CN111272841A - Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material and preparation method and application thereof - Google Patents
Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material and preparation method and application thereof Download PDFInfo
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- 238000002360 preparation method Methods 0.000 title claims abstract description 25
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Abstract
The invention discloses an Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material and a preparation method and application thereof. The preparation method of the composite material comprises the following steps: adding copper chloride dihydrate and thiourea into a mixed solution of deionized water and N-N-dimethylformamide, magnetically stirring, and reacting in a reaction kettle to obtain CuS microspheres; dispersing CuS microspheres in deionized water, adding glucose under stirring to obtain a CuS dispersion liquid; adding the prepared silver-ammonia solution into the CuS dispersion liquid, stirring, standing, separating and washing a product to obtain the Ag-CuS core-shell microspheres; and adding the Ag-CuS core-shell microspheres into N, N-dimethylformamide dispersed nitrogen-doped graphene to obtain the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material. The chemically modified electrode prepared from the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material can be used for quickly detecting tyrosine in food, and has the advantages of low detection limit, good stability, simplicity and convenience in operation and the like.
Description
Technical Field
The invention relates to the technical field of material preparation and electrochemical detection, in particular to a nitrogen-doped graphene composite material loaded by Ag-CuS core-shell microspheres and a preparation method and application thereof.
Background
Tyrosine is an important nutritional amino acid, plays an important role in metabolism, growth and development of people and other animals, and is widely applied to industries such as food, feed, medicine, chemical engineering and the like. The abnormality of tyrosine content has direct relation with some diseases of human body, such as dementia and Parkinson's disease caused by high tyrosine content, and doubtful symptoms, depression, albinism, alkaliuria and the like caused by tyrosine deficiency. Therefore, the method for accurately determining tyrosine, which is simple, convenient, rapid and economic, has great practical significance and scientific value. The current methods for detecting tyrosine mainly comprise methods such as high performance liquid chromatography, fluorescence detection method, mass spectrometry detection method, ultraviolet detection method, capillary electrophoresis amperometric detection method, laser-induced fluorescence detection method, gas chromatography, ion exchange chromatography and the like. However, these methods suffer from drawbacks such as long analysis time, high cost, high sample pre-treatment requirements, etc. making them unsuitable for routine analysis and field testing. In recent years, electrochemical techniques have become the most attractive method for measuring tyrosine due to their advantages of high sensitivity, high accuracy, simple operation, fast analysis speed, low cost, etc. In the construction process of the electrochemical detection method, because the bare glassy carbon electrode has low electrocatalytic activity and weak electrochemical response to an analyte, the key for developing a new electrochemical detection method is to prepare a nano composite material with excellent electrocatalytic performance for modification of a working electrode so as to improve the response performance of electrochemical detection. Tyrosine is an oxidizable amino acid, and has obvious electrochemical signal enhancement on various modified electrodes, for example, electrode materials for tyrosine detection are recently reported as follows: two-dimensional MoS2Carbon gold electrode (detection range 0-100 μ M, detection limit 0.5 μ M, Sensors)&Actuators:B.Chemical 2020,303:127229)、Nd2O3Graphene (detection range 0.1 ℃; E)120 μ M, detection limit of 0.03 μ M, Talanta 2020,206:120176), L-cysteine electropolymerized film (detection range of 3.5-96 μ M, detection limit of 1.1 μ M, Materials Science&Engineering C2019, 98: 496-502), electrically reduced graphene (detection range of 0.8-60 μ M, detection limit of 0.07 μ M, Analytical Methods 2015,7(22): 9535-9541), and the like. However, the electrochemical detection methods constructed by these functional materials have the problems of narrow detection range, high detection limit and poor stability, and are not favorable for accurate determination of tyrosine in actual samples. Therefore, the development of an electrode modification material with wide detection range, low detection limit and strong stability for the electrochemical sensing of tyrosine has important application value.
Disclosure of Invention
The invention aims to solve the primary technical problems that in order to overcome the problems of narrow detection range and higher detection limit of a chemically modified electrode for detecting tyrosine in the prior art, the invention provides a preparation method of an Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material; the modified electrode prepared from the material has a wider detection range and an extremely low detection limit for the detection of tyrosine.
The invention aims to solve another technical problem of providing a nitrogen-doped graphene composite material modified electrode loaded by Ag-CuS core-shell microspheres.
The invention further aims to solve the technical problem of providing the application of the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material modified electrode in detecting the tyrosine content in food.
