Paper-based microfluid regulation and control device for realizing adjustable delay based on gray printing

Abstract

The invention discloses a paper-based microfluid regulation and control device for realizing adjustable delay based on laser gray printing, and belongs to the technical field of paper-based microfluidics. According to the device, carbon powder covering layers with different gray levels (5%-30%) and different widths (1-3.5 mm) are constructed in a microfluid channel of a filter paper substrate by utilizing a common laser printer to serve as a delay structure. After thermocuring treatment, the carbon powder is fused and embedded into a paper fiber network, so that the local porosity is reduced, the hydrophobicity is enhanced, and the liquid permeation resistance is remarkably increased. By digitally adjusting the gray value and the width of the delay structure, the continuous regulation and control of the liquid propulsion speed can be realized without external energy driving, and the delay can be controlled in a range from seconds to minutes. Compared with a traditional paper-based time delay method based on a sugar valve, a wax valve or a chemical valve, the method has the advantages that preparation is easy and convenient, cost is low, parameters can be accurately and digitally designed, and reproducibility is high. The device can be widely applied to sequential control of multi-step reaction, automatic color development process and logic function expansion of paper-based analysis equipment.

Description

Technical Field

[0001] This invention belongs to the field of microfluidics technology, specifically relating to a paper-based microfluidic control device that regulates the permeability of paper-based materials through laser grayscale printing, thereby achieving output with different time delays. It is used for fluid timing control, automatic execution of multi-step reactions, and functional expansion of paper-based sensors. Background Technology

[0002] Paper-based microfluidic devices are widely used in bioanalysis, environmental monitoring, and point-of-care testing (POCT) due to their low cost, lack of external pump drive, and simple fabrication process. However, existing paper-based microfluidic technologies still have significant shortcomings in fluid timing control: the liquid is driven by capillary forces in the fiber network, resulting in a fixed and difficult-to-adjust velocity, making it difficult to automatically complete multi-step reactions in sequence.

[0003] Existing delay methods include sugar valves, wax valves, PNIPAM temperature-sensitive valves, and swelling gels, but these methods generally have the following drawbacks: (1) they are greatly affected by environmental factors such as humidity and temperature; (2) they are complex to prepare and difficult to precisely control the delay time; (3) they require additional heating or external energy triggering; and (4) they have poor repeatability and stability. Laser printing technology is often used to construct hydrophobic boundaries for paper-based chips, but there are currently no literature reports on achieving programmable adjustment of local permeability of paper-based chips by controlling the printing grayscale level. The "grayscale printing-permeability control" strategy proposed in this invention can achieve high-precision, digitally designed liquid delay, which is an important supplement to existing paper-based fluid control technology. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a paper-based delay device that allows for adjustment of permeation resistance solely based on printing parameters without requiring external drive or chemical triggering, thereby enabling continuous adjustment of liquid propulsion time to meet the needs of multi-step reactions and timing logic.

[0005] This invention provides a paper-based microfluidic control device based on grayscale printing. A time-delay structure is formed by printing a toner coating layer with a grayscale value of 5%–30% and a width of 1–3.5 mm inside the channel. After thermosetting, the toner melts and embeds into the paper fiber network, causing simultaneous changes in local porosity and surface hydrophobicity, thus increasing the resistance to liquid permeation. Continuously adjustable liquid delay can be obtained by digitally adjusting the grayscale and width.

[0006] Compared with the prior art, the present invention has the following advantages:

[0007] (1) The delay can be continuously adjusted: the delay range from several seconds to several minutes can be achieved by combining grayscale G and width L.

[0008] (2) No external energy required: driven entirely by capillary force.

[0009] (3) Digital precision design: The delay length can be preset through drawing software.

[0010] (4) Simple and low cost: It can be completed using a regular laser printer and oven.

[0011] (5) High repeatability: thanks to the stable output of laser printing, the structure is consistent.

[0012] (6) Highly scalable: can be used for sequential triggering and logical automation in multi-step reactions. Attached Figure Description

[0013] Figure 1 This is a schematic diagram showing the preparation process and overall structure of the paper-based grayscale delay device of the present invention.

[0014] Figure 2 These are schematic diagrams of the porosity, contact angle, and SEM microstructure of paper substrates with different gray levels. Figure A shows the porosity variation under different gray levels; Figure B shows the water contact angle variation under different gray levels; Figures C, D, E, F, G, and H are all scanning electron microscope (SEM) images.

