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Hot electron-induced electrochemiluminescence of calcein and calcein-Tb(III) complex at disposable oxide-covered aluminum and polyvinyl butyral-carbon black/metal composite electrodes in aqueous solutions
Abstract
Hot electron-induced electrochemiluminescence (HECL) of calcein and calcein-Tb(III) complex was generated at oxide-covered aluminum electrode during cathodic pulse polarization. The excitation of calcein as a molecule or as a ligand is based on subsequent one-electron oxidation and reduction steps by oxidizing radicals and solvated electrons. During HECL excitation of calcein-Tb(III) solution a reaction product of the calcein is formed that also enables the photoexcitation of Tb(III) via the formed ligand derivative by ligand-sensitized mechanism. The determination of low concentrations of calcein with aluminum electrodes was complicated by a relatively strong background electroluminescence originating from the Al2O3-layer. Polyvinyl butyral-carbon black composite electrodes coated on brass were fabricated to solve this problem and a fifty-fold lower background emission was obtained for these novel composite electrodes in comparison to that of oxide-covered 99.9% pure aluminum electrodes. The obtained detection limits were 3.2·10⁻¹⁰ M for calcein and 6.4·10⁻⁹ M for calcein-Tb(III) at the present composite electrodes. These species could potentially be utilized as electrochemiluminescent labels in bioaffinity assays.
... Ta/Ta 2 O 5 /Pt) [23] and lately novel conductor particlesdoped composite electrodes. [7,13,24,25] Recently studied disposable composite electrodes based on polymers doped with conductor particles provide certain advantages when compared to more traditional insulating film-coated electrode materials by having more stable and reproducible HECL output in a wider pH range, and most importantly, without considerable background emission. [26] Our research group have studied e.g. ...
... [26] Our research group have studied e.g. polyetherimide-carbon black-based electrodes [7], polystyrene-graphite-composite/metal electrodes [24] and polyvinyl butyral-carbon black/metal composite electrodes [25] and presently the use the polystyrene-based composite materials as a solid substrate for an immunoassay [13]. In these previous studies carbon black was the most usable and low-cost conductor particle material. ...
... In these previous studies carbon black was the most usable and low-cost conductor particle material. The main advantage of these novel electrode types are their good tolerance in changes of composite layer thickness and composition of the film [7,13,24,25]. ...
The possibility of using cellulose derivative films as (i) insulating material on metal electrodes or (ii) in composite electrode films on metal to produce hot electron-induced electrochemiluminescence (HECL) was studied. It was shown that the luminophores known to produce HECL at thin insulating film coated cathodes (e.g. Si/SiO2 and Al2O3 electrodes) produced HECL with the present novel electrodes. In the case of composite films consisting of cellulose material doped with conducting carbon particles, the optimal cellulose/carbon black ratios were investigated by measuring the time-resolved HECL (TR-HECL) of an aromatic Tb(III) chelate. In addition to Tb(III) chelate, other well-known labels, fluorescein and Ru(bpy)3²⁺ chelate, were demonstrated to produce strong HECL at the present composite electrodes, which are more environmental friendly in disposable assay cartridges as the plastic-based composites we have studied previously. Thus, it is now possible on the present basis to manufacture biodegradable paper-based assay cartridges with HECL detection of labels at biodegradable electrodes. It was shown that the present composite films are stable over wide pH range, and also time-resolved detection of Ru(bpy)3²⁺ chelate is possible although its luminescence lifetime if quite short. The calibration curves were measured for presently used aromatic Tb(III) chelate and for Ru(bpy)3²⁺. The detection limit (s/n = 3) was 2 · 10⁻¹⁰ M for the Tb(III)-chelate and 4 · 10⁻⁹ M for Ru(bpy)3²⁺ in time-resolved detection mode. The relative standard deviation for Tb(III)-L1 (n = 5) emission at 10⁻⁵ M concentration was 2%. Wide linear range and low detection limits suggests that cellulose based composite electrodes can be used in HECL bioaffinity assays which was finally demonstrated here by an immunometric immunoassay.
