Reduction Of Tetrachloroauric Acid Research Articles

Improvement of Seed-Mediated Growth of Gold Nanoparticle Labels for DNA Membrane-Based Assays.

Gold nanoparticles (AuNPs) are popular labels for colorimetric detection of various analytes, involving proteins, nucleic acids, viruses, and whole cells because of their outstanding optical properties, inertness, and modification variability. In this work, we present an improved approach for enhancement of color intensity for DNA membrane microarrays based on seed-mediated growth of AuNP labels. Biotin-labeled DNA is hybridized with capture oligonucleotide probes immobilized on the microarrays. Then biotin is revealed by a streptavidin-AuNP conjugate followed by the detection of AuNPs. Optimization of seed-mediated enlargement of AuNPs by the reduction of tetrachloroauric acid with hydroxylamine made it possible to change the coloring of specific spots on the microarrays from pink to a more contrasting black with minor background staining. Mean size of the resulting AuNPs was four times larger than before the enhancement. Adjusting the pH of HAuCl4 solution to 3.5 and use of a large excess of hydroxylamine increased the signal/background ratio by several times. The method's applicability was demonstrated for quantification of a short oligonucleotide of 19 bases and full-length TEM-type β-lactamase genes of 860 bp responsible for the development of bacterial resistance against β-lactam antibiotics. Improved protocol for AuNP enlargement may be further transferred to any other membrane-based assays of nucleic acids with both instrumental and visual colorimetric detection.

In Situ Assembly of Gold Nanoparticles in the Presence of Poly-DADMAC Resulting in Hierarchical and Highly Fractal Nanostructures

The presence of the polycationic macromolecule poly(diallyldimethylammonium chloride) (poly-DADMAC) has a strong effect on the shape and size of colloidal gold nanoparticles formed by the reduction of tetrachloroauric acid with ascorbic acid in aqueous solution. It slows down nanoparticle growth and supports the formation of nonspherical, partially highly fractal and hierarchical nanoparticle shapes. Four structural levels have been recognized from the near-spherical gold nanoparticles in the lower nanometer range over compact aggregates in the midnanometer range and flower and star-like particles in the submicron range up to larger filamentous aggregates. High-contrast scanning electron microscope (SEM) images show that single gold nanoparticles and clusters of them are connected by bundles of macromolecules in large aggregates. The investigation showed that a large spectrum of different nanoparticle shapes and sizes can be accessed by tuning the poly-DADMAC concentrations and their ratio to other reactants. The nanoassemblies with a very high specific surface area might be of interest for SERS and heterogeneous catalysis.

Ultrasmall gold and silver/gold nanoparticles (2\u2009nm) as autofluorescent labels for poly(D,L-lactide-co-glycolide) nanoparticles (140\u2009nm)

Ultrasmall metallic nanoparticles show an efficient autofluorescence after excitation in the UV region, combined with a low degree of fluorescent bleaching. Thus, they can be used as fluorescent labels for polymer nanoparticles which are frequently used for drug delivery. A versatile water-in-oil-in-water emulsion-evaporation method was developed to load poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles with autofluorescent ultrasmall gold and silver/gold nanoparticles (diameter 2 nm). The metallic nanoparticles were prepared by reduction of tetrachloroauric acid with sodium borohydride and colloidally stabilised with 11-mercaptoundecanoic acid. They were characterised by UV–Vis and fluorescence spectroscopy, showing a large Stokes shift of about 370 nm with excitation maxima at 250/270 nm and emission maxima at 620/640 nm for gold and silver/gold nanoparticles, respectively. The labelled PLGA nanoparticles (140 nm) were characterised by dynamic light scattering (DLS), scanning electron microscopy (SEM), and UV–Vis and fluorescence spectroscopy. Their uptake by HeLa cells was followed by confocal laser scanning microscopy. The metallic nanoparticles remained inside the PLGA particle after cellular uptake, demonstrating the efficient encapsulation and the applicability to label the polymer nanoparticle. In terms of fluorescence, the metallic nanoparticles were comparable to fluorescein isothiocyanate (FITC).

Bactericidal effect of gentamicin conjugated gold nanoparticles

The authors explored the antibacterial activity of gentamicin conjugated gold nanoparticles against Escherichia coli bacteria by using the disk diffusion method. Gold nanoparticles were prepared by the reduction of tetrachloroauric acid with sodium citrate. Experiments were performed with relatively lower and higher doses of gentamicin, gold nanoparticles, and gentamicin conjugated gold nanoparticles. Atomic force microscopy (AFM) images of the bacterial colonies with and without treatment were taken. Results show that gentamicin used alone in a lower range of doses did not cause any growth inhibition, but when used in conjugation with gold nanoparticles, clear inhibition zones were visible. The ratios of inhibition areas of gold nanoparticles with gentamicin to only gentamicin were more in case of bigger sized gold nanoparticles. AFM images of the bacterial colonies also showed that gentamicin conjugated gold nanoparticles were more effective than other groups in inhibiting bacterial growth.

