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ABSTRACT: In oxygenic plants, photons are captured with high quantum efficiency by two specialized reaction centers (RC) called Photosystem I (PS I) and Photosystem II (PS II). The captured photon triggers rapid charge separation and the photon energy is converted into an electrostatic potential across the nanometer-scale ( ~ 6 nm) reaction centers. The exogenous photovoltages from a single PS I RC have been previously measured using the technique of Kelvin force probe microscopy (KFM). However, biomolecular photovoltaic applications require two-terminal devices. This paper presents for the first time, a micro-device for detection and characterization of isolated PS I RCs. The device is based on an AlGaN/GaN high electron mobility transistor (HEMT) structure. AlGaN/GaN HEMTs show high current throughputs and greater sensitivity to surface charges compared to other field-effect devices. PS I complexes immobilized on the floating gate of AlGaN/GaN HEMTs resulted in significant changes in the device characteristics under illumination. An analytical model has been developed to estimate the RCs of a major orientation on the functionalized gate surface of the HEMTs.
IEEE Transactions on NanoBioscience 10/2011; · 1.28 Impact Factor
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ABSTRACT: This paper describes a highly accurate dose control circuit (DCC) for the emission of a desired number of electrons from vertically aligned carbon nanofibers (VACNFs) in a massively parallel maskless e-beam lithography system. The parasitic components within the VACNF device cause a premature termination of the electron emission, resulting in underexposure of the photoresist. In this paper, we compensate for the effects of the parasitic components and noise while reducing the area of the chip and achieving a precise count of emitted electrons from the VACNFs to obtain the optimum dose for the e-beam lithography.
IEEE Transactions on Instrumentation and Measurement 05/2011; · 1.21 Impact Factor
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ABSTRACT: The incorporation of nanostructured materials as functional elements of microscale devices can enhance the application of these systems for biological interfacing. Vertically aligned carbon nanofibers (VACNFs) have been applied as highly spatially resolved electrodes in electrophysiological interfacing to tissue. Further, their high aspect ratio enables them to penetrate into cells of tissue matrices for intracellular molecular manipulation. To date, studies investigating the interactions of VACNFs with cellular processes have been limited by the use of opaque substrate materials (predominantly silicon) which interferes with optical imaging. In this paper, we discuss improved methods for fabrication of VACNF-based devices on transparent, fused silica substrates and provide data regarding the application of these devices for multimodal neuronal interfacing, including both electrophysiological and genetic manipulation of tissue.
Biomedical Sciences and Engineering Conference (BSEC), 2010; 06/2010
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ABSTRACT: Optimizing wavelength selection for monitoring perfusion during liver transplant requires an in-depth characterization of liver optical properties. With these, the impact of liver absorption and scattering properties can be investigated to select optimal wavelengths for perfusion monitoring. To accomplish this, we are developing a single integrating-sphere-based technique using a unique spatially resolved diffuse reflectance system for multispectral optical properties determination for thick samples. We report early results using a monochromatic source to measure the optical properties of well characterized tissue phantoms made from polystyrene spheres and Trypan blue. The presented results demonstrate the feasibility of using this unique system to measure optical properties of tissue phantoms. We are currently in the process of implementing an automated Levenberg-Marquardt diffuse-reflectance-profile fitting algorithm to enable near realtime robust computation of sample optical properties. Future work will focus on the incorporation of multispectral capability to provide needed data to facilitate development of more realistic liver tissue phantoms.
