Paper-based sensor for creatinine detection and preparation method thereof

Abstract

The invention provides a paper-based sensor for creatinine detection and a preparation method thereof, the paper-based sensor comprises a polylactic acid paper-based material and a colorimetric indicator attached to the polylactic acid paper-based material, and the colorimetric indicator is formed by curing water-based colorimetric indication ink; the water-based colorimetric indication ink comprises a solvent, an indicator, a stabilizer and a thickening agent, the indicator is a meta-dinitro aromatic compound, the stabilizer is a water-soluble inorganic alkaline compound, and the thickening agent is a biomass polysaccharide derivative. The paper-based sensor provided by the invention can be used for portable handheld detection of creatinine in a solution, the level of creatinine is judged through comparison with a colorimetric card, compared with a mainstream enzyme method in the market, the response speed is higher, the cost is lower, and the polylactic acid paper base material and the colorimetric indicator can be naturally degraded, so that the paper-based sensor is more environment-friendly.

Description

Technical Field

[0001] The invention relates to the technical field of creatinine detection, and in particular to a paper-based sensor for creatinine detection and a preparation method thereof. Background Art

[0002] Acute kidney injury (AKI) is currently the most important and common type of kidney disease, accounting for 10% to 15% of all hospitalized patients. In addition, AKI is one of the risk factors for the progression of kidney diseases to end-stage renal disease. If not treated promptly and effectively, it will lead to terrible uremia. The detection marker for kidney diseases including AKI and uremia is serum creatinine. Among the many current analytical methods, the specific identification of target compounds based on optical colorimetry is widely accepted by the academic community for its advantages such as simple operation, cost-effectiveness, and efficient output (can be identified by the naked eye).

[0003] Among the optical colorimetric methods, the Jaffe method is the most mature. The principle of the Jaffe method is that trinitrophenol (picric acid) can combine with creatinine under alkaline conditions to form a relatively stable red product. However, picric acid as an indicator is an unstable and explosive compound. There are safety issues when using it, and it is not suitable for medical places with high safety requirements. Subsequent studies have found that aromatic compounds with meta-nitro groups, which are safer than picric acid, can undergo substitution reactions with creatinine under alkaline conditions to obtain new compounds of different colors. Therefore, some technical solutions use aromatic compounds with meta-nitro groups as indicators. For example, the patent document with application number CN201310548676.X discloses a urine creatinine detection reagent strip and a preparation method thereof. The detection reagent strip includes a substrate and a filter paper sheet. The filter paper sheet is prepared by soaking the filter paper in liquid A and liquid B respectively, taking it out, and drying it. Liquid A is an 80-95 v / v% ethanol solution containing 3.2wt% to 4.8wt% buffer and 1wt% to 1.5wt% surfactant; liquid B is a methanol solution containing 0.8wt% to 1.2wt% 3,5-dinitrobenzoic acid and 0.008wt% to 0.012wt% bromocresol green. Although the above technical solution solves the safety problem caused by picric acid, the solution required for preparing the test strip contains highly toxic methanol, which introduces new safety and environmental problems during the preparation and application process. In addition, the test strip has a long soaking time and low preparation efficiency, and its industrialization prospects are insufficient. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a paper-based sensor for creatinine detection. The sensor has good portability and naked eye recognition, and the production materials do not contain explosive or highly toxic substances. The preparation and application process is safer and simpler, and is suitable for places with high safety requirements.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A paper-based sensor for creatinine detection comprises a polylactic acid paper-based material and a colorimetric indicator attached to the polylactic acid paper-based material, wherein the colorimetric indicator is formed by curing an aqueous colorimetric indicator ink; the aqueous colorimetric indicator ink comprises a solvent, an indicator, a stabilizer and a thickener, wherein the indicator is an aromatic compound of a meta-dinitro group, the stabilizer is a water-soluble inorganic alkaline compound, and the thickener is a biomass polysaccharide derivative.

