Development Of Electrochemical Immunoassay For Sulfonamides In Environmental Water

Sulphonamides(SAs),a group of antibacterial drugs with sulfonamide group,have been widely used to treat diseases and protect the health of humans and animals,promote animal growth.However,the overuse of SAs led to the widespread residue of such substances in water environment.That resulted a series of harm to environment,including the death of a large number of beneficial bacteria,and the emergence of drug-resistant strains,disturbance of aquatic ecosystem.SAs furtherly accumulated in the body along the food chain,which would pose health risks.Hence,it is of great significance for investigating the concentration levels of SAs in aquatic environment to establish a simple and sensitive analysis method.Electrochemical immunoassay is a new analytical method based on specific recognition of antibody and antigen and electrochemical conduction technology.For its advantages of simple operation,fast analysis and small sample volume,this method has become an important one for analyzing trace antibiotic in environment media.However,the ordinary electrochemical immunosensors cannot be applied to detecting trace pollutants in the environment.In this study,several nanomaterials,endowed with unique properties,were applied in electrochemical immunosensors.Meanwhile,these electrochemical immunoassays incorporated some unique signal amplification methods,which realized the sensitive analysis of trace SAs in environmental water samples.The main works and results are as follows:(1)A novel competitive electrochemical immunosensor based on Au nanodendrites(Au NDs)/single-walled carbon nanohorns(SWCNHs)@silver nanoparticles(Ag NPs)was established for sensitive determination of SAs in aquatic environments.The indirectly competitive binding system of the approach was composed of coating antigen that coated on Au NDs/glass carbon electrode(GCE),the target and primary antibody(Ab1).When Ab2@SWCNHs@Ag NPs was captured by coating antigen(Cag)-Ab1 complex,massive Ag+will be released from electrode in the presence nitric acid(HNO3).Consequently,the generated Ag+will significantly amplify the electrochemical signal,which would be recorded by the linear sweep voltametry(LSV).Under the optimal conditions,the immunosensor showed a good linear relationship for sulfamethazine(SMZ)ranged in 0.33-63.81 ng/mL with a detection limit of 0.12 ng/mL(LOD,based on 90%inhibition).In addition,the proposed approach exhibited satisfactory accuracy and precision(recoveries,79.25-119.25%;CV,2.14-9.58%),it can be applied for rapid analysis of the trace pollutants from environmental waters.(2)In the detection process of the above research work,we found that the insulation of antibody-secondary antibody conjugate on the surface of electrodes had an effect on the sensitivity,in this method,the signal amplification method was optimized.In this immunoassay,cetyltrimethylammonium bromide-capped gold nanoparticles(CTAB-Au NPs)were used as a signal amplifier and electrode matrix Dendritic fibrous nanosilica functionalized with silver nanoparticle(DFNS@Ag NPs)as labels were used for triggering signal amplification.Under acidic conditions,massive amounts of the Ag+bound to the surface of the Au NPs dissolved,and consequently,formed Ag+@CTAB-AuNP complexes,which resulted in a distinctly improved peroxidase-like activity and enhanced current response.Furthermore,the destroyed Ab1-Ab2-DFNS conjugation greatly decreased the impedance,bringing about the amplification of the electrochemical signals.After optimization of the parameters,the proposed approach exhibited excellent performance,including good sensitivity(LOD,0.0655 ng/mL)and satisfactory accuracy(recoveries,79.02%-118.39%;CV,3.18%-9.82%),which indicates the great potential of this strategy for the rapid detection of trace pollutants in the environments.(3)In this work a dual signal immunosensor based on rGO@CdS QDs and Au NPs was fabricated for quantitative analysis of SAs.CdS QDs is a kind of nanomaterial with electrochemical and photoelectrochemical activity.At wavelength of 460 nm,the sensing interface with rGO@CdS QDs can generate a photocurrent.Meanwhile,the dissolution of Cd2+was converted into electrical signals.The Au NPs,which has good biocompatibility and conductivity,improved electrical signal and photoelectric signal Compared to with signal electrochemical immunosensor,the dual signal immunosensor exhibits low limit of detection(0.124 ng/mL)and wide detection range(1.09-304.94 ng/mL),which provided a model for the construction of electrochemistry-based dual-reading immunosensors.