CN116037232A

CN116037232A - Surface acoustic wave micro-fluidic chip and substrate structure and preparation method thereof

Info

Publication number: CN116037232A
Application number: CN202310044404.XA
Authority: CN
Inventors: 请求不公布姓名
Original assignee: Shanghai Weiran Technology Co ltd
Current assignee: Shanghai Weiran Technology Co ltd
Priority date: 2023-01-30
Filing date: 2023-01-30
Publication date: 2023-05-02

Abstract

The invention provides a surface acoustic wave micro-fluidic chip, a substrate structure thereof and a preparation method thereof. The surface acoustic wave micro-fluidic chip comprises: the micro-channel device comprises a base and a substrate, wherein interdigital transducers and reflecting grids are distributed on the base, and a micro-channel system and a focusing area are arranged on the substrate; the micro flow channel system includes: a focusing flow passage arranged in the focusing region; the interdigital transducer is provided with a flow channel side close to the focusing flow channel and a reflecting side far away from the focusing flow channel, and is suitable for generating surface acoustic waves to focus particles of the focusing flow channel; the reflection grating is arranged on the reflection side of the interdigital transducer and is suitable for reflecting the surface acoustic wave leaked from the interdigital transducer to the reflection side to the flow channel side. The invention can improve the efficiency of utilizing sound waves.

Description

Surface acoustic wave micro-fluidic chip and substrate structure and preparation method thereof

Technical Field

The invention relates to the technical field of microfluidics, in particular to a surface acoustic wave microfluidic chip for particle focusing, a substrate structure suitable for the surface acoustic wave microfluidic chip and a method for preparing the surface acoustic wave microfluidic chip.

Background

Particle focusing is a pretreatment step necessary for particle/cell detection, counting, sorting and other treatments, particularly in various microfluidic chips, scattered cells/particles in a flow channel need to be gathered in the center of the flow channel by external force, so that the particles sequentially pass through detection or counting points, and the particle focusing has wide application in biochemical fields such as cell sorting, single cell analysis, cell culture, drug manufacturing, single cell sorting and the like.

Based on the external force action mechanism of particle focusing, the micro-fluidic chip particle focusing method can be divided into two major categories, namely passive operation technology and active operation technology. Passive steering techniques induce a fluid to exert a force on the particles based entirely on the geometry of the flow channels or other hydrodynamic sources, which adjusts the force of the flow field on the particles by adjusting the microchannel structure. Active manipulation techniques refer to the application of an external force field in a chip to manipulate particles dispersed in a microchannel, mainly including acoustic force manipulation and electrical manipulation. Acoustic steering applies an acoustic radiation force to the particles by acoustic waves, thereby moving the particles to the location of the acoustic wave pressure node, and electric steering is to generate dielectrophoresis force by using an uneven electric field, so as to cause polarization of the particles, and the particles migrate to a focusing position under the action of the electric field force. The acoustic force manipulation has the advantages of small damage to cells, high focusing speed, good controllability and the like, and has been widely applied to particle focusing in microfluidic chips.

The acoustic force manipulation technology comprises two schemes of acoustic surface wave manipulation and bulk acoustic wave manipulation, and the acoustic surface wave focusing scheme is widely adopted at present, wherein an interdigital transducer on a piezoelectric material (lithium niobate, quartz crystal and the like) is utilized to generate an acoustic surface wave, the acoustic surface wave leaks into a micro-channel in a leaky wave mode and is coupled with particle flow to generate an acoustic flow effect, a fixed pressure node (antinode or node) is generated in the channel, and particles are gathered to the center of the channel under the action of acoustic radiation force by adjusting the relative positions of the channel and the interdigital transducer.

The Chinese patent application with publication number of CN112019185A discloses a full-coverage surface acoustic wave interdigital transducer, which comprises two full-coverage transducers and a micro-channel, as shown in figure 1, wherein when the two transducers are started simultaneously, an enhanced standing wave sound field is formed in the micro-channel under the control of a same-frequency signal and used for controlling biological particles in the channel; when one of the transducers is activated, the transducer forms an enhanced traveling wave acoustic field within the microchannel for controlling biological particles within the channel.

Particle focusing based on the interdigital transducer, however, suffers from the following drawbacks: the sound wave generated by the interdigital transducer can leak and cannot be fully utilized; the side wall of the particle focusing area of the micro-channel has a corner effect, particles in a part of the area are not acted by sound radiation force, the particles are adhered to the side wall of the channel, and the focusing effect is poor.

Disclosure of Invention

The technical problems solved by the technical scheme of the invention are as follows: how to solve the problem of acoustic leakage generated by an interdigital transducer in a microfluidic chip and how to improve the efficiency of acoustic utilization.

In order to solve the technical problems, the technical scheme of the invention provides a surface acoustic wave micro-fluidic chip for focusing particles, which comprises the following components: the micro-channel device comprises a base and a substrate, wherein interdigital transducers and reflecting grids are distributed on the base, and a micro-channel system and a focusing area are arranged on the substrate; the micro flow channel system includes: a focusing flow passage arranged in the focusing region; the interdigital transducer is provided with a flow channel side close to the focusing flow channel and a reflecting side far away from the focusing flow channel, and is suitable for generating surface acoustic waves to focus particles of the focusing flow channel; the reflection grating is arranged on the reflection side of the interdigital transducer and is suitable for reflecting the surface acoustic wave leaked from the interdigital transducer to the reflection side to the flow channel side.

Optionally, the substrate is a lithium niobate substrate, and the substrate is a PDMS substrate.

Optionally, the interdigital transducer is a pair of focusing interdigital electrodes suitable for being arranged in the focusing region, and the focusing interdigital electrodes are arranged perpendicular to the flow direction of the focusing runner particles and suitable for focusing the focusing runner particles in the central region of the focusing runner.

Optionally, the focusing interdigital electrode is formed by magnetron sputtering on a substrate with an interdigital pattern.

Optionally, the focusing interdigital electrode is an Al electrode.

Optionally, the width and the pitch of the fingers of the focusing interdigital electrode are equal to half of the width of the focusing flow channel.

Optionally, the width of the fingers of the focusing interdigital electrode is 25 μm, and the inter-finger distance is 25 μm.

Optionally, the width of the fingers of the focusing interdigital electrode is 35 μm, and the inter-finger distance is 35 μm.

Optionally, the width of the fingers of the focusing interdigital electrode is 50 μm, and the pitch of the fingers is 50 μm.

Optionally, the number of pairs of fingers on each side of the focusing interdigital electrode is 54, the number of pairs of reflecting grids on each side is 16, and the interdigital length is 10 mm.

