Antibacterial Nanocomposites Based on Fe 3

For the vulcanized natural rubber (NR), incorporation of silver nanoparticles (AgNPs) into the NR matrix did not exhibit the bactericidal property against Escherichia coli (E. coli). However, incorporation of AgNPs into polyethylene (PE) matrix showed good antibacterial activities to both Gram-negative and Gram-positive bacteria. In the present work, NR/PE (85/15) blends have been prepared by melt blending with presence of compatibilizer in an internal mixer. To possess antibacterial property, AgNPs (5–10 nm) or Fe3O4–Ag hybrid nanoparticles (FAgNPs, 8 nm/16 nm) were added into PE matrix before its blending with NR component. The tensile test indicated that the presence of compatibilizer in NR/PE blend significantly enhanced the tensile strength and elongation at break (up to 35% and 38% increases, resp.). The antibacterial activity test was performed by monitoring of the bacterial lag-log growth phases with the presence of nanocomposites in the E. coli cell culture reactor. The antibacterial test showed that the presence of FAgNPs in NR/PE blend had a better antibacterial activity than that obtained with the lone AgNPs. Two similar reasons were proposed: (i) the faster Ag+ release rate from the Fe3O4–Ag hybrid nanoparticles due to the electron transfer from AgNP to Fe3O4 nanoparticle and (ii) the fact that the ionization of AgNPs in hybrid nanostructure might be accelerated by Fe3+ ions

The transfer and decay of maternal antibody against Shigella sonnei in a longitudinal cohort of Vietnamese infants.

BACKGROUND: Shigella sonnei is an emergent and major diarrheal pathogen for which there is currently no vaccine. We aimed to quantify duration of maternal antibody against S. sonnei and investigate transplacental IgG transfer in a birth cohort in southern Vietnam. METHODS AND RESULTS: Over 500-paired maternal/infant plasma samples were evaluated for presence of anti-S. sonnei-O IgG and IgM. Longitudinal plasma samples allowed for the estimation of the median half-life of maternal anti-S. sonnei-O IgG, which was 43 days (95% confidence interval: 41-45 days). Additionally, half of infants lacked a detectable titer by 19 weeks of age. Lower cord titers were associated with greater increases in S. sonnei IgG over the first year of life, and the incidence of S. sonnei seroconversion was estimated to be 4/100 infant years. Maternal IgG titer, the ratio of antibody transfer, the season of birth and gestational age were significantly associated with cord titer. CONCLUSIONS: Maternal anti-S. sonnei-O IgG is efficiently transferred across the placenta and anti-S. sonnei-O maternal IgG declines rapidly after birth and is undetectable after 5 months in the majority of children. Preterm neonates and children born to mothers with low IgG titers have lower cord titers and therefore may be at greater risk of seroconversion in infancy

Force-induced remodelling of proteins and their complexes

Force can drive conformational changes in proteins, as well as modulate their stability and the affinity of their complexes, allowing a mechanical input to be converted into a biochemical output. These properties have been utilised by nature and force is now recognised to be widely used at the cellular level. The effects of force on the biophysical properties of biological systems can be large and varied. As these effects are only apparent in the presence of force, studies on the same proteins using traditional ensemble biophysical methods can yield apparently conflicting results. Where appropriate, therefore, force measurements should be integrated with other experimental approaches to understand the physiological context of the system under study

The Role of Maternally Acquired Antibody in Providing Protective Immunity Against Nontyphoidal Salmonella in Urban Vietnamese Infants: A Birth Cohort Study.

BACKGROUND: Nontyphoidal Salmonella (NTS) organisms are a major cause of gastroenteritis and bacteremia, but little is known about maternally acquired immunity and natural exposure in infant populations residing in areas where NTS disease is highly endemic. METHODS: We recruited 503 pregnant mothers and their infants (following delivery) from urban areas in Vietnam and followed infants until they were 1 year old. Exposure to the dominant NTS serovars, Salmonella enterica serovars Typhimurium and Enteritidis, were assessed using lipopolysaccharide (LPS) O antigen-specific antibodies. Antibody dynamics, the role of maternally acquired antibodies, and NTS seroincidence rates were modeled using multivariate linear risk factor models and generalized additive mixed-effect models. RESULTS: Transplacental transfer of NTS LPS-specific maternal antibodies to infants was highly efficient. Waning of transplacentally acquired NTS LPS-specific antibodies at 4 months of age left infants susceptible to Salmonella organisms, after which they began to seroconvert. High seroincidences of S. Typhimurium and S. Enteritidis LPS were observed, and infants born with higher anti-LPS titers had greater plasma bactericidal activity and longer protection from seroconversion. CONCLUSIONS: Although Vietnamese infants have extensive exposure to NTS, maternally acquired antibodies appear to play a protective role against NTS infections during early infancy. These findings suggest that prenatal immunization may be an appropriate strategy to protect vulnerable infants from NTS disease

