Interdigitated Microelectrode Array Research Articles

A novel cleanroom-free technique for simultaneous electrodeposition of polypyrrole onto array of IDuEs: Towards low-cost, stable and accurate point-of-care TBI diagnosis without trained manpower

Drop-casted polypyrrole (PPY) nanomaterial-based point-of-care Traumatic Brain Injury (TBI) immunosensing platforms reported previously demand trained manpower at field-test, due to poor adhesion between nanomaterial and electrode surface, limiting the point-of-care purpose. The usage of conventional clean-room-based physical and chemical vapor deposition techniques in creating strong adhesion is limited on account of cost and process complexity. Addressing this technical gap, we report a novel low-cost clean-room-free technique that can effectively electrodeposit the PPY simultaneously onto the working areas of array of Interdigitated microelectrodes (IDμEs) from the precursor solution. Through optimization of deposition cycles and molar concentration ratio of monomer and oxidizing agents, a high-quality nanomaterial was electrodeposited on IDμEs' surface. Further, by using the electrodeposited PPY as a bioelectrical transducer, the TBI-specific UCHL1 and GFAP target analytes were simultaneously detected in terms of variation of DC-Resistance and AC-Capacitance parameters, recorded through chemiresistive I-V and chemicapacitive C-F responses of bioelectrodes, respectively. Such simultaneous multianalyte-detection in terms of multiple parameters increases the diversity of decision-making parameters by several folds, inherently aids in enhancing the diagnostic accuracy of TBI test kit. Here, the efficiency of the electrodeposited PPY-based chemiresistive and chemicapacitive immunosensing platforms in detecting TBI-specific target analytes simultaneously in real-time human-plasma samples was analyzed in terms of sensitivity, resolution, LoD, RoD, long-term stability (30 weeks), and the same is compared with drop-cast PPY-based immunosensing platform. Notably, the electrodeposited PPY sensing platforms showed superior performance in terms of sensitivity, LoD, device variability and long-term stability without demanding any trained manpower in the field.

In Situ Biosynthesis of FeS Nanoparticles Boosts Current Generation in Bioelectrochemical Systems Through Efficient Electron Transfer.

The utility of electrochemical active biofilm in bioelectrochemical systems has received considerable attention for harvesting energy and chemical products. However, the slow electron transfer between biofilms and electrodes hinders the enhancement of performance and still remains challenging. Here, using Fe3O4 /L-Cys nanoparticles as precursors to induce biomineralization, a facile strategy for the construction of an effective electron transfer pathway through biofilm and biological/inorganic interface is proposed, and the underlying mechanisms are elucidated. Taking advantage of an on-chip interdigitated microelectrode array (IDA), the conductive current of biofilm that is related to the electron transfer process within biofilm is characterized, and a 2.10-fold increase in current output is detected. The modification of Fe3O4/L-Cys on the electrode surface facilitates the electron transfer between the biofilm and the electrode, as the bio/inorganic interface electron transfer resistance is only 16% compared to the control. The in-situ biosynthetic Fe-containing nanoparticles (e.g., FeS) enhance the transmembrane EET and the EET within biofilm, and the peak conductivity increases 3.4-fold compared to the control. The in-situ biosynthesis method upregulates the genes involved in energy metabolism and electron transfer from the transcriptome analysis. This study enriches the insights of biosynthetic nanoparticles on electron transfer process, holding promise in bioenergy conversion.

Optimization of Planar Interdigitated Microelectrode Array for Enhanced Sensor Responses

Immunoassays play a pivotal role in detecting and quantifying specific proteins within biological samples. However, its sensitivity and turnaround time are constrained by the passive diffusion of target molecules towards the sensors. ACET (Alternating Current Electrothermal) enhanced reaction emerges as a solution to overcome this limitation. The ACET-enhanced biosensor works by inducing vortices through electrothermal force, which stirs the analyte within the microchannel and promotes a reaction process. In this study, a comprehensive two-dimensional finite element study is conducted to optimize the binding efficiency and detection time of an ACET-enhanced biosensor without external pumping. Optimal geometries for interdigitated electrodes are estimated to achieve significant improvements in terms of probe utilization and enhancement factor. The study’s findings demonstrate enhancement factors of 3.21, 2.15, and 3.09 along with 71.22%, 75.80%, and 57.52% normalized binding for C-reactive protein (CRP), immunoglobulin (IgG), and SARS-CoV-2, respectively.

