A disposable electrochemical nitrite sensor

Abstract

The present invention provides a disposable nitrite electrochemical sensor, which is prepared by the following steps: Step 1, prepare a tea extract; Step 2, add a certain amount of AgNO3 to the tea extract prepared in Step 1, and perform ultrasonic oscillation to obtain a silver nanoparticle solution containing AgNPs; Step 3, bond a pencil lead to a copper wire, slowly insert it into the tip of a plastic pipette gun, seal both ends of the tip, and then cut the pencil lead into an appropriate length to obtain a pencil lead electrode; Step 4, place the pencil lead electrode in the silver nanoparticle solution prepared in Step 2, and perform electro-polymerization under certain conditions to obtain a pencil lead electrode modified with polytea polyphenol-silver nanoparticles, that is, a disposable nitrite electrochemical sensor.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical sensors, and particularly to a disposable nitrite electrochemical sensor. Background Art

[0002] Nitrite is a common color developer and preservative in meat products. It can not only make the color of meat more vivid but also inhibit the production of botulinum toxin. However, excessive intake of nitrite can cause methemoglobinemia and gastric cancer. Therefore, it is crucial to monitor whether the added amount of nitrite in food exceeds the standard for ensuring human health, and it is necessary to accurately and rapidly detect nitrite in food samples.

[0003] In recent years, some methods for the determination of nitrite have been proposed. In particular, electrochemical sensing methods have attracted much attention due to their advantages such as simple operation, high sensitivity, and fast response speed. In order to obtain better convenience and lower cost, it is necessary to develop a disposable nitrite sensor.

[0004] Silver nanoparticles (AgNPs) have good electrical conductivity, a large specific surface area, and strong electrocatalytic activity, and are an ideal sensing material. However, most of the reported AgNPs are synthesized by chemical methods, which not only easily cause environmental pollution but also result in poor biocompatibility of AgNPs. At the same time, pencil graphite electrode (PGE) materials are easily available, low-cost, and have a simple preparation method, and are an ideal substrate electrode. Therefore, developing a green synthesis method for AgNPs and fixing them on the surface of PGE by a simple and controllable method is crucial for the manufacture of disposable nitrite sensors. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a disposable nitrite electrochemical sensor. AgNO₃ is reduced by tea extract 3 to prepare a silver nanoparticle solution containing AgNPs, and the fixation of AgNPs on the electrode surface is achieved by co-electropolymerization to obtain a pencil graphite electrode modified with polytea polyphenols-silver nanoparticles. A disposable nitrite electrochemical sensor is prepared therefrom. This electrochemical sensor has high sensitivity and is convenient for detection.

[0006] The present invention is implemented as follows:

[0007] The present invention provides a disposable nitrite electrochemical sensor, and the nitrite electrochemical sensor is prepared by the following steps:

[0008] Step 1, prepare tea extract;

[0009] Step 2, add a certain amount of AgNO₃ 3It is added to the tea extract obtained in Step 1, and ultrasonic oscillation is carried out to obtain a silver nanosol containing AgNPs;

[0010] Step 3: Glue the pencil lead to the copper wire, slowly insert it into the plastic pipette tip, seal both ends of the tip, and then cut the pencil lead into an appropriate length to obtain a pencil lead electrode;

[0011] Step 4: Place the pencil lead electrode into the silver nanosol prepared in Step 2, and carry out electro-polymerization under certain conditions to obtain a pencil lead electrode modified with polytea polyphenols-silver nanoparticles, denoted as PTP-AgNPs / PGE, that is, a disposable nitrite electrochemical sensor.

[0012] The sensitive material AgNPs is synthesized from tea extract, and the preparation process is green and environmentally friendly, with the advantages of pollution-free, low cost, simple operation, and less time-consuming. The co-electro-polymerization of AgNPs and PTP makes the electrode surface loose and porous, which is beneficial to increasing the effective area of the electrode, improving the enrichment of nitrite on the electrode surface, and enhancing the sensitivity of the nitrite sensor.

[0013] AgNPs material has good electrical conductivity and can provide a larger surface area for NO 2 - enrichment, ensuring a higher electron transfer rate between NO 2 - and the sensor. In addition, PTP is an oligomer and can also improve the electrocatalytic ability.

[0014] Furthermore, the steps for the nitrite electrochemical sensor to detect nitrite are as follows:

[0015] Using a saturated calomel electrode as the reference electrode, a platinum wire electrode as the counter electrode, and the nitrite electrochemical sensor as the working electrode, a three-electrode system is constructed, and differential pulse voltammetry is used for detection.

