Interdigitated Microelectrodes Research Articles

A Polyvinylpyrrolidone Nanofibrous Sensor Doubly Decorated with Mesoporous Graphene to Selectively Detect Acetic Acid Vapors.

An original approach has been proposed for designing a nanofibrous (NF) layer using UV-cured polyvinylpyrrolidone (PVP) as a matrix, incorporating mesoporous graphene carbon (MGC) nanopowder both inside and outside the fibers, creating a sandwich-like structure. This architecture is intended to selectively adsorb and detect acetic acid vapors, which are known to cause health issues in exposed workers. The nanocomposite MGC-PVP-NFs layer was fabricated through electrospinning deposition onto interdigitated microelectrodes (IDEs) and stabilized under UV-light irradiation. To enhance the adhesion of MGC onto the surface of the nanocomposite polymeric fibers, the layer was dipped in a suspension of polyethyleneimine (PEI) and MGC. The resulting structure demonstrated promising electrical and sensing properties, including rapid responses, high sensitivity, good linearity, reversibility, repeatability, and selectivity towards acetic acid vapors. Initial testing was conducted in a laboratory using a bench electrometer, followed by validation in a portable sensing device based on consumer electronic components (by ARDUINO®). This portable system was designed to provide a compact, cost-effective solution with high sensing capabilities. Under room temperature and ambient air conditions, both laboratory and portable tests exhibited favorable linear responses, with detection limits of 0.16 and 1 ppm, respectively.

3D models of molecularly imprinted polymer nanofilms coupled to interdigitated microelectrodes: A physical performance analysis

This work presents the development of three 3D models in COMSOL Multiphysics® to study the performance of sensing platforms based on molecularly imprinted polymer (MIP) nanofilms (∼50 nm thick) deposited on interdigitated microelectrodes (IDMEs). Polypyrrole and glyphosate were selected as the MIP matrix and the target analyte, respectively. A real prototype was tested to adjust the morphological and electrical parameters of the MIP nanofilm. The prototype and the 3D models were evaluated using electrical impedance spectroscopy. Considering the fill factor concept, the percentage relative change in impedance (Δ|Z|Rel) as the target analyte is attached to the MIP nanofilm was estimated. Three zones appear in the impedance spectra, but only two are related to glyphosate incorporation. In both zones, the impedance increases as the glyphosate fills the MIP nanofilm. The glyphosate incorporation modifies the surface area and affects the electrical properties of the MIP nanofilm seen as a whole. The models reproduce the sensing zones and allow studying the predominant factors in each zone and estimating the performance in terms of Δ|Z|Rel. A Δ|Z|Rel as high as 142% was obtained at 100 mHz under saturation, which agrees with experimental results reported with a similar arrangement. These 3D models, as well as the simulation strategy, are useful in interpreting results related to MIP/IDME-based sensors, which are versatile and easy-to-use devices.

A portable EIS-based biosensor for the detection of microcystin-LR residues in environmental water bodies and simulated body fluids.

Due to the eutrophication of water bodies around the world, there is a drastic increase in harmful cyanobacterial blooms leading to contamination of water bodies with cyanotoxins. Chronic exposure to cyanotoxins such as microcystin leads to oxidative stress, inflammation, and liver damage, and potentially to liver cancer. We developed a novel and easy-to-use electrochemical impedance spectroscopy-based immunosensor by fabricating stencil-printed conductive carbon-based interdigitated microelectrodes and immobilising them with cysteamine-capped gold nanoparticles embedded in polyaniline. It has been also coupled with a custom handheld device enabling regular on-site assessment, especially in resource-constrained situations encountered in developing countries. The sensor is able to detect microcystin-LR up to 0.1 μg L-1, having a linear response between 0.1 and 100 μg L-1 in lake and river water and in serum and urine samples. In addition to being inexpensive, easy to fabricate, and sensitive, it also has very good selectivity.

Rapid assessment of degraded frying oil quality using interdigitated microelectrode capacitive sensors

AbstractFrying oil is essential in food processing, influencing both the taste and safety of fried foods. However, its quality can deteriorate with repeated use, posing potential risks. Many current methods for evaluating its quality, such as spectroscopic techniques, are time‐consuming and costly. Our study introduces an affordable and rapid device that uses electrical capacitance to assess the quality of frying oil. We developed a capacitive sensor equipped with interdigitated microelectrodes (IEMs) to measure the oil's dielectric constant. After calibrating the sensor's features, we achieved highly precise results. Our design utilized Corel software for drafting and CNC machinery for precise sensor fabrication. In air, the sensor's measurements closely aligned with theoretical predictions, registering an R2 value above 0.7. We identified a correlation between frying frequency and significant shifts in the dielectric constant across three oil samples. Using a signal circuit to adjust the oscillation frequency and a microprocessor for data interpretation, we classified oils into three safety categories: safe, moderate, and risky. Our device provides a cost‐effective and user‐friendly solution to assess frying oil quality, proactively addressing health concerns arising from oil degradation.Practical Applications: Our capacitive sensor device can be widely applied in the food industry and restaurants, ensuring the safety and quality of fried products. By using this device, manufacturers and kitchens can make informed decisions about reusing frying oil or replacing it as needed, reducing wasted oil. This cost‐saving device also has the potential to contribute to improving food safety issues.

