Light tunneling via resonant surface plasmon polariton states and the enhanced transmission of periodically nanostructured metal films: An analytical study

An analytical treatment of optical transmission through periodically nanosructured metal films capable of supporting surface-plasmon polaritons is presented. The optical properties of such metal films are governed by surface polariton behavior in a periodic surface structure forming a surface polaritonic crystal. Due to different configurations of the electromagnetic field of surface polariton modes, only states of even Brillouin zones are responsible for the optical transmission enhancement at normal incidence. The transmission enhancement is related to photon tunneling via resonant states of surface polariton Bloch modes in which the energy buildup takes place. Surface polariton states of at least one of the film interfaces contribute to the transmission resonance which occurs due to tunnel coupling between photons and surface polaritons on the opposite interfaces. Under double-resonance conditions, resonant tunneling between surface polariton states of both interfaces is achieved, which leads to further enhancement of the transmission efficiency. The double-resonance conditions occur not only in the case of a film in symmetric environment but can also be engineered for a film on a substrate. Light tunneling via surface polariton states can take place directly through a structured metal film and does not necessarily require holes in a film.

Comparison of a novel spray congealing procedure with emulsion-based methods for the micro-encapsulation of water-soluble drugs in low melting point triglycerides

The particle size characteristics and encapsulation efficiency of microparticles prepared using triglyceride materials and loaded with two model water-soluble drugs were evaluated. Two emulsification procedures based on o/w and w/o/w methodologies were compared to a novel spray congealing procedure. After extensive modification of both emulsification methods, encapsulation efficiencies of 13.04% tetracycline HCl and 11.27% lidocaine HCl were achievable in a Witepsol (R)-based microparticle. This compares to much improved encapsulation efficiencies close to 100% for the spray congealing method, which was shown to produce spherical particles of similar to 58 mu m. Drug release studies from a Witepsol (R) formulation loaded with lidocaine HCl showed a temperature-dependent release mechanism, which displayed diffusion-controlled kinetics at temperatures similar to 25 degrees C, but exhibited almost immediate release when triggered using temperatures close to that of skin. Therefore, such a system may find application in topical semi-solid formulations, where a temperature-induced burst release is preferred.

Solving the problem of diffraction of an optical-band electromagnetic wave by metal nanostructured aperture arrays with the use of the method of impedance boundary conditions

The problem of diffraction of an optical wave by a 2D periodic metal aperture array with square, circular, and ring apertures is solved with allowance for the finite permittivity of a metal in the optical band. The correctness of the obtained results is verified through comparison with experimental data. It is shown that the transmission coefficient can be substantially greater than the corresponding value reached in the case of diffraction by a grating in a perfectly conducting screen.

Review and meta-analysis of the short-term effects of a vegetable oil emulsion on food intake

Several short-term studies have investigated the effects of a vegetable oil emulsion on subsequent food intake, although findings have been inconsistent. This work aimed to review all studies, and investigate differences in study outcomes based on methodology. All known studies were identified. Data were abstracted from published studies (n = 7). Details of unpublished studies were gained from investigators/sponsors (n = 5), or were unavailable for reasons of confidentiality (n = 4). Available data were combined using meta-analyses. A combined appetite suppressant effect of the emulsion compared with control was found for test meal intake at approximately 4, 12 and 36 h post-treatment: smallest combined mean difference (random effects model) = 0.53 MJ (95% confidence interval 0.20, 0.86), P < 0.01. However, considerable heterogeneity (variability) between study results was also found (smallest I2 = 94%, P < 0.01), questioning the predictive validity of the above findings. Meta-regression suggested this heterogeneity to be related to differences in the processed nature of the product, treatment dose and in particular year of study (smallest B = 0.54, 95% confidence interval 0.06, 1.03, P = 0.04), although again heterogeneity was found. The only consistent finding was a lack of effect on food intake 4 h post-preload in studies conducted after 2003. These results suggest a small but inconsistent appetite suppressant effect of the vegetable oil emulsion. However, due to the large heterogeneity, no definitive conclusions can be drawn.

Magneto-optical trapping and background-free imaging for atoms near nanostructured surfaces

We demonstrate a combined magneto-optical trap and imaging system that is suitable for the investigation of cold atoms near surfaces. In particular, we are able to trap atoms close to optically scattering surfaces and to image them with an excellent signal-to-noise ratio. We also demonstrate a simple magneto-optical atom cloud launching method. We anticipate that this system will be useful for a range of experimental studies of novel atom-surface interactions and atom trap miniaturization.

