Ultrabright fluorescent microsphere and its novel application for improving the sensitivity of immunochromatographic assay.

Fluorescent microsphere (FM) is widely used as probe in immunochromatographic assay (ICA). However, the performance of conventional FM is limited because of the aggregation-caused quenching effect. Herein, we compared a kind of conventional FM (DMFFM, loading DMF) with novel aggregation-induced emission FM (AIEFM, loading TCBPE). The fluorescence intensity of DMFFM initially increased and then decreased as the concentrations of the loading DMF increased. The fluorescence intensity of AIEFM increased as the concentrations of the loading TCBPE increased and retained a high value. AIEFM was compared with two commercial FMs purchased from Ocean (OFM) and Merk (MFM). The maximum fluorescence intensity and relative quantum yield of AIEFM was approximately 5 and 4.5 times higher than those of two commercial FMs. We used the novel AIEFM as a probe to improve the sensitivity of ICA. When Escherichia coli O157:H7 was detected as the target, the limit of detection of ICA based on AIEFM, OFM and MFM were 3.98 × 103 CFU/mL, 4.48 × 104 and 2.78 × 104 CFU/mL, respectively. The ICA of AIEFM had 11 and 7 times improvement in sensitivity compared with that of OFM and MFM. Our results could be used as a basis for novel probes in practical ICA applications.

Lateral flow immunoassay integrated with competitive and sandwich models for the detection of aflatoxin M1 and Escherichia coli O157:H7 in milk.

Pathogens, mycotoxins, or antibiotics may exist in a food sample. Micro- and macromolecular substances must be detected quickly. A rapid and convenient lateral flow immunoassay (LFI) integrated with competitive and sandwich models was developed to detect micro- and macromolecular substances. In this study, aflatoxin M1 (AFM1) and Escherichia coli O157:H7 were selected as the micro- and macromolecular substances, respectively. Two test lines in the LFI test strip were evaluated to detect AFM1 and E. coli O157:H7 by competitive and sandwich models. Results showed that the limits of detection for detecting AFM1 and E. coli O157:H7 were 50 pg·mL-1 and 1.58 × 104 cfu·mL-1, respectively. The whole assay time was 30 min. The recoveries of gold nanoparticle-LFI ranged from 78.0 to 111.6% with coefficients of variation in the range of 3.9 to 8.5% for the detection of AFM1. For the detection of E. coli O157:H7, the range of recoveries was from 70.1 to 89.6% with coefficients of variation ranging from 4.9 to 13.0%. This study not only tested sensitivity and specificity, but also was a systematic study of location of 2 test lines of the LFI test strip integrated with competitive and sandwich models.