Immunoassay lateral flow devices

Nanoparticles, e.g., silicon, gold, silver (Dequaire et al., 2000), are often used as materials for protein labeling in immunoassays, especially in lateral flow device (LFD), where they are responsible for visualization of the results. Their advantage lies in the fact that they enhance the optical signal, and reduce the background interference (Schneider et al., 2000 Lochner et al., 2003 Matveeva et al., 2005 Chumbimuni-Torres et al., 2006 Li et al., 1999 Peng et al., 2007a). 

Latex and nanogoldparticles. Latex particles are sold in a variety of colors that can be visualized with the naked eye. Nanogold particles can be used alone or in combination with silver to increase sensitivity. Both t) pes of particles are commonly used in rapid immunoassays such us lateral flow devices. 

O Keeffe M, Crabbe P, Salden M, Wichers J, van Peteghem C, Kohen E, Pieraccini G, Moneti G, Preliminary evaluation of a lateral flow immunoassay device for screening urine samples for the presence of sulphamethazine, J. Immun. Meth. 2003 278 117-126. 

Enzyme immunoassays, in a card-test format, are also used for screening carcasses by testing of urine for specific antimicrobial residues such as sulfadimidine and chloramphenicol. The sol particle immunoassay uses adsorption of specific antibodies to dyed colloidal particles (e.g., carbon) as a mechanism for making directly visible the presence of residues (i.e., antigen) in the sample. A lateral flow membrane device is used to identify residue-positive samples through the absence of color formation at the test capture zone (Figure 5). 

One very prominent area, which is only rather loosely connected to pharmaceutical fields, but which is nevertheless an essential aspect of health-related research, and in which cellulose-based materials, namely different paper types, play a fundamental role, is the development of paper-based disposable point-of-care diagnostics tools and low-cost diagnostics tools [49-51], Although the concept of using cellulose-based materials as an essential part is not new as such—basically every commercially available lateral flow immunoassay (e.g., pregnancy tests) contains a specialized paper as an integral part—the development of devices completely made out of paper-like materials has revolutionized the field, and surprisingly simple but powerful devices made out of paper have been developed and tested rmder real conditions in field trials various assay formats have been realized, and it is expected that these devices will have an impact on health care systems due to their cost-effectiveness. 

As a POC (point of care) device semi-quantitative flow-immunoassay methods for the detection of antibodies or antigens had been developed and are well establish in e.g. pregnancy tests. This format is also known as strip test, one step strip test, immunochromatographic test, rapid flow diagnostic, rapid immunoassay or lateral flow immunoassay (LFI). The label is anyway a colored colloidal particle. Additionally to metal colloids, carbon (black) and silica or latex (various colors) are in use. 

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