First Nano-Infrared Spectroscopy and Imaging Measurements of Single Phospholipid Bilayers

Scattering-mode Scanning Near-Field Optical Microscopy (sSNOM) allows one to obtain absorption spectra in the mid-IR region for samples as small as 20 nm in size. This configuration has made it possible to measure FTIR spectra of the protein complement of membranes. (Amenabar 2013) We now show that mid-IR sSNOM has the sensitivity required to measure spectra of phospholipids in individual bilayers in the spectral range 800 cm^-1–1400 cm^-1. We have observed the main absorption bands of the dipalmitoylphosphatidylcholine headgroups in this spectral region above noise level. We have also mapped the phosphate absorption band at 1070 cm^-1 simultaneously with the AFM topography. We have shown that we could achieve sufficient contrast to discriminate between single and multiple phospholipid bilayers and other structures, such as liposomes. This work opens the way to further research that uses nano-IR spectroscopy to describe the biochemistry of cell membranes and model systems.