Infrared nanospectroscopy and nanoimaging of individual cell membranes and microvesicles exposed to air

We use mid-infrared laser absorption nanospectroscopy and nanoimaging, assisted by atomic force microscopy, to study individual hundred-nanometer-sized cell-membrane patches and microvesicles loaded with proteins. The patches and the microvesicles were sparsely deposited on flat gold surfaces and exposed to air for up to 48 hours. The viability of the transmembrane protein Channelrhodopsin, contained in individual membrane patches with lateral size of 500 nm and thickness of 7 nm, was verified by absorption-difference nanospectroscopy. The physical integrity of spherical microvesicles, produced by mouse cell cultures, of diameters distributed around 160 nm was observed by nanoimaging performed 24 hours after drop-casting. The protein cargo of an individual microvesicle was identified by the acquisition of the local infrared absorption spectrum both immediately after deposition and again 24 hours after deposition. The results suggest that infrared nanospectroscopy and nanoimaging may be regarded as potentially useful techniques to assess the stability of e.g. individual hundred-nanometer-sized virus particles deposited on solid surfaces exposed to air for many hours.