Method for detecting N < 3-> by using carboxylated multi-walled carbon nanotube functionalized screen-printed electrode

Abstract

The invention discloses an azide ion electrochemical sensor prepared on the basis of a carboxylated multi-walled carbon nanotube modified screen-printed electrode. The preparation method comprises the following steps: preparing 2mg / mL electrode modification liquid by taking carboxylated multi-walled carbon nanotubes as a modification material and acetic acid solvent, and dispensing 2mu L of electrode modification liquid on a working carbon electrode of a screen-printed electrode to prepare the N3 <-> electrochemical sensor. The concentration of azide ions in a solution is detected by utilizing an electrochemical analysis method, and the sensor has the advantages of easiness in preparation, portability, sensitivity, low price, small required detection amount and the like.

Description

[0001] Technical field: The present invention relates to the field of electrochemical detection technology in analytical chemistry, and in particular to a carboxylated multi-walled carbon nanotube functionalized screen-printed electrode for detecting N3 - method. Background Art

[0002] Electrochemical analysis has the advantages of high sensitivity, good real-time performance and portability, and has great advantages in the field of azide ion detection. Usually, electrochemical analysis is based on a three-electrode system, which is connected in an electrolytic cell to form a circuit to complete the detection. Some platinum and gold electrodes have low detection sensitivity for azide ions. Although highly boron-doped diamond (BDD electrode) and highly oriented pyrolytic graphite (HOPG) have high sensitivity, they are expensive and difficult to prepare. In addition, these electrodes need to undergo some complex pretreatments such as polishing before operation, and the cost is high. The system is complex and not easy to carry. Compared with traditional electrodes, screen-printed electrodes have the advantages of low cost, good stability, easy portability, small amount of detection solution required and simple operation.

[0003] Some blank screen-printed electrodes have poor electrochemical activity due to the preparation process or carbon paste, so the screen-printed electrodes are usually modified to improve their detection performance. The modification method of screen-printed electrodes is more convenient than that of traditional electrodes. At the same time, screen-printed electrodes are more suitable for trace detection, so they have great development prospects. In recent years, carboxylated multi-walled carbon nanotubes have been widely used as a nanomaterial in the study of modified electrodes. They have the advantages of good hydrophobicity, large surface area, many adsorption active sites, conductivity and good potential response. Combining them with screen-printed electrodes to prepare electrochemical sensors can achieve more stable and sensitive electrochemical sensors that can be used for ion detection in the production process. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the prior art and provide a carboxylated multi-walled carbon nanotube functionalized screen-printed electrode for detecting N3 - The method optimizes the detection conditions of the electrochemical sensor and utilizes electrochemical analysis to detect the concentration of azide ions in the solution. The detection method has the advantages of easy preparation, portability, sensitivity, low price, and small detection amount.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] One of the purposes of the present invention is to provide a method for preparing an electrode modification solution, the method comprising the following steps:

[0007] Step 1: Measure 1 mL of glacial acetic acid into a 2 mL threaded transparent sample bottle, use an analytical balance to weigh 2 mg of carboxylated multi-walled carbon nanotubes (MWCNTs-COOH), add to 1 mL of glacial acetic acid, cap and shake to disperse it in the solvent, then put it into a 100 W ultrasonic cleaning machine, time it for 20 minutes, ultrasonically mix it, take it out after the ultrasonic machine stops working, and store it at room temperature;

[0008] The second object of the present invention is to provide a method for functionalizing screen-printed electrodes with carboxylated multi-walled carbon nanotubes, the method comprising the following steps:

[0009] Step 1: Apply 1 μL of the modified solution droplet on the working carbon electrode of the pretreated screen-printed electrode, air-dry naturally until the solvent evaporates (about 2 hours or more), and use deionized water to wash the unmodified material on the electrode surface until the shape and current size of the cyclic voltammetry curve in the PBS buffer solution are similar. After drying completely at room temperature, it is used for testing;

[0010] The third object of the present invention is to provide the functional screen-printed electrode in detecting N3 - The electrode uses electrochemical detection mechanism to detect N3 - After electrochemical oxidation, an oxidation peak appears at the oxidation potential, that is, as N3 - With the increase of concentration, the oxidation peak response current is enhanced, thus achieving the - Detection.

