Polyfluorene Conjugated Polymer Fluorescence Sensor Of The Synthesis, Design And Applied Research

Water-soluble conjugated polyelectrolytes (CPEs) are an interesting class of organic macromolecules withπ-conjugated backbones and charged side chains, which combine the unique optoelectronic properties of traditional conjugated polymers with aqueous solubility and electrostatic behaviors of polyelectrolytes. During the past decades, CPs have been employed in the detection of various analytes such as metal ions, small biomolecules, DNA, and proteins. However, the field of conjugated polyelectrolytes is still far from mature, and the future promises new exciting synthesis method and detection systems. In this dissertation, we focused on the synthesis of conjugated polyelectrolytes with high water-solubility and high quantum yields by means of structure design and the control of CPEs aggregation. Furthermore, Highly sensitive and selective chemosensors and biosensors have been developed based on these conjugated polyelectrolytes. The results are summarized as follows:1. New water-soluble hyperbranched polyfluorenes bearing carboxylate side chains have been synthesized via the simple "A2+B2+C3" protocol based on Suzuki coupling polymerization. The linear polyfluorene analogue LPFA was also synthesized for comparative investigation. The optical properties of the neutral precursory polymers in CHCl3 and final carboxylic-anionic conjugated polyelectrolytes in buffer solution were investigated. The obtained hyperbranched polyelectrolyte HPFA2 with lower content of branch unit (2%) showed excellent solubility and high fluorescence quantum yield (φF=89%) in aqueous solution. Fluorescence quenching of HPFA2 by different metal ions was also investigated, the polyelectrolyte showed high selectivity for Hg2+ and Cu2+ ions relative to other various metal ions in buffer solution. The Stern-Volmer constant Ksv was determined to be 0.80×106 M-1 for Hg2+ ions and 3.11×106 M-1 for Cu2+ ions respectively, indicating the potential application of HPFA2 as a highly selective and sensitive chemosensor for Hg2+ and Cu2+ ions in aqueous solution.2. A simple and sensitive assay using carboxylic acid-functionalized polyfluorene containing 5% benzo[2,1,3]thiadiazole (PFCOOH-BT5) for trace detection of diamines and biogenic polyamines was demonstrated. The optical properties of PFE-BT5, PFCOONa-BT5, and PFCOOH-BT5 in appropriate solvents were investigated to evaluate the effect of side-chain modification on the intrinsic BT emission. Addition of diamines and biogenic polyamines can lead to denser polymer aggregation, which is responsible for more efficient FRET of PFCOOH-BT5 from fluorene segments to BT units and thus fluorescence color change from blue to orange. In contrast,1,3-propanediol was found to induce no significant variations in the PL spectra of PFCOOH-BT5, which suggested that the analyte-induced aggregation was dominantly caused by the electrostatic interactions between the carboxylic acid functional groups and multiamines. This ratiometric fluorescence sensor takes advantage of the signal amplification of conjugated polymers and can detect diamines and biogenic polyamines at concentration level as low as 2 uM, indicating that PFCOOH-BT5 can serve as a highly sensitive sensor for diamines and biogenic polyamines.3. A series of carboxylate-containing fluorene-based anoinic water-soluble conjugated polymers, which are specially designed to link fluorene with alternating moieties such as 5% benzo[2,1,3]thiadiazole (BT) and amine groups have been synthesized via the Pd-catalyzed suzuki-coupling reaction, respectively. These polymers had good solubility in water and showed different responses for metal ions in aqueous environments. After investigation of the UV-vis absorption spectra and PL emission spectra, we found that the energy or electron-transfer reactions were the main reason for fluorescence quenching of these polymers. On the other hand, interchain aggregation caused by metal ions also lead to fluorescence quenching for these polymers.4. A completely water-soluble and highly fluorescent conjugated polyfluorene(PF) was rationally designed and synthesized as a signal amplifying unit and chemically modified with carboxylic functional groups at the sidechains of the polymer to bioconjugate with amine functionalized singlestranded oligonucleotides as a receptor using carbodiimide chemistry. This approach allows the functional groups on the polymers to be effectively linked to DNA without obvious damage to the conjugatedπ-system of the polymers. A simple and highly sensitive assay based on this new hybrid bio/-synthetic sensory conjugated polyelectrolytes were developed to achieve selective detection of the target oligonucleotides labeled with a chromophore dye(FAM). DNA detection results using the PF-ssDNA hybrid system confirmed large signal amplification by means of efficient FRET energy transfer from the energy harvesting PF to the fluorescent dye(FAM) attached to the complementary probe DNA. To realize label-free detection, a new DNA intercalating dye(SYBR Green I) were also used in combination with the anionic conjugated polymers. A DNA detection study by using the resulting PF-ssDNA/intercalating dye complex showed not only signal-amplification properties but also sensitive FRET efficiency from polyfluorenes-ssDNA bioconjugate(PF-ssDNA)to SYBR Green...