A Homogeneous Immunoassay of Thyroxine Based on Microchip Electrophoresis and Chemiluminescence Detection

A homogeneous chemiluminescent immunoassay of thyroxine (T4) present in serum samples is described. The proposed method deployed the competitive immunoreaction of T4 and horseradish peroxidase (HRP)-labeled T4 (HRP–T4) with anti-T4 mouse monoclonal antibody (Ab). HRP–T4 and the HRP–T4–Ab complex were separated and quantified by using microchip electrophoresis (MCE) with chemiluminescence (CL) detection. The MCE separation was accomplished within 60 s. Highly sensitive CL detection was achieved by means of HPR-catalyzed luminol-H₂ O₂ reaction. The linear range for T4 was 5–250 nM with a detection limit of 2.2 nM (S/N = 3).