Defects within a self-assembled monolayer (SAM) of dodecanethiol on gold have been used as nucleation sites for the electrodeposition of mushroom shaped platinum nanoparticles (PtNPs). The top surfaces of these PtNPs were then decorated with a layer of silver creating a hemispherical – platinum : silver core : shell nanoparticle (Pt–AgNP). Thiolated probe strand miRNA was then immobilised onto the upper silver surface. These regioselectively modified particles were desorbed by applying a current jump to yield nanoparticles capable of hybridising to a complementary miRNA target with electrocatalysis occurring on the non-functionalized lower surface. A second electrode was functionalized with single stranded capture miRNA that has a sequence that is complementary to an miRNA, miR-132, associated with the childhood cancer, Neuroblastoma but leaves a section of the target available to bind the nucleic acid sequence on the core : shell Pt–AgNPs. Following hybridization of the target and capture strands the surface was exposed to the miRNA labelled electrocatalytic Pt–AgNPs. The concentration of the target was then determined by monitoring the current associated with the reduction of hydrogen peroxide in a solution of H2SO4. Calibration plots of the log[miRNA] vs. faradaic current were linear from 1 aM to 1 μM and aM concentrations could be detected without the need for chemical amplification of the target, e.g., using PCR or NASBA. The regioselectively modified particles were also immobilised within the interior of gold microcavity arrays via miRNA hybridisation and their Raman properties investigated.

•Direct detection of miRNA associated with neuroblastoma without amplification.•Electrocatalytic current of H2O2 at triangular silver nanoplates (TSNPs) measured.•TSNPs immobilised in gold microcavities via miRNA hybridisation.•SERS enhancement of hybridisation event of TSNPs in gold microcavities.Triangular silver nanoplates (TSNPs) have been functionalised with probe strand miRNA that is complementary in part to the target nucleic acid, miR-132-3p, that is associated with neuroblastoma. These TSNPs were immobilised in gold microcavities via complementary miRNA hybridisation and can give plasmonic enhancement of the Raman response. Optimum enhancement can be achieved by using different excitation wavelengths and changing the distance between the nanoplate and the surface of the cavity. As silver is electrocatalytically active to the reduction of hydrogen peroxide, these probe-functionalised TSNPs can be used in a miRNA assay where a linear response was obtained for target concentrations from 100 fM to 1 μM target concentration, with a current generated of 100 μA.Download high-res image (91KB)Download full-size image

The ability of a molecular beacon to detect miR-132, a microRNA associated with the childhood cancer neuroblastoma, is reported in solution and within live cells. The stem-loop structure comprises a sequence complementary to miR-132, modified with a 6-FAM dye and dabcyl quencher on either end. In the absence of the target, self-binding occurs bringing the luminophore and quencher into close proximity, significantly decreasing the emission intensity. In the presence of miR-132, the signal is greatly enhanced, with a linear increase in intensity for mole ratios of beacon-to-target between 0.25 and 2.00. The structure differentiates between target and mismatched nucleic acid sequences, e.g., in the presence of a single-base mismatch, no increase in emission intensity beyond the background is observed. The stem-loop can be introduced into neuroblastoma cancer cells by electroporation, allowing miR-132 to be imaged within live cells. miR-132 appears to be localized within the nucleus of the cells, where its concentration is of the order of 1 μM. Significantly, transfection of the cells with a miR-132 mimic causes the emission intensity to more than double, demonstrating the sensitivity of the approach to changes in miR-132 concentration in live cells. This behavior opens up significant theranostic applications, such as the possibility of rapidly identifying retinoic acid resistant patients as well as providing a means to monitor therapeutic efficacy.

•Rapid charge transport through polyaniline–ruthenium metal complex composite•Composites yield highly efficient electrochemiluminescence.•Metal complexes in a conducting polymer matrix can lead to bright ECL.Electrochemiluminescent films have been formed by electrodepositing polyaniline, PANI, in the presence of [Ru(bpy)2PIC]2 +; bpy is 2,2′-bipyridyl and PIC is (2,2′-bipyridyl)-2(4-carboxylphenyl) imidazo [4,5][1,10] phenanthroline. The homogeneous charge transport diffusion coefficient, DCT, for the Ru2 +/3 + couple within the PANI film is 2.6 ± 0.9 × 10− 10 cm2s− 1. The large DCT facilitates a fast regeneration of Ru3 + and, coupled to a relatively rigid microenvironment, results in a high ECL intensity in the presence of tripropylamine as a co-reactant compared to [Ru(bpy)3]2 +. Significantly, despite the conducting nature of the polymer backbone, the [Ru(bpy)2PIC]2 + loaded PANI has the highest efficiency, 1.00%, yet reported for a surface confined ruthenium complex.

