Potentiometric Detection of Single Protein Molecules in Solution by Nanoimpact Method

Nanoscale electrochemical methods based on nanopores and nanoelectrodes have gained enormous popularity for single-entity detection and analysis. This work integrates two aforementioned methods in one nanopipette apex to simultaneously monitor the ionic current and surface potential changes at the nanopore and the nanoelectrode when a protein translocates through the nanopore or collides with the nanoelectrode. In this presentation, I will demonstrate a facile potentiometric method of detecting protein at the single-molecule level in solution based on the nanoimpact events of proteins at the nanoelectrode, which is further supported by molecular dynamics (MD) simulation. Proteins, such as ferritin, hemoglobin, cytochrome-c, and lysozyme are tested to validate the method. When a protein molecule arrives at the vicinity of the electrically floating nanoelectrode, open-circuit potential (OCP) changes are detected at the nanoelectrode. Compared with the ionic current change, the OCP changes can be detected with better signal-to-noise ratio and higher time resolution. The nanopipette based novel potentiometric detection method provides new opportunities to study various biological entities at a single-entity level with close to physiological conditions.