Surface-Bonding-Enhanced Self-Co-Reactant Electrogenerated Chemiluminescence for Sensitive and Selective Detection of Thioglycolic Acid in Cosmetics

Thioglycolic acid (TGA) is an organic compound widely used in cosmetics that cause a variety of health problems when overexposed to it. So far many attempts have been made to develop methods for TGA detection, but most of them need sophisticated instrumentations and are a little bit complicated. Therefore, a simple, cheap and sensitive detection method of TGA is highly desired. Herein, we demonstrated for the first time an Au−S bonding amplified, highly sensitive electrochemiluminescence (ECL) sensing method for TGA detection using tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) as a luminophore and TGA as a self-co-reactant, via an anodic reaction at the Au electrode surface. Due to different molecular coordination environments of the TGA at the electrode surface, the ECL signal intensity of the developed ECL system gives much higher ECL signal in borate buffer than phosphate buffer of the same pH. Under the optimized experimental conditions, the ECL intensity has a direct relationship with the concentration of TGA in the range of 0.03 μM to 300 μM and a limit of detection of 0.013 μM (3σ/m). The reported ECL system has further been applied for the detection of TGA in cosmetics with acceptable recoveries.     

共晶诱导增强的电化学发光9,10-二苯基蒽-苝微晶构建高效尿酸传感器

采用表面活性剂辅助自组装方法, 制得非共平面分子9,10-二苯基蒽(DPA)与平面型分子苝(Pe)形成的具有共晶诱导增强效应的电化学发光(ECL)新材料. DPA的引入不仅可以有效降低Pe分子因π-π作用聚集 引起的聚集诱导猝灭(ACQ)效应, 导致Pe分子的ECL发射从二聚体或多聚体激发态(¹Pe^2*)转变为单体激 发态(¹Pe^*); 还发挥了供体分子的作用, 为受体分子Pe提供了有效的能量传递, 进一步增强了ECL响应. 将该共晶发光材料修饰到玻碳电极表面构建了新型ECL尿酸传感器, 其对尿酸检测的线性范围为0.01 μmol/L~ 5.0 mmol/L, 检出限为4.0 nmol/L, 具有良好的选择性和稳定性.     

Self-enhanced multicolor electrochemiluminescence by competitive electron-transfer processes

Controlling electrochemiluminescence (ECL) color(s) is crucial for many applications ranging from multiplexed bioassays to ECL microscopy. This can only be achieved through the fundamental understanding of high-energy electron-transfer processes in complex and competitive reaction schemes. Recently, this field has generated huge interest, but the effective implementation of multicolor ECL is constrained by the limited number of ECL-active organometallic dyes. Herein, the first self-enhanced organic ECL dye, a chiral red-emitting cationic diaza [4]helicene connected to a dimethylamino moiety by a short linker, is reported. This molecular system integrates bifunctional ECL features (i.e. luminophore and coreactant) and each function may be operated either separately or simultaneously. This unique level of control is enabled by integrating but decoupling both molecular functions in a single molecule. Through this dual molecular reactivity, concomitant multicolor ECL emission from red to blue with tunable intensity is readily obtained in aqueous media. This is done through competitive electron-transfer processes between the helicene and a ruthenium or iridium dye. The reported approach provides a general methodology to extend to other coreactant/luminophore systems, opening enticing perspectives for spectrally distinct detection of several analytes, and original analytical and imaging strategies.

Controlling electrochemiluminescence (ECL) color(s) is crucial for many applications ranging from multiplexed bioassays to ECL microscopy.     