Blood platelet adhesion is crucial in dictating haemocompatibility of medical implants and in platelet capture in diagnostics. Understanding the role of platelet activation in dictating platelet adhesion at chemically modified interfaces is important but relatively unexplored. Using scanning electron microscopy and confocal fluorescence microscopy a quantitative assessment of capture of blood platelets at self-assembled monolayers and mixed monolayers (SAMs) on gold as a function of the activation status of the platelets was conducted. Single and mixed monolayers were prepared using thiol-functionalized arginine-glycine-aspartic acid (RGD), C-Ahx-GRGDS (Ahx = aminohexanoic acid linker), thiolated poly(ethylene)glycol (PEG-COOH) and 1-octanethiol. When incubated with suspensions of resting platelets, RGD promoted platelet adhesion compared to bare or alkanethiol modified gold. Increasing the alkanethiol ratio in the deposition solution decreased the extent of platelet adhesion. Platelet adhesion increased approximately 3 fold at PEG-COO- modified surfaces compared to RGD-alone. Platelets adhered to RGD or mixed RGD:alkane SAM surfaces were found to be captured in their resting state. In contrast, platelets captured at PEG-COO- SAM surfaces were activated by these substrates. The effect of treating platelets with the chemical activators, Mn2+ or DTT or the physiological activator, thrombin, on the capture efficiency and activation at RGD modified surfaces was also investigated. Mn2+ treated platelets presented similar adhesion to untreated platelets, while surprisingly DTT yielded a very significant decrease in platelet adhesion. And, any platelets that were captured, were in a resting state. Thrombin activated platelets were captured with similar efficiencies as untreated platelets. However, the platelets captured were fully activated. The distinction between capture of chemically and physiologically activated platelet is interesting and likely to originate from differences in the conformation of the integrin induced by each process. Finally, platelet adhesion to each surface could be reversed by incubation with a solution of linear or cyclical RGD or PEG-COO- for the RGD and PEGCOO- surfaces respectively. The specificity of platelet removal confirmed that platelet adhesion at RGD surfaces is occurring through integrin–RGD interactions.

Spontaneously adsorbed monolayers have been formed on gold electrodes using a Keggin polyoxotungstate with covalently attached alkanethiol linkers of two different lengths. Films of both polyoxotungstates show two well-defined reduction processes associated with the polyoxotungstate centers where the ionic liquid, [BMIM][BF4], acts as supporting electrolyte. The surface coverages are both less than that expected for a close-packed monolayer. For the short and long linkers, the voltammetric response can be described in terms of the Butler–Volmer response involving a surface confined species using standard heterogeneous electron transfer rate constants of 170 and 140 s–1 for the first reduction and 150 and 100 s–1 for the second reduction processes, respectively. The rate of electron transfer to a solution phase redox probe, ferrocyanide, is significantly more sensitive to the length of the linker than the rate of electron transfer to the tungstate centers. This behavior probably arises due to potential-induced changes in the film structure.

Platinum nanoparticles, functionalised regioselectively with probe strand DNA, have been immobilised within the interior of gold nanocavity arrays via DNA hybridisation. The immobilised nanoparticles are highly electrocatalytic and show significantly higher currents for the reduction of hydrogen peroxide than uniformly functionalised particles.

Ovarian cancer cells, SKOV3, have been immobilized onto platinum microelectrodes using anti-EPCAM capture antibodies and detected with high sensitivity using electrochemical impedance. The change in impedance following cell capture is strongly dependent on the supporting electrolyte concentration. By controlling the concentration of Dulbecco’s phosphate buffered saline (DPBS) electrolyte, the double layer thickness can be manipulated so that the interfacial electric field interacts with the bound cells, rather than simply decaying across the antibody capture layer. Significantly, the impedance changes markedly upon cell capture over the frequency range from 3 Hz to 90 kHz. For example, using an alternating-current (ac) amplitude of 25 mV, a frequency of 81.3 kHz, and an open circuit potential (OCP) as the direct-current (dc) voltage, a detection limit of 4 captured cells was achieved. Assuming an average cell radius of 5 μm, the linear dynamic range is from 4 captured cells to 650 ± 2 captured cells, which is approximately equivalent to fractional coverages from 0.1% to 29%. An equivalent circuit that models the impedance response of the cell capture is discussed.

•Cysteamine linked BODIPY films on platinum generate significant electrochemiluminescence.•Potential at which electrochemiluminescence occurs can be controlled by the co-reactant.•Electrochemiluminescence can be generated for adsorbates close to a metal surface.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 1-2 nmol cm− 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.

