Patent Publication Number: US-9421543-B2

Title: Hydrodynamic filter unit, hydrodynamic filter including the hydrodynamic filter unit, and method of filtering target material by using the hydrodynamic filter unit and the hydrodynamic filter

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2011-0061799, filed on Jun. 24, 2011, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     Often it is useful to detect target materials on the basis of certain properties of those target materials, for example, size or mass. Target materials can be labelled and then may be detected by using a probe. Alternatively, target materials may be stained and detected based on the properties of the stain. However, when it is desirable to detect target materials on the basis of the size of the target materials, a filter, particularly, a hydrodynamic filter is useful. A hydrodynamic filter is a system for capturing target materials in a fluid by flowing the fluid through the filter. There is a need for hydrodynamic filters and related compositions or methods for effectively detecting target materials. 
     SUMMARY OF THE INVENTION 
     A hydrodynamic filter unit is provided herein, which is useful for detecting target materials in a fluid. According to an aspect of the present invention, the hydrodynamic filter unit comprises: a fluid chamber; an inlet channel connected to the fluid chamber into which a fluid comprising a target material is introduced; a plurality of outlet channels connected to the fluid chamber through which the fluid is discharged; and a plurality of capturing portions disposed in connection portions to which the fluid chamber and the plurality of outlet channels are connected. 
     Each of the plurality of capturing portions may comprise a pair of protrusion portions protruding from the connection portions. 
     The hydrodynamic filter unit may further comprise an accumulation prevention portion disposed between the plurality of outlet channels, and protruding from an inside surface of the fluid chamber. 
     The shape of each of the plurality of capturing portions and the accumulation prevention portion may be formed according to the shape of the target material to be detected. 
     According to one aspect of the invention, the pair of protrusion portions may have a round end portion. 
     According to another aspect of the present invention, a plurality of hydrodynamic filter units can be arranged in a sequence, thereby providing a hydrodynamic filter sequence. 
     A hydrodynamic filter also is provided, which comprises a plurality of hydrodynamic filter sequences, each comprising a plurality of hydrodynamic filter units. 
     The hydrodynamic filter may further include: a body portion comprising the plurality of hydrodynamic filter sequences (e.g., surrounding, encompassing, or otherwise holding or housing the plurality of hydrodynamic filter sequences). 
     The hydrodynamic filter may further comprise an inlet portion and an outlet portion that are connected to the body portion. 
     A ratio of a width to a length of the body portion optionally ranges from about 3:1 to about 100:1. 
     The hydrodynamic filter may further comprise convex portions disposed in a front surface and a rear surface of the plurality of hydrodynamic filter sequences, and protruding from the front surface and the rear surface. 
     An n th  hydrodynamic filter sequence and an (n+1) th  hydrodynamic filter sequence among the plurality of hydrodynamic filter sequences may be disposed in a zigzag arrangement (n is a natural number). In other words, in a plurality of hydrodynamic filter sequences arranged parallel to one another, an n th  hydrodynamic filter sequence and an (n+1) th  hydrodynamic filter sequence can be arranged in an offset manner, such that a filter unit of the nth filter sequence is not directly in-line with a filter unit of the (n+1) th  hydrodynamic filter sequence. When arranged in this way, a fluid path through the filter sequences is varied. 
     A filtering method also is provided, the method comprising introducing a fluid comprising a target material into a hydrodynamic filter unit, as described herein, through the inlet channel; capturing the target material in the hydrodynamic filter unit; and discharging a remaining part of the fluid from the hydrodynamic filter unit (i.e., to the outside of the hydrodynamic filter unit) through the outlet channel. 
     The filtering method may further comprise attaching any one or more of a bead, hydrogel, nano particle, or aptamer to the target material before the introducing of the fluid into the hydrodynamic filter unit. 
     Each of the plurality of capturing portions of the hydrodynamic filter unit may include a pair of protrusion portions protruding from the connection portions, and the target material is captured in at least one of the pairs of protrusion portions. The remaining part of the fluid may be discharged through the other pairs of protrusion portions without capturing the target material. 
     In another aspect, the hydrodynamic filter unit is part of a hydrodynamic filter comprising a plurality of hydrodynamic filter units or a plurality of hydrodynamic filter sequences, the filtering method comprising introducing the fluid comprising the target material into the hydrodynamic filter; capturing the target material in the hydrodynamic filter; and discharging a remaining part of the fluid from the hydrodynamic filter (i.e., to the outside of the hydrodynamic filter). 
     All other aspects of the filtering method are as described with respect to the hydrodynamic filter unit and hydrodynamic filter. 
