Terbium(III) chelate as an efficient donor for multiple-wavelength fluorescent acceptors.

The emission spectra of the lanthanide chelates enable them to act as a donor for several acceptors emitting at different wavelengths. Fluorescence resonance energy transfer between terbium(III) chelate labeled antibody Fab fragment (donor) and a 17beta-estradiol conjugated to Alexa Fluor 488, 555, 594 or 680 (acceptor) was employed to study the functionality of the terbium(III) chelate as an efficient donor for several acceptors emitting from green to far-red. During measurement, the sensitized emission of the acceptor was measured at acceptor specific wavelength. All the tested dyes proved to be efficient acceptors, and they were successfully used in the competitive homogeneous E2 assay. The highest signal to background ratio and the best assay performance was obtained with Alexa Fluor 680, due to the very low donor emission background at the far-red area. In addition, the sensitized emission of both Alexa Fluor 488 and 680 could be measured simultaneously without significant cross talk.