Ultrasensitive competitive electrochemiluminescence immunoassay for the β-adrenergic agonist phenylethanolamine A using quantum dots and enzymatic amplification

Abstract

We have designed an ultrasensitive electrochemiluminescence (ECL) immunoassay for the determination of the β-adrenergic agonist phenylethanolamine A (PA). It is based on the use of L-cysteine-capped CdSe quantum dots (QDs) immobilized on a glassy carbon electrode (GCE) with the help of chitosan. PA (the antigen) was linked to the surface of the GCE by using glutaraldehyde where it competes with the PA in the sample solution to bind to the antibody. Upon formation of the immunocomplex, a second antibody labeled with horseradish peroxidase was immobilized on the surface of the modified GCE. The ECL emission decreases due to steric hindrance by the immunocomplex which slows down the electron transfer rate of the reduction of dissolved oxygen, and this decrease can be strongly amplified by using an enzymatic cycle to consume the self-produced coreactant H2O2. Under optimal conditions, the ECL intensity measured in this competitive immunoassay is related to the concentration of PA over a range as wide as from 0.05 to 1,000 ng mL−1. The lower detection limit is 15 pg mL−1 at the S/N ratio of 3. This ECL immunoassay is rapid, sensitive, selective, acceptably precise, and extends the application of QDs-based ECL to immunoassays of β-agonists.