The technical problem to be solved by the invention is realized by the following technical scheme:
a preparation method of a nitrogen-doped graphene composite material loaded by Ag-CuS core-shell microspheres comprises the following steps:
(1) synthesizing CuS microspheres: weighing 0.3-0.5 mmol of copper chloride dihydrate and 0.8-1.2 mmol of thiourea, adding 7-8 mL of deionized water and 7-8 mL of N, N-dimethylformamide, stirring for 30-60 min, transferring the mixed solution to a hydrothermal reaction kettle, placing the reaction kettle in an oven for constant temperature reaction at 160-180 ℃ for 5-8 hours, and after the reaction is completed, separating and washing the product to obtain CuS microspheres;
(2) preparing a CuS microsphere dispersion liquid: dispersing the obtained CuS microspheres in 4-6 mL of water, and adding 0.7-0.8 g of glucose under the stirring condition to obtain a CuS microsphere dispersion liquid;
(3) preparing a silver ammonia solution: 0.08 to 0.12g of AgNO3Dissolving the silver-ammonia solution in 0.8-1.2 mL of water, and adding 0.5-0.6 mol/L of ammonia water solution until the generated precipitate disappears to obtain the silver-ammonia solution;
(4) dropwise adding the prepared silver ammonia solution into the CuS microsphere dispersion liquid, stirring for 30-60 min, standing for 70-100 min, and separating and washing a product to obtain Ag-CuS core-shell microspheres;
(5) and adding 0.4-0.6 mg of Ag-CuS core-shell microspheres into 4-6 mL of N, N-dimethylformamide dispersed nitrogen-doped graphene with the concentration of 0.8-1.2 mg/mL, performing ultrasonic treatment for 50-80 min, and performing centrifugal drying to obtain the Ag-CuS core-shell microsphere-loaded nitrogen-doped graphene composite material.
Preferably, step (1) is specifically: weighing 0.4mmol of copper chloride dihydrate and 1mmol of thiourea, adding 7.5mL of deionized water and 7.5mL of N, N-dimethylformamide, stirring for 45min, transferring the mixed solution into a hydrothermal reaction kettle, placing the reaction kettle in an oven for reacting for 6 hours at a constant temperature of 170 ℃, and after the reaction is finished, separating and washing the product to obtain the CuS microspheres.
Preferably, the step (2) is specifically: the obtained CuS microspheres were dispersed in 5mL of water, and 0.75g of glucose was added under stirring to obtain a CuS microsphere dispersion.
Preferably, step (3) is specifically: 0.1g of AgNO3Dissolving in 1mL of water, and adding 0.55mol/L ammonia water solution until the generated precipitate disappears to obtain the silver-ammonia solution.
Preferably, step (5) is specifically: and adding 0.5mg of Ag-CuS core-shell microspheres into 5mL of N, N-dimethylformamide dispersed nitrogen-doped graphene with the concentration of 1mg/mL, performing ultrasonic treatment for 60min, and performing centrifugal drying to obtain the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material.
The invention also provides the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material prepared by the preparation method.
The invention provides a brand new Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material prepared by a brand new method, which is prepared by attaching silver nanoparticles to CuS microspheres built by nanosheets to form core-shell structure microspheres, and then further loading the microspheres on nitrogen-doped graphene to form the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material; the material is used for modifying the surface of the electrode, so that the detection limit of electrochemical detection can be obviously reduced, the detection range can be widened, and the anti-interference performance can be enhanced.
In the field of electrochemical detection, those skilled in the art will recognize that for the use of nanocomposites to prepare electrodes for the determination of the content of a particular chemical component or species, the inventors are required to prepare different nanocomposites based on the nature of the particular chemical species being determined. The quality of the detection limit, sensitivity, stability, anti-interference performance and other effects of the prepared electrode on the substance to be measured is mainly determined by the preparation method of the nano composite material. The preparation method of the nano composite material mainly comprises the selection of raw materials, the proportion of the raw materials, the reaction conditions of each step and the like. For the nano composite material used as the electrode, the selection and the proportion of raw materials in the preparation method and the difference of reaction conditions of each step can cause the great difference of the electrical properties of the electrode obtained by subsequent preparation, thereby causing the great difference of the effects of detection limit, detection range, sensitivity, stability, anti-interference performance and the like.
Tyrosine has the defects of weak electrocatalytic oxidation signal, incapability of detecting the content of low-concentration tyrosine and the like on an unmodified working electrode. According to the characteristics of tyrosine, in order to obtain a tyrosine detection electrode with a wide detection range and a low detection limit, the inventor obtains the nitrogen-doped graphene composite material loaded by the Ag-CuS core-shell microspheres through a large number of experiments by continuously adjusting the raw material composition, the proportion and the process parameters in the preparation process, and the nitrogen-doped graphene composite material modified electrode loaded by the Ag-CuS core-shell microspheres prepared by the material has excellent electrochemical response performance, can obviously reduce the detection limit of tyrosine in a sample, and improves the linear range, the stability and the anti-interference performance of detection.
The invention also provides a nitrogen-doped graphene composite material modified electrode loaded by the Ag-CuS core-shell microspheres, which takes the nitrogen-doped graphene composite material loaded by the Ag-CuS core-shell microspheres as an electrode modified material.
Preferably, the nitrogen-doped graphene composite material modified electrode loaded by the Ag-CuS core-shell microspheres is prepared by the following method:
ultrasonically dispersing the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material in an organic solvent to obtain an electrode modification solution;
and dropwise adding the electrode modification solution on the surface of the glassy carbon electrode, and drying to obtain the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material modified electrode.
