Structural effects of amphiphilic protein/gold nanoparticle hybrid based nanozyme on peroxidase-like activity and silver-mediated inhibition

Abstract

Understanding structure–property correlations of nanozymes is critical in the rational design and fabrication of nanozymes with effective activity and smart multifunction. Here, an amphiphilic protein, β-casein, was chosen as a flexible modifier to fabricate a β-casein–AuNP hybrid nanozyme. The physicochemical properties including protein surface density and particle sizes can be easily controlled by the molar ratio of [precursor]/[protein]. Then, the structure–property correlation of the nanozyme was systematically investigated. Both the surface density of the protein and the nanoparticle size influence the peroxidase-like activity and silver-mediated inhibition. β-Casein–AuNP with a moderate AuNP core size and protein surface density has the lowest apparent K_m value of CM–AuNPs with TMB and H₂O₂, and hence the highest enzyme activity. Furthermore, the silver ion has been found to selectively inhibit the catalytic activity of β-casein–AuNPs due to the capping microenvironment provided by the protein. Since the bound silver ions can be effectively reduced to Ag⁰ by protein on the AuNP surface, the highest inhibition potency by silver is obtained for a β-casein–AuNP nanozyme with the lowest protein surface density and largest particle size. Importantly, a β-casein–AuNP (4.3 nm) based silver sensor is highly sensitive for sensing silver ions with a wide linear range of 0.1–10 μM, and has a low detection limit of 10 nM. The fundamental understanding of the structure–property relationship of nanozymes could provide guidance in the further development of easily prepared, effective, and low-cost nanozymes and their utilization in numerous areas.