Gold Salts Research Articles

Synthesis of gold organometallics at the nanoscale

We report the synthesis of aryldiazonium tetrachloroaurate(III) salts [X-4-C6H4N≡N]AuCl4 (X = F, Cl, Br, I, CN, NO2) and their mild reduction to covalently functionalized nanoparticles. The synthesis of the salts was carried out by the oxidation of anilines, dissolved in HCl, using sodium nitrite followed by the exchange of the counter anion with [AuCl4]- in water. In another procedure, the anilines were protonated with H[AuCl4] in acetonitrile followed by one-electron oxidation using nitrosonium salt [NO]X (X = BF4−, PF6−). Raman and ATR-FTIR spectroscopy displayed the diazonium νN≡N and Raman showed the tetrachloroaurate νAu-Cl stretching frequencies. X-ray crystal structure of [NO2-4-C6H4N≡N]AuCl4 salt showed N≡N bond distance typical of a triple bond. Gold-aryl nanoparticles were constructed by the mild chemical reduction of the diazonium gold(III) salts using 9-borabicyclo[3.3.1]nonane (9-BBN). Nanoparticles hydrodynamic diameter, elemental composition, dynamics information, and stability data were determined. Transmission electron microscopy (TEM) measurements showed limited aggregation due to the small suppressing organic shell. However, dynamic light scattering (DLS) measurements showed considerable aggregation in acetonitrile. X-ray photoelectron spectrometry (XPS) showed the gold core in zero oxidation state and manifested the gold-organic shell connectivity. The –N=N-aryl interfacial formation on the gold surface can be ruled out since the N1s peak assigned to the diazonium moiety showed no sign in the XPS nitrogen area in addition to its absence in the ATR-FTIR spectra. Raman spectroscopy measurements showed a peak assigned to gold-carbon bonding supported by density functional calculations (DFT) on Au20-C6H4-CN model.

Cathodically activated Au/TiO2 nanocomposite synthesized by a new facile solvothermal method: An efficient electrocatalyst with Pt-like activity for hydrogen generation

We report here a facile, template-free and one-step solvothermal approach for the synthesis of high-temperature stable gold/titania nanocomposite (NCs), providing a new, simple, quick and inexpensive wet-chemical route. Our approach is based on the assembly of gold salt and titanium butoxide in dimethyl sulfoxide (DMSO). Also, we present here, for the first time, a cathodically activated Au/TiO2 catalyst with Pt/C activity for the hydrogen evolution reaction (HER) in 0.5 M H2SO4 in the dark. The as-prepared (unactivated) Au/TiO2 NCs exhibits considerable electrocatalytic activity for H2 generation in the dark, with a low onset potential (EHER) of −64 mV vs. RHE, a Tafel slope (-bc) of 60 mV dec−1 and an exchange current density (jo) of 0.12 mA cm−2. Long-term stability and durability tests in 0.5 M H2SO4, employing cyclic voltammetry technique (10,000 of repetitive cycling) and 72 h of chronoamperometry measurements at a high cathodic potential (cathodic activation), reveal that the electrocatalyst activates during such aging processes yielding an activated Au/TiO2 catalyst with Pt/C-like activity for H2 generation (EHER -3 mV, -bc: 35 mV dec−1, and jo: 0.95 mA cm−2). The outstanding HER activity of the activated catalyst is discussed.

