172 research outputs found
Letter to the Editor Concerning Simultaneous, Single-Particle Measurements of Size and Loading Give Insights into the Structure of Drug-Delivery Nanoparticles
The vexing error of excess variance in the sizing of single particles
degrades accuracy in applications ranging from quality control of nanoparticle
products to hazard assessment of nanoplastic byproducts. The particular
importance of lipid nanoparticles for vaccine and medicine delivery motivates
this comment on a publication in ACS Nano. In ref 1, the
benchmark measurements of a nanoparticle standard manifest large errors of the
size distribution that contradict the claim of validation. Such errors can bias
the correlation of fluorescence intensity as an optical proxy for the molecular
loading of lipid nanoparticles and give misleading insights from power-law
models of intensitysize data. Looking forward, measurement error models have
the potential to address this widespread issue.Comment: Peer reviewed and pending acceptance by ACS Nan
Subnanometer traceability of localization microscopy
In localization microscopy, subnanometer precision is possible but supporting
accuracy is challenging, and no study has demonstrated reliable traceability to
the International System of Units (SI). To do so, we measure the positions of
nanoscale apertures in a reference array by traceable atomic-force microscopy,
creating a master standard. We perform correlative measurements of this
standard by optical microscopy, correcting position errors from optical
aberrations by a Zernike calibration. We establish an uncertainty field due to
localization errors and scale uncertainty, with regions of position
traceability to within a 68 % coverage interval of +/- 1.0 nm. These results
enable localization metrology with high throughput, which we apply to measure
working standards, validating the subnanometer accuracy of lithographic pitch
A lateral nanoflow assay reveals nanoplastic fluorescence heterogeneity
Colloidal nanoplastics present technological opportunities, environmental
concerns, and measurement challenges. To meet these challenges, we develop a
lateral nanoflow assay from sample-in to answer-out. Our measurement system
integrates complex nanofluidic replicas, super-resolution optical microscopy,
and comprehensive statistical analyses to measure polystyrene nanoparticles
that sorb and carry hydrophobic fluorophores. An elegant scaling of surface
forces within our silicone devices hydrodynamically automates the advection and
dominates the diffusion of the nanoparticles. Through steric interaction with
the replica structure, the particle size distribution reciprocally probes the
unknown limits of replica function. Multiple innovations in the integration and
calibration of device and microscope improve the accuracy of identifying single
nanoparticles and quantifying their diameters and fluorescence intensities. A
statistical model of the measurement approaches the information limit of the
system, discriminates size exclusion from surface adsorption, and reduces
nonideal data to return the particle size distribution with nanometer
resolution. A Bayesian statistical analysis of the dimensional and optical
properties of single nanoparticles reveals their fundamental structure-property
relationship. Fluorescence intensity shows a super-volumetric dependence,
scaling with nanoparticle diameter to nearly the fourth power and confounding
basic concepts of chemical sorption. Distributions of fluorescivity - the
product of the number density, absorption cross section, and quantum yield of
an ensemble of fluorophores - are ultrabroad and asymmetric, limiting ensemble
analysis and dimensional or chemical inference from fluorescence intensity.
These results reset expectations for optimizing nanoplastic products,
understanding nanoplastic byproducts, and applying nanoplastic standards
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Shotgun metagenome data of a defined mock community using Oxford Nanopore, PacBio and Illumina technologies.
Metagenomic sequence data from defined mock communities is crucial for the assessment of sequencing platform performance and downstream analyses, including assembly, binning and taxonomic assignment. We report a comparison of shotgun metagenome sequencing and assembly metrics of a defined microbial mock community using the Oxford Nanopore Technologies (ONT) MinION, PacBio and Illumina sequencing platforms. Our synthetic microbial community BMock12 consists of 12 bacterial strains with genome sizes spanning 3.2-7.2 Mbp, 40-73% GC content, and 1.5-7.3% repeats. Size selection of both PacBio and ONT sequencing libraries prior to sequencing was essential to yield comparable relative abundances of organisms among all sequencing technologies. While the Illumina-based metagenome assembly yielded good coverage with few misassemblies, contiguity was greatly improved by both, Illumina + ONT and Illumina + PacBio hybrid assemblies but increased misassemblies, most notably in genomes with high sequence similarity to each other. Our resulting datasets allow evaluation and benchmarking of bioinformatics software on Illumina, PacBio and ONT platforms in parallel
Inflation, moduli (de)stabilization and supersymmetry breaking
We study the cosmological inflation from the viewpoint of the moduli
stabilization. We study the scenario that the superpotential has a large value
during the inflation era enough to stabilize moduli, but it is small in the
true vacuum. This scenario is discussed by using a simple model, one type of
hybrid models.Comment: 17 pages, 7 figure
Loop Quantum Cosmology: A Status Report
The goal of this article is to provide an overview of the current state of
the art in loop quantum cosmology for three sets of audiences: young
researchers interested in entering this area; the quantum gravity community in
general; and, cosmologists who wish to apply loop quantum cosmology to probe
modifications in the standard paradigm of the early universe. An effort has
been made to streamline the material so that, as described at the end of
section I, each of these communities can read only the sections they are most
interested in, without a loss of continuity.Comment: 138 pages, 15 figures. Invited Topical Review, To appear in Classical
and Quantum Gravity. Typos corrected, clarifications and references adde
Construction of non-polar mutants in Haemophilus influenzae using FLP recombinase technology
Background
Nontypeable Haemophilus influenzae (NTHi) is a gram-negative bacterium that causes otitis media in children as well as other infections of the upper and lower respiratory tract in children and adults. We are employing genetic strategies to identify and characterize virulence determinants in NTHi. NTHi is naturally competent for transformation and thus construction of most mutants by common methodologies is relatively straightforward. However, new methodology was required in order to construct unmarked non-polar mutations in poorly expressed genes whose products are required for transformation. We have adapted the lambda red/FLP-recombinase-mediated strategy used in E. coli for use in NTHi.
