Electrochemiluminescence
(ECL) is a highly successful technique
used in commercial immunoassays for clinical diagnosis. Developing
an ECL-based multiplex immunoassay, with the potential to enable high-throughput
detection of multiple biomarkers simultaneously, remains a current
research interest yet is limited by a narrow choice of ECL luminophores.
Herein we report the synthesis, photophysics, electrochemistry, and
ECL of several new ruthenium(II) and iridium(III) complexes, three
of which are eventually used as signal reporters for multiplex immunoassay.
The ECL behaviors of individual luminophores and their mixtures were
investigated in multiple modes, including light intensity, spectrum,
and image measurements. The spectral peak separation between Ru(bpy)2(dvbpy)2+ (bpy = 2,2′-bipyridine, dvbpy
= 4,4′-bis(4-vinylphenyl)-2,2′-bipyridine), and Ir(dFCF3ppy)2(dtbbpy)+ (dFCF3ppy
= 3,5-difluoro-2-[5-(trifluoromethyl)-2-pyridinyl]phenyl, dtbbpy =
4,4′-bis(tert-butyl)-2,2′-bipyridine)
was up to 145 nm, thus providing the spectrum-resolved possibility
of identifying light signals. The potential-resolved ECL signals were
achieved for the mixtures of Ir(ppy)3 (ppy = 2-phenylpyridine)
with either Ru(bpy)2(dvbpy)2+ or Ir(dFCF3ppy)2(dtbbpy)+, due to the self-annihilation
ECL of Ir(ppy)3 at higher potentials, as confirmed by electrochemistry-coupled
mass spectrometry. A multiplex immunoassay free of spatial spotting
antibodies on plates or substrates was ultimately devised by combining
luminophore-loaded polymer beads with the homogeneous sandwich immunoreaction.
Using potential and spectrum dual-resolved ECL as the readout signal,
simultaneous recognition of three antigens, namely, carcinoembryonic
antigen (CEA), alpha-fetoprotein (AFP), and beta-human chorionic gonadotropin
(β-HCG), was demonstrated in a single run for a sample volume
of 300 μL. These results contribute to the understanding of
ECL generation by multiple luminophores and devising spot-free multiplex
immunoassays with less sample consumption.