Redox plasticity in copper-doped carbon-dot nanozymes: Determinants of ROS generation and scavenging

Copper-doped carbon-dot (Cu-CD) nanozymes exhibit unusually flexible redox behavior, enabling either reactive oxygen species (ROS) generation or scavenging depending on their composition and surrounding chemical environment. This review examines the physicochemical basis, mechanistic determinants, and biological consequences of this redox plasticity. Particular emphasis is placed on how carbon-core organization, Cu coordination, heteroatom coupling, surface chemistry, and electronic structure influence catalytic state, and how pH, peroxide availability, oxygen tension, and reducing capacity redistribute reaction flux among competing oxidoreductase-like pathways. The review further synthesizes evidence across antibacterial, inflammatory, regenerative, intestinal, and cancer-related systems to distinguish predominantly pro-oxidant, antioxidant, and context-dependent redox phenotypes. Cross-study analysis indicates that Cu incorporation alone is insufficient to predict function; rather, redox outcome emerges from coupled composition–structure–environment relationships. The current evidence supports redox plasticity more strongly than a universally defined reversible switch, revealing important limitations in mechanistic attribution and cross-platform comparability. Accordingly, the review identifies the need for standardized redox metrics, operando mechanistic characterization, reproducible manufacturing, and quantitatively defined switching maps to enable predictive design of Cu-CD nanozymes. This review provides a focused examination of copper-doped carbon-dot nanozymes, emphasizing the mechanistic origins, environmental regulation, and biological implications of their redox plasticity between ROS-generating and ROS-scavenging states.