• Neubert, T.J.; Wehrhold, M.; Kaya, N.S.; Balasubramanian, K.: Faradaic effects in electrochemically gated graphene sensors in the presence of redox active molecules. Nanotechnology 31 (2020), p. 405201/1-15

10.1088/1361-6528/ab98bc
Open Access Version

Abstract:
Field-effect transistors (FETs) based on graphene are promising devices for the direct sensing ofa range of analytes in solution. We show here that the presence of redox active molecules in theanalyte solution leads to the occurrence of heterogeneous electron transfer with graphenegenerating a Faradaic current (electron transfer) in a FET configuration resulting in shifts of theDirac point. Such a shift occurs if the Faradaic current is significantly high, e.g. due to a largegraphene area. Furthermore, the redox shift based on the Faradaic current, reminiscent of adoping-like effect, is found to be non-Nernstian and dependent on parameters known fromelectrode kinetics in potentiodynamic methods, such as the electrode area, the standard potentialof the redox probes and the scan rate of the gate voltage modulation. This behavior clearlydifferentiates this effect from other transduction mechanisms based on electrostatic interactionsor molecular charge transfer doping effects, which are usually behind a shift of the Dirac point.These observations suggest that large-area unmodified/pristine graphene in field-effect sensorsbehaves as a non-polarized electrode in liquid. Strategies for ensuring a polarized interface arediscussed.