Indium Tin Oxide-coated Glass Electrodes Research Articles

Towards Molecularly Imprinted Polypyrrole-Based Sensor for the Detection of Methylene Blue

This study is dedicated to molecularly imprinted polymer-based sensor development for methylene blue detection. The sensor was designed by molecular imprinting of polypyrrole with phenothiazine derivative methylene blue (MB) as a template molecule. The molecularly imprinted polymer (MIP) was deposited directly on the surface of the indium tin oxide-coated glass electrode by potential cycling. Different deposition conditions, the layer’s durability, and thickness impact were analysed. The working electrodes were coated with molecularly imprinted and non-imprinted polymer layers. Potential pulse chronoamperometry and cyclic voltammetry were used to study these layers. Scanning electron microscopy was used to determine the surface morphology of the polymer layers. The change in optical absorption was used as an analytical tool to evaluate the capability of the MIP layer to adsorb MB. Selectivity was monitored by tracking the optical absorption changes in the presence of Azure A. In the case of MB adsorption, linearity was observed at all evaluated calibration plots in the concentration range from 0.1 μM to 10 mM. The novelty of this article is based on the methodology in the fabrication process of the sensors for MB, where MB retains its native (non-polymerised) form during the deposition of the MIP composite.

Investigation of Peptides for Molecular Recognition of C-Reactive Protein-Theoretical and Experimental Studies.

We investigate the interactions between C-reactive protein (CRP) and new CRP-binding peptide materials using experimental (biological and physicochemical) methods with the support of theoretical simulations (computational modeling analysis). Three specific CRP-binding peptides (P2, P3, and P9) derived from an M13 bacteriophage have been identified using phage-display technology. The binding efficiency of the peptides exposed on phages toward the CRP protein was demonstrated via biological methods. Fibers of the selected phages/peptides interact differently due to different compositions of amino acid sequences on the exposed peptides, which was confirmed by transmission electron microscopy. Numerical and experimental studies consistently showed that the P3 peptide is the best CRP binder. A combination of theoretical and experimental methods demonstrates that identifying the best binder can be performed simply, cheaply, and fast. Such an approach has not been reported previously for peptide screening and demonstrates a new trend in science where calculations can replace or support laborious experimental techniques. Finally, the best CRP binder─the P3 peptide─was used for CRP recognition on silicate-modified indium tin oxide-coated glass electrodes. The obtained electrodes exhibit a wide range of operation (1.0-100 μg mL-1) with a detection limit (LOD = 3σ/S) of 0.34 μg mL-1. Moreover, the dissociation constant Kd of 4.2 ± 0.144 μg mL-1 (35 ± 1.2 nM) was evaluated from the change in the current. The selectivity of the obtained electrode was demonstrated in the presence of three interfering proteins. These results prove that the presented P3 peptide is a potential candidate as a receptor for CRP, which can replace specific antibodies.

Symmetric and Asymmetric Supercapacitors of ITO Glass and Film Electrodes Consisting of Carbon Dot and Magnetite

To enhance the energy density, hybrid supercapacitors were fabricated, and their electrochemical features were investigated using a two-electrode configuration. By assembling nitrogen-doped graphene/magnetite (NG/Fe3O4) on indium tin oxide-coated (ITO) glass as a cathode and NG/carbon dots(Cdots)/Fe3O4 on ITO glass as an anode, a much higher gravimetric specific capacitance of 252.2 F/g, at a current density of 0.5 A/g, was obtained from this asymmetric supercapacitor compared with that (212.0 F/g) of a symmetric supercapacitor (NG/Cdots/Fe3O4)//(NG/Cdots/Fe3O4). A gravimetric energy density of 90.1 Wh/kg was obtained for an asymmetric ITO glass device at a specific power density of 400.0 W/kg. On the other hand, when an asymmetric two-electrode cell was fabricated with a Cdots/polypyrrole (PPy)/Fe3O4/TEMPO-oxidized cellulose nanofiber (TOCNF)-film electrode and a Cdots/PPy/TOCNF-film electrode, the specific capacitance (107.1 F/g) at a current density of 0.8 A/g was lower than that (456.4 F/g) of a symmetric (Cdots/PPy/Fe3O4/TOCNF)//(Cdots/PPy/Fe3O4/TOCNF)-film cell. Subsequently, a gravimetric energy density of 40.6 Wh/kg was achieved for a symmetric-film device at a specific power density of 320 W/kg. These results suggest that our method offers an efficient approach to developing symmetric and asymmetric devices consisting of hybrid materials for meeting the ever-increasing demands on energy-storage devices.