Recent Advances in CMOS Electrochemical Biosensor Design for Microbial Monitoring: Review and Design Methodology.

Rapid, high-sensitivity, and real-time characterization of microorganisms plays a significant role in several areas, including clinical diagnosis, human healthcare, early detection of outbreaks, and the protection of living beings. Integrating microbiology and electrical engineering promises the development of low-cost, miniaturized, autonomous, and high-sensitivity sensors to quantify and characterize bacterial strains at various concentrations. Electrochemical-based biosensors are receiving particular attention in microbiological applications among the different biosensing devices. Several approaches have been adopted to design and fabricate cutting-edge, miniaturized, and portable electrochemical biosensors to track and monitor bacterial cultures in real time. These techniques differ in their sensing interface circuits and microelectrode fabrication. The goals of this review are (i) to summarize the current state of CMOS sensing circuit designs in label-free electrochemical biosensors for bacteria monitoring and (ii) to discuss the material and size of the electrodes used in electrochemical biosensors in microbiological applications. In this paper, we reviewed the latest and most advanced CMOS integrated interface circuits that have recently been used in electrochemical biosensors to identify and characterize bacteria species, such as impedance spectroscopy, capacitive, amperometry, and voltammetry, etc. In addition to the interface circuit design, other crucial factors, such as the material and scale of the electrodes, must be considered to increase the sensitivity of electrochemical biosensors. Surveying the literature in this field improves our knowledge about the impact of electrode designs and materials on sensing precision and will help future designers adapt, design, and fabricate appropriate electrode configurations based on their application. Thus, we summarized the conventional microelectrode designs and materials mainly employed in microbial sensors, including interdigitated electrodes (IDEs), microelectrode arrays (MEAs), paper, and carbon-based electrodes, etc.

Label-free impedimetric immunosensor for point-of-care detection of COVID-19 antibodies

The COVID-19 pandemic has posed enormous challenges for existing diagnostic tools to detect and monitor pathogens. Therefore, there is a need to develop point-of-care (POC) devices to perform fast, accurate, and accessible diagnostic methods to detect infections and monitor immune responses. Devices most amenable to miniaturization and suitable for POC applications are biosensors based on electrochemical detection. We have developed an impedimetric immunosensor based on an interdigitated microelectrode array (IMA) to detect and monitor SARS-CoV-2 antibodies in human serum. Conjugation chemistry was applied to functionalize and covalently immobilize the spike protein (S-protein) of SARS-CoV-2 on the surface of the IMA to serve as the recognition layer and specifically bind anti-spike antibodies. Antibodies bound to the S-proteins in the recognition layer result in an increase in capacitance and a consequent change in the impedance of the system. The impedimetric immunosensor is label-free and uses non-Faradaic impedance with low nonperturbing AC voltage for detection. The sensitivity of a capacitive immunosensor can be enhanced by simply tuning the ionic strength of the sample solution. The device exhibits an LOD of 0.4 BAU/ml, as determined from the standard curve using WHO IS for anti-SARS-CoV-2 immunoglobulins; this LOD is similar to the corresponding LODs reported for all validated and established commercial assays, which range from 0.41 to 4.81 BAU/ml. The proof-of-concept biosensor has been demonstrated to detect anti-spike antibodies in sera from patients infected with COVID-19 within 1 h.Photolithographically microfabricated interdigitated microelectrode array sensor chips & label-free impedimetric detection of COVID-19 antibody.

In Situ Confocal Fluorescence Lifetime Imaging of Nanopore Electrode Arrays with Redox Active Fluorogenic Amplex Red.

Direct imaging of electrochemical processes on electrode surfaces is a central part of understanding spatially heterogeneous electrochemical processes on the surfaces. Herein, we report a strategy for the spatially resolved imaging of local faradaic processes on nanoscale electrochemical interfaces. This strategy is based on fluorescence lifetime imaging microscopy (FLIM) with the use of Amplex Red as a fluorogenic redox probe. After verifying the capability of Amplex Red for fluorescence lifetime imaging, we demonstrated the turn-on FLIM-based imaging of faradaic processes on the electrochemical interfaces of different dimensions. In particular, we achieved spatially resolved visualization of the local electrochemical processes occurring on even nanopore electrode arrays as well as conventional microelectrodes, including disk-shaped ultramicroelectrodes and interdigitated array microelectrodes.

