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Planar optical waveguides are an attractive tool for use in analytical chemistry and spectroscopy. Although similar to fiber optics, planar waveguides have been slow to be commercially accepted due to the difficulty of coupling light into the guide. Generally, prism coupling is the method of choice in the laboratory, as efficiencies approaching 80% can be reached. However, prisms are impractical for routine use for several reasons:  expensive positioning equipment is required, coupled power is sensitive to environmental fluctuations, and prism coupling prohibits the fabrication of a truly planar device. The use of thin gratings on the surface of the waveguide allows for a two-dimensional structure to be maintained, while providing enough efficiency to be useful as a sensor. Our research efforts focus on developing a technique to make inexpensive, reproducible gratings that are easy to fabricate. By chemically modifying the surface of a commercial grating with a suitable release agent, it is possible to emboss replica gratings onto a variety of waveguide types. The fabrication of embossed gratings will be described, and their performance on glass, ion-diffused, polymer, and semiconductor waveguides will be presented.

The electrochemistry of [Re III (DIARS) 2 Cl 2 ]Cl in aqueous and aqueousyethanol solvents at bare and Na®on-modi®ed electrodes has been studied by cyclic voltammetry, differential pulse voltammetry, and chronocoulometry. .93 phosphate buffer, and aqueous pH 6.93 phosphate buffer solutions gave formal reduction potentials that fall within the range of À0.319 V to À0.263 V (vs. AgyAgCl) and increase with the dielectric constant of the solvent. In 33 % ethanolyaqueous pH 6.93 phosphate buffer and aqueous pH 6.93 phosphate buffer, both the oxidized and reduced forms of the complex exhibited adsorption at the surface of gold electrodes as shown by cyclic voltammetry and chronocoulometry. An especially sharp reduction wave, which is more negative than the reduction wave in subsequent cycles, was obtained on the ®rst scan in cyclic voltammetry. By comparison, well-de®ned voltammograms were obtained at Na®on-modi®ed glassy carbon. Substantial partitioning into Na®on occurred and a detectable signal was measured for Na®on coated glassy electrodes at concentrations as low as 4X0 Â 10 À10 M by differential pulse voltammetry. Na®on also prevented uric acid, dopamine, DOPAC, and ascorbic acid from interfering with the electrochemical detection of [Re , which is potentially useful for the study of its imaging properties in nuclear medicine.