[0011] Compared with the prior art, the present invention has the following advantages and effects:

[0012] 1. A method for detecting N3 provided by the present invention - The electrochemical sensor is sensitive to N3 - The detection is simple, fast and portable, which makes it have broad application prospects in defense, biology, medicine, environment and other fields. The electrochemical oxidation of azide ions on the screen-printed electrode is a diffusion-controlled process and is irreversible. The electrochemical sensor converts the concentration of azide ions into an electrical signal, with fast detection speed, high sensitivity and strong practicality.

[0013] 2. A carboxylated multi-walled carbon nanotube functionalized screen-printed electrode provided by the present invention for detecting N3 - The method contains N3 - The solution was electrochemically oxidized on the screen-printed electrode functionalized with carboxylated multi-walled carbon nanotubes, and N3 - The higher the concentration, the greater the electrochemical response current, thus achieving the - Quantitative detection of concentration, low detection limit and wide detection range, which greatly improves its use effect.

[0014] 3. A method for detecting N3 provided by the present invention - The electrochemical sensor has a simple preparation process, low cost, and good reproducibility, stability and selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram of the preparation process of the carboxylated multi-walled carbon nanotube functionalized screen-printed electrode provided in Example 1 of the present invention;

[0016] Figure 2 This is a scanning electron microscope image of the carboxylated multi-walled carbon nanotube functionalized screen-printed electrode provided in Example 1 of the present invention;

[0017] Figure 3 The carboxylated multi-walled carbon nanotube functionalized screen-printed electrode provided in Example 2 of the present invention detects N3 - Characterization diagram of electrochemical behavior;

[0018] Figure 4 The carboxylated multi-walled carbon nanotube functionalized screen-printed electrode provided in Example 2 of the present invention detects N3 at different scanning speeds - Cyclic voltammetry curve of

[0019] Figure 5 The carboxylated multi-walled carbon nanotube functionalized screen-printed electrode provided in Example 2 of the present invention detects N3 at different scanning speeds - The relationship between the response current and the scanning speed;

[0020] Figure 6 This is a diagram showing the optimization of the pH value of the base solution of the carboxylated multi-walled carbon nanotube functionalized screen-printed electrode provided in Example 2 of the present invention;

[0021] Figure 7 The carboxylated multi-walled carbon nanotube functionalized screen-printed electrode provided in Example 3 of the present invention detects different concentrations of N3 - Electrochemical response diagram of

[0022] Figure 8 The carboxylated multi-walled carbon nanotube functionalized screen-printed electrode provided in Example 3 of the present invention detects different concentrations of N3 - Fitting diagram of DPV oxidation peak response current and concentration change.

[0023] Fig. 9 This is a reproducibility graph of the carboxylated multi-walled carbon nanotube functionalized screen-printed electrode provided in Example 4 of the present invention;

[0024] Fig.10 This is a stability diagram of the carboxylated multi-walled carbon nanotube functionalized screen-printed electrode provided in Example 4 of the present invention;

[0025] Fig.11 A selectivity diagram of the carboxylated multi-walled carbon nanotube functionalized screen-printed electrode provided in Example 4 of the present invention; DETAILED DESCRIPTION

[0026] The present invention is implemented through the following embodiments, but the conditions and results described in the implementation do not limit the content and rights of the invention.

[0027] Example 1: Carboxylated multi-walled carbon nanotube functionalized screen-printed electrodes

[0028] 1. Preparation of carboxylated multi-walled carbon nanotube functionalized screen-printed electrodes

[0029] 1. Pretreatment of screen printed electrodes:

[0030] 100 μL of 0.1 M PBS (pH=7.5) was dripped onto the screen-printed electrode, and cyclic voltammetry scanning was performed (parameter settings: potential scanning range of -0.5 V to 1.5 V, scanning rate of 100 mV / s, scanning segment number of 40 segments), and then naturally air-dried after scanning.

