Design And Synthesis Of Cationic Conjugated Polyelectrolytes And Their Application On Chemical And Biological Sensors

A series of water-soluble conjugated polyfluorenes were designed and synthesized. Highly sensitive and selective chemosensors and biosensors were developed using these conjugated polymers as optical probes. The results are summarized as follows: 1. The water-soluble cationic polyfluorene (CCP1) containing the imidazole moieties in side chain was designed and synthesized as the fluorescent probe for"turn-on"detection of nitric oxide (NO). The assay benefits from the sensitivity of optical signals from conjugated polymers and the simplicity of fluorescence measurement techniques. The assay contains three elements: a cationic conjugated polymer containing imidazole moieties, Cu²⁺ ions, and the target nitric oxide. The highly fluorescent conjugated polymer coordinates to Cu²⁺ ions through weak N…Cu interactions, and its fluorescence is efficiently quenched via photo-induced electron transfer process ('off'state). In the presence of nitric oxide, the transformation of the paramagnetic Cu²⁺ ion into diamagnetic Cu1+ ion inhibits the quenching and therefore the fluorescence of the conjugate polymer is recovered ('on'state). Other biologically relevant reactive nitrogen species, such as NOBF4, NaNO2 and NaNO3 don't exhibit the fluorescence recovery of conjugated polymer in the same condition as nitric oxide. The cationic conjugated polymer/Cu²⁺ complex can thus be used as the platform to detect nitric oxide in aqueous solution with high sensitivity and selectivity.2. We design and synthesize a new series of water-soluble cationic polyfluorene copolymers containing 2,2'-bipyridyl-phenylene-vinylene moieties in the backbone (PFP-P1-3). Among them, PFP-P2 can be used as selective and sensitive fluorescent probe to detect Cu²⁺ ions in aqueous medium. In the absence of the Cu²⁺ ion, the PFP-P2 exhibits strong fluorescence emission in aqueous solution. Upon adding the Cu²⁺ ion, the PFP-P coordinates to Cu²⁺ ions through weak N…Cu interactions, and its fluorescence is efficiently quenched by the Cu²⁺ ion. By triggering the change of emission intensity of PFP-P, it is suitable to assay Cu²⁺ ions in aqueous solution. The assay benefits from the sensitivity of optical signals from conjugated polymers and the simplicity of fluorescence measurement techniques.3. Water-soluble cationic oligofluorene containing one carboxyl group on side chain (OF1) was synthesized by Suzuki coupling. The presence of terminal ammonium moieties and carboxyl group increases intermolecular electrostatic interactions. The electrostatic forces and hydrophobic interactions lead to the formation of polymeric-like structures for OF 1, which offers it similar light-harvesting ability as that of cationic conjugated polyelectrolytes. This collective optical behavior was studied by fluorescence quenching experiments and fluorescence resonance energy transfer (FRET) experiments with fluorescein-labeled double-stranded DNA (dsDNA-F1).