Picosecond nonlinear optical studies of gold nanoparticles synthesised using coriander leaves (Coriandrum sativum)

The results are presented from the experimental picosecond nonlinear optical (NLO) studies of gold nanoparticles synthesised using coriander leaf (Coriandrum sativum) extract. Nanoparticles with an average size of ～30?nm (distribution of 5–70?nm) were synthesised according to the procedure reported by Narayanan et al. [Mater. Lett. 2008, 62, 4588–4591]. NLO studies were carried out using the Z-scan technique using 2?ps pulses near 800?nm. Open-aperture data suggested saturation absorption as the nonlinear absorption mechanism, whereas closed-aperture data suggested a positive nonlinearity. The magnitude of third-order nonlinearity was estimated to be (3.3?±?0.6)?×?10^?13?esu. A solvent contribution to the nonlinearity was also identified and estimated. A comparison is attempted with some recently reported NLO studies of similar gold nanostructures.     

Highly reproducible solid-phase extraction membrane for removal and surface-enhanced Raman scattering detection of antibiotics

A disposable solid-phase extraction (SPE) membrane was developed for rapid removal and sensitive surface-enhanced Raman scattering (SERS) detection of antibiotics in water samples. The membrane was fabricated on commercially available SPE column by filtration of the activated carbon modified with silver nanoparticles (Ag NPs/AC). The prepared SPE membrane exhibited outstanding preconcentration ability due to the high adsorption properties of AC, and excellent ability to enhance Raman signal resulting from “hot spots” between the embedded Ag NPs, improving the sensitivity of SERS detection. A detection limit (LOD) of 5.0?×?10^?11 and 1.6?×?10^?10 M was achieved for rhodamine 6G and p-aminothiophenol. In addition, the membrane exhibited high reproducibility with spot-to-spot variation in SERS spectral intensity less than 15%. Based on the membrane, the qualitative and quantitative analysis of the antibiotics in aqueous solution was accomplished with the LOD at nM level, demonstrating the feasibility of the disposable SPE membrane for in situ rapid preconcentration and detection.     

In vitro biomechanical properties,fluorescence imaging,surface-enhanced Raman spectroscopy,and photothermal therapy evaluation of luminescent functionalized CaMoO4:Eu@Au hybrid nanorods on human lung adenocarcinoma epithelial cells

Highly dispersible Eu³⁺-doped CaMoO₄@Au-nanorod hybrid nanoparticles (HNPs) exhibit optical properties, such as plasmon resonances in the near-infrared region at 790 nm and luminescence at 615 nm, offering multimodal capabilities: fluorescence imaging, surface-enhanced Raman spectroscopy (SERS) detection and photothermal therapy (PTT). HNPs were conjugated with a Raman reporter (4-mercaptobenzoic acid), showing a desired SERS signal (enhancement factor 5.0 × 10⁵). The HNPs have a heat conversion efficiency of 25.6%, and a hyperthermia temperature of 42°C could be achieved by adjusting either concentration of HNPs, or laser power, or irradiation time. HNPs were modified with antibody specific to cancer biomarker epidermal growth factor receptor, then applied to human lung cancer (A549) and mouse hepatocyte cells (AML12), and in vitro PTT effect was studied. In addition, the biomechanical properties of A549 cells were quantified using atomic force microscopy. This study shows the potential applications of these HNPs in fluorescence imaging, SERS detection, and PTT with good photostability and biocompatibility.     

