M. M. Miller

The BARC biosensor applied to the detection of biological warfare agents.

The Bead ARray Counter (BARC) is a multi-analyte biosensor that uses DNA hybridization, magnetic microbeads, and giant magnetoresistive (GMR) sensors to detect and identify biological warfare agents. The current prototype is a table-top instrument consisting of a microfabricated chip (solid substrate) with an array of GMR sensors, a chip carrier board with electronics for lock-in detection, a fluidics cell and cartridge, and an electromagnet. DNA probes are patterned onto the solid substrate chip directly above the GMR sensors, and sample analyte containing complementary DNA hybridizes with the probes on the surface. Labeled, micron-sized magnetic beads are then injected that specifically bind to the sample DNA. A magnetic field is applied, removing any beads that are not specifically bound to the surface. The beads remaining on the surface are detected by the GMR sensors, and the intensity and location of the signal indicate the concentration and identity of pathogens present in the sample. The current BARC chip contains a 64-element sensor array, however, with recent advances in magnetoresistive technology, chips with millions of these GMR sensors will soon be commercially available, allowing simultaneous detection of thousands of analytes. Because each GMR sensor is capable of detecting a single magnetic bead, in theory, the BARC biosensor should be able to detect the presence of a single analyte molecule.

Detection of a micron-sized magnetic sphere using a ring-shaped anisotropic magnetoresistance-based sensor: A model for a magnetoresistance-based biosensor

We have fabricated micron-sized NiFe ring-shaped sensors that show localized detection of the radial component of the dipolar fringing field from a single, partially magnetized, micron-sized NiFe sphere. Specifically, the anisotropic magnetoresistance response to this fringing field is strongly peaked when the sphere is directly above the center of the ring and rapidly decreases to zero when the sphere is outside the ring. Such a device is a model system for a proposed biosensor array architecture that could operate similarly to high-density random access computer memory.

A DNA array sensor utilizing magnetic microbeads and magnetoelectronic detection

We describe a multi-analyte biosensor that uses magnetic microbeads as labels to detect DNA hybridization on a micro-fabricated chip. The beads are detected by giant magnetoresistance (GMR) magnetoelectronic sensors embedded in the chip. The prototype device is a tabletop unit containing electronics, a chip carrier with a microfluidic flow cell, and a compact electromagnet and is capable of simultaneous detection of eight different analytes.

Hybrid Hall effect device

A novel magnetoelectronic device incorporating a single microstructured ferromagnetic film and a micron scale Hall cross was fabricated and characterized at room temperature. Magnetic fringe fields from the edge of the ferromagnet generate a Hall voltage in a thin film semiconducting Hall bar. The sign of the fringe field, as well as the sign of the output Hall voltage, is switched by reversing the magnetization of the ferromagnet. This new device has excellent output characteristics and scaling properties, and may find application as a magnetic field sensor, nonvolatile storage cell, or logic gate.

Determination of crystallite size in a magnetic nanocomposite using extended x-ray absorption fine structure

An extended x-ray absorption fine structure was collected for a soft magnetic material comprising very fine nanoscale crystallites of nickel within coarser iron matrix grains. Using a simple spherical model and the spectra of bulk standards, the nickel crystallite size was estimated. Comparison with transmission electron microscopy images confirms that this technique yields a size weighted toward smaller crystallites, whereas Scherrer analysis yields sizes weighted toward larger crystallites. The iron crystallite size was also estimated by this technique in order to ascertain the effect of a nonspherical morphology. This technique shows promise for in situ analyses of materials containing nanoscale crystallites and as a complement to Scherrer analyses.

