Abstract:
A particle separating method comprising the following steps is provided. A vibration chamber is vibrated by a vibrating element for changing a volume of the vibration chamber periodically, such that a suspension is pumped into the vibration chamber while the volume of the vibration chamber is increased and pumped out of the vibration chamber while the volume of the vibration chamber is decreased, and a net flow of the suspension in oscillating flow field and toward a trifurcate zone is obtained. Two vortices are generated in an upstream of a center channel of the trifurcate zone. Particles of the suspension are led toward two side channels of the trifurcate zone.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This is a continuation application of patent application Ser. No. 11/779,283, filed on Jul. 18, 2007. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a particle separating method. The suspension, which includes liquid and particles, may be pumped from the inlet chamber and the particles may be removed into the side outlet channels. 
         [0004]    2. Description of Related Art 
         [0005]    Particle separators are essential components in micro-total-analysis-systems (μ-TAS) and are widely used in bio-chemical and biomedical applications. One of the key issues in developing these systems is how simple and high separation performance can be achieved. In the previous studies, two noncontact technologies, dielectrophoresis (DEP) and acoustic wave, were the most frequently used approaches for particle separation in suspension. DEP is the lateral movement of particles induced by polarization effects in non-uniform electric fields. In the DEP devices, mixing particles are injected into a separation chamber and an electric field is applied for separation. The particles are separated on the basis of sizes and DEP properties. Theoretical studies on acoustic radiation forces indicated that a rigid and compressible sphere in a nonviscous fluid can be trapped in such a field. The efficacy of using acoustic force to concentrate small particles in suspension has also been evaluated theoretically and experimentally. That this method could be used to separate particles continuously in a micro-channel was proposed. Those devices adopted acoustic wave and operated in a half wavelength standing wave field. 
         [0006]    In addition, a special design in the geometry of the micro-channel, such as a pinched flow fractionation (PFF), has been used to separate and filter particles of different sizes. Filtration has a critical drawback, namely clogging in the channel, which makes it impossible to separate repetitively. A new hydrodynamic filtration method was developed to avoid this clogging problem, but precise channel geometry and flow rate controls are necessary. While a variety of separators have been studied with DEP, acoustic wave, and PFF in the laminar flow, the oscillating flow generated from a micropump has received much less attention. However, in the miniaturization of bio-detecting applications, the micropump is a necessary component in the system. The flow pattern in the micro-channel is an oscillating flow, not a laminar flow. The flow characteristics of an oscillating flow in the micro-channel were used to achieve particle removal without an external pumping source. This distinct feature makes the present device ideal for a portable μ-TAS or lab-on-a-chip. 
         [0007]    The objective of this patent is to develop a triple-channel particle separation device that can remove the particles from the suspension. The device can be utilized for applications in biomedical and chemical analyses, such as removing red blood cells from the whole blood. This device has been successfully demonstrated to be able to pump fluid and to remove particles without any external pumping devices. This is a definite advantage over other separation techniques such as DEP, acoustic force and PFF, which require a syringe pump or other external driving source. The present device can be fabricated by a simple MEMS process which requires only one photo mask and one ICP etching process. This process not only simplifies the complicated processes of producing separators used in the previous studies but also reduces the cost and enhances the yield. Due to the reduced volume of the particle separating system, the present separator has the potential to be integrated with other detectors for uses in a miniaturized μ-TAS in the future. 
       SUMMARY OF THE INVENTION 
       [0008]    Accordingly, the present invention is directed to a particle separating method, which has a low cost and a better separation effect. 
         [0009]    As embodied and broadly described herein, the present invention provides a particle separating method comprising the following steps. A vibration chamber is vibrated by a vibrating element for changing a volume of the vibration chamber periodically, such that a suspension is pumped into the vibration chamber while the volume of the vibration chamber is increased and pumped out of the vibration chamber while the volume of the vibration chamber is decreased, and a net flow of the suspension in oscillating flow field and toward a trifurcate zone is obtained. Two vortices are generated in an upstream of a center channel of the trifurcate zone. Particles of the suspension are led toward two side channels of the trifurcate zone. 
         [0010]    In an embodiment of the present invention, the net flow of the suspension in oscillating floe field is driven toward the trifurcate zone by the change of the vibration chamber without additional driving apparatus. 
         [0011]    In an embodiment of the present invention, rotating directions of the two vortices are contrary to each other. 
         [0012]    In an embodiment of the present invention, the suspension is pumped into the vibration chamber via a flow directing device that provides a path. A cross section of the path near the vibration chamber is bigger than a cross section of the path away from the vibration chamber. 