Facile chemical synthesis of nano-silver powders for printable electronics applications

In this article, a simple and reproducible technique for the synthesis of silver nanoparticles in organic phase without using external reducing agents is reported. The organic phase contains silver acetate as precursor, oleic acid and oleyl amine as capping molecules and diphenyl ether as solvent. Monodispersed silver nanoparticles with an average size of 5?nm could be easily synthesised at large scale and it was possible to isolate the particles suitable for electronics applications. The formation of silver nanoparticles has been characterised in terms of optical absorption, transmission electron microscopy images and small-angle X-ray scattering. Recovered silver nanoparticles reveal X-ray diffraction of a well grown-up fcc-Ag lattice. Chemical and thermal characterisations of silver nanopowders were carried out using X-ray photoelectron spectroscopy and thermogravimetric analysis, respectively. For the latter purpose, concentrated dispersions of silver nanoparticles were prepared and used for depositing uniform thin layers. Thin films were sintered at low temperature to obtain conductive films and the films were characterised using scanning electron microscope. Electrical conductivity of the conductive films was in the range 2–3?×?10⁴?S?cm^?1.     

Isotropical conductive adhesives with very-long silver nanowires as conductive fillers

Isotropical conductive adhesives (ICAs) have garnered great attention from the researchers in electronic industry as a potential substitute to lead-bearing solders for novel microsystem. In this paper, silver nanowires with a diameter of approximately 390 nm and a length of over 100 μm were synthesized by a polyol process. The ICAs composed of an epoxy-based binder containing silver nanowire were prepared and the curing behaviors, electrical properties, hygroscopicity, and the tensile shear strength of ICAs were investigated. Silver nanowires affect the curing behavior of epoxy resin and reduce the cross-linking density. The resistivity of the ICAs filled with 10, 35 and 45 wt% silver nanowire cured at 150 °C is 8.9 × 10^?3, 1.69 × 10^?5 and 4.9 × 10^?6 Ω cm respectively. The resistivity of the ICAs filled with silver nanowire cured at 150 °C is little change after aged under 85 °C/85 % for 264 h. With the increase of the loading of silver nanowire the tensile shear strength of the ICAs increase. The reasons for the effects of silver nanowires on the curing behavior and the electrical property and hygroscopicity and the tensile shear strength were discussed in terms of the morphology, distribution, and higher activity of silver nanowires.     

Nanospheres Containing Urea: Photothermic Properties

In the present research, nanospheres of chitosan (CS), maltodextrin, and sodium tripolyphosphate (STPP), loaded with urea, were synthesized by using an ionic gelation technique. In the nanosphere synthesis was used a central composite experimental design, obtaining nanospheres with an average size of 275?±?32 nm and 27.5 mV zeta potential. The nanospheres were characterized by their hydrodynamic diameter, polydispersity index, nitrogen content, and thermal properties such as thermal diffusivity (α), effusivity (e), and conductivity (k); also melting temperature was obtained by differential scanning calorimetry. The thermal properties of nanospheres show that the sample with the smallest size has a thermal diffusivity value of (14.4?±?0.4)?×?10^?8 m²·s^?1 and a thermal conductivity value of (6.4?±?0.1)?×?10^?1 W·m^?1·K^?1, and the obtained melting temperature was 157 °C. Higher concentrations of CS increase the values of these thermal properties, probably because chitosan interacts ionically with STPP forming a reticular network due to the opposite charges of both molecules.     

Photothermal Beam Deflection Spectroscopy for the Determination of Thermal Diffusivity of Soils and Soil Aggregates

Photothermal beam deflection spectroscopy (BDS) with a red He–Ne laser (632.8 nm, 35 mW) as an excitation beam source and a green He–Ne laser (543.1 nm, 2 mW) as a probe was used for estimating thermal diffusivity of several types of soil samples and individual soil aggregates with small surfaces (2?×?2 mm). It is shown that BDS can be used on demand for studies of changes in properties of soil entities of different hierarchical levels under the action of agrogenesis. It is presented that BDS clearly distinguishes between thermal diffusivities of different soil types: Sod-podzolic [Umbric Albeluvisols, Abruptic], 29?±?3; Chernozem typical [Voronic Chernozems, Pachic], 9.9?±?0.9; and Light Chestnut [Haplic Kastanozems, Chromic], 9.7?±?0.9 cm²·h^?1. Aggregates of chernozem soil show a significantly higher thermal diffusivity compared to the bulk soil. Thermal diffusivities of aggregates of Chernozem for virgin and bare fallow samples differ, 53?±?4 cm²·h^?1 and 45?±?4 cm²·h^?1, respectively. Micromonoliths of different Sod-podzolic soil horizons within the same profile (topsoil, depth 10–14 cm, and a parent rock with Fe illuviation, depth 180–185 cm) also show a significant difference, thermal diffusivities are 9.5?±?0.8 cm²·h^?1 and 27?±?2 cm²·h^?1, respectively. For soil micromonoliths, BDS is capable to distinguish the difference in thermal diffusivity resulting from the changes in the structure of aggregates.     

