Biomedical subjects

Robert J Forster

Publications and source records attributed to Robert J Forster.

At least 19 recordsLinked to original sources

PubMed2007

16S rRNA gene-based analysis of mucosa-associated bacterial community and phylogeny in the chicken gastrointestinal tracts: from crops to ceca.

Mucosa-associated microbiota from different regions of the gastrointestinal (GI) tract of adult broilers was studied by analysis of 16S rRNA gene sequences. The microbiota mainly comprised Gram-positive bacteria along the GI tract. Fifty-one operational taxonomic units (OTUs) (from 98 clones) were detected in the ceca, as compared with 13 OTUs (from 49 clones) in the crops, 11 OTUs (from 51 clones) in the gizzard, 14 OTUs (from 52 clones) in the duodenum, 12 OTUs (from 50 clones) in the jejunum and nine OTUs (from 50 clones) in the ileum. Ceca were dominantly occupied by clostridia-related sequences (40%) with other abundant sequences being related to Faecalibacterium prausnitzii (14%), Escherichia coli (11%), lactobacilli (7%) and Ruminococcus (6%). Lactobacilli were predominant in the upper GI tract and had the highest diversity in the crop. Both Lactobacillus aviarius and Lactobacillus salivarius were the predominant species among lactobacilli. Candidatus division Arthromitus was also abundant in the jejunum and ileum.

Animals↗

PubMed2006

Photonic and electrochemical properties of adsorbed [Ru(dpp)2(Qbpy)]2+ luminophores.

Dense monolayers of [Ru(dpp)2Qbpy]2+, where dpp is 4,4'-diphenylphenanthroline and Qbpy is 2,2':4,4' ':4'4' '-quarterpyridyl, have been formed by spontaneous adsorption onto clean platinum microelectrodes. The cyclic voltammetry of these monolayers is nearly ideal, and three redox states are accessible over the potential range of +/-1.3 V. Chronoamperometry conducted on the microsecond time scale has been used to probe the dynamics of heterogeneous electron transfer and indicates that the standard heterogeneous electron-transfer rate constant, k degrees , is approximately 106 s-1. The metal complex emits at approximately 600 nm in fluid and solid solution as well as when bound to a platinum electrode surface within a dense monolayer. In the case of the monolayers, it appears that the excited states are not completely deactivated by radiationless energy transfer to the metal because electronic coupling between the adsorbates and the electrode is weak. The dynamics of lateral electron transfer between the electronically excited Ru2+* and ground-state Ru3+ species has been explored by measuring the luminescence intensity after defined quantities of Ru3+ have been produced electrochemically within the monolayer. The rate of lateral electron transfer is between 8 x 106 and 3 x 108 M-1 s-1, indicating efficient electron transfer between adsorbates in close-packed assemblies. Voltammetry conducted at megavolt per second scan rates has been used to directly probe the redox properties of the electronically excited species.

Adsorption↗

PubMed2006

Regulation of rumen fermentation during seasonal fluctuations in food intake of muskoxen.

We studied rumen fermentation of castrated adult muskoxen (Ovibos moschatus; n=4) during periods of low (May) and high (August) food intake. Turnover time (17+/-1.8 h) and volume (26+/-3.9 L) of rumen fluid were consistent between May and August and among days within each season. Rumen temperature did not vary significantly during the day (38.8+/-0.29 degrees C) in either season. Rumen osmolality (271.9+/-16.4 vs. 245.9+/-11.4 mOsm kg(-1)) and pH (6.81+/-0.31 vs. 6.39+/-0.15) were higher in May than in August indicating a shift in the allostatic set point. Rumen fluid pH was more variable in May than in August both before and after a single meal of fermentable substrate even though fermentation acids were lower in May than in August (101.0+/-11.0 vs. 126.0+/-8.74 mM). Changing proportions of minor fermentation acids indicated a shift in metabolic pathways even though bacterial numbers were similar between seasons (6.4+/-5.8x10(9) mL(-1)). Allostatic set points probably alter the homeostatic range of conditions and the microbial diversity of fermentations in herbivores from highly seasonal environments.

Animals↗

PubMed2006

Sensitization of photo-reduction of the polyoxometalate anions [S(2)M(18)O(62)](4-) (M = Mo, W) in the visible spectral region by the [Ru(bpy)(3)](2+) cation.

