Electrochemical sensor constructed by Cu SAs / N-C composite material as well as preparation and application of electrochemical sensor

Abstract

The invention provides an electrochemical sensor constructed by a Cu SAs / N-C composite material as well as preparation and application of the electrochemical sensor. Comprising a working electrode and a sensing material modified on the working electrode, and the sensing material is a Cu SAs / N-C composite material. Therefore, the obtained electrochemical sensor has the beneficial effects of high activity, high sensitivity, excellent stability and reproducibility, simple preparation method and low cost.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, and in particular to electrochemical sensors constructed from Cu SAs / NC composite materials, their preparation, and applications. Background Technology

[0002] Luteolin (3′,4′,5,7-tetrahydroxyflavone) is one of the representative compounds of flavonoids, widely found in many plants. In daily life, luteolin exists either as a glycoside or directly in commonly encountered natural plants, such as *Prunella vulgaris* and chrysanthemum; it is also found in edible vegetables such as celery, bell peppers, and broccoli. Luteolin exhibits a wide range of biological activities, possessing both antioxidant and pro-oxidative properties. Therefore, it is necessary to establish an efficient and stable detection method to determine the luteolin content in pharmaceuticals.

[0003] To date, various analytical methods have been used for the detection of luteolin, but some of these methods have not been adopted due to their complex instrumentation, time-consuming operation, insufficient selectivity, or poor accuracy. Since current methods for detecting luteolin are complex and cumbersome, establishing a rapid, accurate, simple, efficient, and low-cost detection method is of great significance for the research of luteolin in the pharmaceutical field. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides an electrochemical sensor constructed from Cu SAs / NC composite materials, along with its preparation and application, for the rapid detection of luteolin.

[0005] The present invention proposes the following technical solution: According to one aspect of this application, an electrochemical sensor constructed from Cu SAs / NC composite material is provided, characterized in that it includes a working electrode and a sensing material modified on the working electrode; the sensing material is a Cu SAs / NC composite material.

[0006] In some embodiments, the working electrode is a glassy carbon electrode.

[0007] According to another aspect of this application, a method for preparing an electrochemical sensor as described above is provided, comprising the following steps: S1. providing a Cu SAs / NC composite material; S2. pretreating the surface of a working electrode; S3. mixing the Cu SAs / NC composite material obtained in step S1 with anhydrous ethanol, Nafion and deionized water, and subjecting it to ultrasonic treatment to form a homogeneous mixture; S4. drop-coating the mixture obtained in step S3 onto the surface of the working electrode after pretreatment in step S2, and drying it to obtain the electrochemical sensor.

[0008] In some embodiments, the Cu SAs / NC composite material described in step S1 is prepared by the following method: S11: CuSO4•5H2O and 2,2'-bipyridine are dissolved in dimethyl sulfoxide and stirred at room temperature to obtain a mixture; S12: Add carbon black to the mixture from step S11, heat and stir at 80°C to obtain a dispersion; S13: The dispersion obtained in step S12 is heated at 180°C to evaporate and remove dimethyl sulfoxide, resulting in a black solid; S14: After grinding the black solid obtained in step S13, heat it to 700°C at a heating rate of 5°C / min under an inert atmosphere, and calcine it at 700°C for 2 hours to obtain Cu SAs / NC composite material.

[0009] In some implementations... In step S11, the molar ratio of CuSO4·5H2O to 2,2'-bipyridine is 1:10. And / or in step S11, the mass ratio of CuSO4·5H2O to carbon black is 1:5.

[0010] In some implementations, the room temperature stirring time in step S11 is 30 minutes; In step S12 and / or step S12, the heating and stirring reaction is carried out under oil bath conditions for 5 hours. And / or in step S13, the heating and evaporation are carried out at 180°C for 12 hours.

[0011] In some implementations... In step S11, the amount of dimethyl sulfoxide used is 2 mL for every 13.9 mg CuSO4·5H2O.

[0012] According to another aspect of this application, a Cu SAs / NC composite material is provided, which is prepared by the aforementioned method.

