PS-micelles altered the Φ_s distribution histogram.

<p>Figures A and B show the AFM and KPFM images, respectively, of a PC12 cell treated with PS-micelles. C. The Φ_s from B was binned with 40 steps and the histogram was fitted with a two-peak Gaussian model (red line). The two Gaussian distributions were plotted in green and blue. D. Averaged skewness in PC12 cells without treatment (control) or treated with PC- and PS-micelles (PC & PS, respectively). Data are expressed as mean ± SEM, and N = 11 for each group. * indicates <i>p</i><0.05 (by Student's <i>t</i>-test) compared with the control group.</p

Various Φ_s distribution histograms of PC12 cell plasma membrane.

<p>A fixed PC12 cell was air-dried and then a 66 µm² region of the plasma membrane was scanned at a resolution of 256128 pixels. Figures A and B show the simultaneously recorded AFM and KPFM images, respectively. C. The Φ_s from B was binned with 40 steps and the histogram was fitted with a two-peak Gaussian model (red line). The two Gaussian peaks were plotted in green and blue. D–E. Two other representative cells having Φ_s distribution histograms with differing skewness values.</p

An Ultrasensitive Nanowire-Transistor Biosensor for Detecting Dopamine Release from Living PC12 Cells under Hypoxic Stimulation

Dopamine (DA) is an important neurotransmitter that is involved in neuronal signal transduction and several critical illnesses. However, the concentration of DA is extremely low in patients and is difficult to detect using existing electrochemical biosensors with detection limits typically around nanomolar levels (∼10^–9 M). Here, we developed a nanoelectronic device as a biosensor for ultrasensitive and selective DA detection by modifying DNA-aptamers on a multiple-parallel-connected (MPC) silicon nanowire field-effect transistor (referred to as MPC aptamer/SiNW-FET). Compared with conventional electrochemical methods, the MPC aptamer/SiNW-FET has been demonstrated to improve the limit of DA detection to <10^–11 M and to possess a detection specificity that is able to distinguish DA from other chemical analogues, such as ascorbic acid, catechol, phenethylamine, tyrosine, epinephrine, and norepinephrine. This MPC aptamer/SiNW-FET was also applied to monitor DA release under hypoxic stimulation from living PC12 cells. The real-time recording of the exocytotic DA induced by hypoxia reveals that the increase in intracellular Ca²⁺ that is required to trigger DA secretion is dominated by an extracellular Ca²⁺ influx, rather than the release of intracellular Ca²⁺ stores

One-Step Synthesis of Antioxidative Graphene-Wrapped Copper Nanoparticles on Flexible Substrates for Electronic and Electrocatalytic Applications

In this study, we report a novel, one-step synthesis method to fabricate multilayer graphene (MLG)-wrapped copper nanoparticles (CuNPs) directly on various substrates (e.g., polyimide film (PI), carbon cloth (CC), or Si wafer (Si)). The electrical resistivities of the pristine MLG-CuNPs/PI and MLG-CuNPs/Si were measured 1.7 × 10^–6 and 1.4 × 10^–6 Ω·m, respectively, of which both values are ∼100-fold lower than earlier reports. The MLG shell could remarkably prevent the Cu nanocore from serious damages after MLG-CuNPs being exposed to various harsh conditions. Both MLG-CuNPs/PI and MLG-CuNPs/Si retained almost their conductivities after ambient annealing at 150 °C. Furthermore, the flexible MLG-CuNPs/PI exhibits excellent mechanical durability after 1000 bending cycles. We also demonstrate that the MLG-CuNPs/PI can be used as promising source-drain electrodes in fabricating flexible graphene-based field-effect transistor (G-FET) devices. Finally, the MLG-CuNPs/CC was shown to possess high performance and durability toward hydrogen evolution reaction (HER)

Growth of Large-Area Graphene Single Crystals in Confined Reaction Space with Diffusion-Driven Chemical Vapor Deposition

To synthesize large-area graphene single crystals, we specifically designed a low-pressure chemical vapor deposition (LPCVD) reactor with confined reaction space (L 22 mm × W 13 mm × H 50 μm). Within the confined reaction space, a uniform distribution of reactant concentrations, reduced substrate roughness, and the shift of growth kinetics toward a diffusion-limited regime can be achieved, favoring the preparation of large-area, high-quality graphene single crystals. The gas flow field and mass transport pattern of reactants in the LPCVD system simulated with a finite element method support the advantages of using this confined reaction room for graphene growth. Using this space-confined reactor together with the optimized synthesis parameters, we obtained monolayer, highly uniform, and defect-free graphene single crystals of up to ∼0.8 mm in diameter with the field-effect mobility of μ_EF ∼ 4800 cm² V^–1 s^–1 at room temperature. In addition, structural design of the confined reaction space by adjusting the reactor’s dimensions is of facile controllability and scalability, which demonstrates the superiority and preference of this method for industrial applications

Three-Dimensional Heterostructures of MoS₂ Nanosheets on Conducting MoO₂ as an Efficient Electrocatalyst To Enhance Hydrogen Evolution Reaction