Voltammetric, photo-physical and photo-electrochemical properties of the Dawson polyoxometalate anions alpha-[S(2)M(18)O(62)](4-) (M = Mo, W) are presented, both in the presence and absence of a series of [Ru(II)L(n)](+/2+) cations [L(n) = (bpy)(3), (bpy)(2)(Im)(2), (bpy)(2)(dpq), (bpy)(2)(box) and (biq)(2)(box)]. Electrochemical processes for both the anion and Ru(II/III) couples were detected in solutions of the salts [Ru(II)L(n)](2)[S(2)M(18)O(62)] in dimethylformamide (0.1 M Bu(4)NPF(6)) by both cyclic and hydrodynamic voltammetries. Responses were also detected when the solid salts were adhered to the surface of a glassy carbon electrode in contact with an electrolyte in which they are insoluble (CH(3)CN; 0.1M Bu(4)NPF(6)). Photolysis experiments were performed on solutions of the salts [R(4)N](4)[S(2)M(18)O(62)] (R = n-butyl or n-hexyl) and [Ru(II)L(n)](2)[S(2)M(18)O(62)] at 355 and 420 nm in dimethylformamide and acetonitrile in the presence and absence of benzyl alcohol (10% v/v). When associated with [Ru(bpy)(3)](2+), the molybdate anion exhibited a large increase in the quantum yield for photo-reduction at 420 nm. The quantum yield for the tungstate analogue was lower but the experiments again provided clear evidence for sensitization of the photo-reduction reaction in the visible spectral region. The origin of this sensitization is ascribed to the new optical transition observed around 480 nm in static ion clusters {[Ru(bpy)(3)][S(2)M(18)O(62)]}(2-) and {[Ru(bpy)(3)](2)[S(2)M(18)O(62)]} present in solution. Measurable photocurrents resulted from irradiation of solutions of the anions with white light in the presence of the electron donor dimethylformamide. Evidence is also presented for possible quencher-fluorophore interactions in the presence of certain [Ru(II)L(n)](+) cations.

Anions↗

PubMed2006

Adsorption dynamics and electrochemical and photophysical properties of thiolated ruthenium 2,2'-bipyridine monolayers.

A new complex [Ru(bpy)(2)(bpySH)](PF(6))(2), RuBpySH, has been prepared bearing two anchoring groups for surface attachment, where bpy is 2,2'-bipyridyl and bpySH is 5,5'-bis(mercaptomethyl)-2,2'-bipyridine. Monolayers of RuBpySH have been formed on micro and macro platinum electrodes by spontaneous adsorption from micromolar solutions of the complex in 50:50 v/v water/acetone. The monolayers can be reversibly switched between the Ru(2+) and the Ru(3+) forms. Cyclic voltammetry is well-defined with a peak-to-peak splitting of 30 +/- 5 mV and a full width at half-maximum of 110 +/- 10 mV being observed for scan rates up to 5 V s(-1) where the supporting electrolyte is 0.1 M tetrabutylammonium tetrafluoroborate in acetonitrile. Adsorption is irreversible in this system, and the saturation coverage obtained is 8.1 +/- 0.4 x 10(-11) mol cm(-2) when the complex concentration in the deposition solution is between 10 microM and 1.0 mM. The dynamics of adsorption depend markedly on the bulk concentration and are described in terms of irreversible adsorption. Dry monolayers display luminescence properties similar to those of powder samples of the complex, indicating that the monolayer has characteristics of the solid-state sample rather than the solution sample of the complex. Significantly, efficient electrochemiluminescence is generated using tripropylamine as the coreactant. The rate of electron transfer across the electrode/monolayer interface has been probed using high scan rate cyclic voltammetry. The standard heterogeneous electron-transfer rate constant, k degrees , is 0.9 +/- 0.1 x 10(4) s(-1), and there is weak adsorbate-electrode electronic communication.

2,2'-Dipyridyl↗

PubMed2006

Ruminal fermentation and fill change with season in an arctic grazer: responses to hyperphagia and hypophagia in muskoxen (Ovibos moschatus).