Size-Dependent Ripening of Gold Nanoparticles through Repetitive Electrochemical Surface Oxidation-Reduction Cycling

Here we describe the electrochemical size stability of 1.6, 4.1, and 15.1 nm diameter Au nanoparticles (NPs) supported on indium tin oxide-coated glass electrodes (glass/ITO). Anodic stripping voltammetry (ASV) and the electrochemically-measured total surface area-to-volume ratio (SA/V) provide the NP size following surface oxidation-reduction cycling from −0.2 to 1.6 V (vs Ag wire) in 0.1 M HClO4. After 1000 oxidation-reduction cyclic voltammetry (CV) scans, the relative size increases by a factor of 12, 7, and 2 for the 1.6, 4.1, and 15.1 nm diameter Au NPs, respectively. The relative size increase is largest for the smallest NPs, also confirmed by electron microscopy, indicating their lower size stability towards surface oxidation-reduction cycling. The size increase is fastest within the first 200 cycles, which decreases with a further increase in the number of cycles until the Au NP diameter stabilizes. The size transformation is more dramatic at higher Au NP electrode coverage and 30%–100% of the Au dissolves during cycling, depending on the coverage and NP size. Various potential cycling and holding profiles show that the Au NP size increases during reduction of the oxide layer, consistent with an electrochemical Ostwald ripening mechanism.

Electrochemical Detection of Dopamine in Real Samples by an Indium Tin Oxide-Coated Glass Electrode Modified with Carbon Nanotubes

Electrochemical Detection of Dopamine in Real Samples by an Indium Tin Oxide-Coated Glass Electrode Modified with Carbon Nanotubes

Electrochemical sensor for detection of mercury (II) ions in water using nanostructured bismuth hexagons

This study presents a systematic observation of the ability of bismuth nanostructures to detect trace amounts of mercury. Nanostructured hexagons of bismuth were synthesized using electrochemical deposition with potentiostatic mode on indium tin oxide-coated glass electrodes. Regular hexagons composed of nano-sized hexagonal building blocks (edge length $$\approx 80$$ to 700 nm) with well-defined edges were observed in scanning electron microscopy studies. X-ray diffraction pattern indicates the presence of polycrystalline bismuth and bismuth oxide in rhombohedral and cubic phases, respectively. X-ray photoelectron spectroscopy was done to analyze the chemical structure of the prepared nanostructures. Square wave anodic stripping voltammetry technique confirms that these nanostructured electrodes are highly sensitive to $$Hg^{2+}$$ ions down to concentrations as low as 0.74 ppb.

Voltammetric determination of copper and zinc in water using a Ruthenium bipyridyl/Nafion-modified indium tin oxide-coated glass electrode

Chemically-modified Indium Tin Oxide (ITO) coated glass substrates were fabricated by depositing Nafion thin films doped with tris (2,2’-bipyridyl) ruthenium(II) dichloride hexahydrate via drop coating deposition technique. The Nafion volume concentration in the film is 1% (v/v) and the mediator concentration is 5 mg per 1 mL Nafion. The chemically-modified electrodes were characterized by cyclic voltammetry (CV) and were used as working electrodes to detect varying concentrations of copper (Cu2+) and zinc (Zn2+) in a 0.1 M NaCl supporting electrolyte solution via Anodic Stripping Voltammetry (ASV). Cu2+ and Zn2+ ions were successfully determined by ASV. The limits of detection for Cu2+ and Zn2+ were 0.1 ppm and 0.7 ppm, respectively. The modified electrodes were used to determine the presence of Cu2+ and Zn2+ in different real water samples. The presence of Cu2+ was successfully determined in deep well, lake, and tap water samples, while the presence of Zn2+ was successfully determined in sea and tap water samples. Atomic Absorption Spectroscopy (AAS) results confirm the presence of Cu2+ and Zn2+ in the samples.

Oxidation of Highly Unstable <4 nm Diameter Gold Nanoparticles 850 mV Negative of the Bulk Oxidation Potential

Here we describe the oxidation of <4 nm diameter Au nanoparticles (NPs) attached to indium tin oxide-coated glass electrodes in Br(-) and Cl(-) solution. Borohydride reduction of AuCl(4)(-) in the presence of hexanethiol or trisodium citrate (15 min) led to Au NPs <4 nm in diameter. After electrochemical and ozone removal of the hexanthiolate ligands from the thiol-coated Au NPs, Au oxidation peaks appeared in the range 0-400 mV vs Ag/AgCl (1 M KCl), which is 850-450 mV negative of the bulk Au oxidation peak near 850 mV. The oxidation potential of citrate-coated Au NPs is in the 300-500 mV range and those of 4 and 12 nm diameter Au NPs in the 660-780 mV range. The large negative shift in potential agrees with theory for NPs in the 1-2 nm diameter range. The oxidation potential of Au in Cl(-) solution is positive of that in Br(-) solution, but the difference decreases dramatically as the NP size decreases, showing less dependence on the halide for smaller NPs.

