AN OPTICAL FIBER-BASED SPECTROMETER FOR MEASUREMENT OF FLUORESCENCE LIFETIMES

An instrument is described which measures fluorescence intensity and l ifetime properties using a single optical fiber for the development of fiber optic chemical sensors. The instrument utilizes a fast-pulse ni trogen laser for excitation and a digital storage oscilloscope to prov ide time-resolved fluorescence decay curves. The time-resolved measure ments permitted the separation of most of the scattered excitation rad iation from the sample signal and allowed for analysis of samples expo sed to ordinary room lighting. A method for determination of lifetimes from the time-resolved decays was developed based on the time-correla ted single-photon counting method. The new method used reference fluor ophore solutions to determine the instrument response function, includ ing the influence of the optical fiber, and multiple decays were avera ged to improve signal-to-noise and to provide statistical weighting fo r the analysis. The accuracy of the lifetime analysis was demonstrated by comparison of results for Stern-Volmer quenching of quinine sulfat e by chloride ion (slope = 0.115 +/- 0.001, int. = 1.04 +/- 0.04, r(2) = 0.9992) with a literature study on the same system (slope = 0.118 /- 0.002, int. = 1.06 +/- 0.05, r(2) = 0.9986). Measurement of the lif etime of pyrene in ethanol gave 17.8 +/- 0.9 ns, while the value for c oumarin was 3.82 +/- 0.45 ns. When mixed together, two lifetimes with values of 17.43 +/- 0.73 and 3.68 +/- 1.30 ns were determined. (C) 199 4 Academic Press, Inc.