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.

Abstract
Phase-shifted Bragg grating waveguides (PSBGWs) were formed in bulk fused silica glass by femtosecond laser direct writing to produce narrowband (22 +/- 3) pm filters at 1550 nm. Tunable p and other phase shifts generated narrow passbands in controlled positions of the Bragg stopband, while the accurate placement of multiple cascaded phase-shift regions yielded a rectangular-shaped bandpass filter. A waveguide birefringence of (7.5 +/- 0.3) x 10(-5) is inferred from the polarization-induced spectral shifting of the PSBGW narrowband filters. (C) 2012 Optical Society of America

Abstract
Femtosecond laser exposure produces form and stress birefringence in glasses, mainly controlled by laser polarization and pulse energy, which leads to challenges in certain applications where polarization mode dispersion or birefringence splitting is critical for the desired responses from optical devices. In this paper, parallel laser modification tracks with different geometries were applied to preferentially stress the laser-written waveguides and explore the possibility of tuning the waveguide birefringence in devices fabricated in bulk fused silica glass. Polarization splitting in Bragg grating waveguides showed the laser modification tracks to controllably add or subtract stress to the pre-existing waveguide birefringence, demonstrating independence from the nanograting induced form birefringence and the contributions from material stress. Stressing bars are shown that offer tunable birefringence in the range from similar to 0 up to 4.35 x 10(-4), possibly enabling great flexibility in designing polarization dependent devices, as well as making polarization independent devices. (C) 2012 Optical Society of America

Abstract
In this paper we examine the birefringence of buried optical waveguides written with femtosecond lasers in bulk fused silica glass. We report two modes of low and high birefringence associated with strong form birefringence and the orientation of nanogratings that align perpendicular to the writing laser polarization. The birefringence and waveguide losses are characterized over various laser exposure conditions to facilitate the fabrication of low-loss and compact wave retarders and polarization beam splitters for integration into polarization controlled circuits. Zero-order quarter-wave and half-wave retarders together with polarization beam splitters are demonstrated, all operating at telecom wavelengths. Integration of such devices is targeted for application in photonic quantum circuits. © 2012 SPIE.

Abstract
This paper explores Ampere's circuital law (ACL) from an educational perspective. The interchangeability of the amperian loop with the current loop, an intrinsic symmetry of ACL that is seldom addressed in the literature or textbooks, is illustrated here. It is verified that the symmetry axis of a circular current is an amperian loop. The attempt to apply ACL to a finite wire, a common source of student misunderstanding, is used to highlight the limitations of ACL. The generalisation of ACL is illustrated using an instructive example where the displacement current is unconfined and not spatially uniform. This work is primarily intended for teachers and more advanced undergraduate students, who may benefit from the ideas that are presented here.