Anion Adsorption on an Au Colloid Monolayer Based Cysteamine-Modified Gold Electrode

IntroductionThe metal colloids have been investigated for over l40 years since Faraday['] made thefirst approach on gold colloids. Colloidal Au can be used for catalysis['], microanalysis of pro--tein and biosensors[3J and its fine particles have been expected to be a highly efficient thirdnon1inear optical material[4'5J. However, most studies on the surface chemistry of metal parti-cles have been focused on silver[6], the reason is that the plasmon absorption band of that met-al is very str…     

D-glucose-derived polymer intermediates as templates for the synthesis of ultrastable and redispersible gold colloids

A two-stage hydrothermal process was developed for the synthesis of highly dispersed Au colloids. In the first stage, a novel glucose-derived polymer template was prepared by the hydrothermal treatment of glucose at 160 degrees C. This template was then further used in the next step to synthesize highly dispersed gold (Au) colloids by hydrothermal treatment with HAuCl(4.) The templates treated at 160 degrees C with changing reaction times had different templating effects toward Au species. The 3-h treated template was able tightly adhere to the Au colloids. As a result, an unusual stability was observed for the prepared Au particles that could be repeatedly precipitated and redispersed with the template in H(2)O and were also stable against heating (below 160 degrees C) and aging. Meanwhile, the 5-h and 7-h treated templates had much poorer templating effects to Au species, leading to severe aggregation of the Au colloids immobilized on them. The various templating effects were correlated to the different structural features of the templates. Compared to the 5- or 7-h treated templates that were deeply carbonized, the 3-h treated template was only slightly carbonized, thus possessing a lot of functional and hydrophilic O-containing groups that could bind to Au species. These differences in templating ability were also observed in the Au samples prepared by the sonication-assisted method. The highly dispersed Au colloids immobilized on the 3-h treated template were tested for CO oxidation, and a good catalytic activity and stability for CO oxidation was observed.     

From discrete particles to spherical aggregates: a simple approach to the self-assembly of Au colloids

Here we demonstrate a simple, template-free approach to the formation of spherical gold aggregates through the reduction of HAuCl4 by NaBH4, in the presence of cysteine (Cys) as a capping agent. The resulting aggregates are quite stable in solution. The pH of the solution and the molar ratio of Au:Cys are two key empirical factors in the formation of such highly ordered aggregates. At slightly alkaline pH (7-10) and with Au:Cys ratios ranging from 1:0.5 to 1:2, spherical Au aggregates of 30-80 nm are formed. At lower Cys ratios (Au:Cys> or =1:0.5) very loosely linked aggregates are formed; however, at very high Cys ratios (Au:Cys< or =1:3), highly dispersed Au particles of 2-4 nm are obtained, which are virtually indistinguishable from the original colloidal form. Aggregate size is influenced markedly by component concentration; a 3-fold increase in standard levels resulted in Au spherical aggregates of a larger size, 200-500 nm. In addition, we used a combination of Cys and lysine (Lys) as a capping agent/cross-linker and found that the morphology of the Au colloid aggregates can be easily manipulated from a linear to a spherical form by adjusting the proportions of Cys and Lys in the capping agent/cross-linker mixture. The introduction of mercapto (SH)-containing organic acids reduced the cross-linking ability of Cys, especially in the case of long-chain acids. Complete disruption of the spherical aggregates highlights the importance of Cys per se. An explanation of this ordered self-assembly process is proposed, in the context of the known surface chemistry of Au colloids.     

Investigation of the effects of Au-colloid modification on cobalt hexacyanoferrate film growth and mass transport by electrochemical quartz crystal microbalance

The growth of cobalt hexacyanoferrate (CoHCF) films on bare and Au-colloid-modified electrodes in nitrate or sulfate solutions was monitored by electrochemical quartz crystal microbalance. The average efficiency of CoHCF film growth for Au colloid modified electrodes is 23 and 12 ng cm(-2) s(-1) in KNO3 and K2SO4 solutions, respectively, while those values for the bare gold electrode are 15 and 9 ng cm(-2) s(-1), respectively. In K2SO4 solution, the apparent molar masses for the Au-colloid-modified electrode at lower and higher potential is 58.4 and 37.3 g mol(-1), respectively, which is larger than those for the bare gold electrode (51.7 and 26.3 g mol(-1), respectively). The respective results were also obtained in KNO3 solution. Furthermore, the difference of the apparent molar masses at lower and higher potential for Au-colloid-modified electrodes is smaller than that for bare gold electrodes in the same electrolyte. Additionally, the mechanism of charge propagation is dependent on different anions in electrolyte solutions at higher potentials where the second redox reaction of CoHCF occurs. Therefore, the existence of Au colloids can accelerate CoHCF film growth and weaken the effect of anions on mass transport.     

