Gold Bulletin最新文献

A facile approach is proposed for the stabilization of gold nanoparticles within alumina matrix based on fast coprecipitation of colloidal gold and alumina sol in the supercritical carbon dioxide used as antisolvent. Acetylacetone was used as a stabilizer agent for the synthesis of alumina sol. Gold nanoparticles were synthesized from HAuCl₄ directly in liquid alumina sol in reaction with acetylacetone. Acetylacetone played the role of both a stabilizer agent for gold nanoparticles and a reducing agent. Obtained system is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), infrared (IR) spectroscopy, and UV–Vis adsorption spectroscopy. The method allows us to synthesize aerogel-like alumina highly loaded with gold nanoparticles firmly fixed on oxide surface and uniformly distributed within alumina matrix. The proposed approach combines sol-gel and supercritical fluid methods for the synthesis and opens the wide prospects for preparation composites consisting of gold nanoparticles in oxide matrix with a uniform distribution. These gold-bearing systems may be of interest to a wide range of applications.

Herein, a simple method for etching Au_nanorods@SiO₂ surface to obtain Au_nanorods@B-SiO₂ material is reported, which is used for the theoretical study of drug loading and release of composite materials by microcalorimetry. In the presence of surfactant cetyltrime-thylammonium bromide (CTAB), the Au_nanorods@SiO₂ is etched under the strong acid environment with pH of about 2 to obtain the ideal material Au_nanorods@B-SiO₂. Relevant experimental results show that after etching, Au_nanorods@B-SiO₂ still retains the morphology, structure, and composition of a single material, and its LSPR absorption is almost consistent with Au nanorods. The successful preparation of Au_nanorods@B-SiO₂ combines the properties of Au nanorods and silicon dioxide to provide a basic material for medical cancer diagnosis and treatment.

In the past few decades, there have been remarkable advances in our knowledge of gold nanoparticles (AuNPs) and synthesizing methods. AuNPs have become increasingly important in biomedical and industrial applications. As a newly implemented method, AuNPs are being used in nanopackaging industries for their therapeutic and antibacterial characteristics as well as their inert and nontoxic nature. As with other NPs, AuNPs have privileges and disadvantages when utilized in the food sector, yet a significant body of research has shown that, due to the specific nontoxic characteristics, AuNPs could be used to address other NP flaws. In this mini review, we present synthesizing methods, food industry applications, and mechanisms of action of gold nanoparticles. Regarding the investigations, gold nanoparticles can play a major role to reduce microbial load in foodstuff and therefore can be implemented in food packaging as an effective approach.

Understanding the various structures of gold clusters and the interaction modes between Au clusters and biomolecules is an important issue in material science such as biosensors and catalysts. The binding of small gold clusters (Au_n n?=?2–5) with neutral and anionic forms of arginine (Arg) amino acid is investigated in this study using density functional theory (DFT) and B3LYP level. The relative stability among different forms of Au clusters including linear, zigzag, planar, and three-dimensional Au clusters was estimated, initially. The calculated findings show that the zigzag structure for Au₃ and the planar structure for Au₄ and Au₅ are the best form. Furthermore, the different modes of interaction were taken into account from thermodynamic view point between the most stable conformers of Arg and Arg^? with gold clusters. Finally, the arginine is considered as a weak organic acid to investigate the impact of Au clusters on the gas phase acidity. The acidity of isolated arginine and the acidity of [Au_n/Arg] complexes were also compared. Based on the obtained results, upon the complexation with Au clusters at 298?K, for the interaction of Au, Au₂, Au₃, Au₄, and Au₅ clusters with arginine, the gas phase acidity (GPA) of arginine alters from 342.12 to 314.17, 303.04, 299.42, 303.41, and 331.66?kcal/mol respectively. These calculated values predict that when a weak organic acid is complexed with Au clusters, it will be altered to super acid. Furthermore, for isolated and complexed species of Arg, pK_a values were evaluated in water solvent.