[0006] In order to overcome the inconvenience of existing blood tests, based on the inspiration of pH test paper, portable paper-based colorimetric devices have attracted the attention of more and more researchers. For example, the prior art (CN201310548676.X) provides a creatinine detection reagent strip, the paper-based material of the reagent strip is filter paper (i.e., cellulose material), and the cellulose material is fully soaked in liquid A and liquid B in the preparation process, so that 3,5-dinitrobenzoic acid as the main indicator penetrates into the cellulose material, and the creatinine detection reagent strip is obtained after drying. This method has two disadvantages. One is that the cellulose material needs to be fully soaked under strong alkaline conditions during the preparation process, the preparation time is long, the industrialization prospect is insufficient, and the structural strength of the cellulose material will be reduced during the soaking process, and it is easy to be damaged. The second is that the solvent in liquid B is highly toxic methanol, and the preparation process will bring safety and environmental protection problems. In order to solve the above problems, the inventors considered using different methods to combine the paper-based material with the indicator. After comparing different methods, they finally chose a more efficient one, that is, to form a film of ink on the paper-based material by means of scraping, printing, etc., and use the film layer as the color-developing material for creatinine detection. This method has low industrial difficulty, high production efficiency, and a small amount of solvent volatilization during the production process, and has advantages in safety and environmental protection. After determining the preparation method, faced with the choice of paper-based materials and ink, the first thing that can be determined is that when compounds with picric acid-related mechanisms are used as indicators, alkaline substances as stabilizers are generally indispensable for inks. Considering that paper-based materials generally move in processing equipment in a roll-up manner during industrial continuous production, the paper-based materials need to maintain a certain tension. Therefore, it is necessary to ensure the physical strength stability of the paper-based material before and after the combination with the ink to ensure production stability. Although the alkali content in the ink is significantly reduced compared to the immersion method, there is still a risk of corrosion to the paper-based material, which in turn causes changes in the structural strength of the paper-based material, affecting continuous production. For this reason, the inventors ruled out the use of cellulose or other biomass materials affected by strong alkali as paper-based materials. At the same time, considering the adhesion strength requirements between the ink and the paper-based material and the environmental protection requirements when the test paper is used as medical waste, polylactic acid paper-based material was finally selected as the ink adhesion carrier. While determining the paper-based material, the selection of ink components also needs to take into account many aspects. In order to reduce the danger of the indicator itself, the inventors selected an aromatic compound with meta-dinitro group, which is more stable than picric acid and has the same indicating effect after evaluation. In order to solve the safety and environmental protection problems caused by solvent volatilization during ink curing, the inventors chose a water-based ink solution and further used biomass polysaccharide derivatives as thickeners. This type of thickener has a good thickening effect in aqueous solution, a high bonding strength with polylactic acid paper-based materials, and is itself a biomass material, which further improves the degradability of paper-based sensors.

[0007] Based on the above research and development ideas, the present invention provides a paper-based sensor for creatinine detection. The paper-based sensor has a light yellow background color when dry, and exhibits an optical change from light purple to dark purple after being exposed to creatinine solutions with concentrations ranging from low to high in an alkaline environment. Based on a pre-prepared standard colorimetric card, the concentration range of creatinine can be judged by naked eye recognition. Compared with the enzymatic hydrolysis method with a high degree of commercial medical use on the market, the portability of the paper-based sensor provided by the present invention is greatly improved, and the changes in the entire detection process can be identified by the naked eye. The reagent detection time is within 2 minutes, which is convenient and efficient, and the requirements for detection equipment are greatly reduced. The operation process is more streamlined and easy to promote and use. Compared with other creatinine colorimetric test papers, the optical paper-based sensor provided by the present invention is easier to industrialize and continuously produce, and the raw material components do not involve toxic organic solvents, which improves the safety and environmental protection of the production process, and basically all materials can be biodegraded under natural conditions to achieve carbon neutrality.

[0008] Further, the indicator is one or more of 3,5-dinitrobenzoic acid (35DNBA) or 2,4-dinitrobenzoic acid (24DNBA). Preferably, the indicator is 3,5-dinitrobenzoic acid.

[0009] Further, the stabilizer is one or more of potassium hydroxide, sodium hydroxide and sodium carbonate. Preferably, the indicator is potassium hydroxide.

[0010] Furthermore, the thickener is one or more of sodium alginate, methyl cellulose, and hydroxyethyl cellulose.

