Photonic synaptic transistors with new electron trapping layer for high performance and ultra-low power consumption.

Photonic synaptic transistors are being investigated for their potential applications in neuromorphic computing and artificial vision systems. Recently, a method for establishing a synaptic effect by preventing the recombination of electron-hole pairs by forming an energy barrier with a double-layer consisting of a channel and a light absorption layer has shown effective results. We report a triple-layer device created by coating a novel electron-trapping layer between the light-absorption layer and the gate-insulating layer. Compared to the conventional double-layer photonic synaptic structure, our triple-layer device significantly reduces the recombination rate, resulting in improved performance in terms of the output photocurrent and memory characteristics. Furthermore, our photonic synaptic transistor possesses excellent synaptic properties, such as paired-pulse facilitation (PPF), short-term potentiation (STP), and long-term potentiation (LTP), and demonstrates a good response to a low operating voltage of - 0.1 mV. The low power consumption experiment shows a very low energy consumption of 0.01375 fJ per spike. These findings suggest a way to improve the performance of future neuromorphic devices and artificial vision systems.

RGO decorated N-doped NiCo2O4 hollow microspheres onto activated carbon cloth for high-performance non-enzymatic electrochemical glucose detection.

This paper reports the first effective fabrication of a high-performance non-enzymatic glucose sensor based on activated carbon cloth (ACC) coated with reduced graphene oxide (RGO) decorated N-doped urchin-like nickel cobaltite (NiCo2O4) hollow microspheres. Hierarchically mesoporous N-doped NiCo2O4 hollow microspheres were synthesized using a facile solvothermal method, followed by thermal treatment in a nitrogen (N2) atmosphere. Subsequently, they were hydrothermally decorated with RGO nanoflakes. The resulting composite was dip-coated onto ACC, and its electrochemical and glucose sensing performances were investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and chronoamperometric measurements in a three-electrode system. The composite electrode sensor demonstrates admirable sensitivity (6122 µM mM-1 cm-2) with an ultralow detection limit (5 nM, S/N = 3), and it performs well within a substantial linear range (0.5-1.450 mM). Additionally, it exhibits good long-term response stability and outstanding anti-interference performance. These outstanding results can be attributed to the synergistic effects of the highly electrically conductive ACC with multiple channels, the enhanced catalytic activity of highly porous N-doped NiCo2O4 hollow microspheres, and the large electroactive sites provided by its well-developed hierarchical nanostructure and RGO nanoflakes. The findings highlight the enormous potential of the ACC/N-doped NiCo2O4@RGO electrode for non-enzymatic glucose sensing.

NiCo2O4/RGO Hybrid Nanostructures on Surface-Modified Ni Core for Flexible Wire-Shaped Supercapacitor.

In this work, we report surface-modified nickel (Ni) wire/NiCo2O4/reduced graphene oxide (Ni/NCO/RGO) electrodes fabricated by a combination of facile solvothermal and hydrothermal deposition methods for wire-shaped supercapacitor application. The effect of Ni wire etching on the microstructural, surface morphological and electrochemical properties of Ni/NCO/RGO electrodes was investigated in detail. On account of the improved hybrid nanostructure and the synergistic effect between spinel-NiCo2O4 hollow microspheres and RGO nanoflakes, the electrode obtained from Ni wire etched for 10 min, i.e., Ni10/NCO/RGO exhibits the lowest initial equivalent resistance (1.68 Ω), and displays a good rate capability with a volumetric capacitance (2.64 F/cm3) and areal capacitance (25.3 mF/cm2). Additionally, the volumetric specific capacitance calculated by considering only active material volume was found to be as high as 253 F/cm3. It is revealed that the diffusion-controlled process related to faradaic volume processes (battery type) contributed significantly to the surface-controlled process of the Ni10/NCO/RGO electrode compared to other electrodes that led to the optimum electrochemical performance. Furthermore, the wire-shaped supercapacitor (WSC) was fabricated by assembling two optimum electrodes in-twisted structure with gel electrolyte and the device exhibited 10 µWh/cm3 (54 mWh/kg) energy density and 4.95 mW/cm3 (27 W/kg) power density at 200 µA. Finally, the repeatability, flexibility, and scalability of WSCs were successfully demonstrated at various device lengths and bending angles.

Capacitive Force Sensor with Wide Dynamic Range Using Wrinkled Micro Structures as Dielectric Layer.

We propose a wide dynamic range capacitive force sensor with two wrinkle-structured elastomer layers as a dielectric layer. The sensor consists of electrodes on each substrate and two dielectric layers between them. The electrode is made of platinum and fabricated by using a lift-off process. The polyimide film is used as a substrate. Two wrinkle-structured dielectric layers, which are placed in perpendicular direction, are made by poly(dimethylsiloxane) (PDMS) replica molding process. With the pressure applied on the device, dielectric layers deform while decreasing distance between the electrodes and thus increasing the capacitance of the sensor. The orthogonally positioned wrinkled structures make possible to increase the dynamic range of the capacitive cell. The proposed capacitive sensor operates in the pressure range of 1 MPa with the maximum sensitivity of 0.06%/kPa.

Multifunctional Woven Structure Operating as Triboelectric Energy Harvester, Capacitive Tactile Sensor Array, and Piezoresistive Strain Sensor Array.

