Interdigitated Electrodes Research Articles

Spinal cord injury immunosensor: Sensitive detection of S100β on interdigitated electrode sensor

A spinal cord injury is damage to the nerves and cells that receive and provide a signal from the brain to the rest of the body. Spinal injury causes changes in movement, sensation, and strength, affect the body functions near the injury site, and may lead to paralysis. S100β was found as a suitable biomarker for identifying spinal cord injury and its causing problem. Herein, S100β immunoassay was developed on interdigitated electrode sensor to diagnose spinal cord injury. For effective anti-S100β antibody immobilization, the antibody was premixed with 3-Aminopropyl)triethoxsilane and then attached to the hydroxylated interdigitated electrode surface. This method of antibody immobilization enhanced the antibody attachment two-times than the method without premix. Antibody-attached surfaces increased current responses as S100 concentrations increased, and the limit of detection was seen to be 1 pg/mL on the linearity until 3000 pg/mL at an R2 value of 0.9907 [y = 7x - 6.4667]. Further, biofouling experiments with glial fibrillary acidic protein and γ-aminobutyric acid failed to enhance the current response, indicating the specific detection of S100β. This immunoassay identifies S100β at its lower level and helps to diagnose spinal cord injury and its related problem.

4D printing of shape-adaptive tactile sensor with tunable sensing characteristics

Using 4D printing to fabricate tactile sensors is promising, which will bring exciting functionalities to sensors, such as action self-sensing, environment self-adaptation, and self-healing. Here, we introduce 4D printing technology to fabricate the versatile smart tactile sensor with an adjustable measuring range and sensitivity, and shape adaptation for sensing in unstructured objects, which can sense touch from. The 4D-printed sensors (4DPS) with unique coplanar designs are achieved using a multi-material extrusion process for manufacturing interdigital electrodes composed of nanocarbon black/polylactic acid composites and shape memory polyurethane. The variability in the detection range and sensitivity stems from the changes in the electrode height and spacing caused by the deformation of shape memory polymer (SMP) under heat treatment. By setting printing parameters, not only can the diameter of the interdigital electrodes be precisely regulated, but 3D sensors that adapt to different curved surfaces can also be realized by utilizing thermal stress during the printing process. Moreover, the 4DPS is applicable to non-developable surfaces, such as spherical dome surfaces or saddle surfaces. Therefore, the shape-changing tactile sensor may offer great potential in environment self-adaptation and test range self-adjustment for human-robot cooperation in sensing.

Effect of electrode patterns on piezoelectric energy harvesting property of zinc oxide polyvinylidene fluoride based piezoelectric nanogenerator

Renewable energy generation is one of the key strategies to solve energy shortages and environmental problems. Among various techniques of renewable energy generation and harvesting, piezoelectric energy harvesting receives huge consideration due to the enormous demand in self-powered electronic devices. Therefore, the development of a piezoelectric nanogenerator (PENG) with effective piezoelectric energy harvesting performance is very important. Herein, we develop zinc oxide polyvinylidene fluoride based (ZnO@PVDF PENG) device and study on the effects of electrode patterns on the piezoelectric performances of the device. We also investigate real application of the device in our daily life. The findings show that interdigitated electrode patterned ZnO@PVDF PENG present the highest piezoelectric performance by harvesting output current, voltage, and power density of 1.15 μA, 50 V, and 20.10 mW/m2, respectively at 12 N. The device also scavenges energy that has capacity to light 20 green light emitting diodes (LEDs) and display a liquid crystal display (LCD) timer for 1 s. Moreover, the ZnO@PVDF PENG) device shows excellent cyclic charging and discharging property, which is very important for practical applications. Therefore, this PENG device is promising candidate to harvest green and renewable energy and use to power electronic devices.

