Surface hydrophilic modification method of cotton thread, application of surface hydrophilic modification method and cotton thread for tear detection

Abstract

The invention belongs to the field of biomedical materials, and relates to a surface hydrophilic modification method of a cotton thread, application thereof and the cotton thread for tear detection. The surface hydrophilic modification method of the cotton thread comprises the following steps: enabling the cotton thread to react with a chemical coupling agent for a certain time, then adding a hydrophilic modifier containing end amino groups into the system, and continuously reacting for a certain time to obtain the surface hydrophilic cotton thread. The chemical coupling agent is polybasic acyl chloride. The hydrophilic modifier containing the terminal amino group is one of amino-terminated chitosan, amino-terminated glucose and amino-terminated polyethylene glycol. According to the method, the chemical linking agent and hydroxyl on the surface of the cotton thread are subjected to esterification reaction, and then amino in the hydrophilic modifier and residual active sites of the chemical linking agent are subjected to amidation reaction, so that the hydrophilic modifier is linked with the cotton thread. The modified cotton thread is good in hydrophilicity, and tears can be rapidly absorbed.

Description

Technical Field

[0001] The present invention relates to the technical field of biomedical materials, and specifically relates to a method for surface hydrophilic modification of cotton threads, its application, and cotton threads for tear detection. Background Art

[0002] Tears are a liquid secreted by the lacrimal gland and have complex components. Normal tears have multiple functions such as barrier, antibacterial, bactericidal, and immunomodulatory functions, and play an important role in protecting the eyeball and improving visual function. Therefore, changes in tears can reflect eye diseases. In view of this, accurately detecting changes in tears is crucial for diagnosing and managing various eye diseases.

[0003] In the prior art, the tear secretion volume of patients is often detected by tear test strips. In addition, during the research and development of many dry eye drugs, tear detection is also required for animal models after drug administration. However, tear test strips are not convenient to fold during use, and the hands often need to contact the test strips, which is easy to cause contamination. In addition, tear test strips are relatively hard and can easily cause strong irritation to the eyes, resulting in extreme discomfort for patients. Therefore, there is a need to provide a new type of tear detection product that is convenient for packaging and use and does not cause irritation to the eyeball.

[0004] Pure cotton threads have many advantages such as good biosecurity, portability, flexibility, and lightness, and are not likely to irritate the eyes of patients. They are an ideal substrate for preparing tear detection cotton threads. However, some cotton threads have hydrophobic surfaces. Due to the large surface tension of the aqueous solution on the surface of such cotton threads, the natural water absorption effect of the cotton threads is poor, resulting in extremely poor diffusion efficiency of tears on the cotton thread surface, making it difficult to accurately detect the diffusion speed of tears and unable to be used to identify the severity of dry eye symptoms and the therapeutic effect of drugs.

[0005] Therefore, it is necessary to improve the diffusion efficiency of the aqueous solution on the cotton thread surface so that it can be used as a tear detection cotton thread. Summary of the Invention

[0006] (I) Technical Problems to be Solved

[0007] In order to solve the problem that some cotton threads in the prior art have poor surface hydrophilicity, poor diffusion efficiency of tears on the cotton thread surface, and difficulty in accurately detecting the tear diffusion speed, the present invention provides a method for surface hydrophilic modification of cotton threads, its application, and cotton threads for tear detection.

[0008] (II) Technical Solutions

[0009] In order to achieve the above object, the main technical solutions adopted by the present invention include:

[0010] In the first aspect, the present invention provides a method for surface hydrophilic modification of cotton threads, including the following steps:

[0011] React the cotton thread with a chemical linker for a certain period of time, then add a hydrophilic modifier containing a terminal amino group to the system, and continue to react for a certain period of time to obtain a cotton thread with hydrophilic surface;

[0012] The chemical linker is a polyacyl chloride;

[0013] The hydrophilic modifier containing a terminal amino group is one of chitosan capped with amino group, glucose capped with amino group, and polyethylene glycol capped with amino group.

[0014] For the method for surface hydrophilic modification of cotton thread as described above, preferably, the mass ratio of the hydrophilic modifier, the chemical linker, and the cotton thread is (10 - 15):(10 - 15):(1 - 5).

