Chemically catalyzed self-driven conical tube micro-motor and preparation method thereof

Abstract

The present application relates to a chemical catalytic self-propelled conical tube-shaped micromotor and its preparation method. The preparation method of the micromotor is to sequentially tilt deposit a pre-stressed rectangular nanofilm on a sacrifice layer, the nanofilm only has a thickness gradient in one side length direction to form a wedge-shaped thickness, and is equal in thickness in a direction perpendicular to the side length direction. Then the sacrifice layer is dissolved along a direction perpendicular to the thickness gradient of the nanofilm to release the nanofilm, and the nanofilm is self-rolled to generate a conical tube-shaped micromotor under the action of a strain gradient. The method can flexibly adjust the conical angle of the nanofilm by adjusting the tilt angle during deposition of the nanofilm, and can also adjust the length and diameter of the conical tube by changing the area and thickness of the nanofilm. The micromotor uses a bubble generated by catalytic hydrogen peroxide to push the movement. The chemical catalytic self-propelled conical micromotor effectively improves the movement performance of the micromotor and has certain conveying capacity, and has a broad prospect in environmental remediation and drug delivery.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano actuation, and relates to the preparation method and actuation of micro motors in microfluidics. Background Technology

[0002] In recent years, the motion of microsystems in fluid environments has become one of the most challenging areas in micro- and nanotechnology. These microsystems have many names, such as microrobots, micromotors, and microengines, and their driving mechanisms include chemical catalysis, magnetic actuation, and acoustic actuation. Chemically catalytically driven micromotors have attracted widespread attention from researchers due to their simplicity, low cost, and lack of the need for additional complex drive mechanisms. Thanks to their ultra-small size, chemically catalytically driven micromotors can navigate complex environments and can be used to remove pollutants and heavy metals from aqueous solutions or deliver drugs into blood vessels. They hold promise for playing a significant role in biomedicine and environmental remediation.

[0003] Self-rolling technology has become a highly anticipated method for fabricating micromotors due to its unique advantages, such as a wide range of material choices and ease of fabrication of microstructures. Specifically, self-rolling technology is a method for fabricating three-dimensional micro / nanostructures. During manufacturing or growth, stress is intentionally introduced into the nanofilm. Once the constraint between the nanofilm and the substrate is released, the nanofilm can transform into a 3D structure. In 2001, Schmidt first reported the self-rolling of planar nanofilms to form nanotubes. In 2008, Mei proposed an improved method for fabricating self-rolled nanotubes and introduced platinum metal onto the inner surface of the tubes to create chemically catalytically driven micromotors. Around the same time, several researchers explored this field, further optimizing the performance of micromotors by adjusting the nanofilm material, changing the release mechanism, and modifying the driving fuel. Most of these rolled-up nanotubes are cylindrical, with occasional instances of nanofilms rolling into slightly conical shapes. Researchers found that during catalytic driving, the conical nanotubes travel faster than the cylindrical ones. This is because the asymmetric conical structure allows bubbles to be ejected more efficiently along the larger end, thus improving the micromotor's motion performance. Furthermore, the conical micromotor structure offers advantages such as ease of penetration and cutting in invasive biological manipulation. Previous studies have also fabricated conical micromotors using template-assisted electrochemical deposition; however, micromotors produced using this method are limited by the size of the porous template channels, making it difficult to adjust the external dimensions of the conical tube. Summary of the Invention

[0004] To address the shortcomings of currently fabricated conical micromotors, such as poor dimensional adjustability and inefficient motion performance, this invention proposes a chemically catalyzed self-driven conical micromotor and its preparation method.

[0005] To achieve the above objectives, the technical solution adopted by the chemically catalyzed self-driven conical micromotor of the present invention is as follows:

[0006] The micromotor is formed by the oriented self-rolling of three nanofilms, which, when viewed from above, are rectangular with sides of 50-300 μm. The average thickness of the first and second nanofilms is 90-110 nm, and the average thickness of the third nanofilm is 8-12 nm. The nanofilms exhibit a thickness gradient along one side, forming a wedge-shaped thickness with a thickness ratio of 2-5 at both ends, while the thickness is uniform along the direction perpendicular to this side, without a thickness gradient.

[0007] The micromotor adopts a tapered tube design with a length of 70-420μm, a large end diameter of 8-40μm, a small end diameter of 2-10μm, and a taper angle of 4-6°.

