Silicon dioxide-protection boosting the peroxidase-like activity of Fe single-atom catalyst for combining chemo-photothermal therapy

Carbon-based single-atom catalysts (SACs) have been widely studied in the field of biomedicine due to their excellent catalytic performance. However, carbon-based SACs usually aggregate during pyrolysis, which leads to the reduction of catalytic activity. Here, we describe a method to improve the monodispersion of SACs using silicon dioxide as a protective layer. The decoration of silicon dioxide serves as a buffer layer for individual nanoparticles, which is not destroyed during the pyrolysis process, ensuring the single-particle dispersion of the nanoparticles after etching. This approach increased the hydroxyl groups on the surface of Fe-SAC (Fe-SAC-SE) and improved its water solubility, resulting in a four times enhancement of the peroxidase (POD)-like activity of Fe-SAC-SE (58.4 U/mg) than that of non-protected SACs (13.9 U/mg). The SiO2-protection approach could also improve the catalytic activities of SACs with other metals such as Mn, Co, Ni, and Cu, indicating its generality for SACs preparation. Taking advantage of the high POD-like activity, photothermal properties, and large specific surface area of Fe-SAC-SE, we constructed a synergistic therapeutic system (Fe-SAC-SE@DOX@PEG) for combining the photothermal therapy, catalytic therapy, and chemotherapy. It was verified that the photothermal properties of Fe-SAC-SE@DOX@PEG could effectively improve its POD-like activity, exhibiting excellent tumor-killing performance at the cellular level. This work may provide a general approach to improve the performances of SACs for disease therapy and diagnosis.