Biochar-supported copper cobalt thiospinel (Co₂CuS₄) nanozymes for atom-efficient, dual-modal colorimetric sweat...

Nanozymes hold immense promise for point-of-care diagnostics; however, their clinical translation is frequently hindered by the intrinsic conflict between high catalytic activity and biosafety, manifested as low atom utilization and inevitable cytotoxicity at high local dosages. Herein, we report a graphitized pine pollen biochar decorated with Co₂CuS₄ nanocrystals (Co₂CuS₄@BH) that reconciles these competing demands. By exploiting the conductive graphitic matrix of the biochar, we achieve a synergistic enhancement was achieved, boosting the specific activity per metal atom by over 60% compared with pristine Co₂CuS₄. The composite nanozyme exhibits robust catalytic stability across a broad range of physiological environments. Critically, this structural design simultaneously mitigates cytotoxicity (cell viability > 85% at 24 h) and hemolysis (< 2%), an effect attributed to the decentralization of Co₂CuS₄ crystals on the biochar surface, which reduced the localized metal loading and thereby limits the contact area between cells and nanozyme. Integration of Co₂CuS₄@BH with glucose oxidase, a fluorescein pH indicator, and a silk fibroin-F127 hydrogel yielded a background-independent, dual-modal colorimetric sensor. Using 34 engineered features and an XGBoost algorithm, the system predicted glucose concentration and sweat pH with accuracies of 90.5% and 89.2%, respectively, enabling real-time stratification of diabetic risk (Low, Moderate, High, Critical). This work demonstrates that biochar-supported spinel nanozymes can alleviate the classical trade-off between catalytic activity and biocompatibility, opening a new avenue for wearable early-warning diagnostic devices.