Development Of An Immunochromatography Assay With Fluorescent Microspheres For The Rapid Detection Of Ractopamine

Objectives：To establish a fluorescent microsphere immunochromatographic assay forthe detection of ractopamine (RAC) residues based on competition principle.Developping fluorescent microsphere lateral-flow immunochromatographic test stripfor monitoring ractopamine(RAC) in swine urine samples.Methods: The ascites antibody against RAC were purified with ammonium sulfateprecipitation，and the antibody concentration was measured with the BCA kit. Thefluorescent microsphere-antibody complexes were prepared by using3-(ethyliminomethyleneamino)-N,N-dimethyl-propan-1-amine （EDC） at roomtemperature. For the preparation of test strips, the conjugates were dispensed onto theconjugate pad, artificial antigen RAC-BSA was dispensed onto NC membrane as thetest line(T line), and goat anti-mice IgG was prepared and dipensed onto nitrocellulose(NC) membrane as the control line (C line). Then the sample pad, conjugate pad,nitrocellulose membrane and absorbent paper were assembled in turn and cut into teststrips. During detection process, the more RAC presented in samples, the morefluorescent latex particles-labeled anti-RAC McAb would be bound to RAC, the lessfluorescent latex particles-labeled anti-RAC McAb would be bound to RAC-BSA onthe test line, and the test line would be darker under the450nm exciting light. Thefluorescence brightness of the test line could indicate the quantity of the RAC insamples.Results： The RAC-BSA and fluorescent microsphere-antibody complexes weresynthesized successfully. The fluorescent microsphere-antibody complexes could bebound to RAC-BSA well，and have no non-specific reactivity with BSA. A fluorescentmicrosphere lateral-flow immunochromatographic technique for the rapid detection ofractopamine（RAC）in swine urine samples was developed. The minimum limit of thestrips could reach2ngmL-1. The strips had no cross-reaction with clenbuterol (CL) andsalbutamol (SAL).Conclusions：A fluorescent microsphere lateral-flow immunochromatographic assay for RAC detection with low cost, high stability and sensitivity was developed and could beused as an efficient method for rapid screening test of ractopamine residues in swineurine samples.