Field-amplified sample stacking capillary electrophoresis with electrochemiluminescence applied to the determination of illicit drugs on banknotes

Tris(2,2'-bipyridyl)ruthenium (II) complex as a universal reagent for the fabrication of heterogeneous electrochemiluminescence platforms and its recent analytical applications

In recent years, electrochemiluminescence (ECL) has received enormous attention and has emerged as one of the most successful tools in the field of analytical science. Compared with homogeneous ECL, the heterogeneous (or solid-state) ECL has enhanced the rate of the electron transfer kinetics and offers rapid response time, which is highly beneficial in point-of-care and clinical applications. In ECL, the luminophore is the key element, which dictates the overall performance of the ECL-based sensors in various analytical applications. Tris(2,2'-bipyridyl)ruthenium (II) complex, Ru(bpy)32+, is a coordination compound, which is the gold-standard luminophore in ECL. It has played a key role in translating ECL from a "laboratory curiosity" to a commercial analytical instrument for diagnosis. The aim of the present review is to provide the principles of ECL and classical reaction mechanisms-particularly involving the heterogeneous Ru(bpy)32+/co-reactant ECL systems, as well as the fabrication methods and its importance over solution-phase Ru(bpy)32+ ECL. Then, we discussed the emerging technology in solid-state Ru(bpy)32+ ECL-sensing platforms and their recent potential analytical applications such as in immunoassay sensors, DNA sensors, aptasensors, bio-imaging, latent fingerprint detection, point-of-care testing, and detection of non-biomolecules. Finally, we also briefly cover the recent advances in solid-state Ru(bpy)32+ ECL coupled with the hyphenated techniques.

Electrochemiluminescence sensors and forensic investigations: a viable technique for drug detection?

Novel psychoactive substances (NPS) are today considered one of the major ticking public health time bombs in regard to drug abuse. The inability to identify these substances with current screening methods, sees their distribution remain uninterrupted and contributes to the high death rates amongst users. To tackle this problem, it is vital that new robust screening methods are developed, addressing the limitation of those currently in place, namely colour subjectivity and lack of compatibility with the complex matrices these substances may be found within. To this avail, electrochemical methods have been assessed. These low cost and extremely portable sensors have been successfully applied for the direct detection of a broad range of compounds of interest in a range of matrices including, herbal material, commercial drinks and biological fluids (serum, saliva, sweat and urine). With their high versatility, gifted through a significant degree of flexibility in regard to electrode material a range of sensors have to date been reported. In this review the various electrochemical sensors developed to date for NPS detection will be compared and contrasted, with a special focus upon those utilising electrochemiluminescence (ECL) technology.

Ruthenium polypyridine complexes combined with oligonucleotides for bioanalysis: a review

Ruthenium complexes are among the most interesting coordination complexes and they have attracted great attention over the past decades due to their appealing biological, catalytic, electronic and optical properties. Ruthenium complexes have found a unique niche in bioanalysis, as demonstrated by the substantial progress made in the field. In this review, the applications of ruthenium complexes coordinated with polypyridine ligands (and analogues) in bioanalysis are discussed. Three main detection methods based on electrochemistry, electrochemiluminescence, and photoluminscence are covered. The important targets, including DNA and other biologically important targets, are detected by specific biorecognition with the corresponding oligonucleotides as the biorecognition elements (i.e., DNA is probed by its complementary strand and other targets are detected by functional nucleic acids, respectively). Selected examples are provided and thoroughly discussed to highlight the substantial progress made so far. Finally, a brief summary with perspectives is included.

Capillary Electrophoresis with UV Detection to Determine Cocaine on Circulated Banknotes

A new methodology employing capillary electrophoresis with UV detection (CE-UV) was developed, validated, and applied to determine the presence of cocaine on Brazilian banknotes. Some of the banknotes analyzed were obtained directly from general circulation (well used) while others were collected from Automated Teller Machines (ATMs) (relatively new). The background electrolyte optimized using Peakmaster 5.1 software was composed of 60 mmol L−1 TRIS(hydroxymethyl)aminomethane and 20 mmol L−1 2-hydroxyisobutyric acid, at pH 8.4. The separation time achieved for cocaine was only 2.5 minutes. The figures of merit obtained in the evaluation of the proposed method were good linearity (r>0.999) in the concentration range of 0.8–8.0 mg L−1 and acceptable limits of detection and quantification (0.2 mg L−1 and 0.8 mg L−1, resp.). The relative standard deviations of the instrumental precision, repeatability (intraday), and intermediate precision (interday) were less than 4.5% (peak area). The accuracy evaluated through comparing the cocaine results for the banknotes determined by the proposed CE-UV method and using an LC-MS/MS method showed no significant difference between the methods (95% confidence level). In the analysis of the samples cocaine was detected on 93% of the circulating banknotes in amounts ranging from 11.5 μg to 2761.9 μg per note.

