Interdigitated Array Research Articles

MnO2 nanowires modified reduced graphene oxide thick film cathode for aqueous zinc-ion prismatic battery

Aqueous zinc-ion batteries are an excellent alternative to lithium-ion batteries that can meet the energy requirements while also being safe and eco-friendly. However, developing a suitable cathode material with good energy density and high-rate capability is challenging. In this study, we developed an aqueous zinc-ion battery with a high surface area MnO2 nanowires modified reduced graphene oxide nanocomposite screen printed interdigitated array electrodes and a distinctive aqueous electrolyte comprising 1 M each of ZnSO4 and Na2SO4, 0.1 M MnSO4, and 0.8 mM sodium dodecyl sulfate. The charge-discharge curves reveal that the cathode material exhibits a high reversible storage capacity of 164 mAh g−1 at a current density of 50 mA g−1. The battery retained 99.59% of its Coulombic efficiency after 300 cycles when cycled at a high current rate of 300 mA g−1. The prismatic battery realized exhibited a calculated energy density of 505.5 Wh kg−1 which is higher than previously reported works. On account of the large energy density and high rate capability coupled with non-toxic components, low cost and facile fabrication method, the Zn||MnO2/rGO battery shows good promise for energy storage application.

Transport Effects in Electrochemical Biochip Sensors with Redox Cycling Amplification: Computational and Experimental Analysis

In the last few decades, and especially after the COVID-19 pandemic, point-of-care diagnostics and field-deployable biosensors have attracted significant attention. Key components of these instruments are microchips that integrate microfluidics with a sensor (e.g., optical or electrochemical) to provide rapid, low-cost, real-time detection of analyte molecules in very small volumes. Next-generation electrochemical sensors have been miniaturized on solid-state platforms (e.g., arrays and vectors) where the area is limited. However, as the active surface area of the sensors decreases from a few square microns to sub-micron and nanometric scales, the measured currents drop, hence affecting the limit of detection. As the concentration of many analytes in the physiological environment is low, low signal-to-noise ratios have limited the miniaturization of standard electrochemical sensors. One way to increase signal at the sensor output is by redox amplification. To achieve amplification, a second working electrode must be incorporated close to the first working electrode and proper bias must be applied to both. Micrometer-sized interdigitated electrode arrays have been fabricated using robust and scalable processes based on optical lithography and reactive ion-etching techniques. In some cases, IDAs have been integrated into microfluidics devices. The physical and electrochemical phenomena that occur in microfluidic channels under flow have been previously evaluated and showed an increase of current under flow. The effect of redox cycling in microfluidic and nanofluidic systems has also been qualitatively demonstrated. Some studies measured the amplification in the cases with and without flow and showed that the flow itself amplifies the measured electrochemical current, though in most cases, it reduces the amplification factor.Towards a more quantitative investigation, analytical and computational modeling were used, providing meaningful insights into the physics of IDAs without requiring numerous device fabrications. In this work, we used COMSOL Multiphysics to create a full three-dimensional simulation-based model of a real device in order to study the effect of laminar flow on redox cycling, as well as a simplified one-dimensional model for the analysis of transition velocity between different amplification regimes. IDAs with 5-10 mm for both electrodes width and gap were studied numerically and experimentally. The results of the 3D and 1D simulations were consistent between themselves, and also with those of the physical experiments. The relationship between the two mass transfer methods — diffusion and convection — were analyzed at different flow velocities and for different electrode geometries.Here we report a study of transport effects on a microfluidic sensor-chip in which electrochemical sensing is amplified by redox cycling using an interdigitated electrode array (IDA). Our models indicate that there exist two dominant regimes: one which is limited by redox cycling diffusion—a unique feature of IDAs— which is dominant at relatively low flow rates, and another which is limited by convection and has dominant flow effects which are effective at high flow rates (see Figure). The transition velocity between the two sensing regimes depends on the width of the electrode and spacing. It was found to be Vflow [mm/sec]=0.335/L[μm] + 0.04 which is similar to the prediction of Vflow∝1/L obtained from the one-dimensional model.An understanding of the combined effects of redox cycling and convection flow is critical as microfluidic chips with electrochemical sensing amplified by redox cycling using IDAs are becoming widely used in diagnostic assays. The method for prediction of current under any flow rate described here will support technological development of more efficient and accurate devices. Figure 1

