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We demonstrate a flexible biosensor for lactate detection based on l-lactate oxidase immobilized by chitosan film cross-linked with glutaraldehyde on the surface of a graphene nanowall (GNW) electrode. The oxygen-plasma technique was developed to enhance the wettability of the GNWs, and the strength of the sensor's oxidation response depended on the concentration of lactate. First, in order to eliminate interference from other substances, biosensors were primarily tested in deionized water and displayed good electrochemical reversibility at different scan rates (20-100 mV s -1 ), a large index range (1.0 μM to 10.0 mM) and a low detection limit (1.0 μM) for lactate. Next, these sensors were further examined in phosphate buffer solution (to mimick human body fluids), and still exhibited high sensitivity, stability and flexibility. These results show that the GNW-based lactate biosensors possess important potential for application in clinical analysis, sports medicine and the food industry.

Two-dimensional molybdenum disulfide (MoS 2 ) is a promising material for ultrasensitive photodetectors owing to its tunable band gap and high absorption coefficient. However, controlled synthesis of high-quality, large-area monolayer molybdenum disulfide (MoS 2 ) is still a challenge in practical application. In this work, we report a gold foil assistant chemical vapor deposition method for the synthesis of large-size (>400 μm) single-crystal MoS 2 film on a silicon dioxide (SiO 2 ) substrate. The influence of Au foil in enlarging the size of single-crystal MoS 2  is investigated systemically using thermal simulation in Ansys workbench 16.0, including thermal conductivity, temperature difference and thermal relaxation time of the interface of SiO 2 substrate and Au foil, which indicate that Au foil can increase the temperature of the SiO 2 substrate rapidly and decrease the temperature difference between the oven and substrate. Finally, the properties of the monolayer MoS 2 film are further confirmed using back-gated field-effect transistors: a high photoresponse of 15.6 A W -1 and a fast photoresponse time of 100 ms. The growth techniques described in this study could be beneficial for the development of other atomically thin two-dimensional transition metal dichalcogenide materials.

We demonstrate a highly stretchable electronic skin (E-skin) based on the facile combination of microstructured graphene nanowalls (GNWs) and a polydimethylsiloxane (PDMS) substrate. The microstructure of the GNWs was endowed by conformally growing them on the unpolished silicon wafer without the aid of nanofabrication technology. Then a stamping transfer method was used to replicate the micropattern of the unpolished silicon wafer. Due to the large contact interface between the 3D graphene network and the PDMS, this type of E-skin worked under a stretching ratio of nearly 100%, and showed excellent mechanical strength and high sensitivity, with a change in relative resistance of up to 6500% and a gauge factor of 65.9 at 99.64% strain. Furthermore, the E-skin exhibited an obvious highly sensitive response to joint movement, eye movement and sound vibration, demonstrating broad potential applications in healthcare, body monitoring and wearable devices.