Metasurface-enhanced infrared photothermal microscopy toward ultrasensitive chemical analysis

Abstract

Infrared spectroscopy with its rich vibrational information plays a crucial role in biochemical sensing. Metasurface-enhanced infrared spectroscopy amplifies the detection sensitivity by enhancing local electromagnetic fields. However, conventional far-field techniques lack the spatial resolution to image the optical response of a single plasmonic nanostructure. In this work, we introduce mid-infrared (mid-IR) photothermal microscopy to map the hot spot distribution and thermal response of a plasmonic metasurface resonant in the mid-IR spectral range. We demonstrate infrared photothermal detection of proteins and drug molecules around a single nanoantenna. Our metasurface-enhanced infrared photothermal microscope achieves a detection limit as low as 0.24 monolayer surface coverage of bovine serum albumin, paving the way for high-throughput, highly sensitive mid-IR analysis of low-abundance molecules.