Surface coating–modulated peroxidase-like activity of maghemite nanoparticles for a chromogenic analysis of cholesterol

Maghemite (γ-Fe₂O₃) nanoparticles (NPs) emerging as an artificial enzymes have demonstrated an excellent peroxidase-like activity and thus gained much attention in various biological and medical applications. But naked γ-Fe₂O₃ NPs are aqueously instable and prone to aggregation in biological solutions such as blood plasma. Surface coating for γ-Fe₂O₃ NPs is thus necessitated to achieve better stability and biocompatibility. In this work, three typical coating layers including poly(lactic-co-glycolic acid) (PLGA), carboxymethyl chitosan (CMCS), and human serum albumin (HSA) were utilized as modifiers to decorate γ-Fe₂O₃ NPs and fabricate compound NPs including NP_PLGA, NP_CMCS, and NP_HSA, respectively, and subsequently, the peroxidase-like activity of these NPs was evaluated with colorimetric analysis of cholesterol detection. The results showed that the surface coating barely affected peroxidase-like activity of NPs but could remarkably amend stability in the determined pH and temperature ranges. As evidenced with kinetic parameters, the enzymatic catalysis of NPs accorded well with Michaelis–Menten kinetics. Moreover, the catalytic assay demonstrated that the fabricated NP_PLGA, NP_CMCS, and NP_HSA showed a capable catalytic activity using cholesterol as substrate, and especially, the NP_PLGA showed a higher peroxidase-like activity compared with the NP_CMCS and NP_HSA. In conclusion, herein we obtained a coating layer-modulated peroxidase-like activity of γ-Fe₂O₃ NPs for a visualized analysis of cholesterol, which could be extended for cholesterol detection in biomedical analyses in the future.