Density Of AgNPs Research Articles

In situ immobilization of silver nanoparticles for improving permeability, antifouling and anti-bacterial properties of ultrafiltration membrane

In this work, silver nanoparticles (AgNPs) were in situ immobilized on polysulfone (PSf) ultrafiltration membrane via polydopamine (PDA) deposition and in situ reduction of silver ammonia aqueous solution (Ag(NH3)2OH). The adhesive and reductive PDA layer existing on the membrane surface induced the reduction of Ag+ on the site of surface without surface pore blockage, and also favored to the firm attachment and uniform distribution of AgNPs onto the membrane. The diameter and density of the immobilized AgNPs were regulated by changing [Ag(NH3)2]+ ion concentration, which exerted an influence on membrane hydrophilicity and permeation flux. The prepared AgNPs-PDA/PSf membranes were characterized by X-ray photoelectron spectroscopy (XPS), scanning election microscope (SEM), atomic force microscopy (AFM), water contact angle measurement and thermogravimetric analysis (TGA). The results indicated that AgNPs were immobilized on the surface as well as the top layer cross section of the membranes. The increase of Ag+ ion concentration led to an increase in the size and density of AgNPs anchored onto the membrane. Compared with PSf membrane, AgNPs-PDA/PSf (20mM) membrane showed higher water flux, slower flux decline rate during BSA solution filtration and higher flux recovery ratio after simple water flushing. The AgNPs-PDA/PSf (20mM) membrane possessed excellent stability with little release of silver during the filtrate operation or static immersion in water for 12 days. Besides, AgNPs-PDA/PSf (20mM) membrane displayed excellent anti-bacterial and ani-biofouling properties against E. coli and B. subtilis.

Ag doped silicon nitride nanocomposites for embedded plasmonics

The localized surface plasmon-polariton resonance (LSPR) of noble metal nanoparticles (NPs) is widely exploited for enhanced optical spectroscopies of molecules, nonlinear optics, photothermal therapy, photovoltaics, or more recently in plasmoelectronics and photocatalysis. The LSPR frequency depends not only of the noble metal NP material, shape, and size but also of its environment, i.e., of the embedding matrix. In this paper, Ag-NPs have been fabricated by low energy ion beam synthesis in silicon nitride (SiNx) matrices. By coupling the high refractive index of SiNx to the relevant choice of dielectric thickness in a SiNx/Si bilayer for an optimum antireflective effect, a very sharp plasmonic optical interference is obtained in mid-range of the visible spectrum (2.6 eV). The diffusion barrier property of the host SiNx matrix allows for the introduction of a high amount of Ag and the formation of a high density of Ag-NPs that nucleate during the implantation process. Under specific implantation conditions, in-plane self-organization effects are obtained in this matrix that could be the result of a metastable coarsening regime.

Surface area or diameter – which factor really determines the antibacterial activity of silver nanoparticles grown on TiO2coatings?

Titanium dioxide coatings were prepared on Si wafers using the sol–gel method. Four different types of coatings with silver nanoparticles (AgNPs) were synthesized. The diameter and surface density of AgNPs were conditioned by the concentration of Ag+ ions in the initial solution, time and UV illumination source. The bactericidal activity of AgNPs on the titanium dioxide coatings against the S. aureus strain were calculated as the percentage of the inhibition of bacterial growth after 24 hour incubation of microorganisms at 37 °C on TiO2 coatings with AgNPs. Control samples were coated with titanium dioxide without AgNPs. We concluded that the titanium dioxide coatings modified with silver nanoparticles had a high antibacterial activity. Moreover, we demonstrated strong dependence between surface areas of AgNPs and inhibition of bacterial growth. The obtained results evidence that the surface area of AgNPs grown on titanium dioxide coatings is a major factor determining their antimicrobial potential.