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 150 pM to 1 μM 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.

Suspensions of electrocatalytic platinum nanoparticles with radii as small as 78.9 ± 3.5 nm that are functionalised with DNA only in one region have been created using templated electrodeposition. The integrity of the bound DNA following nanoparticle desorption from the electrode is demonstrated by detecting attomolar concentrations of DNA without the need for molecular, e.g., PCR or NASBA, amplification. Double potential step approaches coupled with interface engineering via nucleation sites allows PtNPs to be created with controlled particle size and density in a facile and reproducible manner.

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.

•Self-assembled films of [Ru(bpy)3]2γ*-[W18O54(SO4)2] were prepared at Pt electrodes.•Low electrolyte concentrations are required to maintain film integrity.•Photocatalysis by [W18O54(SO4)2]4− is sensitized by the ruthenium centres.•Photocatalytic performance of the film was optimised under low electrolyte conditions.•The highest photocurrent response from POM films under visible irradiation is reported.Under appropriate conditions, photocatalytic oxidation of benzyl alcohol by Dawson polyoxometalates, POM, can be sensitized by ruthenium(II) polypyridyl complexes under visible irradiation of electrostatic adducts formed between these materials. To realize the potential of such sensitization in a photoelectrochemical cell, thin film assembly of at an electrode interface of such materials is required. However, because they are electrostatically associated, the structural integrity of the Ru-POM complex can be compromised by the contacting electrolyte. Herein, thin layers of an electrostatic adduct formed between the polyoxotungstate γ*-[W18O54(SO4)2]4− and the ruthenium polypyridyl complex [Ru(bpy)3]2+ have been self-assembled on platinum electrodes for the first time, using alternate immersion layer-by-layer assembly. SEM and AFM imaging reveal that the adduct films exhibit a highly nanoporous structure with an average pore diameter of approximately 200 nm; a film morphology that is clearly distinctive from films comprised of either parent ion; [(Hex)4N]4γ*-[W18O54(SO4)2] or [Ru(bpy)3](PF6)2 alone, and indicate that ion-pairing is what drives film porosity. Cyclic voltammetry of the adduct ([Ru–POM]) films was performed on Pt microelectrodes in the absence of, or presence of low levels of added supporting electrolyte to minimise any electrostatic disruption of the ionic film. Low concentrations of supporting electrolyte (1 mM (Bu)4NBF4) decreased the resistance across the cell by an order of magnitude, compared with no electrolyte whilst maintaining the film integrity. Photoelectrochemical studies of [Ru–POM] films using visible light (λ > 400 nm) and benzyl alcohol as the sacrificial electron donor were performed in the absence of added electrolyte. Resonance Raman spectroscopy, along with the extinction of photocurrent on oxidation of the ruthenium center indicate that the benzyl alcohol oxidation is sensitized in the visible spectral region by the ruthenium center. Increasing the surface coverage by adding more layers resulted in a net decrease in photocurrent density due to ion-transport limitations. However, rates of electrochemical re-oxidation of the photochemically reduced films ([Ru–POM]red) increased exponentially with increasing applied overpotential up to the oxidation potential of the ruthenium center. The overall photocurrent was optimized at 59 μA cm−2 in (1 mM (Bu)4NBF4), which is almost an order of magnitude higher than currents generated under the same conditions (at 6.8 μA cm−2) but in the absence of added electrolyte.Graphical abstractThe photocatalytic oxidation of benzylalcohol, sensitized under visible irratdiation at a layer by layer assembled film of γ*-[W18O54(SO4)2]4− and [Ru(bpy)3]2+ is optimised in low electrolyte media under which conditions the electrostatically associated film is stable.

Poly-3,4-ethylenedioxythiophene, PEDOT, films have been deposited on gold electrodes using polymerization from the vapor-phase in which the surface is first covered with a Fe (III) tosylate oxidant and then exposed to 3,4-ethylenedioxythiophene, EDOT, vapor. Gold nanoparticles were then electrodeposited to give a nanocomposite material, PEDOT-AuNP. Thiolated capture strand DNA, that is complementary to the sequence associated with the pathogen S. aureus that causes mammary gland inflammation, was then immobilized onto the gold nanoparticles and the underlying gold electrode. The target oligo was then hybridized to the capture strand DNA. A probe strand, labeled with horse radish peroxidase, was then hybridized to the target. The concentration of the target was determined by measuring the current required to reduce hydroquinone oxidized during the regeneration of the HRP label. Semi-log plots of the pathogen DNA concentration vs. faradaic current are linear from 150 pM to 1 μM and pM concentrations can be detected without the need for molecular, e.g., PCR or NASBA, amplification.Highlights► Gold nanoparticles and PEDOT nanocomposites undergo a strong electronic interaction. ► High sensitivity detection of DNA is enabled by PEDOT-AuNP composites. ► Nanocomposites exhibit excellent discrimination for S. aureus associated with mastitis over S. epidermis.