Laser-direct-writing assisted preparation of flexible humidity sensors based on semi-interpenetrating polymer network for applications in non-contact human-machine interaction

Flexible sensors for non-contact human-machine interaction (HMI) received great attention recently due to increasing requirements for cross-infection of bacteria or virus, which is prominent considering the disaster brought about by COVID-19. Herein, a semi-interpenetrating network of poly(dimethyl diallyl ammonium chloride)/crosslinked poly(vinyl alcohol)/graphene oxide (PDDA/c-PVA/GO) was deposited on polytetrafluoroethylene membrane with interdigital electrodes constructed by reducing GO with laser-direct-writing technology to prepare a flexible humidity sensor (FHS). As-prepared PDDA/c-PVA/GO FHS showed excellent sensing performance, including high response magnitude over wide range of relative humidity (RH) (impedance change of three orders of magnitude between 10 % and 90 % RH), good sensing linearity (R2 = 0.991) on a semi-logarithmic scale, small hysteresis (∼ 4.4 % RH) and resistance to humid environment. Moreover, the FHS exhibited good performance in various scenarios of non-contact HMI, including prompt differentiation of respiration status, speech recognition, accurate measurement of fingertip movement (as small as 2 mm). Specially, a 3 × 3 FHS sensor array could realize accurate non-contact positioning. This work provides a new approach for developing high performance flexible sensors with great application potentials in non-contact HMI.

Classification-Based Evaluation of Multi-Ingredient Dish Using Graphene-Modified Interdigital Electrodes.

A taste sensor with global selectivity can be used to discriminate taste of foods and provide evaluations. Interfaces that could interact with broad food ingredients are beneficial for data collection. Here, we prepared electrochemically reduced graphene oxide (ERGO)-modified interdigital electrodes. The interfaces of modified electrodes showed good sensitivity towards cooking condiments in mixed multi-ingredients solutions under electrochemical impedance spectroscopy (EIS). A database of EIS of cooking condiments was established. Based on the principal component analysis (PCA), subsets of three taste dimensions were classified, which could distinguish an unknown dish from a standard dish. Further, we demonstrated the effectiveness of the electrodes on a typical dish of scrambled eggs with tomato. Our kind of electronic tongue did not measure the quantitation of each ingredient, instead relying on the database and classification algorithm. This method is facile and offers a universal approach to simultaneously identifying multiple ingredients.

Fabrication of carbon nanotube/ titanium dioxide nanomaterials-based hydrogen sensor using novel two-stage dielectrophoresis process

The porosity and large surface area of carbon nanotubes (CNTs) made them a candidate active material for gas sensing applications. However, the responsivity and sensitivity of CNTs toward hydrogen are lower than those of metal oxide semiconductor materials such as TiO2. The addition of TiO2 to CNTs is found to increase the sensitivity of the resulting composite material at the expense of increasing the resistance. This paper presents a new dielectrophoresis (DEP) process to fabricate nanoparticle-based hydrogen sensors at room temperature. The simple and low-cost process is based on tuning the AC signal frequency to deposit different nanoparticles in stages, forming a composite sensing layer across interdigitated electrodes (IDE). The sensing layers have been characterized using field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX), and atomic force microscopy (AFM). Sensors fabricated with only CNTs showed low resistance and weak sensitivity of less than 2%. The sensitivity has increased to 3.42% when CNTs are deposited together with TiO2 in a single stage. However, the sensor shows high resistance because TiO2 particles interrupt the conduction paths of CNTs. A high sensitivity of 15.78% and a low resistance of ∼524 Ω have been achieved when CNTs are deposited individually in the first stage, and followed by depositing the TiO2 in the second stage. This work provides a proof-of-concept that the two-stage DEP enhances the performance of the sensor in terms of sensitivity and resistance compared to single-stage DEP, which is highly desirable in fabricating composite and multi-layer sensing materials.

Graphene Oxide-coated interdigitated electrode for selective detection of mercury ions using self-assembled monolayer of mercaptosuccinic acid

Graphene Oxide-coated interdigitated electrode for selective detection of mercury ions using self-assembled monolayer of mercaptosuccinic acid

Highly Stable Low-Strain Flexible Sensors Based on Gold Nanoparticles/Silica Nanohelices.

