Improving the tissue penetration depth and spatial resolution of fluorescence-based optical nanoprobes remains a grand challenge for their practical applications in in vivo imaging, due to the scattering and absorption and endogenous autofluorescence of living tissues. Here, we present that Ag2S quantum dots (QDs), containing no toxic ions, exhibiting long circulation time and high stability, act as a new kind of fluorescent probes in the second near-infrared window (NIR-II, 1000–1350 nm) which enable in vivo monitoring of lymphatic drainage and vascular networks with deep tissue penetration and high spatial and temporal resolution. In addition, NIR-II fluorescence imaging with Ag2S QDs provide ultrahigh spatial resolution (∼40 μm) that permits us to track angiogenesis mediated by a tiny tumor (2–3 mm in diameter) in vivo. Our results indicate that Ag2S QDs are promising NIR-II fluorescent nanoprobes that could be useful in surgical treatments such as sentinel lymph node (SLN) dissection as well in assessment of blood supply in tissues and organs and screening of anti-angiogenic drugs.

In vivo real-time visualization of tissue blood flow and angiogenesis using Ag2S quantum dots in the NIR-II window