pH and C02 fiber-optic sensors were prepared using self-referencing dyes from the seminaphthorhodamine family (SNARF). The ratio of the emission from the acid and base tautomers of these dyes is insensitive to photobleaching and variations in the excitation intensity. The photophysics of the dyes has been determined. At high concentrations formation of nonfluorescent aggregates of the dyes results in reduced emission yields. The fluorescent lifetimes of the dyes are unaffected by concentration. The p of the dyepolymer composite is sensitive to the structure of the polymer. This sensitivity is attributed to a difference in energy of the conjugate base of the dye as a function of the amount of cross-linking of the polymer. The pH sensors show mpH response in the physiological pH range (6.8-7.S) and fast hydration and response times. The C02 sensors show 1-2 Torr response with partial pressures of C02 in the range of 10-100 Torr and have response and hydration times on the order of several minutes.

An instrument to measure the excited-state lifetimes of phosphorescent materials in real time is described. This apparatus uses pulsed and frequency-doubled Nd:YAG solid-state laser for excitation, sampler for data acquisition, and frequency domain methods for data fitting. The instrument amplifies the ac components of the detector output and band limits the signal to 25 kHz. The fundamental frequency of the excitation is then set to obtain a desired number of harmonics. This band limited signal is sampled and averaged over few thousand cycles in the time domain. The frequency domain representation of the data is obtained by employing fast Fourier transform algorithms. The phase delay and the modulation ratio of each sampled harmonic is then computed. Ten to a hundred values of the phase and modulations are averaged before computing the sensor lifetime. The instrument is capable of measuring precise and accurate excited-state lifetimes from subpicowatt luminescent signals in 100 μm optical fibers. To monitor oxygen for biomedical applications the response time of the system is decreased by collecting only 8 or 16 harmonics. A least-squares fit yields the lifetimes of single exponentials. A component of zero lifetime is introduced to account for the backscatter excitation. The phosphorescence lifetimes measured reproducibly to three parts in a thousand are used to monitor oxygen. Oxygen concentrations are computed employing empirical polynomials. The system drift is less than 1% over 100 h of continuous operation. This instrument is used to measure oxygen concentrations in vitro and in vivo with 2 s update times and 90 s full response times. Examples of measurements in saline solutions and in dogs are presented.

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