[0015] For the method for surface hydrophilic modification of cotton thread as described above, preferably, the polyacyl chloride is one of trimellitic anhydride acyl chloride, isophthaloyl chloride, and terephthaloyl chloride; the cotton thread reacts with the chemical linker in a solvent, and the solvent is a mixture of tetrahydrofuran and water, and the volume ratio of tetrahydrofuran to water is 1:1.

[0016] For the method for surface hydrophilic modification of cotton thread as described above, preferably, the reaction temperature of the cotton thread and the chemical linker is 25 - 40 °C, and the reaction time is 24 - 48 h;

[0017] After adding the hydrophilic modifier containing a terminal amino group, the reaction temperature is 25 - 40 °C, and the reaction time is 24 - 48 h.

[0018] In a second aspect, the present invention provides an application of the cotton thread prepared by the method for surface hydrophilic modification of the above cotton thread in tear detection.

[0019] In a third aspect, the present invention provides a cotton thread for tear detection, which is prepared by soaking the cotton thread prepared by the above method for surface hydrophilic modification in an alkali-responsive dye solution and then drying it.

[0020] For the cotton thread for tear detection as described above, preferably, the alkali-responsive dye solution is an aqueous solution of phenol red.

[0021] For the cotton thread for tear detection as described above, preferably, the concentration of phenol red in the aqueous solution of phenol red is 0.3 - 0.5 mg / mL.

[0022] For the cotton thread for tear detection as described above, preferably, the soaking time is 1 - 3 h.

[0023] For the cotton thread for tear detection as described above, preferably, the drying time is 24 - 48 h.

[0024] (III) Beneficial effects

[0025] The present invention uses polyvalent acyl chloride as a chemical linker. Through the esterification reaction of the chemical linker with the hydroxyl groups on the surface of cotton thread, and then adding a hydrophilic modifier containing an end amino group, such as chitosan capped with amino group, glucose capped with amino group or polyethylene glycol capped with amino group, the amino groups in these hydrophilic modifiers can undergo amidation reaction with the remaining active sites of the chemical linker, thereby realizing the connection between the hydrophilic modifier and the cotton thread.

[0026] After the above modification treatment, the surface of the cotton thread has good hydrophilicity, enabling the aqueous solution to quickly and evenly diffuse on the surface of the cotton thread, and further ensuring that the tear fluid can be rapidly absorbed by the modified cotton thread and diffuse along its length direction, so that it can be used for tear fluid detection and accurately reflect the changes in tear fluid.

[0027] In addition, the hydrophilic modifier materials selected in the present invention all have good biocompatibility and water solubility, which not only ensure the safety of the modified cotton thread, but also can avoid potential irritation or damage to eye tissues. Description of the Drawings

[0028] Figure 1 is the schematic diagram of the preparation principle of chitosan modified cotton thread;

[0029] Figure 2 is the schematic diagram of the preparation principle of polyethylene glycol modified cotton thread;

[0030] Figure 3 is the schematic diagram of the preparation principle of glucose modified cotton thread;

[0031] Figure 4 is the schematic structural diagram of the phenol red cotton thread prepared by the present invention;

[0032] Figure 5 is the Fourier infrared spectrogram of the surface of the cotton thread prepared in Example 1, Example 2 and Example 3;

[0033] Figure 6 is the ultraviolet absorption spectrogram of the phenol red cotton thread prepared in Example 1, Example 2 and Example 3;

[0034] Figure 7 is the comparison chart of the tear fluid diffusivity test results of the phenol red cotton thread prepared in Example 1, Example 2 and Example 3.

[0035]

Description of the Reference Numerals

[0036] 1: Cotton thread matrix; 2: Phenol red dye. Detailed Embodiments

[0037] In order to better explain the present invention for easy understanding, the present invention will be described in detail below in combination with specific embodiments.

[0038] As a natural cellulose material, cotton thread is applied to tear detection due to its low cost, good biocompatibility and other characteristics. It is generally believed in the prior art that cotton thread has hydrophilicity, mainly based on the hydroxyl groups contained in its cellulose molecules. However, the researchers of the present invention found in practical applications that the surface wettability of cotton threads prepared by different production processes varies significantly, and some cotton threads show obvious hydrophobicity, resulting in extremely poor diffusion efficiency and uneven distribution of tears on the surface of the cotton thread, seriously affecting the sensitivity and accuracy of detection.