Flexible strain sensors based on nanoparticle (NP) arrays show great potential for future applications such as electronic skin, flexible touchscreens, healthcare sensors, and robotics. However, even though these sensors can exhibit high sensitivity, they are usually not very stable under mechanical cycling and often exhibit large hysteresis, making them unsuitable for practical applications. In this work, strain sensors based on silica nanohelix (NH) arrays grafted with gold nanoparticles (AuNPs) can overcome these critical aspects. These 10 nm AuNPs are functionalized with mercaptopropionic acid (MPA) and different ratios of thiol-polyethylene glycol-carboxylic acid (HS-PEG7-COOH) to optimize the colloidal stability of the resulting NH@AuNPs nanocomposite suspensions, control their aggregation state, and tune the thickness of the insulating layer. They are then grafted covalently onto the surface of the NHs by chemical coupling. These nanomaterials exhibit a well-defined arrangement of AuNPs, which follows the helicity of the silica template. The modified NHs are then aligned by dielectrophoresis (DEP) between interdigitated electrodes on a flexible substrate. The flexibility, stability, and especially sensitivity of these sensors are then characterized by electromechanical measurements and scanning electron microscopy observations. These strain sensors based on NH@AuNPs nanocomposites are much more stable than those containing only nanoparticles and exhibit significantly reduced hysteresis and high sensitivity at very slight strains. They can retain their sensitivity even after 2 million consecutive cycles with virtually unchanged responsiveness. These improved performances come from their mechanical stability and the use of nanohelices as stable mechanical templates.

High porosity and oxygen vacancy enriched WO3-x thin films for room temperature hydrogen gas sensors

Due to the increase in demand for hydrogen in several fields, sensors that detect the presence of hydrogen gas more precisely even at room temperature (30 °C) are required for its safe use. In this work, we report the hydrogen gas sensing performance of the WO3-x thin film deposited at different oxygen partial pressures (10%, 15%, and 20%) onto SiO2/Si substrate using a radio frequency (RF) magnetron sputtering technique. To study the hydrogen gas sensing performance, Ag/WO3-x/Ag test-device is fabricated by depositing interdigitated Ag electrodes onto the WO3-x gas sensing layer via thermal evaporation. The performance of the obtained sensors is investigated at different hydrogen concentrations (100 ppm–300 ppm) and different operating temperatures (30°C–300 °C). WO3-x thin films deposited at 10% of pO2 show a maximum response of 3.40% for 100 ppm of H2 gas even at room temperature, which is due to the high crystallinity, high porosity, and the presence of more oxygen vacancies. The oxygen vacancies that are created during the reactive magnetron sputtering would enhance the hydrogen adsorption and hence superior hydrogen sensing results achieved. Herein, the response and recovery times are measured in most of the sensing conditions and the sensing mechanism has been discussed.

Dielectrophoretic liquid lens driven by interdigitated sidewall electrodes.

This paper proposes a dielectrophoretic (DEP) liquid lens that is driven by interdigitated electrodes distributed on the sidewalls and has a structure similar to that of the electrowetting one produced by the company Corning. The interdigital electrodes are formed by winding double flexible wire electrodes wrapped in dielectric layers on the sidewall. Compared with the traditional planar electrode DEP lens, the proposed model ensures the stability of the optical axis of the liquid lens, simplifies the construction process of the interdigital electrode, realizes a continuous change in the focus from negative to positive, and reduces the response time. A truncated conical cavity dielectrophoretic liquid lens with an aperture of 5 mm is fabricated. When the voltage is 0-260 Vrms, it can reach shortest negative and positive focal lengths of -100 mm and 100 mm with a driving time of 190 ms and a relaxation time of 133 ms.

Toward Band n78 Shear Bulk Acoustic Resonators Using Crystalline Y-Cut Lithium Niobate Films With Spurious Suppression

This work presents the study of suspended Y-cut Lithium Niobate shear bulk acoustic resonators for wide band filter applications in the frequency range of 3.5-4.5GHz. The resonators consist of a Lithium Niobate film with Aluminum top interdigitated electrodes (IDE) and floating bottom metal plate. Through vertical electric field excitation, shear bulk acoustic waves are generated in each unit cell of the device functioning as a quasi-independent resonator. Measured devices at 3.7GHz having large relative resonance-antiresonance bandwidth of 16.7% (750MHz), with 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm{\Omega }$</tex-math> </inline-formula> impedance at resonance are presented. Suppression of higher order lateral harmonics through etching of trenches in the Lithium Niobate and geometric optimization is discussed.2022-0205

