Electrochemically tuneable multi-colour electrochemiluminescence using a single emitter

Enhanced Electrochemiluminescence of A Macrocyclic Tetradentate Chelate Pt(II) Molecule via Its Collisional Interactions with the Electrode

A macrocyclic tetradentate chelate Pt(II) molecule (Pt1) served as an excellent luminophore in electrochemiluminescence (ECL) processes. The blue ECL of Pt1/S2O82- coreactant system in N,N'-dimethylformamide was found to be 46 times higher than that of the Ru(bpy)2+/S2O82- system or 30 times higher than that of the 9,10-diphenylanthracene/S2O82- system. The unprecedented high ECL quantum efficiencies were caused by the cyclic generation of monomer excited states through collisional interactions of Pt1 molecules with the electrode at an elevated frequency. The ECL is tunable from bright blue to pure white by simply changing the solvent from N,N'-dimethylformamide to dichloromethane. The white ECL of Pt(II) molecule was reported for the first time and the mechanism was proposed to be the simultaneous emissions from the monomer excited state (blue) and excimer (red).

Lighting Up Electrochemiluminescence-Inactive Dyes via Grafting Enabled by Intramolecular Resonance Energy Transfer

Due to near-zero optical background and photobleaching, electrochemiluminescence (ECL), an optical phenomenon excited by electrochemical reactions, has drawn extensive attention, especially for ultrasensitive bioassays. Developing diverse ECL emitters is crucial to unlocking their multiformity and performances but remains a formidable challenge due to the rigorous requirements for ECL. Herein, we report a general strategy to light up ECL-inactive dyes in an aqueous solution via grafting, a well-developed concept for plant propagation since 500 BCE. As a proof of concept, a series of luminol donor-dye acceptor-based ECL emitters were grafted with near-unity resonance energy transfer (RET) efficiency and coarse/fine-tunable emission wavelengths. Rather than the sophisticated design of new skeleton-based molecules to meet all of the prerequisites for ECL in a constrained manner, each unit in the proposed ECL ensemble performed its functions maximally. As a result, beyond traditional two-dimensional (2D) ones, a three-dimensional (3D) coordinate biosensing system, simultaneously showing a calibration curve and selectivity, was established using the new ECL emitter. This lighting up strategy would generally address the scarcity of ECL emitters and enable unprecedented functions.

A redox-mediator pathway for enhanced multi-colour electrochemiluminescence in aqueous solution

The classic and most widely used co-reactant electrochemiluminescence (ECL) reaction of tris(2,2'-bipyridine)ruthenium(ii) ([Ru(bpy)3]2+) and tri-n-propylamine is enhanced by an order of magnitude by fac-[Ir(sppy)3]3- (where sppy = 5'-sulfo-2-phenylpyridinato-C 2,N), through a novel 'redox mediator' pathway. Moreover, the concomitant green emission of [Ir(sppy)3]3-* enables internal standardisation of the co-reactant ECL of [Ru(bpy)3]2+. This can be applied using a digital camera as the photodetector by exploiting the ratio of R and B values of the RGB colour data, providing superior sensitivity and precision for the development of low-cost, portable ECL-based analytical devices.

Dual-potential electrochemiluminescence of single luminophore for detection of biomarker based on black phosphorus quantum dots as co-reactant

Simultaneous cathodic and anodic electrochemiluminescence (ECL) emissions of needle-like nanostructures of Ru(bpy)₃²⁺ (RuNDs) as the only luminophore are reported based on different co-reactants. Cathodic ECL was attained from RuNDs/K₂S₂O₈ system, while anodic ECL was achieved from RuNDs/black phosphorus quantum dots (BPQDs) system. Ferrocene attached to the hairpin DNA could quench the cathodic and anodic ECL simultaneously. Subsequently, the ECL signals recovered in the presence of tumor marker mucin 1 (MUC1), which made it possible to quantitatively detect MUC1. The variation of ECL signal was related linearly to the concentrations of MUC1 in the range 20 pg mL^-1 to 10 ng mL^-1, and the detection limits were calculated to 2.5 pg mL^-1 (anodic system, 3σ) and 6.2 pg mL^-1 (cathodic system, 3σ), respectively. The recoveries were 97.0%, 105%, and 95.2% obtained from three human serum samples, and the relative standard deviation (RSD) is 5.3%. As a proof of concept, this work realized simultaneous ECL emission of  a single luminophore, which initiates a new thought in biomarker ECL detection beyond the traditional ones. Simultaneous cathodic and anodic ECL emissions of RuNDs were reported based on different co-reactants. Ferrocene could quench the ECL emission in the cathode and the anode simultaneously. Thus, an aptasensor was constructed based on the variation of ECL intensity. As a proof of concept, this work realized simultaneous ECL emission of a single luminophore, which initiates a new thought in biomarker ECL detection beyond the traditional ones by avoiding the false positive signals.

