Diffusion boundary layer of a rotating disk electrode as a thin-layer spectroelectrochemical cell

A UV-visible rapid scan spectrophotometer (RSS) was coupled to a Au rotating disk electrode (RDE) for monitoring at near-normal incidence the reflection-absorption spectrum of the diffusion boundary layer in [Fe(CN)(6)](4)(-) aqueous solutions over a potential region in which [Fe(CN)(6)](4-) oxidizes, generating highly absorbing [Fe(CN)(6)](3-) (lambda(max) = 420 nm). Measurements were performed under steady-state conditions at rotation rates, omega, in the range 300 相似文献   

Luminescence-Based Spectroelectrochemical Sensor for [Tc(dmpe)(3)](2+/+) (dmpe = 1,2-bis(dimethylphosphino)ethane) within a Charge-Selective Polymer Film

A spectroelectrochemical sensor consisting of an indium tin oxide (ITO) optically transparent electrode (OTE) coated with a thin film of partially sulfonated polystyrene-blockpoly(ethylene-ran-butylene)-block-polystyrene (SSEBS) was developed for [Tc(dmpe)(3)](+) (dmpe = 1,2-bis(dimethylphosphino)ethane). [Tc(dmpe)(3)](+) was preconcentrated by ion-exchange into the SSEBS film after a 20 min exposure to aqueous [Tc(dmpe)(3)](+) solution, resulting in a 14-fold increase in cathodic peak current compared to a bare OTE. Colorless [Tc(dmpe)(3)](+) was reversibly oxidized to colored [Tc(dmpe)(3)](2+) by cyclic voltammetry. Detection of [Tc(dmpe)(3)](2+) was accomplished through emission spectroscopy by electrochemically oxidizing the complex from nonemissive [Tc(dmpe)(3)](+) to emissive [Tc(dmpe)(3)](2+). The working principle of the sensor consisted of electrochemically cycling between nonemissive [Tc(dmpe)(3)](+) and emissive [Tc(dmpe)(3)](2+) and monitoring the modulated emission (λ(exc) = 532 nm; λ(em) = 660 nm). The sensor gave a linear response over the concentration range of 0.16-340.0 μM of [Tc(dmpe)(3)](2+/+) in aqueous phase with a detection limit of 24 nM.     

Prussian-blue-modified iron oxide magnetic nanoparticles as effective peroxidase-like catalysts to degrade methylene blue with H2O2

Prussian-blue (PB)-modified γ-Fe(2)O(3) magnetic nanoparticles (PBMNPs) were successfully synthesized based on electric interactions between negatively charged [Fe(CN)(6)](4-) and positively charged γ-Fe(2)O(3) nanoparticles. The in situ PB coating was generated by the coordinating reaction between the adsorbed [Fe(CN)(6)](4-) and the ferric ions on the surface of γ-Fe(2)O(3) NPs. The as-prepared PBMNPs were characterized by FT-IR, XRD, TEM, and used to remove organic pollutants from aqueous solution, namely, using methylene blue (MB) as model compound. The experimental results showed that the target compound could be removed efficiently from solution over a wide pH range from 3 to 10 in the presence of PBMNPs as peroxidase-like catalyst and H(2)O(2) as oxidant. Under optimal conditions, MB could be removed completely after 120 min of reaction at 298 K; the chemical oxygen demand (COD) removal efficiency and the total organic carbon (TOC) abatement efficiency were 53.6% and 35%, respectively. Furthermore, the PBMNPs catalysts showed high magnetization, temperature tolerance, long-term storage and operational stability, and they could be readily separated from solution by applying an external magnetic field. Finally, a possible reaction mechanism for MB degradation was also discussed.     

