Gold Nanocrystallites Research Articles

Viability of MDR bacteria against antibacterial biosynthesized ZnO and Au Nanoparticles

Abstract Introduction/Objective: Background Resistant strain diseases are increasing worldwide. Antimicrobials are concerned about pathogen-acquired resistance. Nanotechnology advances enable the creation of novel formulations based on various nanoparticles (NPs) with different sizes and antibacterial characteristics. Methods/Case Report Materials and methods All fungi were isolated and cultivated on malt extract broth. The endophytic fungus was cultured. Zn and Au nanoparticles have been produced by adding 0.1 M, 1 mL of Zn SO4, and HAuCl4 to 10 mL of fungal filtrate. Characterization of nanoparticles by the extracts' UV-visible spectrum shows ZnO NPs and Au NPs' green synthesis. UV-Vis, HR-TEM, XRD patterns, EDX analysis, and a Zeta-sizer characterize NPs' optical properties and morphology. Using 2,3,5-triphenyl tetrazolium chloride, biosynthesized Au and ZnO NPs' MICs against bacteria were determined. The bacterial culture was cultivated until it reached an Mc-Farland standard of 0.5. After that, 10 uL of bacterial suspension was pipetted into 140 uL of nutritional broth with 0.12 to 31.25 ug/mL ZnO and Au NPs. ZnO- and Au-free nutrient broth was used as a control. Wells that didn't turn red was examined for MIC values. Results (if a Case Study enter NA): Results The fungal filtrate's color changed from light yellow to colorless and violet after mixing with ZnSO4 and HAuCl4, respectively, ensuring nanoparticle formation. UV-Vis spectra: ZnO NPs were confirmed by excitonic absorption peaks between 300 and 400 nm; the maximum absorbance peak was 305 nm, while Au NPs' peak was 520 nm. Results showed that Au NPs and ZnO NPs have a hydrodynamic diameter (HD) of 34.88 nm and 15.77 nm, respectively. Our EDX analysis revealed that both nanoparticles have 64.61 and 35.39 % Zn and O stoichiometric mass percent. Energy dispersive X-rays showed a peak optical absorption band at 2.2 keV in gold nanocrystallites. Au NPs and ZnO NPs had MICs of 7.81 and 1.95 ug ml-1 against P. aeruginosa and 3.9 and 0.98 against E. coli, respectively. ZnO NPs' MIC against E. coli and P. aeruginosa is lower than Au NPs'. ZnO NPs increased microbial cell proliferation, and its inhibition was affected by the concentrations, sizes, and forms. Conclusion Our study investigated that the number of pathogens Escherichia coli and Pseudomonas aeruginosa decreases as nanoparticle concentration increases. So, ZnO NPs and Au NPs can inhibit bacterial development and cytoplasmic leak contents at lower concentrations.

Physico-Chemical Alternatives for Synthesis of Metal Nanoparticles Using Fusarium Chlamydosporum

