Biosynthesis and characterization of gold nanoparticles produced by laccase from Paraconiothyrium variabile

During recent years investigation on the development of eco-friendly processes for production of gold nanoparticles (GNPs) have received much attention due to hazardous effects of chemical compounds used for nanoparticle preparation. In the present study, the purified laccase from Paraconiothyrium variabile was applied for synthesis of Au nanoparticles (AuNPs) and the properties of produced nanoparticles were characterized. The UV-vis spectrum of formed AuNPs showed a peak at 530 nm related to surface plasmon absorbance of GNPs represented the formation of gold nanoparticles after 20 min incubation of HAuCl(4) (0.6 mM) in the presence of 73 U laccase at 70°C. Transmission electron microscopy (TEM) image of AuNPs showed well dispersed nanoparticles in the range of 71-266 nm as determined by the laser light scattering method. The pattern of energy dispersive X-ray (EDX) of the prepared GNPs confirmed the structure of gold nanocrystals.     

A Xyloside-Based Ligand to Stabilize Gold Nanoparticles: Preparation and Application

Water-soluble and air-stable gold nanoparticles stabilized by a xyloside-based ligand containing a pyridine ring-functionalized 1,2,3-triazole backbone were prepared in the presence of a reducing agent. During their preparation, UV-vis and NMR spectroscopic techniques were used to study the interaction between the xyloside ligand and Au(III) ions. These AuNPs were characterized by UV-vis spectroscopy, TEM and DLS and showed a small size (average diameter<10 nm determined by TEM). Their catalytic activity was tested in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in water.     

Synthesis, characterization, and self-assembly of protein lysozyme monolayer-stabilized gold nanoparticles

Lysozyme monolayer-protected gold nanoparticles (Au NPs) which are hydrophilic and biocompatible and show excellent colloidal stability (at low temperature, ca. 4 degrees C), were synthesized in aqueous medium by chemical reduction of HAuCl4 with NaBH4 in the presence of a familiar small enzyme, lysozyme. UV-vis spectra, transmission electron microscopy (TEM), atomic force microscopy, and X-ray photoelectron spectroscopy characterization of the as-prepared nanoparticles revealed the formation of well-dispersed Au NPs of ca. 2 nm diameter. Moreover, the color change of the Au NP solution as well as UV-vis spectroscopy and TEM measurements have also demonstrated the occurrence of Ostwald ripening of the nanoparticles at low temperature. Further characterization with Fourier transform infrared spectroscopy (FTIR) and dynamic light scattering indicated the formation of a monolayer of lysozyme molecules on the particle surface. FTIR data also indicated the intactness of the protein molecules coated on Au NPs. All the characterization results showed that the monodisperse Au NPs are well-coated directly with lysozyme. Driven by the dipole-dipole attraction, the protein-stabilized Au NPs self-assembled into network structures and nanowires upon aging under ambient temperature. On the basis of their excellent colloidal stability, controlled self-assembly ability, and biocompatible surface, the lysozyme monolayer-stabilized Au NPs hold great promise for being used in nanoscience and biomedical applications.     

HYDRATED ELECTRON FORMATION IN NANOSECOND and PICOSECOND LASER FLASH PHOTOLYSIS OF HEMATOPORPHYRIN IN AQUEOUS SOLUTION

Nanosecond (lambda exc = 266, 355 and 532 nm) and picosecond (lambda exc = 355 nm) laser flash photolysis of hematoporphyrin (Hp) was performed in neutral (pH 7.4) and alkaline (pH 12) aqueous solution, as well as in the presence of 0.1% Triton X-100. The dependence of the yield of photoproduced hydrated electrons (e-aq) on laser pulse energy was studied over a wide range of energies (0.2 to greater than 1000 mJ cm-2). The results show that e-aq are predominantly formed in a two-photon process at lambda exc = 266 and 355 nm. One-photon quantum yields are higher at lambda exc = 266 nm than at lambda exc = 355 nm. Both one-photon and two-photon pathways are less efficient at higher Hp concentration, reflecting the influence of Hp self-aggregation. Two-photon e-aq formation is more efficient when 30 ps pulses are used for excitation, as compared to 10 ns pulses. No e-aq could be detected at lambda exc = 532 nm. Nanosecond pulse-induced transient spectra obtained at pH 7.4 are also discussed.     

