Influence of nature, concentration and pH of buffer acid–base system on rate determining step of the electrochemiluminescence of Ru(bpy)32+ with tertiary aliphatic amines

Kinetics-Based Ratiometric Electrochemiluminescence Analysis for Signal Specificity: Case Studies of Piperazine Drug Discrimination with Au Nanoclusters

A multi-parameter calibration and analysis strategy has been developed based on the kinetics of charge transfer reactions. Absolute and ratiometric electrochemiluminescence signals are elucidated from single measurements for the detection of hydroxyzine and cetirizine as prototype drugs which greatly enhance the near-infrared electrochemiluminescence from atomically precise Au₂₂ nanoclusters stabilized with lipoic acid ligands on ITO electrodes. The signal-on sensing mechanism eliminates the need for recognition elements and highly excess co-reactants in conventional electrochemiluminescence practice. The rates of sequential charge transfer reactions render specificity in electrochemiluminescence intensity and kinetics toward the target molecular/electronic structures and are conveniently controlled/optimized by operation parameters. Signal kinetic profiles, in stark contrast to steady-state or single-point recordings, not only improve the signal/noise ratio but also offer greater resolving power to differentiate analogue species and nonspecific interference. The fundamental kinetics-based ratiometric concept/strategy is not limited to a specific luminophore or a co-reactant and is thus generalizable. The case studies successfully detect and discriminate drug compounds at sub-nanomolar physiological ranges, with efficacy validated using synthetic urine toward point-of-care applications in therapeutic/abuse drug monitoring.

Ultrasensitive electrochemiluminescence sensor based on perovskite quantum dots coated with molecularly imprinted polymer for prometryn determination

A highly effective molecularly imprinted electrochemiluminescence sensor was constructed for prometryn determination in environmental and biological samples by using perovskite quantum dots coated with a molecularly imprinted silica layer (MIP/CsPbBr₃-QDs) as the recognition and response element. MIP/CsPbBr₃-QDs were immobilized on a glassy carbon electrode (GCE) through electropolymerization, and the electrochemiluminescence (ECL) response of MIP/CsPbBr₃-QDs could be motivated under the condition of H₂O₂ as co-reactant. ECL signal was selectively quenched with prometryn by hindering electron transfer and directly proportional to the logarithm of prometryn concentration (0.10-500.0 μg/L) with a correlation coefficient of 0.9960. Limits of detection in fish and seawater samples were 0.010 μg/kg and 0.050 μg/L, respectively. Excellent recoveries of 88.0%-106.0% were acquired for fish and seawater samples with a relative standard deviation below 4.2%. The constructed MIECL sensor based on MIP/CsPbBr₃-QDs showed good stability, accuracy, and precision for sensitive detection of prometryn in aquaculture products and environmental samples.

Shadow Electrochemiluminescence Microscopy of Single Mitochondria

Mitochondria are the subcellular bioenergetic organelles. The analysis of their morphology and topology is essential to provide useful information on their activity and metabolism. Herein, we report a label-free shadow electrochemiluminescence (ECL) microscopy based on the spatial confinement of the ECL-emitting reactive layer to image single living mitochondria deposited on the electrode surface. The ECL mechanism of the freely-diffusing [Ru(bpy)₃ ]²⁺ dye with the sacrificial tri-n-propylamine coreactant restrains the light-emitting region to a micrometric thickness allowing to visualize individual mitochondria with a remarkable sharp negative optical contrast. The imaging approach named "shadow ECL" (SECL) reflects the negative imprint of the local diffusional hindrance of the ECL reagents by each mitochondrion. The statistical analysis of the colocalization of the shadow ECL spots with the functional mitochondria revealed by classical fluorescent biomarkers, MitoTracker Deep Red and the endogenous intramitochondrial NADH, validates the reported methodology. The versatility and extreme sensitivity of the approach are further demonstrated by visualizing single mitochondria, which remain hardly detectable with the usual biomarkers. Finally, by alleviating problems of photobleaching and phototoxicity associated with conventional microscopy methods, SECL microscopy should find promising applications in the imaging of subcellular structures.

Self-electrochemiluminescence of CdTe nanocrystals capped with 2-diethylaminoethanethiol

The self-electrochemiluminescence of CdTe nanocrystals capped with 2-diethylaminoethanethiol was achieved via protective reagent exchange.

A review of electrogenerated chemiluminescent biosensors for assays in biological matrices

Electrogenerated chemiluminescence (ECL) is the production of light via electron transfer reactions between electrochemically produced reagents. ECL-based biosensors use specific biological interactions to recognize an analyte and produce a luminescent signal. Biosensors fabricated with novel biorecognition species have increased the number of analytes detected. Some of these analytes include peptides, cells, enzymes and nucleic acids. ECL biosensors are selective, simple, sensitive and have low detection limits. Traditional methods use ruthenium complexes or luminol to generate ECL. Nanomaterials can be incorporated into ECL biosensors to improve efficiency, but also represent a new class of ECL emitters. This article reviews the application of ruthenium complex, luminol and nanomaterial-based ECL biosensors to making measurements in biological matrices over the past 4 years.

