Probing Ca²⁺-induced electron transfer on the surface of self-assembled monolayer using SECM

The electron transfer process of protein on the surface of biomembrane is closely related to various physiological phenomena occurring on the biomembrane. Calcium cations (Ca²⁺), as a ubiquitous messenger, induced electron transfer of negatively charged protein on the surface of negatively charged biomembrane is a problem worth exploring. In this work, the 3-Mercaptopropionic acid self-assembled monolayer (MPA SAM) with terminal carboxyl groups was constructed on gold surface as a simplified model for simulated surface of negatively charged biomembrane. The electron transfer of negatively charged redox ion induced by Ca²⁺ on the surface of MPA SAM was investigated using scanning electrochemical microscopy. It was found that Ca²⁺ can induce electron transfer and enhance the electron transfer of negatively charged redox ions. The result is attributed to the reduction of the energy barrier of the electron transfer of negatively charged redox ion on the surface of MPA SAM because Ca²⁺ neutralizes the electrostatic repulsion interaction between negatively charged redox ion and negatively charged carboxylate surface of MPA SAM. The conditions of lower pH also benefit the above-mentioned electron transfer, which further confirms the mechanism of Ca²⁺-induced electron transfer. This work may provide a reference for studying the electron transfer process on the surface of simulated biomembrane.