[0039] Research shows that the surface of such hydrophobic cotton threads usually has dense micro-nano villi or micro-nano structures with multi-level pores. Although this structure may be formed by specific production processes, its negative impact on the liquid diffusion performance has not been fully emphasized. Since the hydrophobic surface is difficult to be quickly wetted by tears, the unmodified cotton thread cannot meet the requirements of rapid and uniform absorption for tear detection. Therefore, it is urgent to improve the hydrophilic properties of such cotton threads through surface modification technology to break through its limitations in biological detection applications.

[0040] In the prior art, the research on the hydrophilic modification of cotton threads mostly focuses on the performance optimization of conventional hydrophilic cotton threads, and there is a lack of targeted solutions for the modification of hydrophobic cotton threads. This results in that some cotton threads prepared by certain processes in actual production cannot be directly used for tear detection due to hydrophobicity problems, restricting their application scope.

[0041] To solve the above problems, the present invention provides a method for hydrophilic surface modification of cotton thread, including the following steps:

[0042] React the cotton thread with a chemical linker for a certain period of time, then add a hydrophilic modifier containing an end amino group to the system, and continue to react for a certain period of time to obtain a cotton thread with a hydrophilic surface.

[0043] The above chemical linker can be polyacid chloride, and the hydrophilic modifier containing an end amino group can be chitosan capped with amino group, glucose capped with amino group or polyethylene glycol capped with amino group.

[0044] The cotton thread surface has abundant hydroxyl functional groups. The present invention uses trimellitic anhydride acyl chloride, isophthaloyl chloride or terephthaloyl chloride as the chemical linker, and through the esterification reaction of the chemical linker with the hydroxyl groups on the surface of white pure cotton thread, then adds a hydrophilic modifier containing an end amino group. The amino groups in these hydrophilic modifiers can undergo amidation reactions with the remaining active sites of the chemical linker, thereby realizing the connection of the hydrophilic modifier to the cotton thread.

[0045] In the present invention, the surface of the cotton thread after modification treatment has good hydrophilicity, and the aqueous solution can rapidly and uniformly diffuse on the surface of the cotton thread, thereby ensuring that the tear fluid can be quickly absorbed by the modified cotton thread and diffuse along its length direction, so that it can be used for tear fluid detection and accurately reflect the changes in tear fluid. The cotton thread prepared by the present invention can be well used for diagnosing dry eye patients and has important application value for clinical diagnosis of dry eye patients. In addition, the hydrophilic modifier materials selected in the present invention all have good biocompatibility and water solubility, which not only ensure the safety of the cotton thread after modification, but also can avoid potential irritation or damage to eye tissues.

[0046] Preferably, the above-mentioned polyacyl chloride can be one of trimellitic anhydride acyl chloride, isophthaloyl chloride, and terephthaloyl chloride. In the above reaction, the mass ratio of the hydrophilic modifier, the chemical linker, and the cotton thread is (10-15):(10-15):(1-5). If the ratios of the hydrophilic modifier and the chemical linker are lower than the above ranges, the hydrophilic modification effect of the cotton thread will be reduced.

[0047] Preferably, the cotton thread reacts with the chemical linker in a solvent, and the solvent is a mixture of tetrahydrofuran and water, and the volume ratio of tetrahydrofuran to water is 1:1.

[0048] Further preferably, the reaction temperature of the cotton thread and the chemical linker is 25-40°C, and the reaction time is 24-48h. After adding the hydrophilic modifier containing terminal amino groups to the reaction system, the reaction temperature is 25-40°C, and the reaction time is 24-48h. If the above reaction time is less than 24h and the temperature is lower than 25°C, the hydrophilic modification effect of the cotton thread will also be reduced.

[0049] If there is no terminal amino group in polyethylene glycol and glucose, after the esterification reaction between the chemical linker and the hydroxyl groups on the surface of the cotton thread, it will not be able to continue the amidation reaction with the hydrophilic modifier, and the hydrophilic modifier cannot be connected to the surface of the cotton thread, so the hydrophilicity of the cotton thread cannot be significantly improved.

