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Biomedical subjects

Timothy G J Jones

Publications and source records attributed to Timothy G J Jones.

17 recordsLinked to original sources
PubMed2006

Voltammetric sizing of a sphere.

The size of a glass sphere positioned in the center of a microdisk electrode is determined by using a simple electrochemical procedure and is confirmed, additionally, by a microscopical measurement of the sphere at the time of the electrochemical measurement. The cyclic voltammetric response of the naked electrode and of the electrode with the sphere positioned in its center is recorded over a wide range of scan rates (0.002-1.5 V s(-1)). The size of the sphere is then determined by comparison of the experimental voltammogram with simulations for each individual scan rate.

Journal Article↗
PubMed2006

Nano-electrochemical detection of hydrogen or protons using palladium nanoparticles: distinguishing surface and bulk hydrogen.

The benefits of using nanoparticle-modified electrodes are exemplified through the electrochemical detection of protons and/or hydrogen. It is shown that a palladium-nanoparticle-modified boron-doped diamond allows voltammetric information relating to the relative roles played by the surface and the bulk metal to be obtained for the proton-hydrogen system at palladium surfaces which is not accessible using palladium macroelectrodes or microelectrodes.

Journal Article↗
PubMed2006

Mathematical modelling and simulation of adsorption processes at spherical microparticles.

A model for the adsorption process at spherical microparticles under transient diffusion conditions has been developed and solved using numerical simulation. This model allowed us to demonstrate that the system is controlled by two main dimensionless parameters: the adsorption rate constant ka' and the saturation parameter beta. Analytical models for the adsorption process at spherical microparticles under steady-state mass transport conditions have been derived. These models use previously developed empirical relationships for the calculation of the mass transfer coefficient (kc). The properties of the system were studied for both the case where mass transport is described by diffusion only and the case where it is the result of a coupled diffusion/convection process. These mathematical tools were then used to analyse the results obtained for the uptake of CuII by glassy carbon powder modified with the monomer L-cysteine methyl ester and to extract a minimum value for the adsorption rate constant which was found to be of the order of 10(-4) cm s(-1).

Journal Article↗
PubMed2005

The electroanalytical detection of hydrazine: a comparison of the use of palladium nanoparticles supported on boron-doped diamond and palladium plated BDD microdisc array.

We show that both a random distribution of palladium nanoparticles supported on a BDD electrode or a palladium plated BDD microelectrode array can each provide a sensing platform for the electrocatalytic detection of hydrazine. The palladium nanoparticle modified electrode displays a sensitivity and limit of detection of 60 mA mol(-1) L and 2.6 microM respectively while the array has a sensitivity of 8 mA mol(-1) L with a detection limit of 1.8 microM. The beneficial cost implications of using palladium nano- or micro-particles in sensors compared to a palladium macroelectrode are evident. Interestingly the array of the nanoparticles shows similar sensitivity and limit of detection to the microelectrode array which probably indicates that the random distribution of the former leads to 'clumps' of nanoparticles that effectively act as microelectrodes.

Boron↗
PubMed2005

Boron-doped diamond microdisc arrays: electrochemical characterisation and their use as a substrate for the production of microelectrode arrays of diverse metals (Ag, Au, Cu)via electrodeposition.

A novel boron-doped diamond (BDD) microelectrode array is characterised with electrochemical and atomic force microscopic techniques. The array consists of 40 micron-diameter sized BDD discs which are separated by 250 microns from their nearest neighbour in a hexagonal arrangement. The conducting discs can be electroplated to produce arrays of copper, silver or gold for analytical purposes in addition to operating as an array of BDD-microelectrodes. Proof-of-concept is shown for four separate examples; a gold plated array for arsenic detection, a copper plated array for nitrate analysis, a silver plated array for hydrogen peroxide monitoring and last, cathodic stripping voltammetry for lead at the bare BDD-array.

Arsenic↗
PubMed2005

All-diamond microelectrode array device.

We report the development of all-diamond microelectrochemical devices, namely, a microelectrode array (MEA), in which a periodic array structure with well-defined diameters, distance, and hexagonal unit cell pattern is micromachined using a combination of state-of-the-art microwave-induced plasma growth and laser ablation shaping techniques to prepare and coat a patterned boron-doped diamond (BDD) substrate with an intrinsic diamond insulating layer. The active BDD element can be tuned to between 10 and 50 microm in diameter with a 10 times diameter center-to-center distance between two adjacent conducting elements, which are exactly coplanar to the dielectric surroundings. This type of device should enable applications in harsh conditions such as high temperature, high pressure, and resistive media under dynamic flow regimes.

Journal Article↗
PubMed2005

4-Nitrobenzylamine partially intercalated into graphite powder and multiwalled carbon nanotubes: characterization using X-ray photoelectron spectroscopy and in situ atomic force microscopy.

We report the characterization of partial intercalation of 4-nitrobenzylamine (4-NBA) into edge-plane or edge-plane-like defect sites on the surface of both graphite powder and "bamboo-like" multiwalled carbon nanotubes (MWCNTs) using X-ray photoelectron spectroscopy (XPS). By comparing the XPS spectra of 4-NBA derivatized graphite powder and MWCNTs with that of graphite powder treated with benzylamine in a similar fashion, we conclude that benzylamine itself does not undergo partial intercalation. Using in situ atomic force microscopy, we are able to observe the partial intercalation of 4-NBA into an edge-plane-like "step" defect on the surface of a highly ordered pyrolytic graphite crystal in real time. Together these observations provide further evidence for the partial intercalation of 4-NBA and lead us to propose a new hypothesis to explain this phenomenon.

