A New Strategy toward Simple Water-Soluble AIE Probes for Hypoxia Detection

Hypoxia-responsive fluorescent probes have emerged as a novel scaffold for tumor diagnosis. However, dilemma often exists between simple synthesis and high water solubility in traditional probes. Owing to the intrinsic property of N-oxides, herein, a new strategy is proposed to design and synthesize probes for in vitro hypoxia imaging. Equipped with tetraphenylethene (TPE), the N-oxides exhibit aggregation-induced emission characteristics and emit no light in aqueous solutions. Interestingly, the N-oxides can be reduced by ferrous ions in different rates. The aggregation of the resulting hydrophobic TPE residues restricts the intramolecular motions of the molecules, which turns-on their fluorescence. The N-O covalent bond of one molecule can be specifically cleaved by cellular reductase overexpressed under hypoxic conditions, and thus turn-on hypoxia imaging in vitro is achieved. The new strategy to design hypoxia imaging probes is extremely valuable and has great potential for application in tumor diagnosis.