Synthesis And Sensor Properties Of Water-Soluble Conjugated Poly (Aromatic Diacetylenes)

Conjugated polymers (CPs) that serve as signal transducers in chemical and biological sensors have been paid much attention. Relative to small molecule counterparts, their advantage is the amplification of the signal by collective optical response. Solubility in aqueous media is essential for interfacing with biological substrates such as proteins and DNA, which is achieved by attaching charged functionalities (sulfonate acid, carboxylic acid, or ammonium) as pendant groups on the conjugated backbone. Their photophysical property, aggregation, and conformation are easily perturbed by external stimuli to result in large changes in measurable optical signals. We and others have utilized this property to detect DNA, RNA, proteins, and metalions.In this paper, two types of novel water-soluble conjugated polymers were designed and synthesized. One is containing diacetylene, carbazole and fluorene moieties in the main chain functionalized with ammonium in the side chains, the other is carbohydrate-functionalized polydiacetylene to improve the water-solubility. In this thesis, aiming for developling higher sensitive DNA and Hg²⁺ detection method based on these novel fluorescent conjugated polymers, four parts of works have been demonstrated as follows:(1) Synthesis of cationic fluorescent conjugated polymers CPF_xC_y and CPFCB_z .The precursor conjugated copolymers CPF_xC_y based different molar ratio of 2,7-diethynylfluorene and 3,6-diethynylcarbazole units in the main chain were prepared by Hay coupling polymerization. Their cationic copolymers were prepared by the methylation of their diethylpropylamino groups with CH3I. CPFCB_z was synthesized as the same method. A comparative study on the optical properties of cationic polymers in DMF and DMF/H2O showed that they underwent water-induced aggregation.(2) DNA detection with cationic fluorescent conjugated polymers CPF_xC_y.The interaction between calf thymus DNA (CT DNA) and cationic conjugated polymers CPF_xC_y by means of absorption and emission spectroscopy was preliminarily investigated. The disturbance by the buffer solution was also studied. The spectral behaviors of cationic fluorescent conjugated polymers with calf thymus DNA showed that a distinct fluorescent quenching took place with minute addition of CT DNA (3.3×10–13 M). The results showed that the polymers containing diacetylene in the main train would be promising biosensor materials for sensitive detection of DNA.(3) The study on Hg²⁺ detection with cationic conjugated polymers.We have developed a new fluorescence turn-on sensor composed of a cationic conjugated polyelectrolyte CPFC and [Fe(CN)]4– for the detection of Hg²⁺ ions. In contrast to previous reports, this sensor does not require fluorescent labels on the oligonucleotide probe, which should significantly reduce the costs. Even with the naked eye, we could identify micromolar Hg (II) ion concentrations from other metal ions. By using the fluorometric method, the detection limit was improved to the nanomolar range (5nM).(4) Synthesis and sensor properties of carbohydrate-functionalized polydiacetylenesPolydiacetylenes (PDAs) undergoes dramatic visible blue-to-red transformations together with fluorescence (none to-red) changes when PDAs are subjected to environmental perturbations, such as temperature and ligand–receptor interactions. The chromatic transitions are easily identified by the naked eye and can also be recorded by conventional high-throughput screening instruments. Here, three carbohydrate-functionalized PDAs(including glucoside, galactoside and mannoside) were designed to be used for ConA and E.coli detection. The results indicate that only mannoside-functionalized PDA is a potential detector for Con A and E.coli.