"Self-assembled monolayers (SAMs) are organized molecular assemblies that are formed by spontaneous adsorption of a compound in solution to a surface (e.g. alkanethiols on gold). The design, preparation, and characterization of several self-assembled monolayers and multilayers on surfaces (gold, indium tin oxide and quartz) are described. The systems were chosen based on their ability to form ordered films and to perform a given device function. SAMs were fabricated with selected functional groups at the air-monolayer interface, capable of complexing metal ions (e.g. dicarboxypyridine, dicarboxybenzene, imidazole, 4-hydroxypyridine) with the purpose of using these SAMs to construct multilayered films. Deposition of a second layer consisting of metal ions (e.g. Cu(II), Co(II) and Fe(III)), occurs by non-covalent metal ligand binding interactions between the metal ion layer and the different organic ligands on the surface. Deposition of subsequent layers was achieved by the incorporation of the appropriate organic ligands and metal ions. These monolayers and multilayered films were characterized by contact angle measurements, ellipsometry, grazing angle FT-IR, cyclic voltammetry and impedance spectroscopy following deposition of each layer on the film. Electrochemical analysis of the multilayered films shows alternating insulating/conducting behavior (cyclic voltammetry) and alternating changes in films capacitance (impedance spectroscopy) depending on the outermost layer of the film. Films capped with an organic layer show low conductivity, while films capped with a metal layer show conducting behavior. The electrochemical behavior of the films is related to the degree of “leakiness” or electrolyte solution permeation through the film, which is high for films with metal layers as the top layer and decreases once the film is capped with an organic layer. The alternating conducting/insulating behavior of the films allows for fabrication of multilayered thin films of variable thickness and tunable conducting properties. Ordered films were fabricated with up to seven layers of dicarboxypyridine and Cu(II), and 4-hydroxypyridine and Fe(III) metal-ligand units. The construction of these films provides an example of molecular films that could function as molecular wires or junctions due to their controllable electrochemical properties. Photocurrent generating films were fabricated by incorporation of chromophore groups (e.g. pyrene, porphyrins) into the multilayered structures. These films generate cathodic or anodic current upon photoexcitation of the chromophores. The monolayers functionalized with different organic ligands were also used to study lanthanide complexation on the surfaces. Successful deposition of different lanthanide ions was achieved from DMSO solutions. Monolayers of a bicyclic structure, 4, 7, 13, 16-tetraoxa-1,10,21-triaza-bicycle[8.8.5] tricosane-19,23-dione, attached to a hexadecanethiol molecule were used to study the ability of metal ion detection on the surface using electrochemical (cyclic voltammetry and impedance spectroscopy) techniques. The SAMs show higher complexation affinity for Li+ than for Na+ or K+. Preliminary studies were also carried out to investigate the ability of different SAMs to cell adhesion interactions. Future experiments will help elucidate a systematic relation of cell adherence and the bulk and molecular-level properties of the functionalized surfaces. The different multilayered films described in this dissertation served as preliminary models for different molecular scale device applications. Current work is focused in the design and preparation of more efficient photocurrent generating films, highly selective sensors for different types of ions, surfaces for cell adhesion and microbial interactions, and the study of other potential applications such as the design of micro and nanofluidic devices. "

Fouling properties of materials such as polyethylene glycol (PEG) have been extensively studied over the past decades. Traditionally, the factors believed to result in protein adsorption resistance have included i) steric exclusion arising from the compression of longer chains and ii) grafting density contribution which may provide shielding from the underlying material. Recent studies have suggested that PEG interaction with water may also play a role in its ability to resist protein adsorption suggesting that steric exclusion may not be the only mechanism occurring during PEG/protein interactions. Star-shaped PEG polymers have been utilized in protein adsorption studies due to their high PEG segment concentration, which allows to increase the PEG chain grafting density compared to that achieved with linear PEG chains. Most studies that have investigated the interactions of tethered linear and star-shaped PEG layers with proteins have considered linear PEG molecules with molecular weights several orders of magnitude smaller than those considered for star-shaped PEG molecules (i.e. 10 000 g/mol vs. 200 000 g/mol, respectively). Additionally, the star-shaped PEG molecules which have been considered in the literature had up to ~70 arms and were therefore modeled by hard-sphere like structures and low chain densities near the surface due to steric hindrance. This resulted in some difficulties to achieve grafted PEG chain overlap for star molecules. Here, triethoxysilane end-functionalized linear PEG molecules have been synthesized and utilized to form star-shaped PEG derivatives based on ethoxy hydrolysis and condensation reactions. This resulted in PEG stars with up to ~4 arms, which were found to result in grafted star-shaped PEG chains with significant chain overlap. Linear PEG derivatives were synthesized so that their molecular weight would match the overall molecular weight of the star-shaped PEG molecules. These 2 PEG molecular architectures were covalently self-assembled to hydroxylated silicon wafers and the thickness, grafting density, and conformation of these films were studied. The adsorption of human albumin (serum protein) on linear and star-shaped PEG films was compared to that obtained on control samples, i.e. uncoated silicon wafers. Both film architectures were found to significantly lower albumin adsorption. / Ph. D.