Peroxidase-like activity of Fe3O4@fatty acid-nanoparticles and their application for the detection of uric acid

Magnetic nanoparticles (MNPs) are used as enzyme mimics owing to the unique properties such as good catalytic activity, high stability and rapid separation. Here, a range of fatty acid (C6–C11) coated Fe3O4 nanoparticles were synthesized, and they possess excellent peroxidase-like catalytic activity, which can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to produce a blue coloration in the presence of hydrogen peroxide (H2O2). The fatty acid coated Fe3O4 nanoparticles can remarkably enhance peroxidase-like activity compared to Fe3O4. The study showed that the appropriate chain length can effectively improve the catalytic efficiency and heptylic acid coated MNPs (Fe3O4@C7 MNPs) showed better peroxidase-like enzyme activity. Based on the steady-state kinetic analysis and Michaelis–Menten model, Fe3O4@C7 MNPs are similar to that of horseradish peroxidase (HRP), indicating their superior affinity for the substrates TMB and H2O2. The peroxidase-like Fe3O4@C7 MNPs catalytic activity was successfully applied for the detection of uric acid (UA) with a limit of detection (LOD) of 2.8 μM. The linear regression equation for uric acid substrate was stated as y = 0.001x + 0.163 with a correlation coefficient of 0.992. The method has the advantages of high sensitivity, good selectivity and cost-effectiveness, and provides an efficient and simple method for the determination of UA concentration in human serum.