Amperometric Cholesterol Biosensor Based On Electropolymerization Of Polypyrrole

Cholesterol, which existing in our blood and being called the total cholesterol as a whole, is the most important steroid in human body. The total cholesterol consists of cholesterol ester and dissociative cholesterol. The desired total plasma cholesterol for an individual is less than 5.2mM (200 mg/dl), and a high level being considered as greater than 6.2mM (240 mg/dl). Cholesterol is routinely measured for the risk assessment of cardiovascular conditions, such as atherosclerosis and hypertension, which can develop into coronary heart disease, myocardial and cerebral infarction (stroke).Electrochemical cholesterol biosensor is mainly based on cholesterol ester, cholesterol oxidase and horseradish peroide. We can use different techniques to immobilize enzymes onto electrode surfaces. Amperometric and potentiometric methods have been researched to determine the level of cholesterol.Recently, there is a considerable attention to amperametric biosensors based on organic conductive polymers. The ability to synthesise conductive electroactive polymers under mild conditions enables to perform the immobilization of a range of biological moieties (enzymes, antibodies, even whole living cells, ect). Polypyrrole and its derivatives play a leading role due to their versatile applicability, high conductivity and good stability. It can be easily formed from aqueous buffered solutions under mildly oxidative conditions and has been widely used for biosensors.This dissertation describes a cholesterol biosensor which is based on screen printed carbon paste electrode. Cholesterol oxidase and horseradish peroxide are immobilized by electropolymerization of polypyrrole. Ferrocyanide works as an eletroactive mediator. Cholesterol (concentration range from Omg/dl to 400mg/dl) is detected by an amperometric method. Reaction principles, modification of electrode surface and enzyme immobilization are discussed. Parameters of electropolymerization and other factors which may influence the response of the biosensor are analyzed.Experimental results indicate that eletropolymerization of polypyrrole can effectively immobilize cholesterol oxidase and horseradish peroxide on carbon paste electrodes. There is a potentical to realize miniature cholesterol biosensors for massive industrial production at low cost.