Copper-doped Coptidis Rhizoma-derived carbon dots (Cu-CR-CDs) nanozymes exhibit intestinal protective effects against Escherichia coli-induced diarrhea

Escherichia coli ( E. coli )-induced diarrhea remains a major health challenge in yaks, leading to substantial economic losses in plateau livestock production. Meanwhile, the widespread use of antibiotics has accelerated the emergence of antimicrobial resistance, underscoring the urgent need for green and sustainable antibacterial alternatives. In this study, copper-doped Coptidis Rhizoma -derived carbon dots (Cu-CR-CDs) were successfully synthesized and systematically evaluated for their antibacterial, antioxidant, and intestinal barrier protective effects both in vitro and in vivo . Cu-CR-CDs exhibited a uniform spherical morphology with an average diameter of 3.48 nm, and copper incorporation markedly enhanced its free radical scavenging capacity and conferred with multiple enzyme-like activities, including peroxidase-, superoxide dismutase-, and glutathione peroxidase-like activities. Compared with CR-CDs, Cu-CR-CDs demonstrated significantly enhanced antibacterial activity against E. coli , primarily by disruption of bacterial membrane integrity, increasing permeability, inducing leakage of intracellular biomolecules, inhibiting biofilm formation, and promoting intracellular reactive oxygen species (ROS) generation. In vitro experiments showed that Cu-CR-CDs effectively protected RAW264.7 macrophages and Caco-2 epithelial cells from H 2 O 2 -induced oxidative stress and lipopolysaccharide-induced inflammatory injury through scavenging intracellular ROS, suppressing pro-inflammatory cytokine production, and restoring tight junction protein expression. In vivo , oral administration of Cu-CR-CDs markedly alleviated E. coli –induced diarrhea in mice, reduced intestinal mucosal damage, restored villus structure, mitigated epithelial barrier function, and attenuated systemic inflammation. Moreover, Cu-CR-CDs reshaped gut microbiota composition by decreasing the relative abundance of harmful bacteria (e.g., Proteobacteria, Deferribacteres, and Desulfovibrio ) while increasing beneficial taxa such as Muribaculum, Prevotellaceae, and Akkermansia . Collectively, these results demonstrate that Cu-CR-CDs, as a multifunctional nanozyme with superior performance over CR-CDs, exhibiting potent antibacterial and therapeutic effects against enteric infections, thereby highlighting their potential as a promising nanotherapeutic strategy for the treatment of bacterial diarrhea.