Preparation method and application of a nitrite electrochemical sensor based on polydopamine nanosphere composite material

Abstract

The application discloses a preparation method and application of a nitrite electrochemical sensor based on a polydopamine nanosphere composite material, and belongs to the fields of functional nanocomposite materials and sensing technologies. The prepared polydopamine nanospheres are ultrasonically treated in a hexadecyltrimethylammonium bromide solution, a polydopamine nanosphere / hexadecyltrimethylammonium bromide composite is obtained through electrostatic action, and the composite is drop-coated on a clean electrode surface, and is dried at room temperature to obtain an electrochemical sensor, which can be applied to the detection of nitrite in cured meat. The nanomaterial composite material is simple to prepare and low in cost, and the prepared nitrite electrochemical sensor has high sensitivity, a low detection limit, a wide detection range, a fast detection speed and good reproducibility.

Description

Technical Field

[0001] This invention belongs to the field of functional nanocomposite materials and electrochemical sensing and analysis technology, specifically relating to a method for preparing and applying a nitrite electrochemical sensor based on polydopamine nanosphere composite materials. Background Technology

[0002] Nitrites resemble table salt in appearance and taste. Appropriate addition of nitrites to food can enhance color and flavor, and is widely used in the processing of cured meats, bacon, and pickles. However, excessive addition can cause serious safety problems, leading to nitrite poisoning. Nitrite poisoning causes severe tissue hypoxia in humans, resulting in shock, cyanosis, and death if not treated promptly. Infants and young children are extremely sensitive to nitrites; ingestion can cause hypoxia, cyanosis, and other symptoms, and in severe cases, even death. According to China's National Food Safety Standard (GB2760-2014), the residual amount of nitrite in cured meat products must not exceed 30 mg / kg. An adult ingesting 0.2-0.5g can cause poisoning, and 3g can be fatal. Therefore, quantitative detection of nitrites is of great significance in food analysis.

[0003] Currently, most technologies for detecting nitrite in cured meat products employ laboratory-based analytical methods such as chromatography, spectrophotometry, and capillary electrophoresis. These methods involve complex and time-consuming sample pretreatment processes, require professional technicians, and are costly. Summary of the Invention

[0004] To address the aforementioned problems, the purpose of this invention is to propose a method for preparing a nitrite electrochemical sensor based on polydopamine nanosphere composite materials and its application.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0006] A method for preparing a nitrite electrochemical sensor based on polydopamine nanosphere composite material involves first preparing polydopamine nanospheres, then combining the polydopamine nanospheres with hexadecyltrimethylammonium bromide to prepare a polydopamine nanosphere composite material, and finally modifying the polydopamine nanosphere composite material dispersion onto an electrode. The polydopamine nanospheres in the composite material are negatively charged nanospheres with a Zata potential of -22 mV and a diameter of 200-300 nm. The specific steps include:

[0007] Step 1: Dopamine hydrochloride was added to Tris buffer, followed by isopropanol. The mixture was magnetically stirred under light-shielded conditions to obtain polydopamine nanospheres. The concentration of dopamine hydrochloride in the Tris buffer was 1 mg / mL; the volume ratio of isopropanol to Tris buffer was 4:10. The stirring speed was 600 rpm for 72 hours. The resulting polydopamine nanospheres had a Zata potential of approximately -22 mV and a diameter of approximately 250 nm.

[0008] Step 2: Add polydopamine nanospheres to an aqueous solution of hexadecyltrimethylammonium bromide. Using ultrasound, the cationic surfactant hexadecyltrimethylammonium bromide is electrostatically adsorbed onto the negatively charged polydopamine nanospheres, resulting in a polydopamine nanosphere / hexadecyltrimethylammonium bromide composite dispersion.

[0009] Preferably, the sonication time is 30 minutes, the concentration of polydopamine nanospheres in the solution is 1.0 mg / mL, and the concentration of hexadecyltrimethylammonium bromide aqueous solution is 0.25 mg / mL.

[0010] Step 3: The composite dispersion of polydopamine nanospheres / hexadecyltrimethylammonium bromide is applied to the surface of a glassy carbon electrode by drop casting.

[0011] Preferably, the amount of the polydopamine nanospheres / cetyltrimethylammonium bromide composite dispersion used for drop casting is 0.5–0.7 μL / mm. 2 .

[0012] This invention also provides an application of an electrochemical sensor for nitrite based on polydopamine nanosphere composite materials. The electrochemical sensor is used as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum wire electrode as the counter electrode, forming a three-electrode system for the electrochemical detection of nitrite. The electrochemical detection uses the concentration-oxidation peak current standard curve method to calculate the nitrite concentration of the sample solution. Specifically, the following steps are included:

[0013] (a): A three-electrode working system was constructed by using a polydopamine nanosphere composite material-based nitrite electrochemical sensor as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum wire electrode as the counter electrode.

