A method for detecting chromium (vi) ions based on oxide nanoszyme test strip

Abstract

The application provides a method for detecting chromium (VI) ions based on an oxide nanometer enzyme (Cu-CeO 2 NPs) test strip. The application belongs to the technical field of heavy metal ion detection, and relates to a preparation of a Cu-CeO 2 NPs test strip and a new method for detecting chromium (VI) ions in water. The test strip is prepared by treating and drying a chromogenic reagent, a substrate, a buffer solution and a catalyst. The method is as follows: a vacuum-sealed test strip is taken out, a sample to be detected is dropped on the test strip, and a photo is taken by using a smart phone after reaction is completed. After the photo collected by the smart phone is processed by a corresponding software (ColorDetector), an RGB value is obtained, a standard curve is drawn according to the correlation between the R value read by the software and the chromium (VI) ions, and the concentration of the corresponding chromium (VI) ions in the sample to be detected can be measured by using a linear equation. The method has the advantages of high speed, simple operation and no need of large equipment, and has great advantages in real-time, rapid and visualized analysis of actual samples.

Description

Technical Field

[0001] This invention belongs to the field of hexavalent chromium(VI) ion detection technology, and relates to the preparation of a test strip based on oxide nanozymes and its method for detecting chromium(VI) ions by combining it with a smartphone. Background Technology

[0002] Hexavalent chromium (Cr(VI)) is a well-known, highly soluble, and toxic carcinogen. Ingestion of chromium(VI) compounds has been reported to be associated with respiratory cancers and other adverse reactions. Therefore, the U.S. Environmental Protection Agency recommends that the concentration of Cr(VI) in drinking water should be less than 0.1 mg / mL. -1 However, Cr(VI) is widely used in many industrial processes, including planting, dye and pigment manufacturing, leather tanning, and wood preservation. Given the increasing threat of Cr(VI) exposure in the environment, developing highly sensitive and selective methods for Cr(VI) determination is crucial. Analysis of Cr(VI) in environmental samples typically employs methods such as UV-Vis spectrophotometry, luminescence methods, atomic emission spectrometry, X-ray fluorescence spectrometry, and atomic absorption spectrometry. However, these methods are often complex, require expensive specialized equipment, and atomic absorption spectrometry (AAS) and inductively coupled plasma atomic emission spectrometry can only obtain information on the total concentration of chromium. Colorimetric methods are highly attractive because they are easily read with the naked eye, offering advantages such as simplicity, speed, and low cost, without requiring any complex instruments. However, simple naked-eye detection strategies have some problems in practical use, such as background color interference and the potential for significant deviations in analytical results due to subjective color judgments. Therefore, exploring a real-time, rapid, and visualized method for chromium(VI) ion detection is of great significance. This invention combines colorimetry with a smartphone, using a color reading program to numerically read colors. By converting the colors of the test strips into digital color information, it eliminates analytical errors caused by subjective color judgment in naked-eye colorimetric analysis, thus improving the accuracy of the analysis results. The purpose of combining test strips with smartphones is to solve the problems of cumbersome operation, dependence on professional equipment and technicians, and subjective errors in existing chromium (VI) ion detection methods, demonstrating significant advantages and commercial potential.

[0003] Nanoenzymes are artificial enzyme systems based on nanomaterials that can replace traditional biological enzymes by mimicking the catalytic sites of natural enzymes. Nanoenzymes exhibit excellent enzyme-like activity, which can be modulated through size control, doping, and surface modification. Doping cerium oxide nanoparticles with various metals (alkali metals, rare earth elements, and transition metals, etc.) enhances the surface Ce content. 3+Higher catalytic efficiency is achieved by increasing the content of cations. When cations of appropriate radius partially replace cerium, the activation degree of oxygen in the cerium lattice increases, the oxygen storage capacity associated with oxygen-rich vacancies increases, and ultimately, the catalytic activity is improved. Therefore, the cerium dioxide system with the addition of a second transition metal ion exhibits higher catalytic activity than the undoped cerium dioxide system. The synergistic effect of copper and cerium dioxide in this invention, with Cu-CeO2NPs exhibiting good activity, has great practical value and research significance in biosensing, actual sample detection and analysis, and clinical diagnosis. However, there are currently no reports on methods for detecting chromium(VI) ions based on Cu-CeO2NPs.

[0004] Therefore, it is of great significance to develop a test strip for detecting chromium(VI) ions based on oxide nanozymes (Cu-CeO2NPs) and combine it with a smartphone app to determine the content of chromium(VI) ions in actual samples. Summary of the Invention

[0005] To address the shortcomings of existing methods for detecting chromium (VI) ions, the purpose of this invention is to provide a novel method for detecting the concentration of chromium (VI) ions in water, thereby enabling real-time, rapid, and visualized detection of chromium (VI) ions in actual samples.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for detecting chromium(VI) ions using a nano-enzyme-based test strip combined with a smartphone, wherein the main reagent formulation of the chromium(VI) ion detection test strip is as follows:

[0008] Buffer solution pH = 3-6

[0009] The concentration of the colorimetric reagent is 1-8 μmol / L.