The invention also provides an application of the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material modified electrode in detection of tyrosine content in food.
Preferably, the detection is performed by differential pulse voltammetry, and the specific method comprises the following steps:
forming a three-electrode system by taking the nitrogen-doped graphene composite material modified electrode loaded by the Ag-CuS core-shell microspheres as a working electrode, a platinum electrode as a counter electrode and a saturated calomel electrode as a reference electrode, and connecting the three-electrode system after assembling with an electrochemical workstation to form an electrochemical detection device;
preparing a standard solution and an actual sample solution to be detected;
measuring the oxidation peak current value of tyrosine in different standard solutions by using a differential pulse voltammetry, obtaining a linear equation according to the relation between the oxidation peak current value of tyrosine and the concentration of the tyrosine, measuring the oxidation peak current value of tyrosine in an actual sample solution to be measured by using the differential pulse voltammetry, and converting the tyrosine concentration according to the obtained linear equation to obtain the tyrosine content in the actual sample to be measured;
wherein the linear equation in the range of 0.3-300 mu mol/L is as follows: i.e. ip=0.0183c+1.9233×10-7(R20.9927), the linear equation is in the range of 300-4000 mu mol/L: i.e. ip=0.00348c+3.640×10-6(R20.9898), the linear equation is as follows within the range of 4000-7000 mu mol/L: i.e. ip=0.01124c+2.581×10-5(R20.9855); c in the equation is tyrosine concentration, and the unit is mol/L; i.e. ipThe unit is A for the oxidation peak current value obtained by differential pulse voltammetry;
the detection conditions of the differential pulse voltammetry are as follows: the pH value of the detection base solution is 3.96, the enrichment time is 60s, the potential increment is 4mV, the amplitude is 50mV, the primary pulse width is 0.2s, the secondary pulse width is 0.05s, the sample measurement width is 0.0167s, and the pulse period is 0.5 s.
Has the advantages that: (1) the invention solves the defects of long analysis time, high cost, high sample pretreatment requirement and the like of methods such as a high performance liquid chromatography method, a fluorescence detection method, a mass spectrometry detection method, an ultraviolet detection method, a capillary electrophoresis amperometric detection method, a laser-induced fluorescence detection method, a gas chromatography and an ion exchange chromatography, and provides a brand-new Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material for preparing a modified electrode, which is prepared by a brand-new method; (2) the electrode prepared by the material can be used for quantitatively detecting tyrosine in food, and has the advantages of wide detection range, low detection limit, strong anti-interference performance and the like; (3) the data of the examples show that the prepared electrode has a linear range of 0.3-7000 mu mol/L and a detection limit of 1.0 multiplied by 10 for tyrosine measurement-4The detection range and detection limit of the micro-mol/L electrode are greatly improved compared with those of a chemically modified electrode and an unmodified electrode reported in the prior art, and the obvious progress is achieved; (4) the electrode can be reused after being stored at room temperature for one month, and the peak current can reach more than 95% of the initial value, which shows that the storage stability of the electrode is excellent; (5) the modified electrode prepared by the method has no obvious interference on the detection of tyrosine under the coexistence condition of sodium nitrite, hydrogen peroxide, tryptophan, L-cysteine, paracetamol, tartrazine, vanillin, salbutamol, 5-hydroxytryptamine, caffeic acid, ferric chloride and other substances.
Drawings
Fig. 1 is a scanning electron microscope image of nitrogen-doped graphene (a), a CuS microsphere-loaded nitrogen-doped graphene composite material (B), and an Ag-CuS core-shell microsphere-loaded nitrogen-doped graphene composite material (C); and ultraviolet spectrograms (D) of the CuS microsphere-loaded nitrogen-doped graphene composite material and the Ag-CuS core-shell microsphere-loaded nitrogen-doped graphene composite material.
Fig. 2 is an X-ray powder diffraction pattern (a), a photoelectron spectrum (B) and an energy spectrum element analysis pattern (C) of the Ag-CuS core-shell microsphere-loaded nitrogen-doped graphene composite material.
Fig. 3 is a cyclic voltammogram (a) and a differential pulse voltammogram (B) of a glassy carbon electrode (a), a nitrogen-doped graphene modified electrode (B), a nitrogen-doped graphene composite material (c) loaded by a CuS microsphere and a nitrogen-doped graphene composite material modified electrode (d) loaded by an Ag-CuS core-shell microsphere in a 7mmol/L tyrosine solution.
FIG. 4 is a cyclic voltammetry curve (B) of oxidation peak current values (A) of 1mmol/L tyrosine on a nitrogen-doped graphene composite material modified electrode loaded by Ag-CuS core-shell microspheres at different enrichment times and under different pH values (the pH values of a-i are 9.92-3.05).