Green Formation of Nano-Hexagon from Nano-Triangle of Gold Nanoparticles Using Palm Oil Fronds Extracts

A simple method to synthesized nanoparticles was satisfied by reduction of tetrachloroauric acid in the presence of palm oil fronds extracts as capping and reduced agents. The as-synthesized gold nanoparticles structures have a triangular and hexagonal shape that are of tens of nanometre in size. It was realized that good control shape of nano-hexagonal gold nanoparticles were obtained from nano-triangular gold nanoparticles in the absence of any soft template. The production techniques of the gold nanoparticles were examined by using UV-vis spectroscopy, EFTEM and XRD patterns, which showed peaks at (111), (200), (220), (311) and (222), that described the preferential structure of the AuNPs as face-centered cubic crystal

Detection of helminth ova genera using in-situ biosynthesis of gold nanoparticles

In this study, a presumptive colorimetric method was used to detect and differentiate the ova of two major soil transmitted helminths in wastewater, Ascaris and Trichuris. Gold nanoparticles were synthesised following the reduction of tetrachloroauric acid by the surface moiety of Ascaris suum, resulting in a colour change. In contrast there was no colour change with Trichuris suis indicating the absence of gold nanoparticle synthesis. Analysis of the ova using scanning electron microscopy (SEM) revealed that the synthesis of nanoparticles on the surface of ova was confirmed as gold nanoparticles (91 w/w %) by energy dispersive X-ray analysis (EDX). This study indicated that the surface moieties of helminth ova could be a potential target for ova detection and differentiation using the biosynthesis of nanoparticles by colorimetry methods.Three advantages:•Simple colorimetry based method requiring no sophisticated devices.•No trained personnel required.•Cost-effective and can be a potential candidate for biosensors.

Nano-radiogold-decorated composite bioparticles

Hybrid composite bioparticles modified with stable and radioactive gold nanoparticles were prepared via reduction of tetrachloroauric acid within Lactobacillus rhamnosus cells. The resulting biocomposite material was characterized using a number of physicochemical techniques, including microscopic, spectroscopic and thermal methods.The bacterial particles act as a type of template for gold deposition. Gold nanoparticles of approximately 3.7 nm diameter are formed and are uniformly distributed within the bacterial cell, including its hydrogel outer shell. For radioactive gold-198, the β− radiation emitted from the biocomposite particles can be used for therapeutic purposes, as demonstrated in vitro in cancer cell cultures. The antitumor activity can be further enhanced by incorporation of doxorubicin, a cytostatic drug, within composite particles. The cell viability data indicate the considerable synergistic effect of β− radiation and doxorubicin on breast cancer cells (MCF-7). The antitumor action of the biocomposite particles is very promising for new anticancer therapies.

Solution NMR Spectroscopy with Isotope-Labeled Cysteine (13C and 15N) Reveals the Surface Structure of l-Cysteine-Coated Ultrasmall Gold Nanoparticles (1.8 nm).

Ultrasmall gold nanoparticles with a diameter of 1.8 nm were synthesized by reduction of tetrachloroauric acid with sodium borohydride in the presence of l-cysteine, with natural isotope abundance as well as 13C-labeled and 15N-labeled. The particle diameter was determined by high-resolution transmission electron microscopy and differential centrifugal sedimentation. X-ray photoelectron spectroscopy confirmed the presence of metallic gold with only a few percent of oxidized Au(+I) species. The surface structure and the coordination environment of the cysteine ligands on the ultrasmall gold nanoparticles were studied by a variety of homo- and heteronuclear NMR spectroscopic techniques including 1H-13C-heteronuclear single-quantum coherence and 13C-13C-INADEQUATE. Further information on the binding situation (including the absence of residual or detached l-cysteine in the solution) and on the nanoparticle diameter (indicating the well-dispersed state) was obtained by diffusion-ordered spectroscopy (1H-, 13C-, and 1H-13C-DOSY). Three coordination environments of l-cysteine on the gold surface were identified that were ascribed to different crystallographic sites, supported by geometric considerations of the nanoparticle ultrastructure. The particle size data and the NMR-spectroscopic analysis gave a particle composition of about Au174(cysteine)67.