[0008] The nanofilm was formed by sequentially sputtering copper / chromium / silver onto a substrate with a sacrificial layer using an angled deposition technique; the deposition angle was 45-75°, and the copper sputtering rate was [missing information]. Argon pressure is 0.2-0.3 Pa; the nanofilm has built-in compressive stress and a thickness of 90-110 nm; the deposition rate of sputtered chromium... Argon pressure was 0.8-1.1 Pa; the nanofilm had internal tensile strain and a thickness of 90-110 nm; the deposition rate of sputtered silver was... The argon pressure is 0.8-1.1 Pa, and the thickness of the nanofilm is 8-12 nm;

[0009] After the nanofilm is deposited, it is released directionally using a triaxial slide. By rotating the fine-tuning knob, the substrate with the nanofilm is moved downwards; as the sacrificial layer is gradually dissolved, the nanofilm begins to curl along a direction perpendicular to the thickness gradient. Due to the difference in curvature at both ends of the nanofilm, a conical micromotor is eventually formed.

[0010] The fabrication principle of the micromotor is as follows: Based on the self-rolling principle, three rectangular nanofilms are sequentially and obliquely deposited on a substrate with a sacrificial layer. The rectangular nanofilms exhibit a thickness gradient along one side, forming a wedge-shaped thickness. However, the thickness is uniform along the direction perpendicular to this side, with no thickness gradient. During deposition, the first nanofilm incorporates compressive stress, the second layer incorporates tensile stress, and the third layer is a functional nanofilm with catalytic activity. When the sacrificial layer dissolves along the direction perpendicular to the thickness gradient of the nanofilm, the release of internal stress leads to strain. This strain gradient triggers roll-up, with the roll-up direction aligned with the direction of the sacrificial layer's dissolution. For a specific nanofilm system, under a constant strain gradient, the curvature of the rolled-up nanofilm is primarily determined by its thickness. The roll-up curvature at the thicker end of the nanofilm is less than that at the thinner end. This difference ultimately results in a conical structure for the nanofilm.

[0011] The micromotor can adjust the thickness gradient of the nanofilm by changing the tilt angle during nanofilm deposition, thereby enabling flexible adjustment of its cone angle.

[0012] The micromotor can adjust the length and diameter of the tapered tube by changing the area and thickness of the nanofilm.

[0013] The micromotor operates in a mixed solution of 5% (V / V) hydrogen peroxide and 10% (V / V) sodium dodecyl sulfate (surfactant).

[0014] The working principle of the micromotor is as follows: the functional nanofilm on the inner surface of the conical micromotor acts as a catalyst in the hydrogen peroxide solution, catalyzing the decomposition of hydrogen peroxide to produce water and oxygen. These oxygens gather into large bubbles and are ejected from the large end opening of the conical micromotor. The recoil force generated by the ejection of the bubbles drives the micromotor to move.

[0015] The micromotor is used as follows: The micromotor is placed in a solution of 5% (v / v) hydrogen peroxide and 10% (v / v) sodium dodecyl sulfate (surfactant). The surfactant reduces the surface tension of the solution, making it easier for the rolled-up conical micromotor to be filled by the aqueous solution, thereby promoting the generation of bubbles inside the tube. The functional nanofilm on the inner surface of the micromotor catalyzes the hydrogen peroxide to generate bubbles, which are continuously ejected outwards from the larger end of the micromotor, generating a driving force that propels the micromotor forward.

[0016] The small end of the micromotor can capture and transport the target substance under catalytic drive.

[0017] Compared to the conical micromotor fabricated by template-assisted electrochemical deposition, the self-rolling multi-layered conical structure of the micromotor provides a larger surface area in the same space, resulting in higher catalytic efficiency and effectively improving the micromotor's loading capacity and motion performance.

[0018] The micromotor is prepared by sequentially and obliquely depositing prestressed rectangular nanofilms with wedge-shaped thicknesses on a sacrificial layer. Then, the sacrificial layer is dissolved along the thickness gradient direction perpendicular to the nanofilm to allow the nanofilm to be released in an oriented manner. Under the action of the strain gradient, the nanofilm self-rolls into a conical micromotor.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The micromotor described in this invention can adjust the length and diameter of the tapered tube by changing the area and thickness of the nanofilm;

[0021] (2) The micromotor described in this invention can flexibly adjust its cone angle by adjusting the tilt angle during deposition;

[0022] (3) The micro motor described in this invention has good conveying capacity and can capture and convey particles in some microfluids;

[0023] (4) The micro motor described in this invention has high motion performance and can be used for transporting heavy objects and long-distance movement; Attached Figure Description