Fig. 5 is a differential pulse voltammetry curve (a) obtained by continuously adding tyrosine with different concentrations to an acetic acid base solution (pH 3.96) of a nitrogen-doped graphene composite material modified electrode loaded by an Ag-CuS core-shell microsphere and a linear relationship diagram (B) in different concentration ranges.
Detailed Description
The present invention is further explained below with reference to specific examples, which are not intended to limit the present invention in any way.
Example 1 preparation of nitrogen-doped graphene composite material loaded with Ag-CuS core-shell microspheres
(1) Synthesizing CuS microspheres: weighing 0.4mmol of copper chloride dihydrate and 1mmol of thiourea, adding 7.5mL of deionized water and 7.5mL of N, N-dimethylformamide into a small beaker, magnetically stirring for 45min, transferring the mixed solution into a hydrothermal reaction kettle with a polytetrafluoroethylene lining, placing the reaction kettle into an oven for constant-temperature reaction at 170 ℃ for 6 hours, naturally cooling to room temperature after the reaction is finished, and then centrifuging, and washing the product with absolute ethyl alcohol and deionized water for 3 times respectively to obtain CuS microspheres;
(2) preparing a CuS microsphere dispersion liquid: dispersing the obtained CuS microspheres in 5mL of water, and adding 0.75g of glucose under the condition of vigorous stirring to obtain a CuS microsphere dispersion liquid;
(3) preparing a silver ammonia solution: 0.1g of AgNO3Dissolving in 1mL of water, and slowly adding 0.55mol/L ammonia water solution until the generated precipitate disappears to obtain silver ammonia solution;
(4) dropwise adding the prepared silver ammonia solution into the CuS microsphere dispersion liquid, stirring for 40min, standing for 90min, centrifuging, and washing the product with absolute ethyl alcohol and deionized water for 3 times respectively to obtain Ag-CuS core-shell microspheres;
(5) and adding 0.5mg of Ag-CuS core-shell microspheres into 5mL of N, N-dimethylformamide dispersed nitrogen-doped graphene with the concentration of 1mg/mL, performing ultrasonic treatment for 60min, and performing centrifugal drying to obtain the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material.
Comparative example 1 preparation of CuS microsphere-loaded nitrogen-doped graphene composite material
(1) Synthesizing CuS microspheres: weighing 0.4mmol of copper chloride dihydrate and 1mmol of thiourea, adding 7.5mL of deionized water and 7.5mL of N, N-dimethylformamide into a small beaker, magnetically stirring for 45min, transferring the mixed solution into a hydrothermal reaction kettle with a polytetrafluoroethylene lining, placing the reaction kettle into an oven for constant-temperature reaction at 170 ℃ for 6 hours, naturally cooling to room temperature after the reaction is finished, and then centrifuging, and washing the product with absolute ethyl alcohol and deionized water for 3 times respectively to obtain CuS microspheres;
(2) and adding 0.5mg of CuS microspheres into 5mL of N, N-dimethylformamide dispersed nitrogen-doped graphene with the concentration of 1mg/mL, performing ultrasonic treatment for 60min, and performing centrifugal drying to obtain the CuS microsphere-loaded nitrogen-doped graphene composite material.
The difference between the comparative example 1 and the example 1 is that the reaction step of silver ammonia solution and the CuS microspheres is not carried out in the preparation process, and the nitrogen-doped graphene loaded by the CuS microspheres is directly synthesized.
The morphology and optical characteristics of the Ag-CuS core-shell microsphere-loaded nitrogen-doped graphene composite material prepared in example 1 are as follows: fig. 1 is a scanning electron microscope image of nitrogen-doped graphene (a), a CuS microsphere-loaded nitrogen-doped graphene composite material (B), and an Ag-CuS core-shell microsphere-loaded nitrogen-doped graphene composite material (C); and ultraviolet spectrograms (D) of the CuS microsphere-loaded nitrogen-doped graphene composite material and the Ag-CuS core-shell microsphere-loaded nitrogen-doped graphene composite material. It can be seen from fig. 1(a) that the surface with nitrogen-doped graphene has more pronounced wrinkles due to the nitrogen doping, and such a multi-wrinkled surface facilitates its loading with metal particles. Fig. 1(B) shows that the CuS microspheres are loaded on the surface of the nitrogen-doped graphene, and the CuS microspheres are built by the nanosheets, so that the overall appearance of the microspheres also presents a carnation-like structure. FIG. 1(C) shows that a large amount of silver nanoparticles are deposited on the surface of a CuS microsphere through silver mirror reaction to form an Ag-CuS core-shell microsphere, and the Ag-CuS microsphere is successfully loaded on nitrogen-doped graphene to form the composite material to be prepared by the invention; the composite material integrates the large specific surface area and the core-shell structure of graphene, and is beneficial to high dispersibility and stability of surface metal particles, the composite structure is beneficial to effectively improving the electrocatalytic activity of the composite material, and the sensing performance and the stability of the composite material modified electrode are enhanced. As can be seen from fig. 1(D), compared with the ultraviolet pattern of the CuS microsphere-loaded nitrogen-doped graphene composite material, the ultraviolet pattern of the Ag-CuS core-shell microsphere-loaded nitrogen-doped graphene composite material has an obvious characteristic peak of metallic Ag at a wavelength of 360nm, which confirms that Ag is successfully deposited on the CuS microsphere to form the Ag-CuS core-shell microsphere.
