CN109701673B

CN109701673B - Preparation method of three-dimensional large-scale high-precision microfluidic channel

Info

Publication number: CN109701673B
Application number: CN201910056960.2A
Authority: CN
Inventors: 程亚; 徐剑; 林子杰; 李晓龙; 方致伟
Original assignee: East China Normal University
Current assignee: East China Normal University
Priority date: 2019-01-22
Filing date: 2019-01-22
Publication date: 2021-06-25
Anticipated expiration: 2039-01-22
Also published as: CN109701673A

Abstract

The invention discloses a preparation method of a three-dimensional large-scale high-precision microfluidic channel. First, ultra-short pulse laser direct writing is used to irradiate the inside of a transparent material to generate a high-precision three-dimensional microchannel pattern and a method for connecting the surface of the sample and the internal microchannel. Several auxiliary channel patterns were obtained, and then the above patterns were selectively removed by wet chemical etching treatment to obtain a composite through structure composed of three-dimensional microchannels and auxiliary channels with unlimited three-dimensional size and shape, which were hollow and connected. The surface opening of the auxiliary channel is melted and closed to realize the controllable preparation of a three-dimensional large-scale high-precision three-dimensional microfluidic channel. The invention can improve the efficiency, quality and overall size of three-dimensional microchannel preparation by using carbon dioxide laser melting and closing auxiliary channels, and is suitable for high-performance manufacturing and integration of commercial and industrial three-dimensional microfluidic systems.

Description

Preparation method of three-dimensional large-size high-precision microfluidic channel

Technical Field

The invention relates to a method for manufacturing a three-dimensional micro-channel and a micro-fluidic device, in particular to a method for preparing a three-dimensional large-size high-precision micro-fluidic channel by using ultrashort pulse laser. The invention is suitable for the fields of commercial-grade and industrial-grade microfluidic devices, application and the like.

Background

The micro-fluidic technology can realize rapid, accurate and controllable operation and treatment on micro-scale fluid, has the remarkable advantages of high flux, high efficiency, high sensitivity, low energy consumption and the like, and has shown important application prospect in the fields of chemistry and chemical industry, biological pharmacy, medical diagnosis, photonics and the like. The microchannel is used as a core unit of the microfluidic chip, and the high-performance and multifunctional preparation technology of the microchannel has important significance for improving the development of the microfluidic technology. Compared with the two-dimensional micro-channel which is widely used at present, the three-dimensional micro-channel can provide more flexible and efficient micro-scale space fluid control capability for further innovation of the micro-fluidic technology.

Transparent materials, especially quartz glass materials, are one of the substrates widely used in microfluidic chips and devices at present due to their high heat resistance and chemical stability, low thermal expansion coefficient, wide spectral transmission range and good biocompatibility. Currently, the most representative technique for preparing three-dimensional micro-channels in transparent materials is ultrashort pulse laser micromachining. Highly nonlinear modifications such as nano-gratings, micro-cavities and the like can be induced in the transparent material by regulating and controlling the pulse energy of the focused ultrashort pulse laser, and then a microchannel structure with a flexible and controllable three-dimensional spatial configuration can be prepared by different ways. At present, there are two main technical approaches which have the most extensive research and application prospects. One approach is to directly three-dimensionally ablate transparent materials with liquid-assisted ultrashort pulsed lasers. For example, a method of using water-assisted femtosecond laser to ablate a porous glass material and close a nanopore at a high temperature can realize microchannel preparation (y. Liao, et al, opt. lett. 2010, 35, 3225-. Another approach is to induce selective chemical etching of transparent materials using ultrashort pulsed laser irradiation. The method can realize high-performance preparation of the three-dimensional uniform microchannel, but due to the intrinsic limitation of the chemical etching process and the chemical etchant, the uniform three-dimensional microchannel structure with unlimited length (such as more than centimeter level) is difficult to obtain along with the increase of the etching time. In order to break through the limitations, a plurality of auxiliary channels for communicating the sample surface and the micro-channel are prepared while the three-dimensional micro-channel is prepared, and uniform three-dimensional micro-channel preparation without limit on length can be realized (S. Ho, et al. appl. Phys. A2012, 106, 5-13; S. He, et al. Opt. Lett. 2012, 37, 3825-3827). However, it should be noted that the three-dimensional micro-channel prepared as described above is mainly bonded by Polydimethylsiloxane (PDMS) film to realize surface closure of the auxiliary channel, and the material of the closure region is mainly PDMS film. Therefore, the stability and safety of microfluidic operation are limited to some extent by the thickness of the PDMS film and the strength of the seal between it and the transparent material. The method can be well applied to microfluidic research at a general laboratory level, but for commercial and industrial microfluidic application occasions, particularly continuous flow microscale organic chemical reactions with long time consumption and harsh conditions, the chemical stability and the mechanical property of the PDMS material of the auxiliary channel closed region are greatly tested, so that the sealing property and the safety of the method have great challenges. Therefore, the auxiliary channel closing technology based on a new principle is sought, and the method has important significance and practical value for preparing the three-dimensional large-size high-precision microfluidic channel.