We studied castrated adult muskoxen fed a standard diet of grass hay and supplement throughout the year to determine seasonal changes in digesta passage, fill, and fermentation without the confounding effects of reproductive demands or changes in food quality. Although food intake increased by 74% between spring and autumn, mean retention times of fluid and particulate digesta markers were maintained between seasons in both the rumen (9-13 h) and the intestines (27-37 h). The rumen contained 84.5% of digesta and accounted for 79% of dry matter digestion in the whole digestive tract. Ruminal fluid space and whole-gut digesta fill increased by 31%-34%, while ruminal rates of in situ degradation increased by more than 100% between spring and autumn for cellulose and hemicellulose. Hyperphagia in autumn was accompanied by increased bacterial counts in ruminal fluid (30%), declines in ruminal pH, and increases in the concentration of fermentation acids (16%) when compared with spring hypophagia. Consumption of fresh hay and supplement increased the concentrations of acids most markedly during winter and spring when bacterial counts were low. Low food intakes in winter and spring may limit the microbial population, whereas hyperphagia in autumn may foster a much more active microflora that requires consistent supplies of substrate. Plasticity of fill and fermentation in muskoxen minimizes winter costs and maximizes nutrients and energy gained from coarse forages in small home ranges throughout the year.

Animals↗

PubMed2006

Production and characterization of a polyclonal antibody for Os(II) and Ru(II) polypyridyl complexes.

The characterization of a polyclonal antibody produced via immunization with an [Os(bpy)(2)dcbpy] hapten is described. Bpy is 2,2'-bipyridine and dcbpy is 2,2'-bipyridine-4,4'-dicarboxylic acid. The cross-reactivity of the antibody for the Ru(II) analogue of the hapten was also investigated. Large increases in the emission and luminescent lifetime of a series of Os and Ru complexes were observed on binding of the antibody. Association equilibrium constants were derived from luminescence titration data and were found to be 5.6 x 10(8) and 5.0 x 10(8)M(-1) for [Os(bpy)(2)dcbpy] and [Ru(bpy)(2)dcbpy], respectively. Spectroscopic changes were likely due to the exclusion of H(2)O from the complex/antibody binding cleft and blocking of vibrational relaxation pathways of the Os/Ru excited state. D(2)O/H(2)O experiments confirmed that the antibody protected approx. 82% of [Os(bpy)(2)dcbpy] and 80% of [Ru(bpy)(2)dcbpy] from excited state deactivation by the aqueous solvent.

Animals↗

PubMed2006

Effect of surface immobilization on the electrochemiluminescence of ruthenium-containing metallopolymers.

The effect of surface confinement on the electrochemiluminescence (ECL) properties of metallopolymer [Ru(bpy)2(PVP)10]2+, where bpy is 2,2'-bipyridyl and PVP is poly(4-vinylpyridine), is reported. Immobilizing a luminescent material on an electrode surface can substantially modulate its photophysical properties. Significantly, our study revealed that the overall efficiency of the ECL reaction for the metallopolymer film is almost four times higher, at 0.15%, than the highest value obtained for [Ru(bpy)2(PVP)10]2+ dissolved in solution, (phi(ECL) = 0.04%). Electrochemistry has been used to create well-defined concentrations of the quencher Ru3+ within the film. Analysis of both the steady-state luminescence and lifetimes of the film reveals that static quenching by electron transfer between the photoexcited Ru2+ and the Ru3+ centers is the dominant quenching mechanism. The bimolecular rate of electron transfer is (2.5 +/- 0.4) x 10(6) M(-1) s(-1). The implications of these findings for ECL-based sensors, in terms of optimum luminophore loading, is considered.

Journal Article↗

PubMed2005

Fullerene bridged metallocyclodextrin donor-acceptor complexes: optical spectroscopy and photophysics.

Two pyridine substituted beta-cyclodextrins have been synthesized and coordinated to the photoactive metal centres, [Ru(II)(bpy)2] and [Re(I)(CO)3bpy], where bpy is 2,2'-bipyridyl. The photophysical and electrochemical properties of these model complexes have been examined and compared with dinuclear complexes formed when C60 was included between two cyclodextrin cavities of the metallocyclodextrin units. On inclusion of C60, significant quenching of the emission of the luminophores is observed. Concentration and laser power dependence confirm that this quenching is intramolecular. The quenching process is interpreted in terms of a photoinduced electron transfer between the photosensitizer and C60 centre on the basis of spectroscopic and electrochemical evidence. Rate constants of 1.3 +/- 0.1 x 10(8) and 7.0 +/- 0.4 x 10(7) s(-1) have been determined for the Ru and Re based complexes, respectively. Significantly, these large rate constants indicate that that there is substantial electronic communication across the cyclodextrin at least for excited state processes.

2,2'-Dipyridyl↗

PubMed2005

Photophysics of ruthenium polypyridyl complexes formed with lacunary polyoxotungstates with iron addenda.

