127 research outputs found
The application of chiral metamaterials for sensing and active plasmonics
Chirality, the property of asymmetry, is ubiquitous in nature, observed in the handednesses of molecules to the twist of galaxies. This work concern artificial chiral metamaterials, periodic arrays of chiral metal nanostructures. The extraordinary properties that they exhibit are determined not only by the materials from which they are constructed, as in traditional materials, but by the size, shape and spacing of nanostructures which constitute them. The chirality of the structures mean that they strongly interact with the chiral manifestation of light, circularly polarised light. It is this interaction that is the theme that runs through this work. Two applications of chiral metamaterials are investigated here. The first is their use for the detection of chiral biological material. Arrays of gammadion nanostructures are created using state of the art electron beam lithography fabrication techniques in the James Watt Nanofabrication Centre. The effect of deformations to the nanostructure geometry and morphology on their interaction with circularly polarised light is investigated. In particular focus is the effect on the circular dichroism (CD) spectra and levels of enhanced optical chirality, a parameter which has been related to the enhancement of the interaction of light with chiral molecules. It is shown here that whilst geometric changes do not have a significant effect on CD spectra, surface roughness on the surface of the nanostructure can support optical chirality ‘hotspots’. These enhancements are, however, not as large as those observed for electric field enhancements commonly exploited for surface enhanced Raman spectroscopy. It is subsequently shown through numerical simulation that the sensing capabilities of the gammadion nanostructure is correlated to its thickness. This is reconciled within a framework of an interference mechanism for the “dissipation” of optical chirality into chiral material currents. The presence of a chiral dielectric can cause an asymmetric change to the phase difference between two spatially separated chiral modes resulting in asymmetric changes to their chiral optical properties. The second application is in the field of active plasmonics, which allows for the properties of metamaterials to be tuned post-fabrication by changing their size and shape using an external stimulus. Current approaches can require complex fabrication techniques which are inherently high cost. Here, a simple and novel approach is described which allows the chiral optical properties, namely the optical rotatory dispersion spectra, to be controlled electrically through a flexoelectric effect. The flexoelectric element, a lead zirconate titanate film, does not require high temperature processing and so can be integrated with polymer-based material
RUNX-mediated growth arrest and senescence are attenuated by diverse mechanisms in cells expressing RUNX1 fusion oncoproteins
RUNX gene over-expression inhibits growth of primary cells but transforms cells with tumor suppressor defects, consistent with reported associations with tumor progression. In contrast, chromosomal translocations involving RUNX1 are detectable in utero, suggesting an initiating role in leukemias. How do cells expressing RUNX1 fusion oncoproteins evade RUNX-mediated growth suppression? Previous studies showed that the TEL-RUNX1 fusion from t(12;21) B-ALLs is unable to induce senescence-like growth arrest (SLGA) in primary fibroblasts while potent activity is displayed by the RUNX1-ETO fusion found in t(8;21) AMLs. We now show that SLGA potential is suppressed in TEL-RUNX1 but reactivated by deletion of the TEL HLH domain or mutation of a key residue (K99R). Attenuation of SLGA activity is also a feature of RUNX1-ETO9a, a minor product of t(8;21) translocations with increased leukemogenicity. Finally, while RUNX1-ETO induces SLGA it also drives a potent senescence-associated secretory phenotype (SASP), and promotes the immortalisation of rare cells that escape SLGA. Moreover, the RUNX1-ETO SASP is not strictly linked to growth arrest as it is largely suppressed by RUNX1 and partially activated by RUNX1-ETO9a. These findings underline the heterogeneous nature of premature senescence and the multiple mechanisms by which this failsafe process is subverted in cells expressing RUNX1 oncoproteins
Active chiral plasmonics: flexoelectric control of nanoscale chirality
The ability to electrically control the optical properties of metamaterials is an essential capability required for technological innovation. The creation of dynamic electrically tuneable metamaterials in the visible and near IR region are important for a range of imaging and fibre optic technologies. However current approaches require complex nanofabrication processes which are incompatible for low cost device production. Here, we report a novel simple approach for electrical control of optical properties which utilises a flexoelectric dielectric element to electromechanically manipulate the form factor of a chiral nanostructure. By altering the dimensions of the chiral nanostructure, we allow the polarisation properties of light to be electrically controlled. The flexoelectric element is part of a composite metafilm that is templated on to a nanostructured polymer substrate. Since the flexoelectric element does not require in situ high temperature annealing it can be readily combined with polymer‐based substrates produced by high throughput methods. This is not the case for piezoelectric elements, routinely used in microelectromechanical (MEM) devices which require high temperature processing. Consequently, combining amorphous flexoelectric dielectric and low‐cost polymer‐based materials provides a route to the high throughput production of electrically responsive disposable metadevices