[0024] Figure 1 : Schematic diagram of the nanofilm structure of this invention;

[0025] Figure 2 : A partial magnified view of the nanofilm structure of this invention;

[0026] Figure 3 : Schematic diagram of the directional self-rolling process of the nanofilm in this invention;

[0027] Figure 4 : Schematic diagram of the micromotor structure of this invention;

[0028] Figure 5 : Schematic diagram of the micromotor manufacturing process of this invention;

[0029] Figure 6 The manufacturing process of the micro motor of this invention Figure 1 ;

[0030] Figure 7 The manufacturing process of the micro motor of this invention Figure 2 ;

[0031] Figure 8 The manufacturing process of the micro motor of this invention Figure 3 ;

[0032] Figure 9 The manufacturing process of the micro motor of this invention Figure 4 ;

[0033] Figure 10 The micromotor manufacturing process of this invention Figure 5 ;

[0034] Figure 11 The micromotor manufacturing process of this invention Figure 6 ;

[0035] Figure 12 The micromotor manufacturing process of this invention Figure 7 ;

[0036] Figure 13 The micromotor manufacturing process of this invention Figure 8 ;

[0037] Figure 14 The micromotor manufacturing process of this invention Figure 9 ;

[0038] Figure 15 The micromotor manufacturing process of this invention Figure 10 ;

[0039] In the figure: 1. Copper nanofilm, 2. Chromium nanofilm, 3. Silver nanofilm, 4. Compressive stress, 5. Tensile stress, 6. Conical micromotor, 7. Glass substrate I, 8. Polyimide film, 9. SU-8 negative photoresist, 10. Photomask, 11. SU-8 photomask, 12. Glass substrate II, 13. Positive photoresist, 14. Nanofilm, 15. Three-axis slide, 16. Fine-tuning knob, 17. Glass substrate II with nanofilm, 18. Acetone, 19. Beaker. Detailed Implementation

[0040] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings. The content mentioned in the embodiments is only used to explain the present invention and is not intended to limit the scope of the present invention.

[0041] The self-driven catalytic micromotor in this invention is fabricated using a self-coiling technique. The attached figure shows the specific process flow:

[0042] Step 1: Making the SU-8 mask:

[0043] (1) Appendix Figure 6 Glass substrate I7 ​​is a glass slide, which is cleaned with deionized water and baked on a baking table at 110°C for 30 minutes.

[0044] (2) Appendix Figure 7 A polyimide film 8 with a thickness of 25 μm is adhered to the glass substrate I7;

[0045] (2) Appendix Figure 8A layer of SU-8 negative adhesive 9 is spin-coated onto the polyimide film 8, with an adhesive layer thickness of 50μm-80μm;

[0046] (3) Pre-baking: First, bake at a constant temperature of 65℃ for 30 minutes, then bake at a constant temperature of 95℃ for 60 minutes, and then cool naturally to room temperature to obtain cured SU-8 negative adhesive 9.

[0047] (4) Appendix Figure 9 The photomask 10 is placed on the surface of the cured SU-8 negative adhesive 9 and pressed firmly. Exposure is then performed using an exposure machine with a UV light intensity of 5 mW / cm². 2 Exposure time: 2 minutes;

[0048] (5) Post-baking: First, bake at 65℃ for 15 minutes, then bake at 95℃ for 40 minutes, then cool naturally to room temperature, and finally ultrasonically develop and clean with deionized water to leave SU-8 film structure on the substrate.

[0049] (6) Appendix Figure 10 The substrate with the SU-8 membrane was ultrasonically cleaned for 15 minutes. A sharp blade was inserted between the SU-8 membrane and the polyimide membrane to peel off the SU-8 membrane, resulting in a patterned SU-8 mask 11.

[0050] Step 2: Tilting sputtering of nanofilms:

[0051] (1) Appendix Figure 11 For the glass substrate II12, a glass slide can be used. It should be cleaned with deionized water and baked on a baking table at 110°C for 30 minutes.

[0052] (2) Appendix Figure 12 A layer of positive photoresist 13 with a thickness of 1-2 μm is spin-coated onto a glass substrate II12.

[0053] (3) Appendix Figure 13 The SU-8 mask 11 is attached above the positive photoresist 13, and the gap between the photoresist layer 13 and the mask 11 is minimized as much as possible during attachment.