Electrochemical and spectroscopic investigation of the reduction of dimethylglyoxime at mercury electrodes in the presence of cobalt and nickel

Voltammograms (polarograms) obtained from solutions of cobalt and nickel containing dimethylglyoxime (dmgH(2)) are widely used for the trace determination of these metals. Detailed electrochemical and spectroscopic studies on the reduction process observed in the analytically important ammonia buffer media at mercury dropping, hanging, and pool electrodes are all consistent with an overall 10-electron reduction process, in which both the dmgH(2) ligand and cobalt ions are reduced in the adsorbed state: Co(II) + 2dmgH(2) ? (solution) [Co(II)(dmgH)(2)] + 2H(+); [Co(II)(dmgH)(2)] + Hg ? (electrode) [Co(II)(dmgH)(2)](ads)Hg; and [Co(II)(dmgH)(2)](ads)Hg + 10e(-) + 10H(+) → Co(Hg) + 2[2,3-bis(hydroxylamino)butane]. The limited solubility of the nickel complex in aqueous media restricts the range of studies that can be undertaken with this system, but an analogous mechanism is believed to occur. Low-temperature voltammetric studies in dichloromethane at a frozen hanging mercury drop electrode and in situ electron spin resonance electrochemical measurements on more soluble analogues of the dimethylglyoxime complexes are consistent with an initial one-electron reduction step being available in the absence of water. Deliberate addition of water to acetone solutions enables the influence of the aqueous environment on voltammograms and polarograms to be examined. The results of the present study are compared with the wide range of mechanisms proposed in other studies.     

Fluorophilic ionophores for potentiometric pH determinations with fluorous membranes of exceptional selectivity

Ionophore-doped sensor membranes exhibit greater selectivities and wider measuring ranges when they are prepared with noncoordinating matrixes. Since fluorous phases are the least polar and least polarizable liquid phases known, a fluorous phase was used for this work as the membrane matrix for a series of ionophore-based sensors to explore the ultimate limit of selectivity. Fluorous pH electrode membranes, each comprised of perfluoroperhydrophenanthrene, sodium tetrakis[3,5-bis(perfluorohexyl)phenyl]borate, and one of four fluorophilic H(+)-selective ionophores were prepared. All the ionophores are highly fluorinated trialkylamines containing three electron withdrawing perfluoroalkyl groups shielded from the central nitrogen by alkyl spacers of varying lengths: [CF(3)(CF(2))(7)(CH(2))(3)](2)[CF(3)(CF(2))(6)CH(2)]N, [CF(3)(CF(2))(7)(CH(2))(3)](2)(CF(3)CH(2))N, [CF(3)(CF(2))(7)(CH(2))(3)](3)N, and [CF(3)(CF(2))(7)(CH(2))(5)](3)N. Their pKa values in the fluorous matrix are as high as 15.4 +/- 0.3, and the corresponding electrodes exhibit logarithmic selectivity coefficients for H(+) over K(+) as low as <-12.8. The pKa and selectivity follow the trends expected from the degree of shielding and the length of the perfluoroalkyl chains of the ionophores. These electrodes are the first fluorous ionophore-based sensors described in the literature. The selectivities of the sensor containing [CF(3)(CF(2))(7)(CH(2))(5)](3)N are not only greater than those of analogous sensors with nonfluorous membranes but were of the same magnitude as the best ionophore-based pH sensors ever reported.     

Simple template-free solution route for the synthesis of Ni(SO(4))(0.3)(OH)(1.4) nanobelts and their thermal degradation

Nanobelts of nickel hydroxyl sulfate have been prepared on a large scale via a simple template-free hydrothermal reaction on the basis of a complex [Ni(NH(3))(6)](2+) formed with Ni(2+) and ammonia in an ethanol-water solution. The as-synthesized nanobelts were single crystals, with several tens of microns in length and 50-150?nm in width. The nanobelts were enclosed by top surfaces (100) and side surfaces (001) and their growth direction was parallel to [010]. The function of aqueous ammonia and ethanol was discussed. Furthermore, nanostructures of a mixture of crystralline NiO and amorphous nickel sulfate with various morphologies, such as nanobelts, porous nanobelts, and nanoparticles, were obtained by the thermal treatment of the as-synthesized Ni(SO(4))(0.3)(OH)(1.4) nanobelts at different temperatures.     

