Interdigitated Array Research Articles

Low-Frequency Impedance-Based Cell Discrimination Considering Ion Transport Model in Cell Suspension.

Low-frequency impedance-based (LFI) cell discrimination as a novel non-destructive and non-invasive cell discrimination is proposed. LFI cell discrimination discriminates the cell type by considering an ion transport model in cell suspension. Ion transport model in cell suspension is constructed on the basis of Fick's laws of diffusion in the extracellular region under ion permeability P which represents the characteristics of cell type. P is achieved using the ion transport model equation through an iterative curve fitting to an ion concentration in extracellular region obtained from low-frequency impedance which is assumed to be linearly related to the ion concentration in extracellular region. In experiment, the electrical impedance spectra from the frequency of 200kHz to 2.0MHz are measured over time during producing ions from intracellular region to extracellular one in cell suspension using an impedance analyzer and an interdigitated array electrode system. As a target cell type, two different cell types based on Medical Research Council 5 (MRC-5), which are different in intracellular component are used. The curve fitting is performed for the low-frequency impedance at 200kHz at which impedance reflects the ion concentration in extracellular region in order to obtain P of each cell type. As a result, each cell type has its own P. The proposed LFI cell discrimination successfully discriminates the cell type.

In Situ Real-Time Monitoring of ITO Film under a Chemical Etching Process Using Fourier Transform Electrochemical Impedance Spectroscopy.

As a novel approach to the in situ real-time investigation of an ITO electrode during the wet etching process, step-excitation Fourier-transform electrochemical impedance spectroscopy (FT-EIS) was implemented. The equivalent circuit parameters (e.g., Rct, Cdl) continuously obtained by the FT-EIS measurements during the entire etching process showed an electrode activation at the initial period as well as the completion of etching. The FT-EIS results were further validated by cyclic voltammograms and impedance measurements of partially etched ITO films using ferri- and ferrocyanide solution in combination with FESEM imaging, EDS, XRD analyses, and COMSOL simulation. We also demonstrated that this technique can be further utilized to obtain intact interdigitated array (IDA) electrodes in a reproducible manner, which is generally considered to be quite tricky due to delicacy of the pattern. Given that the FT-EIS allows for instantaneous snapshots of the electrode at every moment, this work may hold promise for in situ real-time examination of structural, electrokinetic, or mass transfer-related information on electrochemical systems undergoing constantly changing, transient processes including etching, which would be impossible with conventional electroanalytical techniques.

Laser-engraved ammonia sensor integrating a natural deep eutectic solvent

Ammonia is a naturally-occurring gas, present throughout the atmosphere at sub-ppb concentrations. As result of various processes, significantly higher concentrations can be found in the areas surrounding industrial and agricultural operations. In such cases, the presence of NH3 in air is not only associated with a very pungent odor but can also affect the environment, animals, plants, and humans. Aiming to provide a simple platform to monitor NH3 in air, a paper-derived gas sensor, integrating a natural deep eutectic solvent (NADES) was developed. The herein described paper-derived ammonia gas sensor was fabricated using direct laser scribing, to form a carbon-based interdigitated array. Characterization and optimization (using chemometrics) were performed to develop a material with the lowest possible resistivity. A unique feature of the proposed sensor is that it integrates a natural deep eutectic solvent formed with lactic acid:glucose:water (LGH). This NADES conveys selectivity toward ammonia (over methanol, ethanol, 1-propanol, and water) and greatly enhances the sensitivity of the sensor (over the plain carbon array). The resistance of the sensor was dependent on the NH3 concentration in the 0.11–40.6% range and rendered an estimated limit of detection of 0.33%. Although the sensitivity of the sensor is lower than that of others based on metallic oxides, the herein described approach represents a low-cost, portable, and simple way to address the need of emerging markets such as the NH3-based fuel industry or waste treatment where most of the current sensors would be saturated.

