Fluid dynamic focusing device

Abstract

A hydrodynamic focusing device, preferably implemented as a microfluidic device, comprises a first flow channel (4), a second, smaller flow channel (8), an enclosure region (12) coaxially connected between the first flow channel (4) and the second flow channel (8), and a chimney (14) comprising a body (16) and a sample fluid inlet (18), the chimney extending from a preferably sloped wall (20) delimiting the enclosure region (12) and into the enclosure region (12). The body (16) and the sample fluid inlet (18) each are formed with an elongated, preferably tear-drop shaped profile having a front edge (28) facing the first flow channel (4) and opposite long edges (30a, 30b) tapering towards a back edge (32).

Description

Technical Field

[0001] This invention relates to a hydrodynamic focusing device. Background Technology

[0002] The need to analyze, classify, or otherwise dispose of single particles in a flowing sample fluid often requires focusing the sample fluid into a precise, uniform flow. Such focusing is typically achieved by encapsulating the sample fluid with a sheath fluid and spatially compressing it into an extremely thin and precisely positioned flow. Hydrodynamic focusing devices typically consist of two main components: a first channel, which includes an encapsulation region; and a second channel, which is typically the channel in which measurements are performed on the sample fluid. The sheath fluid flows in the first channel to encapsulate and focus a second sample fluid flow introduced into the sheath fluid via a sample fluid inlet at the encapsulation region. This second sample fluid typically contains the artificial or biological particles to be measured.

[0003] The volumetric sheath fluid flow is significantly larger than the volumetric sample fluid flow, typically 30 times larger. The sheath fluid flow is introduced into the first channel and used to focus the sample fluid flow into the second channel. The second channel has a smaller cross-section than the first channel, typically approximately 0.2 x 0.2 mm. 2 This allows lasers or other known measurement modes to query the sample particles now flowing in a column in the sample liquid at the measurement area of ​​the second channel.

[0004] To achieve effective focusing of the sample fluid, it is crucial to position the inlet of the sample fluid flow in such a way that the sample fluid becomes completely encapsulated by the flowing sheath fluid. A conventional method for addressing this problem is to introduce the sample fluid flow via a needle inlet coaxially positioned with the sheath fluid flow in the encapsulation zone of the first channel. However, depending on the needle size, this method can be prone to clogging. The method also requires very precise alignment between mechanical components. Furthermore, from an economic perspective, it is desirable to manufacture such devices using methods such as injection molding, additive manufacturing, or photolithography. However, achieving the geometry described above, which allows the sample fluid inlet to be completely surrounded by the sheath fluid flow, is extremely difficult.

[0005] EP 1281059 describes a hydrodynamic focusing apparatus that addresses problems associated with conventional methods. This hydrodynamic focusing apparatus employs a short tube or 'flue' inlet for the sample fluid, which protrudes perpendicularly to the flow direction of the sheath fluid into the encapsulation zone of a first channel, such that a 'plume' of the sample fluid from the flue will migrate downstream toward a second channel as the sheath fluid flows.

[0006] The advantages of using a flue design are primarily manufacturing-related, as the design does not have a negative slip angle, meaning it lacks overhang structures. This enables numerous cost-effective manufacturing techniques, such as injection molding, additive manufacturing, or photolithography. However, the flue itself introduces significant interference into the sheath flow. This, in turn, negatively impacts the shape of the focused sample fluid in the measurement region. The primary cause of this interference is the wake effect downstream of the flue. Flow conditions in the wake region will tend to widen and distort the plume from the inlet flue, negatively affecting measurement quality due to differences in, for example, sample fluid velocity, measurement laser illumination intensity, and optical focus.

[0007] An alternative hydrodynamic focusing device has been developed, disclosed in US 9784644. This device essentially replaces the flue of the device described in EP 1281059 with a specifically shaped island in which a sample fluid inlet is formed. The island is shaped to reduce the wake effect associated with known flues. The device generally includes: a microfluidic chip in which a first channel for carrying sheath fluid is formed; a rhomboid chamber coaxial with the first channel to form an encapsulation region; a central rhomboid island projecting into and concentrically positioned within the chamber, the island having smaller lateral and vertical dimensions than the chamber, allowing sheath fluid to flow from the channel through the chamber, around the lateral sides of the island, and above the top surface of the island; a sample fluid inlet through the island, terminating at the top surface of the island; and a second channel for receiving sheath fluid from the chamber and the encapsulated, focused sample fluid, having a smaller cross-section than the first channel. Any sample fluid introduced into the microfluidic device through the sample fluid inlet is thus carried downstream along the top surface of the island and laterally confined by the sheath fluid, which forms a barrier below the sample fluid. As the sample fluid flows horizontally out of the top surface of the island, a portion of the sheath fluid already flowing around the island confines the sample fluid from below, and the sample fluid becomes hydrodynamically focused.

