Proteins are basic building blocks of life. The chemistry and structure of proteins are essential for their biological function. Indeed, the structure of proteins determines their mechanical and catalytic properties (e.g. enzymes). Such functions literally shape all living beings. Furthermore, the protein structure also plays a major role in many diseases. For example, the secondary structure of a protein (whether it has helical (alpha-) or sheet-like (beta-) internal substructures) is highly relevant in the pathogenous mechanism leading to Alzheimer, Parkinson, and other neuro-degenerative diseases. Although a variety of methods have been developed to study the protein chemistry and structure, recognizing and mapping the secondary structure on the nanometer scale, or even with single protein sensitivity, is still a major challenge. A new infrared spectroscopy technique, called nano-FTIR, has now enabled nanoscale chemical imaging and probing of protein's secondary structure with enormous sensitivity. nano-FTIR is an optical technique that combines scattering-type scanning near-field optical microscopy (s-SNOM) and Fourier transform infrared (FTIR) spectroscopy. The latter is a tool often used for studying secondary structure of proteins that, however, does not allow for nanoscale mapping of proteins by itself. In nano-FTIR, a sharp metalized tip is illuminated with a broadband infrared laser beam, and the backscattered light is analyzed with a specially designed Fourier transform spectrometer. With this technique, the researchers could now demonstrate local infrared spectroscopy of proteins with a spatial resolution of less than 30 nm.
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