[0011] When selecting thickeners, the inventors found that inks with sodium alginate added had significantly higher viscosity than inks with the same mass of cellulose thickeners added. In addition, when the inventors used cellulose paper-based materials for ink attachment in the early stages of the study, they found that inks with sodium alginate added had a lower degree of corrosion on cellulose paper-based materials than inks with cellulose thickeners added. The inventors inferred that the mechanism is that the colloidal hydrolysis products of sodium alginate at the interface between the ink and the cellulose paper-based materials can slow down the corrosion of alkali on the cellulose paper-based materials, thus playing a protective role. Therefore, the preferred thickener is ammonium alginate. In some cases, the polylactic acid paper-based materials of the present invention may also need to be compounded with other types of paper-based materials. In this case, the use of sodium alginate as a thickener can avoid the corrosion of other types of paper-based materials by inks.

[0012] Furthermore, the method for preparing the aqueous colorimetric indicator ink comprises the following steps: Provide an indicator that changes color with creatinine; dissolving the indicator in an aqueous stabilizer solution to obtain a uniform solution; The uniform solution is mixed with a thickener and stirred sufficiently to obtain an aqueous colorimetric indicator ink free of solid insoluble matter.

[0013] Furthermore, the concentration of the stabilizer aqueous solution is 0.5-0.8M.

[0014] Furthermore, the concentration of the indicator in the homogeneous solution is 0.2-0.4M.

[0015] Furthermore, the mass concentration of the thickener in the aqueous colorimetric indicator ink is 1wt%~3wt%.

[0016] Another object of the present invention is to provide a method for preparing the above-mentioned paper-based sensor for creatinine detection, which comprises the following steps: s1. Prepare polylactic acid paper-based material; s2, applying water-based colorimetric indicator ink on the polylactic acid paper-based material; s3. Dry the aqueous colorimetric indicator ink on the polylactic acid paper-based material to obtain a paper-based sensor for creatinine detection.

[0017] Furthermore, in s2, the applied thickness of the aqueous colorimetric indicator ink is 250-1000 μm; in s3, the polylactic acid paper substrate is treated in a blower at 30-50° C. for 20-60 minutes to dry the aqueous colorimetric indicator ink.

[0018] In summary, the application of the present invention can achieve the following beneficial effects: 1. The paper-based sensor provided by the present invention can be portable and handheld to detect creatinine in a solution, and the level of creatinine can be determined by comparing it with a colorimetric card. Compared with the mainstream enzyme method on the market, it has a faster response speed and lower cost.

[0019] 2. The paper-based sensor provided by the present invention is composed of a polylactic acid paper-based material and a colorimetric indicator formed by an aqueous colorimetric indicator ink. Both the polylactic acid paper substrate and the colorimetric indicator can be naturally degraded, which is more environmentally friendly.

[0020] 3. The colorimetric indicator of the paper-based sensor provided by the present invention is formed by curing the aqueous ink. The aqueous ink does not contain organic solvents, and no volatile harmful substances are generated during the drying and curing process of the ink. The preparation is safer, and the processing cost of a part of the volatile harmful substances is saved during industrial production, which has industrial prospects.

[0021] 4. The paper-based material of the paper-based sensor provided by the present invention has strong adhesion to the ink, and the structural strength of the paper-based material is basically not affected by the strong alkalinity of the ink. The unrolled paper-based material is not easy to break during continuous production, and is suitable for industrial production. DETAILED DESCRIPTION

[0022] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Example 1 This embodiment provides a paper-based sensor for creatinine detection, which includes a polylactic acid paper-based material and a colorimetric indicator attached to the polylactic acid paper-based material, wherein the colorimetric indicator is formed by curing an aqueous colorimetric indicator ink.

[0024] ① The preparation method of the aqueous colorimetric indicator ink is as follows: 3,5-Dinitrobenzoic acid was selected as an indicator for color change reaction with creatinine; A 0.6M potassium hydroxide aqueous solution was prepared, and 3,5-dinitrobenzoic acid was added to the aqueous solution and stirred thoroughly to obtain a uniform solution, so that the concentration of 3,5-dinitrobenzoic acid in the uniform solution was 0.3M; Sodium alginate was added to the homogeneous solution, and the solution was mechanically stirred for 2 hours to obtain an aqueous colorimetric indicator ink, wherein the mass concentration of sodium alginate was 2 wt %.

