Cotton fiber / nitrocellulose composite membrane as well as preparation method and application thereof

Abstract

The invention provides a cotton fiber / nitrocellulose composite membrane and a preparation method and application thereof.The preparation method comprises the following steps that S1, a cotton pulp board is beaten into cotton fiber-containing cotton pulp, the cotton fiber-containing cotton pulp is added into an acetic acid buffer solution of sodium periodate, a first reaction is conducted, an obtained product is washed and then added into a NaBH4 solution, and a second reaction is conducted; carrying out a second reaction, and washing the obtained product to obtain cotton fibers oxidized by sodium periodate; and S2, mixing the cotton fibers oxidized by sodium periodate with a cellulose nitrate and carboxymethyl cellulose suspension, carrying out suction filtration to form a membrane, so as to obtain an ox-CF / NC / CMC composite membrane, immersing the ox-CF / NC / CMC composite membrane into a gelatinized cationic starch suspension, taking out the membrane, and drying the membrane, so as to obtain the ox-CF / NC / CMC / CS composite membrane. The protein adsorption performance and the color development performance of the composite membrane are enhanced.

Description

Technical Field

[0001] This invention relates to paper-based colorimetric sensors, specifically a cotton fiber / cellulose nitrate composite membrane, its preparation method, and its applications. Background Technology

[0002] Paper-based colorimetric sensors, with their high sensitivity, rapid response, and excellent color recognition capabilities, have become an important tool in modern detection technology. Their greatest advantages lie in their extremely low cost, ease of use, portability, and good biocompatibility, often being designed for single use. These advantages make them demonstrate enormous application potential in areas such as point-of-care medical diagnostics (e.g., pregnancy test strips, blood glucose testing), rapid food safety testing (e.g., pesticide residues, heavy metal analysis), on-site environmental monitoring (e.g., water quality assessment), and smart packaging. Nitrocellulose membranes (NC membranes), with their high protein binding capacity and stable capillary flow characteristics, have become a core material in the field of biodetection, used as a substrate in the fabrication of paper-based colorimetric sensors; for example, early pregnancy test strips based on lateral flow chromatography have already been applied. However, the market mainly relies on imports for NC membranes, resulting in high costs and unstable supply. Therefore, developing domestically produced NC membranes to break the foreign monopoly and expand the supply channels of upstream raw materials in the in vitro diagnostics field is of great significance. Currently, cotton fiber / cellulose nitrate composite membranes have been used in the preparation of side-flow chromatography test strips for the detection of HIV targets. However, these methods suffer from weak color development intensity and poor uniformity, limiting the practical application of research findings in commercial production. Therefore, enhancing the color development performance of cotton fiber / cellulose nitrate composite membranes has significant practical implications and application value. Summary of the Invention

[0003] To address the issues of weak color intensity and poor uniformity in existing cotton fiber / cellulose nitrate composite membranes, this invention provides a cotton fiber / cellulose nitrate composite membrane, its preparation method, and its application. This composite membrane exhibits enhanced protein adsorption and color development properties.

[0004] This invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for preparing a cotton fiber / cellulose nitrate composite membrane, comprising the following steps: S1, the cotton pulp board is pulped into cotton pulp containing cotton fibers. The cotton pulp containing cotton fibers is added to sodium periodate acetate buffer solution for the first reaction. The resulting product is washed and then added to NaBH4 solution for the second reaction. The resulting product is washed to obtain cotton fibers oxidized by sodium periodate. S2, cotton fibers oxidized by sodium periodate are mixed with nitrocellulose and carboxymethyl cellulose suspensions, filtered to form a membrane, and then the ox-CF / NC / CMC composite membrane is obtained. The ox-CF / NC / CMC composite membrane is then immersed in a gelatinized cationic starch suspension, removed and dried to obtain the ox-CF / NC / CMC / CS composite membrane.

[0005] Preferably, in S1, the reaction temperature of the first reaction is 25~45℃, and the reaction time is 2~6h.

[0006] Preferably, in S1, the reaction temperature of the second reaction is 25~30℃, and the reaction time is 10~30min.

[0007] Preferably, in S1, the sodium periodate concentration in the sodium periodate acetate buffer solution is 10~90mM.

[0008] Preferably, in S1, the concentration of the NaBH4 solution is 50~100mM.

[0009] Preferably, in S1, the beating degree of the cotton pulp is 60° SR.

[0010] Preferably, in S2, the mass content of carboxymethyl cellulose in the ox-CF / NC / CMC composite membrane is 0.1%~2%.

[0011] Preferably, in S2, the mass content of gelatinized cationic starch in the ox-CF / NC / CMC / CS composite membrane is 0.5%~2%.

[0012] Preferably, in S2, the mass ratio of cotton fibers oxidized by sodium periodate to nitrocellulose is 9:1 to 1:9.

[0013] Preferably, in S2, the drying temperature is 25~45℃.

[0014] Secondly, the present invention provides a cotton fiber / cellulose nitrate composite membrane obtained by the preparation method described above.

