The Factors Affecting the Electrochemiluminescence of Tris(2,2′-bipyridyl)Ruthenium(II)/Tertiary Amines

A novel and efficient electrochemiluminescence sensing strategy for the determination of trimethylamine oxide in seafood

A novel and efficient electrochemiluminescence (ECL) sensing strategy and a solid-state ECL sensor was proposed to detect trimethylamine oxide (TMAO), which is widely presented in marine species and has important physiological functions. TMAO was reduced by Fe(II)-EDTA complex to trimethylamine, acting as coreactant, to amplify the ECL response of the Ru (bpy)32+ system. To improve the detection sensitivity and efficiency, a robust solid-state ECL probe was prepared and a flow injection ECL detection system was established with a specially designed flow ECL unit, under the excitation of stepping pulse potentials. Under optimized experimental conditions, the developed ECL sensor worked well for TMAO detection in a wide linear range of 10.00 μM to 1.00 mM with a limit of detection of 3.41 μM. It was successfully applied to determine TMAO in various species of seafood samples. This work provides a promising strategy for TMAO detection.

Nano-matrixes propped self-enhanced electrochemiluminescence biosensor for microRNA detection

MicroRNAs (miRNA) are the potential biomarker for breast cancer, a biosensor for detecting miRNA-21 was successfully prepared by covalently linking carbohydrazide (CON4H6) and tris (4,4 '- dicarboxylic acid-2,2' - bipyridyl) ruthenium dichloride (Ru (dcbpy)32+) as a self-enhanced emitter (Ru-CON4H6). The biosensor was prepared by coating the electrode with mesoporous silica encapsulated Ru-CON4H6 as luminophores (RMSNs) to covalently link a couple of DNA strands (Q1-H2). The RMSNs coated electrode exhibited strong ECL emission due to the intramolecular electron transfer between the electrochemically oxidized Ru (dcbpy)32+ and co-reactant CON4H6. In the presence of target miRNA-21 and an assistant hairpin H1, H2 could be released from the surface through a strand displacement reaction (SDR), and the reserved Q1 could form G-quadruplex upon the addition of K+. The formed G-quadruplex then interacted with Q2-Fc in the presence of Mg2+ to form a DNA complex on the biosensor surface, which quenched the nano-matrixes propped self-enhanced ECL emission through the electron exchange between Fc and electrode or oxidized ECL intermediates. Under optimal conditions, the ECL decrease showed a correlation with target concentration, leading to a biosensing method for sensitive detection of miRNA-21. The proposed ECL method demonstrated a detectable concentration range from 0.1 fM to 1 nM along with a detection limit of 0.03 fM, good accuracy, and acceptable reproducibility, showing that the self-enhanced ECL biosensing strategy supported by nano-matrix provided a new way for the ultrasensitive detection of miRNA, and promoted the development of breast cancer diagnosis.

Facile nano-free electrochemiluminescence biosensor for detection of sulphamethoxazole via tris(2,2'-bipyridyl)ruthenium(II) and N-methyl pyrrolidone recognition

The electrochemiluminescence (ECL) system based on the ruthenium complex has become a powerful tool in the field of analytical chemistry. However, the non-aqueous ECL luminescence system, which does not involve complex nano-modification, has not been widely used for the determination of analytes. In this study, N-methyl pyrrolidone was selected as the solvent, and it could also act as a co-reactant of [inline-formula removed]. Based on this, a simple ECL system without nanomaterials was established. Strong ECL was generated. Furthermore, a quenching effect between the excited state of [inline-formula removed] and sulphamethoxazole (SMZ) was observed. Based on this, a sensitive ECL sensor for detecting SMZ is constructed. A linear relationship between ECL signal quenching intensity (ΔI) and the logarithm of SMZ concentration (log C) in the concentration range of 1 × 10^-7-1 × 10^-5 mol/l is obtained. The limit of detection is as low as 3.33 × 10^-9 mol/l. The method has been applied to the detection of SMZ in tap water samples with different concentration levels with satisfactory results, and the recovery was 95.3-102.6%.

