A microfluidic mixing device based on in-line injection and methods of use thereof

Abstract

This invention discloses a microfluidic mixing device based on tandem injection and its usage method, belonging to the field of microfluidic chip technology. The invention employs a tandem mixing chamber design, allowing two fluids of different concentrations to be alternately injected into the mixing chamber. Through the flow channel structure, a three-layer parallel laminar fluid structure can be spontaneously formed at the inlet cross-section of the mixing chamber. After passing through the mixing channel, the mixed fluids of the three-layer structure achieve efficient mixing through molecular diffusion based on the expanded contact area. This structure doubles the diffusion contact area between fluids without introducing chaotic convection or an external energy field, significantly enhancing the molecular diffusion mixing efficiency at low Reynolds numbers (Re). It enables efficient mixing under low Reynolds number conditions through a simple, low-cost flow channel design without external energy input, while maintaining low flow resistance.

Description

Technical Field

[0001] This invention belongs to the field of microfluidic chip technology, specifically relating to a microfluidic mixing device based on tandem sample introduction and its usage method. Background Technology

[0002] Microfluidic chip technology has become an important platform in fields such as biology, chemistry, and medicine due to its advantages of low sample consumption, fast reaction speed, and high integration. However, in micrometer-scale channels, fluid flow is usually in a low Reynolds number laminar state, and mixing between fluids mainly depends on slow molecular diffusion, which severely limits the efficiency of analyses involving rapid reactions.

[0003] To address this bottleneck, researchers have conducted long-term research. One mainstream approach is to design complex microchannel geometries, such as constructing serpentine channels, placing periodic barriers within the channels, or creating three-dimensional segmented-reconstructed channels, in order to induce chaotic convection in laminar flow or increase the stretching and folding of the fluid interface. While these methods can improve mixing efficiency to some extent, their improvements often come at the cost of significantly increasing fluid flow resistance (i.e., pressure drop), which not only increases driving energy consumption but may also adversely affect other sensitive units integrated on the same chip. Furthermore, complex three-dimensional microstructures also increase the design and fabrication difficulty and cost of the chip.

[0004] Another approach involves introducing external energy fields to actively disturb the fluid, such as applying acoustic, electric, magnetic, or thermal fields to directly disrupt the laminar interface. This type of active mixing strategy can typically achieve efficient mixing over a wide flow rate range without necessarily leading to increased pressure drop. However, its drawbacks are equally apparent: it requires additional external drive devices and control systems, making the entire system complex, bulky, and costly, contradicting the original intention of highly integrated and portable microfluidic technology. More importantly, some energy fields may adversely affect bioactive samples, limiting its application in the life sciences.

[0005] Existing microfluidic mixing technology faces a dilemma: passive mixers sacrifice structural simplicity and low energy consumption in pursuit of efficiency; while active mixers offer controllable efficiency but introduce system complexity and potential sample interference.

[0006] Therefore, developing a novel microfluidic mixing scheme that can achieve efficient mixing under low Re numbers by means of a simple and low-cost channel design without external energy input, while maintaining low flow resistance, has become an important technical challenge in this field. Summary of the Invention

[0007] Therefore, the purpose of this invention is to provide a microfluidic mixing device based on tandem injection and its usage method, which can achieve efficient mixing under low Re number conditions, with only a simple and low-cost flow channel design and no external energy input, while maintaining low flow resistance.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] In a first aspect, the present invention provides a high-efficiency microfluidic mixing chip, wherein mixing chamber a and mixing chamber b are connected in series, mixing chamber b is connected to a mixing channel, mixing chamber a is connected to inlet channel a, mixing chamber b is connected to inlet channel b, and a microelectrode structure is provided below the outlet of the mixing channel.

[0010] Among them, the high-efficiency microfluidic mixing chip is a PDMS-glass composite chip, which includes a microchannel structure and a microelectrode structure; the series-connected mixing chambers a and b, mixing channel, inlet channel a, and inlet channel b together form a microchannel structure, forming a series-connected sample injection channel layout, with a microchannel structure height of 60 micrometers.

