A Highly Fluorescent Tumor-Targeting Photosensitizer for DSLR Camera Image-Guided Two-Photon Photodynamic Therapy
Fluorescence image-guided photodynamic therapy (PDT) enables real-time monitoring of photosensitizer biodistribution and metabolism for optimized treatment timing. However, its application remains limited by reliance on high-end imaging systems. To address this, we designed three novel small-molecule photosensitizers (TTNb, TTAn, TTPh) based on a 2-vinylbenzoic acid scaffold, functionalized at the 5-position with nitro, amino, or hydrogen groups. Replacing the nitro group with amino or hydrogen switched aggregation behavior from aggregation-induced emission (AIE) to aggregation-caused quenching (ACQ), accompanied by a red-to-green fluorescence shift and subcellular relocation from liposomes to lysosomes. These findings establish design principles for ratiometric nitroreductase probes and enable systematic comparison between AIE and ACQ photosensitizers. Among these, TTAn exhibited superior cellular uptake (2800 times higher than Ce6 in Eca-109 cells), specific lysosomal targeting, balanced reactive oxygen species (singlet oxygen/superoxide anion) generation, and intense fluorescence. Under white light irradiation, TTAn achieved an IC50 of 21 nM, surpassing Ce6 by 50-fold. Notably, TTAn produced strong fluorescence in mice tumors under both one- and two-photon excitation, detectable using conventional imaging tools (smartphones, DSLR cameras) or even visible to the naked eye, confirming outstanding tumor specificity. Leveraging these advantages, TTAn enabled successful image-guided two-photon PDT in Eca-109 tumor-bearing mice with a single treatment, demonstrating potent therapeutic efficacy and biosafety. This work provides a strategic blueprint for developing small-molecule theranostic agents that operate without complex fluorescence imaging systems.