Interdigitated Electrodes Research Articles

High transmittance, fast response, and high contrast ratio smart window with lateral driving electrophoretic display

Smart windows can dynamically control the optical transmittance of natural light and efficiently reduce the energy consumption of buildings. Currently, the practical application of smart windows is limited by high power consumption, low transmittance, and complicated preparation process. Developing smart windows with fast response and high transmittance is challenging. Herein, we fabricated a smart window based on electrophoretic display (EPD) technology, which can switch between white and transparent states by changing the stacking states of the electrophoretic particles on electrodes. To further increase the transmittance of the smart window, the polyvinyl alcohol (PVA) hydrophilic layer was spin-coated on the electrode to reduce the adhesion of particles. Compared with other EPD smart window technologies, our device exhibits the fastest response time of up to 375 ms at 30 V, high transmittance of up to 78% at 632 nm, and a high contrast ratio of up to 89. In addition, to reduce the particle’s lateral diffusion and improve our device's stability, the microcup array was aligned on the interdigital electrode. The particles can be driven and stacked onto the side walls of the microcup to achieve a transparent state. This work demonstrated that the EPD device would provide a promising future for practical smart windows with high transmittance and fast response time.

NOx Sensor Constructed from Conductive Metal-Organic Framework and Graphene for Airway Inflammation Screening.

The detection of nitric oxide in human exhaled breath (EB) has received wide attention due to its close relationship with respiratory tract inflammation. Herein, a ppb-level NOx chemiresistive sensor was prepared by assembling graphene oxide (GO) with a conductive π-d conjugated metal-organic framework Co3(HITP)2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) in the presence of poly(dimethyldiallylammonium chloride) (PDDA). The construction of a gas sensor chip was achieved by drop-casting the GO/PDDA/Co3(HITP)2 composite onto ITO-PET interdigital electrodes, followed by in situ reduction of GO to reduced graphene oxide (rGO) in hydrazine hydrate vapor. Compared with bare rGO, the nanocomposite shows significantly improved sensitivity and selectivity for NOx among various gas analytes owing to its folded and porous structure as well as its numerous active sites. The limit of detection (LOD) for NO and NO2 can reach as low as 11.2 and 6.8 ppb, respectively, and the response/recovery time to 200 ppb NO is 24/41 s. These results indicate that rGO/PDDA/Co3(HITP)2 can achieve a sensitive and fast response toward NOx at room temperature (RT). Additionally, good repeatability and long-term stability were observed. Furthermore, the sensor shows improved humidity tolerance owing to the presence of hydrophobic benzene rings in Co3(HITP)2. To demonstrate its ability in EB detection, EB samples collected from healthy individuals were spiked with a certain amount of NO to simulate the EB of respiratory inflammatory patients. The sensor can successfully distinguish healthy people from the simulated patients. Furthermore, in real clinical sample detection, the sensor can further differentiate acute respiratory inflammatory patients from the chronic ones.

Excellent electrochemical performance of all-solid-state planar on-chip micro-supercapacitors with narrow interdigital electrode configuration

As a popular direction of research in micro-energy storage devices, improving the comprehensive performance of all-solid-state planar on-chip micro-supercapacitors (MSCs) has received increasing attention. Graphene quantum dots (GQDs) are a new type of nano-scale electrode materials that can improve the electrochemical performance of devices. In addition, the doping of nitrogen/oxygen heteroatoms can further improve the electrochemical activity of the electrode materials. In this paper, nitrogen-oxygen co-doped graphene quantum dots (NO-GQDs) were used as electrode materials, and a modified liquid-air interface self-assembly method was used to fabricate the electrode films. Finally, the MSCs with narrow interdigital electrode configuration were prepared by photolithography with an electrode width/interdigital gap of 3 μm/1 μm. The prepared MSCs have excellent electrochemical performance, including an area capacitance of 150.63 μF cm−2, an energy density of 20.92 nWh cm−2, a power density of 175.49 μW cm−2, a relaxation time constant of 3.53 μs, and a capacitance retention of 90.42%. As shown by the results, the combination of NO-GQDs and narrow interdigital electrode configuration provides a significant improvement in the comprehensive electrochemical performance of the all-solid-state planar on-chip MSCs.