[0015] Thirdly, the present invention provides the application of the cotton fiber / cellulose nitrate composite membrane as a substrate in the preparation of paper-based colorimetric sensors.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention modifies cotton fiber / cellulose nitrate composite membranes based on the synergistic effects of physical and chemical methods, enhancing the color development intensity and uniformity of the membranes. The invention involves depositing carboxymethyl cellulose onto the cotton fiber / cellulose nitrate composite membrane via vacuum filtration, and then impregnating and modifying the membrane with gelatinized cationic starch. The addition of carboxymethyl cellulose and cationic starch alters the pore size of the membrane, influencing the transport and distribution of chromogenic substances and thus enhancing its color development performance. Simultaneously, sodium periodate (NaIO4) is used to oxidize the cotton fibers. Sodium periodate selectively oxidizes the secondary hydroxyl groups at the C2-C3 positions of cellulose, breaking the C-C bonds and generating dialdehyde cellulose (containing two aldehyde groups). This imbues the surface of the cotton fiber / cellulose nitrate composite membrane with aldehyde groups, which enhance the adsorption of proteins on the membrane surface through covalent bonding, thereby improving its color development performance. Furthermore, the oxidation by sodium periodate reduces the pore size of the membrane, further enhancing its color development performance, thus expanding the application prospects of cotton fiber / cellulose nitrate composite membranes in paper-based bioassays. Cotton fibers oxidized with sodium periodate are reacted in a NaBH4 solution to reduce the highly reactive and unstable aldehyde groups generated by oxidation to stable hydroxyl groups, thereby stabilizing the material structure. The cotton fiber / cellulose nitrate composite membrane obtained by this invention, based on the synergistic effect of physical and chemical modification, has the advantages of low cost, portability, simple operation, and mass production, and can be used in the preparation of paper-based colorimetric sensors. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The morphology, pore size, and protein adsorption properties of the unmodified CF / NC composite membrane in Comparative Example 1 and the CF / NC / CMC and CF / NC / CS composite membranes prepared by physical modification method in Comparative Example 2 are shown in Figure A. A is an electron micrograph; B is a protein adsorption standard curve; C is the protein adsorption performance. Wherein, 0.1%CMC represents CF / NC / 0.1%CMC, 1%CMC represents CF / NC / 1%CMC, 2%CMC represents CF / NC / 2%CMC, 0.5%CS represents CF / NC / 0.5%CS, 1%CS represents CF / NC / 1%CS, and 2%CS represents CF / NC / 2%CS.

[0019] Figure 2The color development performance of the unmodified CF / NC composite film in Comparative Example 1 and the CF / NC / CMC / and CF / NC / CS composite films prepared by physical modification method in Comparative Example 2 is shown in Figure A. A is the color development image; B is the radial distribution of the color signal analyzed according to Image J; C is the planar distribution of the color signal analyzed according to Image J. Wherein, 0.1%CMC represents CF / NC / 0.1%CMC, 1%CMC represents CF / NC / 1%CMC, 2%CMC represents CF / NC / 2%CMC, 0.5%CS represents CF / NC / 0.5%CS, 1%CS represents CF / NC / 1%CS, and 2%CS represents CF / NC / 2%CS.

[0020] Figure 3 The infrared spectrum and protein adsorption properties of cotton fibers oxidized with sodium periodate are shown in Comparative Example 3; A is the infrared spectrum; B is the protein adsorption standard curve; C is the protein adsorption properties.

[0021] Figure 4 To illustrate the color development performance of cotton fibers oxidized with sodium periodate in Comparative Example 3; A is the color development image; B is the radial distribution of the color signal analyzed using ImageJ; C is the planar distribution of the color signal analyzed using ImageJ.

[0022] Figure 5 Electron micrographs (A) of the unmodified CF / NC composite membrane, the CF / NC / 0.1%CMC / 0.5%CS composite membrane prepared by physical modification, the ox-CF / NC composite membrane prepared by chemical modification, and the ox-CF / NC / 0.1%CMC / 0.5%CS composite membrane prepared by synergistic physicochemical modification prepared for this invention are shown. The pore size of the CF / CNF paper-based material was measured using ImageJ software based on the scanning electron microscope results (B). In A, (a) is the CF / NC composite membrane of Comparative Example 1; (b) is the CF / NC / 0.1%CMC / 0.5%CS composite membrane of Comparative Example 2; (c) is the ox-CF / NC composite membrane of Comparative Example 3; and (d) is the ox-CF / NC / 0.1%CMC / 0.5%CS composite membrane of Example 1.

[0023] Figure 6 The protein adsorption standard curve (A) of the cotton fiber / cellulose nitrate composite membrane prepared by the present invention, and the protein adsorption amount curve (B) of the CF / NC composite membrane of Comparative Example 1, the CF / NC / 0.1%CMC / 0.5%CS composite membrane of Comparative Example 2, the ox-CF / NC composite membrane of Comparative Example 3, and the ox-CF / NC / 0.1%CMC / 0.5%CS composite membrane of Example 1.

[0024] Figure 7Image J shows the pigment color development images (A) of the CF / NC / 0.1%CMC / 0.5%CS composite film of Comparative Example 2, the ox-CF / NC composite film of Comparative Example 3, and the ox-CF / NC / 0.1%CMC / 0.5%CS composite film of Example 1, and analyzes the radial distribution (B) and planar distribution (C) of the color signal based on Image J. Detailed Implementation

[0025] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0026] It should be noted that the process equipment or apparatus not specifically mentioned in the following embodiments are all conventional equipment or apparatus in the art.

[0027] It should be noted that the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or apparatuses. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not intended to limit the order of the method steps or define the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0028] Comparative Example 1 The preparation of unmodified cotton fiber / cellulose nitrate composite membrane includes the following steps: Step 1: Prepare cotton pulp with an oven-dry content of 26.11% at a freeness of 60° SR using a trough beater.

[0029] Step 2: Weigh out cotton pulp containing 0.4536g of cotton fiber (octane-dry weight) and 0.05g of nitrocellulose (octane-dry weight), dissolve them in 50mL of deionized water, mix and stir to obtain mixture 1; vacuum filter mixture 1, dry it to obtain CF / NC composite membrane, at which point the basis weight of the paper base material is 80g / m³. 2 .

[0030] Comparative Example 2 The preparation of cotton fiber / cellulose nitrate composite membranes by physical modification includes the following steps: Step 1: Prepare cotton pulp with an oven-dry content of 26.11% at a freeness of 60° SR using a trough beater.

