Interdigitated Electrodes Research Articles

Nanoquantification of RUNX2 by a 1,1′-carbonyldiimidazole-diamond mediated sandwich assay for osteogenic differentiation

Adipose tissue-derived stem cells (ADSCs) possess the capability to modulate the immune response and alleviate inflammation, rendering them a promising therapeutic option for various conditions, including autoimmune diseases, cardiovascular diseases, and tissue injuries. The osteogenic differentiation in ADSCs plays a pivotal role in fracture healing, bone growth, and the overall bone turnover process, governed by intricate interactions. Runt-related Transcription Factor 2 (RUNX2) is a key player in mineralized tissue generation and is typically found in the early stages of osteogenic differentiation. The objective of this study was to develop a high-affinity sandwich biosensor for the quantification of RUNX2. 1,1′-Carbonyldiimidazole-modified nanodiamond was immobilized on an amine-modified interdigitated electrode surface, followed by the use of a capture antibody to facilitate antigen interaction. A sandwich assay was conducted with the antibody, and the limit of detection for RUNX2 was calculated as 0.1 ng/mL, with a regression value (R2) of 0.9914 over a linear range of 1–2000 ng/mL. Furthermore, biofouling experiments with a nonimmune antibody, BSA, and TNF-α did not yield any current responses, indicating the specific detection of RUNX2. Additionally, RUNX2-spiked serum exhibited an increasing current response at all concentrations, confirming the selective detection of RUNX2.

All Screen Printed and Flexible Silicon Carbide NTC Thermistors for Temperature Sensing Applications.

In this study, Silicon Carbide (SiC) nanoparticle-based serigraphic printing inks were formulated to fabricate highly sensitive and wide temperature range printed thermistors. Inter-digitated electrodes (IDEs) were screen printed onto Kapton® substrate using commercially avaiable silver ink. Thermistor inks with different weight ratios of SiC nanoparticles were printed atop the IDE structures to form fully printed thermistors. The thermistors were tested over a wide temperature range form 25 °C to 170 °C, exhibiting excellent repeatability and stability over 15 h of continuous operation. Optimal device performance was achieved with 30 wt.% SiC-polyimide ink. We report highly sensitive devices with a TCR of -0.556%/°C, a thermal coefficient of 502 K (β-index) and an activation energy of 0.08 eV. Further, the thermistor demonstrates an accuracy of ±1.35 °C, which is well within the range offered by commercially available high sensitivity thermistors. SiC thermistors exhibit a small 6.5% drift due to changes in relative humidity between 10 and 90%RH and a 4.2% drift in baseline resistance after 100 cycles of aggressive bend testing at a 40° angle. The use of commercially available low-cost materials, simplicity of design and fabrication techniques coupled with the chemical inertness of the Kapton® substrate and SiC nanoparticles paves the way to use all-printed SiC thermistors towards a wide range of applications where temperature monitoring is vital for optimal system performance.

Fabrication of Flexible Capacitive Pressure Sensors by Adjusting the Height of the Interdigital Electrode

Fabrication of Flexible Capacitive Pressure Sensors by Adjusting the Height of the Interdigital Electrode

Direct laser writing of MnOx decorated laser-induced graphene on paper for sustainable microsupercapacitor fabrication

Laser-induced graphene (LIG) on paper is a popular choice for fabricating flexible micro-supercapacitors (MSCs) as it is a simple and sustainable process. However, carbon-based MSC electrodes have limited energy densities. To address this challenge, this study presents a highly reproducible and cost-effective method for decorating manganese oxide (MnOx) on interdigital LIG MSC electrodes, fabricated via a single-step direct laser writing (DLW) process on paper substrates. The paper fibers embedded with MnOx precursors are transformed into graphene through laser processing while reducing the salt, resulting in the formation of MnOx-LIG. The resulting MnOx-LIG-MSC exhibits a specific capacitance of 12.30 mF cm−2 (0.05 mA cm−2) with a 60 % retention at 1000 bending cycles (30°), due to the pseudocapacitive contribution of MnOx. Furthermore, the devices exhibit high electrochemical stability, retaining 190 % of the initial specific capacitance after 10,000 cycles, and a high energy density of 2.6 μWh cm−2 (at a power of 0.109 mW cm−2). The study demonstrates that manganese oxide-based LIG-MSCs have the potential to be used as energy storage devices for portable, low-cost, and flexible paper electronics.