[0011] The electrodes or electrode arrays are precisely aligned with the mixing channel to facilitate real-time monitoring of fluid concentration using electrochemical impedance spectroscopy.

[0012] Based on the above technical solution, further, the radii of the inlet channel a and the inlet channel b are 0.5mm, the radii of the mixing chamber a and the mixing chamber b are 1.5mm, the distance between the inlet channel a and the inlet channel b is 5mm, the cross-sectional dimensions at the connection between the mixing channel and the mixing chamber b are 0.1mm × 0.06mm, the mixing channel has a U-shaped main channel section, the vertical section of the main channel section is 4mm long, and the radius of the arc section of the main channel section is 1mm.

[0013] Based on the above technical solution, the microelectrode structure is further described as a finger-shaped cross electrode array, and the electrode includes a 10nm thick chromium adhesion layer and a 100nm thick gold conductive layer.

[0014] The 10nm thick chromium adhesion layer and the 100nm thick gold conductive layer ensure good conductivity and adhesion to the glass substrate.

[0015] Based on the above technical solution, the mixing chamber a, the mixing chamber b, the inlet channel a, the inlet channel b, and the mixing channel are further prepared using soft photolithography, and the microelectrode structure is prepared by photolithography, sputtering, and lift-off processes.

[0016] The use of soft lithography technology gives the microchannel structure good flexibility and sealing properties.

[0017] Based on the above technical solution, the microelectrode structure is located on the surface of the glass substrate, and the mixing chamber a, the mixing chamber b and the mixing channel are bonded to the glass substrate through oxygen plasma surface hydrophilication treatment.

[0018] The microchannel structure is bonded to the glass substrate through oxygen plasma surface hydrophilization treatment, forming a closed microchannel system.

[0019] The glass substrate serves as the carrier substrate for the microelectrode, ensuring structural stability and electrical detection performance.

[0020] Secondly, the present invention provides a method for fabricating the above-mentioned high-efficiency microfluidic hybrid chip, comprising the following steps: Fluid a and fluid b are sequentially injected into inlet channel a and inlet channel b, respectively, with the flow rate fraction of fluid b being... φ = v 2 / ( v 1+ v 2), of which v 1 represents the average flow velocity of inlet channel a. v 2 represents the average flow velocity of inlet channel b. φ The adjustment range is 10%-90%, and the initial concentration ratio of fluid a to fluid b is 1:9-9:1.

[0021] Based on the above technical solution, further, before injection, fluid a and fluid b are stored in liquid storage devices corresponding to inlet channel a and inlet channel b, respectively, and fluid a and fluid b are injected into inlet channel a and inlet channel b by injection pump.

[0022] The syringe pump is a high-precision syringe pump, and the flow rate ratio of the two fluids is set according to the target concentration gradient.

[0023] Based on the above technical solution, further, fluid a and fluid b form a three-layer parallel laminar fluid structure in the mixing chamber b, in which fluid a encloses fluid b, and fluid a and fluid b form a mixed solution in the mixing channel.

[0024] Among them, under the action of the flow channel structure of the mixing chamber b, a stable three-layer fluid structure is formed, in which fluid a encloses fluid b.

[0025] Within the main channel section, the two fluids achieve efficient mixing through molecular diffusion, based on the expanded contact area.

[0026] Based on the above technical solution, furthermore, an electrochemical impedance spectroscopy device is connected to the microelectrode structure to detect the impedance signal of the mixed solution, wherein the detection frequency range is 1Hz-10Hz. 6 Hz.

[0027] Among them, the electrochemical impedance spectroscopy device measures the impedance signal of the fluid at the outlet of the mixing channel in real time, and verifies the generated concentration gradient based on the correspondence between impedance and concentration.

[0028] Based on the above technical solution, further, when the Re number is adjusted within the range of 0.15-75, the mixing index at the outlet is not less than 92%.