Size and stability modulation of ionic liquid functionalized gold nanoparticles synthesized using Elaeis guineensis (oil palm) kernel extract

Bio-synthesis approach for gold nanoparticles (AuNPs) has received tremendous attention as an efficient and eco-friendly process. However, kinetic growth and colloidal stability of AuNPs synthesized by this process remained challenging. In this study, Elaeis guineensis (oil palm) kernel (OPK) extract prepared in an ionic liquid (IL)[EMIM][OAc] (1-ethyl-3-methylimidazolium acetate) was employed to control and tune the size and morphology of AuNPs. Synthesized AuNPs were characterized using UV-vis spectrophotometer, dynamic light scattering (DLS) and transmission electron microscopy (TEM) to observe any changes in absorbance, surface charge and particle size, respectively. IL mediated AuNPs were examined for 120 days and found well dispersed and stable at room temperature. UV-vis analysis demonstrated that volume of extract played an important role to control the stability of AuNPs. After 120 days, only 8.86% reduction from maximum absorbance was observed using 2 mL of volume of extract, which was elevated to 47.64% in case of 0.3 mL. TEM analysis was performed periodically after day 1, day 30, day 60, day 90 and day 120 and minor increase in the size was observed. Insignificant change in zeta potential value after 120 days supported enhanced stability of IL mediated AuNPs. Crystalline nature of AuNPs was confirmed by X-ray diffraction (XRD) pattern. The particles size and zeta potential of AuNPs was measured as 8.72 nm and −18.7 mV, respectively. However, the absence of [EMIM][OAc] from OPK extract resulted into larger particles size (9.64 nm), low zeta potential value (−13.9 mV) and enhanced aggregation of particles. Finally, experimental data were used to predict the theoretical and the experimental settling time for AuNPs to evaluate colloidal stability.     

Spectroscopic and microscopic investigation of gold nanoparticle formation: ligand and temperature effects on rate and particle size

We report a spectroscopic and microscopic investigation of the synthesis of gold nanoparticles (AuNPs) with average sizes of less than 5 nm. The slow reduction and AuNP formation processes that occur by using 9-borabicyclo[3.3.1]nonane (9-BBN) as a reducing agent enabled a time-dependent investigation based on standard UV-vis spectroscopy and transmission electron microscopy (TEM) analyses. This is in contrast to other borohydride-based syntheses of thiolate monolayer protected AuNPs which form particles very rapidly. We investigated the formation of 1-octadecanethiol (ODT) protected AuNPs with average diameters of 1.5-4.3 nm. By studying the progression of nanoparticle formation over time, we find that the nucleation rate and the growth time, which are interlinked with the amount of ODT and the temperature, influence the size and the size dispersion of the AuNPs. High-resolution TEM (HRTEM) analyses also suggest that the nanoparticles are highly single crystalline throughout the synthesis and appear to be formed by a diffusion-controlled Ostwald-ripening growth mechanism.     

Novel small stable gold nanoparticles bearing fluorescent cysteine-coumarin probes as new metal-modulated chemosensors

Emissive molecular probes based on amino acid moieties are very appealing because of their application as new building blocks in peptide synthesis. Two new bioinspired coumarin probes (L1 and L2) were synthesized and fully characterized by elemental analysis, infrared, (1)H NMR, (13)C NMR, UV-vis absorption and emission spectroscopy, matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF-MS), lifetime measurements, and X-ray crystal diffraction. Their sensing ability toward alkaline earth, transition, and post-transition metal ions (Ca(2+), Zn(2+), Cd(2+), Cu(2+), Ni(2+), Hg(2+), Ag(+), and Al(3+)) and their acid-base behavior (H(+), OH(-)) were explored in absolute ethanol by absorption and fluorescence spectroscopy. Compound L1 shows a strong complexation constant with the soft metal ions Zn(2+), Cd(2+), and Ag(+). Compound L2 shows a high fluorescence quantum yield, and it could be used as a non-pH-dependent fluorescent biological probe. Very small gold nanoparticles (AuNPs) using compounds L1 and L2 as stabilizers were obtained by using a reductive method and were characterized by UV-vis, light scattering, and transmission electron microscopy (TEM). Dynamic light scattering and TEM studies show that the formation of small nanoparticles is around 4.27 ± 0.64 nm for L1 and around 2.69 ± 0.96 nm for L2. The new stable Cou@AuNPs behaved as supramolecular chemosensors, which have been selective for the heavy element Hg(2+), with a concomitant change of color from pink to dark red/brown and an increase of size up to 100-fold.     

