Seeing the unseen: NIR probes for reactive nitrogen species biosensing and bioimaging.

Reactive nitrogen species (RNS) play a crucial role in both health and disease, making their accurate and sensitive detection essential. However, their transient nature (∼milliseconds), high reactivity, and low abundance (nM-μM) in complex biological environments present significant challenges. Near-infrared (NIR) fluorescent probes have emerged as a promising solution for in vivo RNS imaging due to their enhanced sensitivity, spatiotemporal resolution, and deep tissue penetration. This review highlights recent advances in the design strategies, sensing mechanisms, and applications of NIR fluorescent probes in bioimaging. Additionally, we address current challenges and discuss future directions to advance the development of improved probes with potential for clinical translation, as well as the next generation of NIR probes for RNS biosensing and bioimaging.