Simultaneous Measurement System for an Adsorbed Substance on a Glass Slab Optical Waveguide and a Dissolved Substance in Liquid-Phase by Visible Absorption Spectrometryt

Abstract

A slab optical waveguide (SOWG) is an element which can transmit light through a thin layer with a minimum attenuation of the light power. Since the refractive index of the thin layer (guiding layer) is higher than those of the outer atmosphere, typically air and a solvent, and of the substrate of the SOWG (Fig. 1), incident light is transmitted through the guiding layer based on total reflection. When the SOWG is applied to spectroscopic measurements, an evanescent wave from the SOWG surface is used for exciting an analyte. Thus, only the surface phenomena of the SOWG can be observed. Moreover, the guiding layer is so thin that the number of reflections often becomes more than one hundred per 1 cm, which results in a remarkable enhancement of the sensitivity. Recently, the SOWG has often been applied to analytical chemistry, e.g., opto-chemical sensorsl-4, opto-biosensors5-', and highly sensitive spectroscopic measurements of a thin film and its surface.g-11We have also been applying the glass SOWG to an absorption detector of flow analysis to detect trace amounts of several dyes and iron(II).12-14 These analytes were adsorbed onto the SOWG and detected by this method. In principle, the SOWG absorption detector is sensitive to an adsorbed chromophore onto the SOWG surface, while it is almost insensitive to a dissolved substance in solution. Thus, the sample matrix scarcely interferes with the SOWG measurements. Moreover, the SOWG detector showed a fairly high sensitivity for those analytes, i, e., several-times better than conventional spectrophotometry with a 0.5 ml of sample. In these studies, however, only less than 1% of the analytes was adsorbed onto the SOWG surface. Hence, further improvements in the sensitivity could be achieved if greater adsorption of analytes could be achieved. For such purpose, it is necessary to understand the adsorption mechanism of analytes onto the glass surface. In this study, we developed a simultaneous measurement system for both an adsorbed substance onto the SOWG surface and a dissolved substance in a flow cell by visible absorption spectrometry. This system was applied to a study of the adsorption behavior of Methylene Blue (MB) onto the SOWG surface.

Adsorption Behavior of Cytochrome c, Myoglobin and Hemoglobin in a Quartz Surface Probed Using Slab Optical Waveguide (SOWG) Spectroscopy

“…2,3 The reported nomenclature in the literature include slab optical waveguide (SOWG) spectroscopy, 4-17 the integrated optical waveguideattenuated total reflection technique (IOW-ATR) [18][19][20][21][22][23][24][25][26][27] and optical waveguide lightmode spectroscopy (OWLS). 1,[28][29][30][31][32][33][34][35][36][37][38] These techniques have been successfully used in real-time studies on the adsorption of dye molecules 11,12,[14][15][16] and proteins 4,8,[18][19][20][21][22][23][24][25][28][29][30][31][32][33][34][35][36][37]…”

“…Since the interacting photons come from the waveguiding surface, one advantage of ITR-based spectroscopy is its ability to interact mostly with the adsorbed molecules and much less with those in the bulk solution. Some of the research groups that are actively involved in studying protein adsorption on surfaces based on ITR are Jeremy Ramsden's group in Basel, Switzerland, 28-37 Scott Saavedra's group in Arizona, [18][19][20][21][22][23][24][25][26][27] Paul R. Van Tassel's group in Wayne, USA 38,40 and some research groups in Japan [4][5][6][7][8][9][10][11][12][13][14][15][16][17]39 and elsewhere. 41,42 In this work we investigated, under various solution conditions, the adsorption behavior of hemoglobin, myoglobin and cytochrome c in a bare quartz surface.…”

Adsorption of Methylene Blue onto Silylated Silica Surfaces, Studied Using Visible Attenuated Total Reflection Spectroscopy with a Slab Optical Waveguide

“…In order to develop a new sensing system, an understanding of the dynamics of molecules residing at interfaces is necessary. In particular, we have been studying the adsorption behavior of methylene blue (MB) on glass surfaces 21,22 because this m olecule is used as a probe to study interfaces using various methods. 4,16,23 M oreover, MB is an important reagent that is widely used in analytical chemistry, e.g., in extraction-spectrophotometric measurem ent of anionic surfactants.…”