Highly sensitive electroluminescence immunoassay for Hg(II) ions based on the use of CdSe quantum dots, the methylmercury-6-mercaptonicotinic acid-ovalbumin conjugate, and a specific monoclonal antibody

We have designed a rapid and ultrasensitive electrochemiluminescent (ECL) competitive immunoassay for the determination of mercury(II) ion. It is based on the use of CdSe quantum dots (QDs), methylmercury-6-mercaptonicotinic acid-ovalbumin as coating antigen and specific monoclonal antibodies (mAbs) against Hg(II). The latter is quite selective for Hg(II). The coating antigen was immobilized on the surface of a gold electrode via reaction between the functional groups of cysteamine and glutaraldehyde. The mercury(II) ions in a sample and the coating antigen compete for binding sites of QD-labeled monoclonal antibody which binds specifically to Hg(II) ions. The ECL of the system decreases with increasing concentration of Hg(II) because less QD-labeled mAbs are present on the surface of the electrode. Under optimal conditions, the decrease of ECL intensity is linearly related to the logarithm of the Hg(II) concentration in the range from 0.02 to 100 ng mL⁻¹, with a detection limit of 6.2 pg mL⁻¹. As far as we know, this is the first report on an ECL immunoassay for Hg(II) based on a specific monoclonal antibody. The favorable results obtained when this method was applied to real samples indicate that this detection scheme can widely enlarge the applicability of detecting heavy metal ions by exploiting the ECL of QDs for immunoassays. (author)