Reduction Of Au Ions Research Articles

An evanescent waves sensor based on polydopamine-gold coated chalcogenide tapered fiber for enzyme activity profiling

In this research, we demonstrate a high-sensitivity tapered fiber (TF) sensor made of As2S3 chalcogenide glass coated with polydopamine (PDA) and gold nanoparticles (AuNPs). The presence of in-situ grown AuNPs on the PDA-coated TF surface via the reduction of Au ions by catechol groups in PDA, facilitated efficient light coupling with evanescent waves, thereby improving the IR absorption of molecules. The sensor was utilized to measure the activity of the glucose oxidase enzyme as a point-of-concept analyte. This process of enzyme catalyzing the conversion of glucose to hydrogen peroxide and Gluconic acid can be recorded by the sensor. In investigating the enzyme activity and D-glucose oxidation kinetics, we monitored the intensity of the Gluconic acid band at 5.764 μm, which arises from the C=O stretching vibration, as a function of time. The estimated enzyme activity using the PDA/AuNPs-coated TF sensor was 103.66 ± 2.87 Umg−1 when the enzyme activity of the sample was 100 Umg−1 which is consistent with standard value. The Lineweaver–Burk plot yielded the following kinetic constants: Km = 16.10 ± 1.63 mM and Vmax = 93.72 ± 12.71 μmol/min. Results suggest that this sensor has great application potential in various enzyme activity applications.

In vitro assessment of antimicrobial, anti-inflammatory, and schistolarvicidal activity of macroalgae-based gold nanoparticles

There is a growing need to improve facile, eco-friendly, and cheap approaches for nanoparticle (NP) synthesis. Green protocols have been investigated for the fabrication of NPs using several natural sources as plants, algae, fungi, and bacteria. Thus, the present study proposed a rapid, convenient, and efficient biosynthesis of gold NPs (Au-NPs) using the ethanolic extracts of three macroalgae, i.e., Cystoseira myrica, C. trinodis, and Caulerpa prolifera. The reduction of Au ions and the fabrication of Au-NPs were validated using ultraviolet-visible (UV–Vis) spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), and zeta potential analysis. The produced Au-NPs were tested for their antibacterial, antifungal, anti-inflammatory, and schistolarvicidal activity. Results revealed the formation of Au-NPs with an average size of 12.6–15.5 nm and different shapes that are mainly spherical with pure crystalline nature. The strong antibacterial activities of C. trinodis– and C. myrica–based Au-NPs against E. coli (inhibition zones of 22 and 19 mm) and against Staphylococcus aureus (inhibition zones of 18 and 20.5 and mm) were recorded, respectively. On the other hand, the high antifungal activity of C. trinodis Au-NPs against Aspergillus niger and Alternaria alternate showed the inhibition zones of 18 and 17 mm, respectively. The high antifungal activity of C. trinodis Au-NPs against Candida albicans (inhibition zone 16 mm) was also recorded. Regarding anti-inflammatory and schistolarvicidal activity, Au-NPs fabricated using C. myrica showed 64.2% of the inhibitory effect on protein denaturation and recorded the highest schistolarvicidal activity against Schistosoma mansoni cercariae that sank and died after 7 min. Overall, these findings proved that macroalgal ethanolic extracts can be effectively used for the biosynthesis of Au-NPs. These Au-NPs offer a significant alternative antimicrobial, anti-inflammatory, and schistolarvicidal agents. for biomedical uses.

Influences of petroleum hydrocarbon pyrene on the formation, stability and antibacterial activity of natural Au nanoparticles

The effect of pyrene on the formation of naturally Au nanoparticles (AuNPs) in the presence of humic acid (HA) under UV irradiation is described. TEM, EDS, FTIR and XPS were carried out to prove the formation of AuNPs and display their morphologies and formation mechanism. There are little differences between size, morphology and function groups of surface coated materials of AuNPs formed with and without pyrene. With the presence of HA, pyrene showed an inhibiting effect on the reduction of Au ion via competition for O2•-, thereby decreasing the production of AuNPs. However, AuNPs formed by HA-pyrene showed higher stability than AuNPs formed by HA with the sedimentation rates of 4.13% and 13.68% respectively after 30-d standing. As for the antibacterial activities against Staphylococcus aureus and Escherichia coli, AuNPs formed by HA-pyrene were more toxic than AuNPs formed by HA. Meanwhile, changes of environmental factors such as temperature, pH and ionic strength exhibited similar influence trend on the formation of AuNPs in the presence and absence of pyrene. The results suggest that the typical petroleum hydrocarbon pyrene contained in spilled oil could influence the formation, fate and ecotoxicity of AuNPs.

