Synthesis and fluorescent properties of dendritic polyelectrolyte fluorophores

Abstract

Water soluble fluorophores containing multiple fluorogenic moieties are of interests for chemical analysis and highly sensitive medical diagnosis. The fluorophores with controllable numbers of fluorogenic units can provide good mechanistic understanding and experimental reproducibility. In this thesis, a series of nine variously charged dendritic fluorophores (charges: 6C⁻, 3C⁻, 2C⁻N⁰, C⁻2N⁰, 2C⁻N⁺, 2C⁰N⁺, C⁰2N⁺, 3N⁺, and 6N⁺) composed of exact numbers of the para-phenyleneethynylene (PPE) fluorogenic branches and anionic carboxylate or cationic ammonium peripheral groups are synthesized via Sonogashira coupling. The first generation anionic dendrimer, 6C⁻ exhibits a highly selective fluorescence quenching by Hg²⁺ ions with quenching efficiency Ksv of 33,700 M⁻¹ in the presence of Triton X-100 surfactant. The nine fluorophores are assembled into an array for protein analysis. Using principal component analysis (PCA) and factorial discriminant analysis (FDA), the optimum detection wavelength is located at 500 nm and the number of sensing elements is reduced from nine to two (C⁰2N⁺ and 3C⁻) with 100% discriminating accuracy. The cellulose nanofiber mats doped with 3C⁻ fluorophore are fabricated by electrospinning technique. The mats can be applied as a reusable solid-state fluorescent sensing device for metalloproteins such as hemoglobin which shows high Ksv of 1.7×10⁶ M⁻¹. The findings in this thesis work have established a new interesting class of fluorophores useful for sensing applications in aqueous media.