Millimeter-deep micron-resolution vibrational imaging by shortwave infrared photothermal microscopy

TL;DR

This paper introduces a shortwave infrared photothermal microscope capable of millimeter-deep vibrational imaging with sub-micron resolution, enabling detailed chemical imaging in thick biological tissues with high sensitivity.

Contribution

The development of SWIP microscopy provides a new method for deep-tissue vibrational imaging with high resolution and sensitivity, surpassing previous limitations in tissue depth and chemical contrast.

Findings

Achieves millimeter-deep imaging with sub-micron resolution.

Detects nanoparticles with high sensitivity, 63 times more than photoacoustic signals.

Successfully images lipids and tissue structures in various biological samples.

Abstract

Deep-tissue chemical imaging plays a vital role in biological and medical applications. Here, we present a shortwave infrared photothermal (SWIP) microscope for millimeter-deep vibrational imaging with sub-micron lateral resolution and nanoparticle detection sensitivity. By pumping the overtone transition of carbon-hydrogen bonds and probing the subsequent photothermal lens with shortwave infrared light, SWIP can obtain chemical contrast from microparticles located millimeter-deep in a highly scattering phantom. By fast digitization on the optically probed signal, the amplitude of photothermal signal is shown to be 63 times larger than that of photoacoustic signal, thus enabling highly sensitive detection of nanoscale objects. SWIP can resolve the intracellular lipids across an intact tumor spheroid and the layered structure in millimeter-thick liver, skin, brain, and breast tissues. Together, SWIP microscopy fills a gap in vibrational imaging with sub-cellular resolution and millimeter-level penetration, which heralds broad potential for life science and clinical applications.