Supramolecular self-assembly of DNA and cationic polythiophene: from polyplexes to fibers

Cationic polythiophenes constitute an interesting class of polymers for prospective applications in imaging, gene delivery and biosensing, as they combine solubility in aqueous media and have sensitive optical properties for the detection of biomolecules such as DNA. Here, we study the supramolecular self-assembly of poly[3-(6'-(trimethylphosphonium)hexyl)thiophene-2,5-diyl] (P3HT-PMe3) with various types of DNA, like single-stranded oligonucleotides or long genomic DNA. Self-assembly in buffered aqueous solution yields polyplexes (polymer/DNA complexes) with hydrodynamic radius ranging from 7 nm to around 25 nm, as observed by Taylor Dispersion Analysis. In these polyplexes, the achiral polymer presents chiroptical signals induced by supramolecular organization along chiral DNA. When the solution of long DNA/P3HT-PMe3 is deposited on surfaces, the formation of µm-long fibers occurs, as evidenced by microscopy techniques. Those fibers are formed by compaction of the polyplexes and condensation of DNA, and the fluorescence of the polymer is homogeneous along these fibers.