Stable solutions of gold nanoparticles with an average diameter of 13 nm and C_Au = 5×10^–4 M were obtained by the reduction of HAuCl₄ with an equivalent amount of sodium sulfite at 80–100 °C in the presence of 2% PEG 6000 as a stabilizer: AuCl₄^– + 3/2 SO₃^2– + 3/2 H₂O → Au⁰ + 3/2 SO₄^2– + 3 H⁺ + 4 Cl^–. The resulting solutions of nanoparticles do not contain additional components capable of complexation, redox, and acid-based interactions. The effect of additives of thiourea, cysteine, thiomalate, and glutathione at various pH on the stability of such solutions to the aggregation has been studied. It was shown that the values of the protonation constants and charges of species of a thiol-containing component are not the only factors determining stability. Using thiomalate (HTM^2–) as an example, it was shown also that at pH 7–8, the chemisorption is not followed by the release of H⁺ ions into the solution.

The paper reports a simple enzyme-free colorimetric sensor for the detection of cardiac marker, Troponin I (cTnI) based on the self-assembly of gold nanorods (AuNRs) on heparin. The sensing system consists of a purple colour solution of Hexadecyltrimethylammonium bromide (CTAB) stabilised AuNRs self-assembled in presence of heparin due to the electrostatic interaction resulting in the reduction of surface plasmon absorption (SPR) of AuNRs and hence colour quenching/change of solution from red to blue. However, in the presence of cTnI, the electrostatic balance was disturbed due to the strong complex forming tendency between heparin and cTnI which was attributed due to the stronger complex forming tendency between the sulphate and carboxylate group of glycosaminoglycans and heparin binding proteins present in cTnI. Hence, the AuNRs are left free in the solution and retains the native red colour of the solution. As the concentration of cTnI in the solution was increased, the colour gradually changes from blue to red there by enabling the sensing of cTnI. The above mechanisms were confirmed by transmission electron microscopy. The AuNR aggregation was found to be inversely proportional to the concentration of cTnI. The change in absorbance of AuNRs with different concentrations of cTnI was monitored by UV-Visible spectroscopy. Using this sensor system, cTnI in the range of 0.5–15 ng/mL could be measured with a detection limit of 0.4 ng/mL. The system also showed good selectivity in presence of different competing substances under the same experimental conditions. The method appears to be simple, cost effective, and would be highly be beneficial in rural health care centres where high tech diagnostic aids are inaccessible.

This article reports a simple one-step method for anisotropic gold nanoparticle synthesis for plasmonic photothermal therapy medical purposes, using 1,4-bis[(2-ethylhexyl) oxy]-1,4-dioxo-2-butanesulfonic acid-sodium (AOT) reverse micelles as nanoreactor, where under specific condition, AOT acts as both a reducing and stabilizing agent. Obtained AuNPs were functionalized by attaching compounds derived from 2-aminopteridin-4(3H)-ona (pterin family) such as (2S)-2-[(4-{[(2-amino-4-hydroxypteridin-6-yl) methyl] amino} phenyl) formamido] pentanedioic acid (folic acid/FA) and 2-amino-4-hydroxypteridine-6-carboxylic acid (PCA) in order to evaluate its effect as targets for folate receptor-mediated cellular uptake in HeLa and normal human endocervical cells. The nanoconjugates were characterized through transmission electron microscopy (TEM), ultraviolet-visible, fluorescence, and Fourier transform infrared spectroscopies. Results showed an effective photothermal response of AuNPs in solution under NIR exposure with concentration dependence and none effect of the conjugation. In vitro studies in HeLa cells showed a concentration-dependent cytotoxicity of AuNPs; thus, conjugation to biomolecules such as FA or PCA has provided a biocompatible coating onto AuNPs and made them highly cytocompatible. Results demonstrated despite AF and PCA are analogue molecules, the folate receptors in HeLa cells are specific, and the different chemical groups available on the AuNPs surface have drastically different cell membrane penetration properties. The specific cell uptake through folate receptor (FR) was observed for short treatment time, while for a long treatment time, other mechanisms as penetration or adhesion were shown involved. In the particular case, of AF@AuNPs, the cell uptake through FR-mediated endocytosis was evidenced to have been decreasing cell viability in 24% after 2 h of treatment and 5 min under NIR exposure. This was confirmed by morphological changes in cells, as well the selective uptake of the FA@AuNPs by HeLa cells compared to normal cells, due folate receptor overexpression in HeLa cells. The findings from this study will have implications in the chemical design of nanostructures for plasmonic photothermal therapy. The obtained results provide evidences at in vitro level to support the fact that AF@AuNP nanoconjugate will accumulate in the affected tissue preferentially through the EPR (enhanced permeability and retention) effect by folate-targeting mechanism which will significantly enhance the efficacy of NIR-induced local photothermal effects.

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.