Showing papers by "Deyu Li published in 2007"

SiO2-coated porous anodic alumina membranes for high flow rate electroosmotic pumping

Abstract: Electroosmotic pumping has been extensively used in lab-on-a-chip devices and micropumps for microelectronic cooling. High flow rate per unit area with a low applied voltage is a key performance requirement to achieve compact design and efficient operation. In this paper, we report work on using SiO2-coated porous anodic alumina membranes for high flow rate electroosmotic pumping under low applied voltages. High quality porous alumina membranes of controllable pore diameters in the range of 30‐100 nm and pore lengths of 60‐100 μm were fabricated by electrochemical anodization. The pores are straight, uniform and hexagonally close-packed with a high porosity of up to 50% of the total area. The inner surface of the pore was coated conformally with a thin layer (∼ 5n m) of SiO 2 to achieve a high zeta potential. The electroosmotic pumping performance of the fabricated anodic alumina membranes, coated and uncoated, was investigated using standard relevant aqueous electrolyte buffer solutions. The high zeta potential of the SiO2 coating increases the pumping flow rate even though the coating reduces the porosity of the membrane. Results show that nanostructured SiO2-coated porous anodic alumina membranes can provide a normalized flow rate of 0.125 ml min −1 V −1 cm −2 under a low effective applied voltage of 3 V. This compares favourably with other microporous materials such as glass frits.

Wide-spectrum, ultrasensitive fluidic sensors with amplification from both fluidic circuits and metal oxide semiconductor field effect transistors

Abstract: The authors report a sensing scheme to detect the translocation of small particles through a fluidic channel. The device connects the gate of a metal oxide semiconductor field effect transistor (MOSFET) with a fluidic circuit and monitors the FET’s drain current to detect particles. They demonstrate that amplification can be achieved from both the fluidic circuit and the MOSFET. The results show that a 0.7% volume ratio of the particle to the sensing microchannel can lead to 28%–56% modulation of the MOSFET’s drain current. The minimum volume ratio detected is 0.006%, which is about ten times smaller than the lowest detectable volume ratio reported in the literature.

Molecular dynamics simulations of ion distribution in nanochannels

Abstract: Molecular dynamics simulations of ion distribution in a nanochannel were performed using a three region simulation domain including two bulk regions on each side of the nanochannel. This scheme allows the study of ion concentration and distribution inside the nanochannel under a given bulk electrolyte concentration, i.e. when the molecular system reaches equilibrium, the concentrations of the counter- and co-ions inside the nanochannel corresponding to a bulk electrolyte will emerge naturally. Our approach is in sharp contrast to the common practice in modeling electric double layers where the number of ions in the nanochannel is assigned somewhat arbitrarily, corresponding to an unknown bulk concentration.

Molecular Dynamics Simulation of Thermal Conductivity of Nanocrystalline Composite Films

Abstract: The effectiveness of a thermoelectric device is measured by the figure of merit ZT, which is inversely proportional to the thermal conductivity. Superlattice materials often have a reduced thermal conductivity because of the introduction of interface scattering and, therfore, improved performance. The present work is focused on the effective thermal conductivity of nanocomposite films. This configuration could also improve ZT because of phonon-interface scattering introduced by the nanocrystals. The effects of crystal size and mass fraction is studied numerically using a molecular dynamics simulation. Results indicate that a reduction in the effective thermal conductivity can be achieved with the addition of a nanocrystal.© 2007 ASME

Ultra-sensitive fluidic sensors by integrating fluidic circuits and mosfets

Abstract: Nanofluidic sensors have been developed over the past decade and demonstrated the capability of sensing single DNA molecules. One important and promising class of nanofluidic devices detects single molecules by inserting a nanopore or nanochannel between two fluid cells and inducing an ionic current by applying an electric bias across the nanopore or nanochannel. When molecules are translocated through the nanopore/nanochannel, a modulation of the baseline ionic current can be observed. In this scheme, the ionic current modulation is approximately the same as the channel resistance modulation, requiring the channel size to be comparable to the molecules to be detected. Here we report on a new sensing scheme to detect the translocation of particles through a fluidic channel, which amplifies the resistance modulation by up to 75 times. In this scheme, the device connects the gate of a MOSFET with a fluidic circuit and monitors the modulation of MOSFET’s drain current to detect particles. We demonstrate that amplification can be achieved from both the fluidic circuit and the MOSFET. For a 9.86 μm diameter polystyrene bead that occupies 0.7% of the total volume of the sensing channel, results show that the drain current of the MOSFET is blocked by 30–46%. We also demonstrate the capability of this device to distinguish particles with similar sizes but different surface charges as they translocate through the sensing channel. More interestingly, the experiments with CD4+ T lymphocyte cells show another modulation pattern: the MOSFET’s drain current is first enhanced and then blocked, which is not fully understood and needs further investigation. Although at this moment the device is based on microchannels and the particles detected are micron-size beads and cells, we expect that the same scheme can be applied to nanofluidic circuits for single molecule detection.Copyright © 2007 by ASME