Comparing Nanozymes Catalytic Activity and Applications

Nanozymes (NZs), nanomaterials with intrinsic catalytic properties able to mimic natural enzymes, are gaining increasing interest among the scientific community in virtue of their properties that make them valuable alternative to natural enzymes in several fields from biosensing to nanomedicine. The field is rapidly evolving, with ongoing discoveries of new nanomaterials able to mimic more and more diverse enzymatic activities. However, most of the articles focus on specific application, often overlooking catalytic properties investigations. The works that report NZ activity characterization, often suffer for the lack of standardized protocols to evaluate their potential, preventing meaningful comparison with other reports and overall hampering the progress of the field. To address some of these challenges, in this thesis, we developed solid and reproducible Standard Operating Procedures (SOPs) to characterize NZ enzyme-like activities, using Platinum NZs (PtNZs) as a case study, owing to their highly efficient oxidoreductase-like activities. Analysing PtNZ catalase- (CAT-), peroxidase- (POD-) and oxidase-like (OX-like) activities, we addressed several fundamental aspects, often overlooked in literature, potentially responsible to results’ misinterpretations in the literature. With this implemented characterization workflow, we found that PtNZs can perform an extraordinary CAT-like activity, with an efficacy similar to the one of natural enzymes, confirming their great potential as antioxidant therapeutic. Leveraging on the developed SOPs, we also analysed and compared the catalytic activities of several metal and metal-oxide NZs including Pt, Palladium (Pd), Gold (Au), Ceria and Iron oxide (IO) NZs. The results of this study help to identify what should be the best NZ candidate for a specific application, for instance PtNZ present the more efficiency CAT-like activity, Ceria NZ is the best in phosphatase- (PHOS-)like activity, and AuNZ might be preferred choice for GOX-like activity in colorimetric assay. Overall, noble-metals NZs demonstrated higher catalytic performances than metal-oxide ones for all the oxidoreductase-like activities. Interestingly, we also observed that NZs POD- and OX-like activities are substrate dependent, and that different NZs preferentially react with different substrates. Finally, exploiting the theoretical knowledge gained on the POD-like activity of noble-metal NZs for application in the field of environmental remediation, we employed AuNZs to efficiently degrade different synthetic dyes (Rhodamine B, Methylene blue and Methyl orange), which are typically resistant to biodegradation and thus are considered persistent pollutant in aqueous bodies. We also gained some important insights on the degradation pathway of the pollutants treated with the NZ that resulted substantially different from the one of a natural POD enzyme (i.e. HRP). Finally, we developed a proof-of-concept system, immobilizing AuNZs on a membrane, which allow for an easier recovery and reuse of the catalyst, which showed excellent performance also with simulated real samples.