Self-photo-oxidation for extending visible light absorption of carbon dots and oxidase-like activity

Carbon dots (C-dots) are attractive for their low cost, excellent optical properties, and low toxicity, but most C-dots are limited by their UV absorbance, especially for photodynamic therapy (PDT) applications. Developing rational and simple strategies to obtain C-dots with longer excitation/emission wavelengths remains a challenge. Previous work showed that C-dots can produce a high yield of reactive oxygen species (ROS) upon UV light illumination. We herein show that the produced ROS can lead to further oxidation and growth of C-dots, leading to visible light absorption (400 nm–650 nm) and extend fluorescence emission from blue to green. In addition, the light-treated C-dots showed boosted peroxidase and oxidase mimicking activity than the initial C-dots in the absence of light. In the presence of visible light, the catalytic efficiency of the light-treated C-dots is 11-fold much higher than the pristine C-dots. The light-treated C-dots can be used as a PDT agent due to the extended excitation and visible photo-oxidative activity, simultaneously providing a highly efficient cancer therapy. This study provides a simple way to modify C-dots leading to novel properties.