[0016] Furthermore, Step 1 is specifically to heat tea in ultrapure water to boiling, filter and then centrifuge, and the supernatant is the tea extract.

[0017] Furthermore, the specific conditions for electro-polymerization in Step 4 are: using cyclic voltammetry, the potential range is -0.8V - 1.8V, the scanning rate is 50mV / s, and the number of polymerization cycles is 5.

[0018] Furthermore, the detection bottom solution used for detecting nitrite is a phosphate buffer solution with 0.1M pH = 4.0, containing 2mM nitrite.

[0019] Furthermore, the potential range for detection is 0.2V to 1.3V.

[0020] The present invention has the following beneficial effects:

[0021] 1. The present invention uses electrochemical polymerization to co-electropolymerize a tea polyphenol-silver nanoparticle composite film on the surface of a pencil core electrode to prepare a nitrite electrochemical sensor (PTP-AgNPs / PGE). The surface of PTP-AgNPs / PGE is uneven, the specific surface area of the electrode is relatively large, the electron transfer rate is increased, and it has a catalytic effect on the reaction of nitrite occurring on the electrode surface.

[0022] 2. The sensitive material AgNPs in the present invention is green synthesized from tea extract, which conforms to the concept of ecological environmental protection and sustainable development.

[0023] 3. The nitrite sensor prepared by the present invention has the advantages of a wide linear range (0.02 - 1160 μM), high sensitivity (50 nA / μM in the concentration range of 0.02 - 860 μM; 140 nA / μM in the concentration range of 860 - 1160 μM), low detection limit (4 nM), short response time (about 2 s), good reproducibility, and good anti-interference ability. Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 SEM images of the pencil core electrode (A), PTP / PGE (B), and PTP-AgNPs / PGE (C) in Example 1 of the present invention;

[0026] Figure 2 Differential pulse voltammograms of different electrodes in Example 2 of the present invention;

[0027] Figure 3 For different concentrations of AgNO 3 solution, different polymerization cycles, and different pH values on the oxidation peak current of NO 2 - ;

[0028] Figure 4 Detection result graph in Example 4 of the present invention;

[0029] Figure 5 Reproducibility detection graph of the nitrite sensor in Example 4 of the present invention;

[0030] Figure 6Results of the selective evaluation of the sensor in Example 5 of the present invention;

[0031] Figure 7 Results of the detection of nitrite in food samples by the sensor in Example 6 of the present invention. Detailed implementation manners

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] Example 1

[0034] In this example, a disposable nitrite electrochemical sensor was prepared, and the preparation steps are as follows:

[0035] Step 1: Prepare tea extract. Heat 5 g of Enshi selenium tea in 50 mL of ultrapure water until boiling and filter. Then centrifuge the filtrate at 10,000 rpm for 5 min, and filter the supernatant with a 0.22 μm microporous membrane. The obtained filtrate is the tea extract;

[0036] Step 2: Prepare silver nanoparticle solution. Add 0.2 mM AgNO 3 to 5 mL of tea extract, and ultrasonically oscillate at room temperature for 5 min to obtain a silver nanoparticle solution containing AgNPs;

[0037] Step 3: Prepare a pencil core electrode. Firmly bond a 2-cm pencil core to a copper wire with conductive silver glue, then carefully and slowly insert it into the tip of a plastic pipette. Seal both ends of the pipette tip with AB glue, and then cut the exposed length of the pencil core to 5 mm to obtain a pencil core electrode;

[0038] Step 4: Prepare an electrochemical sensor. Using cyclic voltammetry, place the pencil core electrode in the silver nanoparticle solution and perform electro-polymerization under the conditions of potential range: -0.8 V - 1.8 V; scan rate: 50 mV / s; number of polymerization cycles: 5 cycles to fix AgNPs on the electrode surface, and obtain a pencil core electrode modified with polyphenol - silver nanoparticles (PTP - AgNPs / PGE), which is a disposable nitrite electrochemical sensor.

[0039] For further comparison, a pencil core electrode modified with polyphenol (PTP / PGE) was prepared, which was also manufactured according to the above similar steps. The difference is that the electro-polymerization solution is tea extract without AgNPs.