Cyclometalated iridium(III) chelates-a new exceptional class of the electrochemiluminescent luminophores

Recent development of the phosphorescent cyclometalated iridium(III) chelates has enabled, due to their advantageous electrochemical and photo-physical properties, important breakthroughs in many photonic applications. This particular class of 5d(6) ion complexes has attracted increasing interest because of their potential application in electroluminescence devices with a nearly 100 % internal quantum efficiency for the conversion of electric energy to photons. Similar to electroluminescence, the cyclometalated iridium(III) chelates have been successfully applied in the electricity-to-light conversion by means of the electrochemiluminescence (ECL) processes. The already reported ECL systems utilizing the title compounds exhibit extremely large ECL efficiencies that allow one to envisage many potential application for them, especially in further development of ECL-based analytical techniques. This review, based on recently published papers, focuses on the ECL properties of this very exciting class of organometallic luminophores. The reported work, describing results from fundamental as well as application-oriented investigations, will be surveyed and briefly discussed. Graphical abstract Depending on the chemical nature of the cyclometalated irdium(III) chelate different colours of the emitted light can be produced during electrochemical excitation.

A novel electrochemiluminescent immunosensor based on CdS-coated ZnO nanorod arrays for HepG2 cell detection

In this work, the highly oriented CdS-coated-ZnO nanorod arrays have been fabricated. The CdS-coated-ZnO nanorod arrays show high electrochemiluminescence intensity, fast response and good stability. All of the desirable properties spur the development of an ECL immunosensor for the detection of the liver cancer cell line (HepG2 cells). Two successive modification steps of 3-aminopropyltriethoxysilane and gold nanoparticles onto the CdS-coated-ZnO nanorod arrays not only offer the substrates for conjugation of antibody, but also effectively enhance the ECL signal, resulting in production of the high performance ECL immunosensor. The ECL immunosensor exhibits a sensitive response to HepG2 cells in a linear range of 300-10,000 cells mL(-1) with a detection limit of 256 cells mL(-1). The proposed sensor characteristics of high specificity, good reproducibility and remarkable stability will provide a sensitive, selective, and convenient approach for the clinical detection of cancer cells.

Glucose sensing by electrogenerated chemiluminescence of glucose-dehydrogenase produced NADH on electrodeposited redox hydrogel

In this work, we report a new sensing approach based on electrogenerated chemiluminescence (ECL) in an electrodeposited redox hydrogel using glucose dehydrogenase as a model system. The ECL-hydrogel films were electrodeposited by potential cycling of a PBS solution containing [poly(4-vinylpyridine)Ru(2,2'-bipyridine)(2)Cl(-)](+/2+). The film was easily prepared in a rapid, reproducible and well-controlled one-step procedure. The deposited hydrogel film is permeable to water-soluble chemicals and biochemicals, like enzyme substrates and coenzymes. Electrochemistry and ECL of NADH were studied at the level of the hydrogel film. Results indicate that ECL emission occurs at a relatively low anodic potential compared to the classical Ru(bipy)(3)(2+) complex. This is an important advantage since the measurements performed with the ECL hydrogel are thus less sensitive to interfering species. An ECL oxidative-reductive mechanism is presented for the ECL-hydrogel. Then we showed that the intensity of the ECL of NADH produced by the enzymatic activity varies with the enzyme substrate concentration. Such sensing approach combines enzymatic selectivity with the ECL advantages at low oxidation potential.

Electrochemical aptasensor using the tripropylamine oxidation to probe intramolecular displacement between target and complementary nucleotide for protein array

Tripropylamine (TPA) has different oxidation efficiency at double stranded (ds)-and single stranded (ss)-DNA-modified electrodes. Using this property, a simple but sensitive biosensor using TPA oxidation to probe the intramolecular displacement was constructed with the analysis of lysozyme as model for the first time. After the complementary ss-DNA strand of anti-lysozyme aptamer was immobilized onto gold electrode via gold-thiol bond, the incubation with the aptamer resulted in the formation of ds-DNA. Lysozyme (in 10 μL sample) binding with aptamer displaced the complementary strand because of the high affinity of lysozyme and its aptamer, corresponding to the dissociation of the ds-DNA. The modified electrode was swept in 20mM TPA solution from 0.2 to 0.95 V. The difference in oxidation current was used to quantify the content of lysozyme with a linear range from 1.0 pM to 1.1 nM. That means 10 amol or 6.0 × 10(6) lysozyme molecules can be detected. Because the signal is produced from the preconcentrated TPA at the electrode surface, the high sensitivity is achieved over the single site labelling strategy. The proposed method is simple, stable, specific, and time-saving while the complicated sample pre-treatment and the labelling to the DNA strand are avoided. The biosensor was validated by the analysis of the diluted egg white sample directly. The recovery and reproducibility were 93.3-100% and 1.4-4.2%, respectively.