Detection of Tomato Ringspot Virus Based on Microfluidic Impedance Sensor.

A microfluidic impedance sensor embedded with gold interdigitated array microelectrodes was utilized to rapidly detect Tomato Ringspot Virus (ToRSV) and achieve efficient and precise detection. The electrochemical impedance spectrum was obtained by immobilizing ToRSV antibody on the surface of a gold interdigital array microelectrode and mixing it with ToRSV to generate an impedance change. The electrochemical impedance spectrum was obtained. The equivalent circuit was established to analyze the mechanism of impedance change, and the quantitative linear relationship between ToRSV concentration and impedance was established. According to an equivalent circuit analysis, ToRSV increases the solution resistance Rs, the electron transfer resistance Ret on the electrode surface, and the double layer capacitance Cdl, resulting in an increase in impedance. The results reveal that the ToRSV concentration detected in the range of 0.001 to 10 μg/mL ranges from 248.8 to 687.2 kΩ at the ideal detection frequency of 10.7 Hz, with a good linear connection, R2 = 0.98. When this method’s detection limit is tested, the impedance value is 367.68 kΩ. 0.0032 μg/mL was the detection limit. The sensor is quick and easy to use, has high detection sensitivity, and can be used to detect other plant viruses.

A highly sensitive, easy-and-rapidly-fabricable microfluidic electrochemical cell with an enhanced three-dimensional electric field

An NP-μFEC is a reusable, novel microfluidic electrochemical cell with multiple non-planar interdigitated microelectrode arrays, minimal sample volume, and enhanced electric field penetration for highly sensitive electrochemical analysis. (i) The NP-μFEC features spatial 3-electrode architecture, and a small sample volume (∼4 μL). (ii) Here, [Fe(CN)6]3-/4- redox couple are used as an electrochemical reporter. The effects on the electrochemical properties of NP-μFEC due to the change in the reference electrode (RE) and counter electrode (CE)'s position with respect to the working electrode (WE) position are analyzed. For NP-μFEC, the position of the RE with respect to the WE does not affect the CV, DPV electrochemical profiles. However, the spacing between the CE and WE plays a significant role. (iii) The enhanced three-dimensional electric field penetration in NP-μFEC is validated by finite element analysis simulation using COMSOL Multiphysics. (iv) Without electrode surface modifications, NP-μFEC shows a detection limit (DL) of ∼2.54 × 10−6 M for aqueous [Fe(CN)6]3-/4- probe. (v) The DL for Cu2+, Fe3+, and Hg2+ are 30.5±9.5 μg L−1, 181±58.5 μg L−1, and 12.4±1.95 μg L−1, respectively, which meets the US Environmental Protection Agency (EPA)'s water contamination level for Cu, Fe, and is close to that for Hg (EPA limits are 1300 μg L−1, 300 μg L−1, and 2 μg L−1, respectively). (vi) Further, using a pressure-sensitive adhesive layer to form the channel and create the NP-μFEC configuration simplifies the manufacturing process, making it cost-effective and allowing for rapid adoption in any research lab. NP-μFEC is used to detect heavy metal ions in water. This demonstrates that cost-effective, easy-to-fabricate NP-μFEC can be a new sensitive electrochemical platform.

Label-free, ultrasensitive and rapid detection of FDA-approved TBI specific UCHL1 biomarker in plasma using MWCNT-PPY nanocomposite as bio-electrical transducer: A step closer to point-of-care diagnosis of TBI