[0008] However, depending on the flow conditions, there is a risk that the sample fluid flow may spread across the island's surface and become distorted in unpredictable ways. Furthermore, particles in the sample fluid may be trapped at the island's surface, which in turn can lead to unpredictable flow characteristics. Summary of the Invention

[0009] According to a first aspect of the invention, a hydrodynamic focusing apparatus is provided, comprising: a first flow channel; a second flow channel having a smaller cross-section than the cross-section of the first flow channel; an encapsulation region coaxially connected between the first and second flow channels; and a flue including a body and a sample fluid inlet, the body extending from the wall of the encapsulation region into the encapsulation region and having smaller lateral and vertical dimensions than the encapsulation region; wherein the body and the sample fluid inlet each form an elongated profile having a front edge facing the first flow channel and long edges that taper relative to each other toward a rear edge.

[0010] A more hydrodynamically efficient shape for the flue has the advantage of suppressing any wake effect. In some embodiments, the flue is configured to have a trailing edge angle of about 30° or less (i.e., the angle formed at the trailing edge of the flue between the tangents of the long edge of the flue). With this configuration, it has been found that the wake effect can be substantially eliminated or at least measurably reduced.

[0011] Since the flue body is not large enough in the direction of fluid flow through the encapsulation zone to act as a support for the sample fluid, smearing of the sample fluid and capture of particles can be avoided.

[0012] In some embodiments, the flue slopes from its extending base plate toward the second flow channel, wherein the slope begins at a distance (upstream or downstream) from the center of the leading edge, said distance being selected so that the upward sheath flow influences the morphology of the encapsulated sample fluid. This distance is typically within 1.5 times the height of the first flow channel immediately upstream of the leading edge, and in some embodiments, zero times. This has the advantage of making it easier to adjust the morphology of the hydrodynamically focused sample fluid.

[0013] In some embodiments, the first flow channel, the second flow channel, and the encapsulation region are formed as a portion of a substrate, such as the substrate of a microfluidic chip, wherein a lens is also formed in the substrate at a location below the measurement region of the second flow channel, and the lens is optically connected to the measurement region through an optically transparent material portion of the substrate.

[0014] According to a second aspect of the present invention, a method for hydrodynamically focusing a sample fluid using a hydrodynamic focusing apparatus according to a first aspect of the present invention is provided, the method comprising: (i) allowing a sheath fluid to flow through a first flow channel into an encapsulation region; (ii) introducing a sample fluid into the encapsulation region through a sample fluid inlet of a flue such that the sample fluid is hydrodynamically focused by the sheath fluid as it exits the flue; and (iii) allowing the encapsulated, hydrodynamically focused sample fluid to flow out of the encapsulation region and into a second flow channel.

[0015] Unless otherwise specifically stated, directions and dimensions will be referred to herein with respect to the channels or other features described and the flow within those channels or other features. Thus, “axial,” “flow direction,” or “upstream / downstream” will refer to a direction generally parallel to or consistent with the fluid flow through the channels or other features. The term “bottom” or “base” will refer to the wall of a channel or other feature (e.g., formed in a chip substrate) intended to be the lowest inner surface of the chamber or feature in use. Similarly, “top” or “top plate” will refer to the wall of a channel or other feature (e.g., a barrier formed by a layer applied over the chip substrate) intended to be the highest inner surface of the chamber or feature in use. The term “above” will refer to a direction generally away from the base of the channel or other feature. Similarly, “lateral” or “horizontal” will refer to a direction generally toward or away from the sidewalls (not the top or bottom walls) of the channel or other feature. Corresponding terms will be interpreted in a similar manner. In some descriptions, the direction or dimension may be additionally or alternatively represented by X, Y, and Z, which are mutually orthogonal directions, wherein the X and Y directions lie in a plane parallel to the direction in which the fluid flows through the channel or other feature. Attached Figure Description

[0016] Exemplary embodiments of the invention will now be explained in more detail with reference to the accompanying drawings, in which:

