CN104266680A - Microfluidics droplet detection system and method based on capacitive sensor - Google Patents

Abstract

A microfluidic droplet detection system based on a capacitive sensor, characterized in that it includes a droplet microfluidic chip, a DC voltage regulator circuit unit, a signal detection circuit unit, and a computer; wherein the droplet microfluidic chip is The chip structure that integrates the capacitive sensor and the microchannel that generates the micro-droplet; the droplet detection method includes sample pumping, droplet formation, and droplet detection; its advantages: ① simple structure; ② detection by the change of capacitance value ; ③ fast detection, small system size and can be integrated; ④ suitable for the analysis of expensive samples and reagents; ⑤ easy to process and manufacture, easy to implement.

Description

A microfluidic droplet detection system and detection method based on capacitive sensor

(1) Technical field:

The invention belongs to the field of microfluidic chip analysis, in particular to a capacitive sensor-based microfluidic droplet detection system and detection method.

(two) background technology:

The microfluidic chip integrates the basic operation units involved in the fields of biology and chemistry, such as sample preparation, reaction, separation, detection, cell culture, sorting, and lysis, on a chip of several square centimeters. A network of microchannels is formed to run through the entire system with controllable fluids to replace various functions of conventional chemical or biological laboratories. The biggest advantage of microfluidic chips is the flexible combination and large-scale integration of various unit technologies on an overall controllable micro platform, which makes microfluidic chips likely to become an important platform for the development of biochemical analysis technology in the future. Droplet microfluidics is an emerging technology developed in the past decade. The main research content is to generate and manipulate nanoliter or even picoliter droplets in a closed microchannel network.

The biggest feature of droplet microfluidics is that the two liquids that form the droplet are immiscible, such as water and oil, and there is no diffusion between the liquid inside the droplet and the liquid outside, so that each droplet can be regarded as a separate The reaction chamber in the droplet is not affected by the completion of the reaction conditions, and there is no cross-contamination between samples. For droplets, the characteristics of droplet size, shape, velocity and content concentration have a significant impact on the final biochemical expression and test results. Therefore, real-time detection of droplet characteristics is very necessary. Researchers have proposed many detection methods, such as optical detection methods. Huebner et al. used laser-induced fluorescence to detect droplets, which can capture the geometric changes of droplets. Tkaczyk et al. mixed fluorescein in the droplets, and the laser light excited by the laser was reflected to the multi-channel photon counter and photomultiplier tube to detect the average length and average interval of the droplets. The detection method of laser-induced fluorescence is highly capable of single-molecule detection. However, fluorescent labeling may cause changes in the biochemical activity of the analyte, affecting the reliability of the results. What the photomultiplier tube detects is the average information of the droplet, and the droplet cannot be precisely controlled. Moreover, the above two detection methods all require large-scale experimental instruments, which is not conducive to integration.

(3) Contents of the invention:

The object of the present invention is to provide a microfluidic droplet detection system and detection method based on a capacitive sensor, which can overcome the deficiencies of the prior art, and is a simple structure and easy to process that can be applied to microfluidic droplets. And the realized system, and its detection method has high detection speed and high precision.

The technical solution of the present invention: a microfluidic droplet detection system based on a capacitive sensor, characterized in that it includes a droplet microfluidic chip, a DC voltage stabilizing circuit unit, a signal detection circuit unit, and a computer; wherein the liquid The droplet microfluidic chip is a chip structure that integrates a capacitive sensor and a microchannel that generates microdroplets; the droplet microfluidic chip is composed of an upper sheet, a lower sheet, and a capacitive sensor bonded to each other; the lower sheet The sheet is a microchannel sheet, which is welded with a sample I inlet, a sample II inlet, a droplet outlet, a cross, an electrode terminal, a sample I channel, a sample II channel, and a droplet generation channel; the sample I inlet is connected to the sample I channel Connected; the sample II inlet is connected to the sample II channel; the sample I channel and the sample II channel are connected to the droplet generation channel through the intersection; the droplet generation channel is connected to the droplet outlet; the capacitance sensor is placed The top of the droplet generation channel is connected with the electrode terminal; the upper chip has a groove for placing a capacitive sensor; the output end of the DC voltage stabilizing circuit unit and the input end of the signal detection circuit unit are respectively connected to the droplet microflow The electrode terminals on the control chip are connected; the computer is bidirectionally connected to the signal detection circuit unit, and its output terminal is connected to the input terminal of the DC voltage stabilizing circuit unit.