[0010] Substrate concentration 2-14 μmol / L

[0011] Catalyst concentration 50-500 μg / mL

[0012] No water added

[0013] The buffer solution is an acetate-sodium acetate buffer solution;

[0014] The colorimetric reagent is 3,3',5,5'-tetramethylbenzidine (TMB).

[0015] The substrate solution is an H2O2 solution.

[0016] The catalyst is Cu-CeO2NPs.

[0017] In a preferred embodiment, the specific formulation of the chromium ion detection reagent is as follows:

[0018] The buffer solution has a pH of 4.0.

[0019] The concentration of the colorimetric reagent is 4 μmol / L.

[0020] Substrate concentration 10 μmol / L

[0021] Catalyst concentration 200 μg / mL

[0022] Mix the above reagent solution according to the specific volume ratio of chromium(VI) ion detection reagent: substrate solution: colorimetric reagent: buffer solution: catalyst = 1:1:1:1. Then, drop 8 μL of chromium(VI) ion detection reagent onto the test strip. After drying, cool to room temperature and vacuum dry before storage. The method for detecting chromium(VI) ions using the prepared dried test strip in conjunction with a smartphone includes the following steps:

[0023] (1) Prepare a series of chromium(VI) ion standard solutions into test solutions, and drop 8 μL of each solution onto the prepared dry test strips. After reacting for 10 min, perform RGB analysis on the test strip color using the smartphone color reading application ColorDetector to obtain the R value. Establish a colorimetric signal-concentration standard curve for chromium(VI) ion detection with chromium(VI) ion concentration as the x-axis and R value as the y-axis;

[0024] (2) Process the actual liquid sample to prepare the test reagent, repeat the operation in (1) to obtain the R value of the actual sample, substitute it into the signal standard curve of chromium (VI) ion detection, and the concentration of chromium (VI) ions in the actual liquid sample can be obtained.

[0025] The present invention will be further explained and described below:

[0026] The principle of this invention is based on the following: Peroxidase (POD) is a highly active enzyme that catalyzes the oxidation of substrates using hydrogen peroxide as an electron acceptor. POD-like activity refers to functional nanomaterials that can mimic the catalytic activity of peroxidase, and they have received widespread attention and application in fields such as biomedical diagnostics, bioimaging, antibacterial and antimicrobial coatings. Under the catalytic action of Cu-CeO2 nanoparticles, H2O2 can oxidize TMB to ox-TMB, accompanied by a significant color change. A characteristic peak of ox-TMB at 652 nm can be found in a mixed solution of TMB, H2O2, and Cu-CeO2 NPs. This indicates that Cu-CeO2 nanoparticles can catalyze the oxidation of TMB in the presence of H2O2. Since Cr(VI) can also oxidize TMB, it effectively affects the amount of ox-TMB in the system and the color of the system. Therefore, in the presence of different concentrations of Cr(VI), the intensity of the ox-TMB characteristic peak at 652 nm changes, and the color of the mixture changes to varying degrees, which can be used to detect Cr(VI). The ColorDetector app on a smartphone can read color data, enabling visualization and quantitative testing of Cr(VI) concentration in water.

[0027] In this invention, the selectivity of the method is also tested to exclude other interfering substances (KMnO4, Fe). 3+ Na + ,K + Ag + Cd 2 + Cu 2+ Ni 2+ ,Pb 2+ ,Zn 2+ ,Cr 3+ The detection process is similar to that for Cr(VI), except that the detection solution for interfering substances is used instead of the detection solution for Cr(VI). Among these, KMnO4 and Fe... 3+ It may interfere with the detection process of Cr(VI). Experiments have shown that using ethylenediaminetetraacetic acid (EDTA) can eliminate Fe... 3+ Interference, therefore, in the presence of ethylenediaminetetraacetic acid, Fe 3+ The influence of KMnO4 is negligible. The concentration of Cr(VI) in industrial wastewater is much higher than that of KMnO4, so the interference of KMnO4 can be ignored in the detection of Cr(VI). Therefore, Cu-CeO2 nanoparticles have good selectivity for the detection of Cr(VI) and can be used for the detection of real samples.

[0028] The innovation of this invention compared with existing Cr(VI) detection methods lies in:

[0029] 1. This invention utilizes readily available oxide nanozymes to construct a chromium(VI) ion detection method, which exhibits high sensitivity and high selectivity compared to other colorimetric methods for Cr(VI) detection.

