Showing papers by "Deyu Li published in 2008"

On-chip counting the number and the percentage of CD4+ T lymphocytes.

Abstract: A novel technique is reported for counting the number and the percentage of CD4+ T lymphocytes in a polydimethylsiloxane (PDMS) microchannel. This system integrates optical fluorescence detection with resistive pulse sensing enhanced by a metal oxide semiconductor field effect transistor (MOSFET). The MOSFET signal indicates the total number of the cells passing through the detection channel, while the concurrent fluorescence signal records only the number of cells tagged with a specific fluorescent dye. The absolute count of the CD4+ T cells and its percentage to the total lymphocytes can be analyzed by combining the two counting results, which shows comparable accuracy to those from the commercial flow cytometer. The fastest observed counting rate for a single-channel microchip is 8.5 cells per second. This technique is highly promising as it could greatly reduce the cost for HIV diagnosis and treatment and make it accessible to resource-poor developing countries.

Microfluidic differential resistive pulse sensors.

Abstract: This study demonstrates an on-chip resistive pulse-sensing scheme with a design of symmetric mirror channels, which significantly reduces the noise and achieves better signal-to-noise ratio. Polystyrene particles of different sizes have been detected with the developed sensing scheme and a record low volume ratio of the particle to the sensing channel, or 0.0004%, has been detected with particles of 520 nm in diameter in a sensing aperture of 50×16×20 μm3. This volume ratio is about ten times lower than the lowest volume ratio reported in the literature including that specified for commercial Coulter counters.

Electroosmotic Flow in Nanotubes with High Surface Charge Densities

Abstract: The ion distribution and electroosmotic flow of sodium chlorine solutions confined in cylindrical nanotubes with high surface charge densities are studied with molecular dynamics (MD). To obtain a more practical physical model for electroosmotic driven flow in a nanoscale tube, the MD simulation process consists of two steps. The first step is used to equilibrate the system and to obtain a more realistic ion distribution in the solution under different surface charge densities. Then, an external electric field is acted to drive the liquids. The simulation results indicate that with the increase of the surface charge density, both the thickness of the electric double layer and the peak height of the counterion density increase. However, the phenomenon of charge inversion does not occur even as the surface charge density increases to −0.34 C/m2, which is rather difficult to reach for real materials in practical situations. This simulation result confirms the recent experimental observation that monovalent i...

Experimental characterization of a metal-oxide-semiconductor field-effect transistor-based Coulter counter.

Abstract: We report the detailed characterization of an ultrasensitive microfluidic device used to detect the translocation of small particles through a sensing microchannel. The device connects a fluidic circuit to the gate of a metal-oxide-semiconductor field-effect transistor (MOSFET) and detects particles by monitoring the MOSFET drain current modulation instead of the modulation in the ionic current through the sensing channel. The minimum volume ratio of the particle to the sensing channel detected is 0.006%, which is about ten times smaller than the lowest detected volume ratio previously reported in the literature. This volume ratio is detected at a noise level of about 0.6% of the baseline MOSFET drain current, clearly showing the amplification effects from the fluidic circuits and the MOSFETs. We characterize the device sensitivity as a function of the MOSFET gate potential and show that its sensitivity is higher when the MOSFET is operating below its threshold gate voltage than when it is operating above the threshold voltage. In addition, we demonstrate that the device sensitivity linearly increases with the applied electrical bias across the fluidic circuit. Finally, we show that polystyrene beads and glass beads with similar sizes can be distinguished from each other based on their different translocation times, and the size distribution of microbeads can be obtained with accuracy comparable to that of direct scanning electron microscopy measurements.

Report on the Seventh U.S.–Japan Joint Seminar on Nanoscale Transport Phenomena—Science and Engineering

Abstract: The seventh US–Japan Joint Seminar on Nanoscale Transport Phenomena was held in Shima, Japan, from December 11 to 14, 2011 The goals of this joint seminar were to provide a critical assessment of the state of the art and future directions in the field of nanoscale transport phenomena and energy conversion processes, to foster US–Japan collaborations, and to provide international exposure to a new generation of scientists in this field Issues discussed in the joint seminar were organized in 10 topical sessions, including (1) nanoscale thermophysical measurements; (2) optical characterization; (3) thermal and molecular transport; (4) phonon transport modeling; (5) energy storage and conversion; (6) nanoscale fluidics and phase change phenomena; (7) biological and organic systems; (8) interfacial thermal transport; (9) novel thermoelectric and thermal management materials; and (10) nanocarbon materials and devices In addition to these topical sessions, the joint seminar featured an opening plenary ses

Measurement of Budding Yeast Growth Rate With MOSFET-Based Microfluidic Coulter Counters

Abstract: Many bioassays are performed on an ensemble of cells and assay results depend crucially on the state of cells relative to one another. If the cells in the ensemble are disordered with respect to one variable, then the measurements that depend on that variable are confounded by averaging. One solution to this is to maintain the cell cycle synchrony for the cells in the ensemble. To do this, it is extremely important to accurately measure the cell growth rate. For example, the volume growth rate of budding yeast is closely linked to many aspects of the cell cycle. Therefore, investigation of the volume growth rate of budding yeast has become an appealing research topic because of its important implications in achieving cell cycle synchrony. In this paper, we report on applications of novel microfluidic sensing technique to measure the volume growth rate of individual budding yeast. We apply our recently developed MOSFET-based microfluidic Coulter counters to detect the volume of budding yeast when it is translocated through the sensing aperture forth and back, controlled by adjusting the direction of electroosmotic flow inside the microfluidic device. Our results indicate that because of the enhanced sensitivity of the MOSFET-based microfluidic Coulter counter, it is possible to measure the volume growth rate of individual budding yeast over its whole cell cycle. The measurement results clearly showed the volume growth of the individual budding yeast.Copyright © 2008 by ASME

Thermal Bubble Nucleation in Nanochannels: Simulations and Strategies for Nanobubble Nucleation and Sensing

Abstract: Progress in the state of the art of nanofabrication now allows devices that may enable the experimental sensing of bubble nucleation in nanochannels, and the direct measurement of the bubble nucleation rate in nanoconfined water and other fluids. In this paper we report on two aspects in achieving this goal: 1) new molecular dynamics simulations of nanobubble formation in nanoconfined argon and water model systems and 2) an ultrasensitive nanofluidic device architecture potentially able to detect individual nanobubble nucleation events.