A Novel Fullerene Hydroxamic Acid for the Liquid–Liquid Extraction,Separation, Preconcentration,and Spectrophotometric and ICP‐AES Determination of Vanadium

Abstract

A new reagent N‐phenyl‐(1,2 methanofullerene C₆₀)61‐formohydroxamic acid (PMFFA) is reported for extraction and trace determination of vanadium(V) in nutritional and biological substrates. The extraction mechanism of vanadium from 6 M HCl media is investigated. The influence of PMFFA, diverse ions, and temperature on the distribution constant of vanadium examined. The over all stability constant (log β₂ K _e ) and extraction constant (K _ex) are 20.89 ± 0.02 and 8.0 ± 0.02 × 10^?15, respectively in chloroform. The thermodynamics parameters are calculated and kinetics of vanadium transport is discussed. The system obeys Beer's law in the range of 3.2–64.0 ng mL^?1 of vanadium(V). The molar absorptivity is 7.96 × 10⁵ L mol^?1 cm^?1, at 510 nm. The PMFFA–vanadium(V) complex chloroform extract in chloroform was directly inserted into plasma for ICP‐AES measurement, which increases the sensitivity by 50 folds and obey Beer's law in the range of 50–1200 pg mL^?1 of vanadium(V). The method is applied for determination vanadium in real standard samples, sea water, and environmental samples.     

An effective three-dimensional surface-enhanced Raman scattering substrate based on oblique Si nanowire arrays decorated with Ag nanoparticles

Silicon nanowire arrays (SiNWAs) decorated with metallic nanoparticle heterostructures feature promising applications in surface-enhanced Raman scattering (SERS). However, the densely arranged SiNWAs are usually inconvenient for the following decoration of metallic nanoparticles, and only the top area of silicon nanowires (SiNWs) contributes to the SERS detection. To improve the utilization of the heterostructure, herein, oblique SiNWAs were grown separately, and Ag nanoparticles (AgNPs) were uniformly deposited by magnetron sputtering to get the three-dimensional (3D) SiNWAs decorated with AgNPs (AgNPs-SiNWAs) SERS substrate. The large open surfaces of oblique SiNWs would create more surface area available for the formation of hotspots and improve the adsorption and excitation of analyte molecules on the wire. The optimized AgNPs-SiNWAs substrate exhibits high sensitivity in detecting chemical molecule Rhodamine 6G, and the detection limit can reach 1 × 10^?10 M. More importantly, the substrate also can be used as an effective DNA sensor for label-free DNA detection.     

Determining the number of layers in graphene films synthesized by filtered cathodic vacuum arc technique

We have synthesized graphene film by the filtered cathodic vacuum arc (FCVA) technique and determined the number of layers in graphene films by various techniques. Amorphous carbon (a-C) films of different thicknesses (1, 2, 3, 6, 10 and 18 nm) were synthesized by the FCVA technique on Si/SiO₂/Ni substrate and then annealed in vacuum at 800°C and cooled down to room temperature naturally to obtain graphene. Prepared graphene films were transferred on different substrates and characterized by the Raman spectroscopy, UV-VIS-NIR spectroscopy, high-resolution transmission electron microscopy (HRTEM), optical microscopy, atomic force microscopy (AFM) and sheet resistance to determine the number of layers present in the graphene films. Raman spectra of the prepared graphene films exhibit that there is red shift in the position of D, G and 2 D peak. The value of I_2D/I_G varied from 0.18 to 0.51, I_D/I_G varied from 0.82 to 1.02 and full width at half maximum of 2 D peak varied from 101.2 to 128.0 cm^?1, for different thicknesses of graphene films, respectively. The value of transmittance decreases from 97 to 63.7% and that of sheet resistance increases from 460 to 1400 Ω/square with the increase in the thickness of the prepared graphene film. The HRTEM and AFM study revealed that the graphene synthesis from 1 nm thick a-C film possesses a single layer structure.     