Preparation of Gold Nanoparticles Using 2-Ethoxyethanol, 2-Methoxyethanol and 1,3-Butyleneglycol Supported in Chitosan

The aim of this work was to prepare and characterize several properties of Au nanoparticles colloids prepared by the “chemical liquid deposition” method, which involves the co-deposition of metallic Au with organic vapors (2-ethoxyethanol, 2-methoxyethanol and 1,3-butylenglycol at 77 K). AuNPs supported on chitosan were performed by solvated metal atom dispersed method. Then, colloids were characterized by transmission electron microscopy (TEM), electron diffraction (ED), UV–Vis spectroscopy, electrophoretic mobility, physical stability, medium–far infrared spectroscopy and thermogravimetric analysis. These studies had demonstrate that Au nanoparticles solvated with 1,3-butylenglycol and 2-ethoxyethanol, shows higher stability, due to their high dielectric constant and a better NPs solvation. TEM analysis showed a size distribution between 4.61 and 48.8 nm. From ED, a face-centered cubic structure was found. UV–Vis analysis showed lower stability of nanoparticles solvated with 2-methoxyethanol. FTIR spectra showed that the solvent was incorporated and surround the Au NPs. The thermograms shows that thermal decomposition of AuNPs–chitosan decreases with the metal presence. Bioassays of acute toxicity on fishes with AuNPs–chitosan with 1,3-butylenglycol were carried out due to the lower toxicity. The bioassay showed that 0.94 mL/L produce mortality of 50 % (LD 50) of fishes exposed 96 h calculated with a confidence interval of 0.810–1.148 mL/L.     

Effect of Pluronic P103 Concentration on the Simple Synthesis of Ag and Au Nanoparticles and Their Application in Anatase-TiO2 Decoration for Its Use in Photocatalysis

Silver and gold nanoparticles were synthesized under environmentally-friendly reaction conditions by using a biodegradable copolymer and water as a solvent. The triblock copolymer Pluronic P103 was utilized as a stabilizing agent or soft template to produce Ag and Au nanoparticles (NPs) of different sizes. Moreover, in the synthesis of Au NPs, the polymer acted as a reducing agent, decreasing the number of reagents used and consequently the residues produced, hence, rendering the procedure less complicated. It was observed that as the concentration of the polymer increased, the size of the metallic NPs augmented as well. However, AgNPs and AuNPs prepared with 1 and 10 wt% Pluronic P103, respectively, showed a significant decrease in particle size due to the presence of polymeric soft templates. The hybrid materials (metal/polymer) were characterized by UV-Vis spectroscopy, DLS, and TEM. The pre-synthesized nanoparticles were employed to decorate anatase-TiO₂, and the composites were characterized by DRS, XRD, BET surface area measurements, the TEM technique with the EDS spectrum, and XPS spectroscopy to demonstrate NPs superficial incorporation. Finally, methylene blue was used as a probe molecule to evidence the effect of NPs decoration in its photocatalytic degradation. The results showed that the presence of the NPs positively affected methylene blue degradation, achieving 96% and 97% removal by utilizing TAg0.1 and TAu10, respectively, in comparison to bare anatase-TiO₂ (77%).     

