| In recent years,food safety issues have become the focus of attention including veterinary drug residues,pesticide residues,the addition of prohibited compounds,and pathogens pollution problems.At the same time,food safety testing technology has also been the community’s general concern.Lateral flow assay(LFA)based on antigen-antibody specific reaction is sensitive,rapid,high-throughput,low-cost,and suitable for on-site screening when compared to the conventional instrument detection methods.Early LFA can only acquire qualitative or semi-quantitative detection result by naked eye observation.With the development of optical detection equipment,LFA combined with portable optical reader can achieve high sensitivity quantitative detection.Some new nanoparticles with unique light absorption or fluorescence spectral properties as labels can also be used in LFA to improve detection sensitivity or reduce the limit of detection.LFA has become an important means of food safety testing.In the second chapter,a method for the quantitative detection of florfenicol by colloidal gold lateral flow immunoassay was developed.Five parameters including pH value in the process of conjugation between the colloidal gold and antibody,the amount of the immunogold,concentration of the antigen on T line,and detection time were optimized.With a colloidal gold strip reader,the signal intensity of T line and C line on lateral flow strips was recorded.The AT/AC ratio of negative control and positive samples were defined as B0 and BX,and the standard curve was established by plotting the BX/B0 ratio against the concentration of florfenicol.This assay showed a good linear range from 0.1 to 1.5 ng/mL with the limit of detection of 0.08 ng/mL,while the result could be obtained within 15 min.It was a convenient,rapid and quantitative method which could be used for screening a large batch of samples on site.In the third chapter,we study the effect of different labels on the sensitivity of lateral flow assay.Time-resolved fluorescent nanobeads,fluorescent microspheres,quantum dots,and colloidal gold-based lateral flow assay(TRFN-LFA,FM-LFA,QD-LFA,and CG-LFA)were first systematically compared for the quantitative detection of ractopamine in swine urine based on competitive format.The optimal process parameters of the four LFAs were determined.The limits of detection(LOD)of TRFN-LFA,FM-LFA,QD-LFA,and CG-LFA were 7.2,14.7,23.6,and 40.1 pg/mL in swine urine samples,respectively.The sensitivity of TRFN-LFA was highest.In the quantitative determination of ractopamine(RAC)in swine urine samples,TRFN-LFA exhibited a wide linear range of 5 pg/mL to 2,500 pg/mL with a reliable coefficient of correlation(R2= 0.9803).Relatively narrow linear ranges of 10 pg/mL to 500 pg/mL(FM-LFA)and 25 pg/mL to 2,500 pg/mL(QD-LFA and CG-LFA)were acquired.Approximately 0.005 μg of anti-RAC polyclonal antibody(pAb)was used in each TRFN-LFA test strip,whereas 0.02,0.054,and 0.15 μg of pAb were used in each of the FM-LFA,QD-LFA,and CG-LFA test strips,respectively.In addition,TRFN-LFA required the least RAC-BSA antigens and exhibited the shortest detection time compared with the other lateral flow assays.Analysis of the RAC in swine urine samples showed that the result of TRFN-LFA was consistent with that of liquid chromatography-tandem mass spectrometry(LC-MS/MS)and a commercial enzyme-linked immunosorbent assay(ELISA)kit.The results showed that TRFN-LFA had unique advantages in detecting RAC in swine urine,and TRFN-LFA has potential application value for detection of small molecules in food safety. |
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