Discovered triethylamine as impurity in synthetic DNAs for and by electrochemiluminescence techniques

The purity of the synthetic oligonucleotides is very important because it is crucial for the accuracy of the established biological assays. Herein, it was discovered that one impurity in synthetic DNAs might affect the experiment results of electrochemiluminescence (ECL) detection techniques, which was never reported before. According to a series of experiments using ECL detection methods combined with capillary electrophoresis (CE) (CE-ECL), the impurity was identified as triethylamine (TEA), which came from incomplete removal after HPLC purification of synthetic DNAs. Moreover, CE-ECL technique was for the first time to be proposed for discovering, identifying and sensitive determining the possible impurity such as TEA in various DNA samples, which was usually neglected by other detection techniques for purification quality control of synthetic oligonucleotides. A detection range from 5.00×10(-10) to 2.00×10(-5) M with a detection limit as low as 50 nM (S/N=3) was reached for TEA. Through further designed ECL methods and data analysis, situations which would be really affected by the impurity of TEA were studied. To avoid or eliminate the impact of the TEA impurity on ECL applications, judgment basis for choosing purification ways was discussed according to individual requirements.

Dispersive liquid-liquid microextraction prior to field-amplified sample injection for the sensitive analysis of 3,4-methylenedioxymethamphetamine, phencyclidine and lysergic acid diethylamide by capillary electrophoresis in human urine

A novel capillary zone electrophoresis (CZE) with ultraviolet detection method has been developed and validated for the analysis of 3,4-methylenedioxymethamphetamine (MDMA), lysergic acid diethylamide (LSD) and phencyclidine (PCP) in human urine. The separation of these three analytes has been achieved in less than 8 min in a 72-cm effective length capillary with 50-μm internal diameter. 100 mM NaH(2)PO(4)/Na(2)HPO(4), pH 6.0 has been employed as running buffer, and the separation has been carried out at temperature and voltage of 20°C, and 25kV, respectively. The three drugs have been detected at 205 nm. Field amplified sample injection (FASI) has been employed for on-line sample preconcentration. FASI basically consists in a mismatch between the electric conductivity of the sample and that of the running buffer and it is achieved by electrokinetically injecting the sample diluted in a solvent of lower conductivity than that of the carrier electrolyte. Ultrapure water resulted to be the better sample solvent to reach the greatest enhancement factor. Injection voltage and time have been optimized to 5 kV and 20s, respectively. The irreproducibility associated to electrokinetic injection has been correcting by using tetracaine as internal standard. Dispersive liquid-liquid microextraction (DLLME) has been employed as sample treatment using experimental design and response surface methodology for the optimization of critical variables. Linear responses were found for MDMA, PCP and LSD in presence of urine matrix between 10.0 and 100 ng/mL approximately, and LODs of 1.00, 4.50, and 4.40 ng/mL were calculated for MDMA, PCP and LSD, respectively. The method has been successfully applied to the analysis of the three drugs of interest in human urine with satisfactory recovery percentages.

Applications of tris(2,2'-bipyridyl)ruthenium(II) in electrochemiluminescence

Electrochemiluminescence (ECL) of tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)(3)(2+)] has received considerable interest over broad applications due to its remarkably high sensitivity and extremely wide dynamic range. After a brief introduction of the ECL of Ru(bpy)(3)(2+), an overview of our recent research on enhanced ECL, fabrication of solid-state ECL sensors, analytical application of an effective bioassay, and alignment of ECL with capillary electrophoresis (CE) and microchip CE is discussed in detail. Finally, we conclude with a look at the future challenges and prospects of the development of ECL.

