New developments in particle-based immunoassays: Introduction
There have been many innovations in diagnostics since white latex particles or microspheres were first used in medical diagnostic applications as "latex" agglutination tests (LAT) in the late 1950's. These innovations include colored particles permitting multivalent (or simultaneous) analyses, and special devices for simplifying test execu- tion and result interpretation. Dyed agglutinated particles caught on filters form the ba- sis of another class of tests. Sensitive particle-enhanced turbidimetric assays are in common use and are read with clinical chemistry analyzers via spectrophotometric or nephelometric methods. Particle capture ELISA tests and assays are in common use. The popular new strip tests for pregnancy, ovulation, drugs of abuse in urine, and many other tests all use dyed microspheres (and some use wo types of microspheres). Solid phase assays and tests use particles as a solid phase for positive or negative cap- ture of a wide variety of analytes. Solid-liquid separations can be made by centrifugal density separation, or filtration, or via magnetic separation of superparamagnetic parti- cles. Single microsphere (and perhaps single molecule sensitivity?) assays are now possible in flow cytometers.