Label-free optical imaging of ion channel activity on living cells

Abstract: Deciphering ion channel activity and signaling interactions within cells is one of the key tasks of neuroscience. Currently, measuring this electrophysiological activity is done using patch-clamp1-4 or voltage-sensitive imaging5-8. Unfortunately, these techniques are unable to balance between single-channel sensitivity and highthroughput detection. Here we introduce a label-free electrochemical-modulated interferometric scattering microscope (EM-iSCAT) to measure ion channel activity on living cells at both whole-cell and single-channel levels. We visualize the cellular responses dynamics to osmotic stimulation, and record open-close trajectories of single N-methyl-D-aspartate receptors channels with a frame rate of 1.5 kHz. Furthermore, we localize and distinguish different kinds of ion channels (Na+, K+, Ca2+) on cell membrane and monitor spatio-temporal heterogeneous responses between different cells in a network. The high-throughput and single-channel sensitive nature of EMiSCAT microscopy allows monitoring simultaneously the activity of individual channels, their localization, and clustering in the cellular community. Our imaging concept opens the possibility to study any kind of ion channels, and more broadly, cell communication mediated by ion channels.