Ultrasensitive in vivo infrared spectroscopic imaging via oblique photothermal microscopy

• Published in: Nature communications Vol. 16; no. 1; pp. 6065 - 15
• Main Authors: Li, Mingsheng, Xiao, Sheng, Ni, Hongli, Ding, Guangrui, Yuan, Yuhao, Marar, Carolyn, Mertz, Jerome, Cheng, Ji-Xin
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 02.07.2025; Nature Publishing Group; Nature Portfolio
• Subjects: 140/125; 631/1647/245/2226; 639/624/1107/510; 639/624/1107/527/2257; 9/10; Animals; Efficiency; Female; Humanities and Social Sciences; Humans; Infrared analysis; Infrared imaging; Infrared spectroscopy; Lasers; Mice; Microscopy; Microscopy - instrumentation; Microscopy - methods; Monte Carlo simulation; multidisciplinary; Photons; Propagation; Science; Science (multidisciplinary); Sensitivity; Sensors; Skin; Skin - diagnostic imaging; Skin - metabolism; Spectrophotometry, Infrared - methods; Spectrum analysis
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-025-61332-w

In vivo IR spectroscopy faces challenges due to poor sensitivity in reflection mode and low resolution at micrometer scale. To break this barrier, we report an oblique photothermal microscope (OPTM) to enable ultrasensitive IR spectroscopic imaging of live subjects at sub-micron resolution. Classic photothermal measurement captures only a small fraction of probe photons through an iris to extract the photothermal signal. Instead, OPTM uses a differential split detector placed on the sample surface to collect 500-fold more photons and suppress the laser noise by 12 fold via balanced detection. Leveraging its improved sensitivity, OPTM enables low-dose IR imaging of skin without photodamage. Depth-resolved in vivo OPTM imaging of metabolic markers beneath mouse and human skin is shown. Furthermore, we demonstrate in vivo OPTM tracking of topical drug contents within mouse and human skin. Collectively, OPTM presents a highly sensitive imaging platform for in vivo and in situ molecular analysis. Authors report an oblique photothermal microscope system for ultrasensitive infrared spectroscopic imaging of live subjects at sub-micron resolutions. The method enables low-dose skin imaging without photodamage, and is a highly sensitive platform for in vivo and in situ molecular analysis.