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 o f peroxide is reported. The HRP is immobilized within two different matrixe s: (1) graphite paste electrode and (2) a new organically modified sol-gel glass (ormosil) electrode. The direct electron transfer From these two matr ixes has been studied based on cyclic voltammetry and amperometric measurem ent. 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 a t -0.2 V versus Ag/AgCl, whereas, direct bioelectrochemical response of bio sensor 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 us ing the data on cyclic voltammograms of soluble ferrocene at the surface of paste and ormosil modified electrodes. The data on peak current versus squ are root of scan rate shows linear relation and passes through origin while using HRP modified paste electrode, whereas, the same has positive interce pt while using ormosil modified peroxide biosensor suggesting well-behaved diffusion limited conditions within paste matrix and poor diffusion kinetic s of mass transport within ormosil matrix. The ormosil-based peroxide biose nsor is developed using a bilayer of ormosil within which HRP is sandwiched between two layers. The new ormosil matrix with and without encapsulated H RP is analyzed by scanning electron microscopy (SEM). The HRP encapsulated ormosil electrode shows greater than 90% reproducible response for more tha n 3 months when stored in dry condition at 4 degreesC. The typical calibrat ion curves on the subsequent additions of peroxide of ormosil-based biosens or 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 conc entrations, direct reduction of peroxide near -0.2 V versus Ag/AgCl, the ki netics of electron transfer due to direct oxidation of peroxide at 0.7 V ve rsus Ag/AgCl on bare glassy carbon electrode, and direct electron transfer from enzymatically oxidized peroxidase are discussed. (C) 2001 Elsevier Sci ence B.V. All rights reserved.