Abstract

Chemical imaging is an essential tool for label-free visualization of biomolecules and materials in complex living systems. Infrared spectroscopic imaging has been an important approach towards this direction, which, however, is thus far mostly applicable to dried samples, has low spatial resolution, and lacks optical sectioning capabilities. Here, we overcome these limitations through sensing vibrational absorption induced photothermal effect by a visible laser beam. Our mid-infrared photothermal (MIP) approach reached 10 μM detection sensitivity and sub-micron lateral spatial resolution. Such performance has exceeded the diffraction limit of infrared microscopy and allowed label-free three-dimensional chemical imaging of live cells and organisms. Distributions of endogenous lipid and exogenous drug inside single cells were visualized. In vivo MIP imaging of lipids and proteins in C. elegans were demonstrated. The reported MIP imaging technology promises broad applications from monitoring metabolic activities to high-resolution mapping of drug molecules in living systems, which are beyond the reach of current infrared microscopy.

© 2017 Optical Society of America