[0017] Figure 1 A plan view showing an embodiment of the hydrodynamic focusing device according to the present invention;

[0018] Figure 2 exhibit Figure 1 The embodiment of the hydrodynamic focusing device described herein is shown along the side view of AA;

[0019] Figure 3 Describe the focusing mode of the sample fluid, wherein (i) there is no wake effect; (ii) it is customized using the tilt of the base plate of the encapsulation region; and (iii) there is a wake effect; and

[0020] Figure 4 This section describes certain design aspects of the flue of the device according to the invention. Detailed Implementation

[0021] Now consider Figure 1 and Figure 2An example of the hydrodynamic focusing apparatus 2 according to the invention is described below. The hydrodynamic focusing apparatus 2 here includes: a first flow channel 4 for a sheath fluid flow 6; a second flow channel 8 for a flow of fluid 10 encapsulated over a sample; an encapsulation region 12 coaxially connected between the first flow channel 4 and the second flow channel 8, and integral with the first flow channel 4 here; and a flue 14 including a flue body 16 and a sample fluid inlet 18 housed therein. The flue body 16 extends from the wall (or base plate) 20 of the encapsulation region 12 and into the encapsulation region 12, and is configured to have smaller lateral (X' and 'Y') and vertical ('Z') dimensions compared to the lateral (X' and 'Y') and vertical (Z') dimensions of the encapsulation region 12. The sample fluid inlet 18 terminates at a first end 22 within the encapsulation region 12, coinciding with the end of the body 16, and connects to the sample fluid flow 26 at an opposite end 24.

[0022] The flue body 16 and the sample fluid inlet 18 are substantially concentric and together form the flue 14, which has a generally elongated profile in a plane parallel to the general direction of fluid flow through the encapsulation region 12 from the first flow channel 4 to the second flow channel 8. In this embodiment, the flue 14 has an arcuate nose or 'front edge' 28 and tapers along its generally relatively long edges 30a, 30b to form a narrower tail or 'rear edge' 32. Figure 1 and Figure 2 In the embodiments described herein, both the flue body 16 and the sample fluid inlet 18 are symmetrically teardrop-shaped and extend from the base plate 20, centered between the opposing walls 34, 36 of the encapsulation region 12. This teardrop shape is particularly effective in terms of hydrodynamics, but it should be understood that other hydrodynamically effective shapes of the flue 14 may be employed, provided that the shape conforms to the general form described above. Furthermore, in some embodiments, one or both of the long edges 30a, 30b are flexible, and in some embodiments, the teardrop shape is asymmetrical. In some embodiments, the flue body may be inclined relative to the vertical direction in the direction of the sheath fluid flow 6 from the first flow channel 4 toward the second flow channel 8. This provides a vector component of the sample fluid flow 26 in the direction of the sheath fluid flow 6, which facilitates the encapsulation of this sample fluid flow 26.

[0023] Upon encountering the leading edge 28 of the flue 14, the sheath fluid flow 6 is split by the leading edge 28 into: flow 6i, which flows around the flue along a path between the long edge 30a of the flue 14 and the opposing wall 34 of the encapsulation region 12; flow 6ii, which flows around the flue along a path between the long edge 30b of the flue 14 and the opposing wall 36 of the encapsulation region 12; and flow 6iii, which flows along a path between the first end 22 of the sample fluid inlet 18 and the cover 46 (or top plate) of the encapsulation region 12, which is generally opposite to the wall 20 (or bottom plate) from which the flue body 16 extends. Sheath fluid flows 6i, 6ii, and 6iii recombine after the trailing edge 32 of the flue 14. During the simultaneous flow of the sheath fluid 6 through the encapsulation zone 12, the sample fluid flow 26, which exits the sample fluid inlet 18 at its end 22, is encapsulated by the sheath fluid 6 after the rear edge 32, so as to travel as a hydrodynamically focused encapsulated sample fluid flow 10 toward the second flow channel 8.

