Colorimetric sensing of ascorbic acid based on OsNPs-BSA-MnO₂ nanosheets with peroxidase-like activity

Resolving the aggregation of osmium (Os) nanozyme is important for improving its catalytic activity. Herein, Os nanoparticles-Bovine serum albumin-MnO₂ composite nanosheets (OsNPs-BSA-MnO₂) were synthesized by loading Os NPs on BSA-MnO₂ nanosheets. The Os NPs well dispersed on the surface of the nanosheets. The composite exhibited specific peroxidase-like activity with negligible oxidase-like activity. The catalytic mechanism was proved due to the generation of ·OH. Steady-state kinetics revealed stronger affinity for both H₂O₂ and 3,3',5,5'-tetramethylbenzidine (TMB) substrate. Interestingly, OsNPs-BSA-MnO₂ composite nanosheets exhibited a much lower activation energy than other osmium-based nanozymes, indicating superior catalytic performance. Moreover, ascorbic acid could effectively inhibit the catalytic activity of composite nanosheet. Thus, a colorimetric method for ascorbic acid detection was established with the limit of detection (LOD) of 1.69 μM and excellent selectivity. For practical application, ascorbic acid in Water-soluble C100 and fetal bovine serum was detected with satisfactory recoveries.