A sensitive choline biosensor with supramolecular architecture

A sensitive biosensor with supramolecular architecture was designed and implemented here to detect choline. Choline oxidase and horseradish peroxidase were assembled onto the polymer of thiolated β-cyclodextrin and platinum nanoparticles modified gold electrode through 1-adamantane carboxylic acid coupling. Square wave voltammetry showed that the reduction currents at 0.38 mV had a linear relationship with the logarithms of choline concentrations in the range of 10⁻⁹-10⁻² M, and the detection limit was down to 0.1 nM. Such biosensor also exhibited excellent selectivity, reproducibility and stability.     

Oligothiophene isocyanides for platinum-based molecular electronic applications

Understanding molecular orientation on a metal surface is key to designing molecular electronic device junctions. Though platinum device electrodes are of particular interest as a more stable alternative to the often used gold electrodes, the chemisorption of conducting molecules onto platinum surfaces has not been thoroughly studied. We present herein the first detailed study of the ability and manner in which soluble oligothiophene isocyanides, of lengths ranging from 2 to 7 nm, chemisorb onto platinum surfaces and nanoparticles. It was found that these oligothiophene isocyanides stand at a 41 degrees angle from the platinum surface normal, suggesting their applicability in molecule-bridged platinum electrode devices.     

Self-metallization of photocatalytic porphyrin nanotubes

Porphyrin nanotubes represent a new class of nanostructures for which the molecular building blocks can be altered to control their structural and functional properties. Nanotubes containing tin(IV) porphyrins are photocatalytically active and can reduce metal ions from aqueous solution. The metal is deposited selectively onto tube surfaces, producing novel composite nanostructures that have potential applications as nanodevices. Two examples presented here are nanotubes with a continuous gold wire in the core and a gold ball at the end and nanotubes coated with platinum nanoparticles mainly on their outer surfaces. The latter are capable of photocatalytic reduction of water to hydrogen.     

A fire-assay and wet chemical method for the determination of palladium, platinum, gold, and silver in ores and concentrates

A method is presented for the determination of palladium, platinum, gold and silver in ores and concentrates by a fire-assay and wet chemical technique. After parting of the lead assay button with dilute nitric acid, and separation of the solution from the residue, the palladium and platinum in the solution are precipitated by the addition of stannous chloride, with tellurium as collector. The resulting precipitate is combined with the gold residue and dissolved in aqua regia, then the solution is analysed for palladium, platinum and gold by atomic-absorption spectrophotometry (AAS). Silver is determined in the original solution by AAS before the reduction step.     

Extractive separation and spectrophotometric determination of palladium and platinum with dithizone in the presence of stannous chloride

The conditions [acid used, presence of chloride and tin(II)] for the extractive separation and spectrophotometric determination of palladium and platinum as the dithizonates Pd(HDz)(2) and Pt(HDz)(2) have been examined. In the absence of stannous chloride platinum does not undergo extraction. Conditions for the separation and determination of these metals in the presence of mercury, gold and copper, which are also extracted with dithizone into carbon tetrachloride or chloroform under the conditions suitable for palladium (1M sulphuric acid/0.1M hydrochloric acid), have been defined. The mercury and gold dithizonates are formed quickly and can be removed before the palladium and platinum compounds have had time to form. They can be decomposed with iodide. Copper dithizonate is decomposed by reduction with tin(II). The proposed procedure has been applied to the determination of palladium in technical platinum metal.     

Extraction of gold, palladium and platinum from chloride, bromide and iodide solution with di-n-octyl sulphide (DOS) in cyclohexane

The extraction of gold, palladium and platinum from hydrochloric acid, hydrobromic acid and iodide media by solutions of di-n-octyl sulphide in cyclohexane was examined. From distribution data it was concluded that the monosolvates AuX(3).DOS and disolvates PdX(2).2DOS are extracted. Extraction of platinum was efficient only from iodide solutions; a disolvate PtI(4).2DOS was formed. The possibility of separation of gold and palladium from platinum by extraction from bromide or chloride solutions and simultaneous extraction of palladium and platinum from an iodide medium was demonstrated.     