Optionally, the micro flow channel system further includes: a particle inlet, a particle outlet, a primary sheath fluid inlet, a secondary sheath fluid inlet, a primary sheath fluid outlet, and a secondary sheath fluid outlet; the focusing flow channel is provided with an inlet end and an outlet end, the inlet end is connected to the particle inlet so as to flow in particles before focusing, and the outlet end is connected to the particle outlet so as to flow out particles after focusing; sheath liquid enters the inlet end of the focusing flow channel from the first sheath liquid inlet and the second sheath liquid inlet, so that particles before focusing entering from the particle inlet move to the central area of the focusing flow channel in advance.

Optionally, the width of the focusing flow channel is 50 μm, the width of the particle inlet is 50 μm, the width of the particle outlet is 50 μm, the widths of the first sheath liquid inlet and the second sheath liquid inlet are respectively 10 μm, and the widths of the first sheath liquid outlet and the second sheath liquid outlet are respectively 10 μm.

Optionally, the width of the focusing flow channel is 70 μm, the width of the particle inlet is 50 μm, the width of the particle outlet is 50 μm, the widths of the first sheath liquid inlet and the second sheath liquid inlet are respectively 10 μm, and the widths of the first sheath liquid outlet and the second sheath liquid outlet are respectively 10 μm.

Optionally, the width of the focusing flow channel is 100 μm, the width of the particle inlet is 70 μm, the width of the particle outlet is 70 μm, the widths of the first sheath liquid inlet and the second sheath liquid inlet are 20 μm respectively, and the widths of the first sheath liquid outlet and the second sheath liquid outlet are 20 μm respectively.

In order to solve the technical problem, the technical scheme of the invention also provides a substrate structure suitable for the surface acoustic wave micro-fluidic chip, which comprises: the device comprises a substrate, interdigital transducers distributed on the substrate and a reflecting grating; the substrate is suitable for bonding and packaging with a substrate of the microfluidic chip, and a micro-channel system and a focusing area are arranged on the substrate; the micro flow channel system includes: a focusing flow passage arranged in the focusing region; the interdigital transducer is provided with a flow channel side close to the focusing flow channel and a reflecting side far away from the focusing flow channel, and is suitable for generating surface acoustic waves to focus particles of the focusing flow channel; the reflection grating is arranged on the reflection side of the interdigital transducer and is suitable for reflecting the surface acoustic wave leaked from the interdigital transducer to the reflection side to the flow channel side.

In order to solve the technical problems, the technical scheme of the invention also provides a method for preparing the surface acoustic wave micro-fluidic chip, which comprises the following steps:

preparing a substrate, wherein interdigital transducers and reflecting grids are distributed on the substrate;

preparing a substrate, wherein a micro-channel system and a focusing area are arranged on the substrate;

packaging the substrate and the substrate through oxygen plasma bonding to obtain the surface acoustic wave micro-fluidic chip;

the micro flow channel system includes: a focusing flow passage arranged in the focusing region; the interdigital transducer is provided with a flow channel side close to the focusing flow channel and a reflecting side far away from the focusing flow channel, and is suitable for generating surface acoustic waves to focus particles of the focusing flow channel; the reflection grating is arranged on the reflection side of the interdigital transducer and is suitable for reflecting the surface acoustic wave leaked from the interdigital transducer to the reflection side to the flow channel side.

Optionally, the preparing the substrate includes:

washing and irradiating a substrate to make the substrate hydrophilic;

disposing a layer of photoresist on the substrate and exposing to light to form a desired pattern;

and removing residual glue of the substrate with the pattern and performing magnetron sputtering coating to prepare the interdigital transducer and the reflecting grating.

Optionally, the washing and irradiating the substrate to make the substrate hydrophilic includes:

the substrate was washed with acetone, absolute ethanol and deionized water for 15min, respectively, and irradiated with a UV-UV washer for 25min to make the surface hydrophilic.

Optionally, disposing a layer of photoresist on the substrate and exposing to light to form a desired pattern includes:

uniformly throwing a layer of photoresist on the substrate by using a photoresist homogenizer, and then placing the substrate on a hot plate for pre-baking to volatilize a photoresist solvent so as to arrange the photoresist on the substrate;

the prepared mask plate with the electrode pattern is placed on a base coated with photoresist, exposed under a photoetching machine, and then the substrate is subjected to post-baking, and a required pattern is formed on the base through development.

Optionally, the removing the residual glue of the patterned substrate and performing magnetron sputtering coating to prepare the interdigital transducer and the reflective grating includes:

and (3) putting the substrate with the pattern into oxygen plasma to remove residual photoresist, performing magnetron sputtering coating, pre-sputtering for 5min with 120W power, performing formal sputtering for 20min, and removing redundant photoresist with acetone after sputtering is finished so as to prepare the interdigital transducer and the reflecting grating on the substrate.

Optionally, the preparing the substrate includes:

washing and irradiating a silicon substrate to make the silicon substrate hydrophilic;

spin-coating photoresist on the silicon substrate and baking the silicon substrate for the first time;

cooling the baked silicon substrate to room temperature for exposure and performing secondary baking;

cooling the exposed silicon substrate and performing cyclic development;

placing the developed silicon substrate in a vacuum drying oven for standing to evaporate the retained photoresist;

placing the prepared substrate material prepolymer into a vacuum box for vacuumizing;

and pouring the substrate material prepolymer on a micro-channel template and solidifying the substrate material prepolymer to form the micro-channel system.

Optionally, the cleaning and irradiating the silicon substrate to make the silicon substrate hydrophilic includes: and cleaning the silicon substrate by using acetone, absolute ethyl alcohol and deionized water respectively for 15min, and irradiating the silicon substrate by using a UV (ultraviolet) cleaning machine for 25min to make the surface hydrophilic.

Optionally, the spin coating the photoresist on the silicon substrate and baking the silicon substrate for the first time includes: spin-coating SU-8 photoresist on the silicon substrate, placing the uniformly-glued silicon substrate on a hot plate with the temperature of 45 ℃ and keeping for 5min; then, the hot plate temperature was set to 65℃and kept for 2 hours, completing the first baking of the silicon substrate.

Optionally, the cooling the baked silicon substrate to room temperature for exposure and performing the second baking includes:

cooling the silicon substrate after the first baking to room temperature, exposing the silicon substrate on a photoetching machine, and placing the exposed silicon substrate on a hot plate at 65 ℃ for 2min; and then the temperature of the hot plate is adjusted to 95 ℃ and kept for 10 minutes, so as to finish the second baking of the silicon substrate.

Optionally, the cooling the exposed silicon substrate and performing cyclic development includes:

after the silicon substrate was cooled to room temperature, it was placed in propylene glycol methyl ether acetate and isopropanol solution, respectively, and cyclic development was performed for 15 seconds, until no white precipitate appeared.

Optionally, the placing the developed silicon substrate in a vacuum drying oven for standing to evaporate the remaining photoresist includes: the developed silicon substrate was placed in a vacuum oven at 135 c for 10min and the remaining SU-8 photoresist solvent was evaporated.