Optically transparent diamond electrode for use in ir transmission spectroelectrochemical measurements

A new analytical spectroelectrochemical methodology is reported on that utilizes an optically transparent boron-doped diamond thin film. The film was deposited on undoped Si by microwave-assisted chemical vapor deposition using a 4-h growth with a 0.5% CH4/H2 source gas mixture and 2 ppm B2H6 added for boron doping. The thin-film electrode possessed a transparency of 40-60% in the mid- and far-IR regions of the electromagnetic spectrum. The physical, electrical, optical, and electrochemical properties of the electrode were characterized by scanning electron microscopy, Raman spectroscopy, X-ray diffraction, four-point probe electrical resistance measurements, IR spectroscopy, and cyclic voltammetry. The film's electrochemical behavior was evaluated using both aqueous (Fe(CN)(6)3-/4-, methyl viologen, Ru(NH3)(6)3+/2+, and IrCl(6)2-/3-) and nonaqueous (ferrocene) redox systems. The film exhibited a low and stable background current and a nearly reversible voltammetric response for all these redox systems. The diamond/Si optically transparent electrode (OTE) and a thin-layer transmission cell were used to record the spectroelectrochemical response for 10 mM Fe(CN)(6)3-/4- in 1 M KCl. Difference IR spectra (oxidized minus reduced), recorded at various applied potentials, showed that the CN vibrational mode at 2039 cm-1 for Fe(CN)(6)4- reversibly shifted to 2116 cm-1 upon oxidation to Fe(CN)(6)3-, as expected. Difference IR spectra (oxidized minus reduced) were also recorded for 20 mM ferrocene in 0.1 M TBABF4/CH3CN. A shift of the C-H bending mode of the cyclopentadienyl ring from 823 to 857 cm-1 occurred upon oxidation of ferrocene to ferricenium. The key finding from the work is that the diamond OTE provides sensitive, reproducible, and stable spectroelectrochemical responses for aqueous and nonaqueous redox systems in the mid- and far-IR.     

Electrochemical sensing of DNA hybridization based on duplex-specific charge compensation

A nonlabeling voltammetric detection method for DNA hybridization has been developed, in which [Fe(CN)(6)](3-) in solution can readily approach an electrode surface covered with a charge-compensated DNA duplex layer and thus provides a strong redox-sensing current. Charge compensation for negative charges on the DNA backbone has been specifically accomplished on DNA duplexes by discouraging nonspecific binding of positively charged intercalating molecules with single strands. A pretreatment of DNA-modified electrodes with sodium dodecyl sulfate before the intercalator binding process is essential in preventing the nonspecific binding. Since ferricyanide, the only electrochemically active species, is present in the voltammetric solution, the detection signal can be amplified by increasing its concentration. Combination of the duplex-specific charge compensation with the signal amplification has achieved a remarkable signal difference: in 30 mM [Fe(CN)(6)](3-), the area ratio between cyclic voltammograms of the hybridized and unhybridized electrodes is approximately 200 when 3,6-diaminoacridine is used as the intercalator. High sensitivity of the method has been demonstrated by detecting 10 fM (100 zmol in amount) of a target probe DNA.     

Controlled self-assembly of metal-organic frameworks on metal nanoparticles for efficient synthesis of hybrid nanostructures

We report a novel approach for synthesizing inorganic nanoparticle/metal-organic frameworks (MOFs) heterostructured nanocomposites by self-assembly of MOFs on nanoparticles. This approach involves the synthesis of Au nanoparticles and preferential growth of [Cu(3)(btc)(2)](n) frameworks consisting of Cu(2+) ions and benzene-1,3,5-tricarboxylate (btc) on nanoparticles. Aggregates consisting of 11-mercaptoundecanoic acid (MUA)-stabilized Au nanoparticles linked by Cu(2+) ions were necessary for preferential self-assembly of [Cu(3)(btc)(2)](n) frameworks on the aggregates, resulting in the formation of Au nanoparticles/[Cu(3)(btc)(2)](n) nanocomposites. The present approach was confirmed to be applicable for other hybrids consisting of Au nanoparticles and tetragonal [Cu(2)(ndc)(2)(dabco)](n) frameworks.     