Synergistic effect of AgBiS2 segregated NaV3O8 nanostructures in direct conversion X-ray sensors

Synergistic nanostructures possess enriched electrical and optical properties compared to conventional nanostructures. 1D-3D synergized nanostructure was implied to elucidate the performance of the X-ray sensor for the first time. Current research in X-ray detection only focuses on implementing high attenuating material based on oxides/ perovskites in developing X-ray sensors. Herein we approached tailoring the performance of an X-ray sensor with a synergistic nanostructure composed of sodium vanadium oxide (NaV3O8) with substantial grain boundary (GB) segregation of silver bismuth sulfide (AgBiS2), enabling the structured arrangement of nanostructured grains at the surface of NaV3O8 nanorods. Then, it was coated as a thick film on top of the interdigitated electrodes by glass rod sliding technique to readout the dose-dependent X-ray sensing capability. From the X-ray impinged photocurrent characteristics, the sensor with 75 wt% AgBiS2 segregated NaV3O8 exhibits superior sensitivity 82.6 nC mGy-1 cm-2 and low-noise equivalent dose rate 1.04 mGy Hz-0.5 for 2.49 mGy s-1 than other compositions. These experimental findings explore the implication of synergistic nanostructures as active layers in direct conversion X-rays sensors for improved charge extraction and enhancement in X-ray impinged photocurrent at low dose rates.

Interdigital flexible tactile sensor based on Velostat

PurposeTactile sensation is an important sensory function for robots in contact with the external environment. To better acquire tactile information about objects, this paper aims to propose a three-layer structure of the interdigital flexible tactile sensor.Design/methodology/approachThe sensor consists of a bottom electrode layer, a middle pressure-sensitive layer and a top indenter layer. First, the pressure sensitive material, structure design, fabrication process and circuit design of the sensor are introduced. Then, the calibration and performance test of the designed sensor is carried out. Four functions are used to fit and calibrate the relationship between the output voltage of the sensor and the contact force. Finally, the contact force sensing test of different weight objects and the flexible test of the sensor are carried out.FindingsThe performance test results show that the sensitivity of the sensor is 0.93 V/N when it is loaded with 0–3 N and 0.23 V/N when it is loaded with 3–5 N. It shows good repeatability, and the cross-interference between the sensing units is generally low. The contact force sensing test results of different weight objects show that the proposed sensor performs well in contact force. Each part of the sensor is a flexible material, allowing the sensor to achieve bending deformation, so that the sensor can better perceive the contact signs of the grasped object.Practical implicationsThe sensor can paste the surface of the paper robot’s gripper to measure the contact force of the grasping object and estimate the contour of the object.Originality/valueIn this paper, a three-layer interdigital flexible tactile sensor is proposed, and the structural parameters of the interdigital electrode are designed to improve the sensitivity and response speed of the sensor. The indenter with three shapes of the prism, square cylinder and hemisphere is preliminarily designed and the prism indenter with better conduction force is selected through finite element analysis, which can concentrate the external force in the sensing area to improve the sensitivity. The sensor designed in this paper can realize the measurement of contact force, which provides a certain reference for the field of robot tactile.

Deep-Learning Enabled Active Biomimetic Multifunctional Hydrogel Electronic Skin.

There is huge demand for recreating human skin with the functions of epidermis and dermis for interactions with the physical world. Herein, a biomimetic, ultrasensitive, and multifunctional hydrogel-based electronic skin (BHES) was proposed. Its epidermis function was mimicked using poly(ethylene terephthalate) with nanoscale wrinkles, enabling accurate identification of materials through the capabilities to gain/lose electrons during contact electrification. Internal mechanoreceptor was mimicked by interdigital silver electrodes with stick-slip sensing capabilities to identify textures/roughness. The dermis function was mimicked by patterned microcone hydrogel, achieving pressure sensors with high sensitivity (17.32 mV/Pa), large pressure range (20-5000 Pa), low detection limit, and fast response (10 ms)/recovery time (17 ms). Assisted by deep learning, this BHES achieved high accuracy and minimized interference in identifying materials (95.00% for 10 materials) and textures (97.20% for four roughness cases). By integrating signal acquisition/processing circuits, a wearable drone control system was demonstrated with three-degree-of-freedom movement and enormous potentials for soft robots, self-powered human-machine interaction interfaces of digital twins.