Dynamic-coupling analyses of cells localization by the negative dielectrophoresis

Negative dielectrophoresis is widely used in cell localization for long-term observations such as the impedance analysis, in vivo drug screening, and cell patterns. However, the coupling effect of AC electrokinetics, including negative dielectrophoresis, AC electroosmosis, and electrothermal flow is still unclear. This work investigated cell localization based on the dynamic-coupling of dielectrophoresis, AC electroosmosis, and electrothermal flow. A two-dimensional finite element model that consisted of interdigitated array electrodes was established. The effects of system parameters on the capture efficiency were investigated, when the medium conductivity was in the range of 0.001–1 S/m. The selection of the medium conductivity is suggested to be the first step of the experiment design. Then, the choice of AC frequency and AC amplitude requires balancing the effects of transmembrane potential and temperature rise on cell viability. Besides, particular electrode spacing is evidenced to be only efficient for a specific cell diameter. Thus, the electrode spacing of the microfluidic chip needs to be optimized according to the cell's diameter.

An Electrochemical Study with Three Redox Substances on a Carbon Based Nanogap Electrode Array

An Electrochemical Study with Three Redox Substances on a Carbon Based Nanogap Electrode Array

A Flexible and Printable Chemiresistor Sensor Array for Detection and Recognition of Aging-Associated Human Body Odor

Introduction Human skin emits a variety of volatile organic compounds that are perceived as unique body odor [1]. It has been believed human body odor contains a large amount of information related to body chemistry of individuals. During recent years, there has been great interest in aging-associated body odors since some compounds have been identified existing in specific age groups [2]. For example, diacetyl has been found is a key contributor for middle-aged male odor [3]. 2-nonenal has been detected only in people over the age of 40 (old person smell) [4]. Organic acids (such as hexanoic acid and its derivatives) are characteristic odor of young ages due to their active activity of eccrine sweat glands [2]. The detection and recognition of aging-associated body odor may suggest many potential applications. However, the assessment of body odor at present mainly depends on human panelist and lack of effective sensing approaches. In this work, a flexible and printable chemiresistor sensor is developed for the detection and recognition of aging-associated odor compounds. The fabrication process of the sensor, the selection method of sensitive materials, and the pattern recognition of an optimized sensor array on three typical odor substances (hexanoic acid, diacetyl and 2-nonenal) are introduced. Materials and Method The chemiresistor sensor was prepared by using conductive composites of carbon black (CB) with various sensing materials. Many materials have been reported that can be used in the fabrication of CB-based chemiresistor sensors including polymers, lipopolymers, low volatility organic molecules, intrinsic conducting polymers, gas chromatography stationary materials, and so on. How to select those materials that are suitable for the sensing of body odor is a problem. In this work we investigated and compared the performance of about fifty materials commercially available. The chemiresistor sensors were prepared by mixing CB and the sensitive materials in tetrahydrofuran (or chloroform) with appropriate critical concentrations. Interdigitated array (IDA) electrode was prepared by a commercial inkjet printer using Ag conductive ink and polyethylene terephthalate (PET) film. The CB suspensions of different sensing materials were dropcast automatically by a digital dispenser on the IDA electrode to fabricate the array sensors. The performance of the sensitive materials was evaluated by their response on five McReynolds test probes (benzene, 1-butanol, 2-pentanone, nitropropane and pyridine). The selectivity of sensor channels were analysis by principle component analysis (PCA) as well as multivariate analysis of covariance (MANCOVA). A 6-channel sensor array optimized according to F-values of Wilk’s Λ statistic was used for pattern recognition of hexanoic acid, diacetyl and 2-nonenal. Vapors with standard concentration (from several ppm to several tens of ppm) were generated by a calibration gas generation system (GASTEC, Japan). The response of chemresistor sensor was recorded by a home-made multiple channel sensing device and control software system. Results and Conclusions Figure 1 shows the illustrated experimental setup used for the generation and sensing of odor samples with standard concentrations. The flexible IDA electrode with 8 channels basically was prepared by a low cost inkjet printing process. The McReynolds probe compounds are generally used in gas chromatography to assess the separation capability of gas chromatography stationary phase. Here we use them as a reference to select the sensitive materials for the fabrication of sensor array. Figure 2a shows the response characteristics of twenty-four materials on the five McReynolds probes (The details of these materials was not disclosed in view of business consideration). Figure 2b shows the ordered F-value of the above 24 materials by analysis of MANCOVA. A large F-value means that the variable has high selectivity [5]. That is to say, the materials holds high discrimination ability in the array. The chemiresistor sensor array can be then optimized by comprehensive consideration both the selectivity (F-value) and sensitivity (response intensity over 5 ‰). For example, the red mark in figure 2b lists an optimized sensor array including 6 channels ( No.13, 34, 32, 20, 23 and 16). Figure 3 shows the PCA result of the optimized sensor array on the McReynolds probes. The five compounds are well separated in the PCA plot which demonstrates that the optimized sensor array may exhibit a broad range of ability to discriminate odorant molecules. This result provides us a guiding principle to design sensor arrays for different sensing targets. The sensor array is then used for sensing of hexanoic acid, diacetyl and 2-nonenal. The PCA plot shown in figure 4 demonstrates that it succeeds in the detection and recognition of aging-associated human body odors. Considering the excellent body odor sensing performance as well as printable and flexible characteristics, it is promising that the chemiresistor sensor array can be further developed as a wearable device and applied for body odor-related biomedical and health application.

