Growth of centimeter-scale single-crystal graphene on polycrystalline copper foil for ultrahigh sensitive sweat sensors

The low-cost growth of wafer-scale single-crystal (SC) shows great potential in its practical application. Epitaxial growth of large-area SC graphene on pre-produced SC metal foil with a specific index surface has been reported, which requires a high cost and complexity of operational processes. Here, we demonstrate an easy and low-cost approach for the growth of wafer-scale SC graphene on polycrystalline copper foil, the growth kinetics and the lattice orientation for graphene growth controlled by induced surface steps. Despite graphene domains grown across the Cu grain boundary, the domains have a common crystal orientation at the macroscale induced by the surface steps. This work demonstrates the polycrystalline Cu foil can also grow graphene domains with unidirectional alignment and seamless stitching on the large area. The wearable 2D graphene array sensors have also been developed for the detection of interleukin-6 (IL-6) in sweat, which can locate and detect infection or disease in a non-invasive way. Our growth method and novel application put up a new way of production and utilization of SC two-dimensional (2D) materials.