title: The electroactive integrated optical waveguide:  ultrasensitive spectroelectrochemistry of submonolayer adsorbates.
abstract: Highly sensitive spectroelectrochemistry of adsorbed films on ITO is demonstrated with the electroactive integrated optical waveguide (EA-IOW). The EA-IOW, a single-mode planar waveguide coated with an ITO layer, is ∼10(4)-fold more sensitive to changes in absorbance occurring during electrochemical events versus a single-pass transmission spectroelectrochemical experiment, as demonstrated by reduction of surface-adsorbed methylene blue. Furthermore, the EA-IOW is selective to near-surface events, as it is relatively insensitive to absorbance by solutions of dissolved chromophores at <1 mM. The EA-IOW is also used to monitor the formation of Prussian Blue during the reduction of ferricyanide, an event that is not easily followed using current-detected cyclic voltammetry, due to interfering faradaic and non-faradaic electrochemical events. The optical background of the EA-IOW is potential-dependent and is explained by ion diffusion into the ITO and by voltage-dependent changes in optical constants for the material. Finally, the high sensitivity of the EA-IOW (relative to other evanescent-field-based spectroelectrochemical techniques) is discussed in terms of its design.
authors.affiliation: Department of Chemistry and Optical Sciences Center, University of Arizona, Tucson, Arizona 85721.
authors.forename: D R
authors.initials: DR
authors.lastname: Dunphy
authors.forename: S B
authors.initials: SB
authors.lastname: Mendes
authors.forename: S S
authors.initials: SS
authors.lastname: Saavedra
authors.forename: N R
authors.initials: NR
authors.lastname: Armstrong