Plasmon enhanced CuS@Au Nanozyme assisted dual mechanism colorimetric monitoring of food freshness at near-neutral pH.

Nanozymes have garnered growing interest due to their potential to act as substitutes for natural enzymes across a range of biomedical applications, including biosensing, catalysis, and immunoassays. Conventional approaches in biosensing application face several challenges due to their complicated methodology and high cost, thus restricting their application in on-site detection. To overcome these challenges, herein, we developed gold coated copper sulfide (CuS@Au) nanozymes possessing synergistic peroxidase mimetic activity. Reports support this observation and can be assumed due to noncovalent Cu+(d10)-Au+(d10) metallophilic interactions. Peroxidase mimetic activity was evaluated and validated using chromogenic substrate TMB in the presence of H2O2, found to obey Michaelis-Menten enzymatic equation. In comparison to many reported nanozymes, advancement of developed system is to possess catalytic potential at physiological pH, which proves to more important in biological system. Developed nanozyme was further applied as colorimetric biosensor for rapid and sensitive detection of xanthine and ascorbic acid in biological matrices. Colorimetric sensing primarily based on xanthine (presence of xanthine oxidase) and ascorbic acid, ability to promote and inhibit the oxidation of TMB, respectively. Results showed that for xanthine and ascorbic acid, linear detection range were 0-750 μM and 10-200 μM with detection limit of 1.42 μM and 2.4 μM, respectively. Further, colorimetric method was also efficiently used in detection of xanthine and ascorbic in real samples with high recovery. Overall, the CuS@Au nanozyme exhibits significant peroxidase-like activity, characterized by its affordability, high efficiency, and cost effectiveness, thereby offering an effective and sensitive platform for monitoring xanthine and ascorbic acid as a substitute for conventional methods.