Experimental and theoretical determination of the plasmonic responses and shape distribution of colloidal metallic nanoparticles.

The optical properties of gold and silver nanoparticles (NPs) dispersed in water and distributed in shape are investigated by introducing a shape distributed effective medium theory (SDEMT). This model takes into account the variation of depolarization parameter induced by a NP shape distribution. Simulations show that the shape distribution induces an inhomogeneous broadening and a decrease of the amplitude of the plasmon band. The number of plasmon bands and their positions depend on both the mean value of depolarization parameter and the NP material. By fitting the measured absorption spectra with the SDEMT, we unambiguously demonstrate that the depolarization parameter distribution, i.e., the shape distribution of nanoparticles can be deduced from absorption spectra.

An Analysis of the Structures at Risk from Percutaneous Pinning of Distal Radius Fractures and a Comparison of Two Pinning Techniques: A Cadaveric Study.

Background: A stab incision and blunt dissection prior to wire placement are believed to decrease the risk of injury to underlying structures during percutaneous pinning of distal radius fractures (DRF). However, only a few studies have compared stab incision and blunt dissection to direct wire placement. The aim of this cadaveric study is to analyse the structures at risk during percutaneous pinning of DRF and compare the two methods of wire placement. Methods: A total of 10 cadavers (20 upper limbs) were divided into two groups of five each. Five 2.0 mm Kirschner (K)-wires were inserted into the distal radius under fluoroscopic control in a standard fashion to simulate percutaneous pinning of DRF. In group 1, the K-wires were inserted directly, whereas in group 2, the wires were inserted after making a stab incision and blunt dissection to reach the bone. Each cadaveric limb was then dissected carefully to measure the distance of the K-wires from the branches of the superficial radial nerve (SRN), the cephalic vein and the first dorsal compartment and to determine the structures injured (pierced or in close contact) by the K-wires. Results: Out of the 100 K-wires placed, 18 wires were in close contact or pierced an underlying structure. These included 11 wires injuring tendons, six wires injuring branches of the SRN and one wire injuring the cephalic vein. Direct wire placement (group 1) resulted in injury to eight structures (44.4%) while stab incision and blunt dissection prior to wire placement (group 2) resulted in injury to 10 structures (55.5%). This difference was not statistically significant. Conclusions: Percutaneous pinning of DRF is associated with a high risk of injury to the extensor tendons and branches of the SRN. This risk is not reduced by making a stab incision and blunt dissection prior to K-wire placement.

Spatially controlled synthesis of silver nanoparticles and nanowires by photosensitized reduction.

The present paper reports on the spatially controlled synthesis of silver nanoparticles (NPs) and silver nanowires by photosensitized reduction. In a first approach, direct photogeneration of silver NPs at the end of an optical fiber was carried out. Control of both size and density of silver NPs was possible by changing the photonic conditions. In a further development, a photochemically assisted procedure allowing silver to be deposited at the surface of a polymer microtip was implemented. Finally, polymer tips terminated by silver nanowires were fabricated by simultaneous photopolymerization and silver photoreduction. The silver NPs were characterized by UV-visible spectroscopy and scanning electron microscopy.

Wavelength-scale light concentrator made by direct 3D laser writing of polymer metamaterials.

We report on the realization of functional infrared light concentrators based on a thick layer of air-polymer metamaterial with controlled pore size gradients. The design features an optimum gradient index profile leading to light focusing in the Fresnel zone of the structures for two selected operating wavelength domains near 5.6 and 10.4 µm. The metamaterial which consists in a thick polymer containing air holes with diameters ranging from λ/20 to λ/8 is made using a 3D lithography technique based on the two-photon polymerization of a homemade photopolymer. Infrared imaging of the structures reveals a tight focusing for both structures with a maximum local intensity increase by a factor of 2.5 for a concentrator volume of 1.5 λ3, slightly limited by the residual absorption of the selected polymer. Such porous and flat metamaterial structures offer interesting perspectives to increase infrared detector performance at the pixel level for imaging or sensing applications.