Scanning Electrochemical Potential Microscopy Imaging Horseradish Peroxidase on HOPG

Abstract

Electrochemical scanning tunneling microscopy (EC-STM) has been successfully applied to study the electron-transfer (ET) reactions of biomolecules at solid-liquid interfaces.1–4 However, there are still limitations, including requirement of sample conductivity and potential damage to the biomolecules from strong tunneling current, to be overcome.A different type of probe microscopy, scanning electrochemical potential microscopy (SECPM), can be used as a promising alternative. SECPM shares the similar hardware setup with EC-STM, except for the current amplifier being substituted by a potentiometer to measure the local electrochemical potential as feedback signal. This feature enables SECPM to work on less conductive biomolecular samples. It has been shown that SECPM is capable of imaging horseradish peroxidase (HRP) at single molecular level under in situ conditions, with image resolution comparable or even better than EC-STM (Figure 1). 5 The electrochemical double layer (EDL) existing at the solid-liquid interface in an electrochemical cell can be investigated by SECPM using tip-distance curves. Preliminary results will be shown.In this work, we use SECPM to image HRP molecules adsorbed on HOPG under in situ conditions, with varying electrochemical potentials applied to the substrate. HRP redox reactions were controlled by varying the substrate potential, and the corresponding change of the potential distribution in the EDL covering the adsorbed HRP surface was recorded by SECPM. The experimental results could offer a novel perspective to understand how the ET reactions influences the EDL, and then help the further research on biosensors and EDL capacitors.This work is supported in part by the North-East Centre for Energy Materials (EP/R021503/1) funded by EPSRC.