Publications

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Flow cytometry is an indispensable tool in clinical diagnostics, for example in cancer, AIDS, infectious disease outbreaks, microbiology, and others. The cost and size of existing cytometers precludes their entry into field clinics, water monitoring, agriculture/veterinary diagnostics, and rapidly deployable biothreat detection. Much of the cost and footprint of conventional cytometers is dictated by the high speed achieved by cells or beads in a hydrodynamically focused stream. This constraint is removed by using ultrasonic focusing in a parallel microfluidic architecture. In this paper, we describe our progress towards a microfabricated flow cytometer that uses bulk and microfabricated planar piezoelectric transducers in glass microfluidic channels. In addition to experimental data, initial modeling data to predict the performance of our transducers are discussed.

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A microflame-based detector suit has been developed for sensing of a broad range of chemical analytes. This detector combines calorimetry, flame ionization detection (FID), nitrogen-phosphorous detection (NPD) and flame photometric detection (FPD) modes into one convenient platform based on a microcombustor. The microcombustor consists in a micromachined microhotplate with a catalyst or low-work function material added to its surface. For the NPD mode a low work function material selectively ionizes chemical analytes; for all other modes a supported catalyst such as platinum/alumina is used. The microcombustor design permits rapid, efficient heating of the deposited film at low power. To perform calorimetric detection of analytes, the change in power required to maintain the resistive microhotplate heater at a constant temperature is measured. For FID and NPD modes, electrodes are placed around the microcombustor flame zone and an electrometer circuit measures the production of ions. For FPD, the flame zone is optically interrogated to search for light emission indicative of deexcitation of flame-produced analyte compounds. The calorimetric and FID modes respond generally to all hydrocarbons, while sulfur compounds only alarm in the calorimetric mode, providing speciation. The NPD mode provides 10,000:1 selectivity of nitrogen and phosphorous compounds over hydrocarbons. The FPD can distinguish between sulfur and phosphorous compounds. Importantly all detection modes can be established on one convenient microcombustor platform, in fact the calorimetric, FID and FPD modes can be achieved simultaneously on only one microcombustor. Therefore, it is possible to make a very universal chemical detector array with as little as two microcombustor elements. A demonstration of the performance of the microcombustor in each of the detection modes is provided herein.

Detailed studies of the properties of ceramic CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) have clarified the physics of this interesting material and revealed several features not reported before. The dielectric relaxational properties of CCTO are explained in terms of a capacitive-layer model, as for an inhomogeneous semiconductor, consisting of semiconducting grains and insulating grain boundaries as also concluded by others. The kinetics of the main [low-temperature (T)] relaxation reveal that two different thermally activated processes in CCTO grains control the dynamics. A likely candidate defect responsible for the two processes is the oxygen vacancy which is a double donor. A higher-T relaxation is determined by grain boundary conduction. Both Nb and Fe doping lowered both the apparent dielectric constant {var_epsilon}{prime} and the dielectric loss, but increased Fe doping led to more dramatic effects. At 3 at.% Fe doping, the anomalous {var_epsilon}{prime}(T) response was removed, making the CCTO an intrinsic, very-low-loss dielectric. The intrinsic {var_epsilon}{prime}({approx}75) and its T dependence are measured and shown to be largely determined by a low-lying soft TO phonon. At low T, cubic CCTO transforms into an antiferromagnetic phase at T{sub N} = 25 K. T{sub N} is essentially independent of Nb doping (up to 4 at.%) and of hydrostatic pressure (up to {approx}7 kbar), but decreases significantly with Fe doping. Analysis of the high-T dependence of the magnetic susceptibility provided insight into the role of Fe as a dopant. Finally, an {var_epsilon}{prime}(T) anomaly associated with the onset of antiferromagnetic order has been discovered, providing evidence for coupling between the polarization and sublattice magnetization. The possible origin of this coupling is discussed.

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Solution stamping nanolithography (SSNL) was used to print patterns of metallic copper and high-temperature-superconducting YBa{sub 2}Cu{sub 3}O{sub 7}. SSNL combines soft lithography and chemical-solution deposition to achieve direct printing of inorganic materials. The size of the printed patterns is determined by both the stamp feature size and the wetting properties of the solution.