Simultaneous determination of palladium, platinum, rhodium and gold by on-line solid phase extraction and high performance liquid chromatography with 5-(2-hydroxy-5-nitrophenylazo)thiorhodanine as pre-column derivatization regents

In this paper, 5-(2-hydroxy-5-nitrophenylazo)thiorhodanine (HNATR) was synthesized. A new method for the simultaneous determination of palladium, platinum, rhodium and gold ions as metal-HNATR chelates was developed using a rapid analysis column high performance liquid chromatography equipped with on-line solid phase extraction technique. The samples (Water, human urine, geological samples and soil) were digested by microwave acid-digestion. The palladium, platinum, rhodium and gold ions in the digested samples were pre-column derivatized with HNATR to form colored chelates. The Pd-HNATR, Pt-HNATR, Rh-HNATR and Au-HNATR chelates can be absorbed onto the front of the enrichment column when they were injected into the injector and sent to the enrichment column [Zorbax Stable Bound, 10 mm x 4.6 mm, 1.8 microm] with a buffer solution of 0.05 mol L(-1) phosphoric acid as mobile phase. After the enrichment had finished, by switching the six ports switching valve, the retained chelates were back-flushed by mobile phase and travelling towards the analytical column. These chelates separation on the analytical column [Zorbax Stable Bound, 10 mm x 4.6 mm, 1.8 microm] was satisfactory with 72% acetonitrile (containing 0.05 mol L(-1) of phosphoric acid and 0.1% of Triton X-100) as mobile phase. The palladium, platinum, rhodium and gold chelates were separated completely within 2.5 min. Compared to the routine chromatographic method, more then 80% of separation time was shortened. By on-line solid phase extraction system, a large volume of sample (10 mL) can be injected, and the sensitivity of the method was greatly improved. The detection limits (S/N=3, the sample injection volume is 10 mL) of palladium, platinum, rhodium and gold in the original samples reaches 1.4, 1.8, 2.0 and 1.2 ng L(-1), respectively. The relative standard deviations for five replicate samples were 2.4-3.6%. The standard recoveries were 88-95%. This method was applied to the determination of palladium, platinum, rhodium and gold in human urine, water and geological samples with good results.     

高效铂-纳米多孔金催化剂的设计和制备

使用去合金法制备了孔径和孔壁均匀的纳米多孔金(NPG)电极.研究发现NPG对甲酸、甲醛的氧化具有很高的电催化活性.如在NPG基体再沉积微量的铂,不仅明显改善了NPG的结构稳定性,而且由于Pt、Au两组分之间的协同效应而使该催化剂对有机小分子的电催化氧化具有比纯铂更高的催化活性和更强的抗催化毒物能力.     

Surface-enhanced vibrational spectroscopy of B vitamins: what is the effect of SERS-active metals used?

Surface-enhanced Raman scattering (SERS) spectroscopy and surface-enhanced infrared absorption (SEIRA) spectroscopy are analytical tools suitable for the detection of small amounts of various analytes adsorbed on metal surfaces. During recent years, these two spectroscopic methods have become increasingly important in the investigation of adsorption of biomolecules and pharmaceuticals on nanostructured metal surfaces. In this work, the adsorption of B-group vitamins pyridoxine, nicotinic acid, folic acid and riboflavin at electrochemically prepared gold and silver substrates was investigated using Fourier transform SERS spectroscopy at an excitation wavelength of 1,064 nm. Gold and silver substrates were prepared by cathodic reduction on massive platinum targets. In the case of gold substrates, oxidation–reduction cycles were applied to increase the enhancement factor of the gold surface. The SERS spectra of riboflavin, nicotinic acid, folic acid and pyridoxine adsorbed on silver substrates differ significantly from SERS spectra of these B-group vitamins adsorbed on gold substrates. The analysis of near-infrared-excited SERS spectra reveals that each of B-group vitamin investigated interacts with the gold surface via a different mechanism of adsorption to that with the silver surface. In the case of riboflavin adsorbed on silver substrate, the interpretation of surface-enhanced infrared absorption (SEIRA) spectra was also helpful in investigation of the adsorption mechanism.     

Preparation of polymer-protected gold/platinum bimetallic clusters and their application to visible light-induced hydrogen evolution

The dispersions of polymer-protected gold/platinum bimetallic clusters were easily and reproducibly prepared by refluxing the mixed solutions of tetrachloroaureic(III) acid and hexachloroplatinic(IV) acid in ethanol/water (1/1) at 90 ∼ 95 °C for 2 h in the presence of a protective polymer such as poly(N-vinyl-2-pyrrolidone) (PVP). The gold/platinum bimetallic clusters thus obtained were very small, well dispersed and very stable. The UV-Vis spectra and the transmission electron micrographs have indicated that each bimetallic particle has an alloy structure consisting of both gold and platinum atoms, and that the surface of the cluster particle is rich in platinum atoms and the inner core in gold atoms. The gold/platinum bimetallic clusters were used as the multi-electron redox catalysts for visible light-induced hydrogen evolution from water. The rate of hydrogen evolution depended on the mole ratio of the gold/platinum bimetallic clusters. The bimetallic clusters at the mole ratio of Au/Pt = 2/3 were the most active catalyst. The in-situ UV-Vis spectra during the reaction have indicated that the order of the aggregation in the two kinds of metal atoms is very important for structure determination of the Au/Pt bimetallic clusters. The protective polymer PVP plays a role not only in protecting hydrophobic colloidal particles in an aqueous solution, but also in determining the metal composition of the cluster surface.     

