Effects of crystal structure on the activity of MnO2 nanorods oxidase mimics

The crystal structures would directly affect the physical and chemical properties of the surface of the material, and would thus influence the catalytic activity of the material. alpha-MnO2, beta-MnO2 and gamma-MnO2 nanorods with the same morphology yet different crystal structures were prepared and tested as oxidase mimics using 3,3',5,5'-tetramethylbenzidine (TMB) as the substrate. beta-MnO2 that exhibited the highest activity had a catalytic constant of 83.75 mu mol center dot m(-2)center dot s(-1), 2.7 and 19.0 times of those of alpha-MnO2 and gamma-MnO2 (30.91 and 4.41 mu mol center dot m(-2)center dot s(-1)), respectively. The characterization results showed that there were more surface hydroxyls as well as more Mn4+ on the surface of the beta-MnO2 nanorods. The surface hydroxyls were conducive to the oxidation reaction, while Mn4+ was conducive to the regeneration of surface hydroxyls. The synergistic effect of the two factors significantly improved the activity of beta-MnO2 oxidase mimic. Using beta-MnO2, a beta-MnO2-TMB-GSH system was established to detect the content of glutathione (GSH) rapidly and sensitively by colorimetry. This method had a wide detection range (0.11-45 mu M) and a low detection limit (0.1 mu M), and had been successfully applied to GSH quantification in human serum samples.