Study Of Cholesterol Biosensor

Cholesterol existing in our blood, which is the most important steroid in human body and be called total cholesterol as a whole, consists of cholesterol ester and dissociative cholesterol. Normal human blood serum contains 120—260mg/dl (3.1 — 6.7mM) cholesterol. Current medical research indicates that there is a strong positive correlation between high serum cholesterol level and arteriosclerosis, hypertension and myocardial infarction. So the determination of cholesterol is important for clinical diagnosis.This work of this dissertation is a part of the 863 program of China. The aim is to develop a portable and easily operational full blood cholesterol biosensor. The biosensor we designed used carbon paste as electrodes. Enzymes were immobilized on the surface of electrodes through special bio-immobile technology. The biosensor can rapidly detect cholesterol using 2ul whole blood. We investigate the effect of manufacture procedure and testing condition on sensor performance. Experimental results indicate that the most suitable working voltage applied on working electrode is 300mV, and the response time is 180 sec. In the range of 100—400mg/dl, the sensor has a good linearity, sensitivity, reasonable repetition and conservation time. The sensor is relatively cheap and easy to use so that it is suitable for mass product for clinic screen and family use.Carbon nanotube is a kind of novel nano-material. It has a wide application in biosensor because of the special physical and chemical property and the high surface area possessing abundant acidic sites. The carbon nanotube modified carbon paste electrode has more effective electrode surface, which is propitious to the immobilization of enzyme, promotes electron transfer to enhance the response current. The linear range and sensitivity have been improved. We construct the theoretical model to explain this result for future research.As one of the most used conducting polymer, polypyrrole is applied in biosensors extensively. In this dissertation, the conditions of the preparation of polypyrrole-cholesterol oxidase electrode were also discussed. The cholesterol oxidase could be immobilized in the polypyrrole membrane when the pyrrole is polymerized on the electrode. In the experiments, the concentration of pyrrole, the concentration of enzyme, the pH of buffer solution and the electric charge significantly effect on the preparation of the electrode. Our experimental results show that the response of polypyrrole-cholesterol oxidase electrode operates optimally when the enzyme concentration is 16mg/ml, the pyrrole concentration is 0.5M, the LiClO₄ concentration is 0.5M, the pH of buffer solution is 8.0, the polymerization potential is 0.9V(vs. Ag/AgCl) and the polymerization charge is 3.5mC.