| Fenitrothion,with chemical name O,O-dimethyl O-（3-methyl-4-nitrophenyl）phosphorothioate,is a kind of organophosphorus pesticides,with contact action and stomach poison effects and broad insecticidal spectrum.Fenitrothion has special effects to the larva of pink rice borer,striped rice borer,yellow rice borer and rice leaf roller,as well as the coleopera and the hemiptera insects.Its mechanism of action is inhibition of the activity of acetylcholinesterase,resulting in plenty of acetylcholine accumulate at the synapse,leading to the overactivity of acetylcholine receptors on postsynaptic membrane,and a long period of excited time for the postsynaptic nerve fibers,while the nerve impulses in the synapse is blocked.Poisoned insects will be paralyzed and dead after being excited and spasmodic.1-（6-chloro-3-pyridylmethyl）-N-nitromidazolidin-2-ylideneamine,chemical name of imidacloprid,is one kind of chloronicotinyl insecticide,with multiple functions such as contact action,stomach toxicity and systemic action,aiming at homoptera insects like aphid,leafhopper,planthopper and thysanoptera insects such as thrip.Imidacloprid is the first chloronicotinyl insecticide acting on the nicotinic acetylcholine receptors with fast-acting property and a long longevity of residue.The residue problems arising from the unreasonable use of fenitrothion and imidacloprid need to be solved by establishing a rapid detection method to ensure environmental safety and human health.Currently reported pesticide detection methods mainly are gas chromatography（GC）,gas chromatography-mass spectrometry（GC-MS）,high performance liquid chromatography（HPLC）and liquid chromatography-mass spectrometry（HPLC-MS）.As traditional detection methods,these methods can detect the residual pesticide in agricultural products effectively,but they also need time-consuming sample pretreatment,high cost,large instruments,professional operators and maintenance personnel,making they unsuitable for on-site test,while electrochemical detection technology and immunochromatography strip can make up the defects of above-metioned technologies to meet the requirements of on-site rapid detection.On this research,we established an novel electrochemical detection method for fenitrothion,the concrete steps were as follows:with the dry and clean glassy carbon electrode modified by graphene oxide dispersion,we used square wave voltammetry to scan the potential range from 0.2 V to 1.0 V,which showed the irreversible reduction peaks,after accumulation time of 120s by time-current cerve,then accumulated for another 240s to scan from-0.6 V to 0.3 V to show the reversible oxidation peak.We quantify the content of fenitrothion by the oxidation peak current ultimately.During the experiment,there are two steps for accumulation,thus we named this method as a two-step accumulation way.This method has a linear range from 1 ng·mL-1 to 400 ng·mL-I,and the linear equation is ipa（μA）= 0.133 c(ng·mL-1)+ 0.953（R2 = 0.999）,with a detection limit of 0.1 ng·mL-1（S/N = 3）.We also established another method which was scanning the reversible oxidation peak directly after a period of accumulation time according to other researchers.To distinguish the method we described before,we call it one-step way in this article.This method has a linear range from 50 ng·mL-1-1600 ng·mL-1,and the linear equation is ipa（μA）= 0.002 c(ng·mL-1)+ 0.037（R2 = 0.997）,with a detection limit of 40 ng·mL-1（S/N=3）。Comparing two methods,it turned out that the two-step accumulation way we established do have a stronger detection signal and a higher sensitivity.On the basis of this electrochemical detection method we established,we did some research about immunochromatography strip to capture fenitrothion specificly.The concrete steps were as follows:coating a certain amount of fenitrothion antibody on the strip and drying by vacuum oven,preparing a certain concentration of standard solution to pipet on sample pad,after specificity binding of antibody and antigen by chromatography,washing redundant fenitrothion with washing buffer and dissociating the antigen-antibody complex with acidic buffer,and detecting by electrochemical workstation finally.In this part we mainly optimized the parameters such as suitable NC membrane for assembling the immunochromatography strip,reaction buffer concentration and washing beffer concentration in this non-cpmpete immunoreaction system.We also explored the electrochemical signal of imidacloprid,optimized some parameters of the immunochromatography strip for the detection of imidacloprid which was established by Dr Fang Qingkui,including working buffer pH and salt ionic strength.There is a prospect for combination of two methods to detect imidacloprid. |
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