An ormosil-based peroxide biosensor - a comparative study on direct electron transport from horseradish peroxidase

An ormosil-based peroxide biosensor, based on direct electron transfer from horseradish peroxidase (HRP) encapsulated within ormosil in the presence of peroxide is reported. The HRP is immobilized within two different matrixes: (1) graphite paste electrode and (2) a new organically modified sol-gel glass (ormosil) electrode. The direct electron transfer From these two matrixes has been studied based on cyclic voltammetry and amperometric measurement. In both cases, direct electron transfer takes place between 0.1 and -0.2 V versus Ag/AgCl, however, the direct bioelectrochemical response of HRP is influenced by direct reduction of peroxide even in the absence of HRP at -0.2 V versus Ag/AgCl, whereas, direct bioelectrochemical response of biosensor at 0.05 V versus Ag/AgCl is only the function of enzymatic reaction. The mass transfer kinetics within these two matrixes have been analysed using the data on cyclic voltammograms of soluble ferrocene at the surface of paste and ormosil modified electrodes. The data on peak current versus square root of scan rate shows linear relation and passes through origin while using HRP modified paste electrode, whereas, the same has positive intercept while using ormosil modified peroxide biosensor suggesting well-behaved diffusion limited conditions within paste matrix and poor diffusion kinetics of mass transport within ormosil matrix. The ormosil-based peroxide biosensor is developed using a bilayer of ormosil within which HRP is sandwiched between two layers. The new ormosil matrix with and without encapsulated HRP is analyzed by scanning electron microscopy (SEM). The HRP encapsulated ormosil electrode shows greater than 90% reproducible response for more than 3 months when stored in dry condition at 4 degreesC. The typical calibration curves on the subsequent additions of peroxide of ormosil-based biosensor at 0.05 V versus Ag/AgCl and at -0.2 V versus Ag/AgCl are reported. The various parameters such as inhibition of peroxidase at higher peroxide concentrations, direct reduction of peroxide near -0.2 V versus Ag/AgCl, the kinetics of electron transfer due to direct oxidation of peroxide at 0.7 V versus Ag/AgCl on bare glassy carbon electrode, and direct electron transfer from enzymatically oxidized peroxidase are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.