| Organophosphorus compounds(OPs) and carbamate are widely used as pesticides, insecticides and chemical warfare agents.These compounds affect the nervous system by inhibiting acetylcholinesterase(AChE) function of regulating the neurotransmitter acetylcholine.Traditionally,the widely used methods for determination of organophosphorus pesticides are liquid/gas chromatography,mass chromatography and Spectroscopy,these methods are sensitive and allow discrimination among different organophosphorus compounds but they are expensive and require a long time not to satisfy the need of fast detection.Meanwhile,immunoassay and biosensor are sensitive and fast.As a comparison,biosensor based on enzyme inhibition technique provided a promising way to detect organophosphorus pesticides which was both rapid and simple. With this method a mass of samples could be detected quickly and no expensive instruments.So we placed emphasis on studying of biosensor based on carbon nanotubes(CNTS) and enzyme,the carbon nanotubes is as a directly immobolilization material of AChE.So the biosensor have good stability and sensitivity.1.A three-electrode analysis system linked to CHI800 electrochemical analyzer was used as a detection system,before pretreating and electrochemical activation process, CNTS pioneer layer was electroposited at 1.70V for 2h,the modified electrode showed a good character in detection of[Fe(CN)6]3-/[Fe(CN)6]4-,which paved the way of the detection of thiocholine(TCh) and seldom provided in references.2.Because the detection of pesticides residue was based on the detection of TCh, electrochemical properties of thiocholine were studied carefully,the concentration of TCh was determined by Ellman method and electrochemical technique and the same results was given,and the peak current has good linearity with concentration of TCh.So this results tell us the electrochemical technique is reliable and intensive. 3.According to the electrochemical properties of Tch,modification technique of multi-walled carbon nanotubes(MWNTs) towards glass carbon electrode(GCE) was studied,firstly,MWNTs was functionized to be good dispersion,biocompatible, anti-fouling and good electroactalatical.Then drop method and a controllable layer-by-layer(LBL) self-assembly modification technique of multi-walled carbon nanotubes(MWNTs) towards glass carbon electrode(GCE) was studied,by LBL, the bilayer membranes of PDDA and MWNTs,which were fabricated by alternate immersion of GCE in 1.0%poly(diallyldimethylammonium chloride)(PDDA) solution and 1mg·L-1MWNTs dispersed in pH 9.18 borate buffer solution for 15 minutes either,were self-assembled to GCE after two hours' electro-deposition of MWNTs at the voltage of 1.70 V.The modified GCE with five self-assembled {PDDA/MWNTs}n bilayers showed good sensitivity,stability,and high reproducibility towards the detection of 5×10-3mol·L-1 TCh.In comparison with bare GCE,the obtained oxidative potential decreased from 0.65V to 0.35V,and the peak current value increased by almost 100 percent,the peak current also has good linearity with concentration of TCh.Meanwhile,the modified GCE showed a low even lower oxidative potential of 0.30 V,the detection limit of less than 7.500×10-7 mol·L-1 with current-time techniques.4.Direct immobilization methods of AChE to MWNTs were also studied and make a comparasion to enzyme immobilization to membrane,the direct immobilization of AChE to modified electrode was finished by LBL self-assembly technique in PDDA solution and AChE solution,the activity of AChE was 0.010U,it is stable and repeatable,the changes of current response in the obstained biosensor has good linearity with enzyme inhibition rates,so pesticides residue can be detected by this biosensor practically and intensively.5.There is a good linearity of enzyme inhibition rate and -lg value of concentration of both the organophosphorus compounds(methamidophos and dichlorvos) and carbamates pesticides(carbaryl and carbofuran) in the range of 10-10-10-7g·L-1.In the detection of water samples with pesticides concentration of 10-8g·L-1 of carbaryl, carbofuran,methamidophos and dichlorvos,the average recoveries are 108%,124%, 130%and 112%separately.So the enzyme sensor may have a good use in the rapid detection of organophosphorus and carbamates pesticides.
|
PDF Full Text Request