         [0013]    According to the present invention, the vibration chamber vibrated by vibrating element can drive the suspension to move towards a fixed direction. Therefore, the suspension moves towards a fixed flow direction under the vibration effect of the vibrating element. Additionally, the present invention utilizes the vortices generated in an upstream of a center channel of the trifurcate zone to lead particles of the suspension toward two side channels of the trifurcate zone 
         [0014]    In order to make the aforementioned and other objects, features, and advantages of the present invention comprehensible, preferred embodiments accompanied with figures are described in detail below. 
         [0015]    It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0016]    The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
           [0017]      FIG. 1A  is a schematic top view of a triple-channel particle separation device according to an embodiment of the present invention. 
           [0018]      FIG. 1B  is a schematic sectional view of  FIG. 1A  taken along the section line A-A′. 
           [0019]      FIG. 1C  is a schematic sectional view of  FIG. 1A  taken along the section line B-B′. 
           [0020]      FIG. 1D  is a physical diagram of the particle separation device according to an embodiment of the present invention. 
           [0021]      FIG. 2A  is a schematic view of the movement of the particles under the effect of the oscillating flow field in the junction of the triple channels of the particle separation device of the present invention. 
           [0022]      FIG. 2B  shows the measurement result of the oscillating flow field with the particle image velocimetry in the junction of the triple channels of the particle separation device of the present invention. 
           [0023]      FIG. 3A  shows the condition of injecting the suspension into the triple-channel particle removal device with a syringe pump, in which the particles are distributed in the three channels. 
           [0024]      FIG. 3B  shows the actual operation results of the triple-channel particle separation device of the present invention, in which the particles in the suspension move towards the side outlet channels on the two sides, so as to be separated. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0025]      FIG. 1A  is a schematic top view of a triple-channel particle separation device according to an embodiment of the present invention.  FIG. 1B  is a schematic sectional view of  FIG. 1A  taken along the line A-A′.  FIG. 1C  is a schematic sectional view of  FIG. 1A  taken along the line B-B′.  FIG. 1D  is a physical diagram of the triple-channel particle separation device. Referring to  FIGS. 1A ,  1 B,  1 C, and  1 D, a triple-channel particle separation device  100  is suitable for separating particles contained in the suspension, in which the fluids are liquid. The triple-channel particle separation device  100  mainly includes a body  200  and a vibrating element  300 . The body  200  mainly includes an upper substrate  200   a  and a lower substrate  200   b.  The upper substrate  200   a  is disposed on a bonding surface  202  of the lower substrate  200   b,  and the upper substrate  200   a  and the lower substrate  200   b  are made of, for example, glass, silicon wafer, acryl, polymethyl methacrylate (PMMA), polydimethyl siloxane (PDMS) or the like. 
         [0026]    The lower substrate  200   b  has a recess pattern located on a bonding surface  202  of the lower substrate  200   b,  and the recess pattern forms a inlet chamber  210 , a vibration chamber  220 , a center outlet chamber  230 , two side outlet chambers  240 , a junction of triple channels  250 , a transport channel for the suspension  260 , a center outlet channel  261 , two side outlet channels  262 , a flow directing device  270 , and a taper  280  between the upper substrate  200   a  and the lower substrate  200   b.    
         [0027]    It should be noted that, this embodiment is not used to limit the present invention, and in other embodiments of the present invention, the recess pattern can be further formed on the upper substrate  200   a.  Additionally, in another embodiment of the present invention, the upper substrate  200   a  and the lower substrate  200   b  may both have recess patterns. 
         [0028]    The inlet chamber  210  is suitable for accommodating the suspension, and the fluids are liquid. One end of the flow directing device  270  is connected to the inlet chamber  210 , and the other end is connected to the vibration chamber  220 . One end of the transport channel for the suspension  260  is connected to the vibration chamber  220 , and the other end is connected to the junction of the triple channels  250 . 
         [0029]    Additionally, in the present invention, the body  200  merely has an inlet chamber  210  and a flow directing device  270  disposed therein, and the number of the inlet chamber  210  and the flow directing device  270  is not limited in the present invention. The body  200  may further have a plurality of inlet chambers  210  and flow directing devices  270  with the same number. 
         [0030]    The vibrating element  300  is disposed on the surface of the lower substrate  200   b,  and the position of the vibrating element  300  corresponds to the vibration chamber  220 . The vibrating element  300  is, for example, a piezoelectric film, and suitable for receiving an electronic signal to generate harmonic vibrations in the vibrating direction D. The waveform of the electronic signal is, for example, a square wave or other signal waveforms that can make the vibrating element  300  generate the harmonic vibrations in the vibrating direction D. Additionally, although the lower substrate  200   b  merely has a vibrating element  300  disposed on the surface thereof in this embodiment, to the number of the vibrating element  300  is not limited in the present invention. The upper substrate  200   a  may also have a vibrating element  301  on the surface thereof. 