Miniaturized Flexible Non-Contact Interface Based on Heat Shrinkage Technology.

High-performance miniaturized flexible sensors are becoming increasingly important in wearable electronics. However, miniaturization of devices often requires high-precision manufacturing processes and equipment, which limits the commercialization of flexible sensors. Therefore, revolutionary technologies for manufacturing miniaturized flexible sensors are highly desired. In this work, a new method for manufacturing miniaturized flexible humidity sensor by utilizing heat shrinkage technology is presented. This method successfully achieves much smaller sensor and denser interdigital electrode. Utilizing this method, a miniaturized flexible humidity sensor and array are presented, fabricated by anchoring nano-Al2 O3 into carbon nano-tube as the humidity sensitive film. This heat shrinkage technology, forming wrinkle structure on the humidity sensitive film, endows the sensor with a high sensitivity over 200% (ΔR/R0 ) at humidity levels ranging from 0 to 90%RH and a fast recovery time (0.5s). The sensor allows non-contact monitoring human respiration and alerting in case of an asthma attack and the sensor array can be adaptively attached to the wrist as a non-contact human-machine interface to control the mechanical hand or computer. This work provides a general and effective heat shrinkage technology for the development of smaller and more efficient flexible circuits and sensor devices.

Design and experimental investigation of interdigitated electrode architecture for tunable liquid crystal-based metasurfaces with rapid responses

In this paper, an interdigitated electrode architecture is investigated, which can be used to tune the permittivity of liquid crystal (LC) in metasurfaces with rapid responses. The interdigitated electrodes are composed of two groups of cross-distributed comb grids, where external bias voltages can be applied to each group of comb grids. By continuously adjusting the bias voltages through the grids, the orientation of the liquid crystal molecules can be dynamically controlled due to the excited electrostatic field. Hence the permittivity of the LC and the electromagnetic responses of the metasurface can be tuned arbitrarily by the external biasing. Three kinds of interdigitated electrodes with different fitting ratios were developed to explore the working of the interdigitated electrode architecture. The response time of these interdigitated electrodes and their influence on frequency tunability were analyzed in detail. The measured absorption spectra of interdigitated electrodes with 7, 9, and 11 grids per unit cell with identical periodicity indicate that the fill density of comb grids has a negligible effect on the frequency tunability. However, the fill density has a significant impact on the response time of the LC metamaterial in the interdigitated electrodes. Moreover, the response time was further reduced by 65% with the increase in the number of grids. The proposed architecture and its design provide new insight into developing tunable LC metasurfaces with rapid responses.

3D-Printed Flexible PVDF-TrFE Composites with Aligned BCZT Nanowires and Interdigital Electrodes for Piezoelectric Nanogenerator Applications

Piezoelectric nanogenerators based on piezoelectric nanocomposites have attracted much interest in recent decades owing to their excellent piezoelectric properties and application in self-powered systems and wearable sensors. As a promising piezoelectric ceramic filler in composite-based generators, one-dimensional (1D) piezoelectric nanowires were filled into a polymer matrix to enhance its dielectric and piezoelectric properties. In this paper, flexible PVDF-TrFE composite films containing highly aligned Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZT) nanowires (NWs) have been manufactured via a direct-ink writing method. The effect of BCZT NW content on the dielectric, ferroelectric, and piezoelectric properties was investigated using multiphysics modeling and detailed experiments. An optimum composite composition was discovered, and the piezoelectric composite film with 15 wt % BCZT NWs possessed the highest energy harvesting figure of merit of 5.3 × 10–12 m2/N. Interdigital electrodes were combined with the composite to fabricate a patterned piezoelectric nanogenerator, where the piezoelectric nanogenerator can produce an open-circuit output voltage of 17 V, and the maximum output power density could reach 5.6 μW/cm2. This work provides opportunities for the optimization and fabrication of piezoelectric materials for energy-harvesting and sensing applications.