Roles of superchirality and interference in chiral plasmonic biodetection
Chiral plasmonic nanostructures enable ≤pg detection and characterization of biomaterials. The sensing capabilities are associated with the chiral asymmetry of the near fields, which locally can be greater than equivalent circularly polarized light, a property referred to as superchirality. However, sensing abilities do not simply scale with the magnitude of superchirality. We show that chiral molecular sensing is correlated to the thickness of a nanostructure. This observation is reconciled with a previously unconsidered interference mechanism for the sensing phenomenon. It involves the “dissipation” of optical chirality into chiral material currents through the interference of fields generated by two spatially separated chiral modes. The presence of a chiral dielectric causes an asymmetric change in the phase difference, resulting in asymmetric changes to chiroptical properties. Thus, designing a chiral plasmonic sensor requires engineering a substrate that can sustain both superchiral fields and an interference effect
Collaboration of MYC and RUNX2 in lymphoma simulates T‐cell receptor signaling and attenuates p53 pathway activity
MYC and RUNX oncogenes each trigger p53‐mediated failsafe responses when overexpressed in vitro and collaborate with p53 deficiency in vivo. However, together they drive rapid onset lymphoma without mutational loss of p53. This phenomenon was investigated further by transcriptomic analysis of premalignant thymus from RUNX2/MYC transgenic mice. The distinctive contributions of MYC and RUNX to transcriptional control were illustrated by differential enrichment of canonical binding sites and gene ontology analyses. Pathway analysis revealed signatures of MYC, CD3, and CD28 regulation indicative of activation and proliferation, but also strong inhibition of cell death pathways. In silico analysis of discordantly expressed genes revealed Tnfsrf8/CD30, Cish, and Il13 among relevant targets for sustained proliferation and survival. Although TP53 mRNA and protein levels were upregulated, its downstream targets in growth suppression and apoptosis were largely unperturbed. Analysis of genes encoding p53 posttranslational modifiers showed significant upregulation of three genes, Smyd2, Set, and Prmt5. Overexpression of SMYD2 was validated in vivo but the functional analysis was constrained by in vitro loss of p53 in RUNX2/MYC lymphoma cell lines. However, an early role is suggested by the ability of SMYD2 to block senescence‐like growth arrest induced by RUNX overexpression in primary fibroblasts
Addiction to Runx1 is partially attenuated by loss of p53 in the Eμ-Myc lymphoma model
The Runx genes function as dominant oncogenes that collaborate potently with
Myc or loss of p53 to induce lymphoma when over-expressed. Here we examined the
requirement for basal Runx1 activity for tumor maintenance in the Eµ-Myc model
of Burkitt’s lymphoma. While normal Runx1fl/fl lymphoid cells permit mono-allelic
deletion, primary Eµ-Myc lymphomas showed selection for retention of both alleles
and attempts to enforce deletion in vivo led to compensatory expansion of p53null blasts
retaining Runx1. Surprisingly, Runx1 could be excised completely from established Eµ-
Myc lymphoma cell lines in vitro without obvious effects on cell phenotype. Established
lines lacked functional p53, and were sensitive to death induced by introduction of a
temperature-sensitive p53 (Val135) allele. Transcriptome analysis of Runx1-deleted
cells revealed a gene signature associated with lymphoid proliferation, survival
and differentiation, and included strong de-repression of recombination-activating
(Rag) genes, an observation that was mirrored in a panel of human acute leukemias
where RUNX1 and RAG1,2 mRNA expression were negatively correlated. Notably,
despite their continued growth and tumorigenic potential, Runx1null lymphoma cells
displayed impaired proliferation and markedly increased sensitivity to DNA damage
and dexamethasone-induced apoptosis, validating Runx1 function as a potential
therapeutic target in Myc-driven lymphomas regardless of their p53 status
Low-mass lithium-rich AGB stars in the Galactic bulge: evidence for Cool Bottom Processing?
Context: The stellar production of the light element lithium is still a
matter of debate.
Aims: We report the detection of low-mass, Li-rich Asymptotic Giant Branch
(AGB) stars located in the Galactic bulge.
Methods: A homogeneous and well-selected sample of low mass, oxygen-rich AGB
stars in the Galactic bulge has been searched for the absorption lines of Li.
Using spectral synthesis techniques, we determine from high resolution UVES/VLT
spectra the Li abundance in four out of 27 sample stars, and an upper limit for
the remaining stars.
