RECENT DEVELOPMENTS IN FREQUENCY-DOMAIN FLUOROMETRY
A description is given of variable-frequency phase-modulation fluorometers along with their design and operating principles. To illustrate the obtainable resolution the authors present results for the resolution of two and three-component mixtures of fluorophores, the resolution of complex anisotropy decays from non-spherical molecules and the determination of time-resolved emission spectra in the presence of time-dependent spectral relaxation. At present, the resolution obtainable with the frequency-domain fluorometers appears to be at least equivalent to that obtained with pulsed mode-locked laser sources with single photon counting. These mode-locked sources can also be used for phase fluorometry.