     Additional aspects of the invention will be apparent from the detailed description of the invention and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIGS. 1A and 1B  are a plan view and a perspective view of a hydrodynamic filter unit according to an embodiment of the present invention, respectively; 
         FIG. 2  is a plan view of a hydrodynamic filter unit according to another embodiment of the present invention; 
         FIG. 3  is a plan view of a hydrodynamic filter unit according to another embodiment of the present invention; 
         FIG. 4  is a plan view of a hydrodynamic filter unit according to another embodiment of the present invention; 
         FIG. 5  is a plan view of a hydrodynamic filter unit according to another embodiment of the present invention; 
         FIG. 6  is a plan view of a hydrodynamic filter according to an embodiment of the present invention; 
         FIG. 7  is a plan view of hydrodynamic filter sequences included in the hydrodynamic filter of  FIG. 6 ; 
         FIGS. 8A through 8D  are plan views of a hydrodynamic filter unit for explaining a sequential filtering process; and 
         FIG. 9  is a plan view of a hydrodynamic filter for explaining a filtering process. 
     
    
    
     DETAILED DESCRIPTION 
     Various example embodiments will now be described more fully with reference to the accompanying drawings in which some example embodiments are shown. 
     Detailed illustrative example embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative and provided for purposes of describing exemplary embodiments. This invention may, however, be embodied in many alternate forms; the invention should not be construed as limited to the embodiments set forth herein. On the contrary, the invention is considered to cover all modifications, equivalents, and alternatives of the subject matter described herein, including modifications, equivalents, and alternatives of particular embodiments. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these terms are only used to distinguish one element from another and are not intended to otherwise limit the scope of the invention. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. Furthermore, an embodiment comprising a first and second element might also be configured to comprise additional elements (third, fourth, etc.) even though such additional elements are not shown. 
     As used herein, the term “and/or,” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
     It will be understood that when an element or layer is referred to as being “formed on” or “disposed on” another element or layer, it can be directly or indirectly formed on the other element or layer. That is, for example, intervening elements or layers may be present. In contrast, when an element or layer is referred to as being “directly formed on” or “directly disposed on” another element, there are no intervening elements or layers present. Other words used to describe the relationship between elements or layers should be interpreted in a like fashion (e.g., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.). 
     As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. In the drawings, the same reference numerals denote the same elements, and sizes of elements may be exaggerated for clarity and convenience. 
       FIGS. 1A and 1B  are a plan view and a perspective view of a hydrodynamic filter unit  100  according to an embodiment of the present invention, respectively. 
     Referring to  FIGS. 1A and 1B , the hydrodynamic filter unit  100  may include a fluid chamber  10 , an inlet channel  20  that is connected to the fluid chamber  10  and into which a fluid including a target material  50  is introduced, a plurality of outlet channels  30  and  35  that are connected to the fluid chamber  10  and through which the fluid is discharged, and a plurality of capturing portions  41  and  43  that are respectively disposed in connection portions to which the fluid chamber  10  and the outlet channels  30  and  35  are connected and capture the target material  50 . The term “connection portion” as used herein refers to the region at which two or more elements are coupled, connected, or otherwise meet. For instance, the inlet channel is connected to the fluid chamber at or by way of a connection portion, and each of the outlet channels is similarly connected to the fluid chamber at or by way of a connection portion. The connection portion can be an element that couples two or more other elements, and can be separate from the two or more other elements or can be an integral part of the two or more other elements. 
     The hydrodynamic filter unit  100  can have a planar shape that is polygonal such as rectangular. The hydrodynamic filter unit  100  may be formed of a silicon based polymer material or other type of polymer material. The hydrodynamic filter unit  100  may be formed of, for example, acrylate, polymethylacrylate, COO (Cyclic Olefin Copolymer), polymethylmethacrylate (PMMA), polycarbonate, polystyrene, polyimide, epoxy resin, polydimethylsiloxane (PDMS), parylene, etc. In addition, the hydrodynamic filter unit  100  may be formed by etching a silicon wafer, a silicon-on-glass (SOG) wafer, etc. 
     The fluid chamber  10  may be disposed in one region of the hydrodynamic filter unit  100 . For example, when the planar shape of the hydrodynamic filter unit  100  is rectangular, the fluid chamber  10  may be disposed in a center portion of the rectangular shape of the hydrodynamic filter unit  100 . The hydrodynamic filter unit  100  may have a circular shape or an oval shape, and additionally have polygonal shapes such as a triangular shape, a rectangular shape, etc. The fluid chamber  10  may be connected to the inlet channel  20  and the outlet channels  30  and  35 . 
     The inlet channel  20  is connected to the fluid chamber  10 , and thus the fluid including the target material  50  may be introduced into the fluid chamber  10 . The inlet channel  20  may be tapered toward the fluid chamber  10  from the outside of the hydrodynamic filter unit  100 . That is, the inlet channel  20  may have a tapered structure in which the inlet channel  20  becomes narrow toward the inside of the hydrodynamic filter unit  100 . 
