Presence Of Colloidal Gold Research Articles

Investigation of the Pigments and Glassy Matrix of Painted Enamelled Qing Dynasty Chinese Porcelains by Noninvasive On-Site Raman Microspectrometry

A selection of 15 Chinese painted enameled porcelains from the 18th century (Qing dynasty) was analyzed on-site by mobile Raman and XRF microspectroscopy. The highly prized artifacts are present in the collections of the Musée du Louvre in Paris and Musée Chinois at Fontainebleau Castle in France. In the painted enamels, pigments such as Naples yellow lead pyrochlore, hematite, manganese oxide and carbon and opacifiers such as lead arsenates were detected. The glassy matrices of the enamels mainly belonged to lead-rich and lead-alkali glass types according to the Raman spectra obtained. The glaze and body phases of the porcelain artifacts were also analyzed. The detection of lead arsenate apatite in some of the blue enamels was significant, indicating the use of arsenic-rich European cobalt ores (smalt) and possibly mixing with Asian cobalt. This characteristic phase has also been identified in French soft-paste porcelains and glass decor and high-quality Limoges enamels from the same period. Based on the shape of the Raman scattering background, the presence of colloidal gold (Au° nanoparticles) was identified in red, orange and pink enamels. Different types of Naples yellow pigments were also detected with Sb-rich, Sn-rich and mixed Sb–Sn–(Zn, Fe?) compositions in the yellow enamels. The results were compared to previous data obtained on Chinese cloisonné and painted enameled metalware and Limoges enamels as well as French enameled watches.

Non-Invasive On-Site Raman Study of Pigments and Glassy Matrix of 17th–18th Century Painted Enamelled Chinese Metal Wares: Comparison with French Enamelling Technology

A selection of 10 Chinese enamelled metal wares dating from the 17th–18th centuries (Qing Dynasty) was analysed on-site by mobile Raman microspectroscopy. These wares display cloisonné and/or painted enamels and belong to the collections of Musée du Louvre in Paris and Musée Chinois at the Fontainebleau Castle in France. Pigments (Naples yellow lead pyrochlore, hematite, manganese oxide etc.), opacifiers (fluorite, lead arsenates) and corresponding lead-based glassy matrices were identified. One artefact was also analysed by portable X-ray fluorescence spectrometry (pXRF) in order to confirm the Raman data. In some of these metal wares, it is suggested that cassiterite was unpredictably used as an opacifier in some parts of the decor. The results are compared to previous data obtained on Chinese cloisonné and Limoges enamels as well as recent data recorded on painted enamelled porcelains of the Qing Dynasty. Lead arsenate apatite detected in some of the 17th–18th century blue enamelled decors is related to the use of arsenic-rich European cobalt ores, as also characterized in French soft-paste porcelain and glass decors and high-quality Limoges enamels for the same period. However, lead arsenate could then also have been deliberately used for white opacification. The specific Raman signature displaying the shape of the Raman scattering background indicates the presence of colloidal gold (Au° nanoparticles) in red to violet enamelled and cloisonné areas. At least three types of Naples yellow lead pyrochlore pigments identified with Sb-rich, Sn-rich and mixed Sb–Sn–(Zn, Fe?) compositions prove the use of European pigments/recipes.

Pigments and glassy matrix of the 17th–18th century enamelled French watches: A non-invasive on-site Raman and pXRF study

Abstract Twelve rare watches with painted enamels, mostly produced in France, from the 17th and 18th centuries in the collections of Musee du Louvre in Paris were analysed on-site in order to characterize the materials used in their enamels and the enamelling technique. All the watches were analysed by mobile Raman microspectroscopy and five of them were also analysed by pXRF. Pigments (Naples Yellow pyrochlore, hematite, carbon, lapis lazuli, arsenic sulphide, manganese oxides), opacifiers (cassiterite, lead arsenates) and corresponding lead-rich glassy silicate matrices were identified by one or two methods. Similar to the oil painting or tempera techniques, different hues of the related enamels were obtained by mixing many colouring agents, rather than using ‘pure’ enamels as in the case of Limoges enamelled objects. Lead arsenate apatite detected in some of the 17th century blue enamels is related to the use of European arsenic-rich cobalt ores, as also characterized in the blue (soft-paste) porcelain decors and high-quality Limoges enamels. The presence of colloidal gold (Au° nanoparticles) was indirectly detected by the Raman technique in the 18th century watches and confirmed by pXRF. At least three types of Naples Yellow pigment were identified with Sb-rich, Sn-rich and mixed Sb-Sn-Fe-Zn compositions.