Abstract Introduction/Objective Background: Synthesizing metal nanoparticles (NPs) by chemical or physical methods is difficult due to energy and time consumption, equipment costs, and chemical toxicity. Chemosynthesis-derived NPs are unstable, limiting their biological applications. Thus, identifying alternative green sources to address these drawbacks is difficult scientifically. The hardest part of green metal nanoparticle synthesis is finding a nontoxic natural product and an eco-friendly solvent. Objectives: Isolation of fungal endophytes from Eucalyptus sideroxylon leaves to synthesize ZnO and Au nanoparticles. Methods/Case Report Materials and methods: We used healthy Eucalyptus sideroxylon plant samples from the desert research center to separate endophytes. All fungi were grown on malt extract broth on a rotary shaker at 28 °C (120 rpm) for 96 hours after isolation. Biomass components were removed by filtration and washing in distilled water. Nanoparticles came from biomass cell filtrate. 0.1 M, 1 mL of Zn SO4, and HAuCl4 were added to 10 mL of fungal filtrate and agitated for 24 hours in the dark at room temperature to make Zn and Au nanoparticles separately. Characterization of nanoparticles shows a green synthesis of ZnONPs and AuNPs. Results (if a Case Study enter NA) Results: Fungal endophytes' filtrates were mixed with 1mM Zn SO4 and HAuCl4 solutions to test their extracellular biosynthesis of ZnO and Au NPs. The fungal filtrate became colorless and violet after mixing with Zn SO4 and HAuCl4. Only FI-03 is from 13 (FI-01 to FI-013). The most potent fungal strain for Zn O NP and Au NP nanoparticle synthesis was Fusarium Chlamydosporum. Pure, mostly spherical ZnO and Au NPs averaged 19.3 and 22.1 nm. UV-Vis absorption: Excitonic absorption peaks of ZnO NPs were between 300 and 400 nm. ZnO NPs' maximum absorption peak was 305 nm, while Au NPs' peak was 520 nm. One absorption peak indicates metallic gold nanoparticles. Au and ZnO NPs aggregate the most due to their hydrophilicity, HD of 34.88 and 15.77 nm, and PdI of 0.77, 1.00, and 0.952. Gold face-centered cubic fcc structure dominates Au NPs' XRD pattern. EDX shows 64.61 and 35.39 percent Zn and O, respectively, in both nanoparticles. The optical absorption band of gold nanocrystallites peaked at 2.2 keV in energy-dispersive X-rays. Conclusion Endophytic fungus biosynthesizes ZnO and Au NPs, which are bioactive compounds for medicine and food without toxic chemicals and are environmentally friendly.

Fabrication of Antibacterial Metal Surfaces Using Magnetron-Sputtering Method.

One-hundred-nanometer films consisting of silver, copper, and gold nanocrystallites were prepared, and their antibacterial properties were quantitatively measured. The magnetron-sputtering method was used for the preparation of the metallic films over the glass plate. Single- and double-layer films were manufactured. The films were thoroughly characterized with the XRD, SEM, EDS, and XPS methods. The antibacterial activity of the samples was investigated. Gram-negative Escherichia coli, strain K12 ATCC 25922 (E. coli), and Gram-positive Staphylococcus epidermidis, ATCC 49461 (S. epidermidis), were used in the microbial tests. The crystallite size was about 30 nm in the cases of silver and gold and a few nanometers in the case of copper. Significant oxidation of the copper films was proven. The antibacterial efficacy of the tested samples followed the order: Ag/Cu > Au/Cu > Cu. It was concluded that such metallic surfaces may be applied as contact-killing materials for a more effective fight against bacteria and viruses.

Environmentally benign rapid biosynthesis of extracellular gold nanoparticles using Aspergillus flavus and their cytotoxic and catalytic activities

In this study, the rapid biosynthesis of gold nanoparticles (AuNPs) by Aspergillus flavus culture supernatant was achieved by reducing 1 mM of chloroauric acid (HAuCl4) within 2 min at pH 7 and 30 °C. The biosynthesized nanoparticles exhibited maximum absorbance at 545 nm in UVvis spectroscopy. Transmission electron microscopy exhibited that AuNPs tend to take nearly spherical shapes with an average size of 12 nm. Fourier transform infrared analysis indicated that carboxyl, amine, and hydroxyl groups may participate in the biosynthesis and stabilization of AuNPs. Its zeta potential was found to be -33.01 mV. Energy dispersive X-rays showed a strong and typical beak of gold nanocrystallites with 80.84 % of analyzed sample. X-Ray diffraction spectrum displayed Bragg reflections identical to the gold nanocrystals. The results confirmed that biosynthesized AuNPs are a potent anticancer agent against A549, HepG2 and MCF7 cell lines with IC50 value 53.5, 60.7 and 100 μg/mL, respectively. Crystal violet assay confirmed the cytopathic effects of AuNPs on HepG2 and A549 cell lines. Annexin-V FITC assay and cell cycle confirmed the apoptotic effect and cell cycle arrest in G2/M phase, respectively for A549 cell line. Moreover, the results showed a degradation efficiency of AuNPs to 4-nitrophenol within 16 min.