[0031] 2. Preparation of carboxylated multi-walled carbon nanotube modification solution:

[0032] Measure 1 mL of glacial acetic acid into a 2 mL threaded transparent sample bottle, use an analytical balance to weigh 2 mg of carboxylated multi-walled carbon nanotubes (MWCNTs-COOH), add it to 1 mL of glacial acetic acid, seal the bottle, and shake to disperse it in the solvent. Then put it into a 100 W ultrasonic cleaning machine, set the timer for 20 minutes, and mix it with ultrasound. After the ultrasound machine stops working, take it out and store it at room temperature.

[0033] 3. Preparation of carboxylated multi-walled carbon nanotube functionalized screen-printed electrodes:

[0034] The working electrode was modified by drop coating method. 1 μL of modification liquid was drop coated on the working carbon electrode of the pretreated screen-printed electrode, and naturally air-dried until the solvent evaporated (about 2 h or more). Deionized water was used to wash the unmodified material on the electrode surface until the shape and current size of the cyclic voltammetry curve in PBS buffer solution were similar. After completely drying at room temperature, it was used for testing.

[0035] The preparation process of carboxylated multi-walled carbon nanotube functionalized screen-printed electrodes is as follows: Figure 1 shown.

[0036] 2. Morphological Characterization of Carboxylated Multi-walled Carbon Nanotube Functionalized Screen-printed Electrodes

[0037] 1. Characterization by scanning electron microscopy (SEM), such as Figure 2As shown, it can be found that compared with the unmodified screen-printed electrode, the surface roughness of the electrode modified with carboxylated carbon nanotubes has a slight change, indicating that the nanomaterial has been modified to the surface of the working electrode, and there are obvious cracks on the surface of the modified electrode, which has a larger specific surface area.

[0038] Example 2: Carboxylated multi-walled carbon nanotube functionalized screen-printed electrodes in N3 - Electrochemical characterization in solution

[0039] Take the carboxylated multi-walled carbon nanotube functionalized screen-printed electrode prepared in Example 1, and drop 100 μL of 10 mM N3 - pH 7.5 PBS buffer solution without N3 - The cyclic voltammetry curves were characterized by using a pH 7.5 PBS buffer solution. Figure 3 As shown in the figure, it can be seen that a very obvious oxidation peak appears, but no reduction peak appears, indicating that the electrochemical reaction is irreversible. In addition, the MWCNTs-COOH / SPE at different scan rates was tested at pH 7.5 containing 1mmol / L N3 - The cyclic voltammetry curves in PBS buffer solution show that with the increase of the scan rate (20, 40, 60, 80, 100 mV / s from bottom to top), the oxidation peak current also increases, and the oxidation peak potential shifts positively, such as Figure 4 As shown. Figure 4 Provide data to plot the relationship between oxidation peak current and scan rate, such as Figure 5 As shown, it can be seen that in the scan rate range of 20 to 100 mV / s, the oxidation peak current is linearly correlated with the square root of the scan rate, and the correlation coefficient is above 0.99, and the linear relationship is good. This indicates that the electrochemical oxidation of azide ions on the screen-printed electrode is a diffusion-controlled process.

[0040] N3 - It has different stabilities at different pH values, and the pH of the working environment of the electrochemical sensor in the future application also has a certain range. In order to make the sensor achieve the best detection state of azide ions, the pH value of the test environment is optimized. The electrochemical response of the MWCNTs-COOH / SPE electrode to azide ions in the range of different pH values ​​of 6 to 11 is tested. Figure 6As shown in the figure, the activity of the modified electrode shows a trend of increasing first and then decreasing with the increase of pH value. Between pH 6 and 7.5, the oxidation peak response current increases with the increase of pH value; in the pH range of 7.5 to 11, the oxidation peak response current decreases with the increase of pH value. Therefore, it can be seen that when the pH value is 7.5, the performance of MWCNTs-COOH / SPE electrode in testing azide ions is the best. This phenomenon of increasing first and then decreasing may be due to the fact that azide is easy to exist in the form of protons in a low pH environment and is difficult to oxidize. In a strong alkaline environment, the decrease in response current may be due to the competition between hydroxide ions and azide ions, resulting in detection interference.

