Ruthenium(II)-Phenanthroline-Biotin Complexes: Synthesis and Luminescence Enhancement upon Binding to Avidin

We report the synthesis, characterization, and avidin-binding properties of two novel ruthenium complexes, [Ru(bpy)2(phenbiotin)][PF6]2 1 and [Ru(phen)2(phen-biotin)][PF6]2 2 (bpy = 2,2ʹ-bipyridine; phen = 1,10-phenanthroline, phen-biotin = 5(10-amidobiotinyl)-1,10-phenanthroline)). We demonstrate that both biotinylated compounds bind to avidin through their biotin moieties with high affinity and in a 4:1 ratio. The binding of compounds 1 and 2 to avidin results in an enhancement in luminescence intensity (~1.4×, ~1.6×, respectively), relative to the unbound biotinylated ruthenium complexes. This behavior is markedly different from biotinylated organic dyes, whose fluorescence is quenched upon binding to avidin. Thus, rutheniumbiotin complexes 1 and 2 can form the basis of new, simplified biotin-avidin assays, which involve luminescence detection of the relevant biotinylated molecule through cross-linking with avidin.