[0031] Step 2: Weigh 0.5g of carboxymethyl cellulose powder, dissolve it in 50mL of deionized water, and stir until completely dissolved to obtain a 1% (m / v) carboxymethyl cellulose suspension; weigh 1g of cationic starch, dissolve it in 50mL of deionized water, and stir in an oil bath at 67℃ for 1h to gelatinize the starch to obtain a 2% (m / v) gelatinized cationic starch suspension, which is mixture 2.

[0032] Step 3: Weigh out cotton pulp containing 0.4536g of cotton fiber (octane-dry weight) and 0.05g of nitrocellulose (octane-dry weight), dissolve in 50mL of deionized water, and mix to obtain mixture 1. Take 50.4μL, 504μL, and 1008μL of carboxymethyl cellulose suspension respectively, add to mixture 1, and prepare mixtures with different carboxymethyl cellulose addition amounts of 0.1%, 1%, and 2% (the percentage of carboxymethyl cellulose in the total mass (octane-dry weight) of cotton fiber and nitrocellulose). Vacuum filter and dry to obtain CF / NC / 0.1%CMC, CF / NC / 1%CMC, and CF / NC / 2%CMC composite films. At this time, the basis weight of the paper base material is 80g / m³. 2 .

[0033] Step 4: Weigh out cotton pulp containing 0.4536g of cotton fiber (octane-dry weight) and 0.05g of nitrocellulose (octane-dry weight), dissolve them in 50mL of deionized water, and mix to obtain mixture 1. Vacuum filter and dry mixture 1 to obtain CF / NC composite membrane. Take 126μL, 252μL, and 504μL of mixture 2 respectively and dilute them to 15mL with deionized water to prepare mixtures 2 with different concentrations of cationic starch: 0.5%, 1%, and 2% (the percentage of cationic starch in the total mass (octane-dry weight) of cotton fiber and nitrocellulose). Then, immerse the CF / NC composite membrane in mixture 2, remove it, and dry it at 37℃ to obtain CF / NC / 0.5%CS, CF / NC / 1%CS, and CF / NC / 2%CS composite membranes. At this time, the basis weight of the paper base material is 80g / m³. 2 .

[0034] Step 5: Bovine serum albumin (BSA) was selected as the model sample for protein adsorption. First, a standard curve was constructed by measuring the absorbance of serially diluted BSA buffer using a UV spectrophotometer. Then, the prepared CF / NC / 0.1%CMC, CF / NC / 1%CMC, CF / NC / 2%CMC, CF / NC / 0.5%CS, CF / NC / 1%CS, and CF / NC / 2%CS composite membranes were cut into 1cm × 1cm paper pieces and incubated in 400 μL of BSA solution at room temperature for 2 h. After adsorption, the remaining volume was measured using a pipette, and the absorbance of the residual BSA solution was measured at 280 nm using a UV spectrophotometer. The concentration of the remaining BSA was calculated using the standard curve. Finally, the amount of unadsorbed protein was calculated using the formula (residual protein adsorption = residual BSA concentration × residual volume), thus evaluating the protein adsorption capacity of the composite membrane. All experiments were repeated three times.

[0035] Step 6: Punch holes in each of the prepared composite membranes into circular paper discs with a diameter of 5 mm for later use. Dilute the food coloring in a gradient of 50, 60, 70, 80, 100, 200, 400, 600, 800, 1000, 2000, and 0 times. Use a pipette to add 0.5 μL of each concentration of food coloring to the circular paper discs prepared with the composite membrane. Observe the color development performance by taking a picture using a mobile phone (Huawei P50, professional mode: ISO: 50, S: 1 / 250). To fully determine the uniformity of the colorimetric signal, this study used ImageJ software to analyze the distribution of the colorimetric signal from three aspects: visual observation, radial distribution of the color signal, and planar distribution, thereby verifying the optimization effect of the composite membrane construction on paper-based detection.

[0036] Comparison of the experimental results of various composite membranes revealed that 0.1% carboxymethyl cellulose (the percentage of carboxymethyl cellulose in the total mass (dry weight) of cotton fiber and nitrocellulose) and 0.5% cationic starch (the percentage of cationic starch in the total mass (dry weight) of cotton fiber and nitrocellulose) were the optimal addition amounts. Based on these conditions, composite membranes were prepared for subsequent experiments. The preparation process is as follows: Weigh cotton pulp containing 0.4536g of cotton fiber (octane-dry weight) and 0.05g of nitrocellulose (octane-dry weight), dissolve them in 50mL of deionized water, and mix to obtain mixture 1. Add 50.4μL of 1% (m / v) carboxymethyl cellulose suspension to mixture 1 according to the 0.1% carboxymethyl cellulose addition amount, vacuum filter, and dry to obtain a CF / NC / 0.1%CMC composite membrane. Dilute 126μL of mixture 2 with deionized water to 15mL according to the 0.5% cationic starch ratio. Immerse the CF / NC / 0.1%CMC composite membrane in mixture 2, remove it, and dry it at 37℃ to obtain a CF / NC / 0.1%CMC / 0.5%CS composite membrane. At this point, the basis weight of the paper-based material is 80g / m³. 2 .

[0037] To investigate the effect of the physically modified cotton fiber / cellulose nitrate composite membrane characteristics on color development performance, this invention observed the morphology, pore size, and protein adsorption properties of the cotton fiber / cellulose nitrate composite membrane. Figure 1 ) and color rendering properties ( Figure 2 ).

