Emmanuel Topoglidis - Academia.edu (original) (raw)

Papers by Emmanuel Topoglidis

Analytical Methods, 2019

This work presents a simple and efficient preparation method for microperoxidase-11 (MP11) modifi... more This work presents a simple and efficient preparation method for microperoxidase-11 (MP11) modified mesoporous SnO 2 films on ITO glass substrates (MP11/DDAB/SnO 2 /ITO) for the development of a sensitive electrochemical drug sensor for the determination of antimalarial endoperoxide artemisinin (ART). Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Fourier Transform-Infrared Spectroscopy (FT-IR) and UV-vis absorption spectroscopy were used to characterize the resultant modified electrodes. The properties of the electrode enable a high MP11 loading to be achieved in a stable and functional way allowing the direct reduction and oxidation of the immobilized undecapeptide. The MP11 modified electrodes exhibited significant catalytic activity for the electrochemical reduction of ART around À0.43 V vs. Ag/AgCl in NaH 2 PO 4 pH 7 buffer by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results showed a sensitive response; the cathodic catalytic current was linearly proportional to the concentration of ART in the range 0-150 mM (R ¼ 0.9895) when using DPV with a limit of detection of 17 mM. This type of sensor has demonstrated good repeatability, reproducibility and stability and was found to be applicable for use in determining ART concentrations in extracts from the plant Artemisia annua purchased from local pharmaceutical stores. Finally due to the optical transparency of the SnO 2 film electrodes, the reaction of immobilized MP11 with ART was also monitored using UV-vis spectroscopy indicating the formation of MP11/ART adducts on the surface of the film electrode.

ChemBioChem, Nov 24, 2003

De novo designed synthetic redox proteins (maquettes) are structurally simpler, working counterpa... more De novo designed synthetic redox proteins (maquettes) are structurally simpler, working counterparts of natural redox proteins. The robustness and adaptability of the maquette protein scaffold are ideal for functionalizing electrodes. A positive amino acid patch has been designed into a maquette surface for strong electrostatic anchoring to the negatively charged surfaces of nanocrystalline, mesoporous TiO 2 and SnO 2 films. Such mesoporous metal oxide electrodes offer a major advantage over conventional planar gold electrodes by facilitating formation of high optical density, spectroelectrochemically active thin films with protein loading orders of magnitude greater (up to 8 nmol cm À2) than that achieved with gold electrodes. The films are stable for weeks, essentially all immobilized-protein display rapid, reversible electrochemistry. Furthermore, carbon monoxide ligand binding to the reduced heme group of the protein is maintained, can be sensed optically and reversed electrochemically. Pulsed UV excitation of the metal oxide results in microsecond or faster photoreduction of an immobilized cytochrome and millisecond reoxidation. Upon substitution of the heme-group Fe by Zn, the lightactivated maquette injects electrons from the singlet excited state of the Zn protoporphyrin IX into the metal oxide conduction band. The kinetics of cytochrome/metal oxide interfacial electron transfer obtained from the electrochemical and photochemical data obtained are discussed in terms of the free energies of the observed reactions and the electronic coupling between the protein heme group and the metal oxide surface.

Colloid and Polymer Science, Jun 25, 2018

Multi-walled carbon nanotubes (MWCNTs) were incorporated into the active layer of mesoporous TiO ... more Multi-walled carbon nanotubes (MWCNTs) were incorporated into the active layer of mesoporous TiO 2 films resulting in MWCNTs-TiO 2 nanocomposites with improved electrical conductivity. These MWCNTs-TiO 2 nanocomposite films were prepared by a direct mixing method and the Bdoctor blade^technique. The films were sintered at various annealing temperatures (300, 350, 400, and 450°C) in order to examine the effect of annealing temperature to the morphology and electrochemical activity of the films. The presence of anatase TiO 2 and MWCNTs has been confirmed by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy, while conductivity and electrochemical properties of the nanocomposite MWCNΤs-TiO 2 films were examined via cyclic voltammetry (CV) and spectroelectrochemistry. After successful protein immobilization (Cyt-c), the electrochemical and spectroelectrochemical behavior of these hybrid electrodes (Cyt-c/MWCNTs-TiO 2) was examined in detail and particularly the effect of MWCNTs on the interfacial electron transfer between the film electrode and the adsorbed protein molecules.

Biochemical Society Transactions, Feb 1, 2000

Bioelectrochemistry, Nov 1, 2008

Hybrid protein films incorporating Cyt-c immobilized on TiO 2 films were prepared and characteris... more Hybrid protein films incorporating Cyt-c immobilized on TiO 2 films were prepared and characterised optically with UV-visible spectroscopy and electrochemically with cyclic voltammetry, and their conductivity properties were studied in detail. In addition the effects of a thin overlayer coating of a second metal oxide such as SiO 2 , Al 2 O 3 , ZrO 2 and MgO 2 were studied and the effects over the electrochemical properties of the hybrid working electrodes were discussed.

