The Impact of Pesticides - Academy Publish

Wang, 2010) and tetracyanoquinodimethane (Martorell et al, 1997) have been usedto reduce the overvoltage of oxidation and enhance the sensitivity of the detection.The ideal biosensor fabrication method should employ mild chemical conditions,allow for large quantities of enzyme to be immobilized, provide a favorablemicroenvironment to maintain the enzyme activity, and provide a large surface areafor enzyme-substrate contact within a small total volume. Barriers to mass transportof substrate and product should be minimized, and a chemically and mechanicallyrobust system should be provided.Joshi et al (2005) demonstrated a low cost disposable biosensor for the sensitivedetection of OP pesticides by using CNTs. A film of acid functionalized MWCNTwas cast on the surface of the screen-printed electrode by drop drying. Then AChEwas immobilized on the CNT film by dropping 10 µL of AChE solution and dryingat room temperature under a current of air and the electrode was carefully washedwith buffer to remove loosely adsorbed enzyme molecules and bonded CNTs. Todetermine relative inhibition, the AChE-functionalized MWCNT-SPE electrode wasimmersed in a cell containing 2 mL of pH 7.4, 50 mM phosphate buffer with 0.1 MKCl under constant stirring. The potential was poised at 200 mV (vs. Ag/AgCl).After current stabilization, acetylthiocholine iodide substrate was added to a finalconcentration of 1.75 mM. This value of current corresponded to I 0 , the currentbefore inhibition. A known concentration of paraoxon was then dropped on to theelectrode and incubated for 30 minutes. After incubation, the electrode was washedwith the buffer and the response was measured again as described above, thissecond value corresponded to I i , the current after inhibition. The relative inhibition(RI, %) was determined according to the following formula: RI (%) = [(I 0 -I i )/I 0 ]*100 and then related to the inhibitor concentration. The biosensor detected aslow as 0.5 nM (0.145 ppb) of the paraoxon with good precision, electrode toelectrode reproducibility and stability.Upadhyay et al (2009) have proposed a sensitive amperometric biosensor by usinggold–platinum bimetallic nanoparticles modified glassy carbon electrode for thesensitive detection of organophosphate pesticides, carbamates and nerve agent. TheOP pesticide (paraoxon ethyl), carbamate (aldicarb) and nerve agent (sarin) weredetected by utilizing the unique properties of Au–Pt bimetallic NPs, by using thebienzyme (AChE and ChOx) approach .This novel system has been developed byelectrodeposition of the Au–Pt bimetallic NPs on the 3-aminopropyltriethoxy silane(3-APTES) modified glassy carbon (GC) electrode. Then AChE and ChOx arecoimmobilized on the Au–PtNPs modified electrode by cross-linking enzymes and3-APTES through glutaraldehyde. In this bienzyme system, AChE rapidlyhydrolyzes acetylcholine into acetate and choline. The choline is subsequentlyoxidized by ChOx and H 2 O 2 is produced, and finally H 2 O 2 is detectedamperometrically. By using this method paraoxon ethyl, sarin, and aldicarb could bedetected up to 150–200 nM, 40–50 nM, and 40–60 µM respectively at 30–40%inhibition level of AChE enzyme and followed linearity in wide range concentration.AcademyPublish.org - The Impact of Pesticides402