Electrochemical Surface Plasmon Resonance Sensing using a van der Waals Heterostructure

Coupling surface plasmon resonance (SPR) sensing with electrochemistry (EC) is a promising analytical strategy to obtain information about interfacial phenomena in heterogeneous reactions. Typical EC-SPR sensors utilize a metal film both as the plasmonic material and as the working electrode. In this configuration, the eigenmodulation of the plasmonic properties of the metal film under applied potential results in a background signal, which hampers the unambiguous interpretation of the sensor response due to redox reactions. Here, a new strategy is presented to overcome this disadvantage by using a van der Waals heterostructure (vdW-HS) as the working electrode. The vdW-HS comprises of a graphene / hexagonal boron nitride (hBN) stack on a gold film of a standard SPR sensor. It is shown here that the background signal is completely suppressed enabling the unambiguous analysis of SPR sensor response due to electrochemical reactions. It is further observed that the potential dependent plasmonic signals are not just a reproduction of the electrochemical current and subtle differences can be traced back to the diffusive nature of the redox active species. Finally, it is demonstrated that EC-SPR can be used as a complementary method to distinguish if the electrochemical response is mainly surface-bound or due to diffusion.