Photocatalytic activity of hybrid gold-titania nanocomposites

This paper describes a new and straightforward approach for the synthesis of high temperature stable hybrid Au/TiO2 nanocomposites (NCs). This novel approach allows one to produce Au cores decorated with titanium dioxide (TiO2) nanoparticles owing to a modified solvothermal process that makes use of gold salt HAuCl4 and Titanium(IV) butoxide as the gold and titanium precursors, and Dimethyl Sulfoxide (DMSO) as a solvent. The structure and morphology of the Au/TiO2 nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Energy Dispersive X-ray Fluorescence (EDXRF), high-resolution transmission electron microscopy (HRTEM), Raman and photoluminescence spectroscopies. Based on FTIR and TDA/TGA measurements, a proposed mechanism for the formation of Au/TiO2 NCs in DMSO (without adding of any other reagents) is discussed in this contribution. Optical absorption measurement showed that the Au/TiO2 NCs exhibit a UV significant absorption peak clearly blue-shifted with respect to that of bulk TiO2. The produced nanocomposites consist of monodisperse quasi-spherical AuNPs core decorated with TiO2 anatase phase (average size of 11 nm). The hybrid Au/TiO2 NCs exhibit a high thermal stability at higher temperature. The high crystalline quality, together with the easy synthesis process, makes the Au/TiO2 NCs a promising candidate for many applications such as optoelectronics and water photolysis for hydrogen production.

Cage Encapsulated Gold Nanoparticles as Heterogeneous Photocatalyst for Facile and Selective Reduction of Nitroarenes to Azo Compounds.

A discrete nanoscopic organic cage (OC1R) has been synthesized from a phenothiazine based trialdehyde treating with chiral 1,2-cyclohexanediamine building block via dynamic imine bond formation followed by reductive amination. The cage compound has been characterized by several spectroscopic methods, which advocate that OC1R has trigonal prismatic shape formed via [2 + 3] self-assembled imine condensation followed by imine reduction. This newly designed cage has aromatic walls and porous interior decorated with two cyclic thioether and three vicinal diamine moieties suitable for binding gold ions to engineer the controlled nucleation and stabilization of ultrafine gold nanoparticles (AuNPs). The functionalized confined pocket of the cage has been used for the controlled synthesis of AuNPs with narrow size distribution via encapsulation of Au(III) ions. Inductively coupled plasma mass spectrometric (ICP-MS) analysis revealed that the composite Au@OC1R has very high (∼68 wt %) gold loading. In distinction, reduction of gold salts in absence of the cage yielded structureless agglomerates. The fine-dispersed cage anchored AuNPs (Au@OC1R) have been finally used as potential heterogeneous photocatalyst for very facile and selective conversion of nitroarenes to respective azo compounds at ambient temperature in just 2 h reaction time. Exceptional chemical stability and reusability without any agglomeration of AuNPs even after several cycles of use are the potential features of this material. The composite Au@OC1R represents the first example of organic cage supported gold nanoparticles as photocatalyst.

Gold-carbon nanoparticles mediated delivery of BSA: Remarkable robustness and hemocompatibility

There is a tremendous interest in the fabrication of novel hemocompatible nanoparticles for applications in theranostics. In this context, bovine serum albumin (BSA) conjugates with the water-soluble and super robust gold-aryl nanoparticles truncated with carboxylic functionals were synthesized. The gold-aryl nanoparticles were fabricated by the mild reduction of the diazonium gold(III) salt [HOOC-4-C6H4N≡N]AuCl4. The gold core size and the presence of BSA sheath encapsulating Au−COOH nanoparticles were concluded from transmission electron microscopy (TEM). Clear spectral changes supported by quantitative X-ray photoelectron spectrometry (XPS) surface analysis are visible: the C1s/Au4d intensity ratio increased sharply and the gold features were very well attenuated after BSA attachment, which brings more nitrogen essentially due to NH-C = O peptide links. The conjugation of BSA with Au−COOH nanoparticles resulted in the isoelectric point (pI) change from 4.7 to a range of 4.1-5.0. The robustness of the bioconjugates can be concluded based on the high ζ-potential values and the resistance to drastic pH conditions. The high encapsulation efficiency percentage (EE%) calculated using Bradford protein assay was in a range of 90.0–94.6% under physiological pH values. Taken together, overall studies imply the presence of interaction between the Au−COOH nanoparticles and BSA. In this study we investigated the interaction of gold nanoparticles and their BSA conjugates with human red blood cells (RBCs), which might cause cell deformity and hemolysis. To elaborate on the uniqueness of the bioconjugates, they showed negligible hemolysis or morphology deformation to cells membrane visualized using light and phase contrast microscopes. Quantitative measurements of hemoglobin leached out of the cell membrane using UV–vis showed negligible hemolysis. The high physiological stability of the conjugates fosters their applications in intravenous drug delivery supported by the long blood circulation half-life.

