ITO Electrode Surface Research Articles

On an Electrode Modified by a Supramolecular Ruthenium Mixed Valence (RuII/RuIII) Diphosphine-Porphyrin Assembly

Three novel polymetallic ruthenium (III) meso-tetra(4-pyridyl)porphyrins containing peripheral "RuCl(3)(dppb)" moieties have been prepared and characterized. The X-ray structure of the tetraruthenated {NiTPyP[RuCl(3)(dppb)](4)} porphyrin complex crystallizes in the triclinic space group P1. This structure is discussed and compared with the crystal data for the mer-[RuCl(3)(dppb)(py)]. The {TPyP[RuCl(3)(dppb)](4)} and {CoTPyP[RuCl(3)(dppb)](4)} porphyrins were used to obtain electrogenerated films on ITO and glass carbon electrode surfaces, respectively. Such tetraruthenated porphyrins form films of a mixed-valence species {TPyP[Ru(dppb)](4)(muCl(3))(2)}(2n)(4n2+) and {CoTPyP[Ru(dppb)](4)(muCl(3))(2)}(2n)(4n2+) on the electrode surface. The modified electrode with {CoTPyP[RuCl(3)(dppb)](4)} is very stable and can be used to detect organic substrates such as catechol.

Hydrophilic carbon nanoparticle-laccase thin film electrode for mediatorless dioxygen reduction: SECM activity mapping and application in zinc-dioxygen battery

Laccase from Cerrena unicolor was adsorbed on hydrophilic carbon nanoparticles (diameter = ca. 7.8 nm) modified with phenyl sulfonate groups and immobilized on an ITO electrode surface in a sol–gel processed silicate film. As shown by scanning electron and atomic force microscopies, the nanoparticles are evenly distributed on the electrode surface forming small aggregates of tens of nanometers in size. The mediator-free electrode exhibits significant and pH-dependent electrocatalytic activity towards dioxygen reduction. The maximum catalytic current density (95 μA cm −2) is obtained at pH 4.8 corresponding to maximum activity of the enzyme. Under these conditions dioxygen electroreduction commences at 0.575 V vs. Ag|AgCl sat, a value close to the formal potential of the T1 redox centre of the laccase. The scanning electrochemical microscopy images obtained in redox competition mode exploiting mediatorless electrocatalysis show that the laccase is evenly distributed in the composite film. The obtained electrode was applied as biocathode in a zinc-dioxygen battery operating in 0.1 M McIlvaine buffer (pH 4.8). It provides 1.48 V at open circuit and a maximum power density 17.4 μW cm −2 at 0.7 V.

Synthesis, photophysical and electrophosphorescent properties of mononuclear Pt(II) complexes with arylamine functionalized cyclometalating ligands

Abstract Four cyclometalated Pt(II) complexes, i.e., [(L2)PtCl] (1b), [(L3)PtCl] (1c), [(L2)PtC CC6H5] (2b) and [(L3)PtC CC6H5] (2c) (HL2 = 4-[p-(N-butyl-N-phenyl)anilino]-6-phenyl-2,2′-bipyridine and HL3 = 4-[p-(N,N′-dibutyl-N′-phenyl)phenylene-diamino]-phenyl-6-phenyl-2,2′-bipyridine), have been synthesized and verified by 1H NMR, 13C NMR and X-ray crystallography. Unlike previously reported complexes [(L1)PtCl] (1a) and [(L1)PtC CC6H5] (2a) (HL1 = 4,6-diphenyl-2,2′-bipyridine), intense and continuous absorption bands in the region of 300–500 nm with strong metal-to-ligand charge transfer (1MLCT) (dπ(Pt) → π∗(L)) transitions (e ∼ 2 × 104 dm3 mol−1 cm−1) at 449–467 nm were observed in the UV–Vis absorption spectra of complexes 1b, 1c, 2b and 2c. Meanwhile, with the introduction of electron-donating arylamino groups in the ligands of 1a and 2a, complexes 1b and 2b display stronger phosphorescence in CH2Cl2 solutions at room temperature with bathochromically shifted emission maxima at 595 and 600 nm, relatively higher quantum yields of 0.11 and 0.26, and much longer lifetimes of 8.4 and 4.5 μs, respectively. An electrochromic film of 1b-based polymer was obtained on Pt or ITO electrode surface, which suggests an efficient oxidative polymerization behavior. An orange multilayer organic light-emitting diode with 1b as phosphorescent dopant was fabricated, achieving a maximum current efficiency of 11.3 cd A−1 and a maximum external efficiency of 5.7%. The luminescent properties of complexes 1c and 2c are dependent on pH value and solvent polarity, which is attributed to the protonation of arylamino units in the C^N^N cyclometalating ligands.