[0013] According to another aspect of this application, an application of the electrochemical sensor as described above in the detection of luteolin is provided.

[0014] In some embodiments, the detection is performed in PBS with a pH of 3.90-7.00.

[0015] Compared with the prior art, this application has the following advantages: 1. High activity and high sensitivity: Copper single-atom doped nitrogen-carbon spheres are used as the sensing material. The atomically dispersed copper sites provide extremely high catalytic activity and abundant active sites, which significantly enhances the current response of the sensor, thereby achieving high-sensitivity detection of the target.

[0016] 2. Excellent stability and reproducibility: Rigorous electrode pretreatment and performance verification procedures ensure the high uniformity of the sensor substrate. Simultaneously, the NC carrier exhibits good stability, preventing the aggregation and loss of single-atom sites, thus guaranteeing the long-term stability of the sensor and excellent reproducibility across different batches.

[0017] 3. The preparation method is simple and the cost is low: the entire preparation process does not require complex and expensive equipment, is easy to operate, and is easy to mass-produce, and has a good commercial prospect. Attached Figure Description

[0018] Figure 1 These are TEM images of Cu SAs / NC prepared in this application; Figure 2 This is the HAADF diagram of Cu SAs / NC prepared in this application; Figure 3 This is an EDX elemental distribution diagram of each component in the Cu SAs / NC prepared in this application; Figure 4 The different electrodes in this application are in a solution containing 0.1 mol / L KCl and 0.005 mol / L Fe[(CN)6]. 3- / 4- CV diagram in solution; Figure 5 The cyclic voltammetry curves of Cu SAs / NC / GCE in this application in PBS solution at pH=5.51 without luteolin (a) and with 10 μmol / L luteolin (b) are shown. Figure 6 This is a cyclic voltammetric curve of the response of GCE (a), NC / GCE (b), and Cu SAs / NC / GCE (c) to luteolin in PBS solution at pH=5.51 in this application. Figure 7 This is a cyclic voltammetric response diagram of Cu SAs / NC / GCE to luteolin detection in PBS buffer solutions at different pH values ​​in this application; Figure 8 This is a graph showing the relationship between the redox peak potential and pH value in this application; Figure 9 This is a cyclic voltammogram of Cu SAs / NC / GCE in this application at different scan rates in a PBS solution containing 10 µmol / L luteolin at pH=5.51. Figure 10 This is a graph showing the relationship between the redox peak current of luteolin and the scan rate in this application; Figure 11 This is a graph showing the relationship between peak potential and lnυ in this application; Figure 12 This is a DPV curve of Cu SAs / NC / GCE for detecting different concentrations of luteolin in this application; Figure 13 This is a graph showing the linear relationship between peak current and concentration in this application. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] I. Experimental Reagents and Instruments (a) Experimental reagents Table 1 Experimental Reagents

[0021] (II) Experimental Instruments Table 2 Experimental Instruments

[0022] II. Solution Preparation (a) Preparation of test electrode solution and impedance solution Weigh the reagents according to Table 2-3 to prepare 250 mL of test electrode solution containing 1 mol / L KCl and 1 mmol / L K3[Fe(CN)6] and K4[Fe(CN)6]; prepare 250 mL of impedance solution containing 0.1 mol / L KCl and 5 mmol / L K3[Fe(CN)6] and K4[Fe(CN)6].

[0023] Table 3 Preparation of test electrode solution and impedance solution

[0024] (ii) Preparation of PBS buffer solutions with different pH values Weigh the medicines according to Table 4 to prepare 250 mL of PBS buffer solutions with different pH values, and use a pH meter to measure and adjust to the required pH value.

[0025] Table 4. Masses of Na2HPO4·12H2O and NaH2PO4 required for different pH values

[0026] (III) Preparation of test solution Take about 2g of the powder (passed through a No. 2 sieve), accurately weigh it, place it in a stoppered conical flask, accurately add 25ml of 85% methanol, weigh it, heat under reflux for 1.5 hours, cool it, weigh it again, make up the lost weight with 85% methanol, shake well, filter it, and take the filtrate to obtain the product.

