Date of Graduation

Spring 5-20-2016

Document Type

Thesis

Degree Name

Master of Science in Chemistry

College/School

College of Arts and Sciences

Department/Program

Chemistry

First Advisor

Lawrence Margerum

Second Advisor

William Melaugh

Third Advisor

Ryan West

Abstract

A series of silica nanoparticle-based fluorescent chemosensors were synthesized for the sensitive and selective detection of Cu2+ ions in aqueous solution and subsequent CN- ion detection. Silica nanoparticles (SNP) were modified with branching polyamidoamine (PAMAM) dendrimers, which function as selective turn-off Cu2+ ion chelators and platforms for the attachment of rhodamine isothiocyanate (RITC) or fluorescein isothiocyanate (FITC) fluorescent dyes. In the presence of Cu2+ ions, the emission of the fluorescent dye is quenched by Forster resonance energy transfer (FRET) and is dependent upon dendrimer generation, pH, fluorescent dye, and surface charge. The quenching effectiveness was analyzed by Stern-Volmer quenching analysis and increased with dendrimer generation up to G4, yielding a Stern-Volmer quenching constant of 14 (±2) x 105 M-1 and a limit of detection of 0.2 µM Cu2+ under optimal conditions (SNPG4-FITC). Furthermore, the fluorescence can be fully restored by the subsequent addition of CN- ions, which is surprisingly effective compared to other strong anion chelators like EDTA and azide at low concentrations, reaching a turn-on detection limit of 1 µM CN- (SNPG4-FITC). The turn-off, turn-on fluorescent chemosensing systems were also used as FRET sensors for 8-Anilino-1-naphthalenesulfonic acid (ANS) to prove the applicability of the systems as small organic molecule sensors. In the future, the same SNPGx-Dye sensing system can be customized to sense additional analytes like polycyclic aromatic hydrocarbons, explosives, and amino acids.

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