     A first capturing portion  40  may be disposed in the connection portion where the inlet channel  20  and the fluid chamber  10  are connected to each other and capture the target material  50 . That is, the first capturing portion  40  may be disposed in one tapered end portion of the inlet channel  20 . The first capturing portion  40  may include a pair of protrusion portions that protrude from the connection portion. The pair of protrusion portions is tapered toward end portions thereof so that the first capturing portion  40  may well capture the target material  50 . The ends of the pair of protrusion portions may be sharp or blunt and may be modified in various ways. The size of the first capturing portion  40  is a distance d 1  between the pair of protrusion portions, and may be adjusted according to sizes of target materials to be captured. The size d 1  of the first capturing portion  40  may be several μm through several hundred μm. For example, the size d 1  of the first capturing portion  40  may be about 1 μm through about 500 μm, and more particularly, about 5 μm through about 100 μm. 
     The plurality of outlet channels  30  and  35  may include, for example, the first and second outlet channels  30  and  35 . The first and second outlet channels  30  and  35  are connected to the fluid chamber  10  and may discharge the fluid introduced into the fluid chamber  10  to the outside of the hydrodynamic filter unit  100 . The first and second outlet channels  30  and  35  are connected to the fluid chamber  10  in a different direction, for example, in an opposite direction, from the inlet channel  20  and may be spaced apart from each other. The first and second outlet channels  30  and  35  may be tapered toward the fluid chamber  10  from the outside of the hydrodynamic filter unit  100 . That is, the first and second outlet channels  30  and  35  may have a tapered structure in which the first and second outlet channels  30  and  35  become narrow toward the inside of the hydrodynamic filter unit  100 . The first and second outlet channels  30  and  35  may reduce half a maximum flow speed of the fluid in the fluid chamber  10  compared to one outlet channel. 
     The plurality of capturing portions  41  and  43  may include, for example, the second and third capturing portions  41  and  43 . The second and third capturing portions  41  and  43  are disposed in the connection portions to which the fluid chamber  10  and the outlet channels  30  and  35  are connected and may capture the target material  50 . That is, the second and third capturing portions  41  and  43  may be disposed in the tapered end portions of the first and second outlet channels  30  and  35 , respectively. Each of the second and third capturing portions  41  and  43  may include a pair of protrusion portions that protrude from the connection portions. The pair of protrusion portions is tapered toward end portions thereof so that the second and third capturing portions  41  and  43  may well capture the target material  50 . The ends of the pair of protrusion portions may be sharp or blunt and may be modified in various ways. 
     The sizes of the second and third capturing portions  41  and  43  are distances d 2  and d 3  between the pair of protrusion portions, and may be adjusted according to sizes of target materials to be captured. The sizes d 2  and d 3  of the second and third capturing portions  41  and  43  may be several μm to several hundred μm. For example, the sizes d 2  and d 3  of the second and third capturing portions  41  and  43  may be about 1 μm to about 500 μm, and more particularly, about 5 μm to about 100 μm. Meanwhile, the sizes d 2  and d 3  of the second and third capturing portions  41  and  43  may be smaller than the size d 1  of the first capturing portion  40 . When the size d 1  of the first capturing portion  40  is greater than the sizes d 2  and d 3  of the second and third capturing portions  41  and  43 , the target material  50  may be easily introduced into the fluid chamber  10 , and may be captured by the second capturing portion  41  or the third capturing portion  43 . Further, the size d 2  of the second capturing portion  41  may be different from the size d 3  of the third capturing portion  43 . For example, when the size d 2  of the second capturing portion  41  is smaller than the size d 3  of the third capturing portion  43 , the second capturing portion  41  may capture a target material, i.e., another target material, smaller than the target material  50  captured by the third capturing portion  43 . 
     A height h of the hydrodynamic filter unit  100  may be greater than the size of the target material  50 . The greater the height h of the hydrodynamic filter unit  100 , the smaller the shear force in the hydrodynamic filter unit  100  and smaller the pressure applied to the target material  50 . The height h of the hydrodynamic filter unit  100  may be several μm to several hundred μm. For example, the height h of the hydrodynamic filter unit  100  may be about 10 μm to about 500 μm, and more particularly, about 20 μm to about 200 μm. 
     The target material  50  to be captured by the hydrodynamic filter unit  100  may, for example, be any of various biological materials. Biological materials may include cells or other biological molecules. Cells may include, for example, cancer cells, red blood cells (RBCs), white blood cells (WBCs), phagocytes, animal cells, and plant cells. Biological molecules may include various biomolecules constituting a living organism, such as proteins, lipids, DNAs, and RNAs, but the present embodiment is not limited thereto. If target material  50  comprises biological molecules, since sizes of the biological molecules range from several nanometers (nm) to several hundred nanometers (nm), a size of the hydrodynamic filter unit  100 , i.e. a size of a capturing portion, may range from several nanometer (nm) to several hundred nanometers (nm). In this regard, the target material  50  may include, for example, cells such as circulating tumor cells (CTCs) included in blood. The number of CTCs may be so small that only one CTC is detected from among about 10 9  cells. For example, in the case of breast cancer, about 5 CTCs or less may be detected in about 7.5 ml of blood, and in the case of colon cancer, 3 CTCs or less may be detected in about 7.5 ml of blood. Accordingly, it is very important to capture such a small number of CTCs without loss. Also, since CTCs are easily destroyed, external environmental factors that may destroy CTCs should be minimized. 