Fig. 2 is an X-ray powder diffraction pattern (a), a photoelectron spectrum (B) and an energy spectrum element analysis pattern (C) of the Ag-CuS core-shell microsphere-loaded nitrogen-doped graphene composite material. As can be seen from fig. 2A, the X-ray powder diffraction shows diffraction peaks of (101), (102), (103), (006), (110), (108) and (116) planes of copper sulfide; meanwhile, typical diffraction peaks of metal silver or silver oxide at 32.2 °, 38.3 °, 44.5 °, 46.7 °, 54.9 °, 57.2 °, 68.2 ° and 74.8 ° can be seen; a diffraction peak of the graphene appears at 23.2 degrees, which shows that the composite material contains Ag, CuS and nitrogen-doped graphene, and no obvious other peak is seen, thus the prepared material is mainly the nitrogen-doped graphene composite material loaded by the Ag-CuS core-shell microspheres. As can be seen from the photoelectron spectroscopy and the energy spectroscopy element analysis diagrams of fig. 2B and C, the material prepared in this example contains elements of C, O, N, Cu, S and Ag, and it can be seen from the measurement of the photoelectron spectroscopy that the atomic percentage contents of these elements are 72.92%, 23.48%, 0.68%, 0.82%, 1.07% and 1.02%, respectively. The characterization method proves the successful preparation of the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material.
Example 2 preparation of nitrogen-doped graphene composite material modified electrode loaded with Ag-CuS core-shell microspheres
Using 0.3 μm and 0.05 μm Al2O3Polishing a glassy carbon electrode (the diameter of which is 3mm) on sand paper by using the powder, grinding the glassy carbon electrode into a smooth mirror surface, then ultrasonically cleaning the glassy carbon electrode for 5min by using dilute nitric acid, acetone and distilled water in a ratio of 1:1 in sequence, and then baking the glassy carbon electrode under an infrared lamp for standby application to obtain the well-treated glassy carbon electrode. Then, 1mg of the Ag-CuS core-shell microsphere-loaded nitrogen-doped graphene composite material prepared in the example 1 is added into 3mL of N, N-dimethylformamide, ultrasonic dispersion is carried out for 10min to obtain a dispersion liquid of the Ag-CuS core-shell microsphere-loaded nitrogen-doped graphene composite material, 7 μ L of the dispersion liquid is dropwise added on the surface of the treated glassy carbon electrode, and the surface is baked under the irradiation of an infrared lamp to obtain the Ag-CuS core-shell microsphere-loaded nitrogen-doped graphene composite material modified electrode (namely, the chemical modified electrode for detecting tyrosine).
For comparison, the nitrogen-doped graphene composite material loaded by the Ag-CuS core-shell microspheres is replaced by the nitrogen-doped graphene composite material loaded by the nitrogen-doped graphene in the step (5) in example 1 and the nitrogen-doped graphene composite material loaded by the CuS microspheres prepared in comparative example 1 by the above method, so as to prepare the nitrogen-doped graphene modified electrode and the nitrogen-doped graphene composite material modified electrode loaded by the CuS microspheres.
Example 3 detection Performance of Nitrogen-doped graphene composite modified electrode loaded with Ag-CuS core-shell microspheres
In this example, each modified electrode prepared in example 2 was used as an experimental object, and a platinum counter electrode and a saturated calomel reference electrode were combined to form a three-electrode system, which was connected to a CHI660 electrochemical workstation (shanghai chenhua instruments ltd) to perform electrochemical performance detection.
