A surface acoustic wave microfluidic device for separating particles with a wide particle size distribution

Abstract

The application discloses a surface acoustic wave micro-fluidic device for separating particles with wide particle size distribution, and belongs to the cross field of surface acoustic wave and micro-fluidic technology, and specifically relates to the following technical scheme: a surface acoustic wave micro-fluidic device for separating particles with wide particle size distribution, comprising 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, the rest of the side walls are the PDMS substrate, and the interdigital electrodes are arranged on the piezoelectric substrate; the separation region flow channel is an axisymmetric structure, comprising 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, 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 separation region flow channel and the interdigital electrodes is 10 DEG to 75 DEG, and the application can realize single-step separation of multiple particles with different particle size distribution ranges within the range of minimum critical particle size and maximum critical particle size.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of surface acoustic wave and microfluidic technology, and specifically relates to a surface acoustic wave microfluidic device for separating particles with a wide particle size distribution. Background Technology

[0002] Surface acoustic waves (SAWs) are mechanical waves that propagate along the surface of an elastic solid, with their energy concentrated at a depth of about one wavelength below the material's surface. Since the commercialization of SAW devices in radar and communications in the 1960s, this technology has been widely used in the manufacture of various sensors, radio frequency filters, microfluidic chips, and other microelectromechanical systems (MEMS) devices, and has significant application value in the field of particle separation.

[0003] In the field of particle separation, traditional techniques such as centrifugation, filtration, and electrophoresis generally face problems such as low separation efficiency, high cost, complex equipment, or damage to samples. For example, centrifugation relies on the inertial force generated by high-speed rotation, making it difficult to achieve precise separation of particles at the microscale; filtration is easily affected by clogging and is difficult to separate nanoparticles; electrophoresis is sensitive to the conductivity of the solution, and the Joule heat generated during separation can easily lead to the inactivation of biological samples. In recent years, the development of microfluidic technology has promoted the advancement of miniaturized separation technology, among which sonophoresis, which uses acoustic waves, such as surface acoustic waves (SAWs), has significant advantages. SAW microfluidic separation devices are usually fabricated by bonding interdigital transducers to a polydimethylsiloxane (PDMS) substrate. After bonding, the cavity between the PDMS substrate and the interdigital transducer forms a microchannel. The interdigital transducer utilizes the piezoelectric effect and inverse piezoelectric effect of piezoelectric substrates, such as lithium niobate substrates and quartz substrates, to generate SAWs. Inputting a specific frequency electrical signal into the interdigital transducer can excite surface acoustic waves, thereby generating controllable acoustic radiation force and acoustic flow effect in the microchannel, thus achieving non-contact manipulation of micron and submicron particles. Its core advantages include: (1) no physical contact is required, avoiding sample contamination; (2) the separation effect can be controlled in real time by adjusting parameters such as input frequency and power, ensuring separation accuracy; (3) the device has a compact structure and is easy to integrate with microfluidic systems; (4) it is suitable for biocompatible scenarios and causes less damage to living biological particles.

[0004] However, existing surface acoustic wave (SAW) microfluidic separation technology still faces significant challenges in separating particles with a wide particle size distribution: (1) it typically requires two or more sets of interdigital transducers for multi-step separation, increasing the complexity of the flow channel design and significantly increasing the design and manufacturing costs of the device; (2) the particle size resolution (the minimum particle size difference that can be separated within the target particle size distribution range) is low, making it impossible to accurately separate particles with a specific narrow particle size distribution within the target particle size distribution range. Therefore, a novel SAW microfluidic separation device is needed that can separate particles with a wide particle size distribution in a single step and has high particle size resolution. Summary of the Invention

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

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A surface acoustic wave (SAW) microfluidic device for separating particles with a wide particle size distribution includes interdigitated 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 sidewalls are PDMS substrates. The interdigitated electrodes are disposed on the piezoelectric substrate. The separation region flow channel has 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 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 interdigitated electrodes is 10°-75°. This invention can achieve single-step separation of multiple particles with different particle size distribution ranges within the range of minimum and maximum critical particle sizes. The ratio of the maximum critical particle size to the minimum critical particle size is the product of the first power of the flow rate ratio and the sound pressure ratio. The minimum critical particle size is set as the minimum particle size of the target particle.

[0008] Furthermore, when there is one set of interdigitated electrodes, the interdigitated electrodes are located below the flow channel in the separation region; when there are two sets of interdigitated electrodes, the two sets of interdigitated electrodes are distributed on both sides of the flow channel in the separation region.

[0009] Furthermore, the interdigital electrodes and the piezoelectric substrate together form an interdigital transducer. The types of 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.

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

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

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

[0013] The flow 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 separation zone to the cross-sectional area of ​​the inlet channel I of the separation zone, preferably between 2 and 36. The inlet channel I, main outlet channel I, and branch outlet channels II are all straight 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, and v l λ is the liquid velocity near the particle, λ is the wavelength of the sound wave, θ is the angle between the interdigitated electrode fingers and the axis of symmetry of the flow channel in the separation region, and β is the velocity of the liquid near the particle. l φ represents the compressibility of the liquid, and φ is the acoustic contrast factor. v within the flow channel of the separation region. l The two physical quantities affecting the critical particle size, p0 and p1, are regularly distributed within the flow channel space of the separation region, resulting in a decrease in the critical particle size along the axis of symmetry starting from the end of the inlet channel I of 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, as well as particles with a particle size ranging between the minimum and maximum critical particle sizes, flow out from the branch outlet channel II.