Results: Two stars in our sample have a solar Li abundance or above; these
stars seem to be a novelty, since they do not show any s-element enhancement.
Two more stars have a Li abundance slightly below solar; these stars do show
s-element enhancement in their spectra. Different scenarios which lead to an
increased Li surface abundance in AGB stars are discussed.
Conclusions: Of the different enrichment scenarios presented, Cool Bottom
Processing (CBP) is the most likely one for the Li-rich objects identified
here. Self-enrichment by Hot Bottom Burning (HBB) seems very unlikely as all
Li-rich stars are below the HBB mass limit. Also, the ingestion of a low mass
companion into the stars' envelope is unlikely because the associated
additional effects are lacking. Mass transfer from a former massive binary
companion is a possible scenario, if the companion produced little s-process
elements. A simple theoretical estimation for the Li abundance due to CBP is
presented and compared to the observed values.Comment: 5 pages, 3 figures, accepted by A&A Letter
Detecting antibody–antigen interactions with chiral plasmons: factors influencing chiral plasmonic sensing
Chiral near fields possessing enhanced asymmetry (superchirality), created by the interaction of light with (chiral) nanostructures, potentially provide a route to novel sensing and metrology technologies for biophysical applications. However, the mechanisms by which these near fields lead to the detection of chiral media is still poorly understood. Using a combination of numerical modeling and experimental measurements on an antibody–antigen exemplar system, important factors that influence the efficacy of chiral sensing are illustrated. It is demonstrated that localized and lattice chiral resonances display enantiomeric sensitivity. However, only the localized resonances show a strong dependency on the structure of the chiral media detected. This can be attributed to the ability of birefringent chiral layers to strongly modify the properties of near fields by acting as a sink/source of optical chirality, and hence alter inductive coupling between nanostructure elements. In addition, it is highlighted that surface morphology/defects may amplify sensing capabilities of localized chiral plasmonic modes by mediating inductive coupling
Observations of Neutron-Capture Elements in the Early Galaxy
Neutron-capture elements in low metallicity Galactic halo stars vary widely
both in overall contents and detailed abundance patterns. This review discusses
recent observational results on the n-capture elements, discussing the
implications for early Galactic nucleosynthesis of: (a) the star-to-star
``bulk'' variations in the n-capture/Fe abundance ratios; (b) the distinct
signature of rapid n-capture synthesis events in many (most?) of the lowest
metallicity stars; (c) the existence of metal-poor stars heavily enriched in
the products of slow n-capture synthesis reactions; and (d) the now-routine
detection of radioactive thorium (and even uranium in one and possibly two
cases) in the spectra of metal-poor stars.Comment: 8 pages, 3 figures; To appear in the Proceedings of the 7th
International Conference on Nuclei in the Cosmo
Correlation between technetium and lithium in a sample of oxygen-rich AGB variables
The aims of this paper are: 1) to revisit the Tc content of a sample of
oxygen-rich asymptotic giant branch (AGB) variables and 2) to increase the
number of such stars for which the Li abundance has been measured to provide
constraints on theoretical models of extra-mixing processes. To this end, we
analysed high-resolution spectra of 18 sample stars for the presence of
absorption lines of Tc and Li. The abundance of the latter was determined by
comparing the observed spectra to hydrostatic MARCS model spectra. Bolometric
magnitudes were established from near-IR photometry and pulsation periods. We
reclassify the star V441 Cyg as Tc-rich, and the unusual Mira star R Hya, as
well as W Eri, as Tc-poor. The abundance of Li, or an upper limit to it, was
determined for all of the sample stars. In all stars with Tc we also detected
Li. Most of them have a Li content slightly below the solar photospheric value,
except for V441 Cyg, which has ~1000 times the solar abundance. We also found
that, similar to Tc, a lower luminosity limit seems to exist for the presence
of Li. We conclude that the higher Li abundance found in the cooler and higher
luminosity objects could stem from a Li production mechanism operating on the
AGB. The stellar mass might have a crucial influence on this (extra-mixing)
production mechanism. It was speculated that the declining pulsation period of
R Hya is caused by a recent thermal pulse (TP). While not detecting Tc does not
rule out a TP, it indicates that the TPs are not strong enough to drive
dredge-up in R Hya. V441 Cyg, on the other hand, could either be a low-mass,
intrinsic S-star that produced its large amount of Li by extra-mixing
processes, or an intermediate-mass star (M>=M_sun) undergoing Li production due
to hot bottom burning.Comment: 12 pages, 7 figures, accepted for publication in A&
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