[0025] ② The preparation method of the paper-based sensor is as follows: Choose commercially available weight 120g m -2 Polylactic acid paper is used as the paper base material; The paper base material was fixed, and a water-based colorimetric indicator ink was applied on the surface of the paper base material by a doctor blade method. The amount of ink applied was 50 g·m -2 , so that an ink layer with a thickness of about 500 μm is attached to the surface of the paper base material; The paper-based material with the ink layer attached is sent into a blower box, the temperature is set to 40° C., and the blower is treated for 30 minutes to dry and solidify the ink layer to form a colorimetric indicator, thereby obtaining a paper-based sensor for creatinine detection.

[0026] Example 2 This embodiment provides a paper-based sensor for creatinine detection, which includes a polylactic acid paper-based material and a colorimetric indicator attached to the polylactic acid paper-based material, wherein the colorimetric indicator is formed by curing an aqueous colorimetric indicator ink.

[0027] ① The preparation method of the aqueous colorimetric indicator ink is as follows: 2,4-Dinitrobenzoic acid was selected as an indicator for color change reaction with creatinine; A 0.6M potassium hydroxide aqueous solution was prepared, and 2,4-dinitrobenzoic acid was added to the aqueous solution and stirred thoroughly to obtain a uniform solution, so that the concentration of 2,4-dinitrobenzoic acid in the uniform solution was 0.3M; Sodium alginate was added to the homogeneous solution, and the solution was mechanically stirred for 2 hours to obtain an aqueous colorimetric indicator ink, wherein the mass concentration of sodium alginate was 2 wt %.

[0028] ② The preparation method of the paper-based sensor is similar to that of Example 1.

[0029] Example 3 This embodiment provides a paper-based sensor for creatinine detection, which includes a polylactic acid paper-based material and a colorimetric indicator attached to the polylactic acid paper-based material, wherein the colorimetric indicator is formed by curing an aqueous colorimetric indicator ink.

[0030] ① The preparation method of the aqueous colorimetric indicator ink is as follows: 3,5-Dinitrobenzoic acid was selected as an indicator for color change reaction with creatinine; A 0.4M potassium hydroxide aqueous solution was prepared, and 3,5-dinitrobenzoic acid was added to the aqueous solution and stirred thoroughly to obtain a uniform solution, so that the concentration of 3,5-dinitrobenzoic acid in the uniform solution was 0.3M; Sodium alginate was added to the homogeneous solution, and the solution was mechanically stirred for 1 hour to obtain an aqueous colorimetric indicator ink, wherein the mass concentration of sodium alginate was 2 wt %.

[0031] ② The preparation method of the paper-based sensor is similar to that of Example 1.

[0032] Example 4 This embodiment provides a paper-based sensor for creatinine detection, which includes a polylactic acid paper-based material and a colorimetric indicator attached to the polylactic acid paper-based material, wherein the colorimetric indicator is formed by curing an aqueous colorimetric indicator ink.

[0033] ① The preparation method of the aqueous colorimetric indicator ink is as follows: 3,5-Dinitrobenzoic acid was selected as an indicator for color change reaction with creatinine; A 0.5M potassium hydroxide aqueous solution was prepared, and 3,5-dinitrobenzoic acid was added to the aqueous solution and stirred thoroughly to obtain a uniform solution, so that the concentration of 3,5-dinitrobenzoic acid in the uniform solution was 0.3M; Sodium alginate was added to the homogeneous solution, and the solution was mechanically stirred for 1 hour to obtain an aqueous colorimetric indicator ink, wherein the mass concentration of sodium alginate was 2 wt %.

[0034] ② The preparation method of the paper-based sensor is similar to that of Example 1.

[0035] Example 5 This embodiment provides a paper-based sensor for creatinine detection, which includes a polylactic acid paper-based material and a colorimetric indicator attached to the polylactic acid paper-based material, wherein the colorimetric indicator is formed by curing an aqueous colorimetric indicator ink.

