Plasmonic surface lattice resonances on arrays of different lattice symmetry

Arrays of metallic particles may exhibit optical collective excitations known as surface lattice resonances (SLRs). These SLRs occur near the diffraction edge of the array and can be sharper than the plasmon resonance associated with the isolated single particle response. We have fabricated and modeled arrays of silver nanoparticles of different geometries. We show that square, hexagonal, and honeycomb arrays show similar SLRs; no one geometry shows a clear advantage over the others in terms of resonance linewidth. We investigate the nature of the coupling between the particles by looking at rectangular arrays. Our results combine experiment and modeling based on a simple coupled-dipole model.Royal SocietyLeverhulme Trus

Exploration of how light interacts with arrays of plasmonic, metallic nanoparticles

The content of this thesis is based upon the interaction of light with metallic nanoparticles arranged in different array geometries. An incident electric field (light) can force the conduction electrons of a metallic nanoparticle to oscillate. At particular frequencies, in the optical regime for gold and silver particles, absorption and scattering of the light by the particle is enhanced, corresponding to the particle plasmon resonance. The spectral position and width of the particle plasmon resonance of an isolated single particle may be tuned by adjusting its size and shape, thus changing the surface charge distribution. Periodic arrays of particles offer additional control over the frequency and width of the resonance attributed to the re-radiating (scattering) property of plasmonic particles. By fabricating arrays with a pitch comparable to the wavelength of an isolated single particle plasmon resonance, a coherent interaction between particles may be produced, known as surface lattice resonances (SLRs). The electromagnetic coupling between in-plane particle plasmon modes for different particle array geometries is explored through experiment and theory. Firstly, SLRs in square, hexagonal and honeycomb arrays are investigated by normal-incidence extinction measurements and compared to a simple-coupled dipole model. Secondly, to verify the nature of the coupling between the scattered electric field associated with particle resonances, the incident electric field polarization-dependence of the extinction of rectangular arrays and chains is studied. Thirdly, the optical response of square arrays with a symmetric two-particle basis is investigated, particularly the retardation of the scattered electric field between particles in a pair. Fourthly, square arrays with an asymmetric two-particle basis are fabricated to explore the symmetric (dipole moments of both particles are parallel) and anti-symmetric (dipole moment of both particles anti-parallel) SLRs, excited by normal-incidence light.EPSR

Asymmetric dot dimers – optical properties and interactions

We present a study of the rich optical behaviour of the dark (grey) modes exhibited by asymmetric dot dimers and how this behaviour is modified upon interaction between dimers

A Study in Asymmetry: Resonances in Arrays of Asymmetric Disc Dimers (Invited)

Published

Dietary Supplementation with Soluble Plantain Non-Starch Polysaccharides Inhibits Intestinal Invasion of Salmonella Typhimurium in the Chicken

Soluble fibres (non-starch polysaccharides, NSP) from edible plants but particularly plantain banana (Musa spp.), have been shown in vitro and ex vivo to prevent various enteric pathogens from adhering to, or translocating across, the human intestinal epithelium, a property that we have termed contrabiotic. Here we report that dietary plantain fibre prevents invasion of the chicken intestinal mucosa by Salmonella. In vivo experiments were performed with chicks fed from hatch on a pellet diet containing soluble plantain NSP (0 to 200 mg/d) and orally infected with S.Typhimurium 4/74 at 8 d of age. Birds were sacrificed 3, 6 and 10 d post-infection. Bacteria were enumerated from liver, spleen and caecal contents. In vitro studies were performed using chicken caecal crypts and porcine intestinal epithelial cells infected with Salmonella enterica serovars following pre-treatment separately with soluble plantain NSP and acidic or neutral polysaccharide fractions of plantain NSP, each compared with saline vehicle. Bacterial adherence and invasion were assessed by gentamicin protection assay. In vivo dietary supplementation with plantain NSP 50 mg/d reduced invasion by S.Typhimurium, as reflected by viable bacterial counts from splenic tissue, by 98.9% (95% CI, 98.1–99.7; P<0.0001). In vitro studies confirmed that plantain NSP (5–10 mg/ml) inhibited adhesion of S.Typhimurium 4/74 to a porcine epithelial cell-line (73% mean inhibition (95% CI, 64–81); P<0.001) and to primary chick caecal crypts (82% mean inhibition (95% CI, 75–90); P<0.001). Adherence inhibition was shown to be mediated via an effect on the epithelial cells and Ussing chamber experiments with ex-vivo human ileal mucosa showed that this effect was associated with increased short circuit current but no change in electrical resistance. The inhibitory activity of plantain NSP lay mainly within the acidic/pectic (homogalacturonan-rich) component. Supplementation of chick feed with plantain NSP was well tolerated and shows promise as a simple approach for reducing invasive salmonellosis