[0030] 2. By using the ColorDetector app on a smartphone to convert the color of the test strip into digital color information, the analysis error caused by subjective color judgment in naked-eye colorimetric analysis is eliminated, thus improving the accuracy of the analysis results.

[0031] 3. The test strips are easy to use and do not require professional operation, making them particularly suitable for rapid on-site detection of chromium (VI) content. Attached Figure Description

[0032] Figure 1 (AB) are transmission electron microscopy (TEM) images (A) and elemental mapping images (B) of Cu-CeO2NPs; (C) is a high-resolution TEM image of Cu-CeO2NPs.

[0033] Figure 2 (A) XRD images of Cu-CeO2NPs, CeO2 NPs and CuO NPs; (B) XPS full spectrum of Cu-CeO2NPs and CeO2NPs; (C) UV-Vis spectrum of Cu-CeO2NPs, CeO2 NPs and CuO NPs.

[0034] Figure 3 Feasibility diagram for detecting chromium(VI) ions in Cu-CeO2 NPs: (A) UV-Vis spectra at different Cr(VI) concentrations (0, 0.08, 0.16, 0.24, 0.32, 0.4, 2.0, 4.0, 8.0, 12.0, 16.0, 20.0, 24.0, 32.0, 40.0 μM); (B) Linear relationship between different Cr(VI) concentrations and the characteristic peak intensity of ox-TMB at 652 nm. In the range of 0.08–40 μM, the linear correlation equation between Cr(VI) concentration and absorbance at 652 nm is y = 0.0139x + 0.188(R0). 2 =0.998).

[0035] Figure 4 (A) The selectivity for chromium(VI) ion detection, against chromium(VI) ions and other potential interfering substances (KMnO4, Fe). 3+ Na + K + Ag + Cd 2+ Cu 2+ Ni 2+ Pb 2+ Zn2+ Cr 3+ The selectivity of Cu-CeO2 NPs indicates that Cu-CeO2 NPs can selectively detect Cr(VI). All experiments were performed at pH 4.0. Figure 4 (B) shows the linear curve and corresponding test strip color images for chromium (VI) ion detection using test strips in conjunction with a smartphone. The test strip color gradually darkens with increasing Cr(VI) concentration. Within the range of 0.40-200 μM, the Cr(VI) concentration exhibits a good linear relationship with the R value in the RGB values ​​acquired by the smartphone and processed by the corresponding software. The linear equation is y = -0.390x + 202(R). 2 =0.995), and the detection limit is 0.30 μM. This indicates that the Cu-CeO2NPs-based test strip combined with a smartphone system can be used for the detection of chromium(VI) ions. Detailed Implementation

[0036] The present invention will be further described below with reference to the embodiments.

[0037] A series of chromium(VI) ion standard solutions (0.4, 0.8, 1.2, 1.6, 2.0, 10, 20, 40, 80, 120) were prepared, and 8 μL of each solution was added dropwise to prepared dry test strips. After reacting for 10 min, the color of the test strips was analyzed using the ColorDetector smartphone color reading application to obtain the R value. A colorimetric signal-concentration standard curve for chromium(VI) ion detection was established with chromium(VI) ion concentration as the x-axis and R value as the y-axis, yielding the linear equation y = -0.390x + 202(R). 2 =0.995).

[0038] Example 1

[0039] This example demonstrates the determination of hexavalent chromium in a tap water sample, including the following steps:

[0040] (1) Sample preparation: After centrifugation at 10,000 rpm for 10 min, the sample was filtered through a 0.22 μm membrane.

[0041] (2) Testing using the standard addition method:

[0042] Eight microliters of the treated experimental sample were placed on the test strip. After 10 minutes, a photo was taken using software on a smartphone. The photo taken by the smartphone was processed by the corresponding software, and the R1 value read by the software was recorded. Then, standard solutions with different Cr(VI) concentrations (0, 0.20, 2.00, 20.00 μM) were added to the sample. The detection procedure was the same as before the addition of the spike, and the R values ​​after the addition of the spike were recorded. The chromium ion concentration in Example 1 was calculated from the R values ​​before and after the addition of the spike, as shown in Table 1.

[0043] (3) Recovery rate and precision determination: When a 20.00 μM standard chromium ion solution was added to tap water, the chromium ion concentration calculated by the test strip combined with a smartphone was 20.72 μM, so the recovery rate was 101.8%, and the relative standard deviation of three repeated experiments was 3.87%. The chromium ion concentration, recovery rate and relative standard deviation detected in tap water with the addition of standard solutions of different Cr(VI) concentrations (0, 0.20, 2.00, 20.00 μM) are similar and can be found in Table 1.

