Interdigitated Electrodes Research Articles

Editable 3D Micro-Supercapacitor with High Energy Density Based on Mortise–Tenon Joint Structures

Three-dimensional micro-supercapacitors (3D MSCs) have accelerated the development of microenergy-storage modules for miniaturized and portable electronics. However, the low energy density, complex construction strategy, and low assembly accuracy of a 3D MSC restrict its practical application. Herein, we design a simple construction strategy for a 3D MSC with high energy density by mortise and tenon structures. Wood-derived carbon modified by nitrogen-doped carbon nanotube arrays (N-CNT-WDC) provides an ordered ion transport channel and a large active specific surface area, availing the improvement of the energy density of a 3D MSC. Its strong carbon skeleton structure supports the construction of 3D interdigital electrodes with a tenon structure by laser, realizing precise and regulable assembly of 3D MSCs through a mortise and tenon joint. The prepared 3D MSC based on N-CNT-WDC shows an excellent volumetric capacitance of 93.66 F cm-3, a high volumetric energy density of 12 mW h cm-3 at 600 mA cm-3, and an 85% retention rate of capacitance after 10,000 cycles of charge and discharge at 1000 mA cm-3. Furthermore, the mortise and tenon structure realizes diversified integration of 3D MSCs, making the integrated manufacturing of 3D microdevices more convenient and promoting their application in microelectronic devices.

A Robust and Adhesive Hydrogel Enables Interfacial Coupling for Continuous Temperature Monitoring

AbstractContinuous temperature monitoring by flexible hydrogel‐based electronics achieves rapid advances, overcoming the drawbacks of rigid and unportable thermocouples. However, an open question is whether and how the thermosensitive hydrogel designing can prevent mechanical mismatching between devices and skin‐tissues and reduces interfacial failure. Herein, a versatile hydrogel‐based thermistor epidermal sensor (HTES) paradigm is engineered consisting of thermosensitive and self‐adhesive function layer (PEST) in tandem with a surface spraying Ag interdigital electrode. Leveraging the advantage of catechol chemistry inspired tannic acid‐coated cellulose nanocrystals, the resultant PEST achieves the adhesion‐cohesion equilibrium along with superior thermosensitivity. The assembled HTES thereby yields unprecedented features of superior thermosensitivity (TCR = 1.43% °C−1), exceptional mechanical integrity (hammering 200 cycles, current variation <9%), impressive interfacial compatibility (adhesion strength, 25 kPa), and environmental stability (thermosensation retention of 98% over 5 days). By in‐situ microstructure observation, the unique geometrical synchronization of HTES with arbitrary curvilinear surfaces (e.g., sphere, cone, and saddle) stemming from elastic dissipation and discrete rupture of the adhesive fibrillar bridges is validated, affording competitive advantages than that of the state‐of‐the‐art thermistor electronics for alleviating the interfacial deterioration, which dramatically inspires advanced HTES design strategies and paves the way for commercialization of attachable thermistor electronics.

Chemiresistors with In2O3 Nanostructured Sensitive Films Used for Ozone Detection at Room Temperature.

Detection of greenhouse gases is essential because harmful gases in the air diffuse rapidly over large areas in a short period of time, causing air pollution that will induce climate change with catastrophic consequences over time. Among the materials with favorable morphologies for gas detection (nanofibers, nanorods, nanosheets), large specific surfaces, high sensitivity and low production costs, we chose nanostructured porous films of In2O3 obtained by the sol-gel method, deposited on alumina transducers, with gold (Au) interdigitated electrodes (IDE) and platinum (Pt) heating circuits. Sensitive films contained 10 deposited layers, involving intermediate and final thermal treatments to stabilize the sensitive film. The fabricated sensor was characterized using AFM, SEM, EDX and XRD. The film morphology is complex, containing fibrillar formations and some quasi-spherical conglomerates. The deposited sensitive films are rough, thus favoring gas adsorption. Ozone sensing tests were performed at different temperatures. The highest response of the ozone sensor was recorded at room temperature, considered to be the working temperature for this specific sensor.

