On the formation and extent of uptake of silver nanoparticles by live plants

In this work we investigate the limits of uptake of metallic silver by two common metallophytes, Brassica juncea (BJ) and Medicago sativa (MS) and assess the form and distribution of the metal once sequestered by the plants. BJ accumulated up to 12.4 wt.% silver when exposed to an aqueous substrate containing 1,000 ppm AgNO₃ for 72 h, however silver uptake was largely independent of exposure time and substrate silver concentration. MS accumulated up to 13.6 wt.% silver when exposed to an aqueous substrate containing 10,000 ppm AgNO₃ for 24 h. In contrast to BJ there was a general trend for MS showing an increase in metal uptake with a corresponding increase in the substrate metal concentration and exposure time. In both cases the silver was stored as discrete nanoparticles, with a mean size of ∼50 nm. According to the hyperaccumulation definition of Brooks et al. (Brooks RR, Chambers MF, Nicks LJ, Robinson BH (1998) Phytomining. Trends Plant Sci 3:359–362), this is the first report of the hyperaccumulation of silver in any plant species.     

SERS activity of carbon nanotubes modified by silver nanoparticles with different particle sizes

A two-dimensional (2D) surface-enhanced Raman scattering (SERS) substrate is fabricated by decorating carbon nanotube (CNT) films with Ag nanoparticles (AgNPs) in different sizes, via simple and low-cost chemical reduction method and self-assembling method. The change of Raman and SERS activity of carbon nanotubes/Ag nanoparticles (CNTs/AgNPs) composites with varying size of AgNPs are investigated by using rhodamine 6G (R6G) as a probe molecule. Meanwhile, the scattering cross section of AgNPs and the distribution of electric field of CNTs/AgNPs composite are simulated through finite difference time domain (FDTD) method. Surface plasmon resonance (SPR) wavelength is redshifted as the size of AgNPs increases, and the intensity of SERS and electric field increase with AgNPs size increasing. The experiment and simulation results show a Raman scattering enhancement factor (EF) of 10⁸ for the hybrid substrate.     

Superhydrophobic conductive textiles with antibacterial property by coating fibers with silver nanoparticles

Silver nanoparticles (Ag NPs) were produced on cotton fibers by reduction of [Ag(NH₃)₂]⁺ complex with glucose. Further modification of the fibers coated by Ag NPs with hexadecyltrimethoxysilane led to superhydrophobic cotton textiles. Scanning electron microscopy images of the textiles showed that the treated fibers were covered with uniform Ag NPs, which generate a dual-size roughness on the textiles favouring the formation of superhydrophobic surfaces, and the Ag NPs formed dense coating around the fibers rendering the intrinsic insulating cotton textiles conductive. Antibacterial test showed that the as-fabricated textiles had high antibacterial activity against the gram-negative bacteria, Escherichia coli. These multifunctional textiles might find applications in biomedical electronic devices.     

Highly bacterial resistant silver nanoparticles: synthesis and antibacterial activities

In this article, we describe a simple one-pot rapid synthesis route to produce uniform silver nanoparticles by thermal reduction of AgNO₃ using oleylamine as reducing and capping agent. To enhance the dispersal ability of as-synthesized hydrophobic silver nanoparticles in water, while maintaining their unique properties, a facile phase transfer mechanism has been developed using biocompatible block co-polymer pluronic F-127. Formation of silver nanoparticles is confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–vis spectroscopy. Hydrodynamic size and its distribution are obtained from dynamic light scattering (DLS). Hydrodynamic size and size distribution of as-synthesized and phase transferred silver nanoparticles are 8.2 ± 1.5 nm (σ = 18.3%) and 31.1 ± 4.5 nm (σ = 14.5%), respectively. Antimicrobial activities of hydrophilic silver nanoparticles is tested against two Gram positive (Bacillus megaterium and Staphylococcus aureus), and three Gram negative (Escherichia coli, Proteus vulgaris and Shigella sonnei) bacteria. Minimum inhibitory concentration (MIC) values obtained in the present study for the tested microorganisms are found much better than those reported for commercially available antibacterial agents.     

