Gold nanoparticles of different shape for bicolor lateral flow test

Spherical gold nanoparticles are the most commonly used marker in lateral flow assays. However, the widespread practice of using identical coloration for the test and control zones of test strips can lead to erroneous interpretations of the assay's results. We propose an immunochromatographic test strip with lines of different colors. For this purpose, gold nanoparticles of different shapes were used, namely blue nanoflowers in the test zone and red gold nanospheres in the control zone. A detailed synthesis procedure for nanoparticles and their conjugates is considered and design parameters for optimal results are described. For the first time, nanoparticles of different shapes have been combined in the test strip with indirect labeling of specific antibodies (via their interaction with labeled secondary antibodies). Using the T-2 toxin (T2T) as an example, an instrumental detection limit of 30 pg/ml and a working range 0.06-0.9 ng/mL were achieved in an analysis of water-organic corn extracts.

A new kind of highly sensitive competitive lateral flow immunoassay displaying direct analyte-signal dependence. Application to the determination of the mycotoxin deoxynivalenol

A new kind of competitive immunochromatographic assay is presented. It is based on the use of a test strip loaded with (a) labeled specific antibodies, (b) a hapten-protein conjugate at the control zone, and (c) antibodies interacting with the specific antibodies in the analytical zone. In the case where a sample does not contain the target antigen (hapten), all labeled antibodies remain in the control zone because of the selected ratio of reactants. The analytical zone remains colorless because the labeled antibodies do not reach it. If an antigen is present in the sample, it interferes with the binding of the specific antibodies in the control zone and knocks them out. Some of these antibodies pass the control zone to form a colored line in the analytical zone. The intensity of the color is directly proportional to the amount of the target antigen in the sample. The assay has an attractive feature in that an appearance in coloration is more easily detected visually than a decoloration. Moreover, the onset of coloration is detectable at a lower concentration than a decoloration. The new detection scheme was applied to the determination of the mycotoxin deoxynivalenol. The visual limit of detection is 2 ng·mL^-1 in corn extracts (35 ng per gram of sample). With the same reagents, this is lower by a factor of 60 than the established test strip. The assay takes only 15 min. This new kind of assay has wide potential applications for numerous low molecular weight analytes. Graphical abstract Competitive immunochromatography with direct analyte-signal dependence is proposed. It provides a 60-fold decrease of the detection limit for mycotoxin deoxynivalenol. The analyte-antibody-label complexes move along the immobilized antigen (control zone) and bind with anti-species antibodies (test zone).

Comparison of Fluorescent Microspheres and Colloidal Gold as Labels in Lateral Flow Immunochromatographic Assays for the Detection of T-2 Toxin

A new highly specific and sensitive monoclonal antibody (MAb) to T-2 toxin (T-2) was produced, providing an IC50 value of 1.02 ng/mL and negligible cross-reactivity (CR) to other related mycotoxins. Based on the new MAb, a lateral-flow immunochromatographic assay (LFIA) using colloidal gold (CG) and fluorescent microspheres (FMs) as labels was proposed for T-2. Under the optimized conditions, in rapid qualitative assay, the cut-off values of the CG-LFIA were 400 μg/kg in rice and 50 μg/L in fresh milk, and the cut-off values of the FMs-LFIA were 100 μg/kg in both rice and chicken feed. For the quantitative assay with the FMs-LFIA, the limit of detection (LOD) were 0.23 μg/kg and 0.41 μg/kg in rice and chicken feed, respectively, and the average recoveries ranged from 80.2% to 100.8% with the coefficient of variation (CV) below 10.8%. In addition, we found that the CG-LFIA could tolerate the matrix effect of fresh milk better than the FMs-LFIA, while the FMs-LFIA could tolerate the matrix effect of chicken feed better than CG-LFIA under the same experimental conditions. These results provide a certain reference for the selection of appropriate labels to establish a rapid LFIA in various biological samples.