A vibrating membrane ejector for direct ink writing of printed electronics

Direct ink writing (DIW) represents a technical branch of additive manufacturing technology, particularly suitable for prototyping or small-batch printing production of printed electronic components. However, the existing print heads required for near or sub-100 μm line width are quite sophisticated, limiting the accessibility and application of the DIW method. This paper reports the use of the vibrating membrane ejector (VME) as a new option for the print head of DIW. The structure of the VME-based print head was specially designed for this purpose. Finite element modeling and analysis of the VME’s vibration characteristics were performed to provide insights into the ejection conditions and behaviors. The factors influencing the size of printed structures were identified and analyzed through the printing of a metal–organic complex silver (Ag) ink. After optimizing several operational parameters to limit the spreading effects and suppress the satellite droplets, the DIW printed line width has reached about 100 μm. The effectiveness of the VME-based print head was further demonstrated through the DIW fabrication of interdigitated electrodes and microstrip transmission lines. This highlights the versatility of the VME-based print head as a practical tool for device prototyping and ink development in the field of printed electronics.

Rapid and Sensitive Detection by Combining Electric Field Effects and Surface Plasmon Resonance: A Theoretical Study.

Surface plasmon resonance (SPR) has been extensively employed in biological sensing, environmental detection, as well as chemical industry. Nevertheless, the performance possessed by conventional surface plasmon resonance (SPR) biosensors can be further limited by the transport of analyte molecules to the sensing surface, noteworthily when small molecules or low levels of substances are being detected. In this study, a rapid and highly sensitive SPR biosensor is introduced to enhance the ability of the target analytes' collection by integrating AC electroosmosis (ACEO) and dielectrophoresis (DEP). Both the above-mentioned phenomena principally arise from the generation of the AC electric fields. This generation can be tailored by shaping the interdigitated electrodes (IDEs) that also serve as the SPR biomarker sensing area. The effects exerted by different parameters (e.g., the frequency and voltage of the AC electric field as well as microelectrode structures) are considered in the iSPR (interdigitated SPR) biosensor operation, and the iSPR biosensors are optimized with the sensitivity. The results of this study confirm that the iSPR can efficiently concentrate small molecules into the SPR sensing area, such that SPR reactions achieve an order of magnitude increase, and the detection time is shortened. The rapid and sensitive sensor takes on critical significance in the development of on-site diagnostics in a wide variety of human and animal health applications.

A hybrid wind and raindrop energy harvesting operating on Savonius turbine

In offshore environments, abundant wind and rainfall resources await development, representing significant untapped energy potential for powering Internet of Things (IoT) devices. Triboelectric Nanogenerators (TENGs) are particularly suited for capturing continuous motion in offshore environments, presenting a reliable solution for sustainable energy generation in IoT applications. Herein, we propose a wind-droplet hybrid generator (WDHG) tailored for adaptive environmental energy harvesting, explicitly targeting the demanding conditions prevalent in offshore environments. The WDHG combines the efficiency of a helical Savonius TENG with the versatility of an interdigitated electrode TENG, enabling simultaneous wind and rain energy harvesting. The helical Savonius TENG exhibits superior aerodynamic performance, producing an output power ranging from 0.39 to 2.10 mW with wind speeds increasing from 0.75 to 6.84 m/s. Additionally, the droplet TENG generates a power output of 35.90 mW/m2 under rainfall at 70 mm/min. Optimizations include not only the comparative analysis of helical Savonius turbines and the variation in pole-pair numbers but also adjustments in fluorinated ethylene propylene (FEP) film thickness and electrode gap length for interdigitated electrode, alongside the development of a tailored power management circuit (PMC) featuring dual bridge rectifiers, a buck circuit module, and a smart load switch. The PMC enables continuous operation of a low-powered digital thermohygrometer under conditions of 4.5 m/s wind speed, and drives a 20-second wake BLE server under 7.2 m/s wind speeds. Integration of the WDHG with offshore wind and raindrop extends energy harvesting capabilities, exhibiting a great potential of providing reliable power source for IoT devices.

