Gold Bulletin最新文献

The color of fine gold shows paradoxical variations that have tentatively been explained by metallurgic factors. Measurements and digital photographs show a significantly redder color than predicted by theory. A novel purely optical explanation based on the multiple reflection in grooves is suggested. The analysis in the colorimetric space RGB of the photographs of several fine gold samples and coins confirms that the gold red shift comes from minute grooves that seem black but that in fact have an extremely dark orange/red color.

In this work, we proposed one simple and effective chiral-sensing method for the discrimination of carnitine enantiomers. The gold nanorods (AuNRs) were used as colorimetric probes to recognize carnitine enantiomers in this method. l-Carnitine can induce rapidly the blue-to-gray change of AuNR solution color, whereas d-carnitine cannot induce the obvious change of the color. Based on this distinct difference of color, a visual method for recognition of carnitine enantiomers was suggested. This method has been applied to detect the enantiometric excess of l-carnitine in the range of ??100~100%. The presented chiral measurement can be performed with a simple ultraviolet-visible spectrometer and even the naked eyes. In this method, AuNRs need no modification with chiral molecule, and the chiral recognition is based on the inherent chirality of AuNRs. This new method opens up possibility for fast and easy assay of carnitine enantiomers.

This report provides a method to estimate how much the photocurrents can be increased by adding gold nanoparticles in P3HT:PCBM films, without having to carry out the complex process of fabricate a whole cell. The tuning effect of varying the gold nanoparticle concentration on optical properties of these films was analyzed by measuring optical absorption. To estimate the contribution of the optical absorption variation, theoretical photocurrents generated for these films as active layers were calculated using a photonic flux density equation. With this methodology, it is possible to estimate the amount of energy that can be harvest with a given gold nanoparticle concentration. Improvements up to 26% were obtained compared with films without added gold nanoparticles.

The aim of this research was to describe a facile protocol to obtain biocompatible gold nanoparticles (AuNPs) suitable for microbial optical sensing. For this purpose, polycationic poly-L-lysine (PLL) was employed as both reducing and stabilizing agent in order to obtain an optically active microbial nanotag based on the electrostatic interaction with negatively charged cell envelopes. A one-pot procedure was developed to produce homogeneous, positively charged AuNPs. The as-synthesized particles, named PLL@AuNPs, exhibited maximal surface plasmon resonance (SPR) at 532 nm, a FCC crystalline nature, and sizes ranging from 20 to 25 nm, according to spectroscopy, X-ray diffractometry (XRD), transmission electron microscopy (TEM), and dynamic light scattering (DLS) analyses. The reduction of gold ions by PLL was featured by Fourier-transform infrared (FTIR) absorption bands of various functional groups. Zeta potential analysis confirmed the high cationic feature with a value of + 57 mV. The applicability of the particles to tag bacterial cell surfaces was exemplified by their adherence to Escherichia coli, a bacterial species commonly used to monitor fecal pollution in water sources. Finally, the potential of this tagging approach for microbial sensing through surface-enhanced Raman scattering (SERS) was explored.

One-step laser-assisted fabrication of elongated Au nanoparticles (NPs) and their subsequent fragmentation and agglomeration are experimentally studied. The generation of elongated Au NPs is carried out via laser ablation of a solid Au target in water using an ytterbium-doped fiber laser source with pulse duration of 200?ns and pulse energy of 1?mJ. Extinction spectrum of the resulting particles exhibits an increase in the absorption in visible red and near IR spectral regions. This change in absorption is accounted for by the longitudinal plasmon resonance of the electrons in elongated Au NPs and is corroborated by the TEM images. The effect of additional laser exposure on the elongated Au NPs produced using this method is studied, as well. Laser pulse energies and exposure times are varied. Possible processes of laser-assisted formation of elongated Au NPs in aqueous solutions of calcium chloride and magnesium sulfate and their following interaction with pulsed laser radiation are discussed.