Engineering in Medicine and Biology Society, 2009. EMBC 2009. Annual International Conference of the IEEE; 10/2009
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ABSTRACT: The development and refinement of a microfluidic-based alginate bead generator system for bacterial encapsulation is presented. The resulting microgels have application for the encapsulation of single cells, and can allow for small scale, clonal expansion of thousands of isolated cells in parallel. PDMS based microfluidic chips were fabricated using conventional lithography techniques to produce both externally gelled and directly gelled alginate microspheres using a controlled, water-in-oil emulsion system. The production of directly gelled beads, formed by the in-chip mixing of aqueous alginate and calcium chloride solutions dispersed within an organic carrier flowstream is qualitatively compared to a system, which produces beads and relies on diffusion of a crosslinking agent from the carrier fluid to cause gelation (external gelation). While the direct gelation scheme allows the use of biocompatible oils as the organic carrier, it also has a detrimental effect on device stability often resulting in clogging and gel-streaming at the microfluidic interface of these solutions. A design for the continuous production of directly gelled beads was evaluated in terms of the threshold flow conditions and reagent concentrations that did not result in clogging or streaming. Monodisperse alginate microgels of 30 mum diameter were produced at frequencies of over 500 beads per second. The beads could be completely dispersed into aqueous media using an off-chip washing protocol to remove the organic phase. The microgels effectively encapsulated individual or small numbers of GFP-expressing Escherichia. coli, which could be subsequently clonally expanded. The described microfluidic platform is a robust front-end sample preparation technology that shows strong potential for use in drug delivery systems, biosensors, and other cell-based microcompartmentalization applications. The co-culturing of microbial colonies in a large population of alginate beads will allow for functional -
sorting and genetic analyses at the single cell level.
Biomedical Science & Engineering Conference, 2009. BSEC 2009. First Annual ORNL; 04/2009
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ABSTRACT: Optimizing wavelength selection for monitoring perfusion during liver transplant requires an in-depth characterization of liver optical properties. With these, the impact of liver absorption and scattering properties can be investigated to select optimal wavelengths for perfusion monitoring. To accomplish this, we are developing a single integrating-sphere-based technique using a unique spatially resolved diffuse reflectance system for multispectral optical properties determination for thick samples. We report early results using a monochromatic source to measure the optical properties of well characterized tissue phantoms made from polystyrene spheres and Trypan blue. The presented results demonstrate the feasibility of using this unique system to measure optical properties of tissue phantoms. We are currently in the process of implementing an automated Levenberg-Marquardt diffuse-reflectance-profile fitting algorithm to enable near realtime robust computation of sample optical properties. Future work will focus on the incorporation of multispectral capability to provide needed data to facilitate development of more realistic liver tissue phantoms.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2009; 2009:6565-8.
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ABSTRACT: A current mode multi-channel ADC has been designed in a 0.5-mum bulk CMOS process. The ADC is capable of supporting multiple channels with an input current range of 10 muA to 80 muA. The main blocks in the ADC include a current ramp generator, multiple current comparators and a 12-bit Gray code counter. Simulation results are presented that predict 12-bit resolution, sampling rates up to 20 Ksps, and a per-channel power consumption of less than 2 mW using a Wilkinson architecture with 8 channels.
Signals and Electronic Systems, 2008. ICSES '08. International Conference on; 10/2008
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ABSTRACT: A multichannel low power analog-to-digital converter (ADC) designed, fabricated and tested in 0.5-mum Silicon Germanium BiCMOS process is reported. The 12-bit ADC features 8 input channels, each having a 10-Ksps sampling rate and an input voltage range of 1.2 V. The ADC architecture, comprised of a ramp generator, comparators, and a Gray code counter, is discussed along with design details of the primary blocks. Measurement data shows a differential nonlinearity of less than 0.5 LSB and an approximate accuracy of 10 bits.
Circuits and Systems, 2008. MWSCAS 2008. 51st Midwest Symposium on; 09/2008
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C. Ulaganathan,
N. Nambiar,
B. Prothro,
R. Greenwell,
S Chen,
B.J. Blalock,
C.L. Britton, M.N. Ericson,
H. Hoang,
R. Broughton,
K. Cornett,
G Fu,
H. A. Mantooth,
J.D. Cressler,
R. W. Berger
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ABSTRACT: A instrumentation channel has been designed, implemented and tested in a 0.5-μm SiGe BiCMOS process. The circuit features a reconfigurable Wheatstone bridge network that interfaces a range of external sensors to signal processing circuits. Also, analog sampling has been implemented in the channel using a flying capacitor configuration. Measurement results show the instrumentation channel supports input signals up to 200Hz.
