Abstract

Abstract
The Bruggeman effective medium is used to study the transition to hyperbolic dispersion of visible light in thin-film metal-dielectric composite metamaterial of varying mixing proportion. This transition is experimentally demonstrated by the detection of the swap between the refracted birefringence components in fabricated composites of silver nanowires embedded in anodic aluminium oxide. Three refraction regimes are observed in a single composite using excitation radiation on both sides of the transition.

Abstract
The sol-gel method was employed to obtain poly(oxyethylene) (POE)/siloxane hybrids (di-ureasils) doped with erbium triflate (Er(CF3SO3)(3)). The host hybrid matrix employed is composed of a siliceous framework to which short POE chains are covalently bonded through urea linkages (-NH(C(=O)NH-). Xerogels with infinity > n >= 5 (where n, salt composition, is the molar ratio of OCH2CH2 moieties per Er3+ ion) were analyzed. Samples with n >= 20 are amorphous. Those with n > 20 are thermally stable up to about 325 degrees C. In the di-ureasils proposed, the Er3+ ions are active at room temperature (RT). Concentration effects on the quenching of the 1.53 mm emission intensity (excited at 488 nm) are negligible.

Abstract

Abstract
Microcystin-LR (MC-LR) is a dangerous toxin found in environmental waters, quantified by high performance liquid chromatography and/or enzyme-linked immunosorbent assays. Quick, low cost and on-site analysis is thus required to ensure human safety and wide screening programs. This work proposes label-free potentiometric sensors made of solid-contact electrodes coated with a surface imprinted polymer on the surface of Multi-Walled Carbon NanoTubes (CNTs) incorporated in a polyvinyl chloride membrane. The imprinting effect was checked by using non-imprinted materials. The MC-LR sensitive sensors were evaluated, characterized and applied successfully in spiked environmental waters. The presented method offered the advantages of low cost, portability, easy operation and suitability for adaptation to flow methods. (C) 2012 Elsevier Ltd....Selection and/or peer-review under responsibility of the Symposium Cracoviense Sp. z.o.o.

Abstract
The present work reports new sensors for the direct determination of Microcystin-LR (MC-LR) in environmental waters. Both selective membrane and solid contact were optimized to ensure suitable analytical features in potentiometric transduction. The sensing layer consisted of Imprinted Sol-Gel (ISG) materials capable of establishing surface interactions with MC-LR. Non-Imprinted Sol-Gel (NISG) membranes were used as negative control. The effects of an ionic lipophilic additive, time of sol-gel polymerization, time of extraction of MC-LR from the sensitive layer, and pH were also studied. The solid contact was made of carbon, aluminium, titanium, copper or nickel/chromium alloys (80 : 20 or 90 : 10). The best ISG sensor had a carbon solid contact and displayed average slopes of 211.3 mV per decade, with detection limits of 7.3 x 10(-10) M, corresponding to 0.75 mu g L-1. It showed linear responses in the range of 7.7 x 10(-10) to 1.9 x 10(-9) M of MC-LR (corresponding to 0.77-2.00 mu g L-1), thus including the limiting value for MC-LR in waters (1.0 mu g L-1). The potentiometric-selectivity coefficients were assessed by the matched potential method for ionic species regularly found in waters up to their limiting levels. Chloride (Cl-) showed limited interference while aluminium (Al3+), ammonium (NH4+), magnesium (Mg2+), manganese (Mn2+), sodium (Na+), and sulfate (SO42-) were unable to cause the required potential change. Spiked solutions were tested with the proposed sensor. The relative errors and standard deviation obtained confirmed the accuracy and precision of the method. It also offered the advantages of low cost, portability, easy operation and suitability for adaptation to flow methods.