     Since the hydrodynamic filter unit  100  may capture the target material  50  in any of the first through third capturing portions  40 ,  41 , and  43 , target material  50  is more likely to be captured. Since cells (e.g., CTCs) are surrounded by flexible cell membranes, some of the cells (e.g., CTCs) may be deformed to some extent, for instance, by the hydrostatic pressure of fluid flow through the hydrodynamic filter unit. In this instance, and in other circumstances, the target material can comprise elements that have different shapes or sizes. The portion of the target material  50  having one shape or size, for instance, undeformed CTCs, may be captured by the first capturing portion  40 , and the target material  50  having a different shape or size, for instance, deformed CTCs, may be captured by the second capturing portion  41  or the third capturing portion  43 , thereby reducing the amount of target material (e.g., number of CTCs) that are not filtered and, thus, are lost. Since the hydrodynamic filter unit  100  may filter only desired target material, a time taken to analyze target material may be reduced. Also, since there is often no need to separate the desired target molecules from other materials, efficiency and convenience may be improved. 
     Meanwhile, if the hydrodynamic filter unit  100  includes one outlet channel, if a capturing portion captures a target material, the outlet channel is blocked. Then, since a fluid is continuously introduced into a fluid chamber through an inlet channel, a pressure of the fluid chamber rises, and high pressure may be applied to the target material. The target material may be discharged to the inlet channel or the outlet channel and lost. However, when, for example, the third capturing portion  43  captures the target material  50 , although the target material  50  blocks the second outlet channel  35 , the fluid may be discharged to the first outlet channel  30  including the second capturing portion  41  that does not capture the target material  50 . Further, molecules, other than the target material  50 , along with the fluid may be discharged to the first outlet channel  30 . Thus, the pressure of the fluid chamber  10  drops, thereby preventing high pressure from being applied to the target material  50  and the target material  50  from being lost. 
     Referring to  FIG. 1A , to further describe the hydrodynamic filter unit  100 , the hydrodynamic filter unit  100  may include a first portion  11 , a second portion  13  spaced apart from the first portion  11  and facing the first portion  11 , and a third portion  15  disposed between the first and second portions  11  and  13 . An inlet channel  20  may be disposed between front end portions of the first and second portions  11  and  13 . The third portion  15  may be disposed between rear end portions of the first and second portions  11  and  13 , the rear end portion being that end portion or region of the first and second portions furthest from the inlet chamber. A first outlet channel  30  may be formed between the first and third portions  11  and  15 . A second outlet channel  35  may be formed between the second and third portions  13  and  15 . Meanwhile, the hydrodynamic filter unit  100  may include more portions (e.g., a fourth portion, fifth portion, sixth portion, etc.) arranged relative to the first, second, and third portions so as to provide more outlet channels (e.g., a third outlet channel, fourth outlet channel, fifth outlet channel, etc.). 
     The first portion  11  may include first and second protrusions  21  and  31  that are formed in a first side direction that may face the second portion  13 . The second portion  13  may include third and fourth protrusions  23  and  39  formed toward the first portion  11 . The third portion  15  may include a fifth protrusion  33  formed toward the first portion  11  and a sixth protrusion  38  formed toward the second portion  13 . 
     The portions can be arranged such that the protrusions of the portions define a fluid chamber and capturing portions. The first protrusion  21  may correspond to the third protrusion  23 . The first capturing portion  40  may be formed by the first and third protrusions  21  and  23 . The second protrusion  31  may correspond to the fifth protrusion  33 . The second capturing portion  41  may be formed by the second and fifth protrusions  31  and  33 . The fourth protrusion  39  may correspond to the sixth protrusion  38 . The third capturing portion  43  may be formed by the fourth and sixth protrusion  39  and  38 . 
       FIG. 2  is a plan view of a hydrodynamic filter unit  110  according to another embodiment of the present invention. The differences between the hydrodynamic filter unit  100  described with reference to  FIGS. 1A and 1B  and the hydrodynamic filter unit  110  will now be described in detail. 
     Referring to  FIG. 2 , the hydrodynamic filter unit  110  may include the fluid chamber  10 , the inlet channel  20  that is connected to the fluid chamber  10  and into which a fluid including the target material  50  is introduced, the outlet channels  30  and  35  that are connected to the fluid chamber  10  and through which the fluid is discharged, and the capturing portions  41  and  43  that are respectively disposed in connection portions to which the fluid chamber  10  and the outlet channels  30  and  35  are connected and capture the target material  50 . 
