Quasi-spherical gold nanoparticles as peroxidase-like nanozymes for broad-range colorimetric detection of hydrogen peroxide and glucose.

Gold-based (Au-based) nanozymes have emerged as promising substitutes for natural peroxidase enzymes, exhibiting distinctive advantages such as high stability, cost-effectiveness, and relatively good catalytic activity. However, to further enhance their catalytic performance, considerable efforts have been devoted to designing and synthesizing Au-based nanozymes with more sophisticated nanostructures. In this work, quasi-spherical gold nanoparticles (Au NPs) with an average size of 15-20 nm were facilely synthesized via a simple chemical reduction method and investigated for their peroxidase-like (POD-like) catalytic activity. Their catalytic activity was confirmed using 3,3',5,5'-tetramethylbenzidine (TMB) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as chromogenic substrates. Steady-state kinetic analysis yielded apparent K m values of 0.75 ± 0.2 mM for TMB and 0.036 ± 0.005 mM for H2O2, indicating favorable H2O2 affinity and supporting the strong H2O2 responsiveness of the Au NPs nanozyme. Based on TMB oxidation, the Au NPs system enabled colorimetric determination of H2O2 over a broad working range of 0.059 µM-97 mM, and was further extended to glucose detection over 0.5-300 µM through a glucose oxidase-mediated reaction. The practical applicability of Au NPs nanozyme was further supported by H2O2 determination in spiked bottled mineral water, giving recoveries of approximately 94-105%.