Gold nanorods exhibit intense optical absorption bands in the near-infrared region of principal interest for applications in biomedical optics, which originate from sharp plasmon resonances. This high absorbance, combined with the biochemical inertness and targetability of gold nanoparticles, makes these materials excellent candidates to provide contrast in photoacoustic imaging and for other applications such as the selective hyperthermia of cancer. One issue demoting the potential of gold nanorods as contrast agents in photoacoustic applications is their limited photostability, which falls below relevant permissible exposure limits. In particular, when gold nanorods are resonantly excited by laser pulses in the nanosecond duration regime, there may occur phenomena like reshaping into rounder nanoparticles as well as fragmentation and sublimation, which modify their optical absorption bands and hinder their efficiency of photoacoustic conversion. Here we investigate the influence of nanoparticle size on the photostability and reproducibility of photoacoustic conversion of gold nanorods embedded in biomimetic phantoms. We compare samples containing gold nanorods with different sizes but the same shapes and overall optical densities. We demonstrate clear size effects as the thresholds of optical fluences for nanoparticle deformation improve from below 2 to above 6 mJ/cm2 with nanoparticle miniaturization from 22 to 5 nm effective radii. We interpret these results in terms of a better thermal coupling and faster heat dissipation from smaller nanoparticles to their environment, originating from their larger specific surface area.

The determination of the magnetic properties of molecular magnets in environments similar to those used in spintronic devices is fundamental for the development of applications. Single-molecule magnets (SMMs) are molecular cluster systems that display magnetic hysteresis of dynamical origin at low temperature. [1,2] As they behave like perfectly monodisperse nanomagnets and show clear macroscopic quantum effects in their magnetic properties, [3] they are extremely appealing candidates for the forthcoming generation of molecular devices: they have been proposed as efficient systems for quantum computation, [4] ultra-high-density magnetic recording media, [5] and molecular spintronic systems. [6][7][8] These attractive possibilities have stimulated the creativity of chemists and materials scientists in developing several different ways of organizing such systems into addressable nanostructured materials. In particular inclusion into Langmuir-Blodgett (LB) films, [9] mesoporous silica, [10] polymeric matrices, [11] and ultrathin films [12] have been devised and studied. The most appealing approaches, both from the applicative and speculative points of view, are the functionalization and binding of such clusters on conducting surfaces [13,14] as well as their incorporation into break-junctions, [6][7][8]15] where a single molecule is directly accessible. These results have led to the creation of the first SMM-based molecular spintronic devices, [15] in which the electronic transport properties are modulated by the magnetic state of a single SMM cluster. The considerable difficulties linked to the interpretation of such results have recently stimulated much theoretical work, [6][7][8] and a number of predictions have been made. Both topological [8] and quantum tunneling [7] effects on the transport in the Kondo regime have been predicted, and several peculiar fingerprints of the SMM behavior should be apparent in transport measurements. [6,15] Interesting effects are also predicted when addressing a SMM on a surface with a tunneling current. [16] Although the influence of the surroundings on the magnetic properties of SMMs has been pointed out in several theoretical and experimental works, [17] our understanding of SMM behavior almost totally relies on measurements performed on crystalline samples. Magnetic measurements on SMMs that lie in environments similar to those of spintronic devices have not been reported up to now, mainly because of the very high sensitivity required. In this Communication we try to fill this void by using high-sensitivity instrumentation, based on magneto-optical (MO) techniques on a variety of materials.

We present an experimental study of the radiative recombination dynamics in size-controlled anatase TiO2 nanoparticles in the range 20–130 nm. From time-integrated photoluminescence spectra and picosecond time-resolved experiments as a function of the nanoparticle size, excitation density, and temperature, we show that photoluminescence comes out from a bulk and a surface radiative recombination. The spectral shift and the different time dynamics provide a clear distinction between them. Moreover, the intrinsic nature of the emission is also proven, providing a quantitative evaluation of volume and surface contributions.

No abstract

We report new advancements in the biomedical exploitation of plasmonic nanoparticles as an effective platform for the photothermal repair of biological tissue. Chitosan films are loaded with gold nanorods with intense optical absorption in the "therapeutic window" of deepest light penetration through the body, and then activated by near infrared laser excitation to give adhesion with adjacent connective tissues. The adhesion consists of 0.07 mm(2) welds of ~20 kPa tensile strength at the film/tissue interface, which are obtained by administration of pulses with duration in the hundreds of millisecond timescale from a diode laser at ~130 J cm(-2). We investigate the adhesive effect as a function of pulse power and duration and identify an optimal operative window to achieve effective and reproducible welds with minimal detrimental superheating. These results may prove valuable to standardize laser bonding techniques and meet current needs for new knowledge which is urged by the penetration of nanotechnology into biomedical optics.

No abstract

We report the observation of weak localization of light in a semiconductor microcavity. The intrinsic disorder in a microcavity leads to multiple scattering and hence to static speckle. We show that averaging over realizations of the disorder reveals a coherent backscattering cone that has a coherent enhancement factor > or =2, as required by reciprocity. The coherent backscattering cone is observed along a ring-shaped pattern due to confinement by the microcavity.

Ref. [82] was not included in the originally published version of this article. It should be added to the second paragraph on page 7179, which then reads as follows: "More recently, the notion to exploit the natural tropism of cells, such as tumor-associated macrophages, [35][36][37][38][39] T cells, [40,82] mesenchymal stem cells, [41][42][43] and neural stem cells, [44,45] has begun to emerge as a radical alternative."Ref.