A green approach for the synthesis of gold nanotriangles using aqueous leaf extract of Callistemon viminalis

In this present work, we developed a green method for the synthesis of stable Au NPs that does not require any of the conventional stabilizing ligands. This synthesis can be performed in minutes rather than hours, under very mild conditions using aqueous leaf extract of Callistemon viminalis. Gold nanotriangles so prepared were well characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), quasi elastic light scattering (QELS), UV-visible spectroscopy techniques etc. Powder X-ray diffraction plot revealed the presence of only gold in zero oxidation state.     

Surface plasmon-based nanopatterning assisted by gold nanospheres

A pulsed laser is used to produce surface plasmon excitation in a monolayer of gold (Au) spheres to nanopattern a silicon substrate. An electrodynamic model accompanies the experimental data, based on the numerical solution to the complete Maxwell's equations including near-?and far-field effects and reflection from the substrate. The Drude-employing finite-difference time-domain method describes the deformation and enhancement of the laser pulse around the boundary of a Au sphere and the resulting distribution of intensity incident upon the substrate. The effect of the incident laser angle on the plasmon generation and lithographic potential is studied.     

Extracellular synthesis gold nanotriangles using biomass of Streptomyces microflavus

Applications of nanotechnology and nano‐science have ever‐expanding breakthroughs in medicine, agriculture and industries in recent years; therefore, synthesis of metals nanoparticle (NP) has special significance. Synthesis of NPs by chemical methods are long, costly and hazardous for environment so biosynthesis has been developing interest for researchers. In this regard, the extracellular biosynthesis of gold nanotriangles (AuNTs) performed by use of the soil Streptomycetes. Streptomycetes isolated from rice fields of Guilan Province, Iran, showed biosynthetic activity for producing AuNTs via in vitro experiments. Among all 15 Streptomyces spp. isolates, isolate No. 5 showed high biosynthesis activity. To determine the bacterium taxonomical identity at genus level, its colonies characterised morphologically by use of scanning electron microscope. The polymerase chain reaction (PCR) molecular analysis of active isolate represented its identity partially. In this regard, 16S rRNA gene of the isolate was amplified using universal bacterial primers FD1 and RP2. The PCR products were purified and sequenced. Sequence analysis of 16S rDNA was then conducted using National Center for Biotechnology Information Basic Local Alignment Search Tool method. The AuNTs obtained were characterised by ultraviolet–visible spectroscopy, atomic force microscopy, transmission electron microscopy and energy dispersive X‐ray spectroscopy, Fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction spectroscopy analyses. The authors results indicated that Streptomyces microflavus isolate 5 bio‐synthesises extracellular AuNTs in the range of 10–100 nm. Synthesised SNPs size ranged from 10 to 100 nm. In comparison with chemical methods for synthesis of metal NPs, the biosynthesis of AuNTs by Streptomyces source is a fast, simple and eco‐friendly method. The isolate is a good candidate for further investigations to optimise its production efficacy for further industrial goals in biosynthesis of AuNTs.Inspec keywords: microorganisms, cellular biophysics, gold, nanobiotechnology, renewable materials, DNA, proteins, nanoparticles, scanning electron microscopy, genetics, biochemistry, enzymes, molecular configurations, bioinformatics, ultraviolet spectra, visible spectra, atomic force microscopy, transmission electron microscopy, X‐ray chemical analysis, Fourier transform spectra, infrared spectra, X‐ray diffraction, biological techniques, nanofabricationOther keywords: extracellular synthesis, biomass, Streptomyces microflavus, nanotechnology, nanoscience, biosynthesis, gold nanotriangles, Streptomycetes spp. isolates, rice fields, Guilan Province, Iran, bacterium taxonomical identity, genus level, scanning electron microscope, polymerase chain reaction, PCR, molecular analysis, 16S rRNA gene, universal bacterial primer FD1, universal bacterial primer RP2, sequence analysis, National Center for Biotechnology Information, ultraviolet‐visible spectroscopy, atomic force microscopy, transmission electron microscopy, energy dispersive X‐ray spectroscopy, Fourier transform infrared spectroscopy, FTIR, X‐ray diffraction spectroscopy, Basic Local Alignment Search Tool method, size 10 nm to 100 nm, Au     

