CN109603935B

CN109603935B - Micro-fluidic chip processing method based on plug-in capillary

Info

Publication number: CN109603935B
Application number: CN201811631341.3A
Authority: CN
Inventors: 申峰; 代建峰; 刘赵淼
Original assignee: Beijing University of Technology
Current assignee: Beijing University of Technology
Priority date: 2018-12-29
Filing date: 2018-12-29
Publication date: 2021-03-30
Anticipated expiration: 2038-12-29
Also published as: CN109603935A

Abstract

The invention discloses a micro-channel liquid drop three-dimensional generation method based on an inserted capillary, which changes the generation mode of generating liquid drops on the traditional two-dimensional plane, only needs to process a main channel on the lower wall surface of a PDMS microchip by using a soft lithography method, a capillary tube is arranged on a side channel and is vertically inserted into the main channel, the insertion position and the depth are controllable, and liquid drops with different sizes and frequencies required by production are generated by using the same PDMS channel by changing the position and the depth of the capillary tube inserted into the micro-channel. The process can be applied to the field of visualization research of related micro-channel three-dimensional flow fields such as controllable droplet generation of the micro-channel technology and the like.

Description

Micro-fluidic chip processing method based on plug-in capillary

Technical Field

The invention relates to a novel micro-fluidic chip processing technology, which can generate liquid drops with different sizes at the same position according to different requirements. The process belongs to the field of three-dimensional flow field visualization research related to a micro-channel controllable droplet generation technology and the like.

Background

The microfluidic technology refers to the technology and science for controlling fluid with volume from nanoliter to picoliter in a micron-sized mechanism to realize fluid flow, heat transfer and chemical reaction, is widely applied to the fields of biology, chemical medicine, energy, aerospace and the like, has the characteristics of high generation rate, short reaction time, sufficient mixing, no cross contamination and the like, belongs to the new technology in the 21 st century, and is fast in development and applied in recent years in the microfluidic technology at home and abroad. The microfluidic core technical content comprises: the method comprises the steps of designing and manufacturing a micro-channel structure, driving and controlling micro-nano-scale fluid, and integrating and packaging a micro-fluidic device and a system. At present, the microchannel manufacturing material mainly comprises monocrystalline silicon, glass and a high polymer, and in recent years, a mode of processing a microchannel by using the high polymer Polydimethylsiloxane (PDMS) as a material becomes a main mode for manufacturing a microfluidic chip. In the process of processing the microfluidic chip, a liquid PDMS reagent is poured on a silicon chip male die with a carved micro-channel, then the silicon chip male die is taken down after being solidified, a sunken micro-channel is formed on one side surface of the silicon chip male die, then the micro-channel is adhered on a smooth glass plate or a PDMS bottom plate to form a micro-channel with a sealed middle, then holes are punched at the inlet and outlet positions of the micro-channel, and a tiny tube is inserted to realize the inlet and outlet of fluid in the micro-channel. The capillary tube is adopted to replace a disperse phase inlet, which is a new emerging method in recent years, and the liquid drop generated by the capillary tube has the advantages of reducing the occurrence of the wall sticking phenomenon of the discrete liquid drop, simple and uniform structure, easy functionalization of the surface, reduction of the processing difficulty of the chip, reduction of the chip cost and the like. At present, a capillary is placed at a position of a template channel printed in advance to replace a channel inlet in the conventional PDMS type micro-channel, but with the rapid development of the microfluidic technology, higher requirements can be generated on the size, the distance, the frequency and the position of a liquid drop in the liquid drop generation process, and the liquid drop with single size and frequency generated by only using one template obviously cannot meet the requirements on processing and production and is also greatly wasted on resources. Therefore, the invention processes a device for vertically inserting the capillary at any position on the template without printing the disperse phase channel in advance, realizes the control of the generation size, frequency and position of the liquid drop, and perfects the traditional PDMS processing technology. At present, the traditional PDMS type microfluidic chip processing technology mainly comprises three parts, namely channel pouring, chip bonding and chip cutting, more liquid drops are generated in a two-dimensional capillary-free mode, the wall sticking phenomenon is serious in the liquid drop generation process, the accurate control of the liquid drop generation can be influenced, and the wall sticking phenomenon in the liquid drop generation process can be effectively reduced in a capillary-inserted type liquid drop three-dimensional generation mode, so that the size, the distance and the frequency of the liquid drop generation process can be accurately controlled and predicted. In the traditional liquid drop generation, due to the characteristics of the cured PDMS material, the roughness of the cutting section of the blade and the PDMS model is large and the transparency is poor in the chip cutting process, so that the observation of the internal micro-channel from the side surface of the chip cannot be directly realized. The device can carry out secondary processing and pouring on the side surface of the channel, improve the three-dimensional observation problem in the liquid drop generation process and deepen the comprehensive observation and analysis of the liquid drop generation process. The scheme is simple and reliable, the processing cost is low, the chip processing can be completed in a common biological laboratory, and certain scientific research and application values are achieved.