Synthesis of copper nanoparticles catalyzed by pre-formed silver nanoparticles

Synthesis of well dispersed copper nanoparticles was achieved by reduction of copper nitrate in aqueous solution using hydrazine monohydrate as a reducer in the presence of preformed silver nanoparticles as catalysts. It has been demonstrated that addition of silver nanoparticles to the reaction mixture leads to formation of aqueous dispersion of copper nanoparticles and also results in a drastic reduction in reaction time compared to procedures reported in the literature. The absorption spectrum of the dispersions, HR-TEM and STEM images and XRD pattern indicate the formation of copper nanoparticles with particle size in the range of 5–50 nm.     

Mixing thiols on the surface of silver nanoparticles: preserving antibacterial properties while introducing SERS activity

The purpose of the study was to prepare and characterize nanosuspensions that can maintain high and extended supersaturation to improve the dissolution and absorption of poorly soluble 10-hydroxycamptothecin (10-HCPT). 10-HCPT oral nanosuspensions (HCPT-Nanosuspensions) were produced on a laboratory-scale by microprecipitation- high pressure homogenization method. The particle morphology and the physical state were studied using transmission electron microscopy, X-ray powder diffraction (XRPD), and differential scanning calorimetry (DSC). Supersaturated dissolution tests were carried out with the paddle method. Caco-2 cell experiments were performed to imitate the oral absorption. The in vivo pharmacokinetics studies were undertaken in rats following oral administration. The 10-HCPT nanoparticles were 135 nm in dimension before lyophilization and were claviform or lump in shape. XRPD and DSC both confirmed that a portion of 10-HCPT was present in a crystalline state in nanosuspension. Supersaturated dissolution tests showed HCPT-Nanosuspensions could maintain high supersaturated level for an extended period time. The cell experiment on HCPT-Nanosuspensions showed a significantly higher uptake and greater membrane permeability compared with the other formulations. The pharmacokinetic test exhibited HCPT-Nanosuspensions had a similar pharmacokinetic performance with 10-HCPT solution. In conclusion, highly and extendedly supersaturated HCPT-Nanosuspensions have been prepared which could result in high peak concentration (C _max) and great exposure (AUC) after oral administration.

     

One-step synthesis and antibacterial property of water-soluble silver nanoparticles by CGJ bio-template

In this article, a new synthetic method of nanoparticles with fresh Chinese gooseberry juice (CGJ) as bio-template was developed. One-step synthesis of highly water-soluble silver nanoparticles at room temperature without using any harmful reducing agents and special capping agent was fulfilled with this method. In the process, the products were obtained by adding AgNO₃ to CGJ, which was used as reducing agent, capping agent, and the bio-template. The products of silver nanoparticles with diameter of 10–30 nm have strong water solubility and excellent antibiotic function. With the same concentration 0.047 μg mL⁻¹, the antibacterial effect of water-soluble silver particles by fresh CGJ was 53%, whereas only 27% for silver nanoparticles synthesized using the template method of fresh onion inner squama coat (OISC). The excellent water solubility of the products would enable them have better applications in the bio-medical field. The synthetic method would also have potential application in preparing other highly water-soluble particles, because of its simple apparatus, high yield, mild conditions, and facile operation.     

Raman spectra of benzoic acid enhanced by the silver nanoparticles of various sizes

Using sodium borohydride as the reducing agent and polyvinyl pyrrolidone (PVP, MW = 10 000) as the stabilizer, we obtained silver nanoparticles of various diameters (8–78 nm) from silver nitrate aqueous solutions in the concentration range from 0.001 to 0.1 M. The surface‐enhanced Raman scattering (SERS) from benzoic acid's ring‐breathing mode at 1003 cm⁻¹ was detected from its dilute solutions (∼10⁻² M) doped with these silver nanoparticles under 488‐nm laser excitation. The observed size dependences of SERS intensities fit quite well with those calculated by Schatz's theoretical model for spherical silver nanoparticles. The only exception occurred with the smallest particles (8 nm), possibly due to the failure of Maxwell's electromagnetic theory used in this model. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and optical properties of silver nanoparticles in ORMOCER

Experimental results on synthesis of metal nanoparticles in ORMOCER by ion implantation are presented. Silver ions were implanted into organic/inorganic matrix at an accelerating energy of 30?keV and doses in the range of 0.25?10¹⁷ to 0.75?10¹⁷?ion/cm². The silver ions form metal nanoparticles, which demonstrate surface plasmon absorption at the wavelength of 425?C580?nm. The nonlinear absorption of new composite materials is measured by Z-scan technique using 150?fs laser pulses at 780?nm wavelength. ORMOCER matrix shows two-photon nonlinear absorption, whereas ORMOCER with silver nanoparticles demonstrates saturated absorption. Some optical applications of these composite materials are discussed.     

