Immunoassay by detecting enhanced resonance light scattering signals of immunocomplex using a common spectrofluorometer

A sensitive, highly specific immunoassay method has been developed by measuring the enhanced resonance light scattering (RLS) signals of immunoreactions with simultaneously scanning both the excitation and the emission monochromators of a common spectrofluorometer. For a given content of antibody (Ab), the RLS signals of an immunoreaction follow Gaussian distribution with antigen (Ag) concentration. The central position of the Gaussian curve represents the concentration of given Ab, and the half bandwidth has proved to be a characteristic constant of a given Ab–Ag immunoreaction. With the RLS signals, the limit of detection for human immunoglobulin G (HIgG) in serum samples could reach 10 ng ml−1, and the concentration of HIgG in blood serum samples could be detected with the recovery of 90.2–107.7% and R.S.D. of 0.8–2.7%. The results of determination for three human serum samples are identical to those obtained by immunoturbidimetry.