials behave indistinguishably. We were also able to demonstrate the predictability of water content based on one samples IS measurements. We propose that by extracting the resonant frequencies from the measurements and identifying the resistance of the sample at those frequencies, we can use a regression to predict the water content of the mixture within 1.5 Wt%. Our results show that in the case of 15 − 50μm starch grains, there is a sharp increase in capacitance resulting from the addition of water (10–30 Wt%) which may increase risks of auto-ignition by approaching the Minimum Ignition Energy (MIE). This research offers useful information on how to use IS techniques for understanding both the starch properties and their moisture condition at the same time. This information will allow the industry to asses not only the quality but also the storage safety and handling conditions.

Inkjet Printed Interdigitated Biosensor for Easy and Rapid Detection of Bacteriophage Contamination: A Preliminary Study for Milk Processing Control Applications

Bacteriophages are responsible for significant material and time losses in the dairy industry. This because these viruses infect the selected lactic starter cultures used for milk fermentation, i.e., the first stage toward cheese production. Standard detection techniques are time- and labor-consuming, causing huge costs related to production plant sanitation and product wasting. A new type of biosensor for early detection of bacteriophage contamination is highly demanded by the milk processing market, and inkjet-printed electrochemical sensors could be the answer. Inkjet printing is a well-known technology that has been revisited in recent years, using silver nanoparticle (AgNP) based inks for low-cost and easy fabrication of sensing and biosensing systems on flexible and eco-compatible substrates. In this research, we studied inkjet printing for the manufacturing of both interdigitated electrodes arrays (IDEAs), and a versatile system to monitor bacterial cultures by electrochemical impedance spectroscopy (EIS). In particular, we studied this biosensing system for the detection of bacteriophages by comparing its performance with standard microbiological methods. We performed electrical and morphological characterizations of the devices produced with a consumer-use inkjet printer with commercial AgNPs ink on flexible substrates, such as office paper, polyethylene (PET), and photo paper. We used light microscopy optical analysis, profilometry, atomic force microscopy (AFM), and scanning electron microscopy (SEM) imaging to define the objects resolution, their real dimensions, and thickness. We also investigated the devices’ conductivity and layout, by EIS measurements with a standard buffer solution, i.e., phosphate buffered saline (PBS). Finally, we tested our system by monitoring Lactococcus lactis cultures and bacteriophage infection. We compared the results to those obtained by two standard microbiological methods in terms of response time, proving that our technique requires less than half the time of other methods and no specialized personnel.

Halogen Bonding Interactions for Aromatic and Nonaromatic Explosive Detection.

Improved sensing strategies are needed for facile, accurate, and rapid detection of aromatic and nonaromatic explosives. Density functional theory was used to evaluate the relative binding interaction energies between halogen-containing sensor model molecules and nitro-containing explosives. Interaction energies ranged from -18 to -14 kJ/mol and highly directional halogen bonding interactions were observed with bond distances ranging between 3.0 and 3.4 Å. In all geometry optimized structures, the sigma-hole of electropositive potential on the halogen aligned with a lone pair of electrons on the nitro-moiety of the explosive. The computational results predict that the strongest interactions will occur with iodine-based sensors as, of all the halogens studied, iodine is the largest, most polarizable halogen with the smallest electronegativity. Based on these promising proof-of-concept results, synthetically accessible sensors were designed using 1,4-dihalobenzene (X = Cl, Br, and I) with and without tetra-fluoro electron withdrawing groups attached to the benzene ring. These sensing molecules were embedded onto single walled carbon nanotubes that were mechanically abraded onto interdigitated array electrodes, and these were used to measure the responses to explosive model compounds cyclohexanone and dimethyl-dinitro-benzene in nitrogen gas. Amperometric current-time curves for selectors and control molecules, including concentration correlated signal enhancement, as well as response and recovery times, indicate selector responsiveness to these model compounds, with the largest response observed for iodo-substituted sensors.

Impedimetric array in polymer microfluidic cartridge for low cost point-of-care diagnostics

Deep Vein Thrombosis and pulmonary embolism (DVT/PE) is one of the most common causes of unexpected death for hospital in-patients. D-dimer is used as a biomarker within blood for the diagnosis of DVT/PE. We report a low-cost microfluidic device with a conveniently biofunctionalised interdigitated electrode (IDE) array and a portable impedimetric reader as a point-of-care (POC) device for the detection of D-dimer to aid diagnosis of DVT/PE. The IDE array elements, fabricated on a polyethylenenaphtalate (PEN) substrate, are biofunctionalised in situ after assembly of the microfluidic device by electropolymerisation of a copolymer of polypyrrole to which is immobilised a histidine tag anti-D-Dimer antibody. The most consistent copolymer films were produced using chronopotentiometry with an applied current of 5μA for a period of 50 s using a two-electrode system. The quality of the biofunctionalisation was monitored using optical microscopy, chronopotentiometry curves and impedimetric analysis. Measurement of clinical plasma sample with a D-dimer at concentration of 437 ng/mL with 15 biofunctionalised IDE array electrodes gave a ratiometric percentage of sample reading against the blank with an average value of 124 ± 15 at 95% confidence. We have demonstrated the concept of a low cost disposable microfluidic device with a receptor functionalised on the IDE array for impedimetric detection towards POC diagnostics. Changing the receptor on the IDE array would allow this approach to be used for the direct detection of a wide range of analytes in a low cost manner.