Comparison of voltammetric data obtained for the trans-[Mn(CN)(CO)2[P(OPh)3](Ph2PCH2PPh2)]0/+ process in BMIM.PF6 ionic liquid under microchemical and conventional conditions

Conventional cyclic voltammetric studies on the oxidation of millimolar concentrations (mg masses) of trans-[Mn(CN)(CO)(2)[P(OPh)(3)](Ph(2)PCH(2)PPh(2))] (trans-Mn) dissolved in milliliter volumes of bulk ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM.PF(6)), give rise to a reversible [trans-Mn](0/+) process. In this study, it is shown that equally well-defined reversible voltammetry can be more economically obtained under microchemical ionic liquid conditions by employing a chemically modified electrode (microg quantities of trans-Mn adhered to a glassy carbon electrode covered with microliter volumes of water-immiscible BMIM.PF(6)) in contact with aqueous (0.1 M KPF(6)) electrolyte. The ability to obtain electrochemical data that are directly relatable to bulk ionic liquid media under these microchemical conditions is principally associated with the dissolution of electrogenerated solid [trans-Mn](+) in the layer of water-immiscible BMIM.PF(6) present at the electrode/ionic liquid/aqueous electrolyte interface. If the BMIM.PF(6) layer is sufficiently thick, mass transport of the dissolved species is governed by semi-infinite linear diffusion. Under these conditions, the voltammetric waveshape and position, but not the current magnitude are the same as those found when conventional bulk ionic liquid conditions are employed. In contrast, use of very thin layers produces voltammograms that exhibit the characteristics expected for a reversible process in which the mass transport process is predominantly governed by finite rather than semi-infinite diffusion. A theoretical model has been developed that describes the transformation from thick- to thin-layer type behavior as the thickness of the ionic liquid layer is decreased.     

Stable tris(2,2'-bipyridine)ruthenium(III) for chemiluminescence detection

Two exceedingly stable [Ru(bipy)(3)](3+) reagents were prepared by dissolving either [Ru(bipy)(3)](ClO(4))(2) in acetonitrile (containing 0.05 M HClO(4)) or [Ru(bipy)(3)]Cl(2)·6H(2)O in 95:5 glacial acetic acid-acetic anhydride (containing 0.05 M H(2)SO(4)) followed by oxidation with PbO(2). These conveniently prepared solutions provide highly reproducible chemiluminescence detection over long periods of analysis, avoiding the need for recalibration or preparation of fresh reagent solutions and without the complications associated with online chemical or electrochemical oxidations. The reagent prepared in acetonitrile produced much greater signal intensities with a range of analytes and was deemed most suitable for high-performance liquid chromatography (HPLC) with postcolumn chemiluminescence detection.     

Large-amplitude Fourier transformed high-harmonic alternating current cyclic voltammetry: kinetic discrimination of interfering Faradaic processes at glassy carbon and at boron-doped diamond electrodes

Significant advantages of Fourier transformed large-amplitude ac higher (second to eighth) harmonics relative to responses obtained with conventional small-amplitude ac or dc cyclic voltammetric methods have been demonstrated with respect to (i) the suppression of capacitive background currents, (ii) the separation of the reversible reduction of [Ru(NH(3))(6)](3+) from the overlapping irreversible oxygen reduction process under conditions where aerobic oxygen remains present in the electrochemical cell, and (iii) the kinetic resolution of the reversible [Ru(NH(3))(6)](3+/2+) process in mixtures of [Fe(CN)(6)](3-) and [Ru(NH(3))(6)](3+) at appropriately treated boron-doped diamond electrodes, even when highly unfavorable [Fe(CN)(6)](3-) to [Ru(NH(3))(6)](3+) concentration ratios are employed. Theoretical support for the basis of kinetic discrimination in large-amplitude higher harmonic ac cyclic voltammetry is provided.     