Slight pH Fluctuations in the Gold Nanoparticle Synthesis Process Influence the Performance of the Citrate Reduction Method.

Gold nanoparticles (AuNPs) are currently under intense investigation for biomedical and biotechnology applications, thanks to their ease in preparation, stability, biocompatibility, multiple surface functionalities, and size-dependent optical properties. The most commonly used method for AuNP synthesis in aqueous solution is the reduction of tetrachloroauric acid (HAuCl4) with trisodium citrate. We have observed variations in the pH and in the concentration of the gold colloidal suspension synthesized under standard conditions, verifying a reduction in the reaction yield by around 46% from pH 5.3 (2.4 nM) to pH 4.7 (1.29 nM). Citrate-capped AuNPs were characterized by UV-visible spectroscopy, TEM, EDS, and zeta-potential measurements, revealing a linear correlation between pH and the concentration of the generated AuNPs. This result can be attributed to the adverse effect of protons both on citrate oxidation and on citrate adsorption onto the gold surface, which is required to form the stabilization layer. Overall, this study provides insight into the effect of the pH over the synthesis performance of the method, which would be of particular interest from the point of view of large-scale manufacturing processes.

Simple size-controlled synthesis of Au nanoparticles and their size-dependent catalytic activity

The controlled preparation of Au nanoparticles (NPs) in the size range of 6 to 22 nm is explored in this study. The Au NPs were prepared by the reduction of tetrachloroauric acid using maltose in the presence of nonionic surfactant Tween 80 at various concentrations to control the size of the resulting Au NPs. With increasing concentration of Tween 80 a decrease in the size of produced Au NPs was observed, along with a significant decrease in their size distribution. The size-dependent catalytic activity of the synthesized Au NPs was tested in the reduction of 4-nitrophenol with sodium borohydride, resulting in increasing catalytic activity with decreasing size of the prepared nanoparticles. Eley-Rideal catalytic mechanism emerges as the more probable, in contrary to the Langmuir-Hinshelwood mechanism reported for other noble metal nanocatalysts.

Optimization of Gold Nanoparticles Synthesis using Design of Experiments Technique

Gold nanoparticles are considered the newest drug carriers for different diseases. Therefore it is appropriate continuous optimization of their preparation. In this study, gold colloids with an average size of 1 - 26 nm were obtained by the reduction of tetrachloroauric acid with trisodium citrate. The nanomaterials were characterized by UV-Vis spectroscopy and dynamic light scattering technique. In addition, zeta potential was measured for samples synthesized in order to determine the stability of the colloids. A Two-level Full Factorial design was chosen to determine the optimum set of process parameters (chloroauric acid concentration and sodium citrate concentration) and their effect on various gold nanoparticles characteristics (size and zeta potential). These effects were quantified using Design of Experiments (DoE) with 5 runs and 1 centerpoint. The selected objective and process model in this investigation are screening and interaction. Findings from this research show that to obtain particles larger than 35 nm, it is recommended to increase sodium citrate concentration, at low chloroauric acid values. These conditions will help to achieve smaller zeta potential, too.

Polyurethane-gold and polyurethane-silver nanoparticles conjugates for efficient immobilization of maltogenase

Preparation of polyurethane microparticles (PU) modified with gold (Au-NPs) or silver nanoparticles (Ag-NPs) for maltogenase immobilization was presented. The PU/Au-NPs and PU/Ag-NPs conjugates were prepared via adsorption of already synthesized nanoparticles on PU or via synthesis of nanoparticles within bulk of PU. Au-NPs of different size and Ag-NPs, synthesized by reduction of tetrachloroauric acid and silver nitrate with sodium citrate, were characterized by UV–vis and Dynamic Light Scattering technique. The best results (immobilization yield 90.0% and efficiency 83.5%) were achieved, when maltogenase was immobilized onto PU modified with Au-NPs(13nm) by adsorption method. Immobilized maltogenase was stable in time, after 25days of storage 95.2-98.6% of initial enzyme activity was remained. Moreover, the results revealed that stability of enzyme was improved upon immobilization on PU/Au-NPs(13nm) in comparison to PU without Au-NPs. Enhancement of photoluminescence after enzyme immobilization confirmed the successful attachment of maltogenase to PU/Au-NPs or PU/Ag-NPs via metal nanoparticles.