Disclosure of Invention

The invention aims to provide a preparation method of a three-dimensional large-size high-precision microfluidic channel aiming at the technical challenge of the preparation of the three-dimensional microfluidic channel by using ultrashort pulse laser.

The specific technical scheme for realizing the purpose of the invention is as follows:

a preparation method of a three-dimensional large-size high-precision microfluidic channel comprises the following steps:

step 1: ultrashort pulse laser irradiation

Fixing a transparent material sample on a programmable high-precision three-dimensional displacement platform, focusing ultrashort pulse laser on the transparent material through a microscope objective, driving the displacement platform to move and starting ultrashort pulse laser irradiation at the same time, and directly writing a pre-designed high-precision three-dimensional micro-channel pattern and a plurality of auxiliary channel patterns for connecting the sample and an internal micro-channel in the transparent material;

step 2: selective chemical etching

And placing the transparent material sample irradiated by the ultrashort pulse laser into a chemical etching solution, and performing space selective etching removal on the directly-written three-dimensional micro-channel and auxiliary channel patterns so as to obtain a hollow and communicated composite through structure consisting of the three-dimensional micro-channel and the auxiliary channel with three-dimensional geometric configurations and unlimited lengths in the transparent material sample.

And step 3: carbon dioxide laser irradiation

The surface openings of the single auxiliary channels are irradiated in sequence by focusing carbon dioxide laser, and all the auxiliary channels are melted and sealed under the irradiation of the carbon dioxide laser, so that the controllable preparation of the three-dimensional large-size high-precision microfluidic channel is realized.

The pulse width of the ultrashort pulse laser is 10 fs-20 ps, the repetition frequency is 1 kHz-60 MHz, and the numerical aperture of the focusing objective lens is 0.1-1.4.

The transparent material is various transparent glass, transparent crystal and transparent polymer materials.

The chemical corrosion solution is 5-20 mol/L potassium hydroxide solution or 1-20% hydrofluoric acid solution at the temperature of 80-95 ℃.

The large size is that the length of the micro-channel in one direction or three dimensions is 1-100 cm.

The high precision is that the width of the one-way or three-dimensional characteristic of the micro-channel is 10-500 mu m.

Compared with the prior art, the invention has the advantages that:

1) and large size and high precision. The introduction of the auxiliary channel can obviously improve the efficiency of the selective chemical etching laser modification area, and the shortening of the corrosion time and the strengthening of the selective etching process can greatly improve the processing size, the processing quality and the processing precision of the three-dimensional uniform microfluidic channel prepared by the ultrashort pulse laser. In principle, with the aid of the auxiliary channel, virtually any length of microchannel can be achieved while maintaining a high machining precision. It should be noted that, in order to avoid the influence of the larger dead volume generated by the sealed auxiliary channel on the microfluidic operation effect, the distance between the processed auxiliary channel and the surface is generally dozens of micrometers, which has a great limit to the processing of the three-dimensional large-size microfluidic channel to a certain extent. The invention can realize the closing of the auxiliary channel with the depth of mm level by regulating the technical conditions of carbon dioxide laser melting, such as focusing depth and the like, has the technical capability of realizing the closing of the auxiliary channel with different depths, and has application advantages for preparing three-dimensional multilayer large-size complex microfluidic channels.

2) And the controllable auxiliary channel closing capacity is stabilized. The focused carbon dioxide laser is utilized to irradiate the single auxiliary channel, so that the transparent material at the periphery of the auxiliary channel can generate a spatial local controllable high-temperature melting area, and the transparent material generates melting migration under the action of high temperature, so that the inner wall of the auxiliary channel collapses to generate closure. The dynamic process of auxiliary channel closure can be controlled by the irradiation conditions of the carbon dioxide laser, such as irradiation power, irradiation time, focused light spot size, focusing depth and the like, and the closed processing window of the channel is stable, free of cracks and good in repeatability.

