Fiber-optic pH sensing system with microscopic spatial resolution

Acidity of an environment expressed as pH is one of the key biological parameters. An optical sensing scheme together with the use of optical fiber probes can bring advantages to the pH monitoring such as fine spatial resolution, less interference with biological material or immunity to the electromagnetic field. An optical pH-sensor with fine spatial resolution suitable for measurement of pH in near-neutral range is presented and the influence of sensing probe preparation process onto the sensor performance is discussed in the paper. The sensor is based on an ion pair of 8-hydroxypyrrene-1,3,6-pyrene trisulfonic acid trisodium salt (HPTS) and hexadecyltrimethylammonium bromide (CTAB) immobilized by a sol-gel method on the tip of tapered-fiber probes. It was found that the sensor performance is affected significantly by the shape of the sensing layer.