Multiphoton ionization and Coulomb explosion of C2H5Br clusters: a mass spectrometric and charge density study

Using time‐of‐flight mass spectrometry (TOFMS), laser‐induced photochemistry of ethyl bromide clusters has been investigated at three different wavelengths (viz. 266, 355 and 532 nm) utilizing nanosecond laser pulses of ~5 × 10⁹ W/cm². An interesting finding of the present work is the observation of multiply charged atomic ions of carbon and bromine at 355 and 532 nm, arising from the Coulomb explosion of (C₂H₅Br)_n clusters. At 266 nm, however, the (C₂H₅Br)_n clusters were found to exhibit the usual multiphoton dissociation/ionization behaviour. The TOFMS studies are complemented by measuring the total charge density of the ionized volume at 266, 355 and 532 nm, using the parallel plate method, and the charge densities were found to be ~2 × 10⁹, 6 × 10⁹ and 2 × 10¹¹ charges/cm³, respectively. The significantly higher charge density and the presence of energetic, multiply charged atomic ions at 532 nm are explained by the higher ponderomotive energy of the 532 nm photon, coupled with the Coulomb stability of the residual multiply charged ethyl bromide clusters generated upon laser irradiation, due to their larger effective cluster size at 532 nm than at 355 and 266 nm. Copyright © 2011 John Wiley & Sons, Ltd.     

Microwave-Assisted Green Synthesis of Gold Nanoparticles Using Olibanum Gum (Boswellia serrate) and its Catalytic Reduction of 4-Nitrophenol and Hexacyanoferrate (III) by Sodium Borohydride

In this work we report straightforward, an economically viable, one-step microwave-assisted green synthesis of well stabilized gold nanoparticles (AuNPs) by reducing chloroauric acid with natural water soluble olibanum gum (Boswellia serrate). The olibanum gum acts as a dual role of reducing and capping agent for synthesis of AuNPs. The formation of AuNPs was confirmed using UV–Vis spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy and electron diffraction. The results indicated that the synthesized NPs were well dispersed and spherical in shape had an average diameter of 3 ± 2 nm. The reaction parameters significantly affected the formation of NPs, as the concentration of gum and irradiation time increases the formation of NPs particles increases and size of particles are reduced. In addition, it has been shown that these olibanum gum capped AuNPs functioned as effective homogeneous catalyst for the reduction of two model reactions hexacyanoferrate(III) and 4-nitrophenol by sodium borohydride. The kinetic investigations were carried out at different amount of AuNPs and different temperatures.     

Electrochemical solid-state phase transformations of silver nanoparticles

Adenosine triphosphate (ATP)-capped silver nanoparticles (ATP-Ag NPs) were synthesized by reduction of AgNO(3) with borohydride in water with ATP as a capping ligand. The NPs obtained were characterized using transmission electron microscopy (TEM), UV-vis absorption spectroscopy, X-ray diffraction, and energy-dispersive X-ray analysis. A typical preparation produced ATP-Ag NPs with diameters of 4.5 ± 1.1 nm containing ~2800 Ag atoms and capped with 250 ATP capping ligands. The negatively charged ATP caps allow NP incorporation into layer-by-layer (LbL) films with poly(diallyldimethylammonium) chloride at thiol-modified Au electrode surfaces. Cyclic voltammetry in a single-layer LbL film of NPs showed a chemically reversible oxidation of Ag NPs to silver halide NPs in aqueous halide solutions and to Ag(2)O NPs in aqueous hydroxide solutions. TEM confirmed that this takes place via a redox-driven solid-state phase transformation. The charge for these nontopotactic phase transformations corresponded to a one-electron redox process per Ag atom in the NP, indicating complete oxidation and reduction of all Ag atoms in each NP during the electrochemical phase transformation.     

Formulation of gold nanoparticles with hibiscus and curcumin extracts induced anti-cancer activity