Detection and discrimination of single nucleotide polymorphisms by exploiting metal ion-mediated DNA duplex

Detection of mutant DNA is necessary for early diagnosis of disease. In particular, detection of single nucleotide polymorphisms (SNPs) has become an important method for monitoring cancer and obtaining theragnostic information about it. SNPs are very difficult to detect selectively because of their similarity with wildtype DNA. In this paper, the specific binding between metal ion and DNA mismatch was used to achieve highly sensitive and selective SNP detection. Cytosine-cytosine (C-C) mismatched nucleobases capture silver (Ag) ions, and thymine-thymine (T-T) mismatched nucleobases capture mercury (Hg) ions. Metal ions bound between DNA could be reduced using a reducing agent (hydroquinone). In addition, gold (Au) amalgam could be formed around the DNA mismatch by the reduction of Au ion and mercury ion bound between T-T mismatches. Differential pulse voltammetry (DPV) was used to measure signals which are mediated by silver and Au amalgam. The detection limit of point mutation DNA obtained by the proposed detection method is 20 pM. In addition, by comparing the values of the DPV peaks by silver and Au amalgam, the types of DNA point mutations including cytosine or thymine (CT, CC, TT, AC, and TG) could be distinguished. The results obtained from our proposed method suggest its potential for diagnosing cancer patients.

Photochemical synthesis of ZnO@Au nanorods as an advanced reusable SERS substrate for ultrasensitive detection of light-resistant organic pollutant in wastewater

The prospect of wielding surface-enhanced Raman spectroscopy (SERS) as a powerful technique for ultrasensitive detection of organic molecules in wastewater has received extensive attention in environmental surveillance. Based on ultraviolet (UV, 405 nm) laser irradiation of ZnO nanorods in HAuCl4 solution, ZnO@Au nanorods with controllable Au nanoparticles were successfully fabricated and established as an advanced SERS-based substrate. The reduction of Au ions was driven by the generation of electron-hole pairs via UV laser excitation of semiconductor-based nanomaterials, resulting in the moderate overgrowth of Au nanoparticles on the ZnO nanorods. The Au composition-dependent SERS analysis of crystal violet (CV) molecules revealed that the ZnO@Au nanorods with 16.21% Au contents exhibited optimized SERS activity in comparison with other nano-substrates in this paper. Furthermore, the detection limit of light-resistant methyl blue (MB) dye molecules was achieved at nanomole (nM) level of 10−9 M (0.8 μg/L), providing ultrasensitive detection of organic pollution in wastewater. Even after twenty recycles, the excellent reusability of this novel substrate with 65% original SERS intensity was achieved by subsequently eliminating the residual MB molecules via photocatalytic degradation. Therefore, the as-prepared ZnO@Au nanorods can serve as a cost-effective, clean, reusable and active SERS substrate for ultrasensitive monitoring of light-resistant organic pollutant in natural ecosystems.

(Invited) Development of Newfangled Nanotechnologies By Introducing Ionic Liquid to Vacuum Devices

