We report a macromolecular end-capping approach to improve the detection sensitivity of cationic conjugated polymer (CCP) based DNA detection. A phenylethynyl anthracene (PEA) end-capped cationic polyfluorene (PF) derivative (P1) is synthesized via Suzuki coupling. Due to efficient fluorescence resonance energy transfer (FRET) from the polymer backbone to the end-capper PEA units, the polymer (P1) fluorescence is dominated by the emission from PEA even in dilute aqueous solution. Pi emission has a better spectral overlap with fluorescein (Fl) absorption compared to that for uncapped PF (P2). In addition, the intra and intermolecular energy transfer for P1 is more efficient in the presence of DNA due to complexation-induced polymer aggregation. These impart a combinatorial FRET between P1 and an Fl-labeled probe which is more efficient than that between P2 and the same probe. P1 thus offers a better DNA detection sensitivity relative to P2 and opens up new opportunities to improve the performance of CCP based biosensors involving FRET.