Promotion and inhibition of oxidase-like nanoceria and peroxidase-like iron oxide by arsenate and arsenite

Comparison of the peroxidase activities of iron oxide nanozyme with DNAzyme and horseradish peroxidase

Peroxidase-based assays are the most extensively used in bioanalytical sensors because of their simple colorimetric readout and high sensitivity owing to enzymatic signal amplification. To improve the stability, modification, and cost of protein-based enzymes, such as horseradish peroxidase (HRP), various enzyme mimics, such as DNAzymes and nanozymes, have emerged over the last few decades. In this study, we compared the peroxidase activities of HRP, a G-quadruplex (G4)-hemin DNAzyme, and Fe₃O₄ nanozymes in terms of activity and stability under different conditions. The reactions were much slower at pH 7 than at pH 4. At pH 4, the turnover rate of HRP (375 s^-1) was faster than that of G4 DNAzyme (0.14 s^-1) and Fe₃O₄ (6.1 × 10^-4 s^-1, calculated by surface Fe concentration). When normalized to mass concentrations, the trend was the same. Through observation of the reaction for a long time of 2 h, the changes in the color and UV-vis spectra were also different for these catalysts, indicating different reaction mechanisms among these catalysts. Moreover, different buffers and nanozyme sizes were found to influence the activity of the catalysts. Fe₃O₄ showed the highest stability compared to HRP and G4 DNAzyme after a catalytic reaction or incubation with H₂O₂ for a few hours. This study helps to understand the properties of catalysts and the development of novel catalysts with enzyme-mimicking activities for application in various fields.

Nanozyme's catalytic activity at neutral pH: reaction substrates and application in sensing

Nanozymes exhibit their great potential as alternatives to natural enzymes. In addition to catalytic activity, nanozymes also need to have biologically relevant catalytic reactions at physiological pH to fit in the definition of an enzyme and to achieve efficient analytical applications. Previous reviews in the nanozyme field mainly focused on the catalytic mechanisms, activity regulation, and types of catalytic reactions. In this paper, we discuss efforts made on the substrate-dependent catalytic activity of nanozymes at neutral pH. First, the discrepant catalytic activities for different substrates are compared, where the key differences are the characteristics of substrates and the adsorption of substrates by nanozymes at different pH. We then reviewed efforts to enhance reaction activity for model chromogenic substrates and strategies to engineer nanomaterials to accelerate reaction rates for other substrates at physiological pH. Finally, we also discussed methods to achieve efficient sensing applications at neutral pH using nanozymes. We believe that the nanozyme is catching up with enzymes rapidly in terms of reaction rates and reaction conditions. Designing nanozymes with specific catalysis for efficient sensing remains a challenge.