Mechanisms for Fluorescence Lifetime-Based Sensing

Molecular Mechanisms for Fluorescence Lifetime-Based Sensing 

Th fluorescence lifetime of a sample is the mean duration of time the fluorophore remains in the excited state. Following pulsed excitation, the intensity decays of many fluorophores are single exponential 2 23  

Nonradiative processes (knr) can occur with a wide range of rate constants. Molecules with high knr values display low quantum yields due to rapid depopulation of the excited state by this route. The measured lifetime in the absence of collisional or energy transfer quenching is usually referred to as To, and is given by to = (kr + knr).  

There are two widely used methods for measuring fluorescence lifetimes, the time-domain and frequency-domain or phase-modulation methods. The basic principles of time-domain fluorometry are described in Chapter 1, Vol.l of this series(34) and those of frequency-domain in Chapter 5, Vol. 1 of this series. 35) Good accounts of time-resolved measurements using these methods are also given elsewhere/36,37) It is common to represent intensity decays of varying complexity in terms of the multiexponential model 

This fact can be understood by recognizing that the a,r, product represents the area under the decay curve which is due to the component with the lifetime t,-. 

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