Mid-wave infrared photothermal microscopy for molecular and metabolic imaging in deep tissues and spheroids

TL;DR

This paper introduces mid-wave infrared photothermal microscopy for high-resolution, deep-tissue molecular and metabolic imaging, overcoming water background issues and enabling detailed functional imaging in 3D biological systems.

Contribution

It presents a novel MWIP microscopy technique operating in the 2000-2500 nm range, achieving deep tissue imaging with high contrast and molecular specificity.

Findings

Achieved a detection limit of 0.12% for DMSO.

Demonstrated depth-resolved imaging up to 500 micrometers in tissues.

Enabled tracking of transdermal drug transport and metabolic processes in spheroids.

Abstract

High-resolution chemical imaging within deep tissues and intact spheroids remains a grand challenge. Here, we introduce mid-wave infrared photothermal (MWIP) microscopy operating in the underexplored 2000-2500 nm spectral window for submicron-resolution molecular and metabolic imaging in intact tumor spheroids and deep tissues. A dark-field photothermal detection scheme significantly suppresses water background and enhances contrast. By accessing strong carbon-hydrogen combination absorptions, a detection limit of 0.12% for dimethyl sulfoxide is achieved, comparable to stimulated Raman scattering microscopy. Depth-resolved imaging of endogenous biomolecules up to 500 micrometers in excised mouse skin and brain tissues is demonstrated. MWIP further enables depth-resolved tracking of transdermal drug transport via carbon-deuterium overtone absorption. Using deuterium metabolic probes, fatty-acid metabolism is imaged at 200 micrometers deep within intact tumor spheroids through carbon-deuterium overtone and combination bands. Collectively, MWIP offers a platform for functional imaging of 3D biological systems in their native environments.