<title>Copalis technology: immunoassay diagnostics using latex microparticles and colloidal gold</title>

Abstract

Copalis<SUP>TM,1</SUP> (coupled particle light scattering) is an innovative particle-based homogeneous immunoassay technology that allows rapid, sensitive, simultaneous determination of multiple analytes in a single fluid sample. Particles, their aggregates and cells are differentiated on the basis of light scatter measurements as they flow across a finely focused elliptical beam produced by a semiconductor laser. Two distinct complementary test formats have been developed, one based on particle self-agglutination and the other based on binding of colloidal gold particles to latex micro-spheres. In the first format, particle self- agglutination gives rise to dimers and oligomers which are classified and enumerated from the light scatter histogram. The extent of agglutination determines the test result. The second format uses micron-sized latex micro-spheres as the carriers onto which varying amounts of colloidal gold particles are bound in sandwich or competitive immunoassay formats. The main characteristic of this type of immunoassay is the relative broadening of light scatter histogram peaks for particles coated with colloidal gold. The extent of broadening is used to determine the concentration of the analyte. With both formats, the use of latex particles of different sizes in the same reaction mixture allows multiple simultaneous assays. This technology yields an analytical sensitivity of 10<SUP>-13</SUP> M, an improvement by several orders of magnitude over other homogeneous assay technologies.