Preparation and characterization of noble metal nanocolloids by silk fibroin in situ reduction

Silk fibroin (SF) is a natural protein from silkworm. It represents Chinas resplendent civili-zation as dress materials in the past 5000 a. To this day, the silk output in China is about 90000 tons per year, which is about 70% of the world overall output. In the past decade, it has been found that silk fibroin has special properties for being used as healthy foods, cosmetics, enzyme immobilizing materials, cell culture medium, biosensor, artificial skin, artificial muscle, perme-able membran…     

Preparation and characterization of noble metal nanocolloids by silk fibroin <Emphasis Type="Italic">in situ</Emphasis> reduction

Noble metal nanocolloids are prepared from their precursors by in situ reduction of a silk fibroin solution at room temperature without any reducing agent. The mechanism, the effects of pH and the molar ratio of the reactants on the reduction reaction are studied by UV-Vis spectroscopy. The structure of the colloids is characterized by FT-IR, TEM and AFM. According to the TEM images, the gold-silk fibroin colloid is a nanostructured bioconjugate with novel core-shell, while the silver-silk fibroin colloid tends to be congregated as clusters having more than ten nanoparticles of silver-silk fibroin. The gold colloid is highly dispersed and stable while the silver colloid is less dispersed and stable than the gold colloid.     

Cationic gold carbonyl complex on a phosphine support

A cationic gold carbonyl complex has been synthesized and characterized using several techniques including X-ray crystallography. [(Mes(3)P)Au(CO)][SbF(6)] (Mes = 2,4,6-Me(3)C(6)H(2)) has a linear, two-coordinate gold atom. This compound displays the CO stretching frequency at 2185 cm(-1). The (13)C NMR signal of the gold-bound (13)CO appears as a doublet centered at δ 182.6 ((2)J(C,P) = 115 Hz). A computational study shows that the Au-CO bond consists of electrostatic attraction, Au ← CO donation, and significant Au → CO π-back-bonding components. Polarization of the CO bond caused by the electrostatic effect of the cationic gold center is mainly responsible for the large blue shift in the CO stretching frequency.     

Surface adsorption and transfer of organomercaptans to colloidal gold and direct identification by matrix assisted laser desorption/ionization mass spectrometry

The adsorption characteristics of two different organomercaptan adsorbates, 5-((2-(and-3)-S-(acetylmercapto)succinoyl)amino)fluorescein (SAMSA) and the peptide Cys-Lys-Trp-Ala-Lys-Trp-Ala-Trp (CKWAKWAK), on colloidal Au were studied, and the conjugates produced were characterized by UV-vis spectroscopy, transmission electron microscopy, and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Fluorescence difference measurements of free thiols in solution were used to assemble surface adsorption isotherms on Au colloid revealing surface coverages of 1.0 x 10(14) molecules cm(-2) for SAMSA and 3.1 x 10(14) molecules cm(-2) for CKWAKWAK. The free energies of adsorption were calculated to be -48.4 kJ/mol for SAMSA and -49.2 kJ/mol for CKWAKWAK. UV-visible absorption spectroscopy and transmission electron microscopy reveal that the thiol/colloid conjugates flocculate under conditions where the net charge per colloid is small or neutral and that flocculated colloids can be resuspended by a change in pH to more basic for the acidic SAMSA/Au conjugates or to more acidic for the basic CKWAKWAK/Au conjugates. The reversible flocculation allows the conjugates to be readily separated from free adsorbate in solution and thereby prepared for further characterization. CKWAKWAK/colloid conjugates were analyzed by MALDI-MS, and the mass spectra show (M + H)(+), (M + Na)(+), and (M + K)(+) ions attributable to the peptide. The manipulations studied here constitute a powerful complement to microfluidic-based separation and analysis methods. Conjugating mass-limited analytes to Au colloids makes it possible to sequester and transfer small quantities of analytes with high efficiency.     

