Tapered-Fiber Optical Sensor for Physiological pH Range

Optical sensors brings new possibilities to biological, medical, and environmental applications, since they are small, immune to electromagnetic field and their potential unwanted interaction with measured samples is limited. This paper describes influence of composition of pH-sensitive layers to their performance and application of these layers in a tapered-fiber optical pH sensor. The sensitive layers were based on ion-pair of 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt and hexadecyltrimethylammonium bromide, which was immobilized in xerogel matrices composed of ethyltriethoxysilane (ETES) and (3-glycidoxypropyl)-trimethoxysilane (GLYMO) in different ratios. The best performance was obtained for layers with ETES:GLYMO ratio of 40:60. Their detection range was in the interval of pH from 5.75 to 7.25. Proved stability of sols and coated optical substrates makes the practical application of these sensing layers feasible and the tested tapered-fiber probes are suitable for detection of small samples of volumes of microliters.