Novel biogenic gold nanoparticles catalyzing multienzyme cascade reaction: Glucose oxidase and peroxidase mimicking activity

Enzyme-mimicking nanoparticles or nanozymes have received increasing interest as potentially viable alternatives to overcome natural enzyme limitations including low thermal stability and high cost of synthesis, isolation, and purification. Nanomaterial-based biomimetic catalysts with multiple functions are essential to address challenges in artificial enzyme mimicking processes. Here, we report novel gold nanoparticles (AuNPs) catalyzing multienzyme cascade reaction (glucose oxidase and peroxidase mimicking activity) synthesized via a green process using gallnut extract (GNE) as a reducing and capping agent. First, with glucose oxidase mimicking activity, glucose is oxidized to gluconic acid and H2O2. Second, the in situ generated H2O2 by glucose oxidation assists the subsequent peroxidase mimicking reaction that oxidizes the chromogenic substrate 3,3',5,5'-tetramethylbenzidine. The synthesized GNE-based AuNPs showed an optimum catalytic activity at 40 degrees C within a pH range of 6-8. Apparent Michaelis constant (K-m) values for glucose and H2O2 were estimated to be 0.089 and 0.118 mM, respectively. These low K-m values demonstrate the strong affinity of the synthesized GNE-based AuNPs towards both substrates. GNE-based AuNPs exhibited an average zeta-potential value of -32.2 mV, indicating good physical stability of the nanosuspension. The nanoparticles displayed good reproducibility with long-term stability during storage at 4 degrees C for 10 days. In addition, the green synthesized AuNPs showed higher dual enzyme mimicking activity compared to chemically synthesized AuNPs due to their unique rhombic dodecahedron morphology. This work provides new insights regarding the investigation of green synthesized nanoparticles as multienzyme substitutes for glucose oxidase and peroxidase in different applications such as diagnostic kits for glucose level detection.