One of fascinate features that ionic liquid (IL) possesses is extremely low vapor pressure, which enable us to put IL in a vacuum chamber. There are many vacuum devices that have been designed for solid samples, as a matter of course. However, an ability to make wet condition in vacuum system by introducing IL into it allows us to develop newfangled technologies in analytical chemistry and nanomaterial synthesis fields. In this paper, two topics on in situ electron microscope observation of reactions in IL and facile way to synthesis nanoparticles using a sputtering instrument onto IL are described. Regarding the use of IL for electron microscope observation, we have found the fascinate fact that IL drops give scanning electron microscope (SEM) images without any charging.1 In other words, IL behaves like a conducting material for electron microscope observation. It was also found that IL behaves like a transparent material for SEM observation when its thickness is less than 1 micro meter. Based on these facts, we started to develop ways to conduct in situ electron microscope observation of chemical reactions. Electrically conducting polypyrrole film deposited on an electrode surface was the first sample and changes in its thickness upon redox reaction in IL electrolyte were observed by SEM.2 As another electrochemical reaction, we attempted to observe deposition of Ag metal on an electrode from IL containing Ag+ ions. Nucleation and nuclear growth were dominant when Ag deposition was moderately conducted. Howerver, when the deposition rate was accelerated so as to make the diffusion-controlled condition, growth of Ag metal with dendriform was clearly observed.3 When we observed IL dissolving Na[AuCl4] by SEM, it was found that Au particles appeared in the IL, resulting from reduction of Au ions by electron beam irradiation.4 On the basis of this finding, attempt was made to observe generation and growth of Au nanoparticles by a transmission electron microscope (TEM). Figure 1 shows time course of two Au nanoparticles (diameter = ca. 5 nm). Each particle shows fringes reflecting crystal lattice of Au and it is obvious that coalescence gives a larger Au nanoparticles by production of one Au crystal from two crystals.5 The metal sputtering instrument is useful for depositing a metal thin layer on a substrate surface. The sample was limited to solid materials because the metal sputtering must be conducted under reduced pressure. Our first attempt was to subject IL to Au sputtering and observation of the resulting IL by TEM, giving us a chance to discover synthesis of Au nanoparticles suspended in IL.6 Nanoparticles of several kinds of metals and metal oxides including alloy nanoparticles can be prepared by this method.7 The noble nanoparticles including Au and Pt can be adsorbed on carbon substance surfaces by putting IL containing metal nanoparticles on the substance and heating it. This way is exploitable for preparation of Pt-carbon catalysts for fuel cells.8 Furthermore, adsorption of Pt nanoparticles on surfaces of carbon nanotubes (CNTs) was possible by the similar way as shown in Figure 2.9 Electrochemical measurements of the prepared Pt nanoparticle-adsorbed CNTs revealed that this material possesses distinct catalytic activities toward O2 reduction.

Radiolytic preparation of thin Au film directly on resin substrate using high-energy electron beam

A novel method for preparing thin Au films directly on resin substrates using an electron beam was developed. The thin Au films were prepared on a resin substrate by the reduction of Au ions in an aqueous solution via irradiation with a high-energy electron beam (4.8MeV). This reduction method required 7s of the irradiation time of the electron beam. Furthermore, no reductant or catalyst was needed. As the concentration of Au ions in the precursor solution was increased, the amount of Au deposited on the resin substrate increased, too, and the structure of the prepared Au film changed. As a result, the film color changed as well. Cross-sectional scanning electron microscope images of the thus-prepared Au film indicated that the Au films were consisted of two layers: a particle layer and a bottom bulk layer. There was strong adhesion between the Au films and the underlying resin substrates. This was confirmed by the tape-peeling test and through ultrasonic cleaning. After both processes, Au remained on the resin substrates, while most of the particle-like moieties were removed. This indicated that the thin Au films prepared via irradiation with a high-energy electron beam adhered strongly to the resin substrates.

Preparation of a Colloid Solution of Au/Silica Core-Shell Nanoparticles Surface-Modified with Cellulose and its X-ray Imaging Properties

Preparation of a Colloid Solution of Au/Silica Core-Shell Nanoparticles Surface-Modified with Cellulose and its X-ray Imaging Properties Objective: The aim of this paper is to describe the preparation of a colloid solution of Au nanoparticles that are coated with silica and simultaneously surface modified with carboxymethylcellulose (CMC) (Au/SiO2/CMC) and to investigate the X-ray imaging of mice using the colloid solution. Methods: The reduction of Au ions (III) with sodium citrate produced Au nanoparticles, and amino groups were introduced on the surface of the Au nanoparticles by using (3-aminopropyl)-trimethoxysilane. The Au nanoparticles with amino groups were silica coated by a sol-gel process using tetraethylorthosilicate, (3-aminopropyl)- triethoxysilane, water and sodium hydroxide in ethanol (Au/SiO2- NH2). After concentrating the as-prepared Au/SiO2-NH2 particle colloid solution by centrifugation, CMC was immobilized on the Au/ SiO2-NH2 particle surface with the addition of CMC to the Au/SiO2- NH2 particle colloid solution. Results: The Au/SiO2/CMC particles, with a size of 67.4 ± 5.4 nm containing a core of a single Au nanoparticle with a size of 17.9 ± 1.3 nm, were produced using the preparation conditions adopted in the present work. A computed tomography (CT) value that was as high as 344 ± 12 Hounsfield units (HU) was recorded for the Au/SiO2/CMC particle colloid solution with an Au concentration of 0.043 M. Its converted value was calculated by dividing the Au concentration into the recorded CT value and was 8.0×103 HU/M. This value was larger than that of Iopamiron 300, a commercial X-ray contrast agent. The Au/SiO2/CMC particle colloid solution was injected into the tail vein of a mouse and could be used to image the tissues. Conclusion: The Au/SiO2/CMC particle colloid solution obtained in the present work was successfully used for X-ray imaging.

