Parallel Comparative Studies on Composition-dependent Peroxidase-like Catalytic Activity of Ultrasmall Ferrite Nanoparticles

Abstract

Ferrite nanoparticles, known for their enzyme-like catalytic activity, have gained significant attention as innovative nanozymes for various catalysis medicine applications. However, the relationship between catalytic activity and ultrasmall ferrite nanoparticle composition remains unclear, which hinders the development of ferrite-based nanozymes with high catalytic performance. Here, we have synthesized a series of ultrasmall ferrite nanozymes for studying the composition dependent peroxidase (POD)-like activity. Initially, the size and surface charge were regulated to assess their impact on POD-like activity. The results indicate that smaller ferrite nanozymes with a negative charge exhibited superior activity when using TMB as the substrate. Subsequently, we examined the ultrasmall ferrite nanozymes with the same size and surface charge but different compositions (CoFe2O4, MnFe2O4, and γ-Fe2O3), and comprehensively investigated the effect of composition on POD-like activity. The results show that the POD-like activity is closely related to the composition of the ultrasmall ferrite nanozymes and the activity order towards TMB is found to be CoFe2O4 > MnFe2O4 > γ-Fe2O3. By comparing the catalytic performance of nanoparticles with different compositions, the influence of composition on their activity are elucidated. Furthermore, we determined that the optimal pH and temperature for the POD-like catalytic activity of ultrasmall CoFe2O4 nanozyme were pH=4-4.5 and 30 oC. Under these optimal catalytic conditions, the ultrasmall CoFe2O4 nanozymes exhibited a higher POD-like activity, resulting in increased tumor cell staining intensity. This suggests that ultrasmall CoFe2O4 nanozymes may serve as a viable alternative to horseradish peroxidase for immunohistochemical staining applications. This work provides experimental evidence for designing efficient ultrasmall ferrite catalysts for nanozyme catalysis medicine applications.