Investigation of Glucose Oxidation on Gold Nanocrystallites Modified Cobalt and Cobalt-Boron Coatings

Herein, the electrochemical oxidation of glucose has been investigated on the Co and CoB alloy coatings, which were deposited on the copper substrate (Cu) and subsequently modified with a small amount of Au nanocrystallites (termed as the AuCo/Cu and AuCoB/Cu catalysts), with the aim to use them as the anode catalysts for direct glucose fuel cells (DGFCs). The catalysts have been prepared via a simple electroless Co deposition method followed by a spontaneous Au galvanic displacement from the Au(III)-containing solution. The activity of the prepared catalysts for the oxidation of glucose in an alkaline medium has been examined by cyclic voltammetry and chrono-techniques.In conclusion, the Co and CoB alloy coatings, which were modified with a small amount of Au nanocrystallites in the range from 11 to 14 µg Au cm–2, exhibit a significantly higher activity for the oxidation of glucose as compared to that of bare Au, Co and CoB alloy catalysts. Furthermore, the process of glucose oxidation has been significantly shifted to more negative potential domain at the both AuCo/Cu and AuCoB/Cu catalysts, indicating the higher activity of the latter catalysts as compared to that of the unmodified Co/Cu and CoB/Cu catalysts and the bare Au electrode. In addition, approximately 22 and even 67 times higher glucose oxidation current density values have been obtained at the AuCo/Cu and AuCoB/Cu catalysts, respectively, as compared to those for the unmodified CoB/Cu and Co/Cu. The prepared AuCo/Cu and AuCoB/Cu catalysts, which have been prepared with very small amount of Au nanocrystallites, seem to be a promising anode material for DGFCs.

Plasmon-Enhanced Two-Photon Absorption of Infrared Femtosecond Laser Pulses in Thin Gold Films

The transmission of femtosecond laser pulses of the near-infrared range (wavelength of 1030 nm) through nanocrystalline gold films with a variable thickness (15–90 nm) has been experimentally studied for various intensities of laser radiation in the range of 1–10 TW/cm2. A dip in the transmission coefficient at the wave-length of pump pulses at moderate radiation intensities is due to two-photon transitions from d bands with a high density of states to s and p bands with a low density of states and their saturation at higher intensities. The cross section is estimated for two-photon absorption in gold films enhanced by plasmon resonance of gold nanocrystallites at the wavelength of the second harmonic of exciting radiation, which is compared to values for gold films and various plasmon nanostructures known for other spectral ranges.

Medium constituents mediated engineering for size and shape tuning of gold nanocrystallites

Abstract The current investigation introduces the utilization of cell culture mediums as a novel source for the one-plot synthesis as well as stabilization of metal nanoparticles. By varying the medium constituents we could control the size and shape distributions of the gold nanoparticles. Nanospheres of diameter 24 ± 6 nm and 19 ± 5 nm were produced using DMEM and M199 mediums respectively, nanoneedles of 150 ± 50 nm using RPMI medium and nanoflowers of 60 ± 25 nm using IMDM medium, with an overall yield of 91 ± 2%. A remarkable decrease in the reaction duration (

Recrystallization and formation of spheroidal gold particles in amorphous-like AlN–TiB2–TiSi2 coatings after annealing and subsequent implantation

The recrystallization of the structure of an X-ray amorphous AlN–TiB2–TiSi2 coating containing short-range order regions with characteristic sizes of 0.8–1.0 nm has been performed using a negative gold ion (Au–) beam and high-temperature annealing. Direct measurements using methods of high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectral (EDXS) microanalysis have demonstrated that thermal annealing at a temperature of 1300°C in air results in the formation of nanoscale (10–15 nm) phases AlN, AlB2, Al3O3, and TiO2, whereas the ion implantation of negative ions Au– leads to a fragmentation (decrease in the size) of nanograins to 2–5 nm with the formation of spheroidal gold nanocrystallites a few nanometers in size, as well as to the formation of an amorphous oxide film in the depth (near-surface layer) of the coating due to ballistic ion mixing and collision cascades.

Surface plasmon resonance caused by gold nanoparticles formed on sprayed TiO2 films

Titania films covered by gold nanoparticles are prepared by combination of spray pyrolysis and spin-coating methods. Proposed combination of techniques is prospective for photovoltaic coatings with plasmonic properties. The prepared TiO2 films with Au nanoparticles demonstrate variation in size of the gold nanocrystallites from 36 to 56nm depending on the concentration of the HAuCl4∙3H2O solution and plasmonic light extinction in the spectral range of 600–650nm. It is shown that gold nanocrystallites enhance Raman scattering from the underlying thin TiO2 film.