Results
A cassette containing a spectinomycin resistance gene and an rpsL gene flanked by FRT sites was constructed. A PCR amplicon containing 50 base pairs of DNA homologous to the 5' and 3' ends of the gene to be disrupted and the cassette was generated, then recombineered into the target NTHi gene, cloned on a plasmid, using the lambda recombination proteins expressed in E. coli DY380. Thus, the gene of interest was replaced by the cassette. The construct was then transformed into a streptomycin resistant NTHi strain and mutants were selected on spectinomycin-containing growth media. A plasmid derived from pLS88 with a temperature sensitive replicon expressing the FLP recombinase gene under the control of the tet operator/repressor was constructed. This plasmid was electroporated into the NTHi mutant at the permissive temperature and FLP expression was induced using anhydrotetracycline. The recombinase recognizes the FRT sites and eliminates the antibiotic cassette by site-specific recombination, creating the unmarked non-polar mutation. The plasmid is cured by growth of cells at the restrictive temperature.
Conclusion
The products of the genes in the NTHi pilABCD operon are required for type IV pilus biogenesis and have a role in transformation. We demonstrated the utility of our methodology by the construction of a non-polar pilA mutation in NTHi strain 2019 and complementation of the mutation with a plasmid containing the pilA gene. Utilization of this approach allowed us to readily generate unmarked non-polar mutations in NTHi genes.This work was supported by NIH grants R01DC007464 to RSM, R01DC003915 to Lauren Bakaletz and a subcontract from N01AI30040 to Michael Apicella. We thank Michael Apicella for the gifts of NTHi strains 2019 and 2019 rpsL
Adherence to physical activity guidelines in older adults, using objectively measured physical activity in a population-based study.
BACKGROUND: Physical activity (PA) levels in older adults decline with age. The prevalence and correlates of adherence to current UK PA guidelines in older adults has not been studied using objectively measured PA, which can examine precisely whether PA is carried out in bouts of specified length and intensity.
METHODS: Free living men and women aged 70-93 years from 25 towns in the United Kingdom, participating in parallel on-going population based cohort studies were invited (by post) to wear a GT3x accelerometer over the hip for one week in 2010-12. Adherence to UK PA guidelines was defined as ≥150 minutes/week of moderate or vigorous PA (MVPA) in bouts of ≥10 minutes; the effect of different intensities and durations were examined.
RESULTS: 1593 men and 857 women participated (responses 51% and 29% respectively). 15% men and 10% women achieved ≥150 minutes/week of MVPA (defined as >1040 cpm) in bouts lasting ≥10 minutes. With MVPA defined as >1952 cpm, prevalences were 7% and 3% respectively. Those adhering to guidelines were younger, had fewer chronic health conditions, less depression, less severe mobility limitations, but higher exercise self-efficacy and exercise outcomes expectations. They rated their local environment more highly for social activities and leisure facilities, having somewhere nice to go for a walk and feeling safe after dark, They left the house on more days per week, were more likely to use active transport (cycle or walk) and to walk a dog regularly.
CONCLUSIONS: Few older adults attain current PA guidelines. Health promotion to extend the duration of moderate-intensity activity episodes to 10 minutes or more could yield important health gains among older adults. However future studies will need to clarify whether attaining guideline amounts of PA in spells lasting 10 minutes or more is critical for reducing chronic disease risks as well as improving cardiometabolic risk factors
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