Anticancer activity of Sasa borealis leaf extract-mediated gold nanoparticles

Advancements in metal nanoparticle synthesis using plant extracts and their anticancer activity have received significant attention in recent years. The green approach for the synthesis of gold nanoparticles (AuNPs) using leaf extract of Sasa borealis is reported in this study. Synthesis of AuNPs was performed at 50 °C, and nanoparticle formation was observed after 20 min incubation. AuNPs formation was confirmed by the UV–visible spectrum peak at 542 nm. The synthesized AuNPs were oval, spherical with sizes around 10–30 nm observed using the transmission electron microscope. Energy dispersive X-ray analysis was utilized for the detection of elemental compound. The face centered cubic structure was confirmed by X-ray diffraction pattern. The reduction of tetrachloroauric acid into AuNPs by the phytochemical compounds of S. borealis extract was determined by Fourier transform infrared spectroscopy and the presence of biomolecules was studied by GC–MS. The synthesized AuNPs was tested for toxic effect on HEK293 cells and anticancer activity on AGS cells by WST-1® assay. Condensation or fragmentation is a characteristics of apoptosis, which was confirmed by 4,6-diamidino-2-pheynylindole dihydrochoride (DAPI) staining. The S. borealis-mediated AuNPs have good activity as an anticancer agent and it will be beneficial in cancer therapeutics.

Gentamicin-gold nanoparticles conjugate: a contrast agent for X-ray imaging of infectious foci due to Staphylococcus aureus.

There is no optimal imaging method for the detection of unknown infectious foci in some diseases. This study introduces a novel method in X-ray imaging of infection foci due to Staphylococcus aureus by developing a contrast agent based on gold nanoparticles (GNPs). GNPs in spherical shape were synthesised by the reduction of tetrachloroauric acid with sodium citrate. Then gentamicin was bound directly to citrate functionalised GNPs and the complex was stabilised by polyethylene glycol. The interaction of gentamicin with GNPs was confirmed by ultraviolet-visible and Fourier transform infrared spectroscopies. The stability of complex was studied in human blood up to 6 h. The stability of conjugate was found to be high in human blood with no aggregation. The biodistribution study showed localisation of gentamicin-GNPs conjugate at the site of Staphylococcal infection. The infection site was properly visualised in X-ray images in mouse model using the gentamicin-GNPs conjugate as a contrast agent. The results demonstrated that one may consider the potential of new nanodrug as a contrast agent for X-ray imaging of infection foci in human beings which needs more investigations.

Synthesis of Gold Nanoparticles with Polyamidoamine (Pamam) Generation 4 Dendrimer as Stabilizing Agent for CT Scan Contrast Agent

SummaryGold nanoparticles have great potential in biomedical applications as both a therapeutic and diagnostic agents. Pamam dendrimers are spherical, highly branched macromolecules with a narrow polydispersity to encapsulate and stabilize metal nanoparticles. In the preparation of metal nanoparticles, stabilizers play an important role in controlling particle size. The objectives of this study were to synthesize and characterize of gold nanoparticles. The gold nanoparticles were prepared by reduction of tetrachloroauric acid using sodium borohydride with and without addition of pamam generation 4 dendrimer as stabilizing agent. Gold nanoparticles stabilized pamam generation 4 dendrimer were characterized by Uv‐Vis spectrometry, transmission electron microscopy (TEM), dynamic light scattering (DLS) and zetasizer. The result showed that UV–vis absorption spectra of gold nanoparticles without pamam G4 dendrimer at 530 nm while absorption spectra of gold–pamam G4 dendrimer at 280 nm. The absorbance peak at 280 nm related to individual of gold nanoparticle encapsulated pamam dendrimer. TEM analysis exhibits the occurrence aggregation of gold nanoparticles without pamam G4 dendrimer. DLS analysis exhibit gold nanoparticles has a particles size 88‐252 nm while gold‐pamam G4 dendrimer nanoparticles 2‐15 nm. The addition of pamam generation 4 dendrimer on preparation of gold nanoparticles could prevent aggregation of nanoparticles through entrapment in cavity or core molecules. Au‐PAMAM G4 nanoparticles 0.1 mg/ml has a greater Hounsfield unit (HU) value than iodine at the same concentration, so it has better contrast properties.

Synthesis of mercaptopropyl-(phenylene)s-benzoates passivated gold nanoparticles: Implications for plasmonic photovoltaic cells