[0036] ① The preparation method of the aqueous colorimetric indicator ink is as follows: 3,5-Dinitrobenzoic acid was selected as an indicator for color change reaction with creatinine; A 0.8M potassium hydroxide aqueous solution was prepared, and 3,5-dinitrobenzoic acid was added to the aqueous solution and stirred thoroughly to obtain a uniform solution, so that the concentration of 3,5-dinitrobenzoic acid in the uniform solution was 0.3M; Sodium alginate was added to the homogeneous solution, and the solution was mechanically stirred for 1 hour to obtain an aqueous colorimetric indicator ink, wherein the mass concentration of sodium alginate was 2 wt %.

[0037] ② The preparation method of the paper-based sensor is similar to that of Example 1.

[0038] Example 6 This embodiment provides a paper-based sensor for creatinine detection, which includes a polylactic acid paper-based material and a colorimetric indicator attached to the polylactic acid paper-based material, wherein the colorimetric indicator is formed by curing an aqueous colorimetric indicator ink.

[0039] ① The preparation method of the aqueous colorimetric indicator ink is as follows: 3,5-Dinitrobenzoic acid was selected as an indicator for color change reaction with creatinine; A 1.0 M potassium hydroxide aqueous solution was prepared, and 3,5-dinitrobenzoic acid was added to the aqueous solution and stirred thoroughly to obtain a uniform solution, so that the concentration of 3,5-dinitrobenzoic acid in the uniform solution was 0.3 M; Sodium alginate was added to the homogeneous solution, and the solution was mechanically stirred for 1 hour to obtain an aqueous colorimetric indicator ink, wherein the mass concentration of sodium alginate was 2 wt %.

[0040] ② The preparation method of the paper-based sensor is similar to that of Example 1.

[0041] Example 7 This embodiment provides a paper-based sensor for creatinine detection, which includes a polylactic acid paper-based material and a colorimetric indicator attached to the polylactic acid paper-based material, wherein the colorimetric indicator is formed by curing an aqueous colorimetric indicator ink.

[0042] ① The preparation method of the aqueous colorimetric indicator ink is as follows: 3,5-Dinitrobenzoic acid was selected as an indicator for color change reaction with creatinine; A 0.6M potassium hydroxide aqueous solution was prepared, and 3,5-dinitrobenzoic acid was added to the aqueous solution and stirred thoroughly to obtain a uniform solution, so that the concentration of 3,5-dinitrobenzoic acid in the uniform solution was 0.3M; Sodium alginate was added to the homogeneous solution, and the solution was mechanically stirred for 2 hours to obtain an aqueous colorimetric indicator ink, wherein the mass concentration of sodium alginate was 0.5 wt %.

[0043] ② The preparation method of the paper-based sensor is similar to that of Example 1.

[0044] Example 8 This embodiment provides a paper-based sensor for creatinine detection, which includes a polylactic acid paper-based material and a colorimetric indicator attached to the polylactic acid paper-based material, wherein the colorimetric indicator is formed by curing an aqueous colorimetric indicator ink.

[0045] ① The preparation method of the aqueous colorimetric indicator ink is as follows: 3,5-Dinitrobenzoic acid was selected as an indicator for color change reaction with creatinine; A 0.6M potassium hydroxide aqueous solution was prepared, and 3,5-dinitrobenzoic acid was added to the aqueous solution and stirred thoroughly to obtain a uniform solution, so that the concentration of 3,5-dinitrobenzoic acid in the uniform solution was 0.3M; Sodium alginate was added to the homogeneous solution, and the solution was mechanically stirred for 2 hours to obtain an aqueous colorimetric indicator ink, wherein the mass concentration of the sodium alginate was 1 wt %.

[0046] ② The preparation method of the paper-based sensor is similar to that of Example 1.

[0047] Example 9 This embodiment provides a paper-based sensor for creatinine detection, which includes a polylactic acid paper-based material and a colorimetric indicator attached to the polylactic acid paper-based material, wherein the colorimetric indicator is formed by curing an aqueous colorimetric indicator ink.