Distinct plasmonic manifestation on gold nanorods induced by the spatial perturbation of small gold nanospheres

The plasmon coupling between a Au nanorod and a small Au nanosphere has been studied with scattering measurements, electrodynamic simulations, and model analysis. The spatial perturbation of the nanosphere leads to distinct spectral changes of the heterodimer. The plasmonic responses, including Fano resonance, are remarkably sensitive to the nanosphere position on the nanorod, the gap distance, and the nanocrystal dimensions. The nanosphere dipole is intriguingly found to rotate around the nanorod dipole to achieve favorable attractive interaction for the bonding dipole-dipole mode. The sensitive spectral response of the heterodimer to the spatial perturbation of the nanosphere offers an approach to designing plasmon rulers of two spatial coordinates for sensing and high-resolution measurements of distance changes.     

Hybridized surface-plasmon resonances of platinum colloid-adsorbed gold nanospheres

The surface-plasmon resonances of gold nanospheres dispersed in water split into two bands and shift to the red with the adsorption of colloidal platinum. These spectral changes are quite different from both the calculated and the experimental spectral variations of gold nanospheres with the thickness of coating platinum. Thus, these spectral changes have been attributed to the elementary plasmon interactions of the core gold and the adsorbed colloidal platinum as well as to the modification of the medium refraction index of the gold nanospheres. A simple and intuitive picture has been drawn to describe the hybridization plasmon interactions of a platinum colloid-adsorbed gold nanosphere.     

Structure-dependent coherent acoustic vibrations of hollow gold nanospheres

Hollow gold nanospheres (HGNs) were excited with ultrashort laser pulses, and the coherent vibrational response was examined using femtosecond time-resolved transient absorption. The results indicated that HGNs support an isotropic mode, resulting in periodic modulation of the surface plasmon differential absorption. Two different categories of coherent acoustic vibrations, which depend on particle dimensions, were observed for HGNs. Further, the vibration launching mechanism was dependent upon the dimensions of the HGN. Coherent vibrations in HGNs characterized by small outer radii (<10 nm) and low cavity-radius-to-outer-shell radius aspect ratios (<0.5) were excited by a direct mechanism, whereas the vibrations observed for the larger particles (>25 nm OR) with higher aspect ratios (>0.5) resulted from an indirect mechanism. These findings may be significant for developing a predictive understanding of nanostructure optical and mechanical properties.     

Magnetization reversal in nanotriangles fabricated by nanosphere lithography

We report on the magnetization reversal behavior of sub 100-nm triangular shaped Ni₈₀Fe₂₀ dot array fabricated by nanosphere lithography. Hysteresis loops measured by magneto-optical Kerr effect magnetometry are classified into single and double-switched loops in 45 nm, 80 nm and 100 nm triangular nanomagnets. Micromagnetic simulations show that a plateau observed in the double-switched loop in the 100-nm triangular nanomagnet is due to the formation of a metastable mediating V state.     

Synthesis of bismuth micro- and nanospheres by a simple refluxing method

Well-separated bismuth micro- and nanospheres were successfully prepared from bismuth citrate and urea by a simple refluxing reaction at 198 °C in ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP). The products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDX). The larger Brunauer–Emmett–Teller (BET) surface area of these micro- and nanospheres was found to be 17.34 m²/g by the results of N₂ adsorption. It was found that the amount of PVP have an influence on the morphologies of bismuth nanostructure. The possible growth mechanism of bismuth micro- and nanospheres was also discussed.     

