Fluorescence sensing platform for sarcosine analysis based on nitrogen-doping copper nanosheets and gold nanoclusters

Herein, nitrogen-doped copper nanosheet (CuT@N NS) was obtained by pyrolysis of the tryptophan-based Cu-containing nanosheet (CuT NS) and graphitic carbon nitride (g-C₃N₄). The high Cu loading (8.62 wt%) on the nitrogen-doped carbon-nanosheets endowed CuT@N NS with prominent peroxidase-mimicking activity. A fluorometric sensing platform comprising CuT@N NS with exceptional catalytic performance and 5-methyl-2-thiouracil capped gold nanoclusters (AuNCs) was successfully constructed for the determination of sarcosine. Under appropriate conditions, sarcosine oxidase (SOx) recognized and oxidized the sarcosine substrate to generate H₂O₂. The as-obtained CuT@N NS then decomposed H₂O₂ into superoxide radicals (O₂^•-) and further promoted the reaction between 4-aminoantipyrine (AAP) and phenol to form pink-red quinone-imine dye (p-QID, absorbance at 508 nm). When excited at 380 nm, the orange-emitting AuNCs peak at 560 nm was quenched by the produced p-QID via inner filter effect (IFE). Thus, a CuT@N NS/AuNCs-based fluorometric sensing strategy for sarcosine analysis was constructed. Impressively, the outputting fluorometric signal revealed a wide linear range of 7.5-1100 μmol L^-1 with the detection limit of 4.69 μmol L^-1. These findings not only expanded the applications of nanozyme in bioanalysis, but also provided a sensitive and effective approach for monitoring the levels of sarcosine.