Time-resolved fluorescence of a new europium chelate complex : demonstration of highly sensitive detection of protein and DNA samples

Safety and environmental considerations have made it desirable to develop nonradioactive detection technologies that offer detection limits comparable to those of radioisotopes. Although fluorometric methods are widely used for biochemical and biological analyses, disadvantages of organic fluorochromes, such as overlap of background fluorescence with emission spectra and "inner-filter effects", have resulted in less than optimum detection limits and prevented broad applications. Innovative new fluorometric techniques, however, continue to reduce detection limits and expand utility into specific new applications. The luminescence properties of europium chelates include exceptional Stokes' shifts (200-300 nM), narrow emission line spectra, long wavelength emission (615 nM), and long fluorescence lifetimes (600-1000 mu s). While each of these characteristics is important, the latter is key to achieving low detection limits, in that short-lived background fluorescence and scattered excitation radiation can be efficiently eliminated by measuring fluorescence emission at a delay (100-400 mu s) after the excitation pulse.