64 research outputs found
Far-Field Plasmonic Resonance Enhanced Nano-Particle Image Velocimetry within a Micro Channel
In this paper, a novel far-field plasmonic resonance enhanced
nanoparticle-seeded Particle Image Velocimetry (nPIV) has been demonstrated to
measure the velocity profile in a micro channel. Chemically synthesized silver
nanoparticles have been used to seed the flow in the micro channel. By using
Discrete Dipole Approximation (DDA), plasmonic resonance enhanced light
scattering has been calculated for spherical silver nanoparticles with
diameters ranging from 15nm to 200nm. Optimum scattering wavelength is
specified for the nanoparticles in two media: water and air. The
diffraction-limited plasmonic resonance enhanced images of silver nanoparticles
at different diameters have been recorded and analyzed. By using standard PIV
techniques, the velocity profile within the micro channel has been determined
from the images.Comment: submitted to Review of Scientific Instrument
Naturally occurring nanoparticles from English ivy: an alternative to metal-based nanoparticles for UV protection
<p>Abstract</p> <p>Background</p> <p>Over the last decade safety concerns have arisen about the use of metal-based nanoparticles in the cosmetics field. Metal-based nanoparticles have been linked to both environmental and animal toxicity in a variety of studies. Perhaps the greatest concern involves the large amounts of TiO<sub>2 </sub>nanoparticles that are used in commercial sunscreens. As an alternative to using these potentially hazardous metal-based nanoparticles, we have isolated organic nanoparticles from English ivy (<it>Hedera helix</it>). In this study, ivy nanoparticles were evaluated for their potential use in sunscreens based on four criteria: 1) ability to absorb and scatter ultraviolet light, 2) toxicity to mammalian cells, 3) biodegradability, and 4) potential for diffusion through skin.</p> <p>Results</p> <p>Purified ivy nanoparticles were first tested for their UV protective effects using a standard spectrophotometric assay. Next the cell toxicity of the ivy nanoparticles was compared to TiO<sub>2 </sub>nanoparticles using HeLa cells. The biodegradability of these nanoparticles was also determined through several digestion techniques. Finally, a mathematical model was developed to determine the potential for ivy nanoparticles to penetrate through human skin. The results indicated that the ivy nanoparticles were more efficient in blocking UV light, less toxic to mammalian cells, easily biodegradable, and had a limited potential to penetrate through human skin. When compared to TiO<sub>2 </sub>nanoparticles, the ivy nanoparticles showed decreased cell toxicity, and were easily degradable, indicating that they provided a safer alternative to these nanoparticles.</p> <p>Conclusions</p> <p>With the data collected from this study, we have demonstrated the great potential of ivy nanoparticles as a sunscreen protective agent, and their increased safety over commonly used metal oxide nanoparticles.</p
Self-Retracting Motion of Graphite Microflakes
We report the observation of a novel phenomenon, the self-retracting motion
of graphite, in which tiny flakes of graphite, after being displaced to various
suspended positions from islands of highly orientated pyrolytic graphite,
retract back onto the islands under no external influences. Our repeated
probing and observing such flakes of various sizes indicate the existence of a
critical size of flakes, approximately 35 micrometer, above which the
self-retracting motion does not occur under the operation. This helps to
explain the fact that the self-retracting motion of graphite has not been
reported, because samples of natural graphite are typical larger than this
critical size. In fact, reports of this phenomenon have not been found in the
literature for single crystals of any kinds. A model that includes the static
and dynamic shear strengths, the van der Waals interaction force, and the edge
dangling bond interaction effect, was used to explain the observed phenomenon.
These findings may conduce to create nano-electromechanical systems with a wide
range of mechanical operating frequency from mega to giga hertzs
Ultraviolet Extinction and Visible Transparency by Ivy Nanoparticles
Though much research has been conducted for nanoparticles, naturally occurring nanoparticles have not yet been well explored for their diverse properties and potential applications. This paper reports the optical absorption and scattering properties of nanoparticles secreted by English ivy. Both experimental and theoretical studies have been conducted. Strong ultraviolet extinction and excellent visible transparency are observed, compared to the inorganic TiO2 and ZnO nanoparticles at similar concentrations. The contributions of absorption and scattering to the total extinction are quantified by simulation of the Mie scattering theory
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