Hypoxia-Responsive Molecular Probe Lighted up by Peptide Self-Assembly for Cancer Cell Imaging

Hypoxia is a characteristic feature of most solid tumors, which promotes the proliferation, metastasis, and invasion of tumors and stimulates the resistance of cancer treatments, leading to the serious consequences of tumor recurrence. The exploration of hypoxia detection technology will aid tumor diagnosis and treatment. Fluorescence imaging technology is an accurate and efficient hypoxia detection technology. It has attracted significant research interest, but designing novel fluorescence probes, especially stimuli-responsive probes with high sensitivity and low toxicity is still challenging. In this work, we report a hypoxia-responsive molecular bioprobe lighted up by peptide self-assembly, which contains aggregationinduced emission (AIE) fluorescent molecule TPE, hypoxia-responsive azo group (-N═N-), the self-assembling peptide GFFY, and targeting ligand RGD. The resulting peptide derivative TPE-GFFY-N═N-EERGD forms supramolecular nanofibers but emit weak fluorescence because the azobenzene moiety can effectively quench the fluorescence of the TPE dye. However, the fluorescence-quenched nanofibers could be lighted up dramatically when the azo group is reduced. More importantly, this "turn-on" supramolecular fluorescence bioprobe enables effective detecting tumor hypoxia due to the overexpressed azoreductase in the tumor microenvironment. This work affords a paradigm of designing environmentsensitive fluorescent molecular probes for tumor hypoxia imaging.