Prototype reflectivity analyses of hydrogen storage levels in single-walled carbon nanotubes.

A prototype case study is presented that examines the level of hydrogen content in H-SWNTs using the Surface Plasmon Resonance technique. The damping effect and the angular shift in the resonance minimum of an SWNT-gold interface due to the presence of hydrogen is analyzed using a parametric model, which is based on the concept of an effective permittivity. The new approach provides for a non-invasive analysis of the level of hydrogen content in H-SWNTs and is potentially extendable to other carbon-based hydrogen storage materials.

Surface patterning of polychloromethylstyrene films.

We describe and characterize a simple process for the fabrication of patterned materials on polychloromethylstyrene thin film surfaces under ambient conditions. Patterned deep UV exposure (approximately 60 mJcm(-2), 193 nm) efficiently oxidizes the surface C-Cl bonds of the polymer film, producing an aldehyde species as the major photoproduct. Reductive amination in the presence of ammonium ion and cyanoborohydride reductant selectively converts the aldehyde into an alkylamine, which leads to an amine reactivity template on the film surface. The amines formed are sufficiently reactive to selectively and covalently bind fluorescent dye or electroless Ni metal to the template, which results in negative tone features with micron-scale resolutions (mask limited) in each case. Spectroscopic characterizations of the polymer surface following the photochemical transformation, reductive amination, and grafting steps are presented in support of the process. A key advantage of the method is the use of safe solvents, such as water or simple alcohols, to effect the reductive amination and grafting reactions. This approach mitigates waste disposal and associated environmental concerns, increasing the attractiveness of our method for use with high-throughput track-line processing equipment.

Fabrication of patterned DNA surfaces.

Two photolithographic methods are described for the formation of patterned single or multiple DNA species on SiO2 substrates. In the first approach, substrates are treated with a photochemically labile organosilane monolayer film. Irradiation of these surfaces with patterned deep UV (193 nm) light results in patterned chemically reactive groups which are then reacted with heterobifunctional crosslinking molecules. Covalent attachment of modified synthetic DNA oligomers to the crosslinker results in stable DNA patterns. Alternatively, a photoresist is spin-coated over a silane film which had been previously modified with the heterobifunctional crosslinker. Upon patterned irradiation and subsequent development, the underlying crosslinker-modified layer is revealed, and is then reacted with a chemically modified DNA. Feature dimensions to 1 micron are observed when a single fluorescent DNA is attached to the surface. By performing sequential exposures, we have successfully immobilized two distinguishable DNA oligomers on a single surface. Synthetic DNA immobilized in this manner retains the ability to hybridize to its complementary strand, suggesting that these approaches may find utility in the development of miniaturized DNA-based biosensors.

Fabrication of surfaces resistant to protein adsorption and application to two-dimensional protein patterning.

Proteins were attached in defined geometric patterns on a surface. A prerequisite to making a pattern of proteins is generation of surfaces resistant to nonspecific protein adsorption. This was accomplished via oxidation of the thiol terminus of an organosilane self-assembled monolayer film by deep ultraviolet (DUV) irradiation. The resultant surface exhibited marked resistance to protein adsorption. Using a mask to protect regions of the silanized surface from irradiation, proteins were selectively adsorbed or attached via covalent linkage at locations protected from the DUV light. Antibodies immobilized in patterns using this procedure retained their antigen-binding capability. Thus chemistry and DUV lithography were combined to create patterns of active biomolecules which could be used in the microfabrication of electronic devices and biosensors.

Deep UV photochemistry of chemisorbed monolayers: patterned coplanar molecular assemblies.

Deep ultraviolet (UV) irradiation is shown to modify organosilane self-assembled monolayer (SAM) films by a photocleavage mechanism, which renders the surface amenable to further SAM modification. Patterned UV exposure creates alternating regions of intact SAM film and hydrophilic, reactive sites. The exposed regions can undergo a second chemisorption reaction to produce an assembly of SAMs in the same molecular plane with similar substrate attachment chemistry. The UV-patterned films are used as a template for selective buildup of fluorophores, metals, and biological cells.