[0029] Among them, when Re=7.5, the mixing index of the initial section of the main mixing channel reaches 92.5%.

[0030] Specifically, solution resistance parameters are extracted based on an equivalent circuit model, and the generated concentration gradient is verified using the correlation between solution resistance and concentration. The deviation between the solution resistance and manually prepared standard solutions is verified to be no more than 3%, ensuring the accuracy of concentration control.

[0031] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention employs a series mixing chamber design, allowing two fluids of different concentrations to be alternately injected into the mixing chamber. Through the flow channel structure, a three-layer parallel laminar fluid structure can be spontaneously formed at the inlet cross-section of the mixing chamber. After the three-layer fluid structure passes through the mixing channel, it achieves efficient mixing through molecular diffusion based on the expanded contact area. This structure doubles the diffusion contact area between fluids without introducing chaotic convection or an external energy field, significantly enhancing the molecular diffusion mixing efficiency at low Reynolds numbers (Re). It can achieve efficient mixing under low Reynolds number conditions with only a simple and low-cost flow channel design, without the need for external energy input, while maintaining low flow resistance.

[0032] 2. The chip of the present invention integrates microelectrodes and, combined with electrochemical impedance spectroscopy, can perform label-free, real-time, and quantitative verification of the concentration gradient generated during the mixing process.

[0033] 3. The present invention has a simple structure, low processing cost, high mixing efficiency and low pressure drop, and is particularly suitable for microfluidic applications that require rapid and uniform mixing or controllable concentration gradient generation, such as biochemical analysis, drug screening and nanomaterial synthesis. Attached Figure Description

[0034] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0035] Figure 1 Here is a geometric model diagram of the tandem injection system of Embodiment 1 of the present invention: C-1 is an enlarged view of the structure of the mixing chamber b, and S-1 is an enlarged cross-sectional view of the connection between the mixing channel and the mixing chamber b; Figure 2This is a schematic diagram of the microfluidic chip fabrication process according to Embodiment 1 of the present invention: In the image: 1. Glass slide; 2. Spin coating of LN35cp photoresist; 3. Exposure; 4. Development; 5. Sputtering; 6. Lifting; 7. Silicon wafer; 8. Spin coating of SU-8 2050 photoresist; 9. Exposure; 10. Development; 11. Casting PDMS; 12. Film removal and trimming; 13. Rendering of the integrated microfluidic chip after bonding. Figure 3 The following are the results of the influence of Re on the mixing performance in Example 2 of the present invention: (a) Concentration characterization diagram of tandem injection mode under different Re, (b) Line graph of expected concentration at the outlet under different Re, (c) Line graph of mixing index at S-1 and S-8 sections under different Re; Figure 4 The following are the results of the influence of φ on the expected concentration in Example 2 of the present invention: (a) is a concentration characterization diagram of the tandem injection mode under different φ, (b) is a bar chart of the expected concentration at the outlet under different φ, and (c) is a line graph of the concentration difference at the outlet under different φ. Figure 5 The following are the results of the NaCl impedance signal verification concentration gradient in Example 3 of this invention: (a) is a schematic diagram of the impedance signal verification system, (b) is the impedance Bode plot of the response at different concentrations, and (c) is the solution resistance result obtained from the equivalent circuit. Detailed Implementation

[0036] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0037] Example 1 This embodiment describes the chip structure design and fabrication.

[0038] like Figure 2 As shown, the high-efficiency microfluidic hybrid chip in this embodiment adopts a PDMS-glass composite structure.

[0039] Microelectrode fabrication: On a cleaned glass substrate (75mm × 25mm), a negative photoresist LN35cp was spin-coated, and a mask for forming a finger-shaped interdigitated electrode pattern was formed by UV lithography and development. Subsequently, a 10nm chromium adhesion layer and a 100nm gold conductive layer were sequentially deposited by magnetron sputtering. Finally, the interdigitated electrodes on the glass substrate were obtained through a lift-off process.

