CLASSIFICATION of lateral flow tests

Lateral flow assays can be developed to be used in a dipstick format or in a cassette. Both dipsticks and cassette tests will work in a similar way, it is just dependent on the industry, sample matrix, and the market requirement, as to which format is suitable.

1 Sandwich format

The sandwich assay format is typically used for detecting relatively large analytes. If the analyte has at least two distinct binding sites (i.e. epitopes), a "sandwich" assay can be developed where an antibody to one epitope is conjugated to the nanoparticle and an antibody to another epitope is immobilized at the test line. The sandwich format results in a signal intensity that is proportional to the amount of analyte present in the sample.

2 Competitive format

A competitive format is used for detecting analytes in which the analyte is too small for two antibodies to bind simultaneously, such as vitamins and antibiotics. In a competitive assay, the test line contains the target analyte molecule (usually a protein-analyte complex). The nanoparticles are conjugated to an antibody that recognizes the analyte. If the analyte is not present in the sample, the nanoparticle antibody conjugates will bind to the analyte at the test line, resulting in high signal intensity. If the target analyte is present in the sample, the analyte will bind to the antibodies on the nanoparticle surface and prevent the nanoparticle from binding to the test line. This will reduce the signal at the test line resulting in a signal intensity that is inversely proportional to the amount of analyte present in the sample.

3 Multiplexed lateral flow assays

Both sandwich and competitive assays can be developed to include one or more test lines.
A multiplexed assay may be used for detecting multiple targets in a single test rather than using many individual tests. In situations where only a small sample volume is available a multiplex assay allows you to maximize its use to assist diagnosis where the presence of a number of markers together is required. It confirms the presence of multiple contaminants during high volume food and feed testing. It offers cost-saving benefits to end-users in a laboratory or in-the-field by testing for different targets simultaneously. Multiplexed testing will save time in remote or agricultural areas where resources are limited.

Guidence of GeneMedi's protocol / procedure for the diagnostics application:          1. CLIA          2. ELISA: (1) Direct ELISA (2) Indirect ELISA (3) Competitive ELISA (4) Sandwich ELISA          3. LFIA: (1) Sandwich format (2) Competitive format (3) Multiplexed lateral flow assays          4. PETIA          5. Immunonephelometry          6. IHC          7. FACS: (1) Antibody titration protocol using 96 well plates (2) Protocol for cell sorting          8. Octet system    Summary of the advantages and disadvantages of the different immunoassay