Intensity modulation of UV light in gas sensor array to discriminate several analytes at room temperature

AbstractIn this study, a gas sensor array along with intensity modulation of UV light was utilized to discriminate several gases at room temperature. The sensor array was consisted of two interdigitated microelectrodes and TiO2 nanofibres were electrospun on them and calcined at 540°C for 90 min. One of these sensors was coated by 2‐nm Pt using the DC sputtering method and the other one remained uncoated. In each experiment, the sensor array was located at a distance of 30 mm from a 365‐nm UV LED. For intensity modulation of UV light, a staircase waveform voltage was applied to the UV LED. The voltage was included of three voltage steps and the measured powers at a distance of 30 mm from the UV‐LED were about 450, 560, and 680 µW/cm2, respectively. Analytes including acetone, ethanol, methanol, 2‐propanol, and carbon monoxide (CO) at various concentrations ranging from 50 to 500 ppm were examined. Three‐dimensional Principal Component Analysis mapping was successfully used for the segregation of all examined gases. The examinations revealed that using sensor array along with intensity modulation of UV light is an effective method for discrimination of several analytes at room temperature.

Screen-printed interdigitated microelectrodes employment in dielectrophoretic manipulation of MWCNTs.

As key enablers of Industry 4.0 and Internet of Things, sensors are among the first devices which are to encounter fast physical transformation (from rigid to flexible) as of large-scale utilization of printing technologies. In order to step-up this process, adaptation of conventional fabrication technologies (based on metallization) employed in sensors' development should be tested and demonstrated. Within thispaper, we are reporting the functionality of dielectrophoresis (DEP)for electromanipulation of multi-walled carbon nanotubes (MWCNTs) as sensing element, at the level of printed interdigitated electrodes. First, we present the flatbed screen-printed process of interdigitated microelectrodes on flexible substrate with tailored geometries employed afterwards for generating convenient dielectrophoretic forces of optimal magnitude and frequency for trapping MWCNTs. Successful dielectrophoresis operability of MWCNTs across silver-based screen-printed μIDE (interdigitated microelectrodes) provided with electrode gaps of ≈ 150μm was validated and suitable values of the signal frequencies for avoiding parasitic electrokinetic phenomena (AC electro-osmosis, electrothermal effect) occurring simultaneously with DEP were identified. Time-dependent effect of DEPover MWCNTs bridges formation is discussed, as well as voltage magnitude contribution.

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.

Simple Electroosmotic Pump and Active Microfluidics with Asymmetrically Coated Microelectrodes

Electroosmotic pumps can deliver liquid without moving parts, making them suitable for microfluidic and lab‐on‐chip systems. Previously, alternating current electroosmotic pumps were constructed using pairs of coplanar asymmetrical interdigitated microelectrodes on the same substrate. In this work, a simpler micropumping system is developed, separating the electrodes on two substrates and breaking the symmetry by half‐depositing electrodes with 3D microstructures. Numerical simulation models of the pumping system and experimental velocity profiles are used to explain the fluid motion mechanism and structure‐dependent pumping performance. In addition to its efficiency and simplicity, this new pumping system also allows for the creation of a microvortex device and an active microfluidics device. This scalable micropumping system provides a way to pump liquids at microscopic or macroscopical scale in complex microfluidics systems.

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.

Plasma-based diagnostic and screening platform using a combination of biosensing signals in Alzheimer's disease

Using biosensor to screen for Alzheimer's disease (AD) facilitates early detection of AD with high sensitivity and accuracy. This approach overcomes the limitations of conventional AD diagnostic methods, such as neuropsychological assessment and neuroimaging analysis. Here, we propose a simultaneous analysis of signal combinations generated by four crucial AD biomarkers (Amyloid beta 1–40 (Aβ40), Aβ42, total tau 441 (tTau441), and phosphorylated tau 181 (pTau181)) by inducing a dielectrophoretic (DEP) force on fabricated interdigitated microelectrode (IME) sensor. By applying an optimal DEP force, our biosensor selectively concentrates and filters the plasma-based AD biomarkers, exhibiting high sensitivity (limit of detection <100 fM) and selectivity in the plasma-based AD biomarkers detection (p < 0.0001). Consequently, it is demonstrated that a complex combined signal comprising four AD-specific biomarker signals (Aβ40− Aβ42+ tTau441− pTau181) can differentiate between patients with AD and healthy subjects with high accuracy (78.85%) and precision (80.95%) (p < 0.0001).

