Surface acoustic wave microfluidic device for separating particles with wide particle size distribution

Abstract

A surface acoustic wave micro-fluidic device for separating particles with wide particle size distribution belongs to the crossing field of surface acoustic wave and micro-fluidic technology, and adopts the specific scheme that the surface acoustic wave micro-fluidic device for separating particles with wide particle size distribution comprises an interdigital electrode, a piezoelectric substrate, a PDMS (Polydimethylsiloxane) substrate and a separation area flow channel, the bottom surface of the separation area flow channel is a piezoelectric substrate, the other side walls are PDMS substrates, and the interdigital electrode is arranged on the piezoelectric substrate; the separation area flow channel is of an axial symmetry structure and comprises an inlet channel I, a main outlet channel I and at least two branch outlet channels II, the inlet channel I and the main outlet channel I are located on the symmetry axis, and all the branch outlet channels II are symmetrically distributed on the two sides of the main outlet channel I; and the included angle between the symmetry axis of the flow channel in the separation area and the finger strip of the interdigital electrode is 10-75 degrees. The single-step separation of various particles with different particle size distribution ranges within the minimum critical particle size range and the maximum critical particle size range can be realized.

Description

Technical Field

[0001] The present invention belongs to the cross - field of surface acoustic wave and microfluidic technology, and particularly relates to a surface acoustic wave microfluidic device for separating particles with a wide particle size distribution. Background Art

[0002] Surface Acoustic Wave (SAW) is a mechanical wave propagating along the surface of an elastic solid, and its energy is concentrated within a depth range of about one wavelength below the material surface. Since the commercialization of surface acoustic wave devices in the radar and communication fields in the 1960s, this technology has been widely used in the manufacture of various micro - electromechanical system devices such as sensors, radio frequency filters, and microfluidic chips, and has important application value in the field of particle separation.

[0003] In the field of particle separation, traditional techniques such as centrifugal separation, filtration, and electrophoresis separation generally face problems such as low separation efficiency, high cost, complex equipment, or damage to samples. For example, centrifugal separation relies on the inertial force generated by high - speed rotation and is difficult to achieve precise separation of particles at the micro - scale; filtration is easily affected by clogging and is difficult to separate nanoparticles; electrophoresis technology is sensitive to the conductivity of the solution, and the Joule heat generated during separation easily causes inactivation of biological samples. In recent years, the development of microfluidic technology has promoted the progress of miniaturized separation technology, among which the acoustic streaming technology using sound waves, such as surface acoustic waves, has significant advantages. A surface acoustic wave microfluidic separation device is usually prepared by bonding an interdigital transducer and a polydimethylsiloxane (PDMS) substrate. After bonding, the cavity between the PDMS substrate and the interdigital transducer forms a microchannel. The interdigital transducer uses the piezoelectric effect and inverse piezoelectric effect of a piezoelectric substrate, such as a lithium niobate substrate or a quartz substrate, to generate surface acoustic waves. Inputting an electrical signal with a specific frequency into the interdigital transducer can excite surface acoustic waves, and then generate controllable acoustic radiation force and acoustic streaming effect in the microchannel, thereby realizing non - contact manipulation of micron - and sub - micron - sized particles. Its core advantages include: (1) no physical contact, avoiding sample contamination; (2) the separation effect can be adjusted in real time by adjusting parameters such as input frequency and power to ensure separation accuracy; (3) the device structure is compact and easy to integrate with the microfluidic system; (4) suitable for biocompatible scenarios with low damage to living biological particles.

[0004] However, when separating particles with a wide particle size distribution, there are still significant challenges in existing surface acoustic wave microfluidic separation technologies: (1) Usually, more than two sets of interdigital transducers are required for multi-step separation, increasing the complexity of the flow channel design and significantly increasing the device design and manufacturing costs; (2) The particle size resolution (the minimum particle size difference of particles that can be separated within the target particle size distribution range) is low, and particles with a specific narrow particle size distribution within the target particle size distribution range cannot be accurately separated. Therefore, a new type of surface acoustic wave microfluidic separation device that can separate particles with a wide particle size distribution in a single step and has a high particle size resolution is needed. Summary of the Invention