Enhancement of high-TC superconducting thin film devices by nanoscale polishing

The effects of mechanical nanoscale polishing on the superconducting parameters of YBa2Cu3O7−δ (YBCO) thin films and bi-crystal grain boundary Josephson junctions have been investigated. We prepared samples with additional gold nanocrystallites in the YBCO film. As they are distributed throughout the whole YBCO film, they provide a low-resistance ohmic contact even if parts of the film are removed. Polishing was performed either before or after the patterning and did not change the properties of the grain boundary. However, nanopolishing reduces the film roughness in a significant way, which makes it an indispensable tool for the preparation of integrated superconducting circuits. We also succeeded in tuning the IC and RN of the Josephson junctions of direct current superconducting quantum interference devices (dc-SQUIDs) by systematically reducing the film thickness, which opens up new possibilities in the application of magnetic field sensors.

Biofabrication of discrete spherical gold nanoparticles using the metal-reducing bacterium Shewanella oneidensis

Nanocrystallites have garnered substantial interest due to their various applications, including catalysis and medical research. Consequently important aspects of synthesis related to control of shape and size through economical and non-hazardous means are desirable. Highly efficient bioreduction-based fabrication approaches that utilize microbes and/or plant extracts are poised to meet these needs. Here we show that the γ-proteobacterium Shewanella oneidensis can reduce tetrachloroaurate (III) ions to produce discrete extracellular spherical gold nanocrystallites. The particles were homogeneously shaped with multiple size distributions and produced under ambient conditions at high yield, 88% theoretical maximum. Further characterization revealed that the particles consist of spheres in the size range of ∼2–50 nm, with an average size of 12 ± 5 nm. The nanoparticles were hydrophilic and resisted aggregation even after several months. Based on our experiments, the particles are likely fabricated by the aid of reducing agents present in the bacterial cell membrane and are capped by a detachable protein/peptide coat. Ultraviolet–visible and Fourier transform infrared spectroscopy, X-ray diffraction, energy dispersive X-ray spectra and transmission electron microscopy measurements confirmed the formation, surface characteristics and crystalline nature of the nanoparticles. The antibacterial activity of these gold nanoparticles was assessed using Gram-negative ( Escherichia coli and S. oneidensis) and Gram-positive ( Bacillus subtilis) bacterial species. Toxicity assessments showed that the particles were neither toxic nor inhibitory to any of these bacteria.

Field emission properties of composite nano-Au/DLC films prepared by CVD technique

Nanocrystalline gold incorporated diamond-like carbon (nano-Au/DLC) films were deposited by capacitively coupled plasma (CCP) r.f. chemical vapour deposition (CVD) technique. Gold content in the DLC matrix was controlled by the amount of argon in the argon + methane mixture in the plasma. Field emission properties of these films were studied critically. Bonding environment (sp 2/sp 3 ratio) in these films was obtained from Raman measurements. Modification of the surface with the incorporation of gold nanocrystallites and associated modulation of sp 2/sp 3 ratio in the films culminated in improved field emission properties. Fowler–Nordheim model was used to ascertain the work function ( ϕ) which varied between 19 and 64 meV. The field factor ( β) varied between 172 and 1050.

Dynamics of low-coordinated surface atoms on gold nanocrystallites

The authors highlight the importance of transient configurations of atoms on the surface of nanocrystallites, and present methodologies for their investigation. A Monte Carlo method has been developed and is used to simulate the thermodynamic equilibrium of nanometer sized Au nanocrystallites, both free and supported on a MgO(100) surface. The authors find that appreciable numbers of atoms transiently occupy adatom positions on Au(111) facets, even at room temperature. This type of dynamically appearing site is usually neglected in relation to catalysis but may have a significant activity (for CO oxidation, for example). They also observe a complex solid-solid roughening transition which involves a variety of transient local atom configurations on the surface of nanocrystallites.