[0038] Figure 1 Electron micrographs (A) of the unmodified CF / NC composite membrane of Comparative Example 1 and the CF / NC / CMC / and CF / NC / CS composite membranes prepared by physical modification method of Comparative Example 2 are shown. The pore size of the CF / CNF paper-based material was measured using ImageJ software based on the scanning electron microscope results. Figure 1 The results from the study A showed that the pore size of cotton fibers was significantly reduced after the addition of CMC and CS through physical methods. Quantitative results of pore size analysis revealed the following pore sizes: CF / NC (40.7693±22.79μm) > CF / NC / 0.5%CS (19.79±11.06μm) > CF / NC / 0.1%CMC (16.38±6.97μm) > CF / NC / 1%CS (11.90±7.02μm) > CF / NC / 2%CS (10.70±7.45μm) > CF / NC / 2%CMC (10.60±4.72μm) > CF / NC / 1%CMC (8.48±2.11μm). Furthermore, a decrease in pore size error was observed, indicating that the structure of the physically modified cotton fiber / cellulose nitrate composite membrane was more uniform. This is because carboxymethyl cellulose and cationic starch, as fillers, fill or even block the macroporous structure of cotton fibers, thereby changing the pore size of the cotton fibers.

[0039] Figure 1 Figure B is the protein adsorption standard curve, used to calculate the amount of protein adsorbed on paper-based materials. From... Figure 1 As shown in Figure C, compared to the unmodified cotton fiber / nitrocellulose composite membrane in Comparative Example 1, the physically modified cotton fiber / nitrocellulose composite membrane showed an increase in BSA adsorption capacity. The order was: CF / NC / 0.1%CMC (49.39±2.54μg) > CF / NC / 1%CMC (48.54±8.56μg) > CF / NC / 0.5%CS (42.98±2.41μg) > CF / NC / 2%CS (40.84±5.86μg) > CF / NC (39.77±2.32μg) > CF / NC / 2%CMC (38.33±4.87μg) > CF / NC / 1%CS (28.88±6.13μg). By comparing the protein adsorption performance of different composite membranes, it can be seen that adding trace amounts of carboxymethyl cellulose and cationic starch can improve the protein adsorption performance of paper-based materials.

[0040] Figure 2 Table A presents visual observation of the color development images of different concentrations of food coloring from Comparative Example 2; quantitative analysis of grayscale values ​​was performed using ImageJ software. Figure 2 As can be seen from Figure B, compared to the unmodified cotton fiber / nitrocellulose composite membrane in Comparative Example 1, the higher the concentration of carboxymethyl cellulose and cationic starch, the lower the gray value, indicating a deeper color development. The gray values ​​of the membrane with added carboxymethyl cellulose are: CF / NC (165.19) > CF / NC / 0.1%CMC (162.75) > CF / NC / 1%CMC (160.73) > CF / NC / 2%CMC (156.74); the gray values ​​of the membrane with added cationic starch are: CF / NC (161.79) > CF / NC / 0.5%CS (157.41) > CF / NC / 1%CS (154.46) > CF / NC / 2%CS (146.80). The planar distribution of the composite membrane's color development was analyzed using ImageJ software. Figure 2 As can be seen from Figure C, the color development on the surface of the physically modified cotton fibers is more uniform, which may be due to the effect of physical modification on the pore size of the paper base surface, thereby improving the color uniformity. Considering both protein adsorption and color development performance, a carboxymethyl cellulose addition of 0.1% (the percentage of carboxymethyl cellulose in the total mass (ocean-dry weight) of cotton fibers and nitrocellulose) and a cationic starch addition of 0.5% (the percentage of cationic starch in the total mass (ocean-dry weight) of cotton fibers and nitrocellulose) were selected as the basis for subsequent research.

[0041] Comparative Example 3 The preparation of cotton fiber / cellulose nitrate composite membranes by chemical modification includes the following steps: Step 1: Prepare cotton pulp with an oven-dry content of 26.11% at a freeness of 60° SR using a trough beater.

[0042] Step 2: Add cotton pulp containing 2g of cotton fiber (ocean-dry weight) to 100mL of mixture 3 containing 10mM, 50mM, and 90mM sodium periodate respectively. React at 25℃. After reacting for 4 hours, centrifuge and wash three times. Add 100mL of mixture 4 and react for 30 minutes. Wash again to obtain cotton fiber oxidized with sodium periodate (store at 4℃ for later use). Mixture 3 is an acetate buffer solution containing sodium periodate (pH≈4.7), and mixture 4 is a 100mM NaBH4 solution. Step 3: Weigh out cotton pulp containing 0.4536g of cotton fiber (octane-dry weight) oxidized with sodium periodate and 0.05g of nitrocellulose (octane-dry weight), dissolve in 50mL of deionized water, mix and stir to obtain mixture 5. Filter to obtain an ox-CF / NC composite membrane. Dry the prepared ox-CF / NC composite membrane at 37℃ to obtain a cotton fiber / nitrocellulose composite membrane. At this point, the basis weight of the paper-based material is 80g / m³. 2 .

[0043] Step 4: Bovine serum albumin (BSA) was selected as the model sample for protein adsorption. First, a standard curve was constructed by measuring the absorbance of serially diluted BSA buffer using a UV spectrophotometer. Then, the prepared cotton fiber / nitrocellulose composite membrane was cut into 1cm × 1cm paper pieces and incubated in 400 μL of BSA solution at room temperature for 2 h. After adsorption, the remaining volume was measured using a pipette, and the absorbance of the residual BSA solution was measured at 280 nm using a UV spectrophotometer. The concentration of the remaining BSA was calculated using the standard curve. Finally, the amount of unadsorbed protein was calculated using the formula (residual protein adsorption = residual BSA concentration × residual volume), thus evaluating the protein adsorption capacity of the cotton fiber / nitrocellulose composite membrane. All experiments were repeated three times.

[0044] Step 5: Perforate the prepared cotton fiber / nitrocellulose composite membrane into circular paper discs with a diameter of 5 mm for later use. Dilute the food coloring serially at concentrations of 50, 60, 70, 80, 100, 200, 400, 600, 800, 1000, 2000, and 0. Use a pipette to add 0.5 μL of each concentration of food coloring to the perforated circular paper discs. Observe the color development performance by taking a picture using a mobile phone (Huawei P50, professional mode: ISO: 50, S: 1 / 250). To fully assess the uniformity of the colorimetric signal, this study uses ImageJ software to analyze the distribution of the colorimetric signal from three aspects: visual observation, radial distribution of the color signal, and planar distribution. This verifies the optimization effect of the cotton fiber / nitrocellulose composite membrane construction on paper-based detection.

[0045] To investigate the influence of the properties of the cotton fiber / cellulose nitrate composite membrane prepared after chemical modification on its color development performance, this invention observed the infrared spectrum and protein adsorption performance of the cotton fiber / cellulose nitrate composite membrane. Figure 3 ) and color rendering properties ( Figure 4 ).

[0046] Figure 3 In section A, the surface functional groups of the ox-CF / NC composite membrane prepared from cotton fibers oxidized with sodium periodate in Comparative Example 3 were characterized by FTIR. The results showed that the ox-CF / NC composite membrane prepared from cotton fibers oxidized with sodium periodate exhibited high surface functional groups at 1741.3 cm⁻¹. -1 The characteristic absorption peak of the aldehyde group appeared on both sides, at 2916.9 cm⁻¹. -1 and 2848 cm -1 The presence of aldehyde characteristic peaks indicates successful oxidation of the cotton fibers.

[0047] Figure 3 Figure B is the protein adsorption standard curve, used to calculate the amount of protein adsorbed on the subsequent paper-based material. From... Figure 3 As shown in Figure C, the order of BSA adsorption capacity of cotton fiber / nitrocellulose composite membranes prepared from cotton fibers modified with different concentrations of sodium periodate is: (50mM NaIO4)ox-CF / NC (66.47±1.17μg) > (90mM NaIO4)ox-CF / NC (61.47±1.58μg) > (10mM NaIO4)ox-CF / NC (55.47±6.98μg). By comparing the protein adsorption performance of different composite membranes, it can be seen that the protein adsorption performance is optimal when the sodium periodate concentration is 50mM.

[0048] Figure 4 Table A presents visual observation of the color development images of different concentrations of food coloring in Comparative Example 3; quantitative analysis of grayscale values ​​was performed using ImageJ software. Figure 4 As can be seen in Figure B, compared to the unmodified cotton fiber / nitrocellulose composite membrane in Comparative Example 1, the higher the sodium periodate concentration, the lower the gray value, indicating a deeper color development. The gray values ​​for different concentrations are: (90mM NaIO4)ox-CF / NC (140.52) > (50mM NaIO4)ox-CF / NC (143.71) > (10mM NaIO4)ox-CF / NC (158.26). The planar distribution of the composite membrane's color development was analyzed using ImageJ software. Figure 4 As shown in Figure C, the color development of cotton fibers became more uniform with increasing sodium periodate concentration after chemical modification. This is likely due to the effect of chemical modification on the pore size of the paper substrate surface, thereby improving the color uniformity. Considering both protein adsorption and color development performance, we selected cotton fibers oxidized with 50 mM sodium periodate.

[0049] Example 1 The preparation of a cotton fiber / cellulose nitrate composite membrane based on the synergistic effect of physical and chemical modification includes the following steps: Step 1: Prepare cotton pulp with an oven-dry content of 26.11% for cotton fibers at a beating degree of 60° SR using a trough beater.

[0050] Step 2: Weigh 0.5g of carboxymethyl cellulose powder, dissolve it in 50mL of deionized water, and stir until completely dissolved to obtain a 1% (m / v) carboxymethyl cellulose suspension; weigh 1g of cationic starch, dissolve it in 50mL of deionized water, and stir in an oil bath at 67℃ for 1h to gelatinize the starch to obtain a 2% (m / v) gelatinized cationic starch suspension, i.e., mixture 2.

[0051] Step 3: Add 2g of cotton pulp (octane-dry weight) containing cotton fibers from Step 1 to 100mL of mixture 3 containing 50mM sodium periodate and react at 25℃. After reacting for 4 hours, centrifuge and wash three times. Add 100mL of mixture 4 and react for 30 minutes, then wash to obtain cotton fibers oxidized with sodium periodate (store at 4℃ for later use). Mixture 3 is an acetate buffer solution with added sodium periodate (pH≈4.7), and mixture 4 is a 100mM NaBH4 solution.

[0052] Step 4: Weigh cotton pulp containing 0.4536g of cotton fiber (octane-dry weight) oxidized with sodium periodate and 0.05g of nitrocellulose (octane-dry weight), dissolve in 50mL of deionized water and mix to obtain mixture 5; according to the addition amount of 0.1% carboxymethyl cellulose (the percentage of carboxymethyl cellulose in the total mass (octane-dry weight) of cotton fiber and nitrocellulose), take 50.4μL of 1% (m / v) carboxymethyl cellulose suspension and add it to mixture 5 and vacuum filter to obtain ox-CF / NC / 0.1%CMC composite membrane; according to the addition amount of 0.5% cationic starch (the percentage of cationic starch in the total mass (octane-dry weight) of cotton fiber and nitrocellulose), take 126μL of mixture 2 and dilute it to 15mL with deionized water, immerse the ox-CF / NC / CMC composite membrane in this mixture 2, take it out and dry at 37℃ to obtain ox-CF / NC / 0.1%CMC / 0.5%CS composite membrane. At this time, the basis weight of the paper base material is 80g / m 2 .

[0053] Step 5: Bovine serum albumin (BSA) was selected as the model sample for protein adsorption. First, a standard curve was constructed by measuring the absorbance of serially diluted BSA buffer using a UV spectrophotometer. Then, the prepared cotton fiber / nitrocellulose composite membrane was cut into 1cm × 1cm paper pieces and incubated in 400 μL of BSA solution at room temperature for 2 h. After adsorption, the remaining volume was measured using a pipette, and the absorbance of the residual BSA solution was measured at 280 nm using a UV spectrophotometer. The concentration of the remaining BSA was calculated using the standard curve. Finally, the amount of unadsorbed protein was calculated using the formula (residual protein adsorption = residual BSA concentration × residual volume), thus evaluating the protein adsorption capacity of the cotton fiber / nitrocellulose composite membrane. All experiments were repeated three times.