[0005] To solve the problems in the background technology, the present invention provides a surface acoustic wave microfluidic device for separating particles with a wide particle size distribution.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A surface acoustic wave microfluidic device for separating particles with a wide particle size distribution includes interdigital electrodes, a piezoelectric substrate, a PDMS substrate, and a separation region flow channel. The bottom surface of the separation region flow channel is the piezoelectric substrate, and the remaining side walls are the PDMS substrate. The interdigital electrodes are arranged on the piezoelectric substrate; the separation region flow channel is an axisymmetric structure, including an inlet channel I, a main outlet channel I, and N branch outlet channels II, where N is an even number and N≥2; the inlet channel I and the main outlet channel I are located on the axis of symmetry, and all the branch outlet channels II are symmetrically distributed on both sides of the main outlet channel I. The angle between the axis of symmetry of the separation region flow channel and the finger bars of the interdigital electrodes is 10°-75°. The present invention can achieve single-step separation of particles with various particle size distribution ranges within the range of the minimum critical particle size and the maximum critical particle size. The ratio of the maximum critical particle size to the minimum critical particle size is the product of the square root of the flow rate ratio and the sound pressure ratio, and the minimum critical particle size is set as the minimum particle size of the target particles.

[0008] Further, when the number of interdigital electrodes is one set, the interdigital electrodes are located below the separation region flow channel; when the number of interdigital electrodes is two sets, the two sets of interdigital electrodes are distributed on both sides of the separation region flow channel.

[0009] Further, the interdigital electrodes and the piezoelectric substrate together form an interdigital transducer, and the types of the interdigital transducer include a single-ended bidirectional interdigital transducer, a single-ended unidirectional interdigital transducer, a combination of a single-ended unidirectional and bidirectional interdigital transducer, a double-ended bidirectional interdigital transducer, a double-ended unidirectional interdigital transducer, or a combination of a double-ended unidirectional and bidirectional interdigital transducer.

[0010] Further, the height of the separation region flow channel is 20-500μm.

[0011] Further, the number N of the branch outlet channels II is 2, 4, 6, 8, 10, 12, 14 or 16.

[0012] The sound pressure ratio is the ratio of the maximum effective sound pressure to the peak value of the nearest effective sound pressure at the end of the inlet channel I on the symmetry axis of the flow channel in the separation region, obtained by simulation or amplitude measurement (the effective sound pressure shows periodic changes), and the value is preferably between 1 and 5.

[0013] The flow rate ratio is the ratio of the sum of the cross-sectional areas of the main outlet channel I and all branch outlet channels II of the flow channel in the separation region to the cross-sectional area of the inlet channel I in the separation region, and the value is preferably between 2 and 36. The inlet channel I, the main outlet channel I, and the branch outlet channels II are all straight flow channels.

[0014]

[0015] Critical particle size D p,crit The expression is

[0016]

[0017] In the formula, p0 is the sound pressure, μ is the viscosity of the liquid, v l is the liquid flow velocity near the particle, λ is the sound wave wavelength, θ is the angle between the finger bars of the interdigital electrode and the symmetry axis of the flow channel in the separation region, β l is the compressibility of the liquid, and φ is the acoustic contrast factor. In the flow channel of the separation region, v l , p0, two physical quantities affecting the critical particle size, are regularly distributed in the space of the flow channel in the separation region, resulting in a decreasing critical particle size along the symmetry axis direction starting from the end of the inlet channel I in the separation region. During the separation process, small particles with a particle size lower than the minimum critical particle size flow out from the main outlet channel I; large particles with a particle size exceeding the maximum critical particle size, and particles with a particle size distributed within the range between the minimum and maximum critical particle sizes flow out from the branch outlet channels II.

[0018] Further, the material of the piezoelectric substrate is lithium niobate, lithium tantalate, aluminum nitride, gallium nitride or quartz, and the material of the interdigital electrode is gold, aluminum, copper, titanium, palladium, chromium, molybdenum or platinum.

[0019] Further, the thickness of the interdigital electrode is 40 - 300 nm.

[0020] Further, the surface acoustic wave microfluidic device further includes a liquid inlet region flow channel, the outlet channel III of the liquid inlet region flow channel is communicated with the inlet channel I of the separation region flow channel, and the inlet channel II of the liquid inlet region flow channel includes an intermediate liquid inlet channel and two sheath liquid inlet channels.

[0021] Further, the two sheath liquid inlet channels are symmetrically distributed on both sides of the middle liquid inlet channel.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) The number of critical particle sizes (the critical value of particle size, particles with a size smaller than this critical value in the separation region move along the streamline direction; particles with a size larger than this critical value move along the direction parallel to the fingers of the interdigital electrode) of traditional surface acoustic wave microfluidic separation devices is usually within 5; compared with traditional surface acoustic wave microfluidic separation devices, the present invention optimizes the microchannel topology structure and the interdigital transducer design in the separation region, and physical quantities such as liquid flow velocity and sound pressure in the flow channel in the separation region during the separation process are regularly distributed in the flow channel space, and the number of critical particle sizes in a single-step separation of the separation device can be increased to dozens. Therefore, the surface acoustic wave microfluidic device for separating particles with a wide particle size distribution described in the present invention can separate particles with a wide particle size distribution, that is, it can single-step separate various particles with different particle size distribution ranges within the range of the minimum critical particle size and the maximum critical particle size, and the particle size resolution is significantly improved. Compared with traditional surface acoustic wave microfluidic separation devices, the number of critical particle sizes is increased from less than 5 to dozens, and the particle size resolution is significantly improved.

