Advantages of fluorescent microspheres compared with colloidal gold as a label in immunochromatographic lateral flow assays

Label selection is of vital importance for immunochromatographic assays. In this study, the fluorescent microsphere test strip and colloidal gold immunochromatographic test strip (FM-ICTS and CG-ICTS) were developed for the detection of Escherichia coli O157:H7 on the basis of the sandwich format. Two types of labels, namely, colloidal gold particles (CG) and carboxyl-modified fluorescent microspheres (FMs), were compared while coupling with anti-E. coli O157:H7 monoclonal antibody (mAb). The FM-ICTS and CG-ICTS were also compared. Results show that the coupling rate between FMs and mAb was higher than that between CG and mAb. Under optimum conditions, the sensitivity of FM-ICTS was eight times higher than that of CG-ICTS. Approximately 0.1 μg of mAb was used in every FM-ICTS, whereas 0.4 μg of mAb was used in every CG-ICTS. The coefficient of variation of FM-ICTS and CG-ICTS was 4.8% and 16.7%, respectively. The FM-ICTS and CG-ICTS can be stored at room temperature for 12 months and specific to five E. coli O157:H7 strains. Milk sample inoculated with E. coli O157:H7 were tested by the FM-ICTS and CG-ICTS. The FM-ICTS sensitivity was 10(4) CFU/ml while the CG-ICTS sensitivity was 10(5) CFU/ml. The sensitivity, consumption of antibodies, and coefficient of variation of FM-ICTS were better than those of CG-ICTS for the detection of E. coli O157:H7.