Chemical interactions at molecular interfaces have been studied by integrated optics evanescent wave surface-enhanced Raman spectroscopy (IO-EWSERS). We describe methods to decorate planar glass waveguides with two-dimensional aggregates of Rayleigh limit silver particles by covalent attachment of them through a propane thiolate moiety grafted to the glass surface in a prior step. The evanescent field of the propagating transverse electric waves is enhanced by coupling with surface plasmon modes of the metal particles. Surface tethering and orientations of 2-and 4-mercaptopyridine (MPy) on Ag particles are studied through a comparative analysis of their SER spectra on silver metal liquid-like films (MELLFs), Ag hydrosols, and the colloid functionalized waveguide. Both molecules adopt roughly perpendicular orientations when bonded through the sulfur atom to silver. Overcoating the silver adlayer on the waveguide converts the construction into a sensing "optical chemical bench" (OCB). Accordingly, reversible acidbase titration of surface-bound 4-Mpy could be examined. In contrast, Cu 2+ is coordinated irreversibly. X-ray photoelectron spectroscopy gives insight into the OCB fabrication and sensing process as the structure is evaluated step by step from a silica substrate surface to the copper ion at the outermost layer. The EWSER experiment is sensitive to perturbations of the vibrational structure of the heterocycle adsorbate at sub-monolayer coverage. The experiment can be conducted without photodegradation at relatively low laser power on inexpensive waveguides.

Pyrazinamide (pza) and 2-mercaptopyridine (2-MPy) are shown to form Ag colloid-adsorbate films at the interface between an aqueous Ag colloid and a solution of an adsorbate in dichloromethane. By contrast, under the same conditions, 4-mercaptopyridine (4-MPy) forms Ag organosol aggregates by the interface transfer of adsorbate-covered Ag colloidal particles from the aqueous phase to the organic phase. This result confirms that formation of Ag colloid-adsorbate films is an adsorbate specific process. Transmission electron and optical microscopy and surface plasmon adsorption measurements are used to characterize the morphology of the deposited Ag colloid-adsorbate structures while SERS spectra of the incorporated adsorbates probe their internal structure. Furthermore, we demonstrate that, for a particular adsorbate, the process of Ag colloid-adsorbate film formation, the morphology of the deposited films, and the SERS spectra are substantially influenced by the Ag content of the parent colloid (Ag-pza and Ag-4-MPy films) and/or by the concentration of the adsorbate in the organic phase (Ag-2-MPy films). We propose that the observed differences in the rates of formation of the films, their morphology, and the orientation of the adsorbate with respect to the Ag surface are related to differences in the actual surface coverage of Ag colloidal particles by adsorbate molecules.

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