We present a study of the trapping properties of Au nanorods of different aspect ratios in an optical tweezers and comparison with other characterization techniques like transmission electron microscope (TEM) imaging and dynamic light scattering (DLS). This study provides information on the dynamics and orientation of Au nanorods inside an optical trap based on a time study of their localised surface plasmon resonance (LSPR) features. The results indicate that the orientation of the Au nanorods trapped in our optical tweezers varies with time and LSPR spectra can provide information on the angle of the nanorod with respect to the direction of propagation of the trapping laser.
Nanoparticles and products incorporating nanoparticles are a growing branch of nanotechnology industry. They have
found a broad market, including the cosmetic, health care and energy sectors. Accurate and representative determination
of particle size distributions in such products is critical at all stages of the product lifecycle, extending from quality
control at point of manufacture to environmental fate at the point of disposal. Determination of particle size distributions
is non-trivial, and is complicated by the fact that different techniques measure different quantities, leading to differences
in the measured size distributions.
In this study we use both mono- and multi-modal dispersions of nanoparticle reference materials to compare and contrast
traditional and novel methods for particle size distribution determination. The methods investigated include ensemble
techniques such as dynamic light scattering (DLS) and differential centrifugal sedimentation (DCS), as well as single
particle techniques such as transmission electron microscopy (TEM) and microchannel resonator (ultra high-resolution
mass sensor).
We give an overview of the design and planned operation of the metrological Scanning Probe Microscope (mSPM)
currently under development at the National Measurement Institute Australia (NMIA) and highlight the metrological
principles guiding the design of the instrument. The mSPM facility is being established as part of the nanometrology
program at NMIA and will provide the link in the traceability chain between dimensional measurements made at the
nanometer scale and the realization of the SI meter at NMIA. The instrument will provide a measurement volume of
100 μm × 100 μm × 25 μm with a target uncertainty of 1 nm for the position measurement.
Three different methods for extracting zinc oxide (ZnO) and titanium dioxide (TiO2) nanoparticles from commercially
available sunscreen were investigated to determine the most appropriate route for producing a sample suitable for
measuring the primary particle size. Direct dilution of the formulation, centrifugal methods and chemical washing were
trialed in combination with ultrasonic processing and surfactant addition to generate samples that are suitable for particle
size analysis. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were used to monitor the
extraction and re-dispersion process. Washing with hexane, methanol and water to remove the formulation, in
combination with pulsed high-powered ultrasonication and the addition of a charge-stabilizing surfactant was found to be
the most efficient way of producing de-agglomerated samples. DLS measurements gave average hydrodynamic particle
diameters of 87 nm for ZnO and 76 nm for TiO2, compared to equivalent spherical particle diameters of 21 ± 12 nm for
ZnO (81 particles) and 19 ± 14 nm for TiO2 (81 particles) obtained from TEM analysis.
ZnO nanoparticles are a challenging material to disperse and stabilize due to their high density, tendency to aggregate
and chemical properties. Manufactured ZnO nanoparticles often posses a high degree of size and shape dispersity, adding
additional complexity to both sample preparation and subsequent characterization. In this paper, procedures for
achieving stable and representative dispersions of ZnO nanoparticles from commercially available sources are discussed,
and the average particle size determined from dynamic light scattering measurements is qualitatively evaluated against
transmission electron microscopy images. The results highlight a number of important issues that need to be taken into
consideration when performing a metrological assessment of particle sizes and size distributions in such systems.
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