Scanning Probe Nano-Infrared Imaging and Spectroscopy of Biochemical and Natural Materials.

The mid-infrared with a characteristic wavelength of 3-20 μm is important for a wealth of technologies. In particular, mid-infrared spectroscopy can reveal material composition and structure information by fingerprinting chemical bonds' infrared resonances. Despite these merits, state-of-the-art mid-infrared techniques are spatially limited above tens of micrometers due to the fundamental diffraction law. Herein, recent progress in the scanning probe nanoscale infrared characterization of biochemical materials and natural specimens beyond this spatial limitation is reviewed. By leveraging the strong tip-sample local interactions, scanning probe nano-infrared methods probe nanoscale optical and mechanical responses to disclose material composition, heterogeneity, orientation, fine structure, and phase transitions at unprecedented length scales. These advances, therefore, revolutionize the understanding of a broad range of biochemical and natural materials and offer new material manipulation and engineering opportunities close to the ultimate length scales of fundamental physical, chemical, and biological processes.