The incorporation of gold nanoparticles in heterojunction solar cells is expected to increase the efficiency due to plasmon effects, but the literature studies are sometimes controversial. In this work, gold nanoparticles passivated with (Ph)n–(CH2)3SH (n=1, 2, 3) have been synthesized by reduction of tetrachloroauric acid with sodium borohydride in two ways: (1) one-phase where both the thiol and the gold salt are solubilized in a mixture of methanol with acetic acid: Au-s-(Ph)n or (2), two-phase, using tetraoctylammonium bromide (TOAB) to transfer gold from water to toluene where the thiol is solubilized, Au(TOAB)-s-(Ph)n. The morphological, experimental and simulated optical properties were studied and analyzed as a function of the thiol and of the synthetic procedure in order to correlate them with the efficiency of plasmonic hybrid solar cells in the following configuration ITO/PEDOT:PSS/P3HT:PCBM-C60:Au-nanoparticles/Field’s metal, where PEDOT:PSS is poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), P3HT is poly(3-hexylthiophene-2,5-diyl) and PCBM-C60 is [6,6]-Phenyl C61 butyric acid methyl ester. Our findings indicate that the gold nanoparticles incorporation is affecting the electrical properties of the active layer giving a maximum efficiency for Au-s-(Ph)3. Moreover, TOAB, which is usually used in the synthesis of thiol passivated gold nanoparticles, has negative effects in both plasmonic and electrical properties. This result is important for optoelectronic applications of gold nanoparticles prepared with any procedures that involve TOAB.

Synthesis of Chiral Gold Nanoparticle by Direct Reduction with L and D-Serine and Enhanced Anti-Mycobacterial Activity by D-Serine Protected Gold Nanoparticle

Current situation demands more biocompatible and non-toxic nanostructures. Towards this the present study describes the synthesis of gold nanoparticle by direct reduction of tetrachloroauric acid with both D- and L-enantiomeric forms of the amino acid serine. The formation of nanoparticle was confirmed by examining different physical characteristics like surface plasmon resonance. Moreover, the retention of chirality of the reduced particle was also evident from circular dichroism spectroscopy experiment. In addition, the shielding of the nanoparticle by respective amino acid was confirmed by Scanning Electron Microscope and Energy Dispersive X-ray Analysis (SEM-EDAX). As D-serine is known to be active against Mycobacteria, examination of the biological activity of the D-serine protected particle was performed against the same. The result showed higher inhibitory activity of the particle against Mycobacterium smegmatis than D-serine alone. Thus the present study describes a new protocol for the synthesis of chiral gold nanoparticle that can be beneficial in enantioselective biological applications.

Gold–platinum alloy nanoparticles through water-in-oil microemulsion

Au–Pt alloy nanoparticles have been synthesized by the reduction of tetrachloroauric acid (HAuCl4) and chloroplatinic acid (H2PtCl6) using sodium borohydride in water-in-oil (w/o) microemulsion of water/Triton X-100/cyclohexene/1-hexanol at 25 ± 2 °C. The observed nanoparticles looked like a chain with diameter of 2.5 nm. The particles formation was characterized by UV–visible spectrometry and transmission electron microscopy images. The particles are crystalline confirmed by high-resolution transmission electron microscopy and diffraction pattern. A bright-field and dark-field images were compared to find out the nature of the nanochains.

Controlled formation of gold nanoflowers by reduction of tetrachloroauric acid with thermally treated glucose in alkaline solution

Herein, thermally treated glucose in alkaline solution at 60°C for 10min was used to reduce tetrachloroauric acid for the preparation of gold nanoflowers within the size range of 50–520nm. The use of the glucose activated for a longer period of time led to the formation of gold nanoparticles with less anisotropic characteristics. The degradation of glucose in alkaline solution results in enediols and carboxylates. It was suggested that the product has stronger reduction ability and limited protection effect for tetrachloroauric acid and gold nanoparticles, respectively, contributes to the controlled formation of gold nanoflowers. The as-prepared gold nanoflowers showed better surface enhanced Raman scattering (SERS) activity than citrate or PVP coated ones when rhodamine 6G (R6G) was used as probe molecule.

Continuous-Microflow Synthesis and Morphological Characterization of Multiscale Composite Materials Based on Polymer Microparticles and Inorganic Nanoparticles

This paper presents a new route to the synthesis of uniform and size-controlled inorganic/organic composite microparticles by means of microreaction technology. Au-nanoparticles in the range of 3 to 14 nm are synthesized by reduction of tetrachloroauric acid, while ZnO-nanoparticles (200–2000 nm) are synthesized in a continuous-flow two-step process using microtube arrangements for microsegmented flow. Both inorganic nanoparticles have a well-controlled size and narrow size distribution. Upon surface modification, the nanoparticles are then mixed on one hand with an acrylate-based monomer and, on the other hand, with an aqueous solution of acrylamide. Both solutions were then emulsified into uniform core-shell droplets by means of a capillary-based microfluidic device. Droplet's shell was hardened through UV-induced polymerization, whereas the core led to a hydrogel upon thermal-induced polymerization. Core-shell polymer microparticles (200–300 µm) with inorganic nanoparticles selectively incorporated int...