[0018] Furthermore, the piezoelectric substrate is made of lithium niobate, lithium tantalate, aluminum nitride, gallium nitride, or quartz, and the interdigitated electrodes are made of gold, aluminum, copper, titanium, palladium, chromium, molybdenum, or platinum.

[0019] Furthermore, the thickness of the interdigitated electrode is 40-300 nm.

[0020] Furthermore, the surface acoustic wave microfluidic device also includes a liquid inlet channel, the outlet channel III of which is connected to the inlet channel I of the separation channel, and the inlet channel II of the liquid inlet channel includes an intermediate liquid inlet channel and two sheath liquid inlet channels.

[0021] Furthermore, the two sheath fluid inlet channels are symmetrically distributed on both sides of the intermediate fluid inlet channel.

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

[0023] (1) The number of critical particle sizes (the critical value of particle size; particles smaller than this critical value move along the streamline direction in the separation region; particles larger than this critical value move along the direction parallel to the interdigital electrode strips) in traditional surface acoustic wave (SAW) microfluidic separation devices is usually less than 5. Compared with traditional SAW microfluidic separation devices, this invention optimizes the microchannel topology and interdigital transducer design in the separation region. During the separation process, physical quantities affecting the critical particle size, such as liquid velocity and sound pressure, are regularly distributed in the channel space, increasing the number of critical particle sizes in a single-step separation to dozens. Therefore, the SAW microfluidic device for separating particles with wide particle size distribution described in this invention can separate particles with wide particle size distribution, that is, it can separate multiple particles with different particle size distribution ranges within the minimum and maximum critical particle size ranges in a single step, and the particle size resolution is significantly improved. Compared with traditional SAW 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 requires only one single-ended interdigital transducer or a set of double-ended interdigital transducers, and the device structure is simple. Attached Figure Description

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

[0026] Figure 2 This is a top view of the flow channel in the liquid inlet area;

[0027] Figure 3 This is a top view of the flow channel in the separation area;

[0028] Figure 4 This is a complete structural diagram of a surface acoustic wave microfluidic device with a symmetry axis and an interdigitated electrode with an angle of 45° between the fingers and the electrodes, and 8 branch outlet channels II.

[0029] Figure 5 This is the actual structural diagram of the separation region flow channel with an angle of 60° between the axis of symmetry and the interdigitated electrode strips, and 8 branch outlet channels II.

[0030] Figure 6 This is a fluorescence micrograph of the movement of polystyrene particles without an applied electrical signal;

[0031] Figure 7This 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 interdigitated electrode in Example 3.

[0032] Figure 8 This 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 interdigitated electrode in Example 3;

[0033] Figure 9 This 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 interdigitated electrode in Example 3;

[0034] Figure 10 This is a schematic diagram of a combined structure of a single-ended unidirectional and bidirectional interdigital transducer.

[0035] Figure 11 This is a top view of the flow channel in the separation region using a dual-ended bidirectional interdigital transducer;

[0036] In the figure, 1. Interdigitated electrode, 2. Piezoelectric substrate, 3. PDMS substrate, 4. Separation zone flow channel, 5. Liquid inlet zone flow channel, 6. Single-ended unidirectional interdigitated transducer, 7. Single-ended bidirectional interdigitated 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

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within 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 interdigitated electrode 1, a piezoelectric substrate 2, a PDMS substrate 3, and a separation region channel 4. The bottom surface of the separation region channel 4 is the piezoelectric substrate 2, and the remaining sidewalls are the PDMS substrate 3. The interdigitated electrode 1 is disposed on the piezoelectric substrate 2. A cross-sectional schematic diagram is shown below. Figure 1As shown, the separation region flow channel 4 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, and the two branch outlet channels II 43 are symmetrically distributed on both sides of the main outlet channel I 42. The angle between the axis of symmetry of the separation region flow channel 4 and the finger strip of the interdigital electrode 1 is 30°. Figure 3 As shown. This method achieves single-step separation of multiple particles with different size distributions, all within the range of the minimum and maximum critical particle sizes. The ratio of the maximum to the minimum critical particle size is the product of the flow rate ratio raised to the power of half and the sound pressure ratio. The sound pressure ratio is the ratio of the maximum effective sound pressure value along the axis of symmetry of the separation zone flow channel 4, obtained through simulation or amplitude measurement, to the nearest neighbor effective sound pressure peak value at the end of inlet channel I 41. 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 separation zone flow channel 4 to the cross-sectional area of ​​the inlet channel I 41. Inlet channel I 41, main outlet channel I 42, and 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 also includes a liquid inlet channel 5, the outlet channel Ⅲ 51 of the liquid inlet channel 5 is connected to the inlet channel Ⅰ 41 of the separation channel 4, and the inlet channel Ⅱ 52 of the liquid inlet channel 5 includes an intermediate liquid inlet channel 521 and two sheath liquid inlet channels 522.