[0050] As Figure 1 shown, if chitosan capped with amino groups is used as the hydrophilic modifier and trimellitic anhydride acyl chloride is used as the chemical linker, the reaction principle is:

[0051] The surface of the cotton thread has abundant hydroxyl functional groups, which can undergo an esterification reaction with the acyl chloride groups in the polyacyl chloride, thereby introducing a chemical linker on the surface of the cotton thread. After adding chitosan capped with amino groups, the anhydride in trimellitic anhydride acyl chloride can further undergo an amidation reaction with the terminal amino groups on the chitosan to modify the chitosan on the surface of the cotton thread. If the polyacyl chloride is isophthaloyl chloride or terephthaloyl chloride, the acyl chloride groups contained therein can undergo an amidation reaction with the terminal amino groups on the chitosan to modify the chitosan on the surface of the cotton thread.

[0052] AsFigure 2 As shown, if amino-terminated polyethylene glycol is used as the hydrophilic modifier and trimellitic anhydride acyl chloride is used as the chemical linker, the reaction principle is as follows:

[0053] The cotton thread surface has abundant hydroxyl functional groups, which can undergo an esterification reaction with the acyl chloride groups in the polyacyl chloride, thereby introducing a chemical linker on the cotton thread surface. After adding amino-terminated polyethylene glycol, the anhydride in trimellitic anhydride acyl chloride can further undergo an amidation reaction with the terminal amino group on the polyethylene glycol to modify the polyethylene glycol on the cotton thread surface. If the polyacyl chloride is isophthaloyl chloride or terephthaloyl chloride, the acyl chloride groups contained therein can undergo an amidation reaction with the terminal amino group on the polyethylene glycol to modify the polyethylene glycol on the cotton thread surface.

[0054] Similarly, as Figure 3 shown, if amino-terminated glucose is used as the hydrophilic modifier and trimellitic anhydride acyl chloride is used as the chemical linker, the reaction principle is as follows:

[0055] The cotton thread surface has abundant hydroxyl functional groups, which can undergo an esterification reaction with the acyl chloride groups in the polyacyl chloride, thereby introducing a chemical linker on the cotton thread surface. After adding amino-terminated glucose, the anhydride in trimellitic anhydride acyl chloride can further undergo an amidation reaction with the terminal amino group on the glucose to modify the glucose on the cotton thread surface. If the polyacyl chloride is isophthaloyl chloride or terephthaloyl chloride, the acyl chloride groups contained therein can undergo an amidation reaction with the terminal amino group on the glucose to modify the glucose on the cotton thread surface.

[0056] The cotton thread prepared by the surface hydrophilic modification method of the cotton thread of the present invention can be used in tear detection.

[0057] In addition, the cotton thread is white while the tear is a colorless and transparent liquid, and the diffusion process of the tear on the cotton thread surface is difficult to identify. Therefore, in addition to the need to improve the hydrophilicity of the tear detection cotton thread, it is also necessary to solve the problem of visualizing the tear diffusion on the cotton thread surface.

[0058] To solve the above problems, the present invention also provides a cotton thread for tear detection, which is prepared by soaking the cotton thread prepared by the above surface hydrophilic modification method in an alkali-responsive dye solution and then drying it.

[0059] The above alkali-responsive dye solution is preferably a phenol red aqueous solution, the concentration of the phenol red dye in the phenol red aqueous solution is 0.3 - 0.5 mg / mL, the soaking time is preferably 1 - 3 h, and the drying time is preferably 24 - 48 h.

[0060] To visually monitor the diffusion behavior of tears on the cotton thread surface in real time, the present invention adsorbs the alkali-responsive phenol red dye on the cotton thread surface. Since tears are weakly alkaline, it can change the phenol red from yellow to red, thereby achieving the goal of visually observing the tear diffusion degree with the naked eye.

[0061] As Figure 4 shown, the phenol red cotton thread for tear detection prepared by the present invention includes a cotton thread matrix 1 (which has been subjected to surface hydrophilic modification treatment) and a phenol red dye 2. The phenol red cotton thread for tear detection is in an overall strip shape, and the length can be 7.5 cm. There are creases on the cotton thread, and the length of the creases can be 3 - 5 mm. The part above the creases is used for adhering to the inner eyelid to directly contact tears.

[0062] To further clarify the solution of the present invention and its technological progressiveness, the following will be described in combination with specific examples and technical effects.

