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)

Detection of K⁺ Efflux from Stimulated Cortical Neurons by an Aptamer-Modified Silicon Nanowire Field-Effect Transistor

The concentration gradient of K⁺ across the cell membrane of a neuron determines its resting potential and cell excitability. During neurotransmission, the efflux of K⁺ from the cell via various channels will not only decrease the intracellular K⁺ content but also elevate the extracellular K⁺ concentration. However, it is not clear to what extent this change could be. In this study, we developed a multiple-parallel-connected silicon nanowire field-effect transistor (SiNW-FET) modified with K⁺-specific DNA-aptamers (aptamer/SiNW-FET) for the real-time detection of the K⁺ efflux from cultured cortical neurons. The aptamer/SiNW-FET showed an association constant of (2.18 ± 0.44) × 10⁶ M^–1 against K⁺ and an either less or negligible response to other alkali metal ions. The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) stimulation induced an outward current and hyperpolarized the membrane potential in a whole-cell patched neuron under a Na⁺/K⁺-free buffer. When neurons were placed atop the aptamer/SiNW-FET in a Na⁺/K⁺-free buffer, AMPA (13 μM) stimulation elevated the extracellular K⁺ concentration to ∼800 nM, which is greatly reduced by 6,7-dinitroquinoxaline-2,3-dione, an AMPA receptor antagonist. The EC₅₀ of AMPA in elevating the extracellular K⁺ concentration was 10.3 μM. By stimulating the neurons with AMPA under a normal physiological buffer, the K⁺ concentration in the isolated cytosolic fraction was decreased by 75%. These experiments demonstrate that the aptamer/SiNW-FET is sensitive for detecting cations and the K⁺ concentrations inside and outside the neurons could be greatly changed to modulate the neuron excitability