Influence of Three Anionic Gemini Surfactants with Different Chain Lengths on the Optical Properties of a Cationic Polyfluorene

The effects of three sulfonate gemini surfactants with different hydrophobic chain lengths (8, 10, and 12 carbon atoms) on the optical properties of a fluorene-based conjugated cationic polymer poly­{[9,9-bis­(6′-<i>N</i>,<i>N</i>,<i>N</i>-trimethylammonium)­hexyl]-fluorene-phenylene} bromide (PFP) dissolved in DMSO–water solutions (4% v/v) or water were investigated, respectively. When surfactants with PFP dissolved in DMSO–water solutions (4% v/v) are incubated, a decrease in photoluminescence (PL) intensity and a red shift of emission maxima are obtained at low surfactant concentrations. Intriguingly, two different Stern–Volmer constants (<i>K</i>_SV1 and <i>K</i>_SV2) are obtained and analyzed in detail for the first time. Further increase in the surfactant concentration enhanced PL intensity, and distinct blue shifts of both absorption and emission maxima are observed. Importantly, the turning point between the emission quenching and enhancement is closely related to the hydrophobic chain length: the longer the chain length, the earlier the turning point appears. Simulation studies provide strong evidence to explain these phenomena. Surface tension measurements show more insight on the interactions between PFP and surfactant. On the contrary, no emission quenching is obtained at low surfactant concentrations for PFP dissolved in water

Amplified Fluorescent Sensing of DNA Using Graphene Oxide and a Conjugated Cationic Polymer

We explore the interactions between a fluorescein (FAM)-labeled single-stranded DNA (P), graphene oxide (GO), and a cationic conjugated polymer, poly [(9,9-bis­(6′-<i>N</i>,<i>N</i>,<i>N</i>-trimethylammonium)­hexyl)-fluorenylene phenylene dibromide] (PFP). It is found that the fluorescence change of P-GO-PFP system is dependent on the addition order of P and PFP. When adding PFP into P/GO complex, the fluorescence resonance energy transfer (FRET) from PFP to P is inefficient. If P is added to PFP/GO complex, efficient FRET is obtained. This may be attributed to the equal binding ability for P and PFP to GO. The results of time-resolved fluorescence and fluorescence anisotropy support the different fluorescent response under different addition order of P and PFP to GO. Based on the above phenomenon, we demonstrate a method to reduce the high background signal of a traditional PFP-based DNA sensor by introducing GO. In comparison to the use of single PFP, the combination of PFP with GO-based method shows enhanced sensitivity with a detection limit as low as 40 pM for target DNA detection