Thin films of polyoxometalates that are sensitized with a Ru(II) metallopolymer generate significant photocurrents in the presence of benzyl alcohol and visible light. Significantly, the photocurrent generated by the tungstate based adduct, α-[P2W18O62]6−, is approximately seven fold larger than that found for the Dawson polyoxomolybdate α-[S2Mo18O62]4−.

Suspensions of electrocatalytic gold nanoparticles with radii as small as 83 ± 13 nm that are functionalised with DNAonly in one region have been created using templated electrodeposition. The integrity of the bound DNA following nanoparticle desorption from the electrode is demonstrated by detecting picomolar concentrations of DNA without the need for molecular, e.g., PCR or NASBA, amplification.

Self-assembled monolayers (SAMs) of dodecanethiol have been formed on gold electrodes to produce nanoscale defects. These defects define nucleation sites for the electrodeposition of mushroom shaped platinum nanoparticles (PtNPs). The top surfaces of these PtNPs have been selectively functionalized with single stranded probe DNA. These regioselectively modified particles were desorbed by applying a current jump to yield nanoparticles capable of biorecognition on the top curved side and efficient electrocatalysis on the nonfunctionalized lower surface. A second electrode was functionalized with single stranded capture DNA that has a sequence that is complementary to the pathogen, Staphylococcus aureus but leaves a section of the target available to bind the probe strand immobilized on the PtNPs. Following hybridization of the target and capture strands, the surface was exposed to the probe DNA labeled electrocatalytic PtNPs. Target binding was detected by monitoring the current associated with the reduction of hydrogen peroxide in a solution of 0.01 M H2SO4. Calibration plots of the log[DNA] versus faradaic current were linear from 10 pM to 1 μM and picomolar concentrations could be detected without the need for amplification of the target, for example, using PCR or NASBA. As well as a wide dynamic range, this detection strategy has an excellent ability to discriminate DNA mismatches and a high analytical sensitivity.

A novel electrochemiluminescent reagent, 2,6-Diethyl-1,3,5,7-tetramethyl-8-[(2-fluorophenyl)-6-methoxy-1,5-naphthyridine-3-carboxy]-4,4′‐difluoroboradiazaindacene, BODIPY-COOH, capable of direct conjugation to a wide range of biomolecules has been developed. BODIPY-COOH shows a high fluorescence quantum yield, ϕ = 0.67 ± 0.03, which significantly exceeds the range of 0.33 to 0.41 previously reported for structurally similar dyes. In the presence of persulfate, the dye generates significant electrochemiluminescence, ECL. Significantly, at high concentrations, quenching of the ECL is observed due to dimerisation.Highlights► BODIPY dye generates significant electrochemiluminescence in the presence of persulfate. ► At high concentrations, BODIPY dyes show trivial quenching of the ECL and tend to dimerise. ► Carboxy functionalised BODIPY dyes are useful for biomolecule labelling.

Electrodes, modified with [Ru(bpy)2PVP10]n(ClO4)2 metallopolymer:gold nanoparticle composites, are used for the high sensitivity detection of nicotinamide adenine dinucleotide, NADH, using electrochemiluminescence, ECL; bpy is 2,2′-bipyridyl and PVP is poly (4-vinylpyridine). Incorporation of 12.5 nm gold nanoparticles protected with 4-dimethylaminopyridine, DMAP-AuNPs, causes the overall ECL efficiency to decrease with increasing nanoparticle loading. However, the absolute emission intensity and signal-to-noise ratio are both higher for the nanocomposite than for the parent metallopolymer. The ECL intensity depends linearly on [NADH] from 10 fM to 10 μM with a limit of detection, LOD, of 5 fM. The wide dynamic range and low limit of detection make these nanocomposite films attractive for biosensor development.Highlights► Metallopolymer–nanoparticle composites exhibit enhanced electrochemiluminescence intensity. ► Nanocomposites allow direct ECL detection of NADH at femtomolar concentrations. ► Electrochemiluminescence intensity varies linearly with [NADH] over nine orders of magnitude. ► In nanocomposites, ECL efficiency decreases with increasing nanoparticle loading. ► Electrochemiluminescence quenching in nanocomposites is described by the Perrin Model.