Traumatic Brain Injury (TBI), a major cause of mortality and neurological disability affecting people of all ages worldwide, remains a diagnostic and therapeutic challenge to date. Rapid, ultra-sensitive, selective, and wide-range detection of TBI biomarkers in easily accessible body fluids is an unmet clinical need. Considering this, in this work, we report the design and development of a facile, label-free, highly stable and sensitive, chemi-impedance-based sensing platform for rapid and wide range detection of Ubiquitin-carboxy terminal hydrolase L1 (UCHL1: FDA-approved TBI specific plasma biomarker), using carboxylic functionalized MWCNTs embedded polypyrrole (PPY) nanocomposites (PPY/f-MWCNT). The said nanocomposites were synthesized using chemical oxidative polymerization method. Herein, the functionalized MWCNTs are used as conducting fillers so as to increase the polymer's dielectric constant according to the micro-capacitor model, thereby augmenting both DC electrical conductivity and AC dielectric property of the nanocomposite. The proposed immunosensing platform comprises of PPY/f-MWCNT modified interdigitated microelectrode (IDμEs) array, on which anti-UCHL1-antibodies are immobilized using suitable covalent chemistry. The AC electrical characterization of the nanocomposite modified IDμEs, with and without the antibodies, was performed through generic capacitance vs. frequency (C–F, 1 KHz – 1 MHz) and capacitance vs. applied bias (C–V, 0.1 V–1 V) measurements, using an Agilent B1500A parametric analyzer. The binding event of UCHL1 peptides to anti-UCHL1-antibodies was transduced in terms of normalised changes in parallel capacitance, via the C–F analysis. Further, we have tested the detection efficiency of the said immunoassay against UCHL1 spiked human plasma samples in the concentration range 10 fg/mL – 1 μg/mL. The proposed sensing platform detected UCHL1 in spiked-plasma samples linearly in the range of 10 fg/mL – 1 ng/mL with a sensitivity and LoD of 4.22 ((ΔC/C0)/ng.mL−1)/cm2 and 0.363 fg/mL, respectively. Further, it showed excellent stability (30 weeks), repeatability, reproducibility, selectivity and interference-resistance. The proposed approach is label-free, and if desired, can be used in conjunction with DC measurements, for biosensing applications.

Designing Sensitivity: A Comparative Analysis of Microelectrode Topologies for Electrochemical Oxygen Sensing in Biomedical Applications.

The monitoring of dissolved oxygen is a key parameter in many fields, namely the treatment and monitoring of various cerebral traumas. Leveraging existing manufacturing techniques, electrochemical sensors hold the potential for compact, simple, and scalable dissolved oxygen sensors. Past studies have focused on the general design of such sensors, but a comparative study on the impact of microelectrode geometries for cerebral applications has been forthcoming. We present here the results of a characterization study conducted across solid-state sensors with varying microelectrode geometries. The electrode structures were covered with a Nafion membrane and included variations of the classic interdigitated microelectrode array in addition to a circular microelectrode array variation. Voltage sweeps were conducted while monitoring the devices’ sensing current responses across a 50.3 mmHg change in dissolved oxygen within a deionized aqueous solution. Half of the devices were identified as ultramicroelectrode designs that presented a greater dependence on electrode spacing and topology. The ultramicroelectrode-style (UME) interdigitated electrode (IDE) topology presented the greatest signal response at 25.24 nA/mmHg, an approximate eight-fold improvement in sensitivity from a non-UME variation with a sensitivity of 2.98 nA/mmHg. The design presented a linear response from 8.3 mmHg to 58.6 mmHg with r2 = 0.9743. The sensitivity improvement was attributed to the ultramicroelectrode structure’s amplifying diffusive feedback, which was enabled by the IDE topology and short electrode spacings.

Micropatterned PEDOT with Enhanced Electrochromism and Electrochemical Tunable Diffraction

Micro-nanofabrication of conductive polymers (CPs) with functional structures is in great demand in organic electronic devices, micro-optics, and flex sensors. Here, we report the fabrication of micropatterned poly(3,4-ethylenedioxythiophene) (PEDOT) and its applications on flexible electrochromic devices and tunable diffractive optics. The localized electropolymerization of 3,4-ethylenedioxythiophene at the electrode/agarose gel stamping interface through an electrochemical wet stamping (E-WETS) technique is used to fabricate PEDOT with functional microstructures. PEDOT microdots, micro-rectangles, and interdigitated array microelectrodes are fabricated with submicron tolerance and ∼2 μm smallest feature size. Furthermore, the flexible PEDOT electrochromic devices consisting of the logo of Xiamen University are fabricated with a reversible switch of absorptivity. The improved optical and coloration-amperometric responses of electrochromism are demonstrated because of the enhanced charge transport rate of the micropatterned PEDOT. The electrochromism of the 2D PEDOT micropatterns is further used as a binary diffractive optical element to modulate the intensity and efficiency of diffracted 2D structural light because of the switchable absorptivity during doping and dedoping processes. When the potential is switched from 1 to -1 V to tune the absorptivity at ∼600 nm from low to high, the intensity of zero-order diffraction light spot decreases with the intensity of other order diffraction light spots increasing dramatically. The results demonstrate that E-WETS provides an alternative method for the fabrication of CPs with functional micro-nanostructures. The electrochemical tunable diffraction with high reversibility and fast response is of potential applications in micro-optics and flex sensors.