Development of functional nucleic acid sensor for detection of locust pheromone 4-vinylanisole

In recent years, locust plagues have occurred frequently in the world, causing great concern. In this work, we developed a portable, stand-alone functional nucleic acid sensor to detect the locust pheromone 4-vinylanisole (4VA) to monitor the population dynamics of locusts and achieve early warning of locust disasters. A high-affinity aptamer sequence with a 4VA KD value of 269.25 ± 90.65 nM was obtained by selecting the 4VA DNA aptamer. The Apt@AuNPs@MOF (Apt: aptamer, AuNPs: gold nanoparticles, and MOF: metal–organic framework) functional nucleic acid sensor was designed on this basis, and its performance was tested. The results showed that the sensor based on the screened DNA aptamers had apparent selectivity for 4VA. At room temperature, it could respond to 1 ppm of 4VA gas within a minute. The sensitivity was 1.107 × 10−3, and the average response/recovery time was 103.1 ± 28.0 s/80.1 ± 17.4 s. The sensor was assembled with a composite adsorption tube for enrichment of gas sample, which allowed for the detection as low as 1 ppb of 4VA. It can be concluded that a gas sensor integrated with a high-affinity DNA aptamer and an interdigitated electrode automated biosensing platform provides a promising strategy on real-time monitoring the locust pheromone 4VA in ambient air for timely warning and prevention of locust plagues.

Mechano-control of Extracellular Electron Transport Rate via Modification of Inter-heme Coupling in Bacterial Surface Cytochrome

Bacterial outer-membrane multi-heme cytochromes (OMCs) mediate extracellular electron transport (EET). While heme alignment dictates the rate of EET, control of inter-heme coupling in a single OMC remains challenging, especially in intact cells. Given that OMCs diffuse and collide without aggregation on the cell surface, the overexpression of OMCs could increase such mechanical stress to impact the OMCs' protein structure. Here, the heme coupling is modified via mechanical interactions among OMCs by controlling their concentrations. Employment of whole-cell circular dichroism (CD) spectra of genetically engineered Escherichia coli reveals that the OMC concentration significantly impacts the molar CD and redox property of OMCs, resulting in a 4-fold change of microbial current production. The overexpression of OMCs increased the conductive current across the biofilm on an interdigitated electrode, indicating that a higher concentration of OMCs causes more lateral inter-protein electron hopping via collision on the cell surface. The present study would open a novel strategy to increase microbial current production by mechanically enhancing the inter-heme coupling.

Micro-Cup Architecture for Printing and Coating Asymmetric 2d-Material-Based Solid-State Supercapacitors.

High energy density micro-supercapacitors (MSCs) are in high demand for miniaturized electronics and microsystems. Research efforts today focus on materials development, applied in the planar interdigitated, symmetric electrode architecture. Anovel "cup & core" device architecture that allows for printing of asymmetric devices without the need of accurately positioning the second finger electrode here have been introduced. The bottom electrode is either produced by laser ablation of a blade-coated graphene layer or directly screen-printed with graphene inks to create grids with high aspect ratio walls forming an array of "micro-cups". A quasi-solid-state ionic liquid electrolyte is spray-deposited on the walls; the top electrode material -MXene inks- is then spray-coated to fill the cup structure. The architecture combines the advantages of interdigitated electrodes for facilitated ion-diffusion, which is critical for 2D-material-based energy storage systems by providing vertical interfaces with the layer-by-layer processing of the sandwich geometry. Compared to flat reference devices, volumetric capacitance of printed "micro-cups" MSC increased considerably, while the time constant decreased (by 58%). Importantly, the high energy density (3.99 µWh cm-2 ) of the "micro-cups" MSC is also superior to other reported MXene and graphene-based MSCs.

ZnO photoconductive synaptic devices for neuromorphic computing

In the field of artificial intelligence, neuromorphic computing offers the allure of human brain simulation. The capacity of optoelectronic synapses to intelligently handle optoelectronic input signals makes them a key component of neuromorphic computing. In this work, we fabricated ZnO-based optoelectronic synapses and investigated their electronic and photonic synaptic plasticity. The device fabrication process flow is as follows: photolithography is performed on ITO glass, followed by hydrochloric acid etching and degumming to obtain interdigital electrodes on the glass substrate, and a ZnO film is grown on the interdigitated electrodes by magnetron sputtering. A good Ohmic contact is formed between the ZnO and ITO electrodes, and the device exhibits a linear relationship between current and voltage under dark field conditions, and exhibits excellent synaptic properties and sensitivity in UV switching response experiments. Additional processes were subsequently introduced through growing ZnO nanowires and annealing, and the synaptic properties of ZnO device were improved. The shift from short-term to long-term memory, short-term plasticity, long-term plasticity, paired-pulse facilitation, and learning to experience behavior are only a few of the synaptic activities of the nervous system that have been successfully described. The manufactured array device also includes a special memory recall feature that may retrieve previous optoelectronic data. This work will advance the field of artificial intelligence and stimulate additional study on optoelectronic synapses.

