A novel method for fabricating optical fluid variable focus microlens arrays

Abstract

This invention discloses a novel method for fabricating a photofluidic variable-focus microlens array, belonging to the field of microfluidics. First, a liquid polymer is cast onto a microfluidic mold and cured to obtain an elastomer film with microchannels. Next, a microlens array is fabricated within the microchannels using a near-field electro-inking system. Then, a microfluidic chip with the embedded microlens array is prepared through encapsulation. Finally, the focal length of the microlens array is adjusted by introducing solutions of different refractive indices into the microfluidic channels. The fabrication method of this invention allows control of the microlens size by controlling the deposition time of the printed droplets. The focal length of the microlenses can be adjusted by changing the liquid in the microfluidic channels. This invention does not require complex process steps or expensive processing equipment, representing a flexible manufacturing method.

Description

Technical Field

[0001] This invention relates to the field of microfluidics, specifically to a novel method for fabricating an optofluidic variable-focus microlens array. Background Technology

[0002] Variable-focus microlens arrays have attracted increasing attention in the fields of miniaturized optical systems and optical sensing due to their unique zoom characteristics. In particular, microlens arrays based on solution refractive index zoom have found wide applications in biochemical analysis, cell imaging, and cell detection.

[0003] Current research on variable-focus microlens arrays can be divided into two categories: zooming based on lens geometry and zooming based on liquid refractive index. For zooming based on lens geometry, several methods exist, such as using pressure, hydrodynamics, electrowetting, or other physical effects to change the curvature of the microlens. However, all these lenses require an external actuator to adjust their shape, and their operation is complex, hindering their integration into compact microchips. Zooming based on liquid refractive index offers another effective method for focal length adjustment. For example, liquid crystal tunable lenses achieve zooming by changing the refractive index of the lens by altering the alignment of liquid crystal molecules; however, the complex manufacturing methods and zooming mechanisms limit their application.

[0004] Changing the focal length of a microlens through a solution is a novel zoom technique, but fabricating microlens arrays within narrow microfluidic channels remains a pressing challenge. Traditional microlens array fabrication methods, such as photolithography and soft lithography, require high substrate flatness, making them difficult to implement in microchannels. Subtractive manufacturing methods, such as femtosecond laser direct writing, can produce high-performance microlens arrays; however, these methods dictate that the microlens array material is the same as the substrate, limiting material selection and making it difficult to fabricate microlens arrays on polydimethylsiloxane. Therefore, developing a low-cost, high-efficiency, and simplified method for fabricating microlens arrays in microfluidic channels is an urgent problem to be solved. Summary of the Invention

[0005] In order to overcome the above-mentioned shortcomings in the prior art, the present invention aims to provide a controllable fabrication method for a microlens array in a microfluidic channel. This method adopts an additive manufacturing approach, which can print high-viscosity UV-curable adhesive and can use liquid to change the focal length of the microlenses in the microfluidic channel, thereby achieving controllable adjustment of the focal length.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A novel method for fabricating an optical fluid variable focus microlens array includes the following steps:

[0008] (1) Preparation of polymer films with microchannels: polymer films with microchannels are prepared by casting using microfluidic molds;

[0009] (2) Fabrication of microlens array in microchannel: First, a microdroplet array is prepared by printing UV-curable adhesive on a substrate using a near-field electro-inking system; then, the microdroplet array is exposed and cured under a UV lamp to form a microlens array; finally, a microlens array based on medium refractive index zoom is prepared by encapsulation.

[0010] (3) Adjusting the focal length by introducing a solution: By introducing solutions with different refractive indices into the microfluidic channel, the focal length of the microlens array can be adjusted.

[0011] In step (1) above, the polymer film is polydimethylsiloxane (PDMS).