[0041] Example 3: Carboxylated multi-walled carbon nanotube functionalized screen-printed electrodes at different concentrations of N3 - Response current in solution

[0042] The carboxylated multi-walled carbon nanotube functionalized screen-printed electrode prepared in Example 1 and the optimal detection pH value of 7.5 in Example 2 were tested for 5×10 -5 ~1×10 -3 The DPV current response curve of the electrochemical sensor within the mol / L azide ion concentration range is as follows: Figure 7 As shown. The relationship between the sensor response current and the azide ion concentration is obtained by data fitting, as shown in Figure 8 As shown, the linear relationship is: y = 0.01283x + 4.8119, the correlation coefficient R 2 =0.9927, sensitivity is 12.83μA / mM. According to the detection limit calculation formula LOD=3σ / S (where σ is the relative standard deviation of the blank sample response 0.0446; S is the sensitivity), the detection limit of the electrochemical sensor for azide ions is calculated to be 10.4μM.

[0043] Example 4: Detection of N3 by carboxylated multi-walled carbon nanotube functionalized screen-printed electrodes - Performance evaluation

[0044] The carboxylated multi-walled carbon nanotube functionalized screen-printed electrode prepared in Example 1 and the optimal detection pH value of 7.5 in Example 2 were used to test the reproducibility, stability and selectivity of the electrochemical sensor.

[0045] To evaluate the reproducibility of the screen-printed electrodes after functionalization, 1 mmol / L N3 - As a unified detection concentration, the current response of 8 screen-printed electrodes purchased from the same batch after being modified with the same material was tested. The test results are as follows: Fig. 9As shown, the oxidation peak currents of the 8 electrodes tested were all around 18.7 μA, and the calculated result of the relative deviation of the 8 groups of response currents tested was 3.3%. The human error of the same batch was within an acceptable range, which shows that the functionalized screen-printed electrode electrochemical sensor has good reproducibility.

[0046] To evaluate N3 - To test the stability of the electrochemical sensor, the four prepared electrodes were placed in a sealed bag and stored in a refrigerator at 4°C. One electrode was taken out every 2 days and the performance of the taken electrodes was tested. The test solution was also 1mmol / L N3 - The stability was evaluated by testing the oxidation peak response current signal of the electrochemical sensor stored for 2 days, 4 days, 6 days, and 8 days in a pH 7.5 phosphate buffer solution. The test results are shown in Fig.10 As shown in the figure, it can be seen that N3 - The electrochemical sensor was stored in a refrigerator at 4°C for 8 days, and its response current to azide ions did not change significantly, and the relative standard deviation was within 10%, which shows that N3 - Electrochemical sensors have good long-term storage capabilities.