Direct electron transfer of cytochrome C and its electrocatalytic properties on multiwalled carbon nanotubes/ciprofloxacin films

In this study, stable and homogenous thin films of multiwalled carbon nanotubes (MWCNTs) were obtained on conducting surface using ciprofloxacin (CF, fluoroquinolone antibiotic) as an effective-dispersing agent. Further, MWCNTs/CF film modified electrodes (glassy carbon and indium tin oxide-coated glass electrode) are used successfully to study the direct electrochemistry of proteins. Here, cytochrome C (Cyt-C) was used as a model protein for investigation. A MWCNTs/CF film modified electrode was used as a biocompatible material for immobilization of Cyt-C from a neutral buffer solution (pH 7.2) using cyclic voltammetry (CV). Interestingly, Cyt-C retained its native state on the MWCNTs/CF film. The Cyt-C adsorbed MWCNTs/CF film was characterized by scanning electron microscopy (SEM), UV–visible spectrophotometry (UV-vis) and CV. SEM images showed the evidence for the adsorption of Cyt-C on the MWCNTs/CF film, and UV–vis spectrum confirmed that Cyt-C was in its native state on MWCNTs/CF film. Using CV, it was found that the electrochemical signal of Cyt-C was highly stable in the neutral buffer solution and its redox peak potential was pH dependent. The formal potential (−0.27 V) and electron transfer rate constant (13 ± 1 s−1) were calculated for Cyt-C on MWCNTs/CF film modified electrode. A potential application of the Cyt-C/MWCNTs/CF electrode as a biosensor to monitor H2O2 has been investigated. The steady-state current response increases linearly with H2O2 concentration from 2 × 10−6 to 7.8 × 10−5 M. The detection limit for determination of H2O2 has been found to be 1.0 × 10−6 M (S/N = 3). Thus, Cyt-C/MWCNTs/CF film modified electrode can be used as a biosensing material for sensor applications.

Electrochemical Impedance Immunosensor for the Detection of C-Reactive Protein in Aqueous Solution

A label-free electrochemical impedance immunosensor is reported by immobilizing protein antibody, αCRP-Ab, through a self assembled monolayer (SAM) of 3-aminopropyltriethoxysilane (APTES) using a cross linker, Bis[sulfosuccinimidyl] suberate (BS3), on indium tin oxide (ITO) coated glass electrode. The immunosensor (αCRP-Ab/BS3/APTES/ITOglass) was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrochemical techniques. The electrochemical performance of the immunosensor was studied by electrochemical impedance spectroscopy. The results showed an increasing electron-transfer resistance with the immobilization of CRP antibody (αCRP-Ab) on the modified ITO coated glass electrode surface and on their coupling with protein CRP antigen (αCRP-Ag) at the immunosensor surface in the presence of [Fe(CN)6]3−/4− as redox probe. The immunosensor exhibits an electrochemical impedance response to antigen, αCRP-Ab, concentrations in a linear range from 8.5 ng to 9.12 μg mL−1 a with a lowest detection limit of 3.5 ng mL−1 antigen.

Electro-reduction of oxygen and electro-oxidation of methanol at Pd monolayer-modified macroporous Pt electrode

With polystyrene latex spheres self-assembled on indium tin oxide-coated glass electrode as templates, highly ordered macroporous Pt was prepared by electrochemical deposition. Then, the macroporous Pt was modified by Pd monolayer involving the galvanic displacement of Cu monolayer formed by under-potential deposition on macroporous Pt. Electrocatalytic properties of the Pd-modified macroporous Pt electrode for oxygen reduction were investigated by cyclic voltammetry and chronoamperometry in O2-saturated solution containing 0.1 M HClO4. Methanol electro-oxidation on the Pd-modified macroporous Pt surfaces in 0.5 M H2SO4 containing 1 M CH3OH was studied by cyclic voltammetry. The corresponding results showed that Pd-modified macroporous Pt electrode had negative catalytic activity for methanol oxidation in compared with macroporous Pt. However, Pd-modified macroporous Pt electrode had positive electrocatalytic activity to O2 reduction.

