Determination Of Methyl Parathion In Soil And Water Samples Based On New Electrochemical Sensors

Pesticides play an important role in the high productivity achieved in agriculture throughthe control of pests. However, pesticides are intentionally toxic, and the presence of pesticideresidues in food, water, and soil has become a major issue in environmental chemistry.Worldwide, organophosphorus pesticides （OPs） compounds account for over38%of thetotal pesticides used. Their toxicity is based on the inhibition of acetylcholinesterase （AChE,EC3.1.1.7）, which is essential for the functioning of the centralnervous system of humansand insects. This results in the accumulation of the acetylcholine neurotransmitter, whichinterferes with muscular responses and causes respiratory and myocardial malfunctions andeven death. As a result, effective monitoring of OPs in the environment is very desirable.Among many analysis methods, electrochemical analysis has been confirmed as one of themost promising method for pesticide measurement by virtue of its simplicity, rapidity, highsensitivity and versatility. In this paper, four different electrochemical sensors were fabricatedbased on new nanomaterials and their applications in OPs determination were investigated.The main contents could be divided into four aspects as follow:（1） A sensitive acetylcholinesterase biosensor was fabricated based on dual-signalamplification. A large amount of enzyme was immobilized on a glassy carbon electrode viaspecific binding between functionalized ZnSe quantum dots and acetylcholinesterase, and agraphene-chitosan nanocomposite was introduced as electrode modifier that improvesresponse. These two factors render the biosensor highly sensitive to acetylthiocholine chloride.Organophosphate pesticides were detected with this biosensor using methyl parathion as amodel enzyme inhibitor. Under optimal conditions, there is a linear relationship between thepercentage of inhibition（I%）and the log of the concentration of methyl parathion in the0.5nM to0.5μM range, with a0.2nM detection limit （at an S/N of3）. The biosensor displaysacceptable reproducibility and relatively good storage stability. It was successfully employedto the determination of methyl parathion in spiked water and soil samples.（2） A novel method was proposed for ultra-trace detection of pesticides combining electrochemical reduction of Ellman′s reagent （DTNB） with AChE inhibition. Theamperometric biosensor, fabricated by immobilizing AChE on multi-walled carbonnanotubes-chitosan （MWCNTs-Chi） nanocomposites modified glassy carbon electrode,enjoyed high sensitivity owing to the excellent conductivity and favorable biocompatibility ofMWCNTs-Chi nanocomposites. Meanwhile, the sensitivity of the biosensor was furtherenhanced using the electrochemical reduction signal of DTNB for determination. Underoptimum conditions, methyl parathion was detected based on its inhibition effect on AChEactivity and the subsequent change in electrochemical reduction response of DTNB. Goodrelationship was obtained between the reduction current and pesticide concentration in theranges of5.0×10^-7-1.0×10^-12M with a detection limit of7.5×10^-13M （S/N=3）. Moreover,the proposed protocol was successfully employed for the determination of methyl parathion inspiked water and soil samples.（3） A novel multi-walled carbon nanotubes-CeO₂-Au nanocomposite（MWCNTs-CeO₂-Au） was synthesized by a facile two-step precipitation method and usedfor solid-phase extraction of methyl parathion （MP）. The MWCNTs-CeO₂-Aunanocomposite combined the individual properties of MWCNTs （high conductivity andexceptional adsorption affinity） and nanoparticles （high surface area and special catalyticactivity）, and realized the efficient enrichment and electrochemical stripping voltammetricdetection of MP. An ultra-low detection limit of7.5×10^-11M （S/N=3） for MP wasobtained at MWCNTs-CeO₂-Au nanocomposite modified electrode, suggesting the highsensitivity of the nanocomposite based electrochemical sensor. Moreover, the proposedelectrochemical sensor was successfully employed for the determination of MP in water andsoil samples.（4） With the assistance of ultrasound, graphene quantum dots （GQDs） weresuccessfully prepared via cleaving graphene oxide under acid conditions and werecharacterized by TEM and FT-IR. Then, a novel OPs electrochemistry sensor was fabricatedby electro-polymerization melamine film onto GODs modified glassy carbon electrode（PAM/GODs/GCE）. A large amount of MP was absorbed on the electrode surface via thestatic electricity and hydrogen bonds between PAM film and MP molecules. GQDs wereintroduced as electrode modifier that improves the electrode response. In addition, sensitivityof the sensor was further enhanced by the catalytic action of PAM and GODs towards theelectrochemistry reduction of MP. Under optimum conditions, good relationship was obtained between the reduction current and pesticide concentration in the ranges of0.1nM to50nm,with a detection limit of0.06nM （S/N=3）. Moreover, the proposed protocol wassuccessfully employed for the determination of MP in spiked water and soil samples.