Inorganic Chemistry Communications, Dec 1, 2006

... 40 (2001), p. 155. José V. Ros-Lis, R. Martínez-Mañez and Juan Soto, Chem. Commun. (2002), p.... more ... 40 (2001), p. 155. José V. Ros-Lis, R. Martínez-Mañez and Juan Soto, Chem. Commun. (2002), p. 2248. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (97) P. Azenbadrer Jr., Daniel S. Tyson, Karolina Jursikova and Felix N. Castellano, J. Am. Chem. Soc. ...

Bioelectrochemistry, Jun 1, 2004

Protein film cyclic voltammetry is a well-established technique for the study of redox proteins i... more Protein film cyclic voltammetry is a well-established technique for the study of redox proteins immobilised on electrode surfaces. In this paper, we use nanostructured SnO 2 electrodes to demonstrate that cyclic voltabsorptometry is an effective, complimentary approach to such studies of protein redox function. We exemplify this approach using two different redox systems: microperoxidase-11 (MP-11) and flavodoxin Desulfovibrio vulgaris Hildenborough (Fld). Both systems were immobilised on nanocrystalline SnO 2 electrodes and the resulting films investigated by simultaneous cyclic voltammetry and voltabsorptometry. We demonstrate that cyclic voltabsorptometry allows the unambiguous and background free observation of redox reactions for both systems studied.

Chemical Communications, Jun 13, 2002

Transient optical spectroscopies and photocurrent action spectra are used to demonstrate photoind... more Transient optical spectroscopies and photocurrent action spectra are used to demonstrate photoinduced charge separation between zinc-substituted cytochrome c and a nanocrystalline TiO 2 electrode.

Journal of the American Chemical Society, Jun 1, 2004

In this paper, we report a spectroelectrochemical investigation of proton-coupled electron transf... more In this paper, we report a spectroelectrochemical investigation of proton-coupled electron transfer in flavodoxin D. vulgaris Hildenborough (Fld). Poly-L-lysine is used to promote the binding of Fld to the nanocrystalline, mesoporous SnO2 electrodes. Two reversible redox couples of the immobilized Fld are observed electrochemically and are assigned by spectroelectrochemistry to the quinone/semiquinone and semiquinone/hydroquinone couples of the protein's flavin mononucleotide (FMN) redox cofactor. Comparison with control data for free FMN indicates no contamination of the Fld data by dissociated FMN. The quinone/ semiquinone and semiquinone/hydroquinone midpoint potentials (E q/sq and Esq/hq) at pH 7 were determined to be-340 and-585 mV vs Ag/AgCl, in good agreement with the literature. Eq/sq exhibited a pH dependence of 51 mV/pH. The kinetics of these redox couples were studied using cyclic voltammetry, cyclic voltabsorptometry, and chronoabsorptometry. The semiquinone/quinone reoxidation is found to exhibit slow, potential-independent but pH-sensitive kinetics with a reoxidation rate constant varying from 1.56 s-1 at pH 10 to 0.0074 s-1 at pH 5. The slow kinetics are discussed in terms of a simple kinetics model and are assigned to the reoxidation process being rate limited by semiquinone deprotonation. It is proposed that this slow deprotonation step has the physiological benefit of preventing the undesirable loss of reducing equivalents which results from semiquinone oxidation to quinone.

Coatings, Feb 3, 2020

A TiO 2 thin film, prepared on fluorine-doped indium tin oxide (FTO)-coated glass substrate, from... more A TiO 2 thin film, prepared on fluorine-doped indium tin oxide (FTO)-coated glass substrate, from commercial off-the-shelf terpinol-based paste, was used to directly adsorb Ag plasmonic nanoparticles capped with polyvinylpyrollidone (PVP) coating. The TiO 2 film was sintered before the surface entrapment of Ag nanoparticles. The composite was evaluated in terms of spectroelectrochemical measurements, cyclic voltammetry as well as structural methods such as scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). It was found that the Ag nanoparticles are effectively adsorbed on the TiO 2 film, while application of controlled voltages leads to a fully reversible shift of the plasmon peak from 413 nm at oxidation inducing voltages to 440 nm at reducing voltages. This phenomenon allows for the fabrication of a simple photonic switch at either or both wavelengths. The phenomenon of the plasmon shift is due to a combination of plasmon shift related to the form and dielectric environment of the nanoparticles.

Materials Chemistry Frontiers, 2018

It is possible that methylamine by being reduced could escape to the environment, thus, forcing t... more It is possible that methylamine by being reduced could escape to the environment, thus, forcing the remaining perovskite to form other perovskite-like chemical moieties based on low dimensional arrangement of PbBr6 octahedra, rather than PbBr2.