The sample I inlet is a continuous phase inlet, which is composed of a continuous phase sample I inlet and a continuous phase sample I inlet II; the sample I inlet I and the sample I inlet II are respectively pumped into the sample I by the pump I; the sample II inlet is the discrete phase inlet, and the sample II inlet is pumped into the sample II through the pump II; the pump I and the pump II are respectively connected to the sample I inlet and the sample II inlet through pipelines, and the sample is pumped into the droplet microfluidic chip channel.

There are two electrode terminals, respectively electrode terminal I and electrode terminal II; the electrode terminal I is connected to the output terminal of the DC voltage stabilizing circuit; the electrode terminal II is connected to the input terminal of the signal detection circuit connect.

The microchannel for generating microdroplets in the droplet microfluidic chip is a Ψ-shaped channel composed of a sample I channel, a sample II channel and a droplet generating channel.

There are two sample I channels, namely sample I channel I and sample I channel II.

The sample II channel and the droplet generation channel are straight channels.

The sample I channel I and the sample I channel II are channels with a straight front end and a curved rear end; the straight front channel parts are parallel to each other and are in parallel relationship with the sample II channel; the curved channel part at the rear end is a 1/4 circle bend channel; the sample I channel I, sample I channel II, sample II channel and the droplet generation channel are connected at the intersection.

The size of the intersection is smaller than the cross-sectional size of the sample I channel I, sample I channel II, sample II channel and droplet generation channel on the chip, and it is easy to form droplets during the droplet preparation process.

The cross-sectional size of the sample I channel I, the sample I channel II, the sample II channel and the droplet generation channel is 200 μm*200 μm; the size of the intersection is 100 μm*100 μm.

The center line of the capacitive sensor coincides with the center line of the droplet generation channel, and there is no interlayer between the two; the capacitive plate of the capacitive sensor is located at the outlet end of the droplet generation channel, and the center line of the capacitive plate is in line with the outlet end of the droplet generation channel. The centerlines of the droplet generation channels coincide.

The material for making the droplet microfluidic chip is polydimethylsiloxane; the capacitive sensor is a planar interdigitated structure, and the material is a mixture of silver and polydimethylsiloxane.

The signal detection circuit unit is composed of a frequency modulation circuit containing an oscillation module, a frequency voltage f/V conversion circuit and a low-pass filter circuit; the input end of the frequency modulation circuit receives the signal of the electrode terminal II of the droplet microfluidic chip, Its output end is connected with a low-pass filter circuit through a frequency-voltage f/V conversion circuit; the output end of the low-pass filter circuit is connected with a computer.

A microfluidic droplet detection method based on a capacitive sensor, characterized in that it comprises the following steps:

①Pump I is connected to the inlet I of sample I and inlet II of sample I through two Teflons, and pump II is connected to the inlet of sample II through Teflon to press the sample into the channel of the droplet microfluidic chip, and sample I passes through sample I Inlet I and sample I inlet II enter the droplet microfluidic chip, and at the same time, sample II enters the droplet microfluidic chip from the sample II inlet, and the two samples pass through sample I channel I and sample I channel II respectively; sample II channel flows into the droplet microfluidic chip , and form droplets at the intersection, the size, shape, generation frequency, and velocity of the droplets are affected by the inlet velocity of sample I, the viscosity of sample I, and the interfacial tension between sample I and sample II;

②The DC voltage stabilization circuit provides power for the sensor capacitor. The droplets obtained in step ① flow through the capacitive sensor through the droplet generation channel. Due to the difference in the dielectric constant of the two liquids, the capacitance of the capacitive sensor will change. The capacitance will drive the external signal detection circuit to work;

③The frequency modulation circuit of the signal detection circuit unit receives the signal of capacitance change, and the changed capacitance also makes the oscillation module in the frequency modulation circuit generate different frequency values when resonating;

