Gold Bulletin最新文献

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.

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.