Swirl-like Acoustofluidic Stirring Facilitates Microscale Reactions in Sessile Droplets.

Sessile droplets play a crucial role in the microreactors of biochemical samples. Acoustofluidics provide a non-contact and label-free method for manipulating particles, cells, and chemical analytes in droplets. In the present study, we propose a micro-stirring application based on acoustic swirls in sessile droplets. The acoustic swirls are formed inside the droplets by asymmetric coupling of surface acoustic waves (SAWs). With the merits of the slanted design of the interdigital electrode, the excitation position of SAWs is selective by sweeping in wide frequency ranges, allowing for the droplet position to be customized within the aperture region. We verify the reasonable existence of acoustic swirls in sessile droplets by a combination of simulations and experiments. The different periphery of the droplet meeting with SAWs will produce acoustic streaming phenomena with different intensities. The experiments demonstrate that acoustic swirls formed after SAWs encountering droplet boundaries will be more obvious. The acoustic swirls have strong stirring abilities to rapidly dissolve the yeast cell powder granules. Therefore, acoustic swirls are expected to be an effective means for rapid stirring of biomolecules and chemicals, providing a new approach to micro-stirring in biomedicine and chemistry.

Low-Cost, High-Sensitivity Paper-Based Bacteria Impedance Sensor Based on Vertical Flow Assay

This study proposes a low-cost, portable paper-fluidic vertical flow assay bacterium counter with high accuracy. We designed sensors with low fabrication costs based on e-beam evaporation and three-dimensional printing based on the impedance measurement principle. Interdigitated (IDT) electrodes were coated on the filter membrane by e-beam evaporation with a shadow mask. We could print wafer-scale frames with low melting temperature three-dimensional-printing materials for confining liquid bacterial samples within the IDT sensing region. This novel fabrication technique significantly reduced the chip’s cost to less than 1% of that of silicon-based chips. Two equivalent circuit models were proposed for different concentration ranges to analyze the principle of paper-based impedance bacterial sensors. We proposed an improved model based on the Randles model for low concentrations by considering the leaky double-layer capacitor effect and spherical diffusion from the nano-structural electrodes of the gold-coated filter membrane. The phenomenon in which charge transfer resistance, Rct, declines at high concentration ranges was found and explained by the pearl chain effect. The pearl effect could cause a false-negative at high concentrations. We modeled the pearl chain effect as an R and C, connected parallel to the low-concentration model. When users properly applied both models for analyses, this sensor could quantitatively measure cell concentrations from 400 to 400 M per milliliter with superior linearity.

Fe-based metal-organic framework as a chemiresistive sensor for low-temperature monitoring of acetone gas

This work demonstrates the potential of a novel iron-based metal-organic framework (Fe-MOF or VNU-15) to effectively detect low-concentration volatile organic compounds (VOCs), particularly acetone (CH3COCH3). A facile solvothermal strategy was used to synthesize Fe-MOFs, comprising Fe(II)/Fe(III) and two distinct linkers—BDC (benzene-1,4-dicarboxylate) and NDC (naphthalene-2,6-dicarboxylic acid). As a first step, Fe-MOFs were characterized to determine their pure phase formation and identify their structural and morphological characteristics. Fe-MOFs processed via the solvothermal method demonstrated high crystallinity, high thermal stability, polyhedral crystal-shaped surface morphology, and a surface area of 735 m2g−1, making them suitable for gas-sensing applications. Laboratory-scale gas-sensing devices were fabricated by printing Fe-MOF powder onto patterned interdigitated electrodes, with performance measurements conducted on these devices in response to exposure to various target gases at temperatures between 25 and 200 °C and gas concentrations between 1 and 10 ppm. Gas-sensing tests confirmed that the VNU-15 sensor selectivity detects CH3COCH3 with a gas response of 1.68–10 ppm and a response time of 64 s, followed by a recovery time of 166 s at 50 °C. This study demonstrates the feasibility of using novel MOF-based sensing channels as low-temperature gas sensors, providing new insights into gas-sensing technology.

Mammalian Cell-Growth Monitoring Based on an Impedimetric Sensor and Image Processing within a Microfluidic Platform.