A electrochemiluminescence aptasensor for detection of thrombin incorporating the capture aptamer labeled with gold nanoparticles immobilized onto the thio-silanized ITO electrode

A novel electrochemiluminescence (ECL) aptasensor was proposed for sensitive and cost-effective detection of the target thrombin adopted an aptamer-based sandwich format. To detect thrombin, capture aptamers labeled with gold nanoparticles (AuNPs) were first immobilized onto the thio-silanized ITO electrode surface through strong Au–S bonds. After catching the target thrombin, signal aptamers tagged with ECL labels were attached to the assembled electrode surface. As a result, an AuNPs-capture-aptamer/thrombin/ECL-tagged-signal-aptamer sandwich type was formed. Treating the resulting electrode surface with tri- n-propylamine (TPA) and applying a swept potential to the electrode, ECL response was generated which realized the detection of target protein. Spectroscopy and electrochemical impedance techniques were used to characterize and confirm the fabrication of the ECL aptasensor. AuNPs amplification and smart sensor fabrication art were implemented for the sensitive and cost-effective detection purpose. Signal-to-dose curve excellently followed a sandwich format equation and could be used to quantify the protein, and the detection limit was estimated to be 10 nM. Other forms of thrombin such as β- and γ-thrombins had negligible response, which indicated a high specificity of α-thrombin detection. The aptasensor opened up new fields of aptamer applications in ECL domain, a highly sensitive technique, and had a promising perspective to be applied in microarray analysis.

Preparation and characterization of poly[Ni( salen)(crown receptor)]/multi-walled carbon nanotube composite films

Nanocomposite films comprising multi-walled carbon nanotubes (MWCNTs) embedded within poly[Ni(3-Mesalophen-b15-c5)] were deposited on Pt and ITO electrode surfaces by the potentiodynamic polymerisation of [Ni(3-Mesalophen-b15-c5)] from solutions containing dispersed MWCNTs. Composites incorporating carbon nanotubes subject to a range of oxidising pre-treatments were compared with those incorporating untreated carbon nanotubes and with the pure polymer. In both cases, the use of CH 3CN and CH 2Cl 2 as fabrication and characterization media were explored. Films were characterized by voltammetry, electrochemical impedance spectroscopy and scanning electron microscope (SEM). The coating of the carbon nanotubes with polymer varied significantly with pre-treatment and solvent medium; this influenced the final composite morphology and electrical properties. Performance enhancement of the polymer component by the presence of the carbon nanotubes was manifested through the ability to store charge and the ease with which this could be accomplished; these were parameterized via increased redox capacitance and decreased charge-transfer resistance, respectively. Correlation of impedance parameters with SEM images provided a morphological rationale for composite electrical properties.

Structure, surface topography and electrochemical properties of cast films formed by fullerenes and their compositions with salt matrices

Some properties of films based on fullerene and pyridyl substituted fullerenopyrrolidines were studied. Both direct casting and immobilizing electroactive substances in the tetraoctylammonium bromide (TOAB) or tetraphenylphosphonium bromide matrices were used for modification of the ITO electrode surface. In accordance with X-ray diffraction, pyridyl substituted fullerenopyrrolidines are amorphous, and the lamellar structure of TOAB is retained when fullerene is present in the film. The differences, which are observed in the absorption spectra of the cast coatings of the individual fullerenes or fullerenes in the TOAB matrix as compared with solution spectra testify to the electronic interaction between fullerene molecules in a solid phase. At that, the quaternary ammonium salt participates immediately in the coating self-organization. Atomic force microscopy showed that both the solution composition and addends in the C 60 molecules influence the film morphology. Disintegration of fullerenes in the TOAB matrix and their interaction with hydrocarbon chains of TOAB provide the hydrophobic surrounding required for reversible electrochemical reduction of fullerene on an electrode in an aqueous solution. The differences observed for C 60 embedded in the tetraphenylphosphonium bromide and TOAB films accentuate the role of a layered structure of the matrix for the reversible electrochemical behavior of fullerene in aqueous solution.