Circuits and Systems, 2008. MWSCAS 2008. 51st Midwest Symposium on; 09/2008
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S.A. Eliza,
S.K. Islam,
T. Rahman,
R. Vijayaraghavan,
T. Grundman,
B. Blalock,
S.J. Randolph,
L.R. Baylor,
T.S. Bigelow,
W.L. Gardner, M.N. Ericson,
J.A. Moore
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ABSTRACT: Field emission (FE) of electrons from nanostructured graphitic carbon-based materials has been an area of intense investigation in recent years. Each field emitting device has control gates and an electron emitting cathode, which emits electron when a sufficient voltage is applied at the gate electrode. Recently, a technique for fabricating gated cathode structures that uses a single in situ grown vertically aligned carbon nanofiber (VACNF) as a FE element has been reported. This paper presents digitally addressable VACNFs for implementation of massively parallel maskless lithography.
Semiconductor Device Research Symposium, 2007 International; 01/2008
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ABSTRACT: This paper presents for the first time a micro-sensor for detecting Photosystem I (PS I) reaction centers. In oxygenic plants, photons are captured with high quantum efficiency by two specialized reaction centers, Photosystems I and II (PS I and PS II). Photon capture triggers rapid charge separation and the conversion of light energy into an electric voltage across the nanometer-scale (~6 nm) reaction centers. AlGaN/GaN based high electron mobility transistors (HEMTs) show high current throughputs and greater sensitivity to surface charges. PS I molecules were chemically immobilized on the HEMT device and significant changes in the transistor characteristics were noticed. With zero gate bias and 5 V at drain terminal, drain current changes by about 5 mA for 6muL drop of PS I solution. The difference between light and dark measurements is ~0.8 mA. Test results demonstrate that this approach is a potential candidate for detection and characterization of biomolecular photodiodes -PS I reaction centers.
Sensors, 2007 IEEE; 12/2007
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ABSTRACT: We present a discussion of the use of vertically- aligned carbon nanofibers (VACNFs) as nanoscale elements that directly interface to biological whole-cell systems. VACNFs are compatible with a large subset of microfabrication processes, thereby enabling their incorporation into mesoscale hybrid systems that provide addressability of the VACNFs as either bulk electrode material, or as individually addressed nanoelectrodes. These VACNF devices are compatible with cell cultures, and electrochemical addressability of nanofibers can be maintained for extended periods within cell cultures. We present results that demonstrate possible use of VACNF devices as electrical and genetic substrates for tissue scaffolding applications.
Engineering in Medicine and Biology Society, 2007. EMBS 2007. 29th Annual International Conference of the IEEE; 09/2007
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ABSTRACT: The digital electrostatically focused e-beam array direct-write lithography (DEAL) concept is currently under development at Oak Ridge National Laboratory (ORNL) . This concept incorporates a digitally addressable field-emission array (DAFEA) employing electrostatic focusing with an integrated dose control circuit to function as the write head for an e-beam lithography tool. Electron beams from each emitter cathode are individually addressable, thus enabling parallel patterning of a target substrate by multiple electron sources.
Vacuum Nanoelectronics Conference, 2007. IVNC. IEEE 20th International; 08/2007
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ABSTRACT: We present a discussion of the use of vertically-aligned carbon nanofibers (VACNFs) as nanoscale elements that directly interface to biological whole-cell systems. VACNFs are compatible with a large subset of microfabrication processes, thereby enabling their incorporation into mesoscale hybrid systems that provide addressability of the VACNFs as either bulk electrode material, or as individually addressed nanoelectrodes. These VACNF devices are compatible with cell cultures, and electrochemical addressability of nanofibers can be maintained for extended periods within cell cultures. We present results that demonstrate possible use of VACNF devices as electrical and genetic substrates for tissue scaffolding applications.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2007; 2007:5381-3.