[0063] Example 1

[0064] This example provides a preparation method for a cotton thread for tear detection, including the following steps: adding the cotton thread and trimellitic anhydride acyl chloride into a mixed solvent of tetrahydrofuran and water with a volume ratio of 1:1, and reacting at 35 °C for 36 h. Then adding chitosan to the reaction system, and the mass ratio of chitosan, trimellitic anhydride acyl chloride, and the cotton thread is 12:12:3, and continuing to react at 35 °C for 36 h to obtain a surface-hydrophilic cotton thread. Soaking the surface-hydrophilic cotton thread in a phenol red solution with a concentration of 0.5 mg / mL for 2 h, and then drying it for 36 h to obtain the phenol red cotton thread for tear detection.

[0065] Example 2

[0066] This example provides a preparation method for a cotton thread for tear detection, including the following steps: adding the cotton thread and trimellitic anhydride acyl chloride into a mixed solvent of tetrahydrofuran and water with a volume ratio of 1:1, and reacting at 25 °C for 48 h. Then adding amino-terminated polyethylene glycol to the reaction system, and the mass ratio of amino-terminated polyethylene glycol, trimellitic anhydride acyl chloride, and the cotton thread is 10:10:5, and continuing to react at 25 °C for 48 h to obtain a surface-hydrophilic cotton thread. Soaking the surface-hydrophilic cotton thread in a phenol red solution with a concentration of 0.4 mg / mL for 1 h, and then drying it for 24 h to obtain the phenol red cotton thread for tear detection.

[0067] Example 3

[0068] This example provides a preparation method for a cotton thread for tear detection, including the following steps: adding the cotton thread and trimellitic anhydride acyl chloride into a mixed solvent of tetrahydrofuran and water with a volume ratio of 1:1, and reacting at 40 °C for 24 h. Then adding amino-terminated glucose to the reaction system, and the mass ratio of amino-terminated glucose, trimellitic anhydride acyl chloride, and the cotton thread is 15:15:1, and continuing to react at 40 °C for 24 h to obtain a surface-hydrophilic cotton thread. Soaking the surface-hydrophilic cotton thread in a phenol red solution with a concentration of 0.3 mg / mL for 3 h, and then drying it for 48 h to obtain the phenol red cotton thread for tear detection.

[0069] Comparative Example 1

[0070] This comparative example provides a cotton thread for tear detection, which is different from Example 1 in that no hydrophilic modification treatment is carried out.

[0071] Comparative Example 2

[0072] This comparative example provides a preparation method of a cotton thread for tear detection, which is different from Example 2 in that the polyethylene glycol does not contain a capped amino group.

[0073] Comparative Example 3

[0074] This comparative example provides a preparation method of a cotton thread for tear detection, which is different from Example 2 in that the glucose does not contain a capped amino group.

[0075] Test Example 1

[0076] The Fourier transform infrared spectra of the tear detection phenol red cotton threads prepared in Examples 1-3 were obtained respectively, and Figure 5 . As Figure 5 shown, the characteristic peak at 3402 cm -1 is attributed to the hydroxyl peak, and the characteristic peak at 2928 cm -1 is attributed to the methylene peak. These characteristic peaks are all characteristic peaks of chitosan, polyethylene glycol and glucose in Examples 1-3. The characteristic peak at 1633 cm -1 is attributed to the infrared absorption peak of the amide functional group, indicating that an amidation reaction has occurred. The above characteristic peaks prove that chitosan, polyethylene glycol and glucose were successfully grafted onto the surface of the cotton thread in Examples 1-3 respectively.

[0077] Test Example 2

[0078] The ultraviolet absorption spectra of the tear detection phenol red cotton threads prepared in Examples 1-3 and the standard phenol red sample solution were obtained respectively, and Figure 6 to characterize whether the phenol red dye is adsorbed on the surface of the modified cotton thread. It can be seen from Figure 6 that compared with the standard phenol red sample solution, the cotton threads modified with three different hydrophilic modifiers in Examples 1-3 all showed the same maximum absorption peak (430 cm -1 ) as the phenol red solution in aqueous solution, proving that the phenol red dye can be effectively adsorbed on the surface of the hydrophilic modified cotton thread and stably retained in the air.