Single-step electrochemical deposition of high performance Au-graphene nanocomposites for nonenzymatic glucose sensing

In this paper, high-quality three-dimensional (3D) nanocomposites (Au nanoparticles anchored on graphene, denoted as Au-gra) were synthesized by a simple electrochemical approach, in which the reduction of Au ions and graphene oxide were achieved with a one-step process. The resulting hybrids were characterized by field-emission scanning electron microscopy (FE-SEM), Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). It is found that Au nanoparticles have been successfully supported on the surface of graphene, and the nanocomposites uniformly modified on the electrode with 3D porous structures. Based on cyclic voltammetry and amperometric results, Au-gra efficiently catalyzed the oxidation of glucose in neutral media (0.1M PBS, pH 7.4) and exhibited a rapid response time (about 3s), a broad linear range (0.1–16mM), good stability, and sensitivity estimated to be 4.56μAcm−2mM−1 (R=0.992, 285.8μAcm−2mM−1 vs. geometric area). The electrochemical experiments were performed at a relatively low detection potential (i.e., 0V), under which the impact from the oxidation of common interfering species could be effectively limited. These results indicated a great potential of Au-gra in fabricating novel non-enzymatic glucose sensors with high performance.

Dual stimuli-sensitive dendrimers: Photothermogenic gold nanoparticle-loaded thermo-responsive elastin-mimetic dendrimers

Dendrimers are synthetic macromolecules with unique structures that can work as nanoplatforms for both photothermogenic gold nanoparticles (AuNPs) and thermosensitive elastin-like peptides (ELPs) with valine-proline-glycine-valine-glycine (VPGVG) repeats. In this study, photothermogenic AuNPs were loaded into thermo-responsive elastin-mimetic dendrimers (dendrimers conjugating ELPs at their periphery) to produce dual stimuli-sensitive nanoparticles. Polyamidoamine G4 dendrimers were modified with acetylated VPGVG and (VPGVG)2, and the resulting materials were named ELP1-den and ELP2-den, respectively. The AuNPs were prepared by the reduction of Au ions using a dendrimer-nanotemplated method. The AuNP-loaded elastin-mimetic dendrimers exhibited photothermal properties. ELP1-den and ELP2-den showed similar temperature-dependent changes in their conformations. Phase transitions were observed at around 55°C and 35°C for the AuNP-loaded ELP1-den and AuNP-loaded ELP2-den, respectively, but not for the corresponding PEGylated dendrimer. In contrast to the AuNP-loaded PEGylated dendrimer, AuNP-loaded ELP2-den readily associated with cells and induced efficient photocytotoxicity at 37°C. The cell association and the photocytotoxicity properties of AuNP-loaded ELP2-den could be controlled by temperature. These results therefore suggest that dual stimuli-sensitive dendrimer nanoparticles of this type could be used for photothermal therapy.

Study of Vegetable Biodiesel Enhanced by Gold Nanoparticles Using Thermal-Lens Technique

In this work, experimental results for the enhancement of the thermal diffusivity of a colloidal suspension of gold nanoparticles in biodiesel oil are reported. Different concentrations of Au nanoparticles are prepared using a microemulsion method, by simultaneous reduction of Au ions in the presence of hydrazine as a reducing agent. The thermal diffusivity was found to increase with increasing nanoparticle concentration.

