Organic probes for NO-activatable biomedical imaging: NIR fluorescence, self-luminescence, and photoacoustic imaging.

Nitric oxide (NO) is a crucial signaling molecule involved in diverse physiological and pathological processes, making its precise detection essential for exploring its biological roles. Optical imaging is particularly attractive for NO detection due to its non-invasive nature, high sensitivity, and excellent spatial resolution. However, it suffers from limited tissue penetration and low signal-to-background ratios resulting from strong light scattering and autofluorescence. To overcome these challenges, several advanced imaging strategies have been developed, including near-infrared (NIR) fluorescence imaging that leverages optical regions with less light-tissue interactions, self-luminescence imaging that avoids the need for real-time light excitation, and photoacoustic imaging that detects acoustic signals with minimal attenuation. This review systematically summarizes recent advances in organic molecular probes for NO detection using these imaging modalities, focusing on their design strategies, recognition mechanisms, and biological applications. Finally, current challenges and future directions are discussed to guide the development of next-generation NO probes for both fundamental research and clinical translation.