Development of interdigitated electrode based enzyme sensor for triglyceride monitoring using engineered oxygen insensitive glycerol 3-phosphate oxidase

Triglycerides (TG) are an important biomarker of various diseases including hyper-lipidemia. Current emergent requirements for TG sensing include the development of electrochemical sensors for easy, cost-effective, disposable and single use triglyceride sensors. We propose a TG sensor using an engineered glycerol 3-phosphate oxidase (GlpO) and electrochemical detection. In this study, we aimed to develop an electrochemical TG sensor based on engineering the oxidative half reaction of GlpO to be oxygen insensitive, with the employment of an interdigitated electrode (IDE). To construct an oxygen insensitive mutant GlpO, we constructed a double mutant, Met104Phe/Asp169Glu, which revealed an engineered GlpO exhibiting repressed oxidase activity, while its dye-mediated dehydrogenase activity enhanced. The electrochemical enzyme sensor was constructed for the measurement of TG based on engineered GlpO using disposable screen-printed carbon electrode (SPCE) or disposable IDE using Ru complex as the electron mediator. By using the disposable IDE sensor, a highly sensitive electrochemical sensor for Glp was achieved, with the sensitivity of 0.4 µA/mM. The improved sensitivity was 2.4 times higher than that of SPCE (0.17 µA/mM), with LOD of 0.022 mM. Furthermore, the dry sensor strip, where the double mutant GlpO and Ru complex were dropcasted and dried on the IDE, was prepared and the Glp concentration was successfully measured in the delipidized serum solution. Therefore, by the employment of the established pretreatment method for TG to release Glp, a highly sensitive, accurate, easy and rapid electrochemical measurement method for TG will be developed using constructed M104F/D169E mutant GlpO with the combination of IDE.

Optimal interdigitated electrode sensor design for biosensors using multi-objective particle-swarm optimization

<p>Interdigitated electrodes (IDEs) are commonly employed in biological cellular characterization techniques such as electrical cell-substrate impedance sensing (ECIS). Because of its simple production technique and low cost, interdigitated electrode sensor design is critical for practical impedance spectroscopy in the medical and pharmaceutical domains. The equivalent circuit of an IDE was modeled in this paper, it consisted of three primary components: double layer capacitance, C<sub>dl</sub>, solution capacitance, C<sub>Sol</sub>, and solution resistance, R<sub>Sol</sub>. One of the challenging optimization challenges is the geometric optimization of the interdigital electrode structure of a sensor. We employ metaheuristic techniques to identify the best answer to problems of this kind. multi-objective optimization of the IDE using multi-objective particle swarm optimization (MOPSO) was achieved to maximize the sensitivity of the electrode and minimize the Cut-off frequency. The optimal geometrical parameters determined during optimization are used to build the electrical equivalent circuit. The amplitude and phase of the impedance versus frequency analysis were calculated using EC-LAB® software, and the corresponding conductivity was determined.</p>

Simulation Studies on the Design and Analysis of Interdigital and Fractal-Based Micro-Supercapacitors

Micro supercapacitors (MSC) are recently replacing traditional batteries in flexible and portable electronic devices owing to their outstanding features such as high power density and long cycle life. In-plane supercapacitors are usually built in an interdigital electrode (IDE) structure because of its fabrication simplicity and flexibility. This helps to reduce ion diffusion length and enables easy on-chip integration of the device. Recent researches show that by replacing the interdigital electrode structure with the new architecture technique of Fractal electrode design, the effective area of the electrode-electrolyte interface and capacitance can be increased. This work investigates the effect of the device architecture on the energy storage capacity of in-plane MSCs. IDE and Fractal-based electrodes are simulated using COMSOL Multiphysics and analyzed for performance using cyclic voltammetry, galvanic charge-discharge technique and electric field distribution. The results indicate that the device with fractal design has more areal capacitance than the traditional interdigital structure. The highest capacitance was achieved by the proposed Sierpinski Fractal electrode design which exhibited 85.59% more areal capacitance than the conventional IDE. This can be attributed to the significant increase in effective electrode area and the edging effect of the electric field in the sharp edges of fractal electrodes.