X-ray-induced reduction of Au ions in an aqueous solution in the presence of support materials and in situ time-resolved XANES measurements.

Synchrotron X-ray-induced reduction of Au ions in an aqueous solution with or without support materials is reported. To clarify the process of radiation-induced reduction of metal ions in aqueous solutions in the presence of carbon particles as support materials, in situ time-resolved XANES measurements of Au ions were performed under synchrotron X-ray irradiation. XANES spectra were obtained only when hydrophobic carbon particles were added to the precursor solution containing Au ions. Changes in the shape of the XANES spectra indicated a rapid reduction from ionic to metallic Au in the precursor solution owing to synchrotron X-ray irradiation. In addition, the effects of the wettability of the carbon particles on the deposited Au metallic spots were examined. The deposited Au metallic spots were different depending on the relationship of surface charges between metal precursors and support materials. Moreover, a Au film was obtained as a by-product only when hydrophilic carbon particles were added to the precursor solution containing the Au ions.

Synthesis of Graphene-Gold Nanocomposites via Sonochemical Reduction

A Reduced reduced graphene oxide (RGO)-gold (Au) nanoparticle (NP) nanocomposite was synthesized by simultaneously reducing the Au ions and depositing Au NPs on onto the surface surface of the RGOsRGO simultaneously. To facilitate the reduction of Au ions and the generation of oxygen functionalities for anchoring the Au NPs on the RGOsRGO, ultrasound irradiation was applied to the mixture of reactants. The functional groups were investigated with FT-IR spectra. From the Raman and XPS spectra, the oxygen groups were identified as hydroxyl, epoxy, and carboxyl groups, the same as the one from graphene oxide (GO). As a result, the dense and uniform deposition of nanometer-sized Au NPs with nanometer size was observed on the RGO sheets sheet was observed with from the TEM imagesimage. The Oxygen oxygen functional groups that formed on the surface surface of the RGOs RGO seemed to have served serve as links for Au NPs NP attachment, through the electrostatic attraction of Au ions. Hybrid materials could thus be produced in a short time, with a high yield, by via ultrasound application. Besides, it ultrasound application could can readily take goldAu- binding- peptide (GBP)-modified biomolecules, readily implying its possibility in possible biological applications.

In situ growth approach for preparation of Au nanoparticle-doped silica aerogel

Gold (Au) nanoparticle-doped silica aerogels were prepared via the in situ growth approach. The Au ions were reduced to Au nanoparticles by hydroxylamine during the prehydrolysis oligomer process. Then, the samples were followed through with continuous supercritical extraction with CO 2. Ultraviolet–visible (UV–Vis) spectrophotometry was employed following the reduction of Au ions and the growth of Au nanoparticles. The size of the Au particles at the inner surface of the silica aerogel was within the 5–7 nm range. The morphology and microstructure characteristics of both silica aerogel and Au-doped samples were obtained through SEM, HRTEM, BET, and BJH. The total pore volume of obtained aerogel ranged within 2.9–3.45 cm −3/g, and the mean pore diameter was about 15 nm.

Effect of aging on the electrocatalytic activity of gold nanoparticles

The electrocatalytic activities of freshly prepared nanomaterials do not represent normal activities, if they change with aging. We report the dependence of the electrocatalytic activity of gold nanoparticles (AuNPs) upon aging. The activities of AuNPs prepared by four different methods (electrodeposition; reduction of Au ions with NaBH 4, citrate, and ascorbate, respectively) slowly decrease with aging in the electrooxidation of H 2O 2 or formic acid, both in air and in solution. The possible origin of this effect is discussed.

Preparation of Core–Shell Organic–Inorganic Nanocomposite Particles Based on Phase Separation of a Polymer Blend

Abstract Polymer nanoparticles with phase-separation structures can be prepared by simple solvent evaporation process from block copolymer or polymer blend solution (self-organized precipitation (SORP)). In this report, core–shell organic–inorganic nanocomposite particles were prepared by combination of block copolymer stabilizing Au nanoparticles and polymer blend. Block copolymer stabilizing Au NPs were prepared by reduction of Au ion in their micelles. Nanocomposite particles of poly(methyl methacrylate) (PMMA) and block copolymer stabilizing Au NPs are successfully prepared by using the SORP method.

