OPTICAL FIBER-BASED SENSOR FOR CALCIUM USING HYDROPHOBICALLY ASSOCIATED CALCEIN AND LASER-INDUCED FLUORESCENCE DETECTION

An optical fiber-based sensor for Ca2+ has been developed using hydrop hobically associated calcein. In this measurement protocol, the optica l fiber surface is derivatized with a C-18 moiety thereby allowing spe cific reagents to be reproducibly associated with the surface through a hydrophobic process. The C-18 surface is shown to provide significan t immunity from chemical degradation at the extremes of the pH scale, at elevated temperatures, and in the presence of specific organic solv ents. This capability was exploited in the development of an optical f iber sensor for Ca2+ using C-12-derivatized calcein as the sensing rea gent. The reagent can be reproducibly associated with the optical fibe r surface and used to quantitate Ca2+ at pH 12. The derivatized calcei n exhibited enhanced fluorescent properties at pH 12 in the absence of Ca2+ which limited the quantitative capabilities of the sensor. As no w configured, the optical fiber-based sensor has a demonstrated limit- of-detection for Ca2+ of 20 ppb (0.5 mu M) (SNR = 2) in a probe volume of 20 mu l, or less. (C) 1994 Academic Press, Inc.