Multifunctional Probe Based on Cationic Conjugated Polymers for Nitroreductase-Related Analysis: Sensing, Hypoxia Diagnosis, and Imaging.

Nitroreductase (NTR) is overexpressed in hypoxic tumors. Moreover, hypoxia is usually considered as the most important feature of various diseases. Thus, it is important to build a sensitive and selective method for NTR detection and hypoxia diagnosis. Herein, a new cationic conjugated polymer (PBFBT-NP) with p-nitrophenyl group in the side chain was designed and synthesized as a fluorescent probe for the detection of NTR. In the absence of NTR, the fluorescence of PBFBT-NP was quenched due to photoinduced electron transfer (PET). On the contrary, in the presence of NTR, NTR can specifically react with p-nitrophenyl group to form p-aminophenyl group, which leads to the PET being inhibited and the polymer's fluorescence significantly increasing (>110-fold). The sensitive and selective NTR sensing method in vitro is thus constructed with a low detection limit of 2.9 ng/mL. Moreover, the hypoxic status of tumor cells can be visualized by fluorescence bioimaging with very low cytotoxicity. Interestingly, the probe was successfully used for imaging an NTR-expressed microorganism, such as E. coli, and showed excellent antibacterial activity against E. coli under white light irradiation. In brief, this multifunctional probe is promising for widespread use in NTR-related biological analysis.