Low‐Temperature Resistant Stretchable Micro‐Supercapacitor Based on 3D Printed Octet‐Truss Design (Small 23/2023)

Micro-Supercapacitors In article number 2207634, Hui Ying Yang and co-workers develop an innovative stretchable micro-supercapacitor with excellent resistance to freezing. Using digital light processing (DLP) 3D printing technology, an interdigital electrode with octet-truss lattice structure has been designed to enhance the electrochemical performance of the micro-supercapacitor. It is anticipated that the proposed design concept will be applicable for next-generation stretchable electronics.

A Smart Gas Sensor Using Machine Learning Algorithms: Sensor Types Based on IED Configurations, Fabrication Techniques, Algorithmic Approaches, Challenges, Progress, and Limitations: A Review

Over the past decade, Machine Learning and Artificial Intelligence have attracted great interest in research and various practical applications. Currently, smart, fast, highly sensitive with excellent selectivity are becoming increasingly interesting due to the high need for environmental safety and medical applications. The main challenge is to improve sensor selectivity, which requires the combination of interdisciplinary research areas to successfully develop smart gas/chemical sensing devices with better performance. In this review, we present a few principles of gas sensing based on low-cost interdigitated electrodes (IDE), such as electrochemical, resistive, capacitive and acoustic sensors. In addition, the most important current methods for improving gas sensing performance, the different materials, the different techniques used to fabricate IDE gas sensors, their advantages and limitations are presented. In addition, a comparison between different machine learning and artificial intelligence algorithms for pattern recognition and classification algorithms is also discussed. The discussion then establishes application cases of smart machine learning algorithms, which provide efficient data processing methods, for the design of smart gas sensors which are highly selective. In addition, the challenges and limitations of machine learning in gas sensor applications are critically discussed. The study shows the importance of machine learning with the need for structural optimization to develop and improve smart, sensitive and selective sensors.

All Resistive Pressure-Temperature Bimodal Sensing E-Skin for Object Classification.

Electronic skin (E-skin) with multimodal sensing ability demonstrates huge prospects in object classification by intelligent robots. However, realizing the object classification capability of E-skin faces severe challenges in multiple types of output signals. Herein, a hierarchical pressure-temperature bimodal sensing E-skin based on all resistive output signals is developed for accurate object classification, which consists of laser-induced graphene/silicone rubber (LIG/SR) pressure sensing layer and NiO temperature sensing layer. The highly conductive LIG is employed as pressure-sensitive material as well as the interdigital electrode. Benefiting from high conductivity of LIG, pressure perception exhibits an excellent sensitivity of -34.15 kPa-1 . Meanwhile, a high temperature coefficient of resistance of -3.84%°C-1 is obtained in the range of 24-40°C. More importantly, based on only electrical resistance as the output signal, the bimodal sensing E-skin with negligible crosstalk can simultaneously achieve pressure and temperature perception. Furthermore, a smart glove based on this E-skin enables classifying various objects with different shapes, sizes, and surface temperatures, which achieves over 92% accuracy under assistance of deep learning. Consequently, the hierarchical pressure-temperature bimodal sensing E-skin demonstrates potential application in human-machine interfaces, intelligent robots, and smart prosthetics.

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.

Facile Self-Assembly of Exfoliated Graphene/PANI Film for High-Energy Zn-Ion Micro-Supercapacitors.

