Development Of The Detection Method To Enhance The Sensitivity Of Immunochromatographic Strip

Many detection methods of food, including liquid chromatographic mass spectrometry, gas chromatographic mass spectrometry, high performance liquid chromatographic, and Enzyme-linked immunosorbent assay, have been recently developed. However, the disadvantages such as expensive instrument, tedious sample pretreatment and professional personnel limit the application of these methods in on-site detection. Immunochromatographic test strip(ICTS) presents four advantages, including a user-friendly format, a short period of time required to acquire test results, long-term stability over a wide range of climates, and relatively inexpensive production. These characteristics make ICTS an ideal choice for the primary screening of samples in spot. Nevertheless, the sensitivity of ICTS is low, and the application of it was limited. In this study, the methods of improving the sensitivity of ICTS were explored.A colloidal gold immunochromatographic signal-amplifying test strip with a sandwich format was successfully developed to detect Escherichia coli O157:H7. The detection signal was improved by addition of enhancers(HAu Cl4 and NH2OH·HCl) to the NC membrane of a conventional ICTS. The detection sensitivities of the test strip before and after signal amplification were 4×104 and 5×103 CFU/m L,respectively, as determined by a colloidal gold strip reader. An 8-fold increase in sensitivity after signal amplification was accomplished within 20 min. No cross-reactivity with 27 non-target strains was observed. Compared with conventional test strip, the time required to detect E. coli O157:H7 in spiked milk samples for signal-amplifying test strip was shortened by 1.5 h. The colloidal gold immunochromatographic signal-amplifying test strip thus provides a novel method for determining E. coli O157:H7 and is rapid, sensitive, convenient, and suitable for on-site detection.The appropriate probe materials play a significant role in improving the detection sensitivity of test strip. In this study, hollow Ag-Au Nanoparticles(NPs) labeled ICTS was successfully developed for the detection of clenbuterol(CLE) on the basis of the competitive binding format. The hollow Ag-Au NPs materials with different Ag/Au ratio and different aperture size were synthesized by adding different volume of HAu Cl4 to CTAC capped Ag NPs solution. The surface of hollow Ag-Au NPs acquired was covered by a bilayer of CTAC molecules which was positively charged. It was successful to change the positive-charged surface of hollow Ag-Au NPs to a negative-charged surface by adding MUA solution. The different MUA capped hollow Ag-Au NPs was labeled separately with anti-CLE monoclonal antibody to acquire hollow Ag-Au NPs probes and applied on ICTS for the detection of CLE. Results showed the Ag/Au ratio of hollow Ag-Au NPs acquired decreased from 12.69:1 to 4.78:1, 1.77:1, 1:1.02, and 1:2.17 with the addition of HAu Cl4 solution. When the Ag/Au ratio of hollow Ag-Au NPs was 4.78:1, the limit of detection hollow Ag-Au NPs test strip was at 2 ng/m L within 15 min, which is 10-fold lower than that of conventional test strip. The optimized hollow Ag-Au NPs labeled test strip is an ideal candidate for rapid detection of CLE in food samples.