Fabrication of organic shell-covered gold nanospheres with near-infrared absorption

A simple protocol is developed for the fabrication of stable organic shell-covered gold nanospheres with near-infrared absorption characteristics. The designed strategy mainly concentrates on two steps: (i) the polymerization of gold nanoparticles (AuNPs) induced by 1,2-ethanedithiol in water/ethanol; (ii) conjugation of the polymerized AuNPs with marocyclic compound for the formation of the organic shell. In the first step, the 1,2-ethanedithiol containing two thiols towards both ends of the chain enables the successful polymerization of AuNPs due to the forceful appetency of thiols to AuNPs. In the second step, the polymerized AuNPs are covered by the marocyclic compound attributing to the hydrogel-bonding effect between NH and SH. Because of the organic shell, the stability and dispersibility of the obtained nanospheres are improved. The optical properties of the fabricated gold nanospheres (400 nm average diameter) are well investigated by the UV-vis absorption spectroscopy which exhibit intense near-infrared absorption at 972 nm in acetone. The strategy developed in this study is promising in that excellent stability and dispersibility of gold nanospheres can be achieved in a facile and economic way.     

Irreversible adsorption of gold nanospheres on fiber optical tapers and microspheres

We study the adsorption of gold nanospheres onto cylindrical and spherical glass surfaces from quiescent particle suspensions. The surfaces consist of tapers and microspheres fabricated from optical fibers and were coated with a polycation, enabling irreversible nanosphere adsorption. Our results fit well with theory, which predicts that particle adsorption rates depend strongly on surface geometry and can exceed the planar surface deposition rate by over two orders of magnitude when particle diffusion length is large compared to surface curvature. This is particularly important for plasmonic sensors and other devices fabricated by depositing nanoparticles from suspensions onto surfaces with non-trivial geometries.     

Synthesis and characterization of fluorescent chitosan-ZnO hybrid nanospheres

Hybrid hollow nanospheres of chitosan-ZnO (CS-ZnO Nps) were successfully prepared by the in situ growing of ZnO quantum dots (QDs) in an aqueous solution consisting of a cationic polymer CS and an anionic monomer acrylic acid (AA), followed by the polymerization of AA and selectively crosslinking of CS with glutaraldehyde. The as-prepared nanospheres were characterized by transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), UV-visible spectrometer (UV) and fluorescence spectrophotometer (PL). ZnO QDs were dispersed evenly in the shell of hybrid nanospheres, with its dimension less than 5 nm. These fluorescent CS-ZnO Nps were expected to be simultaneously used as biological fluorescent labeling and a carrier for guest materials.     

Large-scale preparation of polyaniline nanospheres anchored with thiol-stabilized gold nanoparticles

Reported herein is the preparation of a new nanostructured composite consisting of PANI(SH) (where PANI(SH) is poly(aniline-co-4-aminothio phenol)) and gold nanoparticles (AuNPs)) via "seed"-induced bulk polymerization. The PANI(SH)-AuNPs composite was designated as PANI(SH)-Au-NS(P). The composite was characterized in terms of its morphology and structural, thermal, and electrochemical properties. The field emission scanning electron microscopy (FESEM) image of PANI(SH)-Au-NS(P) revealed the presence of PANI(SH) nanospheres (sizes: approximately 150-250 nm) with finely distributed AuNPs (approximately 10 nm). The usefulness of PANI(SH)-Au-NS(P) as an electrocatalyst towards the oxidation of methanol was tested.     

