Fluorescence spectroscopy is widely used in various fields of chemistry, biology and medicine in particular due to the high sensitivity and selectivity of the method. Also there is considerable interest in fluorescence techniques for trace metal detection, and for the recognition and measurement of metal components in various systems, especially in biological materials. The introduction of metal chelating groups into the structure of fluorescent dyes is designed to produce derivatives that undergo changes in fluorescence intensity or wavelength upon formation of the complexes, thus producing a metal ion detection and quantitative analysis. More recently, fluoroionophores consisting of fluorophores linked to a crown ether, i.e. ionophores able to complex ions, offered a new powerful tool of investigation because a large change in the photophysical properties may be observed upon metal ion binding. Application of these compounds to the recognition and measurement of metal cations in solution at low concentration have been reported.