Study On Enzymatic Electrode Biosensor For The Detection Of Pesticides

Organophosphorus and carbamate pesticides accounted for a large part in China’s pesticide market.Enzyme inhibition method is a rapid screening detection method for pesticide residues based on the principle that pesticides can inhibit the activity of enzyme.Electrochemical biosensors,with high sensitivity and selectivity and quick response,is suitable for the field test of pesticide.It has a broad application prospect in the field of rapid detection of pesticide residues.In this thesis,the enzymatic electrode biosensor was based on enzyme inhibition method.mainly includes four parts:1)A conductive composite graphite electrode was fabricated by using thick-film technology.The electric catalytic activity of compound electrode was characterized by using cyclic voltammetry in potassium ferricyanide or hydroquinone solution,which shows good electrochemical catalytic properties and high electrode response sensitivity.2)Take adequate amount of Chitosan/acetic acid solution and TCNQ saturated liquid mixture together,then modified on the composite graphite electrode surface by using the drop coating method,enzyme electrode was obtained by modified with acetyl cholinesterase on the composite membrane,then tested in the acetylcholine chloride buffer solution by cyclic voltammetry,the results show that TCNQ can reduce the work potential of enzyme electrode and can get a higher response current at +0.3 6 V.3)Using the orthogonal test to optimize the immobilization conditions of enzyme,the optimum conditions for enzyme immobilization was as follow:glutaraldehyde(5μL 1%);Bovine serum albumin(BSA 5μL 1%);chitosan/TCNQ film layer(12 μl);enzyme amount per electrode(0.8U);temperature for enzyme immobilization(4℃);time for enzyme immobilization(8 h).4)The enzymatic electrode biosensor was constructed by using the method of adsorption-cross linking to fix acetyl cholinesterase,the working conditions of the biosensor were optimized.The modified electrodes have been characterized by using scanning electron microscopy(SEM)and electrochemical impedance spectroscopy(EIS).The biosensor was adopted to detect dursban and carbosulfan and the results exhibited that the responses to both pesticide was sensitive and enzymatic inhibition ratio has a good linear relationship with the logarithm of pesticide concentrations in a certain scope.The detection limit of dursban is 0.2×10-10 lol/L and the detection limit of carbosulfan is 1.0×10-11 mol/L.When the biosensor was used for the actual sample testing,the recovery rate of two kinds of pesticide are between 94-101%.