In recent years, advancements in microfluidic and sensor technologies have led to the development of new methods for monitoring cell growth both in macro- and micro-systems. In this paper, a microfluidic (MF) platform with a microbioreactor and integrated impedimetric sensor is proposed for cell growth monitoring during the cell cultivation process in a scaled-down simulator. The impedimetric sensor with an interdigitated electrode (IDE) design was realized with inkjet printing and integrated into the custom-made MF platform, i.e., the scaled-down simulator. The proposed method, which was integrated into a simple and rapid fabrication MF system, presents an excellent candidate for the scaled-down analyses of cell growths that can be of use in, e.g., optimization of the cultivated meat bioprocess. When applied to MRC-5 cells as a model of adherent mammalian cells, the proposed sensor was able to precisely detect all phases of cell growth (the lag, exponential, stationary, and dying phases) during a 96-h cultivation period with limited available nutrients. By combining the impedimetric approach with image processing, the platform enables the real-time monitoring of biomasses and advanced control of cell growth progress in microbioreactors and scaled-down simulator systems.

A Degradable Sensor Based on Insect Protein for Postsurgical Diagnosis of Joint Health

AbstractDegradable electronics have received extensive attention due to their potential to construct ‘green’ electronics and implantable medical devices. However, in the development of degradable devices, the contradiction between the strict requirements for biodegradability and the pursuit of device performance has brought considerable challenges to the selection of materials. This paper reports a biodegradable flexible tactile sensor (BFTS) based on chitosan film doped with Ostrinia furnacalis cuticular protein (OfCPH‐1) as substrate and Zn as the interdigital electrode. The BFTS maintains a precise and stable response to microdistance, and it is completely degraded in 3 h through the solubility test in Stroke‐physiological saline solution. Furthermore, the BFTS has been tested in complications monitoring after meniscal removal surgery by the dynamic detection of articular cartilage wear and effusion of joint. These results indicate that the BFTS has potential application as implantable medical devices.

Investigation into the influence of interdigital parameters on electrochemical performance for in-plane supercapacitors via mathematical modeling and conformal mapping techniques

Herein, we propose a mathematical model and corresponding analytical transformation approach based on the conformal mapping technique and equivalent circuit conversion method to investigate the influence of interdigital parameters such as electrode length (Le), width (We), and spacing (De) on the electrochemical performance of in-plane supercapacitors (SCs) fabricated via CO2 laser processing on polyimide film and encapsulation with PVA/H3PO4 gel electrolyte. We conclude from the experiments that the small gap ensures a compact structure, a high electrode utilization rate, and a short anion/cation transport channel, while the large electrode area generates a sufficient electrostatic double-layer effect to improve areal capacitance. Furthermore, interdigital length and width are particularly sensitive to capacitve performance, implying that electrode area plays a critical role. Eventually, the optimal electrode parameters are 10 mm (Le), 1.5 mm (We), and 0.35 mm (De), delivering high areal capacitance (2.43 mF/cm2), relatively low resistance (≈46 Ω) and excellent areal energy density (225 μWh/cm2) and power density (3.65 mW/cm2). Because the experimental values are compatible with the simulation curves and the different percentages between them are controlled within 13 %, the mathematical model has theoretical significance for the design of interdigital electrodes.

Facile and Controllable Ultrasonic Nebulization Method for Fabricating Ti3C2Tx‐Based Strain Sensor and Monitoring of Human Motion and Sound Wave

AbstractFlexible and wearable electronic devices hold great potential in electronic skins, health monitoring systems and soft robotics. Among them, flexible strain sensors with high performance are key components for wearable health monitoring devices. However, the facile and controllable preparation of highly sensitive sensors still faces significant challenges. By virtue of excellent conductivity of 2D transition metal carbids (MXenes), this work reports a facile and low‐cost fabrication strategy for large‐scale production of strain sensors. The sensitive layer is deposited on flexible interdigital electrodes by ultrasonic nebulization of Ti3C2Tx nanosheets. By controlling the nebulization time, different thicknesses of Ti3C2Tx films has a great influence on the performance of strain sensors. The Ti3C2Tx‐based strain sensor exhibits good sensing performances such as high GF (19.1) in the low strain range (≈0.25%–1.14%), short response time (0.7 s), and stable durability (over 1000 cycles). In practice, the potential applications of the strain sensor in sound frequency detection, human physiological signal monitoring and facial expression recognition are demonstrated. Finally, this work integrates the strain sensor with a miniaturized analyzer to assemble a wearable motion monitoring device for mobile healthcare. This study provides a facile strategy for fabricating flexible strain sensors in the field of wearable electronics.

Three Different Rapidly Prototyped Polymeric Substrates With Interdigitated Electrodes for Escherichia coli Sensing: A Comparative Study.