A glassy carbon electrode modified with C-dots and silver nanoparticles for enzymatic electrochemiluminescent detection of glutamate enantiomers

This paper describes an electrochemiluminescent (ECL) based method for chiral recognition and detection of both glutamate (Glu) enantiomers. The luminophore luminol (Lum) was used as both the reductant and stabilizer of Ag nanoparticles (AgNP-Lum) which were combined with carbon quantum dots (C-dots) and placed on a glassy carbon electrode (GCE) along with the enzyme glutamate oxidase (GluOx). The use of these materials is found to result in strong amplification of ECL. The nanomaterials used were characterized by transmission electron microscopy (TEM) and Fourier transform infrared (FTIR). The stepwise fabrication of the electrode was verified by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Under optimized conditions and by applying a typical potential of 0.6 V, the ECL increases linearly in the 5.0 μM to 5.0 mM Glu concentration range, with a 1.6 μM lower detection limit and satisfactory selectivity. A Glu logic gate idea has been designed that is based on this enzymatic biosensor.

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Graphical abstract Schematic presentation of the electrochemiluminescent (ECL) biosensor. A glassy carbon electrode (GCE) was modified with C-dots and silver nanoparticles which were deoxidized by luminol (AgNP-Lum) for enzymatic specific detection.

     

Disposable electrochemiluminescent biosensor using bidentate-chelated CdTe quantum dots as emitters for sensitive detection of glucose

A novel disposable solid-state electrochemiluminescent (ECL) biosensor was fabricated by immobilizing glucose oxidase and surface-unpassivated CdTe quantum dots (QDs) on a screen-printed carbon electrode (SPCE). The surface morphology of the biosensor was characterized with scanning electron microscopy and atomic force microscopy. With dissolved O(2) as an endogenous coreactant, QDs/SPCE showed strong ECL emission in pH 9.0 HCl-Tris buffer solution with low ECL peak potential at -0.89 V. The ECL intensity was twice that with hydrogen peroxide as coreactant at the same concentration. This phenomenon meant the ECL decreased upon consumption of dissolved O(2) and thus could be applied to the construction of oxidase-based ECL biosensors. With glucose oxidase as a model enzyme, the biosensor showed rapid response to glucose with a linear range of 0.8 to 100 μM and a detection limit of 0.3 μM. Further detection of glucose contained in human serum samples showed acceptable sensitivity and selectivity. This work provided a promising application of QDs in ECL-based disposable biosensors.     

A ruthenium(II) complex based turn-on electrochemiluminescence probe for the detection of nitric oxide

Electrochemiluminescence (ECL) detection technique using bipyridine-ruthenium(II) complexes as probes is a highly sensitive and widely used method for the detection of various biological and bioactive molecules. In this work, the spectral, electrochemical and ECL properties of a chemically modified bipyridine-ruthenium(II) complex, [Ru(bpy)(2)(dabpy)](2+) (bpy: 2,2'-bipyridine; dabpy: 4-(3,4-diaminophenoxy)-2,2'-bipyridine), were investigated and compared with those of its nitric oxide (NO)-reaction derivative [Ru(bpy)(2)(T-bpy)](2+) (T-bpy: 4-triazolephenoxy-2,2'-bipyridine) and [Ru(bpy)(3)](2+). It was found that the ECL intensity of [Ru(bpy)(2)(dabpy)](2+) could be selectively and sensitively enhanced by NO due to the formation of [Ru(bpy)(2)(T-bpy)](2+) in the presence of tri-n-propylamine. By using [Ru(bpy)(2)(dabpy)](2+) as a probe, a sensitive and selective ECL method with a wide linear range (0.55 to 220.0 μM) and a low detection limit (0.28 μM) was established for the detection of NO in aqueous solutions and living cells. The results demonstrated the utility and advantages of the new ECL probe for the detection of NO in complicated biological samples.     