The interactions between luminophore [Ru(bpy)3]2+, and the lacunary Dawson heteropolyanions, [P2W17O61(FeOH2)]7-, [P2W17O61(FeBr)]6- and [P2W17O61]10- were investigated using a combination of photophysics, optical and Raman spectroscopy. Extensive quenching of the excited state of [Ru(bpy)3]2+ was observed in each case. Quenching is attributed to the formation of association complexes between [Ru(bpy)(3)]2+ and the heteropolyanions in which the charge on the heteropolyanions is fully compensated for by the ruthenium polypyridyl species. The interaction appears to be principally electrostatic in nature producing [Ru(bpy)3]3.5[P2W17O61(FeOH2)], [Ru(bpy)3]3[P2W17O61(FeBr)] and [Ru(bpy)3]5[P2W17O61]10-. The association constants for formation of the clusters were obtained from photophysical studies and surprisingly, despite the electrostatic nature of the interaction, there was no correlation between the charge on the polyoxometallate and the association constant. In particular, the unsubstituted lacunary, [P2W17O61]10-, showed considerably weaker association compared to the transition metal substituted lacunaries, in spite of its 10- charge. Difference absorption spectroscopy revealed a new transition at ca. 480 nm for each of the cluster complexes. From resonance Raman spectroscopy the origin of this transition was found to involve the polyoxometallate. Unlike previously reported adducts, the cluster complexes formed were not luminescent. In all cases the cluster complexes exhibit remarkable photostability, with no photodecomposition or photo-induced ligand exchange reactions evident in acetonitrile, under conditions where [Ru(bpy)3]2+ alone exhibits considerable photolability.

Acetonitriles↗

PubMed2005

Conducting polymers containing in-chain metal centers: electropolymerization of oligothienyl-substituted {M(tpy)2} complexes and in situ conductivity studies, M = Os(II), Ru(II).

The electropolymerization of a series of Ru and Os bis-terpyridine complexes that form rodlike polymers with bithienyl, quaterthienyl, or hexathienyl bridges has been studied. Absorption spectroscopy, scanning electron microscopy, and cyclic voltammetry have been used to characterize the monomers and resulting polymer films. The absolute dc conductivity of the quaterthienyl-bridged {Ru(tpy)2} and {Os(tpy)2} polymers is unusually large and independent of the identity of the metal center at 1.6 x 10(-3) S cm(-1). The maximum conductivity occurs at the formal potential of each redox process, which typically is observed for systems where redox conduction is the dominant charge transport mechanism. Significantly, the dc conductivity of the metal-based redox couple observed in these polymers is 2 orders of magnitude higher thanthat of a comparable nonconjugated system.

Journal Article↗

PubMed2005

Storage lipid accumulation and acyltransferase action in developing flaxseed.

Investigations of storage lipid synthesis in developing flaxseed (Linum usitatissimum) provide useful information for designing strategies to enhance the oil content and nutritional value of this crop. Lipid content and changes in the FA composition during seed development were examined in two cultivars of flax (AC Emerson and Vimy). The oil content on a dry weight basis increased steadily until about 20 d after flowering (DAF). The proportion of alpha-linolenic acid (alpha-18:3, 18:3cisDelta9,12,15) in TAG increased during seed development in both cultivars while the proportions of linoleic acid (18:2cisDelta9,12) and saturated FA decreased. The developmental and substrate specificity characteristics of microsomal DAG acyltransferase (DGAT, EC 2.3.1.20) and lysophosphatidic acid acyltransferase (LPAAT, EC 2.3.1.51) were examined using cultivar AC Emerson. The maximal acyltransferase specific activities occurred in the range of 8-14 DAF, during rapid lipid accumulation on a per seed basis. Acyl-CoA of EPA (20:5cisDelta5,8,11,14,17) or DHA (22:6 cis4,7,10,13,16,19) were included in the specificity studies. DGAT displayed enhanced specificity for alpha-18:3-CoA, whereas the preferred substrate of [PAAT was 18:2-CoA. Both enzymes could use EPA- or DHA-CoA to varying extents. Developing flax embryos were able to take up and incorporate these nutritional FA into TAG and other intermediates in the TAG-formation pathway. This study suggests that if the appropriate acyl-CoA-dependent desaturation/elongation pathways are introduced and efficiently expressed in flax, this may lead to the conversion of alpha-18:3-CoA into EPA-CoA, thereby providing an activated substrate for TAG formation.

Acetyl Coenzyme A↗

PubMed2005

Naturally occurring DNA transfer system associated with membrane vesicles in cellulolytic Ruminococcus spp. of ruminal origin.