Quantification of the Interaction between Charged Guest Molecules and Chemisorbed Monothiolated β-Cyclodextrins

The quantification of small molecules in aqueous solution by surface bound supramolecular host molecules is an important goal in the research field of chemo- and biosensor development. In this paper we present an attempt to quantify the interaction of different charged guest molecules with chemisorbed monothiolated β-cyclodextrin monolayers by means of impedance spectroscopy in the presence of the redox couple [Fe(CN)(6)](3)(-)/[Fe(CN)(6)](4)(-). Self-assembled monolayers of mercaptopropane-N-mono-6-deoxy-β-cyclodextrin amide (MPA-CD) on gold surfaces were formed with coverage of 99-100%. The inclusion of charged guest molecules was detected by monitoring the changes in the charge-transfer resistance, which is sensitive to the surface charge density in terms of repulsion or attraction of the redox active ions. Adsorption of positively charged 1-adamantanamino hydrochloride (1-ADHC) led to a considerable increase in the charge-transfer resistance, whereas the inclusion of both negatively charged 1-adamantanecarboxylic acid (1-ADC) and 2-(p-toluidinyl)naphthalene-6-sulfonate (2,6-TNS) caused a decrease. Applying the Frumkin correction to obtain the surface charge density and the Gouy-Chapman-Stern theory to account for the electrochemical double layer, we were able to quantify the binding of the charged guest molecules in terms of binding isotherms. The isotherms display a distinct two step adsorption process probably owing to the presence of two energetically different binding sites on the surface. Complete reversibility of the binding process of the guest molecules could be demonstrated by the addition of β-cyclodextrin in solution, which allowed the reuse of the functionalized surfaces.     

Fluorescence quenching of the europium tetracycline hydrogen peroxide complex by copper (II) and other metal ions

The europium-tetracycline complex [Eu(Tc)] is known to show only weak fluorescence with an emission maximum at 615 nm. On addition of hydrogen peroxide (HP), the strongly fluorescent [Eu(Tc)(HP)] complex is formed, which displays a 15-fold stronger luminescence intensity. This study describes the decrease in luminescence intensity of the [Eu(Tc)(HP)] complex in aqueous solution in the presence of Cu2+, Fe3+, Ag+, Al3+, Zn2+, Co2+, Ni2+, Mn2+, Ca2+, and Mg2+. Static and dynamic quenching can be induced by Cu2+, and these processes were quantified by means of their quenching constants. Stern-Volmer plots were also derived from lifetime imaging measurements accomplished by the rapid lifetime determination (RLD) technique based on microwell plate assays, and also by the time-correlated single photon counting (TCSPC) technique. According to those data, a time-resolved fluorescent method for copper determination can be proposed that is based on dynamic quenching of the [Eu(Tc)(HP)] complex by Cu2+ ions. The response to copper concentrations is linear up to 1.6 micromol L(-1), providing a detection limit of 0.2 micromol L(-1).     

Ion-Pair Extraction of Metalloporphyrins into Acetonitrile for Determination of Copper(II)