[0012] In step (2) above, when preparing the microlens array in the microchannel, NOA 61 UV-curable adhesive with a viscosity of 300 mPa, NOA 63 UV-curable adhesive with a viscosity of 2000 mPa, NOA65 UV-curable adhesive with a viscosity of 1200 mPa, or NOA 68 UV-curable adhesive with a viscosity of 5000 mPa are selected at room temperature. A nozzle with an internal diameter of 0.1-50 μm is selected for printing. The droplet array is printed into the microfluidic channel using a near-field electro-inking system. The droplet size is adjusted by adjusting parameters such as time and voltage.

[0013] In step (2) above, when fabricating the microlens array in the microchannel, a power density of 1000 mJ / cm² is selected. 2 The wavelength of the ultraviolet lamp was 355nm, and the exposure time was 30 minutes.

[0014] In step (3) above, the focal length of the microlens array is only related to the refractive index of the solution, and the focal length of the microlens increases with the increase of the refractive index of the solution.

[0015] The design principle of this invention is as follows:

[0016] This invention is based on near-field electrohydrodynamic inkjet printing (E-jet Printing). A voltage is applied between the printhead and the substrate, creating an electric field that concentrates charge at the tip. The polarized printing solution, under the influence of the electric field, generates shear force, causing the meniscus at the tip to become a cone shape, known as a Taylor cone. When the shear force generated by the charge overcomes the surface tension of the solution, tiny droplets are produced. The solidification of this microdroplet array forms a microlens array.

[0017] The advantages and beneficial effects of this invention are as follows:

[0018] 1. This invention is a direct-write additive manufacturing method with a simple process flow. It can achieve precise printing of microlenses through the movement of a moving platform, and the size and morphology of the microlens array can be precisely controlled according to different setting parameters.

[0019] 2. This invention is a high-efficiency inkjet printing technology that reduces the viscosity of printing materials and the requirements for substrate materials, enabling the fabrication of microlens arrays in microfluidic channels.

[0020] 3. This invention enables controllable adjustment of the microlens focal length through a solution;

[0021] 4. The manufacturing method of the present invention does not require expensive instruments and complex process steps, the processing materials are readily available, and the manufacturing cost is low; Attached image description:

[0022] Figure 1 A schematic diagram illustrating the fabrication of a polymer film with microchannels;

[0023] Figure 2 A schematic diagram illustrating the printing of microlenses in microchannels using a near-field electro-inking system;

[0024] Figure 3 This is a schematic diagram of a microfluidic chip with a microlens array after packaging.

[0025] Figure 4 This is a schematic diagram of injecting a solution into a microfluidic chip with a microlens array.

[0026] In the figure: 1-microfluidic mold, 2-polymer; 3-microlens; 4-solution. Detailed implementation method:

[0027] The embodiments of the present invention will be described in detail below with reference to the technical solutions and accompanying drawings.

[0028] This invention provides a controllable fabrication method for a microlens array in a microfluidic channel, the method comprising the following steps:

[0029] Step 1: Preparation of polymer films with microchannels: Polymer films with microchannels are fabricated by casting using a microfluidic mold;

[0030] Step 2: Fabrication of microlens array in microchannels: First, a microdroplet array is prepared by printing UV-curable adhesive on a substrate using a near-field electro-inking system; then, the microdroplet array is exposed and cured under a UV lamp to form a microlens array; finally, a microlens array based on medium refractive index zoom is prepared by encapsulation.

[0031] Step 3: Adjusting the focal length by introducing solutions: The focal length of the microlens array is adjusted by introducing solutions with different refractive indices into the microfluidic channel.

[0032] As a further aspect of the present invention: Step 1 is specifically performed as follows: PDMS and curing agent (Sylgard 184, Dow Corning) are mixed at a mass ratio of 10:1. The resulting mixture is poured onto a mold and cured at 80°C for 2 hours. Finally, the cured PDMS is peeled off the mold to obtain a PDMS film with microchannels.

[0033] As a further aspect of the present invention: Step 2 is specifically operated as follows: Select NOA 61 UV-curable adhesive with a viscosity of 300 mPa, NOA 63 UV-curable adhesive with a viscosity of 2000 mPa, NOA65 UV-curable adhesive with a viscosity of 1200 mPa, or NOA 68 UV-curable adhesive with a viscosity of 5000 mPa at room temperature; select a nozzle with an internal diameter of 0.1-50 μm for printing; use a near-field electro-inking system to print the droplet array into the microfluidic channel; and adjust the droplet size by adjusting parameters such as time and voltage.