Optionally, placing the prepared substrate material prepolymer into a vacuum box for vacuumizing comprises:

uniformly mixing the substrate material glue and the curing agent in a culture dish according to the mass ratio of 10:1, and stirring for 20 minutes by using a glass rod until uniform small bubbles appear on the surface of the mixture;

Placing the prepared substrate material prepolymer into a vacuum box for vacuumizing until no bubbles appear on the surface and the inside of the mixture, so as to complete the configuration of the substrate material prepolymer.

Optionally, the pouring the substrate material pre-polymer on a micro-fluidic channel template and curing the substrate material pre-polymer to form the micro-fluidic channel system includes:

pouring the substrate material prepolymer on a runner template, and baking in an oven at 100 ℃ for 1 hour to solidify the substrate material, thereby obtaining the substrate with the micro runner system.

The technical scheme of the invention has the beneficial effects that at least:

according to the technical scheme, the interdigital transducer and the reflecting grating are arranged on the substrate of the surface acoustic wave microfluidic chip, so that the problem of energy efficiency waste caused by sound wave leakage of the interdigital transducer in the prior art can be solved. According to the technical scheme, the reflection grating is added on the reflection side, far away from the flow channel, of the interdigital transducer, so that sound waves on the reflection side of the interdigital transducer can be reflected back to the flow channel side, close to the flow channel, of the interdigital transducer, the utilization rate of sound wave energy of the surface acoustic wave micro-fluidic chip can be improved, and the focusing effect is better and the focusing speed is faster under the energy of the same input signal.

In the alternative scheme of the technical scheme, the corresponding sheath liquid inlet and sheath liquid outlet are arranged at the runner inlet and the runner outlet, so that particles entering the runner are far away from the corner effect of the side wall of the runner based on the sheath liquid pre-focusing, and all the particles are moved to the central area of the runner, thereby solving the problem that the particles adhere to the side wall of the runner when the particles are focused, improving the focusing effect of the particles and increasing the flow velocity of a sample.

Drawings

Other features, objects and advantages of the present invention will become more apparent upon reading of the detailed description of non-limiting embodiments, given with reference to the accompanying drawings in which:

fig. 1 is a schematic structural diagram of a full-coverage surface acoustic wave interdigital transducer provided in the prior art;

fig. 2 is a schematic structural diagram of a saw micro-fluidic chip for focusing particles according to the technical scheme of the present invention;

fig. 3 is a schematic structural diagram of another saw micro-fluidic chip for focusing particles according to the technical scheme of the present invention;

fig. 4 is a schematic diagram of a substrate structure suitable for a surface acoustic wave micro-fluidic chip according to the technical scheme of the present invention;

fig. 5 is a schematic flow chart of a method for preparing a surface acoustic wave micro-fluidic chip according to the technical scheme of the present invention;

Fig. 6 is a schematic structural diagram of a saw micro-fluidic chip for focusing particles according to an application example of the present invention;

fig. 7 is a schematic structural diagram of a micro-fluidic channel system according to an application example of the present invention;

FIG. 8 is a schematic flow chart of a preparation method of a lithium niobate substrate according to the technical scheme of the present invention;

fig. 9 is a schematic flow chart of a preparation method of a PDMS micro-channel according to the present invention.

Detailed Description

In order to better and clearly show the technical scheme of the invention, the invention is further described below with reference to the accompanying drawings.

Example 1

A surface acoustic wave microfluidic chip for particle focusing as shown in fig. 2, comprising: a base 1 and a substrate 2.

Interdigital transducers

4a and 4b and reflecting

grids

5a and 5b are distributed on the substrate, and a micro-channel system w and a focusing region j are arranged on the substrate 2.

With continued reference to fig. 2, the micro flow channel system w includes: a focusing flow path L provided in the focusing region j. The focusing flow path L has a particle inlet and a particle outlet. The interdigital transducer 4a is provided with a flow channel side d1 close to the focusing flow channel L and a reflection side d2 far from the focusing flow channel L, and the interdigital transducer 4b is provided with a flow channel side d3 close to the focusing flow channel L and a reflection side d4 far from the focusing flow channel L.

The interdigital transducer 4a is adapted to generate a surface acoustic wave to focus the particles in the focusing flow path L. The reflection grating 5a is disposed on the reflection side d2 of the interdigital transducer 4a, and is adapted to reflect the surface acoustic wave leaking from the interdigital transducer 4a to the reflection side d2 to the flow path side d1 of the interdigital transducer 4a, so as to save energy consumption.

Similarly, the interdigital transducer 4b is adapted to generate a surface acoustic wave to focus the particles in the focusing flow path L. The reflection grating 5b is arranged on the reflection side d4 of the interdigital transducer 4b, and is suitable for reflecting the surface acoustic wave leaked from the interdigital transducer 4b to the reflection side d4 to the flow channel side d3 of the interdigital transducer 4b, so that the energy consumption is further saved.

The surface acoustic wave micro-fluidic chip of the embodiment can reflect and utilize the leakage sound wave of the interdigital transducer by arranging the corresponding reflecting grating on the reflecting side of the interdigital transducer. The leakage sound wave of the interdigital transducer can be reflected to the side of the flow back channel through the reflecting grating, and the surface acoustic wave micro-fluidic chip of the embodiment has better focusing effect and focusing speed under the energy of the same input signal.

Specifically, in this embodiment, the substrate 1 may be a lithium niobate substrate, and the substrate 2 may be a PDMS substrate.

The

interdigital transducers

4a, 4b may in particular consist of focusing interdigital electrodes. The focusing interdigital electrode is formed by arranging a plurality of interdigital electrodes according to preset interdigital widths and interdigital intervals, and the interdigital electrodes are also provided with pins. The direction of alignment of these interdigital electrodes is perpendicular to the direction of flow of the particles in the focusing flow path L. When the interdigital electrodes work, the surface acoustic waves emitted by the interdigital electrodes can enable particles in the focusing flow channel L to focus on the flow channel central area of the focusing flow channel L.

The interdigital electrode may be specifically constituted of an Al (aluminum) electrode. In this embodiment, the inter-finger width and inter-finger pitch of the inter-finger electrodes are equal to half the width of the focusing flow channel L. The focusing flow path L width k is illustrated in fig. 2.

More specifically, in this embodiment, the focusing flow channel has a flow channel width of 50 μm (micrometers), and the interdigital electrodes can be arranged in an arrangement of 25 μm in interdigital width and 25 μm in interdigital pitch to realize

interdigital transducers

4a and 4b.

In other examples, the focusing flow channel has a flow channel width of 70 μm, and the interdigital electrodes may be arranged in an arrangement of 35 μm interdigital width and 35 μm interdigital distance to realize

interdigital transducers

4a, 4b. Alternatively, the width of the focusing flow channel may be 100 μm, and the interdigital electrodes may be arranged with an interdigital width of 50 μm and an interdigital pitch of 50 μm, so as to realize

interdigital transducers

4a and 4b.

