A mitochondria-targeted near-infrared fluorescent probe with a large Stokes shift for detecting nitroreductase activity in cells and mouse tumors

The hypoxic as a typical indicator, is closely involved with grow, invasion, metastasis and drug resistance of tumors. The upregulation of nitroreductase (NTR) has been universally used for assessing the hypoxic degrees of tumor cells and solid tumors. The fluorescence imaging technique, an important analytical instrument, has the ability to in suit detect the NTR activity and assess the hypoxia degree of tumors. Therein, we proposed a near-infrared (NIR) fluorescent probe (MTR), which detected mitochondrial NTR activity, thereby evaluating the degree of hypoxia in mouse tumors. The probe MTR demonstrated outstanding detection performance toward NTR in the buffer system, such as high selectivity, lower detection limit, large Stokes shift and NIR emission. Moreover, the probe MTR mainly concentrated within the mitochondria and detected NTR activity under hypoxic conditions. Employing this probe, the ascending of NTR activity was monitored in mouse tumors. Therefore, this work provides a decent practical tool for the detection and diagnosis of tumor hypoxia.