Dayeong JEON, Wook Jae YOO, Jeong Ki SEO, Sang Hun SHIN, Ki-Tek HAN, Seon Geun KIM, Jang-Yeon PARK, and Bongsoo LEE^*

School of Biomedical Engineering, College of Biomedical and Health Science, Research Institute of Biomedical Engineering, Konkuk University, Chungju 380-701, Korea

(Received August 15, 2012; Revised November 1, 2012; Accepted November 6, 2012)

In this study, we developed a fiber-optic pH sensor based on a sol–gel film immobilized with neutral red (NR). A sol–gel film was prepared by mixing tetramethylorthosilicate (TMOS), trimethoxymethylsilane (MTMS), ethanol (EtOH), distilled water (H₂O), and NR powder. Accordingly, the thin pH sol–gel film was fabricated through a sol–gel process with a dip-coating method. The thickness and diameter of the fabricated pH sol–gel film are 0.11 and 0.6 mm, respectively. We measured the optical absorbance and the light intensity with the spectra of reflected light, which change with the color variation of the pH sol–gel film in the fiber-optic sensing probe. From the experimental results, we demonstrated that the proposed fiber-optic pH sensor has good reversibility, reproducibility, and a fast response time, in which the optical properties of the NR-based pH sol–gel film change with the pH value.

Key words: fiber-optic sensor, pH sensor, sol–gel, neutral red, optical fiber

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