Ultrasensitive monitoring of DNA damage associated with free radicals exposure using dynamic carbon nanotubes bridged interdigitated electrode array

There are currently increasingly concerns over DNA damage related to free radicals due to their vital roles in human health, especially high-performance detection method. Herein, we report an ultra- sensitive monitoring of DNA damage associated with free radicals exposure using interdigitated electrode (IDE) array for the first time. The proposed IDE array was equipped with DNA-wrapped carbon nanotube-based bridges, which utilized the DNA damage mechanism due to the free radicals’ attack and the efficient electrical detection nature of the interdigitated electrode. Experiments have been performed, and the results showed the device’s capability for detecting DNA damage induced by multiple free radicals generated from different sources, including the Fenton reaction, UV radiation and cigarette smoke, showing the promising ability for DNA damage detection. In addition, the carbon nanotubes bridge-based interdigitated electrode sensor enabled different levels of sensing of DNA damage with great sensitivity and a wide detection range. It was illustrated that the ultrasensitive detection of free radicals generated from ultraviolet radiation (15 min – 125 min), cigarette smoke tar (1 μg/mL to 10 μg/mL) and Fenton reaction under different concentration of H2O2 (2.5 pM – 100 pM), have been detected successfully. Typically, the IDE array supports further performance improvement for the electrochemical detection in an ultrasensitive and high throughput route.

A high-energy aqueous on-chip lithium-ion capacitor based on interdigital 3D carbon microelectrode arrays

There is a growing interest in the development of high energy on-chip capacitive energy storage units for application in microelectronic devices. Lithium-ion capacitor (LIC) typically comprising battery-type and capacitor-type electrodes offer the opportunity for an improved energy density in capacitive energy storage. In this work, an aqueous on-chip LIC was fabricated using carbon microelectromechanical systems (C-MEMS) technique. Oxygen plasma-treated 3D carbon microelectrode arrays served as the capacitor-type electrode in the LIC, while LiFePO4 integrated on the 3D carbon microelectrode arrays was used as the battery-type cathode. Electrochemical performance evaluation shows that the aqueous on-chip LIC can deliver an areal density up to ~5.03 μWh cm−2, which is ~5 times higher than the oxygen plasma-treated symmetric carbon microelectrode-based electrochemical capacitor.

Influence of the Substrate on the Optical and Photo-electrochemical Properties of Monolayer MoS2.

Substrates influence the electrical and optical properties of monolayer (ML) MoS2 in field-effect transistors and photodetectors. Photoluminescence (PL) and Raman spectroscopy measurements have shown that conducting substrates can vary the doping concentration and influence exciton decay channels in ML-MoS2. Doping and exciton decay dynamics are expected to play a major role in the efficiency of light-driven chemical reactions, but it is unclear to what extent these factors contribute to the photo(electro)catalytic properties of ML-MoS2. Here, we report spatially resolved PL, Raman, and photo-electrochemical current measurements of 5-10 μm-wide ML-MoS2 triangles deposited on pairs of indium-doped tin oxide (ITO) electrodes that are separated by a narrow insulating quartz channel [i.e., an ITO interdigitated array (IDA) electrode]. Optical microscopy images and atomic force microscopy measurements revealed that the ML-MoS2 triangles lie conformally on the quartz and ITO substrates. The PL spectrum of MoS2 shifts and decreases in intensity in the ITO region, which can be attributed to differences in nonradiative and radiative exciton decay channels. Raman spectra showed no significant peak shifts on the two substrates that would have indicated a substrate-induced doping effect. We spatially resolved the photo-electrochemical current because of hole-induced iodide oxidation and observed that ML-MoS2 produces lower photocurrents in the quartz region than in the ITO region. The correlated PL, Raman, and photocurrent mapping data show that the MoS2/quartz interface diminishes fast nonradiative exciton decay pathways but the photocurrent response in the quartz region is likely limited by inefficient in-plane carrier transport to the ITO electrode because of carrier recombination with S vacancies in MoS2 or charged impurities in the quartz substrate. Nonetheless, the experimental methodology presented herein provides a framework to evaluate substrate engineering strategies to tune the (photo)electrocatalytic properties of two-dimensional materials.