Electrochemically activated polyaniline based ambipolar organic electrochemical transistor

AbstractThe organic electrochemical transistors (OECTs) are largely applied as bio‐ and ion‐sensor devices due to their performance in an aqueous environment with electrochemical doping/dedoping (reversible redox reactions) of the semiconducting layer through ion injection and also low (around 1 V) operation potentials. Aiming for the complementary circuits’ development and improvement of the sensors device, we report the application of spin coated polyaniline (PANI) in ambipolar OECT. The OECT operation is based on electrochemical protonation/deprotonation of PANI upon applied gate potential that was verified by cyclic voltammograms (CV) of PANI sample. The device operates in accumulation mode with on‐currents on the milliampere range due to the use of interdigitated array (IDA) microelectrodes architecture with a larger active area. Acid (HCl) doped PANI were applied in OECT device for comparison, and it presented improved performance with increasing drain‐source current up to 38%, reaching 4.8 mA for the n‐type device. This current increase is due to the narrower bandgap of doped PANI that affects the injection barrier. The HCl doped PANI was evaluated by UV‐Vis spectrophotometry and CV analysis. Using deionized water as electrolyte defunctionalized the PANI‐based OECT (no current modulation observed) because the absence of ions in the electrolyte interrupts the electrochemical doping. This is the opposite for the poly(3‐hexylthiophene) (P3HT)‐based electrolyte‐gated organic field‐effect transistor (EGOFET) due to the polymeric hydrophobicity nature that allows for field‐effect modulation in the electrolyte/semiconductor interface. The results presented may open new possibilities for bio‐ and ion‐sensors devices.

Sensitivity Analysis of a Portable Wireless PCB-MEMS Permittivity Sensor Node for Non-Invasive Liquid Recognition.

Dielectric characteristics are useful to determine crucial properties of liquids and to differentiate between liquid samples with similar physical characteristics. Liquid recognition has found applications in a broad variety of fields, including healthcare, food science, and quality inspection, among others. This work demonstrates the fabrication, instrumentation, and functionality of a portable wireless sensor node for the permittivity measurement of liquids that require characterization and differentiation. The node incorporates an interdigitated microelectrode array as a transducer and a microcontroller unit with radio communication electronics for data processing and transmission, which enable a wide variety of stand-alone applications. A laser-ablation-based microfabrication technique is applied to fabricate the microelectromechanical systems (MEMS) transducer on a printed circuit board (PCB) substrate. The surface of the transducer is covered with a thin layer of SU-8 polymer by spin coating, which prevents it from direct contact with the Cu electrodes and the liquid sample. This helps to enhance durability, avoid electrode corrosion and contamination of the liquid sample, and to prevent undesirable electrochemical reactions to arise. The transducer’s impedance was modeled as a Randles cell, having resistive and reactive components determined analytically using a square wave as stimuli, and a resistor as a current-to-voltage converter. To characterize the node sensitivity under different conditions, three different transducer designs were fabricated and tested for four different fluids, i.e., air, isopropanol, glycerin, and distilled water—achieving a sensitivity of 1.6965 +/− 0.2028 εr/pF. The use of laser ablation allowed the reduction of the transducer footprint while maintaining its sensitivity within an adequate value for the targeted applications.