A New Methodology for Quantitative LSPR Biosensing and Imaging

A new quantitative analysis methodology for localized surface plasmon resonance (LSPR) biosensing which determines surface-receptor fractional occupancy, as well as an LSPR imaging technique for the spatiotemporal mapping of binding events, is presented. Electron beam nanolithography was used to fabricate 20 × 20 arrays of gold nanostructures atop glass coverslips. A single biotinylated array was used to measure the association kinetics of neutravidin to the surface by spectroscopically determining the fractional occupancy as a function of time. By regenerating the same array, a reliable comparison of the kinetics could be made between control samples and neutravidin concentrations ranging from 1 μM to 50 nM. CCD-based imagery of the array, taken simultaneously with the spectroscopic measurements, reveals the binding of neutravidin to the surface as manifested by enhanced scattering over the majority of the resonance peak. The temporal resolution of the LSPR imaging technique was 200 ms and the spatial resolution was 8 μm(2).

Magnetoelectronic latching Boolean gate

Abstract We present a magnetoelectronic device family with the unique characteristic that the “family” is composed of a single device that can perform any of several Boolean functions, with the function dynamically determined during the operation by the manner in which the device is addressed. As the device operates in a latching mode, it also performs a nonvolatile storage function. Integration of logic and memory is achieved, so that memory and processing functions can be dynamically apportioned.

Evaluation of Methods for Measuring Particulate Matter Emissions from Gas Turbines

The project SAMPLE evaluated methods for measuring particle properties in the exhaust of aircraft engines with respect to the development of standardized operation procedures for particulate matter measurement in aviation industry. Filter-based off-line mass methods included gravimetry and chemical analysis of carbonaceous species by combustion methods. Online mass methods were based on light absorption measurement or used size distribution measurements obtained from an electrical mobility analyzer approach. Number concentrations were determined using different condensation particle counters (CPC). Total mass from filter-based methods balanced gravimetric mass within 8% error. Carbonaceous matter accounted for 70% of gravimetric mass while the remaining 30% were attributed to hydrated sulfate and noncarbonaceous organic matter fractions. Online methods were closely correlated over the entire range of emission levels studied in the tests. Elemental carbon from combustion methods and black carbon from optical methods deviated by maximum 5% with respect to mass for low to medium emission levels, whereas for high emission levels a systematic deviation between online methods and filter based methods was found which is attributed to sampling effects. CPC based instruments proved highly reproducible for number concentration measurements with a maximum interinstrument standard deviation of 7.5%.

Magnetism and structure of ZnxFe3−xO4 films processed via spin-spray deposition

Zn-ferrite films, ZnxFe3−xO4 where the Zn:Fe ratio ranges from 0.36 to 0.76, were grown on glass substrates using a spin spray technique. Films are shown using scanning electron microscopy and atomic force microscopy to be dense and granular with an average grain size ∼0.3 μm. X-ray diffraction indicates that the films are a Fd3m symmetry consistent with a pure spinel ferrite phase. The films’ coercive fields have a strong positive correlation with the film roughness indicating the dominance of a physical domain wall pinning mechanism. The films are smooth and magnetically soft near the ZnFe2O4 stoichiometry. All films, including those near the ZnFe2O4 stoichiometry, display ferrimagnetic behavior with compensation temperatures well above the bulk Neel temperature of 9.5 K; this is attributed to the cation disorder measured in the Zn cation distribution.

Factors affecting performance of NiO biased giant magnetoresistance structures

We have made spin‐valve structures of Permalloy/Cu/Co by sputtering or electron‐beam deposition onto the antiferromagnetic oxide NiO. The oxides were made either by deposition of the metals and subsequent oxidation or by growing them in situ using reactive sputtering. The magnetic properties of the giant magnetoresistance structures were studied by magnetoresistance, vibrating sample magnetometry, and ferromagnetic resonance methods. The oxides were characterized by x‐ray diffraction and atomic force microscopy. We studied surface roughness and structure as functions of thickness and oxidation temperature and correlated the oxide properties with the magnetic performance. We found that the metal layer roughened during the postdeposition oxidation process and that the resulting oxide layers were very effective in pinning the direction of the magnetic moment of adjacent metal films. Coercive fields over 500 Oe were obtained for Co overlayers on NiO films but the exchange bias field was generally less than 10...