In the case where the flow channel width of the focusing flow channel is 50 μm, the particle inlet width may be 50 μm and the particle outlet width may be 50 μm. In the case where the flow channel width of the focusing flow channel is 70. Mu.m, the particle inlet width may be 50. Mu.m, and the particle outlet width may be 50. Mu.m. In the case where the flow channel width of the focusing flow channel is 100 μm, the particle inlet width is suitably 70 μm, and the particle outlet width is suitably 70 μm.

In other examples according to the present disclosure, the interdigital transducer 4a may be specifically configured by 54 pairs of interdigital electrodes, where the 54 pairs of interdigital electrodes are disposed on one side of the focusing channel, and the interdigital electrodes have corresponding pins, and the interdigital spaces according to the present embodiment are disposed between the pins. The interdigital transducer 4a is further provided with 16 pairs of reflecting grids (5 a) on the reflecting side d2 of the interdigital electrode thereof so as to reflect the surface acoustic wave leaking from the reflecting side d2 generated when the interdigital electrode is operated by 54 pairs of the interdigital electrode, and the particles in the flow channel can be continuously focused on the flow channel side d1 of the interdigital transducer 4a by utilizing the reflected sound wave. The length of the interdigital electrodes and the reflecting grating between the pins can be 10 mm.

Similarly, on the other side of the focusing flow path, the interdigital transducer 4b is correspondingly formed by 54 pairs of interdigital electrodes, the 54 pairs of interdigital electrodes are arranged on the other side of the focusing flow path, the interdigital electrodes of the interdigital transducer 4b also have corresponding pins, and the interdigital intervals according to the embodiment are arranged among the pins. The interdigital transducer 4b is also provided with 16 pairs of reflecting grids (5 b) on the reflecting side d4 of the interdigital electrode thereof so as to reflect the surface acoustic wave leaked from the reflecting side d4 generated when the interdigital transducer 4b works, and the reflected sound wave can be utilized to continuously focus particles in a flow channel on the flow channel side d3 of the interdigital transducer 4 b. The length of the interdigital electrodes and the reflecting grating between the pins can be 10 mm.

In the technical scheme of the invention, the reflecting grating can be prepared from the same material Al as the interdigital electrode and is prepared by photoetching and magnetron sputtering together. The reflecting grids can be rectangular arrays, the width of each reflecting grid is the same as the width of each interdigital electrode, the spacing between every two adjacent reflecting grids is the same as the spacing between the interdigital electrodes, the height of each reflecting grid is the same as the height of each interdigital electrode, and the length of each reflecting grid can be 10mm so as to fully reflect sound waves. In a specific example, the distance between the reflective grating array and the interdigital electrode array may be an acoustic wavelength (the acoustic wavelength may be set to a value according to the acoustic wavelength emitted by the actual interdigital transducer electrode array), so that the acoustic wave reflected by the reflective grating may be overlapped with the acoustic wave before reflection to maximize the utilization of the acoustic wave.

Example two

Although the first embodiment adds the reflecting grating structure on the basis of the interdigital transducer in the prior art so as to solve the problem of focusing energy consumption leakage of the surface acoustic wave micro-fluidic chip. However, when the acoustic wave is transmitted into the flow channel, there is a rayleigh Li Jiao, and an area within the rayleigh angle does not have acoustic radiation force, which is called a corner effect area, and particles in the area are not affected by the acoustic radiation force, so that the micro-fluidic chip is easy to adhere to the flow channel wall when focusing the particles.

Therefore, the first embodiment is based on the first embodiment and assisted by focusing with sheath liquid, the particles such as sample particles are pushed to the central area far away from the wall of the flow channel by the sheath liquid, and then act on the fluid domain by acoustic surface waves, and the particles are focused on the central area of the flow channel under the action of acoustic radiation force, so that the three-dimensional focusing of the particles is realized.

Based on the saw microfluidic chip as shown in the first embodiment, the saw microfluidic chip as shown in fig. 3 includes, in addition to: the

interdigital transducers

4a and 4b and the

reflective gratings

5a and 5b distributed on the substrate 1, the substrate 2 is provided with a micro-channel system w and a focusing region j, and the method further comprises the following steps: a sheath liquid inlet 6a, a sheath liquid inlet 6b, a sheath liquid outlet 7a, and a sheath liquid outlet 7b.

With continued reference to fig. 3, the focusing flow path L has an inlet port r1 connected to the particle inlet and an outlet port r2 connected to the particle outlet. The particle inlet is the particle before the focusing flow path L flows into the focusing through the inlet port r1, and the inlet port r1 is not located in the focusing region j but may be provided at the flow path port before the focusing flow path enters the focusing region j. The particle outlet is the focused particle flowing out of the focusing flow channel L through the outlet end r2, and the inlet end r2 is not in the focusing region j, but can be arranged at the flow channel port after the focusing flow channel enters the focusing region j.

With continued reference to fig. 3, in this embodiment, after the sample particles enter the focusing flow channel for focusing, the width of the sample flowing into the focusing flow channel decreases with the increase of the sheath flow velocity in the focusing flow channel, and also decreases with the increase of the included angle of the sheath flow focusing structure. Here, the total flow rate of the sheath liquid entering from both sides of the sheath liquid inlet 6a and the sheath liquid inlet 6b may be specifically set to be equal to the flow rate of the sample entering the particle inlet, the inlet angle of the sheath liquid may be set to α1=α2=45°, the angle of the sheath liquid outlet may be set to α3=α4=45°, and the sample particles may be held in the center region of the flow channel while controlling the width of the sample flowing into the focusing flow channel so as to maintain symmetry.

The inlet end r1 of the focusing flow channel is connected to the

sheath fluid inlets

6a, 6b: sheath liquid enters the focusing flow passage L from the sheath liquid inlet 6a and the sheath liquid inlet 6b respectively, a first preset included angle alpha 1 is formed between the direction of the sheath liquid entering the inlet end r1 from the sheath liquid inlet 6a and the direction of the particles entering the focusing flow passage L from the particle inlet, a second preset included angle alpha 2 is formed between the direction of the sheath liquid entering the inlet end r1 from the sheath liquid inlet 6b and the direction of the particles entering the focusing flow passage L from the particle inlet, and the first preset included angle alpha 1 is equal to the second preset included angle alpha 2.

The outlet end r2 of the focusing flow channel is connected to the sheath fluid outlets 7a, 7b: the sheath liquid flows out of the focusing flow passage L from the sheath liquid outlet 7a and the sheath liquid outlet 7b respectively, the direction of the sheath liquid flowing out of the outlet end r2 from the sheath liquid outlet 7a and the direction of the particles flowing out of the focusing flow passage L from the particle outlet have a third preset included angle alpha 3, and the direction of the sheath liquid flowing out of the outlet end r2 from the sheath liquid outlet 7b and the direction of the particles flowing out of the focusing flow passage L from the particle outlet have a fourth preset included angle alpha 4, wherein the third preset included angle alpha 3 is equal to the fourth preset included angle alpha 4.

