Insights into electrochemiluminescent enhancement through electrode surface modification

The electrochemiluminescent (ECL) properties of a luminescent metal centre, [Ru(bpy)(3)](2+), can be significantly modulated through its electronic interaction with neighbouring centres and the polymer backbone used to confine it on an electrode surface. From the perspective of ECL based sensing devices, an increase in the ECL efficiency of a metallopolymer film can result in enhanced sensor sensitivity and selectivity. This work probes the ECL properties of both conjugated, [Ru(bpy)(2)(PPyBBIM)(10)](2+), and non-conjugated, [Ru(bpy)(2)(PVP)(10)](2+), ruthenium based metallopolymer films based on a well documented reaction with sodium oxalate, where bpy is 2,2'-bipyridyl, PPYBBIM is poly[2-(2-pyridyl)-bibenzimidazole] and PVP is poly(4-vinylpyridine). Through a combination of ground state electrochemical studies and ECL measurements, the ECL efficiency for each film is determined. This study reveals that despite a dramatic influence in charge transfer rates between metal centres, as observed for the conducting polymer, mediated through the conducting polymer backbone, a corresponding increase in ECL efficiency is not always observed. The degree of communication between the adjacent excited state metal centres are an important consideration for ECL enhancement however self quenching, luminophore distribution and film porosity must also be considered

Ground and excited state communication within a ruthenium containing benzimidazole metallopolymer

Emission spectroscopy and electrochemistry has been used to probe the electronic communication between adjacent metal centres and the conjugated backbone within a family of imidazole based metallopolymer, [Ru(bpy)2(PPyBBIM)n]2+, in the ground and excited states, bpy is 2,2’-bipyridyl, PPyBBIM is poly[2-(2-pyridyl)-bibenzimidazole] and n = 3, 10 or 20. Electronic communication in the excited state is not efficient and upon optical excitation dual emission is observed, i.e., both the polymer backbone and the metal centres emit. Coupling the ruthenium moiety to the imidazole backbone results in a red shift of approximately 50 nm in the emission spectrum. Luminescent lifetimes of up to 120 ns were also recorded. Cyclic voltammetry was also utilized to illustrate the distance dependence of the electron hopping rates between adjacent metal centres with ground state communication reduced by up to an order of magnitude compared to previously reported results when the metal to backbone ratio was not altered. DCT and De values of up to 3.96 x 10-10 and 5.32 x 10-10 cm2S-1 were observed with corresponding conductivity values of up to 2.34 x 10-8 Scm-1

