An analytical model of label-free nanoscale chemical imaging reveals avenues toward improved spatial resolution and sensitivity

Abstract

Atomic force microscopy–infrared spectroscopy (AFM-IR) is a widely used scanning probe technique for label-free photothermal nanoscale chemical imaging, with diverse applications spanning single protein spectroscopy to analyzing nanoscale chemical, physical, and optical phenomena. However, the understanding of spatial resolution of the technique is limited to few specific, simple geometries (spheres, pillars, etc.). We introduce an analytical model of AFM-IR verified by numerical simulations and experiments that describes experimental data well for complex sample geometries. The model allows to reason about the spatial resolution and sensitivity of the technique and can give guidance for optimizing experimental parameter for sensitivity and resolution and interpreting results. Beyond this, it can be a stepping stone toward superresolution AFM-IR or nanoscale chemical tomography.