Molybdenum disulfide (MoS₂) is a promising catalyst for hydrogen evolution reaction (HER) because of its unique nature to supply active sites in the reaction. However, the low density of active sites and their poor electrical conductivity have limited the performance of MoS₂ in HER. In this work, we synthesized MoS₂ nanosheets on three-dimensional (3D) conductive MoO₂ via a two-step chemical vapor deposition (CVD) reaction. The 3D MoO₂ structure can create structural disorders in MoS₂ nanosheets (referred to as 3D MoS₂/MoO₂), which are responsible for providing the superior HER activity by exposing tremendous active sites of terminal disulfur of S₂^–2 (in MoS₂) as well as the backbone conductive oxide layer (of MoO₂) to facilitate an interfacial charge transport for the proton reduction. In addition, the MoS₂ nanosheets could protect the inner MoO₂ core from the acidic electrolyte in the HER. The high activity of the as-synthesized 3D MoS₂/MoO₂ hybrid material in HER is attributed to the small onset overpotential of 142 mV, a largest cathodic current density of 85 mA cm^–2, a low Tafel slope of 35.6 mV dec^–1, and robust electrochemical durability

Tuning Rashba Spin–Orbit Coupling in Gated Multilayer InSe

Manipulating the electron spin with the aid of spin–orbit coupling (SOC) is an indispensable element of spintronics. Electrostatically gating a material with strong SOC results in an effective magnetic field which can in turn be used to govern the electron spin. In this work, we report the existence and electrostatic tunability of Rashba SOC in multilayer InSe. We observed a gate-voltage-tuned crossover from weak localization (WL) to weak antilocalization (WAL) effect in quantum transport studies of InSe, which suggests an increasing SOC strength. Quantitative analyses of magneto-transport studies and energy band diagram calculations provide strong evidence for the predominance of Rashba SOC in electrostatically gated InSe. Furthermore, we attribute the tendency of the SOC strength to saturate at high gate voltages to the increased electronic density of states-induced saturation of the electric field experienced by the electrons in the InSe layer. This explanation of nonlinear gate voltage control of Rashba SOC can be generalized to other electrostatically gated semiconductor nanomaterials in which a similar tendency of spin–orbit length saturation was observed (e.g., nanowire field effect transistors), and is thus of broad implications in spintronics. Identifying and controlling the Rashba SOC in InSe may serve pivotally in devising III–VI semiconductor-based spintronic devices in the future

Intrinsic Electron Mobility Exceeding 10³ cm²/(V s) in Multilayer InSe FETs

Graphene-like two-dimensional (2D) materials not only are interesting for their exotic electronic structure and fundamental electronic transport or optical properties but also hold promises for device miniaturization down to atomic thickness. As one material belonging to this category, InSe, a III–VI semiconductor, not only is a promising candidate for optoelectronic devices but also has potential for ultrathin field effect transistor (FET) with high mobility transport. In this work, various substrates such as PMMA, bare silicon oxide, passivated silicon oxide, and silicon nitride were used to fabricate multilayer InSe FET devices. Through back gating and Hall measurement in four-probe configuration, the device’s field effect mobility and intrinsic Hall mobility were extracted at various temperatures to study the material’s intrinsic transport behavior and the effect of dielectric substrate. The sample’s field effect and Hall mobilities over the range of 20–300 K fall in the range of 0.1–2.0 × 10³ cm²/(V s), which are comparable or better than the state of the art FETs made of widely studied 2D transition metal dichalcogenides

Improving Nanowire Sensing Capability by Electrical Field Alignment of Surface Probing Molecules

We argue that the structure ordering of self-assembled probing molecular monolayers is essential for the reliability and sensitivity of nanowire-based field-effect sensors because it can promote the efficiency for molecular interactions as well as strengthen the molecular dipole field experienced by the nanowires. In the case of monolayers, we showed that structure ordering could be improved by means of electrical field alignment. This technique was then employed to align multilayer complexes for nanowire sensing applications. The sensitivity we achieved for detection of hybridization between 15-base single-strand DNA molecules is 0.1 fM and for alcohol sensors is 0.5 ppm. The reliability was confirmed by repeated tests on chips that contain multiple nanowire sensors

High Performance and Bendable Few-Layered InSe Photodetectors with Broad Spectral Response

Two-dimensional crystals with a wealth of exotic dimensional-dependent properties are promising candidates for next-generation ultrathin and flexible optoelectronic devices. For the first time, we demonstrate that few-layered InSe photodetectors, fabricated on both a rigid SiO₂/Si substrate and a flexible polyethylene terephthalate (PET) film, are capable of conducting broadband photodetection from the visible to near-infrared region (450–785 nm) with high photoresponsivities of up to 12.3 AW^–1 at 450 nm (on SiO₂/Si) and 3.9 AW^–1 at 633 nm (on PET). These photoresponsivities are superior to those of other recently reported two-dimensional (2D) crystal-based (graphene, MoS₂, GaS, and GaSe) photodetectors. The InSe devices fabricated on rigid SiO₂/Si substrates possess a response time of ∼50 ms and exhibit long-term stability in photoswitching. These InSe devices can also operate on a flexible substrate with or without bending and reveal comparable performance to those devices on SiO₂/Si. With these excellent optoelectronic merits, we envision that the nanoscale InSe layers will not only find applications in flexible optoelectronics but also act as an active component to configure versatile 2D heterostructure devices