Abstract: Anew amperometric sensor for free cholesterol has been fabricated based on a high electrocatalytic activity of cobalt protoporphyrin to the oxidation of H₂O₂.Alayer of cobalt pro-toporphyrin was absorbed on the glassy carbon electrode, the enzyme film consisting of bovine serum albumin and cholesterol oxidase was put on it, then a layer of poly(ο-phenylenediamine) film was electropolymerized out of the enzyme film to avoid interference and fouling.The linear range of concentration was 0.1 mmol/L -2 mmol/L.The response time was less than 30 s.The electrode was used for 150 times assays without loss of any enzymatic activity.

Key words: Cobalt protoporphyrin, Modified electrode, Cholesterol oxidase