This paper presents a power-generating sensor array in a flexible and stretchable form. The proposed device is composed of resistive strain sensors, capacitive tactile sensors, and a triboelectric energy harvester in a single platform. The device is implemented in a woven textile structure by using proposed functional threads. A single functional thread is composed of a flexible hollow tube coated with silver nanowires on the outer surface and a conductive silver thread inside the tube. The total size of the device is 60 × 60 mm² having a 5 × 5 array of sensor cell. The touch force in the vertical direction can be sensed by measuring the capacitance between the warp and weft functional threads. In addition, because silver nanowire layers provide piezoresistivity, the strain applied in the lateral direction can be detected by measuring the resistance of each thread. Last, with regard to the energy harvester, the maximum power and power density were measured as 201 µW and 0.48 W/m², respectively, when the device was pushed in the vertical direction.

ECG Monitoring Garment Using Conductive Carbon Paste for Reduced Motion Artifacts.

The heart is a fundamental organ of the human circulatory system and the continuous measurement of electrocardiogram (ECG) signals is of great importance for pre-detection of heart diseases. Dry electrodes that do not require electrolyte gel have been developed for wearable ECG monitoring applications. However, this kind of electrode often introduces motion artifacts because of the high contact impedance between the electrode and skin. We propose a wearable ECG monitoring garment that employs electrodes made of conductive carbon-based paste. This paste is directly applied to the skin and after drying for 5 min, it forms a patch electrode that is detachable and flexible. The contact impedance between the patch electrode and the skin is very low because the paste covers the skin in a conformal manner. The experimental results show that the contact area of the carbon-based paste on the skin replica is almost 100%. At frequencies under 10 Hz, the contact impedance of the patch electrode is of 70.0 kΩ, much lower than the typical 118.7 kΩ impedance of a Ag/AgCl electrode. We also demonstrate that the ECG signals measured using the custom-designed garment and the patch electrodes are very stable even during actions such as walking and running.

Nanostructure Modified Microelectrode for Electrochemical Detection of Dopamine with Ascorbic Acid and Uric Acid.

Dopamine (DA) is one kind of neurotransmitter in central nervous system which is indicator of neural disease. For this reason, determination of DA concentration in central nervous system is very important for early diagnosis of neural disease. In this study, we designed micro electrode array and fabricated by MEMS technology. Furthermore, we fabricated 3-D conducting nanostructure on electrode surface for enhanced sensitivity and selectivity due to increased surface area. Compared with macro and normal micro electrode, the 3-D nanostructure modified micro electrode shows better electrical performance. These surface modified pin type electrode was applied to detect low concentration of DA and successfully detect various concentration of DA from 100 µM to 1 µM with linear relationship in the presence of ascorbic acid and uric acid. From these results, our newly designed electrode shows possibility to be applied as brain biosensor for neural disease diagnosis such as Parkinson's diseases.

Microfluidic chips designed for measuring biomolecules through a microbead-based quantum dot fluorescence assay.

This chapter introduces the demonstration of specific antibody detection by using a microbead-based assay with quantum dot (QD) fluorescence on a polydimethylsiloxane (PDMS) microfluidic chip. The microfluidic chip is designed to isolate a single microbead where the binding reaction of antibodies occurs on the surface. The microfluidic chip is fabricated on a glass substrate using a transparent silicone elastomer, PDMS, for easy access of monitoring and flexible gate operations to capture the single microbead. For antibody detection, a sequence of functionalized assays has been performed in the fabricated chip, including the capturing of microbeads, antibody injection into a microchamber, quantum dot injection, and fluorescence detection. Various concentrations of human IgG antibodies have been introduced to bind to a single microbead captured and isolated inside a designated microchamber in a small volume of 75 pL. Fluorescence detection is monitored using a CCD camera after the second binding with the QDs conjugated with anti-human IgG. In this experiment, a human IgG antibody concentration below 0.1 microg/mL has been successfully detected.

Fabrication of complex multilevel microchannels in PDMS by using three-dimensional photoresist masters.

This paper demonstrates a new method of implementing complex microchannels in PDMS, which is simply constructed using three-dimensional photoresist structures as a master mold for the PDMS replica process. The process utilizes UV-insensitive LOR resist as a sacrificial layer to levitate the structural photoresist. In addition, the thickness of photoresist structures can be controlled by multi-step UV exposure. By using these techniques, various three-dimensional photoresist structures were successfully implemented, including the recessed cantilevers, suspended bridges, and the complex plates with micro-pits or micro-villi. We demonstrate that the three-dimensional photoresist structures are applicable to implementing complex multiple microchannels in PDMS by using the PDMS replica method.

Micro/Nanofluidic device for single-cell-based assay.

In this paper we have proposed and demonstrated a microfluidic device for a fast and parallel single-cell based assay. The proposed device is designed to passively capture single-cells or beads on multiple cell-positioning sites by a pre-defined fluidic stream and inject specific reagents or drugs onto each isolated single-cell. The device consists of surface-modified silicon channels capped with a grooved polydimethylsiloxane (PDMS) cover layer. A cell capture experiment has been performed using polystyrene beads as well as CHO DG44 living cells, and successful positioning of a single-cell on the cell-positioning sites was achieved. Also, we have demonstrated independent drug injection into a specific target cell.