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

[0043] Example 2:

[0044] The difference between this embodiment and Embodiment 1 is that the angle between the axis of symmetry of the separation region flow channel 4 and the interdigitated electrode 1 is 45°, and the number of branch outlet channels II 43 is 8. The complete structural diagram of the surface acoustic wave microfluidic separation device is shown below. Figure 4 As shown.

[0045] Example 3:

[0046] The difference between this embodiment and Embodiment 1 is that: the angle between the axis of symmetry of the separation region flow channel 4 and the interdigitated electrode 1 is 60°, the number of branch outlet channels II 43 is 8, and from left to right on one side of the axis of symmetry 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 follows: Figure 5 As shown. The flow rates of the particulate-containing liquid (intermediate liquid) and sheath fluid were set to 100 nL / min and 1000 nL / min, respectively, and the power gain of the power amplifier was 30.6 dB. Fluorescence micrographs of particle motion without an applied electrical signal are shown below. Figure 6 As shown in the figure. During the separation process, a signal generator produces a sinusoidal signal with a peak-to-peak voltage of 700mV and a frequency of 54MHz. After being amplified by a power amplifier, the signal is input into the interdigital transducer of the surface acoustic wave microfluidic device. The separation effect of the device is characterized using a dispersion containing polystyrene particles with particle sizes ranging from 300-800nm, 1.5-2.5μm, and 4-5.8μm. The fluorescence micrograph is shown in the figure. Figure 7-9 As shown. By Figure 7-9 It is known 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 4.0-5.5μm, 2.4-4.0μm, and 1.6-2.4μm, respectively. Simultaneously, particles with a particle size distribution range of 1.6-5.5μm can be separated using the above three branch outlets. The number of interdigitated electrode strips corresponding to the three branch outlets, i.e., the number of critical particle sizes, is 80, and the average particle size resolution is (5.5-1.6) / 80 = 0.049μm.

[0047] Example 4:

[0048] The difference between this embodiment and Embodiment 1 is that the interdigitated transducers used are a combination of a single-ended unidirectional interdigitated transducer 6 and a single-ended bidirectional interdigitated transducer 7; all other aspects are the same as in Embodiment 1. A schematic diagram of the combined structure of the single-ended unidirectional interdigitated transducer 6 and the single-ended bidirectional interdigitated transducer 7 is shown below. Figure 10 As shown.

[0049] Example 5:

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

[0051] In embodiments 1-5 of this invention, admittance curves are obtained based on interdigital transducer parameters, and the piezoelectric equation for the admittance curve is expressed as follows:

[0052] T = cS - eE

[0053] D=εE-eS

[0054] Where T is the stress matrix, c is the piezoelectric material stiffness matrix, 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 piezoelectric material dielectric matrix; 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] Wherein, e11, e12, e13, e14, e15, e16, e21, e22, e23, e24, e25, e26, e31, e32, e33, e34, e35, and e36 are the piezoelectric coefficients of the corresponding directions of the piezoelectric material. Based on the above equations, the theoretical admittance curve of the interdigital transducer is determined by finite element simulation and the geometric parameters are adjusted. The interdigital transducer is manufactured, and the actual admittance curve of the interdigital transducer is obtained by testing. Based on the actual admittance curve, the geometric dimensions and process parameters are further adjusted, and finally the geometric dimensions and process parameters of the interdigital transducer that meet the requirements are determined.

[0057] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider 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: The system includes an interdigitated 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 sidewalls are the PDMS substrate (3). The interdigitated electrode (1) is disposed on the piezoelectric substrate (2). The separation region flow channel (4) has an axisymmetric structure, including an inlet channel I (41), a main outlet channel I (42), and N branch outlet channels II (43), where N is an even number and N≥2. The inlet channel I (41) and the main outlet channel I... (42) Located on the axis of symmetry, all branch outlet channels II (43) are symmetrically distributed on both sides of the main outlet channel I (42). From the inlet channel to the outlet channel, the flow channel gradually expands in a cone shape. The main outlet channel I (42) and N branch outlet channels II (43) are located at the end of the expansion section. The angle between the axis of symmetry of the separation region flow channel (4) and the finger strip of the interdigitated electrode (1) is 10°-75°, realizing the single-step separation of particles with different particle size distribution ranges within the range of minimum critical particle size and maximum critical particle size.

2. 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 interdigital electrodes (1) is one set, the interdigital electrodes (1) are located below the flow channel (4) in the separation region; when the number of interdigital electrodes (1) is two sets, the two sets of interdigital electrodes (1) are distributed on both sides of the flow channel (4) in the separation region.

3. The surface acoustic wave microfluidic device for separating particles with a wide particle size distribution according to claim 1, characterized in that: The interdigital electrode (1) and the piezoelectric substrate (2) together form an interdigital transducer. The types of 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.

4. 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 zone channel (4) is 20-500 μm.

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

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

Images