Embedded Micro-Interdigitated Flow Fields for Efficient Intercalation-Based Desalination at Seawater Scale

During the past decade, intensifying water crises around the globe have motivated research in electrochemical desalination. Among such technologies, Faradaic deionization (FDI) has shown great promise for seawater desalination with the use of intercalation electrode materials that possess at least ten-fold higher charge storage concentration (~5 M) than seawater salinity (~0.5 M). Despite many efforts focused either on developing electrode materials or modifying flow-cell architectures, the promise of intercalative FDI was not previously realized experimentally. This work demonstrates for the first time salt removal approaching seawater-level salinity by using a flow cell containing symmetric cation intercalation electrodes separated by an anion-exchange membrane [Do et al., Energy Environ. Sci., 16, 3025–3039 (2023)]. We show removal of 96% of salt from ~500 mM NaCl feeds with ~50% water recovery at a thermodynamic energy efficiency (TEE) of 7%. In addition, the flow cell readily produces fresh water (< 0.017 M NaCl) from brackish water with 40% TEE and substantially lowered hypersaline brine concentration from 0.78 M down to 0.23 M at 11.7% TEE. We note that (1) scaling up the charge capacity of intercalation electrodes is crucial to improve salt removal in FDI and (2) rational design of flow-through electrodes is equally important to make FDI more energy-efficient by mitigating pumping energy consumption. Upscaling was achieved by using large-area electrodes with high areal loading of nickel hexacyanoferrate (NiHCF), up to 21 mg cm-2. Pumping energy was drastically reduced by embedding an interdigitated array of 70 µm wide channels into the NiHCF electrodes using laser micromaching to form novel embedded, micro-interdigitated flow fields (eµ-IDFFs). The dimensions of the eµ-IDFFs were tailored for our low-permeability electrodes based on analytical and numerical modeling, resulting in two orders of magnitude improvement in the apparent hydraulic permeability of these electrodes while minimizing active-material loss. Evidence of water transport between diluted and concentrated streams, as well as feed-concentration-dependent charge efficiency were reported, which potentially contributed to energy efficiency and water recovery losses, motivating their investigation to further improve FDI performance. In addition to their application toward desalination, the present eµ-IDFFs show promise for use in electrochemical energy storage and conversion processes that employ nanomaterials

Exploring charge regeneration effect in interdigitated array electrodes-based TENGs for a more than 100-fold enhanced power density

The vast potential of harnessing high entropy and abundantly available mechanical energy through triboelectric nanogenerators (TENGs) has attracted significant attention in recent years. However, the cost of harvesting this energy has often outweighed the energy collected. Recent advancements in TENGs for blue energy harvesting from water flow have shown great promise. In this study, we present a novel approach to optimize the performance of interdigitated electrode array-based TENGs operating in free-standing mode (IDA-FTENG) by introducing a gap-to-width ratio (GWR) relationship for the electrodes and its impact on the charge regeneration effects. We investigate the dependence of the charge regeneration effect on GWRs and the number of electrode pairs to enhance the performance of IDA-FTENGs, employing a rapid and industrially scalable laser scribing process for fabricating the devices. An optimized device, featuring a maximum of 34 interdigitated electrode grids, demonstrates a 140-fold increase in power density compared to conventional single electrode pair TENGs (SEP-TENGs). Furthermore, power density projections indicate that the optimized IDA-FTENGs can compete with current solar cells, if designed suitably. We showcase the applicability of the proposed IDA-FTENG devices in self-powered sensors, autonomous wireless operations, security monitoring, and smart home systems.

