New developments in particle-based tests and immunoassays.

Latex agglutination tests were invented in 1957. Thirty years later, new tests are still being devised and applied to new analytes. Reproducibility and readability continue to improve. Qualitative tests have now evolved to quantitative particle immunoassays: agglutination is detected by spectrophotometers or nephelometers, in tubes or 96-well plates. These same particles are now also being used in particle capture ELIST and ELISA (enzyme linked immunosorbent tests and assays) where particles are caught upon a filter and act as supports for sandwich tests (those "+/-" or "blue-dot" tests). These also can be quantified, as in the Abbott IM x assay system. Dyed microspheres now function as the color tags in over-the-counter sandwich-type pregnancy tests. In the future, results from assays using this technology could be read on reflectometers (strip readers). Currently, magnetic particles are used in solid phase radioimmunoassays and DNA probes.