Patent Publication Number: US-2011056834-A1

Title: Dielectrophoresis-based microfluidic system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a microfluidic system, and more particularly to a dielectrophoresis-based microfluidic system. 
     2. Description of Related Art 
     At present, microfluidic systems, or called microfluidic chips, are developed widely. Since microfluidic systems have the advantages of rapid reaction rate, high sensitivity, high reproducibility, low costs, low pollution, and so on, they are widely used in various applications such as biological application, medical application, and photoelectric application and so on. 
     A basic structure of a conventional microfluidic system includes a substrate in which one channel or a plurality of channels in micrometer size, or called microchannels, are formed. Fluid may fill in the microchannels and then flow in the microchannels. 
     Additionally, some microfluidic systems further include pumps for providing power for fluid so that the fluid can flow in microchannels successfully. 
     However, the above-mentioned microfluidic systems have the shortcoming of fixed microfluidic networks. Once a microfluidic system is manufactured, its microfluidic network is fixed and cannot be changed to make fluid flow in different directions. Furthermore, the placement of the pumps increases the overall dimensions of the microfluidic systems, thereby reducing the transportability. 
     Hence, the inventors of the present invention believe that the shortcomings described above are able to be improved and finally suggest the present invention which is of a reasonable design and is an effective improvement based on deep research and thought. 
     SUMMARY OF THE INVENTION 
     A main objective of the present invention is to provide a dielectrophoresis-based microfluidic system which has unfixed virtual channels. 
     To achieve the above-mentioned objective, a dielectrophoresis-based microfluidic system in accordance with the present invention is provided. The dielectrophoresis-based microfluidic system includes: a first electrode plate which has a first substrate and an electrode layer disposed on one side surface of the first substrate; a second electrode plate which has a second substrate and a plurality of electrodes, wherein the electrodes are disposed on one side surface of the second substrate which is opposite to the electrode layer, and arranged in a microchannel pattern; and a spacing structure which is disposed between the first electrode plate and the second electrode plate so that a space is formed between the first electrode plate and the second electrode plate. 
     The dielectrophoresis-based microfluidic system of the present invention has the efficacy as following: the channels of the microfluidic system are virtual channels formed by the plurality of electrodes, thereby avoiding that conventional real channels limit flow directions of pumped fluid. As long as users apply voltage to different electrodes, the pumped fluid can flow to different locations, thereby achieving the intended result of programmable fluid manipulation. Additionally, since the present invention does not require a pump, the overall dimension of the present invention is smaller. 
     To further understand features and technical contents of the present invention, please refer to the following detailed description and drawings related the present invention. However, the drawings are only to be used as references and explanations, not to limit the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a first embodiment of a dielectrophoresis-based microfluidic system of the present invention; 
         FIG. 2  is a planar cross-sectional view of the first embodiment of the dielectrophoresis-based microfluidic system of the present invention; 
         FIG. 3  is a schematic view of a microchannel pattern of the first embodiment of the dielectrophoresis-based microfluidic system of the present invention; 
         FIG. 4  is a schematic view of the first embodiment of the dielectrophoresis-based microfluidic system of the present invention, connected with a driving circuit board and a controller; 
         FIG. 5  is a schematic view of the first embodiment of the dielectrophoresis-based microfluidic system of the present invention, in a used state; 
         FIG. 6  is a first schematic view of the first embodiment of the dielectrophoresis-based microfluidic system of the present invention separating DNA sample liquid; 
         FIG. 7  is a second schematic view of the first embodiment of the dielectrophoresis-based microfluidic system of the present invention separating DNA sample liquid; 
         FIG. 8  is a perspective view of a second embodiment of the dielectrophoresis-based microfluidic system of the present invention; 
         FIG. 9  is a perspective view of a third embodiment of the dielectrophoresis-based microfluidic system of the present invention; 
         FIG. 10  is a perspective view of a fourth embodiment of the dielectrophoresis-based microfluidic system of the present invention; 
         FIG. 11  is a schematic view of a microchannel pattern of a fifth embodiment of the dielectrophoresis-based microfluidic system of the present invention; and 
         FIG. 12  is a perspective view of a sixth embodiment of the dielectrophoresis-based microfluidic system of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides a dielectrophoresis-based microfluidic system with unfixed virtual channels for users to manipulate microfluids programmably. The dielectrophoresis-based microfluidic system can be referred as “microfluidic system” for short below. 