Endomicroscopic and transcriptomic analysis of impaired barrier function and malabsorption in environmental enteropathy

Introduction: Environmental enteropathy (EE) is associated with growth failure, micronutrient malabsorption and impaired responses to oral vaccines. We set out to define cellular mechanisms of impaired barrier function in EE and explore protective mechanisms. Methods: We studied 49 adults with environmental enteropathy in Lusaka, Zambia using confocal laser endomicroscopy (CLE); histology, immunohistochemistry and mRNA sequencing of small intestinal biopsies; and correlated these with plasma lipopolysaccharide (LPS) and a zinc uptake test. Results: CLE images (median 134 for each study) showed virtually ubiquitous small intestinal damage. Epithelial defects, imaged by histology and claudin 4 immunostaining, were predominantly seen at the tips of villi and corresponded with leakage imaged in vivo by CLE. In multivariate analysis, circulating log-transformed LPS was correlated with cell shedding events (β = 0.83; P = 0.035) and with serum glucagon-like peptide-2 (β = -0.13; P = 0.007). Zinc uptake from a test dose of 25mg was attenuated in 30/47 (64%) individuals and in multivariate analysis was reduced by HIV, but positively correlated with GLP-2 (β = 2.72; P = 0.03). There was a U-shaped relationship between circulating LPS and villus surface area. Transcriptomic analysis identified 23 differentially expressed genes in severe enteropathy, including protective peptides and proteins. Conclusions: Confocal endomicroscopy, claudin 4 immunostaining and histology identify epithelial defects which are probably sites of bacterial translocation, in the presence of which increased epithelial surface area increases the burden of translocation. GLP 2 and other protective peptides may play an important role in mucosal protection in EE

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

Excitonic surface lattice resonances (dataset)

University of Exeter Physics and AstronomyThrough the use of analytic models and numerical simulation we show how molecular materials may be used to produce nanoparticles that exhibit localized surface exciton polariton modes when the molecules have a strong excitonic transition. Such particles display electric field enhancement and field confinement similar to those associated with the localized surface plasmon polariton modes of metallic nanoparticles. We further show that periodic arrays of suitable molecular nanoparticles may support surface lattice resonances that arise as a result of coherent interactions between the particles. These results demonstrate that excitonic molecular materials are an interesting alternative to metals for nanophotonics; they offer the prospect of both fabrication based on supramolecular chemistry and optical functionality arising from the way the properties of such materials may be controlled with ligh

Surface lattice resonances in plasmonic arrays of asymmeric disc dimers (dataset)

Provides research data for the article "Surface Lattice Resonances in Plasmonic Arrays of Asymmeric Disc Dimers".Final published version available from the publisher via DOI: 10.1021/acsphotonics.5b00727.The article associated with this dataset is in ORE: http://hdl.handle.net/10871/25440We study regular wavelength scale arrays of metallic dimers. By employing dimers made up of two different sized discs, we are able to couple to array-based collective surface lattice resonances of both bright and dark, that is symmetric and antisymmetric, dimer modes and to show that the degree of asymmetry can be used to control the relative strength of the two surface-lattice modes. The collective nature of these excitations can even lead to an antisymmetric surface-lattice resonance that is stronger than the symmetric one; this is in stark contrast to the dark and bright nature of the underlying modes of the individual dimers. We verify these experimental findings, derived from extinction measurements, by comparison with both analytical and numerical modeling.The Leverhulme TrustPhysical Sciences Research Council (U.K.