Smartphone-powered, ultrasensitive, and selective, portable and stable multi-analyte chemiresistive immunosensing platform with PPY/COOH-MWCNT as bioelectrical transducer: Towards point-of-care TBI diagnosis

Traumatic Brain Injury, one of the significant causes of mortality and morbidity, affects worldwide and continues to be a diagnostic challenge. The most desirable and partially met clinical need is to simultaneously detect the disease-specific-biomarkers in a broad range of readily available body fluids on a single platform with a rapid, low-cost, ultrasensitive and selective device. Towards this, an array of interdigitated microelectrodes was fabricated on commercially existing low-cost single-side copper cladded printed-circuit-board substrate followed by the bioelectrodes preparation through covalent immobilization of brain injury specific biomarkers on carboxylic functionalized multi-walled carbon nanotubes embedded polypyrrole nanocomposite modified interdigitated microelectrodes. Subsequently, the immunological binding events were transduced as the normalized change in bioelectrode resistance with and without the target analyte via current-voltage analysis. As proof of concept, current-voltage responses were primarily recorded using a conventional probe station, and later, a portable handheld-electronic-readout was developed for the point-of-care application. The data compilation and analysis were carried out using the in-house developed android-based mobile app. Notably, the smartphone powered the readout through a PL-2303 serial connector, avoiding integrating power sources with the readout. Further, this technology can be adapted to other point-of-care biosensing applications.

Synthesised silver nanoparticles mediate interdigitated nanobiosensing for sensitive Pneumonia identification

Pneumonia is a life-threatening disease and at present, a large population of humans is affected by pneumonia worldwide. It is a serious issue causing complications of acquired immune deficiency syndrome infection. Most people are affected in low-and middle-income countries. Until now pneumonia is mainly diagnosed by smear microscopy and is not easily available in the area of low-income settings. This research was conducted with a sensing strategy on interdigitated microelectrode (IDME) to identify the lower level of the target, ‘procalcitonin’. In addition, procalcitonin can distinguish the community-acquired viral pathogens, which helps to provide a suitable treatment. IDME was physically modified by a silver nanoparticle, and an anti-procalcitonin antibody was attached to a silver nanoparticle with amine and aldehyde linkers. On this IDME, procalcitonin was quantified in a dose-dependent manner (10–320 ng/mL) and calculated the detection limit to 10 ng/mL on a linear coefficient regression analysis [y = 2.2821×−2.6871; R2 = 0.9904]. Specific performances with control proteins that did not increase the current were revealed the specific identification of procalcitonin. This experiment created a sensing strategy to identify procalcitonin as a suitable biomarker.

Amplification-free, highly sensitive electrochemical DNA-based sensor for simultaneous detection of stx1 and stx2 genes of Shiga toxin-producing E. coli (STEC)

Shiga toxin-producing E. coli (STEC) is a food-borne pathogen of significant public health concern, due to the severity of the illness it can cause at a low infection dose. The key targets in molecular-based assays to detect STEC are stx1 or stx2 genes, coding for the ability to produce Shiga T Toxin 1 and 2, respectively. The most commonly used molecular detection techniques, such as PCR and real-time PCR, are considerably time-consuming and there is an urgent need for a more rapid screening assay which could be used in agri-food settings. In this work, an amplification-free multiplex electrochemical sensor for the simultaneous detection of stx1 and stx2 genes was developed using a silicon-based chip comprising six interdigitated gold microelectrodes (IDE) sensors. Two probes complementary to stx1 and stx2 genes were immobilised on a single chip allowing for multiplex detection. The selectivity of the multiplex sensor was confirmed using fluorescence and electrochemistry. The developed assay conditions allowed for an improved limit of detection of three orders of magnitude compared to the previous reports achieving an amplification-free limit of detection of 100 zM (10−19 M) for both, stx1 and stx2 genes. The developed sensor was validated using chromosomal DNA extracted from bacterial cultures containing either no virulence genes, stx1 gene only, and both stx1 and stx2. Such multiplex sensors, if combined with on-chip DNA extraction, could revolutionise the point-of-use detection of STEC as well as other pathogens for instance on-farm or in the food industry.

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.