Polypyrrole films functionalized with pendant titanocene dichloride complexes: Ellipsometric study of the electropolymerization process

Electrochemical and ellipsometric methods have been used to study the electropolymerization process of a functionalized monomer, Tc3Py (in which pyrrole is covalently bonded with titanocene dichloride complex) on platinum electrode from a dilute monomer solution in acetonitrile. The deposition has been performed in the potentiodynamic regime. A new method for the acquisition and treatment of ellipsometric data has been proposed which allowed us to analyze the evolution of the film properties at each potential. The model of a single uniform layer was unable to describe the ellipsometric experimental observations with the necessary precision. A proper fitting of the data has been achieved considering a model of two layers having identical values of the refractive index but different values of the extinction coefficient (higher absorption for the outer layer). The analysis of the calculated values of the optical parameters of these layers has led to the assumption that both layers represent morphologically the same medium (i.e. that the whole polymer film is uniform) while the higher extinction coefficient of the external layer was due to a penetration into it of solute oligomers possessing an intensive absorption at the wavelength of the observation, 633 nm. The dependences of the thicknesses of each layer and of the whole film on the cycle number have been established, the increment of the growth (5.5 nm per cycle) being constant within the whole deposition procedure. The variation of the optical constants of the layers during the potential cycling was determined and interpreted. The calculated values for the extinction coefficients and the layer thicknesses have been used to estimate how the film absorbance changes during the potential cycling. Its comparison with the same characteristic measured directly in a spectroelectrochemical cell for a film deposited at the ITO electrode surface has provided an extra evidence in favor of the above hypothesis on the film being a morphologically uniform material, with incorporated solute oligomers in its outer layer.

Electrochemical and photoelectrochemical response of electrodes coated with LB films of an azopolymer

This paper describes the electrochemical and photoelectrochemical behaviour of electrodes coated with Langmuir–Blodgett (LB) films of an azopolymer. The coating material used is a pyridine azopolymer (PAzPy) obtained by free radical polymerization of 6-[2-(4-pyridyazo)phenoxy]hexyl methacrylate (AzPy). Cyclic voltammetry experiments of LB films deposited at several transference surface pressures were performed to analyze the effect of the molecular packing on the electrochemical response. The influence of the pH of the electrolytic solution was also considered. AFM images have helped in the interpretation of the molecular architecture influence on the redox activity of the films. From the experimental results it was concluded that PAzPy is situated with the nitrogen from the pyridine group close to the ITO electrode surface in the LB films, which allows a direct electron transfer between the electrode surface and the azobenzene group leading to a quick electrochemical response of the films. The azobenzene electrochemical activity and the kinetics of the process are also highly dependent on the proton transfer process between the electrolytic solution and the azobenzene unit. The efficiency of the proton transfer process is determined by the pH of the electrolytic solution as well as by the molecular architecture of the film. The results presented in this paper show that, under optimal conditions, both the percentage of electroactive azobenzene chromophores and the standard heterogeneous rate constant of electron transfer are higher for PAzPy arranged in LB films compared with the values so far reported for azobenzenes of lower molecular weight.

A novel sensitive solid-state electrochemiluminescence sensor material: [formula omitted] doped SiO 2@MWNTs coaxial nanocable

A simple, large scale, and one-step process for the preparation of tris(2,2′-bipyridyl)ruthenium(I) ( Ru ( bpy ) 3 2 + ) doped SiO 2@carbon nanotubes (MWNTs) coaxial nanocable used for an ultrasensitive electrochemiluminescence (ECL) is presented for the first time. More importantly, a directly coated as-formed functional material on ITO electrode surface exhibits excellent ECL behavior, good stability, and high sensitivity in the presence of tripropylamine (TPA). This novel functional material will find potential applications in biosensor, electrophoresis and electroanalysis.

Application of the Double Pulse Potential Chronoamperometry Technique to Modify the ITO Electrode Surface

This paper proposes the application of the Double Pulse Potential Chronoamperometry (DPPC) technique to modify the ITO electrode surface in order to increase the electrode activity for chlorophenol detection. This technique consists in the application of two sets of potential pulses (anodic and cathodic). We used Ni-triethylenediamine as the electrode-modifying agent. We characterized the modified electrodes using SEM and Cyclic Voltammetry (CV), and determining the amount of film immobilized over the electrode area. We also applied CV to detect 2,4-dichlorophenol using the chemically modified electrodes (CMEs). The application of DPPC led to CMEs with a higher capacity to detect 2,4-DCP than that of the CMEs obtained by Chemisorption and CV.

Electrochemical synthesis and characterization of poly[3-(ω-bromoalkyl)thiophene

A novel series of functionalized polythiophenes incorporating 3-(ω-bromoalkyl) pendants are synthesized by electrochemical polymerization. The effect of the solvent on the electrosynthesis is investigated. The polymeric films are characterized using cyclic voltammetry, FT-IR, AFM and SEM microscopy. The poly[3-(6-bromohexyl)thiophene] film cast on GC or ITO electrode surface is compared with a sample obtained by a chemical method.