[0024] (2) The present invention only requires a single-ended interdigital transducer or a group of double-ended interdigital transducers, and the device structure is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a cross-sectional schematic diagram of the surface acoustic wave microfluidic device of the present invention;

[0026] Figure 2 is a top view schematic diagram of the flow channel in the liquid inlet region;

[0027] Figure 3 is a top view schematic diagram of the flow channel in the separation region;

[0028] Figure 4 is a complete structure diagram of a surface acoustic wave microfluidic device with an included angle of 45° between the axis of symmetry and the fingers of the interdigital electrode and 8 branch outlet channels II;

[0029] Figure 5 is an actual structure diagram of the separation region flow channel with an included angle of 60° between the axis of symmetry and the fingers of the interdigital electrode and 8 branch outlet channels II;

[0030] Figure 6 is a fluorescence micrograph of the movement of polystyrene particles when no electrical signal is applied;

[0031] Figure 7It is a fluorescence micrograph of the movement of polystyrene particles with a particle size distribution range of 300 - 800 nm when an electrical signal is applied to the interdigital electrodes in Example 3;

[0032] Figure 8 It is a fluorescence micrograph of the movement of polystyrene particles with a particle size distribution range of 1.5 - 2.5 μm when an electrical signal is applied to the interdigital electrodes in Example 3;

[0033] Figure 9 It is a fluorescence micrograph of the movement of polystyrene particles with a particle size distribution range of 4 - 5.8 μm when an electrical signal is applied to the interdigital electrodes in Example 3;

[0034] Figure 10 It is a schematic structural diagram of the combination of a single - end unidirectional and a bidirectional interdigital transducer;

[0035] Figure 11 It is a top - view schematic diagram of the separation - region flow channel using a double - end bidirectional interdigital transducer;

[0036] In the figure, 1. Interdigital electrode, 2. Piezoelectric substrate, 3. PDMS substrate, 4. Separation - region flow channel, 5. Inlet - region flow channel, 6. Single - end unidirectional interdigital transducer, 7. Single - end bidirectional interdigital transducer, 41. Inlet channel Ⅰ, 42. Main outlet channel Ⅰ, 43. Branch outlet channel Ⅱ, 431. First channel, 432. Second channel, 433. Third channel, 434. Fourth channel, 51. Outlet channel Ⅲ, 52. Inlet channel Ⅱ, 521. Intermediate - liquid inlet, 522. Sheath - liquid inlet. Detailed implementation manners

[0037] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0038] Example 1:

[0039] A surface acoustic wave microfluidic device for separating particles with a wide particle - size distribution includes an interdigital electrode 1, a piezoelectric substrate 2, a PDMS substrate 3, and a separation - region flow channel 4. The bottom surface of the separation - region flow channel 4 is the piezoelectric substrate 2, and the remaining side walls are the PDMS substrate 3. The interdigital electrode 1 is disposed on the piezoelectric substrate 2; the cross - sectional schematic diagram is as Figure 1As shown, the flow channel 4 in the separation region has an axisymmetric structure, including an inlet channel I 41, a main outlet channel I 42, and two branch outlet channels II 43. The inlet channel I 41 and the main outlet channel I 42 are located on the axis of symmetry. The two branch outlet channels II 43 are symmetrically distributed on both sides of the main outlet channel I 42. The included angle between the axis of symmetry of the flow channel 4 in the separation region and the finger bars of the interdigital electrode 1 is 30°, as Figure 3 shown. Single-step separation of particles with different particle size distribution ranges within the range of the minimum critical particle size and the maximum critical particle size is achieved. The ratio of the maximum critical particle size to the minimum critical particle size is the product of the square root of the flow rate ratio and the sound pressure ratio. The sound pressure ratio is the ratio of the maximum effective sound pressure to the peak value of the nearest effective sound pressure at the end of the inlet channel I 41 on the axis of symmetry of the flow channel 4 in the separation region obtained by simulation or amplitude measurement. The flow rate ratio is the ratio of the sum of the cross-sectional areas of the main outlet channel I 42 and all branch outlet channels II 43 of the flow channel 4 in the separation region to the cross-sectional area of the inlet channel I 41. The inlet channel I 41, the main outlet channel I 42, and the branch outlet channels II 43 are all straight flow channels.

