High-Throughput White Blood Cell (Leukocyte) Enrichment from Whole Blood Using Hydrodynamic and Inertial Forces.

A microfluidic chip, which can separate and enrich leukocytes from whole blood, is proposed. The chip has 10 switchback curve channels, which are connected by straight channels. The straight channels are designed to permit the inertial migration effect and to concentrate the blood cells, while the curve channels allow the Dean flow to further classify the blood cells based on the cell sizes. Hydrodynamic suction is also utilized to remove smaller blood cells (e.g., red blood cell (RBC)) in the curve channels for higher separation purity. By employing the inertial migration, Dean flow force, and hydrodynamic suction in a continuous flow system, our chip successfully separates large white blood cells (WBCs) from the whole blood with the processing rates as high as 1 × 108 cells/sec at a high recovery rate at 93.2% and very few RBCs (~0.1%).

Electroosmotic flow control in microfluidic chips using a self-assembled monolayer as the insulator of a flow field-effect transistor.

A novel concept for electroosmotic flow (EOF) control in a microfluidic chip is presented by using a self-assembled monolayer as the insulator of a flow field-effect transistor. Bidirectional EOF control with mobility values of 3.4 × 10(-4) and -3.1 × 10(-4) cm(2)/V s can be attained, corresponding to the applied gate voltage at -0.8 and 0.8 V, respectively, without the addition of buffer additives. A relatively high control factor (approximately 400 × 10(-6) cm(2)/V(2) s) can be obtained. The method presented in this study offers a simple strategy to control the EOF.

Nanocapillary electrophoretic electrochemical chip: towards analysis of biochemicals released by single cells.

A novel nanocapillary electrophoretic electrochemical (Nano-CEEC) chip has been developed to demonstrate the possibility of zeptomole-level detection of neurotransmitters released from single living cells. The chip integrates three subunits to collect and concentrate scarce neurotransmitters released from single PC-12 cells, including a pair of targeting electrodes for single cells captured by controlling the surface charge density; a dual-asymmetry electrokinetic flow device for sample collection, pre-concentration and separation in a nanochannel; and an online electrochemical detector for zeptomole-level sample detection. This Nano-CEEC chip integrates a polydimethylsiloxane microchannel for cell sampling and biomolecule separation and a silicon dioxide nanochannel for sample pre-concentration and amperometric detection. The cell-capture voltage ranges from 0.1 to 1.5 V with a frequency of 1-10 kHz for PC-12 cells, and the single cell-capture efficiency is optimized by varying the duration of the applied field. All of the processes, from cell sampling to neurotransmitter detection, can be completed within 15 min. Catecholamines, including dopamine and norepinephrine (noradrenaline) released from coupled single cells, have been successfully detected using the Nano-CEEC chip. A detection limit of 30-75 zeptomoles was achieved, which is close to the levels released by a single neuron in vitro.

Microfluidic systems for biosensing.

In the past two decades, Micro Fluidic Systems (MFS) have emerged as a powerful tool for biosensing, particularly in enriching and purifying molecules and cells in biological samples. Compared with conventional sensing techniques, distinctive advantages of using MFS for biomedicine include ultra-high sensitivity, higher throughput, in-situ monitoring and lower cost. This review aims to summarize the recent advancements in two major types of micro fluidic systems, continuous and discrete MFS, as well as their biomedical applications. The state-of-the-art of active and passive mechanisms of fluid manipulation for mixing, separation, purification and concentration will also be elaborated. Future trends of using MFS in detection at molecular or cellular level, especially in stem cell therapy, tissue engineering and regenerative medicine, are also prospected.

Nanostructured pillars based on vertically aligned carbon nanotubes as the stationary phase in micro-CEC.

We present a micro-CEC chip carrying out a highly efficient separation of dsDNA fragments through vertically aligned multi-wall carbon nanotubes (MWCNTs) in a microchannel. The vertically aligned MWCNTs were grown directly in the microchannel to form straight nanopillar arrays as ordered and directional chromatographic supports. 1-Pyrenedodecanoic acid was employed for the surface modification of the MWCNTs' stationary phase to adsorb analytes by hydrophobic interactions. This device was used for separating dsDNA fragments of three different lengths (254, 360, and 572 bp), and fluorescence detection was employed to verify the electrokinetic transport in the MWCNT array. The micro-CEC separation of the three compounds was achieved in less than 300 s at a field strength of 66 V/cm due to superior laminar flow patterns and a lower flow resistance resulting from the vertically aligned MWCNTs being used as the stationary phase medium. In addition, a fivefold reduction of band broadening was obtained when the analyte was separated by the chromatographic MWCNT array channel instead of the CE channel. From all of the results, we suggest that an in situ grown and directional MWCNT array can potentially be useful for preparing more diversified forms of stationary phases for vertically efficient chip-based electrochromatography.

Dual-asymmetry electrokinetic flow focusing for pre-concentration and analysis of catecholamines in CE electrochemical nanochannels.

In this research, a technique incorporating dual-asymmetry electrokinetic flow (DAEKF) was applied to a nanoCE electrochemical device for the pre-concentration and detection of catecholamines. The DAEKF was constructed by first generating a zeta-potential difference between the top and bottom walls, which had been pre-treated with O2 and H2O surface plasma, respectively, yielding a 2-D gradient shear flow across the channel depth. The shear flow was then exposed to a varying zeta-potential along the downstream direction by control of the field-effect in order to cause downward rotational flow in the channel. By this mechanism, almost all of the samples were effectively brought down to the electrode surface for analysis. Simulations were carried out to reveal the mechanism of concentration caused by the DAEKF, and the results reasonably describe our experiment findings. This DAEKF technique was applied to a glass/glass CE electrochemical nanochip for the analysis of catecholamines. The optimum detection limit was determined to be 1.25 and 3.3 nM of dopamine and catechol, respectively. A detection limit at the zeptomole level for dopamine can be obtained in this device, which is close to the level released by a single neuron cell in vitro.

Three-electrode electrochemical detector and platinum film decoupler integrated with a capillary electrophoresis microchip for amperometric detection.

This article demonstrates that a three-electrode electrochemical (EC) detector and an electric decoupler could be fabricated in the same glass chip and integrated with an O2-plasma-treated PDMS layer using microfabrication techniques to form the capillary electrophoresis (CE) microchip. The platinized decoupler could mostly decouple the electrochemical detection circuit from the interference of an separation electric field in 10 mM 2-(N-morpholino)ethanesulfonic acid (MES, pH 6.5) solution. The baseline offset of background current recorded from the working electrode with and without application of a separation electric field was maintained at less than 0.05 pA in 10 mM MES. In addition, the platinized pseudoreference electrode was demonstrated to offer a stable potential in electrochemical detection. As a consequence, the limit of detection of dopamine was 0.125 microM at a S/N = 4. The responses for dopamine to different concentrations were found to be linear between 0.25 and 50 microM with a correlation coefficient of 0.9974 and a sensitivity of 11.76 pA/microM. The totally integrated CE-EC microchip should be able to fulfill the ideal of miniaturization and commercialization.