... R þ hn ðRadiative transitionÞ (4) There are several reports about ECL of Eu(III) and Tb(III) complexes in an aqueous medium. [21][22][23][24][25][26][27][28][29][30][31][32] Lis et. al., reported ECL on Tb(III)-doped Al/Al 2 O 3 electrode, [25] and ECL of Eu(III) complexes with Kegging polyoxomatalates [26] and coumarine-3carboxylic acid. ...
... al., performed ECL measurements for Eu(III) and Tb(III) complexes using Al/Al 2 O 3 and polystyrenegraphite composite electrodes. [21,24,29,31] Some of the ECL measurements needed high applied voltage (e. g., 40 V), and the mechanism is probably similar to that of the electroluminescence (the excited states are formed by recombination of a hole and electron). Some analytical applications using ECL of Tb(III) complexes in an aqueous solution were also reported. ...
We report the electrochemical properties, and electrogenerated chemiluminescence (ECL) of eight different organometallic complexes of Eu(III) and Tb(III), Eu(dbm)3phen, Eu(dbm)3bath, Eu(fod)3phen, Eu(tta)3phen, Tb(acac)3phen, Tb(acac)3bath, Tb(fod)3phen, and Tb(tmhd)3bpy in acetonitrile, where phen, bath, and bpy are 1, 10‐phenanthroline, bathophenanthroline, 2,2′‐bipyridyl, respectively, and the anionic ligands, acac⁻, dbm⁻, fod⁻, and tta⁻ are the enolate forms of acetylacetone, dibenzoylmethanate, 6,6,7,7,8,8,8‐heptafluoro‐2,2‐dimethyl‐3,5‐octanedione, and thenoyltrifluoroacetone, respectively. The electronic states of the neutral and some charged states of the complexes were clarified with density functional theory calculations. The ECL spectra were recorded by using S2O8²⁻ as a coreactant, and for all complexes, sharp ECL spectra, which are attributable to the f‐f transitions, were observed. On the potential‐dependent ECL spectra, broad ECLs, which were originated from the ligands, were also detected. Based on the ECL behavior and the electronic states, the mechanisms of the intraconfigurational ECL were discussed.
... Insulating polymer material surrounds the carbon black particles and enables electrons to be transported through the thin composite layer with very low IR-loss, and finally hot electrons to be emitted at the electrode/solution interface. The main advantage of these novel electrodes over traditional insulating thin-film covered electrodes is their insensitivity to composite layer thickness and composition of the film [9,15,21,22]. Compared to thin insulating film-coated electrode materials, such as aluminum or silicon, composite electrodes are found to have a more stable and reproducible HECL output in a wider pH range, and most importantly, without considerable background emission [15,23,24]. ...
Novel hot electron-emitting working electrodes and conventional counter electrodes were created by screen printing. Thus, low-cost disposable electrode chips for bioaffinity assays were produced to replace our older expensive electrode chips manufactured by manufacturing techniques of electronics from silicon or on glass chips. The present chips were created by printing as follows: (i) silver lines provided the electronic contacts, counter electrode and the bottom of the working electrode and counter electrode, (ii) the composite layer was printed on appropriate parts of the silver layer, and (iii) finally a hydrophobic ring was added to produce the electrochemical cell boundaries. The applicability of these electrode chips in bioaffinity assays was demonstrated by an immunoassay of human C-reactive protein (i) using Tb(III) chelate label displaying long-lived hot electron-induced electrochemiluminescence (HECL) and (ii) now for the first time fluorescein isothiocyanate (FITC) was utilized as an a low-cost organic label displaying a short-lived HECL in a real-world bioaffinity assay.