     Please refer to  FIG. 1  and  FIG. 2  illustrating a first preferred embodiment of the dielectrophoresis-based microfluidic system  1  according to the present invention, which includes a first electrode plate  11 , a second electrode plate  12  and a spacing structure  13 . 
     The following is to demonstrate the features of each of components and then the connection relationship between the components. Each direction (up, down, front, rear, left or right) in the following description is only used to express a relative direction, and doesn&#39;t limit the actual used directions of the dielectrophoresis-based microfluidic system  1 . 
     The first electrode plate  11  includes a first substrate  111 , an electrode layer  112  and a first hydrophobic layer  113 . The first substrate  111  is a rectangular plate of which a material may be glass, silicon substrate, poly-dimethylsiloxane (PDMS), polyethylene terephthalate (PET), polyethylene naphthalate (PEN) or a flexible polymer material etc. 
     The electrode layer  112  is disposed on the bottom surface of the first substrate  111  and covers the whole bottom surface of the first substrate  111 . The material of the electrode layer  112  may be a conductive metal material, a conductive polymer material or a conductive oxide material etc., such as Cr/Cu metal or indium tin oxide (ITO) etc. 
     The electrode layer  112  is deposited on the first substrate  111  via E-beam evaporation, physical vapor deposition, sputtering etc. 
     The first hydrophobic layer  113  is disposed on the bottom surface of the electrode layer  112  and covers the whole bottom surface of the electrode layer  112 . The material of the first hydrophobic layer  113  may be a hydrophobic material such as Teflon and so on. The effect is that the pumped fluid  4  mentioned below (please refer to  FIG. 5 ) has a hydrophobic characteristic, or the surface of the first electrode plate  11  is hydrophobic to the pumped fluid  4 , which is convenient for driving the pumped fluid  4 . The first hydrophobic layer  113  is deposited on the electrode layer  112  via physical or/and chemical deposition or spin coating etc. 
     Even if the first hydrophobic layer  113  is not disposed on the electrode layer  112 , it will not cause that the pumped fluid  4  cannot be driven. Furthermore, if the pumped fluid  4  has a good hydrophobic characteristic itself, or its surface energy is large, then it is not required to dispose the first hydrophobic layer  113  on the electrode layer  112 . In other words, for the first electrode plate  11 , the first hydrophobic layer  113  is optional. 
     The above is the illustration for the first electrode plate  11 , and the following is to describe the second electrode plate  12 . 
     The second electrode plate  12  includes a second substrate  121 , a plurality of electrodes  122 , a dielectric layer  123  and a second hydrophobic layer  124 . 
     The second substrate  121  is similar to the first substrate  111 , that is, the second substrate  121  is a rectangular plate and the material of the second substrate  121  may be glass, silicon substrate, poly-dimethylsiloxane (PDMS), polyethylene terephthalate (PET), polyethylene naphthalate (PEN) or a flexible polymer material etc. 
     The electrodes  122  are disposed on the top surface of the second substrate  121 . The material of the electrodes  122  is similar to that of the conductive layer  121  and may be a conductive metal material, a conductive polymer material or a conductive oxide material etc., such as Cr/Cu metal or Indium tin oxide (ITO) etc. The shape and the arrangement of the electrodes  122  depend on a particular microchannel pattern. 
