Journal of Analytical & Bioanalytical Techniques
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Optical fiber technology provides a promising technique for chemical sensors covering a wide range of application areas.
Monitoring of pH is an important task in various applications such as clinical blood analysis, industrial wastewater
treatment, and food processing. In this study, we demonstrate a novel evanescent wave fiber-optic pH sensor coupled with
a polyelectrolyte thin film of poly(acrylic acid) (PAA) and poly(allyamine hydrochloride) (PAH) via layer-by-layer (LbL)
Optical fiber with a diameter of 200 μm (silica-core, polymer-clad) was obtained from BAS Inc, Japan. First, a clad-removed
section of optical fiber was bended in U-type using a flame and treated with 1 wt% ethanolic KOH (ethanol/water=3:2, v/v) for
a negatively charged surface. Then, LbL deposition was performed for the deposition of a PAH/PAA alternate thin film onto
the surface of the bended fiber core.
The pH measurements were carried out using different pH solutions from pH 3 to pH 9 and the intensity change was much
larger in the pH range from 7 to 9 than in the acidic range. The pH sensing mechanism of the current sensor system is based
on the refractive index change of the coated film due to the binding of H
or OH- ions. Plausibly, this optical response reflects
the change in electrostatic interaction between the PAH and PAA layers, indicating reversible morphological changes (swelling
and shrinkage) inside the film. Furthermore, the current pH sensor showed good repeatability and high durability.
Hirofumi Okuda received his bachelor degree in 2014 from the University of Kitakyushu (Japan) and now he is a master course student in the same University. His
research interests include optical fiber sensors for chemical and biomedical applications
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