FLIM-Guided Self-Reporting of PDT Efficacy Using a Mitochondria-Targeted, Viscosity-Sensitive Quinolinium Probe

Abstract

Mitochondrial viscosity plays a pivotal role in microenvironment of mitochondria, and is closely associated with pathological conditions. As a light-activated treatment for cancer and infections, Photodynamic Therapy (PDT) relies on reactive oxygen species (ROS) generation by photosensitizers to induce cell apoptosis, and mitochondria are prime targets of PDT. However, current photosensitizers lack realtime feedback on therapeutic efficacy. Herein, we report Mito-Qu and Mito-QuE, two quinolinium-based multifunctional fluorescent probes for mitochondrial targeting and viscosity response based on the D-π-A structure to overcome these limitations. Mito-Qu and Mito-QuE reveal an exceptionally large Stokes shift of 179 nm and 186 nm and exhibit viscosity-sensitive emission via a twisted intramolecular charge transfer (TICT) mechanism, making them robust sensors for monitoring mitochondrial viscosity dynamics. Also, further experiments suggest Mito-Qu as a sensitive monitor for mitochondrial viscosity monitoring and self-reporting PDT efficacy via both confocal imaging and FLIM, providing a blueprint for developing next-generation organelletargeted probes for intracellular microenvironment monitoring.