[0040] The pencil core electrode, PTP / PGE, and PTP-AgNPs / PGE were characterized by scanning electron microscopy ( Figure 1 ), as Figure 1 shown in A, a typical graphite sheet structure appeared on the surface of the pencil core electrode. As Figure 1 shown in B, an obvious thin film was observed on the surface of PTP / PGE. As Figure 1 shown in C, the co-electropolymerization of AgNPs and PTP made the electrode surface loose and porous, which was beneficial to increasing the effective area of the electrode, improving the enrichment of nitrite on the electrode surface, and enhancing the sensitivity of the sensor. The obvious difference in the surface morphologies of PTP / PGE and PTP-AgNPs / PGE also indicated the successful co-electropolymerization of AgNPs and tea polyphenols.

[0041] Example 2

[0042] Using the nitrite electrochemical sensor prepared in Example 1 as the working electrode, the saturated calomel electrode as the reference electrode, and the platinum wire electrode as the counter electrode, a three-electrode system was constructed. Using 0.1 M phosphate buffer solution (PB) with pH = 4.0 as the detection base solution, differential pulse voltammetry (DPV) was used to measure nitrite (2 mM) in the PB solution, and the potential range during detection was 0.2 V to 1.3 V.

[0043] For further comparison, the electrochemical responses of the pencil core electrode, PTP / PGE, and PTP-AgNPs / PGE in the presence of 2 mM nitrite and blank experiments were conducted. The results are as Figure 2 shown. Curve a is the differential pulse voltammogram of PTP-AgNPs / PGE in 0.1 M phosphate buffer solution (pH = 4.0, containing 2 mM nitrite). Curve b is the differential pulse voltammogram of PTP / PGE in 0.1 M phosphate buffer solution (pH = 4.0, containing 2 mM nitrite). Curve c is the differential pulse voltammogram of the pencil core electrode in 0.1 M phosphate buffer solution (pH = 4.0, containing 2 mM nitrite). Curve d is the control differential pulse voltammogram of PTP-AgNPs / PGE in 0.1 M phosphate buffer solution (pH = 4.0, without nitrite).

[0044] Obviously, the electrochemical signal of NO 2 - on PTP-AgNPs / PGE is higher than that of other electrodes, indicating its good electrocatalytic performance. Because AgNPs have good conductivity, they can provide a larger surface area for NO 2 - enrichment, ensuring a higher electron transfer rate between NO 2 - and the sensor. In addition, PTP is an oligomer, which can also improve the electrocatalytic ability.

[0045] Example 3

[0046] To improve the electrocatalytic performance of the sensor towards nitrite, various conditions were optimized through experiments:

[0047] When preparing the silver nanoparticles solution, 0 mM, 0.1 mM, 0.2 mM, 0.3 mM, 0.4 mM, and 0.5 mM of AgNO 3 solution was added to the tea extract respectively, and then PTP-AgNPs / PGE (i.e., the nitrite sensor) was prepared according to the above method. The effect of the nitrite sensor prepared with AgNO 3 solution at different concentrations on the oxidation peak current of NO 2 - was tested, and the results are shown in Figure 2 (a); when the concentration of the AgNO 3 solution was 0.2 mM, the oxidation peak current of NO 2 - reached the maximum value. Therefore, when preparing the silver nanoparticles solution, the optimal concentration of the AgNO 3 solution added to the extract was 0.2 mM;

[0048] When co-electropolymerizing tea polyphenols and AgNPs, cyclic voltammetry scans were performed 0, 5, 10, 15, and 20 cycles respectively to prepare PTP-AgNPs / PGE with different cycle numbers. The effect of the nitrite sensor prepared with different polymerization cycle numbers on the oxidation peak current of NO 2 - was tested, and the results are shown in Figure 2 (b); when the polymerization cycle number was 5, the oxidation peak current of NO 2 - reached the maximum value. Therefore, the optimal polymerization cycle number was 5;

[0049] PTP-AgNPs / PGE was placed in phosphate buffer solutions with pH values of 2.0, 3.0, 4.0, 5.0, 6.0, and 7.0 respectively, and the effect of the nitrite sensor on the oxidation peak current of NO 2 - under phosphate buffer solutions with different pH values was tested, and the results are shown in Figure 2 (c); when the pH of the phosphate buffer solution was 4.0, the oxidation peak current of NO 2- reached the maximum value. Therefore, the optimal pH of the detection base solution was 4.0.