Piezoelectric quartz crystal impedance and electrochemical impedance study of HSA-diazepam interaction by nanogold-structured sensor

Human serum albumin (HSA) was immobilized on the surface of colloidal Au and exposed to diazepam. Colloidal Au were at first self-assembled on the gold electrode through the thiol groups of a 1,6-hexanedithiol monolayer. The real-time course of the resonant frequency and equivalent circuit parameters of the sensor during the protein-diazepam binding was determined for the first time by piezoelectric quartz crystal impedance (PQCI). On the basis of the multidimensional information provided by the PQCI analysis, it was concluded that the decrement of the observed frequency was mainly ascribable to the mass loading on the sensor surface. Compared with a bare gold electrode, the gold electrode self-assembled from nanogold colloids exhibits maintained biocompatibility, increased capacity, and more bioactivity. Cyclic voltammetry and electrochemical impedance techniques were used to investigate the immobilization of HSA and the interaction between HSA and diazepam. Results testified that gold colloid could play the role of an efficient electron-conducting tunnel and have a very high ratio of surface to volume. Additionally, the kinetics of the binding process was investigated. The estimated binding constant (K) and the number of binding site (n) on one HSA molecule were 1.66 x 10(6) mol l(-1) and 1.28, respectively.     

Gold complexes with dithiothiophene ligands: a metal based on a neutral molecule

The gold complexes n-Bu4N[Au(alpha-tpdt)2] (5), n-Bu4N[Au(dtpdt)2] (4) and n-Bu4N[Au(tpdt)2] (6) based on new dithiothiophene ligands (alpha-tpdt= 2,3-thiophenedithiolate, dtpdt=2,3-dihydro-5,6-thiophenedithiolate and tpdt = 3,4-thiophenedithiolate) have been prepared and characterised. These gold(III) complexes are diamagnetic, but they can be oxidised with iodine to the paramagnetic compounds [Au(alpha-tpdt)2] (8), [Au(dtpdt)2] (7) and n-Bu4N[[Au(tpdt)2]n-2] (9), which were isolated as fine powders and which exhibit paramagnetic susceptibilities that are almost temperature independent with room temperature values of 2.5 x 10(-4), 2.0 x 10(-4) and 5 x 10(-4) emu x mol(-1), respectively. Interestingly, the neutral complex [Au(alpha-tpdt)2] (8) as a polycrystalline sample displays the properties of a metallic system with a room temperature electrical conductivity of 6 S x cm(-1) and a thermoelectric power of 5.5 microVK(-1); this is the first time that this metallic property has been observed in a molecular system based on a neutral species.     

Isolable, gold carbonyl complexes supported by N-heterocyclic carbenes

Cationic gold carbonyl complexes supported by N-heterocyclic carbene ligands, SIDipp and IDipp, have been synthesized. [(SIDipp)Au(CO)][SbF(6)] has a linear, two-coordinate gold center. [(SIDipp)Au(CO)][SbF(6)] and [(IDipp)Au(CO)][SbF(6)] display ?ν(CO) values at 2197 and 2193 cm(-1), respectively. Computational studies on [(SIMe)Au(CO)](+) indicate the presence of a strong Au(I)-CO bond.     

Hematite spindles with optical functionalities: growth of gold nanoshells and assembly of gold nanorods

The layer-by-layer (LBL) assembly method, combined with the seeded growth technique, have been used to deposit gold shells on the surface of hematite (alpha-Fe(2)O(3)) spindles. While the LBL method yields dense coatings of preformed Au nanoparticles, when AuCl(-)(4) ions are further reduced by a mild reducing agent, thicker, rough nanostructured shells can be grown. The deposition process was monitored by TEM and UV-visible spectroscopy, demonstrating a gradual change in the optical features of the colloids as the surface is more densely covered. The particles so-prepared can find useful applications in cancer therapy and as SERS substrates. Additionally, we show that Au nanorods can be assembled on hematite spindles, providing a flexible way to tune the optical properties of the resulting composite colloids.     