Real-time, Economical Identification of Microplastics Using Impedance-based Interdigital Array Microelectrodes and k-Nearest Neighbor Model

Real-time, Economical Identification of Microplastics Using Impedance-based Interdigital Array Microelectrodes and k-Nearest Neighbor Model

Integrated interdigital electrode and thermal resistance micro-sensors for electric vehicle battery coolant conductivity high-precision measurement

Monitoring the conductivity of battery coolant is extremely important as it can significantly improve the safety of electric vehicles. The conductivity of coolant should be maintained in the range of 0-10 μS/cm to ensure the insulation level, requiring high-precision measurement of ultra-low detection range. However, polarization and capacitive effects, temperature effects, as well as poor stability, all pose significant challenges to achieving high-precision conductivity measurements. This work describes a novel integrated conductivity and temperature (CT) micro-sensor for the conductivity high-precision measurement of electric vehicle battery coolant. An interdigital micro-electrode is fabricated for conductivity sensing and a thin-film platinum resistor is employed as temperature sensor cell. The integrated CT sensor demonstrates an acceptable limit of detection with a resolution of 0.1 μS/cm. Besides, high-precision signal acquisition and processing circuit is designed for sensors and a desirable measuring full-scale error is observed. Compared to the current method of using bulky metal electrodes prepared by mechanical process as conductivity sensor, the proposed sensor can be mass produced by Micro-Electro-Mechanical System (MEMS), and favorable consistency, high sensitivity, excellent stability, smaller size are obtained. Consequently, the as-proposed CT micro-sensor has an opportunity to be developed as a competitive device for online conductivity monitoring in battery coolant.

An alternating current electrokinetics biosensor for rapid on-site serological screening of Taenia solium cysticercosis infection.

Cysticercosis, caused by Taenia solium infection, is a leading cause of acquired epilepsy in many developing countries. Several types of immunoassays have been developed for the detection of Taenia solium infection in both infected humans and livestock animals. However, these methods require central laboratory facilities and are both time- and labor-consuming with longer than desired turnaround time. In this work, we demonstrated that AC electrokinetics (ACEK) capacitive sensing can be used to realize point-of-care immunosensor in general, with the on-site screening of Taenia solium infection as an example here. The sensor employs interdigitated microelectrodes (IDME) functionalized with a recombinant Taenia solium antigen, rT24H, to detect anti-rT24H antibodies in clinical serum samples. ACEK capacitive sensing method interrogates the IDME sensors with a special AC signal, which serves the dual purposes of enriching target antibodies by ACEK effects and directly measuring the capacitance change induced by specific binding. First, to characterize the ACEK biosensor as an immunosensor in general, IgG in phosphate-buffered saline buffer was tested against IDME sensors functionalized with anti-IgG. The limit of detection of the sensor was 24.1fg/mL, and the linear dynamic range was 0.1-100pg/mL. To test the clinical usage of this sensor, ACEK capacitive sensors with rT24H probe were used to test clinical serum samples from patients with or without Taenia solium infection. The diagnostic sensitivity of the ACEK capacitive sensor for Taenia solium infection was found to be 88.24%. ACEK capacitive immunosensors have shown good potential for point-of-care diagnostics.

Electrical and dielectric characterization of a biological liquid using an interdigitated microelectrodes

Electrical and dielectric characterization of a biological liquid using an interdigitated 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.

Microfluidic Device with Room Temperature Ionic Liquids for Detecting Low Concentrations of CO2

In this work we report the use of a gas sensor that can be used in inline configuration for applications like organ-on-a-chip. The key element of the device is a microfluidic channel with a thickness of 140 μm and width of 500 μm. This microfluidic channel is sandwiched between a top and bottom substrate, each substrate containing microelectrodes making this a non-planar interdigitated microelectrode (NP-IμE) configuration. Room temperature ionic liquids (RTILs) are used as electrolyte in the microfluidic channel. Due to the dimensions of the microfluidic channel only low volume of RTILs are required as electrolyte. RTILs can be tuned to selectively capture specific gases. This in addition to other favourable properties such as wide electrochemical window, thermal stability and negligible vapor pressure makes it a good candidate as the selective electrolyte in electrochemical gas sensor. The use of NP-IμE makes the electric field penetrate through the channel. This allows us to register the perturbations in signal caused by absorption of CO2 from the entire cross-section of the channel, thereby increasing the sensitivity of the device (as compared to a planar architecture). 1-ethyl-3-methylimidazolium 2-cyanopyrolide ([EMIM][2-CNpyr]) was used as the RTIL, as it has been shown to be a good sorbent of CO2 with high capacity at low partial pressures due to its chemical affinity. The RTILs exposed to different concentrations of CO2 was injected into the microfluidic channel. Cyclic Voltammetry (CV), Differential pulse voltammetry (DPV) and Electrochemical impedance spectroscopy (EIS) experiments were done using our microfluidic device. During the CV and DPV experiments, RTIL exposed to CO2 shows a reduction peak (of CO2). This along with the changes in EIS spectrum (Nyquist plot) can be used to detect the presence of CO2. We used CO2 as a test gas to analyse the sensitivity of our microfluidic device combined with RTIL. In future we will be using this same setup to sense biomarker gases and other toxic gases by changing the RTIL and tuning its affinity towards the target analytes.