     The hydrodynamic filter unit  110  may further include an accumulation prevention unit  60  disposed between the capturing portions  41  and  43 . The accumulation prevention unit  60  may be disposed between the outlet channels  30  and  35 , i.e., between the capturing portions  41  and  43 . The accumulation prevention unit  60  may be a region protruding from an inside surface of the fluid chamber  10 . Thus, the accumulation prevention unit  60  may prevent molecules other than the target material  50  from being accumulated between the capturing portions  41  and  43 . For example, when CTCs are captured by the third capturing portion  43 , the accumulation prevention unit  60  may prevent RBCs or WBCs other than CTCs from being accumulated between the capturing portions  41  and  43 . Thus, the hydrodynamic filter unit  110  prevents molecules other than the target material  50  to be captured from being accumulated in the fluid chamber  10  and captures the target material  50 , thereby increasing purity of the target material  50  to be filtered. 
       FIG. 3  is a plan view of a hydrodynamic filter unit  120  according to another embodiment of the present invention. The differences between the hydrodynamic filter units  100  and  110  described with reference to  FIGS. 1A, 1B, and 2 , and the hydrodynamic filter unit  120  will now be described in detail. 
     Referring to  FIG. 3 , the hydrodynamic filter unit  120  may include the fluid chamber  10 , the inlet channel  20  that is connected to the fluid chamber  10  and into which a fluid including the target material  50  is introduced, the outlet channels  30  and  35  that are connected to the fluid chamber  10  and through which the fluid is discharged, and capturing portions  45  and  47  that are respectively disposed in connection portions to which the fluid chamber  10  and the outlet channels  30  and  35  are connected and capture the target material  50 . The hydrodynamic filter unit  120  may further include an accumulation prevention unit  65  disposed between the capturing portions  45  and  47 . 
     Shapes of the second and third capturing portions  45  and  47  and the accumulation prevention unit  65  may be formed according to the shape of the target material  50  to be captured. That is, the shapes of the second and third capturing portions  45  and  47  and the accumulation prevention unit  65  may be formed in such a way that a contact area of the target material  50  and the second and third capturing portions  45  and  47  and the accumulation prevention unit  65  may be maximized. For example, when the target material  50  is spherical, the shapes of the second and third capturing portions  45  and  47  and the accumulation prevention unit  65  may be half-spherical. Thus, an external force applied to the captured target material  50  is distributed to the contact area of the target material  50  and the second and third capturing portions  45  and  47  and the accumulation prevention unit  65 , and thus the hydrodynamic filter unit  120  may more stably capture the target material  50  and reduce stress applied to the target material  50 . 
       FIG. 4  is a plan view of a hydrodynamic filter unit  130  according to another embodiment of the present invention. The differences between the hydrodynamic filter units  100 ,  110 , and  120  described with reference to  FIGS. 1A, 1B, 2, and 3 , and the hydrodynamic filter unit  130  will now be described in detail. 
     Referring to  FIG. 4 , the hydrodynamic filter unit  130  may include the fluid chamber  10 , the inlet channel  20  that is connected to the fluid chamber  10  and into which a fluid including the target material  50  is introduced, the outlet channels  30  and  35  that are connected to the fluid chamber  10  and through which the fluid is discharged, and a plurality of capturing portions  41 ′ and  43 ′ that are respectively disposed in connection portions to which the fluid chamber  10  and the outlet channels  30  and  35  are connected and capture the target material  50 . 
     A first capturing portion  40 ′ may be disposed in a connection portion to which the inlet channel  20  and the fluid chamber  10  are connected and capture the target material  50 . That is, the first capturing portion  40 ′ may be disposed in one tapered end portion of the inlet channel  20 . The first capturing portion  40 ′ may include a pair of protrusion portions that protrude from the connection portion. The pair of protrusion portions may have round end portions. If the protrusion portions are round, the target material  50  may be prevented from being damaged due to the protrusion portions. 
     The capturing portions  41 ′ and  43 ′ may include second and third capturing portions  41 ′ and  43 ′. The second and third capturing portions  41 ′ and  43 ′ may be disposed in the connection portions to which the fluid chamber  10  and the outlet channels  30  and  35  are connected and capture the target material  50 . That is, the second and third capturing portions  41 ′ and  43 ′ may be disposed in the tapered end portions of the first and second outlet channels  30  and  35 , respectively. Each of the second and third capturing portions  41 ′ and  43 ′ may include a pair of protrusion portions that protrude from the connection portion. The pair of protrusion portions may have round end portions. If the protrusion portions are round, the target material  50  may be prevented from being damaged due to the protrusion portions. Thus, hydrodynamic filter unit  130  may prevent the target material  50  from being damaged due to the protrusion portions of the first through third capturing portions  40 ′,  41 ′, and  43 ′. 