Green Synthesis of Gold Nanoparticles using Arabidopsis thaliana and Dunaliella salina Cell Cultures

The ability of the suspension culture of Arabidopsis thaliana cells and Dunaliella salina microalga to reduce gold ions with the formation of nanoparticles is shown. The average diameter of gold nanoparticles obtained using D. salina for synthesis appeared to be less than when using A. thaliana cells: 8 and 25 nm, respectively. Freshly prepared culture media used for growing cells of both dunaliella and arabidopsis did not reduce gold salts with the formation of nanoparticles. After the cells were grown and freed by centrifugation and/or filtration, culture media turned out to be capable of gold reduction.

Sintering-Induced Nucleation and Growth of Noble Metal Nanoparticles for Plasmonic Resonance Ceramic Color

This study demonstrates the formation of nanoparticles (NPs) from metal salts within ceramic glazes, such that the use of this colorant technology is more accessible to artisans, employs less metal content, is less environmentally harmful, and allows for the use of traditional kilns. Gold NPs have been demonstrated to possess a specific, low material loading use as a ceramic glaze colorant via plasmon resonance. Pre-synthesized gold NPs that are added to ceramic glazes have been found to significantly change in size after firing in both reductive and oxidative atmospheres, but still maintain some size relationships and color properties. Unfortunately, it is not viable for the art community to fabricate and employ gold NP systems with high precision in a studio setting; however, the use of noble metal salts or metal oxides are realistic. To that end, this work investigates spontaneous gold and silver NP synthesis by the firing-induced development of NPs from metallic salts included within the glaze materials. Glaze samples with gold and silver salts are fired in reductive and oxidative environments, yielding a range of surface plasmon coloring effects for ceramic coloring. Additionally, the use of gold NP waste (precipitated Au NPs waste) was added to wet ceramic glazes to investigate firing effects on NPs precipitate and potential use as an alternative colorant. Sintering-induced NP nucleation and growth was observed after firing in both oxidation and reduction environments, although to differing degrees. The direct noble metal salt application process eliminates the need for preliminary gold NP synthesis, thus allowing for more practical and environmentally friendly methods in creating plasmonic resonance ceramic coloring, potentially reflective of the processes employed in ancient nanoparticle glasses.

Plasmonic Effects, Size and Biological Activity Relationship of Au-Ag Alloy Nanoparticles

The plasmonic effects of Au-Ag alloy nanoparticles, gold nanoparticles (AuNPs), and silver nanoparticles (AgNPs) are studied and compared to their size. Various factors that affect the size of alloy nanoparticles are varied such as concentration and ratio of gold and silver salt, time of addition of reducing agent, temperature and pH. Addition of reducing agent at different time intervals for the synthesis of pure and alloy Au-Ag NPs shows a gradual increase in size, as well as increase in heterogeneity of nanoparticles with delayed addition of reducing agent. Temperature dependent alloy nanoparticles also shows a gradual increase in size with increase in temperature. pH dependent alloy nanoparticles show decrease in size with increase in pH from 4 to 8. Their size is characterized by SEM and corelated with UV-Vis spectroscopy. Furthermore, alloy nanoparticles synthesized by varying temperature are also characterized for their antibacterial studies against Escherichia coli and Staphylococcus aureus strains. Nanoparticles synthesized at high temperature (100°C) have shown higher bioactivity against both organisms due to small and uniform size nanoparticles, while nanoparticles synthesized at lower temperature (50°C) have lower biological activity. Alloy nanoparticles synthesized at 60°C and 70°C are more active against E. coli while those of 80°C and 90°C are more active against S. aureus.

