[OPTICAL REVIEW Vol. 18, No. 1 (2011) 139-143]
© 2011 The Japan Society of Applied Physics

Measurements of Spectral Responses for Developing Fiber-Optic pH Sensor

Wook Jae YOO, Ji Yeon HEO, Kyoung Won JANG, Jeong Ki SEO, Jin Soo MOON, Jang-Yeon PARK, Byung Gi PARK1, Seunghyun CHO2, and Bongsoo LEE*

School of Biomedical Engineering, College of Biomedical and Health Science, Research Institute of Biomedical Engineering, Konkuk University, Chungju 380-701, Korea
1Department of Energy and Environment Engineering, College of Engineering, Soonchunhyang University, Asan 336-745, Korea
2Department of Organic Materials and Fiber Engineering, College of Engineering, Soongsil University, Seoul 156-743, Korea

(Received May 31, 2010; Accepted October 26, 2010)

In this study, we have fabricated a fiber-optic pH sensor, which is composed of a light source, a pH-sensing probe, plastic optical fibers and a spectrometer, for determining the degree of infection by Helicobacter pylori in the stomach. As pH indicators, phenol red and m-cresol purple are used, and pH liquid solutions are prepared by mixing phenol red or m-cresol purple solutions and various kinds of pH buffer solutions. The light emitted by a light source is guided by plastic optical fibers to the pH liquid solution, and the optical characteristic of a reflected light is changed according to the color variations of the pH indicator in the pH-sensing probe. Therefore, we have measured the intensities and wavelength shifts of the reflected lights, which change according to the color variations of indicators at different pH values, by using a spectrometer for spectral analysis. Also, the relationships between the pH values of liquid solutions and the optical properties of the modulated lights are obtained on the basis of the changes of the colors of indicators.

Key words: fiber-optic sensor, m-cresol purple, phenol red, plastic optical fiber, pH sensor

*E-mail address: bslee@kku.ac.kr