[0040] Microchannel fabrication: Standard soft lithography was employed. SU-8 2050 photoresist was spin-coated onto a silicon wafer, and a microchannel male mold with a height of 60 μm was fabricated through photolithography and development. PDMS prepolymer and curing agent were mixed at a 10:1 ratio, degassed, and then poured onto the mold. The mixture was cured at 80°C for 2 hours, and then peeled off to obtain a PDMS layer with a microchannel structure. Holes were drilled in the PDMS channel layer to form fluid inlets and outlets.

[0041] Chip integration: The glass substrate with electrodes and the PDMS channel layer are treated with oxygen plasma to modify their surfaces to be more hydrophilic. Then, under a microscope, they are precisely aligned and light pressure is applied to permanently bond them together, forming a closed integrated microfluidic chip. After bonding, the working area of ​​the microelectrodes is located directly below the mixing chamber or the downstream main channel.

[0042] Three-layer structure, such as Figure 1 In S-1, blue represents fluid a, yellow represents fluid b, and fluid a encloses fluid b in a three-layer parallel laminar flow fluid structure. The three-layer structure is... Figure 3 and Figure 4 This is also reflected in S-1.

[0043] Example 2 Study on the influence of operating parameters on the chip prepared in Example 1.

[0044] To comprehensively evaluate chip performance, COMSOL Multiphysics software was used to establish a model that perfectly matches the experimental results, and simulations were performed by coupling laminar flow and rarefaction mass transfer physics fields. The key operating parameters, Reynolds number and... φ The impact. For example... Figure 3 As shown. Simulation studies were conducted within the Re number range of 0.15 to 75. At low Re numbers, mixing was dominated by diffusion, and the three-layer flow structure was stable. As the Re number increased to 7.5, the convection effect strengthened, and mixing was significantly enhanced, reaching a peak MI (92.5%) at the S-1 section. With further increases in the Re number, the initial mixing efficiency decreased due to the shortened fluid residence time, but due to strong convective disturbances, the outlet mixing index remained above 99%, as shown. Figure 3 c. Throughout the entire Re number study range, the expected export concentration remained stable between 0.492 and 0.530, very close to the theoretical perfect mixture value of 0.5. Figure 3 b demonstrates the chip's hybrid robustness over a wide Re number range. For example... Figure 4 As shown. By adjusting the ratio of the second inlet flow velocity to the total flow velocity ( φ The study investigated the chip's ability to precisely control the concentration of the output solution, ranging from 10% to 90%. Figure 4 As shown in b, the actual measured value of the outlet concentration is in high agreement with the theoretical value, with a maximum deviation of only 0.013 ( φWhen the percentage is 20%, the minimum deviation is 0.00121. φ =70% (e.g., when =70%). Figure 4 As shown in Figure c, the concentration difference at the outlet is introduced, which is the absolute value of the difference between the theoretical value and the actual value. The concentration difference is... φ =10% is 0.012, then in φ At 20%, it increased slightly to 0.013, and then generally showed a downward trend. φ The minimum value of 0.00121 is reached when the percentage is 70%. φ When the flow rates were further increased to 80% and 90%, the concentration difference slightly increased again, reaching 0.0058 and 0.0084 respectively. The actual values ​​closely approximate the theoretical values, indicating that the tandem injection mode can effectively achieve controllable mixing of the fluid under different flow rate distribution conditions and accurately reflect the dominant role of the inlet flow rate ratio on the outlet concentration. This result not only verifies the accuracy of the simulation model but, more importantly, demonstrates that this chip can precisely control the concentration of the output solution and achieve a stable concentration gradient generation function by simply adjusting the flow rate ratio of the two inlets.

[0045] Example 3 Regarding the chip prepared in Example 1, a hybrid verification method based on impedance detection was used. like Figure 5 As shown. To verify the accuracy of the concentration gradient generated by the chip in practical applications, an impedance detection system was built as follows. Figure 4 a. Using manual preparation and via this chip respectively. φ The NaCl solutions of specific concentrations were tested in real time under conditions of 25%, 50%, and 75%.

[0046] Methods and Systems: Connect the chip-integrated microelectrodes to an impedance analyzer. For example... Figure 5 b. Measure the impedance spectra of NaCl solutions with different concentrations. Extract the solution resistance Rs by fitting an equivalent circuit, such as... Figure 5 As shown in Figure c, for the same target concentration, the resistance value of the solution generated by the chip is almost identical to the resistance value of the manually prepared standard solution. φ At 50%, the chip value is 389.25Ω, and the manual value is 388.05Ω. This result fully confirms that the tandem injection mixing chip described in this invention can accurately and reliably generate the expected concentration gradient, and that integrated impedance detection is an effective in-situ verification method.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-efficiency microfluidic hybrid chip, characterized in that, Mixing chamber a and mixing chamber b are connected in series, mixing chamber b is connected to the mixing channel, mixing chamber a is connected to the inlet channel a, mixing chamber b is connected to the inlet channel b, and a microelectrode structure is provided below the outlet of the mixing channel.

2. The high-efficiency microfluidic hybrid chip according to claim 1, characterized in that, The radii of the inlet channel a and the inlet channel b are 0.5 mm, the radii of the mixing chamber a and the mixing chamber b are 1.5 mm, the distance between the inlet channel a and the inlet channel b is 5 mm, the cross-sectional dimensions at the connection between the mixing channel and the mixing chamber b are 0.1 mm × 0.06 mm, the mixing channel has a U-shaped main channel section, the vertical section of the main channel section is 4 mm long, and the radius of the arc section of the main channel section is 1 mm.

3. The high-efficiency microfluidic hybrid chip according to claim 1, characterized in that, The microelectrode structure is a finger-shaped cross electrode array, and the electrode includes a 10 nm thick chromium adhesion layer and a 100 nm thick gold conductive layer.

4. The high-efficiency microfluidic hybrid chip according to claim 1, characterized in that, The mixing chamber a, the mixing chamber b, the inlet channel a, the inlet channel b, and the mixing channel are fabricated using soft photolithography, and the microelectrode structure is fabricated using photolithography, sputtering, and lift-off processes.

5. A high-efficiency microfluidic hybrid chip according to claim 1, characterized in that, The microelectrode structure is located on the surface of the glass substrate, and the mixing chamber a, the mixing chamber b and the mixing channel are bonded to the glass substrate through oxygen plasma surface hydrophilication treatment.

6. The method for fabricating a high-efficiency microfluidic hybrid chip as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Fluid a and fluid b are sequentially injected into inlet channel a and inlet channel b, respectively, with the flow rate fraction of fluid b being... φ = v 2 / ( v 1+ v 2), of which v 1 represents the average flow velocity of inlet channel a. v 2 represents the average flow velocity of inlet channel b. φ The adjustment range is 10%-90%, and the initial concentration ratio of fluid a to fluid b is 1:9-9:

1.

7. The preparation method according to claim 6, characterized in that, Before injection, fluid a and fluid b are stored in liquid storage devices corresponding to inlet channel a and inlet channel b, respectively. Fluid a and fluid b are injected into inlet channel a and inlet channel b by injection pump.

8. The preparation method according to claim 6, characterized in that, The fluid a and the fluid b form a three-layer parallel laminar fluid structure in the mixing chamber b, in which the fluid a encloses the fluid b, and the fluid a and the fluid b form a mixed solution in the mixing channel.

9. The preparation method according to claim 8, characterized in that, An electrochemical impedance spectroscopy device is connected to the microelectrode structure to detect the impedance signal of the mixed solution, wherein the detection frequency range is 1Hz-10Hz. 6 Hz.

10. The preparation method according to claim 8, characterized in that, When the Re number is adjusted within the range of 0.15-75, the mixing index at the outlet is not less than 92%.

Images