[0014] (b): The three-electrode working system was immersed in the prepared supporting electrolyte of nitrite at different concentrations, and electrochemical detection was performed to obtain the electrochemical oxidation signal of nitrite and to plot the concentration-oxidation peak current standard curve.

[0015] (c): The three-electrode working system is immersed in the actual sample solution to be tested and electrochemical detection is performed. The concentration of nitrite in the sample solution to be tested is calculated based on the plotted concentration-oxidation peak current standard curve.

[0016] As a preferred method, the electrolyte in the electrochemical detection system is a 0.1 mol / L pH 4.0 phosphate buffer solution, the electrochemical detection adopts the differential pulse voltammetry method, the potential window is 0.5V-1.1V, the enrichment potential is 0.3V, and the enrichment time is 30 seconds.

[0017] The beneficial effects of this invention are as follows: This invention introduces a polydopamine nanosphere / hexadecyltrimethylammonium bromide composite material with good stability and signal amplification into the construction of a nitrite sensor. Combined with the advantages of electrochemical analysis technology, such as high sensitivity, low detection cost, and ease of use, ultrasensitive detection of nitrite is achieved. The nitrite electrochemical sensor prepared by this invention has a wide detection range, fast detection speed, and good reproducibility. The detection limit of the electrochemical sensor constructed by this invention for nitrite is 0.08 μM, which can successfully detect the nitrite content in actual samples and is expected to be applied in the field of food testing. Attached Figure Description

[0018] Figure 1 Scanning electron microscope (SEM) image (A) and transmission electron microscope (TEM) image (B) of polydopamine nanospheres;

[0019] Figure 2 Differential pulse curves of different electrodes (bare glassy carbon electrode a, polydopamine nanosphere modified electrode b, and polydopamine nanosphere / hexadecyltrimethylammonium bromide composite modified electrode c) in phosphate buffer solution containing 0.2 mmol / L sodium nitrite (0.1 mol / L pH 4.0);

[0020] Figure 3 Differential pulse voltammetry curves and magnified views of the low-concentration region of the polydopamine nanosphere / hexadecyltrimethylammonium bromide composite modified electrode in phosphate buffer solutions containing sodium nitrite at different concentrations;

[0021] Figure 4 The graph shows the linear relationship between sodium nitrite concentration and oxidation peak current. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] In this invention, all water used in the experiments was deionized water, all reagents used in the experiments were analytical grade, and all experiments were conducted at room temperature.

[0024] The application principle of the present invention will be described in detail below with reference to the accompanying drawings.

[0025] Example 1

[0026] Fabrication of a nitrite electrochemical sensor based on polydopamine nanosphere composite material

[0027] Preparation and characterization of A1 polydopamine nanospheres

[0028] Accurately weigh 100 mg of dopamine hydrochloride, add 100 mL of Tris buffer and 40 mL of isopropanol, and stir magnetically for 72 hours under light protection. After the reaction is complete, remove the material and centrifuge. Wash three times each with ethanol and deionized water, and then dry at 60 °C for 6 hours to obtain polydopamine nanospheres.

[0029] The morphology of the prepared polydopamine nanospheres was characterized, such as... Figure 1 As shown in scanning electron microscopy (SEM) image (A) and transmission electron microscopy (TEM) image (B), the polydopamine nanospheres are spheres with a diameter of approximately 250 nm. The zeta potential of the prepared polydopamine nanospheres was measured to be -22 mV.

[0030] Preparation of A2 polydopamine nanospheres / hexadecyltrimethylammonium bromide composite material

[0031] 1.0 mg of polydopamine nanospheres were added to 1 mL of a 0.25 mg / mL hexadecyltrimethylammonium bromide aqueous solution and sonicated for 30 minutes to obtain a polydopamine nanosphere / hexadecyltrimethylammonium bromide composite solution.

[0032] Preparation of A3 nitrite electrochemical sensor

[0033] A glassy carbon electrode with a diameter of 3 mm was polished with Al2O3 polishing powders of 0.3 μm and 0.05 μm. The polished electrode was then ultrasonically washed with anhydrous ethanol and ultrapure water to obtain a smooth electrode surface, and then naturally dried at room temperature for later use.