Quenching Behavior of the Electrochemiluminescence of Ru(bpy)32+/TPrA System by Phenols on a Smartphone-Based Sensor

Phenolic compounds such as vanillic and p-coumaric acids are pollutants of major concern in the agro-industrial processing, thereby their effective detection in the industrial environment is essential to reduce exposure. Herein, we present the quenching effect of these compounds on the electrochemiluminescence (ECL) of the Ru(bpy)₃²⁺/TPrA (TPrA=tri-n-propylamine) system at a disposable screen-printed carbon electrode. Transient ECL profiles are obtained from multiple video frames following 1.2 V application by a smartphone-based ECL sensor. A wide range of detection was achieved using the sensor with limit of detection of 0.26 μM and 0.68 μM for vanillic and p-coumaric acids, respectively. The estimated quenching constants determined that the quenching efficiency of vanillic acid is at least two-fold that of p-coumaric acid under the current detection conditions. The present ECL quenching approach provided an effective method to detect phenolic compounds using a low-cost, portable smartphone-based ECL sensor.     

Synergistic Enhancement Effects of Carbon Quantum Dots and Au Nanoclusters for Cathodic ECL and Non‐enzyme Detections of Glucose

In this study, we found that glucose enhance electrochemiluminescence (ECL) intensity of both Au nanoclusters (Au NCs) and carbon quantum dots (CQDs) with K₂S₂O₈ as the co‐reactants. The enhancing effects by Au NCs and CQDs were overlapped, enabling the detection of glucose. The increased ECL intensity of glucose was linear with the logarithm of concentrations of glucose in the range of 50 μM–3.0 mM, and the limit of detection is 20 μM. Anti‐interruption ability was achieved, and ascorbic acid, urea, and uric acid had little influence to glucose detection. This method realized the direct detection of glucose by enhancing ECL of Au NCs and CQDs, which was fast and economic, possessing potential applications for glucose detection in human serum.     

Ultrasensitive Electrochemiluminescence Biosensor for mRNA Based on Polymerase Assisted Signal Amplification

A novel biosensor for ultra‐trace mRNA sensing was constructed based on isothermal circular strand‐replacement polymerization (CSRP) to amplify the electrochmeiluminescence (ECL) signal by combining quantum dots (CdTe) as luminophore. After the hairpin‐like capture DNA was opened by hybridization with target mRNA, the additive primer (DNA1) was able to get access to its complementary sequence which is partially belong to the stem part and triggered a polymerization of DNA strand, leading to the release of target mRNA and another polymerization cycle. The remaining sequence of the stem part continued to hybridize with QDs labeled DNA, accomplishing ECL signal amplification. Target mRNA could be specifically assayed with a linear relationship between the signal intensity and the logarithm of concentrations of target DNA in the range of 1.0×10⁻¹⁴∼5.0×10⁻¹⁰ M, with a low detection limit of 1.4×10⁻¹⁵ M. The signal could discriminate perfect matched target mRNA from 1‐base mismatch sequence. This proposed ECL biosensor exhibited an efficient performance in serum sample, opening new opportunities for genetic target analysis in diagnostic and clinic biomedical fields.     

Scanning electrochemical microscopy study of ion annihilation electrogenerated chemiluminescence of rubrene and [Ru(bpy)3]2+

Scanning electrochemical microscopy (SECM) was used for the study of electrogenerated chemiluminescence (ECL) in the radical annihilation mode. The concurrent steady-state generation of radical ions in the microgap formed between a SECM probe and a transparent microsubstrate provides a distance-dependent ECL signal that can provide information about the kinetics, stability, and mechanism of the light emission process. In the present study, the ECL emission from rubrene and [Ru(bpy)(3)](2+) was used to model the system by carrying out experiments with the SECM and light-detecting apparatus inside an inert atmosphere box. We studied the influence of the distance between the two electrodes, d, and the annihilation kinetics on the ECL light emission profiles under steady-state conditions, as well as the ECL profiles when carrying out cyclic voltammetry (CV) at a fixed d. Experimental results are compared to simulated results obtained through commercial finite element method software. The light produced by annihilation of the ions was a function of d; stronger light was observed at smaller d. The distance dependence of the ECL emission allows the construction of light approach curves in a similar fashion as with the tip currents in the feedback mode of SECM. These ECL approach curves provide an additional channel to describe the reaction kinetics that lead to ECL; good agreement was found between the ECL approach curve emission profile and the simulated results for a fast, diffusion-limited second-order annihilation process (k(ann) > 10(7) M(-1) s(-1)). In the CV mode at fixed distance, the ECL emission of rubrene showed two distinct signals at different potentials when fixing the substrate to generate the radical cation and scanning the tip to generate the radical anion. The first signal (pre-emission) corresponded to an emission well before reaching the generation of the radical anion and was more intense on Au than on Pt. The second ECL signal showed the expected steady-state behavior from the second-order annihilation reaction and agreed well with the simulation. A comparison of the emission obtained with rubrene and [Ru(bpy)(3)](2+) to test the direct formation of lower energy triplets directly at the electrode showed that triplets are not the cause of the pre-emission observed. Wavelength selection experiments for the rubrene system showed that the pre-emission ECL signal also appeared slightly red-shifted with respect to the main luminophore emission; a possible explanation for this phenomenon is inverse photoemission, where the injection of highly energetic holes by the oxidized species into the negatively biased tip electrode causes emission of states in the metal that appear at a different wavelength than the singlet emission from the ECL luminophore.     