Humidity Sensor Composed of Laser-Induced Graphene Electrode and Graphene Oxide for Monitoring Respiration and Skin Moisture.

Respiratory rate and skin humidity are important physiological signals and have become an important basis for disease diagnosis, and they can be monitored by humidity sensors. However, it is difficult to employ high-quality humidity sensors on a broad scale due to their high cost and complex fabrication. Here, we propose a reliable, convenient, and efficient method to mass-produce humidity sensors. A capacitive humidity sensor is obtained by ablating a polyimide (PI) film with a picosecond laser to produce an interdigital electrode (IDE), followed by drop-casting graphene oxide (GO) as a moisture-sensitive material on the electrode. The sensor has long-time stability, a wide relative humidity (RH) detection range from 10% to 90%, and high sensitivity (3862 pF/%RH). In comparison to previous methods, the technology avoids the complex procedures and expensive costs of conventional interdigital electrode preparation. Furthermore, we discuss the effects of the electrode gap size and the amount of graphene oxide on humidity sensor performance, analyze the humidity sensing mechanism by impedance spectrum, and finally perform the monitoring of human respiratory rate and skin humidity change in a non-contact manner.

Hierarchical α-MoO3: A versatile eco-friendly material for humidity-assisted ammonia sensing and efficient catalytic activity in wastewater treatment

In this work, a facial synthesis of α-MoO3 nanoparticles was done by chemical co-precipitation method. The synthesized α-MoO3 nanomaterials have been reported for sensing and photocatalysis applications together. For sensing, the α-MoO3 was coated on FTO based interdigitated electrodes, and the prepared sensor was tested for numerous concentrations of ammonia (100–600 ppm) under different relative humidity levels (11–33%−56–75% −95% RH). The response and recovery time of α-MoO3 based sensor for 500 ppm of NH3 were 8 s and 11 s under 95% RH, respectively. The prepared α-MoO3 based sensor exhibits high selectivity and stability towards ammonia. To analyze the photocatalytic activity of prepared α-MoO3 nanoparticles, the photodegradation of methylene blue (MB) and methyl orange (MO) under visible light irradiation was studied. The first-order reaction rate constant for MB dye is 0.02434 min−1, and for MO dye is 0.01111 min−1. Finally, the maximum degradation efficiency for MB and MO dyes was calculated to be 95% and 73%, respectively. The given data conclude that the synthesized α-MoO3 nanoparticles can be used as an effective NH3 sensor as well as an efficient photocatalyst in organic dye degradation.

Characterization and performance evaluation of fully biocompatible gelatin-based humidity sensor for health and environmental monitoring

Biomaterials will have far reaching effects on solving the ever-rising environmental problems caused by the presently used toxic materials. Disposal of hazardous materials based electronic devices is causing a huge environmental problem in the form of electronic wastes (E-wastes). This study is an effort to contribute in the reduction of E-wastes by presenting the design, fabrication, and performance evaluation of a fully biocompatible humidity sensor with gelatin as the active layer. Gelatin is an excellent choice for humidity sensing because it is a hygroscopic material with the natural ability to attract and absorb water molecules, allowing for an effective detection and measurement of humidity levels in its surrounding environment. We patterned highly conductive (2.05 μΩ-cm) gold (Au) interdigitated electrode (IDE) (50 nm thickness) structure on a glass substrate by using thermal vacuum evaporation followed by the deposition of gelatin thin film by using cost effective technique of spin coating (at 1,500 rpm for 15 s). The device size was 25 mm × 22 mm with a line spacing of 1.50 mm between IDEs. Electrical characterisation was carried out to determine necessary performance parameters of the fully biocompatible humidity sensor and the obtained results exhibited a fast response/recovery time (4/6.30 s), wide operating range (15 %RH to 86 %RH), highly repeatable behaviour of 3 different samples and long lifetime (1 month). Wide variation in the resistance of sensor was observed at extreme humidity sensors ranging from 2.45 MΩ (15 %RH) to 0.12 MΩ (86 %RH). The fabricated sensor was used for the practical applications of health monitoring, touch less sensing, and environment monitoring. Moisture content of multiple commercially available moisturizers was determined by using gelatin based fully biocompatible humidity sensor and the obtained results showed that moisturizing cream had highest moisture content of 87 %RH (0.1 MΩ), followed by 80 %RH (0.30 MΩ) of rose water, and 72 %RH (0.67 MΩ) of baby oil.

