Nanoscale resolution in infrared imaging of protein-containing lipid membranes

The precise imaging of biomolecular entities contributes to an understanding of the relationship between their structure and function. However, the resolution of conventional infrared microscopic imaging is diffraction limited and does not exceed a few micrometres. Atomic force microscopy, on the other hand, can detect infrared absorption down to the sub-micrometer level. In the present report, we demonstrate that for multi-bilayer lipid samples containing the plant photosynthetic pigment-protein complex LHCII, the resolution of this latter technique can be better than 20 nm. Such a high resolution is attributable to two factors: (i) the relatively high infrared absorption by the complex that is integrated perpendicular to the plane of the multilayer film, and (ii) the distinctly different mechanical properties and thermal conductivity of the lipid and protein components of the sample.