Highly luminescent metallopolymers have been prepared from condensation reactions between the primary alkyl amines contained within a poly(styrene-p-(aminomethyl)styrene) polymer backbone and carboxylic acid groups on [Ru(bpy)2(CAIP)](ClO4)2, where CAIP is 2-(4-carboxyphenyl)imidazo[4,5-f][1,10]phenanthroline. The photophysical properties of these metallopolymers including emission and absorption spectroscopy, luminescent lifetimes and time-resolved emission anisotropy show strong solvent and pH dependence. These properties are rather insensitive to the loading of the metal centres on the polymer backbone suggesting weak electronic interactions between adjacent centres and the polymer backbone. The polymers form continuous films when drop-cast at an indium tin oxide interface and retain their strong luminescence. This processability and intense luminescence make them potentially useful for sensing and display applications.

Ink jet printed carbon nanotube forest arrays capable of detecting picomolar concentrations of immunoglobulin G (IgG) using electrochemiluminescence (ECL) are described. Patterned arrays of vertically aligned single walled carbon nanotube (SWCNT) forests were printed on indium tin oxide (ITO) electrodes. Capture anti-IgG antibodies were then coupled through peptide bond formation to acidic functional groups on the vertical nanotubes. IgG immunoassays were performed using silica nano particles (Si NP) functionalized with the ECL luminophore [Ru(bpy)2PICH2]2+], and IgG labelled G1.5 acid terminated PAMAM dendrimers. PAMAM is poly(amido amine), bpy is 2,2′-bipyridyl and PICH2 is (2-(4-carboxyphenyl)imidazo[4,5-f][1,10]phenanthroline). The carboxyl terminal of [Ru(bpy)2PICH2]2+ (fluorescence lifetime ≈ 682 ± 5 ns) dye was covalently coupled to amine groups on the 800 nm diameter silica spheres in order to produce significant ECL enhancement in the presence of sodium oxalate as co-reactant in PBS at pH 7.2). Significantly, this SWCNT-based sensor array shows a wide linear dynamic range for IgG coated spheres (106 to 1012 spheres) corresponding to IgG concentrations between 20 pM and 300 nM. A detection limit of 1.1 ± 0.1 pM IgG is obtained under optimal conditions.Highlights► Ink jet printed highly sensitive vertically aligned SWCNT forest-ITO ECL sensor array. ► Silicate nanoparticles decorated with an ECL generating metal complex produce a significantly brighter emission. ► Wide linear dynamic range for IgG (20 pM to 300 nM) with detection limit as low as 1.1 ± 0.1 pM.

Thin films of the adduct formed from the electrostatic association of the metallopolymer, [Ru(bpy)2(PVP)10]2+, and the Dawson polyoxomolybdate α-[Mo18O54(SO4)2]4–, POMo, have been formed on ITO electrodes using an alternate immersion approach. The Ru/POMo ratio is 4.5:1, which exceeds the 2:1 ratio expected on the basis of the charges of the Ru2+ and POMo4– building blocks. This behavior arises because of the polymeric character of the cation. In the presence of a substrate that has an abstractable proton such as benzyl alcohol, these ruthenium-sensitized polyoxomolybdate films generate significant photocurrents under visible irradiation. Significantly, increasing the surface coverage of the adduct from 1.4 × 10–10 to 8.1 × 10–10 mol cm–2 does not measurably increase the photocurrent observed. Scan-rate-dependent cyclic voltammetry reveals that the rate of homogeneous charge transport through the film is slow, which most likely results in only a fraction of the film thickness being active for photoelectrocatalysis. The photocurrent increases markedly when the driving force for the oxidation of POMo5–, created by the photoelectrocatalytic oxidation of benzyl alcohol, is increased. This result is consistent with the dynamics of heterogeneous electron transfer being centrally important to the regeneration of the photoelectrocatalyst. A system in which the surface coverage and applied overpotential are optimized produces a photocurrent density of 190 ± 18 nA cm–2 under 480 ± 5 nm irradiation.

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.

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.