[0048] ① The preparation method of the aqueous colorimetric indicator ink is as follows: 3,5-Dinitrobenzoic acid was selected as an indicator for color change reaction with creatinine; A 0.6M potassium hydroxide aqueous solution was prepared, and 3,5-dinitrobenzoic acid was added to the aqueous solution and stirred thoroughly to obtain a uniform solution, so that the concentration of 3,5-dinitrobenzoic acid in the uniform solution was 0.3M; Sodium alginate was added to the homogeneous solution, and the solution was mechanically stirred for 2 hours to obtain an aqueous colorimetric indicator ink, wherein the mass concentration of sodium alginate was 3 wt %.

[0049] ② The preparation method of the paper-based sensor is similar to that of Example 1.

[0050] Example 10 This embodiment provides a paper-based sensor for creatinine detection, which includes a polylactic acid paper-based material and a colorimetric indicator attached to the polylactic acid paper-based material, wherein the colorimetric indicator is formed by curing an aqueous colorimetric indicator ink.

[0051] ① The preparation method of the aqueous colorimetric indicator ink is as follows: 3,5-Dinitrobenzoic acid was selected as an indicator for color change reaction with creatinine; A 0.6M potassium hydroxide aqueous solution was prepared, and 3,5-dinitrobenzoic acid was added to the aqueous solution and stirred thoroughly to obtain a uniform solution, so that the concentration of 3,5-dinitrobenzoic acid in the uniform solution was 0.3M; Sodium alginate was added to the homogeneous solution, and the solution was mechanically stirred for 2 hours to obtain an aqueous colorimetric indicator ink, wherein the mass concentration of sodium alginate was 4 wt %.

[0052] ② The preparation method of the paper-based sensor is similar to that of Example 1.

[0053] Embodiment 11 This embodiment provides a paper-based sensor for creatinine detection, which includes a polylactic acid paper-based material and a colorimetric indicator attached to the polylactic acid paper-based material, wherein the colorimetric indicator is formed by curing an aqueous colorimetric indicator ink.

[0054] ① The preparation method of the aqueous colorimetric indicator ink is as follows: 3,5-Dinitrobenzoic acid was selected as an indicator for color change reaction with creatinine; A 0.6M potassium hydroxide aqueous solution was prepared, and 3,5-dinitrobenzoic acid was added to the aqueous solution and stirred thoroughly to obtain a uniform solution, so that the concentration of 3,5-dinitrobenzoic acid in the uniform solution was 0.1M; Sodium alginate was added to the homogeneous solution, and the solution was mechanically stirred for 2 hours to obtain an aqueous colorimetric indicator ink, wherein the mass concentration of sodium alginate was 2 wt %.

[0055] ② The preparation method of the paper-based sensor is similar to that of Example 1.

[0056] Example 12 This embodiment provides a paper-based sensor for creatinine detection, which includes a polylactic acid paper-based material and a colorimetric indicator attached to the polylactic acid paper-based material, wherein the colorimetric indicator is formed by curing an aqueous colorimetric indicator ink.

[0057] ① The preparation method of the aqueous colorimetric indicator ink is as follows: 3,5-Dinitrobenzoic acid was selected as an indicator for color change reaction with creatinine; A 0.6M potassium hydroxide aqueous solution was prepared, and 3,5-dinitrobenzoic acid was added to the aqueous solution and stirred thoroughly to obtain a uniform solution, so that the concentration of 3,5-dinitrobenzoic acid in the uniform solution was 0.2M; Sodium alginate was added to the homogeneous solution, and the solution was mechanically stirred for 2 hours to obtain an aqueous colorimetric indicator ink, wherein the mass concentration of sodium alginate was 2 wt %.

[0058] ② The preparation method of the paper-based sensor is similar to that of Example 1.

[0059] Example 13 This embodiment provides a paper-based sensor for creatinine detection, which includes a polylactic acid paper-based material and a colorimetric indicator attached to the polylactic acid paper-based material, wherein the colorimetric indicator is formed by curing an aqueous colorimetric indicator ink.

