Probing Local Potentials inside Metallic Nanopores with SERS and Bipolar Electrochemistry

It is essential to understand the local potential distribution of solid-state nanopores in nanofluidic systems. However, applying gate voltage or adding external electrical probes tends to disturb the electric field and/or flow patterns. To solve this problem, an approach is described to monitor the local potential using electrochemical surface enhanced Raman spectroscopy (EC-SERS) in two types of nanocavity pores: doubled-sided gold nanopores (MM nanopores) and single-sided gold nanopores with a dielectric passivation layer on the backside (MD nanopores). Numerical simulations predict an electrical polarization reversal in the two nanopore geometries. Consequently, the redox SERS changes of Nile Blue A on the two gold nanopores are found to be reversed, which is consistent with the variation of polarizations. The driving voltage of metallic nanopore devices is about an order of magnitude lower than that of microfluidic bipolar devices. Our method will not only prove valuable for the design of metallic nanopores, but also will find applications in the measurement of contactless metallized nanofluidic devices.