[0027] (iv) Preparation of luteolin standard solution Accurately weigh 14.5 mg of luteolin [batch number C17069542] and dissolve it in 5 mL of anhydrous ethanol. Disperse the solution ultrasonically for 10 min to prepare a concentration of 0.01 mol / L. Pipette 0.5 mL of the 0.01 mol / L luteolin solution into 4.5 mL of anhydrous ethanol; this solution is 1 mmol / L luteolin. Prepare luteolin solutions with concentrations of 0.1 mmol / L and 0.001 mmol / L using the same method. Store the solutions at low temperature for later use.

[0028] III. Examples (I) Example 1 Synthesis of Cu SAs / NC CuSO4•5H2O (13.9 mg) and 2,2'-bipyridine (88.1 mg) were dissolved in 2 mL of dimethyl sulfoxide and stirred at room temperature for 30 min. 70.2 mg of carbon black was added, and the mixture was heated in an oil bath to 80 °C and magnetically stirred for 5 h. The resulting dispersion was then heated at 180 °C for 12 h to evaporate the dimethyl sulfoxide, yielding a black solid. The obtained black solid was ground into powder using a mortar and pestle, then transferred to a ceramic crucible and placed in a tube furnace. Next, under a nitrogen atmosphere, the black solid was heated to 700 °C at a rate of 5 °C per minute, and then maintained at 700 °C for 2 h.

[0029] (II) Example 2: Preparation of Electrochemical Sensor 1. Working electrode pretreatment The glassy carbon electrode was polished with 0.3 μm Al2O3 powder to make it smooth, and then cleaned with deionized water. The working electrode was placed in a test electrode solution containing 1 mol / L KCl and 1 mmol / L K3[Fe(CN)6] and K4Fe(CN)6 and tested by cyclic voltammetry. It can be used when the difference between the redox peak potentials (ΔE) is less than 79 mV.

[0030] 2. Constructing Cu SAs / NC / GCE sensors Mix 5 mg Cu SAs / NC, 390 μL anhydrous ethanol, 10 μL Nafion, and 100 μL deionized water, and sonicate. Store at room temperature.

[0031] (III) Example 3 Electrochemical Detection Luteolin was detected using a Cu SAs / NC / GCE sensor, and the specific steps are as follows: (1) In a solution containing 0.1 mol / L KCl and 5 mmol / L [Fe(CN)6] 3- / 4- In solution, the electrochemical behavior of GCE, NC / GCE and Cu SAs / NC / GCE was compared by cyclic voltammetry.

[0032] (2) Evaluate the electrochemical activity of electrodes modified with different materials for the detection of luteolin.

[0033] (3) In a PBS buffer system containing 10 μmol / L luteolin, the effect of pH (3.90-7.00) on the detection performance of luteolin was systematically investigated, and the optimal pH value of 5.51 was found.

[0034] (4) By cyclic voltammetry at different scan rates, the mechanism of Cu SAs / NC / GCE detection of luteolin was compared and the number of electrons transferred was calculated.

[0035] (5) Under the condition of optimal pH 5.51, the concentration of luteolin was detected by differential pulse voltammetry (DPV) in the potential range of -0.1 to 0.8 V. The relationship between luteolin concentration and current response, as well as its detection line and linear range, were analyzed.

[0036] IV. Experimental Results and Characterization (a) TEM characterization To prepare Cu SAs / N-CSs nanomaterials with good morphology and hollow structure, the reaction temperature and time of Cu SAs / N-CSs nanomaterials were optimized.

[0037] Figure 1 The TEM image of Cu SAs / NC prepared in this application confirms that no metal clusters or nanoparticles appeared on the carbon black support (Figure 1). The HAADF image of Cu SAs / NC (Figure 2) also confirms this conclusion. Figure 3 The image shows the elemental distribution of CuSAs / NC catalysts by energy dispersive X-ray spectroscopy (EDX). As can be seen from the image, Cu, N, and O exhibit extremely high uniformity of dispersion on the carbon support.

