34 research outputs found
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