Sheath liquid enters the inlet end r1 of the focusing flow channel from the

sheath liquid inlets

6a and 6b, so that particles (before focusing) of the focusing flow channel entering from the particle inlet are moved to the central area of the focusing flow channel L in advance, and the particles before focusing are pre-focused on the central area of the flow channel before entering into the focusing area j, thereby avoiding the particles from falling into corner effect areas and improving the focusing effectiveness of the particles.

Based on the size of the focusing flow path of the first embodiment, the widths of the

sheath liquid inlets

6a, 6b and the widths of the sheath liquid outlets 7a, 7b may be configured accordingly:

when the flow channel width of the focusing flow channel L was 50. Mu.m, the particle inlet width was 50. Mu.m, the particle outlet width was 50. Mu.m, the widths of the

sheath liquid inlets

6a, 6b were 10. Mu.m, and the widths of the sheath liquid outlets 7a, 7b were 10. Mu.m, respectively.

When the flow channel width of the focusing flow channel L was 70. Mu.m, the particle inlet width was 50. Mu.m, the particle outlet width was 50. Mu.m, the widths of the

sheath liquid inlets

When the flow channel width of the focusing flow channel L was 100. Mu.m, the particle inlet width was 70. Mu.m, the particle outlet width was 70. Mu.m, the widths of the

sheath liquid inlets

6a, 6b were 20. Mu.m, and the widths of the sheath liquid outlets 7a, 7b were 20. Mu.m.

Example III

Based on the above embodiments, the present embodiment provides a microfluidic chip applicable to the first and second embodiments, as shown in fig. 4, which is a substrate structure, including: a substrate (not shown in fig. 4), an interdigital transducer 4a, an interdigital transducer 4b, a reflective grating 5a, and a reflective grating 5b distributed on the substrate. The substrate is suitable for bonding and packaging with the micro-fluidic chip substrate described in the first embodiment and the second embodiment. As can be seen from fig. 4, the interdigital transducer 4a, the interdigital transducer 4b, the reflective grating 5a, and the reflective grating 5b are operated by applying corresponding voltages (+10v to-10v) to the pins. The interdigital transducer 4a and the reflecting grating 5a, the interdigital transducer 4b and the reflecting grating 5b are arranged by taking the central line of the flow channel as a symmetrical line. Other specific implementations of this embodiment may refer to the first embodiment and the second embodiment, and are not described herein.

Example IV

A method for preparing a surface acoustic wave microfluidic chip as shown in fig. 5, comprising the steps of:

step S100, preparing a substrate, wherein interdigital transducers and reflecting grids are distributed on the substrate;

step S101, preparing a substrate, wherein a micro-channel system and a focusing area are arranged on the substrate;

and step S102, packaging the substrate and the substrate through oxygen plasma bonding to obtain the surface acoustic wave micro-fluidic chip.

The micro flow channel system in step S102 includes: a focusing flow passage arranged in the focusing region; the interdigital transducer is provided with a flow channel side close to the focusing flow channel and a reflecting side far away from the focusing flow channel, and is suitable for generating surface acoustic waves to focus particles of the focusing flow channel; the reflection grating is arranged on the reflection side of the interdigital transducer and is suitable for reflecting the surface acoustic wave leaked from the interdigital transducer to the reflection side to the flow channel side.

Specifically, the preparation of the substrate in step S100 includes the following steps: washing and irradiating a substrate to make the substrate hydrophilic; disposing a layer of photoresist on the substrate and exposing to light to form a desired pattern; and removing residual glue of the substrate with the pattern and performing magnetron sputtering coating to prepare the interdigital transducer and the reflecting grating. More specifically: the washing and irradiating the substrate to render the substrate hydrophilic includes: the substrate was washed with acetone, absolute ethanol and deionized water for 15min, respectively, and irradiated with a UV-UV washer for 25min to make the surface hydrophilic. The disposing a layer of photoresist on the substrate and exposing to light to form a desired pattern includes: uniformly throwing a layer of photoresist on the substrate by using a photoresist homogenizer, and then placing the substrate on a hot plate for pre-baking to volatilize a photoresist solvent so as to arrange the photoresist on the substrate; the prepared mask plate with the electrode pattern is placed on a base coated with photoresist, exposed under a photoetching machine, and then the substrate is subjected to post-baking, and a required pattern is formed on the base through development. The steps of removing the residual glue of the substrate with the pattern and performing magnetron sputtering coating to prepare the interdigital transducer and the reflecting grating include: and (3) putting the substrate with the pattern into oxygen plasma to remove residual photoresist, performing magnetron sputtering coating, pre-sputtering for 5min with 120W power, performing formal sputtering for 20min, and removing redundant photoresist with acetone after sputtering is finished so as to prepare the interdigital transducer and the reflecting grating on the substrate.

Specifically, the preparation of the substrate in step S101 includes the following steps: washing and irradiating a silicon substrate to make the silicon substrate hydrophilic; spin-coating photoresist on the silicon substrate and baking the silicon substrate for the first time; cooling the baked silicon substrate to room temperature for exposure and performing secondary baking; cooling the exposed silicon substrate and performing cyclic development; placing the developed silicon substrate in a vacuum drying oven for standing to evaporate the retained photoresist; placing the prepared substrate material prepolymer into a vacuum box for vacuumizing; and pouring the substrate material prepolymer on a micro-channel template and solidifying the substrate material prepolymer to form the micro-channel system. More specifically, in the above process: the cleaning and irradiating the silicon substrate to make the silicon substrate hydrophilic includes: and cleaning the silicon substrate by using acetone, absolute ethyl alcohol and deionized water respectively for 15min, and irradiating the silicon substrate by using a UV (ultraviolet) cleaning machine for 25min to make the surface hydrophilic. The spin coating photoresist on the silicon substrate and baking the silicon substrate for the first time comprises: spin-coating SU-8 photoresist on the silicon substrate, placing the uniformly-glued silicon substrate on a hot plate with the temperature of 45 ℃ and keeping for 5min; then, the hot plate temperature was set to 65℃and kept for 2 hours, completing the first baking of the silicon substrate. The step of cooling the baked silicon substrate to room temperature for exposure and performing second baking comprises the following steps: cooling the silicon substrate after the first baking to room temperature, exposing the silicon substrate on a photoetching machine, and placing the exposed silicon substrate on a hot plate at 65 ℃ for 2min; and then the temperature of the hot plate is adjusted to 95 ℃ and kept for 10 minutes, so as to finish the second baking of the silicon substrate. The cooling and cyclic developing of the exposed silicon substrate comprises the following steps: after the silicon substrate was cooled to room temperature, it was placed in propylene glycol methyl ether acetate and isopropanol solution, respectively, and cyclic development was performed for 15 seconds, until no white precipitate appeared. The step of placing the developed silicon substrate in a vacuum drying oven for standing to evaporate the retained photoresist comprises the following steps: the developed silicon substrate was placed in a vacuum oven at 135 c for 10min and the remaining SU-8 photoresist solvent was evaporated. Placing the prepared substrate material prepolymer into a vacuum box for vacuumizing, wherein the step of vacuumizing comprises the following steps of: uniformly mixing the substrate material glue and the curing agent in a culture dish according to the mass ratio of 10:1, and stirring for 20 minutes by using a glass rod until uniform small bubbles appear on the surface of the mixture; placing the prepared substrate material prepolymer into a vacuum box for vacuumizing until no bubbles appear on the surface and the inside of the mixture, so as to complete the configuration of the substrate material prepolymer. The pouring the substrate material prepolymer on a micro-channel template and solidifying the substrate material prepolymer to form the micro-channel system comprises the following steps: pouring the substrate material prepolymer on a runner template, and baking in an oven at 100 ℃ for 1 hour to solidify the substrate material, thereby obtaining the substrate with the micro runner system.

