Impurity-induced peroxidase mimicry of nanoclay and its potential for the spectrophotometric determination of cholesterol

A green version of the "Fe" impurity-induced peroxidase mimicry exhibited by simple and cheap substrate "nanoclay (NC)" along with the highly sensitive amperometric and spectrophotometric determination of cholesterol is demonstrated. The "Fe" impurity can act as the catalyst center for hydrogen peroxide reduction similar to the horseradish peroxidase (HRP)-catalyzed reaction. The Michaelis-Menten constant for the NC-catalyzed reaction is found to be lower than that of the HRP-catalyzed reaction indicating high affinity for the substrate. The NC-modulated peroxidase-like catalytic activity originates from the electron transfer between the reducing substrate in the catalyst center and H2O2 with the intermediate generation of hydroxyl radicals. The peroxidase mimicry is successfully applied for the low-potential electrochemical detection of H2O2 (linear detection range 1.96-10.71 mM, R-2 = 0.97). The H2O2 sensing platform is further modified with cholesterol oxidase (CHOx) for the spectrophotometric (linear detection range 50-244 mu M, R-2 = 0.99) and amperometric detection of cholesterol (linear detection range 0.099-1.73 mM, R-2 = 0.998).