W. Grant McGimpsey

Photocurrent generation in noncovalently assembled multilayered thin films.

Multilayered photocurrent generating thin films were fabricated by templated noncovalent assembly via stepwise assembly of molecular components. Each of films I-IV contained an underlying self-assembled monolayer (SAM) consisting of an alkanethiol linked covalently to a 2,6-dicarboxypyridine ligand that served as a binding site for attaching additional molecular components. The SAM subsequently was functionalized by sequential deposition of Cu(II), Co(II), or Fe(III) ions followed by a variety of substituted 2,6-dicarboxypyridine ligands as a means to incorporate one or more layers of pyrene chromophores into the film. The films were characterized by contact angle measurements, ellipsometry, grazing incidence IR, cyclic voltammetry, and impedance spectroscopy after deposition of each layer, confirming the formation of ordered, stable layers. Following incorporation into a three-electrode system, photoexcitation resulted in the generation of a cathodic photocurrent in the presence of methyl viologen and an anodic photocurrent in the presence of triethanolamine. Using this strategy, systems were fabricated that produced up to 89 nA/cm(2) of reproducible photocurrent.

A multilayered approach to complex surface patterning.

A method for developing complex nanopatterns on surfaces has been developed by combining self-assembly, photolabile protecting groups, and multilayered films. An o-nitrobenzyl protecting group has been incorporated into molecular level films utilizing thiol-gold interactions. When the o-nitrobenzyl group is cleaved by ultraviolet light, a carboxylic acid terminated layer remains on the surface and is available for activation and further functionalization through amide bond formation. Using this method, multilayered films have been constructed and characterized by contact angle goniometry, cyclic voltammetry, grazing incidence infrared spectroscopy, and X-ray photoelectron spectroscopy measurements. Complex surface patterns can be achieved by creating a surface array using a photomask and then further functionalizing the irradiated area through covalent coupling. Fluorophores were attached to the deprotected regions, providing visual evidence of surface patterning using fluorescence microscopy. This approach is universal to bind moieties containing free amine groups at defined regions across a surface, allowing for the development of films with complex chemical and physicochemical properties.

Immobilization of Acetylcholinesterase in Lipid Membranes Deposited on Self-Assembled Monolayers

Human red blood cell acetylcholinesterase was incorporated into planar lipid membranes deposited on alkanethiol self-assembled monolayers (SAMs) on gold substrates. Activity of the protein in the membrane was detected with a standard photometric assay and was determined to be similar to the protein in detergent solution or incorporated in lipid vesicles. Monolayer and bilayer lipid membranes were generated by fusing liposomes to hydrophobic and hydrophilic SAMs, respectively. Liposomes were formed by the injection method using the lipid dimyristoylphosphatidylcholine (DMPC). The formation of alkanethiol SAMs and lipid monolayers on SAMs was confirmed by sessile drop goniometry, ellipsometry, and electrochemical impedance spectroscopy. In this work, we report acetylcholinesterase immobilization in lipid membranes deposited on SAMs formed on the gold surface and compare its activity to enzyme in solution.