[0054] Step 6: Perforate the prepared cotton fiber / nitrocellulose composite membrane into circular paper discs with a diameter of 5 mm for later use. Dilute the food coloring in a gradient of 50, 60, 70, 80, 100, 200, 400, 600, 800, 1000, 2000, and 0 times. Use a pipette to add 0.5 μL of each concentration of food coloring to the perforated circular paper discs. Observe the color development performance by taking a picture using a mobile phone (Honor 500, Professional Mode: ISO: 50, S: 1 / 100). To fully determine the uniformity of the colorimetric signal, this study uses ImageJ software to analyze the distribution of the colorimetric signal from three aspects: visual observation, radial distribution of the color signal, and planar distribution, thereby verifying the optimization effect of the cotton fiber / nitrocellulose composite membrane construction on paper-based detection.

[0055] Example 2 A method for preparing a cotton fiber / cellulose nitrate composite membrane based on the synergistic effect of physical and chemical modification includes the following steps: Step 1: Prepare cotton pulp with an oven-dry content of 26.11% at a freeness of 60° SR using a trough beater.

[0056] Step 2: Weigh 0.5g of carboxymethyl cellulose powder, dissolve it in 50mL of deionized water, and stir until completely dissolved to obtain a 1% (m / v) carboxymethyl cellulose suspension; weigh 1g of cationic starch, dissolve it in 50mL of deionized water, and stir in an oil bath at 67℃ for 1h to gelatinize the starch to obtain a 2% (m / v) gelatinized cationic starch suspension, i.e., mixture 2.

[0057] Step 3: Add 2g of cotton pulp (octane-dry weight) containing cotton fibers from Step 1 to 100mL of mixture 3 containing 50mM sodium periodate and react at 30℃. After reacting for 4 hours, centrifuge and wash three times, then add 100mL of mixture 4 and react for 30 minutes. Wash again to obtain cotton fibers oxidized with sodium periodate (store at 4℃ for later use). Mixture 3 is an acetate buffer solution with added sodium periodate (pH≈4.7), and mixture 4 is a 100mM NaBH4 solution.

[0058] Step 4: Weigh cotton pulp containing 0.4536g of cotton fiber (octane-dry weight) oxidized with sodium periodate and 0.05g of nitrocellulose (octane-dry weight), dissolve in 50mL of deionized water and mix to obtain mixture 5. Add 50.4μL of 1% (m / v) carboxymethyl cellulose suspension to mixture 5 according to the 0.1% carboxymethyl cellulose addition amount (the percentage of carboxymethyl cellulose in the total mass (octane-dry weight) of cotton fiber and nitrocellulose), vacuum filter, and dry to obtain an ox-CF / NC / CMC composite membrane. Add 126μL of mixture 2 to 15mL of mixture 2 according to the 0.5% cationic starch addition amount (the percentage of cationic starch in the total mass (octane-dry weight) of cotton fiber and nitrocellulose), dilute with deionized water, and immerse the ox-CF / NC / 0.1%CMC composite membrane in mixture 2. Remove and dry at 37℃ to obtain an ox-CF / NC / 0.1%CMC / 0.5%CS composite membrane. At this point, the basis weight of the paper-based material is 80g / m³. 2 .

[0059] Step 5: Bovine serum albumin (BSA) was selected as the model sample for protein adsorption. First, a standard curve was constructed by measuring the absorbance of serially diluted BSA buffer using a UV spectrophotometer. Then, the prepared cotton fiber / nitrocellulose composite membrane was cut into 1cm × 1cm paper pieces and incubated in 400 μL of BSA solution at room temperature for 2 h. After adsorption, the remaining volume was measured using a pipette, and the absorbance of the residual BSA solution was measured at 280 nm using a UV spectrophotometer. The concentration of the remaining BSA was calculated using the standard curve. Finally, the amount of unadsorbed protein was calculated using the formula (residual protein adsorption = residual BSA concentration × residual volume), thus evaluating the protein adsorption capacity of the cotton fiber / nitrocellulose composite membrane. All experiments were repeated three times.

[0060] Step 6: Perforate the prepared cotton fiber / nitrocellulose composite membrane into circular paper discs with a diameter of 5 mm for later use. Dilute the food coloring in a gradient of 50, 60, 70, 80, 100, 200, 400, 600, 800, 1000, 2000, and 0 times. Use a pipette to add 0.5 μL of each concentration of food coloring to the perforated circular paper discs. Observe the color development performance by taking a picture using a mobile phone (Honor 500, Professional Mode: ISO: 50, S: 1 / 100). To fully determine the uniformity of the colorimetric signal, this study uses ImageJ software to analyze the distribution of the colorimetric signal from three aspects: visual observation, radial distribution of the color signal, and planar distribution, thereby verifying the optimization effect of the cotton fiber / nitrocellulose composite membrane construction on paper-based detection.

[0061] Example 3 A method for preparing a cotton fiber / cellulose nitrate composite membrane based on the synergistic effect of physical and chemical modification includes the following steps: Step 1: Prepare cotton pulp with an oven-dry content of 26.11% at a freeness of 60° SR using a trough beater.

[0062] Step 2: Weigh 0.5g of carboxymethyl cellulose powder at a mass ratio of 1%, dissolve it in 50mL of deionized water, and stir until completely dissolved to obtain a 1% (m / v) carboxymethyl cellulose suspension; weigh 1g of cationic starch at a mass ratio of 2%, dissolve it in 50mL of deionized water, and stir in an oil bath at 67℃ for 1h to gelatinize the starch to obtain a 2% (m / v) gelatinized cationic starch suspension, i.e., mixture 2.