A glucose biosensor based on electrodeposited biocomposites of gold nanoparticles and glucose oxidase enzyme.

Electrodeposition was used for the codeposition of glucose oxidase enzyme and a gold nanoparticle-silicate network onto an indium tin oxide (ITO) glass electrode. This co-entrapment of glucose oxidase enzyme in a gold nanoparticle-silicate network imparts biocatalytic activity to the film. The gold nanoparticles in the network catalyse the oxidation and reduction of H2O2, the by-product of the enzymatic reaction. The low operating potential of the sensor eliminates the interference from common interferents, such as acetaminophen, ascorbic acid, dopamine, etc.     

The Electrochemical Detection of Arsenic(III) at a Silver Electrode

A study of three electrode substrates namely gold, platinum and silver, for arsenic detection via anodic stripping voltammetry is reported. Hitherto it has been accepted that gold is the most suitable metallic surface for use in this context, as suggested by Forsberg and co‐workers (Forsberg, G.; O'Laughlin, J. W.; Megargle, R. G. Anal. Chem. 1975, 47, 1586.). We revisit these experiments and find that by switching from hydrochloric acid to nitric acid the oxidation of silver that had previously masked the arsenic stripping signal at this surface is shifted considerably enough to allow a clear, analytically reliable As(III) stripping signal to be detected. In contrast to silver and gold platinum is found to have poor performance as an electrode substrate for arsenic detection. Using ASV a LOD of 6.3×10^?7 M is found for As(III) detection at a silver electrode, similar to that which we have previously reported at a gold electrode (A. O. Simm, C. E. Banks and R. G. Compton. Electroanalysis, 2005, 17, 335.) The use of ultrasound was then investigated to further reduce the LOD, which was found to be 1.4×10^?8 M. Apart from reduced cost of silver it also has an added advantage over gold in that it has a higher hydrogen reduction overvoltage enabling a 100 mV more negative deposition potential to be used before the onset of hydrogen evolution when compared to a gold electrode.     

火试金减杂-电感耦合等离子体原子发射光谱法（ICP-AES）法测定高冰镍的金、银、铂、钯含量

建立了火试金减杂-电感耦合等离子体原子发射光谱法（ICP-AES）测定高冰镍中金、银、铂、钯含量的分析方法。实验采用火试金富集、熔融、灰吹得到合粒,通过减杂法得到银含量,通过ICP-AES法测定得到金、铂、钯含量。金、银、铂、钯的加标回收率在99.53%-101.83%之间,相对标准偏差小于3%。此方法快速、简洁,准确度高、精密度好,能够满足高冰镍的测定需求。     

Microelectrodes modification through the reduction of aryl diazonium and their use in scanning electrochemical microscopy (SECM)

This work is devoted to the study of the electrochemical grafting of nitrophenyl groups onto platinum ultramicroelectrode (UME). The grafting was made using the electrochemical reduction of nitrophenyldiazonium. Our results demonstrate the possibility to reduce the diazonium onto Pt UME. As consequence the electrochemical reduction leads to the attachment of nitrophenyl groups onto the UME surface. Following that, the modified UME was characterized using electrochemical techniques. In addition, the electrochemical response of the modified UME in the presence of reversible redox couple, ferrocene, has been studied. The main remark is that the steady state current observed at the UME is not affected by the presence of the nitrophenyl layers. Finally, from this last point we demonstrate the possibility to achieve scanning electrochemical microscopy (SECM) using modified platinum UME.     

Studies on the extraction of platinum metals with tri-iso-octylamine from hydrochloric and hydrobromic acid: separation and determination of gold, palladium and platinum

The extraction of Pd(II), Rh(III), Ir(III), Au(III) and Pt(IV) from hydrochloric and hydrobromic acid with 5% tri-iso-octylamine solution in carbon tetrachloride has been studied. The gold extract from hydrochloric acid is yellow and absorbs at 325 nm, the palladium compound is red and absorbs at 290 nm and 467 nm, and the platinum compound is blood-red and shows absorption at 268 nm. The gold, palladium and platinum extracts from hydrobromic acid are crimson. reddish brown and blood-red, with maximum absorption at 260, 345 and 300 nm respectively. Methods have been devised for the separation of gold from platinum and for its determination and also for the simultaneous determination of palladium and platinum.     