This work delves upon the development of different types of miniaturized and 3D printed devices having interdigitated electrodes (IDEs) for the detection of Escherichia coli (E. coli) bacteria. The IDEs were fabricated using different approaches including laser-induced graphene (LIG) on polyamide, direct laser writing on glass, and polymeric 3D printing technique, and their suitability for bacteria detection has been compared. The electrochemical impedance spectroscopy (EIS) technique was employed to detect the E. coli bacteria in the prepared miniaturized devices, and the sensory response was compared. EIS was performed in the frequency range between 1 Hz to 1 MHz to record the bacterial growth and activities as a function of change in electrical impedance, and detection performance of the different miniaturized devices with IDEs were compared. It was observed that the LIG-based IDE sensor provided better sensitivity compared to that of the other two approaches. The obtained results indicate that the magnitude of impedance changes by around 2.5 [Formula: see text] per doubling of E.coli cells. With fast and flexible fabrication process capabilities, such microdevices may be used as suitable IDE sensors for microscale pathogenic detection for biomedical and clinical analysis.

Enhanced low-dose x-ray sensing nature of nanocrystalline CaWO4 sensor

Extensive research on the development of superior sensitive X-ray sensors by many researchers is due to their increased demand in numerous fields, like medical radiography, security inspection, and scientific research areas. Especially in healthcare, repeated or long-term high-dose X-ray exposure on patients may cause serious health hazards. Therefore, developing a superior sensing low dose X-ray sensor is essential. In this present work, a nanocrystalline CaWO4 thick film above an interdigitated electrode was developed as a direct conversion X-ray sensor that operates at different low doses (mGy) using an intraoral pulsed X-ray (70 keV) machine. The X-ray instigated photocurrent of nano-CaWO4 thick film was examined under different applied bias to obtain superior sensitivity of the device. The nano-CaWO4 thick film exhibit sensitivity of 10 nC/mGycm3 at 0.20 mGy (0.06 s) low dose under 5 V applied bias. A suitable mechanism was proposed to explain the nano-CaWO4 thick film sensing behaviour at different biased conditions.

A Transparent Conductive Layer with an Interdigitated Electrode and Its Effect on Heat Generation

在這篇論文中，基於銦錫氧化物(ITO)加熱裝置依然存在許多問題，為了解決問題，本論文使用不同比例的指叉狀電極遮罩來蒸鍍電極在ITO上，並對其做深入研究。<br>在我們會使用到熱蒸鍍機，並以鋁作為電極，蒸鍍在ITO玻璃上，使用不比例的指叉狀遮罩來蒸鍍鋁於ITO的系統，其中指叉狀電極的比例分別為為1:1(sample02)，2:1(sample03)，3:2(sample04)，以及無指叉狀的電極(sample01)，而在這次的實驗中，我們所改變的參數只有指叉狀電極的比例，其他的參數則沒有改變，鋁圈數量是固定四圈，蒸鍍環境也都是固定的真空值，蒸鍍電流則是固定在70A，以便探討不同電極的影響。<br>在蒸鍍結束後，我們分別對不同比例指叉狀電極的樣品進行電學特性以及溫升的量測，結果表明1:1的電阻值約為68Ω，溫升速率約為0.617°C/s，2:1的電阻值約為100Ω，溫升速率約為0.335°C/s，3:2的電阻值約為100Ω，溫升速率約為0.314°C/s，1:1的電阻值是最小的，溫升速率是最快的，相較於其它比例的樣品是最高的，在蒸鍍不同指叉狀電極的時候，並不是電極數越多越好，而要考慮有效發熱面積與其他因素。In this paper, based on the existing ITO heating device, the effect is not as good as expected. Therefore, we use different types of metal masks to evaporate the electrode on a single layer of indium tin oxide (ITO). Do in-depth research, and this experiment is mainly divided into two parts. <br>In the first part, we will use a thermal evaporator, and use aluminum as the electrode to evaporate on the ITO glass, and use a non-proportional interdigitated mask to evaporate the aluminum on the ITO system. The proportion of the interdigitated electrode is They are 1:1 (sample2), 2:1 (sample3), 3:2 (sample4), and non-digital electrodes (sample1). In this experiment, the only parameter we changed was the fingers. The ratio of the shaped electrodes and other parameters have not changed. The number of aluminum circles is fixed four circles, the evaporation environment is also a fixed vacuum value, and the evaporation current is fixed at 70A to explore the influence of different electrodes. <br>After the evaporation, we measured the electrical characteristics and temperature rise of samples with different ratios of interdigitated electrodes. The results showed that the 1:1 resistance value is about 68Ω, and the temperature rise rate is about 0.617°C/s. 2:1 resistance value is about 100Ω, temperature rise rate is about 0.335°C/s, 3:2 resistance value is about 100Ω, temperature rise rate is about 0.314°C/s, 1:1 resistance value is the smallest Yes, the temperature rise rate is the fastest, which is the highest compared to other proportions of samples. When evaporating different interdigitated electrodes, it is not that the more electrodes are better, but the effective heating area and other factor.