Colorimetric and dynamic light scattering detection of DNA sequences by using positively charged gold nanospheres: a comparative study with gold nanorods

We introduce a new genosensing approach employing CTAB (cetyltrimethylammonium bromide)-coated positively charged colloidal gold nanoparticles (GNPs) to detect target DNA sequences by using absorption spectroscopy and dynamic light scattering. The approach is compared with a previously reported method employing unmodified CTAB-coated gold nanorods (GNRs). Both approaches are based on the observation that whereas the addition of probe and target ssDNA to CTAB-coated particles results in particle aggregation, no aggregation is observed after addition of probe and nontarget DNA sequences. Our goal was to compare the feasibility and sensitivity of both methods. A 21-mer ssDNA from the human immunodeficiency virus type 1 HIV-1 U5 long terminal repeat (LTR) sequence and a 23-mer ssDNA from the Bacillus anthracis cryptic protein and protective antigen precursor (pagA) genes were used as ssDNA models. In the case of GNRs, unexpectedly, the colorimetric test failed with perfect cigar-like particles but could be performed with dumbbell and dog-bone rods. By contrast, our approach with cationic CTAB-coated GNPs is easy to implement and possesses excellent feasibility with retention of comparable sensitivity--a 0.1 nM concentration of target cDNA can be detected with the naked eye and 10 pM by dynamic light scattering (DLS) measurements. The specificity of our method is illustrated by successful DLS detection of one-three base mismatches in cDNA sequences for both DNA models. These results suggest that the cationic GNPs and DLS can be used for genosensing under optimal DNA hybridization conditions without any chemical modifications of the particle surface with ssDNA molecules and signal amplification. Finally, we discuss a more than two-three-order difference in the reported estimations of the detection sensitivity of colorimetric methods (0.1 to 10-100 pM) to show that the existing aggregation models are inconsistent with the detection limits of about 0.1-1 pM DNA and that other explanations should be developed.     

Synthesis of uniform and stable silver nanoparticles by a gold seed-mediated growth approach in a buffer system

A seeding growth approach to the preparation of silver nanoparticles with a controllable size was developed. It contained a two-step reaction: the first step was gold seed clusters quickly generated by a chemical reaction using sodium borohydride as a reducing reagent; the second one was controllable silver nanoparticles were grown at the mild condition by using the mixed reducing reagents (hydroxylamine hydrochloride and sodium hydroxide) to form a buffer system. The gold core was beneficial for the crystalline of silver cations to form the nanoparticles and the buffer system which was composed of hydroxylamine hydrochloride and sodium hydroxide, and was helpful for controlling the size and shape of the as-prepared silver nanoparticles. These as-prepared nanoparticles were characterised by X-ray powder diffraction, UV-Vis spectroscopy (UV-Vis) and transmission electron microscopy along with energy dispersive X-ray spectroscopy. The results indicated that the obtained silver nanoparticles are highly crystallised with an average diameter around 10?nm. The content of gold seeds and the mild reaction rate controlled by the buffer system were considered to be key factors in the control of silver nanoparticles’ morphology and size. A possible mechanism of the silver nanoparticles formed was also proposed.     

Synthesis of gold nanotubes by sputtering of gold into porous materials

Hollow 1-D gold nanostructures with controlled morphology could be readily obtained by RF-sputtering of gold into porous matrices (polycarbonate, polyester), used as scaffolds at low temperatures. Post-synthesis membrane etching by oxygen plasmas or in solution enabled the preparation of free-standing Au nanotubes maintaining the original morphology, that are attractive elements in device structures, such as biosensors for DNA chips or nanoelectrode ensembles. The present results appear extremely promising for the scale-up of different kinds of 1-D materials.     

Synthesis of carbonated hydroxyapatite nanospheres through nanoemulsion

This study investigated the nanoemulsion technique as a means to synthesize carbonated hydroxyapatite (CHAp) nanospheres which could be used to produce composite tissue engineering scaffolds. CHAp nanospheres were successfully synthesized by mixing an acetone solution of Ca(NO₃)₂ · 4H₂O with an aqueous solution of (NH₄)₂HPO₄ and NH₄HCO₃. Four reaction temperatures, namely, 4, 25, 37 and 55 °C, were investigated and no surfactant was added in all nanoemulsion processes. Wet slurries of CHAp from the nanoemulsions were freeze-dried to obtain dry powders. X-ray diffraction (XRD) results showed that the as-synthesized CHAp nanoparticles were mainly in an amorphous state. After calcination at 900 °C, the apatite became well crystallized. Fourier transform infrared (FTIR) spectroscopy showed that the CHAp was B-type substitution. Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the CHAp particles were spherical in shape and that their sizes were in the nanometer range. The successful synthesis of CHAp nanospheres is a critical step forward in our efforts to fabricate bone tissue engineering scaffolds using the selective laser sintering technology.     

