Fluorescence Energy Transfer to Dye-Labeled DNA from a Conjugated Polyelectrolyte Prequenched with a Water-Soluble C₆₀ Derivative

The emission of the cationic polyelectrolyte 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 × 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.