Effect of CTAB coating on structural, magnetic and peroxidase mimic activity of ferric oxide nanoparticles

In the present work, pristine and cetyl trimethyl ammonium bromide (CTAB)-coated ferric oxide nanoparticles $$(\hbox {CTAB@Fe}₂\hbox {O}₃ \hbox { NPs})$$ were synthesized and studied as enzyme mimics. The w/w ratio of $$\hbox {Fe}₂\hbox {O}₃$$ to CTAB was varied as 1:1 and 1:2. Transmission electron microscopic analysis revealed that pristine NPs had an average size of 50 nm, whereas the presence of CTAB resulted in the formation of nanorods with length of 130 nm. BET studies confirmed enhancement of surface area on CTAB coating, which was maximum for w/w ratio 1:1. The synthesized pristine NPs and CTAB-coated NPs were evaluated for their peroxidase mimic activity using o-dianisidine dihydrochloride as substrate. Optimum pH, temperature, substrate and NPs concentration for the reaction were 1, $$25^\circ {\mathrm{C}}$$ , $$0.16~\hbox {mg}~\hbox {ml}^-1$$ and $$1~\hbox {mg}~\hbox {ml}^-1$$ , respectively. Peroxidase mimic activity of $$\hbox {CTAB@Fe}₂\hbox {O}₃\hbox { NPs}$$ (w/w 1:1) was higher than that of pristine NPs. However, further increase in CTAB coating (w/w 1:2) resulted in lowering of peroxidase mimic activity. Kinetic analysis was carried out at optimized conditions; maximum velocity ( $$V_{\mathrm{max}})$$ and Michaelis constant ( $$K_{\mathrm{m}})$$ value of $$\hbox {CTAB@Fe}₂\hbox {O}₃\hbox { NPs}$$ at 1:1 w/w ratio were 7.69 mM and $$1.12~\upmu \hbox {mol}~\hbox {s}^-1$$ , respectively.