A new xanthene-based platform for developing NIR fluorogenic probes for in vivo bioimaging

Fluorescence imaging has attracted much attention due to its unique advantages. In particular, near-infrared (NIR, 650-900 nm) probes are beneficial since they can greatly reduce the interference of autofluorescence and cause negligible photodamage to organisms. Rhodamine B, a kind of xanthene dyes, is widely used for constructing fluorogenic probes because of its outstanding photophysical properties. However, its short absorption and emission wavelengths (<590 nm) impede the bioapplication in living mice. Herein, by extending the conjugated structure of xanthene, we present a novel fluorophore F3 with high quantum yield (& phi; = 16.1%), NIR fluorescence (maxima emission at 770 nm), as well as the tunable fluorescence off-on switch via the incorporation of analyte-specific moieties. As a proof of concept, we synthesize two NIR fluorescence probes (F3ONOO and F3NTR) for peroxynitrite (ONOO-) and nitroreductase (NTR) based on fluorophore F3. Using the two probes, we have realized fluorescence imaging of not only ONOO- fluctuations in hepatotoxicity, but also NTR changes in tumor mice, demonstrating the feasibility of the platform for developing activatable NIR fluorogenic probes for other biospecies in the future.