Emerging biomedical and advanced applications of time-resolved fluorescence spectroscopy.

Time-resolved fluorescence spectroscopy is presently regarded as a research tool in biochemistry, biophysics, and chemical physics. Advances in laser technology, the development of long-wavelength probes, and the use of lifetime-based methods, are resulting in the rapid migration of timeresolved fluorescence to the clinical chemistry lab, the patient's bedside, and even to the doctor's office and home health care. Additionally, time-resolved imaging is now a reality in fluorescence microscopy and will provide chemical imaging of a variety of intracellular analytes and/or cellular phenomena. Future horizons of state-of-the-art spectroscopy are also described. Two photon-induced fluorescence provides an increased information content to time-resolved data. Two photoninduced fluorescence, combined with fluorescence microscopy and time-resolved imaging, promises to provide detailed three-dimensional chemical imaging of cells. Additionally, it has recently been demonstrated that the pulses from modern picosecond lasers can be used to quench and/or modify the excited-state population by stimulated emission since the stimulated photons are directed along the quenching beam and are not observed. The phenomenon of light quenching should allow a new class of multipulse time-resolved fluorescence experiments, in which the excited-state population is modified by additional pulses to provide highly oriented systems.