Immunonephelometric assays

Nephelometry, the measurement of scattered light, determines the size, shape, and concentration of the scattering particles (at least in theory). For the applications of nephelometry in immunoassays, the scatterers are the antigen-antibody complexes formed. The rationale for using nephelometry includes the advantages of greater simplicity and improved precision as compared to other assay methods. There are, however, other factors which limit the immunological assays in which nephelometry is employed, most notably its sensitivity to noise due to dust and occasional large aggregates of antigen-antibody complexes. Nephelometers commercially available for immunoassays use a variety of light sources; most measure the scattered light at a single angle, and several incorporate microcomputers. A review of the theory of light scattering by small spheres is introduced to indicate fashions in which future developments may make nephelometry the method of choice for an even wider range of immunoassays.