Modelling study on heated couple stress fluid peristaltically conveying gold nanoparticles through coaxial tubes: A remedy for gland tumors and arthritis

This paper represents an innovative technique to cure some of the fatal diseases such as rheumatoid arthritis and tumors by injected nano-size gold particles (gold salt in the veins through a hotted slim tube. In the proposed model large atomic number enables gold particles in attaining further heat and conveys medicine to the effected organs and erodes malign tissues or cells. The couple stress fluid is treated as blood inside the two coaxial tubes containing nanoparticles. The inner tube is considered to be rigid in configuration while the outer is elastic or flexible to eventuate a sinusoidal wave once the fluid passes within the gap of tubes. A set of nonlinear and coupled mathematical equations governing the flow model has been converted into a system of ordinary differential equations using suitable transformations prior to seeking an analytical solutions. A comprehensive parametric study has also been made to make the presented analysis more realistic to ensure that the presented study adheres with the physical phenomenon. Effects of velocity, temperature and concentration of the particles are examined corresponding to variate physical parameters contributing in the flow. Besides, highlighting graphically, the impact of each sundry parameters has been explained in detail at the end. It is worth mentioning that the results for Newtonian fluid can be obtained from the reported results by taking couple stress parameter is zero.

PRIMITIVE TECHNIQUES: FROM ‘CUSTOMARY’ TO ‘ARTISANAL’ MINING IN FRENCH WEST AFRICA

AbstractSince the commodity boom of the early 2000s, the visibility of ‘artisanal’ or ‘small-scale’ mining has grown in media coverage and development policies focused on Africa. This article argues that the regulatory category of ‘artisanal’ mining in Africa originated during the colonial period as ‘customary mining’. I build this case through a regional case study of mining policies in the colonial federation of French West Africa, where a single decree accorded African subjects ‘customary rights’ to seasonally mine gold and rock salt in restricted areas. By contrast, colonial citizens, mostly Europeans, accessed stable mining titles. Customary mining rights never codified actual African mining ‘customs’, as colonial officials argued. Rather, this law marked the boundary between the technological status of French subjects and citizens. Core elements of this colonial legal framework have been incorporated into postcolonial policies governing the rights of citizens to mineral resources in Africa.

Synthesis of gold-coated CoFe2O4 and their potential in magnetic hyperthermia

CoFe2O4 nanoparticles (CFO) were synthesized via co-precipitation method and then gold coating (Au@CFO) was carried out by direct reduction of gold salt using citric acid and sodium citrate. Au coating was systematically observed by UV–Vis spectroscopy and afterwards confirmed by scanning electron microscopy, energy dispersive X-ray spectroscopy and Fourier-transform infrared spectroscopy. Gel electrophoresis was used to check the dispersive stability of Au@CFO dispersion which showed no agglomeration and indicated uniform size distribution. Magnetic characteristics before and after coating were studied via hysteresis loops which indicated reduction in magnetization of CFO after Au coating. Radio frequency (RF) heating measurements were done on powder and dispersed samples to evaluate their magnetic heating. Specific loss power was calculated from RF heating, which was greater for powdered samples than the dispersion of Au@CFO nanoparticles, but temperature can be controlled to reach the therapeutic range with respect to time and concentration.

Effects of Different Glide Path Files on Apical Debris Extrusion in Curved Root Canals