[0047] Verify the effect of fluoride, chloride, nitrate and phosphate anions on N3 - Interference of electrochemical sensor detection. 1mM N3 was tested at pH 7.5. - 10 mM F - , 10 mM Cl - 、10mM NO3 - The current response when 0.1M PBS coexists, and the selectivity test results of the electrochemical sensor are shown in Fig.11 As shown. According to the data in the figure, it can be seen that after adding excessive interfering ions, the sensor's detection response to azide ions has no obvious change. The relative standard deviation of the four groups is calculated to be 3.9%, which is within the acceptable range. In addition, when only interfering ions exist in the detection solution and no azide ions are added, the electrochemical sensor performs cyclic voltammetry scanning on it and no oxidation peak appears. The baseline background current generated is also very different from the response current when azide ions are detected. This shows that the presence of fluoride ions, chloride ions and nitrate ions basically do not interfere with the detection of azide ions and can be ignored.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A carboxylated multi-walled carbon nanotube functionalized screen-printed electrode for detecting N3 - The method is characterized in that The following steps are involved: Step 1, preparation of carboxylated multi-walled carbon nanotube modification solution: Measure 1 mL of glacial acetic acid into a 2 mL threaded transparent sample bottle, use an analytical balance to weigh 2 mg of carboxylated multi-walled carbon nanotubes (MWCNTs-COOH), add to 1 mL of glacial acetic acid, cap and shake to disperse in the solvent, then put into a 100 W ultrasonic cleaning machine, time for 20 min, ultrasonically mix, take out after the ultrasonic machine stops working, and store at room temperature; Step 2. Preparation of carboxylated multi-walled carbon nanotube functionalized screen-printed electrodes: Take 2 μL of the modification solution obtained in step 1 and drop it on the working carbon electrode of the pretreated screen-printed electrode. Let it air-dry naturally until the solvent evaporates (about 2 hours or more). Use deionized water to wash the unmodified material on the electrode surface until its cyclic voltammetry curve shape and current size in PBS buffer solution are similar. After completely drying at room temperature, apply it to the test. Step 3: Performance test of carboxylated multi-walled carbon nanotube functionalized screen-printed electrodes: The electrodes prepared in step 2 were used to prepare N3 - The solution was characterized by cyclic voltammetry to analyze its electrochemical behavior and determine the N3 - Optimal detection conditions; detection of different concentrations of N3 by differential pulse voltammetry (DPV) - , establish the standard curve equation.

2. The carboxylated multi-walled carbon nanotube functionalized screen-printed electrode according to claim 1 is prepared in the presence of N3 - Electrochemical behavior in solution, characterized by: Add 100 μL of 10 mM N3 - pH 7.5 PBS buffer solution without N3 - The cyclic voltammetry curves were characterized in pH 7.5 PBS buffer solution to observe the redox peak state; the MWCNTs-COOH / SPE at different scan rates was tested in pH 7.5 containing 1mmol / L N3 - The cyclic voltammetry curves in PBS buffer solution were fitted with the square root relationship between the oxidation peak current and the scan rate to analyze the N3 - Oxidation process at the electrode.

3. The carboxylated multi-walled carbon nanotube functionalized screen-printed electrode according to claim 1 is prepared in the presence of N3 - The detection conditions in solution are optimized, characterized in that: The electrochemical response of MWCNTs-COOH / SPE to azide ions was tested in the pH range of 6 to 11, and the optimal detection conditions were determined by the trend change of the peak current affected by pH value.

4. The performance evaluation of the carboxylated multi-walled carbon nanotube functionalized screen-printed electrode for detecting N3 according to claim 1, characterized in that: The response currents of 8 groups of the same electrodes were tested, and the relative standard deviations of the 8 groups of data were calculated to evaluate the reproducibility of the functionalized electrodes. The four prepared electrodes were placed in a sealed bag and stored in a refrigerator at 4°C. One electrode was taken out every 2 days, and the performance of the taken electrodes was tested. The relative standard deviations of the response currents of the 5 groups were calculated to evaluate the stability of the functionalized electrodes. The reproducibility of the functionalized electrodes in the presence of fluoride, chloride, nitrate and phosphate anions was verified. - Interference detected by electrochemical sensors, comparing the response current, to determine whether the presence of fluoride ions, chloride ions and nitrate ions interferes with the detection of azide ions.

5. A carboxylated multi-walled carbon nanotube functionalized screen-printed electrode as claimed in claim 1 for detecting N3 - The application is characterized by: Test 5×10 -5 ~1×10 -3 DPV current response curve of the electrochemical sensor in the range of mol / L azide ion concentration. - The relationship between concentration and oxidation peak response current was fitted to obtain the standard curve equation and calculate N3 - Detection limit.

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