Liquid phase Peak Force Infrared Microscopy: Super-resolution Infrared Microscopy in the Aqueous Phase

Infrared spectroscopy and microscopy directly couples to molecular functional groups, providing chemical information without extrinsic labels. However, conventional infrared spectroscopy and microscopy have two main limitations: lack of spatial resolution due to Abbe’s diffraction limit, and restriction of applications in the aqueous conditions due to strong infrared attenuation. On the other hand, many meaningful biological processes and chemical transformation happen in the liquid phase. The understanding of them requires insights from the nanoscale. With the support from Beckman Foundation, we have developed the liquid-phase peak force infrared (LiPFIR) microscopy to deliver both label-free super spatial resolution at 10 nm and compatibility with liquid-phase measurement. We have demonstrated the method on a range of samples, from tracking the surface re-organization of polymers in organic solvent, hydrogen-deuterium isotope exchange and ethanol-induced denaturation of proteins, to imaging of cellular structures in aqueous phases. The LiPFIR microscopy bypasses the two limitations of infrared spectroscopy and microscopy. It will enable label-free spectroscopic investigations of chemical reactions and biomolecular transformations from the tens of nanometer scale.