[0034] Preparation of an electrochemical sensor based on an electrode modified with polydopamine nanospheres: 1.0 mg of polydopamine nanospheres prepared in step A1 were added to 1 mL of aqueous solution and sonicated for 30 minutes to obtain a polydopamine nanosphere solution. 4 μL of the polydopamine nanosphere solution was transferred by pipette and dropped onto the electrode surface. The solution was then allowed to air dry at room temperature to obtain an electrochemical sensor based on an electrode modified with polydopamine nanospheres. The sensor was stored at 4 °C for later use.

[0035] Preparation of an electrochemical sensor based on a polydopamine nanosphere / hexadecyltrimethylammonium bromide composite modified electrode: 4 μL of the polydopamine nanosphere / hexadecyltrimethylammonium bromide composite solution prepared in step A2 was pipetted onto the electrode surface and allowed to air dry at room temperature to obtain the electrochemical sensor based on the polydopamine nanosphere / hexadecyltrimethylammonium bromide composite modified electrode, which was stored at 4℃ for later use.

[0036] Example 2

[0037] Nitrite concentration detection test

[0038] B1 testing method

[0039] The electrochemical detection system for nitrite employs a classic three-electrode system: a working electrode, a reference electrode, and a counter electrode. The working electrode is the modified electrode prepared in step A3, the counter electrode is a platinum wire electrode, and the reference electrode is a saturated calomel electrode. The assay solution is 20 mL of 0.1 mol / L phosphate buffer solution (pH 4.0). The method used is electrochemical differential pulse voltammetry, with a scan range of 0.5 V to 1.1 V, a pulse amplitude of 50 mV, and a pulse width of 50 ms.

[0040] B2 Electrochemical signals of nitrite were tested using different electrodes.

[0041] The electrochemical signals of nitrite were tested using the polydopamine nanosphere modified electrode and the polydopamine nanosphere / hexadecyltrimethylammonium bromide composite modified electrode prepared in step A3, as well as the bare glassy carbon electrode. Figure 2 Differential pulse curves of different electrodes (bare glassy carbon electrode a, polydopamine nanosphere modified electrode b, and polydopamine nanosphere / hexadecyltrimethylammonium bromide composite modified electrode c) in phosphate buffer solution (0.1 mol / L pH 4.0) containing 0.2 mmol / L sodium nitrite. Figure 2 As can be seen, the oxidation peak current value of curve a is 1.83 μA, that of curve b is 4.84 μA, and that of curve c is 10.12 μA. Curve c shows a significant increase in oxidation peak current value compared to curves a and b, which may be attributed to the synergistic effect between polydopamine nanospheres and hexadecyltrimethylammonium bromide in the polydopamine nanosphere / hexadecyltrimethylammonium bromide composite modified electrode. The polydopamine nanosphere / hexadecyltrimethylammonium bromide composite modified electrode can significantly improve the sensitivity of sodium nitrite detection.

[0042] B3. Plot the standard concentration working curve.

[0043] First, the polydopamine nanosphere / hexadecyltrimethylammonium bromide composite modified electrode prepared in step A3 of Example 1 was immersed in 20 mL of phosphate buffer solution (0.1 mol / L pH 4.0) containing different concentrations of nitrite. After enrichment at 0.3 V for 30 seconds and equilibration for 10 seconds, differential pulse voltammetry was used to detect and analyze the nitrite. The nitrite was oxidized on the modified electrode, and the peak current value of the oxidation peak increased with increasing nitrite concentration. Figure 3 Then, based on the obtained data, construct a relational expression, such as... Figure 4 As shown, within the range of 0.2 μmol / L to 2000 μmol / L, there are two linear relationships between the concentration of nitrite and the oxidation peak current. Specifically, within the range of 0.2 μmol / L to 200 μmol / L, the linear relationship between the concentration of nitrite and the oxidation peak current is given by the equation Ipa(μA) = 0.0511c(μmol / L) + 0.0159(R). 2 =0.997), and within the range of 200 μmol / L to 2000 μmol / L, there is a linear relationship between the concentration of nitrite and the oxidation peak current, with the linear equation being Ipa(μA) = 0.0511c(μmol / L) + 0.0159(R). 2 =0.998). Based on a signal-to-noise ratio of 3, the detection limit can be calculated to be 0.08 μmol / L. This demonstrates that the sensor manufactured using this method exhibits good stability and a low detection limit for nitrite detection.