IntroductionCreating a glide path before root canal preparation with nickel-titanium rotary files is essential to prevent the file fracture and to maintain the original root canal configuration. Both rotary glide path files and manual K-files are used to create a glide path. The aim of this study was to compare the amount of apically extruded debris after using different glide path files before preparing curved root canals with the WaveOne Gold single-file reciprocating system (Dentsply Maillefer, Ballaigues, Switzerland). MethodsSixty extracted mandibular first molar teeth with curved mesial roots were selected for this study. The mesial roots of the teeth were removed from the cementoenamel junction. Cone-beam computed tomographic imaging was used to evaluate the curvature of the mesial root canals. Specimens were randomly divided into 6 experimental groups according to the root canal preparation (n = 10): group G-File, a glide path with G-Files (Micro-Mega, Besancon, France) + WaveOne Gold preparation; group One G, a glide path with One G (Micro-Mega, Besancon, France) + WaveOne Gold preparation; group ProGlider, a glide path with ProGlider (Dentsply Maillefer) + WaveOne Gold preparation; group PathFile, a glide path with PathFiles (Dentsply Maillefer) + WaveOne Gold; group K-files, a glide path with a K-file + WaveOne Gold preparation; and group without a glide path, WaveOne Gold preparation without a glide path file. Roots were attached to preweighed Eppendorf tubes. All instruments were used according to the manufacturers' instructions. During root canal preparation, a total of 8 mL distilled water was used for each specimen. Apically extruded debris was collected in Eppendorf tubes. After the completion of root canal preparation, Eppendorf tubes were removed from the specimens and stored in an incubator at 68°C for 5 days. Eppendorf tubes were weighed after evaporation to calculate the amount of extruded debris. The data were statistically analyzed with 1-way analysis of variance and post hoc Tukey honest significant difference tests (P = .05). ResultsA statistically significant difference was observed between the One G and K-File groups. The One G group was associated with significantly less debris extrusion than the K-file group. There was no statistically significant difference between K-files and ProGlider, G-Files, PathFiles, and WaveOne Gold without a glide path, and also there was no statistically significant difference between One G and ProGlider, G-Files, PathFiles, and WaveOne Gold without a glide path. All experimental groups caused apical debris extrusion. ConclusionsUnder the conditions of this in vitro study, all rotary path file systems were associated with similar apical debris extrusion before preparing root canals with the WaveOne Gold single-file reciprocating system. K-files caused more apically extruded debris than the One G files.

Biocompatible Gold Nanoparticles Ameliorate Retinoic Acid-Induced Cell Death and Induce Differentiation in F9 Teratocarcinoma Stem Cells.

The unique properties of gold nanoparticles (AuNPs) have attracted much interest for a range of applications, including biomedical applications in the cosmetic industry. The current study assessed the anti-oxidative effect of AuNPs against retinoic acid (RA)-induced loss of cell viability; cell proliferation; expression of oxidative and anti-oxidative stress markers, pro- and anti-apoptotic genes, and differentiation markers; and mitochondrial dysfunction in F9 teratocarcinoma stem cells. AuNPs were prepared by reduction of gold salts using luteolin as a reducing and stabilizing agent. The prepared AuNPs were spherical in shape with an average diameter of 18 nm. F9 cells exposed to various concentrations of these AuNPs were not harmed, whereas cells exposed to RA exhibited a dose-dependent change in cell viability and cell proliferation. The RA-mediated toxicity was associated with increased leakage of lactate dehydrogenase, reactive oxygen species, increased levels of malondialdehyde and nitric oxide, loss of mitochondrial membrane potential, and a reduced level of ATP. Finally, RA increased the level of pro-apoptotic gene expression and decreased the expression of anti-apoptotic genes. Interestingly, the toxic effect of RA appeared to be decreased in cells treated with RA in the presence of AuNPs, which was coincident with the increased levels of anti-oxidant markers including thioredoxin, glutathione peroxidases, glutathione, glutathione disulfide, catalase, and superoxide dismutase. Concomitantly, AuNPs ameliorated the apoptotic response by decreasing the mRNA expression of p53, p21, Bax, Bak, caspase-3, caspase-9, and increasing the expressions of Bcl-2 and Bcl-Xl. Interestingly, AuNPs not only ameliorated oxidative stress but also induced differentiation in F9 cells by increasing the expression of differentiation markers including retinoic acid binding protein, laminin 1, collagen type IV, and Gata 6 and decreasing the expressions of markers of stem cell pluripotency including Nanog, Rex1, octamer-binding transcription factor 4, and Sox-2. These consistent cellular and biochemical data suggest that AuNPs could ameliorate RA-induced cell death and facilitate F9 cell differentiation. AuNPs could be suitable therapeutic agents for the treatment of oxidative stress-related diseases such as atherosclerosis, cancer, diabetes, rheumatoid arthritis, and neurodegenerative diseases.