Carbon optically transparent electrodes for electrogenerated chemiluminescence

This study investigates pyrolyzed photoresist film (PPF)-based carbon optically transparent electrodes (C-OTEs) for use in electrogenerated chemiluminescence (ECL) studies. Oxidative-reductive ECL is obtained with a well-characterized ECL system, C8S3 J-aggregates with 2-(dibutylamino)ethanol (DBAE) as coreactant. Simultaneous cyclic voltammograms (CVs) and ECL transients are obtained for three thicknesses of PPFs and compared to nontransparent glassy carbon (GC) and the conventional transparent electrode indium tin oxide (ITO) in both front face and transmission electrode cell geometries. Despite positive potential shifts in oxidation and ECL peaks, attributed to the internal resistance of the PPFs that result from their nanoscale thickness, the PPFs display similar ECL activity to GC, including the low oxidation potential (LOP) observed for amine coreactants on hydrophobic electrodes. Reductive-oxidative ECL was obtained using the well-studied ECL luminophore Ru(bpy)(3)(2+), where the C-OTEs outperformed ITO because of electrochemical instability of ITO at very negative potentials. The C-OTEs are promising electrodes for ECL applications because they yield higher ECL than ITO in both oxidative-reductive and reductive-oxidative ECL modes, are more stable in alkaline solutions, display a wide potential window of stability, and have tunable transparency for more efficient detection of ECL.     

Capillary electrophoresis–electrochemiluminescence detection method for the analysis of ibandronate in drug formulations and human urine

A simple, rapid and sensitive CE method coupled with electrochemiluminescence (ECL) detection for direct analysis of ibandronate (IBAN) has been developed. Using a buffer solution of 20 mM sodium phosphate (pH 9.0) and a voltage of 13.5 kV, separation of IBAN in a 30‐cm length capillary was achieved in 3 min. ECL detection was performed with an indium tin oxide working electrode bias at 1.6 V (versus a Pt wire reference) in a 200‐mM sodium phosphate buffer (pH 8.0) containing 3.5 mM Ru(bpy)₃²⁺ (where bpy=2,2′‐bipyridyl). Derivatization of IBAN prior to CE‐ECL analysis was not needed. Linear correlation (r=0.9992, n=7) between ECL intensity and analyte concentration was obtained in the range of 0.25–50 μM IBAN. The LOD of IBAN in water was 0.08 μM. The developed method was applied to the analysis of IBAN in a drug formulation and human urine sample. SPE using magnetic Fe₃O₄@Al₂O₃ nanoparticles as the extraction phase was employed to pretreat the urine sample before CE‐ECL analysis. The linear range was 0.2–12.0 μM IBAN in human urine (r=0.9974, n=6). The LOD of IBAN in urine was 0.06 μM. Total analysis time including sample preparation was <1 h.     

