Synthesis And DNA Sensor Properties Of Water-soluble Diketopyrrolopyrrole (DPP)-Containing Conjugated Polyelectrolytes

Water-soluble cationic conjugated polyelectrolytes (CCPs) combine the properties ofpolyelectrolytes with the useful optical and electronic functions of the organic π-conjugatedbackbone. The delocalized electronic structure of CCPs makes them have a large number ofabsorbing units, and excitation energy along the whole backbone can transfer to an acceptorby electron transfer or fluorescence resonance energy transfer (FRET), resulting in theamplification of the fluorescence signal, which highly improves the detection sensitivity. Theparticular characteristics make them successfully be utilized in DNA detection based on theelectrostatic interaction with the negatively charged phosphate backbone of DNA.1,4-Diketo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP) and their derivatives have excellentchemical and thermal stability and high photoluminescence efficiency. The incorporation ofnarrow bandgap DPP in the wide bandgap fluorene-based cationic polyelectrolytes (CPs)might form an energy donor-acceptor molecule architectures, in which DPP units serve as anacceptor of fluorescence resonance energy transfer (FRET), which is important forcolorimetric sensor. To our best knowledge, there is no report on DPP-containing CPs forbiological sensing.In this article, a series of water-soluble conjugated copolymers (P1and P2) containingfluorene, diacetylene and DPP moieties in the main chain were synthesized and characterized.The water-induced aggregation of the cationic conjugated polymers in DMF/H2O and theFRET from fluoreneethynylene segments to DPP units were studied. The disturbance by ionswas also studied. The responses of P1and P2toward CT DNA were studied by the UV-visabsorption and emission spectra. The results show that P1and P2have strong electrostaticinteractions with negatively charged DNA and the FRET is more efficient from theblue-emitting fluoreneethynylene segments to DPP units, resulting in color change from blueto red, which allows naked-eye detection of DNA.In this article, a series of water-soluble conjugated copolymers (P3-6) were also synthesizedand characterized. P3-4are linear conjugated polymers; P5-6are hyperbranched conjugatedpolymers; P3and P5contain fluorene, triphenylamine, diacetylene and DPP moieties in themain chain. The FRET from fluoreneethynylene segments to DPP units and the disturbance by ions were studied. The results of the interaction between DNA and P3or P5show that P5is more sensitive, because its hyperbranched structure offers multiple exciton migrationchannels and diffusion pathways.The DPP-based water-soluble cationic conjugated polyelectrolytes might be a prospectivesensor in detection of DNA. The hyperbranched conjugated polymers exhibit manyadvantages in sensing DNA, such as high sensitivity and high selectivity.