The effects of conductivity and electrochemical doping on the reduction of methemoglobin immobilized in nanoparticulate TiO 2 films

Methemoglobin (bovine) is immobilized from aqueous phosphate buffer (pH 5.5) solution into thin porous TiO 2 (anatase) films at ITO electrode surfaces. Films of TiO 2 are produced in a deposition process employing 40 nm diameter TiO 2 nanoparticles suspended in dry methanol followed by calcination. The pore size in these films is sufficient for methemoglobin (ca. 6 nm diameter) to diffuse into the porous structure (over several hours) and to remain immobilized in electrochemically active form. The electrochemical reduction of methemoglobin immobilized in TiO 2 and immersed in aqueous phosphate buffer at pH 5.5 is observed in two steps with (i) a small quasi-reversible voltammetric response at − 0.16 V vs. SCE (Process 1) and (ii) an irreversible reduction peak at ca. − 0.5 V vs. SCE (Process 2). The irreversible response is recovered only after slow chemical re-oxidation of hemoglobin to methemoglobin. At sufficiently negative applied potential “electrochemical doping” of the TiO 2 host is observed to lead to a considerably enhanced reduction Process 1. TiO 2 can be temporarily switched from a non-conducting (irreversible electron transfer) into a conducting (reversible electron transfer) state.

Poly(3,4-ethylenedioxythiophene) (PEDOT)-Coated Silica Spheres: Electrochemical Modulation of the Optical Properties of a Hydrogel-Stabilized Core−Shell Particle Suspension

In situ electrochemical methods involving both oxidative and reductive mediators were employed to modify the oxidation state (doping level) of PEDOT polymers in colloidal PEDOT-coated silica core−shell particles that were prepared as a dispersion encapsulated in a hydrogel matrix. The hydrogel-stabilized PEDOT particle suspensions were prepared as thin films (several hundred micrometers thick) on an ITO electrode surface and were equilibrated with an aqueous electrolyte containing a cocktail of redox mediators prior to mounting in a transmission-mode spectroelectrochemical cell. The modifications of the redox states of the PEDOT coating induced a change in the absorbance characteristics of the hydrogel films. The coated particles exhibited a maximum absorption peak centered at 800 nm in their doped (oxidized) state that could be significantly reduced through the electrochemical de-doping (reduction) of the PEDOT-coating on the particles.

Electrochemical properties of core-shell TiC–TiO2nanoparticle films immobilized at ITO electrode surfaces

Titanium carbide (TiC) nanoparticles are readily deposited onto tin-doped indium oxide (ITO) electrodes in the form of thin porous films. The nanoparticle deposits are electrically highly conducting and electrochemically active. In aqueous media (at pH 7) and at applied potentials positive of 0.3 V vs. SCE partial anodic surface oxidation and formation (at least in part) of novel core-shell TiC-TiO2 nanoparticles is observed. Significant thermal oxidation of TiC nanoparticles by heating in air occurs at a temperature of 250 degrees C and leads first to core-shell TiC-TiO2 nanoparticles, next at ca. 350 degrees C to TiO2 (anatase), and finally at temperatures higher than 750 degrees C to TiO2 (rutile). Electrochemically and thermally partially oxidized TiC nanoparticles still remain very active and for some redox systems electrocatalytically active. Scanning and transmission electron microscopy (SEM and TEM), temperature dependent XRD, quartz crystal microbalance, and voltammetric measurements are reported. The electrocatalytic properties of the core-shell TiC-TiO2 nanoparticulate films are surveyed for the oxidation of hydroquinone, ascorbic acid, and dopamine in aqueous buffer media. In TiC-TiO2 core-shell nanoparticle films TiO2 surface reactivity can be combined with TiC conductivity.

Highly Selective Response of Dopamine Against its Metabolite and Interfering Molecules at Sputtered ITO Electrode Surface

The highly selective detection of dopamine (DA) against 3,4-dihydroxyphenylacetic acid (DOPAC), L-ascorbic acid (AA), and uric acid (UA) was studied using a sputter deposited indium tin oxide electrode. The sensitivity of the electrode surface was more than 100 times higher for DA than for DOPAC, AA and UA as revealed by voltammograms obtained in a phosphate buffer. The DA response is linear from 10−6 to 10−3 M in the presence of 0.1 mM AA, suggesting that high selectivity is achieved in the mixed solution.

