Difference mid-IR nanospectroscopy on individual patches of purple membranes: The proton pump activity of bacteriorhodopsin at the nanoscale

Conformational changes of the light-sensitive membrane receptor and proton pump bacteriorhodopsin is investigated by tip-enhanced mid-infrared nanospectroscopy on individual cell membrane patches, with a dramatic increase of sensitivity (in terms of number of probed molecules) compared with standard mid-infrared spectroscopy.