A simple route to CoFe2O4 nanoparticles with shape and size control and their tunable peroxidase-like activity

Abstract

Recent studies have suggested that the physical and chemical properties of nanoparticles (NPs) strongly depend on local chemical composition, size, and shape. Here, we report a new precursor-mediated growth of monodisperse magnetic cobalt ferrite (CoFe₂O₄) NPs with controlled size and shape. CoFe₂O₄ NPs with near corner-grown cubic, near cubic and polyhedron shape can be successfully prepared by simply tuning the amount of iron and cobalt acetylacetonates in oleic acid. Interestingly, the product shape varies from near corner-grown cubic to starlike by only changing the reaction temperature from 320 °C to 330 °C. These CoFe₂O₄ NPs exhibit size and shape-dependent peroxidase-like activity towards 3,3′,5,5′-tetramethylbenzdine (TMB) in the presence of H₂O₂, and thus exhibited different levels of peroxidase-like activities, in the order of spherical > near corner-grown cubic > starlike > near cubic > polyhedron; this order was closely related to their particle size and crystal morphology. CoFe₂O₄NPs exhibited high stability in HAc–NaAc buffer (pH = 4.0) and high activity over a broad pH (2.5–6.0). Furthermore, the Michaelis constants K_m value for the CoFe₂O₄ NPs (0.006 mM) with TMB as the substrate was lower than HRP (0.062 mM) and Fe₃O₄ NPs (0.010 mM). After further surface functionalization with folic acid (FA), the folate-conjugated CoFe₂O₄ nanoparticles allow discrimination of HeLa cells (folate receptor overexpression) from NIH-3T3 cells (without folate receptor expression). Such investigation is of great significance for peroxidase nanomimetics with enhanced activity and utilization.