The Zn-ion micro-supercapacitor (ZMSC) is a promising candidate for developing miniaturized and integrated energy storage devices. To achieve high-performance functional groups with simple processing to composite with rod-like active PANI fibers, we prepared exfoliated graphene (EG) with an appropriate amount of O-containing functional groups. The appropriate O content simultaneously facilitated self-assembly of the EG and PANI fibers and maintained the electric conductivity of the composite, producing a free-standing EG/PANI film without additional conductive additives or current collectors. As an interdigital electrode for the ZMSC, the EG/PANI film showed ultrahigh capacitance of 1.8 F cm-2 at 2.6 mA cm-2 (361.3 F g-1 at 0.5 A g-1) and landmark energy density of 755.8 μWh cm-2 at 2.3 mW cm-2 (148.2 Wh kg-1 at 451.7 W kg-1). The facile preparation of the high-performance EG/PANI electrode provides a potential path for practical applications with ZMSCs.

Directional Activated Exciton Highway via Fractal Electric Field Modulation for Ultrasensitive Carbon Nanotube-Based Sensors.

The electrical vapor sensor based on carbon nanotubes (CNTs) has attracted wide attention due to its excellent conductivity, stable interfacial structure, and low dimensional quantum effects. However, the conductivity and contact interface activity were still limited by the random distribution of coated CNTs, which led to limited performance. We developed a new strategy to unify the CNT directions with image fractal designing of the electrode system. In such a system, directional aligned CNTs were gained under a well-modulated electric field, leading to microscale CNT exciton highways and molecule-scale host-guest site activation. The carrier mobility of the aligned CNT device is 20-fold higher than that of the random network CNT device. With excellent electrical properties, such modulated CNT devices based on fractal electrodes behave as an ultrasensitive vapor sensor for methylphenethylamine, a mimic of illicit drug methamphetamine. The detection limit reached as low as 0.998 ppq, 6 orders of magnitude sensitive than the reported 5 ppb record based on interdigital electrodes with random distributed CNTs. Since the device is easily fabricated in wafer-level and compatible with the CMOS process, such a fractal design strategy for aligned CNT preparation will be widely applied in a variety of wafer-level electrical functional devices.

Piezoelectric ZnO nanoarrays for catalytic detection of H2O2 with ultra sensitivity

Piezo-electrocatalytic semiconductors with the piezoelectric effect and catalytic properties offer unprecedented opportunities in a variety of applications of chemical sensors, electrocatalysts, and photocatalysis. Herein, we demonstrate a flexible piezo-electrocatalytic sensor based on ZnO nanoarrays for ultrasensitive detection of hydrogen peroxide (H2O2), an important substance in many biologic and medical fields. In situ growth of ZnO nanoarrays on flexible gold interdigital electrodes can effectively couple electrical excitation and external strain-induced piezoelectric polarization to promote catalytic reactions. Therefore, the piezo-electrocatalytic sensor measured by chronoamperometry exhibits an unexpectedly high sensitivity of 487 μA mM−1 cm−2, which is superior to previous results. By using finite element analysis, we simulate the piezoelectric effect of ZnO to elucidate the charge transfer between the strained ZnO and H2O2. This work demonstrates a versatile platform of a flexible piezo-electrocatalytic sensor that can use external mechanical energy to improve chemical and biologic detection.

Flexible microfluidic triboelectric sensor for gesture recognition and information encoding

Flexible triboelectric sensor has a broad application prospects in self-powered human-machine interface. However, due to the complexity of real environment, the output signal is easily disturbed, thus resulting in low reliability. Here, a flexible microfluidic triboelectric sensor (FMTS) was proposed by counting the number of wave peaks in output waveform. With a high transmittance of 82%, the FMTS shows bendable, twistable and conformable characteristics so that can be operated attached to skin. Based on triboelectrification and electrostatic induction between liquid stream, microchannel and interdigital electrodes, it enables to generate quantifiable voltage wave peaks. The FMTS has a maximum sensitivity of 0.418 kPa−1 and a wide detection range from 2.38 to 58.12 kPa with the microchannel width of 500 µm. For demonstration, a FMTS is attached to the finger, and the number of peaks is used to determine the angle of finger bending with a resolution of 10°. The machine learning approach is employed to achieve accurate recognition of five gestures with an accuracy of 99.2%. The information can also be defined by using waveforms generated by different combinations of movements. An encoding system that recognizes eight types of information with an accuracy of up to 98.8% is finally demonstrated.