Electrochemical Impedance Spectroscopy for Ion Sensors with Interdigitated Electrodes: Capacitance Calculations, Equivalent Circuit Models and Design Optimizations.

Electrochemical impedance spectroscopy (EIS) is becoming more and more relevant for the characterization of biosensors employing interdigitated electrodes. We compare four different sensor topologies for an exemplary use case of ion sensing to extract recommendations for the design optimizations of impedimetric biosensors. Therefore, we first extract how sensor design parameters affect the sensor capacitance using analytical calculations and finite element (FEM) simulations. Moreover, we develop equivalent circuit models for our sensor topologies and validate them using FEM simulations. As a result, the impedimetric sensor response is better understood, and sensitive and selective frequency ranges can be determined for a given sensor topology. From this, we extract design optimizations for different sensing principles.

Cesium ion-guided detection of trichloroethylene in air

Whereas the close associations of cesium ion with organochlorine compounds have been previously documented, the present report is the first attempt to exploit these interactions to create a trichloroethylene (TCE)-selective sensor. Gold monolayer-protected clusters peripherally functionalized with Cs+ ions were used to prepare a chemiresistance film on MEMS-fabricated interdigitated electrodes. Vapor sensing properties of the cesium-rich chemiresistor were determined using a panel of chlorinated hydrocarbons including TCE as well as polar and non-polar VOCs for comparison. The sensor was selective and highly sensitive toward VOCs containing a 1,2-dichloro group at concentrations as low as 0.1 ppm. The results suggest the key interaction contributing to sensor response is a bidentate, metallocycle-like coordination of the 1,2-dichloro group to the cesium cations at the sensor surface.

Fabrication and Implementation of PVA Thin Film-based Relative Humidity Sensor

This paper presents the fabrication of polyvinyl alcohol (PVA)-based relative humidity sensors using copper interdigitated electrodes (IDEs). These sensors were fabricated by patterning copper IDEs onto FR4 fiberglass substrates and coating them with a thin film of PVA. By varying the number of IDE electrode pairs and the concentration of PVA, the sensors exhibited different resistance values, demonstrating an inverse relationship with the number of IDE electrodes and PVA concentration. Additionally, the thickness of the sensing layer, controlled by spin coating speed, affected the resistance of the sensors. The fabricated sensors achieved a humidity measurement range from 50% to 99% RH based on resistance changes. Furthermore, an interface circuit was designed to integrate the fabricated sensors with an ESP8266 microcontroller, achieving accurate measurements above 74% RH.

Comparative Study of Field-Effect Transistors Based on Graphene Oxide and CVD Graphene in Highly Sensitive NT-proBNP Aptasensors.

Graphene-based materials are actively being investigated as sensing elements for the detection of different analytes. Both graphene grown by chemical vapor deposition (CVD) and graphene oxide (GO) produced by the modified Hummers' method are actively used in the development of biosensors. The production costs of CVD graphene- and GO-based sensors are similar; however, the question remains regarding the most efficient graphene-based material for the construction of point-of-care diagnostic devices. To this end, in this work, we compare CVD graphene aptasensors with the aptasensors based on reduced GO (rGO) for their capabilities in the detection of NT-proBNP, which serves as the gold standard biomarker for heart failure. Both types of aptasensors were developed using commercial gold interdigitated electrodes (IDEs) with either CVD graphene or GO formed on top as a channel of liquid-gated field-effect transistor (FET), yielding GFET and rGO-FET sensors, respectively. The functional properties of the two types of aptasensors were compared. Both demonstrate good dynamic range from 10 fg/mL to 100 pg/mL. The limit of detection for NT-proBNP in artificial saliva was 100 fg/mL and 1 pg/mL for rGO-FET- and GFET-based aptasensors, respectively. While CVD GFET demonstrates less variations in parameters, higher sensitivity was demonstrated by the rGO-FET due to its higher roughness and larger bandgap. The demonstrated low cost and scalability of technology for both types of graphene-based aptasensors may be applicable for the development of different graphene-based biosensors for rapid, stable, on-site, and highly sensitive detection of diverse biochemical markers.