Thermoplastic Electrode Arrays in Electrochemical Paper-Based Analytical Devices.

Electrochemical paper-based analytical devices (ePADs) have garnered significant interest as an alternative to traditional benchtop methods due to their low cost and simple fabrication. Historically, ePADs have relied almost exclusively on single electrode detection, limiting potential gains in sensitivity and selectivity achievable with multiple electrodes. Herein we describe incorporation of thermoplastic electrode (TPE) arrays into flow ePADs. Quasi-steady flow was solely generated by capillary action through a fan-shaped paper device. The electrode arrays were fabricated using a simple solvent-assisted method with inexpensive materials (i.e., graphite and thermoplastic binder). These electrodes can be employed as an array of individually addressable detectors or connected as an interdigitated electrode array. The TPEs were characterized through SEM, optical profilometry and cyclic voltammetry. Chronoamperometry was used to characterize the flow-based TPE-ePADs. Trace detection of a ferrocene complex (FcTMA+) was demonstrated through generation-collection experiments, achieving a limit of detection of 0.32 pmol. These TPE arrays containing ePADs show great promise as a rapid, sensitive, and low-cost sensor for point-of-need (PON) applications.

Microfluidic based impedance biosensor for pathogens detection in food products.

A MEMS-based impedance biosensor was designed, fabricated, and tested to effectively detect the presence of bacterial cells including E. coli O157:H7 and Salmonellatyphimurium in raw chicken products using detection region made of multiple interdigitated electrode arrays. A positive dielectrophoresis based focusing electrode was used in order to focus and concentrate the bacterial cells at the centerline of the fluidic microchannel and direct them toward the detection microchannel. The biosensor was fabricated using surface micromachining technology on a glass substrate. The results demonstrate that the device can detect Salmonella with concentrations as low as 10 cells/mL in less than 1 h. The device sensitivity was improved by the addition of the focusing electrodes, which increased the signal response by a factor between 6 and 18 times higher than without the use of the focusing electrodes. The biosensor is selective and can detect other types of pathogen by changing the type of the antibody immobilized on the detection electrodes. The device was able to differentiate live from dead bacteria.

A Self-Adaptive and Wide-Range Conductivity Measurement Method Based on Planar Interdigital Electrode Array

Conductivity is a crucial parameter in water quality detection, which can roughly represent overall concentration of various inorganic ions. However, traditional conductivity sensors can only afford high performance measurement in a relatively low range while the concentration may vary much more in realworld water environment. This paper proposes a high-precision and wide-range measurement method based on a novel planar interdigital electrode sensor array and a self-adaptive algorithm. The array is composed of 3 pairs of planar electrodes with various cell constants aiming at different subdivided conductivity sections. The follow-up circuit and the self-adaptive algorithm keep the optimal electrode pair dominates the output of the array. Numerical simulations were utilized to optimize sensor parameters before fabrication. PCB manufacturing technique was used which guaranteed a relatively low manufacturing cost and stable performance. Experiments were conducted to verify the sensing performance and results showed that the array can maintain precise measurement from 0.5μs/cm to 500ms/cm.

3D impedimetric sensors as a tool for monitoring bacterial response to antibiotics.

The presence of antimicrobial contaminants like antibiotics in the environment is a major concern because they promote the emergence and the spread of multidrug resistant bacteria. Since the conventional systems for the determination of bacterial susceptibility to antibiotics rely on culturing methods that require long processing times, the implementation of novel strategies is highly required for fast and point-of-care applications. Here the development and characterization of a novel label-free biosensing platform based on a microbial biosensor approach to perform antibiotic detection bioassays in diluted solution is presented. The microbial biosensor is based on a three-dimensional interdigitated electrode array (3D-IDEA) impedimetric transducer with immobilized E. coli bacteria. In 3D-IDEA to increase the sensitivity to superficial impedance changes the electrode digits are separated by insulating barriers. A novel strategy is employed to selectively immobilize bacteria in the spaces over the electrode digits between the barriers, referred to here as trenches, in order to concentrate bacteria, improve the reproducibility of the E. coli immobilization and increase the sensitivity for monitoring bacterial response. For effective attachment of bacteria within the trenches an initial anchoring layer of a highly charged polycation, polyethyleneimine (PEI), was used. To facilitate immobilization of bacteria within the trenches and prevent their deposition on top of the barriers an important novelty is the use of poly(N-isopropylmethacrylamide) p(NIPMAM) microgels working as antifouling agents, deposited on top of the barriers by microcontact printing. The reported microbial biosensor approach allows the bacterial response to ampicillin, a bacteriolytic antibiotic, to be registered by means of impedance variations in a rapid and label-free operation that enables new possibilities in bioassays for toxicity testing.