Search

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.

Abstract: The correlation between the structure of a series of uranyl minerals of the type [(UO2)8O2(OH)12] and M[(UO2)xOy(OH)z] (M=Na, x=4, y=2, z=5; M=K2, x=6, y=4, z=6; M=Ca, x=6, y=4, z=6), and their electrochemical properties have been investigated by using solid‐state cyclic voltammetry. Solid‐state electrochemical investigations at near‐neutral pH values reveal that all minerals undergo redox reactions in the potential range from −0.72 to −0.91 V vs. Ag/AgCl. This process is assigned to the U(VI)/U(V) redox couple and a further reduction, observed between −0.95 and −1.20 V, is associated with the U(V)/U(IV) reduction. The nature of the reduced products has been probed by using vibrational spectroscopy and SEM−EDX, and was found to be UO2+x. The mechanism of reduction has been elucidated and shown to be dominated by two independent one‐electron transfer reactions with disproportionation playing at most a minor role. The rate of charge propagation through the solid deposits, characterized by the homogeneous charge‐transport diffusion coefficient, DCT, is much lower in these minerals than structurally related systems with ion, rather than electron, transfer being rate limiting. Overall, the insights into the nature and rate of redox conversion suggest that the uranyl minerals formed by the oxidative corrosion of spent nuclear fuels are not electrochemically innocent. [ABSTRACT FROM AUTHOR]

Highlights: [•] Gold nanoparticles and polyaniline nanocomposites undergo a strong electronic interaction. [•] High sensitivity detection of DNA is enabled by PANI–AuNP composites. [•] Nanocomposites exhibit excellent discrimination for S. aureus associated with mastitis over S. epidermidis. [ABSTRACT FROM AUTHOR]

Abstract: DNA capture surfaces represent a powerful approach to developing highly sensitive sensors for identifying the cause of infection. Electrochemically deposited polypyrrole, PPy, films have been functionalized with electrodeposited gold nanoparticles to give a nanocomposite material, PPy–AuNP. Thiolated capture strand DNA, that is complementary to the sequence from the pathogen Staphylococcus aureus that causes mammary gland inflammation, was then immobilized onto the gold nanoparticles and any of the underlying gold electrode that is exposed. A probe strand, labelled with horse radish peroxidase, HRP, was then hybridized to the target. The concentration of the target was determined by measuring the current generated by reducing benzoquinone produced by the HRP label. Semi-log plots of the pathogen DNA concentration vs. faradaic current are linear from 150pM to 1μM and pM concentrations can be detected without the need for molecular, e.g., PCR or NASBA, amplification. The nanocomposite also exhibits excellent selectivity and single base mismatches in a 30 mer sequence can be detected. [Copyright &y& Elsevier]

The photophysical and electrochemical properties of a novel metallopolymer containing [Re(bpy)(CO)3]+ moieties coordinated to a poly(4-vinylpyridine) polymer chain are reported. Significantly, the release of the metal complexes can be triggered by oxidation or reduction of the rhenium complex. Solvent rapidly binds to the vacant coordination site to give a luminescent product. The redox and photophysical properties of the parent metallopolymer and the released solvated complex are compared. Along with photoemission, the metallopolymer generates significant electrogenerated chemiluminescence upon reduction in the presence of benzoyl peroxide as coreactant. [ABSTRACT FROM AUTHOR]

Abstract: Nanocomposite polymer films of [Ru(bpy)2(PVP)10]2+ metallopolymer and gold monolayer-protected clusters (MPCs) have been formed. Cyclic voltammetry of the films has been performed in both acidic (0.1M H2SO4) and neutral (0.1M Na2SO4) pH electrolyte solution. In acidic electrolyte, the protecting monolayers is desorbed as the gold surface is oxidized. Transmission electron microscopy of the nanocomposite following electrochemical cycling reveals aggregates of “naked” MPCs. In sharp contrast, in neutral pH electrolyte, the MPCs are stable towards voltammetric cycling and no gold oxide formation is evident in the voltammetry. The homogeneous charge-transfer diffusion coefficient, DCT , was determined for a range of nanocomposite films as the MPC mole fraction is systematically varied. When acidic electrolyte is used, DCT decreases from 2.8±0.5×10−10 to 1.5±0.1×10−11 cm2 s−1 as the MPC mole fraction is increased from 0 to 0.45. In contrast, the DCT determined in neutral electrolyte is universally lower than that determined in acidic electrolyte, it increases by over two orders of magnitude from 2.6±0.9×10−15 to 4.0±0.5×10−13 cm2 s−1 as MPC mole fraction increases from 0.05 to 0.5. [Copyright &y& Elsevier]

Presents a detailed spectroscopic and electrochemical study of a series of novel phenolate bound complexes. Probing of the origins of LUMO and HOMO in the complexes; Extent of orbital mixing; Assessment of the stabilities of the oxidized complexes.

