Heat transfer from nanoparticles for targeted destruction of infectious organisms

© 2017 Informa UK Limited, trading as Taylor & Francis Group. Whereas the application of optically or magnetically heated nanoparticles to destroy tumours is now well established, the extension of this concept to target pathogens has barely begun. Here we examine the challenge of targeting pathogens by this means and, in particular, explore the issues of power density and heat transfer. Depending on the rate of heating, either hyperthermia or thermoablation may occur. This division of the field is fundamental and implies very different sources of excitation and heat transfer for the two modes, and different strategies for their clinical application. Heating by isolated nanoparticles and by agglomerates of nanoparticles is compared: hyperthermia is much more readily achieved with agglomerates and for large target volumes, a factor which favours magnetic excitation and moderate power densities. In contrast, destruction of planktonic pathogens is best achieved by localised thermoablation and very high power density, a scenario that is best delivered by pulsed optical excitation

Synthesis and optical properties of hybrid and alloy plasmonic nanoparticles

Synthesis and optical properties of hybrid and alloy plasmonic nanoparticles hybrid systems that display a plasmon resonance in the visible or near-visible regions of the spectrum are studied. In the hybrid system, also called passive metallo-dielectric hybrids, the functionalities of the parts remain reasonably independent. The optical properties of these structures are explained by the properties of the individual parts, except for some bathochromic shifting of the plasmon resonance of the metallic component due to the increase in local dielectric constant due to the other component. Metal-metal hybrids and their closely related alloyed nanoparticles exhibit more complex behavior. The plasmon resonance or resonances of the parts can be enhanced, shifted, or suppressed. In the case of core-shell particles, the dielectric properties of the shell material will dominate above some modest thickness, and in the limit, the result is as if the hybrid was composed throughout of the shell material

Thermal stresses and cracking in absorptive solar glazing

The emerging popularity of absorptive, as opposed to reflective, solar glazing coatings on windows has generated renewed interest in thermally induced cracking of glass structures. Here we analyse the stresses on glass coated with absorptive solar glazing films caused by uneven solar illumination. It is shown that the occasionally reported brittle fracture of such structures can be readily explained as being the result of differential thermal expansion of the glass. The magnitude of the effect is linearly proportional to the shading coefficient of the glass and is also influenced by the manner in which the glass is supported. © 2005 Elsevier Ltd. All rights reserved

Precious metal core-shell spindles

A simplified method to produce spindle-shaped particles with a hematite core and a silica shell is described. The silica shell can, in turn, serve as the substrate for an outer coating of Ag or Au nanoparticles. The resulting multilayer core-shell particles display a flexible optical extinction spectrum, due primarily to the sensitivity of their plasmon resonance to the morphology of the precious metal outer coating. © 2007 American Chemical Society

Therapeutic possibilities of plasmonically heated gold nanoparticles

Nanoparticles of gold, which are in the size range 10-100 nm, undergo a plasmon resonance with light. This is a process whereby the electrons of the gold resonate in response to incoming radiation causing them to both absorb and scatter light. This effect can be harnessed to either destroy tissue by local heating or release payload molecules of therapeutic importance. Gold nanoparticles can also be conjugated to biologically active moieties, providing possibilities for targeting to particular tissues. Here, we review the progress made in the exploitation of the plasmon resonance of gold nanoparticles in photo-thermal therapeutic medicine. © 2005 Elsevier Ltd. All rights reserved

Optical properties and plasmon resonances of titanium nitride nanostructures

We examine the optical properties of nanostructures comprised of titanium nitride, TiN, an electrically conducting intermetallic-like compound. This material can be deposited in the form of durable films by physical vapor deposition. Use of nanosphere templating techniques extends the range of nanostructures that can be produced to include the versatile semi-shell motif. The dielectric properties of TiN1 - x depend upon stoichiometry and are favorable for plasmon resonance phenomena in the mid-visible to near-infrared range of the spectrum and for x≈0. We analyze the optical phenomena operating in such structures using a combination of experiment and simulation and show that semi-shells of TiN exhibit a tunable localized plasmon resonance with light. The material is, however, unsuitable for applications in which a long-distance surface plasmon polariton is desired. © 2010 IOP Publishing Ltd