       FIG. 5  is a plan view of a hydrodynamic filter unit  140  according to another embodiment of the present invention. The differences between the hydrodynamic filter units  100 ,  110 ,  120 , and  130  described with reference to  FIGS. 1A, 1B, 2, 3, and 4 , and the hydrodynamic filter unit  140  will now be described in detail. 
     Referring to  FIG. 5 , the hydrodynamic filter unit  140  may include the fluid chamber  10 , the inlet channel  20  that is connected to the fluid chamber  10  and into which a fluid including the target material  50  is introduced, the outlet channels  30 ,  35 , and  37  that are connected to the fluid chamber  10  and through which the fluid is discharged, and the capturing portions  41 ,  43 , and  49  that are respectively disposed in connection portions to which the fluid chamber  10  and the outlet channels  30 ,  35 , and  37  are connected and capture the target material  50 . 
     The fluid chamber  10  may be connected to the inlet channel  20  and the first through third outlet channels  30 ,  35 , and  37 . If the hydrodynamic filter unit  140  is, for example, rectangular, the inlet channel  20  and the first through third outlet channels  30 ,  35 , and  37  may be disposed in four side surfaces of the hydrodynamic filter unit  140 , respectively. As described above, the first capturing portion  40  may be disposed in the connection portion to which the inlet channel  20  and the fluid chamber  10  are connected and capture the target material  50 . The second through fourth capturing portions  41 ,  43 , and  49  may be disposed in the connection portions to which the fluid chamber  10  and the outlet channels  30 ,  35 , and  37  are connected and capture the target material  50 . That is, the second through fourth capturing portions  41 ,  43 , and  49  may be respectively disposed in the tapered end portions of the outlet channels  30 ,  35 , and  37 , respectively. Each of the second through fourth capturing portions  41 ,  43 , and  49  may include a pair of protrusion portions that protrude from the connection portions. The pair of protrusion portions becomes narrow toward end portions thereof so that the second through fourth capturing portions  41 ,  43 , and  49  may well capture the target material  50 . The ends of the pair of protrusion portions may be sharp or round and may be modified in various ways. 
     Although a plurality of the target materials  50  are captured, the hydrodynamic filter unit  140  including the outlet channels  30 ,  35 , and  37  and the capturing portions  41 ,  43 , and  49  may discharge the fluid and molecules other than the target materials  50  through a capturing portion that fails to capture the target material  50  and an outlet channel. Thus, the fluid chamber  10  maintains low pressure, thereby preventing high pressure from being applied to the target material  50  and preventing the target material  50  from being lost. 
     Referring to  FIG. 5 , to further describe the hydrodynamic filter unit  140 , the hydrodynamic filter unit  140  may include first through fourth portions  71 ,  73 ,  75 , and  77 . The first through fourth portions  71 ,  73 ,  75 , and  77  may be spaced apart from each other with respect to the fluid chamber  10 . The inlet channel  20  may be disposed between the first and second portions  71  and  73 . The first through third outlet channels  30 ,  35 , and  37  may be disposed between the first and third portions  71  and  75 , between the third and fourth portions  75  and  77 , and between the second and fourth portions  73  and  77 , respectively. 
       FIG. 6  is a plan view of a hydrodynamic filter  200  according to an embodiment of the present invention. 
     Referring to  FIG. 6 , the hydrodynamic filter  200  may include an inlet portion  210 , a body portion  220 , and an outlet portion  230 . The hydrodynamic filter  200  may include a plurality of the hydrodynamic filter units  100  described above. The hydrodynamic filter  200  may include a plurality of hydrodynamic filter sequences  240  including the plurality of hydrodynamic filter units  100 . Meanwhile, the hydrodynamic filter  200  may include the hydrodynamic filter units  110 ,  120 ,  130 , and  140 . 
     The inlet portion  210  and the outlet portion  230  may be disposed to face each other with the body portion  220  therebetween. The inlet portion  210  may be connected to the body portion  220  so that a fluid including target materials may be introduced into the body portion  220  from the outside. When a predetermined pressure is applied through the inlet portion  210 , the fluid may flow through the body portion  220 . A connection portion to which the inlet portion  210  and the body portion  220  are connected may be widened toward the body portion  220 . Also, the other connection portion to which the outlet portion  230  and the body portion  220  are connected may be widened toward the body portion  220 . Meanwhile, the outlet portion  230  may discharge a fluid filtered by the hydrodynamic filter  200  to the outside, and the filtered fluid may again be introduced into the inlet portion  210  and may again be filtered by the hydrodynamic filter  200 . 