Synthesis of gold nanoparticles: an ecofriendly approach using Hansenula anomala

This work describes a bioassisted approach for the preparation of metal nanoparticles using yeast species Hansenula anomala. Gold nanoparticles were prepared using gold salt as the precursor, amine-terminated polyamidoamine dendrimer as the stabilizer, and the extracellular material from H. anomala as the bioreductant. It could also be demonstrated that, using our approach, small molecules such as cysteine can act as stabilizers as well. This synthetic approach offers a greener alternative route to the preparation of gold sols that are devoid of cellular and toxic chemical components. The ability of as-synthesized gold sol to function as biological ink for producing patterns for the analysis of fingerprints and to act as an antimicrobial reagent is evaluated. The generality of this toxin-free synthetic approach to other metals was assessed using palladium and silver.     

Size-dependent effect of gold nanospheres on the acoustic pressure pulses from laser-irradiated suspensions

We carried out the experimental measurements of photoacoustic responses, where the suspensions of spherical gold nanoparticles (NPs) of different diameters (20, 40, and 50 nm) in water at different concentrations and different temperatures (4 and 20 °C) were irradiated by 0.8-ns laser pulses. In the case of 20 °C, the values of photoacoustic signals normalized by the light absorbance of the NP suspension decreased with increasing the NP size. The photoacoustic signals at 4 °C were significantly reduced compared with those at 20 °C. These experimental results are in fair agreement with the estimations from our phenomenological model, where the acoustic pressure pulse is represented by a sum of two contributions from the NPs and the surrounding liquid medium.     

Multichannel biosensing platform of surface-immobilized gold nanospheres for linear and nonlinear optical imaging

What we believe to be a new label-free multichannel biosensing platform is proposed. It is composed of surface-immobilized gold nanospheres (SIGNs) above a gold surface with a nanogap supported by a merocyanine self-assembled monolayer. The circular SIGN spots with a diameter of 120 microm were arrayed for multichannel biosensing on a glass slide. Two kinds of sensing methods were examined: One is a reflectivity measurement of a blue ray and the other is a second-harmonic generation measurement. It was found that the SIGN system can be used as a promising platform for multichannel biosensing in both sensing methods.     

Acousto-plasmonic and surface-enhanced Raman scattering properties of coupled gold nanospheres/nanodisk trimers

This work is devoted to the fundamental understanding of the interaction between acoustic vibrations and surface plasmons in metallic nano-objects. The acoustoplasmonic properties of coupled spherical gold nanoparticles and nanodisk trimers are investigated experimentally by optical transmission measurements and resonant Raman scattering experiments. For excitation close to resonance with the localized surface plasmons of the nanodisk trimers, we are able to detect several intense Raman bands generated by the spherical gold nanoparticles. On the basis of both vibrational dynamics calculations and Raman selection rules, the measured Raman bands are assigned to fundamental and overtones of the quadrupolar and breathing vibration modes of the spherical gold nanoparticles. Simulations of the electric near-field intensity maps performed at the Raman probe wavelengths showed strong localization of the optical energy in the vicinity of the nanodisk trimers, thus corroborating the role of the interaction between the acoustic vibrations of the spherical nanoparticles and the surface plasmons of the nanodisk trimers. Acoustic phonons surface enhanced Raman scattering is here demonstrated for the first time for such coupled plasmonic systems. This work paves the way to surface plasmon engineering for sensing the vibrational properties of nanoparticles.