     Please further refer to  FIG. 3 , the microchannel pattern includes a plurality of quadrate reservoirs  122 A and a plurality of long-strip-shaped channels  122 B. Each of the reservoirs  122 A and the channels  122 B is one of the electrodes  122 . Each channel  122 B is connected with other three channels  122 B (there are spaces between the channels) to form a cruciform channel, and each reservoir  122 A is connected with several channels  122 B located on more peripheral positions. The functions of the reservoirs  122 A and the channels  122 B will be explained in the following operating instructions of the microfluidic system  1 . 
     The manufacturing process for the electrodes  122  is as following: depositing a layer of material on the second substrate  112  via E-beam evaporation, physical vapor deposition, or sputtering etc. and removing unwanted materials via etching and so on to form the plurality of electrodes  122  arranged in the microchannel pattern. The electrodes  122  may also be manufactured via other processes, such as lift-off and so on. 
     The dielectric layer  123  is disposed on the electrodes  122  and covers all of the electrodes  122 . The material of the dielectric layer  123  may be various dielectric materials, such as parylene, positive photoresist, negative photoresist, materials with high dielectric constant, or materials with low dielectric constant. 
     The second hydrophobic layer  124  is disposed on the top surface of the dielectric layer  123  and covers the whole dielectric layer  123 . The material of the second hydrophobic layer  124  is similar to that of the first hydrophobic layer  113  and may be a hydrophobic material such as Teflon and so on. The effect is that the pumped fluid  4  (please refer to  FIG. 5 ) has a hydrophobic characteristic, or the second electrode plate  12  is hydrophobic to the pumped fluid  4 , which is convenient for driving the pumped fluid  4 . 
     The dielectric layer  123  is formed by depositing the material of the dielectric layer  123  on the second substrate  121  and the electrodes  122 , and the second hydrophobic layer  124  may also be formed by depositing the material of the second hydrophobic layer  124  on the dielectric layer  123 . 
     Additionally, for the second electrode plate  12 , the dielectric layer  123  is optional. That is, as long as the dielectric characteristic of the pumped fluid  4  meets the applied requirements, it doesn&#39;t need the dielectric layer  123  existing in the second electrode plate  12 . For the second electrode plate  12 , the second hydrophobic layer  124  is optional. As long as the pumped fluid  4  has the hydrophobic characteristic itself, or the surface of the electrode plate  12  is hydrophobic to the pumped fluid  4 , it does not need to dispose the second hydrophobic layer  124  on the dielectric layer  123 . 
     The above is the illustration of the second electrode plate  12 , and the following is the illustration for the spacing structure  13 . The spacing structure  13  includes four spacers  131 , each of which may be an insulating spacer. The four spacers  131  are arranged in a continuous frame structure. 
     The above is the explanation of each of components of the microfluidic system  1 , and then the connection relationship between the components is to be explained. The first electrode plate  11  and the second electrode plate  12  are arranged in parallel. The electrode layer  112  is opposite to the electrodes  122 . The spacers  131  of the spacing structure  13  are disposed between the first electrode plate  11  and the second electrode plate  12 , so that a space  14  is defined between the first electrode plate  11  and the second electrode plate  12 . 
     Please refer to  FIG. 4 , the microfluidic system  1  is further mounted on a driving circuit board  2  and electrically connected with the driving circuit board  2  by wires or connectors, so that the driving circuit board  2  provides voltage to the electrode layer  112  and the electrodes  122  of the microfluidic system  1 . 
     A controller  3  (for example, a desktop computer, a notebook computer, a personal digital assistant or a mobile phone etc.) is connected with the driving circuit board  2  with or without wires. Users can set various control programs in the controller  3 , so that the controller  3  can send a control signal to the driving circuit board  2  according to the control programs and the driving circuit board  2  can supply voltage for different electrodes  122  according to the control signal. 
     Please refer to  FIG. 5 , during using the microfluidic system  1 , at first, injecting one kind of pumped fluid  4  into the microfluidic system  1 , that is, placing the pumped fluid  4  in the space  14  on one or a plurality of electrodes  122  (reservoirs  122 A). Then, injecting one kind of surrounding fluid  5  into the space  14  to surround the pumped fluid  4 . The pumped fluid  4  and the surrounding fluid  5  is injected into the space  14  through an opening  114  of the first electrode plate  11 , and the opening  114  is located over the reservoirs  122 A. 