For hot electron-induced electrochemiluminescence (HECL), developing facile and controllable insulating layer on the electrode surface is key to the effective electron tunneling. Herein, a polystyrene modified glassy carbon electrode based the spin-coating was proposed for HECL. The constructed interface was characterized by atomic force microscopy (AFM). And HECL performance was investigated in details using the system of Ru(bpy)3²⁺ and S2O8²⁻. The as-prepared film shows the stable and reproducible HECL performance and the HECL mechanism was discussed using ECL spectra and hydrated electron quenchers. Finally, on the basis of the inhibition of SO4•-, the present polystyrene film was applied to the detection of rutin in the range of 0.1-1.3 μM with a detection limit of 90 nM (S/N = 3).
The development of the hot electron‐induced cathodic electrochemiluminescence (HECL) often accompanied with the advance in the electrode materials and instruments. In this work, dimethyl silicone oil was employed as the coating layer for initiating the HECL. The insulating layer was obtained by simple drop casting and subsequent polishing, which can withstand high voltage and meet the requirement of HECL. With the as‐prepared interface, the quantitative detection of puerarin in the aqueous solution was achieved based on the quenching effect on the SO4·‐.
Tb(III) chelates exhibit intense hot electron-induced electrogenerated chemiluminescence during cathodic polarization of metal/polystyrene-graphite (M/PG) electrodes in fully aqueous solutions. The M/PG working electrode provides a sensitive means for the determination of aromatic Tb(III) chelates at nanomolar concentration levels with a linear log-log calibration curve spanning more than five orders of magnitude. The charge transport and other properties of these novel electrodes were studied by electrochemiluminescence measurements and cyclic voltammetry. The present composite electrodes can by utilized both under pulse polarization and DC polarization unlike oxide-coated metal electrodes which do not tolerate cathodic DC polarization. The present cost-effective electrodes could be utilized e.g. in immunoassays where polystyrene is extensively used as a solid phase for various bioaffinity assays by using electrochemiluminescent Tb(III) chelates or e.g. Ru(bpy)3²⁺as labels.
Various luminophores produce strong electrogenerated chemiluminescence during cathodic pulse polarization of the present insulating film-covered carbon paste electrodes in fully aqueous solutions. First electrodes made of a commercial conductive carbon paste were successfully utilized as working electrodes and their surface was characterized by ESCA. Then custom in-laboratory made improved composite electrodes were manufactured from the same insulating polymer and conducting carbon black particles. The relationship between the amount of carbon present on the composite electrode, in the bulk and on the surface, and the intensity of electrogenerated chemiluminescence was studied further. The overall performance of these composite electrodes makes them viable low-cost replacements for metal/insulator type electrodes such as oxide-coated silicon electrodes.
Tris(2,2′-bipyridine)ruthenium(II) chelate exhibits strong electrogenerated chemiluminescence during cathodic high-voltage pulse-polarization of pointed Pt electrode in aqueous solutions. The present method is based on a field emission or other type of tunnel emission of hot electrons into an aqueous electrolyte solution. The method allows the detection of tris(2,2′-bipyridine)ruthenium(II) and its derivatives below nanomolar concentration levels and yields linear log-log calibration plots spanning several orders of magnitude of concentration.
The hydroxyl radical ((•)OH) is one of the most powerful oxidizing agents, able to react unselectively and instantaneously with the surrounding chemicals, including organic pollutants and inhibitors. The (•)OH radicals are omnipresent in the environment (natural waters, atmosphere, interstellar space, etc.), including biological systems where (•)OH has an important role in immunity metabolism. We provide an extensive view on the role of hydroxyl radical in different environmental compartments and in laboratory systems, with the aim of drawing more attention to this emerging issue. Further research on processes related to the hydroxyl radical chemistry in the environmental compartments is highly demanded. A comprehensive understanding of the sources and sinks of (•)OH radicals including their implications in the natural waters and in the atmosphere is of crucial importance, including the way irradiated chromophoric dissolved organic matter in surface waters yields (•)OH through the H2O2-independent pathway, and the assessment of the relative importance of gas-phase vs aqueous-phase reactions of (•)OH with many atmospheric components. Moreover, considering the fact that people spend so much more time in dwellings than outside, the impact of the reactivity of indoor hydroxyl radicals on health and well-being is another emerging research topic of great concern.
