Gauging surface charge distribution of live cell membrane by ionic current change using scanning ion conductance microscopy

The distribution of surface charge and potential of cell membrane plays an indispensable role in cellular activities. However, probing surface charge of live cells in physiological conditions, until recently, remains an arduous challenge owing to lack of effective methods. Scanning ion conductance microscope (SICM) is an emerging imaging technique for imaging live cell membrane in its native state. Here, we introduce a simple SICM based imaging technique to effectively map the surface charge distribution of soft substrates including cell membrane by utilizing the higher surface charge sensitivity of the ionic current when the nanopipette tip is close to the substrate with a relatively high current change. This technique was assessed on charged model substrates made by polydimethylsiloxane, and the surface charge sensitivity of ionic current change was supported by finite element method simulations. With this method, we can distinguish the surface charge difference between cell membrane and the supporting collagen matrix. We also observed the surface charge change induced by the small membrane damage after 1% dimethyl sulfoxide (DMSO) treatment. This new SICM technique provides opportunities to study interfacial and cell membrane processes with high spatial resolution.