A benzoindole-based fluorescent probe for nitroreductase imaging in living cells under hypoxia conditions

• A novel fluorescent NTR probe NFP-NTR based on the benzo[ cd ]indol fluorophore was designed for nitroreductase imaging in living cells under hypoxia conditions. • The probe NFP-NTR showed excellent sensitive capability with calculated limit detection of 17 ng/mL. • The probe NFP-NTR displayed high selectivity towards NTR over other analytes. • The probe NFP-NTR was successfully employed as a desirable tool for cellular imaging of endogenous NTR in Hela cells at the condition of hypoxia. Nitroreductase (NTR) plays a vital part in the activation of drugs and the biodegradation of nitroaromatic compounds. With the enhanced expression level of NTR in hypoxic solid tumors, it has been widely used as one of the biomarkers to evaluate the degree of tumor hypoxia. In this work, we reported a benzoindole-based fluorescent probe NFP-NTR for nitroreductase detection. NFP-NTR can react with NTR specifically to cleave the p-nitrobenzyl ether bond when nicotinamide adenine dinucleotide (NADH) is present, showing significant fluorescence augment characteristics. Encouragingly, NFP-NTR exhibited excellent selectivity and satisfactory sensitivity, with a detection limit of 17 ng/mL. In addition, this probe has been successfully used to image live Hela cells under hypoxic conditions with low cytotoxicity, indicating that probe NFP-NTR has great potential to further elucidate more biological applications of NTR.