Surface electrochemistry of CO on reconstructed gold single crystal surfaces studied by infrared reflection absorption spectroscopy and rotating disk electrode

The electrooxidation of CO has been studied on reconstructed gold single-crystal surfaces by a combination of electrochemical (EC) and infrared reflection absorption spectroscopy (IRAS) measurements. Emphasis is placed on relating the vibrational properties of the CO adlayer to the voltammetric and other macroscopic electrochemical responses, including rotating disk electrode measurements of the catalytic activity. The IRAS data show that the C-O stretching frequencies are strongly dependent on the surface orientation and can be observed in the range 1940-1990 cm(-1) for the 3-fold bridging, 2005-2070 cm(-1) for the 2-fold bridging, and 2115-2140 for the terminal position. The most complex CO spectra are found for the Au(110)-(1 x 2) surface, i.e., a band near 1965 cm(-1), with the second, weaker band shifted positively by about 45 cm(-1) and, finally, a weak band near 2115 cm(-1). While the C-O stretching frequencies for a CO adlayer adsorbed on Au(111)-(1 x 23) show nu(CO) bands at 2029-2069 cm(-1) and at 1944-1986 cm(-1), on the Au(100)-"hex" surface a single CO band is observed at 2004-2029 cm(-1). In the "argon-purged" solution, the terminal nu(CO) band on Au(110)-(1 x 2) and the 3-fold bridging band on the Au(111)-(1 x 23) disappear entirely. The IRAS/EC data show that the kinetics of CO oxidation are structure sensitive; i.e., the onset of CO oxidation increases in the order Au(110)-(1 x 2) > or = Au(100)-"hex" > Au(111)-(1 x 23). Possible explanations for the structure sensitivity are discussed.     

Formation of nonclassical carbonyls of Au3+ in zeolite NaY: characterization by infrared spectroscopy

Adsorption of CO on gold supported in zeolite NaY at 85 K led to the formation of (i) various carbonyls and isocarbonyls typical of the zeolite and (ii) carbonyls formed at cationic gold sites (observed in the 2186-2171 cm(-1) region). Analysis of the behavior of the bands allows their assignment to carbonyls of Au(3+) ions. At temperatures higher than 220 K, CO adsorption led to the formation of a new type of Au(3+)-CO species (2207 cm(-1)). Once formed, these complexes could be transformed into the dicarbonyls Au(3+)(CO)(2) when the sample was cooled to 85 K in the presence of CO. The results are explained by migration of Au(3+) ions to more accessible positions within the zeolite at increasing temperatures. When a CO molecule is already adsorbed, it stabilizes the Au(3+) ion in the new position, and a second CO molecule can be coordinated, thus forming a geminal species. These results are the first evidence of Au(3+)(CO)(2) complexes.     

Photo-formation of gold nanoparticles: photoacoustic studies on solid monoliths of Au(III)-chitosan-silica aerogels

Photo-formation of gold nanoparticles in the solid monoliths of Au(III)-chitosan-silica aerogels with different Au/NH(2) molar ratios has been investigated using photoacoustic spectroscopy. Upon exposing to 320 nm UV light, a new absorption feature in the visible region around 525 nm could be seen due to the surface plasmon resonance of gold particles that are generated as a result of UV-induced reduction of Au(III) to Au(0). The plasmon band becomes stronger and shows saturation effects upon increasing the UV exposure time. A blue shift of about 7 nm is also noticed on exposing the sample (Au/NH(2)=1/5) for 6h, indicating a slight decrease in the nanoparticle size due to light-induced annealing with increasing the UV exposure time. The PA signals monitored as a function of chopping frequency show omega(-1) dependence, implying the thermally thin character of Au(III)-chitosan-silica aerogels.     

Synthesis and optical properties of nanorattles and multiple-walled nanoshells/nanotubes made of metal alloys

The galvanic replacement reaction between silver and chloroauric acid has been exploited as a powerful means for preparing metal nanostructures with hollow interiors. Here, the utility of this approach is further extended to produce complex core/shell nanostructures made of metals by combining the replacement reaction with electroless deposition of silver. We have fabricated nanorattles consisting of Au/Ag alloy cores and Au/Ag alloy shells by starting with Au/Ag alloy colloids as the initial template. We have also prepared multiple-walled nanoshells/nanotubes (or nanoscale Matrioshka) with a variety of shapes, compositions, and structures by controlling the morphology of the template and the precursor salt used in each step of the replacement reaction. There are a number of interesting optical features associated with these new core/shell metal nanostructures. For example, nanorattles made of Au/Ag alloys displayed two well-separated extinction peaks, a feature similar to that of gold or silver nanorods. The peak at approximately 510 nm could be attributed to the Au/Ag alloy cores, while the other peak was associated with the Au/Ag alloy shells and could be continuously tuned in the spectral range from red to near-infrared.     