3) Good mechanical pressure resistance and safe and reliable micro-fluidic application capability. The closed area with the thickness of hundreds of microns can be realized by controlling the parameters of carbon dioxide laser melting processing, meanwhile, the closed area can be extended to the vicinity of the microfluidic channel in the transparent material, the characteristic that the closed area bonded with the PDMS film is only sealed on the surface of the transparent sample is obviously different, and the pressure resistance in the long-time continuous flow working occasion of commercialization and industrialization is better. Moreover, as the material of the closed area of the carbon dioxide laser melting auxiliary channel is formed by melting and transferring the transparent material (the same as the substrate material), the carbon dioxide laser melting auxiliary channel has intrinsic chemical inertia to the load fluid for microfluidic operation, and compared with the method for bonding and closing the auxiliary channel by the PDMS film, the method has better chemical stability, safety and reliability and wider applicability in various microfluidic application technical fields.

Drawings

FIG. 1 is a schematic diagram of a process for preparing a three-dimensional large-sized high-precision microfluidic channel;

FIG. 2 is an optical microscopic cross-sectional view of a single microchannel and auxiliary channel obtained after selective chemical etching of a laser modified quartz glass sample;

FIG. 3 is an optical microscopic cross-sectional view of a carbon dioxide laser melt inducing closure of a single auxiliary channel in the vicinity of a microchannel;

FIG. 4 is an optical microscopic cross-sectional view of a three-dimensional spiral microchannel and an auxiliary channel obtained after selective chemical etching of a laser modified quartz glass sample;

fig. 5 is an optical microscopic cross-sectional view of the closure of the secondary channel near the carbon dioxide laser melt-induced spiral channel.

Detailed Description

The present invention will be further described with reference to the following examples and drawings, but the scope of the present invention should not be limited thereto.

Example 1

Step 1: ultrashort pulse laser irradiation

As shown in FIG. 1, a sample of six-sided polished clean quartz glass having dimensions of 100 mm × 5 mm × 2 mm was fixed on a three-dimensional displacement table; the central wavelength of the laser is 1026 nm, the repetition frequency is 250 kHz, and the pulse width is 270 fs; and directly writing the modified pattern by focusing laser by using a microscope objective with the numerical aperture of 0.25. Linearly polarized light processing is adopted, and the polarization direction is perpendicular to the direct writing direction. The length of a direct-writing three-dimensional U-shaped micro-channel pattern is 80 mm, the pattern is 300 micrometers below the surface of quartz glass, the length of a plurality of auxiliary channel patterns connecting the surface of a sample and the micro-channel is 300 micrometers, and the distance between the auxiliary channels is 1 mm. The average power of laser irradiation was 800 mW, and the scanning speed was 5 mm/s.

Step 2: selective chemical etching

And (3) putting the quartz glass sample subjected to laser irradiation into 10 mol/L potassium hydroxide solution (85 ℃) for ultrasonic-assisted corrosion until all laser space selectivity modified areas are removed, so as to obtain a composite through structure consisting of a three-dimensional micro-channel with the length of 80 mm and an auxiliary channel. FIG. 2 is a typical cross-sectional view of a single auxiliary channel adjacent to a microchannel obtained by selective chemical etching, and it can be seen that the introduction of the auxiliary channel allows the diameter of the prepared microchannel to maintain good uniformity.

And step 3: carbon dioxide laser irradiation

Focusing carbon dioxide laser by using a zinc selenide (ZnSe) lens with a focal length of-20 cm, sequentially aligning the ZnSe lens with a surface opening of each auxiliary channel for irradiation, wherein the average irradiation power is-9W, the single irradiation time is 25 s, and the auxiliary channels are melted and sealed under the irradiation of the carbon dioxide laser, so that a three-dimensional U-shaped micro-channel with the length of-80 mm is prepared. FIG. 3 is a cross-sectional view of the carbon dioxide laser melting induced auxiliary channel closure, and it can be observed that the thickness of the glass layer in the closed region can reach 156 μm.

