Using adsorption kinetics to assemble vertically aligned nanorods at liquid interfaces for metamaterial applications.

Vertically aligned monolayers of metallic nanorods have a wide range of applications as metamaterials or in surface enhanced Raman spectroscopy. However the fabrication of such structures using current top-down methods or through assembly on solid substrates is either difficult to scale up or have limited possibilities for further modification after assembly. The aim of this paper is to use the adsorption kinetics of cylindrical nanorods at a liquid interface as a novel route for assembling vertically aligned nanorod arrays that overcomes these problems. Specifically, we model the adsorption kinetics of the particle using Langevin dynamics coupled to a finite element model, accurately capturing the deformation of the liquid meniscus and particle friction coefficients during adsorption. We find that the final orientation of the cylindrical nanorod is determined by their initial attack angle when they contact the liquid interface, and that the range of attack angles leading to the end-on state is maximised when nanorods approach the liquid interface from the bulk phase that is more energetically favorable. In the absence of an external field, only a fraction of adsorbing nanorods end up in the end-on state (≲40% even for nanorods approaching from the energetically favourable phase). However, by pre-aligning the metallic nanorods with experimentally achievable electric fields, this fraction can be effectively increased to 100%. Using nanophotonic calculations, we also demonstrate that the resultant vertically aligned structures can be used as epsilon-near-zero and hyperbolic metamaterials. Our kinetic assembly method is applicable to nanorods with a range of diameters, aspect ratios and materials and therefore represents a versatile, low-cost and powerful platform for fabricating vertically aligned nanorods for metamaterial applications.

Adsorption trajectories of nonspherical particles at liquid interfaces.

The adsorption of colloidal particles at liquid interfaces is of great importance scientifically and industrially, but the dynamics of the adsorption process is still poorly understood. In this paper we use a Langevin model to study the adsorption dynamics of ellipsoidal colloids at a liquid interface. Interfacial deformations are included by coupling our Langevin dynamics to a finite element model while transient contact line pinning due to nanoscale defects on the particle surface is encoded into our model by renormalizing particle friction coefficients and using dynamic contact angles relevant to the adsorption timescale. Our simple model reproduces the monotonic variation of particle orientation with time that is observed experimentally and is also able to quantitatively model the adsorption dynamics for some experimental ellipsoidal systems but not others. However, even for the latter case, our model accurately captures the adsorption trajectory (i.e., particle orientation versus height) of the particles. Our study clarifies the subtle interplay between capillary, viscous, and contact line forces in determining the wetting dynamics of micron-scale objects, allowing us to design more efficient assembly processes for complex particles at liquid interfaces.

Density functional theory for the crystallization of two-dimensional dipolar colloidal alloys.

Two-dimensional mixtures of dipolar colloidal particles with different dipole moments exhibit extremely rich self-assembly behaviour and are relevant to a wide range of experimental systems, including charged and super-paramagnetic colloids at liquid interfaces. However, there is a gap in our understanding of the crystallization of these systems because existing theories such as integral equation theory and lattice sum methods can only be used to study the high temperature fluid phase and the zero-temperature crystal phase, respectively. In this paper we bridge this gap by developing a density functional theory (DFT), valid at intermediate temperatures, in order to study the crystallization of one and two-component dipolar colloidal monolayers. The theory employs a series expansion of the excess Helmholtz free energy functional, truncated at second order in the density, and taking as input highly accurate bulk fluid direct correlation functions from simulation. Although truncating the free energy at second order means that we cannot determine the freezing point accurately, our approach allows us to calculate ab initio both the density profiles of the different species and the symmetry of the final crystal structures. Our DFT predicts hexagonal crystal structures for one-component systems, and a variety of superlattice structures for two-component systems, including those with hexagonal and square symmetry, in excellent agreement with known results for these systems. The theory also provides new insights into the structure of two-component systems in the intermediate temperature regime where the small particles remain molten but the large particles are frozen on a regular lattice.

Crossover between liquidlike and gaslike behavior in CH_{4} at 400 K.

We report experimental evidence for a crossover between a liquidlike state and a gaslike state in fluid methane (CH_{4}). This crossover is observed in all of our experiments, up to a temperature of 397 K, 2.1 times the critical temperature of methane. The crossover has been characterized with both Raman spectroscopy and x-ray diffraction in a number of separate experiments, and confirmed to be reversible. We associate this crossover with the Frenkel line-a recently hypothesized crossover in dynamic properties of fluids extending to arbitrarily high pressure and temperature, dividing the phase diagram into separate regions where the fluid possesses liquidlike and gaslike properties. On the liquidlike side the Raman-active vibration increases in frequency linearly as pressure is increased, as expected due to the repulsive interaction between adjacent molecules. On the gaslike side this competes with the attractive van der Waals potential leading the vibration frequency to decrease as pressure is increased.

Spectroscopy and single-molecule emission of a fluorene-terthiophene oligomer.