Thin layers of an electrostatically associated adduct formed between the polyoxomolybdate, [S2Mo18O62]4−, and the metallopolymers [Ru(bpy)2(PVP)10]2+ or [Ru(bpy)2(CO-P PIC)7]2+ have been deposited onto electrodes using alternate immersion layer-by-layer assembly; PVP is poly(4-vinylpyridine), bpy is 2,2ʹ′-bipyridyl, CO-P is poly[(4-(aminomethyl)styrene)1 (4-vinylpyridine)6] and PIC is 2-(4-carboxyphenyl) imidazo [4,5-f][1,10] phenanthroline. Raman spectroscopy reveals that the Ru-PVP:POM films exhibit an additional vibrational mode at 900 cm− 1 that is not present in either of the components suggesting significant electronic communication between the ruthenium centres and the polyoxomolybdate. Despite the similarity of their redox and photonic properties, this optical transition is absent in the Ru-Co-P:POM layers. Significantly, the Ru-PVP:POM films generate a higher photocurrent (38 ± 1 nA cm− 2) than the Ru-Co-P:POM films (8.9 ± 0.8 nA cm− 2) or [S2Mo18O62]4− films (9.7 ± 1.1 nA cm− 2) under visible irradiation.► Metallopolymer-polyoxometallate films photocatalytically oxidise benzyl alcohol. ► Photocurrent intensity depends on new optical transition observed in Raman. ► Subtle changes in metallopolymer structure significantly affects photocurrent.

Phase-modulated electrochemiluminescence (ECL), induced by modulating the applied potential, is reported for thin films of the metallopolymer, [Ru(bpy)2PVP10]2+, where bpy is 2,2′-bipyridyl and PVP is Poly 4-vinyl pyridine. Using a frequency of 0.25 Hz and an amplitude of 60 mV, a detection limit of 5 μM was obtained for oxalate which is a factor two lower than that obtained using a static DC potential. Significantly, the modulation technique shows higher sensitivity with a slope equal to 15.6 intensity units mM− 1 which is an order of magnitude larger than the unmodulated signal. The phase-modulated approach significantly increases the ECL signal-to-noise ratio, allows ECL measurements to be recorded under ambient light conditions and decreases the measurement time.► Thin ruthenium containing metallopolymer films deposited. ► Novel potential modulated electrochemiluminescence detection approach. ► High calibration sensitivity and ultrasensitive detection of oxalate. ► Electrochemiluminescence can be performed under ambient light conditions.

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 metallopolymers, [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 × 10−10 and 5.32 × 10−10 cm2 S−1 were observed with corresponding conductivity values of up to 2.34 × 10−8 S cm−1.

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 (0.1 M H2SO4) and neutral (0.1 M 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, DCTdecreases 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.Highlights► Nanocomposites of a metallopolymer and monolayer-protected gold clusters. ► Voltammetry in acidic electrolyte removes monolayer and triggers aggregation. ► Conductivity increases with increasing nanoparticle loading in neutral electrolyte. ► Enhanced electrical conductivity with preserved metallopolymer photonic properties.

The fabrication of nanoscale photonic and electronic devices will rely heavily on bottom up approaches for producing highly organized functional materials. These approaches offer distinct advantages over conventional lithography especially in terms of the spatial precision with which such structures can be built. One of the key barriers to producing operational devices is that of connectivity between the nanoscale and macroscopic world. Interfacial supramolecular chemistry provides this connectivity by combining writeable/addressable surfaces with functional materials. Tremendous progress has been made in the area of interfacial assembly over the past decade. The chemistry for creation of mono- and multilayer assemblies is now well established and increasingly, photoaddressability is being incorporated into such films. Coordination compounds are valuable components in interfacial photonic arrays because they can be “programmed” to perform multiple functions such as surface immobilization, electron transfer and light emission with relative synthetic ease. In particular, coordination compounds, e.g., osmium, ruthenium, rhodium polypyridyl complexes, are attractive as their optical transitions are usually well defined, and in the case of charge transfers, strongly allowed, typically occurring in the visible spectral region. Their luminescence can be used as a probe of the interfacial environment or for creating light addressable functionality within a film. Also, they frequently exhibit reversible electrochemical responses across a number of different oxidation states. Although exploitation of such coordination compounds is not as extensive as organic fluorphores, the number of photoactive interfacial films, incorporating photochemically active coordination compounds is growing significantly. Here, we review some key examples, focusing on how coordination compounds can be exploited to drive layer formation and photophysical and photochemical events at interfaces.

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.