Synthesis and characterization of myristic acid capped silver nanoparticles

Reduction of silver myristate (AgMy) under mild thermal reaction conditions in a dipolar aprotic solvent i.e. N, N-dimethylformamide (DMF) has been carried out. UV–visible absorption measurements of dried and re-dispersible brown flocculants showed broad features of surface plasmon resonance (SPR) due to silver nanoparticles. The freshly isolated particles showed absorption bands at 414 and 485 nm, respectively, due to inter-particle coupling or clustering of silver ions and silver atoms. X-ray diffraction (XRD) pattern of fcc zero-valent silver resulted in crystallite size of about 10 nm. Scanning electron microscopy (SEM) revealed formation of rod shaped silver with increasing reaction temperature. Thermal analysis (TGA) showed about 10% weight loss due to organic capping.     

One-step synthesis of silver nanoparticles in an aqueous solution and their antibacterial activities

A one-step simple synthesis of silver colloid nanoparticles with controllable sizes is presented in this research. In the synthesis, an amino-terminated hyperbranched polymer (HBP-NH₂) was applied as a stabilizer and a reductant. The syntheses, performed at various initial AgNO₃ concentrations (0.28–0.56 g/l) in a 2 g/l HBP-NH₂ aqueous solution, produced silver colloid nanoparticles having average sizes from 3 to 30 nm with narrow size distributions. The formation of silver colloid nanoparticles was characterized by Fourier Transform Infrared Spectrophotometry (FTIR), Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM), UV/Visible Absorption Spectrophotometry, and X-ray Diffraction (XRD) measurements. The results indicated that both particle size and the UV absorption are strongly dependent on the initial AgNO₃ concentrations. The silver colloid nanoparticles, prepared with a 0.35 g/l AgNO₃ aqueous solution in the presences of 2 g/l HBP-NH₂, showed good antibacterial activities against Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus). A very low concentration of nano-silver (as low as 3.0 ug/ml Ag) also gave excellent antibacterial performance.     

Synthesis of graphene oxide sheets decorated by silver nanoparticles in organic phase and their catalytic activity

The graphene oxide(GO) sheets decorated by Ag nanoparticles were prepared using a liquid–liquid two-phase method at the room temperature. The synthesized samples existed in the organic phase and were characterized by X-ray diffraction, transmission electron microscopy, UV–vis spectroscopy and Raman spectra. The results demonstrate that these silver-nanoparticles with diameter of about 10 nm assembled on graphene oxide sheets are flexible and can form stable suspensions in organic phase. Raman signals of graphene oxide sheets are increased by the attached silver nanoparticles, displaying higher surface-enhanced Raman scattering activity. Furthermore, Ag/GO are found to serve as effective catalysts to activate the reduction of 4-nitrophenol (4NP) in the presence of NaBH₄.     

Synthesis and characterization of iron-based alloy nanoparticles for magnetorheological fluids

The borohydride reduction method was used to synthesize the Fe-based alloy nanoparticles in an aqueous medium for MR fluids. The effect of ethanol content in the reaction medium on the synthesis of Fe–Co–B nanoparticles was studied first. With increasing the ethanol content from 0 to 40 vol%, the average diameters of Fe–Co–B nanoparticles were decreased from 170 to 35 nm. The possible mechanism for the effect of ethanol has been proposed. Among the four types of Fe-based alloys particles synthesized in this work, Fe–B had the highest magnetization saturation M_s, while M_s decreased in an order of Fe–B>Fe–Co–B>Fe–Cr–B>Fe–Ni–B. A magnetic field of 3000 Oe was able to increase M_s by about 5–6% for each type of iron-based alloy. Under a magnetic field, chain structures of nanoparticles were always formed. When a strong magnetic field such as 3000 Oe was applied, the particles were “squeezed” into chains.     