[0015] Figure 3 These are schematic diagrams showing the liquid delay curves corresponding to different gray levels under a fixed width condition. Figure A shows the effect of gray level variation (5%-30%) on the average delay time under a fixed width value (e.g., 1 mm); Figure B shows the effect of gray level variation on the average delay time under a fixed width value (e.g., 3 mm).

[0016] Figure 4 The graphs show the liquid delay relationship for different widths under a fixed grayscale condition. Figure A shows the linear relationship between the delay structure width (1.0-3.5mm) and the average delay time when the grayscale is fixed at 10% (low grayscale); Figure B shows the relationship curve between the delay structure width and the average delay time when the grayscale is fixed at 25% (high grayscale).

[0017] Figure captions: 1 - Schematic diagram of the preparation process: filter paper is printed with grayscale toner, the toner adheres to the pores, and is fixed by heating and drying to form hydrophobic strips; 2 - Microscopic image of the thermosetting toner: SEM magnification shows the molten state of the toner; 3 - Comparison of simulation effects: fluid state of the simulated empty channel and the delay channel; 4 - Experimental control diagram: comparison of the actual liquid flow between the blank control channel and the delay device channel. Detailed Implementation

[0018] Example 1: Device Preparation

[0019] (1) Design: Design the microfluidic channel pattern using drawing software. The channel width is set to 2.5 mm, and the boundary is formed by a hydrophobic barrier using black lines. A rectangular area is designed inside the channel as a delay structure, with a grayscale value set to 5%–30% and a width of 1 mm–3.5 mm. Specific test widths include 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, and 3.5 mm. (2) Printing: Place the qualitative filter paper in a laser printer and print the designed pattern. (3) Thermal curing: Place the printed paper in an oven and heat at 180°C for 90 minutes. Figure 1 As shown in sections 1 and 2, this step allows the toner to melt and permeate the paper fibers, stabilizing the structure and forming a hydrophobic barrier.

[0020] Example 2: Mechanism Verification

[0021] To verify the impact of grayscale printing on paper properties, SEM characterization and contact angle testing were performed, and the results are as follows: Figure 2 As shown. Comparison Figure 2 The SEM image (CH) shows that the blank filter paper (G=0%) has a loose and porous fiber network. Figure 2 C, F). When the printing grayscale is 5% ( Figure 2 D, G), a small amount of toner adheres to the fiber; when the gray level increases to 20% ( Figure 2 E, H), a large amount of molten carbon powder fills the gaps between fibers, significantly reducing the porosity of the paper. Figure 2 Data from A shows that as the gray value increases from 1% to 35%, the porosity gradually decreases. Figure 2 Data from B shows that the water contact angle on the paper surface increases significantly with increasing grayscale value, indicating enhanced hydrophobicity. The decrease in porosity and the increased hydrophobicity together increase fluid resistance, thus achieving the time delay.

[0022] Example 3: Delay Performance Test

[0023] To verify the effect of different grayscale values ​​and structural widths on liquid passage time, delay structures with grayscale values ​​ranging from 5% to 40% and widths from 1 to 3.5 mm were designed. Liquid was dripped into the channel inlet, and the time it took for the liquid front to pass through the delay region was recorded. The test results correspond to... Figure 3 and Figure 4 .

[0024] (I) Grayscale adjustment delay performance under fixed width conditions

[0025] 1. Figure 3 A: Grayscale effect under low width condition (L = 1 mm)

[0026] With a fixed width of 1 mm for the delay structure, the influence of structures with grayscale values ​​ranging from 5% to 40% on liquid propulsion behavior was investigated. Test results showed that when the grayscale value was between 5% and 25%, the liquid could smoothly penetrate the delay structure, and the passage time gradually increased with increasing grayscale value. When the grayscale value reached 30%, the liquid could still pass through slowly, but a significant delay was observed, and the passage time was significantly prolonged. When the grayscale value reached 35% and 40%, the liquid front failed to penetrate the area within a test time exceeding ten minutes, indicating difficulty in flow.

[0027] The above phenomena indicate that, under low width conditions (1 mm), 30% is the upper limit of grayscale range for achieving high latency, while 35%–40% grayscale leads to a sharp increase in permeation resistance, making it difficult for liquid to pass through. This part is recorded as the upper limit of experimental behavior and does not constitute the working mode of this invention.