Spontaneously adsorbed monolayers of [Co(ttp-CH2-SH)2](PF6)2 have been formed on platinum microelectrodes by exposure to micromolar solutions of the complex in 0.1 M TBABF4 in acetonitrile, ttp-CH2-SH is 4′-(p-(thiolmethyl)-phenyl)-2,2′:6′,2″-terpyridine. Resonance Raman spectroscopy on roughened polycrystalline platinum macro electrodes show that the molecule undergoes adsorption through the sulphur atom onto the platinum surface. The monolayers show reversible and well defined cyclic voltammetry when switched between Co2+ and Co3+ forms, with a peak to peak splitting of 0.040 ± 0.005 V up to 200 V s−1 and an FWHM of 0.138 ± 0.010 V. Adsorption is irreversible leading to the maximum surface coverage, 6.3 ± 0.3 × 10−11 mol cm−2 for 2.5 ≤ [Co(ttp-CH2-SH)2] ≤ 10 μM. The rate of monolayer formation appears to be controlled not by mass transport or interfacial binding but by surface diffusion of the complex. The surface diffusion coefficient is 5.5 ± 1.1 × 10−7 cm2 s−1 indicating that prior to formation of an equilibrated monolayer, the adsorbates have significant mobility on the surface. The electron transfer process across the monolayer–electrode interface has been probed by high speed chronoamperometry and the standard heterogeneous electron transfer rate constant, k°, is approximately 3.06 ± 0.03 × 104 s−1. The reorganization energy is at least 18.5 kJ mol−1.

Electrodeposition of gold island films of nanometre dimensions (<100 nm) on fluorine-doped tin oxide (FDTO) coated glass is reported. The effect of altering the overpotential of the potentiostatic transient, the use of both nucleation and growth pulses as well as the immobilisation of a spontaneously adsorbed monolayer of, 3-aminopropyldimethylmethoxysilane, is reported. Deposits ranging from isolated particles to dense arrays of nanometre dimension particles have been formed. For example, by using a 10 ms nucleation pulse at −1200 mV followed by growth at 600 mV, a high particle density (46 particles/μm2) and a mean particle size of 36 nm with an RSD of 29% were obtained. Double potential step approaches coupled with interfacial engineering via monolayer formation allows gold nanoparticles to be created on optically transparent FDTO with controlled particle size, density and particle size distribution in a facile, inexpensive, reproducible manner.

The potential, time, and concentration dependence of the potentiostatic electropolymerisation of the thienyl-substituted transition metal complex [Os(bttpy)22+] onto platinum disk microelectrodes is reported, bttpy is 4′-(5-(2,2′-bithienyl))-2,2′:6′,2″-terpyridine. Oxidative electropolymerisation of the thienyl bridges is highly efficient with an electropolymerisation efficiency of 36 ± 3% being observed across a wide range of potentials and monomer concentrations. The osmium centres are oxidised when polymerisation proceeds and the deposited polymer is highly conducting allowing high surface coverage films, up to 6 × 10−7 mol cm−2, to be deposited within 60 s. SEM imaging reveals that smooth films can be produced using moderate overpotentials for electrodeposition. Significantly, diffusional mass transport controls the rate of film deposition allowing the radial diffusion field found at microelectrodes to be exploited to favour film growth co-planar with the electrode surface. The electropolymerisation rate increases approximately linearly with increasing monomer concentration from approximately 8 to 400 μM and this first-order dependence likely arises from mass transport limitations. The rate of homogeneous charge transport through potentiostatically deposited films, characterised by D1/2C, where D is the apparent charge transport diffusion coefficient and C is the concentration of osmium centres, is 3.5 ± 0.5 × 10−7 mol cm−2 s−1/2 and is largely insensitive to the deposition potential, and is very similar to that previously observed for potentiodynamically deposited films. This charge transport parameter is approximately two orders of magnitude larger than those found for non-conjugated bridges and is interpreted in terms of resonant superexchange across the quaterthienyl bridge.

Solid deposits of the dimeric complex [Os(bpy)2Cl 4-bpt Os(bpy)2Cl]PF6, where bpy is 2,2′-bipyridyl and bpt is 3,5-bis(pyridin-4-yl)-1,2,4,-triazole have been deposited onto platinum microelectrodes. These layers exhibit unusually ideal electrochemical responses over a wide range of electrolyte compositions and pH values. Scanning electron microscopy reveals that repeated switching of the redox composition of these layers does not induce any significant structural change within the deposits. Cyclic voltammetry (CV) has been used to determine the apparent charge transport diffusion coefficient, DCT, describing homogeneous charge transport through the deposit. DCT is independent of the electrolyte concentration suggesting that electron self-exchange between adjacent redox centres limits the overall rate of charge transport through the solid. In 1.0 M LiClO4 and 1.0 M HClO4, DCT values of 2.0±0.1×10−10 and 1.7±0.4×10−10 cm2 s−1 are observed, corresponding to second order electron transfer rate constants of 1.8×107 and 3.0×107 M−1 s−1, respectively. The rate of heterogeneous electron transfer across the electrode ∣ deposit interface has been determined using fast scan CV. The standard heterogeneous electron transfer rate constant, k°, is 1.08±0.05 cm s−1 irrespective of the electrolyte pH. Significantly, this value is less than one order of magnitude smaller than that determined for a monomeric complex containing the same bridging ligand and redox active metal centre.