Development of Colloidal Gold-Based Immunochromatographic Assay for Rapid Detection of Goose Parvovirus.

Goose parvovirus (GPV) remains as a worldwide problem in goose industry. For this reason, it is necessary to develop a new diagnostic approach that is easier and faster than conventional tests. A rapid immunochromatographic assay based on antibody colloidal gold nanoparticles specific to GPV was developed for the detection of GPV in goose allantoic fluid and supernatant of tissue homogenate. The monoclonal antibodies (Mab) was produced by immunizing the BALB/c mice with purified GPV suspension, and the polyclonal antibody (pAb) was produced by immunizing the rabbits with recombinant VP3 protein. The colloidal gold was prepared by the reduction of gold salt with sodium citrate coupled with Mab against GPV. The optimal concentrations of the coating antibody and capture antibody were determined to be 1.6 mg/ml and 9 μg/ml. With visual observation, the lower limit was found to be around 1.2 μg/ml. Common diseases of goose were tested to evaluate the specificity of the immune colloidal gold (ICG) strip, and no cross-reaction was observed. The clinical detection was examined by carrying out the ICG strip test with 92 samples and comparing the results of these tests with those obtained via agar diffusion test and polymerase chain reaction (PCR) test. Therefore, the ICG strip test was a sufficiently sensitive and accurate detection method for a rapid screening of GPV.

Capping of supramolecular curcubit[7]uril facilitates formation of Au nanorods during pre-reduction by curcumin

Curcumin being biologically available and non-toxic natural compound is an attractive and alternative green reagent for the reduction of gold salts to elemental gold. Here, we bring new insight that shape and size of the Au nanoparticles (NPs) can be tuned by using curcumin in combination with supramolecular host molecule such as curcubit[7]uril (CB[7]) as stabilizing agent. It is found that AuNPs prepared using curcumin alone in aqueous environment gives spherical and smaller size, 10–20 nm, particles with its surface Plasmon resonance peak at ∼536 nm. At the same time when CB[7] is used as a capping agent along with curcumin, larger size NPs and at higher concentration (∼50 μM) of CB[7] Au nanorods (NRs) are formed with a broad surface Plasmon resonance spectrum peaked at ∼610 nm. Thus, CB[7] at higher concentration ultimately helps to form Au NRs. Formation of AuNPs and AuNRs has been confirmed by XRD and conjugation of CB[7] and curcumin is established by FT-IR and TGA data. However, these particles aggregate in solution to form particles between 200 nm and 300 nm with a polydispersity of 0.25 as observed in DLS. Zeta potential measurement indicates formation of stable nanoparticles/nanorods without further precipitation within time. Kinetic study shows that the half-life for the formation of AuNP/NRs is ∼36 min, whereas degradation of curcumin during synthesis has a half-life of ∼10 min, this discrepancy suggests some amount of curcumin degrades on its own during this process besides acting as reducing agent.

Natural Triterpenoid-Tailored Phosphate: In Situ Reduction of Heavy Metals Spontaneously to Generate Electrochemical Hybrid Gels.

In this work, we reported a biocompatible nature product-based soft material which could convert heavy metals to nanoparticles (NPs) in situ spontaneously in a simple step. We have designed and synthesized a natural triterpenoid-tailored phosphate (methyl glycyrrhetate phosphate (MGP)), and this amphiphilic MGP could form the stable hydrogel and extract gold salt from water, followed by spontaneous in situ AuNP formation without external reductants. Notably, the AuNPs were mainly localized on nanofibers instead of gel cavities, and the resulting MGP-AuNPs hybrid gel exhibited attractive electrocatalytic and conductive properties. In addition, as an efficient leaching extraction agent, MGP hydrogel showed higher affinity toward heavy metals over other common metals on account of the high reduction potential of heavy metals. Our work not only provides a novel yet simple way in generating electrochemical hybrid gels by in situ reduction of heavy metals spontaneously but also expands the application of nature product-based functional materials.