We study the thiophene-based oligomer poly[2,7-(9,9-bis(2'-ethylhexyl)fluorene)-alt-2,5-terthiophene] (PF3T) in solution and when dispersed at low concentration into a polynorbornene matrix. We find that at high concentration in solution the 0-0 electronic transition observed in fluorescence is suppressed, a result indicative of the formation of weakly coupled H-aggregates. At low concentration in a polymer matrix, emission from both single molecules and molecular aggregates is observed. We find that the fluorescence spectra of most PF3T emitters are composed of a number of relatively narrow emission features, indicating that the emission usually occurs from multiple chromophores. A small number of PF3T molecules are however characterized by single chromophore emission, spectral blinking, and narrowed emission peaks.

Single molecule spectroscopy of red- and green-emitting fluorene-based copolymers.

Single molecule fluorescence spectroscopy is used to study the optical properties of two polymers: a fluorene-based statistical copolymer that contains a low fraction (10%) of a red-emitting thiophene group, and the green-emitting polymer poly(9,9-dioctylfluorene-alt-benzothiadiazole). These polymers were studied when isolated at a low concentration in a polymer matrix (either polynorbornene or polystyrene). For the red-emitting polymer, we compare the relative emission intensity from the green-emitting benzothiadiazole groups with the red-emitting thiophene. We find that red emission from the thiophenes is significantly suppressed in the single molecule regime, suggesting that interchain energy transfer dominates intrachain processes in such polyfluorene copolymers. We then use fluorescence spectroscopy and polarization anisotropy measurements to show that the conformations of both polymers are dependent on their host matrix, adopting a more collapsed, globular conformation in polystyrene and a more extended chain conformation in polynorbornene.

Refractive index dependence of L3 photonic crystal nano-cavities.

We model the optical properties of L3 photonic crystal nano-cavities as a function of the photonic crystal membrane refractive index n using a guided mode expansion method. Band structure calculations revealed that a TE-like full band-gap exists for materials of refractive index as low as 1.6. The Q-factor of such cavities showed a super-linear increase with refractive index. By adjusting the relative position of the cavity side holes, the Q-factor was optimised as a function of the photonic crystal membrane refractive index n over the range 1.6 to 3.4. Q-factors in the range 3000-8000 were predicted from absorption free materials in the visible range with refractive index between 2.45 and 2.8.

Blockade of CD40-CD40 ligand interactions protects against radiation-induced pulmonary inflammation and fibrosis.

This study investigated whether CD40-CD40 ligand (L) interactions are important in mediating ionizing radiation-induced lung toxicity. Radiotherapy is a key component in the management of malignant diseases and is a conditioning regimen for bone marrow transplantation. Unfortunately, radiation therapy is particularly toxic to the lung, potentially inducing a fatal pneumonitis and fibrosis, thus limiting its effectiveness. There are no therapies that protect against the development of radiation-induced lung toxicity. Using a mouse model of radiation-induced lung toxicity, a monoclonal anti-CD40L antibody (MR1) that disrupts CD40-CD40L interactions was tested for the ability to reduce lung injury. C57BL/6 mice were pretreated with either nothing, MR1, or hamster IgG 24 h prior to a single dose of 15 Gray ionizing radiation to the thorax. During the following 26 weeks, mice continued to receive MR1 or hamster IgG twice per week. MR1 protected against death from radiation pneumonitis and fibrosis and dramatically reduced lung pathology as evidenced by a limited influx of inflammatory cells, minimal collagen deposition, and septal thickening. MR1 also prevented radiation-induced pulmonary mastocytosis and blunted expression of cyclooxygenase-2, a proinflammatory enzyme responsible for prostaglandin synthesis. Disruption of CD40-CD40L interactions may offer a new mode of intervention to protect against radiation-induced pulmonary toxicity.

Disruption of the CD40-CD40 ligand system prevents an oxygen-induced respiratory distress syndrome.

Oxygen therapy is a mainstay treatment for infants and adults with poor lung function. Unfortunately, oxygen itself is toxic and incites respiratory cell damage and inflammation. Therapies for oxygen-induced lung damage are nonexistent. Employing a mouse model of hyperoxic lung injury, a monoclonal anti-CD40 ligand (L) antibody (MR1), which disrupts CD40-CD40L interactions, was tested for the ability to reduce pulmonary injury. Intraperitoneal administration of MR1, either before or after oxygen exposure, was remarkably effective in reducing and in many cases preventing lung injury. The pro-inflammatory enzyme cyclooxygenase-2 (Cox-2), responsible for prostaglandin production, is massively up-regulated in the lungs after hyperoxic exposure. Immunohistochemical staining for Cox-2 revealed that MR1 greatly reduces the oxygen-induced induction of Cox-2. The remarkable effectiveness of MR1 in blunting hyperoxic lung injury in this preclinical model may be relevant to the hundreds of thousands of patients who require treatment with high oxygen and who are at risk for developing severe pulmonary inflammation and consequent fibrosis. Strategies to disrupt CD40-CD40L interactions may offer a new mode of intervention for oxygen-induced acute respiratory distress syndrome and other inflammatory lung disorders.

