Anionic surfactant sensor based on a hetero-core structured optical fiber

A simple method of fiber optic spectrophotometric measurement for anionic surfactant is described. The probe was fabricated from hetero-core structured fiber optic that consisted of multi mode fibers and a short length of single mode fiber which was inserted in the multi mode fibers. The sensor surface was treated with octyltrimethoxysilane to adsorb the surfactant-methylene blue complex via hydrophobic interaction between the octyl group on the fiber surface and the hydrophobic group of the surfactant. Methylene blue—anionic surfactant complex adsorbed on the sensor surface caused propagating light loss because of evanescent wave interaction that was generated at the cladding. The propagating loss spectrum of the fiber showed a peak at around 610 nm. Absorbance increases with the concentration of the surfactant to reach an upper level at a concentration of 30?μm. The response time is within 30 min.