[0040] Furthermore, the interdigital electrode 1 and the piezoelectric substrate 2 together form an interdigital transducer. In this embodiment, a single-ended bidirectional interdigital transducer 7 is used, and the interdigital electrode 1 is located below the flow channel 4 in the separation region.

[0041] Furthermore, the surface acoustic wave microfluidic device further includes a liquid inlet region flow channel 5. The outlet channel III 51 of the liquid inlet region flow channel 5 is connected to the inlet channel I 41 of the flow channel 4 in the separation region. The inlet channel II 52 of the liquid inlet region flow channel 5 includes an intermediate liquid inlet channel 521 and two sheath liquid inlet channels 522.

[0042] Furthermore, the two sheath liquid inlet channels 522 are symmetrically distributed on both sides of the intermediate liquid inlet channel 521, which is a conventional design. The top view schematic diagram is as Figure 2 shown.

[0043] Example 2:

[0044] The difference between this embodiment and Example 1 is that the included angle between the axis of symmetry of the flow channel 4 in the separation region and the finger bars of the interdigital electrode 1 is 45°, and the number of branch outlet channels II 43 is 8. The complete structure diagram of the surface acoustic wave microfluidic separation device is as Figure 4 shown.

[0045] Example 3:

[0046] The difference between this embodiment and Embodiment 1 is that the included angle between the symmetry axis of the separation region flow channel 4 and the finger bars of the interdigital electrode 1 is 60°, the number of branch outlet channels II 43 is 8, and from left to right on one side of the symmetry axis are the first channel 431, the second channel 432, the third channel 433, and the fourth channel 434. The structure of the separation region flow channel 4 is as Figure 5 shown. The flow rates of the particle-containing liquid (intermediate liquid) and the sheath liquid are set to 100 nL / min and 1000 nL / min respectively, and the power gain of the power amplifier is 30.6 dB. When no electrical signal is applied, the fluorescence micrograph of the particle motion situation is as Figure 6 shown. During the separation process, the signal generator generates a sinusoidal signal with a peak-to-peak voltage of 700 mV and a frequency of 54 MHz, which is amplified by the power amplifier and then input into the interdigital transducer of the surface acoustic wave microfluidic device. A dispersion liquid containing polystyrene particles with particle size distribution ranges of 300 - 800 nm, 1.5 - 2.5 μm, and 4 - 5.8 μm respectively is used to characterize the separation effect of the device, and the fluorescence micrograph is as Figures 7 - 9 shown. It can be seen from Figures 7 - 9 that the particle size distribution ranges that can be separated by the second channel 432, the third channel 433, and the fourth channel 434 of the branch outlet channel II 43 are 4.0 - 5.5 μm, 2.4 - 4.0 μm, and 1.6 - 2.4 μm respectively. At the same time, using the above three branch outlets can separate particles with a particle size distribution range of 1.6 - 5.5 μm. The number of finger bars of the interdigital electrode corresponding to the three branch outlets, that is, the number of critical particle sizes, is 80, and the average particle size resolution is (5.5 - 1.6) / 80 = 0.049 μm.

[0047] Embodiment 4:

[0048] The difference between this embodiment and Embodiment 1 is that the type of the interdigital transducer used is a combination of a single-ended unidirectional interdigital transducer 6 and a single-ended bidirectional interdigital transducer 7, and the rest are the same as Embodiment 1. The combined structural schematic diagram of the single-ended unidirectional interdigital transducer 6 and the single-ended bidirectional interdigital transducer 7 is as Figure 10 shown.

[0049] Embodiment 5:

[0050] The difference between this embodiment and Embodiment 1 is that the type of the interdigital transducer is a double-ended bidirectional interdigital transducer, and two interdigital transducers 1 are distributed on both sides of the separation region flow channel 4. The top view schematic diagram is as Figure 11 shown.

[0051] In Embodiments 1 - 5 of the present invention, admittance curves are obtained based on the parameters of the interdigital transducer, and the expression of the piezoelectric equation for obtaining the admittance curve is:

[0052] T = cS - eE

[0053] D = εE - eS

[0054] Where T is the stress matrix, c is the stiffness matrix of the piezoelectric material, S is the strain matrix, e is the piezoelectric stress matrix of the piezoelectric material, E is the electrostatic field strength, D is the electric displacement, and ε is the dielectric matrix of the piezoelectric material; the resonant frequency and electromechanical coupling coefficient of the interdigital transducer are adjusted according to the piezoelectric stress matrix e, and the piezoelectric stress matrix is:

[0055]

[0056] Where e11, e12, e13, e14, e15, e16, e21, e22, e23, e24, e25, e26, e31, e32, e33, e34, e35, e36 are the piezoelectric coefficients of the piezoelectric material in the corresponding directions; based on the above equations, the theoretical admittance curve of the interdigital transducer is determined by the finite element simulation method and the geometric parameters are adjusted; the interdigital transducer is manufactured, the actual admittance curve of the interdigital transducer is measured, and the geometric dimensions and process parameters are further adjusted according to the actual admittance curve, and finally the geometric dimensions and process parameters for preparing the interdigital transducer meeting the requirements are determined.

