Nanopipette-Based Probe Deciphering Nanoscale Charge Distribution of Graphene Layers Affecting Peptide Binding and Assembling

Layered nanomaterials, such as graphite and MoS₂, have attracted much attention due to the amazing electrical and optical properties of their single layers, which are useful for nanoelectronics and biosensing devices. Revealing the chemical environments of graphene layers, e.g., surface charge, is important since it has a critical effect on local electron mobility and biomolecular binding. However, charge distributions from different layers in liquid, with nanoscale resolution, are rarely investigated. Here, we revealed charge distributions on graphite flakes with different layers by nanopipette-based ion conductance microscopy under varied electrolyte concentrations and bias voltage conditions. We demonstrated distinct charge distributions from ultrathin layers (TLs), few layers (FLs), and bulk multilayers (MLs) of graphite flakes, where the underlying substrate could induce charge doping for TL-graphene but had no effect on FL and ML. Also, surface charges derived from each layer showed different sensitivities to electrolyte concentrations and bias voltages. Moreover, graphene defects were found to have an effect on local surface charges. Besides, we examined the binding and assembling behaviors of a designed peptide sequence on different graphene layers. The number and length of peptide nanowires exhibited a correlation with surface charge from different layers of a graphite flake. This work sheds light on the role of surface charge in determining graphene quality, providing potential applications for nanodevices such as graphene biosensing and nanoelectronics.