High performance multilayer heterogeneous resonators based on 128° YX lithium niobate and diamond composite films for 5 GHz and beyond

The advent of the new 5G communication standard has introduced demanding requirements for the performance of RF front-end filters, necessitating high frequency, large bandwidth, and other improved parameters. Consequently, researchers have been actively investigating the potential of surface acoustic wave resonators and film bulk acoustic resonators to address these needs, leading to the development of numerous novel structures. Through finite element simulation, a new heterogeneous stack structure Al/LN/diamond/Si with an interdigitated electrode resonant cavity is proposed. And the advantageous role of a diamond thin film in the surface acoustic wave resonant structure, including the excitation of high-frequency acoustic resonance modes and modulation of the electromechanical coupling coefficient has been studied. This structure holds promise for addressing the increasing demands for high-frequency, large-bandwidth RF front-end filters in the context of the new 5G communication standard. The results show that the central resonant frequency of the new structure resonator is 5284 MHz, the electromechanical coupling coefficient is 10.96%, and the Q factor value is 10 316, which has potential application value in the field of high-frequency filtering.

Capacitive, Highly Selective Zeolite-Based Ammonia Sensor for Flue Gas Applications

The selective detection of different gas components will remain of huge importance in the future, either in the ambient air or in flue gases, e.g., for controlling purposes of combustion processes. The focus here is on the development of a highly selective ammonia sensor that will be exemplarily used in the flue gas of biomass combustion plants with catalysts for nitrogen oxide reduction. Such applications require a robust sensor design, in this case, based on a ceramic substrate. The gaseous ammonia is detected with the help of a zeolite film, whose selective adsorption properties towards ammonia are already intensively being used in the field of flue gas catalysis. The adsorption and desorption of ammonia on the gas-sensitive zeolite film lead to changes in the dielectric properties of the functional material. Using an interdigital electrode (IDE) structure below the zeolite film, the capacitance was determined as a measure of the ammonia concentration in the gas. In this context, the fabrication of all layers of the sensor in the thick film with subsequent laser patterning of the IDE structure enables a cost-efficient and effective method. The functionality of this sensor principle was extensively tested during measurements in the laboratory. A high and fast response to ammonia was detected at different sensor temperatures. In addition, very low cross-sensitivities to other gas components such as water (very low) and oxygen (zero) were found.

Enhanced Electrical Injury Using Triangular Interdigitated Electrodes for Catheter-Based Irreversible Electroporation

Irreversible electroporation (IRE) is a promising nonthermal ablation technique that uses high-voltage electrical pulses to create permanent pores in the cell membrane of target tissue. Recently, endoscopic IRE with catheter-based electrodes has attracted significant attention as a potential alternative tool for gastrointestinal tumors, but it has been challenged owing to the limited electric field distribution in an in-plane electrode configuration, in which rectangular interdigitated electrodes (IDEs) are commonly used. Herein, we report an enhanced electrical injury in tissue using triangular IDEs that cause strong electric fields to be induced at the tip of the electrode fingers. A set of 10 pulses with a duration of 100 μs and a frequency of 1 Hz were delivered to the tissue, and a finite element method was used to calculate the electrical injury in the gastrointestinal model. The probability of cell death by electrical injury at the triangular IDEs increases by approximately 10 times compared to that of conventional rectangular IDEs at the same electrode distance. These results could potentially pave the way toward designing electrodes in catheter-based IRE devices.