Tris(2,2'-bipyridyl)ruthenium(II) chemiluminescence

Fabrication of an all-in-one self-enhanced solid-state electrochemiluminescence sensing platform for the selective detection of spermine

The fabrication of an all-in-one solid-state ECL sensing platform is beneficial not only for expediting the miniaturization of sensing devices, but also, more importantly, for enabling point-of-care applications. In the present work, a self-enhanced solid-state ECL sensing platform is fabricated using newly synthesised silica polyethylene nanoparticles (SiO2-PEI NPs) which generate a co-reactant in situ and easily self-assemble with Ru(bpy)32+ and shows selective and sensitive detection of spermine at physiological pH (7.4). Spermine induces the maximum ECL emission intensity compared to other biogenic amines due to the presence of two secondary amines. A possible ECL reaction mechanism has been proposed based on CV and ECL experiments, DFT calculations, and in situ ECL spectrum analysis. The developed solid-state sensor showed a linear increase in ECL intensity with increasing spermine concentration in the range of 10 nM to 100 nM with an LOD of 12.2 nM. Compared to other biogenic amines in previous works, chemically synthesised SiO2-PEI NPs used in the present study act as an effective label- and enzyme-free sensor, and the new method is observed to be simple and cost-effective, to overcome various limitations of solution-phase ECL and to avoid the usage of any noble metals.

Chemiluminescence and electrochemiluminescence of water-soluble iridium(III) complexes containing a tetraethylene-glycol functionalised triazolylpyridine ligand

BACKGROUND

Iridium(III) complexes, exhibiting high luminescence quantum yields and a wide range of emission colours, are promising alternatives to tris(2,2'-bipyridine)ruthenium(II) for chemiluminescence (CL) and electrochemiluminescence (ECL) detection. This emerging class of reagent, however, is limited by the poor solubility of many iridium(III) complexes in aqueous solution, and lack of understanding of their remarkably variable selectivities towards different analytes.

RESULTS

Seven [Ir(C^N)2(pt-TEG)]+ complexes, exhibiting a wide range of reduction potentials and emission energies, were examined with six model analytes. For CL, cerium(IV) was used as the oxidant. The alkylamine analytes generally produced greater CL and ECL with the more readily oxidised Ir(III) complexes (C^N = piq, bt, ppy), predominantly through the 'direct' pathway requiring oxidation of both metal complex and analyte. Aniline derivatives that did not also contain secondary or tertiary alkylamines elicited CL from the less readily oxidised complexes (C^N = df-ppy-CF3, df-ppy) via energy transfer. The most difficult to oxidise complexes (C^N = df(CF3)-ppy-Me, df(CN)-ppy) gave poor responses due to the limited potential window of the solvent and inefficiency of energy transfer to their high energy excited states. Greater CL and/or ECL intensities were generally obtained for each analyte with at least one Ir(III) complex than with [Ru(bpy)3]2+; superior limits of detection for two analytes were demonstrated.

SIGNIFICANCE

This exploration of CL/ECL in which the properties of luminophore, analyte and oxidant are all varied provides a new understanding of the influence of the metal-complex potentials and excited state energy on the light-producing and quenching pathways, and consequently, their distinct selectivity towards different analytes. These findings will guide the development of water-soluble Ir(III) complexes as CL and ECL reagents.

Electrochemiluminescence of a First-Row d6 Transition Metal Complex

We report the electrochemiluminescence (ECL) of a 3d6 Cr(0) complex ([Cr(LMes)3]; λem=735 nm) with comparable photophysical properties to those of ECL-active complexes of 4d6 or 5d6 precious metal ions. The electrochemical potentials of [Cr(LMes)3] are more negative than those of [Ir(ppy)3] and render the [Cr(LMes)3]* excited state inaccessible through conventional co-reactant ECL with tri-n-propylamine or oxalate. ECL can be obtained, however, through the annihilation route in which potentials sufficient to oxidise and reduce the luminophore are alternately applied. When combined with [Ir(ppy)3] (λem=520 nm), the annihilation ECL of [Cr(LMes)3] was greatly enhanced whereas that of [Ir(ppy)3] was diminished. Under appropriate conditions, the relative intensities of the two spectrally distinct emissions can be controlled through the applied potentials. From this starting point for ECL with 3d6 metal complexes, we discuss some directions for future development.

