In Vivo Microendoscopy in the Near-Infrared II Window.

Non-invasive fluorescence endoscopy of deep biological tissues beyond the mucosa, or trans-intestinal imaging in live mammals with high spatiotemporal resolution, remains challenging due to light scattering. Here, we developed a near-infrared II (NIR-II) microendoscopy with imaging wavelength extended to 1700 nm, enabling deep intestinal imaging beyond the mucosa and transrectal imaging at sub-10-µm resolution without any invasive surgery. It facilitated real-time visualization of the relative motion of vascular networks across different layers of the mouse rectum. Featuring a specially designed large field of view, the NIR-II microendoscopy enabled non-invasive transrectal imaging of the entire lumbar lymph node for the first time, revealing abnormal lymphatic drainage in tumor-bearing mice. In vivo longitudinal imaging of healthy mice and colitis-bearing mice mapped distinct fluorescence patterns in rectal vasculature and lumbar lymph nodes, enabling observation of lesions in acute colitis at the initial stage, and opening new possibilities for studying the interaction between the intestinal microenvironment and lymphatic systems.