[0060] ① The preparation method of the aqueous colorimetric indicator ink is as follows: 3,5-Dinitrobenzoic acid was selected as an indicator for color change reaction with creatinine; A 0.6M potassium hydroxide aqueous solution was prepared, and 3,5-dinitrobenzoic acid was added to the aqueous solution and stirred thoroughly to obtain a uniform solution, so that the concentration of 3,5-dinitrobenzoic acid in the uniform solution was 0.4M; Sodium alginate was added to the homogeneous solution, and the solution was mechanically stirred for 2 hours to obtain an aqueous colorimetric indicator ink, wherein the mass concentration of sodium alginate was 2 wt %.

[0061] ② The preparation method of the paper-based sensor is similar to that of Example 1.

[0062] Embodiment 14 This embodiment provides a paper-based sensor for creatinine detection, which includes a polylactic acid paper-based material and a colorimetric indicator attached to the polylactic acid paper-based material, wherein the colorimetric indicator is formed by curing an aqueous colorimetric indicator ink.

[0063] ① The preparation method of the aqueous colorimetric indicator ink is as follows: 3,5-Dinitrobenzoic acid was selected as an indicator for color change reaction with creatinine; A 0.6M potassium hydroxide aqueous solution was prepared, and 3,5-dinitrobenzoic acid was added to the aqueous solution and stirred thoroughly to obtain a uniform solution, so that the concentration of 3,5-dinitrobenzoic acid in the uniform solution was 0.5M; Sodium alginate was added to the homogeneous solution, and the solution was mechanically stirred for 2 hours to obtain an aqueous colorimetric indicator ink, wherein the mass concentration of sodium alginate was 2 wt %.

[0064] ② The preparation method of the paper-based sensor is similar to that of Example 1.

[0065] Performance Test: (1) Performance test of paper-based sensors and comparison of indicators Experimental protocol: A series of creatinine solutions of standard concentrations were prepared, and the paper-based sensors prepared in Example 1 and Example 2 were respectively taken, and creatinine solutions of different concentrations were used to produce a color reaction with the paper-based sensors to obtain standard colorimetric cards for 3,5-dinitrobenzoic acid paper-based sensors and 2,4-dinitrobenzoic acid paper-based sensors, respectively.

[0066] A creatinine solution of another concentration, which has been preliminarily analyzed for creatinine level by an enzymatic method, is taken. The paper-based sensors of Example 1 and Example 2 are used to perform a color reaction with the creatinine solution, respectively, and the creatinine level is determined by a standard colorimetric card.

[0067] Experimental results: The paper-based sensors of Examples 1 and 2 can both undergo a color development reaction and determine the level range of creatinine, and the range is consistent with the enzymatic method. The purple-red color of the paper-based sensor begins to fade after about 7 to 8 minutes until it turns into the yellow background color of the paper-based sensor, which has sufficient observation time. Therefore, the present invention can achieve portable detection of creatinine; the color development effect of the paper-based sensor of Example 1 is more significant and easier to observe than that of Example 2, and the preferred indicator is 3,5-dinitrobenzoic acid.

[0068] (2) Effect of different alkalinity on water-based colorimetric indicator ink The preparation conditions of the inks in Examples 1, 3, 4, 5, and 6 were observed. The inks in Examples 1, 4, 5, and 6 did not contain insoluble solids, while the ink in Example 3 contained solid insolubles.

[0069] The paper-based sensors prepared in Examples 1, 3, 4, 5, and 6 were used to detect creatinine, and their color development was observed and recorded. The paper-based sensors prepared in Examples 1, 4, and 5 faded 7 to 8 minutes after the color development reaction occurred, and the paper-based sensor prepared in Example 6 faded about 5 minutes after the color development reaction occurred. The color development effects of Examples 1, 4, 5, and 6 were relatively uniform and could be compared with the colorimetric card. There were obvious color differences in different areas of Example 3, making it difficult to analyze the creatinine level.

[0070] In summary, in the present invention, the optimal range of the stabilizer aqueous solution is 0.5~0.8M. When it is lower than this range, the indicator cannot be completely dissolved, resulting in the paper-based sensor being unable to perform its detection function normally. When it is higher than this range, the color development is unstable and the fading speed is fast, making it difficult to accurately reflect the level of creatinine.