Development of conductive carbon-based interdigitated electrode array integrated with microfluidic channel for blood glucose sensing

PurposeThis study aims to provide a microfluidic blood glucose sensing platform based on integrated interdigitated electrode arrays (IDEAs) on a flexible quartz glass substrate, adhering closely to pertinent electrochemical characterizations.Design/methodology/approachSensors are the key elements of the modern electronics era through which all the possible physical quantities can be detected and converted into their equivalent electrical form and processed further. But to make the sensing environment better, various types of innovative architectures are being developed nowadays and among them interdigitated electrodes are quite remarkable in terms of their sensing capability. They are a well-qualified candidate in the field of gas sensing and biosensing, but even their sensitivities are getting saturated due to their physical dimensions. Most of the thin film IDEAs fabricated by conventional optical lithographic techniques do not possess a high surface-to-volume ratio to detect the target specified and that reduces their sensitivity factor. In this context, a classic conductive carbon-based highly sensitive three dimensional (3D) IDEA-enabled biosensing system has been conceived on a transparent and flexible substrate to measure the amount of glucose concentration present in human blood. 3D IDEA possesses a way better capacitive sensing behavior compared to conventional thin film microcapacitive electrodes. To transmit the target biological analyte sample property for the detection purpose to the interdigitated array-based sensing platform, the design of a microfluidic channel is initiated on the same substrate. The complex 3D Inter Digital array structure improves the overall capacitance of the entire sensing platform and the reactive surface area as well. The manufactured integrated device displays a decent value of sensitivity in the order of 5.6 µA mM−1 cm−2.FindingsDevelopment of a low-cost array-based integrated and highly flexible microfluidic biochip to extract the quantity of glucose present in human blood.Originality/valuePotential future research opportunities in the realm of integrated miniaturized, low-cost smart biosensing systems may arise from this study.

Electrical modeling of an electrochemical sensor operating at the redox cycling mode

In this work, the direct current vs. voltage (DC) characteristics, and the alternate current (AC) impedance of a 1D four-electrode electrochemical cell, operating under redox-cycling conditions, are presented and discussed. The analysis refers to a four-electrode electrochemical system with one positively biased working electrode, one negatively biased working electrode, one auxiliary electrode, and one reference electrode operating in a redox cycling mode. This configuration is useful, for example, for electrochemical biosensors that can benefit from the inherent redox-cycling amplification of the apparatus. An aqueous buffered electrolyte is assumed, containing electrochemically active species that can be oxidized on the anode, with a positive overpotential. Meanwhile, the product of the oxidation reaction can diffuse to the other working electrode which has a negative overpotential, where the product is reduced. The analysis in this paper assumes that oxidation is the dominant mechanism at the anode, reduction is the dominant mechanism at the cathode, and the transport between them is dominated by diffusion. Since it is a 1D model, an ideal lossless redox cycling, i.e. both working electrodes’ currents (anodic and cathodic) are of the same magnitude with opposite signs, is assumed. Next, the small signal (AC) impedance of the electrochemical cell was calculated assuming that the AC signal modifies the oxidation reaction rate at the anode while the reduction reaction rate at the cathode is fixed. The impedance under redox cycling is calculated vs. frequency for various oxidation and reduction rates and both Bodé and Nyquist plots of the impedance are presented. The last part of the paper presents measured data for both DC and AC (i.e. Bodé and Nyquist plots) experiments with interdigitated array (IDA) electrodes, 5 & 10 μm spacing, operating under redox cycling conditions. The DC measurements were conducted in a 6 mM ferricyanide [K3Fe(CN)6] in 0.1 M Phosphate Buffer Saline (PBS) solution, pH 7.4. The AC measurements were conducted in 10 mM & 100 nM ferricyanide (K3Fe(CN)6) in 100 mM KNO3 aqueous electrolyte. A critical discussion follows the results section where the highlights and problems of the models are discussed.

An electrochemical aptasensor based on ACEK enrichment for detection of AFB1

Aflatoxin B1 (AFB1), known for its high toxicity, poses a serious threat to the agriculture and food chain, thereby impacting human health. Herein, a facile electrochemical aptasensor was developed based on alternating current electrokinetic enrichment for rapid and sensitive detection of AFB1. Alternating electric fields on the interdigital electrode array was introduced to improve the sensitivity and time, because the target could be manipulated for migrating from the solution to the sensing interface instead of aimless random motion, leading to the enrichment of the target. The biosensor achieved the trace detection of AFB1, demonstrating a remarkable detection limit of 9.55 × 10−6 ng/mL, and the linear range of 10−3–102 ng/mL. Furthermore, the biosensor was successfully employed for the detection of AFB1 in actual peanuts and peanut oil, demonstrating its great application potential in food analysis.