Synthesis and characterization of silver nanoparticles from (bis)alkylamine silver carboxylate precursors

A comparative study of amine and silver carboxylate adducts [R₁COOAg-2(R₂NH₂)] (R₁ = 1, 7, 11; R₂ = 8, 12) as a key intermediate in NPs synthesis is carried out via differential scanning calorimetry, solid-state FT-infrared spectroscopy, ¹³C CP MAS NMR, powder X-ray diffraction and X-ray photoelectron spectroscopy, and various solution NMR spectroscopies (¹H and ¹³C NMR, pulsed field gradient spin-echo NMR, and ROESY). It is proposed that carboxyl moieties in the presence of amine ligands are bound to silver ions via chelating bidentate type of coordination as opposed to bridging bidentate coordination of pure silver carboxylates resulting from the formation of dimeric units. All complexes are packed as lamellar bilayer structures. Silver carboxylate/amine complexes show one first-order melting transition. The evidence presented in this study shows that phase behavior of monovalent metal carboxylates are controlled, mainly, by head group bonding. In solution, insoluble silver salt is stabilized by amine molecules which exist in dynamic equilibrium. Using (bis)amine-silver carboxylate complex as precursor, silver nanoparticles were fabricated. During high-temperature thermolysis, the (bis)amine-carboxylate adduct decomposes to produce silver nanoparticles of small size. NPs are stabilized by strongly interacting carboxylate and trace amounts of amine derived from the silver precursor interacting with carboxylic acid. A corresponding aliphatic amide obtained from silver precursor at high-temperature reaction conditions is not taking part in the stabilization. Combining NMR techniques with FTIR, it was possible to follow an original stabilization mechanism.

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Graphical abstract The synthesis of a series (bis)alkylamine silver(I) carboxylate complexes in nonpolar solvents were carried out and fully characterized both in the solid and solution. Carboxyl moieties in the presence of amine ligands are bound to silver ions via chelating bidentate type of coordination. The complexes form layered structures which thermally decompose forming nanoparticles stabilized only by aliphatic carboxylates.

     

Tissular localization and excretion of intravenously administered silica nanoparticles of different sizes

The nanotoxicology as a new subdiscipline of nanotechnology needs to be studied in vivo. To do so, it is essential to understand certain pharmacological information of the nanoparticles in vivo. Silica nanoparticles (SiNPs) have been developed for a number of biomedical uses; however, research on their tissular localization and excretion has been limited. In this study, we analyzed the localization of intravenously administered SiNPs with sizes of 20 and 80 nm in liver and spleen and quantitatively investigated the excretion of SiNPs through urine and feces. The results of the tissular localization study showed that the SiNPs were located in liver evenly; however, they were mainly accumulated in the white pulp of spleen. The quantitative excretory assay found the renal excretion being the main excretion pathway of SiNPs and indicated that the accumulated excretory rate of 80 nm SiNPs through urine was higher than that of 20 nm SiNPs because of the higher hemoconcentration. Further analysis of radioactive substances in the excreta showed the convincing confirmatory evidence that the SiNPs of both the sizes of 20 and 80 nm could be excreted through urine. These results provide important information on in vivo distribution and excretion of SiNPs.     

Synthesis and characterization of silver nanoparticles in a nanoporous glass

We obtained a metal-dielectric composite by thermal restoration of silver atoms from an alcohol solution of a precursor in nanoporous glass with pores with a radius of 2 nm. The concentration, size, and asphericity degree of metal nanoparticles formed in the pores are characterized according to the measured extinction spectra of the material.     

Synthesis and functionalization of magnetite nanoparticles with different amino-functional alkoxysilanes

Superparamagnetic iron oxide (SPIO) nanoparticles show great promise for many biotechnological applications. This paper addresses the synthesis and characterization of SPIO nanoparticles grafted with three different alkoxysilanes: 3-aminopropyl-triethoxysilane (APTES), 3-aminopropyl-ethyl-diethoxysilane (APDES) and 3-aminopropyl-diethy-ethoxysilane (APES). SPIO nanoparticles with an average particle diameter of 10 nm were prepared by chemical sonoprecipitation. As confirmed by Fourier transform infrared (FTIR) spectroscopy, silylation of these nanoparticles occurs through a two-step process. Decreasing the number of alkoxide groups reduced the concentration of free amino groups on the SPIO surface ([SPIO-NH₂]—APTES>APDES>APES). This phenomenon results from steric contributions and the formation of H-bonded amines provided by the ethyl groups present in the APDES and APES molecules. A simulation of SPIO nanoparticles in a saline physiologic solution shows that the ethyl groups impart larger steric stability onto the ferrofluids, which reduces aggregation. The magnetization (M) versus magnetic field (H) curves show that the synthesized iron oxide nanoparticles display superparamagnetic behavior. The zero-field cooling (ZFC) and field cooling (FC) curves show that the changes in the blocking temperature depend on the alkoxysilane-functionalized particle surface.