Progress in Procalcitonin Detection Based on Immunoassay

Procalcitonin (PCT) serves as a crucial biomarker utilized in diverse clinical contexts, including sepsis diagnosis and emergency departments. Its applications extend to identifying pathogens, assessing infection severity, guiding drug administration, and implementing theranostic strategies. However, current clinical deployed methods cannot meet the needs for accurate or real-time quantitative monitoring of PCT. This review aims to introduce these emerging PCT immunoassay technologies, focusing on analyzing their advantages in improving detection performances, such as easy operation and high precision. The fundamental principles and characteristics of state-of-the-art methods are first introduced, including chemiluminescence, immunofluorescence, latex-enhanced turbidity, enzyme-linked immunosorbent, colloidal gold immunochromatography, and radioimmunoassay. Then, improved methods using new materials and new technologies are briefly described, for instance, the combination with responsive nanomaterials, Raman spectroscopy, and digital microfluidics. Finally, the detection performance parameters of these methods and the clinical importance of PCT detection are also discussed.

Determination of pioglitazone hydrochloride by flow injection chemiluminescence tris(2,2'-bipyridyl)ruthenium(II)-silver(III) complex system

A novel flow injection-chemiluminescence (FI-CL) approach is proposed for the assay of pioglitazone hydrochloride (PG-HCl) based on its enhancing influence on the tris(2,2'-bipyridyl)ruthenium(II)-silver(III) complex (Ru(bipy)₃ ²⁺ -DPA) CL system in sulfuric acid medium. The possible CL reaction mechanism is discussed with CL and ultraviolet (UV) spectra. The optimum experimental conditions were found as: Ru(bipy)₃ ²⁺ , 5.0 × 10^-5  M; sulfuric acid, 1.0 × 10^-3  M; diperiodatoargentate(III) (DPA), 1.0 × 10^-4  M; potassium hydroxide, 1.0 × 10^-3  M; flow rate 4.0 ml min^-1 for each flow stream and sample loop volume, 180 μl. The CL intensity of PG-HCl was linear in the range of 1.0 × 10^-3 to 5.0 mg L^-1 (R²  = 0.9998, n = 10) with limit of detection [LOD, signal-to-noise ratio (S/N) = 3] of 2.2 × 10^-4  mg L^-1 , limit of quantification (LOQ, S/N = 10) of 6.7 × 10^-4  mg L^-1 , relative standard deviation (RSD) of 1.0 to 3.3% and sampling rate of 106 h^-1 . The methodology was satisfactorily used to quantify PG-HCl in pharmaceutical tablets with recoveries ranging from 93.17 to 102.77 and RSD from 1.9 to 2.8%.

Flow injection-chemiluminescence determination of cetirizine dihydrochloride in pharmaceuticals using tris(2,2'-bipyridyl)ruthenium (II)-Ag(III) complex reaction

A simple and sensitive flow injection-chemiluminescence (FI-CL) method was developed for determination of cetirizine dihydrochloride (CTZH) in pharmaceuticals. The method is primarily based on the enhancement effect of CTZH on the tris(2,2'-bipyridyl)ruthenium (II)-diperiodatoargentate (III) ([Ru(bpy)₃ ]²⁺ -Ag(III) complex) CL system in an acidic medium. The optimum investigated variables of the CL reaction were: [Ru(bpy)₃ ]²⁺ , 50 × 10^-6 mol/L; sulfuric acid, 1.0 × 10^-3 mol/L; Ag(III) complex, 100 × 10^-6 mol/L; potassium hydroxide, 1.0 × 10^-3 mol/L; flow rate, 3.0 ml/min and sample loop volume, 300 μl. The detection and quantification limits were 2.0 × 10^-4 and 5.0 × 10^-4 mg/L (S/N of 3 and 10) respectively with a linear calibration range of 5.0 × 10^-4 to 7.5 mg/L (R² = 0.9999, n = 11), injection throughput of 110/h and the relative standard deviations of 1.5-3.5% over the range studied. The methodology was successfully applied to determine CTZH in different pharmaceutical samples and validated with a high-performance liquid chromatography method, and resulted in the recovery of 94.6-108.6%. The probable CL reaction mechanism is described in brief.

