Bioelectrochemical characteristics of cholesterol oxidase immobilized in apolyaniline film

Cholesterol oxidase has been immobilized in polyaniline film by the electro chemical doping method. The measurements of the response current are carrie d out in the solutions containing cholesterol and Triton X-100 of 5% and 1% , respectively. The latter is necessary for solubilizing cholesterol. The r esponse current of the polyaniline cholesterol oxidase electrode increases with increasing potential from 0.35 to 0.60 V (vs. SCE). A maximum response current occurs at 0.60 V, which is independent of the concentration of Tri ton X-100. The response current of the enzyme electrode at TritbnX-100 of 1 % is about twice as high as that at Triton X-100 of 5%; The optimum pH and the optimum temperature of the immobilized cholesterol oxidase are 7.26 and 35 degrees C, respectively. The activation energy of the enzyme-catalyzed reaction is 71.1 kJ mol(-1) at Triton X-100 of 5% and 67.4 kJ mol(-1) at Tr iton X-100 of 1%. The apparent Michaelis-Menten constant K-m' is 2.72 mmol dm(-3) at 0.45 V and 3.26 mmol dm-3 at 0.60 V for Triton X-100 of 5%, and 0 .51 mmol dm(-3) at 0.45 V and 0.56 mmol dm(-3) at 0.60 V for Triton X-100 o f 1%. The response current of the enzyme electrode increases linearly with increasing concentration of cholesterol in the range 0.05-0.5 mmol dm(-3) a t 0.45 V and 0.05 to 0.2 mmol dm(-3) at 0.60 V for Triton X-100 of 5%, and 0.01 to 0.1 mmol dm(-3) at both potentials of 0.45 and 0.60 V for Triton X- 100 of 1%. The response current of the enzyme electrode drops to 51% of its initial value after 11 days. During this period, this enzyme electrode is employed to determine the substrate solved in Triton X-100 of 1% at differe nt conditions for 230 times. Thus, the polyaniline cholesterol oxidase elec trode can be used to determine cholesterol concentration. (C) 1999 Elsevier Science S.A. All rights reserved.