Photoswitchable Antioxidant and Prooxidant Activities of Mg-Doped Carbon Dot Nanozymes as Antibacterial and Anti-Inflammatory Agents

Multienzymatic nanozymes hold great potential in therapeutics due to their higher catalytic efficiency and multifunctionality. However, flexibly switching the antioxidant and prooxidant activities of multienzymic nanozymes at the same lesion remains a challenge. Herein, we design magnesium-doped carbon dot (Mg-CD) nanozymes with photoswitchable antioxidant and prooxidant activities under physiological conditions. The Mg-CD nanozymes exhibit superoxide dismutase (SOD)-like activity and can scavenge singlet oxygen and hydroxyl radicals without illumination. Interestingly, the antioxidant activity can be converted to oxidase-like activity under visible light illumination, producing singlet oxygen and superoxide anions. The mechanism of the switchable activities is attributed to the fact that coordination between magnesium and the CD skeleton enhances the excited-state electron transfer of singlet states and the energy transfer of triplet electrons. Therefore, Mg-CDs can act as antibacterial and anti-inflammatory agents. Mg-CDs exhibit antibacterial rates exceeding 99% within 5 min under illumination. They can scavenge reactive oxygen species, thereby showing excellent capacity in treating inflammatory wounds caused by lipopolysaccharide. These photoswitchable antioxidant and prooxidant activities of CD nanozymes offer an effective strategy for better manipulating the versatility of nanozymes, expanding their intelligent biomedical applications.