Self-assembled monolayers and electrostatically self-assembled multilayers of polyalkylviologens on sulfonate-modified gold and indium–tin–oxide electrodes

Self-assembly (SA) of polyviologens with linear alkyl spacers PVn ( n = 3–10) on sulfonate-primed gold and ITO electrode surfaces has been investigated by CV, QCM, XPS and AFM. The polymers form stable and relatively dense monolayers even from 10 −4 M PVn concentration. The viologen surface density is decreased as n is increased but for n = 10 and on alkylsulfonate-primed surfaces a strong adsorption takes place, with decreased redox potential and very narrow cyclic voltammogram of the absorbed layer due to organized structures on the surface. Stable and regular electrostatically self-assembled (ESA) multilayers are built on sulfonate-primed surfaces with PV3 and polysulfonates. From XPS analysis, the composition of the PVn/polysulfonate multilayers corresponds to a 1:1 ratio of polyanion and polycation charges, i.e., no extra non-polymeric ion is present, independently from the alkane chain length. The rate of electron transfer within the multilayers (diffusion coefficient = ca. 10 −9 cm 2 s −1) is higher than for analogous bulk materials.

Mesoporous TiO2carboxymethyl-γ-cyclodextrate multi-layer host films: effects on adsorption and electrochemistry of 1,1′-ferrocenedimethanol

TiO2 (anatase) nanoparticles are readily deposited layer-by-layer in the form of thin films with a carboxymethyl-γ-cyclodextrate binder. Electron microscopy, voltammetric, and quartz crystal microbalance data demonstrate that the film grows homogeneously and is electrically connected to the ITO electrode surface. 1,1′-Ferrocenedimethanol is employed as an adsorbing redox system to study the voltammetric characteristics of the mesoporous host film. The binding constants for the homogeneous complexation of 1,1′-ferrocenedimethanol with carboxymethyl-γ-cyclodextrin at pH 7, Kred = 1300 ± 200 M−1, and at pH 2, Kred = 1000 ± 200 M−1, are determined assuming 1 ∶ 1 complex formation. In the presence of the TiO2 carboxymethyl-γ-cyclodextrate films, solution phase voltammetric responses are affected due to a lower rate of diffusion of 1,1′-ferrocenedimethanol across the film (possibly due to binding to receptor sites) and due to slow electron transfer at pH 7 but not at pH 2. The TiO2 carboxymethyl-γ-cyclodextrate modified electrode, when dipped into 1,1′-ferrocenedimethanol containing solution, rinsed, and transferred into clean buffer solution, shows characteristic signals for adsorbed 1,1′-ferrocenedimethanol, consistent with weak binding and fast release upon oxidation. There is evidence for two distinct binding sites for 1,1′-ferrocenedimethanol both at pH 7 and at pH 2.

A hydrogen peroxide sensor based on the peroxidase activity of hemoglobin immobilized on gold nanoparticles-modified ITO electrode

A novel ITO electrode surface modified with spherical and rod-shaped gold nanoparticles was prepared by a surfactant-assisted seeding growth approach, which provided a biocompatible matrix for the immobilization of hemoglobin (Hb). By electrochemical impedance measurements, gold nanoparticles modification and Hb immobilization on the electrode surfaces were characterized using [Fe(CN) 6] 3−/[Fe(CN) 6] 4− redox probe. Owing to the promoted electron transfer of Hb by gold nanoparticles, the Hb immobilized gold nanoparticles-modified ITO (Hb/Au/ITO) electrode exhibited an effective catalytic response to the reduction of H 2O 2 with good reproducibility and stability. The linear relationship existed between the catalytic current and the H 2O 2 concentration in the range of 1 × 10 −5 to 7 × 10 −3 M. The detection limit (S/N = 3) was 4.5 × 10 −6 M.

Electropolymerization of Bithienyl-appended Cerium(III) Triple Decker Porphyrin Complex

Abstract A cerium(III) triple decker porphyrin complex bearing bithienyl substituents (1) at the peripheral meso-positions was synthesized. Electrochemical polymerization of the triple decker porphyrin gave a unique polymer film on the ITO electrode surface without decomposition.

Organosilicate thin film containing Ru(bpy)32+ for an electrogenerated chemiluminescence (ECL) sensorElectronic supplementary information (ESI) available: experimental details. See http://www.rsc.org/suppdata/cc/b3/b303766e/

An insoluble organosilicate gel containing a Ru(bpy)32+ complex was formed on an ITO electrode surface and its ECL responses toward several analytes were investigated for the sensitive ECL sensor application having long-term stability.