Nanoscale self-assembly of conjugated polyelectrolytes

Abstract

Layer-by-layer (LBL) self-assembly of functional charged molecules is a versatile and efficient technique for preparation of ultrathin film which finds its applications in bioassays and other biomedical applications. The motivation of this PhD work was to study optical signal transduction in LBL film using conjugated molecules which are of vital importance due to their signal quenching and amplification capability by fluorescence resonance energy transfer (FRET). Prior to study in film, novel light harvesting water soluble oligo and polyfluorenes have been synthesized and investigated in solution with a view to achieving structure-property relationships and subsequently discovering potential energy donor for bioassay. The major modes of modification of fluorene backbone that have been focused are oligomeric and end-capping approaches. In this connection, electrostatic layer-by-layer self-assembly of the most efficient cationic oligofluorene has been performed followed by surface characterization. A simpler PNA-probe based DNA assay has been demonstrated on surface with excellent signal amplification (via FRET) and selectivity. Moreover, FRET based sensitive detection of protein (immobilized by click chemistry) on the surface has been accomplished which takes the advantage of charged surface of immobilized protein to assemble multiple layers of charged oligofluorene. Anionic conjugated polyfluorene derivatives have been presented as potential reporters of metal ions at low concentration with selectivity towards copper ion by fluorescence quenching in both solution and LBL film. In a word, this study paves a way towards more sensitive biodetection using conjugated oligo and polyelectrolytes in LBL self-assembly platform.