Electrochemiluminescent & amperometric detection of DNA & DNA damage

Some ruthenium and osmium complexes and metallopolymers have been synthesised and characterised using viscosity, spectroscopic and electrochemical techniques. The obtained results showed that the photochemical and electrochemical properties of the monomeric complexes, i.e. M(bpy)32+ and M(bpy)2(pic)22+, where bpy is 2,2’bipyridyl and pic is 4-picoline, accurately predict the properties o f the analogous polymeric material, M(bpy)2(PVP)io2+, where PVP is poly-4-vinylpyridine. However, the excited state lifetimes and quantum yield of photoluminescence are considerable lower for the polymeric materials than for the analogous M(bpy)32+ complexes. The Ru(bpy)2(PVP)i02+ polymer is an effective mediator for the oxidation of the DNA base guanine using thin films of these materials on electrode surfaces. The film thickness and electrode potential were systematically varied in both sulphuric acid and PBS electrolyte showing that charge transport through the film is a diffusion-like process and the charge transport diffusion coefficient, DCT is approximately 2 x 10'11 cm V . This charge transport rate is independent of the concentration of the electrolyte, indicating an open porous layer structure. The osmium metallopolymer, Os(bpy)2(PVP)io +, was also shown to be an effective mediator for the oxidation of the biomarker 8-oxoguanine. The characteristics of this metallopolymer as a thin film were also investigated, yielding similar results to the ruthenium analogue. ECL was demonstrated in solution phase via annihilation between the electrogenerated 3+ and 1+ forms of the compounds. The ECL spectrum for Ru(bpy)2(PVP)102+ was similar to the photoluminescence, suggesting that the same orbitals are responsible for the emission, whether the excited state was formed electrochemically or photochemically. The ECL efficiencies (ecl) followed the same order as the photoluminescent efficiencies (4>p). The effects of quenchers and self quenching as well as the temperature dependence of the luminescence was investigated, yielding information on the quenching constant, kq, and the activation energies for both the monomeric and polymeric materials. Electrodes modified with thin films containing one or both of the redox polymers and DNA were used for dual amperometric and electrochemiluminescent detection of DNA damage, either by the formation of adducts by chemically generated damage or oxidative DNA damage, for use as a toxicity screening sensor. This system provides fast and accurate responses to the production of DNA adducts, which cause disruption of the DNA helical structure and to oxidative DNA damage in comparison to the methods already in use. The combined amperometric and electrochemiluminescent detection provided a more sensitive and selective sensor for this type of analysis, immobilisation of the chemiluminescent reagent has a number of advantages over solution-phase ECL-based systems; conserves reagent, is simpler and more cost effective and has an additional level of selectivity. It also allowed for the utilisation of thin films containing both the redox polymers and DNA, which resulted in quick easy analysis of potential toxins

Separate Refining Versus Mixed Refining of an “Easy” and “Hard” Refining Pulp

A study of the strength development (mullen and tear) of mixtures of easy and hard refining pulp, in which the pulps were refined as a mixture with that in which they were separately refined, and then mixed, reveals that separate refining develops mullen to the same extent as does mixed refining, but that a higher tearing resistance at the same freeness and mullen can be obtained with separate refining

Electrochemiluminescence detection of methamphetamine in biological matrices

We have studied an electrochemical detection method for the stimulants in the forensic samples using electrochemiluminescence (ECL). In this context, amphetamine type stimulant (methamphetamine (MA)) has been studied as co-reactants in the [Ru(bpy)3]2+ (where bpy is 2,2’-bipyridine) ECL system. This approach is developed based on a glassy carbon electrode modified with [Ru(bpy)3]2+ /Nafion composite film. LoD, LoQ and linear working range for MA are studied currently. The ECL intensity was found to be concentrations over the range of 5 x 10-8 to 2.5 x 10-4mol/L. LoD for MA is 1.94 x 10-10 mol/L. The regression coefficient is 0.9931 for the experiment. Our approach was applied in different medium such as saliva and human serum to detect MA This technique is simple, rapid, selective and sensitive, and shows potential for the high throughput quantitation of MA. the results show that the present electrochemical approach seems to provide a sensitive detection of MA in forensic applications

Electrochemiluminescent detection of methamphetamine and amphetamine

Direct detection of amphetamine type stimulants (ATS) including methylamphetamine (MA) in street samples and biological matrices without the need for pretreatment or extraction is a great challenge for forensic drug analysis. Electrochemical techniques, such as electrochemiluminescence (ECL), are promising tools for this area of analysis. This contribution focuses on the electrochemical and photochemical properties of [Ru(bpy)3]2+ nafion composite films and their subsequent use for the detection of ATS in particular MA. Under optimised conditions, the response linearly increased with the concentration over the concentration range 50 pM <[MA]< 1 mM while an equivalent dynamic range was obtained for amphetamine with a correlation coefficient of 0.9903 and 0.9948 respectively. The ECL signal was monitored at ~620 nm, representing the λmax for the [Ru(bpy)3]2+ nafion composite films. This wavelength is shifted by approximately 15 nm compared to the photoexcited λmax for the same system. The modified films were formed by direct interaction with the electrode surface without the need for surface modification or chain linkers. This is a major advantage for the fabrication of any sensor as it reduces the synthesis times resulting in more economically and cheaper production costs. This technique is simple, rapid, selective and sensitive, and shows potential for the high-throughput quantitation of ATS as well as possibilities for adaptation with other techniques such as FIA or LC systems

