Research into the use of DNA molecules as building blocks for nanoelectronics as well as nanosystems continues. Recently, our group has reported significant electrical conductivity in λ-DNA through direct and in-direct measurements involving high-aspect ratio electrodes that eliminate the effect of the substrate. Our results demonstrate that, at moderate to high frequencies, λ-DNA molecular wires show low impedance. In addition, to prove that the conductivity is indeed from DNA bridge, we studied the effect of temperature and UV irradiation on DNA molecular wires. The temperature results indicate that λ-DNA molecular wires have differing impedance responses at two temperature regimes: impedance increases between 4°C - 40°C, then decreases from 40°C to the melting point (~110°C) at which λ-DNA denatures resulting in a complete loss of current transduction. This hysteric and bi-model behavior makes DNA a candidate for nanoelectronics components such as thermal transistors and switches. The data from UV exposure experiments indicates decreased conductivity of λ-DNA molecular wires after UV exposure, due to damage to GC base pairs and phosphate groups reducing the path available for both charge hopping and short-range electron tunneling mechanisms. The lessons learned from these conductivity experiments along with our knowledge of different charge transport mechanisms within DNA can be applied to the design of synthetic molecular wires for the construction of nanoelectronic devices.
Polyvinylidene difluoride (PVDF) is a piezoelectric polymer with a low-cost, high flexibility and biocompatibility that is
suitable for various energy conversion applications between the electrical and mechanical forms of energy. One of the
novel techniques to create PVDF fibers is electro-spinning. In the present work, the above technique has been applied to
develop electro-spun thin-film based on PVDF with the use of high electric field and a high-frequency mechanical
vibratory motion as an electro-spinning setup. The high-frequency vibratory motion is used to create effective fluid
viscous forces to achieve a localized fluid spreading and thinning behavior of extremely thin polymer fiber solution.
We report on the production of thin films of titanium nickelides (TiNi) shape memory alloy, prepared via Current-
Activated Tip-based Sintering (CATS), a new localized powder sintering process. Mechanically alloyed equi-atomic
TiNi powder was tip-sintered at varying currents and cycles of current exposure time. The effect of processing
conditions on the developed localized microstructure and properties are discussed. The number of cycles of current
exposure time and current magnitude were studied. Both number of cycles and current magnitude in general result in an
increase micro-hardness and a reduction in residual porosity in the sintered thin films.
Molecular diagnostic applications for pathogen detections require the ability to separate pathogens such as
bacteria, viruses, etc., from a biological sample of blood or saliva. Over the past several years,
conventional two-dimensional active microarrays have been used with success for the manipulation of
biomolecules including DNA. However, they have a major drawback of inability to process relatively 'largevolume'
samples useful in infectious disease diagnostics applications. This paper presents an active
microarray of three-dimensional carbon electrodes that exploits electrokinetic forces for transport,
accumulation, and hybridization of charged bio-molecules with an added advantage of large volume
capability. Tall 3-dimensional carbon microelectrode posts are fabricated using C-MEMS (Carbon MEMS)
technology that is emerging as a very exciting research area since carbon has fascinating physical,
chemical, mechanical and electrical properties in addition to its low cost. The chip fabricated using CMEMS
technology is packaged and its efficiency of separation and accumulation of charged particle
established by manipulating negatively charged polycarboxylate 2 μm beads in 50 mM histidine buffer.
This paper compares frequency measurements in lead magnesium niobate-lead titanate (PMN-PT) resonators with
conventional quartz crystal microbalance (QCM) resonators when exposed to acetone vapors under identical test
conditions. A pumpless mechanism for driving acetone vapors by convection force was developed in our experimental
setup. The frequency shift recorded in response to acetone vapor exposure for the PMN-PT resonator was more than
10,000 times larger than for the QCM resonator. Our experimental results reinforce the notion that PMN-PT resonators
could be a superior replacement for QCM resonators in a variety of biosensor applications. The experimental setup
heated water to produce acetone vapors, a volatile organic chemical, which were delivered to a sensing chamber to
interact with the sensing unit. Chemical vapors were driven toward the sensing unit and circulated through the system via
a pumpless mechanism by the principle of convection. Both types of resonators displayed a change in frequency as
acetone vapors were applied, but PMN-PT showed a more significant change by several orders of magnitude.
Batteries based on three dimensional microstructures are expected to offer significant advantages in comparison to conventional two dimensional batteries. One of the key elements for creating new types of 3D microbatteries is fabricating high-aspect-ratio carbon structures. Our efforts on building positive photoresist structures include: (1) casting photoresist in 3D molds made by DRIE before pyrolysis; (2) multi-exposure and multi-developing processes, and (3) using embedded masks in multi-layer photoresists. Another effort is the fabrication of high-aspect-ratio carbon structures using negative photoresist. We manufactured high-aspect-ratio (~10:1) carbon posts by pyrolysis from negative photoresists in a simple one-step process. Simulation results showed that current density is strongly influenced by the biasing pattern and the geometry of the electrodes themselves. Current density (and therefore power density) is stronger at the edge of electrodes-implying that closer spacing of the electrodes will provide a denser current concentration. Electrochemical tests demonstrate that these C-MEMS electrodes can be charged/discharged with Li. A C-MEMS battery approach has the potential to solve both manufacturing and materials problems simultaneously.
We describe a micro electro-optical DNA array sensor whose main features are that it is rapid, sensitive, highly accurate and capable of detecting more than one analyte. These features are the consequence of electronic control of three key elements of DNA assays, namely: concentration of the target molecules at the analysis sites, hybridization of the DNA targets to capture probes and discrimination of complementary DNA from non-complementary DNA. The assays are monitored using a scanning confocal optical platform for fluorescence detection. A finite-element based computational model for determining electric field distribution at the biochip electrode array and electrophoretic transport of DNA species is built and analyzed. Comparison of theoretical results for electrophoretic DNA accumulation with those obtained from experiments and a simple analytical model is presented.
In this work, the mechanical design and optimization of high-sensitivity piezoresistive cantilevers used for detecting changes in surface stresses due to binding and hybridization of biomolecules on the surface of the cantilever is investigated. The silicon-based cantilevers are typically of a micron order thickness doped with boron to introduce piezoresistivity. Microcantilever beams can be built as micro-mechanical arrays which could provide a basis for developing devices capable of performing multi-plexed, low-cost genomic and proteomic analyses. This paper provides several design solutions in optimizing the cantilever mechanical design to address the sensitivity required when approaching recognition of single base pairing of DNA molecules. The sensitivity of such piezoresistive cantilevers to the chemo-mechanical stress induced currents depends not only on the cantilever geometric properties, such as depth and width but also on the depth of the piezo layer (dopant) and its doping characteristics. It is often an expensive exercise to determine the optimum design parameters for increased sensitivity, particularly the dopant characteristics for such MEMS devices. A managed solution or parametric solution algorithm based on a finite element simulation is used to help determine optimum location and depth of this piezoresistive layer in the cantilever that maximizes the piezoresistor signals. Further, novel approaches for increasing the sensitivity of piezoresistive cantilevers through selected structural discontinuities are discussed.