Imaging latent fingerprints by electrochemiluminescence

By exposing an electrode surface with a latent fingerprint to electrochemiluminescence (ECL)-generating luminophore, ECL is produced from the surface not covered by the fingerprint, generating a negative image. The fingerprint can also be pre-stained by luminophores, which generates ECL and yields a positive image (right). ITO=indium tin oxide.     

Ultrasensitive Imaging of Cells and Sub-Cellular Entities by Electrochemiluminescence

Here we report on a label-free electrochemiluminescence (ECL) microscopy using exceptionally low concentrations of the [Ru(bpy)₃]²⁺ luminophore. This work addresses the central point of the minimal concentration of the ECL luminophore required to image single entities. We demonstrate the possibility to record ECL images of cells and mitochondria at concentrations down to nM and pM. This is 7 orders of magnitude lower than classically-used concentrations and corresponds to a few hundreds of luminophores diffusing around the biological entities. Yet, it produces remarkably sharp negative optical contrast ECL images, as demonstrated by structural similarity index metric analyses and supported by predictions of the ECL image covering time. Finally, we show that the reported approach is a simple, fast, and highly sensitive method, which opens new avenues for ultrasensitive ECL imaging and ECL reactivity at the single molecule level.     

A Highly Sensitive Electrochemiluminescence Spermine Biosensor Based on Au−Ag Bimetallic Nanoclusters

In this study, we found that spermine (SPM) could enhance electrochemiluminescence (ECL) intensity of Au−Ag bimetallic nanoclusters (Au−Ag BNCs) with triethylamine (TEA) as a co-reactant. An ECL sensor was fabricated to detect SPM, which contained Au−Ag BNCs as ECL emitters and conductive hydrogel containing polyaniline-amino trimethylene phosphonic acid (PANI-ATMP) as an immobilizing matrix. The increased ECL intensity of SPM was linear with the logarithm of concentrations of SPM in the range of 1 pM to 10 μM with high selectivity, excellent stability, and the limit of detection is 0.11 pM (S/N=3). This sensor realized the detection of SPM in urine samples, which was fast and economic, possessing potential applications for SPM detection in clinical and bioanalysis.     

Enhanced electrochemiluminescence from luminol at multi-walled carbon nanotubes decorated with palladium nanoparticles: a novel route for the fabrication of an oxygen sensor and a glucose biosensor

Incorporation of palladium nanoparticles on the surface of multi-walled carbon nanotubes and modification of glassy carbon electrode with the prepared nano-hybrid material led to the fabrication of a novel electrode. The modified electrode showed attractive electrocatalytic activity and sensitizing effect on luminol-O(2) and luminol-H(2)O(2) electrochemiluminescence (ECL) reactions at neutral media. The sensitized luminol-O(2) and luminol-H(2)O(2) reactions were successfully applied for the ECL determination of dissolved O(2) and glucose, respectively. Under the optimal conditions for luminol-O(2) system, the ECL signal intensity of luminol was linear with the concentration of dissolved oxygen in the range between 0.08 and 0.94 mM (r=0.9996) and for luminol-H(2)O(2) system, the ECL signal intensity of luminol was linear with the concentration of glucose in the range between 0.1 and 1000 μM (r=0.9998). The limits of detection (S/N=3) for dissolved oxygen and glucose were 0.02 mM and 54 nM, respectively. The relative standard deviations (RSD) for repetitive measurements of 0.50 mM oxygen (n=10) and 10 μM glucose (n=30) were 3.5% and 0.3%, respectively. Also, under the optimal conditions for luminol-H(2)O(2) system, the ECL signal intensity of luminol was linear with the concentration of H(2)O(2) in the range between 1 nM and 0.45 mM (r=0.9997). The limit of detection (S/N=3) for H(2)O(2) detection was 0.5 nM and the relative standard deviation for repetitive measurements of 10 μM H(2)O(2) (n=10) was 0.8%.     