(1) Comparison of electrocatalytic oxidation performances of different electrodes on tyrosine
Using a glassy carbon electrode, a nitrogen-doped graphene modified electrode, a CuS microsphere-loaded nitrogen-doped graphene composite modified electrode, and the Ag-CuS core-shell microsphere-loaded nitrogen-doped graphene composite modified electrode prepared in example 2, a cyclic voltammogram and a differential pulse voltammogram of 7mmol/L tyrosine in an acetic acid base solution with a pH of 3.96 are measured, which is specifically shown in fig. 3. As can be seen from fig. 3A, tyrosine has an unobvious oxidation peak on the bare glassy carbon electrode, while an oxidation reduction peak of the modified material itself appears on the modified electrode, and the nitrogen-doped graphene composite material loaded by the Ag-CuS core-shell microspheres has oxidation peaks of Ag and CuS at about 0.0V and 0.2V, respectively, and has a reduction peak of Ag-CuS at about-0.1V, which indicates that the nitrogen-doped graphene composite material loaded by the Ag-CuS core-shell microspheres is successfully modified on the surface of the glassy carbon electrode. More importantly, the three modified electrodes have obvious tyrosine oxidation peaks at about 0.9V, and particularly, the oxidation peak current of the tyrosine on the nitrogen-doped graphene composite material modified electrode loaded by the Ag-CuS core-shell microsphere is the largest, so that the modified electrode has the best electrocatalytic oxidation effect on the tyrosine. As can be seen from fig. 3B, the current response of tyrosine on the glassy carbon electrode is very weak, while a significant current response signal appears on the modified electrode. Particularly, on the nitrogen-doped graphene composite material modified electrode loaded by the Ag-CuS core-shell microspheres, the current response signal is most obvious, the oxidation peak current on the modified electrode is about 45 muA, and the oxidation peak current values on the glassy carbon electrode, the nitrogen-doped graphene modified electrode and the nitrogen-doped graphene composite material modified electrode loaded by the CuS microspheres are only 0.6 muA, 7.5 muA and 24 muA. Under the condition that the concentration of tyrosine is increased consistently, compared with other electrodes, the current response of the nitrogen-doped graphene composite material modified electrode loaded by the Ag-CuS core-shell microspheres is maximum, the current value of the nitrogen-doped graphene composite material modified electrode is 75 times that of an unmodified glassy carbon electrode and is 6 times and 1.9 times that of other two comparative modified electrodes, and the nitrogen-doped graphene composite material modified electrode loaded by the Ag-CuS core-shell microspheres has the best electrocatalytic oxidation effect and detection sensitivity on tyrosine, so that the detection limit of tyrosine is reduced, and the detection range of tyrosine is widened.
The operating conditions set by the cyclic voltammetry are as follows: the sweeping speed is 0.05V/s; the potential range is-1.0 to 1.2V.
The detection conditions of the differential pulse voltammetry are as follows: the pH value of the detection base solution is 3.96, the enrichment time is 60s, the potential increment is 4mV, the amplitude is 50mV, the primary pulse width is 0.2s, the secondary pulse width is 0.05s, the sample measurement width is 0.0167s, and the pulse period is 0.5 s.
(2) The Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material prepared by the invention has electrochemical response performance on tyrosine under the conditions of different enrichment times and pH values
The oxidation peak current change condition of tyrosine in the base solution with different enrichment time and pH value is investigated by using differential pulse voltammetry in a three-electrode system with the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material modified electrode prepared in the embodiment 2 as a working electrode. As can be seen from FIG. 4A, the enrichment time is in the range of 2-120 s, the tyrosine oxidation peak increases and then decreases with the increase of the enrichment time, the maximum current value of the tyrosine oxidation peak appears at 60s, and then the maximum current value of the tyrosine oxidation peak slowly decreases with the increase of the enrichment time, so that the optimal enrichment time of tyrosine on the electrode of the invention is 60 s. As can be seen from fig. 4B, tyrosine has a relatively obvious oxidation peak within a pH range of 9.92 to 3.05, the peak current increases first and then decreases with decreasing pH, and the peak current reaches its maximum value when the pH is 3.96, which indicates that the modified electrode prepared by the present invention has the best electrochemical detection effect on tyrosine under a pH of 3.96.
The detection conditions of the differential pulse voltammetry are as follows: potential increment is 4mV, amplitude is 50mV, primary pulse width is 0.2s, secondary pulse width is 0.05s, sample measurement width is 0.0167s, and pulse period is 0.5 s.
(3) The Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material prepared by the invention has the electrochemical detection performance on tyrosine
Preparing a series of tyrosine solutions with the concentration of 0.3-7000 mu mol/L by 0.01mol/L of tyrosine and using an acetic acid buffer solution with the pH value of 3.96 through a dilution method, adjusting the tyrosine with the series of concentrations to the optimal pH value by using a pH meter, and inspecting the nitrogen-doped graphene composite material modified electrode loaded on the Ag-CuS core-shell microsphere in a series of electrodes through a pulse voltammetry methodListing electrochemical detection performance in different concentrations of tyrosine solution. FIG. 5A shows the result of differential pulse voltammetry, and FIG. 5B is obtained by plotting the oxidation peak current value and the tyrosine concentration of FIG. 5A. It can be seen from FIG. 5B that the three-step linear relationship is formed in the concentration range of 0.3-7000. mu. mol/L, wherein the linear equation in the range of 0.3-300. mu. mol/L is: i.e. ip=0.0183c+1.9233×10-7(R20.9927), the linear equation is in the range of 300-4000 mu mol/L: i.e. ip=0.00348c+3.640×10-6(R20.9898), the linear equation is as follows within the range of 4000-7000 mu mol/L: i.e. ip=0.01124c+2.581×10-5(R20.9855); c in the equation is tyrosine concentration, and the unit is mol/L; i.e. ipThe oxidation peak current value obtained by differential pulse voltammetry is represented by A. In acetic acid base solution containing tyrosine standard solution with pH of 3.96, differential pulse voltammetry measurement is carried out under the condition of keeping pH value unchanged without diluting with acetic acid buffer solution until the concentration is low and no pulse voltammetry signal is recorded as detection limit, and the detection limit is found to be 1.0 × 10 in the process-4μmol/L。
The detection conditions of the differential pulse voltammetry are as follows: potential increment is 4mV, amplitude is 50mV, primary pulse width is 0.2s, secondary pulse width is 0.05s, sample measurement width is 0.0167s, and pulse period is 0.5 s.
