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

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%.