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.
The lithium–sulfur (Li–S) battery is one of the most promising next generation energy storage systems due to its high theoretical specific energy. However, the shuttle effect of soluble lithium polysulfides formed during cell operation is a crucial reason for the low cyclability suffered by current Li–S batteries. As a result, an in‐depth mechanistic understanding of the sulfur cathode redox reactions is urgently required for further advancement of Li–S batteries. Herein, the direct observation of polysulfides in a Li‐S battery is reported by an in situ hyphenated technique of electrochemistry and mass spectrometry. Several short‐lived lithium polysulfide intermediates during sulfur redox have been identified. Furthermore, this method is applied to a mechanistic study of an electrocatalyst that has been observed to promote the polysulfides conversion in a Li–S cell. Through the abundance distributions of various polysulfides before and after adding the electrocatalyst, compelling experimental evidences of catalytic selectivity of cobalt phthalocyanine to those long‐chain polysulfide intermediates are obtained. This work can provide guidance for the design of novel cathode to overcome the shuttle effect and facilitate the sulfur redox kinetics.
In many electrochemiluminescent (ECL) systems, coreactants play crucial roles in the redox-induced light emission process at the electrode surface. In this work, a novel and environment-friendly nanoplatform for ECL immunosensing enabled by triethanolamine (TEOA)-modified gold nanoparticles (TEOA@AuNPs) is reported. The monodisperse TEOA@AuNPs are fabricated by one-pot synthesis using TEOA as both reducing and stabilizing agent. Then the TEOA@AuNPs-modified electrode not only acted as coreactant for Ru(bpy) ECL system but also provided a carrier for antibody 1 to form label-free immunosensor through an interaction between antigen and antibody. The unique structure of the TEOA@AuNPs loaded a large amount of coreactant of Ru(bpy), which shortened the electron-transfer distance from the AuNPs surface to the appended TEOA molecules, thereby greatly enhancing the ECL efficiency and amplifying the ECL signal. In addition, Ru(bpy)-doped silica (RuSiO) nanoparticles and antibody 2 were combined to form a composite for labels and a sandwich-type ECL immunosensor has been constructed. The possible mechanism of those ECL systems have also been proposed and confirmed by the EC-MS hyphenated technique. The human cardiopathy biomarker, cardiac troponin I (cTnI), was detected in a wide linear concentration range and the limit of detection (LOD) was 34 or 5.5 fg mL by using the proposed label-free or labeling ECL immunoassay method.
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