④After different frequency values pass through the frequency-voltage f/V conversion circuit, the frequencies generated during these resonances are converted into voltage signals and output to the low-pass filter circuit. The low-pass filter circuit passes signals lower than the cut-off frequency and higher than the cut-off frequency. The frequency signal is filtered out, so that the smooth signal is output to the computer;

⑤The computer outputs a control signal to the DC voltage stabilizing circuit unit, so that the DC stabilizing circuit unit outputs a stable DC voltage; the computer outputs the control signal to the signal detection circuit unit, and the capacitance sensor transmits the capacitance change signal caused by the difference of the droplet to the signal detection The circuit unit is passed to the computer after passing through the signal detection circuit unit, and the computer can intuitively display the test result, thereby realizing the detection of the sample;

⑥Finally, the droplets generated in step ① flow out from the droplet outlet through the droplet generation channel.

The application of the droplet microfluidic chip includes detecting the size, shape, speed, and content characteristics of the droplet; the precise control of the droplet in the microfluidic droplet system and the control of the sample injection in the fields of biology, chemistry, and medicine. Ingredient Control.

The working principle of the present invention: the microfluidic droplet detection chip based on the principle of capacitive sensor integrates droplet generation and droplet detection. The upper and lower pieces and the capacitor are composed of three parts. The capacitor channel is processed on the upper piece, and the microchannel is processed on the lower piece. The capacitor is embedded in the channel of the upper piece. The upper piece and the lower piece are bonded to form a closed microchannel.

The on-chip microchannel is used to generate separated droplets, and the on-chip capacitive sensor is used to detect the droplets; the function of the DC voltage regulator circuit (see Figure 3) is to output DC with stable voltage to supply the normal operation of the capacitive sensor; frequency modulation The circuit (see Figure 4) uses the capacitive sensor as a part of the resonant circuit of the oscillator. When the input quantity causes the capacitance of the capacitive sensor to change, the oscillation frequency f of the oscillator changes; the f/V conversion circuit (see Figure 5) takes The frequency f change signal is converted into a proportionally variable voltage signal. When the input frequency f changes, the output voltage also changes in response; its function is to convert the frequency f of the oscillator in the frequency modulation circuit into a voltage signal output; low-pass filter circuit (see Figure 6) Pass the signal lower than the cutoff frequency, and filter out the signal higher than the cutoff frequency. The function of the low-pass filter circuit here is to smooth the output signal.

The power supply in the DC stabilized circuit (see Figure 3) is 220V50Hz, which is the energy input of the entire circuit, connected with the transformer T, and forms a single-phase bridge rectifier circuit through diodes D1, D2, D3, D4 to output a single-phase sinusoidal voltage , The single-phase sinusoidal voltage is filtered by four capacitors C1, C2, C3, and C4, and the three-terminal voltage regulator U1, U2 and capacitors C5, C6, C7, and C8 form a voltage regulator link, outputting a DC stable ±12V voltage.

R1, R2, R3, R4 and crystal transistor Q1 form an oscillation circuit, C10, C11, C12, L1 and a variable capacitor Cx form a frequency selection network of the oscillator to complete the frequency selection. The change of the variable capacitance Cx leads to the change of the resonant frequency of the resonant circuit composed of the inductor L1 and the variable capacitance Cx, thereby realizing the change of the output frequency of the circuit (see FIG. 4 ).

But the values of the stabilizing capacitor C14, the integrating capacitor C13, and the output pull-up resistors R5 and R9 determine the range in which the frequency is converted to the output voltage. C15, C16, C17, and R7 are used for filtering and anti-interference. Adjust R8 to trigger the operational amplifier inside TD650. TD650 is a chip with integrated frequency voltage (F/V) conversion circuit (see Figure 5).

R11, C18, R12, and C19 in the low-pass filter circuit form a second-order RC filter circuit, and R10 in the circuit forms a feedback network (see Figure 6).

Because sample I and sample II are two kinds of incompatible liquids, the dielectric constants of the two liquids differ greatly, generally a difference of several tens of times, when only sample I flows through the capacitive sensor 5, the dielectric constant is a fixed number , when the droplet containing the sample II in the sample I flows through the capacitive sensor 5 , the dielectric constant changes and thus the capacitance value of the capacitive sensor 5 changes. The changed signal is detected by an external circuit connected to the electrode terminals 7 and 8, thereby realizing the detection of the droplet. The simulation diagram of the droplet generation is shown in FIG. 7 .

The technical principle involved in the present invention: the schematic diagram of liquid droplet detection is shown in Figure 2, it utilizes two different sample solutions to form micro-droplets at the intersection of the chip, and the dielectric constants of the two sample solutions themselves are very large. When the droplet flows through the capacitive sensor connected to the DC voltage regulator circuit (as shown in Figure 3), the capacitance value changes, and the capacitor and the external frequency modulation circuit (as shown in Figure 4) form an LC sine wave Oscillating circuit, the change of the capacitive sensor changes the oscillation frequency of the LC sine wave oscillation circuit, and the f/V conversion circuit (as shown in Figure 5) converts the oscillation frequency of the LC sine wave oscillation circuit into a voltage signal, and the converted voltage The signal has a lot of low-frequency interference signals, which are filtered out by a low-pass filter circuit (as shown in Figure 6) to obtain a smooth voltage signal, so as to realize the change of the droplet by detecting the change of the capacitance.

1. Microfluidic droplet generation technology

Micro-droplet technology is a kind of micro-liquid that uses the interaction between the flow shear force and surface tension of the liquid to divide and separate the continuous fluid into discrete micro-liter, nano-liter and below-volume droplets in the micro-scale channel. droplet generation technology. It is a brand-new technology for manipulating tiny liquid volumes developed in recent years. The size, shape, and generation frequency of droplets can be flexibly adjusted by adjusting the geometric structure, surface chemical properties, fluid flow rate and other conditions of the chip microchannel. There are three main methods of droplet generation, namely T-junction, flow-focusing, and co-axial flow. There are two main types of micro-droplets: gas-liquid phase droplets and liquid-liquid phase droplets. The application of gas-liquid droplets is limited due to their easy volatilization and cross-contamination in microchannels. Liquid-liquid phase droplets are divided into oil-in-water (O/W), water-in-oil (W/O), oil-in-water-in-oil (O/W/O) and water-in-water droplets according to the difference between the continuous phase and the discrete phase. Water-in-oil (W/O/W), etc., can overcome the shortcomings of droplet volatilization and cross-contamination, so it is the focus of the development of microfluidic droplet technology. The liquid-liquid micro-droplet is an ideal microreactor because of its small size, no diffusion between droplet samples, avoiding cross-contamination between samples, stable reaction conditions, and rapid mixing under proper control. It has been widely used in reactions under micro-scale conditions in the fields of chemistry and life sciences, such as: chemical synthesis, microextraction, protein crystallization, enzyme synthesis and its activity analysis, cell embedding, droplet PCR, etc.

2. Microfluidic droplet detection technology

The droplet microfluidic system has the advantages of fast mixing speed, no cross-contamination, low consumption of reagents and samples, and fast droplet generation frequency (up to hundreds to thousands of hertz), and is widely used in single-cell analysis, enzyme Kinetics, protein synthesis and high-throughput screening and other research fields, these related application fields have high requirements for the precision control of samples, so the detection of droplet information is a very important aspect of the wide application of droplet microfluidic systems. protection. Microfluidic droplet detection is mainly to detect information on the size, shape, velocity, and concentration of droplet contents. The detection of these information plays a vital role in the experimental results.

3. Capacitance signal conversion to voltage signal technology

The difference in droplet information causes the capacitance value of the capacitive sensor to change. Since it is difficult to directly measure the change in capacitance value and the accuracy is very low, we cannot directly measure the change in capacitance value to measure the information of the droplet. Converting to an easy-to-measure voltage value for measurement has the advantages of intuition, simplicity, and convenience.

The advantages of the present invention: ①Simple structure, simple manufacture, easy to generate droplets; ②Use two sample solutions with different dielectric constants to form micro-droplets in the chip, so that when they flow through the capacitive sensor, the capacitance value changes , by detecting the change of capacitance to realize the change of the droplet; ③ this detection method has the advantages of fast detection, easy to realize the miniaturization and integration of the entire detection system; ④ due to the use of microfluidic droplet chip, the required sample It has the advantages of less consumption of samples and reagents, and is very suitable for the analysis of expensive samples and reagents; ⑤The external detection circuit of the droplet detection method can be integrated on a circuit board, which has a simple structure, is easy to process and manufacture, and is easy to Realize structural miniaturization and integration.

(4) Description of drawings:

FIG. 1 is a schematic structural diagram of a droplet microfluidic chip in a capacitive sensor-based microfluidic droplet detection system according to the present invention.

FIG. 2 is a block diagram of the overall structure of a capacitive sensor-based microfluidic droplet detection system according to the present invention.

FIG. 3 is a schematic diagram of the working principle of a DC voltage stabilizing circuit unit in a capacitive sensor-based microfluidic droplet detection system according to the present invention.

FIG. 4 is a schematic diagram of the working principle of a frequency modulation circuit in a capacitive sensor-based microfluidic droplet detection system according to the present invention.

5 is a schematic diagram of the working principle of an f/V conversion circuit in a capacitive sensor-based microfluidic droplet detection system according to the present invention.

6 is a schematic diagram of the working principle of a low-pass filter circuit in a capacitive sensor-based microfluidic droplet detection system according to the present invention.

7 is a schematic diagram of simulated droplet generation in a capacitive sensor-based microfluidic droplet detection method according to the present invention.

8 is a schematic diagram of the relationship between the droplet size and the inlet velocity of the sample I in a capacitive sensor-based microfluidic droplet detection method according to the present invention.

9 is a schematic diagram of the relationship between droplet size and sample I viscosity in a capacitive sensor-based microfluidic droplet detection method according to the present invention.

10 is a schematic diagram of the relationship between the droplet size and the interfacial tension between sample I and sample 2II in a capacitive sensor-based microfluidic droplet detection method according to the present invention.

Wherein, 1 is the continuous phase sample I inlet I; 2 is the continuous phase sample I inlet II; 3 is the sample II inlet; 4 is the droplet outlet; 5 is the capacitive sensor; 6 is the intersection; 7 is the electrode terminal I; 8 is the electrode terminal II; 9 is the sample I channel I; 10 is the sample I channel II; 11 is the sample II channel; 12 is the droplet generation channel.

(5) Specific implementation methods:

Embodiment: A microfluidic droplet detection system based on a capacitive sensor, characterized in that it includes a droplet microfluidic chip, a DC voltage stabilization circuit unit, a signal detection circuit unit, and a computer; wherein the droplet microfluidic The control chip is a chip structure that integrates the capacitive sensor and the microchannel that generates the micro-droplet; the droplet microfluidic chip is composed of an upper sheet, a lower sheet, and a capacitive sensor 5 bonded to each other (see Figure 1); The lower sheet is a microchannel sheet, which is welded with sample I inlet, sample II inlet 3, droplet outlet 4, intersection 6, electrode terminal, sample I channel, sample II channel 11 and droplet generation channel 12; The sample I inlet is connected to the sample I channel; the sample II inlet 3 is connected to the sample II channel 11; the sample I channel and the sample II channel 11 are connected to the droplet generation channel 12 through the intersection 6; the droplet The generating channel 12 is connected to the droplet outlet 4; the capacitive sensor 5 is placed above the droplet generating channel 12 and connected to the electrode terminal; the upper chip has a groove for placing the capacitive sensor 5; the DC voltage stabilizing circuit The output end of the unit and the input end of the signal detection circuit unit are respectively connected to the electrode terminals on the droplet microfluidic chip; end connections (see Figure 2).

The sample I inlet is a continuous phase inlet, which is composed of a continuous phase sample I inlet I1 and a continuous phase sample I inlet II2; the sample I inlet I1 and the sample I inlet II2 are respectively pumped into the sample I by the pump I; the sample II The inlet 3 is the discrete phase inlet, and the sample II inlet 3 is pumped into the sample II through the pump II; the pump I and the pump II are respectively connected to the sample I inlet and the sample II inlet through pipelines, and the sample is pumped into the droplet microfluidic chip channel.

There are two electrode terminals, electrode terminal I7 and electrode terminal II8 respectively; the electrode terminal I7 is connected to the output terminal of the DC voltage stabilizing circuit; the electrode terminal II8 is connected to the input terminal of the signal detection circuit connect.

The microchannel for generating microdroplets in the droplet microfluidic chip is a Ψ-shaped channel composed of a sample I channel, a sample II channel 11 and a droplet generating channel 12 .

There are two sample I channels, namely sample I channel I9 and sample I channel II10.

The sample II channel 11 and the droplet generating channel 12 are straight channels.

The sample I channel I9 and the sample I channel II10 are channels with a straight front end and a curved rear end; the straight front channel parts are parallel to each other and are in parallel relationship with the sample II channel 11; the curved channel part at the rear end is 1/4 A round curved channel; the sample I channel I9 , the sample I channel II10 , the sample II channel 11 communicate with the droplet generation channel 12 at the intersection 6 .

The size of the intersection 6 is smaller than the cross-sectional dimensions of the sample I channel I9, sample I channel II10, sample II channel 11 and droplet generation channel 12 on the chip, and it is easy to form droplets during the droplet preparation process.

The cross-sectional size of the sample I channel I9 , sample I channel II10 , sample II channel 11 and droplet generating channel 12 is 200 μm*200 μm; the size of the intersection 6 is 100 μm*100 μm.

The center line of the capacitive sensor 5 coincides with the center line of the droplet generating channel 12, and there is no interlayer between the two; the capacitive plate of the capacitive sensor 5 is positioned at the outlet end of the droplet generating channel 12, and the capacitive plate The centerline of is coincident with the centerline of the droplet generating channel 12.

The material for making the droplet microfluidic chip is polydimethylsiloxane; the capacitive sensor is a planar interdigitated structure, and the material is a mixture of silver and polydimethylsiloxane.

The signal detection circuit unit is composed of a frequency modulation circuit containing an oscillation module, a frequency voltage f/V conversion circuit and a low-pass filter circuit; the input end of the frequency modulation circuit receives the signal of the electrode terminal II8 of the droplet microfluidic chip, Its output end is connected with a low-pass filter circuit through a frequency-voltage f/V conversion circuit; the output end of the low-pass filter circuit is connected with a computer.

A microfluidic droplet detection method based on a capacitive sensor, characterized in that it comprises the following steps:

①Pneumatic pump I is connected to the inlet I1 of sample I and inlet II2 of sample I respectively through two Teflons, and the pneumatic pump II is connected to the inlet of sample II through Teflon to press the sample into the channel of the droplet microfluidic chip. Hexane enters the droplet microfluidic chip through sample I inlet I1 and sample I inlet II2. At the same time, sample II distilled water enters the droplet microfluidic chip from sample II inlet 3. The two samples pass through sample I channel I9 and sample I respectively. Channel II10; sample II flows into channel 11 and forms droplets at the intersection 6. The size, shape, generation frequency, and velocity of the droplets are affected by the inlet velocity of sample I, the viscosity of sample I, and the gap between sample I and sample II. The influence of the interfacial tension; Distilled water is affected by the shear force of hexadecane and the interfacial tension between hexadecane and water at the intersection 6, and the water is divided into individual small droplets; and can be changed by changing the pneumatic The pressure of the pump changes the size and shape of the droplets generated in the chip;

②The DC stabilizer circuit provides power for the sensor capacitor. The droplets obtained in step ① flow through the capacitive sensor through the droplet generating channel 12. Due to the difference in the dielectric constant of the two liquids, the capacitance of the capacitive sensor will change. The capacitance will drive the external signal detection circuit to work;

③The frequency modulation circuit of the signal detection circuit unit receives the signal of capacitance change, and the changed capacitance also makes the oscillation module in the frequency modulation circuit generate different frequency values when resonating;

④After different frequency values pass through the frequency-voltage f/V conversion circuit, the frequencies generated during these resonances are converted into voltage signals and output to the low-pass filter circuit. The low-pass filter circuit passes signals lower than the cut-off frequency and higher than the cut-off frequency. The frequency signal is filtered out, so that the smooth signal is output to the computer;

⑤ The computer outputs a control signal to the DC voltage stabilizing circuit unit, so that the DC voltage stabilizing circuit unit outputs a stable DC voltage; the computer outputs the control signal to the signal detection circuit unit, and the capacitance sensor 5 transmits the capacitance change signal caused by the difference of the droplet to the signal The detection circuit unit is transmitted to the computer after passing through the signal detection circuit unit, and the computer intuitively displays the detection result, thereby realizing the detection of the sample;

⑥Finally, the droplets generated in step ① flow out from the droplet outlet 4 through the droplet generation channel 12 .

The application of the droplet microfluidic chip includes detecting the size, shape, speed, and content characteristics of the droplet; the precise control of the droplet in the microfluidic droplet system and the control of the sample injection in the fields of biology, chemistry, and medicine. Ingredient Control.

The droplet generation is shown in Figure 7. During the generation process, the size of the droplet is changed by changing the inlet velocity of sample I, the viscosity of sample I, and the interfacial tension between sample 1 (continuous phase) and sample II. shape and frequency. Under the condition that the inlet velocity of sample I is different, its simulation result is shown in Figure 8; Under the condition of different viscosity of sample I, its simulation result is shown in Figure 9; The interfacial tension between sample I and sample II Under different conditions, the simulation results are shown in Figure 10.

Claims (10)

1. A microfluidic droplet detection system based on a capacitive sensor, characterized in that it includes a droplet microfluidic chip, a DC voltage regulator circuit unit, a signal detection circuit unit and a computer; wherein the droplet microfluidic The chip is a chip structure that integrates the capacitive sensor and the microchannel that generates the microdroplet; the droplet microfluidic chip is composed of an upper piece, a lower piece and a capacitive sensor bonded to each other; the lower piece is a microchannel A sheet, welded with a sample I inlet, a sample II inlet, a droplet outlet, a cross, an electrode terminal, a sample I channel, a sample II channel and a droplet generation channel; the sample I inlet is connected to the sample I channel; the The sample II inlet is connected to the sample II channel; the sample I channel and the sample II channel are connected to the droplet generation channel through the intersection; the droplet generation channel is connected to the droplet outlet; the capacitance sensor is placed in the droplet generation channel above, and connected to the electrode terminal; the upper chip has a channel for placing the capacitive sensor; the output end of the DC voltage stabilizing circuit unit and the input end of the signal detection circuit unit are respectively connected to the droplet microfluidic chip. The electrode terminals are connected; the computer is bidirectionally connected to the signal detection circuit unit, and its output terminal is connected to the input terminal of the DC voltage stabilizing circuit unit. 2. A kind of microfluidic droplet detection system based on capacitive sensor according to claim 1, is characterized in that described sample I inlet is continuous phase inlet, is made of continuous phase sample I inlet and continuous phase sample I inlet II; The sample I inlet I and the sample I inlet II are respectively pumped into the sample I through the pump I; the sample II inlet is a discrete phase inlet, and the sample II inlet is pumped into the sample II through the pump II; the pump I and the pump II are respectively The sample is pumped into the channel of the droplet microfluidic chip by connecting with the sample I inlet and the sample II inlet through the pipeline. 3. a kind of microfluidic drop detection system based on capacitive sensor according to claim 1, is characterized in that described electrode terminal has two, is respectively electrode terminal I and electrode terminal II; Described electrode terminal Terminal I is connected to the output terminal of the DC voltage stabilizing circuit; the electrode terminal II is connected to the input terminal of the signal detection circuit; the center line of the capacitive sensor coincides with the center line of the droplet generation channel, and there is no gap between the two layer; the capacitive plate of the capacitive sensor is located at the outlet end of the droplet generating channel, and the centerline of the capacitive plate coincides with the centerline of the droplet generating channel. 4. A kind of microfluidic droplet detection system based on capacitive sensor according to claim 1, it is characterized in that the microchannel that produces microdroplet in the droplet microfluidic chip is composed of sample I channel, sample II channel and a Ψ-shaped channel composed of a droplet generating channel; there are two sample I channels, which are sample I channel I and sample I channel II. 5. A kind of microfluidic droplet detection system based on capacitive sensor according to claim 4, it is characterized in that described sample II channel and droplet generation channel are straight channels; Described sample I channel I and sample I channel II It is a channel with a straight front end and a curved rear end; the straight channel parts at the front end are parallel to each other, and are in a parallel relationship with the sample II channel; the curved channel part at the rear end is a 1/4 round curved channel; the sample I channel I, The sample I channel II, the sample II channel communicate with the droplet generation channel at the intersection. 