This paper presents a magnetophoretic separation method on a chip of white blood cells from blood under continuous flow.
The separation of red blood cells from the whole blood is performed using a high gradient magnetic separation method
under continuous flow to trap the particles inside the device. The device is fabricated by microfabrication technology and
enables to capture the red blood cells without the use of labelling tecniques such as magnetic beads. The method consists of
flowing diluted whole blood through a microfluidic channel where a ferromagnetic layer, subjected to a permanent
magnetic field, is located. The majority of red blood cells are trapped at the bottom of the device while the rest of the blood
is collected at the outlet. Experimental results show that an average of 95% of red blood cells are trapped in the device.
Electrorotation method is a useful technique for characterizing dielectric properties of individual cells or particles.
During the electrorotation process, a dielectric cell is subjected to rotating electric field of high frequency and its rotation
speed is monitored. As high conductivity buffer is used in the process, heat is generated which in turn affects cell
rotation performance. In this work, we present temperature analytical results of a 4-electrode electrorotation chip using
finite element method. The simulation conditions include variation of applied voltage, buffer conductivity and material
of the chip. We found that the applied voltage and conductivity of buffer used are two main factors affecting temperature
rise in electrorotation process.
Liquid pumping, mixing and biological cells/reagents delivery in micro- or nano-liter volume is critical in lab-on-chip
systems. We describe a novel AC electro-osmosis device for delivering reagents/cells over large distances without a
global pressure gradient. Our device features facile transport range scalability in x- and y-axes, using continuous flow
in a serpentine microchannel realized by microelectrode pairs arrayed in a unique antiparallel-asymmetric configuration.
Co-planar microelectrodes on glass substrate are fabricated from gold with chromium as seed layer using micro-electromechanical
system (MEMS) technology. Sealed upon the micro-electrodes is an open-ended serpentine microchannel
having width 80μm and depth 45μm; formed by micromolding PDMS with a silicon-based mold. AC signals at 3.5Vpp
and 0.5V DC offset is used to energize the microelectrodes, and polystyrene beads with diameter 5.0μm are used as
tracer particles to visualize flow. Maximum velocity of 871 μm/s was recorded using AC signals at 8 kHz. The ease
of scaling up transport distance range in 2-axes is unique to our device. Scalability in x-axis is achieved by varying the
number of microelectrode pairs; and in y-axis by varying the number of microelectrodes iterations and the
corresponding number of turns in the serpentine microchannel. Being scalable in transporting fluidic volume with high
efficiency under small driving voltages makes our device suitable for miniaturization in a micro-total-analytical-system.
Our device could be applied towards multiple point reagents, biological cells and particles delivery and mixing in a
We present the design and fabrication of a micro-electromechanical system (MEMS) device for cell and particle
delivery using a combination of AC electrokinetic fluidic flow and negative dielectrophoresis (DEP) force. An array of
interdigitated asymmetric microelectrode pairs were used in the planar device. The electrodes produced a net charge in
the surrounding fluid, generating an AC electrokinetic fluidic motion. A non-uniform electric field with low actuation
frequency from the microelectrode pairs resulted in a negative DEP force, which was responsible for pushing delivery
particles away from sedimentation. The experimental results showed that the flow velocity increased rapidly from 267
μm/min to 394 μm/min when the applied frequency was increased from 10 kHz to 70 kHz for a cell-suspending medium
buffer solution with a conductivity of 4.7 μS/cm. A maximum delivery velocity of 801 μm/min was obtained when the buffer conductivity was increased to 47 μS/cm with an actuation frequency of 100 kHz.
This work presents the microfabrication procedures and filtering application of a novel 3-D dielectrophoretic chip that
possesses a structure similar to a classical capacitor. It is made up by bonding two stainless steel meshes on the opposite
sides of a glass frame which is filled with round silica beads. Double filtration actions that are derived from both
mechanical and dielectrophoretic means have been tested with yeast cells and a maximum trapping efficiency of
approximately 75% has been achieved with initial concentration of 5×106 cells/ml. This was done at an applied voltage
of 200 V and a flow rate of 0.1ml/min.
This paper presents a new fabrication process for nanotips array using notching effect of reflected charges on mask (NERCOM). The NERCOM fabrication process is based on two phenomena: flowing of thick photoresist mask after bake and the notching effect of the reflected charges from the photoresist mask in a plasma etching process. Heating the photoresist at different temperature and time will generate different profile of the masking layer walls. During the plasma etching process, the charges (ions and radicals) are reflected by the oblique profile of the masking layer walls and generate an undercut. This phenomenon is utilized with an isotropic etching process in a Deep RIE system to produce tips. Due to the isotropy of the process, the tips are generated. The results indicate that the radii of the tips are in the range of 40 to 60 nm.
