Cationic and anionic conjugated poly electrolytes: aggregation-mediated fluorescence energy transfer to dye-labeled DNA

An electrostatic complex of water-soluble conjugated polyelectrolytes (CPs) between anionic poly(9,9-bis(4′-sulfonatobutyl)fluorene-co-alt-1,4- phenylene) disodium salt (a-PFP) and cationic poly(9,9-bis((6′-N,N,N,- trimethylammonium)hexyl)fluorene-co-2,1,3-bezothiadiazole) dibromide (85:15) (c-PFB₁₅) was tested as a fluorescence resonance energy transfer (FRET) donor to Texas Red (TR)-labeled single-stranded DNA (ssDNA-TR) via two-step FRET processes. Electrostatic complexation of a-PFP and c-PFB ₁₅ in water leads to aggregation of polymer chains, a concomitant reduction of intersegment distances, and energy transfer to the benzothiadiazole (BT) segments. The following complexation with ssDNA-TR leads to energy transfer from BT to TR via two-step FRET processes. This detection schematic shows an FRET-induced signal amplification, which can be achieved by adjusting the charge ratio in the cationic/anionic CP complex and controlling the number density of the binding CPs around the acceptor, resulting in enhanced antenna effects and sensitivity in CP-based FRET DNA detection assays.