Advances in functional assemblies for regenerative medicine

The ability to synthesise bioresponsive systems and selectively active biochemistries using polymer-based materials with supramolecular features has led to a surge in research interest directed towards their development as next generation biomaterials for drug delivery, medical device design and tissue engineering

Single Electron Transistors

Contains description of one research project and a list of publications.Joint Services Electronics Program Contract DAAL03-92-C-0001National Science Foundation Grant ECS 88-13250National Science Foundation Grant ECS 92-0342

BioWires: Conductive DNA Nanowires in a Computationally-Optimized, Synthetic Biological Platform for Nanoelectronic Fabrication

DNA is an ideal template for a biological nanowire-it has a linear structure several atoms thick; it possesses addressable nucleobase geometry that can be precisely defined; and it is massively scalable into branched networks. Until now, the drawback of DNA as a conducting nanowire been, simply put, its low conductance. To address this deficiency, we extensively characterize a chemical variant of canonical DNA that exploits the affinity of natural cytosine bases for silver ions. We successfully construct chains of single silver ions inside double-stranded DNA, confirm the basic dC-Ag+-dC bond geometry and kinetics, and show length-tunability dependent on mismatch distribution, ion availability and enzyme activity. An analysis of the absorbance spectra of natural DNA and silver-binding, poly-cytosine DNA demonstrates the heightened thermostability of the ion chain and its resistance to aqueous stresses such as precipitation, dialysis and forced reduction. These chemically critical traits lend themselves to an increase in electrical conductivity of over an order of magnitude for 11-base silver-paired duplexes over natural strands when assayed by STM break junction. We further construct and implement a genetic pathway in the E. coli bacterium for the biosynthesis of highly ionizable DNA sequences. Toward future circuits, we construct a model of transcription network architectures to determine the most efficient and robust connectivity for cell-based fabrication, and we perform sequence optimization with a genetic algorithm to identify oligonucleotides robust to changes in the base-pairing energy landscape. We propose that this system will serve as a synthetic biological fabrication platform for more complex DNA nanotechnology and nanoelectronics with applications to deep space and low resource environments

Fabrication of Artificial Graphene in a GaAs Quantum Heterostructure

The unusual electronic properties of graphene, which are a direct consequence of its two-dimensional (2D) honeycomb lattice, have attracted a great deal of attention in recent years. Creation of artificial lattices that recreate graphene's honeycomb topology, known as artificial graphene, can facilitate the investigation of graphene-like phenomena, such as the existence of massless Dirac fermions, in a tunable system. In this work, we present the fabrication of artificial graphene in an ultra-high quality GaAs/AlGaAs quantum well, with lattice period as small as 50 nm, the smallest reported so far for this type of system. Electron-beam lithography is used to define an etch mask with honeycomb geometry on the surface of the sample, and different methodologies are compared and discussed. An optimized anisotropic reactive ion etching process is developed to transfer the pattern into the AlGaAs layer and create the artificial graphene. The achievement of such high-resolution artificial graphene should allow the observation for the first time of massless Dirac fermions in an engineered semiconductor.Comment: 13 pages text, 8 figures, plus reference

Responsive biomaterials:advances in materials based on shape-memory polymers

Shape-memory polymers (SMPs) are morphologically responsive materials with potential for a variety of biomedical applications, particularly as devices for minimally invasive surgery and the delivery of therapeutics and cells for tissue engineering. A brief introduction to SMPs is followed by a discussion of the current progress toward the development of SMP-based biomaterials for clinically relevant biomedical applications

Single Electron Transistors

Contains description of one research project.Joint Services Electronics Program Contract DAAL03-89-C-0001Joint Services Electronics Program Contract DAAL03-92-C-0001National Science Foundation Grant ECS 88-1325

Single Electron Transistors

Contains description of one research project.Joint Services Electronics Program Contract DAAL03-89-C-0001National Science Foundation Grant ECS 88-1325

Artificial Atoms

Contains research goals and objectives, reports on six research projects and a list of publications.Joint Services Electronics Program Contract DAAL03-92-C-0001Joint Services Electronics Program Grant DAAH04-95-1-0038National Science Foundation Grant ECS 92-0342

Ultralow Temperature Studies of Nanometer Size Semiconductor Devices

Contains a description on one research project.Joint Services Electronics Program DAAL03-89-C-000

Improved Glass Surface Passivation for Single-Molecule Nanoarrays

Single-molecule fluorescence techniques provide a critical tool for probing biomolecular and cellular interactions with unprecedented resolution and precision. Unfortunately, many of these techniques are hindered by a common problem, namely, the nonspecific adsorption of target biomolecules. This issue is mostly addressed by passivating the glass surfaces with a poly­(ethylene glycol) (PEG) brush. This is effective only at low concentrations of the probe molecule because there are defects inherent to polymer brushes formed on glass coverslips due to the presence of surface impurities. Tween-20, a detergent, is a promising alternative that can improve surface passivation, but it is incompatible with living cells, and it also possesses limited selectivity for glass background over metallic nanoparticles, which are frequently used as anchors for the probe molecules. To address these issues, we have developed a more versatile method to improve the PEG passivation. A thin film of hydrogen silsesquioxane (HSQ) is spin-coated and thermally cured on glass coverslips in order to cover the surface impurities. This minimizes the formation of PEG defects and reduces nonspecific adsorption, resulting in an improvement comparable to Tween-20 treatment. This approach was applied to single-molecule nanoarrays of streptavidin bound to AuPd nanodots patterned by e-beam lithography (EBL). The fluorescence signal to background ratio (SBR) on HSQ-coated glass was improved by ∼4-fold as compared to PEG directly on glass. This improvement enables direct imaging of ordered arrays of single molecules anchored to lithographically patterned arrays of metallic nanodots