Nanostructured Organic and Inorganic Thin Films With Novel Molecular Recognition Properties

"An important theme in surface/interface science is the development of molecular level understandings of interactions at solid-liquid interfaces. The study of molecular recognition at such interfaces is well suited for modeling with self-assembled monolayers of alkanethiols (SAMs). For optimal studies, the SAM must be defect-free. Towards this end, a chemical treatment of the gold substrate was developed, consisting of a sequential treatment in ""piranha"" followed by dilute aqua regia. We found that the SAMs assembled on these treated substrates had exceptional barrier properties as measured by cyclic voltammetry(CV). X-ray diffraction(XRD) indicated that oxidative treatment induces significant bulk recrystallization of the metal. The dynamics suggest that recrystallization results from preferential dissolution of Au and/or impurities present at grain boundaries, leading to unpinning and merger into larger grains. Supported lipid layers were formed via fusion of unilamellar vesicles of 1,2-dimyristoyl-sn-glycero-3-phosphocholine(DMPC) to mixed SAMs containing ferrocene-functionalized hexadecanethiol chains(FcCO 2C16SH). The structures were characterized by several methods, including CV, ellipsometry and surface plasmon resonance(SPR). Studies revealed that the adsorbed DMPC strongly influences the interactions of the tethered ferrocene groups with secondary aqueous molecular redox probes. Permselective properties are seen. We believe that molecular scale defect structures in the adsorbed DMPC layer confer these molecular discrimination properties. Unilamellar vesicles of DMPC and varying quantities of 1,2-dimyristoyl-sn-glycero-3-[phospho-rac-(1-glycerol)(sodium salt)(DMPG) were used to deposit lipid bilayer assemblies on SAMs. The coverages of the layers were measured with SPR and decreased with increasing DMPG. The assembly is reversible and the lipid adlayer removable with ethanol. Effects of the adsorbed lipid layer on the electrochemical interactions of the hybrid lipid/SAM with several redox probes were characterized using CV. At 5%DMPG, the permeabilities of the probes were affected significantly relative to pure DMPC. These effects include a striking observation of an enhanced, ionic-charge-specific molecular discrimination. Taken together, the results suggest that assembly of secondary adsorbate layers of phospholipids provide an interesting method for modifying the electrochemical properties of thiolate SAMs on gold. Such adlayers can exhibit perm-selection towards species in solution. These species therefore do affect the character of structure/property correlations in ways that are complex and potentially useful."

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Twardowski, Mariusz Z.

Contributors dc:contributor

• Nuzzo, Ralph G.

• Engineering, Materials Science

Language dc:language

eng

Identifier

(MiAaPQ)AAI3086204

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/84110