[0044] B4 Actual Sample Detection

[0045] Eight types of cured meat samples were used as actual samples. The cured meat samples were minced using a meat grinder, and 10.0g of the sample homogenate was accurately weighed and added to 300mL of water. The mixture was ultrasonically extracted for 30 minutes, with shaking every 5 minutes to ensure complete dispersion of the solid phase. The sample solution was then heated in a 75℃ water bath for 15 minutes. The sample solution was then cooled to room temperature and centrifuged for 15 minutes at 10000 rpm. After centrifugation, the supernatant was collected, filtered through a disposable microporous membrane using a water-based needle, and purified using a C18 column to obtain the sample extract. A specific volume of the prepared sample solution was aspirated and added to an electrolytic cell. The electrochemical differential pulse voltammetry method described in step B1 was used to detect the nitrite content in the actual sample solution, with three repeated measurements for each sample. The concentration of nitrite in the test solution could be calculated from the response peak current obtained in step B3 based on the standard curve. The results showed that the nitrite content (calculated as NaNO2) in the tested cured meat products was below the maximum residue limit of 30 mg / kg stipulated by the national standard. Simultaneously, the accuracy of the spiked recovery method was verified, and the results showed that the recovery rate of nitrite in the eight actual samples ranged from 98.1% to 104.0%. This indicates that the method has good accuracy and can be used for nitrite analysis in cured meat samples.

[0046] Table 1. Detection of nitrite in actual samples

[0047]

[0048] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a nitrite electrochemical sensor based on polydopamine nanosphere composite material, characterized in that, The polydopamine nanospheres are prepared first, and then the polydopamine nanospheres are compounded with cetyltrimethylammonium bromide to prepare polydopamine nanosphere composite materials, and the polydopamine nanosphere composite materials are modified to the surface of an electrode to prepare a nitrite electrochemical sensor.

2. The method for preparing a polydopamine nanosphere composite-based nitrite electrochemical sensor according to claim 1, characterized in that, The polydopamine nanospheres are negatively charged nanospheres with a Zata potential of -22 mV and a diameter of 200-300 nm.

3. The method for preparing a polydopamine nanosphere composite-based nitrite electrochemical sensor according to claim 1, characterized in that, The method comprises the following steps: Step one: dopamine hydrochloride is added to Tris buffer, isopropanol is added, and polydopamine nanospheres are obtained by magnetic stirring in the dark; Step two: the polydopamine nanospheres are added to a cetyltrimethylammonium bromide aqueous solution, and cetyltrimethylammonium bromide is electrostatically adsorbed onto the surface of the negatively charged polydopamine nanospheres by ultrasonic treatment to obtain a polydopamine nanosphere / cetyltrimethylammonium bromide composite material dispersion; Step three: the polydopamine nanosphere / cetyltrimethylammonium bromide composite material dispersion is modified to the surface of a glassy carbon electrode by drop coating.

4. The method for preparing a polydopamine nanosphere composite-based nitrite electrochemical sensor according to claim 3, characterized in that, The concentration of dopamine hydrochloride in Tris buffer in step one is 1 mg / mL; the volume ratio of isopropanol to Tris buffer is 4:10; and the stirring speed is 600 r / min for 72 hours.

5. The method for preparing a polydopamine nanosphere composite-based nitrite electrochemical sensor according to claim 3, characterized in that, The concentration of polydopamine nanospheres in the solution in step two is 1.0 mg / ml, and the concentration of the cetyltrimethylammonium bromide aqueous solution is 0.25 mg / ml.

6. The method for preparing a polydopamine nanosphere composite-based nitrite electrochemical sensor according to claim 3, characterized in that, The amount of the polydopamine nanosphere / CTAB composite dispersion liquid droplet coating in step three is 0.5-0.7 μL / mm 2 .

7. Use of a polydopamine nanosphere composite-based nitrite electrochemical sensor, characterized in that, The polydopamine nanosphere composite material-based nitrite electrochemical sensor of any one of claims 1-6 is used as a working electrode, a saturated calomel electrode is used as a reference electrode, and a platinum wire electrode is used as a counter electrode to construct a three-electrode working system, and the system is used in the electrochemical detection of nitrite.

8. Use of a polydopamine nanosphere composite-based nitrite electrochemical sensor according to claim 7, characterized in that, The electrochemical detection is performed by using a concentration-oxidation peak current standard curve method to calculate the concentration of nitrite in a sample solution to be detected.

9. Use of a polydopamine nanosphere composite-based nitrite electrochemical sensor according to claim 7, characterized in that, The electrolyte used in the electrochemical detection is a 0.1 mol / L pH 4.0 phosphate buffer solution.

10. Use of a polydopamine nanosphere composite-based nitrite electrochemical sensor according to claim 7, characterized in that, The electrochemical detection method is differential pulse voltammetry, and the potential window is 0.5 V-1.1 V. The enrichment potential is 0.3 V, and the enrichment time is 30 seconds.

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