Mining Metal‐Biomolecular Framework/PANI Composite CO Sensor: Material Synthesis, Gas Sensing Performance and Mechanism

AbstractIn addressing the issue of poor gas sensitivity in semiconductor CO sensor materials used in mining, such as pure PANI. This study utilized an ice‐water bath in combination with an in‐situ polymerization method to synthesize a new composite material consisting of Cu(II)‐racemic glutamate nanofibers and PANI. The morphology, structure, and chemical bonds of the composite material were analyzed using scanning electron microscopy‐energy dispersive spectroscopy (SEM‐EDS) and spectral analysis. The material's ability to detect CO (100–500 ppm) at room temperature was investigated, revealing a response value of up to 6.8 % for 400 ppm CO detection when the composite material was deposited on a ceramic interdigital electrode. The material exhibited good selectivity and responsiveness to CO detection at room temperature, attributed to the heterojunction formed between Cu(II)‐racemic glutamate nanofibers and PANI, which enhanced carrier migration. Consequently, the Cu(II)‐racemic glutamate nanofiber/PANI composite(Cu(II)‐RGlu/PANI) material shows promise as a high‐performance sensing material for CO detection at room temperature and as a low‐power, integrable sensor material for underground coal mines. This research contributes to the development of a theoretical framework for such applications.

The Role of Interdigitated Electrodes in Printed and Flexible Electronics.

Flexible electronics, also referred to as printable electronics, represent an interesting technology for implementing electronic circuits via depositing electronic devices onto flexible substrates, boosting their possible applications. Among all flexible electronics, interdigitated electrodes (IDEs) are currently being used for different sensor applications since they offer significant benefits beyond their functionality as capacitors, like the generation of high output voltage, fewer fabrication steps, convenience of application of sensitive coatings, material imaging capability and a potential of spectroscopy measurements via electrical excitation frequency variation. This review examines the role of IDEs in printed and flexible electronics since they are progressively being incorporated into a myriad of applications, envisaging that the growth pattern will continue in the next generations of flexible circuits to come.

Temperature and frequency dependence of conductivity, density of states, and dielectric permittivity of ternary metal chalcogenide PbSnSe2 flake

The mechanically cleaved flake of ternary metal chalcogenide PbSnSe2 was transferred onto the interdigitated electrodes to form electrical contacts. The temperature dependent (180 K–250 K) electrical properties were then analyzed employing complex impedance spectroscopy from 2 kHz to 2 MHz. A detailed analysis of Nyquist plots proposed the space charge dependent behavior and negative temperature coefficient of PbSnSe2 flake. The AC conductivity followed Jonscher's power law with s-parameter value being less than unity. The values of s-parameter increased with rise in temperature suggesting the presence of non-overlapping small polaron tunneling (NSPT) in the PbSnSe2 flake. From this NSPT model, tunneling distance, hopping energy, and density of states (DOS) were estimated at temperatures from 180 K–250 K. The dielectric permittivity showed dispersion at lower frequencies and the tangent loss was also found to be directly related to temperature. A single semicircular arc in complex modulus analysis showed the dominance of bulk effect in the material.

Self-Powered Biomimetic Pressure Sensor Based on Mn-Ag Electrochemical Reaction for Monitoring Rehabilitation Training of Athletes.