Disclosure of Invention

The invention mainly aims at the modification of a traditional PDMS chip for generating liquid drops by a capillary, and liquid drops with different sizes and frequencies required by production are generated by utilizing the same PDMS channel by changing the position and the depth of the capillary inserted into a microchannel. The invention discloses a manufacturing method of a novel micro-fluidic chip made of PDMS. The process can be applied to the field of visualization research of related micro-channel three-dimensional flow fields such as controllable droplet generation of the micro-channel technology and the like.

The conventional PDMS microfluidic chip is processed as follows:

firstly, processing a male die for pouring a microchannel on a smooth silicon wafer by a photoetching method; the main channel and the side channel are carved on a silicon chip, a PDMS (polydimethylsiloxane) presetting agent A solution and a coagulant B solution are uniformly mixed according to the proportion of 10:1 in a liquid state, the mixed PDMS solution is poured on a male die carved with a micro-channel, then baking and curing are carried out, and a cured PDMS upper layer model is taken down; placing the capillary tube on the well-described side channel, bonding the PDMS lower-layer bottom plate model without any channel after curing with the PDMS upper-layer model with the channel to form a closed microfluidic channel chip, and integrally cutting the chip as required to finish processing. The channel machined in this way can be observed and studied on the front side of the channel by using a microscope. However, only one channel can be machined in one template, and the generated liquid drops can be fixed in the same range.

The invention mainly improves the traditional PDMS chip processing technology, only one main channel is processed when a chip template is processed, a side channel required by a disperse phase does not need to be processed, and then the PDMS template with the main channel and the PDMS lower-layer bottom plate model without any channel are bonded according to the common steps. Finally, the capillary tube is inserted according to the requirement.

On the basis of the technical scheme, the processing process for manufacturing the microfluidic chip comprises the following steps:

first step, pretreatment of channel male die

The required micro-channel male die (1) is processed on a smooth silicon wafer (2) by a photoetching method, the process is the same as the traditional process, and if a plurality of micro-channels are processed on the same silicon wafer, dividing lines among the channels are cancelled, so that the influence of the dividing lines on the final channel side surface observation is avoided.

The second step is that: PDMS casting

Uniformly mixing a pre-setting agent A and a coagulating agent B of a liquid PDMS reagent according to a ratio of 10:1, standing for 30min until bubbles mixed in a solution of the liquid PDMS reagent float upwards (if part of the bubbles cannot float upwards, the bubbles can be blown by a rubber aurilave), pouring the bubble-free mixed solution onto the convex die set manufactured in the previous step, putting the whole into an oven for heating, curing and molding, and taking down the molded PDMS upper layer model, as shown in figure 3.

The third step: inserting capillary

The one-time casting molding template is placed in a horizontal position, and because the position of a dispersed phase inlet where the capillary tube is placed is not preset, the position where the required liquid drop is generated can be vertically punched by a needle according to the requirement of actual working conditions, the advantage of punching by the needle is that impurities cannot be generated, the capillary tube is inserted from the position, and the process and the fourth step can be interchanged to achieve the purpose of generating the liquid drop at any position.

The fourth step: bonded cover plate

A rectangular PDMS cover plate (5) with the thickness of about 2mm slightly larger than the channel size is taken, and an ultraviolet plasma bonding machine is adopted to bond the upper layer model (shown in figure 5) and the cover plate (5) which are molded by casting together.

The fifth step: secondary PDMS casting

Vertically placing the bonded long side face of the microchannel with the capillary in a culture dish container, vertically fixing the microchannel by adopting two small square pieces of glass, then pouring the fully mixed liquid PDMS solution into the culture dish for the second time, completely wrapping the side face of the channel, placing the channel in an oven for heating to solidify and mold the channel, and repeating the operation on the other side.

And a sixth step: chip dicing

And cutting the cured chip into a required shape according to the observation requirement.

On the basis of the technical process flow, the connection relation of all parts of the process is as follows, a channel male die (1) required by an experiment is processed on a round silicon wafer (2) through a photoetching method, then a uniformly mixed liquid PDMS solution is poured on the male die, the male die is taken down after the PDMS solution is solidified, and a micro-channel concave film (3) is formed on a PDMS upper layer model after primary pouring; and then punching a hole at a position where a liquid drop needs to be generated by using a needle, inserting a capillary at a proper position, bonding a PDMS cover plate (5) with a proper size on an upper layer model (4), performing side secondary pouring on the bonded cover plate (5) and the capillary (6) by using a uniformly mixed liquid PDMS solution, heating and curing to form a final model chip as shown in figure 7, and cutting the processed chip according to experimental needs.

Compared with the prior art, the invention has the following technical advantages.

1. The process can greatly save the cost for manufacturing the PDMS microfluidic chip when producing the droplets with different sizes required by the industry, can obtain the droplets with different sizes and intervals only by using the same main channel, and can also randomly change the positions of the generated droplets according to the actual working conditions.