Multi-parameter paper sensor fabricated by inkjet-printed silver nanoparticle ink and PEDOT:PSS

This work presents the evaluation of a multiparametric sensing device on paper fabricated by inkjet printing, for applications such as smart packaging-labeling and disposable biosensors where biocompatibility and low cost are key factors. The device is able to measure simultaneously relative humidity, temperature and compressive and tensile bending. Commercial silver nanoparticle ink and PEDOT:PSS were printed onto inkjet photo glossy paper using a drop-on-demand inkjet printer forming an interdigitated electrode array and a meander shaped micro-ribbon. Humidity measurements revealed that sensor response, which is effectively expressed by the relationship between paper substrate resistance and relative humidity was similar for both materials utilized as electrodes. Temperature coefficients of resistance (TCR) were extracted for Ag-nanoparticle and PEDOT:PSS - based temperature sensors respectively in the range of 25–45 °C. The bending tests indicated that both materials exhibited similar trend in tensile bending, with resistance increasing in a linear manner up to a maximum tensile length of 900 μm. Ag-nanoparticle ink outperformed PEDOT:PSS ink in terms of repeatability, sensitivity and hysteresis. In compressive bending measurements Ag-nanoparticle and PEDOT:PSS gauge factors exhibited similar gauge factor of opposite sign.

Impedimetric aptasensing using a symmetric Randles circuit model

Electrochemical impedance spectroscopy (EIS) applied for aptasensing is being extensively studied for a variety of targets. Substitution of a symmetric electrode configuration for a conventional three-electrode setup on EIS aptasensing is becoming a trend due to its simple and favorable characteristics for biochip fabrication. However, a single Randles circuit is often used for impedance element parameter fitting in symmetric electrode aptasensing without rationalized basis of validity to date. In this work, an AC impedance model is derived for proving the validity of simplifying a symmetric Randles circuits in series into a single one and is examined with aptasensing applications. With the model, circuit parameter relationships can be quantified and correlated between symmetric and three-electrode configurations. The relationships are verified by comparing the fitted parameters obtained from standard gold electrodes (SGEs), microfabricated symmetric Au electrodes, and interdigitated array (IDA) Au electrode chips with different surface and detection conditions. The model is then found valid for different redox species composition (either Fe(CN)63− or Fe(CN)63−/4- is used) and for both blank and aptamer modified surfaces. From aptasensing of thrombin and tumor marker mucin 1 (MUC1), it is proved that the measured dissociation constants (KD: 129.4 nM for thrombin and 16.3 nM for MUC1) remain the same between a symmetric and three-electrode configuration, but the maximum change of charge transfer resistance (Bmax) is doubled in the symmetric one. This means that the symmetric configuration not only yields the same KD, but also results in a doubled binding signal for EIS aptasensing. In addition to the model derivation and experimental validation, specific EIS aptasensing of MUC1 using a symmetric electrode configuration is successfully demonstrated in this work.