Application example 1

As an application example of the present embodiment, a surface acoustic wave microfluidic chip for particle focusing, referring to fig. 6, is composed of a lithium niobate substrate 1',

interdigital transducers

4a, 4b, and a PDMS substrate 2'. The lithium niobate substrate 1 'is distributed with

interdigital transducers

4a and 4b formed by interdigital electrodes, and the PDMS substrate 2' is provided with a micro-channel system w.

Referring to fig. 7, the micro flow channel system w includes: focusing flow path L, sample inlet and sample outlet, sheath fluid inlet 6a and sheath fluid inlet 6b, sheath fluid outlet 7a and sheath fluid outlet 7b. The micro flow channel system w further includes: the

cavities

8a and 8b are used for correspondingly arranging and accommodating the

interdigital transducers

4a and 4b and the reflecting

grids

5a and 5b of the lithium niobate substrate 1'. The interdigital electrodes of the

interdigital transducers

4a and 4b are symmetrically arranged at two sides of the focusing flow channel L, and are particularly symmetrically arranged by taking the central line of the flow channel as a symmetrical line. The lithium niobate substrate 1 'and the PDMS substrate 2' of the micro flow channel system are bonded by oxygen plasma to complete encapsulation.

In the application example, the material of the runner substrate is PDMS, and the runner substrate is prepared by casting a PDMS prepolymer on a runner template, heating, solidifying, cutting and punching. The runner template of the application example is prepared by a photoetching process, the photoresist is SU8-2025, the spin coating rotating speed is 1000 revolutions, the spin coating time is 60s, and the exposure time is 15s. In this application example, the channel width (L) w of the acoustic focusing region in the PDMS channel is 50. Mu.m, the width of the sheath fluid inlet is 10. Mu.m, the width of the sample inlet is 50. Mu.m, the width of the sheath fluid outlet is 10. Mu.m, and the width of the sample outlet is 50. Mu.m.

In this application example, the micro flow channel is a rectangular flow channel, and the flow channel depth is 50 μm. The interdigital electrodes of the

interdigital transducers

4a and 4b are Al electrodes, and are formed by coating a film on a lithium niobate substrate with interdigital patterns through magnetron sputtering, and the thickness is about 240nm. The interdigital pattern can be prepared by photolithography, the interdigital width a is 25 μm, the interdigital distance b is 25 μm, the interdigital pair number on each side is 54 pairs, the reflecting grating on each side is 16 pairs, and the interdigital length is 10mm.

The acoustic wave micro-fluidic chip in the application example is excited by a signal generator and a power amplifier, the signal excitation frequency f is 39.8MHz, and the signal excitation amplitude is 10V. In the application example, the width a and the inter-finger distance b of the inter-finger electrodes are equal to half of the flow channel width w of the sound wave focusing area, the signal excitation frequency f of the sound wave micro-fluidic device is equal to v/4a, and f is also equal to v/2w, wherein v is the propagation speed of the surface acoustic wave on the lithium niobate substrate 1', and the value of v is 3980m/s.

In this application example, the lithium niobate substrate 1 'and the PDMS substrate 2' with the micro flow channels w are bonded by oxygen plasma treatment and heated on a hot plate at 90 ℃ for 8 hours to enhance bonding strength. The acoustic wave microfluidic chip of the application example can realize particle focusing of 6 mu m, 10 mu m and 20 mu m, and the flow rate of a sample can reach 30 mu l (microliter)/min.

Application example two

The application example illustrates a preparation method of a lithium niobate substrate, as shown in fig. 8, comprising the following steps:

step S200, cleaning and irradiating the lithium niobate substrate to make the lithium niobate substrate hydrophilic.

Specifically, the lithium niobate substrate used for experiments can be washed with acetone, absolute ethyl alcohol and deionized water for 15min respectively, and irradiated with a UV (ultraviolet) washing machine for 25min to make the surface hydrophilic.

In step S201, a layer of photoresist is disposed on the lithium niobate substrate and exposed to light to form a desired pattern.

Specifically, a photoresist layer can be uniformly thrown on a lithium niobate substrate by a photoresist homogenizer, and then the lithium niobate substrate is put on a hot plate for pre-baking to volatilize a photoresist solvent, so that the photoresist layer is arranged on the lithium niobate substrate. The prepared mask plate with the electrode pattern is placed on a lithium niobate substrate coated with photoresist, exposed under a photoetching machine, and then the substrate is subjected to post baking, and a required pattern is formed on the lithium niobate substrate through development.

Specifically, the interdigital width of the interdigital pattern is 25 μm, the interdigital distance is 25 μm, the interdigital pair number of each side is 54 pairs, the reflecting grating of each side is 16 pairs, and the interdigital length is 10mm.

And S202, removing the residual glue of the patterned lithium niobate substrate, and performing magnetron sputtering coating to prepare the required electrode.

Specifically, the patterned lithium niobate substrate is put into oxygen plasma to remove residual glue, then magnetron sputtering coating is carried out, power of 120W is used for pre-sputtering for 5min, formal sputtering is carried out for 20min, and acetone is used for removing redundant photoresist after sputtering is finished, so that the required electrode is prepared on the lithium niobate substrate.

Fig. 9 illustrates a method for preparing a PDMS microchannel, comprising the steps of:

step S300, cleaning and irradiating the silicon substrate to make the silicon substrate hydrophilic.

Specifically, the silicon substrate used for experiments was washed with acetone, absolute ethanol and deionized water for 15min, respectively, and irradiated with a UV ultraviolet washer for 25min to make the surface hydrophilic.

Step S301, photoresist is spin-coated on the silicon substrate, and the silicon substrate is baked for the first time.

Specifically, SU-8 photoresist can be spin-coated on a silicon substrate, and the uniformly coated silicon substrate is placed on a hot plate with the temperature of 45 ℃ and kept for 5min; then, the hot plate temperature was set to 65℃and kept for 2 hours, completing the first baking of the silicon substrate.

And step S302, the baked silicon substrate is cooled to room temperature for exposure, and a second baking is carried out.