Electrochemiluminescence Enhancement and Particle Structure Stabilization of Polymer Nanoparticle by Doping Anionic Polyelectrolyte and Cationic Polymer Containing Tertiary Amine Groups and Its Highly Sensitive Immunoanalysis

A doped polymer nanoparticle (dPNP) of electrochemiluminescence (ECL) was prepared via doping the anionic polyelectrolyte polyacrylic acid (PAA) and the cationic polymer poly-ethyleneimine (PEI) into the polymer nanoparticle (PNP), which was self-assembled by Ru(bpy)32+ derivative-grafted PAA (PAA–Ru) with both cations and anions. The good electrical conductivity of the doped polyelectrolyte PAA enhanced the ECL intensity of PNP to 109.1%, and the involvement of a large number of tertiary amine groups of the doped PEI further enhanced that to 127.3%; meanwhile, doping low-molecular-weight PEI into PNP, while simultaneously doping high-molecular-weight PAA, avoided the precipitation of PAA and PEI, due to interaction of the two oppositely charged polymers; and these also made the self-assembly procedure more effective and the nanoparticle structure more stable than PNP and also led to the production of rich residual PAA chains on the surface of dPNP. The storage results showed that the average hydrated particle diameter kept almost constant (197.5–213.1 nm) during 15-day storage and that the nanoparticles have rich surface charge of −11.47 mV (zeta potential), well suspension stability and good dispersity without detectable aggregation in the solution during the storage. Therefore, the nanoparticle is quite suitable for the antibody labeling, immunoassay and the storage. As a result, a high-sensitive ECL immunoassay approach with good precision, accuracy and selectivity was established and an ultra-low detection limit of 0.049 pg mL−1 (S/N = 3) for magnetic bead-based detection of Hepatitis B surface antigen was observed.

A conceptual framework for the development of iridium(iii) complex-based electrogenerated chemiluminescence labels

Translation of the highly promising electrogenerated chemiluminescence (ECL) properties of Ir(iii) complexes (with tri-n-propylamine (TPrA) as a co-reactant) into a new generation of ECL labels for ligand binding assays necessitates the introduction of functionality suitable for bioconjugation. Modification of the ligands, however, can affect not only the photophysical and electrochemical properties of the complex, but also the reaction pathways available to generate light. Through a combined theoretical and experimental study, we reveal the limitations of conventional approaches to the design of electrochemiluminophores and introduce a new class of ECL label, [Ir(C^N)2(pt-TOxT-Sq)]+ (where C^N is a range of possible cyclometalating ligands, and pt-TOxT-Sq is a pyridyltriazole ligand with trioxatridecane chain and squarate amide ethyl ester), which outperformed commercial Ir(iii) complex labels in two commonly used assay formats. Predicted limits on the redox potentials and emission wavelengths of Ir(iii) complexes capable of generating ECL via the dominant pathway applicable in microbead supported ECL assays were experimentally verified by measuring the ECL intensities of the parent luminophores at different applied potentials, and comparing the ECL responses for the corresponding labels under assay conditions. This study provides a framework to tailor ECL labels for specific assay conditions and a fundamental understanding of the ECL pathways that will underpin exploration of new luminophores and co-reactants.

Oxygen-Resistant Electrochemiluminescence System with Polyhedral Oligomeric Silsesquioxane

We report the oxygen-resistant electrochemiluminescence (ECL) system from the polyhedral oligomeric silsesquioxane (POSS)-modified tris(2,2'-bipyridyl)ruthenium(II) complex (Ru-POSS). In electrochemical measurements, including cyclic voltammetry (CV), it is shown that electric current and ECL intensity increase in the mixture system containing Ru-POSS and tripropylamine (TPrA) on the indium tin oxide (ITO) working electrode. The lower onset potential (E_onset) in CV is observed with Ru-POSS compared to tris(2,2'-bipyridyl)ruthenium(II) complex (Ru(bpy)₃²⁺). From the series of mechanistic studies, it was shown that adsorption of Ru-POSS onto the ITO electrode enhances TPrA oxidation and subsequently the efficiency of ECL with lower voltage. Moreover, oxygen quenching of ECL was suppressed, and it is proposed that the enhancement to the production of the TPrA radical could contribute to improving oxygen resistance. Finally, the ECL-based detection for water pollutant is demonstrated without the degassing treatment. The commodity system with Ru(bpy)₃²⁺ is not applicable in the absence of degassing with the sample solutions due to critical signal suppression, meanwhile the present system based on Ru-POSS was feasible for estimating the amount of the target even under aerobic conditions by fitting the ECL intensity to the standard curve. One of critical disadvantages of ECL can be solved by the hybrid formation with POSS.