Nanosphere lithography has been used to create spherical recessed electrodes of nanometre dimensions capable of enhancing fluorescent signals. [ABSTRACT FROM AUTHOR]

The cover picture shows the release of the luminescent rhenium coordination complex (yellow spheres) in solution. This release is triggered by electrochemical stimulus applied through the cable to the metallopolymer, which is represented by the splash of blue paint. The irreversibility of the electrochemical release is highlighted by holes in the graph paper. G. Valenti, F. Paolucci, R. J. Forster, and co‐workers outline the photophysical and electrochemical properties of a novel metallopolymer containing [Re(bpy)(CO)3]+ moieties coordinated to a poly(4‐vinylpyridine) polymer chain in their Full Paper on page 55 ff. Release of the metal complexes can be triggered by oxidation or reduction of the rhenium complex. [ABSTRACT FROM AUTHOR]

Metallopolymer-gold nanocomposites have been synthesized in which the metal complex-Au nanoparticle (NP) mole ratio is systematically varied by mixing solutions of 4-(dimethylamino) pyridine protected gold nanoparticles and a [Ru(bpy)2PVP10]2+ metallopolymer; bpy is 2,2′-bipyridyl and PVP is poly-(4-vinylpyridine). The impact of changing the gold nanoparticle diameter ranging from 4.0 ± 0.5 to 12.5 ± 1 nm has been investigated. The photo induced emission of the metallopolymer undergoes static quenching by the metal nanoparticles irrespective of their size. When the volume ratio of Au NP-Ru is 1, the quenching efficiency increases from 38% to 93% on going from 4.0 ± 0.5 to 12.5 ± 1 nm diameter nanoparticles while the radius of the quenching sphere remains unaffected at 75 ± 5 Å. The conductivity of thin films is initially unaffected by nanoparticle incorporation until a percolation threshold is reached at a mole ratio of 4.95 × 10-2 after which the conductivity increases before reaching a maximum. For thin films of the nanocomposites on electrodes, the electrochemiluminescence intensity of the nanocomposite initially increases as nanoparticles are added before decreasing for the highest loadings. The electrochemiluminescence intensity increases with increasing nanoparticle diameter. The electrochemiluminescence (ECL) emission intensity of the nanocomposite formed using 12.5 nm particles at mole ratios between 5 × 10-3 and 10 × 10-3 is approximately 7-fold higher than that found for the parent metallopolymer. The application of these materials for low cost ECL-based point of care devices is discussed. [ABSTRACT FROM AUTHOR]

Abstract: The photonic and electrochemical properties of a novel Ru–phenolate based metallopolymer are reported. The complex undergoes a ruthenium based reversible oxidation at approximately +0.400V and irreversible box ligand oxidation at +0.800V vs. Ag/AgCl. Oxidation of thin films in aqueous electrolyte at +0.500V reversibly switches the colour from wine red to light green and a red orange colour is observed for mixed redox composition. In contrast, oxidation at potentials more positive than +1.500V shows no visible colour change but produces a change in the near infra-red region. To determine the electrochromic switching rate and to identify the rate determining step of the, scan rate dependent cyclic voltammetry was performed under semi-infinite linear diffusion conditions in aqueous lithium perchlorate. These data reveal that the homogeneous charge transport diffusion coefficient, D CT, is 3.6±0.2×10−13 cm2 s−1, i.e., under these conditions it takes approximately 90s to fully oxidise a 100nm thick film. [Copyright &y& Elsevier]

The effect of surface confinement on the electrochemiluminescence (ECL) properties of metallopolymer [Ru(bpy)2(PVP)10]2+, where bpy is 2,2′-bipyridyl and PVP is poly(4-vinylpyridine), is reported. Immobilizing a luminescent material on an electrode surface can substantially modulate its photophysical properties. Significantly, our study revealed that the overall efficiency of the ECL reaction for the metallopolymer film is almost four times higher, at 0.15%, than the highest value obtained for [Ru(bpy)2(PVP)10]2+ dissolved in solution, (ϕECL = 0.04%). Electrochemistry has been used to create well-defined concentrations of the quencher Ru3+ within the film. Analysis of both the steady-state luminescence and lifetimes of the film reveals that static quenching by electron transfer between the photoexcited Ru2+* and the Ru3+ centers is the dominant quenching mechanism. The bimolecular rate of electron transfer is (2.5 + 0.4) ⊗ 106 M-1 s-1. The implications of these findings for ECL-based sensors, in terms of optimum luminophore loading, is considered. [ABSTRACT FROM AUTHOR]

Abstract: A thin film of the novel surface active ECL luminophore, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, BODIPY, is used to demonstrate that the ECL turn on potential can be controlled through the identity of the co-reactant. The films were very stable when in contact with organic solvents and surface coverages of 1-2nmolcm−2 are observed. Significantly, the potential at which ECL is generated is dictated by the identity of the co-reactant, either benzoyl peroxide or hydrogen peroxide, which opens new avenues for multi-analyte detection by changing the identity of the co-reactant rather than the dye. [Copyright &y& Elsevier]