Colloidal silver-based lateral flow immunoassay for rapid detection of melamine in milk and animal feed

An immunosilver chromatographic strip based on a monoclonal antibody was developed for the detection of melamine (MEL) residues in milk and animal feed. Colloidal silver nanoparticles (AgNPs), of a diameter of approximately 10.4 nm, were surface-modified with trisodium citrate dehydrate (TSC) in order to improve their stability and dispersion. The anti-MEL monoclonal antibody (mAb) was successfully immobilized on the surface of AgNPs by ionic interactions and characterized using XRD, UV-Vis, TEM and XPS analyses. Surface modification of Ag-mAb conjugates with varying cross-reactivity and thermo-stability was employed to design and prepare labels for use in a lateral flow immunoassay (LFIA) to examine whether these factors affect the performance of the assay. The results showed that no cross-reactions with homologues cyanuric acid, ammeline or ammelide were found, and the test strip remained stable after storage for one year at room temperature. Under optimized conditions, a detection limit of 0.30 ppm for standard melamine was achieved, and limits of detection of 0.750 ppm and 0.875 ppm were obtained in milk and animal feed, respectively

Rapid and sensitive detection of Yersinia pestis by lateral-flow assay in simulated clinical samples

Abstract Background Yersinia pestis is a contributing agent to the epidemic disease, plague, which killed an estimated 200 million people during historical times. In this study, a rapid, cheap, sensitive, and specific technique, the lateral flow assay (F1 strips), has been successfully developed to detect this pathogen, by using paired monoclonal antibodies (MAbs) against Y. pestis capsule like fraction 1 (F1) protein. Compared with the polyclonal antibody (PAb) based F1 strips, the Mab-based F1 strips have a remarkable increased detection limitation (10 to 100 folds). Furthermore, besides the limitation and specificity evaluation, the application of this F1 strip on simulated clinical samples indicate the LFA can be a good candidate to detect plague. Methods Recombinant F1 antigen was expressed and purified from a series of works. The various anti-F1 monoclonal antibodies generated from hybridoma cells were screened with the ELISA technique. To evaluate the feasibility of this Y. pestis F1 test strip, the F1 protein/Y. pestis was spiked into simulated clinical samples such as human serum, mouse bronchoalveolar lavage fluids, and mouse blood to mimic natural infection status. Additionally, this technique was applied to detect the Y. pestis in the environment-captured rats, to evaluate the practical usefulness of the strips. Results By using this MAb-based-LFA technique, 4 ng/ml of recombinant F1-protein and 103 CFU/ml of Y. pestis could be detected in less than 10 mins, which is at least 10-folds than that of the PAb format. On the other hand, although various Yersinia strains were applied to the strips, only Y. pestis strain showed a positive result; all other Yersinia species did not produce a positive signal, indicating the high efficiency and specificity of the MAb-based F1-strips. Conclusion Based on our findings, we suggest that the MAb-format-LFA will be valuable as a diagnostic tool for the detection of Y. pestis. This report shows that the F1 strip is sufficient to support not only the detection of plague in simulated clinical samples, but also it may be a good candidate to meet the epidemiological surveillance during an outbreak of the biological warfare