72,723 research outputs found
Antibiotic mediated synthesis of gold nanoparticles with potent antimicrobial activity and their application in antimicrobial coatings
We report a one-pot synthesis of spherical gold nanoparticles (52-22 nm) and their capping with cefaclor, a second-generation antibiotic, without use of other chemicals. The differently sized gold nanoparticles were fabricated by controlling the rate of reduction of gold ions in aqueous solution by varying the reaction temperature (20-70 C). The primary amine group of cefaclor acted as both the reducing and capping agent for the synthesis of gold nanoparticles leaving the b-lactam ring of cefaclor available for activity against microbes. Antimicrobial testing showed that cefaclor reduced gold nanoparticles have potent antimicrobial activity against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria as compared to cefaclor or gold nanoparticles alone. The minimum inhibition concentrations (MICs) of cefaclor reduced gold nanoparticles were 10m gmL1 and 100m gmL1 for S. aureus and E. coli respectively. The cefaclor reduced gold nanoparticles were further coated onto poly(ethyleneimine) (PEI) modified glass surfaces to obtain antimicrobial coatings suitable for biomedical applications and were tested against E. coli as an exemplar of activity. The antimicrobial coatings were very robust under adverse conditions (pH 3 and 10), inhibited the growth of E. coli on their surfaces, and could be used many times with retained activity. Results from a combined spectroscopic (FTIR) and microscopic study (AFM) suggest that the action of these novel particles is through the combined action of cefaclor inhibiting the synthesis of the peptidoglycan layer and gold nanoparticles generating "holes" in bacterial cell walls thereby increasing the permeability of the cell wall, resulting in the leakage of cell contents and eventually cell death
Directed deposition of silicon nanowires using neopentasilane as precursor and gold as catalyst
In this work the applicability of neopentasilane (Si(SiH3)4) as a precursor for the formation of silicon nanowires by using gold nanoparticles as a catalyst has been explored. The growth proceeds via the formation of liquid gold/silicon alloy droplets, which excrete the silicon nanowires upon continued decomposition of the precursor. This mechanism determines the diameter of the Si nanowires. Different sources for the gold nanoparticles have been tested: the spontaneous dewetting of gold films, thermally annealed gold films, deposition of preformed gold nanoparticles, and the use of “liquid bright gold”, a material historically used for the gilding of porcelain and glass. The latter does not only form gold nanoparticles when deposited as a thin film and thermally annealed, but can also be patterned by using UV irradiation, providing access to laterally structured layers of silicon nanowires
Synthesis and Characterization of Coated Gold Nanoparticles with Embedded SERS Tags
Gold nanoparticles were prepared with the potential to operate as drug delivery vehicles. Surface-enhanced Raman spectroscopy (SERS) is of particular importance as an optical bioimaging technique due to its ability to allow deep and high-resolution volumetric imaging of biological tissues. Characterization of the gold nanoparticles with para-mercaptobenzoic acid (pMBA), a SERS active molecule, silver, and a phospholipid bilayer was done using Raman and UV-vis spectroscopy and particle size analysis. Our results indicate successful coating of the gold nanoparticles and show consistent pMBA Raman spectroscopy peaks that will allow for the nanoparticle use in-vivo to be monitored
Tunable variation of optical properties of polymer capped gold nanoparticles
Optical properties of polymer capped gold nanoparticles of various sizes
(diameter 3-6 nm) have been studied. We present a new scheme to extract size
dependent variation of total dielectric function of gold nanoparticles from
measured UV-Vis absorption data. The new scheme can also be used, in principle,
for other related systems as well. We show how quantum effect, surface atomic
co - ordination and polymer - nanoparticle interface morphology leads to a
systematic variation in inter band part of the dielectric function of gold
nanoparticles, obtained from the analysis using our new scheme. Careful
analysis enables identification of the possible changes to the electronic band
structure in such nanoparticles.Comment: 13 pages,7 figures, 1 tabl
Polyelectrolyte-modified cowpea mosaic virus for the synthesis of gold nanoparticles
Polyelectrolyte surface-modified cowpea mosaic virus (CPMV) can be used for the templated synthesis of narrowly dispersed gold nanoparticles. Cationic polyelectrolyte, poly(allylamine) hydrochloride, is electrostatically bound to the external surface of the virus capsid. The polyelectrolyte-coated CPMV promotes adsorption of aqueous gold hydroxide anionic species, prepared from gold(III) chloride and potassium carbonate, that are easily reduced to form CPMV-templated gold nanoparticles. The process is simple and environmentally benign using only water as solvent at ambient temperature
Magnetic moment generation in small gold nanoparticles via the plasmonic inverse Faraday effect
We theoretically investigate the creation of a magnetic moment in gold
nanoparticles by circularly polarized laser light. To this end, we describe the
collective electron dynamics in gold nanoparticles using a semiclassical
approach based on a quantum hydrodynamic model that incorporates the prin-
cipal quantum many-body and nonlocal effects, such as the electron spill-out,
the Hartree potential, and the exchange and correlation effects. We use a
variational approach to investigate the breathing and the dipole dynamics
induced by an external electric field. We show that gold nanoparticles can
build up a static magnetic moment through the interaction with a circularly
polarized laser field. We analyze that the responsible physical mechanism is a
plasmonic, orbital inverse Faraday effect, which can be understood from the
time-averaged electron current that contains currents rotating on the
nanoparticles surface. The computed laser-induced magnetic moments are
sizeable, of about 0.35 muB/atom for a laser intensity of 450 GW/cm2 at plasmon
resonance
Synthesis and self-assembly of lipid (DMPC)-conjugated gold nanoparticles
Bio-conjugated nanomaterials play a promising role in the development of
novel supramolecular structures, molecular machines, and biosensing devices. In
this study, lipid-conjugated gold nanoparticles were synthesized and allowed to
form a self-assembled monolayer structure. The nanoparticles were prepared by a
phase transfer method, which involved the reduction of potassium
tetrachloroaurate (III) by sodium citrate in an aqueous solution and the
simultaneous transfer of the reduced species to an organic medium containing
DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine). The gold nanoparticles were
characterized using UV-Vis spectroscopy and dynamic light scattering (DLS)
particle-size analysis. In addition, the resulting nanoparticles were examined
using transmission electron microscopy (TEM). The Langmuir-Blodgett (LB)
technique was used to assemble the DMPC-capped nanoparticles onto a water
subphase at room temperature. The measurement of the compression isotherm
confirmed the assemblage of lipid capped gold nanoparticles. This method of
synthesis of ordered structures utilizing molecular interactions of lipids will
be useful in developing novel metamaterials and nanocircuits.Comment: 7 pages, 5 Figure
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