(Keynote) Surfactant and Halide Control in Gold Nanorod Synthesis

Gold nanorods have been of continuing interest to many scientists due to their brilliant optical properties that are dictated by particle shape. Nanorods exhibit both transverse and longitudinal plasmon bands that are tunable from the visible into the near-infrared. Applications areas include plasmon-based sensors, diagnostics, imaging agents, and even photothermal therapeutics due to reasonably efficient light-to-heat conversion. The primary synthesis of these materials starts with a gold salt, and various reduction steps with various reducing agents, in the presence of particular surfactants and ions, do produce gold nanorods of tunable aspect ratio; yet the details of the synthetic steps and the "true" source of the symmetry-breaking anisotropy to produce rods instead of spheres are still the subject of debate. In this talk we will examine the state of the art in gold nanorod synthesis, including recent work that used a design-of-experiment multifactorial approach to gain deeper mechanistic insights into synergistic effects between the various reagents in the synthesis.

Preparation, Modification, Characterization, and Biosensing Application of Nanoporous Gold Using Electrochemical Techniques.

Nanoporous gold (np-Au), because of its high surface area-to-volume ratio, excellent conductivity, chemical inertness, physical stability, biocompatibility, easily tunable pores, and plasmonic properties, has attracted much interested in the field of nanotechnology. It has promising applications in the fields of catalysis, bio/chemical sensing, drug delivery, biomolecules separation and purification, fuel cell development, surface-chemistry-driven actuation, and supercapacitor design. Many chemical and electrochemical procedures are known for the preparation of np-Au. Recently, researchers are focusing on easier and controlled ways to tune the pores and ligaments size of np-Au for its use in different applications. Electrochemical methods have good control over fine-tuning pore and ligament sizes. The np-Au electrodes that are prepared using electrochemical techniques are robust and are easier to handle for their use in electrochemical biosensing. Here, we review different electrochemical strategies for the preparation, post-modification, and characterization of np-Au along with the synergistic use of both electrochemistry and np-Au for applications in biosensing.

Preparation and length control of water-dispersible ultrathin gold and silver bimetallic nanowires

Ultrathin nanowires are very attractive because they have unique catalytic and optical properties. Ultrathin nanowires are generally prepared in organic solvents; hence, the preparation of water-dispersible ultrathin nanowires is necessary in order to expand their areas of application. Furthermore, bimetallic nanocrystals are emerging as a new class of material. Herein, we report the preparation of water-dispersible Au–Ag bimetallic ultrathin nanowires by the orient-attachment method using a long-chain amine (C18AA) as the capping agent. These nanowires have an average diameter of 2 nm and lengths of a few micrometers; these lengths are controlled within the nanometer-to-micrometer range by adjusting the [C18AA]/[Au+Ag] molar ratio. In addition, these ultrathin nanowires exhibit a surface-plasmon band in the infrared region.

Synthesis, spectroscopic characterization, crystal structure determination and DFT calculations of [Au(Me2phen)Br2][AuBr2

New mixed valence gold(III/I) salt containing two complexes [Au(Me2phen)Br2][AuBr2] (1) was prepared from the reaction of AuBr3 and 5,6-dimethyl-1,10-phenanthroline (Me2phen) in a mixture of methanol and acetonitrile. Suitable crystals of 1 for X-ray diffraction measurement were obtained by slow evaporation of the resulted red solution at room temperature. This complex was characterized by spectral methods (IR, UV–Vis and 1H NMR), elemental analysis and single-crystal X-ray diffraction. The X-ray structural analysis indicated that the asymmetric unit of 1 contains one [Au(Me2phen)Br2]+ cation and two half anions of [AuBr2]ˉ. Furthermore, the packing diagram of this complex, 3-D structure stabilized by intermolecular Au…Br and Au…π interactions and intermolecular C–H···Br hydrogen bonds. The experimental investigations on complex have been accompanied computationally by the density functional theory (DFT) and time-dependent DFT calculations. The nature of the Au–N bonds was investigated using quantum theory of atoms in molecules. Moreover, natural bond orbital analysis carried out to obtain hyper-conjugative interactions and electron delocalization on the complex.