ZnO based NOx gas and VOC detection sensor fabrication techniques and materials

Nano- or micro-nano gas sensors have attracted a lot of attention since they have the potential for several applications. Utilizing a coplanar integrated design of the microheater and the inter-digitated electrode, a chemo resistive ethanol gas sensor with a thin layer of zinc oxide (ZnO) as a sensing layer has been examined (IDE). The article's conclusion offers potential future paths and research opportunities for improved sensitivity and selectivity for these sensors. SnO2-based sensors have received a lot of attention in the field of hazardous gas detection because of their extraordinary sensitivity. ZnO thin films are created using a chemical method. Gas sensors must have reduced packaging because they are essential in modern industry for managing environmental concerns. Since the gas sensor must operate at temperatures higher than ambient temperature, using the heater is necessary. The heating mechanism for the detecting layer in the various gas sensors that have recently been developed is either external or incorporates additional layers. The suggested architecture might be helpful in cutting down on the number of layers that must be deposited for the sensor and additional heating circuits. A new architecture with a coplanar microheater and IDEs has been created to analyse the gas response. The ongoing work is built on the coplanar microheater with IDEs produced for the ethanol sensor. Additionally, studies have been conducted to examine how the sensor's sensing capabilities are impacted by the integrated architecture. The sensor detects a layer thickness of 430 nm with a sensing response of 110 the sensing layer is active over the substrate. The study's major goal is to show how an integrated coplanar microheater and IDE architecture may be used with ethanol sensor based on ZnO.

CeO2NPs Based Capacitive Sensor for Quantification of Limonin in Citrus Limetta Juice

Citrus fruit juices are beneficial to health immunity due to having antiviral, antifungal, and antioxidant properties. However, acceptability of its juices reduces due to the delayed bitterness caused mainly by the biomolecule limonin. Hence, continuous monitoring of limonin in juices is required to keep its limit within permissible level. Here, CeO2 nanoparticles (NPs) based capacitive sensor has been introduced for the first time to quantify limonin concentration in citrus limetta juice. The CeO2NPs were synthesized through a low-cost and eco-friendly method using Dillenia Indica aqueous extract. The capacitive sensor was designed and simulated using COMSOL multiphysics and fabricated by drop coating of CeO2NPs on interdigitated electrode (IDE) structure patterned on paper substrate. The sensor exhibits an excellent sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim $ </tex-math></inline-formula> 9.62 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm 0.095 \mu \text{F}$ </tex-math></inline-formula> /ppm and a fast response time of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim $ </tex-math></inline-formula> 13 s. The sensor’s performance was validated using high-performance liquid chromatography (HPLC) analysis. The developed sensor assures easy, on-site, eco-friendly, and rapid monitoring of limonin level in citrus juices.

Chemically derived graphene quantum dots for high-strain sensing

Graphene quantum dots (GQDs) refer to graphene fragments with a lateral dimension typically less than 100 nm, which possess unique electrical and optical properties due to the quantum confinement effect. In this study, we demonstrate that chemically derived graphene quantum dots show great potential for making highly stretchable and cost-effective strain sensors via an electron tunneling mechanism. Stretchable strain sensors are critical devices for the field of flexible or wearable electronics which are expected to maintain function up to high strain values (> 30%). However, strain sensors based on conventional materials (i.e. metal or semiconductors) or metal nanoparticles (e.g. gold or silver nanoparticles) only work within a small range of strain (i.e. the former have a working range < 1% and the latter < 3%). In this study, by simply dropcasting solution-processed GQDs between the interdigitated electrodes on polydimethylsiloxane, we obtained devices that can function in the range from 0.06% to over 50% tensile strain with both the sensitivity and working range conveniently adjustable by the concentration of GQDs applied. This study provides a new concept for practical applications of GQDs, revealing the potential of this material for smart applications such as artificial skin, human-machine interfaces, and health monitoring.