Large third-order nonlinearity of nonpolar A-plane GaN film at 800 nm determined by Z-scan technology

We report an investigation on the optical third-order nonlinear property of the nonpolar A-plane GaN film. The film sample with a thickness of ~2?μm was grown on an r-plane sapphire substrate by metal-organic chemical vapor deposition system. By performing the Z-scan method combined with a mode-locked femtosecond Ti:sapphire laser (800?nm, 50?fs), the optical nonlinearity of the nonpolar A-plane GaN film was measured with the electric vector E of the laser beam being polarized parallel (//) and perpendicular (⊥) to the c axis of the film. The results show that both the third-order nonlinear absorption coefficient β and the nonlinear refractive index n₂ of the sample film possess negative and large values, i.e. β_//?=??135?±?29?cm/GW, n_2//?=??(4.0?±?0.3)?×?10^?3?cm²/GW and β_⊥?=??234?±?29?cm/GW, n_2⊥?=??(4.9?±?0.4)?×?10^?3?cm²/GW, which are much larger than those of conventional C-plane GaN film, GaN bulk, and even the other oxide semiconductors.     

Surface-enhanced Raman spectroscopy studies of orderly arranged silica nanospheres-synthesis,characterization and dye detection

Silica nanospheres have been explored much for drug delivery, photocatalysis, sensors and energy storage applications. It also acts as a template for Surface-Enhanced Raman Spectroscopy (SERS) substrates. Uniform nanostructures at low cost with high reproducibility are the major challenges in SERS substrate fabrication. In the present work, silica nanospheres were synthesized using stober method and deposited on to glass slides using Vertical deposition techniques. Different size/thickness of Silver (Ag) nanoparticles were deposited onto silica thin films using sputter deposition technique. The monodispersity of silica nanospheres and size of silver nanoparticles (10 nm, 20 nm and 30 nm) were confirmed by FESEM analysis. The structural properties were confirmed through XRD. UV–Vis analysis revealed that the plasmonic properties of Ag@SiO₂ give high surface plasmons for 30 nm thickness of silver. The binding energy of Ag@SiO₂ confirmed through XPS spectrum. The fabricated SERS substrates were used to detect Rhodamine 6G (R6G), Methylene blue (MB), Methylene violet (MV) and Methyl orange dyes as an analyte molecule with a limit of detection at about 10^?11 mol/L. The addition of SiO₂ nanospheres decreases the Ag oxidation rate and increases their stability. The maximum enhancement factor (1.5?×?10⁷) achieved for 30nm thickness of Ag@SiO₂. The results and technique establish the potential applications and reproducible SERS substrate.

     

Synthesis and antibacterial activity of stable bio-conjugated nanoparticles mediated by walnut (Juglans regia) green husk extract

Nanoparticles have gained significant attention in recent years due to their numerous applications in various aspects of human life. A variety of methods have been investigated for synthesis of nanoparticles among which, biogenic approaches are considered as both simple and eco-friendly. Here, a new single-step biological approach was employed for synthesis of silver chloride nanoparticles (AgCl-NPs) at room temperature, using walnut green husk extract. Macromolecules present in the plant extract, which might act as bio-reductants and/or stabilisers of nanoparticles were characterised by Fourier transform Infrared spectroscopy. X-ray diffraction pattern and transmission electron microscopy revealed that 1 mM of AgNO3 produced mostly spherical nanoparticles in a range of 4–30 nm in diameter with an average of 16 nm. Interestingly, the synthesised nanoparticles showed significant inhibitory effects against Escherichia coli and Staphylococcus aureus clinical isolates. Altogether, these data suggest a new encouraging application of a medicinal plant bound with synthesised AgCl nanoparticles.     