Frontiers of Materials Science, Jan 13, 2018

In this work three different mesoporous TiO2 film electrodes were prepared and used for the immob... more In this work three different mesoporous TiO2 film electrodes were prepared and used for the immobilization of Cytochrome c (Cyt-c). Films prepared via a standard sol-gel route (SG-films) were compared with commercially available benchmark nanotitania materials, namely P25 Degussa (P25-films) and Dyesol nanopaste (Dyesol films). Their properties, film deposition characteristics and their abilities to adsorb protein molecules in a stable and functional way were examined. We investigated whether it is possible, rather than preparing TiO2 films using multistep, lengthy and not always reproducible sol-gel procedures, to use commercially available nanotitania materials and produce reproducible films faster that exhibit all the properties that make TiO2 films ideal for protein immobilization. Although these materials are formulated primarily for dye-sensitized solar cell applications, in this study we found out that protein immobilization is facile and remarkably stable on all of them. We also investigated their electrochemical properties by using cyclic voltammetry and spectroelectrochemistry and found out that not only direct reduction of Fe(III)-heme to Fe(II)-heme of immobilized Cyt-c was possible on all films but that the adsorbed protein remained electroactive.

Journal of Solid State Chemistry, May 1, 2019

Hybrid organic-inorganic semiconductors (HOIS) still remain as research focus due to their except... more Hybrid organic-inorganic semiconductors (HOIS) still remain as research focus due to their exceptional optoelectronics properties, placing them as ideal candidates for use in the field of light emitting diodes and photovoltaics. In the present work, HOIS have been synthesized, characterized as well as adsorbed onto graphite/silica film electrodes (GSiHE), the latter used as simple, low cost, yet sensitive, electrochemical sensors. These composite electrodes have been specifically characterized with electrochemical methods and have been applied in the development of prototype electrochemical drug sensors; a paradigm is provided for a simple, efficient, sensitive and relatively specific sensing of an antihypertensive drug, losartan (LOS). The electrochemical behavior of GSiHE film modified with HOIS was examined by cyclic voltammetry, while its morphology, structural and spectroscopic properties were investigated by field emission scanning electron microscopy, X-ray diffraction, porosimetry, optical and luminescence spectroscopies. Under optimized conditions the modified film electrode demonstrated excellent electrocatalytic activity towards oxidation of LOS in the linear response range for concentrations from 4x10-5 M to 3.2x10-4 M (correlation coefficient 0.989) with the limit of detection computed at 3x10-6 M. The sensor takes advantage of the ability of ions to interact with the HOIS lattice on the GSiHE film; this type of sensor has demonstrated good repeatability, reproducibility and stability and was found to be applicable for use in determining pharmaceutical tablet sample concentrations.

Analytical Chemistry, Oct 22, 1998

We have investigated the use of optically transparent, nanoporous TiO(2) films as substrates for ... more We have investigated the use of optically transparent, nanoporous TiO(2) films as substrates for protein immobilization. Immobilization on such films may be readily achieved from aqueous solutions at 4 °C. The nanoporous structure of the film greatly enhances the active surface area available for protein binding (by a factor of 150 for a 4-μm-thick film). We demonstrate that the redox state of immobilized cytochrome c may be modulated by the application of an electrical bias potential to the TiO(2) film and that the fluorescence yield of immobilized fluorophore-labeled maltose-binding protein may be used to monitor specifically maltose concentration. We conclude that nanoporous TiO(2) films may be useful both for basic studies of protein/electrode interactions and for the development of array-based bioanalytical devices employing both optical and electrochemical signal transduction methodologies.

Analytica Chimica Acta, Feb 1, 2011

In this paper, we employ microperoxidase MP-11 immobilized on mesoporous SnO 2 electrodes in orde... more In this paper, we employ microperoxidase MP-11 immobilized on mesoporous SnO 2 electrodes in order to study its peroxidase activity and reaction mechanism. We demonstrate the catalytic redox chemistry of the immobilized MP-11 via direct interfacial electron transfer without the use of electron mediators. By taking advantage from the optical transparency of the SnO 2 electrodes, optical absorbance spectroscopy is used in order to compliment the data information obtained from electrochemical techniques. The catalytic activity of the immobilized MP-11 is found to proceed via the Fenton reaction, yielding OH radical intermediates. We also demonstrate the viability of using this electrode system as a potential H 2 O 2 biosensor with a sensitivity range of 0.05-30 M.

Electroanalysis, Jun 1, 2005

Emmanuel Topoglidis,*a, c Emilio Palomares,a Yeni Astuti,a Alex Green,a Colin J. Campbell,b James... more Emmanuel Topoglidis,*a, c Emilio Palomares,a Yeni Astuti,a Alex Green,a Colin J. Campbell,b James R. Durranta a Center of Electronic Materials and Devices, Department of Chemistry, Imperial College, London, SW72AZ, UK *e-mail: manosphd@yahoo.com b ...

Electroanalysis, May 1, 2006

Abstract A nanocrystalline TiO2 film is an electrode material with large surface area which allow... more Abstract A nanocrystalline TiO2 film is an electrode material with large surface area which allows high levels of protein adsorption without loss of protein structure or activity. As an optically transparent semiconductor, titania can be used to carry out direct spectroelectrochemistry of proteins ...

Langmuir, Jul 4, 2003

... We, furthermore, demonstrate the development of an electrochemical NO sensor based upon a ...... more ... We, furthermore, demonstrate the development of an electrochemical NO sensor based upon a ... We, therefore, conclude that SnO 2 electrodes show the attractive protein immobilization properties of other nanoporous metal oxide films such as ZnO and TiO 2 and, moreover ...