Electrogenerated chemiluminescence of methyl-9-(p-formylphenyl) acridinium carboxylate fluorosulfonate and its applications to immunoassay

Electrogenerated chemiluminescent (ECL) reaction of an acridinium ester, methyl-9-(p-formylphenyl) acridinium carboxylate fluorosulfonate (MFPA), on the surface of a platinum electrode has been studied using a homemade ECL apparatus. The ECL intensity was affected by the presence of micro amounts of chloride and hydrogen peroxide in the solution. A positive square wave pulse was exerted on the reaction cell. The applied voltage was 2.5 V (vs SCE). This method allowed MFPA to be determined in the range 1.0 x 10(-9)-4.0 x 10(-7) mol L-1. A line calibration plot was constructed in order to evaluate the limit of detection, which was determined to be 2.1 x 10(-10) mol L-1. The application of this method to immunoassay was demonstrated by the determination of human chorionic gonadotropin using MFPA as label. Good correlation was obtained between the results of the proposed method and the other method. A reaction mechanism study showed that MFPA decomposed to N-methylacridone and 4-hydrobenzaldehyde in the alkaline aqueous solution which contained hydrogen peroxide. N-Methyl-acridone could be oxidized to form an excited state molecule at the surface of the electrode. As some of these excited state molecules went to their ground stare, they released light in the visible wavelength range. The ECL intensity enhanced by addition of chloride may be due to the oxidation of the chloride ion to OCl- and the latter acts on MFPA and then gives out luminescence. (C) 1998 Academic Press.