Example 2

Step 1: ultrashort pulse laser irradiation

Taking a clean quartz glass sample with the size of 20 mm multiplied by 10 mm multiplied by 2 mm and six polished surfaces, and fixing the clean quartz glass sample on a three-dimensional displacement table; the central wavelength of the laser is 1026 nm, the repetition frequency is 250 kHz, and the pulse width is 270 fs; a microscope objective with the numerical aperture of 0.25 is adopted to focus laser, a quarter-wave plate is placed in front of the focusing objective to generate circularly polarized light, and then three-dimensional modified patterns are directly written. The transverse length of the direct-written spiral channel pattern is 10 mm, the edge of the pattern is 200 mu m below the surface of the quartz glass, the spiral diameter is 300 mu m, and the thread pitch is 500 mu m. The single length of the auxiliary channel connecting the sample surface and the spiral micro-channel in a direct writing way is 200 μm, and the distance between two adjacent channels is 500 μm. The average power of laser irradiation was 800 mW, and the scanning speed was 5 mm/s.

Step 2: selective chemical etching

And (3) putting the quartz glass sample subjected to laser irradiation into 10 mol/L potassium hydroxide solution (85 ℃) for ultrasonic-assisted corrosion until all laser space selectivity modified areas are removed, thereby obtaining a composite through structure consisting of the three-dimensional spiral micro-channel and the auxiliary channel. FIG. 4 is a typical cross-sectional view of a three-dimensional spiral microchannel and an auxiliary channel obtained by selective chemical etching, and the introduction of the auxiliary channel also allows the preparation of a three-dimensional spiral microchannel having a good uniformity in diameter.

And step 3: carbon dioxide laser irradiation

Focusing carbon dioxide laser by using a zinc selenide (ZnSe) lens with a focal length of-20 cm, sequentially irradiating openings on the surface of each auxiliary channel, wherein the average irradiation power is-7W, the single irradiation time is 25 s, and the auxiliary channels are melted and sealed under the irradiation of the carbon dioxide laser, so that a three-dimensional spiral micro-channel with the transverse length of-10 mm is obtained. FIG. 5 is a cross-sectional view of a plurality of closed auxiliary channels near a three-dimensional spiral channel induced by carbon dioxide laser melting, and it can be observed that all the auxiliary channels are closed after carbon dioxide laser irradiation, and the thickness of a glass layer in a closed area is 85 μm.

Claims

1. a preparation method of a three-dimensional large-scale high-precision microfluidic channel, is characterized in that, the method comprises the following steps:

Step 1: Ultrashort Pulse Laser Irradiation

Fix the transparent material sample on a programmable high-precision three-dimensional displacement platform, focus the ultra-short pulse laser on the transparent material through the microscope objective lens, drive the displacement platform to move and start the ultra-short pulse laser irradiation, inside the transparent material. Directly write out the pre-designed high-precision three-dimensional microchannel pattern and several auxiliary channel patterns for connecting the sample and the internal microchannel;

Step 2: Selective Chemical Etching

The transparent material sample irradiated by ultra-short pulse laser is placed in a chemical etching solution, and the directly written three-dimensional microchannel and auxiliary channel patterns are subjected to spatial selective etching and removal, and then the transparent material sample with three-dimensional geometric configuration, A composite through structure composed of three-dimensional microchannels and auxiliary channels with unlimited length, hollow and connected;

Step 3: CO2 Laser Irradiation

By irradiating the surface opening of a single auxiliary channel with a focused carbon dioxide laser in turn, the transparent material will melt and migrate under the action of high temperature, so that the inner wall of the auxiliary channel collapses and closes, thereby realizing the controllable preparation of three-dimensional large-scale and high-precision microfluidic channels; wherein:

The pulse width of the ultrashort pulse laser is 10 fs-20 ps, the repetition frequency is 1 kHz-60 MHz, and the numerical aperture of the focusing objective lens is 0.1-1.4;

The large size is that the unidirectional or three-dimensional length of the microchannel is 1-100 cm;

The high precision is that the unidirectional or three-dimensional feature width of the microchannel is 10-500 μm.

2. The method according to claim 1, wherein the transparent material is various transparent glass, transparent crystal or transparent polymer material.

3 . The method according to claim 1 , wherein the chemical etching solution is a 5-20 mol/L potassium hydroxide solution or a 1-20% hydrofluoric acid solution at 80-95° C. 4 .