A genetic transformation system with similarities to those reported for gram-negative bacteria was found to be associated with membrane vesicles of the ruminal cellulolytic genus Ruminococcus. Double-stranded DNA was recovered from the subcellular particulate fraction of all the cellulolytic ruminococci examined. Electron microscopy revealed that the only particles present resembled membrane vesicles. The likelihood that the DNA was associated with membrane vesicles (also known to contain cellulosomes) was further supported by the adherence of the particles associated with the subcellular DNA to cellulose powder added to culture filtrates. The particle-associated DNA comprised a population of linear molecules ranging in size from <20 kb to 49 kb (Ruminococcus sp. strain YE73) and from 23 kb to 90 kb (Ruminococcus albus AR67). Particle-associated DNA from R. albus AR67 represented DNA derived from genomic DNA of the host bacterium having an almost identical HindIII digestion pattern and an identical 16S rRNA gene. Paradoxically, particle-associated DNA was refractory to digestion with EcoRI, while the genomic DNA was susceptible to extensive digestion, suggesting that there is differential restriction modification of genomic DNA and DNA exported from the cell. Transformation using the vesicle-containing fraction of culture supernatant of Ruminococcus sp. strain YE71 was able to restore the ability to degrade crystalline cellulose to two mutants that were otherwise unable to do so. The ability was heritable and transferred to subsequent generations. It appears that membrane-associated transformation plays a role in lateral gene transfer in complex microbial ecosystems, such as the rumen.

Animals↗

PubMed2004

Mediated amperometric immunosensing using single walled carbon nanotube forests.

A prototype amperometric immunosensor was evaluated based on the adsorption of antibodies onto perpendicularly oriented assemblies of single wall carbon nanotubes called SWNT forests. The forests were self-assembled from oxidatively shortened SWNTs onto Nafion/iron oxide coated pyrolytic graphite electrodes. The nanotube forests were characterized using atomic force microscopy and resonance Raman spectroscopy. Anti-biotin antibody strongly adsorbed to the SWNT forests. In the presence of a soluble mediator, the detection limit for horseradish peroxidase (HRP) labeled biotin was 2.5 pmol ml(-1) (2.5 nM). Unlabelled biotin was detected in a competitive approach with a detection limit of 16 nmol ml(-1) (16 microM) and a relative standard deviation of 12%. The immunosensor showed low non-specific adsorption of biotin-HRP (approx. 0.1%) when blocked with bovine serum albumin. This immunosensing approach using high surface area, patternable, conductive SWNT assemblies may eventually prove useful for nano-biosensing arrays.

Adsorption↗

PubMed2004

Solvent effects on charge transport through solid deposits of [Os(4,4'-diphenyl-2,2'-dipyridyl)2Cl2].

Mechanically attached, solid-state films of [Os(4,4'-diphenyl-2,2'-dipyridyl)2Cl2] have been formed on gold macro- and microelectrodes and their voltammetric properties investigated. The voltammetric response of these films associated with the Os(2+/3+) redox reaction is reminiscent of that observed for an ideal reversible, solution phase redox couple only when the contacting electrolyte contains of the order of 40% v/v of acetonitrile (ACN). The origin of this effect appears to involve preferential solvation of the redox centres by acetonitrile which facilitates the incorporation of charge compensating counterions. Scanning electron microscopy reveals that voltammetric cycling in 40:60 ACN-H2O containing 1.0 M LiClO4 as the electrolyte induces the formation of microcrystals. Voltammetry conducted under semi-infinite linear diffusion conditions has been used to determine the apparent diffusion coefficient, Dapp, for homogeneous charge transport through the deposit. The dynamics of charge transport decrease with increasing film thickness but appear to increase with increasing electrolyte concentration. These observations suggest that ion transport rather than the rate of electron self-exchange limit the overall rate of charge transport through these solids. When in contact with 40:60 ACN-H2O containing 1.0 M LiClO4 as electrolyte, Dapp values for oxidation and reduction are identical at 1.7 +/- 0.4 x 10(-12) cm2 s(-1). In the same electrolyte, the standard heterogeneous electron transfer rate constant, k(o), determined by fitting the full voltammogram using the Butler-Volmer formalism, is 8.3 +/- 0.5 x 10(-7) cm s(-1). The importance of these results for the rational design of solid state redox active materials for battery, display and sensor applications is considered.

Journal Article↗

PubMed2004

Direct electrochemiluminescence detection of oxidized DNA in ultrathin films containing [Os(bpy)2(PVP)10]2+.

