Analytical Applications Of Supramolecular Materials In Chemical And Biological Sensors

Abstract

Supramolecular materials are complex chemical structures held together by noncovalent interactions such as electrostatic, hydrogen bonding, van der Waals, and donor-acceptor type interactions. Both individual molecules such as dendrimers and molecular assemblies such as lipid bilayers are categorized under supramolecular materials. Analytical applications of supramolecular materials are increasing and being explored due to their fascinating characteristics. In the work reported in this dissertation, use of supramolecular materials to eliminate/minimize some shortcomings in sol-gel based optical chemical sensor materials (dye leaching, low sensitivity) and in fluor doped silica nanoparticle based biolabels (nonspecific adsorption of/to proteins) were explored. In part one, the ability of PAMAM dendrimers to act as anchors for dye molecules was investigated. Binding the dye molecules to PAMAM quantitatively eliminated the leaching of the dye from sol-gel matrices in aqueous solutions. It was shown that this retention of dye is due to the physical entrapment of the PAMAM bound dye molecules. Taking advantage of the available primary amine groups, dye (Nile red) modified PAMAM molecules were further modified with alkyl chains. The alkylated, Nile red modified PAMAM was used with 2,4-dinitrotoluene (analyte) in aqueous media to show that alkyl chains can preconcentrate the analyte in the vicinity of the dye molecules. It was shown that C8 chains provided the better preconcentration out of the three chain lengths (C4, C8, and C18) tested. The fluorescence signal of the C8 modified PAMAM-Nile red was quenched with the addition of 2,4-dinitrotoluene. The non-alkylated version showed no quenching of signal.In part two of this dissertation, a poly(lipid) coated fluor doped silica particles were used as labels for cellular receptors. Using a model system consisting of streptavidin attached to HeLa cell surfaces, it was shown that poly(lipid) layers on silica particles can carry biotinylated lipids and can bind to streptavidin on HeLa cell surfaces. Most importantly the ploy(lipid) coated particles showed about 70% reduction in the nonspecific adsorption of the protein bovine serum albumin compared to bare particles. It was also shown that polymerized lipid layers could withstand much harsher conditions.