Proteins are central to essentially all molecular processes in living organisms, typically carrying out their activities by folding into well-deﬁned three-dimensional structures and by binding to other molecular species to form functional complexes. Infrared (IR) spectroscopy is well established as an important measurement capability for chemically characterizing the secondary structure of proteins both in solution and in the solid state. New nanoscale chemical characterization capabilities, such as photothermal AFM-IR spectroscopy, have enabled the determination of polypeptide conformations in a single protein fibrils and other submicron-sized protein structures, resulting in an improved understanding of such important processes as protein misfolding and aggregation mechanisms.
Until now, however, AFM-IR could only be performed on dried materials, and there is always a concern that the drying out of a protein-containing material may result in a conformational change in the protein backbone structure. The new approach and results described in this paper show that it is now possible to generate nanoscale resolved IR spectra and maps in air and water with comparable signal-to-noise ratio (SNR) and lateral resolution.