[0054] (4) Appendix Figure 14 A copper / chromium / silver three-layer nanofilm 14 was sequentially deposited onto a glass substrate II 12 using a magnetron sputtering stage at an angle of 45-75°. The deposition rate of sputtered copper was... Argon gas pressure was 0.2-0.3 Pa, the nanofilm contained compressive stress, and its thickness was 90-110 nm. The deposition rate of sputtered chromium... Argon pressure was 0.8-1.1 Pa, the nanofilm had internal tensile strain, and a thickness of 90-110 nm. The deposition rate of sputtered silver was... The argon pressure is 0.8-1.1 Pa, and the thickness of the nanofilm is 8-12 nm;

[0055] Step 3: Targeted release of nanofilm:

[0056] Appendix Figure 15 The substrate 17 with the nanofilm is fixed to the triaxial slide 15 with tape, and the vertical movement direction of the triaxial slide 15 is perpendicular to the thickness gradient of the nanofilm. A beaker 19 containing acetone 18 is placed below the triaxial slide 15 to dissolve the photoresist sacrificial layer under the nanofilm. First, the fine adjustment knob 16 is rotated to lower the substrate 17 with the nanofilm to the edge of the acetone surface. Then, the fine adjustment knob 16 is rotated to move the substrate downward at a speed of 40 μm / min. As the substrate 17 with the nanofilm moves downward, the acetone 18 also begins to dissolve the photoresist sacrificial layer between the nanofilm and the substrate until the acetone 19 completely dissolves the photoresist sacrificial layer, and the nanofilm curls up into a conical micromotor.

[0057] Compared to existing technologies, this invention employs tilted sputtering deposition to fabricate a three-layer rectangular nanofilm with a wedge-shaped thickness. Subsequently, a directional release method perpendicular to the thickness gradient is used to study a conical micromotor, a novel self-rolling technique. Compared to existing self-rolling techniques for uniform-thickness nanofilms, this method significantly improves the success rate of conical microtube fabrication. Compared to template-based conical tube fabrication methods, the conical micromotor in this invention allows for flexible adjustment of its cone angle by adjusting the tilt angle during nanofilm deposition. Furthermore, the length and diameter of the conical tube can be adjusted by changing the area and thickness of the nanofilm. This conical micromotor possesses a certain transport capacity, enabling the capture and transport of microparticles in some microfluidics. The conical micromotor exhibits high motion performance and can be used for transporting heavy objects and long-distance movement.

Claims

1. A chemically catalyzed self-driven micromotor, characterized in that: A rectangular nanofilm with a wedge-shaped thickness gradient is sequentially deposited on a sacrificial layer. The sacrificial layer is then dissolved along the thickness gradient direction perpendicular to the nanofilm, releasing the nanofilm. Under the influence of the strain gradient, the nanofilm self-rolls to generate a micromotor. The nanofilm is formed by sequentially sputtering copper / chromium / silver onto a substrate with a sacrificial layer using an angled deposition technique. The deposition angle is 45-75°, the sputtering rate of copper is 5-7 Å / s, the argon pressure is 0.2-0.3 Pa, and the nanofilm thickness is 90-110 nm; the sputtering rate of chromium is 0.8-1 Å / s, the argon pressure is 0.8-1.1 Pa, and the nanofilm thickness is 90-110 nm; the sputtering rate of silver is 1 Å / s, the argon pressure is 0.8-1.1 Pa, and the nanofilm thickness is 8-12 nm. After the nanofilm is deposited, the nanofilm is released in a directional manner using a triaxial slide stage; the substrate with the nanofilm is moved downward by rotating the fine-tuning knob. As the sacrificial layer is gradually dissolved, the nanofilm begins to curl along a direction perpendicular to the thickness gradient. Due to the difference in curvature at both ends of the nanofilm, a conical micromotor is eventually formed.

2. The self-driven micromotor based on chemical catalysis as described in claim 1, characterized in that: It consists of three self-rolled nanofilms, which are rectangular with sides of 50-500 μm. The nanofilms have a thickness gradient along one side, forming a wedge-shaped thickness with a thickness ratio of 2-5 at both ends, while the thickness is uniform along the direction perpendicular to this side.

3. The self-driven micromotor based on chemical catalysis as described in claim 1, characterized in that: The overall structure is a conical tube with a length of 70-420 μm, a large end diameter of 8-40 μm, a small end diameter of 2-10 μm, and a taper angle of 4-6°. The length and diameter of the conical tube are adjusted by adjusting the area and thickness of the nanofilm. The taper of the conical tube is adjusted by adjusting the tilt angle during deposition.

4. The self-driven micromotor based on chemical catalysis as described in claim 1, characterized in that: The nanofilm is patterned using an SU-8 mask.

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