Complete spectrum fiber optic pH sensor based on a novel fluorescent indicator doped porous sol-gel material

摘要

A new fiber optic sensor for monitoring pH made by doping of fluorescent dyes in a sol-gel matrix is demonstrated. The indicator, 5-(and6)-carboxy-2'7'-dichlorofluorescein (CDCF), has a lower average pK$-a$/ than fluorescein due to a chloride functional modification. The absorption and fluorescence spectra of the immobilized dye at various pH levels show that the indicator is sensitive over a wide pH range. Porous sol-gel coatings are used to make the probes, which are incorporated into a bifurcated fiber optic sensor. The entire absorption and fluorescence spectra are continuously monitored using a miniature fiber optic spectrophotometer. The most responsive area of the fluorescence spectrum is selected and is referenced to a point which is insensitive to pH, so that any changes due to environmental effects and fluctuations in the light source are taken into account. Two approaches for referencing are shown, one involving the back-reflected light from the excitation source, and another utilizing the co-doping of the sol-gel with a second fluorescent dye with the same absorption characteristic as CDCF but which is insensitive to pH and fluoresces at a different wavelength.