Horseradish Peroxidase Immobilized on Poly(thiophene-2-aminophenol-3-thiopheneacetic acid) Film Electrode with Au Nanoparticle-Fabrication and Evaluation as Hydrogen Peroxide Sensor

Enzyme immobilized electrode was fabricated by two methods. In one of the methods, gold-nanoparticles (Au-NPs) prepared by gamma-irradiation were loaded into the copolymer film and horseradish peroxidase (HRP) was immobilized into the Au-NPs loaded copolymer film through physical entrapment. In the other method, the Au-NPs was prepared by electrochemical reduction of Au ions on the surface of poly(Th-AP-TAA) and HRP was immobilized into the Au-NPs. The enzyme immobilized electrodes were tested for electrocatalytic activities towards sensing of H2O2.

Reduction of Gold from Plating Wastewater Using TiO<sub>2</sub> Photocatalyst

TiO2 photocatalyst has attracted much attention in recovering valuable metal ions from industrial wastewater because TiO2 shows chemical stability and good wear resistant, and a photocatalytic reaction occurs by illumination of the sun or fluorescent light. In this study, Au removal and recovery in a gilding wastewater using TiO2 photocatalyst was evaluated. Commercially obtained TiO2 powder and TiO2 film prepared by spray and screen print method were used for Au adsorption. The cyanide existed in a plating wastewater was firstly removed with peroxide or persulfate because a driving force for Au ion reduction during photocatalytic process could decrease by the existed cyanide. Compared with persulfate, peroxide shows relatively slow removal rate of cyanide but no precipitation occurs. With respect to photocatalytic reaction of TiO2 powder and film for Au removal and recovery, it was found that the addition of 10 vol% of methanol as a hole scavenger increases the rates of Au ion reduction and Au adsorption on the TiO2 powder and film, subsequently the reaction of Au photoadsorption was completed within 60 min. Au lumps on the TiO2 particles obtained by photocatalytic reduction of TiO2 was confirmed by XRD analysis and TEM observation.

Doughnut-shaped peptide nano-assemblies and their applications as nanoreactors.

Doughnut-shaped nanoreactors, peptide nano-doughnuts, were self-assembled from peptides and organic Au salts. We demonstrated that monodisperse Au nanocrystals were synthesized inside the cavities of peptide nano-doughnuts by the reduction of Au ions and the size of the Au nanocrystal was controlled by the cavity dimension. The Au nanocrystals inside the nano-doughnuts were extracted by destroying the nano-doughnuts via long UV irradiation (>10 h). These features may allow the peptide nano-doughnuts to be applied in the fields of nanomaterial syntheses, controlled release systems, and drug delivery.

Gold-Nanocluster-Doped Inorganic−Organic Hybrid Coatings on Polycarbonate and Isolation of Shaped Gold Microcrystals from the Coating Sol

Au-nanocluster-doped inorganic−organic hybrid coatings on polycarbonate substrates were prepared for the application of abrasion-resistant colored coatings as well as nonlinear optical material. The Au-doped sol was prepared by incorporating HAuCl4·4H2O into a composite sol derived from 3-(glycidoxypropyl)trimethoxysilane, tetraethylorthosilicate, and 3-(methacryloxypropyl)trimethoxysilane via hydrolysis−condensation and epoxy polymerization reactions. When the coated substrates were exposed under UV light, three reactions occurred simultaneously: (i) reduction of Au ions into metallic Au nanoclusters, (ii) polymerization of methacrylate groups, and (iii) strengthening of the silica network. As a result, the UV-cured coatings became reddish-purple and more abrasion-resistant than the polycarbonate substrate. UV−vis spectroscopy and TEM of the films showed a peak at 530 nm due to the surface plasmon resonance of Au nanoclusters and the presence of 8−10 nm spherical Au nanoclusters, respectively. XRD of the films also showed the characteristic peaks of metallic Au nanoclusters. The inorganic−organic hybrid network at the sol stage also acted as a new breeding medium for the generation of shaped (triangular, hexagonal, prismatic, etc.) Au microcrystals from the Au-doped sol without UV irradiation. Electron diffraction suggests that these were single crystals with a preferential growth along the Au (111) plane.