Core-shell Au@Cu2O-graphene-polydopamine interdigitated microelectrode array sensor for in situ determination of salicylic acid in cucumber leaves

The in situ detection of active small molecules in plants is one of the key technologies for the development of precision agriculture. An interdigitated microelectrode (IDME) array electrochemical sensor is constructed herein, with three groups of IDME arrays as a three-electrode system. The core-shell [email protected]2O-graphene (Gr)-polydopamine (PDA) nanoparticles are densely packed on Al microelectrodes using a three-potential step pulse electrodeposition method. Each of the over 2000 individual microelectrodes is approximately 1 μm wide and 1100 μm in length. The sensor has a high response to salicylic acid (SA) due to the synergistic electrocatalysis of [email protected]2O, Gr, and PDA, and the high-density arrangement of the three-electrode unit with microelectrodes. The sensor has a linear concentration range of 0.01–100 μM for SA and the detection limit is as low as 1.16 nM. The SA concentration in cucumber leaves is monitored from the early growth stage to the fruiting stage using the IDME array sensor, and the juice and living stems of the cucumber are detected. The flat structure of the [email protected]2O-Gr-PDA IDME array sensor is suitable for attachment onto plant tissues, especially for the in situ detection of SA in leaves.

In Situ Spectroelectrochemical Characterization Reveals Cytochrome-Mediated Electric Syntrophy in Geobacter Coculture.

Direct interspecies electron transfer (DIET) between microbial species prevails in some key microbial consortia. However, the electron transfer mechanism(s) in these consortia is controversial due to lack of efficient characterization methods. Here, we provide an in situ anaerobic spectroelectrochemical coculture cell (in situ ASCC) to induce the formation of DIET coculture biofilm on the interdigitated microelectrode arrays and characterize the electron transfer directly. Two typical Geobacter DIET cocultures, Geobacter metallireducens and wild-type Geobacter sulfurreducens (G.m&G.s) and G. metallireducens and a G. sulfurreducens strain deficient in citrate synthase (G.m&G.s-ΔgltA), were selected. In situ Raman and electrochemical Fourier transform infrared (FTIR) spectroscopy indicated that cytochromes are abundant in the electric syntrophic coculture. Cyclic voltammetry and potential step experiment revealed a diffusion-controlled electron transfer process and the electrochemical gating measurements further demonstrated a cytochrome-mediated electron transfer in the DIET coculture. Furthermore, the G.m&G.s-ΔgltA coculture displayed a higher redox conductivity than the G.m&G.s coculture, consistent with the existence of an intimate and efficient electrical connection between these two species. Our findings provide the first report of a redox-gradient-driven electron transport facilitated by c-type cytochromes in DIET coculture, supporting the model that DIET is mediated by cytochromes and suggest a platform to explore the other DIET consortia.

Spatial variation of electrical conductance in electrochemically active biofilm growing on interdigitated microelectrode array

Revealing the pathways of electron transport within electrochemically active biofilms (EABs) is of great importance. Here, mixed-culture EABs are grown on three interdigitated microelectrode arrays (IDAs) with different gap widths of 10 μm, 20 μm and 50 μm and their conductances are determined. The maximum conductive current increases with the decrease of the gap width and charge transfer resistance obtained for the biofilm attaching on the electrode is 3–11 fold less than that for biofilm bridging gaps, suggesting high conductance of biofilm closer to the electrode surface. Results from Raman analysis show high abundance of multi-heme cytochromes in biofilm bridging 10 μm gap, leading to small resistance of biofilm growing on the IDA with 10 μm gap. In addition, the maximum conductive current of biofilm bridging gaps at the potential of −0.40 V vs. Ag/AgCl suggests that electron transfer in biofilm growing on IDAs is redox driven. All these results indicate the spatial heterogeneity of electron transport processes acting within biofilm.

Enterotoxigenic Escherichia Coli Detection Using the Design of a Biosensor

The food industry and clinical analysis, among other sectors, require the development of techniques and devices that detect pathogens, while the development of implantable devices needs biocompatible materials with low degradation in biological environment to increase the lifetime of the device. Throughout this work, hydrogenated amorphous silicon-carbon alloy is proposed, obtained, characterized and incorporated into the development of a proposed interdigitated microelectrode array (PIMA) to capture the bacteria of enterotoxigenic Escherichia coli (E. coli, ETEC). a-SixC1-x:H is obtained by the technique of plasma-enhanced chemical vapor deposition (PECVD) using methane and silane as precursor gases under high hydrogen dilution and low power density in order to improve its biocompatibility. Functionally the PIMA is a transducer based on electrical impedance, namely the capture of E. coli bacteria causes changes in the electrical properties of the medium between and on the microelectrodes of the array, which are associated with changes in electrical impedance. The simulations were made with the purpose of knowing the operation that the PIMA would have under operating conditions (with bacterial environment) and of analyzing the design aspects that could affect or increase the sensitivity of the array.

