Clarifying the oxidoreductase behavior of Platinum Nanoparticles

Nanozymes are a class of nanomaterials that display enzyme-like activities providing several advantages compared to natural enzymes, such as lower manufacturing costs, high stability/durability, and easier storability. Platinum nanoparticles (PtNPs) present multi-enzymatic oxidoreductase activity and are recently attracting tremendous interest thanks to their versatility holding great promises for their applications in biosensing and nanomedicine. Despite the rising number of studies on this topic, only a few works investigated the mechanism and the parameters that can influence the PtNPs’ performances. Furthermore, controversial results among these studies highlight the lack of a solid understanding of the mechanism underlying the catalytic properties. However, these aspects are clearly fundamental for the development of new applications and the understanding of PtNPs biological behavior. Aiming to clarify some of these aspects, within this work, we performed multiple systematic studies on Pt-based nanozymes investigating how the most common physical-chemical factors can influence their catalase- (CAT), oxidase- (OX), and peroxidase-like (POD) activities. We showed that PtNPs oxidoreductase properties are deeply interconnected and are affected by pH, temperature, and chemical environment. We observed that most of the colorimetric assays, commonly used in literature to investigate the nanozymes’ activities, can lead to misleading results due to the instability of the chromogenic substrates in testing conditions and to the influence of solvents and buffers employed in the commercial kits. The catalytic activity of PtNPs (in their optimal condition) was comparable to the one of the natural enzymes and even higher in harsh conditions, where their natural counterparts become inactive. This study provides essential insights on the mechanism involved in PtNPs oxidoreductase activities allowing for future sensor implementation and opening new perspectives for future application