Transient Atomic Configurations of Supported Gold Nanocrystallites at Finite Temperature

A Monte Carlo method has been developed to investigate the dynamic configurations of nanometer-sized An nanocrystallites (NCs) supported on the MgO(100) surface. We have found significant concentrations of An atoms that transiently occupy adatom positions on Au(111) facets. Their concentration increases from 10(-4) per NC at 250 K to 10(-2) per NC at 550 K. A complex roughening transition involving the creation of steps on Au(111) facets is observed close to 500 K. The appreciable numbers of various local atom configurations that may transiently appear on NC at finite temperature may be important for many applications using NCs.

Nanocrystalline Domain Identification in Gold Films, by Backscattered Electron Imaging and Energy-Filtered Transmission Electron Microscopy

Gold nanocrystallites dispersed in an inhomogeneous gold matrix are detected by high-resolution scanning electron microscopy using a field emission source and backscattered electron detection in the composition mode, as well as by energy-filtered transmission electron microscopy in the plasmon energy region. The identity of the nanocrystalline domains was established by observing the same evaporated gold film samples but using bright-field, dark-field, electron diffractogram, and electron energy loss spectroscopy images in the transmission electron microscope. Comparison of these images shows that backscattered electron and plasmon energy detection can be used to identify crystalline domains in an otherwise chemically uniform sample.

Structure and Thermodynamics of Self-Assembled Monolayers on Gold Nanocrystallites

Equilibrium structures and thermodynamic properties of dodecanethiol self-assembled monolayers on small (Au140) and larger (Au1289) gold nanocrystallites were investigated with the use of molecular dynamics simulations. Compact passivating monolayers are formed on the (111) and (100) facets of the nanocrystallites, with adsorption site geometries differing from those found on extended flat Au(111) and Au(100) surfaces, as well as with higher packing densities. At lower temperatures the passivating molecules organize into preferentially oriented molecular bundles with the molecules in the bundles aligned approximately parallel to each other. Thermal disordering starts at T ≳200 K, initiating at the boundaries of the bundles and involving generation of intramolecular conformational (gauche) defects which occur first at bonds near the chains' outer terminus and propagate inward toward the underlying gold nanocrystalline surface as the temperature is increased. The disordering process culminates in melting of...

Structure, Dynamics, and Thermodynamics of Passivated Gold Nanocrystallites and Their Assemblies

The structure, dynamics, and thermodynamics of gold nanocrystallites passivated by alkylthiolate monolayers were investigated, using molecular dynamics simulations, in different environmentsas isolated gas-phase clusters, when adsorbed on a graphite surface, and when assembled into three-dimensional superlattices. The packing arrangements and densities of the monolayers passivating the facets of the core gold nanocrystallites differ from those found on extended gold surfaces, exhibiting organization into molecular bundles of preferred orientations which upon heating undergo a reversible melting transition from the ordered bundled state to a uniform intermolecular orientational distribution. The equilibrium geometries of adsorbed nanocrystallites depend on the chain length of the passivating molecules which effectively lubricate the interface between the gold core and the graphite surface conferring high surface mobility to the crystallites, involving a collective slip-diffusion mechanism. The room-tempera...

Atomic-Force Microscopy of Gold Nanocrystallites on Smooth and Stepped Strontium Titanate Surfaces

ABSTRACTWe have studied the nucleation and growth of Au nanocrystallites with dimensions of tens of nanometers on strontium titanate surfaces using an atomic force microscope. Strontium titanate ablated from a pressed pellet target by a KrF laser was deposited on both planar and offcut strontium titanate substrates. In a separate step, submonolayer quantities of gold were deposited, also by pulsed laser deposition, on the strontium titanate. The surfaces were then scanned by an atomic-force microscope to determine the effects of surface defects (such as steps and kinks on offcut surfaces), substrate temperature, and gold ablation yield on the nucleation, growth and size distribution of the nanocrystallites. The competition between diffusion and nucleation on planar vs stepped surfaces was particularly apparent in the AFM images. These results suggest several ways in which lateral decoration of the strontium titanate by the gold nanocrystallites can be achieved, an important step toward designer nonlinear photonic materials.