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Fluorescent probes, widely used in biochemical sciences, can be excellent tools. However, no single probe is good in all situations. For some cellular studies, quantum yield and stability might be the most important traits; whereas, for intramolecular observations, a long lifetime is an attractive fluorescent feature. Particularly useful are new fluorophores that can be excited by the argon laser at its principal 488 and 514 nm lines for uses in flow cytometry, confocal microscopy, DNA sequencing and other areas and fluorophores that have higher photostability than fluorescein. As our ability to measure the properties of the fluorophores increases and becomes more exact, we must continually reexamine the fluorophores we know and reassess the meaning of the data they supply. In addition, we must be aware of the emergence of new biologically applicable fluorescent probes. An example of one of these new species is discussed here. Since most common dyes are non- or weakly-fluorescent, fluorescent probes have been derived from a relatively limited number of aromatic fluorophores. Completely new fluorophores are rarely developed. Wories1 described synthesis and some spectral characterization of a set of dyes having fluorescein-like spectral properties from the 2,2'-pyrromethene-1,1'-borondifluoride complex. Use of similar derivatives of this new fluorophore as laser dyes has recently been reported. Kang and Haugland have prepared a variety of reactive derivatives from this fluorophore for use as fluorescent probes and for preparation of other probes. Among the probes prepared by Wories, et al. is the sodium salt of 3,3',5,5'-tetramethy1-2,2'- pyrromethene-1,1'-borondifluoride-4-sulfonate complex (here called Bodipysulfonate; structure shown in Fig. 1). We have measured the absorption, fluorescence, and lifetimes of this compound, as well as its non-sulfonated parent compound, 3,3',5,5'-tetramethy1-2,2'-pyrromethene-1,1'-borondifluoride which we have termed Bodipy (trademark of Molecular Probes, Inc.) and the complex bound to two different proteins. The results are presented here.
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