| The pesticides which are available not only for crop protection, but also enhances the agricultural output. However, the extensive use of organophosphorus pesticides in agriculture has raised serious problem the environment and food safety. Pesticides are toxic compounds, which have been result in for many ecological problems and damages to human health. Organophosphate (OP) pesticides are widely used in agriculture due to their high toxicity to insects and limited persistence in the environment. The existing in the environment is very harmful for human health as they irreversibly inhibit the catalytic active sites of acetylcholinesterase (ACHE), which catalyses the hydrolysis of neurotransmitter acetylcholine. Among these methods reported for pesticides detection, such as high performance liquid chromatography (HPLC) and gas chromatography (GC) or coupled techniques such as GC-MS are often used as reference methods. Although these high sensitivities, these techniques are expensive, time-consuming and require highly trained personnel. Furthermore, they are not adapted for in situ and real time detection of pollutants. In addition, they are not able to give any information concerning the toxicity of the sample. Therefore, the rapid, highly sensitive, selective, and powerful methods for pesticides is essential that has the important practical significance to the environmental protection and food security.Electrochemical Biosensor combines the analytical power of electrochemical techniques with the specificity of biological recognition processes. It can convert the concentration of an analyte into an electrical signal. For this purpose, a biospecific reagent is either immobilized or retained at a suitable electrode, which converts the biological recognition event into a quantitative amperometric or potentiometric response. Electrochemical Biosensor is an ideal analytical apparatus for in situ analysis due to its high sensitivity, simple sample treatment, inexpensive instrument, and easily operation procedure. Therefore the study of Electrochemical Biosensor has attracted increasing attention.This thesis includes in the followings three chapters. In Chapter 1, the principle, types of electrochemical biosensors, immobilization methods of enzymes were presented and applications of disposable electrochemical biosensors for the determination of organophosphorus pesticide were reviewed.In Chapter 2, a novel amperometric biosensor for the determination of organophosphorus pesticides has been fabricated with acetylcholinesterase (ACHE) immobilized by gold nanoparticals and chitosan/silica sol-gel organic-inorganic hybrid composite film on the surface of the prussian blue modified glassy carbon electrode. The experiments proved that the gold nanoparticals could enhance the current response to paroxon and prussian blue could induce reduce overpotential of thioncholine. Under the optimized conditions, the response of the biosensor fabricated was related linearly to concentration of paraoxon in the range from 5.0×10-8 to 5.0×10-5 g/L at+0.20V(vs. SCE) with a detection limit of 2.0×10-8 g/L.In Chapter 3, a novel disposable organophosphorus electrochemical biosensor has been developed. A highly sensitive electrochemical biosensor for the determination of malathion was fabricated at a screen-printed electrode modified with acetylcholinesterase. The biosensor can reduce overpotential of thioncholine and enhance the examination selectivity and sensitivity with ferrocenemonocarboxylic acid as the electronic mediator. Acetylcholinesterase was immobilized by crossing linking glutaric dialdehyde combined with Nafion to screen printed electrode. It exhibits the merits the high sensitivity, relative small volume and low cost of equipment, the enzyme film stabilizes no easy to remove, measure current stability and the preparation simplicity, its suitability for on-line and in-situ, and so on by compare with the solid electrode. Under the optimized conditions, the response of the electrochemical biosensor fabricated was related linearly to concentration of malathion in the range from 5.0×10-7 to 2.0×10-5 g/L and with a detection limit of 1.2×10-7 g/L. |
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