Photochemical decoration of silver nanoparticles on ZnO nanowires as a three‐dimensional substrate for surface‐enhanced Raman scattering measurement

To increase the sensitivity in surface‐enhanced Raman scattering (SERS) measurement, a three‐dimensional (3D) SERS substrate was prepared by the decoration of silver nanoparticles (AgNPs) on the side walls of ZnO nanowires. The prepared 3D SERS substrates provide the advantages of highly loaded density of AgNPs, with a large specific surface area to interact with analytes, and the ease for the analytes to access the surfaces of AgNPs. To prepare the substrates, ZnO nanowires were first grown on a glass plate by wet chemical method. By treating SnCl2 on the surfaces of ZnO nanowires, Ag seeds could be formed on the side wall of the ZnO nanowires, which were further grown to a suitable size for SERS measurements via photochemical reduction. To optimize and understand the influences of the parameters used in preparation of the substrates, the reaction conditions were systematically adjusted and examined. Results indicated that AgNPs could be successfully decorated on the side wall of the ZnO nanowires only by the assistances of SnCl2. The size and density of AgNPs were affected by both the concentration of silver nitrate and the irradiation time. With optimized condition, the prepared 3D substrates provided an enhancement factor approaching 7 orders of magnitude compared with conventional Raman intensity. Copyright © 2014 John Wiley & Sons, Ltd.

Synthesis of flexible free-standing silver nanoparticles-graphene films and their surface-enhanced Raman scattering activity

A free-standing and flexible silver nanoparticles-graphene (Ag NPs–GE) film with high surface-enhanced Raman scattering (SERS) sensitivity has been developed. First, the high stable and dispersive Ag NPs–GE composite was fabricated by in situ reduction using graphene oxide sheets as substrates and the hydrazine hydrate as a reducing agent in the solvothermal environment. Second, the Ag NPs–GE films can be fabricated through vacuum filtration of the Ag NPs–GE suspension. Transmission electron microscope (TEM) images show that the Ag NPs with an average size of 22 nm and a narrow particle size distribution are uniformly distributed on GE sheets. The coverage density of Ag NPs onto the surface of GE sheets can be successfully controlled by tuning the concentration of silver ion precursor. As-prepared Ag NPs–GE substrates have good SERS sensitivity due to the high SERS-active of Ag NPs. The enhancement factor for 1 × 10−6 M of rhodamine 6G molecules adsorbed onto the surface of substrate is about 2.7 × 105. The SERS activity toward crystal violet and Escherichia coli was also investigated.

A mechanistic study on the effect of a surface protecting agent on electrocrystallization of silver nanoparticles

Surface protecting agent slowed down the kinetics of electrocrystallization due to introduction of a higher activation overpotential at the electrode–electrolyte interface. The true density of AgNPs significantly differs from the calculated values from the SH, SM, SRWBS and HT models.

Generation and Properties of Antibacterial Coatings Based on Electrostatic Attachment of Silver Nanoparticles to Protein-Coated Polypropylene Fibers

We present a simple method for attaching silver nanoparticles to polypropylene (PP) fibers in a two-step process to impart antibacterial properties. Specifically, PP fibers are pretreated by the adsorption from an aqueous solution of heat-denatured lysozyme (LYS) followed by LYS cross-linking using glutaraldehyde and sodium borohydride. At neutral pH, the surface of the adsorbed LYS layer is enriched with numerous positive charges. Silver nanoparticles (AgNPs) capped with trisodium citrate are subsequently deposited onto the protein-coated PP. Nanoparticle binding is mediated by electrostatic interactions between the positively charged LYS layer and the negatively charged AgNPs. The density of AgNPs deposited on PP depends on the amount of protein adsorbed on the surface. UV-vis spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy are employed to follow all preparation steps and to characterize the resulting functional surfaces. The antibacterial activity of the modified surfaces is tested against gram negative bacteria Escherichia coli (E. coli). Overall, our results show that PP surfaces coated with AgNPs exhibit excellent antibacterial activity with 100% removal efficiency.