Consistent patterns of common species across tropical tree communities

Trees structure the Earth’s most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1,2,3,4,5,6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth’s 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world’s most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees.Publisher PDFPeer reviewe

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Water-dispersible magnetic nanoparticles for biomedical applications : synthesis and characterisation

Magnetic nanoparticles have attracted a great attention due to their diverse potential applications in biology and technology and a substantial number of synthetic methods have been developed to produce these materials. Chemical synthesis approaches have been a particular focus of the field, because of their ability to tune the size, shape and composition, as well as surface of the nanoparticles. To produce magnetic nanoparticles for biomedical applications, one of the primary requirements is to make nanoparticles that are dispersible and stable in aqueous medium under physiological conditions. The focus of this thesis has been the development of methods to synthesise magnetic nanoparticles of different compositions and shape that are dispersible and stable in water. Monodisperse water-dispersible magnetic Co nanoparticles were fabricated using a facile reduction method in water in the presence of hydrophilic polymers. The size and shape of the nanoparticles were both tunable by varying the conditions of synthesis. The size of the spherical nanoparticles would be tuned between 2-7.5 nm by changing the concentration of the polymer. The synthesis approach could also be used to produce nanorods of 15 x 36 nm. The spherical nanoparticles were superparamagnetic at room temperature and were stable in water and in electrolyte solutions of up to 0.23 mM NaCI. The preliminary use of the Co nanoparticles as a MRI contrast enhancer was tested and provided evidence that these materials have considerable potential in this application. Using a similar method, water-dispersible and colloidal stable CoPt nanoparticles were prepared. The effect of structure, functional group and combinations of stabilising ligands on the morphology of the nanoparticles was investigated. It was found that multiple-thiol functional groups play a critical role in the formation of hollow nanoparticles. The size of hollow nanoparticles could be tuned in the range of7-54 nm by changing the concentration and molecular weight of the ligands. The hollow nanoparticles were water-dispersible and superparamagnetic at room temperature. They were stable in wide range of pH from I to 12.5 and at electrolyte concentrations as high as 2 M NaCI. An experiment on tracking stem cells labelled with the CoPt hollow nanoparticles indicated that MRl can effectively detect low numbers of labelled cells due to the enhanced contrast provided by the nanoparticles. CoPt hollow nanoparticles may, thus, have potential applications in MRI. CoFe and cobalt ferrite nanoparticles were synthesised by thermal decomposition in organic solvent to take advantage of the superior control over monodispersity and morphology of the nanoparticles afforded by solvent based syntheses. In the case of CoFe nanoparticles, a layer of Pt was also deposited on the nanoparticles to make core/shell structures. Varying reaction conditions, such as reaction time, had an insignificant effect on monodispersity, size and shape of Co Fe nanoparticles. However, these parameters had a substantial impact on the cobalt ferrite nanoparticles. Cobalt ferrite nanoparticles with sizes in a broad range from 4 nm to over 30 nm and diverse shapes including spherical, cubic and star-like, were synthesised by changing surfactant concentration and reaction time. Ligand exchange using hydrophilic silane and/or polymer ligands were demonstrated to be efficacious on CoFe, CoFelPt and cobalt ferrite nanoparticles. After ligand exchange, the nanoparticles were reasonably stable in water. The work presented in this thesis demonstrates that chemical synthesis is an efficient route to the production of magnetic nanoparticles of diverse composition and shape and so magnetic properties. Moreover, these materials were found to be stable in aqueous solutions. However, it is clear that the application of such magnetic nanoparticles in biology and medicine will require substantial further effort in the development of ligand shells able to withstand the rigours of the biological environment. Given the success of chemical synthesis demonstrated in this thesis, the development of ligand shell systems is now a major challenge of the field.EThOS - Electronic Theses Online ServiceGBUnited Kingdo