     It is noted that the dielectric constant of the pumped fluid  4  must be greater than that of the surrounding fluid  5  so that the pumped fluid  4  can flow basing on the dielectrophoresis phenomenon. So the pumped fluid  4  may be water and the surrounding fluid  5  may be air or silicone oil; or alternatively, the pumped fluid  4  may be silicone oil and the surrounding fluid  5  may be air. The above-mentioned pumped fluid  4  and surrounding fluid  5  are only examples and are not merely limited thereto. 
     After the pumped fluid  4  and the surrounding fluid  5  is injected into the microfluidic system  1 , the driving circuit board  2  applies voltage to the electrode layer  112  and one of the electrodes  122 , so that the electric field between the electrode layer  112  and the electrodes  122  changes. The pumped fluid  4  and the surrounding fluid  5  is polarized in varying degrees, so that the pressure difference exists between the pumped fluid  4  and the surrounding fluid  5 , and then the pumped fluid  4  flows in the low-pressure direction. The phenomenon is called a dielectrophoresis phenomenon and the pressure difference between the pumped fluid  4  and the surrounding fluid  5  may be called a dielectrophoresis force. 
     Accordingly, as long as the driving circuit board  2  applies voltage to different electrodes  122 , the pumped fluid  4  will flow towards the electrode  122  to which the voltage is applied; that is, without a pump, the pumped fluid  4  can be controlled to flow towards different directions. 
     In other words, the configuration of the channels of the microfluidic system  1  is unfixed and changeable with applying voltages to different electrodes  122 . Users write control programs to control the driving circuit board  2  to apply voltage to different electrodes  122 , thereby controlling the pumped fluid  4  to flow towards different electrodes  122 . Accordingly, the programmable microfluid control can be achieved. 
     Please refer to  FIG. 6 , the above-mentioned microfluidic system  1  may be used to separate DNA. Inject DNA sample liquid (the pumped fluid)  4  into the left uppermost and the right uppermost reservoirs  122 A, and then inject buffer liquid (the pumped fluid)  4  into the upper middle and the lower middle reservoirs  122 A. 
     Subsequently, applying voltages to four longitudinal channels  1228  between the upper middle reservoir  122 A and the lower middle reservoir  122 A, so that the buffer liquid  4  flows into the four longitudinal channels  122 B. That is, the four longitudinal channels  122 B are filled with the buffer liquid  4 . Further, applying voltages to four transversal channels  122 B between the left uppermost reservoir  122 A and the right uppermost reservoir  122 A, so that the DNA sample liquid  4  flows into the four transversal channels  122 B. That is, the four transversal channels  122 B are filled with the DNA sample liquid  4 . The DNA sample liquid  4  and the buffer liquid  4  flows crosswise. 
     Please refer to  FIG. 7 , finally, applying voltages to four longitudinal channels  122 B between the upper middle reservoir  122 A and the lower middle reservoir  122 A, so that the crossed DNA sample liquid  4  flows towards the lower middle reservoir  122 A basing on the electrophoresis force and electroosmosis, and separates in the channels  122 B basing on the mass-to-charge ratio. 
     The above is the first embodiment of the microfluidic system  1  of the present invention. Please refer to  FIG. 8  illustrating a second embodiment of the microfluidic system  1  of the present invention. The difference between the second embodiment and the first embodiment is that the microfluidic system  1  of the second embodiment further includes a plurality of fence structures  15  disposed on the top surface of the second electrode plate  12  and respectively surrounding each reservoir  122 A. 
     When the pumped fluid  4  is injected into the reservoirs  122 A, the fence structures  15  can help the pumped fluid  4  keep in the reservoirs  122 A and ensure that the amount of the pumped fluid  4  in each reservoir  122 A is equal. 