Three-dimensional carbon interdigitated ring array nanofibers for electrochemical detection of dopamine neurotransmitter

Dopamine (DA) neurotransmitter is a prominent component of the central nervous system and its deficiency contributes to several diseases, such as Parkinson’s disease and schizophrenia, which significantly influence the quality of life of affected individuals. This paper introduces a circular interdigitated ring electrode, the three-dimensional carbon interdigitated ring array nanofibers (3D C-IDRA NFs), for the detection of DA using amperometric detection. The study utilized cyclic voltammetry and chronoamperometry to investigate DA. The integration of carbon nanofibers (CNFs) with 3D C-IDRA demonstrated enhanced surface area, increased current peak, and superior performance compared to the standalone 3D C-IDRA electrode, as evidenced by a redox amplification factor of 2.94 and a collection efficiency of 81.1%. The results highlight that integrating CNFs with 3D C-IDRA improves the electrochemical performance in detecting DA neurotransmitter. Thus, this discovery elucidates the advantageous potential of the 3D C-IDRA NF electrode in a wide range of applications.

10–14GHz and 14–18GHz Interdigital Planar Bandpass Filters for Frequency Multiplexer

This paper presents the design of two wideband bandpass filters (BPF) operating in the 10–14 GHz and 14–18 GHz ranges for a five port 1-18GHz frequency multiplexer. The 10–14 GHz BPF utilises an interdigital array of resonators with asymmetrical widths and is combined with a low-pass filter for wide stopband characteristics. Sharp attenuation in the stop bands is achieved by including quarter wavelength open stubs. The 14–18 GHz BPF incorporates three interdigital resonators with a modified middle resonator, introducing a variable gap width for improved impedance matching. Open-circuited stubs and a bandstop filter further enhance attenuation in the stop bands. Equivalent circuit models accompany both filters. Both filters exhibit excellent performance, as evidenced by the reflection coefficients below −12 dB within their respective frequency ranges. The insertion loss remains below 2.5 dB throughout the passband, indicating efficient signal transmission. Moreover, the group delay for both filters is less than 0.8 ns, indicating minimal signal delay. These results demonstrate the high-quality characteristics of the designed filters, making them suitable for a wide range of applications requiring efficient signal filtering and multiplexing.

Abstract B001: Impedance based biomarker for “smart ROSE” pancreatic cancer detection: Initial results from an ongoing clinical trial with nsCanary

Abstract Pancreatic cancer (PC) accounts for half a million new cases and 4.7% of cancer-related deaths globally in 2020. Endoscopic ultrasound (EUS) guided fine needle biopsies (FNB) are the current standard for confirming suspicious lesions, although their diagnostic accuracy remains below 70% with a non-diagnostic rate of the first procedure as high as 40%. Rapid on-site evaluation (ROSE) was introduced to improve diagnostic accuracy via on-site pathology assessment. However, ROSE availability is often limited due to resource constraints. NovaScan has developed the nsCanary, a ”smart ROSE” device, which uses a bioimpedance spectroscopy biomarker based on the Cole Relaxation Frequency (CRF) to detect cancer in biopsy samples in real-time and on-site. The aim of this study is to present initial results from a clinical trial that validates the nsCanary’s ability to detect PC in biopsy samples. Data were collected with the nsCanary device in an IRB approved double-blind study including a cohort of 44 patients (20 males, 24 females; average age of 63 years; 66% White, 22% African American, 12% Hispanic) undergoing EUS procedures with FNB sampling for suspected PC at the Texas International Endoscopy Center in Houston, TX. The nsCanary is a small desktop instrument that performs spectral bioimpedance analysis to extract the CRF based biomarker in less than 30 seconds without altering the biopsied tissue. A touch panel user interface allows for the user to input information and start the measurement. Obtained biopsy samples were flushed in a disposable strainer in order to drain any excess fluid. A circular disposable electrode, consisting of an interdigitated array with alternating polarities was placed in contact with the sample to perform measurements of complex bioimpedance in the 1 kHz - 10 MHz frequency range. The design of the electrode allows it to sense the signal from samples as small as FNB cores. Samples with CRF value below 1 MHz for every scan were considered noncancerous. Samples with at least one CRF value above 1MHz or absence of CRF reading (i.e., CRF out of range) were considered cancerous. PC assessment provided by nsCanary was validated against histopathology outcomes for each biopsy sample. Pathology results indicated that out of the cancerous lesions observed, there were 7 cases of pancreatic adenocarcinoma, 2 cases of invasive adenocarcinoma, 1 case of ductal adenocarcinoma, and 1 case of metastatic renal cell carcinoma. Findings showed a sensitivity of 81.8%, specificity of 84.8%, PPV of 64.3% and NPV of 93.3% for a total of n=44 patients. The device is low cost, portable, and can be used in the surgical suite without interfering with the standard workflow or affecting the sample for following pathological assessment. The implementation of the nsCanary device into the clinic will adjunctively support the decision-making process by providing immediate feedback on cancer detection and sample adequacy. This will enable endoscopists to diagnose PC on the first biopsy procedure, ultimately facilitating prompt treatment of patients. Citation Format: Federica Dibennardo, Martina Guidetti, Onur Fidaner, Daniel S. Gehrke, Donato Ceres, Margaret C. John, Constantine H. Bovalis, Isaac Raijman, Les Bogdanowicz. Impedance based biomarker for “smart ROSE” pancreatic cancer detection: Initial results from an ongoing clinical trial with nsCanary [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr B001.