Gold nanoparticles (AuNPs) have shown a potential for biological applications due to their biocompatibility and high efficiency in drug delivery. Most of the times, the chemical routs are being used to synthesize the AuNPs products. In this paper, eco-friendly non-chemical rout was used to prepare AuNPs by utilizing hibiscus and curcumin extracts as reducing and stabilizing agents, and subsequently their anticancer activities were investigated. The synthesized AuNPs were characterized by using ultraviolet–visible spectroscopy (UV–Vis spectroscopy), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). UV–Vis spectroscopy analysis confirmed the characteristics absorption peak of gold, and FTIR findings were highlighted the characteristics boding. SEM and TEM analyses showed that the particles were predominantly spherical in shape. The particles were well dispersed when they were prepared under Hibiscus extracts with average size ～ 13 nm. An interesting morphology was observed when AuNPs were prepared with curcumin, where particles displayed an interconnected morphology (average size ～ 18 nm). The anticancer cell activity of AuNPs was studied against human colorectal carcinoma cells (HCT-116) and breast cancer cells (Michigan Cancer Foundation-7 (MCF-7)). The results of anticancer study showed that the treatment of cancer cells with AuNPs decreased the number of cells significantly as compared to control cells. The AuNPs -Hibiscus specimen showed a better inhibiting property than AuNPs -Curcumin, which is attributed to their uniform dispersion and small size.     

Surface microstructure formation by ps‐ and fs‐laser ablation of an elastomer composite

We investigated the laser ablation of an elastomer composite with picosecond‐ (ps‐) and femtosecond‐ (fs‐) pulsed UV lasers (ps‐laser: λ = 263 nm, τ = 8 ps; fs‐laser: λ = 248 nm, τ = 500 fs). Upon laser irradiation, a unique microstructure on the surface of the elastomer composite (acrylate polymer) containing carbon black (particle size: 18–30 nm) was observed. The laser‐ablated surfaces were analyzed by scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS). The formation mechanism is discussed in terms of thermal effects induced by the different pulse durations of the lasers.     

Surface chemical states of gold nanoparticles prepared using the solution-plasma method in a CsCl aqueous solution

In this study, gold nanoparticles (AuNPs) prepared in a 5 mM CsCl aqueous solution using the solution-plasma method are characterized via transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy with synchrotron radiation (SR-XPS). The particle diameter is measured over the process time via TEM. During the solution-plasma process, small particles of 2.1 to 2.2-nm diameter are generated in the CsCl aqueous solution; these particles then enlarge via Ostwald ripening over time until they reach an equilibrium size of ~13 nm after 36 days. In addition, the surface chemical states of the AuNPs are characterized at different depths via SR-XPS. The SR-XPS measurements obtained using incident X-ray energy (hν) of 945.0 eV revealed that Cs─Au, Cl─Au, and Cs─Cl─Au bonds are present 1.2 nm below the surface. The measurements obtained at an incident X-ray energy of 2515.0 eV showed that Cs─Cl─Au bonding is also present 2.5 nm below the surface, indicating that Cs and Cl strongly interact with Au. The TEM and SR-XPS measurements revealed that 2 processes occur cyclically during the growth process via Ostwald ripening: (i) the Cs and Cl in the aqueous solution adsorb on the AuNP surface and (ii) Au atoms subsequently bond to the AuNPs surface.     

Electrostatically self-assembled azides on zinc sulfide nanoparticles as multifunctional nanoprobes for peptide and protein analysis in MALDI-TOF MS

A simple method to synthesize electrostatically self-assembled azides on zinc sulfide nanoparticles (ZnS-N₃ NPs) was described and then it was further applied as a multifunctional nanoprobe such as enriching, desalting, accelerating and separation-/washing free nanoprobes for rapid analysis of peptides and proteins and microwave assisted tryptic digested proteins in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The ZnS-N₃ NPs were characterized by UV-vis, FT-IR, SEM and TEM spectroscopy. The ZnS-N₃ NPs can effectively enrich signal intensities for 2-10 times for various peptides and proteins including HW6, insulin, ubiquitin, cytochrome c, lysozyme, myoglobin and bovine serum albumin (BSA) in MALDI-TOF MS. Furthermore, we also demonstrated that the ZnS-N₃ NPs can serve as accelerating probes for microwave assisted tryptic digestion of proteins in MALDI-TOF MS. The applicability of the present method on complex sample analysis such as milk proteins from cow milk and ubiquitin and ubiquitin like proteins from oyster mushroom were also demonstrated.     