Specifically, the silicon substrate after the first baking is cooled to room temperature, and is exposed on a photoetching machine, and the exposed substrate slice is placed on a hot plate at 65 ℃ and kept for 2min; and then the temperature of the hot plate is adjusted to 95 ℃ and kept for 10 minutes, so as to finish the second baking of the silicon substrate.

Specifically, the channel width of the acoustic focusing area in the PDMS channel is 50um, the width of the sheath liquid inlet is 10um, the width of the sample inlet is 50um, the width of the sheath liquid outlet is 10um, and the width of the sample outlet is 50um.

Step S303, cooling the exposed silicon substrate and performing cyclic development.

Specifically, the silicon substrate was cooled to room temperature and then placed in propylene glycol methyl ether acetate and isopropanol solution, respectively, and each was subjected to cyclic development for 15 seconds until no white precipitate appeared.

And step S304, placing the developed silicon substrate in a vacuum drying oven for standing to evaporate the retained photoresist.

Specifically, the developed silicon substrate is placed in a vacuum drying oven at 135 ℃ for standing for 10min, the residual SU-8 photoresist solvent is evaporated, the adhesion between the photoresist on the substrate sheet and the silicon wafer is firmer, and the preparation of the runner template is completed.

And step S305, placing the prepared PDMS prepolymer into a vacuum box for vacuumizing.

Specifically, the PDMS prepolymer may be configured as follows: uniformly mixing PDMS glue and a curing agent in a mass ratio of 10:1 in a culture dish, and stirring for 20 minutes by using a glass rod until a large number of uniform small bubbles appear on the surface of the mixture. And placing the prepared PDMS prepolymer into a vacuum box for vacuumizing until no bubbles appear on the surface and the inside of the mixture, and completing step S205.

Step S306, pouring the PDMS prepolymer on a runner template, and curing the PDMS prepolymer to form the PDMS micro-runner.

Specifically, the PDMS prepolymer can be poured on a runner template, and baked in an oven at 100 ℃ for 1 hour to solidify the PDMS, so as to obtain the PDMS chip with the micro-runners.

In this application example, the preparation of the lithium niobate substrate can be completed through steps S200 to S202, the preparation of the PDMS substrate can be completed through steps S300 to S306, and the application example can package the lithium niobate substrate and the PDMS substrate through oxygen plasma bonding, so as to obtain the first surface acoustic wave microfluidic chip a.

Unlike the manner of preparing the interdigital electrode and the PDMS runner size based on the present application example, the following dimensions may be referred to in other application examples to prepare the interdigital electrode and configure the PDMS runner:

the interdigital pattern on which the interdigital electrode is prepared can have an interdigital width of 35 μm, an interdigital pitch of 35 μm, a pair number of interdigital pairs per side of 54 pairs, a pair number of reflective gratings per side of 16 pairs, and an interdigital length of 10mm. The channel width of the acoustic focusing area in the PDMS channel is 70 μm, the width of the sheath liquid inlet is 10 μm, the width of the sample inlet is 50 μm, the width of the sheath liquid outlet is 10 μm, and the width of the sample outlet is 50 μm. According to the interdigital pattern size, the interdigital electrode and the PDMS runner size are prepared, and the other surface acoustic wave microfluidic chip b can be prepared.

Alternatively, the interdigital electrodes and PDMS runners may also be configured with reference to the following dimensions:

the interdigital electrode was prepared based on an interdigital pattern having an interdigital width of 50 μm, an interdigital pitch of 50 μm, an interdigital pair number of 54 pairs per side, 16 pairs per side of reflective grating, and an interdigital length of 10mm. The channel width of the acoustic focusing area in the PDMS channel is 100 μm, the width of the sheath liquid inlet is 20 μm, the width of the sample inlet is 70 μm, the width of the sheath liquid outlet is 20 μm, and the width of the sample outlet is 70 μm. According to the interdigital pattern size, the interdigital electrode and the PDMS runner size are prepared, and the acoustic surface wave microfluidic chip c can be prepared.

The foregoing describes specific embodiments of the present invention. It is to be understood that the invention is not limited to the particular embodiments described above, and that various changes and modifications may be made by one skilled in the art within the scope of the claims without affecting the spirit of the invention.

Claims

1. A surface acoustic wave microfluidic chip for particle focusing, comprising: the micro-channel device comprises a base and a substrate, wherein interdigital transducers and reflecting grids are distributed on the base, and a micro-channel system and a focusing area are arranged on the substrate; the micro flow channel system includes: a focusing flow passage arranged in the focusing region; the interdigital transducer is provided with a flow channel side close to the focusing flow channel and a reflecting side far away from the focusing flow channel, and is suitable for generating surface acoustic waves to focus particles of the focusing flow channel; the reflection grating is arranged on the reflection side of the interdigital transducer and is suitable for reflecting the surface acoustic wave leaked from the interdigital transducer to the reflection side to the flow channel side.

2. The saw microfluidic chip for particle focusing of claim 1, wherein the substrate is a lithium niobate substrate and the substrate is a PDMS substrate.

3. The saw micro-fluidic chip for particle focusing according to claim 1, wherein the interdigital transducer is a pair of focusing interdigital electrodes adapted to be disposed in the focusing region, the focusing interdigital electrodes being arranged perpendicular to the flow direction of the focusing channel particles and adapted to focus the focusing channel particles in the central region of the focusing channel.

4. The saw micro-fluidic chip for particle focusing according to claim 3, wherein the focusing interdigital electrode is formed by coating a film on a substrate having an interdigital pattern by magnetron sputtering.

5. The saw micro-fluidic chip for particle focusing according to claim 3 or 4, wherein the focusing interdigital electrode is an Al electrode.

6. The saw micro-fluidic chip for particle focusing according to claim 3 or 4, wherein the interdigital width and interdigital pitch of the focusing interdigital electrode are equal to half of the focusing flow channel width.

7. The saw micro-fluidic chip for particle focusing according to claim 6, wherein the focusing interdigital electrode has an interdigital width of 25 μm and an interdigital pitch of 25 μm.

8. The saw micro-fluidic chip for particle focusing according to claim 6, wherein the focusing interdigital electrode has an interdigital width of 35 μm and an interdigital pitch of 35 μm.

9. The saw micro-fluidic chip for particle focusing according to claim 6, wherein the focusing interdigital electrode has an interdigital width of 50 μm and an interdigital pitch of 50 μm.

10. The saw micro-fluidic chip for particle focusing according to claim 3 or 4, wherein the number of pairs of fingers on each side of the focusing interdigital electrode is 54 pairs, the number of reflection gratings on each side is 16 pairs, and the length of the fingers is 10 mm.