     The body portion  220  may include the hydrodynamic filter units  100  and the hydrodynamic filter sequences  240  including the hydrodynamic filter units  100 . A width w of the body portion  220  may be greater than the length l thereof. For example, a ratio of the width w and the length l of the body portion  220  may be more than 3:1. Further, the ratio of the width w and the length l of the body portion  220  may range from about 3:1 to about 100:1. More particularly, the ratio of the width w and the length l of the body portion  220  may range from about 3:1 to about 50:1 and from about 3:1 to about 30:1. If the width w of the body portion  220  is greater than the length l thereof, a maximum speed of a flow rate and a maximum pressure applied to target materials may be reduced. 
     The hydrodynamic filter sequences  240  may include the hydrodynamic filter units  100  that are spaced apart from each other or are adjoined with each other. The hydrodynamic filter sequences  240  may be spaced apart from each other and arranged in parallel to each other in a direction of the length l of the body portion  220 . Meanwhile, the hydrodynamic filter sequences  240  may include the hydrodynamic filter units  110 ,  120 ,  130 , and  140 . 
       FIG. 7  is a plan view of hydrodynamic filter sequences  241  and  243  included in the hydrodynamic filter  200  of  FIG. 6 . 
     Referring to  FIG. 7 , the n th  (n is a natural number) and (n+1) th  hydrodynamic filter sequences  241  and  243  may be arranged in parallel to each other in a direction of the length l of the body portion  220 . A hydrodynamic filter unit  101  or  102  included in the n th  hydrodynamic filter sequence  241  and a hydrodynamic filter unit  103  included in the (n+1) th  hydrodynamic filter sequence  243  may not be disposed in a line (i.e., may be disposed in an offset manner). That is, hydrodynamic filter units included in the n th  hydrodynamic filter sequence  241  and hydrodynamic filter units included in the (n+1) th  hydrodynamic filter sequence  243  may be disposed in a zigzag manner. Thus, if the n th  hydrodynamic filter sequence  241  and the (n+1) th  hydrodynamic filter sequence  243  are disposed in zigzags, a fluid, target molecules, and other molecules may have various movement paths. Meanwhile, the hydrodynamic filter units included in the n th  hydrodynamic filter sequence  241  and the hydrodynamic filter units included in the (n+1) th  hydrodynamic filter sequence  243  may not be disposed in zigzags and may be disposed in parallel (in alignment) to each other. 
     Convex portions  25 ,  31 , and  33  may be disposed in front surfaces of the n th  hydrodynamic filter sequence  241  and the (n+1) th  hydrodynamic filter sequence  243  into which the fluid is injected and rear surfaces through which the fluid is discharged. The convex portions  25 ,  31 , and  33  may protrude from the front surfaces and the rear surfaces and be referred to as stagnation prevention portions that prevent a stagnation of the fluid. The first convex portion  25  may be disposed between the inlet channels  20  of adjacent hydrodynamic filter units  101  and  102 . The second convex portion  31  may be disposed between the first and second outlet channels  30  and  35 . The third convex portion  33  may be disposed between the second outlet channels  35  of the hydrodynamic filter unit  101  and the first outlet channels  30  of the adjacent hydrodynamic filter unit  102 . The first through third convex portions  25 ,  31 , and  33  may prevent target materials or other molecules from being accumulated due to the stagnant fluid around the n th  hydrodynamic filter sequence  241  and the (n+1) th  hydrodynamic filter sequence  243 . 
     A method of filtering target materials by using a hydrodynamic filter unit or a hydrodynamic filter including the hydrodynamic filter unit will now be described below. 
     Referring to  FIG. 1A , the method may include introducing a fluid including the target material  50  into the hydrodynamic filter unit  100  described above through the inlet channel  20 , capturing the target material  50  in the hydrodynamic filter unit  100 , and discharging a remaining part of the fluid to the outside of the hydrodynamic filter unit  100  through the outlet channel  30  without the captured target material  50 . Meanwhile, the method may include introducing the fluid including the target material  50  into the hydrodynamic filter units  110 ,  120 ,  130 , and  140  described above. 
     The method may further include, before the introducing of the fluid into the hydrodynamic filter unit  100 , attaching at least one binder to the target material  50 . The binder may include bead, hydro gel, nano particles, or aptamer. The aptamer may include DNA, RNA, or peptide. The binder may be selectively or specifically attached to only the target material  50 . Sizes of the target material  50  to which the binder is attached may be increased to make it more likely that the target material  50  is captured by the first through third capturing portions  40 ,  41 , and  43 . For example, if the target material  50  is CTCs, a plurality of beads may be attached onto the CTCs. It may be difficult to elastically deform cell membranes of the CTCs due to the beads attached onto the CTCs. Thus, the captured CTCs to which the beads are attached may be more easily captured by the second capturing portion  41  or the third capturing portion  43  and rarely leak out of the fluid chamber  10 . 