[0034] As a further aspect of the present invention: the specific operation of step 2 is as follows: placing the UV-curable adhesive microdroplet array in a 1000mJ / cm² area. 2 Power density, 355nm ultraviolet (UV) light. After 30 minutes of UV irradiation, the UV-curable adhesive microdroplet array completely cured to form a microlens array.

[0035] As a further aspect of the present invention: Step 2 specifically involves the following steps: During the printing process, the printhead is placed on a three-dimensional moving platform, and the Z-axis height is adjusted so that the distance between the nozzle tip and the substrate is less than or equal to 20 μm. The substrate is placed on a two-dimensional moving platform, and precise deposition of the droplet array is achieved through program commands. The droplet size is controlled by controlling the deposition time of droplets at the same location through program commands. During the printing process, a DC high-voltage power supply is used, with the positive terminal connected to the printhead and the negative terminal connected to the substrate and grounded. After setting the operating voltage, the printing material is ejected from the printhead as a jet.

[0036] As a further aspect of the present invention: Step 3 specifically involves injecting solutions with different refractive indices into the microchannels of the microfluidic chip using an injection pump system. The flow rate of the solution is controlled between 2-6 mm / s by adjusting the injection pump rate. The focal length of the microlens increases with the increase of the solution's refractive index. The focal length is only related to the refractive index of the solution.

[0037] Example 1:

[0038] This embodiment presents a novel method for fabricating an optofluidic variable-focus microlens array. The fabrication process of the microlens array is as follows: Figure 1-4As shown. First, the polymer solution is poured onto a microfluidic mold 1. After curing, the mold is flipped to obtain a polymer film 2 with microchannels, as shown. Figure 1 As shown; then, a microlens array 3 is printed in the microchannels of the polymer film 2 using a near-field electro-inking system, as shown. Figure 2 As shown; next, the microchannel with the microlens array is encapsulated to obtain a microfluidic chip with a microlens array, as shown. Figure 3 As shown; finally, solutions 4 with different refractive indices were introduced into a microfluidic channel to obtain a novel optofluidic variable focus microlens array, as shown. Figure 4 As shown.

[0039] Example 2:

[0040] PDMS and curing agent (Sylgard 184, Dow Corning) were mixed at a mass ratio of 10:1. The mixture was poured onto mold 1 and cured at 80°C for 2 hours. Finally, the cured PDMS was peeled off the mold to obtain a PDMS film 2 with microchannels.

[0041] Select NOA 61 UV-curable adhesive with a viscosity of 300 mPa at room temperature. Choose a nozzle with an internal diameter of 10 μm for printing. Connect the nozzle to the syringe and inject the required printing material (UV-curable adhesive) into the syringe. Squeeze the syringe piston to ensure that the printing material can be extruded smoothly and directly poured into the nozzle. Place the PDMS film 2 with microchannels on the two-dimensional moving platform. Place the nozzle with the needle tip assist device on the Z-axis of the three-dimensional moving platform. Control the three-dimensional moving platform to move the printing needle to the target position on the substrate, and precisely control the distance between the needle tip and the substrate to 20 μm. A high-voltage power supply serves as the driving device for the printing system. The positive terminal of the DC high-voltage power supply is connected to the printhead; the negative terminal is connected to the substrate and grounded, used to form a high-voltage electrostatic field between the printhead and the substrate to drive the printing ink. The power is turned on and the voltage is adjusted to 600V. After the ejected jet stabilizes, the movement path and speed of the two-dimensional moving platform are set via control commands to achieve precise deposition of droplet arrays on the substrate. For the microlens array, the two-dimensional platform movement speed is 5μm / s, and the printing time for each lens is 10s, resulting in a microlens array with an average diameter of 30μm. After printing, a 1000mJ / cm² voltage is applied. 2 After curing with ultraviolet light (UV) at a power density of 355 nm for 30 minutes, a polymer film with microlens array 3 was obtained. The polydimethylsiloxane film and the polymer film with microlens array were subjected to oxygen plasma treatment for 5 minutes. The treated polydimethylsiloxane film and the polymer film with microlens array were then bonded and encapsulated to complete the fabrication of the microfluidic chip with microlens array.