[0028] 2. Figure 3 B: Grayscale effect under height and width conditions (L = 3 mm)

[0029] With a fixed width of 3 mm for the time-delay structure, the liquid passage time showed significant differences with varying grayscale: structures with grayscale values ​​between 5% and 20% could be penetrated by the liquid, and the delay increased progressively with grayscale; at 25% grayscale, the liquid could pass through slowly, but the penetration rate decreased significantly; when the grayscale reached 30%, the liquid failed to penetrate the 3 mm structure during the observation period, exhibiting no flow. These results indicate that under larger width conditions (≥3 mm), the influence of grayscale on penetration resistance is significantly amplified, and the structural grayscale should not exceed 30%, otherwise, liquid will have difficulty passing through.

[0030] (II) Width-adjustable delay performance under fixed grayscale conditions

[0031] 1. Figure 4 A: Width effect under low grayscale conditions (G = 10%)

[0032] Under a fixed grayscale of 10%, time-delay structures of different widths (1–3.5 mm) were tested, and their liquid propulsion characteristics are as follows: the liquid can smoothly penetrate time-delay structures of all width ranges; the passage time increases approximately linearly with the increase of the structure width; the time delay trend indicates that, under low grayscale conditions, the width is a controllable and effective time delay adjustment parameter.

[0033] 2. Figure 4 B: Width Influence under Medium-High Gray Scale Conditions (G = 25%)

[0034] At a fixed gray level of 25%, the influence of width on liquid passage time is significantly enhanced: when the width is 1-2 mm, the liquid can still pass through, but the passage time is greatly extended; when the width reaches 3 mm, the liquid propulsion speed is extremely slow, close to a stop; when the width is further increased to 3.5 mm, the liquid is in a "difficult to penetrate" state, and the error in the value is large.

[0035] (III) The combined effect of grayscale and width on delay performance

[0036] Combination Figure 3 and Figure 4 The following conclusions can be drawn: Gray level determines the density of the carbon layer and is the main influencing factor for controlling permeation resistance. Width determines the effective permeation path length of the liquid in the high-resistance region and has an amplifying effect on the delay effect. Within the controllable range of gray level 5%–30% and width 1–3.5 mm, continuous delay behavior from several seconds to several minutes can be obtained by adjusting the combination of G and L. When the gray level is higher than 35%, or when the gray level is higher than 30% and the structure width is too large, the liquid exhibits a state of difficulty in penetration; this part is recorded as experimental observation and is not within the adjustable range.

Claims

1. A paper-based microfluidic control device for adjustable delay based on grayscale printing, characterized in that, The system includes a filter paper substrate, a hydrophobic channel boundary formed by laser printing, and a grayscale delay structure disposed inside the channel. The grayscale delay structure is a toner coating layer formed by laser printing, with a grayscale value of 5%–30% and a structure width of 1–3.5 mm. When liquid flows through the grayscale delay structure under capillary force, controllable permeation resistance is generated due to the local porosity reduction and hydrophobicity enhancement caused by the toner layer, thereby achieving liquid propulsion delay.

2. The apparatus according to claim 1, characterized in that, The width of the channel is 2.5 mm.

3. The apparatus according to claim 1, characterized in that, The grayscale value of the grayscale delay structure is any value between 5% and 30%; the higher the grayscale value, the denser the toner layer, the larger the paper contact angle and the lower the local porosity, and the lower the liquid penetration rate.

4. The apparatus according to claim 1, characterized in that, The width of the grayscale delay structure can be selected from 1 mm to 3.5 mm; as the width of the delay structure increases, the time required for the liquid to pass through the structure increases non-linearly.

5. The apparatus according to claim 1, characterized in that, After laser printing, the device underwent a 90-minute thermosetting process at 180°C, which melted the toner and allowed it to adhere stably to the inside of the paper fibers, forming a stable penetration control layer.

6. The apparatus according to claim 1, characterized in that, In a microfluidic channel with multiple inlets, different grayscale delay structures with different parameters are set for each inlet to enable sequential arrival of multiple liquids.

7. The apparatus according to claim 1, characterized in that, The method is used for automatic execution of multi-step chemical reactions, timed triggering colorimetric detection, or fluid timing logic control in paper-based microfluidic chips.

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