•Patterned protein surfaces can provide an improved assay for monitoring antiplatelet therapy.•Patterning significantly influences the spreading of platelets compared to conventional, homogeneously coated surfaces.•Electrochemical impedance can be used to rapidly measure the surface coverage of platelets without the need for labelling.A label-free assay is described to monitor the interaction of abciximab, a glycoprotein IIb/IIIa receptor antagonist (ReoPro), with platelets bound to a fibrinogen-functionalised electrode surface. Firstly, fibrinogen is deposited in a defined pattern onto a gold electrode using microcontact printing, and then platelets from whole blood are captured on the patterned surface. Patterning influences the spreading of platelets, which is strikingly different to that observed on homogeneously coated surfaces. The drug–platelet interaction has been investigated using AC impedance on uniform and patterned fibrinogen-modified surfaces. The results demonstrate that patterned fibrinogen surfaces can provide deep insights into the interaction of abciximab with different platelet sub-populations. The key advantages of this approach are that it is rapid, label free and does not require pre-processing of patient blood samples.

Blood platelet adhesion is crucial in dictating haemocompatibility of medical implants and in platelet capture in diagnostics. Understanding the role of platelet activation in dictating platelet adhesion at chemically modified interfaces is important but relatively unexplored. Using scanning electron microscopy and confocal fluorescence microscopy a quantitative assessment of capture of blood platelets at self-assembled monolayers and mixed monolayers (SAMs) on gold as a function of the activation status of the platelets was conducted. Single and mixed monolayers were prepared using thiol-functionalized arginine-glycine-aspartic acid (RGD), C-Ahx-GRGDS (Ahx = aminohexanoic acid linker), thiolated poly(ethylene)glycol (PEG-COOH) and 1-octanethiol. When incubated with suspensions of resting platelets, RGD promoted platelet adhesion compared to bare or alkanethiol modified gold. Increasing the alkanethiol ratio in the deposition solution decreased the extent of platelet adhesion. Platelet adhesion increased approximately 3 fold at PEG-COO- modified surfaces compared to RGD-alone. Platelets adhered to RGD or mixed RGD:alkane SAM surfaces were found to be captured in their resting state. In contrast, platelets captured at PEG-COO- SAM surfaces were activated by these substrates. The effect of treating platelets with the chemical activators, Mn2+ or DTT or the physiological activator, thrombin, on the capture efficiency and activation at RGD modified surfaces was also investigated. Mn2+ treated platelets presented similar adhesion to untreated platelets, while surprisingly DTT yielded a very significant decrease in platelet adhesion. And, any platelets that were captured, were in a resting state. Thrombin activated platelets were captured with similar efficiencies as untreated platelets. However, the platelets captured were fully activated. The distinction between capture of chemically and physiologically activated platelet is interesting and likely to originate from differences in the conformation of the integrin induced by each process. Finally, platelet adhesion to each surface could be reversed by incubation with a solution of linear or cyclical RGD or PEG-COO- for the RGD and PEGCOO- surfaces respectively. The specificity of platelet removal confirmed that platelet adhesion at RGD surfaces is occurring through integrin–RGD interactions.

Thin films of polyoxometalates that are sensitized with a Ru(II) metallopolymer generate significant photocurrents in the presence of benzyl alcohol and visible light. Significantly, the photocurrent generated by the tungstate based adduct, α-[P2W18O62]6−, is approximately seven fold larger than that found for the Dawson polyoxomolybdate α-[S2Mo18O62]4−.

Suspensions of electrocatalytic gold nanoparticles with radii as small as 83 ± 13 nm that are functionalised with DNAonly in one region have been created using templated electrodeposition. The integrity of the bound DNA following nanoparticle desorption from the electrode is demonstrated by detecting picomolar concentrations of DNA without the need for molecular, e.g., PCR or NASBA, amplification.

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 metallopolymers, [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 × 10−10 and 5.32 × 10−10 cm2 S−1 were observed with corresponding conductivity values of up to 2.34 × 10−8 S cm−1.

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.

Platinum nanoparticles, functionalised regioselectively with probe strand DNA, have been immobilised within the interior of gold nanocavity arrays via DNA hybridisation. The immobilised nanoparticles are highly electrocatalytic and show significantly higher currents for the reduction of hydrogen peroxide than uniformly functionalised particles.