Spectrally Resolved, Functional Super-Resolution Microscopy Reveals Nanoscale Compositional Heterogeneity in Live-Cell Membranes

By recording the full fluorescence spectra and super-resolved positions of similar to 10(6) individual polarity sensing solvatochromic molecules, we reveal compositional heterogeneity in the membranes of live mammalian cells with single-molecule sensitivity and similar to 30 nm spatial resolution. This allowed us to unveil distinct polarity characteristics of the plasma membrane and the membranes of nanoscale intracellular organelles, a result we found to be due to differences in cholesterol levels. Within the plasma membrane, we observed the formation of low polarity, raft-like nanodomains upon cholesterol addition or cholera-toxin treatment, but found this nanoscale phase separation absent in native cells. The ultimate sensitivity achieved through examining the spectra of individual molecules thus opens the door to functional interrogations of intracellular physicochemical parameters at the nano scale.