A novel approach for the biosynthesis of silver oxide nanoparticles using aqueous leaf extract of Callistemon lanceolatus (Myrtaceae) and their therapeutic potential

This study describes a novel biological route for the biosynthesis of silver oxide nanoparticles utilising the aqueous extract of Callistemon lanceolatus D.C. leaves. Formation of silver oxide nanoparticles was confirmed by UV–visible spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscope–energy dispersive X-ray spectroscopy and X-ray diffraction spectroscopy analysis. The biologically synthesised silver oxide nanoparticles were found to be 3–30 nm in size with spherical and hexagonal shape by high-resolution transmission electron microscope analysis. Furthermore, the biogenic silver oxide nanoparticles demonstrated significant (p?in vitro antioxidant methods. These particles also exhibited significant (p?相似文献   

Ultrathin Molybdenum Dioxide Nanosheets as Uniform and Reusable Surface‐Enhanced Raman Spectroscopy Substrates with High Sensitivity

Metal oxides have advantages over the traditional noble metals to be used as substrate materials for surface‐enhanced Raman spectroscopy (SERS) with low cost, versatility, and biocompatibility, but their enhancement factors are generally quite low with a poor limit of detection. Here, ultrathin molybdenum dioxide (MoO₂) nanosheets synthesized by chemical vapor deposition demonstrated in large area are used as SERS substrates with superior signal uniformity in the whole area with a limit of detectable concentration down to 4 × 10^?8m and enhancement factor up to 2.1 × 10⁵, exceeding that of 2D materials and comparable to that of noble metal films. More practically important, the planar MoO₂ substrate is more robust than noble metals and shows excellent reusability and uniformity, which is usually prohibited for nanostructured or nanoparticle‐based metal oxide substrates. The enhancement is mainly attributed to the surface plasmon resonance effect as evidenced by the first principle calculations and UV–vis absorption spectroscopy characterization, which can be further increased by decreasing the thickness of the MoO₂ nanosheets. The overall superior performance makes the MoO₂ nanosheets an ideal substrate for practical SERS applications.     

Synthesis,characterization and bactericidal activity of silica/silver core–shell nanoparticles

Silica/silver core–shell nanoparticles (NPs) were synthesized by coating silver NPs on silica core particles (size ~300 ± 10 nm) via electro less reduction method. The core–shell NPs were characterized for their structural, morphological, compositional and optical behavior using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and UV–Visible spectroscopy, respectively. The size (16–35 nm) and loaded amount of silver NPs on the silica core were found to be dependent upon reaction time and activation method of silica. The bactericidal activity of the NPs was tested by broth micro dilution method against both Bacillus subtilis (gram positive) and Escherichia coli ATCC25922 (gram negative) bacterium. The bactericidal activity of silica/silver core–shell NPS is more against E. coli ATCC25922, when compared to B. subtilis. The minimal inhibitory concentration of the core–shell NPs ranged from 7.8 to 250 μg/mL and is found to be dependent upon the amount of silver on silica, the core. These results suggest that silica/silver core–shell NPs can be utilized as a strong substitutional candidate to control pathogenic bacterium, which are otherwise resistant to antibiotics, making them applicable in diverse medical devices.     