Dynamic Interplay between Transport and Reaction Kinetics of Luminophores on the Operation of AC-Driven Electrochemiluminescence Devices

Electrochemiluminescence (ECL) involves light emission accompanied by a series of electrochemical processes on luminophores, which has been recently exploited in a new light-emitting device platform, referred to as the ECL device (ECLD). Here, we investigate the influence of the transport of the ECL luminophores and their reaction kinetics on the emission properties of alternating current-voltage-driven ECLDs. A model based on the diffusion and reaction rate equations is developed to predict the operational frequency ( f)-dependent luminance properties of the ECLD. It is found that more frequent generation of the redox precursors with a shorter time interval enhances their probability of encountering each other, and therefore the luminance of the device increases with increasing f initially. The luminance at a higher f, however, is suppressed eventually due to the decreased rate of the electrode reactions. Using the model, the influence of diffusion and reaction rates on the performance of an ECLD is analyzed separately and systematically. The results provide insight on the operation of this emerging class of a light-emitting device platform.

Enhanced annihilation electrochemiluminescence by nanofluidic confinement

The generation of stable enhanced light emission by electrochemiluminescence in microfabricated nanofluidic electrochemical devices is demonstrated for the first time by exploiting nanogap amplification.

Microfabricated nanofluidic electrochemical devices offer a highly controlled nanochannel geometry; they confine the volume of chemical reactions to the nanoscale and enable greatly amplified electrochemical detection. Here, the generation of stable light emission by electrochemiluminescence (ECL) in transparent nanofluidic devices is demonstrated for the first time by exploiting nanogap amplification. Through continuous oxidation and reduction of [Ru(bpy)₃]²⁺ luminophores at electrodes positioned at opposite walls of a 100 nm nanochannel, we compare classic redox cycling and ECL annihilation. Enhanced ECL light emission of attomole luminophore quantities is evidenced under ambient conditions due to the spatial confinement in a 10 femtoliter volume, resulting in a short diffusion timescale and highly efficient ECL reaction pathways at the nanoscale.

The recognition and electrochemiluminescence response of benzo[6]urils to polycyclic aromatic hydrocarbons

The electrochemiluminescence of benzo[6]urils was discovered and applied for molecular recognition based on the host–guest interactions with polycyclic aromatic hydrocarbons.

Microfluidic photoinduced chemical oxidation for Ru(bpy)33+ chemiluminescence - A comprehensive experimental comparison with on-chip direct chemical oxidation

For the first time, the analytical figures of merit in detection capabilities of the very less explored photoinduced chemical oxidation method for Ru(bpy)₃²⁺ CL has been investigated in detail using 32 structurally different analytes. It was carried out on-chip using peroxydisulphate and visible light and compared with well-known direct chemical oxidation approaches using Ce(IV). The analytes belong to various chemical classes such as tertiary amine, secondary amine, sulphonamide, betalactam, thiol and benzothiadiazine. Influence of detection environment on CL emission with respect to method of oxidation was evaluated by changing the buffers and pH. The photoinduced chemical oxidation exhibited more universal nature for Ru(bpy)₃²⁺ CL in detection towards selected analytes. No additional enhancers, reagents, or modification in instrumental configuration were required. Wide detectability and enhanced emission has been observed for analytes from all the chemical classes when photoinduced chemical oxidation was employed. Some of these analytes are reported for the first time under photoinduced chemical oxidation like compounds from sulphonamide, betalactam, thiol and benzothiadiazine class. On the other hand, many of the selected analytes including tertiary and secondary amines such as cetirizine, azithromycin fexofenadine and proline did not produced any analytically useful CL signal (S/N=3 or above for 1μgmL^-1 analyte) under chemical oxidation. The most fascinating observations was in the detection limits; for example ofloxacin was 15 times more intense with a detection limit of 5.81×10^-10M compared to most lowest ever reported 6×10^-9M. Earlier, penicillamine was detected at 0.1μgmL^-1 after derivatization using photoinduced chemical oxidation, but in this study, we improved it to 5.82ngmL^-1 without any prior derivatization. The detection limits of many other analytes were also found to be improved by several orders of magnitude under photoinduced chemical oxidation.