[0024] Any wake effect downstream of flue 14 will tend to widen and distort the plume of sample fluid exiting sample fluid inlet 18, and negatively affect the shape of the hydrodynamically focused sample fluid. This is in Figure 3 Section (iii) describes a flue with a known construction. This wake effect can be suppressed by employing the more hydrodynamically efficient flue shape of the present invention. Specifically, this is achieved by configuring flue 14 with a trailing edge angle θ of less than approximately 30° (see section [link to original text]). Figure 4 This can essentially eliminate any wake effect (where it is present) and produce a generally circular, hydrodynamically focused sample stream, such as... Figure 3 (i) as explained. Figure 4 As explained, the rear edge angle θ is the angle formed at the rear edge 32 of the flue body 16 between the tangents (dashed lines in the figure) of the corresponding long edges 30a and b of the flue body. In this embodiment, where both long edges 30a and b are straight edges, the tangents will be parallel to these edges 30a and b.

[0025] Usefully, the walls 34, 36 of the encapsulation region 12, which are partially opposite the long edges 30a, 30b of the flue 14, taper toward the second flow channel 8 to facilitate the positioning of the hydrodynamically focused sample fluid 26 relative to the second flow channel 8. The walls 20 extending from the flue body 16 may also be tapered, i.e., inclined, to aid in this positioning.

[0026] It has been found that if the starting point of the inclination of wall 20 is at flue 14 (see...) Figure 4The wall is particularly useful near the point where the inclination of the flue body 16 from its extending wall 20 begins. It has been found that the upward sheath flow direction immediately following the rear edge 32 will affect the morphology of the encapsulated hydrodynamically focused sample fluid and can be used in conjunction with the selection of the shape of the flue 14 to better adjust the morphology of the hydrodynamically focused sample fluid for a specific application. For example, in the case where particles in the sample fluid flow 26 will be measured using a laser at the measurement area 38 of the second flow channel 8. Typically, the illumination from the laser will have a narrow spatial intensity distribution in the direction perpendicular to the flow direction ('X' direction) ('Y' direction). By starting with the inclination of the base plate 20 arranged as described above, the hydrodynamically focused sample fluid can be focused in the 'Y' direction with a relatively reduced size, such as... Figure 3 As explained in (ii), use appropriate hydrodynamic simulation software, such as Siemens Star. TM CCM+ or COMSOL Multiphysics TM The software can easily model the effect of tilting relative to the change in the starting position of flue 14 and determine its effect on the morphology of the sample fluid after hydrodynamic focusing. In this way, it has been found that it is particularly advantageous to begin tilting at a distance from the center C of the leading edge 28 of flue 14, said distance being less than about three times, preferably within about 1.5 times, and more precisely less than one time, the height h of the first flow channel 4 immediately upstream of the leading edge 28 of flue 14.

[0027] In some embodiments, lens 40 may be provided integrally with the hydrodynamic focusing device 2. Lens 40 may be used as a primary focusing lens or a secondary lens. The secondary lens is used only to improve light collection and is required outside the primary focusing lens (not described) of the hydrodynamic focusing device 2. The advantages of using integrating lens 40 as the primary lens include i) saving the cost of an external focusing lens and ii) improving light collection by eliminating refraction in the air. The advantage of using integrating lens 40 as the secondary lens is that it improves light collection by eliminating refraction in the air while leaving the design features of the primary lens to the external primary focusing lens. For the refraction to be eliminated when used as a secondary lens, lens 40 should be hemispherical with its center approximately located in the middle of the second flow channel 8. This is in Figure 1 and Figure 2 This is explained in the text. For both applications, there is also a common advantage regarding optical alignment: this is easy because the distance between lens 40 and the second flow channel 8 is permanently fixed.

[0028] Useful land, and as Figure 1 and Figure 2As illustrated in the embodiments, the hydrodynamic focusing device 2 can be formed on or in the substrate 42 of the microfluidic chip using conventional manufacturing techniques frequently employed by semiconductor chip manufacturers, such as injection molding, additive manufacturing, micromachining, or photolithography, and a separate cover 46 can be applied. A lens 40 may then be formed as a portion of the substrate 42 directly beneath the measurement region 38. The portion 44 of the substrate between the measurement region 38 and the lens 40 is made of an optically transparent material, thereby optically connecting the lens 40 to at least a portion of the measurement region 38.