[0071] (3) Effects of different thickener contents on water-based colorimetric inks The preparation of the inks in Examples 1, 7, 8, 9, and 10 was observed. The viscosity of the inks prepared in Examples 1, 8, 9, and 10 met the standard, and an ink layer of uniform thickness could be formed on the paper-based material by a scraping method. The viscosity of the ink prepared in Example 7 was too low, and it was difficult to maintain the ink layer structure, so it was not suitable for the preparation of a paper-based sensor. The response speed of the paper-based sensor in Example 10 for creatinine detection was significantly slower than that in Examples 1, 8, and 9, which may be because too much polysaccharide polymer caused the color development reaction to have a hysteresis.

[0072] In summary, the thickener concentration in the ink is preferably 1wt%~3wt%. If it is lower than this range, the viscosity of the ink will be too low, making it difficult to form a colorimetric indicator by scraping or printing. If it is higher than this range, the response speed of the detection process will be affected.

[0073] (4) Effect of different indicator contents on indication effect By observing the color development effect of the paper-based sensors prepared in Examples 1, 11, 12, 13, and 14 when detecting creatinine, it was found that when the indicator addition amount was 0.1~0.4M, the color depth of the color development reaction gradually increased with the indicator addition amount, and the color depth no longer showed obvious changes after the addition amount exceeded 0.4M. In addition, when the indicator addition amount was 0.1M, the color change during creatinine detection was insufficient and could not meet the colorimetric requirements.

[0074] In summary, the amount of indicator added to the ink is preferably 0.2-0.4 M. If it is lower than this range, the colorimetric requirements cannot be met, and if it is higher than this range, meaningless costs are added.

[0075] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A paper-based sensor for creatinine detection, characterized in that: It comprises a polylactic acid paper-based material and a colorimetric indicator attached to the polylactic acid paper-based material, wherein the colorimetric indicator is formed by curing an aqueous colorimetric indicator ink; The water-based colorimetric indicator ink comprises a solvent, an indicator, a stabilizer and a thickener. The indicator is an aromatic compound of meta-dinitro, the stabilizer is a water-soluble inorganic alkaline compound, the thickener is a biomass polysaccharide derivative, and the solvent is water.

2. A paper-based sensor for creatinine detection according to claim 1, characterized in that: The indicator is one or more of 3,5-dinitrobenzoic acid (35DNBA) or 2,4-dinitrobenzoic acid (24DNBA).

3. A paper-based sensor for creatinine detection according to claim 1, characterized in that: The stabilizer is one or more of potassium hydroxide, sodium hydroxide and sodium carbonate.

4. A paper-based sensor for creatinine detection according to claim 1, characterized in that: The thickener is one or more of sodium alginate, methyl cellulose and hydroxyethyl cellulose.

5. A paper-based sensor for creatinine detection according to claim 1, characterized in that: The preparation method of the aqueous colorimetric indicator ink comprises the following steps: Provide an indicator that changes color with creatinine; dissolving the indicator in an aqueous stabilizer solution to obtain a uniform solution; The uniform solution is mixed with a thickener and stirred sufficiently to obtain an aqueous colorimetric indicator ink free of solid insoluble matter.

6. A paper-based sensor for creatinine detection according to claim 5, characterized in that: The concentration of the stabilizer aqueous solution is 0.5-0.8M.

7. A paper-based sensor for creatinine detection according to claim 6, characterized in that: The concentration of the indicator in the homogeneous solution is 0.2~0.4M.

8. A paper-based sensor for creatinine detection according to claim 7, characterized in that: The mass concentration of the thickener in the aqueous colorimetric indicator ink is 1 wt % to 3 wt %.

9. The method for preparing a paper-based sensor for creatinine detection according to any one of claims 1 to 8, characterized in that: The following steps are involved: s1. Prepare polylactic acid paper-based material; s2, applying water-based colorimetric indicator ink on the polylactic acid paper-based material; s3. Dry the aqueous colorimetric indicator ink on the polylactic acid paper-based material to obtain a paper-based sensor for creatinine detection.

10. The method for preparing a paper-based sensor for creatinine detection according to claim 9, characterized in that: In s2, the aqueous colorimetric indicator ink is applied to a thickness of 250 - 1000 μm; In s3, the polylactic acid paper substrate is treated in a blower at 30-50° C. for 20-60 minutes to dry the aqueous colorimetric indicator ink.