Self-powered pressure detection using smart wearable devices is the subject of intense research attention, which is intended to address the critical need for prolonged and uninterrupted operations. Current piezoelectric and triboelectric sensors well respond to dynamic stimuli while overlooking static stimuli. This study proposes a dual-response potentiometric pressure sensor that responds to both dynamic and static stimuli. The proposed sensor utilizes interdigital electrodes with MnO2/carbon/polyvinyl alcohol (PVA) as the cathode and conductive silver paste as the anode. The electrolyte layer incorporates a mixed hydrogel of PVA and phosphoric acid. The optimized interdigital electrodes and sandpaper-like microstructured surface of the hydrogel electrolyte contribute to enhanced performance by facilitating an increased contact area between the electrolyte and electrodes. The sensor features an open-circuit voltage of 0.927V, a short-circuit current of 6µA, a higher sensitivity of 14mV/kPa, and outstanding cycling performance (>5000 cycles). It can accurately recognize letter writing and enable capacitor charging and LED lighting. Additionally, a data acquisition and display system employing the proposed sensor, which facilitates the monitoring of athletes' rehabilitation training, and machine learning algorithms that effectively guide rehabilitation actions are presented. This study offers novel solutions for the future development of smart wearable devices.

Skin‐Mount Textile‐Based Flexible Strain Sensors for Physiotherapy

Tremendous development in intelligent wearable gadgets creates opportunities for flexible strain sensors. Comfortable and safe flexible strain sensors have high demand in wearable applications and therefore the textile‐based strain sensors are desired. Achieving attributes like easy fabrication, cost‐effectiveness, high sensitivity, good stability, and portability is still a challenge to overcome. In this regard, textile‐based flexible strain sensors, one on jeans fabric and other on cotton fabric, are presented. A conventional interdigitated electrode structure is adopted and sensors are prepared by facile and economical fabrication process. Both sensors own high sensitivity factors, i.e., gauge factor >200 and stability of ≈10 000 cycles. The anticipated works show a linear response R2 = 0.99, low hysteresis <5%, and minimum resolution <7°. The intended sensors are implemented for real‐time application, i.e., the physiotherapy of the knee and neck. The jeans‐fabric‐based sensor is used for knee therapy and the cotton for neck. The daily therapy sessions are recorded and examined. The sensors respond well to the applied strain during therapy sessions, proving to be an outstanding choice for integration into biomedical wearable devices for therapeutic purposes. The proposed sensors can also be auspicious candidates for targeting many other wearable applications.

Application of a microfluidic electronic tongue based on impedance spectroscopy for coconut water analysis

The food industry has grown with the demands for new products and their authentication, which has not been accompanied by the area of analysis and quality control, thus requiring novel process analytical technologies for food processes. An electronic tongue (e-tongue) is a multisensor system that can characterize complex liquids in a fast and simple way. Here, we tested the efficacy of an impedimetric microfluidic e-tongue setup – comprised by four interdigitated electrodes (IDE) on a printed circuit board (PCB), with four pairs of digits each, being one bare sensor and three coated with different ultrathin nanostructured films with different electrical properties – in the analysis of fresh and industrialized coconut water. Principal Component Analysis (PCA) was applied to observe sample differences, and Partial Least Squares Regression (PLSR) was used to predict sample physicochemical parameters. Linear Discriminant Analysis (LDA) and Partial Least Square − Discriminant Analysis (PLS-DA) were compared to classify samples based on data from the e-tongue device. Results indicate the potential application of the microfluidic e-tongue in the identification of coconut water composition and determination of physicochemical attributes, allowing for classification of samples according to soluble solid content (SSC) and total titratable acidity (TTA) with over 90% accuracy. It was also demonstrated that the microfluidic setup has potential application in the food industry for quality assessment of complex liquid samples.