Aggregation-resistant water-soluble gold nanoparticles

Stable, water-soluble gold nanoparticles, Au NPs, having an average diameter of ca. 4 nm, were prepared using place exchange reactions. The nanoparticles, capped with novel zwitterionic disulfide ligands, showed remarkable stability in saline media with salt concentrations as high as 3.0 M. Similarly, the Au NPs did not precipitate out of solution when charged polyelectrolytes or biopolymers were added, indicating the absence of nonspecific interactions. The stability and degree of association of Au NPs were characterized using UV-vis absorption spectroscopy, quasi-elastic light scattering, and surface-enhanced Raman scattering.     

Catalytic Reduction of p‐Nitrophenol and Hexacyanoferrate (III) by Borohydride Using Green Synthesized Gold Nanoparticles

A simple and green approach for the synthesis of well‐stabilized gold nanoparticles (AuNPs) using gum Acacia (GA) is presented here. The gum acacia acts as the reductant and stabilizer. The synthesized gold nanoparticles were characterized by using ultraviolet visible (UV‐Vis), fourier transform infrared spectroscopy (FTIR), x‐ray diffraction (XRD), dynamic light scattering (DLS) and transmission electron microscopy (TEM) techniques. The UV‐Vis study revealed a distinct surface plasmon resonance at 520 – 550 nm, due to the formation of AuNPs. FTIR analysis showed the evidence that –OH groups present in the gum matrix were responsible in reducing the tetra chloroauric acid into AuNPs. XRD studies confirmed the formation of well crystalline nanoparticles with fcc structure and the particle size ranges from 4 – 29 nm, as indicated by TEM analysis. The synthesized gold nanoparticles exhibited homogeneous catalytic activity. The two model reactions studied were the reduction of p‐nitro phenol and the reduction of hexacyanoferrate (III) by borohydride ions. Both the reactions were monitored by UV‐Vis spectroscopy. The kinetic investigations were carried out for the AuNPs‐catalyzed reactions at different temperatures and different amount of catalyst.     

Gelatin-coated gold nanoparticles as an effective pH-sensitive methotrexate drug delivery system for breast cancer treatment

The present study investigates the synthesis and effectiveness of gold/gelatin nanoparticles (NPs) biopolymer as a carrier for methotrexate (MTX) drug. Two different shapes of gold particles, including spherical AuNPs (50 & 100 nm) and gold nanorods (AuNRs) with three different sizes (20, 50 and 100 nm length) were synthesized using the chemical reduction method. The effect of AuNPs size and shape on the entrapment efficiency (E.E), the release rate of the drug, and cellular uptake were investigated. The surfaces of both AuNPs and AuNRs were coated with a gelatin biopolymer, and the stability and property of the generated compounds were studied. Moreover, MTX as a chemotherapeutic agent was loaded on the gelatin-coated AuNPs/AuNRs complexes. The physicochemical properties of the gelatin-coated AuNPs/AuNRs complexes were studied using ultraviolet-visible (UV–Vis) spectroscopy, dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR) spectroscopy. The E.E and MTX release behavior from the complexes at pH values of 7.4 and 5.4 and temperatures of 37 and 40 °C were investigated in vitro. The cytotoxic effects of AuNPs, AuNPs-Gelatin, AuNPs-Gelatin-MTX, AuNRs, AuNRs-Gelatin, AuNRs-Gelatin-MTX and free MTX were studied. The results indicated that the E.E of AuNPs was higher than that of AuNRs. The highest release rate of the drug was related to the AuNR1-gelatin complex (pH 5.4 and temperature of 40 °C). In addition, MTX loaded AuNR2-gelatin showed the highest cytotoxic effect on the MCF-7 breast cancer cell line so that even its cell cytotoxicity was more than that of the free drug.     

Formation of gold cluster cations by direct laser vaporization

Gold cluster cations, Au⁺_n, with n= 1 to 6 have been produced by direct laser vaporization of gold metal in a Fourier transform ion cyclotron resonance mass spectrometer. Wavelength studies at λ = 532, 355, and 266 nm show similar results. However, the intensities and intensity ratios of the cluster ions strongly depended on laser power at the two longer wavelengths. Ionization energies of Au⁺ , Au⁺₂, and Au⁺₃ have also been estimated.