Technique for detecting changes in fluorescence lifetime by means of optoelectronic circuit auto-oscillation

We present a new, simple, inexpensive, and highly precise approach to excit ed-state fluorescence-lifetime-based measurements. The detection system con sists of a closed-loop optoelectronic arrangement containing a radio freque ncy resonance amplifier, a fluorescence excitation light source, a fiber-op tic delay line, and a photodetector. The system exhibits auto-oscillations in the form of intensity modulation. The oscillation frequency varies with the modulation phase shift of the fluorescent light. This frequency is used as the detection parameter, which is advantageous because frequency may be measured easily, inexpensively, and with high precision. This technique is well suited for chemical or biosensor applications. (C) 2001 Optical Socie ty of America.