Evanescent-Wave Fiber Optic Sensing of the Anionic Dye Uranine Based on Ion Association Extraction.

Takuya Okazaki,Hideki Kuramitz,Tomoaki Watanabe

doi:10.3390/s20102796

Takuya Okazaki, Hideki Kuramitz + Show 1 more

Open Access

https://doi.org/10.3390/s20102796

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Abstract

Herein, we propose an evanescent-wave fiber optic sensing technique for the anionic dye uranine based on ion association extraction. The sensor was prepared by removing a section of the cladding from a multimode fiber and hydrophobization of the exposed core surface. Uranine was extracted in association along with hexadecyltrimethylammonium (CTA) ion onto the fiber surface and detected via absorption of the evanescent wave generated on the surface of the exposed fiber core. The effect of CTA+ concentration added for ion association was investigated, revealing that the absorbance of uranine increased with increasing CTA+ concentration. A change in the sensor response as a function of the added uranine concentration was clearly observed. The extraction data were analyzed using a distribution equilibrium model and a Freundlich isotherm. The uranine concentration in the evanescent field of the fiber optic was up to 54 times higher than that in the bulk solution, and the limit of detection (3σ) for uranine was found to be 1.3 nM.

Highlights

Evanescent field spectroscopy using optical waveguides is an extension of the established spectroscopic technique attenuated total reflection (ATR) spectroscopy
We have developed a sensor for uranine that combines evanescent-wave fiber optics and ion association extraction
We presented an evanescent-wave fiber optic sensing technique for the cationic dye uranine based on ion association extraction

Summary

Introduction

Evanescent field spectroscopy using optical waveguides is an extension of the established spectroscopic technique attenuated total reflection (ATR) spectroscopy. During the last two decades, fiber optics with exposed cores have been applied for the ATR technique [1,2,3,4,5,6]. If any absorbing molecules exist within the evanescent field, the evanescent wave is absorbed and results in attenuation in the amplitude of the propagating wave guided in the fiber core [7]. This phenomenon has been applied to chemosensors and biosensors for numerous analytes, including oxygen, H+ ions (i.e., pH), nitrates, silica, fluorides, melamine, DNA, and Escherichia. The optical signals of such sensors are not affected by solids suspended in the sample solution because the sensing interactions only occur in the evanescent field, which extends only approximately 1 μm from the fiber surface [15]

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