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Advanced Materials 06/2006; 18(13):1689 - 1694. · 13.88 Impact Factor
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ABSTRACT: In this paper, an adaptive filtering algorithm to separate signals due to perfusion and oxygenation has been developed using an 810-nm source, in addition to 660-nm and 940-nm sources, as an internal reference due to its limited oxygen sensitivity. The newly developed algorithm was tested using Monte Carlo simulated data to prove the effectiveness of the 810-nm reference and adaptive algorithm. Following the simulation, an in vitro model was developed to test the algorithm that used a blood flow through system wrapped with tissue. The system had the ability to isolate the effects of perfusion and oxygenation and the algorithm accurately captured the changes in these signals with reliable consistency. Using the serosal surface of the swine jejunum, in vivo data was also taken to analyze the algorithms response to fluctuating perfusion levels like that seen in hemorrhaging or failing transplants. The algorithm was able to extract the perfusion information from the oxygenation information in this in vivo study. Overall, it was shown that an adaptive filtering algorithm using an 810-nm reference has provided a means to separate oxygenation and perfusion.
IEEE Transactions on Biomedical Engineering 01/2006; · 2.28 Impact Factor
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ABSTRACT: A wavelet-based signal processing technique was employed to improve an implantable blood perfusion monitoring system. Data was acquired from both in vitro and in vivo sources: a perfusion model and the proximal jejunum of an adult pig. Results showed that wavelet analysis could isolate perfusion signals from raw, periodic, in vitro data as well as fast Fourier transform (FFT) methods. However, for the quasi-periodic in vivo data segments, wavelet analysis provided more consistent results than the FFT analysis for data segments of 50, 10, and 5 s in length. Wavelet analysis has thus been shown to require less data points for quasi-periodic data than FFT analysis making it a good choice for an indwelling perfusion monitor where power consumption and reaction time are paramount.
IEEE Transactions on Biomedical Engineering 08/2005; · 2.28 Impact Factor
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ABSTRACT: In designing an implantable sensor for perfusion monitoring of transplant organs the ability of the sensor to gather perfusion information with limited power consumption and in near real time is paramount. The following work was performed to provide a processing method that is able to predict perfusion and oxygenation change within the blood flowing through a transplanted organ. For this application, an autocorrelation-based algorithm was used to reduce the acquisition time required for fast Fourier transform (FFT) analysis while retaining the accuracy inherent to FFT analysis. In order to provide data proving that the developed method is able to predict perfusion as accurately as FFT two experiments were developed isolating both periodic and quasi-periodic cardiac frequencies. It was shown that the autocorrelation-based method was able to perform comparably with FFT (limited to a sampling frequency of 300 Hz) and maintain accuracy down to acquisition times as low as 4 s in length.
IEEE Transactions on Biomedical Engineering 08/2005; · 2.28 Impact Factor
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ABSTRACT: A custom simulation tool that combines HSPICE and MATLAB to enable time-domain noise analysis is reported. The simulation technique is based on computing the statistics of a random process by ensemble averaging and is applicable to both linear time-invariant (LTI) and linear time-variant (LTV) systems. MATLAB is used to generate a set of representative noise signals, which are imported into HSPICE for simulation. Once the simulations are complete the results are read back into MATLAB and ensemble statistics are calculated. The MATLAB-generated noise signals have a user-defined white-noise floor and flicker-noise corner frequency and thus are suitable for modeling a wide variety of electronic components, including CMOS transistors and resistors. Simulation results of the time-dependent output noise of a gated integrator and the timing resolution of a gated integrator/comparator detector are presented to highlight both the utility and the versatility of the tool.
IEEE Transactions on Nuclear Science 07/2005; · 1.45 Impact Factor
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ABSTRACT: A summary of measured small-signal parameters and low frequency noise characterized over temperature is presented for N- and P- MOSFETs fabricated in a partially depleted SOI 0.8 mum process. Small-signal dc parameters critical in analog circuit design are reported including device transconductance efficiency (g<sub>m</sub>/I<sub>d</sub>), output resistance (r<sub>ds</sub>), and threshold voltage (V<sub>t</sub>). These parameters are summarized as a function of both gate length (0.8mum, 2.0mum, 5.0mum, and 20mum) and temperature (20deg to 300degC). Noise characterization of these devices is also presented with an emphasis on flicker noise over temperature (20deg to 250degC). Data is presented in terms of both drain current and inversion coefficient, where appropriate. Use of this information provides the designer with an excellent tool for estimating analog circuit performance in applications where wide temperature range performance is required
Aerospace Conference, 2005 IEEE; 04/2005
