On the choice of laser dyes for use in exciting tyrosine fluorescence decays

The choice of laser dyes for exciting tyrosine fluorescence using synchronously pumped cavity-dumped dye laser systems is discussed. Rhodamine 560 was found to be optimal for a system based on an argon-ion pumping laser, whereas rhodamine 575 was preferred using a frequency-doubled Nd:YAG laser. Modifications of our fluorescence decay instrument to permit rejection of multiphoton events using a microchannel plate photomultiplier are described. An example of a four-component resolution of tyrosine decays illustrates the dramatic resolution capabilities attainable.