Collective Response from a Cationic Tetrahedral Fluorene for Label-Free DNA Detection


  • We thank National University of Singapore (NUS ARF R-279-000-197-112 and R-279-000-197-133) and National Institute of Health Grant (GM 62958-01) and the NSF (DMR-0097611) for financial support.


A cationic water-soluble tetrahedral molecule bearing four phenylene-bis(fluorene) optical units, namely tetrakis[4-(2-(9,9,9′,9′-tetrakis(N,N,N-trimethylammoniumhexyl)-7,2′-bifluorenyl))-phenyl]methane hexadecanebromide, was designed and synthesized. Fluorescence resonance energy transfer (FRET) experiments between the tetrahedral molecule and fluorescein-labeled double stranded DNA (dsDNA-Fl) or single stranded DNA (ssDNA-Fl) were undertaken. Due to its specific shape and spatial registry, the tetrahedral molecule shows improved FRET efficiencies to dsDNA-Fl as well as improved selectivity between dsDNA and ssDNA, when compared to a cationic conjugated polymer with similar repeat units. 30-Fold signal amplification for dsDNA/ethidium bromide (EB) and selective response between complementary and non-complementary DNA indicates that tetrahedral molecules could be useful to amplify the optical response from EB-based DNA protocols.