Electrogenerated chemiluminescence in systems with tetraphenylborate anion as a co-reactant

The study of electrogenerated chemiluminescence (ECL) in aqueous and non-aqueous media with tetraphenylborate anion as a co-reactant is reported. The obtained results indicate that tetraphenylborate acts according to an oxidative reduction scheme and forms a strong reducer after being homogeneously oxidized by a radical cation or dication of luminophore. Spectral measurements prove that light emission originates from the luminophore present in solution and practically no emission occurs when only tetraphenylborate ion is oxidized at the electrode. Since the tetraphenylborate ion is a well known analytical reactant and precipitates a number of metal and organic cations its electrochemiluminescent detection can be used for their assay. It can also be applied as an efficient co-reactant for electrogenerated chemiluminescence excitation both in aqueous and non-aqueous media.     

Advances in bipolar electrochemiluminescence for the detection of biorelevant molecular targets

Bipolar electrochemistry (BPE) contrasts very much with conventional electrochemistry because it is based on the control of the solution potential instead of the working electrode potential. In a typical setup, a piece of conducting materials is immersed in an electrolyte and submitted to an electric field. Such conditions split the interfacial nature of the materials into cathodic and anodic domains where electrochemical reactions can readily take place. BPE has many potential applications, and the present contribution aims to focus on recent analytical applications that involve electrogenerated chemiluminescence (ECL) detection. ECL is a special case of luminescence where the excited state of the luminophore is populated after a sequence of reaction that is triggered by an initial electron transfer step occurring at the electrode surface. The coupling between BPE and ECL is a powerful approach because it provides a unique opportunity to combine the intrinsic advantages of both techniques. BPE enables the spatial separation of sensing and reporting poles, whereas ECL provides a simple and sensitive visual readout. This opinion article will describe the experimental possibilities and the most recent applications of BPE/ECL coupling for the detection of biorelevant molecular targets.     

基于花状铂纳米颗粒构建的电致化学发光免疫传感器用于检测载脂蛋白A1

采用一锅合成法制备了新型的具有大比表面积的花状铂纳米颗粒（PtNFs）,并构建了一个高灵敏电致化学发光（ECL）免疫传感器用于检测载脂蛋白A1（Apo-A1）. 该PtNFs用于吸附二抗（anti-Apo-A1）,并用葡糖糖氧化酶（GOD）封闭其表面的非特异性位点,最终制备了PtNFs@anti-Apo-A1@GOD信号探针. 当Apo-A1存在时,通过夹心免疫反应将制备的信号探针捕获于电极表面,并将所制得的电极置于含有葡萄糖的过硫酸根底液中检测. GOD催化葡萄糖产生H₂O₂,H₂O₂在PtNFs的催化下分解并在电极表面原位产生O₂,所产生的O₂能够催化过硫酸根-氧气体系的电致化学发光反应,放大发光信号,提高检测灵敏度. 该传感器在0.1ng•mL^-1 ~ 100 ng•mL^-1范围内对Apo-A1有良好的线性响应,检测下限达到0.03ng•mL^-1,有望应用于临床分析诊断.     

Pressure-responsive AuNPs/Polyacrylamide Nanocomposite Hydrogel with Highly Stable and Tunable Electrochemiluminescence Performances

Synergistically taking the advantage of distinctive porous matrix, luminophore and functional nanoparticles, we prepared functional nanocomposite hydrogel combining the hydrophilic three-dimensional network of hydrogels as matrix for the adsorption of luminophore, Ru(bpy)₃²⁺, and in situ grown gold nanoparticles (AuNPs) as the conductive. Interestingly, the designed nanocomposite hydrogel shows external pressure resposnsive properties, which precisely tune the distance between the AuNPs becomes shorter, resulting in a remarkable amplification of electrochemiluminescence (ECL) signals. Additionally, differing from the poor stability of conventional ECL, uniform dispersion of the Ru(bpy)₃²⁺ over nanocomposite hydrogel significantly enhanced the long term stability of ECL.