     Please refer to  FIG. 9 , illustrating a third embodiment of the microfluidic system  1  of the present invention. The difference between the third embodiment and the first embodiment is that the area of the first electrode plate  11  of the microfluidic system  1  of the third embodiment is larger than that of the second electrode plate  12 , the spacing structure  13  includes four individual spacers  131  respectively located at four corners of the first electrode plate  11  and the second electrode plate  12 , and the reservoirs  122 A are located on the periphery of the first electrode plate  11 . 
     During using the microfluidic system  1 , the pumped fluid  4  is dripped in the reservoirs  122 A of the second electrode plate  12 , and voltage is applied to different electrodes  122  so that the pumped fluid  4  flows between the first electrode plate  11  and the second electrode plate  12  under the effect of dielectrophoresis. 
     Please refer to  FIG. 10 , illustrating a fourth embodiment of the microfluidic system  1  of the present invention. The difference between the fourth embodiment and the third embodiment is that the microfluidic system  1  of the fourth embodiment further includes a plurality of fence structures  15  and a plurality of hydrophilic layers  16  which are respectively prepared on the top surface of the first electrode plate  11  and located over the partial reservoirs  122 A. 
     During using the microfluidic system  1 , the pumped fluid  4  is dropped in the fence structures  15  or on the hydrophilic layers  16 . The pumped fluid  4  is kept in the fence structures  15  or on the hydrophilic surface  16 , and doesn&#39;t flow between the first electrode plate  11  and the second electrode plate  12  until the electrodes  122  are electrified. 
     Furthermore, the fence structures  15  and the hydrophilic layers  16  can be applied in the third embodiment of the microfluidic system  1 , independently, and are not limited in any specific combinations by applying them. In the microfluidic system  1  of the second embodiment, all or partial of the fence structures  15  may be replaced by the hydrophilic layers  16  In other words, the microfluidic system  1  may selectively have one kind of or all kinds of the opening  114 , the fence structures  15  and the hydrophilic layers  16 . 
     Please refer to  FIG. 11 , illustrating a fifth embodiment of the microfluidic system  1  of the present invention. The difference between the fifth embodiment and the above-mentioned embodiments is that the microfluidic pattern formed by the electrodes  122  further includes a plurality of joints  122 C of which each is connected with at least two channels  122 B. The joints  122 C may also be applied voltage to so as to help the pumped fluid  4  change its flow direction. 
     Please refer to  FIG. 12 , illustrating a sixth embodiment of the microfluidic system  1  of the present invention. The difference between the sixth embodiment and the above-mentioned embodiments is that the electrode layer  112  of the first electrode plate  11  does not cover the whole bottom surface of the first substrate  111 , and comprises a plurality of the electrodes  1121 . The electrodes  1121  are arranged in another microchannel pattern, which may be the same to the microchannel pattern of the electrodes  122 . 
     Using the microfluidic system  1  of the sixth embodiment is similar to using the microfluidic system  1  of other embodiments. Voltage is applied to the designated electrode  122  and the corresponding electrode  1121 , and then the pump fluid  4  will flow towards the designated electrodes. 
     Consequently, the dielectrophoresis-based microfluidic system of the present invention has the characteristics as follows: the channels of the microfluidic system are virtual channels formed by a plurality of electrodes, thereby avoiding that conventional real channels limit the flow directions of the pumped fluid. As long as users apply voltages to different electrodes, the pumped fluid can flow in different directions, thereby achieving the intended result of the programmable fluid manipulation. Additionally, since the present invention does not require a pump, the present invention has smaller size and can be manufactured in a semiconductor fabrication process. 
     What are disclosed above are only the specifications and the drawings of the preferred embodiments of the present invention and it is therefore not intended that the present invention be limited to the particular embodiments disclosed. It will be understood by those skilled in the art that various equivalent changes may be made depending on the specifications and the drawings of the present invention without departing from the scope of the present invention.