Study On Homogeneous Electrochemical Methods For The Determination Of Food Contaminants

Food safety has always been regarded as a national public safety problem.In recent years,a variety of food safety problems are endless and be a serious threat to people's health.Electrochemical methods,with a simple instrument,high sensitivity,high selectivity,has been widespread concern.However,the traditional electrochemical methods generally require the complex process of electrode modification and the reproducibility is poor.Therefore,in this paper,the ITO electrode surface with negative charge combined with signal amplification technology,makes it possible to construct a homogeneous electrochemical detection method.It has been applied to the analysis of the food contaminations.The specific contents in the thesis are as follows:In the first chapter,the paper introduced the characteristics and the related application of the electrochemical methods.The modification of traditional electrochemical methods and the homogeneous electrochemical methods were also summarized in this paper.In the second chapter,a homogeneous electrochemical method based on target triggered aptamer hairpin switch and Exonuclease-assisted recycling amplification to detect Ochratoxin A was developed.The metastable hairpin probe(OTA-Hp)was designed which contained the aptamer of OTA.The DNA probe with a methylene blue tag at its 3' terminus(MB-DNA)was designed to be complementary with OTA-Hp.Introduction of OTA into the assay leads to the formation change of OTA-HP from hairpin shape to open form and the hybridization with MB-DNA.The electrochemical signal is amplified through continuous Exo ? cleavage.Under the optimal conditions,the differential pulse voltammetric(DPV)response had a linear relationship with the logarithm of OTA concentration in the range of 1 pg/mL?0.5 ng/mL and the detection limit was 0.58 pg/mL.The detection method was applied to the detection of OTA in wheat quality control samples.In the third chapter,a simple,sensitive,and selective homogeneous electrochemical method for melamine based on DNA triplex structure and Exonuclease ?-assisted recycling amplificationn was designed.The assay combines the advantage of the high selectivity of the DNA triplex structure containing an Abasic site(AP site)to melamine and high efficiency of exonuclease(Exo)?-assisted recycling amplification.T1,T2,poly[dA]probe containing an AP site(8A),and methylene blue-labeled DNA probe(dMB probe)were carefully designed.Melamine can specifically locate in the AP site through hydrogen bonding interaction between thymine and melamine to make T1,T2,and 8A close to each other,therefore forming a stable T-melamine-T DNA triplex structure.Under the optimal conditions,the DPV response had a linear relationship with the logarithm of melamine concentration in the range of 1 nM?0.5 ?M.The developed method has been successfully applied to detect the milk and the migration of melamine from melamine bowl.In the fourth chapter,a homogeneous electrochemical method based on T-Hg2+-T structure was designed to detect mercury ions in tap water samples.This method utilizes T-Hg2+-T structure specific binding to form double-stranded DNA,and Exo ?specifically recognizes the cleavage of double-stranded structure to release the methylene blue DNA signal molecule,resulting in MB-MF with a small amount of negative charge.At the same time,the release of the target mercury ions can also continue to induce new hybridization and produce a large number of MB-MF.MB-MF can be easily close to the negatively charged ITO electrode surface,producing a significant current signal.Under the optimal conditions,the DPV response had a linear relationship with the logarithm of Hg2+ concentration in the range of linear range of 1.0 nM?500 nM and the detection limit was 0.38 nM.