Direct electrochemiluminescence (ECL) involving oxidized DNA was demonstrated in ultrathin films of cationic polymer [Os(bpy)2(PVP)10]2+ [PVP = poly(vinyl pyridine)] assembled layer-by-layer with DNA or oligonucleotides. Electrochemically oxidized Os(II) sites generated ECL from films containing oxo-guanines on DNA formed by chemical oxidation using Fenton reagent. Films combining DNA, [Ru(bpy)2(PVP)10]2+, and [Os(bpy)2(PVP)10]2+ had Os(II) sites that produced ECL specific for oxidized DNA, and Ru(II) sites gave ECL from reaction with oxo-adenines, chemically damaged DNA, and possibly from cleaved DNA strands.

Biosensing Techniques↗

PubMed2004

Modulating the redox properties of an osmium-containing metallopolymer through the supporting electrolyte and cross-linking.

Thin films of the perchlorate salt of an [Os(N,N'-alkylated-2,2'-biimidazole3)2+/3+-containing polymer have been formed on planar platinum microelectrodes. The electrochemical response associated with the Os2+/3+ couple occurs at -0.19 V. In aqueous perchlorate media at near-neutral pH the voltammetric response is close to that expected for an electrochemically reversible reaction involving a surface-confined reactant. Chronoamperometry conducted on a microsecond time scale indicates that the film and solution resistances are comparable for low concentrations of supporting electrolyte. However, for LiClO4 concentrations greater than 0.4 M, RFilm contributes less than 25% of the overall cell resistance. These results suggest that when the film is dehydrated and the density of redox centers is increased, electron or hole hopping dominates the rate of homogeneous charge transport through the film. The rate of homogeneous charge transport, characterized by D(CT)1/2Ceff, where DCT is the homogeneous charge transport diffusion coefficient and Ceff is the effective concentration of osmium centers within the film, depends weakly on the concentration of LiClO4 as supporting electrolyte decreasing from (8.1 +/- 0.16) x 10(-9) to (4.7 +/- 0.4) x 10(-9) mol cm(-2) s(-1/2) as the perchlorate concentration increases from 0.1 to 1.0 M. These values are about 2 orders of magnitude lower than those of the chemically cross-linked chloride salt of the polymer. The rate of heterogeneous electron transfer is unusually rapid in this system and increases from (5.2 +/- 0.4) x 10(-3) to (7.8 +/- 0.4) x 10(-3) cm s(-1) on going from 0.1 to 0.4 M LiClO4 before becoming independent of the supporting electrolyte concentration at (9.2 +/- 0.6) x 10(-3) cm s(-1) for [LiClO4] > or = 0.6 M.

Journal Article↗

PubMed2004

Carbon composite microelectrodes: charge percolation and electroanalytical performance.

Microelectrodes based on two different epoxy-graphite composites (Araldite-M/HY5162 and Araldite-PY302-2/HY943) that are compatible with organic solvents have been developed and characterized. The variation in the bulk conductivity with graphite particle loading is described by percolation theory and indicates that the particles interact strongly with one another. The percolation threshold is 52% v/v loading of graphite, and this composite exhibits a bulk conductivity of 15 S m(-1). Microdisk electrodes of 25-microm diameter were produced by first etching a microcavity at the tip of a platinum microelectrode, which was then packed with a composite containing 60% v/v graphite so as to optimize both electrical conductivity and the electrode stability in acetonitrile and methanol solutions. Solution phase voltammetry of ferrocene is nearly ideal, and the responses are dominated by radial diffusion (slow scan rates) and semi-infinite linear diffusion (fast scan rates). The microelectrodes display high signal-to-noise ratios, good sensitivity, and low detection limits. The response times given by the product of the resistance, R, and capacitance, C, are 7.5 x 10(-4) and 1.4 x 10(-1) s for the Araldite M and PY302-2 composites, respectively. Although these response times are significantly slower than those associated with microelectrodes based on carbon fibers or metal wires, they are sufficient for time-resolved electroanalytical applications. The long response times arise from the large composite resistances, 3.1 x 10(11) and 8.3 x 10(11) Omega cm(-2) for Araldite M and PY302-2, respectively. Voltammetry of ferrocene in the absence of deliberately added supporting electrolyte is also reported. Significantly, indistinguishable slopes and intercepts for a calibration curve of peak current vs ferrocene concentration where 2 < [ferrocene] < 50 microM are obtained in the presence and absence of supporting electrolyte.

Journal Article↗