     Referring to  FIG. 6 , another method may include introducing a fluid including target material  50  into the hydrodynamic filter  200  described above, capturing the target material  50  in the hydrodynamic filter  200 , and discharging a remaining part of the fluid to the outside of the hydrodynamic filter  200 . The method may further include, before the introducing of the fluid into the hydrodynamic filter  200 , attaching at least one binder to the target material  50 . The binder may include bead, hydro gel, nano particles, or aptamer. The aptamer may include DNA, RNA, or peptide. The binder may be selectively or specifically attached to only the target material  50 . 
       FIGS. 8A through 8D  are plan views of a hydrodynamic filter unit for explaining a sequential filtering process. Sizes of first through third capturing portions of the hydrodynamic filter unit may be about 8 μm. A speed of a fluid flowing through the hydrodynamic filter unit may be about 100 μl/min. The target material  50  is a breast cancer cell (MCF-7)  50 . A binder  55  uses a polystyrene or melamine bead. A size of the polystyrene or melamine bead is about 3 μm. 
     Referring to  FIG. 8A , the breast cancer cell  50  to which the bead  55  is attached passes through a first capturing portion. A size of the breast cancer cell  50  to which the bead  55  is attached may be increased to make it more likely that the breast cancer cell  50  is captured by the first through third capturing portions. It may be difficult to elastically deform cell membranes of the breast cancer cell  50 . Thus, the breast cancer cell  50  may rarely leak out of the fluid chamber. 
     Referring to  FIG. 8B , the breast cancer cell  50  that passed the first capturing portion moves to a third capturing portion by using an accumulation prevention portion that protrudes. The accumulation prevention portion may prevent molecules other than the breast cancer cell  50  from being accumulated between a plurality of capturing portions. The accumulation prevention portion may induce the breast cancer cell  50  to move to a second capturing portion or the third capturing portion. 
     Referring to  FIG. 8C , the breast cancer cell  50  was captured in the third capturing portion. The breast cancer cell  50  captured in the third capturing portion blocks a second outlet channel. Nevertheless, a fluid may be discharged to a first outlet channel including the second capturing portion that does not capture the breast cancer cell  50 . Molecules other than the breast cancer cell  50  and the fluid may be discharged to the first outlet channel. Thus, a fluid chamber maintains low pressure, thereby preventing high pressure from being applied to the breast cancer cell  50  and accordingly preventing the breast cancer cell  50  from being lost from the fluid chamber. 
     Referring to  FIG. 8D , although the fluid is continuously introduced into the fluid chamber, the breast cancer cell  50  is being still captured in the third capturing portion. Thus, high pressure is not applied to the breast cancer cell  50  and the breast cancer cell  50  is not lost from the fluid chamber, thereby enhancing a recovery of target molecules. 
       FIG. 9  is a plan view of the hydrodynamic filter for explaining a filtering process. The target material  50  is a breast cancer cell (MCF-7)  50 . Sizes of first through third capturing portions of the hydrodynamic filter unit may be about 8 μm. A speed of a fluid flowing through the hydrodynamic filter unit may be about 100 μl/min. 
     Referring to  FIG. 9 , the hydrodynamic filter includes a plurality of hydrodynamic filter units. The hydrodynamic filter units may form a plurality of hydrodynamic filter sequences arranged in a line. The hydrodynamic filter sequences may be disposed in parallel to each other and disposed in zigzags to each other. That is, hydrodynamic filter units included in an n th  hydrodynamic filter sequence and hydrodynamic filter units included in a (n+1) th  hydrodynamic filter sequence may not be disposed in a line. Thus, if the n th  hydrodynamic filter sequence and the (n+1) th  hydrodynamic filter sequence are disposed in zigzags, a fluid, target molecules, and other molecules may have various movement paths. Convex portions may be disposed in front surfaces of the n th  hydrodynamic filter sequence and the (n+1) th  hydrodynamic filter sequence into which a fluid is injected and rear surfaces through which the fluid is discharged. The convex portions may protrude from the front surfaces and the rear surfaces and be referred to as stagnation prevention portions that prevent a stagnation of the fluid. 
     Each hydrodynamic filter unit may capture one target material  50 . That is, the hydrodynamic filter units may capture a plurality of target materials  50 . If a capturing portion of a hydrodynamic filter unit captures one target material  50 , a newly introduced target material  50  may bypass a different outlet channel. The newly introduced target material  50  may be captured in another capturing portion. Thus, the hydrodynamic filter units may increase capture efficiency of target materials and prevent the target materials  50  from being accumulated in one capturing portion. A flow of a fluid introduced into the hydrodynamic filter units may be prevented from being interfered with due to the accumulated target material  50  or other materials, and fluid stress applied to the target material  50  may be reduced. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof using specific terms, the embodiments and terms have been used to explain the present invention and should not be construed as limiting the scope of the present invention formed by the claims. The preferred embodiments should be considered in a descriptive sense only and not for purposes of limitation. Therefore, the scope of the invention is formed not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention.