CN108654710A - A kind of micro-fluidic chip measured for solution flow rate and microbubble counts - Google Patents

Abstract

The present invention relates to a kind of micro-fluidic chips measured for solution flow rate in microchannel and microbubble counts.The two chips that the chip is mainly made by dimethyl silicone polymer (PDMS) material are bonded, and upper chip includes：Liquid injection hole, injecting hole, gas-liquid converge mouth, double-thermocouple arrangement, positive electrode, negative electrode, liquid outlet groove and microchannel, and lower chip is for encapsulating chip.The real time temperature that double-thermocouple is measured is collected by data acquisition switch unit, and the real-time flow rate that microchannel flow field can be obtained in post-processing is carried out to the measured temperature collected.The whole work counted about microbubble are completed on the chip made by dimethyl silicone polymer (PDMS).Microbubble counting technology is used in microfluidic field, its function is realized in micro-fluidic chip.

Description

A microfluidic chip for solution flow rate measurement and microbubble counting

technical field

The invention relates to the detection field of a microfluidic chip, in particular to a microfluidic chip used for measuring the flow velocity of a solution in a microchannel and counting microbubbles.

Background technique

Microfluidic chip technology integrates the basic operations of biochemical sample extraction, mixing, reaction, detection and preparation on a tiny chip. With the structural feature of microchannel network, the functional modules on the chip are connected, and the fluid in it exhibits completely different flow characteristics from the macroscopic scale.

At present, with the continuous promotion and application of microfluidic technology, the detection of microfluidic chips also involves many aspects, such as ion detection, metabolite detection, water quality, air quality detection, etc. The detection of the solution flow rate and the counting of generated bubbles in the microchannel of the microfluidic chip are a key technology in the field of microfluidics. The application of this technology is related to the improvement of the function of the microfluidic chip.

Contents of the invention

The object of the present invention is to develop a microfluidic chip for measuring the flow velocity of the solution in the microchannel and calculating the number of microbubbles in the channel.

The concrete technical scheme that the present invention adopts is as follows:

A microfluidic chip for solution flow rate measurement and microbubble counting. The main structure is formed by bonding two chips. The structure on the chip includes a liquid injection hole 1, an air injection hole 2, and a gas-liquid confluence port 3 , a double thermocouple arrangement 4, an anode electrode 5 and a cathode electrode 6, a liquid outlet 7 and a microchannel 8.

The production material of the two chips is polydimethylsiloxane (PDMS). In the laboratory, photolithography technology is used to make microchannels 8 on the upper chip 9, and the lower chip 10 is used to package the microchannels. The function of the package is to The microchannel 8 is made into an airtight space to avoid factors such as vibration and dust in the experimental environment from affecting the flow of the solution in the microchannel 8 . The mask plate required for the fabrication of the microchannel 8 by using photolithography technology is drawn by us in CAD drawings and handed over to the microfluidic manufacturer for customization. All chip fabrication work is done independently by us in the laboratory. After the upper chip 9 is manufactured, a hole puncher is used to punch small holes of corresponding sizes in the liquid injection hole 1, the gas injection hole 2, and the liquid outlet groove 7 of the upper chip. Then the upper chip 9 and the lower chip 10 are firmly bonded together, so that the airtightness of the space in the microchannel 8 can be guaranteed, and the flow of the solution in the microchannel 8 will not be affected by air dust in the experimental environment, vibration of the experimental table, etc. factors.

Due to the elasticity of polydimethylsiloxane (PDMS) material, the surface viscosity is large, and there is strong hydrophobicity, the solution cannot form a smooth and continuous flow in the microchannel 8, so we use the Plasma plasma cleaning machine to change The hydrophobic property of the surface of the chip material, due to the strong viscosity of the PDMS material itself, we use this property to firmly bond the two chips together.

On the left side of the chip in Figure 1 is a channel for generating bubbles. The electrolyte solution enters from the liquid phase, that is, the injection hole 1, and injects the electrolyte solution into the channel through the syringe pump to set a stable injection speed; the gas enters from the gas phase, that is, the gas injection hole. 2. Inject gas into the channel by setting a stable value for the output volume of the cylinder. A group of bubbles with approximately stable size is formed at the confluence 3 of the gas phase and the liquid phase. The opening design of the confluence 3 is to stabilize the size of the generated bubbles around a certain value, and the constricted outlet helps to increase the bubble size. Due to the efficiency of formation, the generated bubbles will pass through the microchannel 8 of the chip on the right side one by one.

When making the microchannel of the chip, the double thermocouple arrangement 4 for measuring the flow rate is shown in FIG. 1 . Carefully placed on the sidewall of the microchannel 8, it is necessary to ensure that the probes of the two K-type thermocouples remain on the same plane as the sidewall of the microchannel 8, so as to prevent the probes of the thermocouples from protruding into the microchannel 8. The space itself in the channel 8 is already very narrow, if the thermal detection head of the thermocouple enters the channel, it will affect the laminar flow movement of the aqueous electrolyte solution in the microchannel 8, so when the thermal detection head is placed on the edge of the microchannel 8 , we must pay attention to the correct placement of the thermal detector head position.

The real-time temperature measured by the dual thermocouples is acquired through the data acquisition switch unit. The real-time flow velocity of the flow field in the microchannel can be obtained by post-processing the acquired temperature measurement value. It is a novel exploration to apply the technology of measuring fluid flow rate by dual thermocouples to the microfluidic chip in the field of microfluidics. No one has made such an attempt before, and it is a very important innovation point.

When the electrolyte solution drives the bubbles to flow in the microchannel 8 to the back end of the chip, here is a bubble counting device, where we can count the number of bubbles passing through the microchannel 8 according to the size of the bubbles. When the bubbles pass through the anode electrode 5 When connected to the negative electrode 6, the voltage changes to generate a pulse signal, and the pulse signal is passed to the single-chip controller (MCU) after signal conditioning and A/D conversion. count value. The system can limit the size of the bubbles that need to be counted. For example, when the bubbles with a particle size larger than 75 μm pass through the counting device, a pulse will be activated, and the pulse amount will be set as the boundary line, that is, the value smaller than this pulse amount will not be counted. , the value greater than this pulse amount counts 1, that is, only counts the bubbles with a particle size greater than 75 μm. All the counting work is done on a chip made of polydimethylsiloxane (PDMS). This is an important innovation point at present, applying bubble counting technology in the field of microfluidics and realizing its functions in microfluidic chips.

Description of drawings

A better understanding of the invention, and many of its attendant advantages, will be readily apparent by reference to the following detailed description when considered in conjunction with the accompanying drawings, but the accompanying drawings illustrated herein are intended to provide a further understanding of the invention, constituting the invention A part of the present invention, the exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation of the present invention, wherein:

Fig. 1 is a schematic diagram of the chip-on-chip structure of the device of the present invention.

Fig. 2 is a schematic diagram of the bonding between the upper and lower chips of the device of the present invention.

Fig. 3 is a schematic diagram of the three-dimensional structure of the detection device of the present invention.

Detailed ways

Below in conjunction with accompanying drawing, further illustrate the present invention with embodiment. But this embodiment is only illustrative, and the protection scope of the present invention is not limited by this embodiment.

The structure of a microfluidic chip for solution flow rate measurement and bubble counting is shown in Figure 1. The structure of the chip includes: liquid injection hole 1, gas injection hole 2, gas-liquid confluence port 3, double thermocouple arrangement 4. Anode electrode 5, cathode electrode 6, liquid outlet tank 7, and microchannel 8. The overall chip structure includes an upper chip 9 and a lower chip 10 , as shown in FIG. 2 . After the upper chip and the lower chip are bonded, a complete microfluidic chip for solution flow rate measurement and bubble counting is formed, as shown in FIG. 3 .

In terms of chip production, we use photolithography and etching techniques. Microfabrication using photoresists, masks and ultraviolet light. It consists of three processes: thin film deposition, photolithography and etching. In order to obtain a good photolithographic effect, it is necessary to clean the silicon wafer. The specific method is to soak it in a mixed solution of concentrated sulfuric acid and hydrogen peroxide, then clean it with deionized water, and blow it dry with nitrogen. Before photolithography, use a uniform machine to evenly cover a layer of photoresist on the surface of the silicon wafer. The photoresist can be divided into positive and negative. According to the requirements of making chips, we use negative glue. The model is SU-82050. Purchase From Suzhou Wenhao shares. Then, the design pattern of the microfluidic chip on the mask plate is transferred to the photoresist layer through the principle of exposure imaging. The mask plate is designed by us through CAD software to design the chip pattern, and then handed over to Kunshan Kaisheng Electronics to make it into a physical object. The basic function of the mask plate is to produce different light absorption and transmission capabilities in the graphic area and non-graphic area when ultraviolet light passes through. . The lithography machine was purchased from the Institute of Optoelectronic Technology, Chinese Academy of Sciences, Chengdu, and the model is URE-2000/25. After the photolithography is completed, the excess photoresist on the silicon wafer is washed away with the developer specified for the negative film, and the developer is purchased from Suzhou Wenhao Co., Ltd. In this way, we successfully transferred the pattern on the mask plate to the silicon wafer as a mold for making microchannels. We mix polydimethylsiloxane (PDMS) and curing agent in a ratio of 10:1, and after stirring well, put the container containing the mixture into a vacuum desiccator to completely extract the air bubbles. Then put the silicon wafer mold into the Petri dish and pour the PDMS mixture on it, heat it on the thermostat at a constant temperature of 80 degrees Celsius for one hour, and then use a scalpel to cut the glue according to the edge of the graph, and use a hole puncher Drill holes at the positions of the liquid injection hole 1, the gas injection hole 2 and the liquid outlet groove 7. Finally, the chip was flushed with ethanol, deionized water and nitrogen to remove surface impurities. In the bonding stage, we use a Plasma plasma cleaning machine to process the upper chip 9 and the lower chip 10 respectively. Then the two chips are tightly bonded together, and heated in vacuum for two hours in a vacuum oven at 65 degrees Celsius. At this point, the required chip production is completed.

The making of the chip is a tool for completing the present invention, and the use of the instrument is also a necessary operation for completing the present invention. The two major innovations of the present invention are the combination of two detection technologies, that is, the measurement of microfluid flow velocity by double thermocouples and the counting of microbubbles, with the microfluidic chip. The structure of the microfluidic chip device is pioneered by our laboratory.

The electrolyte solution was injected through the injection hole 1 through the syringe pump, and the liquid phase fluid flow rate of the syringe pump was set at 5 μL/min; nitrogen was injected through the gas injection hole, and the gas phase fluid flow rate of the gas cylinder was set at 5 μL/min. Between the liquid injection hole 1 and the syringe pump, we connect the two with a medical needle tube and a capillary tube, and then fix the needle tube on the syringe pump. The connection between the nitrogen cylinder and the gas injection hole 2 is also connected by a capillary.

At the gas-liquid confluence port 3, independent microbubbles can be continuously generated, and the microbubbles are transported to the area where the double thermocouples are arranged through the microchannel 8. The thermocouples are arranged on the side wall of the channel, and the temperature data acquisition device is connected through the drawn wires to obtain two real-time temperature values. The model of the temperature data acquisition device we adopt is Agilent's 34972A. We use Newton's cooling law and Origin software to obtain the convective heat transfer coefficient, and then obtain the relationship between the convective heat transfer coefficient and the flow field velocity in the microchannel 8 based on empirical formulas, so as to measure the real-time dynamic flow velocity changes in the microchannel.

When a microbubble passes through the positive electrode 5 and the negative electrode 6, it will cause a voltage change to generate a pulse signal. We use signal conditioning and A/D conversion in the subsequent connection circuit to pick up this pulse signal and convert the processed signal Pass it into the single-chip controller, count the number of excited pulses in the single-chip controller, and then use the MDK software to compile the C language program and display the counting result on the LCD display through the communication interface. Because the sizes of the microbubbles generated at the gas-liquid confluence port 3 are different, the sizes of the pulses excited when passing through the anode electrode 5 and the cathode electrode 6 will also be different. We can set a fixed value in programming, which represents the size of the excitation pulse. When the generated pulse value is lower than this fixed value, we will not count it, that is, the microbubbles whose volume does not reach a certain size Not counted. So far, our microfluidic chip has completed the work of microbubble counting.

The above chip manufacturing process and detection method steps are all carried out under the environment of standard atmospheric pressure of 101.325KPa and normal temperature of 20°C. For the first time, the concept of double thermocouple measuring fluid flow rate was applied to the field of microfluidics, and its function was realized in the microfluidic chip; Relevant hardware and software technical support make the counting results more accurate.

The description of the above examples is only used to help understand the core ideas of the present invention; meanwhile, for those of ordinary skill in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application ranges. , the contents of this specification should not be construed as limiting the present invention.

Claims (4)

1. A microfluidic chip for solution flow rate measurement and microbubble counting, characterized in that it is formed by bonding two chips, and the upper chip 9 structure of the microfluidic chip includes a liquid injection hole 1, an air injection hole 2. Gas-liquid confluence port 3, double thermocouple arrangement 4, positive electrode 5 and negative electrode 6, liquid outlet tank 7 and microchannel 8. The lower chip 10 is used for encapsulating the microchannel 8. The function of the encapsulation is to make the microchannel 8 into a closed space, so as to avoid factors such as vibration and dust in the experimental environment from affecting the solution flow in the microchannel 8. 2. A microfluidic chip for solution flow rate measurement and microbubble counting, characterized in that double thermocouples are embedded in the sidewall of the microchannel 8 of the upper chip 9, and the real-time temperature measured is passed through the data acquisition switch The unit is collected. The real-time flow velocity of the flow field in the microchannel can be obtained by post-processing the acquired temperature measurement value. 3. A microfluidic chip used for solution flow rate measurement and microbubble counting, characterized in that when the electrolyte solution drives the bubbles to flow to the back end of the chip in the microchannel 8, we can here pass through according to the size of the bubbles The number of bubbles in the microchannel 8 is counted. When the bubbles pass through the positive electrode 5 and the negative electrode 6, a voltage change is caused to generate a pulse signal. The pulse signal is conditioned by the signal, and after A/D conversion, it is transmitted to the microcontroller (MCU) , count the number of pulses generated by the microcontroller, and then display the count value through the LCD. 4. A microfluidic chip for solution flow rate measurement and microbubble counting, characterized in that we can set a fixed value in programming, this fixed value represents the size of the excitation pulse, when the generated pulse value is low At this fixed value, we do not count, that is, the microbubbles whose volume does not reach a certain size are not counted.