[0063] Step 3: Add 2g of cotton pulp (octane-dry weight) containing cotton fibers from Step 1 to 100mL of mixture 3 containing 50mM sodium periodate and react at 35℃. After reacting for 4 hours, centrifuge and wash three times, then add 100mL of mixture 4 and react for 30 minutes. Wash again to obtain cotton fibers oxidized with sodium periodate (store at 4℃ for later use). Mixture 3 is an acetate buffer solution with added sodium periodate (pH≈4.7), and mixture 4 is a 100mM NaBH4 solution.

[0064] Step 4: Weigh cotton pulp containing 0.4536g of cotton fiber (octane-dry weight) oxidized with sodium periodate and 0.05g of nitrocellulose (octane-dry weight), dissolve in 50mL of deionized water and mix to obtain mixture 5. Add 50.4μL of 1% (m / v) carboxymethyl cellulose suspension to mixture 5 according to the 0.1% carboxymethyl cellulose addition amount (the percentage of carboxymethyl cellulose in the total mass (octane-dry weight) of cotton fiber and nitrocellulose), and vacuum filter to obtain an ox-CF / NC / CMC composite membrane. Add 126μL of mixture 2 to 15mL of deionized water according to the 0.5% cationic starch addition amount (the percentage of cationic starch in the total mass (octane-dry weight) of cotton fiber and nitrocellulose), immerse the ox-CF / NC / CMC composite membrane in mixture 2, remove and dry at 37℃ to obtain an ox-CF / NC / 0.1%CMC / 0.5%CS composite membrane. At this point, the basis weight of the paper-based material is 80g / m³. 2 .

[0065] Step 5: Bovine serum albumin (BSA) was selected as the model sample for protein adsorption. First, a standard curve was constructed by measuring the absorbance of serially diluted BSA buffer using a UV spectrophotometer. Then, the prepared cotton fiber / nitrocellulose composite membrane was cut into 1cm × 1cm paper pieces and incubated in 400 μL of BSA solution at room temperature for 2 h. After adsorption, the remaining volume was measured using a pipette, and the absorbance of the residual BSA solution was measured at 280 nm using a UV spectrophotometer. The concentration of the remaining BSA was calculated using the standard curve. Finally, the amount of unadsorbed protein was calculated using the formula (residual protein adsorption = residual BSA concentration × residual volume), thus evaluating the protein adsorption capacity of the cotton fiber / nitrocellulose composite membrane. All experiments were repeated three times.

[0066] Step 6: Perforate the prepared cotton fiber / nitrocellulose composite membrane into circular paper discs with a diameter of 5 mm for later use. Dilute the food coloring in a gradient of 50, 60, 70, 80, 100, 200, 400, 600, 800, 1000, 2000, and 0 times. Use a pipette to add 0.5 μL of each concentration of food coloring to the perforated circular paper discs. Observe the color development performance by taking a picture using a mobile phone (Honor 500, Professional Mode: ISO: 50, S: 1 / 100). To fully determine the uniformity of the colorimetric signal, this study uses ImageJ software to analyze the distribution of the colorimetric signal from three aspects: visual observation, radial distribution of the color signal, and planar distribution, thereby verifying the optimization effect of the cotton fiber / nitrocellulose composite membrane construction on paper-based detection.

[0067] To investigate the effect of synergistic effects of physicochemical modification on the properties and color development performance of cotton fiber / cellulose nitrate composite membranes, the morphology and pore size of cotton fiber / cellulose nitrate composite membranes from Comparative Examples 1, 2, 3, and 1 were observed. Figure 5 Protein adsorption performance ( Figure 6 ) and color rendering properties ( Figure 7 ).

[0068] Figure 5 Electron micrographs (A) of the unmodified CF / NC composite membrane of Comparative Example 1, the CF / NC / 0.1%CMC / 0.5%CS composite membrane prepared by physical modification method of Comparative Example 2, the ox-CF / NC composite membrane (50mM NaIO4) prepared by chemical modification method of Comparative Example 3, and the ox-CF / NC / 0.1%CMC / 0.5%CS composite membrane prepared by physicochemical synergistic modification in Example 1 are shown. The pore size of the CF / CNF paper-based material was measured using ImageJ software based on the scanning electron microscope results (B). In A, (a) is the CF / NC composite membrane; (b) is the CF / NC / 0.1%CMC / 0.5%CS composite membrane; (c) is the ox-CF / NC composite membrane (50mM NaIO4); and (d) is the ox-CF / NC / 0.1%CMC / 0.5%CS composite membrane.

[0069] Figure 5 The results from the study showed that the pore size of the composite membrane was significantly reduced after adding CMC and CS through physical methods; the pore size of the ox-CF / NC composite membrane was also significantly reduced after oxidizing cotton fibers through chemical methods; and finally, the pore size of the ox-CF / NC / 0.1%CMC / 0.5%CS composite membrane prepared by the synergistic effect of physicochemical methods was smaller than that prepared by single modification methods. Figure 5Figure B shows the quantitative results of the pore sizes of the prepared paper-based materials. Similar to the results of the electron microscopy images, the pore sizes are as follows: CF / NC (40.7693±22.79μm) > CF / NC / 0.1%CMC / 0.5%CS (34.6864±12.33μm) > ox-CF / NC (30.5881±11.73μm) > ox-CF / NC / 0.1%CMC / 0.5%CS (24.6513±9.62μm). A decrease in pore size error can be observed, indicating that the cotton fiber / cellulose nitrate composite membrane prepared by the synergistic effect of physicochemical processes has a more uniform structure. This is because carboxymethyl cellulose and cationic starch, acting as fillers, fill and even block the macroporous structure of the cotton fibers, thereby changing the pore size of the cotton fibers. Sodium periodate oxidation, through chemical modification of the cellulose chains, enhances intermolecular interactions, and optimizes the film-forming process, ultimately promotes the formation of a denser composite membrane with a more uniform pore size distribution.

