Enhanced electrochemiluminescence immunoassay: 1. Wisely using an electronically neutral ruthenium complex luminophore

Abstract

Enhancing signal-to-noise ratio can be achieved either by raising signal level or by reducing noise, or by both. Rather than a commonly held perception that a brighter luminophore is simply used to enhance signal level, this work shows how a heteroleptic and electronically neutral ruthenium(II) complex, Ru(2,2′-bipyridine) (bathophenanthroline disulfonate)[4-(2,2′-bipyridin-4-yl)butanoic acid], was used as a label in electrochemiluminescence (ECL) immunoassay for controlling electrochemically generated noise. The stronger emission combined with its lower sensitivity to the electrode potential enables the brighter luminophore to be used at a lower potential that brings noise down, while maintaining the signal at the same level as that of conventional [Ru(bpy)3]2+ luminophore. The beneficial ECL characteristics demonstrated in homogeneous solution translated into elevated signal-to-noise ratio and improved signal-concentration curve in immunoassay. A first example of using a brighter luminophore in ECL immunoassay from an unusual angle, this work presents an approach to achieving a lower limit of detection through properly balancing the signal level and signal-to-noise ratio.