Mechanically flexible microfluidics for microparticle dispensing based on traveling wave dielectrophoresis

Transdermal delivery has emerged as an attractive drug administration approach. A soft flexible transdermal delivery device that can dispense drugs in an on-demand and controllable manner is promising for healthcare. Here we report a mechanically flexible microfluidic device with on-demand and controllable dispensing capability based on traveling wave dielectrophoresis (twDEP). The device is an integration of a microfluidic channel for microparticle transport and an interdigitated electrode array for phase-shifted electric field generation. Microparticles are used to mimic drug molecules. The twDEP provides a feasible mechanism for microparticle transportation. The on-demand dispensing is achieved upon the application of alternating current (AC) electrical inputs. The dispensing flow velocity controllability lies in the amplitude and frequency of the applied AC potential. The demonstration of controllable microparticle dispensing in the mechanically flexible microfluidic device suggests its usage for transdermal drug dispensing through optimization based on drug properties and integration with drug storage and release components.

The Fabrication of an Impedance Immunosensor Based on Interdigitated Array Microelectrodes and Normalized Impedance Changes for Chlorpyrifos Residue Detection

The Fabrication of an Impedance Immunosensor Based on Interdigitated Array Microelectrodes and Normalized Impedance Changes for Chlorpyrifos Residue Detection

Electrochemical Detection of C-Reactive Protein in Human Serum Based on Self-Assembled Monolayer-Modified Interdigitated Wave-Shaped Electrode.

An electrochemical capacitance immunosensor based on an interdigitated wave-shaped micro electrode array (IDWµE) for direct and label-free detection of C-reactive protein (CRP) was reported. A self-assembled monolayer (SAM) of dithiobis (succinimidyl propionate) (DTSP) was used to modify the electrode array for antibody immobilization. The SAM functionalized electrode array was characterized morphologically by atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy (EDX). The nature of gold-sulfur interactions on SAM-treated electrode array was probed by X-ray photoelectron spectroscopy (XPS). The covalent linking of anti-CRP-antibodies onto the SAM modified electrode array was characterized morphologically through AFM, and electrochemically through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The application of phosphate-buffered saline (PBS) and human serum (HS) samples containing different concentrations of CRP in the electrode array caused changes in the electrode interfacial capacitance upon CRP binding. CRP concentrations in PBS and HS were determined quantitatively by measuring the change in capacitance (ΔC) through EIS. The electrode immobilized with anti-CRP-antibodies showed an increase in ΔC with the addition of CRP concentrations over a range of 0.01–10,000 ng mL−1. The electrode showed detection limits of 0.025 ng mL−1 and 0.23 ng mL−1 (S/N = 3) in PBS and HS, respectively. The biosensor showed a good reproducibility (relative standard deviation (RSD), 1.70%), repeatability (RSD, 1.95%), and adequate selectivity in presence of interferents towards CRP detection. The sensor also exhibited a significant storage stability of 2 weeks at 4 °C in 1× PBS.

High-Frequency Interdigitated Array Electrode-Based Capacitive Biosensor for Protein Detection

This paper reports a study on developing of a protein detection biochip based on interdigitated array electrodes (IDAEs) capacitive immunosensor. The protein after being preconcentrated in a detection region will be selectively captured and detected by the capacitive immunosensor. Using electrical impedance spectroscopy operated at high-frequency in the range of 100 kHz–1 MHz, the capacitance of the gold electrode is determined and the antibody surface modification steps can be also monitored. The experiment results show the capacitance changes in accordance with the adding biochemical layer on gold electrodes for each step of the antibody surface modification. In particular, the total impedance operated at 1 MHz frequency has been seen to change from 2.1 kΩ of bare chip (before antibody surface modification) to 8 kΩ after antibody surface modification process while the serial capacitance is recorded to reduce steadily from 450 pF to 55 pF. Also, the efficiency of protein chip was investigated by implementing the measurement of 10 µM BSA with and without preconcentration process. The measurement results have shown the sensitivity increasing significantly after the protein is preconcentrated in this chip. The results demonstrate high efficiency of protein detection can be achieved by operating high frequency capacitive measurement on IDAEs capacitive immunosensor.