Colloidal gold-loaded, biodegradable, polymer-based stavudine nanoparticle uptake by macrophages: an in vitro study.

We describe the development, evaluation, and comparison of colloidal gold-loaded, poly(d,l-lactic-co-glycolic acid)-based nanoparticles containing anti-acquired immunodeficiency syndrome drug stavudine and uptake of these nanoparticles by macrophages in vitro. WE USED THE FOLLOWING METHODS IN THIS STUDY: drug-excipient interaction by Fourier transform infrared spectroscopy, morphology of nanoparticles by field-emission scanning electron microscopy, particle size by a particle size analyzer, and zeta potential and polydispersity index by a zetasizer. Drug loading and in vitro release were evaluated for formulations. The best formulation was incorporated with fluorescein isothiocyanate. Macrophage uptake of fluorescein isothiocyanate nanoparticles was studied in vitro. Variations in process parameters, such as speed of homogenization and amount of excipients, affected drug loading and the polydispersity index. We found that the drug was released for a prolonged period (over 63 days) from the nanoparticles, and observed cellular uptake of stavudine nanoparticles by macrophages. Experimental nanoparticles represent an interesting carrier system for the transport of stavudine to macrophages, providing reduced required drug dose and improved drug delivery to macrophages over an extended period. The presence of colloidal gold in the particles decreased the drug content and resulted in comparatively faster drug release.

Electrochemical detection of prostate-specific antigen based on gold colloids/alumina derived sol-gel film

An electrochemical immunosensor for total prostate-specific antigen (PSA) was fabricated based on anti-PSA antibody-functionalized gold colloids/alumina sol-gel film. The presence of colloidal gold provides a good microenvironment for the immobilization of biomolecules. The fabrication process of the immunosensor was characterized by cyclic voltammetry. A direct electrochemical immunoassay format was employed to detect PSA on the basis of the potential change before and after the antigen–antibody interaction. Under optimal conditions, the potential change was proportional to PSA concentration ranging from 4.0 to 13 ng mL − 1 with a detection limit of 3.4 ng mL − 1 . In addition, the performance and factors influencing the performance of the immunosensor were investigated and optimized.

DNA dissociation and degradation at gold nanoparticle surfaces

The instability of DNA-functionalized gold nanoparticles (Au-DNA conjugates) upon exposure to high temperatures is characterized using fluorescence spectroscopy, gel electrophoresis and ion-exchange chromatography. Above 70 °C, aqueous Au-DNA conjugates decompose within hours due to both desorption of thiol-terminated DNA from the gold nanoparticle surface and chemical degradation of DNA in the presence of colloidal gold. Although the chemical mechanism for DNA degradation was not identified in this study, the gold surface participates directly in the cleavage reaction. These results have important implications for the use of Au-DNA conjugates in biotechnological and clinical applications that require high temperatures, such as polymerase chain reaction (PCR).

Development of a high analytical performance-tyrosinase biosensor based on a composite graphite–Teflon electrode modified with gold nanoparticles

The design of a new tyrosinase biosensor with improved stability and sensitivity is reported. The biosensor design is based on the construction of a graphite-Teflon composite electrode matrix in which the enzyme and colloidal gold nanoparticles are incorporated by simple physical inclusion. Experimental variables such as the colloidal gold loading into the composite matrix, the enzyme loading and the potential applied to the bioelectrode were optimized. The Tyr-Au(coll)-graphite-Teflon biosensor exhibited suitable amperometric responses at -0.10 V for the different phenolic compounds tested (catechol; phenol; 3,4-dimethylphenol; 4-chloro-3-methylphenol; 4-chlorophenol; 4-chloro-2-methylphenol; 3-methylphenol and 4-methylphenol). The limits of detection obtained were 3 nM for catechol, 3.3 microM for 4-chloro-2-methylphenol, and approximately 20 nM for the rest of phenolic compounds. The presence of colloidal gold into the composite matrix gives rise to enhanced kinetics of both the enzyme reaction and the electrochemical reduction of the corresponding o-quinones at the electrode surface, thus allowing the achievement of a high sensitivity. The biosensor exhibited an excellent renewability by simple polishing, with a lifetime of at least 39 days without apparent loss of the immobilized enzyme activity. The usefulness of the biosensor for the analysis of real samples was evaluated by performing the estimation of the content of phenolic compounds in water samples of different characteristics.