A sensitive, non-damaging electrochemiluminescent aptasensor via a low potential approach at DNA-modified gold electrodes

Electrochemiluminescence (ECL)-based biosensors are often used in the field of DNA- and protein-assay. Although ruthenium complex-based ECL is sensitive, its high exciting potential may lead to oxidation damage to biomolecules. For the first time, a non-damaging, low potential ECL aptasensor was constructed for bioassay with lysozyme as a model. After a single-stranded anti-lysozyme aptamer was attached to a gold electrode, a double stranded (ds)-DNA formed with its complementary strand. Ru(phen)(3)(2+), as an ECL probe, was intercalated into the ds-DNA. The hybridization of lysozyme with its aptamer led to the dissociation of ds-DNA because of the high stability of the aptamer-lysozyme and therefore the Ru(phen)(3)(2+) intercalated into ds-DNA was released. A low potential ECL was observed at the ds-DNA-modified electrode because ds-DNA was able to preconcentrate tripropylamine (TPA) and acted as the acceptor of the protons released from protonated TPAH(+). While the DNA sequence (anti-lysozyme aptamer) was used as the special recognition element for lysozyme, the formed ds-DNA also provided a micro-environment for low potential ECL. The low potential ECL aptasensor achieved the determination of lysozyme with a detection limit of 0.45 pM. The day-to-day precision (RSDs, n = 5) for the determination of lysozyme was lower than 5%, showing the reliability of the aptasensor. The regeneration of the aptasensor confirmed that the low potential for ECL could decrease oxidation damage to biomolecules. Further, the proposed method was successfully used to analyze diluted egg white sample directly. The protocol exhibited a promising platform for sensitive bioassay and could be further applied for the development of other low potential ECL sensing systems.

Label-free electrochemiluminescent aptasensor with attomolar mass detection limits based on a Ru(phen)(3)(2+)-double-strand DNA composite film electrode

Precisely known ligand-induced conformation change and complex chemical labeling of the DNA sequence with probe molecules are often needed for the signal generation in most of the previous aptasensors. Herein, a solution to the above problems was reported by the use of the Ru(phen)(3)(2+) intercalated into double strand DNA (ds-DNA) as an electrochemiluminescence (ECL) probe with thrombin as the target. After the antithrombin thiolated aptamer (27-mer) was attached to a gold electrode, ds-DNA structure was formed with its complementary 20-mer single strand DNA. Instead of the chemical modification of the aptamer or target with the probe molecule, Ru(phen)(3)(2+), as the probe, was intercalated into the ds-DNA structure. After thrombin hybridized with its aptamer, the ds-DNA dissociated and the intercalated Ru(phen)(3)(2+) released because of the higher stability of the aptamer-thrombin complex than that of the aptamer-complementary strand hybrid. The difference in ECL intensity with tripropylamine (TPA) as coreactant before and after the hybridization of thrombin and its aptamer was used to quantify thrombin. Besides the increase in the number of probe molecules over the single-site labeling, a ca. 80-fold improvement on the TPA oxidation at the ds-DNA modified electrode was found over the bare gold electrode. With the two amplification factors, the mass detection limits of 0.2 attomolar for thrombin are obtained. Because of the independence of conformational changes, the present method is readily extended to the targets whose aptamers have no specific conformational changes or other DNA-related detection without the need for chemical labeling.

Electrogenerated chemiluminescence

In electrogenerated chemiluminescence, also known as electrochemiluminescence (ECL), electrochemically generated intermediates undergo a highly exergonic reaction to produce an electronically excited state that then emits light. These electron-transfer reactions are sufficiently exergonic to allow the excited states of luminophores, including polycyclic aromatic hydrocarbons and metal complexes, to be created without photoexcitation. For example, oxidation of [Ru(bpy)(3)](2+) in the presence of tripropylamine results in light emission that is analogous to the emission produced by photoexcitation. This review highlights some of the most exciting recent developments in this field, including novel ECL-generating transition metal complexes, especially ruthenium and osmium polypyridine systems; ECL-generating monolayers and thin films; the use of nanomaterials; and analytical, especially clinical, applications.

Electrochemiluminescence immunosensor based on CdSe nanocomposites

A novel strategy for the enhancement of electrochemiluminescence (ECL) was developed by combining CdSe nanocrystals (NCs), carbon nanotube-chitosan (CNT-CHIT), and 3-aminopropyl-triethoxysilane (APS). A label-free ECL immunosensor for the sensitive detection of human IgG (HIgG) was fabricated. The colloidal solution containing CdSe NCs/CNT-CHIT composite was first covered on the Au electrode surface to form a robust film, which showed high ECL intensity and good biocompatibility. After APS as a cross-linker was covalently conjugated to the CdSe NCs/CNT-CHIT film, the ECL intensity was greatly enhanced. And, an intensity about 20-fold higher than that of the CdSe NCs/CNT-CHIT film was observed. After antibody was bound to the functionalized film via glutaric dialdehyde (GLD), the modified electrode could be used as an ECL immunosensor for the detection of HIgG. The specific immunoreaction between HIgG and antibody resulted in the decrease in ECL intensity. The ECL intensity decreased linearly with HIgG concentration in the range of 0.02-200 ng mL(-1), and the detection limit was 0.001 ng mL(-1). The immunosensor has the advantages of high sensitivity, speed, specificity, and stability and could become a promising technique for protein detection.