Optimizing the depletion width to enhance the performance of CH3NH3PbI3 flexible photodetector based on the piezo-phototronic effect

The research on organic-inorganic hybrid halide perovskites in the field of optoelectronics has greatly advanced the field of photodetection. However, the reported heterojunction structure of perovskite results in complex preparation processes. A simple method was designed to enhance the performance of CH3NH3PbI3 flexible photodetector (PD) by optimizing the depletion width based on the piezo-phototronic effect. Under 5 V bias conditions, when the electrode width of PD is 3, 5, and 8 μm, where the response peaks at 760 nm are 0.06, 0.02, and 0.01 A/W, respectively. This depends on the decrease of electrode width and the increase of depletion width. As the strain increases, the PD response of the interdigital electrode at 3 μm increases from 0.020 to 0.0482 A/W. When the strain is 0.3, the responsiveness increases by 240 %. As the strain increases, the PD response of the interdigital electrode at 5 μm increases from 0.010 to 0.0255 A/W and the PD response of the interdigital electrode at 8 μm increases from 0.006 to 0.0137 A/W. Therefore, devices with a wide depletion width have significant performance advantages. This work improves the responsivity of perovskite flexible PD based on the piezo-phototronic effect by optimizing the depletion width, providing a simple and effective method for manufacturing perovskite thin film devices on high-performance flexible substrates.

Paired Electrosynthesis at Interdigitated Microband Electrodes: Exploring Diffusion and Reaction Zones in the Absence of a Supporting Electrolyte.

Electrosynthesis traditionally requires dedicated reactor systems and an added electrolyte, although some paired electrosynthesis processes are possible at interdigitated microband electrodes simply immersed in solution and without an intentionally added electrolyte. Here, 1,1'-ferrocenedimethanol oxidation and activated olefin electro-hydrogenation reactions are investigated as model processes at a Pt-Pt interdigitated microband array electrode with 5 μm width and with 5 μm interelectrode gap. Voltammetric responses for electro-hydrogenation are discussed, and product yields are determined in methanol (MeOH) in the presence/absence of an added electrolyte (LiClO4). An isotope effect is observed in CH3OD solvent, leading to olefin monodeuteration linked to a fast EC-type process close to the cathode surface (in the cathode reaction zone) rather than to charge annihilation in the interelectrode zone. A finite element simulation is employed to visualize/discuss reaction zones and to contrast the rate of charge annihilation processes with/without a supporting electrolyte.

High-performance triboelectric-electromagnetic hybrid nanogenerator using dual-functional flexible neodymium iron boron/ethyl cellulose (NdFeB/EC) composite films for wind energy scavenging

Triboelectric-electromagnetic hybrid nanogenerator (HNG) with high output performance provides a very promising solution for realizing self-powered microelectronic devices. However, the complex structures and large mass of traditional HNGs make them difficult to prepare and carry. In this study, a rotating HNG based on flexible neodymium iron boron/ethyl cellulose (NdFeB/EC) composite films was designed for wind energy scavenging. A lightweight composite film with triboelectric and ferromagnetic properties, which can significantly reduce the weight of the rotor, was prepared to replace the magnet. Operated at a wind speed of 15.5 m/s, the triboelectric nanogenerator (TENG) unit of the optimized HNG with an interdigitated electrode gap of 2 mm can generate an open-circuit voltage (Voc) and a short-circuit current (Isc) of 55 V and 5.4 μA, respectively. The maximum power of TENG is 99.2 μW under the condition of an external load resistance of 10 MΩ. The corresponding electromagnetic generator (EMG) unit can produce Voc and Isc of approximately 0.16 V and 59.3 μA, delivering an output power of 2.5 μW at a matched loading resistance of 2.3 kΩ. Compared to the individual TENG or EMG units, the HNG exhibited better charging performance. A 470 μF capacitor can charge to 3.4 V within 600 s, and the stored energy can successfully power a commercial soil temperature–humidity meter to work continuously for 75 s and light 30 blue LEDs in parallel. This research is of great scientific significance for developing triboelectric–ferromagnetic dual-functional materials and designing highly integrated and lightweight HNGs.