Studies on the interaction of colloidal gold and serum albumins by spectral methods

The interactions of colloidal gold and serum albumins, including bovine serum albumin (BSA) and human serum albumin (HSA), were studied by fluorescence and absorption spectrometry. Fluorescence quenching spectrometry was applied to study the interactions between colloidal gold and serum albumins. At pH 7.4 phosphate-buffered saline (PBS), the intensity of fluorescence emission spectrum of serum albumins decreased in the presence of colloidal gold, which indicated that colloidal gold quenched the fluorescence of serum albumins. Experimental results indicated that the combination reactions of colloidal gold and serum albumins were static quenching processes. Based on the effect of colloidal gold on fluorescence intensity, the binding constants, the numbers of binding sites and the acting forces between colloidal gold and serum albumins were found.

Radiolytic Control of the Size of Colloidal Gold Nanoparticles

Solutions containing KAu(CN)2 (∼5 × 10-4 M), methanol (0.3 M), and nitrous oxide (2.5 × 10-2 M) are γ-irradiated in the presence of colloidal gold (∼6 × 10-5 M; mean particle size, 15 nm). The hydroxymethyl radicals, •CH2OH, which are generated in these solutions, reduce Au(I) in Au(CN)2-, and the reduced gold is completely deposited on the gold seeds to yield larger particles. The particle growth is followed spectrophotometrically and by electron microscopy. A mechanism is proposed in which the radicals transfer electrons to the gold particles and Au(CN)2- is subsequently reduced by the stored electrons directly at the surface of the particles. In further steps of particle enlargement, Au(CN)2- is reduced in solutions in which the gold particles synthesized in the preceding step serve as seeds, the result being larger and larger gold particles up to 120 nm. The reduction yield is discussed with respect to side reactions of the radicals, such as mutual deactivation and gold-catalyzed H2 formation. The rad...

Catalytic electroreduction of oxygen at a dropping mercury electrode in the presence of colloidal gold

Catalytic electroreduction of oxygen at a dropping mercury electrode in the presence of colloidal gold

Catalytic electroreduction of oxygen at a dropping mercury electrode in the presence of colloidal gold

The electroreduction of oxygen at the DME in the presence of colloidal gold has been studied. The first wave of O2 reduction undergoes an increase of its amplitude, while the second wave is split and partially shifted toward less negative potentials. The first and second wave are both dependent on the colloidal gold concentration, the pH and the temperature. The catalytic exaltation of the first wave is attributed to the decomposition of the hydrogen peroxide produced at the electrode. Comparison between the kinetic constants obtained by employing the equations for the catalytic currents with partial regeneration of depolarizer and those experimentally measured from bulk decomposition of H2O2 show that a primary role must be played by the mercury itself. This assumption is supported by the variation of the visible spectrum of the gold colloid caused by the presence of mercury. Analysis of the polarographic measurements, as well as additional evidence from the pertinent literature, indicates that the most likely mechanisms is Au(Hg) + HO2− → Au(HgO) + HO− Au(HgO) + O2−H → Au(Hg) + HO− + O2

Catalytic electroreduction of oxygen at a dropping mercury electrode in the presence of colloidal gold

Summary The electroreduction of oxygen at the DME in the presence of colloidal gold has been studied. The first wave of O2 reduction undergoes an increase of its amplitude, while the second wave is split and partially shifted toward less negative potentials. The first and second wave are both dependent on the colloidal gold concentration, the pH and the temperature. The catalytic exaltation of the first wave is attributed to the decomposition of the hydrogen peroxide produced at the electrode. Comparison between the kinetic constants obtained by employing the equations for the catalytic currents with partial regeneration of depolarizer and those experimentally measured from bulk decomposition of H2O2 show that a primary role must be played by the mercury itself. This assumption is supported by the variation of the visible spectrum of the gold colloid caused by the presence of mercury. Analysis of the polarographic measurements, as well as additional evidence from the pertinent literature, indicates that the most likely mechanisms is Au(Hg) + HO2− → Au(HgO) + HO− Au(HgO) + O2−H → Au(Hg) + HO− + O2