[0038] (ii) Electrochemical performance Figure 4Under otherwise constant conditions, but with different composite materials, cyclic voltammetry was used to test three electrodes: bare GCE (a), N-CSs / GCE (b), and Cu SAs / NC / GCE (c) in 0.005 mol / L Fe[(CN)6] containing 0.1 mol / L KCl. 3- / 4- Cyclic voltammetry curves in solution, scan rate 100 mV / s. Comparison of curves a, b, and c shows that Cu SAs / NC / GCE in Fe[(CN)6] 3- / 4- The presence of large redox peak currents in the solution indicates that the Cu SAs / NC catalyst can effectively promote the development of probe molecules Fe[(CN)6]. 3- / 4- The electron transfer process can significantly improve its electrochemical reaction kinetics performance, indicating that the synergistic effect of Cu and N-CSs nanomaterials can effectively improve the electrocatalytic activity of the catalyst.

[0039] (III) Characterization of the electrochemical behavior of luteolin Figure 5 The figures show the cyclic voltammetry of Cu SAs / N-CSs / GCE in PBS solution at pH 5.51 with and without luteolin. Curves a and b are the cyclic voltammetry curves without luteolin and with 10 µmol / L luteolin, respectively. Curve a shows that the cyclic voltammetry curve without luteolin does not have a significant redox peak; however, curve b, containing 10 µmol / L luteolin, shows a significant oxidation peak at 0.43 V and a significant reduction peak at 0.31 V. This redox peak is due to the redox reaction of the catechol group on the B ring of luteolin, which imparts good electroactivity to luteolin. These experimental results confirm that the constructed sensor exhibits excellent electrochemical behavior with luteolin.

[0040] Figure 6The figures show the cyclic voltammetry curves of bare GCE (a), NC / GCE (b), and CuSAs / NC / GCE (c) in a PBS solution containing 10 µmol / L luteolin at pH 5.51. The data show that when using bare GCE (curve a) to detect luteolin, a weak oxidation peak appears at 0.41 V and a weak reduction peak appears at 0.37 V. This is because there are insufficient active sites for luteolin on the bare electrode surface, limiting its electrochemical catalytic oxidation efficiency. However, when using NC / GCE to detect luteolin (curve b), a significant oxidation peak appears at 0.40 V and a significant reduction peak appears at 0.37 V. When luteolin was detected using Cu SAs / NC / GCE (curve c), a strong oxidation peak appeared at 0.43 V and a strong reduction peak appeared at 0.36 V. This may be because the 100% utilization of Cu atoms in Cu SAs and the synergistic effect between Cu and NC greatly enhanced the electrochemical activity of the prepared Cu SAs / NC catalyst.

[0041] (iv) Effect of pH To improve the electrochemical performance of Cu SAs / NC / GCE for luteolin detection, the effect of pH on luteolin detection was studied using cyclic voltammetry. In a PBS buffer solution containing 10 µmol / L luteolin, the effects of different pH values ​​(pH = 3.90, 4.46, 5.04, 5.51, 6.03, 6.53, 7.00) on luteolin detection were measured at a scan rate of 100 mV / s. The electrochemical experimental results showed that (…). Figure 7 Within the pH range of 3.90 to 5.51, the oxidation peak current of luteolin gradually increases with increasing pH; within the pH range of 5.51 to 7.00, the peak current gradually decreases with increasing pH, while the redox peak potential decreases with increasing pH. The maximum peak current is obtained at pH=5.51; therefore, this application selects PBS buffer solution with pH=5.51 as the optimal test substrate. Figure 8 This is a curve showing the relationship between redox peak potential and pH. The linear relationship can be expressed as: E pa =-0.061pH+0.76(R) 2 =0.9865), with a slope of -0.061V / pH; E pc = -0.064pH + 0.71 (R) 2=0.9983) and its slope is -0.064 V / pH. Among them, the slope values ​​of -0.061 and -0.064 are close to the theoretical -0.059 V, which indicates that in the process of electrochemical reaction, each electron transfer is accompanied by a simultaneous proton transfer, which conforms to the 1:1 proton-electron co-transfer mechanism.