The synthesis of citrate-modified silver nanoparticles in an aqueous suspension of graphene oxide nanosheets and their antibacterial activity

A composite material consisting of silver nanoparticles (Ag NPs) deposited on graphene oxide (GO) nanosheets is prepared by chemical reduction of Ag metal ions by sodium borohydride (NaBH4) in the presence of trisodium citrate acting as a stabilizing agent to prevent agglomeration of the nanoparticles. The synthesized GO/Ag NPs composite was characterized by UV/vis spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). TEM analysis confirmed a high density of Ag NPs on the GO nanosheets with a particle size range of 2–25nm. The activity of the GO/Ag NPs suspension as an antibacterial agent against Gram positive bacteria Staphylococcus aureus and Bacillus subtilis was investigated. The percentage of the killing bacterial colonies by Ag NPs (without GO) is found to be 96–97% while 100% of killing bacterial colonies is only obtained using GO/Ag NPs suspension. Moreover, it was also observed that leakage of sugars and proteins from the cell wall of both S. aureus and B. subtilis in interaction with GO/Ag NPs suspension is higher compared to Ag NPs (without GO) and GO nanosheets.

Antibacterial and biocompatible surfaces based on dopamine autooxidized silver nanoparticles

AbstractA facile and green method is proposed to immobilize silver nanoparticles (AgNPs) showing antibacterial and biocompatible properties on surfaces of substrates. The adhesive and reductive polydopamine (Pdop) coating was applied on the substrates such as polyethylene, glass, poly(methyl methacrylate), and poly(lactic‐co‐glycolic acid) by simply dipping into dopamine solutions. AgNPs of 50–70 nm formed uniformly on the Pdop‐coated surfaces after immersing in silver nitrate solution where the density of AgNPs was modulated by Pdop immobilization time. Antibacterial efficacy, lactate dehydrogenase assay, and cell morphology observed by microscopy indicated that the as‐prepared AgNPs deposited on Pdop/substrates possessed effective biocidal properties and did not inhibit the growth of L‐929 cells mouse fibroblasts. The proposed method can be easily applied on different substrates and revealed good biocompatibility, which could be further developed for applications in biomaterials. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

Silver nanoparticle–carbon nanotube hybrid films: Preparation and electrochemical sensing

Multi-walled carbon nanotube (MWCNT) multilayer thin films with controlled thickness were pre-assembled on electrodes by alternatively depositing MWCNT and poly(diallyldimethylammonium chloride) (PDDA) via a layer-by-layer self-assembly technique. Silver nanoparticles (Ag NPs) were then electro-deposited on the MWCNT surface from AgNO3 solution using a potentiostatic double pulse technique. The size, density and morphology of silver nanoparticles that electrodeposited on MWCNT were controlled by the pulse parameters. When a voltage pulse of −600mV was used to nucleate silver nanoparticles and a growth pulse of −105mV was applied to grow the particles, silver particles of 10–500nm with varied density could be electro-generated on MWCNT surface. The formation of Ag NPs and the morphology of the MWCNT/Ag NP composite films were characterized by scanning electron microscopy (SEM). The MWCNT/Ag NP composite films exhibited excellent electrocatalytic activity to the reduction of hydrogen peroxide which was also shown to be slightly affected by the size and density of Ag NPs on the film.

Size-dependent surface-enhanced Raman scattering of sodium benzoate on Silver nanoparticles

The absorption spectrum of silver nanoparticles (Ag NPs) with different size and the transmission electron microscopy (TEM) was recorded. Surface-enhanced Raman scattering (SERS) spectra of Sodium Benzoate (SB) adsorbed on Ag NPs with different particle size were studied. The carboxylic group bands were enhanced as the particle size decreases due to the chemisorption of SB on the Ag NPs through it in which the carboxyl group was perpendicular to the surface and the benzene ring parallel to the surface; the SB bands were enhanced as the coverage density of Ag NPs increased.