(5) The Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material modified electrode prepared by the method has the anti-interference capacity and stability.
The anti-interference capability of the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material modified electrode prepared by the embodiment in the tyrosine detection process is examined by a differential pulse voltammetry method. Firstly, connecting a three-electrode system consisting of the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material modified electrode prepared by the method, a platinum electrode and a saturated calomel electrode to an electrochemical workstation, and examining the influence of substances such as sodium nitrite, hydrogen peroxide, tryptophan, L-cysteine, paracetamol, tartrazine, vanillin, salbutamol, 5-hydroxytryptamine, caffeic acid and ferric chloride on the determination of tyrosine under the conditions of 60s of enrichment time, 4mV of potential increment, 50mV of amplitude, 0.2s of primary pulse width, 0.05s of secondary pulse width, 0.0167s of sample measurement width and 0.5s of pulse period in acetic acid base solution with the pH of 3.96. Firstly, taking a differential pulse voltammetry curve of 1mmol/L tyrosine solution without adding interfering substances as a blank control, taking 10mL of 1mmol/L tyrosine solution, adding 0.25mL of 1mmol/L interfering substances, setting other conditions unchanged, and repeating the previous operation. The experimental result shows that the error is controlled to be +/-5%, and the influence of the interference substance on the tyrosine can be ignored. The nitrogen-doped graphene composite material modified electrode loaded by the Ag-CuS core-shell microspheres prepared by the invention has good anti-interference capability.
The stability of the nitrogen-doped graphene composite material modified electrode loaded by the Ag-CuS core-shell microspheres prepared by the embodiment is examined by a differential pulse voltammetry method. Firstly, connecting a three-electrode system consisting of the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material modified electrode prepared in the embodiment, a platinum electrode and a saturated calomel electrode to an electrochemical workstation, measuring an oxidation peak current response value of 1mmol/L tyrosine under the conditions of potential increment of 4mV, amplitude of 50mV, primary pulse width of 0.2s, secondary pulse width of 0.05s, sample measurement width of 0.0167s and pulse period of 0.5s in acetic acid base solution with pH of 3.96, and then storing for 30 days at room temperature and measuring the oxidation peak current response value again under the same conditions. As a result, the current response is maintained above 95% of the initial value after the electrode is stored for 30 days in a room temperature environment, which indicates that the chemically modified electrode for detecting tyrosine provided by the invention has excellent stability.
EXAMPLE 4 method for detecting tyrosine in actual samples
(1) Forming a three-electrode system by taking the nitrogen-doped graphene composite material modified electrode loaded by the Ag-CuS core-shell microspheres as a working electrode, a platinum electrode as a counter electrode and a saturated calomel electrode as a reference electrode, and connecting the three-electrode system to an electrochemical workstation;
(2) preparing a sample solution to be actually detected;
(3) measuring the oxidation peak current value of tyrosine in the sample by using a differential pulse voltammetry method, and converting out the tyrosine concentration according to a linear equation (as described in example 3) so as to obtain the content of tyrosine in the actual sample; the detection conditions of the differential pulse voltammetry are as follows: the pH value of the detection base solution is 3.96, the enrichment time is 60s, the potential increment is 4mV, the amplitude is 50mV, the primary pulse width is 0.2s, the secondary pulse width is 0.05s, the sample measurement width is 0.0167s, and the pulse period is 0.5 s.
EXAMPLE 5 detection of tyrosine in actual samples
Taking a certain brand of yogurt, obtaining supernatant through ultrasound and centrifugation, taking 1mL of supernatant liquid in a 100mL volumetric flask by using a pipette, and fixing the volume to 100mL by using an acetic acid buffer solution with the pH value of 3.96 as an actual sample to be detected. Forming a three-electrode system by taking the nitrogen-doped graphene composite material modified electrode loaded by the Ag-CuS core-shell microspheres as a working electrode, a platinum electrode as a counter electrode and a saturated calomel electrode as a reference electrode, and connecting the three-electrode system to an electrochemical workstation; and (3) determining the content of tyrosine in the sample by using differential pulse voltammetry. Taking 10mL of an actual sample, measuring tyrosine in the actual sample by adopting a differential pulse voltammetry method under the conditions of enrichment time of 60s, potential increment of 4mV, amplitude of 50mV, primary pulse width of 0.2s, secondary pulse width of 0.05s, sample measurement width of 0.0167s and pulse period of 0.5s, then sequentially adding 1mL of tyrosine standard solutions of 0.1mmol/L, 1mL0.3mmol/L and 1mL0.7mmol/L, and observing the peak appearance of tyrosine under the same conditions. The peak current shows a linear increasing trend along with the gradual addition of the standard solution, which indicates that the modified electrode prepared by the invention can be used for detecting tyrosine in an actual sample. The corresponding concentration value of tyrosine in the measured sample is found from the obtained oxidation value and linear relationship chart (see the description in example 3). The tyrosine content of the tested yogurt sample is 5.6 mu mol/L according to the detection method.