Synthesis and assembly of gold nanoparticles in organized molecular films of gemini amphiphiles

Generation and assembly of gold nanostructures were investigated in the organized molecular films of a series of gemini amphiphiles. The chloroauric acid, dissolved in the aqueous subphase, was incorporated into the monolayers of the gemini amphiphiles containing ethyleneamine spacers through an interfacial assembly. The in situ formed complex monolayers were transferred onto solid substrates, and gold nanoparticles were generated in the film by a chemical or photochemical reduction. Discrete gold nanoparticles with an absorption maximum at 550 nm were generated in the films by photoirradiation, while different gold nanostructures were obtained by chemical reduction. Depending on the chemical reductant, various shape and assembly of gold nanostructures were obtained. When reduced by hydroquinone, a tree-branched assembly of the nanoparticles was obtained and the film showed a broad band centered at around 900 nm. When NaBH 4 was applied, crooked nanowires or assembly of nanoparticles were obtained, depending on concentration, and the film showed absorption at 569 or 600 nm. Furthermore, by combining the photochemical and chemical reduction methods, i.e., the chloroaurate ion-incorporated film was initially irradiated with UV light and then subjected to chemical reduction, the optical absorption of the formed gold nanostructures can be regulated.     

Mechanism of selective oxygen reduction on platinum by 2,2'-bipyridine in the presence of methanol

Mechanism of selective oxygen reduction on platinum by 2,2'-bipyridine in the presence of methanol has been investigated by in situ surface-enhanced infrared absorption spectroscopy. The addition of 2,2'-bipyridine caused the decrease of adsorbed water molecules and those existing near the surface of platinum. The formation of both CO and formate, the latter being the intermediate in the non-CO path for methanol oxidation, depressed in the presence of 2,2'-bipyridine, suggests that 2,2'-bipyridine hinders methanol oxidation via both non-CO and CO paths on platinum. The geometrical effect of 2,2'-bipyridine adsorbed onto platinum was also investigated by multisite Monte Carlo simulation. It is indicated that selective oxygen reduction is caused by the difference in the number of required adsorption sites between methanol and dioxygen molecules. The suppression of Pt oxide species by 2,2'-bipyridine is found to be another factor that enhances the oxygen reduction.     

Electrolytically generated silver(II) as a coulometric titrant

The use of electrolytically generated silver(II) as a coulometric titrant has been studied. Difficulties arising from the current efficiency for generation of silver (II) at a platinum or gold electrode and from the reduction of silver(II) by water, have been overcome. The precautions necessary for accurate titrations of oxalic acid, cerium(III), arsenic(III) and vanadium(IV) by amperometric or potentiometric methods are detailed. Manganese and chromium could not be determined directly. Substances which reduce nitric acid could be determined if care was taken.     

Catalytically active platinum blacks prepared by magnetron sputtering in vacuum and their using in fuel cells with solid polymer electrolyte

Highly disperse platinum film were vacuum-plasma-deposited onto titanium foil and gas-diffusion layers. The platinum deposits have complicated structure. By measuring hydrogen desorption peaks, the catalysts’ active specific surface area was determined and the roughness factor calculated. The electrochemical activity of the electrodes on gas-diffusion layers in the oxygen reduction and hydrogen oxidation reactions was determined. It was shown that the catalysts’ specific activity depends on the platinum content and the Nafion-ionomer additive. The high-activity electrodes were tested in Membrane Electrode Assemblies of low-temperature fuel cells.     

Kinetics and mechanism of glucose electrooxidation on different electrode-catalysts: Part II. Effect of the nature of the electrode and the electrooxidation mechanism

A comparative study has been made of glucose electrooxidation on electrodes made of metals of group VIII, Ag, Au, Cu and glassy carbon as well as of phthalocyanines and porphyrins of cobalt, manganese and iron. It is found that considerable electrooxidation currents are observed for iridium and rhodium (group VIII), and for gold and copper (the copper subgroup). In neutral and alkaline solutions, glucose electrooxidation rates on gold considerably exceed those on platinum.Investigations have been carried out into the main regularities of glucose electrooxidation on a gold electrode in a wide range of potentials, glucose concentrations and pH values. The effect of chloride ions, gluconic acid and amino acids on glucose electrooxidation on gold have been studied.Proceeding from the direct comparison of adsorption data with polarization data obtained under the same conditions, a mechanism of glucose electrooxidation on platinum has been suggested. It is also shown that the mechanism of glucose electrooxidation on gold is similar, in many respects, to that on platinum.