Determination of eight illegal drugs in human urine by combination of magnetic solid-phase extraction with capillary zone electrophoresis

Using magnetite/silica/poly(methacrylic acid-co-ethylene glycol dimethacrylate) (Fe(3)O(4)/SiO(2)/poly(MAA-co-EDMA)) magnetic microspheres, a rapid and high-throughput magnetic solid-phase extraction coupled with capillary zone electrophoresis (MSPE-CZE) method was developed for the determination of illegal drugs (ketamine, amphetamines, opiates, and metabolites). The MSPE of target analytes could be completed within 2 min, and the eight target analytes could be baseline separated within 15 min by CZE with 30 mM phosphate buffer solution (PBS, pH 2.0) containing 15% v/v ACN as background electrolyte. Furthermore, hydrodynamic injection with field-amplified sample stacking (FASS) was employed to enhance the sensitivity of this MSPE-CZE method. Under such optimal conditions, the limits of detection for the eight target analytes ranged from 0.015 to 0.105 μg/mL. The application feasibility of MSPE-CZE in illegal drugs monitoring was demonstrated by analyzing urine samples, and the recoveries of target drugs for the spiked sample ranging from 85.4 to 110.1%. The method reproducibility was tested by evaluating the intra- and interday precisions, and relative standard deviations of <10.3 and 12.4%, respectively, were obtained. To increase throughput of the analysis, a home-made MSPE array that has potential application to the treatment of 96 samples simultaneously was used.

Signal-enhancer molecules encapsulated liposome as a valuable sensing and amplification platform combining the aptasensor for ultrasensitive ECL immunoassay

An innovatory ECL immunoassay strategy was proposed to detect the newly developing heart failure biomarker N-terminal pro-brain natriuretic peptide (NT-proBNP). Firstly, this strategy used small molecules encapsulated liposome as immune label to construct a sandwich immune sensing platform for NT-proBNP. Then the ECL aptasensor was prepared to collect and detect the small molecules released from the liposome. Finally, based on the ECL signal changes caused by the small molecules, the ECL signal indirectly reflected the level of NT-proBNP antigen. In this experiment, the cocaine was chosen as the proper small molecule that can act as signal-enhancer to enhance the ECL of Ru(bpy)(3)(2+). The cocaine-encapsulated liposomes were successfully characterized by TEM. The quantificational calculation proved the ∼5.3×10(3) cocaine molecules per liposome enough to perform the assignment of signal amplification. The cocaine-binding ECL aptasensor further promoted the work aimed at amplifying signal. The performance of NT-proBNP assay by the proposed strategy exhibited high sensitivity and high specificities with a linear relationship over 0.01-500 ng mL(-1) range, and a detection limit down to 0.77 pg mL(-1).

Chemiluminescence and electrochemiluminescence detection of controlled drugs

We review the determination of various controlled drugs (opioids, tranquilizers, stimulants, and hallucinogens) using flow-analysis methodologies (flow injection analysis, high performance liquid chromatography, capillary electrophoresis, and microfluidic devices) with chemiluminescence and electrochemiluminescence reagents such as luminol, diaryloxalates, tris(2,2'-bipyridine)ruthenium(II), permanganate, manganese(IV), and sulfite, for industrial, clinical, pharmaceutical, and forensic science applications.

Determination of galanthamine in Bulbus Lycoridis Radiatae by coupling capillary electrophoresis with end-column electrochemiluminescence detection

A novel method for the determination of galanthamine (GAL) in Bulbus Lycoridis Radiatae has been developed based on coupling CE with an end-column tris(2,2'-bipyridyl)ruthenium(II) electrochemiluminescence (ECL). Parameters affecting CE separation and ECL detection were investigated and optimized. Baseline separation of GAL from other components in the Bulbus Lycoridis Radiatae sample was achieved with an 18 mmol/L phosphate running buffer at pH 9.0. Under the optimized conditions: 12 kV CE-separation voltage, ECL detection potential at 1.25 V with 5 mmol/L Ru(bpy)(3)(2+) and 50 mmol/L phosphate buffer at pH 7.5 in the detection reservoir, the linear range of GAL concentration was from 0.8 ng/mL to 2 microg/mL, whereas the detection limit was 0.25 ng/mL (S/N=3). The proposed method was successfully demonstrated for the determination of GAL in Bulbus Lycoridis Radiatae.

Determination of isocyanates by capillary electrophoresis with tris(2,2'-bipyridine)ruthenium(II) electrochemiluminescence

CE with tris(2,2'-bipyridyl) ruthenium(II) (Ru(bpy)(3) (2+)) electrochemiluminescence (ECL) detection for the quantitative determination of isocyanates was first reported. Hexamethylene diisocyanate (HDI) and hexyl isocyanate (HI) were used as the model analytes. Commercially available N,N-diethyl-N'-methylethylenediamine was used as the derivatization reagent. It has both a secondary amine group and a tertiary amine group. The secondary amine group can quantitatively react with isocyanate group, and the tertiary amine group can react with Ru(bpy)(3) (2+) to produce strong ECL signal for sensitive detection. The derivatization reaction was almost instantaneous and is much faster than other reported derivative reactions using other derivative reagents. The urea formed was stable. Linear calibration curve was obtained in the range from 0.01 to 10 microM for HDI, and 0.02 to 20 microM for hexyl isocyanate (HI). The detection limit is 0.01 microM for HDI and 0.02 microM for HI. The method is more sensitive than UV-detection and electrochemical detection. For practical application, recovery higher than 90% for HDI and HI was obtained for foam sample.