This paper presents a new technique for separation of two cell populations in a dielectrophoretic chip with bulk silicon electrode. A characteristic of the dielectrophoretic chip is its "sandwich" structure: glass/silicon/glass that generates a unique definition of the microfluidic channel with conductive walls (silicon) and isolating floor and ceiling (glass). The structure confers the opportunity to use the electrodes not only to generate a gradient of the electric field but also to generate a gradient of velocity of the fluid inside the channel. This interesting combination gives rise to a new solution for dielectrophoretic separation of two cell populations. The separation method consists of four steps. First, the microchannel is field with the cells mixture. Second, the cells are trapped in different locations of the microfluidic channel, the cell population which exhibits positive dielectrophoresis is trapped in the area where the distance between the electrodes is the minimum whilst, the other population that exhibit negative dielectrophoresis is trapped where the distance between electrodes is the maximum. In the next step, increasing the flow in the microchannel will result in an increased hydrodynamic force that sweeps the cells trapped by positive dielectrophoresis out of the chip. In the last step, the electric field is removed and the second population is sweep out and collected at the outlet. The device was tested for separation of dead yeast cells from live yeast cells. The paper presents analytical aspects of the separation method a comparative study between different electrode profiles and experimental results.
This paper presents a characterization of wet etching of glass in HF-based solutions with a focus on etching rate, masking layers and quality of the generated surface. The first important factor that affects the deep wet etching process is the glass composition. The presence of oxides such as CaO, MgO or Al2O3 that give insoluble products after reaction with HF can generate rough surface and modify the etching rate. A second factor that influences especially the etch rate is the annealing process (560°C / 6 hours in N2 environment). For annealed glass samples an increase of the etch rate with 50-60% was achieved. Another important factor is the concentration of the HF solution. For deep wet etching of Pyrex glass in hydrofluoric acid solution, different masking layers such as Cr/Au, PECVD amorphous silicon, LPCVD polysilicon and silicon carbide are analyzed. Detailed studies show that the stress in the masking layer is a critical factor for deep wet etching of glass. A low value of compressive stress is recommended. High value of tensile stress in the masking layer (200-300 MPa) can be an important factor in the generation of the pinholes. Another factor is the surface hydrophilicity. A hydrophobic surface of the masking layer will prevent the etching solution from flowing through the deposition defects (micro/nano channels or cracks) and the generation of pinholes is reduced. The stress gradient in the masking layer can also be an important factor in generation of the notching defects on the edges. Using these considerations a special multilayer masks Cr/Au/Photoresist (AZ7220) and amorphous silicon/silicon carbide/Photoresist were fabricated for deep wet etching of a 500 μm and 1mm-thick respectively Pyrex glass wafers. In both cases the etching was performed through wafer. From our knowledge these are the best results reported in the literature. The quality of the generated surface is another important factor in the fabrication process. We notice that the roughness of generated surface can be significantly improved by adding HCl in HF solution (the optimal ratio between HF (49%) and HCl (37%) was 10/1).
A self-priming and bubble tolerant planar micro-pump, which is fabricated by traditional technology, has been demonstrated and characterized. The micro-pump has a simple three-layered structure. Its two pump housings are made of polycarbonate and they are fabricated by computer numerical control (CNC) machine. The actuation membrane, which acts as the inlet and outlet valve membrane is cast in polydimethylsiloxane (PDMS). Using the PDMS membrane to act as the actuation membrane and valve membrane, we have solved the problem of sealing and poor compression ratio that most silicon based micro-pump faced. From the model of the membrane stroke volume, the flow rate of the pump is insensitive to the pump output pressure, and the output flow rate is linearly varying with actuating frequency. Flow rate up to 1000 ul/min of liquid has been achieved. More than 2m pump-head has been obtained when using water as the pumping medium. The robustness of the pump makes it suitable for disposable applications like biochip system.
In this work we present the dielectrophoretic structure fabricated using two glass wafers and one 0.5 mm thick and highly conductive silicon wafer. In fabricated device the DEP force extends uniformly across the volume of the microfluidic device in the direction normal to the wafer plane. This is achieved by fabricating microfluidic channel walls from doped silicon so that they can also function as DEP electrodes. The advantages of the structure are: electrical leadouts that are free from the fluid leakage usually associated with the lead out recesses, a volume DEP force for deep chambers compared with the surface forces achieved by planar electrodes, no electrical dead volumes as encountered above the thin planar electrodes of alternative technologies, biocompatible silicon oxide passivated surfaces, and no electrochemical effects that arise from edge effects in multi-metal electrodes such as Ti/Au or Cr/Au.