Tunable Fluorescence of a Semiconducting Polythiophene Positioned on DNA Origami

A novel approach for the integration of pi-conjugated polymers (CPs) into DNA-based nanostructures is presented. Using the controlled Kumada catalyst-transfer polycondensation, well-defined thiophene-based polymers with controllable molecular weight, specific end groups, and water-soluble oligoethylene glycol-based side chains were synthesized. The end groups were used for the easy but highly efficient click chemistry-based attachment of end-functionalized oligodeoxynucleotides (ODNs) with predesigned sequences. As demonstrated by surface plasmon resonance spectroscopy, the prepared block copolymers (BCPs), P3(EO)(3)T-b-ODN, comprising different ODN lengths and specific or repetitive sequences, undergo specific hybridization with complementary, thiol-functionalized ODNs immobilized on a gold surface. Furthermore, the site-specific attachment of the BCPs to DNA origami structures is studied. We demonstrate that a nanoscale object, that is, a single BCP with a single ODN handle, can be directed and bound to the DNA origami with reasonable yield, site-specificity, and high spatial density. On the basis of these results, we are able to demonstrate for the first time that optical properties of CP molecules densely immobilized on DNA origami can be locally fine-tuned by controlling the attractive pi-pi-stacking interactions between the CPs. In particular, we show that the fluorescence of the immobilized CP molecules can be significantly enhanced by surfactant-induced breakup of pi-pi-stacking interactions between the CP's backbones. Such molecular control over the emission intensity of the CPs can be valuable for the construction of sophisticated switchable nanophotonic devices and nanoscale biosensors.