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Improved electrochemiluminescence labels for heterogeneous microbead immunoassay

Yu, Linpo, Liu, Yang, Zhou, Ming
Analytical and bioanalytical chemistry 2016 v.408 no.25 pp. 7095-7103
detection limit, electrochemiluminescence, electrochemistry, immunoassays, ruthenium
Ruthenium(II) complexes with carboxylic acid as a bioconjugatable group, i.e., [Ru(bathophenanthroline disulfonate)(2,2′-bipyridine)(4-methyl-4′-(3-carboxypropyl)-2,2′-bipyridine)]⁰, (C₄₉H₃₈N₆O₈S₂Ru), and [Ru(bathophenanthroline disulfonate)₂(4-methyl-4′-(3-carboxypropyl)-2,2′-bipyridine)]²⁻ · 2Na⁺, (C₆₃H₄₄N₆O₁₄S₄RuNa₂) were characterized spectroscopically and electrochemically. As potential labels for electrochemiluminescence (ECL) immunoassays, the ECL intensities of the free labels in homogenous aqueous buffer solutions were compared under a condition that is similar to the one employed by a commercial clinical immunoassay system. The two labels were found to be more emissive and, thus, can be detected at 10⁻ ¹² pM compared with 5× 10⁻¹² pM of the label currently used in the commercial ECL system. Furthermore, the improved ECL emission of the free labels in homogenous solutions was proven to be translated into more intense ECL signal in heterogeneous sandwich immunoassay and, thus, leading to a lower limit of detection in immunoassay. The data obtained from these ECL labels shed light on the further development of ECL-based clinical immunoassay technology. Graphical abstract Electrochemiluminescence immunoassays were carried out with three different ruthenium(II) complex labels. It was proved that the higher signal intensities found with the novel labels in homogeneous solutions were maintained in heterogeneous sandwich format.