Effect of gold nanoparticles on the fluorescence excitation spectrum of α-fetoprotein: local environment dependent fluorescence quenching

The effect of colloid gold nanoparticles (AuNPs) on the fluorescence excitation spectrum of α-fetoprotein (AFP) has been investigated experimentally. The excitation spectral peaks of AFP with low concentration from 0.01 ng ml(-1) to 12 ng ml(-1) increase monotonically with increasing of AFP concentration. When some gold colloids were added to the AFP solution, the excitation peak at 285 nm decreases distinctly. By comparing the excitation peak intensity of AFP solution with gold colloids and without gold colloids at different AFP concentrations, the quenching effect from gold nanoparticle was more effective at lower AFP concentration. So the range of concentration from 0.01 ng ml(-1) to 0.09 ng ml(-1) will be the potential range of applications because of the higher sensitivity. The physical origin based on local field effect was investigated to illuminate this local environment dependent fluorescence quenching. The changing extent of quenching with different AFP concentrations can be attributed to the nonlinear decreasing of the local field factor of gold nanoparticles as a function of environmental dielectric constant.     

Gold colloid analysis by inductively coupled plasma-mass spectrometry in a single particle mode

Analysis in a single particle mode of gold colloids in water has been performed by inductively coupled plasma-mass spectrometry (ICP-MS). The signal induced by the flash of ions due to the ionization of a colloid in the plasma torch can be measured for the ions ¹⁹⁷Au⁺ by the mass spectrometer without interferences. The intensity of the MS signal is recorded in time scan. The recorded peak distributions were analysed as a function of the colloid size for five monodisperse colloids (80-250 nm). This study describes the experimental conditions to analyse gold colloids in a single particle mode. The size detection limit is around 25 nm corresponding to 0.15 fg colloids and one particle per ml may be detected during a 1 min time scan within standard procedure.     

Tricarbonyls of low-coordinated Au(0) atoms in zeolite-supported gold nanoparticles: Evidence from infrared and X-ray absorption spectroscopies

Mononuclear gold complexes in zeolite NaY were synthesized from initially physisorbed Au(CH3)2(C5H7O2) and characterized by X-ray absorption and infrared spectra recorded as the samples were exposed to flowing CO. X-ray absorption spectra demonstrate the formation of zero-valent gold nanoparticles during the CO treatment. Three new nu(CO) bands grew in during this treatment, at 2070, 2033, and 2000 cm(-1), characteristic of carbonyls of Au0. Because the relative intensities of these bands decreased monotonically when the flow of CO was replaced by flowing He, it is inferred that they correspond to a single Au0(CO)3 species, on low-coordinated Au atoms. This is the first example of an Au0(CO)3 species.     

α-MnO2负载纳米Au催化剂低温催化氧化CO和苯的性能

以尿素为沉淀剂用沉积-沉淀法制备了α-MnO2负载Au催化剂xAu/α-MnO2(x=0-7(对应的Au负载量(质量分数)分别为0-7%)),使用X射线粉末衍射(XRD)、N2-吸附/脱附、透射电镜(TEM)、X射线光电子能谱(XPS)和H2-程序升温还原(H2-TPR)等技术对所制样品进行了表征,并测定其对CO和苯的催化氧化性能.XRD结果表明,负载Au对α-MnO2载体结构影响不大,随Au含量的增加,Au颗粒明显增大.N2-吸附/脱附和TEM结果表明,Au的加入对xAu/α-MnO2的比表面积、孔容和孔径等结构性能影响较小,表明Au分布在α-MnO2载体表面,未阻塞其孔道.XPS结果表明,随着Au负载量的增加,xAu/α-MnO2中的O2-/(O22-或O-)、Mn4+/Mn3+和Au3+/Au0的摩尔比在增加,表明其晶格氧、Mn4+和Au3+的浓度在增加.由于贵金属的溢氢作用,Au明显促进xAu/α-MnO2氧化还原能力,其中3Au/α-MnO2具有最高的氧化还原性.负载Au明显影响xAu/α-MnO2样品的催化活性,xAu/α-MnO2的催化性能与Au的分散性、氧化还原性能及表面氧物种的种类密切相关,其中3Au/α-MnO2显示出最佳活性,其催化氧化CO的T90=80°C,苯的T90=200°C.