Electrochemical detection of free-chlorine in Water samples facilitated by in-situ pH control using interdigitated microelectrodes

Residual free-chlorine concentration in water supplies is a key metric studied to ensure disinfection. High residual chlorine concentrations lead to unpleasant odours and tastes, while low concentrations may lead to inadequate disinfection. The concentration is most commonly monitored using colorimetric techniques which require additional reagents. Electrochemical analysis offers the possibility for in-line analysis without the need for additional reagents. Electrochemical-based detection of chlorine is influenced by the solution pH, which defines the particular chlorine ionic species present in solution. As such, controlling the pH is essential to enable electrochemical based detection of residual chlorine in water. To this end, we explore the application of solid state interdigitated electrodes to tailor the in-situ pH of a solution while simultaneously detecting free-chlorine. Finite element simulations and subsequent electrochemical characterization, using gold interdigitated microelectrode arrays, were employed to explore the feasibility of an in-situ pH control approach. In practice, the approach converted residual chlorine from an initial mixture of two species (hypochlorous acid and hypochlorite ion), to one species (hypochlorous acid). Chlorine detection was shown in water samples using this exploratory method, resulting in a two-fold increase in signal response, compared to measurements without pH control. Finally, tap water samples were measured using the in-situ pH control method and the results showed excellent correlation (within experimental error) with a commercial instrument, demonstrating the efficacy of the developed technique. This work establishes the possibility of deploying an electrochemical based reagent-free, in-line chlorine sensor required for water distribution networks.

Rapid and ultrasensitive detection of Salmonella typhimurium using a novel impedance biosensor based on SiO2@MnO2 nanocomposites and interdigitated array microelectrodes

A novel impedance biosensor was developed based on the interdigitated microelectrodes using H2O2 to reduce SiO2@MnO2 nanocomposites into Mn2+, resulting in significant impedance changes in the rapid and ultrasensitive detection of Salmonella typhimurium (S. typhimurium). The captured S. typhimurium monoclonal antibodies (MAb1) were assembled on the outer layer of the magnetic beads (MBs) for specific enrichment and isolation of S. typhimurium cells in complex samples. The recognized S. typhimurium monoclonal antibodies (MAb2) were immobilized on the surface of the SiO2@MnO2 nanocomposites, which could react with the MBs- S. typhimurium conjugates to form the MBs- S. typhimurium -SiO2@MnO2 sandwich complexes. The MnO2 on the surface of the sandwich complexes was reduced into Mn2+ by using H2O2 achieving obvious impedance change that could be detected by the interdigitated microelectrodes. The recoveries for S. typhimurium cells at the concentrations between 2.0 × 101 and 2.0 × 105 CFU/mL were 83.1 %–97.0 % in the spiked milk samples. The limit of detection of this biosensor for S. typhimurium cells in the spiked milk samples was 21 CFU/mL. This approach possesses the merits of simple operation, high sensitivity, and low cost, potentially enabling this device to be a lab-on-a-chip for rapid screening of foodborne pathogens.

Electrokinetic Propulsion of Polymer Microparticulates Along Glassy Carbon Electrode Array

Abstract Dielectrophoresis (DEP) is a force applied to microparticles in nonuniform electric field. This study discusses the fabrication of the glassy carbon interdigitated microelectrode arrays using lithography process based on lithographic patterning and subsequent pyrolysis of negative SU-8 photoresist. Resulting high-resistance electrodes would have the regions of high electric field at the ends of microarray as demonstrated by simulation. The study demonstrates that combining the alternating current (AC) applied bias with the direct current (DC) offset allows the user to separate subpopulations of microparticulates and control the propulsion of microparticles to the high field areas such as the ends of the electrode array. The direction of the movement of the particles can be switched by changing the offset. The demonstrated novel integrated DEP separation and propulsion can be applied to various fields including in vitro diagnostics as well as to microassembly technologies.