We present mid-infrared vibrational spectroscopy and imaging at the nanoscale of individual cell membranes deposited on ultraflat gold substrate by use of resonantly-enhanced mechanical photoexpansion technique. This platform allows one to measure the energy absorbed by the sample by monitoring its local thermal expansion with a nanometer atomic force microscope tip. The observed Amide-I and Amide-II bands of proteins in the spectrum acquired on individual purple membrane flakes, filled with bacteriorhodopsin (bR) molecules, are in good agreement with the far-field infrared spectrum collected on large numbers of membranes. Differences among the relative intensity of the two Amide bands in the near- and far-field spectra are attributed to different orientation of bR protein molecules in the two samples. Strong vibrational contrast imaging at the Amide-I of proteins with a lateral resolution of around 50 nm is reported for individual flakes of both purple membranes and artificial lipid vesicles loaded with channelrhodospin molecules.
V. Giliberti, M. Badioli, L. Baldassarre, A. Nucara, P. Calvani, E. Ritter, L. Puskar, P. Hegemann, U. Schade, and M. Ortolani, "Nanospectroscopy of single purple membranes by mid-IR resonantly-enhanced mechanical photoexpansion," Proc. SPIE 10111, Quantum Sensing and Nano Electronics and Photonics XIV, 101110D (Presented at SPIE OPTO: January 29, 2017; Published: 27 January 2017); https://doi.org/10.1117/12.2253851.
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