Formation of gold nanorods by a stochastic "popcorn" mechanism

Gold nanorods have significant technological potential and are of broad interest to the nanotechnology community. The discovery of the seeded, wet-chemical synthetic process to produce them may be regarded as a landmark in the control of metal nanoparticle shape. However, the mechanism by which the initial spherical gold seeds acquire anisotropy is a critical, yet poorly understood, factor. Here we examine the very early stages of rod growth using a combination of techniques including cryogenic transmission electron microscopy, optical spectroscopy, and computational modeling. Reconciliation of the available experimental observations can only be achieved by invoking a stochastic, "popcorn"-like mechanism of growth, in which individual seeds lie quiescent for some time before suddenly and rapidly growing into rods. This is quite different from the steady, concurrent growth of nanorods that has been previously generally assumed. Furthermore we propose that the shape is controlled by the ratio of surface energy of rod sides to rod ends, with values of this quantity in the range of 0.3-0.8 indicated for typical growth solutions. © 2012 American Chemical Society

X-ray-induced reduction of a surfactant/polyoxotungstate hybrid compound

© 2018 John Wiley & Sons, Ltd. We investigate the spontaneous reduction of a photochromic surfactant/polyoxotungstate hybrid during repeated X-ray photoelectron spectroscopy (XPS) scans and show how this effect may confound attempts to use soft X-rays to characterise materials of this nature. The W4f core-level spectra revealed a progressive increase of W5+ and W4+ species at the expense of W6+ as irradiation time increased. The samples developed a blue colour attributed to the presence of W4+ and/or W5+. The progressive photoreduction is also associated with a shift of the W6+ peak within the W4f spectrum to lower binding energies. This work highlights the need to consider inadvertent changes in oxidation state during X-ray photoelectron spectroscopy characterisation of samples containing photoreducible transition metals

Effect of glass pre-treatment on the nucleation of semi-transparent gold coatings

Coatings of gold nanoparticles with a uniform film texture and a neutral blue hue may be applied to glass by an aqueous process and such coatings have recently been proposed for architectural applications. Here, we show that the optical transmission spectrum of these coatings is directly related to the interplay between the nucleation, growth and aggregation of the particles. In particular, prior treatments of the glass substrate in 1:1 sulfuric acid (H 2SO4), 98% H2SO4 and buffered hydrofluoric acid (HF) exerted a strong influence on the subsequent particle size and coverage, which is explained here in terms of contact angle and its effect on rates of nucleation. The rate of nucleation on the surface treated with HF is estimated to be twice that of the surface treated with 98% H 2SO4. The color of the coatings is the result of inter-particle plasmonic interactions and is, therefore, also controlled by the nature of nucleation and growth process. © 2005 Elsevier B.V. All rights reserved

The apparent optical indices of spongy nanoporous gold

Very thin spongy nanoporous gold films have a unique nanostructure and hence unusual properties. Our interest in these materials is also due to their wide range of potential application (1,2). An optical study for such nanostructured films is of fundamental interest for understanding how light interacts with such a spongy nanoporous structure. In general the gold either percolates or is very closely packed. This surface plasmons, and surface plasmon resonant effects, are expected to play a key role given the large surface area of metal and the metal backbone of the nanostructure. The ropological complexity of the nano-void network is also expected to be a major influence. The optical response has, for a metal system, quite unusual dispersion relations for the effective complex refractive index components n*, k*. Once these are better understood new optical engineering possibilities arise. We are not aware of any optical studies for spongy metal film nanostructures apart from a brief preliminary report of our own on one such film 93) whose nanstructure was different to the spongy nanoporous films presented here. We check the internal consistency and physical accpetability of the results with a Kramers-Kronig analysis of the spectrumn of n*, k* values, because of their unusual spectral character