Nanocomposite multilayer films containing Dawson-type polyoxometalate and cationic phthalocyanine: Fabrication, characterization and bifunctional electrocatalytic properties

Water-soluble cationic phthalocyanine — Alcian blue (AB) and 2:18 tungstophosphate anions (P 2W 18) were alternately deposited on a -aminopropyltriethoxysilane-modified indium tin oxide-coated glass electrodes or quartz substrate through a layer-by-layer method. The resulting organic-inorganic hybrid films were characterized by ultraviolet-visible absorption spectra, cyclic voltammetry and X-ray photoelectron spectra. A stepwise and regular deposition of AB and P 2W 18 in both pure water and 0.01 M poly(styrenesulfonate) (PSS) were investigated. Differences in linear growth were observed between pure water and 0.01 M PSS-based solutions. The voltammetric curves show well-defined anodic and cathodic peaks, which is indicative of both electrocatalytic oxidation and reduction of nitrite.

Electrochemical and Spectroelectrochemical Evidences for Copolymer Formation Between 2-Aminodiphenylamine and Aniline

Electrochemical copolymerization of 2-aminodiphenylamine (2ADPA) with aniline (ANI) was carried out in aqueous hydrochloric acid by using cyclic voltammetry. In addition, cyclic voltammetry was used to evaluate the differences in electrochemical characteristics of the copolymer in comparison with the corresponding homopolymers, polyaniline (PANI) and poly(2-aminodiphenylamine) (P2ADPA). A growth equation of the copolymer films in terms of concentration of 2ADPA and cycle numbers, was deduced as by utilizing the charge associated for film deposition. The variation of peak currents and peak potentials with respect to sweep rates were compared between copolymer and PANI films. Further support for copolymer formation was obtained through spectroelectrochemical studies. This was done by recording UV-visible spectra during constant potential electropolymerization of a mixture of monomers, ANI and 2ADPA, on an indium-tin oxide-coated glass electrode. The appearance of a band at 520 nm in contrast to the spectra of PANI reveals that the copolymer is structurally different from PANI. © 2001 The Electrochemical Society. All rights reserved.

Electroreflectance and surface photovoltage spectroscopies of semiconductor structures using an indium–tin–oxide-coated glass electrode in soft contact mode

Measurements of electroreflectance and surface photovoltage spectroscopy of semiconductor structures are described using a transparent indium–tin–oxide-coated glass electrode in soft contact mode on the semiconductor surface. This improvisation (simplification) reduces the magnitude of the ac modulation voltage necessary for the electroreflectance measurement to less than a volt from about a kV (∼103 V) as required in the conventional contactless setup. This soft contact mode also enhances the sensitivity of the surface photovoltage signal by three orders of magnitude. We also formulate an analytical criterion to extract the transition energies of a quantum well from the surface photovoltage spectrum.

Edge-emission electroluminescence study of as-grown vertical-cavity surface-emitting laser structures

We report polarized edge- and front-emission electroluminescence studies on red-emitting vertical-cavity surface-emitting laser (VCSEL) structures. The measurements were performed nondestructively on pieces of as-grown wafers using indium–tin–oxide-coated glass electrodes. The front-emission spectra helped determine the Fabry–Pérot cavity-mode wavelength, while the edge-emission spectra were used to identify the wavelength of ground-state emission from the quantum wells (QWs) in the active region. However, measurements on edge-emitting laser (EEL) structures with a similar QW active region reveal that the peaks of the edge-emission spectra are always slightly redshifted with respect to front emission. We show that this arises due to reabsorption effects and then appropriately correct for it in the VCSELs by studying such shifts in the equivalent EELs. Thereafter, by comparing the experimental results with theoretical calculations and simulations, we estimate the composition, strain, and material quality of the QWs in the VCSEL active regions. Finally, we comment on the usefulness of comparing the two orthogonally polarized edge-emission spectra.

Chemiluminescence of Luminol Catalyzed by Electrochemically Oxidized Ferrocenes

Ferrocenes oxidized at an indium tin oxide-coated glass electrode catalyze the chemiluminescent reaction of luminol with hydrogen peroxide. The catalytic reaction has been studied with ferrocene derivatives in solution and covalently attached to ovalbumin adsorbed on the electrode. It is shown that chemiluminescence is initiated by electrochemical oxidation of the ferrocene derivative.

Synthesis and electrochemical characterization of bis(fulvalene)diiron electrode films

Electrochemical reduction of newly synthesised bis(fulvalene)diiron derivatives, [Fe2(C10H8)(C10H8–nRn)](R = CClCHCHO, n= 1 or 3), in NBu4ClO4–MeCN leads to the deposition of stable electroactive films on glassy carbon and indium–tin oxide coated glass electrodes. The difference in the number of substituents affects the electropolymerization reaction rate and physical and electrochemical properties of the polymer films. The electrode films control the reversibility in redox reactions of organic and organometallic electron acceptors such as p-benzoquinones and a cobaltocenium salt in acetonitrile.