A novel peroxidase-mimicking Cu,S co-doped carbon dot nanozyme for dual-mode lactate biosensing in serum and sweat.

Lactate monitoring is of considerable importance because it serves as a key indicator of metabolic status and tissue oxygen deficiency. Its concentration is widely used to evaluate disease severity in clinical diagnosis as well as physical fatigue and exercise intensity in sports medicine. In this work, copper-coordinated sulfur-doped carbon dots (Cu-S@CDs) were prepared through a simple solvothermal strategy and exhibited a high quantum yield of 32.89%, with strong emission at 470 nm under an excitation wavelength of 370 nm. In combination with phenol and 4-aminoantipyrine, the obtained probe enabled dual-mode lactate determination based on H2O2 generated by lactate oxidase. The produced pink chromogenic compound not only caused efficient quenching of the Cu-S@CDs fluorescence for fluorometric analysis, but also provided a characteristic absorbance signal at 512 nm for colorimetric measurement. With optimized experimental parameters, the fluorometric assay demonstrated a linear range of 0.02-800 µM, whereas the colorimetric assay showed a linear range of 0.1-750 µM. Application of the developed method to serum and sweat samples produced consistent analytical performance, underscoring its suitability for clinical diagnostic use and tailored health monitoring.