A fast-responsive fluorescent turn-on probe for nitroreductase imaging in living cells

Abstract

Nitroreductase (NTR) may be more active under the environment of hypoxic conditions, which are the distinctive features of the multiphase solid tumor. It is of great significance to effectively detect and monitor NTR in the living cells for the diagnosis of hypoxia in a tumor. Here, we synthesized a novel turn-on fluorescent probeNTR-NO2based on a fused four-ring quinoxaline skeleton for NTR detection. The highly efficient probe can be easily synthesized. The probeNTR-NO2showed satisfactory sensitivity and selectivity to NTR. Upon incubation with NTR,NTR-NO2could successively undergo a nitro reduction reaction and then generateNTR-NH2along with significant fluorescence enhancement (30 folds). Moreover, the fluorescent dyeNTR-NH2exhibits a large Stokes shift (Δλ= 111 nm) due to the intramolecular charge transfer (ICT) process. As a result,NTR-NO2displayed a wide linear range (0-4.5 μg mL−1) and low detection limit (LOD = 58 ng mL−1) after responding to NTR. In addition, this probe was adopted for the detection of endogenous NTR within hypoxic HeLa cells.