| With the improvement of people’s living conditions,the public is increasingly concerned about food safety.Whether toxicants and alkaline phosphatase in agricultural products are out of limits are related to the health of people.Traditional detection methods still suffer from some intrinsic disadvantages,such as requirement of expensive and huge instruments,complicated pretreatments of samples,well-trained operators.They are inapplicable for home use and on-site determination.Rapid detection is simple,portable,cost-effective,time-saving,and has great potential for on-site testing.Therefore,we have studied on the detection of organophosphorus pesticides(Opps),heavy metal and alkaline phosphatase(ALP)by the methods of electrochemistry,electrochemical immunoassay and real-time quantitative polymerase chain reaction(PCR).The aim was to optimize and exploit rapid detection methods which have lower test cost,simpler operation and higher sensitivity for the safety of agricultural products.Main contents and results of the research are summarized as follows:(1)A nano-silver/acetylcholinesterase/chitosan electrode used for the rapid detection of Opps has been fabricated.Silver has its internal advantage in detecting thiocholine at low potential without further modification,which improves the selectivity and anti-interference ability through low oxidation potential.The amperometric response of nano-silver electrode to thiocholine was twice of micro-silver electrode according to the comparison of two electrodes.One percent chitosan solution was used as binder to immobilize nano-silver and enzyme,which allowed the electrode to be prepared at room temperature.In order to solve the problem that traditional insulating ink contains organic solvent,the feasibility of chitosan solution used as insulating ink was verified.So,three percent chitosan solution was used as insulating compound to control the effective area of electrode.The limit of detection of paraoxon was 0.014μM using this electrode.Chinese chives and cabbage were used to evaluate this method.The recoveries of standard addition were 105.11 and 96.41%,respectively.The preparation process of electrodes did not require high temperature and organic solvent,which was safe and environmentally friendly.(2)A kind of electrochemical detection of Opps using pralidoxime chloride as a probe was proposed.Pyraloxime generated an oxidation peak around 0.8 V Opps could reduce the peak current of pyraloxime,and did not change the peak potential.Pralidoxime chloride was used as probe according to this principle.Chlorpyrifos was the representative of hydrolytic method.Fenthion was the representative of enzymatic inhibition method.Methyl parathion was the representative of direct redox method.They proved the universality of our method.The limit of detection was 0.018 μm,0.100 μM,and 0.215 μM,respectively.Chinese cabbage,pakchoi and corn were used to evaluate this method.The recoveries of standard addition were 98.9%,101.2%and 105.0%.It was the first time for pralidoxime chloride to be used as an electrochemical probe to test Opps.This method solved problems of narrow applicability by direct redox method,complex operation and poor stability by enzymatic inhibition method and no commercial Opps hydrolase by hydrolytic method.(3)A screen printed electrode modified with carbon nanodots was fabricated for the determination of cadmium content of edible lily.Carbon nanodots were prepared by centrifuging candle soot.Their diameters were about tens of nanometers.The surface structure of modified carbon working electrode was more uniform.When the performance of electrode was characterized,the modified electrode had smaller peak potential difference and larger peak current,which indicated that the modification of carbon nanodots could improve the performance of electrode.The peak current of cadmium were increased using modified electrode by stripping voltammetry.The limit of detection could reach to 0.91μg/L.The recoveries of standard addition were from 99.2%to 100.8%when using the modified electrode to detect the cadmium content of edible lily.Compared with other synthetic methods of nano-particles,the method of centrifuging candle soot was simpler.It could transform combustion emission to useful substances.The carbon nanodots modified electrode could improve the sensitivity of detection.(4)A detection method of ALP based on PCR was designed.Single stranded DNA with phosphate group at 3’end(ssDNA-3’P)was proved to be the substrate of ALP.We designed two different ssDNA-3’P as asymmetric two-template system,which was able to prevent the PCR process without ALP.When there was ALP in the testing system,the amplification process would carry on,and the fluorescence signal could be detected.After the optimization of concentrations of two different ssDNA-3’P,the detection limit of activity of ALP could reach to 0.03 U/L.The positive bands were between 50 bp and 100 bp observed by gel electrophoresis,which were in line with the designed template length of 70 bp.The results indicated that the target products were obtained by amplification.In conclusion,it was the first time for PCR method to be used to detect ALP.It was a very simple method with high sensitivity,and did not need any other probes and nanoparticles.(5)A kind of anti-passivation ink was created to solve the problem that electrode would be passivated by p-nitrophenol in electrochemical immunoassay.The ink consists of graphene,ionic liquid,chitosan and so on.The anti-passivation ink was used to fabricate working electrode.Silver ink was used to make reference electrode and counter electrode.Three percent chitosan solution was used as insulating ink to control the effective area of electrode.The preparation process of electrode did not use any organic solvent.Compared with glass carbon electrode,screen-printed electrode and graphene modified screen-printed electrode,this electrode had superior performance.It could reduce the oxidation potential and increase the response current of p-nitrophenol.The ionic liquid in electrode had the ability of anti-passivation to p-nitrophenol. |
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