11. The saw micro-fluidic chip for particle focusing of claim 1, wherein the micro-fluidic channel system further comprises: a particle inlet, a particle outlet, a primary sheath fluid inlet, a secondary sheath fluid inlet, a primary sheath fluid outlet, and a secondary sheath fluid outlet; the focusing flow channel is provided with an inlet end and an outlet end, the inlet end is connected to the particle inlet so as to flow in particles before focusing, and the outlet end is connected to the particle outlet so as to flow out particles after focusing; sheath liquid enters the inlet end of the focusing flow channel from the first sheath liquid inlet and the second sheath liquid inlet, so that particles before focusing entering from the particle inlet move to the central area of the focusing flow channel in advance.

12. The saw micro-fluidic chip for particle focusing according to claim 11, wherein the focusing flow channel has a flow channel width of 50 μm, the particle inlet has a width of 50 μm, the particle outlet has a width of 50 μm, the first sheath fluid inlet and the second sheath fluid inlet have widths of 10 μm, respectively, and the first sheath fluid outlet and the second sheath fluid outlet have widths of 10 μm, respectively.

13. The saw micro-fluidic chip for particle focusing according to claim 11, wherein the focusing flow channel has a flow channel width of 70 μm, the particle inlet has a width of 50 μm, the particle outlet has a width of 50 μm, the first sheath fluid inlet and the second sheath fluid inlet have widths of 10 μm, respectively, and the first sheath fluid outlet and the second sheath fluid outlet have widths of 10 μm, respectively.

14. The saw micro-fluidic chip for particle focusing according to claim 11, wherein the focusing flow channel has a flow channel width of 100 μm, the particle inlet has a width of 70 μm, the particle outlet has a width of 70 μm, the first and second sheath inlets have widths of 20 μm, respectively, and the first and second sheath outlets have widths of 20 μm, respectively.

15. A substrate structure suitable for use in a surface acoustic wave microfluidic chip, comprising: the device comprises a substrate, interdigital transducers distributed on the substrate and a reflecting grating; the substrate is suitable for bonding and packaging with a substrate of the microfluidic chip, and a micro-channel system and a focusing area are arranged on the substrate; the micro flow channel system includes: a focusing flow passage arranged in the focusing region; the interdigital transducer is provided with a flow channel side close to the focusing flow channel and a reflecting side far away from the focusing flow channel, and is suitable for generating surface acoustic waves to focus particles of the focusing flow channel; the reflection grating is arranged on the reflection side of the interdigital transducer and is suitable for reflecting the surface acoustic wave leaked from the interdigital transducer to the reflection side to the flow channel side.

16. The substrate structure for a surface acoustic wave microfluidic chip according to claim 15, wherein the substrate is a lithium niobate substrate.

17. The substrate structure for a saw micro-fluidic chip as defined in claim 15, wherein the interdigital transducer is a pair of focusing interdigital electrodes adapted to be disposed on the focusing region, the focusing interdigital electrodes being arranged perpendicular to the flow direction of the focusing channel particles and adapted to focus the focusing channel particles on the central region of the focusing channel.

18. The substrate structure suitable for a saw micro-fluidic chip as recited in claim 17, wherein the focusing interdigital electrode is formed by magnetron sputtering of a coating film on the substrate with an interdigital pattern.

19. The substrate structure for a surface acoustic wave micro-fluidic chip as recited in claim 17 or 18, wherein the focusing interdigital electrode is an Al electrode.

20. The substrate structure for a saw micro-fluidic chip as recited in claim 17 or 18, wherein the width and spacing of the fingers of said focusing finger electrodes is equal to half the width of said focusing channel.

21. The substrate structure for a saw micro-fluidic chip as recited in claim 20, wherein said focusing interdigital electrodes have an interdigital width of 25 μm and an interdigital pitch of 25 μm.

22. The substrate structure for a saw micro-fluidic chip as recited in claim 20, wherein said focusing interdigital electrodes have an interdigital width of 35 μm and an interdigital pitch of 35 μm.

23. The substrate structure for a saw micro-fluidic chip as recited in claim 20, wherein said focusing interdigital electrodes have an interdigital width of 50 μm and an interdigital pitch of 50 μm.

24. The substrate structure suitable for use in a saw micro-fluidic chip as claimed in claim 17 or 18, wherein the number of pairs of fingers on each side of the focusing interdigital electrode is 54 pairs, the number of reflection gratings on each side is 16 pairs, and the length of the fingers is 10 mm.

25. A method of making a surface acoustic wave microfluidic chip comprising:

26. The method of preparing a surface acoustic wave microfluidic chip according to claim 25, wherein the preparing a substrate comprises:

Washing and irradiating a substrate to make the substrate hydrophilic;

27. The method of preparing a saw micro-fluidic chip as recited in claim 26, wherein said washing and irradiating a substrate to make said substrate hydrophilic comprises:

28. The method of preparing a saw microfluidic chip of claim 26, wherein disposing a layer of photoresist on the substrate and exposing to light to form a desired pattern comprises:

29. The method of manufacturing a saw micro-fluidic chip as defined in claim 26, wherein removing the residual glue of the patterned substrate and performing magnetron sputtering coating to manufacture the interdigital transducer and the reflective grating comprises:

30. The method of preparing a surface acoustic wave microfluidic chip according to claim 25, wherein the preparing a substrate comprises:

cooling the exposed silicon substrate and performing cyclic development;

31. The method of preparing a saw micro-fluidic chip as recited in claim 30, wherein said cleaning and irradiating a silicon substrate to make the silicon substrate hydrophilic comprises: and cleaning the silicon substrate by using acetone, absolute ethyl alcohol and deionized water respectively for 15min, and irradiating the silicon substrate by using a UV (ultraviolet) cleaning machine for 25min to make the surface hydrophilic.

32. The method of preparing a saw micro-fluidic chip of claim 30, wherein spin coating a photoresist on the silicon substrate and baking the silicon substrate for the first time comprises: spin-coating SU-8 photoresist on the silicon substrate, placing the uniformly-glued silicon substrate on a hot plate with the temperature of 45 ℃ and keeping for 5min; then, the hot plate temperature was set to 65℃and kept for 2 hours, completing the first baking of the silicon substrate.

33. The method of manufacturing a saw micro-fluidic chip as defined in claim 30, wherein said exposing the baked silicon substrate to light at room temperature and performing a second bake comprises:

34. The method of preparing a saw micro-fluidic chip as recited in claim 30, wherein said cooling the exposed silicon substrate and performing cyclic development comprises:

35. The method of manufacturing a saw micro-fluidic chip as defined in claim 30, wherein placing the developed silicon substrate in a vacuum oven for standing to evaporate the remaining photoresist comprises: the developed silicon substrate was placed in a vacuum oven at 135 c for 10min and the remaining SU-8 photoresist solvent was evaporated.

36. The method of making a saw micro-fluidic chip as recited in claim 30, wherein said placing the pre-polymer of the formulated substrate material into a vacuum box to evacuate comprises:

37. The method of making a saw microfluidic chip of claim 30, wherein said casting said substrate material pre-polymer onto a fluidic channel template and curing said substrate material pre-polymer to form said fluidic channel system comprises: