Photothermal Nanozyme–Mineralized Chlorella for Cascade Photodynamic Therapy and Tumor Microenvironment Remodeling

Solid tumors are characterized by dense stroma, abnormal vasculature, persistent hypoxia, and an immunosuppressive microenvironment, all of which impede therapeutic penetration and limit treatment efficacy. While photodynamic therapy has shown promise in superficial lesions, its application in deep-seated tumors is restricted by poor photosensitizer accumulation and oxygen dependency. To overcome these barriers, we developed a photothermal nanozyme-mineralized Chlorella biohybrid via the in situ biomineralization of gold nanoparticles on the cell surface. The surface-mineralized gold nanoparticles serve a dual function: acting as a photothermal agent and possessing glucose oxidase-mimicking nanozyme activity. Under 808 nm irradiation, the biohybrid generates mild photothermal heating (42-43 °C), which triggers chlorophyll release, reduces cancer-associated fibroblasts, and softens the extracellular matrix to facilitate deep tumor infiltration. Concurrently, the nanozyme catalyzes the oxidation of intratumoral glucose to produce hydrogen peroxide. This self-supplied hydrogen peroxide fuels a hypoxia-tolerant photodynamic cascade where, upon subsequent 660 nm irradiation, the released chlorophyll reacts with hydrogen peroxide to amplify reactive oxygen species generation approximately threefold compared to chlorophyll alone. In three-dimensional tumor spheroids, this sequential irradiation strategy achieved deeper chlorophyll penetration and approximately 95% cell death. Furthermore, the biohybrid significantly suppressed tumor growth and prolonged survival in both subcutaneous and orthotopic colorectal cancer models compared with control groups. This work presents a bio-abiotic integration strategy that combines stromal remodeling, catalytic hydrogen peroxide generation, and light-responsive activation to significantly expand the therapeutic window of hypoxia-tolerant photodynamic therapy, offering a promising therapeutic strategy for deep-seated and refractory solid tumors.