Charge-independent protein adsorption characteristics of epitaxial graphene field-effect transistor on SiC substrate

Abstract

Charge-independent biomolecule detection using field-effect transistors (FETs) with single-crystal and large-area epitaxial graphene films fabricated on SiC substrates is demonstrated. To obtain clean graphene channel surfaces, FETs were fabricated using stencil mask lithography, which is a resist-free fabrication process. Proteins with various isoelectric points (pI: 5.6–9.9) were used as targets. Transfer characteristics [drain current (ID) vs solution-gate voltage (VG) characteristics] were measured by changing the pH of the buffer solution. The ID–VG characteristics exhibited a clear negative gate voltage shift for both positively and negatively charged proteins, indicating that the epitaxial graphene FETs could not detect the charge type of the protein and electrons were doped by the adsorption of both positively and negatively charged proteins. These results cannot be explained by conventional electrostatic effects. Therefore, it can be concluded that the detection of biomolecules by the epitaxial graphene FETs occurred through charge transfer from the proteins. Moreover, the dissociation constants between the proteins and epitaxial graphene films were as small as 100 pM, indicating the high sensitivity of the graphene FETs.