Electrochemical analysis of p-nitrophenol in acidic or alkaline medium using silver nanoparticle decorated multi-walled carbon nanotubes

Silver nanoparticle decorated multi-walled carbon nanotubes (Ag/MWCNT) were prepared by a simple chemical plating method. The Ag/MWCNT nanocomposite modified glassy carbon electrode (Ag/MWCNT/GC) was fabricated. Electrochemical behavior of p-nitrophenol at the Ag/MWCNT/GC was studied by cyclic voltammetry. The Ag/MWCNT/GC electrode shows good electrocatalytic activity for the reduction of p-nitrophenol. Voltammetric determination of p-nitrophenol was carried out. Under optimal experimental conditions, the reduction peak current of p-nitrophenol is linearly proportional to its concentration in a range from 3.0 × 10^?6 to 1.2 × 10^?4 mol L^?1 in acidic medium and 3.5 × 10^?5 to 1.4 × 10^?4 mol L^?1 in alkaline medium, respectively.     

Enhancement of antibacterial properties of Ag nanorods by electric field

Abstract

The effect of an electric field on the antibacterial activity of columnar aligned silver nanorods was investigated. Silver nanorods with a polygonal cross section, a width of 20–60 nm and a length of 260–550 nm, were grown on a titanium interlayer by applying an electric field perpendicular to the surface of a Ag/Ti/Si(100) thin film during its heat treatment at 700 °C in an Ar+H₂ environment. The optical absorption spectrum of the silver nanorods exhibited two peaks at wavelengths of 350 and 395 nm corresponding to the main surface plasmon resonance bands of the one-dimensional silver nanostructures. It was found that the silver nanorods with an fcc structure were bounded mainly by {100} facets. The antibacterial activity of the silver nanorods against Escherichia coli bacteria was evaluated at various electric fields applied in the direction of the nanorods without any electrical connection between the nanorods and the capacitor plates producing the electric field. Increasing the electric field from 0 to 50 V cm^?1 resulted in an exponential increase in the relative rate of reduction of the bacteria from 3.9×10^?2 to 10.5×10^?2 min^?1. This indicates that the antibacterial activity of silver nanorods can be enhanced by applying an electric field, for application in medical and food-preserving fields.     

Facile synthesis of low temperature sintering Ag nanopaticles for printed flexible electronics

Silver nanoparticles with small particle size distribution and good dispersibility were synthesized through a facile chemical reduction method. In the progress, AgNO₃ was used as the precursor, polyacrylic acid and ethanol amine were introduced as the protective agent, hydrazine hydrate was chosen as the reduce agent. Diameter of the resulted monodisperse silver nanoparticles is between 50 and 70 nm. Then, the obtained silver nanoparticles were well dispersed in the oil-based ink, which can be printed on a flexible polyimide substrate to form the conductive printed circuit board through following low temperature annealing treatment. A lowest electricity resistivity of 5.6?×?10^?8 Ω m is obtained which is only 3.5× higher than that of bulk silver.     

Detection of magnetic nanoparticles against proppant and shale reservoir rocks

With the expansion in the production of shale oil and gas, there is a desire to obtain detailed information of the downhole environment resulting from hydraulic fracturing (fracking). Nanomagnetite (nMag) has been proposed as a suitable contrast agent for magnetic imaging. In order to determine its suitability, 15 nm oleic acid-stabilised magnetite nanoparticles were synthesised and the magnetic susceptibility was measured and compared against two types of proppant. Although frac sand is diamagnetic (?0.20 × 10^?5 SI), ceramic proppant is paramagnetic (25.7 × 10^?5 SI) due to the presence of Fe₂O₃. The quantity of the nanoparticles that would be required for differentiation against the background levels in the proppant pack was calculated to be 0.269 g/L for sand and 1.01 g/L for ceramic, which correlates to a minimum of 15,000 kg and 56,000 kg per well, respectively. In order to determine the contrast with the reservoir rock itself, the magnetic susceptibility was mapped for cores from two typical shale gas reservoirs (Harrison and Rackley, Arkansas), which show a general low level of paramagnetism (ca. 45 × 10^?5 SI). However, regions are observed with higher susceptibility (>200 × 10^?5 SI) necessitating the use of 242,000 kg nMag per well in order to provide contrast with the reservoir.