[0050] Example 4

[0051] The sensor was evaluated by the current i-t curve method in 0.1 M phosphate buffer solution, and the working potential was 0.9 V. The results are shown in Figure 4, Figure 4 A is the current response of PTP-AgNPs / PGE to nitrite at different concentrations in 0.1 M phosphate buffer solution, Figure 4 B shows the current response in the lower concentration range, Figure 4 C is the linear relationship between the oxidation peak current and the nitrite concentration. As Figure 4 shown in C, the linear range of this nitrite sensor can be divided into two segments: one is the lower concentration range from 0.02 μM to 860 μM, and the linear equation is Ip (μA) = 0.05c - 1.78, R 2 = 0.971, and the sensitivity is 50 nA / μM; the other is the higher concentration range from 860 μM to 1160 μM, Ip (μA) = 0.14c - 74.44, R 2 = 0.996, and the sensitivity is 140 nA / μM; Figure 4 D shows the detection limit of the sensor. The detection limit and response time of the sensor are measured to be 4 nM and 2 s respectively. Obviously, this nitrite sensor has the advantages of a wide linear range, high sensitivity, low detection limit and fast response.

[0052] Six PTP-AgNPs / PGE electrodes (i.e., nitrite sensors) were prepared by the same method, and 2 mM nitrite was measured in parallel under the same conditions. The relative standard deviation of the detection results was 6.4%, as shown in Figure 5 , indicating that the prepared disposable nitrite sensor has good reproducibility.

[0053] Example 5

[0054] Different interfering elements were set in the detection base solution, and the selectivity of the nitrite electrochemical sensor prepared by the present invention was evaluated by means of the current i-t curve method at a working potential of 0.9 V. The results are as shown in Figure 6 . 50 times of Na+, K+, Ca 2+ and Mg 2+ , 100 times of Cl - , CO 3 2- and NO 3 - have almost no interference on the detection of 1 μM NO 2 - , indicating that the prepared nitrite sensor has good selectivity.

[0055] Example 6

[0056] The nitrite electrochemical sensor prepared in Example 1 was used to determine nitrite in food samples. The samples were processed according to the second method of GB 5009.33-2016. Each sample was measured 5 times in parallel with the sensor, and the measurement results were compared with the results of spectrophotometry. The results are as Figure 7 shown. It can be seen that the disposable nitrite electrochemical sensor prepared by the present invention has good detection accuracy and good application prospects.

[0057] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A disposable nitrite electrochemical sensor, characterized in that, the nitrite electrochemical sensor is prepared by the following steps: Step 1, prepare a tea extract; Step 2: Add a certain amount of AgNO 3 to the tea extract obtained in Step 1, and ultrasonically oscillate to obtain a silver nanoparticle solution containing AgNPs; Step 3, bond a pencil lead to a copper wire, slowly insert it into the tip of a plastic pipette, seal both ends of the tip, and then cut the pencil lead into an appropriate length to obtain a pencil lead electrode; Step 4, place the pencil lead electrode into the nano-silver solution prepared in Step 2, and perform electro-polymerization under certain conditions to obtain a pencil lead electrode modified with poly-tea polyphenol-silver nanoparticles; use a saturated calomel electrode as the reference electrode, a platinum wire electrode as the counter electrode, and the pencil lead electrode modified with poly-tea polyphenol-silver nanoparticles as the working electrode to construct a three-electrode system to obtain the disposable nitrite electrochemical sensor.

2. The disposable nitrite electrochemical sensor according to claim 1, characterized in that, the steps for the nitrite electrochemical sensor to detect nitrite are: Use a saturated calomel electrode as the reference electrode, a platinum wire electrode as the counter electrode, and the pencil lead electrode modified with poly-tea polyphenol-silver nanoparticles as the working electrode to construct a three-electrode system, and perform detection by differential pulse voltammetry.

3. The disposable nitrite electrochemical sensor according to claim 1, characterized in that: Step 1 is specifically to heat tea leaves in ultrapure water until boiling, filter and then centrifuge, and the supernatant is the tea extract.

4. The disposable nitrite electrochemical sensor according to claim 1, characterized in that, the specific conditions for electro-polymerization in Step 4 are: using cyclic voltammetry, the potential range is -0.8V - 1.8V, the scanning rate is 50mV / s, and the number of polymerization cycles is 5.

5. The disposable nitrite electrochemical sensor according to claim 2, characterized in that: The detection base solution is a phosphate buffer solution with 0.1M pH = 4.0 and contains 2mM nitrite.

6. The disposable nitrite electrochemical sensor according to claim 2, characterized in that: The detection potential range is 0.2V to 1.3V.

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