Signal enhancement and low oxidation potentials for miniaturized ECL biosensors via N-butyldiethanolamine

We present studies on ruthenium-based electrochemiluminescence (ECL) focusing on conditions supporting signal enhancement and low oxidation potentials. Low oxidation potentials (LOPs) are especially attractive for miniaturized ECL biosensors, as microfabricated electrodes tend to detach from their support when used with high currents and operated at high potentials. Furthermore, high potentials or current densities can lead to damage of typical biosensor surface coatings and biological probes. The possibility of generating LOP ECL signals at a potential below 900 mV was therefore studied for Ru(bpy)₃²⁺ with two typical coreactants, i.e. 2-(dibutylamino)ethanol (DBAE) and tripropylamine (TPA), as well as with the tertiary amine N-butyldiethanolamine (NBEA). Furthermore, the effect of buffer components and pH values on ECL signal generation was investigated. We could show a significant LOP ECL signal for NBEA. We found that Tris buffer, with its ability to form complexes with transition metal ions, has a positive influence on this ECL signal in terms of signal strength and LOP capabilities. Specifically, at basic pH values significant increases in ECL signals were observed at 900 mV and at 1.2 V. In fact, the ECL signal at 1.2 V was three times higher than the signal observed in phosphate buffer at a pH of 7, and it was thirty times higher than the ECL signal for TPA under these conditions. The LOP signal for NBEA in Tris buffer at pH 8.5 was similar to the signal obtained for TPA in phosphate buffer at pH 8.5 but three times higher than for TPA at pH 7.0. Interestingly, the coreactant DBAE was neither significantly influenced by the buffer system or pH nor did it present a valuable LOP ECL signal. Finally, it was found that high peak currents in cyclic voltammograms are not the indicators for high ECL signals, which should be obvious because the ECL mechanism requires more complex electron transfers. Overall, the standard TPA ECL at 1.2 V in phosphate buffer at pH 7.0 can successfully be replaced by NBEA ECL at 900 mV in Tris at pH 8.5 providing significantly higher signals accompanied by more gentle electrochemical conditions.

Sensitive CE-ECL method with AuNPs-enhanced signal for the detection of β-blockers and the study of drug–protein interactions

A sensitive capillary electrophoresis (CE) system coupled with electrochemiluminescence (ECL) of tris(2,2′-bipyridyl) ruthenium (ii) is described for the detection of propranolol (Pro) and acebutolol (Ace).

Electrogenerated chemiluminescence of the tris(2,2′-bipyridine)ruthenium(ii)/aliphatic amine system: a universal effect of perchlorate salts

Simply adding perchlorate salts leads to enhanced Ru(bpy)₃²⁺ECL emission of different pathways by 1.5–6.6 times with a variety of aliphatic amines as coreactants in a wide pH range from pH 5 to 12.

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.

Novel poly-dopamine adhesive for a halloysite nanotube-Ru(bpy)(3)2+ electrochemiluminescent sensor

Herein, for the first time, the electrochemiluminescent sensor based on Ru(bpy)₃²⁺-modified electrode using dopamine as an adhesive was successfully developed. After halloysite nanotube slurry was cast on a glassy carbon electrode and dried, an alkaline dopamine solution was added on the electrode surface. Initially, polydopamine belts with dimensions of tens to hundreds of nanometers formed via oxidization of the dopamine by ambient oxygen. As the incubation time increased, the nanobelts became broader and then united with each other to form a polydopamine film. The halloysite nanotubes were embedded within the polydopamine film. The above electrode was soaked in Ru(bpy)₃²⁺ aqueous solution to adsorb Ru(bpy)₃²⁺ into the active sites of the halloysite nanotubes via cation-exchange procedure. Through this simple procedure, a Ru(bpy)₃²⁺-modified electrode was obtained using only 6.25 µg Ru(bpy)₃²⁺, 15.0 µg dopamine, and 9.0 µg halloysite nanotubes. The electrochemistry and electrochemiluminescence (ECL) of the modified electrode was investigated using tripropylamine (TPA) and nitrilotriacetic acid (NTA) as co-reactants. The different ECL behaviors of the modified electrode using NTA and TPA as well as the contact angle measurements reflected the hydrophilic character of the electrode. The results indicate that halloysite nanotubes have a high loading capacity for Ru(bpy)₃²⁺ and that dopamine is suitable for the preparation of modified electrodes.