Chemical Sensors Based On Fluorescent Conjugated Polymers

The application of fluorescent biosensor for analytes sensing is one of the hot spot inscience research. Rapid, high selectivity and high sensitivity study of analytes in biologicalchemical information is one of the frontier subjects in the biosensing. And sensitive reagentand exploration is to improve the trace analysis of the measuring methods of selectivity andsensitivity of the key factors. Conjugated polymers have been widely applied in biosensing,and conjugated polyelectrolyte (CPEs) is a kind of ionized in polar solvent functional groupsin the main chain of the conjugated polymers, which is combines traditional conjugatedpolymers excellent photoelectric properties, such as signal amplification and with goodwater-soluble characteristics of polyelectrolyte. Conjugated polyelectrolyte is also widelyapplied light electric parts and chemical sensors and biological imaging, etc. This paper mainwork includes the following aspects:In this paper, Novel self-assembled water-soluble nanomicelles that by introducingcommercialized three block of surfactant Pluronic F127self-assembly with conjugatedpolymers in aqueous solution, and particle size distribution of spherical nanometer micelleswas successfully achieved in50-100nm. Conjugated polymers (CPs) with uniquephotophysical properties and electrical conductivity are considered as promising candidatesfor the development of fluorescent sensors. However, the application of Conjugated polymers(CPs) to bioimaging and sensing in aqueous environment is hindered by their poor watersolubilities, and Conjugated polymers (CPs) is not conducive to implement specific analysisobject in the aqueous solution (Such as DNA and corresponding biochemical processes ofbiological molecules) detection. Therefore, great efforts have been devoted to developingcolloidal stable conjugated polymer nanoparticles (NPs) in aqueous solution. We screeningout the appropriate concentration ratio of Pluronic F127and conjugated polymer, andoptimize the sensor system in the aqueous solution of conjugated polymers. The morphologyof the F127and conjugated polymers/F127micelles were observed with by dynamic lightscattering (DLS) and transmission electron microscopy (TEM). Fluorescence and absorptionspectroscopy characterization methods confirmed that different surfactants and conjugatedpolymer concentration ratios to adjust different luminous efficiency. The Fluorescent nanomicelles exhibited a highly selective fluorescence quenching by the prohibited foodadditive Sudan dyes, while not for the natural pigments: Capsanthin and Beta-carotene. It isalso possible that the trace amount of hydrophobic dye in the aqueous solution can becollected and enriched in the hydrophobic inner part of F127nanomicelles by thehydrophobic–hydrophobic interaction resulting in the enhancement of quenching effect. TheStern-Volmer constants (Ksv) of PF-PE/F127and PFO/F127for Sudan I were1,040,480M-1and665,000M-1, respectively, which were over100times higher than those of the sameconjugated polymers in the orgainc solvents. The detailed photochemical mechanism foramplified fluorescence quenching was revealed to be due to the more suitable matching of theLUMOs (lowest unoccupied molecular orbital) of the conjugated polymers with that of SudanI molecules, thusthe charge transfer between CPs and analytes and the enriching andcollecting effect micelles hydrophobic core. In the same conditions, CPs nanomicellesexhibited strong fluorescence responses toward other azo dyes, such as Sudan II, Sudan IIIand Sudan IV. It allowed the selectively determination of Sudan dye by a fluorescence method.Moreover, this strategy provides a general approach for extending the applications ofconjugated polymers.In the second chapter, the effect of aggregation on the photophysical properties of threewater/alcohol-soluble conjugated polymers (CPEs),poly[9,9-bis((N,N,N-triethylammonium)-hexyl)-2,7-fluorene] dibromide (PF6NBr),poly[9,9-bis(4’-sulfonatobutyl)fluorene-co-alt-1,4-phenylene] sodium salt (PFSO3Na) andpoly[9,9-bis((N-(3-sulfonate-1-propyl)-N,N-diethylammonium)-hexyl)-2,7-fluorene](PF6NSO) has been studied through laser light scatterings (LLS) and quenching experiment.The results obtained by light scatterings reveal that three CPEs form different fluorescenceaggregates in methanol. Furthermore, fluorescence spectroscopy also reveals that CPEs formfluorescent aggregates in a mixture of methanol and water. Fluorescence quenching of thepolymers was examined using methyl viologen (MV2+)and1,2-naphthoquinone-4-sulfonate(NQS-) as a cationic quencher and anionic quencher, respectively.The fluorescence intensity of PF6NBr decreases with increasing concentration, indicatingthat dominated by electrostatic attraction and aggregation induced less fluorescence quenching and the chain conformation controlled, and high concentrations of PF6NBr leadingchain conformation strong aggregation in methanol and cause the less quenching efficiency.In contrast, for both PFSO3Na and PF6NSO, the emission is less quenched in methanol due tothey have a stable state of aggregation in solution.Accordingly, we investigated the quenching properties of three polyelectrolytes atdifferent methanol and water solvent ratio. However, PF6NBr and PF6NSO shows stronglyamplified quenching effect by NQS-, and PFSO3Na shows amplified quenching effect byMV2+in water. The results are explained by polymer is able to fold into an aggregation insolution. With regard to the PF6NBr and PFSO3Na, quenching efficiency of PF6NSO showeda high quenching efficiency due to NQS-break up polymers aggregates and show a betterquenching efficiency compare to MV2+. This work shows that the quenching of the CPEsinvolves electron transfer and is correlated to the conformational changes that occur uponbinding the quenchers to the polyelectrolyte (CPEs), which facilitates the long-distanceexciton rapid migration along CPEs backbone. Our work addresses an important fundamentalissue concerning quencher-induced amplified quenching effect for CPEs. The resultsunderscore the important role played by chain aggregation in promoting efficient excitontransport, which is the key to the amplified quenching effect.