A dual-signal output ratiometric electrochemiluminescent sensor for NADH detection

Ratiometric electrochemiluminescence (ECL) has attracted great attention in the field of electrochemical analysis. In this study, a dual-signal-output ratiometric ECL sensor was developed for the detection of nicotinamide adenine dinucleotide (NADH). Nitrogen-doped graphene quantum dots (NGQDs) exhibit double ECL signal output capability, without the requirement of additional coreactants. NADH can amplify the anodic ECL response of NGQDs, while it can diminish the cathodic ECL response of NGQDs. Based on the principle between relative enhancing ECL intensity ratio and NADH concentrations, the constructed ratiometric ECL sensor was applied to NADH assays, with a wide concentration range of 10-400 μM and a low limit of detection (LOD) of 2.5 μM (S/N = 3). Furthermore, the proposed method was applied for the determination of spiked NADH, which was proved to be feasible in the biological sample matrix. The proposed strategy of modulating multiple-ECL signals of the single NGQD emitter not only provides a new ECL system for the accurate detection of NADH but also broadens the design pathway for ratiometric sensing fabrication.

Highly Efficient Dual-Polar Electrochemiluminescence from Au25 Nanoclusters: The Next Generation of Multibiomarker Detection in a Single Step

For the first time, simultaneous cathodic and anodic electrochemiluminescence (ECL) emissions of bull serum albumin stabilized Au₂₅ nanoclusters (Au₂₅ NCs) as highly efficient bipolar ECL probes were constructed for the single-step and synchronous determination of carcinoembryonic antigen (CEA) and mucin 1 (MUC1) based on different coreactant and coreaction accelerators. Under the potential cathodic scanning, TiO₂ nanosheets (TiO₂ NSs) as cathodic coreaction accelerators could catalyze the reduction of coreactant dissolved O₂ for promoting cathodic ECL emission of Au₂₅ NCs, while, under the potential anodic scanning, Cu₂O@Cu nanoparticles (Cu₂O@Cu NPs) as anodic coreaction accelerators could stimulate the oxidation of coreactant N,N-diethylethylenediamine (DEDA) for enhancing anodic ECL emission of Au₂₅ NCs. Thus, the proposed strategy easily solved one main technical challenge of cross reactions of dual-luminophors for dual-biomarker detection, resulting in great sensitivity and accuracy toward the detection of CEA down to 0.43 pg/mL and MUC1 down to 5.8 fg/mL. As a proof of concept, this work realized single-step and simultaneous detection of dual biomarkers, which initiates a new thought in realizing a new generation of dual-biomarker ECL detection beyond the traditional ones in sensing analysis and diagnostic sensing.

Unusually Strong Electrochemiluminescence from Iridium-Based Redox Polymers Immobilized As Thin Layers or Polymer Nanoparticles

A new class of redox metallopolymer based on cyclometalated iridium(III) centers is described, with unusually intense luminescence properties in aqueous media. We report the facile synthesis, photophysical and electrochemical characterization, supported by DFT calculations and their electrochemiluminescence (ECL) properties which, under some circumstances, are significantly greater than the analogous ruthenium-based materials. The photoluminescence (PL) and ECL of these materials are further dramatically enhanced when dispersed or immobilized as polymeric nanoparticles (PNPs). This aggregation-induced emission (AIE and AIECL) operates by providing important protection for the cyclometalated iridium(III) centers against the types of quenching processes which commonly afflict iridium-based luminophores in aqueous media. The results suggest interesting new avenues of research for the application of such materials in and PL and ECL-based detection and imaging as well as light-emitting devices.

Mixed annihilation electrogenerated chemiluminescence of iridium(iii) complexes

Previously reported annihilation ECL of mixtures of metal complexes have generally comprised Ir(ppy)3 or a close analogue as a higher energy donor/emitter (green/blue light) and [Ru(bpy)3]2+ or its derivative as a lower energy acceptor/emitter (red light). In contrast, here we examine Ir(ppy)3 as the lower energy acceptor/emitter, by combining it with a second Ir(iii) complex: [Ir(df-ppy)2(ptb)]+ (where ptb = 1-benzyl-1,2,3-triazol-4-ylpyridine). The application of potentials sufficient to attain the first single-electron oxidation and reduction products can be exploited to detect Ir(ppy)3 at orders of magnitude lower concentration, or enhance its maximum emission intensity at high concentration far beyond that achievable through conventional annihilation ECL of Ir(ppy)3 involving comproportionation. Moreover, under certain conditions, the colour of the emission can be selected through the applied electrochemical potentials. We have also prepared a novel Ir(iii) complex with a sufficiently low reduction potential that the reaction between its reduced form and Ir(ppy)3+ cannot populate the excited state of either luminophore. This enabled, for the first time, the exclusive formation of either excited state through the application of higher cathodic or anodic potentials, but in both cases, the ECL was greatly diminished by parasitic dark reactions.

Highly efficient electrochemiluminescence labels comprising iridium(iii) complexes

Highly efficient iridium ECL labels exhibiting various emission colors have been developed. Importantly, BSA labeled with the novel iridium labels displays much more intense ECL than the same amount labeled by a traditional ruthenium label in ProCell buffer solution.