Disassembly-Driven Optical Sensors Based On Water-soluble Polythiophene Complexes

Optical sensors based on conjugated polyelectrolytes (CPEs) have attractedwidespread interest due to their unique optoelectronic properties and signalamplification effect. Hitherto, most of these sensors are focused on the detection ofbiomacromolecules, whereas few CPEs can be applied to the detection of smallbio-analytes due to their weak interaction with CPE probes. Therefore, it remains achallenge to fine new approaches that could improve the sensitivity of small bio-analytedetection and discrimination. Poly(3-alkoxy-4-methylthiophene)s, a kind of conjugatedpolymers with sensitive conformation change towards external stimuli, has beenconfirmed to be sensitive colorimetric and fluorescent probes for the detection ofvarious analytes. This dissertation focused on the detection of anionic surfactants anddiscrimination of primary amino acids based on the disassembly of a cationicpoly(3-alkoxy-4-methyl-thiophene) complexes by combining an in-situ premodificationtechnique. The main results are summarized below.(1) Colorimetric and fluorescent dual detection of anionic surfactants has beenrealized based on the assembly-disassembly of a PMTPA complex with an anionic dye,8-hydroxy-1,3,6-pyrenetrisulfnic acid trisodium salt (HPTS). It was demonstrated thatthe addition of HPTS into PMTPA aqueous solution resulted in the formation ofPMTPS/HPTS complex through ionic self-assembly, along with a solution color changefrom yellow to pink and fluorescence quenching of PMPTA and HPTS. Upon theintroduction of anionic surfactants into the complex solution, the disassembly ofPMTPS/HPTS complex was observed due to the competitive binding with PMTPA viaelectrostatic interaction and the synergistic effect arising from the hydrophobicinteraction between long alkyl chains of surfactants. This process can be monitored byrecording absorption spectral changes of PMTPA and fluorescence recovery of HPTSdue to the collapse of PMTPA/HPTS complex, realizing dual detection of anionicsurfactants. The detection limit is evaluated to be the order of109M by fluorescentanalysis.(2) The formation of amphiphilic isoindole derivatives by an in situ reactionbetween OPA, NDM and amino acids has been confirmed by its absorption andemission spectra. It has been confirmed that the amphiphilic isoindole derivatives caninduce the disassembly of a PMPTA complex formed with2-naphthalenesulfonate (NSA) in aqueous solution, through cooperative electrostatic and hydrophobicinteractions. On the basis of these results, a sensory array of wavelengths of PMTPAwas constructed and applied to discriminate primary amino acids. Linear discriminantanalysis and jackknifed classification demonstrates that this array can discriminateamong19primary acids with100%confidence limits.