[0057] In addition, it should be understood that although this specification is described according to the embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A surface acoustic wave microfluidic device for separating particles with a wide particle size distribution, characterized in that: It includes interdigital electrodes (1), a piezoelectric substrate (2), a PDMS substrate (3), and a separation region flow channel (4). The bottom surface of the separation region flow channel (4) is the piezoelectric substrate (2), and the remaining side walls are the PDMS substrate (3). The interdigital electrodes (1) are arranged on the piezoelectric substrate (2). The separation region flow channel (4) is an axisymmetric structure, including an inlet channel I (41), a main outlet channel I (42), and N branch outlet channels II (43). N is an even number and N≥2. The inlet channel I (41) and the main outlet channel I (42) are located on the axis of symmetry. All the branch outlet channels II (43) are symmetrically distributed on both sides of the main outlet channel I (42). The included angle between the axis of symmetry of the separation region flow channel (4) and the finger bars of the interdigital electrodes (1) is 10°-75°, realizing the single-step separation of various particles with different particle size distribution ranges within the range of the minimum critical particle size and the maximum critical particle size.

2. The surface acoustic wave microfluidic device for separating particles with a wide particle size distribution according to claim 1, wherein: The ratio of the maximum critical particle size to the minimum critical particle size is the product of the square root of the flow rate ratio and the sound pressure ratio.

3. The surface acoustic wave microfluidic device for separating particles with a wide particle size distribution according to claim 2, characterized in that: The flow rate ratio is the ratio of the sum of the cross-sectional areas of the main outlet channel I (42) and all the branch outlet channels II (43) of the separation region flow channel (4) to the cross-sectional area of the inlet channel I (41). The inlet channel I (41), the main outlet channel I (42), and the branch outlet channels II (43) are all straight flow channels. The sound pressure ratio is the ratio of the maximum effective sound pressure value on the axis of symmetry of the separation region flow channel (4) obtained by simulation or amplitude measurement to the peak value of the nearest effective sound pressure at the end of the inlet channel I (41).

4. The surface acoustic wave microfluidic device for separating particles with a wide particle size distribution according to claim 3, wherein: The flow rate ratio is 2-36, and the sound pressure ratio is 1-5.

5. The surface acoustic wave microfluidic device for separating particles with a wide particle size distribution according to claim 1, characterized in that: When the number of the interdigital electrodes (1) is one group, the interdigital electrodes (1) are located below the separation region flow channel (4). When the number of the interdigital electrodes (1) is two groups, the two groups of interdigital electrodes (1) are distributed on both sides of the separation region flow channel (4).

6. The surface acoustic wave microfluidic device for separating particles with a wide particle size distribution according to claim 1, wherein: The interdigital electrodes (1) and the piezoelectric substrate (2) together form an interdigital transducer. The types of the interdigital transducers include single-ended bidirectional interdigital transducers, single-ended unidirectional interdigital transducers, combinations of single-ended unidirectional and bidirectional interdigital transducers, double-ended bidirectional interdigital transducers, double-ended unidirectional interdigital transducers, or combinations of double-ended unidirectional and bidirectional interdigital transducers.

7. The surface acoustic wave microfluidic device for separating particles with a wide particle size distribution according to claim 1, characterized in that: The height of the separation region flow channel (4) is 20-500μm.

8. The surface acoustic wave microfluidic device for separating particles with a wide particle size distribution according to claim 1, characterized in that: The number N of the branch outlet channels II (43) is 2, 4, 6, 8, 10, 12, 14, or 16.

9. The surface acoustic wave microfluidic device for separating particles with a wide particle size distribution according to claim 1, wherein: The surface acoustic wave microfluidic device further includes a liquid inlet region flow channel (5). The outlet channel III (51) of the liquid inlet region flow channel (5) is communicated with the inlet channel I (41) of the separation region flow channel (4). The inlet channel II (52) of the liquid inlet region flow channel (5) includes an intermediate liquid inlet channel (521) and two sheath liquid inlet channels (522).

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