Carbon quantum dots modification reduces TiO₂ nanoparticle toxicity in an aquatic food chain

Carbon quantum dots (CQDs) are emerging as a promising zero-dimensional carbon nanomaterial with the potential to enhance the catalytic properties of titanium dioxide nanoparticles (TiO₂ NPs). Although CQDs modification alters the physicochemical properties of TiO₂ NPs, the impact on their toxicity has been rarely explored. In this study, we investigated the effects of CQDs doping on the toxicity, bioaccumulation, and trophic transfer of TiO₂ NPs using a representative aquatic food chain comprising phytoplankton (Scenedesmus obliquus), zooplankton (Daphnia magna), and fish (Danio rerio). Surprisingly, we found CQDs doping significantly reduces the toxicity and bioconcentration of TiO₂ NPs. Mechanistic studies indicate that CQDs doping enhances the hydrogen peroxide (H₂O₂) scavenging ability of CQDs/TiO₂ NPs through the inherent catalase-like activity of CQDs, thereby reducing oxidative stress in organisms. Additionally, CQDs doping inhibits the conversion of photogenerated holes (h⁺) to hydroxyl radical (·OH) on TiO₂ NPs surfaces, leading to decreased free radical release. The increased surface electronegativity of CQDs/TiO₂ NPs also enhances repulsive interactions with organisms, further reducing both their toxicity and bioaccumulation. This study offers a comprehensive assessment of CQDs/TiO₂ NPs toxicity in aquatic ecosystems, providing a proof-of-principle for the development and application of CQDs-related composite nanomaterials.