[0042] (V) Mechanism of luteolin The oxidation mechanism of luteolin on Cu SAs / NC / GCE was investigated using cyclic voltammetry at different scan rates. In a buffer solution containing 10 µmol / L luteolin at pH 5.51, the reaction mechanism on Cu SAs / NC / GCE was studied at scan rates of 10 mV / s, 20 mV / s, 30 mV / s, 40 mV / s, 50 mV / s, 60 mV / s, 70 mV / s, 80 mV / s, 90 mV / s, 100 mV / s, 120 mV / s, 140 mV / s, 160 mV / s, 180 mV / s, 200 mV / s, 250 mV / s, and 300 mV / s. Figure 9 The test results show that the redox peak current exhibits a significant increasing trend with increasing scan rate. Further analysis... Figure 10 The data revealed a strong linear correlation between the scan rate and the corresponding redox peak current, specifically: anodic peak current I... pa =0.21υ+2.55(R 2 =0.9984), cathode peak current I pc =-0.23υ-3.58(R 2 =0.9976). This linear relationship indicates that the oxidation process is dominated by a surface adsorption mechanism. Furthermore, by plotting the relationship between the redox peak potential and the logarithm of the scan rate (…),… Figure 11 This further verifies the conclusion. Based on this, the number of electrons transferred, n, and the charge transfer coefficient, α, involved in the reaction can be calculated. The curve exhibits the following linear relationship: E pa =0.021lnυ+0.034(R 2 =0.9798), E pc =-0.023lnυ+0.46(R 2 =0.9796). Based on the Laviron equation, the number of electrons transferred, n, and the charge transfer coefficient, α, involved in the reaction can be calculated.

[0043] Eq.(3-1) Eq (3-2) In this formula, Epa E represents the anodic polarization potential. pc Represents the anodic polarization potential. The value represents the conditional potential, and R is the molar gas constant with a value of 8.314 J mol. -1 K -1 T is the thermodynamic temperature, measured in Kelvin (K), α is the charge transfer coefficient, n is the number of electrons transferred in the electrode reaction, and F is the Faraday constant, with a value of 96485 C mol. -1 Based on the above formula, the electron transfer number n is close to 2, and the charge coefficient α is 0.48. This data confirms that the oxidation reaction of luteolin on Cu SAs / NC / GCE surfaces follows a two-electron transfer mechanism.

[0044] (vi) Detection of luteolin Differential pulse voltammetry was used to detect different concentrations of luteolin (0.056, 0.15, 0.34, 0.62, 0.99, 1.45, 2.00, 2.72, 3.62, 4.98, 6.82, 7.95, 9.64, 12.04, 15.02, and 18.76 μmol / L) in PBS buffer solution at pH 5.51 using Cu SAs / NC / GCE. The electrochemical sensing performance test data is shown in the graph (…). Figure 12 The results showed that when the concentration of luteolin was in the range of 0.056-18.76 μmol / L, there was a certain relationship between the oxidation peak current and the concentration. A standard curve was established to show the relationship between the oxidation peak current and the luteolin concentration. Figure 13 The linear regression equation obtained is: I pa =-2.97 c-1.72(R 2 =0.9996). Therefore, the linear range of detection is 0.056 μmol / L-18.764 μmol / L, and the limit of detection is 0.017 μmol / L.

[0045] (vii) Determination of luteolin in Prunella vulgaris The constructed electrochemical sensor was used to detect luteolin in Prunella vulgaris using the standard addition method to verify the scientific validity and practicality of the sensor. 5 μL of Prunella vulgaris solution was added to 4995 μL of PBS buffer solution (pH=5.51), and the concentration was determined by differential pulse voltammetry. The test was performed in triplicate, and the luteolin content in Prunella vulgaris was found to be 0.47 mg / g, with an RSD of less than 3%. The feasibility of the method was verified by spiked recovery. 5 mL of PBS buffer solution (pH=5.51) and 5 μL of *Prunella vulgaris* solution were placed in three 10 mL beakers. Luteolin standard solutions with concentrations of 0.10 μmol / L, 1.00 μmol / L, and 5.00 μmol / L were added to each beaker. The constructed sensor was then used for spiked recovery detection of luteolin using differential pulse voltammetry. The results are shown in Table 5. According to the data in the table, the relative standard deviation (RSD) of the electrochemical sensor constructed with Cu SAs / NC catalyst for detecting luteolin concentration in *Prunella vulgaris* was less than 3%. The data indicate that the Cu SAs / NC sensor is practical and can be used to detect luteolin in *Prunella vulgaris*.