Electrochemiluminescence (ECL) sensing properties of water soluble core-shell CdSe/ZnS quantum dots/Nafion composite films

Water soluble positively charged 2-(dimethylamino) ethanethiol (DAET)-protected core-shell CdSe/ZnS quantum dots (QDs) were synthesized and incorporated within negatively charged Nafion polymer films. The water soluble QDs were characterized using UV-visible and fluorescence spectroscopies. Nafion/QDs composite films were deposited on glassy carbon electrodes and characterized using cyclic voltammetry. The electrochemiluminescence (ECL) using hydrogen peroxide as co-reactant was enhanced for Nafion/QDs composite films compared to films of the bare QDs. Significantly, no ECL was observed for Nafion/QDs composite films when peroxydisulfate was used as the co-reactant, suggesting that the permselective properties of the Nafion effectively exclude the co-reactant. The ECL quenching by glutathione depends linearly on its concentration when hydrogen peroxide is used as the co-reactant, opening up the possibility to use Nafion/QDs composite films for various electroanalytical applications

Optimising electrogenerated chemiluminescence of quantum dots via co-reactant selection

We demonstrate that for quantum dot (QD) based electrochemiluminescence (ECL), the commonly used co-reactant does not preform as effectively as potassium persulfate. By exploiting this small change is co-reactant, ECL intensity can be enhanced dramatically in a cathodic based ECL system. However, TPA remains the preferential co-reactant based system for anodic ECL. This phenomenon can be rationalised through the relative energy level profiles of the QD to the co-reactant in conjunction with the applied potential range. This work highlights the importance of understanding the co-reactant pathway for optimising the application of ECL to bioanalytical analysis, in particular for near infrared (NIR) QDs which can be utilised for analysis in blood

The influence of poly (2-methoxyaniline-5-sulfonic acid) on the electrochemical and photochemical properties of a highly luminescent ruthenium complex

Immobilisation of a luminescent material on an electrode surface is well known to substantially modulate its photophysical and electrochemical properties. Here a positively charged ruthenium metal complex ([Ru(bpy)(3)](2+)) is immobilised on all electrode surface by ion paring with a sulfonated conducting polymer poly(2-methoxyaniline-5-sulfonic acid), (PMAS). Significantly, our study reveals that the electron transport between the ruthenium metal centres can be greatly enhanced due to the interaction with the conducting polymer when both are surface confined. Charge transfer diffusion rates in the present system are an order of magnitude faster than those found where the metal centre is immobilised within a non-conducting polymeric matrix. Electron transport appears to be mediated through the PMAS conjugated structure, contrasting with the electron hopping process typically observed in non-conducting metallopolymers. This increased regeneration rate causes the ruthenium-based electrochemiluminescence (ECL) efficiency to be increased. The impact of these observations on the ECL detection of low concentrations of disease biomarkers is discussed. (c) 2007 Published by Elsevier Ltd

The hydrochloride and hydrobromide salt forms of (S)-amphetamine

(S)-Amphetamine hydrochloride, C9H14ClN, has a Z′ = 6 structure with six independent cation, anion pairs. That these are indeed crystallographically independent is supported by different packing orientations of the cations and by observation of a wide range of cation conformations generated by rotation about the phenyl–CH2 bond. The supramolecular contacts about the anions also differ such that both a wide variation in the geometry of the three N–H···Cl hydrogen bonds formed by each chloride anion and differences in C–H···Cl contacts are apparent. (S)-Amphetamine hydrobromide, C9H14BrN, is broadly similar to the chloride in terms of cation conformation, the existance of three N–H···X hydrogen bond contacts per anion and the overall 2 dimensional hydrogen bonded sheet motif. However, only the chloride structure features organic bilayers and Z′ > 1