6. A kind of microfluidic droplet detection system based on capacitive sensor according to claim 1, it is characterized in that the size of described intersection is smaller than sample I channel I, sample I channel II, sample II channel on the chip The cross-sectional size of the droplet generation channel is easy to form droplets in the process of droplet preparation; the cross-sectional size of the sample I channel I, sample I channel II, sample II channel and droplet generation channel is 200 μm*200 μm; The size of the intersection is 100 μm*100 μm. 7. A kind of microfluidic droplet detection system based on capacitive sensor according to claim 1, it is characterized in that the making material of described droplet microfluidic chip is polydimethylsiloxane; Described capacitive sensor is Planar interdigitated structure, the material is a mixture of silver and polydimethylsiloxane. 8. A kind of microfluidic droplet detection system based on capacitive sensor according to claim 1, it is characterized in that said signal detection circuit unit is composed of a frequency modulation circuit containing an oscillation module, a frequency voltage f/V conversion circuit and a low-pass The filter circuit is formed; the input end of the frequency modulation circuit receives the signal of the electrode terminal II of the droplet microfluidic chip, and its output end is connected with the low-pass filter circuit through the frequency voltage f/V conversion circuit; the low-pass filter circuit The output terminal is connected with the computer. 9. A microfluidic droplet detection method based on a capacitive sensor, characterized in that it comprises the following steps: ①Pump I is connected to the inlet I of sample I and inlet II of sample I through two Teflons, and pump II is connected to the inlet of sample II through Teflon to press the sample into the channel of the droplet microfluidic chip, and sample I passes through sample I Inlet I and sample I inlet II enter the droplet microfluidic chip, and at the same time, sample II enters the droplet microfluidic chip from the sample II inlet, and the two samples pass through sample I channel I and sample I channel II respectively; sample II channel flows into the droplet microfluidic chip , and form droplets at the intersection, the size, shape, generation frequency, and velocity of the droplets are affected by the inlet velocity of sample I, the viscosity of sample I, and the interfacial tension between sample I and sample II; ②The DC voltage stabilization circuit provides power for the sensor capacitor. The droplets obtained in step ① flow through the capacitive sensor through the droplet generation channel. Due to the difference in the dielectric constant of the two liquids, the capacitance of the capacitive sensor will change. The capacitance will drive the external signal detection circuit to work; ③The frequency modulation circuit of the signal detection circuit unit receives the signal of capacitance change, and the changed capacitance also makes the oscillation module in the frequency modulation circuit generate different frequency values when resonating; ④After different frequency values pass through the frequency-voltage f/V conversion circuit, the frequencies generated during these resonances are converted into voltage signals and output to the low-pass filter circuit. The low-pass filter circuit passes signals lower than the cut-off frequency and higher than the cut-off frequency. The frequency signal is filtered out, so that the smooth signal is output to the computer; ⑤The computer outputs a control signal to the DC voltage stabilizing circuit unit, so that the DC stabilizing circuit unit outputs a stable DC voltage; the computer outputs the control signal to the signal detection circuit unit, and the capacitance sensor transmits the capacitance change signal caused by the difference of the droplet to the signal detection The circuit unit is passed to the computer after passing through the signal detection circuit unit, and the computer can intuitively display the test result, thereby realizing the detection of the sample; ⑥Finally, the droplets generated in step ① flow out from the droplet outlet through the droplet generation channel. 10. A kind of capacitive sensor-based microfluidic liquid droplet detection method according to claim 9, it is characterized in that the application of the droplet microfluidic chip includes detecting the size, shape, speed, and content characteristics of the liquid droplet ; Precise control of droplets in microfluidic droplet systems and component control of injected samples in the fields of biology, chemistry, and medicine.