[0042] A sucrose solution 4 (0% to 70% by mass) with a refractive index ranging from 1.334 to 1.456 was injected into the microfluidic chip using a syringe pump system. The flow rate of the solution was controlled between 2 and 6 mm / s by adjusting the syringe pump rate. The focal length of the microlens could be adjusted from 87.3 μm to 235.4 μm.

[0043] The examples described above are merely illustrative of the embodiments of the present invention, but should not be construed as limiting the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention.

Claims

1. A method for fabricating a novel optofluidic variable-focus microlens array, characterized in that: The method comprises the following steps: (1) preparing a polymer film with microchannels: using a microfluidic mold to cast a polymer film with microchannels; the specific operation is: mixing PDMS and curing agent at a mass ratio of 10:1, pouring the obtained mixture on the mold and curing at 80°C for 2 hours to make it solidify; finally, the cured PDMS is peeled off from the mold to obtain a PDMS film with microchannels; (2) preparing a microlens array in the microchannel: first, using a near-field electroblotting system to print a UV-curable adhesive in the microchannel to prepare a microdroplet array; then, the microdroplet array is placed under a UV lamp for exposure and curing to form a microlens array; finally, a liquid-optical variable focus microlens array is prepared by encapsulation; during printing, the electroblotting nozzle is placed on a three-dimensional moving platform, the height in the Z direction is adjusted to make the height of the needle tip from the substrate less than or equal to 20 μm, the substrate is placed on a two-dimensional moving platform, and the droplet array is deposited accurately by program instructions; the droplet size is controlled by program instructions controlling the droplet deposition time at the same position; during printing, a direct current high voltage power supply is used, the positive electrode of the power supply is connected to the nozzle, the negative electrode of the power supply is connected to the substrate and grounded, and after setting the working voltage, the printing material is formed into a jet and sprayed out of the electroblotting nozzle; (3) adjusting the focal length by introducing a solution: introducing a solution with different refractive indexes into the microfluidic channel to adjust the focal length of the microlens array; using a syringe pump system to inject a solution with different refractive indexes into the microchannel of the microfluidic chip; the flow rate of the solution is controlled between 2-6 mm / s by adjusting the speed of the syringe pump; the focal length of the microlens increases with the increase of the refractive index of the solution; the focal length is only related to the refractive index of the solution.

2. The method of claim 1, wherein the method comprises: In step (1), the polymer film is polydimethylsiloxane (PDMS).

3. The method of claim 1, wherein the method comprises: In step (2), when preparing a microlens array in the microchannel, the selected UV-curable adhesive is one of NOA 61 UV-curable adhesive with a viscosity of 300 mPa at room temperature, NOA 63 UV-curable adhesive with a viscosity of 1200 mPa, NOA 65 UV-curable adhesive with a viscosity of 2000 mPa, and NOA 68 UV-curable adhesive with a viscosity of 5000 mPa; a needle with an internal diameter of 0.1-50 μm is selected for printing; the droplet array is printed into the microfluidic channel using a near-field electroblotting system; the droplet size is adjusted by adjusting the time, voltage and other parameters.

4. The method of claim 1, wherein the method is characterized by: In step (2), when the microlens array is prepared in the micro-pipe, a wavelength 355 nm ultraviolet lamp with a power density of 1000 mJ / cm 2 is selected, and the exposure time is 30 min.

5. The method of claim 1, wherein the method further comprises: In step (3), the focal length of the microlens array is only related to the refractive index of the solution, and the focal length of the microlens increases with the increase of the refractive index of the solution.

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