305 research outputs found
Targeted Nanodiamonds for Identification of Subcellular Protein Assemblies in Mammalian Cells
Transmission electron microscopy (TEM) can be used to successfully determine
the structures of proteins. However, such studies are typically done ex situ
after extraction of the protein from the cellular environment. Here we describe
an application for nanodiamonds as targeted intensity contrast labels in
biological TEM, using the nuclear pore complex (NPC) as a model macroassembly.
We demonstrate that delivery of antibody-conjugated nanodiamonds to live
mammalian cells using maltotriose-conjugated polypropylenimine dendrimers
results in efficient localization of nanodiamonds to the intended cellular
target. We further identify signatures of nanodiamonds under TEM that allow for
unambiguous identification of individual nanodiamonds from a resin-embedded,
OsO4-stained environment. This is the first demonstration of nanodiamonds as
labels for nanoscale TEM-based identification of subcellular protein
assemblies. These results, combined with the unique fluorescence properties and
biocompatibility of nanodiamonds, represent an important step toward the use of
nanodiamonds as markers for correlated optical/electron bioimaging.Comment: 38 pages, 6 figures, SI section with 3 figure
Nanodiamond landmarks for subcellular multimodal optical and electron imaging.
There is a growing need for biolabels that can be used in both optical and electron microscopies, are non-cytotoxic, and do not photobleach. Such biolabels could enable targeted nanoscale imaging of sub-cellular structures, and help to establish correlations between conjugation-delivered biomolecules and function. Here we demonstrate a sub-cellular multi-modal imaging methodology that enables localization of inert particulate probes, consisting of nanodiamonds having fluorescent nitrogen-vacancy centers. These are functionalized to target specific structures, and are observable by both optical and electron microscopies. Nanodiamonds targeted to the nuclear pore complex are rapidly localized in electron-microscopy diffraction mode to enable "zooming-in" to regions of interest for detailed structural investigations. Optical microscopies reveal nanodiamonds for in-vitro tracking or uptake-confirmation. The approach is general, works down to the single nanodiamond level, and can leverage the unique capabilities of nanodiamonds, such as biocompatibility, sensitive magnetometry, and gene and drug delivery
A combined NMR and DFT study of Narrow Gap Semiconductors: The case of PbTe
In this study we present an alternative approach to separating contributions
to the NMR shift originating from the Knight shift and chemical shielding by a
combination of experimental solid-state NMR results and ab initio calculations.
The chemical and Knight shifts are normally distinguished through detailed
studies of the resonance frequency as function of temperature and carrier
concentration, followed by extrapolation of the shift to zero carrier
concentration. This approach is time-consuming and requires studies of multiple
samples. Here, we analyzed Pb and Te NMR spin-lattice
relaxation rates and NMR shifts for bulk and nanoscale PbTe. The shifts are
compared with calculations of the Pb and Te chemical shift
resonances to determine the chemical shift at zero charge carrier
concentration. The results are in good agreement with literature values from
carrier concentration-dependent studies. The measurements are also compared to
literature reports of the Pb and Te Knight shifts of - and
-type PbTe semiconductors. The literature data have been converted to the
currently accepted shift scale. We also provide possible evidence for the
"self-cleaning effect" property of PbTe nanocrystals whereby defects are
removed from the core of the particles, while preserving the crystal structure.Comment: 34 pages, 9 figure
A standardised sampling protocol for robust assessment of reach-scale fish community diversity in wadeable New Zealand streams
The New Zealand fish fauna contains species that are affected not only by river system connectivity, but also by catchment and local-scale changes in landcover, water quality and habitat quality. Consequently, native fish have potential as multi-scale bioindicators of human pressure on stream ecosystems, yet no standardised, repeatable and scientifically defensible methods currently exist for effectively quantifying their abundance or diversity in New Zealand stream reaches. Here we report on the testing of a back-pack electrofishing method, modified from that used by the United States Environmental Protection Agency, on a wide variety of wadeable stream reaches throughout New Zealand. Seventy-three first- to third-order stream reaches were fished with a single pass over 150-345 m length. Time taken to sample a reach using single-pass electrofishing ranged from 1-8 h. Species accumulation curves indicated that, irrespective of location, continuous sampling of 150 stream metres is required to accurately describe reach-scale fish species richness using this approach. Additional species detection beyond 150 m was rare (<10%) with a single additional species detected at only two out of the 17 reaches sampled beyond this distance. A positive relationship was also evident between species detection and area fished, although stream length rather than area appeared to be the better predictor. The method tested provides a standardised and repeatable approach for regional and/or national reporting on the state of New Zealand's freshwater fish communities and trends in richness and abundance over time
The effect of a massive object on an expanding universe
A tetrad-based procedure is presented for solving Einstein's field equations
for spherically-symmetric systems; this approach was first discussed by Lasenby
et al. in the language of geometric algebra. The method is used to derive
metrics describing a point mass in a spatially-flat, open and closed expanding
universe respectively. In the spatially-flat case, a simple coordinate
transformation relates the metric to the corresponding one derived by McVittie.
Nonetheless, our use of non-comoving (`physical') coordinates greatly
facilitates physical interpretation. For the open and closed universes, our
metrics describe different spacetimes to the corresponding McVittie metrics and
we believe the latter to be incorrect. In the closed case, our metric possesses
an image mass at the antipodal point of the universe. We calculate the geodesic
equations for the spatially-flat metric and interpret them. For radial motion
in the Newtonian limit, the force acting on a test particle consists of the
usual inwards component due to the central mass and a cosmological
component proportional to that is directed outwards (inwards) when the
expansion of the universe is accelerating (decelerating). For the standard
CDM concordance cosmology, the cosmological force reverses direction
at about . We also derive an invariant fully
general-relativistic expression, valid for arbitrary spherically-symmetric
systems, for the force required to hold a test particle at rest relative to the
central point mass.Comment: 14 pages, 2 tables, 5 figures; new version, to match the version
published in MNRA
Marked Campylobacteriosis Decline after Interventions Aimed at Poultry, New Zealand
A population-level food safety response successfully reduced disease incidence
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