This paper reports the fabrication of a three-dimensional (3D) nanowall structure based on the intercalation of calcein into a layered double hydroxide (LDH) by a modified solvothermal direct growth process, and explores its electrogenerated chemiluminescence (ECL) property for detection of dopamine (DA). X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed the calcein/LDH nanowall film possess a preferential orientation with their ab plane perpendicular to the substrate. The nanowall film shows tunable luminescence properties by simple changing the amount of calcein in the LDH interlayer, and the optimum fluorescence intensity occurs in the sample with x = 1.25%. The stable and strong ECL signals suggested that this film possesses excellent operational and storage stability, which is essential for a sensor. The ECL intensity increased linearly with increasing DA concentration from 5.00 × 10-7 to 1.01 × 10-4 M. The detection limit was 3.52 × 10-7 M. The mechanism of the ECL sensor indicates that the 3D micro-morphology of the calcein/LDH nanowall film has a positive influence on the electrochemical property due to its high surface area and reduced interface resistance. Therefore, this work not only provides a preparation method for a chromophore/LDH complex with a 3D micro/nanostructure, but also systematically probed the structure-property relationship of the calcein/LDH nanowall film. According to this strategy, advanced sensors and devices with outstanding optical and electrochemical properties can be achieved.
Chemiluminescence (CL) probes for reactive oxygen species (ROS) are commonly based on a redox reaction between a CL reagent and ROS, leading to poor selectivity towards a specific ROS. The energy-matching rules in chemiluminescence resonance energy transfer (CRET) process between a specific ROS donor and a suitable fluorescence dye acceptor is a promising method for the selective detection of ROS. Nevertheless, higher concentrations of fluorescence dyes can lead to the intractable aggregation-caused quenching effect, decreasing the CRET efficiency. In this report, we fabricated an orderly arranged structure of calcein-sodium dodecyl sulfate (SDS) molecules to improve the CRET efficiency between ONOOH* donor and calcein acceptor. Such the orderly arranged calcein-SDS composites can distinguish peroxynitrite (ONOO-) from a variety of other ROS owing to the energy-matching in CRET process between ONOOH* donor and calcein acceptor. Under the optimal experimental conditions, ONOO- could be assayed in the range of 1.0-20.0 μM, and the detection limit for ONOO- (S/N = 3) was 0.3 μM. The proposed strategy has been successfully applied in both detecting ONOO- in cancer mouse plasma samples and monitoring the generation of ONOO- from SIN-1. Recoveries from cancer mouse plasma samples were in the range of 96-105%. The success of this work provides a unique opportunity to develop a CL tool to monitor ONOO- with high selectivity in a specific manner. Improvement of selectivity and sensitivity of CL probes holds great promise as a strategy for developing a wide range of probes for various ROS by tuning the types of fluorescence dyes.
This paper reports the detection of uranyl ion via fluorescence quenching of a dye molecule followed by the selective photocatalysis of the dye molecule by excited state uranyl. We have found that selectivity can be obtained when calcein, a highly fluorescent fluorescein-type dye, is quenched by complex formation with uranyl in solution at low concentrations. Following the quenching by uranyl, the entire sample is excited at a wavelength that is strongly absorbed by uranyl at 425nm. This produces the excited state uranyl ion that has a large oxidation potential and photocatalytically decarboxylates the dye, breaking the dye/metal bond. The photocatalysis product is highly fluorescent and produces an increase in the fluorescence signal. The detection limit for uranyl via quenching is 60nM and via photocatalysis is 40nM. Interfering metal ions such as iron and chromate have little effect on the amount of fluorescence regenerated since their absorbance bands, modes of quenching, and photochemistry are different from uranyl.
