Activatable near-infrared organic photosensitizers for imaging-guided photodynamic therapy

Photodynamic therapy (PDT) utilizes light to activate photosensitizers (PS), generating reactive oxygen species (ROS), and has excellent spatiotemporal selectivity and non-invasive. However, traditional PS is always in the “on” state and has lower tissue penetration, leading to non-specific accumulation in normal cells and presenting significant safety challenges for PDT. To overcome these problems, the near-infrared (NIR) activatable photosensitizers (aPS) have been developed by modifying groups specifically recognized by biomolecules, such as low pH and specific enzymes. These NIR aPS remain in the “off” state in normal tissues and cannot produce ROS under NIR laser light. After being activated by specific biomarkers, they generate fluorescence and photoacoustic signals to visualize lesion tissues, produce ROS to eliminate tumors and bacteria under NIR laser irradiation. This article systematically summarizes the categories, design strategies, and response mechanisms of aPS. Additionally, we discuss the application prospects of aPS in biomedical fields, along with the challenges and future directions for development.