[0044] Example 2

[0045] This example demonstrates the determination of hexavalent chromium in a river water sample, including the following steps:

[0046] Steps (1) and (2) are the same as in Example 1.

[0047] (3) Determination of recovery rate and precision

[0048] When a 20.00 μM standard chromium ion solution was added to the river water, the chromium ion concentration calculated by the test strip combined with a smartphone was 22.01 μM, resulting in a recovery rate of 103.6%. The relative standard deviation (RSD) of the three replicate experiments was 2.18%. The chromium ion concentrations, recoveries, and RSDs detected in the river water after adding standard solutions of different Cr(VI) concentrations (0, 0.20, 2.00, 20.00 μM) are similarly shown in Table 1.

[0049] Example 3

[0050] This embodiment illustrates the determination of hexavalent chromium in industrial wastewater samples, including the following steps:

[0051] Steps (1) and (2) are the same as in Example 1.

[0052] (3) Determination of recovery rate and precision

[0053] When a 20.00 μM standard chromium ion solution was added to industrial wastewater, the chromium ion concentration calculated by the test strip combined with a smartphone was 28.92 μM, resulting in a recovery rate of 102.9%. The relative standard deviation (RSD) of three repeated experiments was 2.57%. The chromium ion concentrations, recoveries, and RSDs detected in river water with the addition of standard solutions of different Cr(VI) concentrations (0, 0.20, 2.00, 20.00 μM) are similarly shown in Table 1.

[0054] Table 1. Experimental results of Examples 1-3

[0055]

[0056] The recovery rate results verify that the chromium(VI) ion detection reagent of the present invention is reliable.

[0057] The embodiments of the present invention are merely illustrative and are not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for detecting chromium (VI) ions based on oxide nanoszyme test strip, characterized by It comprises the following steps: (1) preparing a color developing test paper strip by formulating a chromium (VI) ion detection reagent, the reagent formula is: The buffer solution is an acetic acid-sodium acetate buffer solution; The color developing reagent is 3,3',5,5'-tetramethylbenzidine (TMB); The substrate solution is H2O2; The catalyst is Cu-CeO2 NPs; (2) dropping an appropriate amount of chromium (VI) ion detection reagent on filter paper, drying, and cooling to room temperature; (3) cutting the dried filter paper into round pieces and storing in vacuum; (4) preparing a series of standard chromium (VI) ion solutions as test reagents, respectively adding 8 microliters of test solution to the prepared test paper strip, after 10 minutes of reaction, under the support of the color reading application program ColorDetector of the smart phone, the color of the test paper strip is analyzed by RGB, taking the chromium (VI) ion concentration as the horizontal coordinate and the R value as the vertical coordinate, a signal standard curve for chromium (VI) ion detection is established; (5) treating the actual liquid sample to prepare a test reagent, repeating the operation in (4), obtaining the R value of the actual sample, and substituting it into the colorimetric signal standard curve for chromium (VI) ion detection to obtain the chromium (VI) ion concentration of the actual liquid sample.

2. A method for detecting chromium (VI) ions based on oxide nanoszyme test strips according to claim 1, characterized by, The specific formula of the chromium (VI) ion detection reagent for preparing the color developing test paper strip is:

3. A method of detecting chromium (VI) ions based on oxide nanoszyme test strip according to claim 1, characterized in that, The specific volume formula ratio of the chromium (VI) ion detection reagent is: Substrate solution: color developing reagent: buffer solution: catalyst = 1:1:1:

1.

4. The method of claim 1, wherein the oxide nanoszyme-based test strip for detecting chromium (VI) ions is characterized by, The preparation method of the catalyst Cu-CeO2 nanoparticles is: copper nitrate dihydrate and ammonia are respectively added to cerium nitrate hexahydrate solution under stirring, after stirring and ultrasonic treatment, the product is obtained by hydrothermal treatment at 180℃ for 6 hours, the product is centrifuged at 10,000 rpm for 10 minutes, and then washed with deionized water for three times, finally, the purified product is dried at 60℃ overnight, after the material is dried overnight, it is fully ground, ultrasonic treated for 3h, and dispersed into a 200 micrograms / milliliter solution for standby.

5. The method of claim 1, wherein the oxide nanoszyme-based test strip for detecting chromium (VI) ions is characterized by Prior to testing on actual liquid samples, centrifuge at 10,000 rpm for 10 min, filter with 0.22 pm membrane, and use ethylenediaminetetraacetic acid to eliminate interference of Fe 3+ .

6. The method of claim 1, wherein the oxide nanoszyme-based test strip for detecting chromium (VI) ions is characterized by The detection results are read by the color reading program of the smart phone, the color of the test paper strip is analyzed by RGB, and the concentration of chromium (VI) ion in the actual liquid sample is calculated by the obtained R value and the standard curve.

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