Designing copper–nickel hybrid nanoparticles based resistive sensor for ammonia gas sensing

Designing advanced and cost-effective materials for ammonia gas sensing is concomitantly a challenging and crucial task. Herein, copper nickel (Cu–Ni) bimetallic hybrid nanoparticles were synthesized by the co-precipitation method for the application of ammonia gas detection. The synthesized nanoparticles (NPs) were characterized by employing UV–Visible spectroscopy which confirmed the band gap of 2.35 eV. FTIR analysis confirmed the stretching oscillation for hybrid Cu–Ni at 455 cm−1. XRD effectively evaluated the overall crystallinity and particle size while SEM confirmed the spherical shaped particles of the Cu–Ni BNPs. For ammonia gas sensing, the synthesized NPs were deposited onto an interdigitated electrode through electrospinning, then, connected through an LCR meter for analysis of different electrical properties. There was a direct relationship between current and voltage depicting the metallic behavior of the Cu–Ni BNPs. The Cu–Ni BNPs based sensor showed excellent performance on low frequencies of 1 kHz and there was an increase in resistance which confirmed that the sensor was a resistive type. The Cu–Ni showed a maximum response of 27s with a 24s recovery. The as-prepared sensing device can be applied for potential use in ammonia detection quantitatively and qualitatively.

Surface Acoustic Waves Equip Materials with Active De‐Icing Functionality: Unraveled Glaze Ice De‐Icing Mechanisms and Application to Centimeter‐Scale Transparent Surfaces

Enabling active de‐icing functionality on low heat conductive and transparent materials is a requirement for several seminal industries in critical economic sectors. However, developing efficient and environmentally friendly de‐icing methods still fails because of compatibility problems with large‐scale devices and real‐world conditions. In this paper, de‐icing several square centimeters covered with thick layers of glaze ice is approached through nanoscale activation by surface acoustic waves (SAWs). De‐icing functionality is demonstrated with a self‐supported piezoelectric material (LiNbO3) and a piezoelectric film (ZnO) deposited on fused silica, the latter system proving the compatibility of the method with materials of practical relevance. Its applicability to large and transparent substrates is demonstrated by placing the interdigitated electrodes (IDTs) required for activation close to the substrate's edges, leaving most of the surface unaltered. The de‐icing mechanism of glaze ice by SAW activation is revealed by simulating the SAW propagation on ice‐covered surfaces and by experimental analysis of the ice melting process. This involves a combination of ice mechanical stress activation and heating through the initially formed water/ice front. Possible Joule effects due to ohmic losses in the IDTs have been discarded, monitoring local temperature variations during SAW activation at and out of resonance conditions.

A Low-Power Sensing System of VEGF Concentration With Noise Reduction Using Subsampling Technique for Cancer Diagnosis

This paper presents a monolithic low-power sensing system for early cancer detection. The system uses a CMOS MEMS capacitive transducer with a gold interdigitated electrode (IDE) and DNA aptamers to sense the concentration of vascular endothelial growth factor (VEGF). When the DNA aptamer is immobilized with the VEGF sensor, it generates an electric double-layer capacitance. The low-noise front-end circuits amplify this capacitance change and convert the signal into the frequency domain. To solve the wide input dynamic range and reduce power consumption, a two-step time-to-digital converter (TDC) is utilized. The proposed sub-sampling (SS) technique provides a higher conversion gain to reject noise interference and overcome the increase in noise floor introduced from the decoder due to lower supply voltage. The sub-sampling delay-locked loop (SSDLL), combined with the calibration circuit, enhances TDC linearity and noise performance while preventing calibration noise from degrading conversion accuracy. Finally, the time-based information is converted into digital codes with high power efficiency for early cancer analysis. The system is fabricated in TSMC 0.35 μm MEMS CMOS process with electroplated gold. Measurement results show that the power consumption of the readout circuit and the overall system is only 18 μW and 60.65 μW, respectively. The proposed system improves jitter by 49% and achieves 0.725 mV/pg-mL sensitivity.