Fully printed minimum port flexible interdigital electrode sensor arrays.

Screen-printed interdigital electrode-based flexible pressure sensor arrays play a crucial role in human-computer interaction and health monitoring due to their simplicity of fabrication. However, the long-standing challenge of how to reduce the number of electrical output ports of interdigital electrodes to facilitate integration with back-end circuits is still commonly ignored. Here, we propose a screen-printing strategy to avoid wire cross-planes for rapid fabrication of flexible pressure sensor arrays. By innovatively introducing an insulating ink to realize electrical insulation and three-dimensional interconnection of wire crossings, the improved sensor array (4 × 4) successfully reduces the number of output ports from 17 to 8. In addition, we further constructed microstructures on the laser-etched electrode surfaces and the sensitive layer, which enabled the sensor to achieve a sensitivity as high as 17 567.5 kPa-1 in the range of 0-50 kPa. Moreover, we integrated the sensors with back-end circuits for the precise detection of tactile and physiological information. This provides a reliable method for preparing high-performance flexible sensor arrays and large-scale integration of microsensors.

Nondestructive dielectric measurement method for orientation distribution of liquid crystal polymers film

Liquid crystal polymers (LCP) are widely used materials in 5G applications. The LCP films easily tend to form an uneven orientation distribution that degrades their service properties. However, tailoring its orientation distribution remains a challenge, primarily because traditional measurement methods are unable to non-destructively measure the orientation distribution of large-area LCP films attributed to penetration depth constraints or sample preparation requirements. Capitalizing on its inherent orientation-induced dielectric anisotropy, we propose a nondestructive dielectric measurement method for the orientation distribution of LCP film using an interdigital electrodes array. Compared to polarized FTIR and WAXS/SAXS, the dielectric method provides a universally applicable solution, even in intricate scenarios like regions with wrinkles in LCP films, films with substantial thickness, and those lacking large-scale structures. Moreover, the accurate measurement of orientation distribution confirms that the large surface roughness and significant variations in thickness distribution are attributed to the uneven orientation distribution. The findings provide a “visual window” for precisely tailoring the orientation structure of LCP films for 5G applications and beyond.