Equilibrium study of ion-pair extraction of a cationic water-soluble porphyrin [5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin, H(2)tmpyp(4+)] and its metalloporphyrins (MP) into the acetonitrile layer, separated by addition of sodium chloride (4.00 mol dm(-)(3)) to a 1:1 (v/v) acetonitrile-water mixed solvent, was carried out to develop a new and useful method for the determination of a subnanogram amount of copper(II). M denotes Zn(2+), Cu(2+), Co(3+), Fe(3+), and Mn(3+), and P(2)(-) is porphyrinate ion. The extraction and dissociation constants of the ion-pair complexes, defined by K(ex) = [MP(ClO(4))(4)](org)[MP(4+)](aq)(-)(1)[ClO(4)(-)](aq)(-)(4), K(dis,1) = [MP(ClO(4))(3)(+)](org)[ClO(4)(-)](org)[MP(ClO(4))(4)](org)(-)(1), and K(dis,2) = [MP(ClO(4))(2)(2+)](org)[ClO(4)(-)](org)[MP(ClO(4))(3)(+)](org)(-)(1), were determined by taking into account the partition constant of sodium perchlorate (K(D) = 1.82 ± 0.01). The equilibrium constants were found to be K(ex)K(dis,1) = (7.2 ± 1.3) × 10(4), (6.4 ± 0.9) × 10(4), (1.35 ± 0.13) × 10(5), (4.8 ± 0.6) × 10(3), (1.23 ± 0.05) × 10(4), and (1.42 ± 0.07) × 10(3) at 25 °C for the free base porphyrin (H(2)tmpyp(4+)) and the metalloporphyrins of zinc(II), copper(II), cobalt(III), iron(III), and manganese(III), respectively. The K(dis,2) values were (2.9 ± 1.4) × 10(-)(2), (3.1 ± 1.1) × 10(-)(2), (8.0 ± 4.9) × 10(-)(3), and (5.1 ± 2.2) × 10(-)(2) for the free base porphyrins and the metalloporphyrins of zinc(II), copper(II), and cobalt(III), respectively. The results were developed for determination of a trace amount of copper(II) (3 × 10(-)(8)-4 × 10(-)(6) mol dm(-)(3)) in natural water samples using H(2)tmpyp(4+) with a molar absorptivity of 3.1 × 10(5) mol(-)(1) dm(3) cm(-)(1) at a precision of 1.3% (RSD). The determination of copper(II) was not interfered by the presence of 10(-)(4) mol dm(-)(3) of Mn(2+), Co(2+), Ni(2+), Hg(2+), Cd(2+), Ag(+), Cr(3+), V(5+), Al(3+), Mg(2+), Ca(2+), Br(-), I(-), SCN(-), and S(2)O(3)(2)(-) and 10(-)(5) mol dm(-)(3) of Fe(3+), Zn(2+), and Pd(2+).     

Electrochemical determination of dopamine based on self-assembled peptide nanostructure

Self-assembled peptide nanostructures are electronically insulating as are most biomaterials derived from natural amino acids. To obtain additional properties and increase the applicability of peptide nanomaterials, some chemical modifications can be performed and materials can be functionalized to form hybrid compounds. In this work, we described the formation of L-diphenylalanine nanotubes (PNTs) with cyclic-tetrameric copper(II) species containing the ligand (4-imidazolyl)ethylene-2-amino-1-ethylpyridine [Cu(4)(apyhist)(4)](4+) in the Nafion membrane on a vitreous carbon electrode surface. This copper complex has been studied as structural and functional models for the active centers of copper containing redox enzymes. Scanning electron microscopy was used to confirm the formation of the nanostructures. The electrochemical properties of the PNT-[Cu(4)(apyhist)(4)](4+)/Nafion film on a glassy carbon electrode were characterized using cyclic voltammetry and square-wave voltammetry and showed high electrocatalytic activity toward the oxidation of dopamine (DA). The detection sensitivity was found to be enhanced by the use of copper(II) complex in the PNTs/Nafion films. Under the optimum conditions, the square-wave voltammetry peak height was linearly related to the DA concentration over two concentration intervals, viz., 5.0-40 μmol L(-1) and 40-1000 μmol L(-1). The detection limit was 2.80 μmol L(-1) (S/N = 3), and ascorbic acid did not interfere with the DA detection. These results suggested that this hybrid bioinorganic system provides an attractive advantage for a new type of electrochemical sensors. The detection sensitivity was found to be enhanced by use of PNTs.     

Characterization of aqueous lead removal by phosphatic clay: equilibrium and kinetic studies

Immobilization of heavy metals from contaminated environments is an emerging field of interest from both resource conservation and environmental remediation points of view. This study investigated the feasibility of using phosphatic clay, a waste by-product of the phosphate mining industry, as an effective sorbent for Pb from aqueous effluents. The major parameters controlling aqueous Pb removal, viz. initial metal ion concentrations, solution pH, sorbent amounts, ionic strength and presence of both inorganic and organic ligands were evaluated using batch experiments. Results demonstrated that aqueous Pb removal efficiency of phosphatic clay is controlled mainly by dissolution of phosphatic clay associated fluoroapatite [Ca(10)(PO(4))(5)CaCO(3)(F,Cl,OH)(2)], followed by subsequent precipitation of geochemically stable pyromorphite [Pb(10)(PO(4))(6)(F,Cl,OH)(2)], which was confirmed by both X-ray diffraction (XRD) and scanning electron microscopic (SEM) analysis. Lead removal efficiency of phosphatic clay increased with increasing pH, sorbent amount and decreasing ionic strength. It also depends on the nature of complexing ligands. Formation of insoluble calcium oxalate and lead oxalate in the presence of oxalic acid explained high uptake of Pb by phosphatic clay from aqueous solution. However, Pb sorption kinetics onto phosphatic clay were biphasic, with initially fast reactions followed by slow and continuous Pb removal reactions. The slow reactions may include surface sorption, co-precipitation and diffusion. The exceptional capability of phosphatic clay to remove aqueous Pb demonstrated its potential as a cost effective way to remediate Pb-contaminated water, soils and sediments.     