Journal Article↗
PubMed2005

Electrochemical ESR and voltammetric studies of lithium ion pairing with electrogenerated 9,10-anthraquinone radical anions either free in acetonitrile solution or covalently bound to multiwalled carbon nanotubes.

The influence of lithium ion pairing on the voltammetric reduction of anthraquinone in acetonitrile is reported. On gold electrodes, the single electron reduction generates a radical anion which forms a complex with lithium cations from the electrolyte. In situ ESR studies support this finding, and signal intensity measurements are used to estimate a value for the complexation equilibrium constant. Values calculated were of the of the order of 6000 mol(-1) dm3. Potential shift measurements and Digisim modeling are shown to be in support of a complexation mechanism in which a little of the complex precipitates on the electrode surface. The effect of lithium ion pairing is also demonstrated for the case in which 1-anthraquinonyl groups are covalently attached to multiwalled carbon nanotubes abrasively immobilized on a basal plane pyrolytic graphite electrode.

Journal Article↗
PubMed2005

Graphite powder and multiwalled carbon nanotubes chemically modified with 4-nitrobenzylamine.

We demonstrate that graphite powder and multiwalled carbon nanotubes (MWCNTs) can be derivatised by 4-nitrobenzylamine (4-NBA) simply by stirring the graphite powder or MWCNTs in a solution of acetonitrile containing 10 mM 4-NBA. We propose that 4-NBA partially intercalates at localised edge-plane or edge-plane-like defect sites and this hypothesis with a range of experimental data provided by electrochemistry in both aqueous and nonaqueous media, electron microscopy and X-ray powder diffraction.

Journal Article↗
PubMed2003

A thin-layer amperometric sensor for hydrogen sulfide: the use of microelectrodes to achieve a membrane-independent response for Clark-type sensors.

An electrochemical cell design of the Clark type including a thin layer of electrolyte in contact with a microelectrode has been successfully applied for the determination of sulfide utilizing its electrochemically initiated reaction with aqueous diethyl-p-phenylenediamine. The analytical parameters obtained were independent of the membrane used to separate the inner chamber and the outside sulfide-containing solution. The independence arises since the thickness of the diffusion layer associated with the microelectrode is small and, in contrast to the conventional macroelectrode Clark electrode, does not impinge on the membrane. This provides an improvement in gas sensor design and development as it obviates the need for membrane calibration and should simplify the application of Clark cells for variable-temperature measurements.

Electrochemistry↗
PubMed2003

Voltammetric characterization of a N,N'-diphenyl-p-phenylenediamine-loaded screen-printed electrode: a disposable sensor for hydrogen sulfide.

The voltammetric response of a 10% (by weight) N,N'-diphenyl-p-phenylenediamine (DPPD) and 90% (by weight) carbon and binder screen-printed electrode has been examined in aqueous media over a range of pH using cyclic voltammetry both in the presence and in the absence of sulfide. In the absence, the screen-printed electrode undergoes an initial oxidative process on the surface of the solid organic particles to form an insoluble layer of the corresponding cation radical salt, DPPD(*)(+)X(-), where X(-) is an anion present in the solution. The charge transfer is thought to occur at the three-phase boundary between solid DPPD, carbon, and the aqueous solution. At higher potentials, a second oxidative wave is observed that is attributed to the oxidation of the bulk DPPD with intercalation of the anion species present to form a solid phase of DPPD(*)(+)X(-). The two voltammetric processes were found to stabilize after repetitive scanning, after which time, sulfide was added to the solution. The voltammetric response was found to respond to sulfide by showing a decrease in both the oxidative and reductive waves, which can be attributed to the sulfide effectively blocking the three-phase boundary. The response was found to be independent of the electrode used and at pH 4 produced a linear range from 20 to 165 microM, and a limit of detection of 7.5 microM for sulfide detection was achieved.

Journal Article↗
PubMed2003

Amperometric determination of sulfide at a pre-oxidised nickel electrode in acidic media.

The electrochemical response of a pre-oxidised nickel electrode to increasing additions of sulfide has been examined and shown to produce a stripping-like voltammetric wave. A mechanism is described based on the formation of nickel sulfide at the electrode surface from a non-electroactive nickel oxide layer. The analytical utility of the approach has been examined and a linear range from 1 to 140 microM and a limit of detection of 0.8 microM is achievable, depending on the accumulation time.

Air Pollutants↗
PubMed2003

Physical adsorption of N,N'-diphenyl-p-phenylenediamine onto carbon particles: application to the detection of sulfide.

The derivatisation of carbon powder by physical adsorption of N,N'-diphenyl-p-phenylenediamine (DPPD) onto the surface of graphite particles (1-2 microm diameter) results in usefully functionalised carbon. The derivatised carbon powders have been studied using cyclic voltammetry by (i) abrasive immobilisation of the powder onto a basal plane pyrolytic graphite electrode (bppg) and (ii) by the manufacture of carbon-epoxy electrodes containing the derivatised carbon. The electrochemical response of the DPPD modified carbon has been examined in the presence of sulfide and possible reactions identified for the behaviour of each electrode substrate. The analytical application of the carbon-epoxy electrode for the sensing of sulfide is reported.

Journal Article↗