Electrodes-oxide-semiconductor device for biosensing: Renewed conformal analysis and multilayer algorithm

Intelligence technologies aim at providing sense organs to machines such as artificial nose or tongue. Inspired by chemically-sensitive devices and antenna couplers, the Insulated Substrate Impedance Transducer (ISIT) reacts to neighboring electro-active targets by changes in its built-in properties, measured through interface electrodes. Exhaustive comprehension of their interactions with medium and substrate is key to ISIT operation and embodiments efficiency. Among simulation approaches, versatile numerical methods, handy conformal analyses and other partial capacitances yet require computational tuning while loosely ensuring previsions quality. The present work then revisits compact modeling of the ideal though essential 2D cases, planar interdigitated electrodes lengthy-fingers arrays on various materials stacks. Starting from a passive membrane with or without back contact, it tackles computability at thin-film and infinite-medium horizons given clear definitions. Optimally simplified formula are proven for membrane thickness down to zero and fingers' spacing around 10 % to 90 % of their periodicity. A straightforward algorithm going beyond “partial-images” is further proposed for multilayers. Sounded for engineers, it is generic, fast and accurate up to 4 arbitrary substrate layers. The method is verified against extensive Finite Elements and validated with measurements in a metallic biolabels sensing application.

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

Essence: A Shear-Enhanced, Flow-through, Nanoporous and Capacitive Electrode Technology with Non-Planar Interdigitated Micro-Electrodes

The most promising biosensor platforms are electrochemical biosensors due to their simple, low manufacturing and usage costs, multiplexed detection capabilities, short response time, as well as ease of miniaturization for portable point-of-care diagnostics. In this talk, we investigate new electrochemical sensing that utilizes a shear-enhanced, flow-through, nanoporous and capacitive electrode technology (hereafter called “ESSENCE”). ESSENCE consists of three layers, a top and bottom nonplanar interdigitated microelectrode array (IDμE) and a middle layer of vertically grown Carbon Nanotubes (CNTs). The fabrication protocol of ESSENCE is unique as unlike most fabrication protocols; it is neither top-down nor bottom-up. We call the technique side-to-side, where the final layer is a sidewall of the device. The steps are: (1) First, fabricate the bottom IDμE on a suitable substrate like glass or silicon. (2) Deposition and the etching process are used to make the microfluidic channel above the bottom IDμE. (3) The catalyst to grow the CNT pillars in the microchannel is patterned on the exposed bottom portion of the channel. (4) A sacrificial layer to support the upper electrode and protect catalyst is introduced on the bottom IDμE. (5) Top electrodes and catalyst are patterned on the top of the sacrificial layer. (6) The CNT’s are grown using well-established techniques. (7) Finally; the chip wall is closed to finish a non-panned interdigitated microfluidic sensor. The functionalization of the CNT is carried out using an in-house on-chip protocol. We exploited the unique electrochemical impedance spectroscopy signal from ESSENCE. Interestingly the tightly packed, porous, flow-through electrode of ESSENCE leads to a substantive increase in diffusion, leading to the formation of the parasitic double layer capacitor at highly elevated frequencies (MHz). This allows for measurement of the charge transfer resistance, an electrochemical signature of the binding of the target biomolecule at high frequencies. This leads to a significant increase in the signal to noise ratio. Further, the nano-porous nature of ESSENCE tremendously boosts the shear force in the device increasing selectivity. Thus, the use of ESSENCE technology boosts both sensitivities (decrease the occurrence of false negatives) and selectivity (decrease the occurrence of false positives), mitigates biofouling and decreases artifacts in the electrochemical signal like the parasitic double layer capacitance (polarization error). Hence, ESSENCE has four significant benefits over the current generation of electrochemical biosensors. (1) The electrode nanoporosity facilitates the development of shear forces of the order of a hydrogen bond, which significantly increases selectivity by mitigating non-specific adsorption. (2) Our preliminary results indicate that the interdigitated, nanoporous microelectrode design, results in a high signal to noise ratio (SNR) which is realized by increases in both sensitivity and specificity. As the ionic flux is confined to nanodomains due to nanostructured electrodes (nanoconfinement effects), it enables the ESSENCE technology to tremendously increase sensitivity and boosts the signal so significantly that even the surface functionalization of the electrodes can be resolved and characterized. (3) The nanoporous electrode architecture increases convective transport of the analyte of interest to the sensing element, thus overcoming diffusion limitations and reducing assay times. Additionally, the convection-mediated transport enhancement negates signal artifacts such as the parasitic double layer capacitance, thus facilitating rapid, high resolutions characterization of the binding signal due to a significant reduction in noise. (4) Finally, given the ease of controlling shear force through flow rate, challenges related to sensitivity and, device selectivity can be decoupled from each other (and each parameter investigated individually) using the shear force as a tuning design parameter. This decoupling allows us to mitigate the problems of biofouling, false positives, and false negatives, among others. Here, electrode fabrication involves many different well-established micro-fabrication techniques. Preliminary tests show very high sensitivity and selectivity with DNA, and a modified ELISA assay for p53, a biomarker for cancer. Acknowledgement: The authors are supported by the National Science Foundation (NSF) Career grant (#1751759): "ASSURED" electrochemical platform for multiplexed detection of Cancer Biomarker Panel using Shear-Enhanced Nanoporous-Capacitive Electrodes Figure Caption: The left figure shows the schematic of the different layers of the ESSENCE electrochemical sensor. The right figure shows an assembled chip with connection wires and inlet/outlet ports for fluid entry. Figure 1