Evaluation of coloured materials in microfluidic flow-cells for chemiluminescence detection

Recent advances in the construction of chemiluminescence flow-cells has included high precision milling of channels into a range of different polymer materials, in efforts to maximise the transfer of light from the chemical reaction to the photodetector. However, little is known of the extent that the colour of polymer materials will influence this transfer. This may become increasingly important as chemiluminescence detection zones are integrated with other operations within microfluidic devices or micro total analysis systems (μTAS). Herein, we compare microfluidic flow-cells fabricated from five polymer sheets (clear, white, black, red, blue), using two flow-cell designs (spiral and serpentine), two modes of photodetection, and four chemiluminescence reactions that provide a range of different emission colours. The direct transfer of light from the reaction within the white flow-cell channel to the photodetector made only minor contributions (10%-20%) to the measured intensity, with the majority of the measured light first interacting with the polymer material into which the channels were machined. The extent that the emitted light was absorbed or reflected by the coloured polymer materials was dependent on not only the properties of the polymer, but also the spectral distribution of the chemiluminescence. The changes in chemiluminescence intensities from absorption of light by the flow-cell materials can be accompanied by distortion of the spectral distribution.

Analytically useful blue chemiluminescence from a water-soluble iridium(III) complex containing a tetraethylene glycol functionalised triazolylpyridine ligand

We examine [Ir(df-ppy)2(pt-TEG)](+) as the first highly water soluble, blue-luminescent iridium(III) complex for chemiluminescence detection. Marked differences in selectivity were observed between the new complex and the conventional [Ru(bpy)3](2+) reagent, which will enable this mode of detection to be extended to new areas of application.

Ruthenium bistridentate complexes with non-symmetrical hexahydro-pyrimidopyrimidine ligands: a structural and theoretical investigation of their optical and electrochemical properties

The optical and electronic properties of six Ru complexes with non-symmetrical tridentate ligands have been investigated and, as corroborated by electrochemical data, the presence of the hpp ligand strongly affects the oxidation potential of the metal ion.

ONO-pincer ruthenium complex-bound norvaline for efficient catalytic oxidation of methoxybenzenes with hydrogen peroxide

A Ru-bound norvaline shows enhanced catalytic activity for the oxidation of methoxybenzenes with unique chemoselectivity.

Anodic Electrogenerated Chemiluminescence of Ru(bpy)3(2+) with CdSe Quantum Dots as Coreactant and Its Application in Quantitative Detection of DNA

In the present paper, we report that CdSe quantum dots (QDs) can act as the coreactant of Ru(bpy)₃²⁺ electrogenerated chemiluminescence (ECL) in neutral condition. Strong anodic ECL signal was observed at ~1.10 V at CdSe QDs modified glassy carbon electrode (CdSe/GCE), which might be mainly attributed to the apparent electrocatalytic effect of QDs on the oxidation of Ru(bpy)₃²⁺. Ru(bpy)₃²⁺ can be intercalated into the loop of hairpin DNA through the electrostatic interaction to fabricate a probe. When the probe was bound to the CdSe QDs modified on the GCE, the intense ECL signal was obtained. The more Ru(bpy)₃²⁺ can be intercalated when DNA loop has larger diameter and the stronger ECL signal can be observed. The loop of hairpin DNA can be opened in the presence of target DNA to release the immobilized Ru(bpy)₃²⁺, which can result in the decrease of ECL signal. The decreased ECL signal varied linearly with the concentration of target DNA, which showed the ECL biosensor can be used in the sensitive detection of DNA. The proposed ECL biosensor showed an excellent performance with high specificity, wide linear range and low detection limit.