2. According to the invention, the liquid PDMS solution is poured twice, so that the processed chip model has no middle bonding surface, the transparency of the side surface is extremely high, the influence of the traditional upper and lower bonding surfaces on side surface observation is avoided, and a more convenient method is provided for liquid drop three-dimensional observation.

3. The materials and appliances adopted by the process are common materials, the sources are rich, the cost is low, and the popularization is facilitated.

Drawings

FIG. 1 is an isometric view of a lithographically processed punch.

Figure 2 is a left side view of the male mold of the photolithographic process.

Fig. 3 is an isometric view of a PDMS top mold formed after casting.

Fig. 4 is a left view of the PDMS upper layer mold formed after casting.

Fig. 5 is an isometric view of the mold after the cover plate has been bonded.

Fig. 6 is a perspective view of the mold after the cover plate is bonded.

Fig. 7 is a left side view of the mold after the cover plate is bonded.

Fig. 8 is an isometric view of a PDMS model inserted into a capillary.

Fig. 9 is a perspective view of a PDMS model inserted into a capillary.

In the figure:

1. photoetching a microchannel male die 2, a silicon wafer 3, pouring a PDMS concave film 4 of the microchannel, pouring a PDMS upper template 5, a PDMS cover plate 6 and a capillary tube

Detailed Description

1. Processing requirements

a) The key link of the invention is to ensure the controllability of the capillary insertion position and depth, in order to ensure the adjustment in the micron-scale range, the capillary insertion depth and angle must be accurately adjusted by adopting a high-speed or inverted microscope after the capillary is inserted, and the height error of not more than 1um and the angle error of not more than 1 degree are ensured, thereby ensuring the generation size, frequency and position of the accurately controllable adjustment liquid drop.

b) The existing microscope can only observe liquid drops from the upper position of the liquid drop generation, in order to observe the complete liquid drop generation process from the side surface, a gap left by bonding of side PDMS and an uneven surface caused by cutting need to be subjected to secondary pouring, the pouring needs to completely cover the side surface, and the side surface condition in the liquid drop generation process can be clearly observed.

c) In order to ensure that liquid drops can be generated smoothly and positive observation in the liquid drop generation process is not influenced, the length of the capillary is determined to be between 1 and 2 cm, and the capillary cannot be too long or too short.

Claims

1. A micro-fluidic chip processing method based on an insertion capillary is characterized in that:

firstly, preprocessing a channel male die;

a required micro-channel male die (1) is processed on a smooth round silicon wafer (2) by a photoetching method, and if a plurality of micro-channels are processed on the same silicon wafer, dividing lines among the channels are cancelled, so that the influence of the dividing lines on the final channel side observation is avoided;

the second step is that: pouring PDMS;

uniformly mixing a pre-setting agent A and a coagulating agent B of a liquid PDMS reagent according to a ratio of 10:1, standing for 30min until bubbles mixed in the solution float; if part of bubbles can not float upwards, the bubbles are blown through by a rubber ear washing ball; pouring the bubble-free mixed solution onto the micro-channel convex die assembly manufactured in the previous step, putting the micro-channel convex die assembly into an oven for heating, curing and molding, and taking down the molded PDMS upper layer model;

the third step: inserting a capillary;

placing the once-casting molding template in a horizontal position, vertically punching a hole at the position where the required liquid drop is generated by using a needle according to the actual working condition requirement because the position of a dispersed phase inlet where the capillary is placed is not preset, wherein the advantage of punching by using the needle is that impurities cannot be generated, inserting the capillary from the position, and preparing and exchanging with the fourth step in the process to achieve the purpose of generating the liquid drop at any position;

the fourth step: bonding a cover plate;

taking a rectangular PDMS cover plate (5) which is 2mm larger than the microchannel in size and 2mm thick, and bonding the upper layer model molded by casting with the cover plate (5) by adopting an ultraviolet plasma bonding machine;

the fifth step: secondary PDMS pouring;

vertically placing the long side face of the bonded microchannel with the capillary in a culture dish container, vertically fixing the microchannel by adopting two small square pieces of glass, then pouring the fully mixed liquid PDMS solution into the culture dish for the second time, completely wrapping the side face of the channel, placing the channel in an oven for heating, curing and molding, and repeatedly operating the other side;

and a sixth step: cutting the chip;

2. The microfluidic chip processing method based on the insertion capillary as claimed in claim 1, wherein: processing a microchannel male die (1) required by an experiment on a circular silicon wafer (2) by a photoetching method, then pouring a uniformly mixed liquid PDMS solution on the microchannel male die, taking down the microchannel male die after curing, and forming a microchannel concave film (3) on a PDMS upper layer model after primary pouring; and then punching a hole at a position where liquid drops need to be generated by using a needle, inserting a capillary (6) at a proper position, bonding a PDMS cover plate (5) with a proper size on an upper layer model, performing side secondary pouring on the model bonded with the PDMS cover plate (5) and the capillary (6) by using a uniformly mixed liquid PDMS solution, heating and curing the model to form a final model chip, and cutting the processed chip according to experimental needs.