Highly-sensitive wearable pressure sensor based on AgNWs/MXene/non-woven fabric

Nowadays, wearable medical devices are getting more and more public attention. As a continuous monitoring device in wearable medical devices, flexible pressure sensors have also attracted much attention in the field of wearable electronics. High sensitivity and long-term durability in a wide linear range are key requirements for making reliable and flexible wearable pressure sensors. Here, a comfortable, flexible, environmentally friendly and wearable non-woven fabric is proposed as a substrate for the pressure sensor. Conductive AgNWs/MXene/non-woven fabric is prepared by a simple dip-coating technique and then an overall sandwich structure is formed between two layers of polydimethylsiloxane (PDMS) film and an Interdigitated Array of Electrodes (IDE). The viscose fibres in nonwovens are rich in hydroxyl groups and their hydrophilicity is more conducive to the attachment of conductive MXene nanosheets to the entangled fibre network of nonwovens. The synergistic effect between Ti3C2Tx and AgNWs, and the unique intercalation structure can build a more effective conductive network. The pressure sensor based on AgNWs/MXene/non-woven fabric has a fibrous entanglement structure and a special sandwich structure of the sensor with high sensitivity (0.25–5 kPa pressure range: 14.28 kPa−1), and have a wide sensing range (0.25–400 kPa), rapid response and recovery times (60 ms/120 ms), excellent stability, and long term durability for use in human motion detection applications. In addition, the wearable pressure sensors was used to detect and discriminate between different signals related to human health, including monitoring human movement and breathing, and 4 × 4 arrays was used to detect stress distribution signals. These results suggest that the sensor can be potentially applied in mobile medical monitoring devices, showing broad potential in a new generation of wearable electronic devices.

NanoIEA: A Nanopatterned Interdigitated Electrode Array-Based Impedance Assay for Real-Time Measurement of Aligned Endothelial Cell Barrier Functions.

A nanopatterned interdigitated electrode array (nanoIEA)-based impedance assay is developed for quantitative real-time measurement of aligned endothelial cell (EC) barrier functions in vitro. A bioinspired poly(3,4-dihydroxy-L-phenylalanine) (poly (l-DOPA)) coating is applied to improve the human brain EC adhesion onto the Nafion nanopatterned surfaces. It is found that a poly (l-DOPA)-coated Nafion grooved nanopattern makes the human brain ECs orient along the nanopattern direction. Aligned human brain ECs on Nafion nanopatterns exhibit increased expression of genes encoding tight and adherens junction proteins. Aligned human brain ECs also have enhanced impedance and resistance versus unaligned ones. Treatment with a glycogen synthase kinase-3 inhibitor (GSK3i) further increases impedance and resistance, suggesting synergistic effects occur on the cell-cell tightness of in vitro human brain ECs via a combination of anisotropic matrix nanotopography and GSK3i treatment. It is found that this enhanced cell-cell tightness of the combined approach is accompanied by increased expression of claudin protein. These data demonstrate that the proposed nanoIEA assay integrated with poly (l-DOPA)-coated Nafion nanopatterns and interdigitated electrode arrays can make not only biomimetic aligned ECs, but also enable real-time measurement of the enhanced barrier functions of aligned ECs via tighter cell-cell junctions.

In situ detection with interdigitated array electrodes towards the platinum-catalyzed oxygen reduction reaction: Size effect and the reaction pathway

Platinum has long been recognized as a vital catalyst in energy conversion and utilization, particularly in oxygen reduction reaction (ORR), due to its exceptional catalytic activity. However, its exorbitant cost and scarcity have motivated researchers to explore the size-activity correlation of Pt catalysts in ORR, aiming to reduce Pt loading density while preserving high catalytic performance. In this work, we concentrate on the interdigitated-array(IDA)-electrodes-based precise detection of the influence of Pt cluster size on catalytic ability, focusing on (1) Direct synthesis of Pt catalyst onto electrodes surface, rather than offline preparation and pasting, to avoid interference from other chemicals and changes to the surface status of catalyst particles; (2) Use of IDA electrodes with largely improved sensitivity for in-situ detection of reaction intermediates (H2O2) and provide insight into the reaction pathway and electron transfer process. It indicates that the specific activity and mass activity are larger for the smaller-sized Pt cluster. Specifically, the proportion of different electron transfer pathways was analyzed with IDA results, and with the same amount of Pt catalyst loading, the smaller-sized Pt cluster produces a higher percent of H2O2; the smaller-sized Pt catalyzed ORR undergoes less proportion of 4-electron pathway than the larger-sized Pt catalyst (about 43% total catalytic current is contributed by the 4-electron pathway for the #6 Pt catalyst, and this number raises to 98% for the #1 Pt catalyst).

