Supramolecular interactions as a basis for differential sensing applications

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University of Alabama Libraries

In this work, we used supramolecular interactions to construct systems that respond to analytical stimuli and report on specific chemical species in solution using optical spectroscopic techniques (e.g. absorbance and fluorescence spectroscopy), affording low cost and high sensitivity. To obtain selectivity, we used cross reactive sensors (organic dyes, conjugated polymers) to generate differential response patterns when exposed to families of subtly different analytes of interest. The differential responses produced large data sets that were interpreted using well established pattern recognition algorithms, such as linear discriminant analysis (LDA) and principal component analysis (PCA). We first report on conditions and methods based on linear discriminant analysis to predict the identity and composition of samples containing metal ion mixtures without prior physical separation, a common shortcoming of these systems. We also report on a higher sensitivity metal ion sensing array composed of novel fluorene based conjugated polymers with high affinity groups to detect nine divalent metal cations down to 500 pM in freshwater, and to 100 nM in seawater samples collected from the Gulf of Mexico. This robust system was sufficiently sensitive for detection below the maximum mandated concentrations set by the US Environmental Protection Agency (EPA) for toxic metals in drinking water and aquatic ecosystems. Similar highly sensitive, fluorene based conjugated polymers were used again to detect pollutants with intrinsic characteristic light absorption such as polycyclic aromatic hydrocarbons (PAHs) and azo textile dyes. Instead of chemical interaction with these analytes, the polymers displayed good spectral overlap with the absorbance spectra of the targets, leading to changes in their optical spectrum caused by the inner filter effect, where the analytes themselves acted as “chemical filters”. Finally, we investigated the nature of the binding interactions between PAH probes and amine terminated poly(amidoamine) (PAMAM) dendrimers. Using time resolved fluorescence, fluorescence anisotropy, and selective quenching experiments, we used two probes, anthracene and pyrene, to highlight distinct binding modes and locations to the polycationic, macromolecular PAMAM hosts, paving the way for future applications of such charged polymers with interesting affinity towards hydrophobic guests.

Electronic Thesis or Dissertation
Organic chemistry, Analytical chemistry