Quantum dot-ruthenium complex dyads: recognition of double-strand DNA through dual-color fluorescence detection

We have developed a new fluorescent ensemble probe comprising an ionic conjugate between water-soluble thioglycolic acid (TGA) capped CdTe quantum dots (QDs) and Ru(bpy)(2)(dppx)(2+) for the dual-color detection of complementary double-stranded DNAs (dsDNA). To provide the platform for DNA detection, the Ru-complex was first employed as an effective fluorescence quencher to TGA capped QDs via photoinduced electron transfer process. Because of its strong binding affinity with Ru(bpy)(2)(dppx)(2+), complementary dsDNA can break up the low fluoresced ionic ensemble, set free the luminescent QDs, and concomitantly generate the Ru(bpy)(2)(dppx)(2+) intercalated DNA complex. Thus, the recognition of dsDNA by Ru(bpy)(2)(dppx)(2+) can be realized via both the restoration of QDs fluorescence and the emergence of a new fluorescence emission signal of the quencher-substrate at 609 nm, while single-stranded DNA, ribonucleic acid, bovine albumin serum, and biological relevant metal ions cannot produce the similar results. Therefore, a simple, fast, sensitive, and highly selective assay for dsDNA has been realized.