Antimicrobial Efficacy of an Innovative Emulsion of Medium Chain Triglycerides against Canine and Feline Periodontopathogens

OBJECTIVES: To test the in vitro antimicrobial efficacy of a non-toxic emulsion of free fatty acids against clinically relevant canine and feline periodontopathogens 
METHODS: Antimicrobial kill kinetics were established utilising an alamarBlue® viability assay against 10 species of canine and feline periodontopathogens in the biofilm mode of growth at a concentration of 0·125% v/v medium chain triglyceride (ML:8) emulsion. The results were compared with 0·12% v/v chlorhexidine digluconate and a xylitol-containing dental formulation. Mammalian cellular cytotoxicity was also investigated for both the ML:8 emulsion and chlorhexidine digluconate (0·25 to 0·0625% v/v) using in vitro tissue culture techniques.
RESULTS: No statistically significant difference was observed in the antimicrobial activity of the ML:8 emulsion and chlorhexidine digluconate; a high percentage kill rate (>70%) was achieved within 5 minutes of exposure and was maintained at subsequent time points. A statistically significant improvement in antibiofilm activity was observed with the ML:8 emulsion compared with the xylitol-containing formulation. The ML:8 emulsion possessed a significantly lower (P<0·001) toxicity profile compared with the chlorhexidine digluconate in mammalian cellular cytotoxicity assays.
CLINICAL SIGNIFICANCE: The ML:8 emulsion exhibited significant potential as a putative effective antimi-crobial alternative to chlorhexidine- and xylitol- based products for the reduction of canine and feline periodontopathogens.

Hyperbolic Polaritonic Crystals Based on Nanostructured Nanorod Metamaterials

Surface plasmon polaritons usually exist on a few suitable plasmonic materials; however, nanostructured plasmonic metamaterials allow a much broader range of optical properties to be designed. Here, bottom-up and top-down nanostructuring are combined, creating hyperbolic metamaterial-based photonic crystals termed hyperbolic polaritonic crystals, allowing free-space access to the high spatial frequency modes supported by these metamaterials.

Surface-Enhanced Raman Spectroscopy as a Probe of the Surface Chemistry of Nanostructured Materials

Surface-enhanced Raman spectroscopy (SERS) is now widely used as a rapid and inexpensive tool for chemical/biochemical analysis. The method can give enormous increases in the intensities of the Raman signals of low-concentration molecular targets if they are adsorbed on suitable enhancing substrates, which are typically composed of nanostructured Ag or Au. However, the features of SERS that allow it to be used as a chemical sensor also mean that it can be used as a powerful probe of the surface chemistry of any nanostructured material that can provide SERS enhancement. This is important because it is the surface chemistry that controls how these materials interact with their local environment and, in real applications, this interaction can be more important than more commonly measured properties such as morphology or plasmonic absorption. Here, the opportunity that this approach to SERS provides is illustrated with examples where the surface chemistry is both characterized and controlled in order to create functional nanomaterials.

Optical bistability in nonlinear surface-plasmon polaritonic crystals

Nonlinear optical transmission through periodically nanostructured metal films (surface-plasmon polaritonic crystals) has been studied. The surface polaritonic crystals have been coated with a nonlinear polymer. The optical transmission of such nanostructures has been shown to depend on the control-light illumination conditions. The resonant transmission exhibits bistable behavior with the control-light intensity. The bistability is different at different resonant signal wavelengths and for different wavelengths of the control light. The effect is explained by the strong sensitivity of the surface-plasmon mode resonances at the signal wavelength to the surrounding dielectric environment and the electromagnetic field enhancement due to plasmonic excitations at the controlled light wavelengths.

Theoretical analysis on microwave heating of oil–water emulsions supported on ceramic, metallic or composite plates

A detailed theoretical analysis has been carried out to study efficient heating due to microwaves for one-dimensional (1D) oil–water emulsion samples placed on various ceramic, metallic (reflective) and ceramic–metallic composite supports. Two typical emulsion systems are considered such as oil-in-water (o/w) and water-in-oil (w/o). A preliminary study has been carried out via average power vs emulsion thickness diagram to estimate microwave power absorption within emulsion samples for various cases. The maxima in average power, also termed as ‘resonances’, are observed for specific emulsion thicknesses and the two consecutive resonances of significant magnitudes are termed as R1 and R2 modes. For both o/w and w/o emulsions, it is observed that microwave power absorption is enhanced in presence of metallic and composite supports during both R1 and R2 modes. The efficient heating strategies characterized by ‘large heating rates’ with ‘minimal thermal runaway’ i.e. uniform temperature distributions within the sample have been assessed for each type of emulsion. Based on the detailed spatial distributions of power and temperature for various cases, SiC-metallic composite support may be recommended as an optimal heating strategy for o/w samples with higher oil fractions (0.45) whereas metallic and Alumina-metallic composite supports may be favored for samples with smaller oil fractions (=0.3) during R1 mode. For w/o samples, SiC-metallic composite support may be suitable heating strategy for all ranges of water fractions during R1 mode. During R2 mode, metallic and Alumina-metallic composite supports are favored for both o/w and w/o emulsion samples. Current study recommends the efficient way to use microwaves in a single mode waveguide and the heating strategy can be suitably extended for heating of any other emulsions for which dielectric properties are easily measurable or available in the literature.

Ionography of nanostructures with the use of a laser plasma of cluster targets

It has been shown that a femtosecond plasma of cluster targets is an almost isotropic source of fast ions and, hence, can be used to obtain ionographic images with a wide field of view. The spatial resolution of the resulting ionographic images is no worse than 600 nm, which corresponds to a uniquely high value of about 105 of the ratio of the field of view to the resolution. The use of 100–300-keV ion fluxes ensures the sensitivity of the method to the sample thickness of no worse than 100 nm even for samples consisting of light chemical elements (C, H). The proposed method can be used to obtain images of low-contrast biological objects, thin films, membranes, and other nanostructured objects.