[0046] Table 5. Determination of luteolin content in Prunella vulgaris (n=3)

[0047] Based on the above experimental results and discussion, the following conclusions can be drawn: (1) Characterization by transmission electron microscopy (TEM) confirmed that Cu single atoms in Cu SAs / NC catalyst are uniformly dispersed in carbon framework.

[0048] (2) The pH value for luteolin detection was optimized by experimental conditions. According to the experimental data, the optimal pH value of the substrate for luteolin detection is 5.51.

[0049] (3) The oxidation mechanism of luteolin on the constructed electrochemical sensor was studied by cyclic voltammetry. The analysis showed that the oxidation of luteolin was surface-controlled, with electron transfer number n=2 and charge coefficient α=0.48.

[0050] (4) Under optimal detection conditions, luteolin at different concentrations was detected by differential pulse voltammetry based on Cu SAs / N-CSs / GCE. The experimental data showed that the linear range of the detection concentration was 0.056 μmol / L-18.764 μmol / L and the detection limit was 0.017 μmol / L.

[0051] The above descriptions are merely some embodiments of the present invention. It should be noted that those skilled in the art can make other modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. An electrochemical sensor constructed from Cu SAs / NC composite material, characterized in that, It includes a working electrode and a sensing material modified on the working electrode; the sensing material is a Cu SAs / NC composite material.

2. The electrochemical sensor according to claim 1, characterized in that, The working electrode is a glassy carbon electrode.

3. A method for preparing an electrochemical sensor as described in claim 1 or 2, characterized in that, Includes the following steps: S1. Provide CuSAs / NC composite material; S2. Pretreat the surface of the working electrode; S3. Mix the CuSAs / NC composite material obtained in step S1 with anhydrous ethanol, Nafion and deionized water, and sonicate to form a homogeneous mixture; S4. Drop the mixture obtained in step S3 onto the surface of the working electrode after pretreatment in step S2, and after drying, obtain the electrochemical sensor.

4. The preparation method according to claim 3, characterized in that, The Cu SAs / NC composite material described in step S1 is prepared by the following method: S11: Dissolve CuSO4•5H2O and 2,2'-bipyridine in dimethyl sulfoxide and mix with stirring at room temperature to obtain a mixture; S12: Add carbon black to the mixture from step S11, heat and stir at 80°C to obtain a dispersion; S13: The dispersion obtained in step S12 is heated at 180°C to evaporate and remove dimethyl sulfoxide, resulting in a black solid; S14: After grinding the black solid obtained in step S13, heat it to 700°C at a heating rate of 5°C / min under an inert atmosphere, and calcine it at 700°C for 2 hours to obtain Cu SAs / NC composite material.

5. The preparation method according to claim 4, characterized in that, In step S11, the molar ratio of CuSO4·5H2O to 2,2'-bipyridine is 1:

10. And / or in step S11, the mass ratio of CuSO4·5H2O to carbon black is 1:

5.

6. The preparation method according to claim 4, characterized in that, The room temperature stirring time in step S11 is 30 minutes; In step S12 and / or step S12, the heating and stirring reaction is carried out under oil bath conditions for 5 hours. And / or in step S13, the heating and evaporation are carried out at 180°C for 12 hours.

7. The preparation method according to claim 4, characterized in that, In step S11, the amount of dimethyl sulfoxide used is 2 mL for every 13.9 mg CuSO4·5H2O.

8. A Cu SAs / NC composite material, characterized in that, It is prepared by the method described in any one of claims 4-7.

9. The application of an electrochemical sensor as described in claim 1 or 2 in the detection of luteolin.

10. The application according to claim 8, characterized in that, The detection was performed in PBS with a pH of 3.90-7.00.

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