Double insulating barrier tunnel emission electrodes were fabricated by adding a new pure aluminum layer upon oxidized aluminum electrodes by vacuum evaporation and thermally oxidizing the new aluminum layer in air at room temperature. Resulting Al/Al2O3/Al/Al2O3 electrodes allow the use of various aluminum alloys in the electrode body necessary for hardness or shaping ability of the electrode while obtaining the luminescence properties of pure aluminum oxide. During electrical excitation of luminescent labels by cathodic hot electron injection into aqueous electrolyte solution, the background noise is mainly based on high-field-induced solid-state electroluminescence and F-center luminescence of the outer aluminum oxide film. The more defect states and/or impurity centers the outer oxide film contains, the higher is the background emission intensity. The present electrode fabrication method provides a considerable improvement in signal-to-noise ratio for time-resolved electrochemiluminescence (TR-ECL) measurements when the original native oxide film of the electrode body contains luminescence centers displaying long-lived luminescence. The excellent performance of the present electrodes is demonstrated by extremely low-level detection of Tb(III) chelates, luminol, Pt(II) coproporphyrin and Tb(III) labels in an immunometric immunoassay by time-resolved electrochemiluminescence.
Tunnel-emitted hot electrons induce the triplet state emission of the ligand of an aromatic Gd(III) chelate while the corresponding Tb(III) chelate shows a metal-centred emission at cathodically pulse–polarised oxide-covered aluminum electrodes in fully aqueous solutions at room temperature.
Modern analytical luminescence methods and their recent applications are reviewed with emphasis on the most sensitive methods that can be expected to be useful in future microanalytical systems such as mu-TAS, lab-on-chip, point-of-care (POC) and high throughput screening (HTS) applications. Photoluminescence (PL) is presently the most important group of analytical techniques utilising luminescence. Because of the rapidly increasing popularity of electrochemiluminescence (ECL) and its applications, we have given particular attention to ECL mechanisms and techniques. Due to the present and future importance of capillary electrophoresis (CE) as a separation method, the CE detection methods based on luminescence are also considered in a relatively detailed way. For those researchers, designing novel experiments and assays, experimental set-ups, and apparatus we include web links to the manufacturers of some fairly rare reagents, as well as modem instrument components. (C) 2003 Published by Elsevier B.V.
Oxide-covered aluminium electrodes as well as other tunnel emission electrodes allow various label molecules having very different redox and optical properties to be excited cathodically. Low detection limits are obtained and the linear calibration concentration range of the labels spans 5 or 6 orders of magnitude. The lowest detection limits are obtained with Tb(III) chelates which can be detected down to picomolar levels in aqueous solution using time-resolved measurement techniques. Luminophores, such as, 9-fluorenylmethyl chloroformate, derivatives of fluorescein and its analogues, aromatic lanthanide(III) chelates, various coumarins and porphyrins can be used as labels emitting in different spectral regions. The extraordinary analytical power of the tunnel emission electrodes lies in the possibility of simultaneously exciting several different labels emitting either in the UV, visible or NIR range and luminescence lifetimes varying from the ns to the ms range. Therefore, wavelength or time discrimination or their combination can be exploited in separation of the electrochemiluminescence signals from different labels.
Rhodamine B (RhB) exhibits strong cathodic electrogenerated chemiluminescence (ECL) in aqueous solutions during high-amplitude pulse polarization at thin oxide film-coated aluminum electrodes. This method allows the detection of RhB below nanomolar concentration level and provides linear calibration plots spanning over several orders of magnitude of concentration. In addition, a relatively long ECL lifetime of RhB provides a basis for time-resolved detection. Thus, widely used RhB-based labels can also be suggested to be usable as electrochemiluminescent labels in fully aqueous solutions in bioaffinity assays such as in immunoassays and DNA-probing assays. Support was obtained for the chemiluminescence generation mechanism to be essentially the same as that of radiochemiluminescence in aqueous solution.