Dual-functional Cu-doped carbon dots for antioxidant cytoprotection and fluorescent detection of tetracycline

Dual‑functional copper‑doped carbon dots (Cu‑CDs) were prepared through a hydrothermal route using eco‑friendly copper citrate as the starting material. The resulting Cu‑CDs exhibited a uniform spherical morphology, stable excitation‑independent blue fluorescence, and reversible Cu⁺/Cu²⁺ redox couples, which collectively contributed to excellent antioxidant and fluorescent sensing performance. Owing to the synergistic effect of surface functional groups and Cu⁺/Cu²⁺ valence cycling, Cu‑CDs could efficiently scavenge ·OH radicals and exhibited much better retention of radical‑scavenging activity under high‑temperature conditions compared with natural ascorbic acid. Cellular experiments on MOVAS cells showed no significant reduction in cell viability under tested conditions (25‑100 µg/mL Cu‑CDs). Cu‑CDs could effectively eliminate intracellular reactive oxygen species and confer protective effects against H₂O₂‑ induced oxidative damage in MOVAS cells. In parallel, a sensitive fluorescent sensing platform for tetracycline detection was developed based on the inner filter effect. This constructed sensor offered dual linear detection ranges of 2-40 µM and 40-118 µM, a low limit of detection of 0.22 µM and exhibited outstanding anti-interference capacity against common metal ions, amino acids and coexisting organic substances. Satisfactory spike recoveries and low RSD values were obtained in pork and milk food matrices, demonstrating reliable practicability for food safety monitoring. Significantly, complementary experiments revealed that the electron‑transfer‑based antioxidant mechanism and the physical IFE‑dependent sensing mechanism operate independently without mutual interference, thereby effectively avoiding the functional crosstalk often seen in conventional dual‑functional carbon dot systems. Altogether, this study provides a simple and green approach to constructing high‑stability multifunctional carbon nanomaterials with promising applications in oxidative stress protection and food safety monitoring.