Faradaic effects in electrochemically gated graphene sensors in the presence of redox active molecules

Tilmann J Neubert,Michel Wehrhold,Nur Selin Kaya,Kannan Balasubramanian

doi:10.1088/1361-6528/ab98bc

Tilmann J Neubert, Michel Wehrhold + Show 2 more

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https://doi.org/10.1088/1361-6528/ab98bc

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Abstract

Field-effect transistors (FETs) based on graphene are promising devices for the direct sensing of a range of analytes in solution. We show here that the presence of redox active molecules in the analyte solution leads to the occurrence of heterogeneous electron transfer with graphene generating a Faradaic current (electron transfer) in a FET configuration resulting in shifts of the Dirac point. Such a shift occurs if the Faradaic current is significantly high, e.g. due to a large graphene area. Furthermore, the redox shift based on the Faradaic current, reminiscent of a doping-like effect, is found to be non-Nernstian and dependent on parameters known from electrode kinetics in potentiodynamic methods, such as the electrode area, the standard potential of the redox probes and the scan rate of the gate voltage modulation. This behavior clearly differentiates this effect from other transduction mechanisms based on electrostatic interactions or 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 sensors behaves as a non-polarized electrode in liquid. Strategies for ensuring a polarized interface are discussed.

Highlights

Analytical graphene devices are emerging as versatile electronic platforms for chemical sensing and biosensing [1,2,3,4]
Graphene devices were fabricated with CVD-grown monolayer graphene as the conduction channel, between two Ti/Pt electrodes on Si/SiO2 substrates. (See section 4 and the supporting information (SI) for details of the fabrication process (with flow chart—figure S1 in the SI) and measurement configuration.) Shortly, graphene was transferred using a metal-ion-free wet transfer strategy followed by removal of trace impurities using electrochemical etching [21, 44] and annealing
We have investigated the interaction of redox active molecules with graphene in detail and found that electron transfer (ET) to these probes causes shifts in the Dirac point, which is termed a Faradaic effect in electrochemically gated graphene Field-effect transistors (FETs)

Summary

Introduction

Analytical graphene devices are emerging as versatile electronic platforms for chemical sensing and biosensing [1,2,3,4]. GFET sensors have been reported for the detection of various analyte species, including enzymes [9], antibodies [10], DNA [11,12,13] and others [2, 4, 14, 15]. In many of these examples, the graphene surface is functionalized with appropriate receptor

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