Location of a S. mansoni circulating antigen using indirect immunofluorescent assay.

Indirect immunofluorescent technique was utilized to determine the location of butanol extracted microsomal antigen of adult S. mansoni. Bright fluorescence was located deep in the gut of both adult S. mansoni and S. haematobium treated with specific IgM monclonal antibody. No fluorescence was observed in any part of schistosomulae. Thus, this butanol extracted antigen may be considered stage and genus specific. The large surface area of the gut promises that enough antigen escapes to be detectable in the circulation of the host. This antigen has the potentiality to be used as a circulating antigen for diagnosis of active Schistosoma infection.

Intestinal parasitic infections in immunosuppressed patients.

Hundred immunosuppressed patients and 50 apparently healthy individuals as control were subjected to stool examination for parasitic infections by the direct smear method and the merthiolate iodine formal-dehyde (MIF) concentration technique. The modified Ziehl-Neelson stain and the aniline carbol methyl violet stain were used to detect Cryptosporidium oocysts. 27 Patients were found positive using the MIF technique while only 13 of them were positive by the direct smear method. Cryptosporidium oocysts were detected in 7 cases using the aniline carbol methl violet stain while only 5 of them were positive by the modified Ziehl-Neelson stain.

A monoclonal antibody-based enzyme immunoassay for detecting parasite antigenaemia and antigenuria in Schistosomiasis mansoni.

Both specific polycolonal antibody and monoclonal antibody against the microsomal antigen of adult S. mansoni were used to detect antigenaemia and antigenuria by antigen-capture sandwich ELISA in the sera and urine of patients infected with S. mansoni and other parasites. Antigenaemia was detected in 22 sera out of 100 of patients infected with S. mansoni but no antigenuria was detected. None of the sera of S. mansoni free patients were positive for microsomal antigen. More standardization of the technique and more refining of the reagents used is required to improve the sensitivity of the test.

Regulation of IgE and cytokine production by cAMP: implications for extrinsic asthma.

Recent investigations indicate that pharmacologic agents which elevate intracellular levels of cyclic AMP (cAMP) also enhance immunoglobulin E (IgE) production. This review proposes that elevation of intracellular cAMP is a prominent mechanism which enhances IgE production. Enhancement is mediated by two mechanisms. First, cAMP-elevating agents directly target B lymphocytes, promoting recombination of the Ig heavy chain loci. Second, these agents indirectly promote IgE production by inducing a T-helper type 2 (Th2) profile of cytokine secretion. In turn, Th2-type cytokines interact with B lymphocytes and direct isotype switching to the epsilon locus. One type of cAMP-elevating agents, the beta2-adrenergic receptor agonists (beta2-agonists), are used to treat asthma. A number of detrimental phenomena have been associated with beta2-agonist use such as, rebound hyperresponsiveness and increases in asthma mortality. This review theorizes that beta2-agonists enhance IgE and Th2 cytokine production and that these mediators exacerbate extrinsic, IgE-dependent asthma.

Effect of ivermectin on survival and fecundity of Culex pipiens the vector of Wuchereria bancrofti in Egypt.

The effect of two different doses of ivermectin on the survival and fecundity of Culex pipiens was evaluated. Female mosquitoes (50 in each group), same age and generation, were fed once on blood from ivermectin-treated rabbits. Comparative treatments consisted of two different doses of ivermectin (0.1 mg or 0.4 mg/kg of body weight), and mosquito groups were fed on the rabbits at 3 days and 10 days post-treatment respectively. Mosquitoes were maintained with 10% sucrose solution, at 25 degrees C and 70% relative humidity. Observations were made at 7, 10, 15, 20, 25, and 30 days post-feeding. Mosquitoes fed on rabbits treated with the small dose at three days post-injection showed reduced survival of 94%, 62%, 44%, 8% and 0%, while the 0.4 while the 0.4 mg/kg of body weight (bw) dose reduced survival to 88%, 60%, 6% and 0%. Survival of the control groups were 100%, 90%, 88%, 68% and 52% respectively. Survival of adult females fed at the lower dose, 10 days post injection were reduced to 92%, 90%, 84% 60% and 44%; while the higher dose reduced survival to 86%, 58%, 34% 22% and 0%. Survival of control groups were 96%, 92%, 84%, 78% and 72% respectively. Fecundity resulting from blood meals at 3 and 10 days post injection were 61% and 85% for the lower dose, and 0% and 42% for the higher dose respectively. Hatching of eggs was 82% and 88% for the 0.1 mg/kg bw dose, and no hatching was observed at the higher dose. Larval survival rates resulting from blood meals taken 3 days and 10 days post-injection of the lower dose were 24% and 25% respectively. However, no larvae survived from the high dose groups. Larval survival rates in control groups were 42% and 40%, respectively. These results provide new information about the effect of ivermectin on the vector of lymphatic filariasis, and add a new dimension to the use of ivermectin in filariasis control.