Steady-state currents of planar interdigitated electrode arrays in shallow cells

Analytical equations for the steady-state current at shallow electrochemical cells with embedded interdigitated electrode (IDE) arrays were found by solving the diffusion equation in steady state using conformal transformations. These equations consider the cases where the IDE is used with an external counter electrode (four-electrode configuration) and where one of its arrays is used as internal counter electrode (three- and two-electrode configuration). Since the expressions for the current depend on Jacobian elliptic functions, we found approximations which depend only on trigonometric and hyperbolic functions which can ease the calculations at the expense of an error below 5%. Additionally, we provide expressions for steady-state voltammograms for the case of Nernstian (reversible) electrode reactions. The obtained theoretical results agree with theoretical and simulation results from the literature and with our own experiments. These results can be useful as criteria for designing electrochemical cells based on IDEs, and as benchmarks for assessing their performance, especially for polymer- or paper-based microfluidics.

Simple and sensitive electrochemical detection of aminopeptidase N using monolayer-modified Au interdigitated array electrodes with moderate electrocatalytic activities

Electrochemical–electrochemical (EE) redox cycling using interdigitated array (IDA) electrodes is a simple and efficient approach for signal amplification. However, IDA electrodes with high or low electrocatalytic activities are inappropriate for obtaining high signal-to-background ratios in serum containing various interfering redox-active species. Accordingly, herein, Au IDA electrodes are modified with a monolayer of 6-mercapto-1-hexanol (MCH) to achieve moderate electrocatalytic activities, and the modified electrodes are applied to the simple and sensitive electrochemical detection of aminopeptidase N (APN) in human serum. APN liberates redox-active species (namely, 4-amino-1-naphthol, AN) via proteolytic cleavage of AN-conjugated substrates, and the released AN participates in the EE redox cycling. Among facilely synthesized five possible AN-conjugated substrates, AN-conjugated alanine is most rapidly cleaved by APN. MCH modification significantly decreases capacitive currents and the occurrences of unwanted faradaic reactions. The detection limit for APN in a 10-fold diluted human serum in the case of EE redox cycling without a washing step (3.8 ng/mL) is 40 times lower than that obtained without EE redox cycling (150 ng/mL). The proposed detection method exhibits high selectivity toward APN regardless of the presence of other proteases. This simple and selective method is practically promising for APN analysis in human serum.

Transport effects in biochip sensors with redox cycling amplification

We report a study of transport effects on a microfluidic sensor-chip in which electrochemical sensing is amplified by redox cycling using an interdigitated electrode array (IDA). A full three-dimensional simulation-based model and a simple one-dimensional model for the transition velocity between the two regimes is presented. These models indicate that there exist two dominant regimes: one which is limited by redox cycling diffusion—a unique feature of IDAs— and another which is limited by convection and has dominant flow effects. The transition velocity between the two sensing regimes was found to be vflow[mmsec]=0.335L[μm]+0.04 which is similar to the prediction of vflow∝1L, obtained from the one-dimensional model.

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.

High Performance Multiple Passband Substrate Integrated Plasmonic Filters

We proposed a new variety of substrate integrated plasmonic filters (SIPFs) with multiple passband characteristics based on the concept of spoof surface plasmon polaritons (SSPPs). By etching a periodic interdigital structure array on the top metal layer of substrate integrated waveguide (SIW), we can achieve high-efficiency microwave SSPP transmission with an insertion loss of 1 dB in the passband of 7.4-12.5 GHz, and a high rejection level of 27 dB in the rejection bands. By introducing antisymmetric C-ring resonators (ASCRs) in the filter structure, the passband number and bandwidth of the filter can be flexibly manipulated. To validate the proposed design, four SSPP filters prototypes are fabricated and tested, showing good filtering performances with a high transmission coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{S}21\mathbf {&gt;}-$ </tex-math></inline-formula> 1 dB) and low reflection coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{S}11\,\,\mathbf { &lt; } - $ </tex-math></inline-formula> 12 dB) in their passbands, and a high rejection level over 15 dB between them. By changing the geometric parameters of ASCR, the number of passbands can be increased from 1 to 3, and the passband center frequency and bandwidth can be engineered accordingly. The proposed SSPP filters with good multiple passband characteristics may have great potential applications in microwave wireless integrated plasmonic circuits and communication systems.