Moving Beyond Fenton-Based Peroxidase Nanozymes for Analytical Sensing: Perspectives on Nonradical Alternatives from...

Artificial enzymes have garnered attention for their potential to overcome the cost and stability limitations of natural enzymes. Among these, nanozymes─solid nanomaterials with enzymatic activity─have emerged as promising alternatives due to their facile synthesis and recyclability. To date, over half of the reported nanozymes mimic peroxidase (POD), catalyzing the oxidation of chromogenic substrates like 3,3',5,5'-tetramethylbenzidine (TMB) with H₂O₂. While many studies have successfully demonstrated the substitution of horseradish peroxidase (HRP) with POD nanozymes in various sensing applications, challenges persist in characterizing their active sites to establish reliable catalytic correlations. Furthermore, unlike HRP, which utilizes H₂O₂ stoichiometrically for TMB oxidation, most POD nanozymes activate H₂O₂ through radical pathways. This results in low H₂O₂ utilization, hindering their practical use in quantitative assays compared to HRP. This perspective offers potential solutions from the standpoint of heterogeneous catalysis, including the use of probe-assisted surface techniques to distinguish active-site reactivity and the design of POD nanozymes that activate H₂O₂ via nonradical pathways to improve H₂O₂-to-substrate stoichiometry. These insights are expected to guide the future development of POD nanozymes, shifting the focus from maximizing OH radical generation to achieving controlled nonradical H₂O₂ activation and thus better mimicking HRP's catalytic behavior.