A Novel Non-Planar, Interdigitated Microelectrode Array with a Porous, Flow-through Working Electrode for Highly Sensitive and Selective Detection of Various Chem/Bio-Molecules

Here we present an electrochemical platform that meets the “ASSURED” criteria for Point-of-Care devices set by the World Health Organization. The proposed research will integrate technologies for 1) a flow-through, nanoporous and capacitive electrode, 2) electrochemical sensor capable of label-free, multiplexed, rapid, portable, sensitive and selective detection, 3) non-planar interdigitated microelectrodes, and 4) integrates multiple electrochemical sensing techniques in one chip. Furthermore, the proposed work assesses the applicability of using this platform technology with both faradaic (cyclic voltammetry) and non-faradaic (electrochemical impedance spectroscopy, EIS) electrochemical measurements from the same sensor. The device architecture consists of three layers, namely, a top and bottom glass layer with gold interdigitated microelectrode array (IDμE) and a middle tape layer with the desired channel pattern. Here, Carbon Nanotubes (CNTs) are loaded in the channel, between the two non-planar interdigitated IDμEs, as shown in the figure below. The microfluidic channel in the device is fabricated using medical grade, acrylic double-sided, pressure-sensitive tapes from ARcare® (Tape No: 90880). The tape is cut into shape using a commercially available cutting machine, Cricut®. The CNTs are oxidized to introduce –COOH group into the nanotubes following established protocols. Post -COOH functionalization, the CNT’s are placed in the channel. The double-sided tape is then ripped off, and the device is closed. This room temperature assembly of the device allows us to do multiple tasks like pre-functionalization of the CNT’s, replacing the CNT’s with other nanomaterials that often do not survive harsh microfluidic chip integration. Post-chip assembly, an in-house EDC-NHS on-chip protocol is used to attach a capture biomolecule (oligo DNA or capture antibody) to the –COOH functionalized CNT. Target biomolecule (target DNA or antigen) attachment to CNTs is sensed by observing the shift in EIS/CV/DPV that occurs because of this binding. As shown in the figure, due to the innovative design of the electrode architecture, the electrodes can be connected in multiple different modes and 2/3 electrode connections. It is worthwhile to note that exchanging the CNT with another material like metal-organic framework (MOF) not only changes the electrochemical signal but also results in entirely new electrochemical measurement methodology. The MOF filled chip has been used for Ultrasensitive Detection of Perfluorooctanesulfonate (PFAS). Further, the chip is also used to cascade multiple electrochemical techniques at the same time for enhanced sensitivity and selectivity. The different electrode connections allow us to obtain a rich plethora of physical and chemical characteristics of the flow-through, nonporous, non-planar interdigitated IDμE system. It has allowed us to optimize the electrode architecture for significant improvement in the sensitivity and selectivity of the electrochemical platform. Acknowledgement: The authors are supported by the National Science Foundation (NSF) Career grant (#1751759): "ASSURED" electrochemical platform for multiplexed detection of Cancer Biomarker Panel using Shear-Enhanced Nanoporous-Capacitive Electrodes. Figure Caption: The left figure shows the schematic of the different layers of the electrochemical sensor. The right figure shows the multitude of electrical connections and electrode set-ups that can be accomplished with this sensor. In particular we show here the sensor in a 3 electrode set-up with a nanoporous flow-through working electrode that is made of CNT trapped between two non-planar interdigitated micoelectrodes. Figure 1