Fiber optic pH/Ca2+ fluorescence microsensor based on spectral processing of sensing signals

In this paper, we describe the fabrication of a dual function pH/Ca2+ fluorescence microsensor. Dextran conjugates of the fluorescence indicators Oregon Green BAPTA-1, a calcium ion probe, and SNARF (seminaphtorhodafluor)-1, a ratiometric pH probe, are immobilized in a 2-hydroxyethyl methacrylate (PHEMA) matrix support adsorbed to the distal end of an optical fiber. Both dyes are excited at 488 nm. The emission peak maximum of Oregon Green Bapta-1 is at 520 nm, and the emission peak maxima of SNARF-1 are at 584 and 630 nm. The pH and [Ca2+] in the analyte sample are determined by spectral processing of the fluorescence sensing signals. The sensor covers a pH range between pH 6 and pH 8, and calcium ion concentrations between 0.03 and 1.5 mu M. The response times of the sensor are about 1 s for pH and 5 s for [Ca2+] changes. The sensor is highly reversible and maintains its function for over 10 days of continuous use. The sensor is stored for 3 months in a dry, light tight environment, at room temperature with no significant degradation of its analytical properties. (C) 1999 Elsevier Science B.V. All rights reserved.