Simultaneous determination of proline and pipemidic acid in human urine by capillary electrophoresis with electrochemiluminescence detection

Pipemidic acid is extensively used in the treatment of Gram-negative urinary tract infections, and the contents of proline in human urine vary in association with chronic uremia. The simultaneous determination of pipemidic acid and proline in human urine is of significance for quality control of the dosage and clinical study. The coupling of Ru(bpy)(3)(2+)-based electrochemiluminescence detection with capillary electrophoresis was developed for the simultaneous determination of proline and pipemidic acid in human urine. Parameters related to the separation and detection were investigated and optimized. The standard curves were linear between 0.1 and 90 µg mL(-1) for proline and between 0.4 and 100 µg mL(-1) for pipemidic acid. Underoptimized conditions, the detection limits (3σ) were 0.02 µg mL(-1) for proline and 0.06 µg mL(-1) for pipemidic acid. Relative standard derivations for the electrochemiluminescence intensity and the migration time were 3.2 and 0.9% for proline and 3.7 and 1.2% for pipemidic acid, respectively. The developed method was successfully applied to determine proline and pipemidic acid in human urine. The result showed that the content and decreasing rates of proline in urine for male were higher than that for female, and the content and decreasing rate of pipemidic acid in urine for male and female were consistent, respectively.

[Ru(bpy)3]2+-doped silica nanoparticles within layer-by-layer biomolecular coatings and their application as a biocompatible electrochemiluminescent tag material

[Ru(bpy)3]2+-doped silica (RuSi) nanoparticles were synthesized by using a water/oil microemulsion method. Stable electrochemiluminescence (ECL) was obtained when the RuSi nanoparticles were immobilized on a glassy carbon electrode by using tripropylamine (TPA) as a coreactant. Furthermore, the ECL of the RuSi nanoparticles with layer-by-layer biomolecular coatings was investigated. Squential self-assembly of the polyelectrolytes and biomolecules on the RuSi nanoparticles gave nanocomposite suspensions, the ECL of which decreased on increasing the number of bilayers. Moreover, factors that affected the assembly and ECL signals were investigated. The decrease in ECL could be assigned to steric hindrance and limited diffusion of the coreactant molecules in the silica matrix after they were attached to the biomolecules. Since surface modification of the RuSi nanoparticles can improve their biocompatibility and prevent leaking of the [Ru(bpy)3]2+ ions, the RuSi nanoparticles can be readily used as efficient and stable ECL tag materials in immunoassay and DNA detection.

Adaptive recognition of small molecules by nucleic acid aptamers through a label-free approach

We report a novel label-free method for the investigation of the adaptive recognition of small molecules by nucleic acid aptamers using capillary electrophoresis analysis. Cocaine and argininamide were chosen as model molecules, and the two corresponding DNA aptamers were used. These single-strand DNAs folded into their specific secondary structures, which were mainly responsible for the binding of the target molecules with high affinity and specificity. For molecular recognition, the nucleic acid structures then underwent additional conformational changes, while keeping the target molecules stabilized by intermolecular hydrogen bonds. The intrinsic chemical and physical properties of the target molecules enabled them to act as indicators for adaptive binding. Thus any labeling or modification of the aptamers or target molecules were made obsolete. This label-free method for aptamer-based molecular recognition was also successfully applied to biological fluids and therefore indicates that this approach is a promising tool for bioanalysis.

Capillary electrophoresis and microchip capillary electrophoresis with electrochemical and electrochemiluminescence detection

Recent advances and key strategies in capillary electrophoresis and microchip CE with electrochemical detection (ECD) and electrochemiluminescence (ECL) detection are reviewed. This article consists of four main parts: CE-ECD; microchip CE-ECD; CE-ECL; and microchip CE-ECL. It is expected that ECD and ECL will become powerful tools for CE microchip systems and will lead to the creation of truly disposable devices. The focus is on papers published in the last two years (from 2005 to 2006).