A REDOX-ACTIVE POLYMER FILM MEDIATED ENZYME ELECTRODE FOR AMPEROMETRIC DETERMINATION OF FREE-CHOLESTEROL

A new amperometric sensor for determination of free cholesterol based on a bilayer-film coating has been fabricated and its sensor characteristics have been examined by cyclic voltammetry and under steady-state conditions. The electrode substrate was coated with two kinds of polymeric films in a bilayer state, i.e., first with the redox-active cobalt tetrakis(omicron-aminophenyl)prophyrin polymer (poly-CoTAPP), and then with the enzyme film consisting of bovine serum albumin and cholesterol oxidase (CHOx). In this sensor system for assay of free cholesterol, oxygen consumption could be monitored by measuring the current for oxygen reduction electrocatalyzed by the inner poly-CoTAPP film according to the following reaction sequence: [GRAPHICS] where reactions 1, 2, and 3 correspond to the cholesterol-cholesterol oxidase enzymatic reaction, the electrocatalytic reduction of O2 by the poly-CoTAPP film, and the electrode reaction of Co(III/II)TAPP couple in the poly-CoTAPP film, respectively. The reproducible relationship between concentration of free cholesterol and sensor output was obtained. The sensitivity and the dynamic range were found to depend on the amount of CHOx confined in the enzyme film.