The purpose of this study was to evaluate the possible synergistic effect of gold nano-therapy (Au-NPs) on Y79 cells treated with ultrasonic hyperthermia. The cells in the presence and absence of gold nanoparticles were subjected to ultrasonic irradiation (3?MHz, 1?W/cm², 40% pulse mode). Gold nanoparticles with an average diameter of 60?nm were synthesized. The cell viability of the Y79 cells was evaluated 48?h after performing 0.5–11?min hyperthermia with and without Au-NPs using the MTT assay. There was no cytotoxicity with 1.7?μg/mL Au-NP concentration. Moreover, the results revealed a significant difference in the cell viability between the control group and the groups with a hyperthermia period of more than 4?min. The results indicated that with increasing the concentration of Au-NPs (1.75, 3.5, 7, 14, 28 and 56?μg/mL), the cytotoxicity increased. The Y79 cell viability of 50% was caused for 9?min hyperthermia time alone and 4.5?min hyperthermia time in the presence of gold nanoparticles. The cell viability of the Y79 cells for a 0.5 to 11?min hyperthermia time, compared with the control group, was 93 to 27% and 95 to 32% with and without Au-NPs, respectively. It is concluded that the cells are more sensitive to hyperthermia induced by ultrasound irradiation in the presence of Au-NPs.

In the present work, sulfur-doped carbon nanotubes (SCNTs) have been prepared using chemical vapor deposition method and various cobalt-containing catalysts. In this line, simple and silica-supported cobalt nanoparticles (Co and Co/SiO₂) and 5 cobalt spinels (MCo₂O₄, M?=?Ni, Cu, Mn, Fe, Cr, and Mg) were used as the growth catalysts and four different temperatures (600, 650, 700, and 750?°C) were used to obtain the optimized condition for the preparation of SCNTs. Among the employed catalysts, Co/SiO₂ at 600?°C showed the higher abilities for the preparation of desired SCNTs. All products were characterized using FESEM, EDS, XRD, Raman, static contact angle, TGA, and DTA analyzes. The electrochemical behaviors of the two best products (SCNTs-Co/SiO₂ and SCNTs-Co) in hydrogen evolution reaction (HER) were examined, which confirmed the higher ability of SCNTs-Co/SiO₂. This best product was decorated with 2, 5, and 10% of gold nanoparticles to examine the effect of gold decoration of the properties and electrochemical abilities of the product. All decorated products exposure the higher electrochemical potencies versus the simple SCNTs and among the decorated products, 10% Au-SCNT was the most appropriate product for this purpose with small differences with the other ones.

Gold, used for jewelry and ornaments at times, is now considered a safe metal for investment. In addition to buying and selling gold physically, some markets offer electronic trade in gold. Trade volume is on surge in these bullion markets with each passing day. Daily opening and closing gold prices are used for analysis for 7740?days. Data series of daily return on investment in gold is split into two data series; first when the price goes up and second when the price goes down, at the day’s end. Statistical properties of three data series are analyzed and probabilities to earn profits are calculated during any day regardless of what types of decisions are going to be made that day. Probabilities of daily return, for both long and short positions, are presented in the form of tables. The expected daily profit of a trader with associated probability is explained in an illustrative example.

Gold nanoparticle thin films were deposited on copper substrate using electrophoretic deposition (EPD) method. At first, gold nanoparticles were synthesized, using pulsed laser ablation method of a high-purity gold target in distilled water. Ablation was carried out, employing the fundamental wavelength of a Q-switched Nd:YAG laser at 1064?nm and pulse width of 7?ns. Suspension of gold nanoparticle was used as the electrolyte of EPD, in which two copper electrodes with 7?mm gap were immersed. Five samples of gold nanoparticle thin films were prepared at different deposition times and applied voltages. Nanoparticles and thin films were characterized by different diagnostics such as X-ray diffraction pattern, atomic force microscopy (AFM), and scanning electron microscopy (SEM) images as well as optical spectroscopy. XRD pattern determined crystalline structure of gold thin films. SEM image showed the effect of deposition time and applied voltage on the morphology of deposited films. AFM results demonstrated the variations in roughness, thickness, and surface quality due to changes in applied voltage and deposition time. Also, the optical properties of thin films were studied by UV-vis reflection spectroscopy.