Fluorescence energy transfer to dye-labeled DNA from a conjugated polyelectrolyte prequenched with a water-soluble C60 derivative

The emission of the cationic polyclectrolyte poly[9,9'-bis(6 ''-N,N,N-trimethylammonium)hexyl)fluorene-alt-4,7-(2,1,3-benzothiadiazole) dibromide] (PFBT) is effectively quenched via photoinduced electron transfer by the negatively charged C-60 derivative sodium diphosphorate methano[60]fullerene (SDPMF). Stern-Volmer analysis shows the quenching constant as high as 2.8 x 10(12) M-1, consistent with the formation of ground state complexes. Addition of Cy5-labeled ssDNA to PFBT leads to concurrent FRET to Cy5 and a quenching of PFBT emission that is intrinsic to the addition of ssDNA. Similar experiments carried out with a solution of PFBT that was prequenched with SDPMF result in a stable PFBT background emission and a clearly observed Cy5 emission rise. These observations were applied to ssDNA assays that take advantage of Cy5-labeled PNA. The result is a FRET-based detection method with more stable and readily quantifiable optical signals.