DNA biosensor for detection of Helicobacter pylori using phen-dione as the electrochemically active ligand in osmium complexes

A surface-based method for the study of the interactions of DNA with redox-active 1,10-phenantroline-5,6-dione (phen-dione) osmium complexes is described. The study was carried out using gold electrodes modified with DNA via adsorption and [Os(bpy)(2)(phe-dione)](3+/2+) (bpy = 2,2'-bipyridyl) or [Os(phen)(2)(phen-dione)](3+/2+) (phen = 1,10-phenantroline) as electrochemical reported molecules. The method, which is simple and reagent-saving, allows the accumulation of osmium complexes within the DNA layer. The amount of osmium complex bound by the adsorbed layer of DNA was determined from the voltammetric charge associated with the osmium redox process of the immobilized metal complex. The quinone moiety of the phen-dione ligand was useful as an indicator for electrochemical DNA sensing because of its redox response at low potentials. A thiol-linked single-stranded Helicobacter pylori DNA probe was immobilized, through S-Au bonds on to a gold electrode (density of modification 86 pmol/cm(2)). Following hybridization with the complementary DNA sequence, the osmium complex was electrochemically accumulated within the double-stranded DNA layer. Electrochemical detection was performed by differential pulse voltammetry over the potential range where the quinone moiety was redox active (i.e., at very low potentials, -0.020 V vs SSCE); with this approach, a sequence of the H. pylori could be quantified over the range from 5 to 20 pmol with a linear correlation of r = 0.9888 and a detection limit of approximately 6 pmol.     

Hybrid oxygen-responsive reflective Bragg grating platforms

Oxygen responsive sensor platforms were fabricated by pin printing tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) ([Ru(dpp)(3)](2+)) doped sols onto wavelength tuned reflective Bragg gratings. In an epi-luminescence configuration, these Bragg gratings (Gr) were designed to selectively reflect the O(2) responsive [Ru(dpp)(3)](2+) emission toward the detector to enhance the detected signal magnitude. The xerogel based sensors were formed onto (i) glass (XGl), (ii) directly on top of the grating (XGrGl), or (iii) on the glass substrate opposite the grating (XGlGr). The results show that all sensors exhibit linear, statistically equivalent O(2) sensitivities, and the XGrGl platform yields up to an 8-fold increase in relative detected analytical signal (RDAS) in comparison to the control (XGl) platform.     

Ionic liquid salt bridge with low solubility of water and stable liquid junction potential based on a mixture of a potential-determining salt and a highly hydrophobic ionic liquid

A new type of ionic liquid salt bridge (ILSB) based on a mixture of pentyltripropylammonium bis(pentafluoroethanesulfonyl)amide, [N(3335)(+)][C(2)C(2)N(-)], and heptadecafluorodecyltrioctylphosphonium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, [TOPH(+)][TFPB(-)], shows a stable phase-boundary potential (Δ(IL)(W)φ) between the ILSB and an aqueous solution of MCl (M = H(+), Li(+), Na(+), and K(+)) over the concentration range from 0.05 mM to 0.5 M with an averaged excursion in 1 h of ±0.3 mV. The reproducibility of Δ(IL)(W)φ is ±0.6 mV on average (95% confidence interval) in KCl solutions in this concentration range. The mixing of the two different types of salts not only increases the stability of the phase-boundary potential but provides us with more freedom in selecting potential-determining salts to design and customize ILSBs for different purposes.