Chemiluminescence detection of MDMA in street drug samples using tris(2,2'-bipyridine)ruthenium(III)

Tris(2,2'-bipyridine)ruthenium(II) chemiluminescence was investigated for the detection of 3,4-methylenedioxymethamphetamine (MDMA) and several related compounds in street drug samples. Optimization using flow injection analysis showed that the selectivity of the reagent can be targeted towards the detection of secondary amines by altering the pH of the reaction environment. The greater selectivity of this mode of detection, compared to UV-absorbance, reduces the probability of false positive results from interfering compounds. The detection limit for MDMA under these conditions was 0.48 μM. A HPLC method incorporating post-column tris(2,2'-bipyridine)ruthenium(II) chemiluminescence detection was applied to the determination of MDMA in five street drug samples. The results obtained were in good agreement with quantification performed using traditional UV-absorbance detection, which demonstrates the viability of this method for confirmatory analysis of drug samples. This is the first report of tris(2,2'-bipyridine)ruthenium(II) chemiluminescence for the detection of MDMA and related amphetamine derivatives.

Simple chemiluminescence determination of ketotifen using tris(1,10 phenanthroline)ruthenium(II)- Ce(IV) system

A new method using chemiluminescence (CL) detection has been developed for the simple determination of ketotifen fumarate (KF). The method is based on the catalytic effect of KF in the CL reaction of tris(1,10 phenanthroline)ruthenium(II), Ru(phen)3 (2+), with Ce(IV) in sulfuric acid medium. The CL response was detected using a lab-made chemiluminometer. Effects of chemical variables were investigated and under optimum conditions, the CL intensity was proportional to the concentration of the drug over the range 0.34-34.00 µg mL(-1) KF. The limit of detection (S/N=3) was 0.09 µg mL(-1). Effects of common ingredients were investigated and the method was applied successfully for determining KF in pharmaceutical formulations and human plasma. The percent of relative standard deviation (n=11) at level of 3.4 µg mL(-1) of KF was 4.6% and the minimum sampling rate was 70 samples per hour. The possible CL mechanism is proposed based on the kinetic characteristic of the CL reaction, CL spectrum, UV-Vis and phosphorescence spectra.

A novel chiral electrochemiluminescence sensor that can discriminate proline enantiomers

A chiral stereoselective electrochemiluminescence (ECL) sensor was constructed by using Ru–AuNPs and β-CD–rGO composites to discriminate proline enantiomers.

An ON1–OFF–ON2 electrochemiluminescence response: combining the intermolecular specific binding with a radical scavenger

The electrochemiluminescence (ECL) technique was combined with the “ON¹–OFF–ON²” strategy based on the chemical reactions and specific binding among different small chemical compounds for the highly sensitive detection of nonelectroactive organophosphate pesticides.

Iridium(iii) N-heterocyclic carbene complexes: an experimental and theoretical study of structural, spectroscopic, electrochemical and electrogenerated chemiluminescence properties

Theoretical and experimental studies of a series of iridium N-heterocyclic carbene complexes.

Annihilation electrogenerated chemiluminescence of mixed metal chelates in solution: modulating emission colour by manipulating the energetics

We demonstrate the mixed annihilation electrogenerated chemiluminescence of tris(2,2'-bipyridine)ruthenium(ii) with various cyclometalated iridium(iii) chelates. Compared to mixed ECL systems comprising organic luminophores, the absence of T-route pathways enables effective predictions of the observed ECL based on simple estimations of the exergonicity of the reactions leading to excited state production. Moreover, the multiple, closely spaced reductions and oxidations of the metal chelates provide the ability to finely tune the energetics and therefore the observed emission colour. Distinct emissions from multiple luminophores in the same solution are observed in numerous systems. The relative intensity of these emissions and the overall emission colour are dependent on the particular oxidized and reduced species selected by the applied electrochemical potentials. Finally, these studies offer insights into the importance of electronic factors in the question of whether the reduced or oxidized partner becomes excited in annihilation ECL.

Ratiometric ECL of heterodinuclear Os–Ru dual-emission labels

The first ratiometric ECL of heterodinuclear Os–Ru dual-emission labels.