Coupling of plasmonic nanoparticles to their environments in the context of van der Waals-Casimir interactions

We present experiments in which the interaction of a single gold nanoparticle with glass substrates or with another gold particle can be tuned by in-situ control of their separations using scanning probe technology. We record the plasmon resonances of the coupled systems as a function of the polarization of the incident field and the particle position. The distinct spectral changes of the scattered light from the particle pair are in good agreement with the outcome of finite difference time-domain (FDTD) calculations. We believe our experimental technique holds promise for the investigation of the van der Waals-Casimir type interactions between nanoscopic neutral bodies.Comment: 9 pages, 7 figure

Plasmonic nanoparticle monomers and dimers: From nano-antennas to chiral metamaterials

We review the basic physics behind light interaction with plasmonic nanoparticles. The theoretical foundations of light scattering on one metallic particle (a plasmonic monomer) and two interacting particles (a plasmonic dimer) are systematically investigated. Expressions for effective particle susceptibility (polarizability) are derived, and applications of these results to plasmonic nanoantennas are outlined. In the long-wavelength limit, the effective macroscopic parameters of an array of plasmonic dimers are calculated. These parameters are attributable to an effective medium corresponding to a dilute arrangement of nanoparticles, i.e., a metamaterial where plasmonic monomers or dimers have the function of "meta-atoms". It is shown that planar dimers consisting of rod-like particles generally possess elliptical dichroism and function as atoms for planar chiral metamaterials. The fabricational simplicity of the proposed rod-dimer geometry can be used in the design of more cost-effective chiral metamaterials in the optical domain.Comment: submitted to Appl. Phys.

Formulation and optimisation of novel transfersomes for sustained release of local anaesthetic

Objective: To investigate the effect of formulation parameters on the preparation of transfersomes as sustained‐release delivery systems for lidocaine and to develop and validate a new high‐performance liquid chromatography (HPLC) method for analysis. Method: Taguchi design of experiment (DOE) was used to optimise lidocaine‐loaded transfersomes in terms of phospholipid, edge activator (EA) and phospholipid : EA ratio. Transfersomes were characterised for size, polydispersity index (PDI), charge and entrapment efficiency (%EE). A HPLC method for lidocaine quantification was optimised and validated using a mobile phase of 30%v/v PBS (0.01 m) : 70%v/v Acetonitrile at a flow rate of 1 ml/min, detected at 255 nm with retention time of 2.84 min. The release of lidocaine from selected samples was assessed in vitro. Key findings: Transfersomes were 200 nm in size, with PDI ~ 0.3. HPLC method was valid for linearity (0.1–2 mg/ml, R2 0.9999), accuracy, intermediate precision and repeatability according to ICH guidelines. The %EE was between 44% and 56% and dependent on the formulation parameters. Taguchi DOE showed the effect of factors was in the rank order : lipid : EA ratio ˃ EA type ˃ lipid type. Optimised transfersomes sustained the release of lidocaine over 24 h. Conclusion: Sustained‐release, lidocaine‐loaded transfersomes were successfully formulated and optimised using a DOE approach, and a new HPLC method for lidocaine analysis was developed and validated

Spontaneous emission in nanoscopic dielectric particles

We report on theoretical studies of the inhibition of the spontaneous emission process in subwavelength dielectric media. We discuss the modification of the spontaneous emission rate as a function of the size and shape of the medium as well as the position of the emitter in it. (C) 2003 Optical Society of America

Design of plasmonic nanoantennae for enhancing spontaneous emission

We apply two- and three-dimensional numerical calculations to study optical nanoantennae made of two coupled gold nanostructures, enclosing a single emitter in their gap. We show that, using structures manufacturable with today's nanotechnology, it is possible to increase the radiative decay rate by three orders of magnitude while keeping a quantum efficiency larger than 80% in the near-infrared regime. We examine the competition between the radiative and nonradiative processes in the presence of the antennae as a function of wavelength and antenna geometry. Our results hold great promise for improving the quantum efficiency of poor emitters such as silicon nanocrystals or carbon nanotubes. (c) 2007 Optical Society of America

Engineering gold nanoantennae to enhance the emission of quantum emitters

We study the fluorescence enhancement of a single emitter coupled to two spherical gold nanoparticles and discuss the differences with respect to coupling to a single one. We also show that by changing the aspect ratio of the nanoparticles we can easily tune the plasmon-mediated enhancement from the infrared to the visible range. We present the fabrication of our nanoantermae by two alternative methods, namely X-ray interference lithography followed by focused ion beam milling and electron beam lithography. The manufactured structures are characterized individually by confocal microscopy