Facile synthesis of iridium nanoparticles with superior peroxidase-like activity for colorimetric determination of H2O2 and xanthine

A facile and efficient method was developed for the preparation of iridium nanoparticles (Ir NPs) with superior peroxidase-like activity. Under the catalytic action of the Ir NPs, the peroxidase substrate 3,3,5,5-tetramathylbenzidine (TMB) can be oxidized by H 2 O 2 to form a blue-colored production oxTMB. Kinetic analysis indicated that the catalytic behavior was in accordance with the typical Michaelis-Menten kinetics and the catalytic reaction followed the ping-pang mechanism. Electron Spin Resonance (ESR) experiment showed that no hydroxyl radical formed in the reaction process. Peroxide substrates with different electron withdrawing ability (benzoyl peroxide, H 2 O 2 and artemisinin) were used to study the catalytic reactions and results indicated that H 2 O 2 can oxidize TMB with much faster rate than artemisinin and slower rate than benzoyl peroxide. These results suggest an electron transfer mechanism was involved in the system of TMB-H 2 O 2 -Ir NPs. By using TMB as the colorimetric substrate, H 2 O 2 can be rapidly determined and the method was extended for the determination of xanthine based on its production of H 2 O 2 in the presence of xanthine oxidase. The prepared Ir NPs exhibit good stability in wide range of pH and temperature. The Ir NPs retained at least 90% of their initial catalytic activity after stored at ambient temperature for three months. The high specificity for H 2 O 2 and the excellent stability of the peroxidase-like Ir NPs showed the great application potential in biotechnology field.