Gold core/ceria shell-based redox active nanozyme mimicking the biological multienzyme complex phenomenon

Abstract

Catalytically active individual gold (Au) and cerium oxide (CeO₂) nanoparticles (NPs) are well known to exhibit specific enzyme-like activities, such as natural catalase, oxidase, superoxide dismutase, and peroxidase enzymes. These activities have been maneuvered to design several biological applications such as immunoassays, glucose detection, radiation and free radical protection and tissue engineering. In biological systems, multienzyme complexes are involved in catalyzing important reactions of essential metabolic processes such as respiration, biomolecule synthesis, and photosynthesis. It is well known that metabolic processes linked with multienzyme complexes offer several advantages over reactions catalyzed by individual enzymes. A functional nanozyme depicting multienzyme like properties has eluded the researchers in the nanoscience community for the past few decades. In the current report, we have designed a functional multienzyme in the form of Gold (core)-CeO₂ (shell) nanoparticles (Au/CeO₂ CSNPs) exhibiting excellent peroxidase, catalase, and superoxide dismutase enzyme-like activities that are controlled simply by tuning the pH. The reaction kinetic parameters reveal that the peroxidase-like activity of this core-shell nanozyme is comparable to natural horseradish peroxidase (HRP) enzyme. Unlike peroxidase-like activity exhibited by other nanomaterials, Au/CeO₂ CSNPs showed a decrease in hydroxyl radical formation, suggesting that the biocatalytic reactions are performed by efficient electron transfers. A significant enzyme-like activity of this core-shell nanoparticle was conserved at extreme pH (2-11) and temperatures (up to 90 °C), clearly suggesting the superiority over natural enzymes. Further, the utility of peroxidase-like activity of this core-shell nanoparticles was extended for the detection of glucose, which showed a linear range of detection between (100 µM to 1 mM). It is hypothesized that the proximity of the redox potentials of Au⁺/Au and Ce (III)/Ce (IV) may result in a redox couple promoting the multienzyme activity of core-shell nanoparticles. Au/CeO₂ CSNPs may open new directions for development of single platform sensors in multiple biosensing applications.

Keywords: Catalase; Enzyme kinetics; Multienzyme complex mimicking nanozymes; Peroxidase; Superoxide dismutase.