[0070] Figure 6 Figure A is the protein adsorption standard curve, used to calculate the protein adsorption capacity of paper-based materials. From... Figure 6 As can be seen from Figure B, compared to the unmodified cotton fiber / nitrocellulose composite membrane of Comparative Example 1, the adsorption capacity of the physically modified cotton fiber / nitrocellulose composite membrane of Comparative Example 2, the chemically modified (50 mM NaIO4) membrane of Comparative Example 3, and the physicochemically synergistically modified cotton fiber / nitrocellulose composite membrane of Example 1 all increased. The order was CF / NC (39.77±2.32 μg) > CF / NC / 0.1%CMC / 0.5%CS (41.19±4.04 μg) > ox-CF / NC (84.79±6.32 μg) > ox-CF / NC / 0.1%CMC / 0.5%CS (104.54±4.31 μg). By comparing the protein adsorption performance of different composite membranes, it can be seen that physicochemical synergistic modification can improve the protein adsorption performance of the composite membrane. The addition of CMC may introduce negatively charged groups, which enhance the adsorption performance of paper-based materials for proteins through electrostatic attraction; while sodium periodate oxidation introduces active groups such as aldehyde groups in situ on the surface of cotton fibers, transforming the material from a physical adsorption carrier into an active interface that can undergo strong covalent bonding, thereby significantly enhancing the protein adsorption performance. Figure 7Figure A shows the color development images of different concentrations of food coloring from Example 1 through visual observation; the grayscale values ​​were quantitatively analyzed using ImageJ software. As shown in Figure B, compared with the unmodified cotton fiber / cellulose nitrate composite membrane of Comparative Example 1, the gray values ​​of the cotton fiber / cellulose nitrate composite membranes of Comparative Example 2 (physically modified), Comparative Example 3 (chemically modified, 50 mM NaIO4), and Example 1 (physicochemically synergistically modified) decreased, indicating that their color development was deeper. By analyzing the average gray value of the colored area, the gray values ​​were: CF / NC (104.14) > CF / NC / 0.1%CMC / 0.5%CS (102.69) > ox-CF / NC (101.23) > ox-CF / NC / 0.1%CMC / 0.5%CS (98.324). By analyzing the planar distribution of the color development of the composite membrane using ImageJ software, Figure C shows that the color development of the cotton fiber surface after physicochemical synergistic modification is more uniform, which may be due to the influence of physicochemical synergistic modification on the pore size of the paper substrate surface, thereby improving the color development uniformity.

[0071] It should be noted that, Figure 2 and Figure 7 Because different photographic equipment is used, the resulting grayscale values ​​are different.

[0072] In summary, this invention successfully prepared a cotton fiber / cellulose nitrate composite membrane based on the synergistic effect of physical and chemical modification. This composite membrane enhances the colorimetric properties by altering the pore size of the fiber surface and the functional groups on the paper substrate surface. This design not only enhances the protein adsorption performance of the composite membrane from a physical perspective but also improves its protein adsorption capacity from a chemical perspective. This invention not only provides a method for preparing a cotton fiber / cellulose nitrate composite membrane with enhanced colorimetric properties but also offers new ideas for the design and application of paper-based biomaterials, demonstrating improved protein adsorption performance and providing new possibilities for future paper-based colorimetric biodetection.

[0073] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A method for preparing a cotton fiber / cellulose nitrate composite membrane, characterized in that, Includes the following steps: S1, the cotton pulp board is pulped into cotton pulp containing cotton fibers. The cotton pulp containing cotton fibers is added to sodium periodate acetate buffer solution for the first reaction. The resulting product is washed and then added to NaBH4 solution for the second reaction. The resulting product is washed to obtain cotton fibers oxidized by sodium periodate. S2, cotton fibers oxidized by sodium periodate are mixed with nitrocellulose and carboxymethyl cellulose suspensions, filtered to form a membrane, and then the ox-CF / NC / CMC composite membrane is obtained. The ox-CF / NC / CMC composite membrane is then immersed in a gelatinized cationic starch suspension, removed and dried to obtain the ox-CF / NC / CMC / CS composite membrane.

2. The method for preparing the cotton fiber / cellulose nitrate composite membrane according to claim 1, characterized in that, In S1, the reaction temperature for the first reaction is 25~45℃, and the reaction time is 2~6h.

3. The method for preparing the cotton fiber / cellulose nitrate composite membrane according to claim 1, characterized in that, In S1, the reaction temperature for the second reaction is 25~30℃, and the reaction time is 10~30min.

4. The method for preparing the cotton fiber / cellulose nitrate composite membrane according to claim 1, characterized in that, In S1, the concentration of sodium periodate in the acetate buffer is 10~90mM.

5. The method for preparing the cotton fiber / cellulose nitrate composite membrane according to claim 1, characterized in that, In S1, the concentration of the NaBH4 solution is 50~100mM.

6. The method for preparing the cotton fiber / cellulose nitrate composite membrane according to claim 1, characterized in that, In S2, the mass content of carboxymethyl cellulose in the ox-CF / NC / CMC composite membrane is 0.1%~2%.

7. The method for preparing the cotton fiber / cellulose nitrate composite membrane according to claim 1, characterized in that, In S2, the mass content of gelatinized cationic starch in the ox-CF / NC / CMC / CS composite membrane is 0.5%~2%.

8. The method for preparing the cotton fiber / cellulose nitrate composite membrane according to claim 1, characterized in that, In S2, the mass ratio of cotton fibers oxidized by sodium periodate to nitrocellulose is 9:1 to 1:

9.

9. A cotton fiber / cellulose nitrate composite membrane obtained by the preparation method according to any one of claims 1 to 8.

10. The application of the cotton fiber / cellulose nitrate composite membrane of claim 9 as a substrate in the preparation of a paper-based colorimetric sensor.

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