Claims

1. A hydrodynamic focusing device (2) comprising a first flow channel (4); a second flow channel (8) dimensioned to have a smaller cross-section than the first flow channel (4); an enclosure region (12) coaxially connected between the first flow channel (4) and the second flow channel (8), the first flow channel (4), the second flow channel (8) and the enclosure region (12) being configured to mutually define a flow direction extending from the first flow channel (4) through the enclosure region (12) and to the second flow channel (8); and a chimney (14) comprising a chimney body (16) and a substantially coaxial sample fluid inlet (18) having a first end (22), the chimney body (16) extending from a wall (20) of the enclosure region (12) to an end disposed in the enclosure region (12), the chimney body having smaller lateral (X, Y) and vertical (Z) dimensions than the enclosure region (12); the first end (22) of the sample fluid inlet (18) terminating within the enclosure region coincident with the end of the chimney body (16) and substantially perpendicular to the flow direction, such that the sample fluid inlet (18) is configured to supply sample fluid (26) into the enclosure region (12) in a direction substantially perpendicular to the flow direction; wherein the chimney body (16) and the sample fluid inlet (18) each form an elongate profile having a rounded leading edge (28) facing the first flow channel (4); an opposing trailing edge (32); and long edges (30a, 30b) connecting the rounded leading edge (28) and the trailing edge (32) and tapering relatively towards the trailing edge (32).

2. The hydrodynamic focusing device (2) of claim 1, wherein the elongate profile of both the chimney body (16) and the sample fluid inlet (18) is teardrop-shaped.

3. The hydrodynamic focusing device (2) of claim 2, wherein the teardrop shape is a symmetrical teardrop shape.

4. The hydrodynamic focusing device (2) of claim 1, wherein the chimney body (16) forms a trailing edge angle Θ of about thirty degrees or less.

5. The hydrodynamic focusing device (2) of claim 1, wherein the wall (20) from which the chimney body (16) extends is inclined towards the second flow channel (8), wherein the inclination begins at a location relative to the chimney (14) selected to produce an upward flow of sheath fluid in the enclosure region (12) to influence the morphology of a coated hydrodynamically focused sample fluid flow (10).

6. The hydrodynamic focusing device (2) of claim 5, wherein the inclination of the wall (20) from which the chimney body (16) extends begins at a distance from a centre (C) of the rounded leading edge (28) that is within about three times a height of the first flow channel (4) immediately upstream of the rounded leading edge (28).

7. The fluid dynamic focusing device (2) of claim 6, wherein the tilt of the wall (20) from which the chimney body (16) extends begins at the center (C) of the rounded front edge (28).

8. The fluid dynamic focusing device (2) of claim 5 or claim 6, wherein the tilt of the wall (20) from which the chimney body (16) extends begins upstream of the chimney (14).

9. The fluid dynamic focusing device (2) of claim 1, wherein the first flow channel (4), the second flow channel (8); the enclosure region (12) and the chimney (14) are formed as part of a substrate (42), wherein further a lens (40) is formed in the substrate at a location below a measurement region (38) of the second flow channel (8), the lens (40) being optically coupled to the measurement region (38) through an optically transparent material portion (44) of the substrate (42).

10. A method of hydrodynamically focusing a sample fluid using the hydrodynamic focusing device (2) according to any one of claims 5 to 8, the method comprising: (i) flowing sheath liquid (6) through the first flow channel (4) into the enclosure region (12); (ii) introducing sample fluid (26) into the enclosure region (12) through a first end (22) of the sample fluid inlet (18) of the chimney (14) located in the enclosure region (12) such that the sample fluid (26) is fluid dynamically focused by the sheath liquid (6) as it exits the chimney; and (iii) flowing the coated fluid dynamically focused sample fluid flow (10) out of the enclosure region (12) and into the second flow channel (8).

10. The fluid dynamic focusing device (2) of claim 1, wherein the first flow channel (4) is formed as a microfluidic channel (4) having a width of 50 micrometers or less.

11. The fluid dynamic focusing device (2) of claim 1, wherein the second flow channel (8) is formed as a microfluidic channel (8) having a width of 50 micrometers or less.

12. The fluid dynamic focusing device (2) of claim 1, wherein the enclosure region (12) is formed as a microfluidic channel (12) having a width of 50 micrometers or less.

13. The fluid dynamic focusing device (2) of claim 1, wherein the chimney (14) is formed as a microfluidic channel (14) having a width of 50 micrometers or less.

14. The fluid dynamic focusing device (2) of claim 1, wherein the sample fluid inlet (18) of the chimney (14) is formed as a microfluidic channel (18) having a width of 50 micrometers or less.

15. The fluid dynamic focusing device (2) of claim 1, wherein the sample fluid outlet (20) of the chimney (14) is formed as a microfluidic channel (20) having a width of 50 micrometers or less.

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