Establishment Of Electrochemical Immunoassay For Sulfadimethoxine

Sulfonamides(SAs)are commonly used for the prevention of bacterial infectious diseases,and could be used as feed additives in animal breeding.However,excessively using of SAs potentially threaten the health of humans,such as leading to the allergic reaction,and even inducing teratogenic and carcinogenic.Among SAs,sulfadimethoxine(SDM)occupies a large proportion in practical application,thus,the the development of a convenient and sensitive detection method against SDM residues in animal derived products is of great importance.The electrochemical immunoassay,based on the use of nanocomposites materials,possess the character of high sensitivity.Besides,the electrochemical immunoassay method based on the use of Ag-GO nanocomposites has not been used in the detection of SDM residues.Therefore,in this study,a rapid and sensitive electrochemical immunosensor analyzing method was established based on Ag-GO nanocomposites to determine the residues of SDM.In present study,silver nitrate(AgNO3)was reduced onto graphene oxide layer by glucose in-situ green reduction method.The Ag-GO nanocomposite was obtained by dispersing the silver nanoparticles and destroying the ordered structure of the GO film layer.The obtained Ag-GO nanocomposites were characterized by scanning electron microscopy(SEM).It can be seen that silver nanoparticles were evenly distributed on the GO layer;The crystal structure was characterized by X-ray diffraction(XRD),which showed that the synthesized silver nanoparticles had the typical diffraction peak of crystal silver.The above characterization techniques proved that the Ag-GO nanocomposite material was successfully synthesized in this study,which can be used to prepare the electrochemical immunosensor.During the preparation of electrochemical immunosensor,Ag-GO-Nf modified materials were obtained by dispersing Ag-GO nanocomposites were using Nafion solution(Nf).Followed by adding Ag-GO-Nf on the surface of gold electrode.Gold nanoparticles(AuNP s)were further deposited on the modified electrode in chloro auric acid solution by potentiostatic deposition method.Specific antibodies were conjunct to modified electrode by Au-N bond,the unbound active siteswas used to block by bovine serum albumin(BSA).Finally,the sample solutions were dripped on modified electrode for testing.The assembly of the electrochemical immunosensor was characterized using cyclic voltammetry and atomic force microscopy.The responses of the electrochemical immunosensor to SDM was studied by differential pulse voltammetry.As a result,the linear detection scale of this established SDM immunosensor ranged from 333 pg mL-1 to 100 ng mL-1 and exhibited a good linear relationship between electric current and the logarithm value of SDM concentration.The linear equation was I=18.46 log(CsDM/ng mL-1)-413.9 with the linear correlation coefficient R as 0.9928.The minimum limit of detection(LOD)was 4 pg mL-1(S/N=3),the minimum limit of quantitation(LOQ)was 13.33 pg mL-1(S/N=10).Moreover,the selectivity,stability and reproducibility of the prepared immunosensor were analyzed and tested,which revealed a good selectivity,high stability and reproducibility.Then the accuracy of this method was tested by the recovery experiment,which showed that the recoveries were 90.69%～111.10%and the relative standard deviation(RSD)was less than 13.75%,indicating that the immunosensor had high accuracy.HPLC was used for the comparative test,and the accuracy of the established electrochemical immunoassay was determined by comparing the results of standard addition recovery test with HPLC.The SDM concentrations span froml ng mL-1 to 500 ng mL-1 when tested by HPLC.The linear relationship was Y=54.55X+41.85 with the linear correlation coefficient R2 as 0.9998.The LOD was 1 ng mL-1(S/N=3),the LOQ was 3.33 ng mL-1(S/N=10).The recovery proportion of standard addition recovery test were 90.00%～96.40%,with the RSD less than 13.75%.The above comparative analyzed information indicate that the established electrochemical immunoassay method had a good accuracy.In conclusion,a label free electrochemical immunosensorwas successfully established in this study based on Ag-GO nanocomposites and gold nanoparticles to determine the SDM residues in animal derived foods.This established sensor revealed a wide detection range and low detection limit,and show a high accuracy in actual sample detection.