         [0031]    In this embodiment, the triple-channel particle separation device  100  further includes an injection pipe  290 , a center outlet pipe  291 , and two side outlet pipes  292 . The injection pipe  290  penetrates through the upper substrate  200   a  to be communicated with the inlet chamber  210 , the center outlet pipe  291  penetrates through the upper substrate  200   a  to be communicated with the center outlet chamber  230 , and the side outlet pipes  292  penetrate through the upper substrate  200   a  to be communicated with the side outlet chamber  240 . In this way, when the vibrating element  300  receives an electronic signal to generate vibrations, the suspension flow into the inlet chamber  210  via the injection pipe  290 , the fluids can be removed out of the triple-channel particle separation device  100  via the outlet pipe  291 , and the particles can be removed out of the triple-channel particle separation device  100  via the outlet pipe  292 , and the action mechanism of the triple-channel particle separation device is illustrated below in great detail. 
         [0032]    Under the condition of oscillating flow field, when the fluid flows through the junction of triple channels, three phenomena are generated and make the particles move towards the side outlet channels on the two sides. First, when the fluid flows in the transport channel, the particles move towards the two sides of the channel. Next, when the fluids move towards the junction of triple channels, the velocity is reduced due to the enlarged cross sectional area, and two recirculation zones are generated at the two sides. The recirculation zone drives the particles to move towards the two sides of the junction of triple channels, and finally, a pair of vortices is generated behind the inlet of the center outlet channel. The vortex can serve as a stopper to block the progressing of the particles, and thus, reducing the cross sectional area of the center outlet channel and enhancing the flow resistance. Moreover, since the vortex is rotated from the center outlet channel to the side outlet channel on the two sides, the particles are driven to move towards the side outlet channel on the two sides. Under the three phenomena, the particles removal effect can be achieved effectively. As the geometrical shape of the channel affects the position of the generated vertex flow field and further influences the separation efficiency, the geometrical shape of the junction of the triple channels is the key point in designing the device of the present invention. 
         [0033]    Through using the measurement technique of micro particle image velocimetry, the flow field characteristics for the junction of the triple channels can be obtained to explain the reasons for the particle separation.  FIG. 2A  is a schematic view of the movement of the particles in the junction of triple channels in the oscillating flow field. In  FIG. 2A , it can be found that the particles move towards the side outlet channels on the two sides under the effect of the flow field.  FIG. 2B  shows the measurement result of the oscillating flow field in the junction of the triple channels. In  FIG. 2B , it can be found that vortices occur behind the inlet of the center outlet channel in the junction of triple channels. The triple-channel particle separation device of the present invention utilizes the vortices to serve as a stopper, and since the vortices occur behind the inlet of center outlet channel, the cross sectional area of the center outlet channel is reduced and the flow resistance is increased. Furthermore, since the vortices rotates from the center outlet channel to the side outlet channels, the particles are driven to move towards the side outlet channels at the two sides, and thus, the particles contained in the suspension are successfully separated. 
         [0034]    In order to prove the feasibility of the present invention, the triple-channel particle separation device is tested and the movement of the particles within the channel is photographed, in which the work fluid is de-ionized water containing fluorescent particles.  FIG. 3A  shows the condition of injecting the suspension into the micro channel with a syringe pump. As shown in  FIG. 3A , it can be seen clearly that the particles are distributed in three channels.  FIG. 3B  shows the actual operation results of the triple-channel particle separation device of the present invention, in which the movement of the particles in the fluids is photographed by utilizing the particle image velocimetry. The result shows that when flowing through the junction of the triple channels, the particles contained in the suspension move towards the side outlet channels on the two sides, instead of being driven towards the center outlet channel. It can be known that the removal efficiency is better, and the particles removal effect can be achieved indeed. 
         [0035]    To sum up, the triple-channel particle separation device of the present invention at least has the following advantages: 
         [0036]    (1) The present invention utilizes the vortices to remove the particle from the suspension. The vortices are generated when the oscillating flow field flows through the junction of the triple channels. Therefore, the different triple channel angle can be designed in the present invention to meet the different requirements for the particle removal without any additional apparatus. 
         [0037]    (2) The volume of the vibration chamber is changed by using a vibrating element in the present invention, so as to drive the fluids in the triple-channel particle separation device. Therefore, it is not necessary for the present invention to connect to any external pumping source, for example, a syringe pump. Additionally, a portable power supply can also be used in the present invention, so that it is convenient to carry along the device of the present invention. Furthermore, the sensors can also be combined with this present device, so that the present invention has the effect of real-time detection. 
         [0038]    (3) The present invention has a simple structure, and thus has the advantage of a low manufacturing cost. 
         [0039]    It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.