[0079] Test Example 3

[0080] The tear test phenol red cotton threads prepared in Examples 1-3 and Comparative Examples 1-3 were cut into strips 7.5 cm long, and creases were set on the cotton threads with a crease length of 3-5 mm. Three volunteers with healthy eyes were selected and denoted as Volunteer A, Volunteer B, and Volunteer C. The tear diffusibility of the hydrophilic modified phenol red cotton threads prepared in Examples 1-3 was tested. Specifically, the crease of the phenol red cotton thread was placed at one-third of the distance from the outer canthus on the conjunctiva of the lower eyelid of the volunteer and taken out after 20 s, and the tear diffusion length (mm) of the phenol red cotton thread was recorded, obtaining Figure 7 。

[0081] By Figure 7 It can be seen that the tear diffusion lengths of Volunteer A, Volunteer B, and Volunteer C on the hydrophilic modified phenol red cotton thread prepared in Example 1 were 26 mm, 18 mm, and 15 mm respectively. The tear diffusion lengths of Volunteer A, Volunteer B, and Volunteer C on the hydrophilic modified phenol red cotton thread prepared in Example 2 were 38 mm, 26 mm, and 27 mm respectively. The tear diffusion lengths of Volunteer A, Volunteer B, and Volunteer C on the hydrophilic modified phenol red cotton thread prepared in Example 3 were 34 mm, 28 mm, and 32 mm respectively.

[0082] Similarly, the tear diffusibility of the phenol red cotton threads prepared in Comparative Examples 1-3 was also tested by Volunteer A, Volunteer B, and Volunteer C respectively. The test method and time were the same as above. Finally, the average value of the tear diffusion lengths of the phenol red cotton threads in Comparative Examples 1-3 was about 3 mm, indicating that the tear diffusibility of the cotton thread without hydrophilic modification was poor and could not be used for tear measurement. In addition, if the hydrophilic modifier did not contain amino groups, it would lead to the failure of hydrophilic modification, and the tear diffusibility of the cotton thread was also poor and could not be used for tear measurement.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for modifying the surface hydrophilicity of cotton thread, characterized in that: The steps include: The cotton thread is allowed to react with the chemical linker for a certain period of time, and then a hydrophilic modifier containing terminal amino groups is added to the system, and the reaction is continued for a certain period of time to obtain a cotton thread with a hydrophilic surface; The chemical linking agent is a polyacyl chloride; The hydrophilic modifier containing terminal amino groups is one of amino-terminated chitosan, amino-terminated glucose and amino-terminated polyethylene glycol.

2. The method for surface hydrophilic modification of cotton thread according to claim 1, characterized in that: The polyacyl chloride is one of trimellitic anhydride chloride, isophthaloyl chloride and terephthaloyl chloride; the mass ratio of the hydrophilic modifier, the chemical linker and the cotton thread is (10-15):(10-15):(1-5).

3. The method for surface hydrophilic modification of cotton thread according to claim 1, characterized in that: The cotton thread reacts with the chemical linker in a solvent, wherein the solvent is a mixture of tetrahydrofuran and water, and the volume ratio of tetrahydrofuran to water is 1:

1.

4. The method for surface hydrophilic modification of cotton thread according to claim 1, characterized in that: The reaction temperature of cotton thread and chemical connecting agent is 25-40°C, and the reaction time is 24-48h; After adding the hydrophilic modifier containing terminal amino groups, the reaction temperature is 25-40° C. and the reaction time is 24-48 hours.

5. Use of cotton thread prepared by the surface hydrophilic modification method of cotton thread according to any one of claims 1 to 4 in tear detection.

6. A cotton thread for tear detection, characterized in that: The cotton thread is prepared by immersing the cotton thread prepared by the surface hydrophilic modification method according to any one of claims 1 to 4 in an alkali responsive dye solution and then drying it.

7. The cotton thread for tear detection according to claim 6, characterized in that: The alkali responsive dye solution is a phenol red aqueous solution.

8. The cotton thread for tear detection according to claim 7, characterized in that: The concentration of phenol red in the phenol red aqueous solution is 0.3-0.5 mg / mL.

9. The cotton thread for tear detection according to claim 6, characterized in that: The soaking time is 1-3h.

10. The cotton thread for tear detection according to claim 6, characterized in that: The drying time is 24-48h.

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