Claims (10)
1. A preparation method of an Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material is characterized by comprising the following steps:
(1) synthesizing CuS microspheres: weighing 0.3-0.5 mmol of copper chloride dihydrate and 0.8-1.2 mmol of thiourea, adding 7-8 mL of deionized water and 7-8 mL of N, N-dimethylformamide, stirring for 30-60 min, transferring the mixed solution to a hydrothermal reaction kettle, placing the reaction kettle in an oven for constant temperature reaction at 160-180 ℃ for 5-8 hours, and after the reaction is completed, separating and washing the product to obtain CuS microspheres;
(2) preparing a CuS microsphere dispersion liquid: dispersing the obtained CuS microspheres in 4-6 mL of water, and adding 0.7-0.8 g of glucose under the stirring condition to obtain a CuS microsphere dispersion liquid;
(3) preparing a silver ammonia solution: 0.08 to 0.12g of AgNO3Dissolving the silver-ammonia solution in 0.8-1.2 mL of water, and adding 0.5-0.6 mol/L of ammonia water solution until the generated precipitate disappears to obtain the silver-ammonia solution;
(4) dropwise adding the prepared silver ammonia solution into the CuS microsphere dispersion liquid, stirring for 30-60 min, standing for 70-100 min, and separating and washing a product to obtain Ag-CuS core-shell microspheres;
(5) and adding 0.4-0.6 mg of Ag-CuS core-shell microspheres into 4-6 mL of N, N-dimethylformamide dispersed nitrogen-doped graphene with the concentration of 0.8-1.2 mg/mL, performing ultrasonic treatment for 50-80 min, and performing centrifugal drying to obtain the Ag-CuS core-shell microsphere-loaded nitrogen-doped graphene composite material.
2. The preparation method of the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material according to claim 1, which is characterized in that,
the step (1) is specifically as follows: weighing 0.4-0.5 mmol of copper chloride dihydrate and 1-1.2 mmol of thiourea, adding 7.5-8 mL of deionized water and 7.5-8 mL of N, N-dimethylformamide, stirring for 45-60 min, transferring the mixed solution to a hydrothermal reaction kettle, placing the reaction kettle in an oven for reacting for 6-8 hours at a constant temperature of 170-180 ℃, and after the reaction is completed, separating and washing the product to obtain CuS microspheres;
most preferably, step (1) is specifically: weighing 0.4mmol of copper chloride dihydrate and 1mmol of thiourea, adding 7.5mL of deionized water and 7.5mL of N, N-dimethylformamide, stirring for 45min, transferring the mixed solution into a hydrothermal reaction kettle, placing the reaction kettle in an oven for reacting for 6 hours at a constant temperature of 170 ℃, and after the reaction is finished, separating and washing the product to obtain the CuS microspheres.
3. The preparation method of the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material according to claim 1, which is characterized in that,
the step (2) is specifically as follows: dispersing the obtained CuS microspheres in 5-6 mL of water, and adding 0.75-0.8 g of glucose under the stirring condition to obtain a CuS microsphere dispersion liquid;
most preferably, step (2) is specifically: the obtained CuS microspheres were dispersed in 5mL of water, and 0.75g of glucose was added under stirring to obtain a CuS microsphere dispersion.
4. The preparation method of the Ag-CuS core-shell microsphere-loaded nitrogen-doped graphene composite material according to claim 1, wherein the step (3) is specifically as follows: 0.1g of AgNO3Dissolving in 1mL of water, and adding 0.55mol/L ammonia water solution until the generated precipitate disappears to obtain the silver-ammonia solution.
5. The preparation method of the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material according to claim 1, which is characterized in that,
the step (5) is specifically as follows: adding 0.5-0.6 mg of Ag-CuS core-shell microspheres into 5-6 mL of N, N-dimethylformamide dispersed nitrogen-doped graphene with the concentration of 1-1.2 mg/mL, performing ultrasonic treatment for 60-80 min, and performing centrifugal drying to obtain the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material;
most preferably, step (5) is specifically: and adding 0.5mg of Ag-CuS core-shell microspheres into 5mL of N, N-dimethylformamide dispersed nitrogen-doped graphene with the concentration of 1mg/mL, performing ultrasonic treatment for 60min, and performing centrifugal drying to obtain the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material.
6. The Ag-CuS core-shell microsphere-loaded nitrogen-doped graphene composite material prepared by the preparation method of any one of claims 1 to 5.
7. A nitrogen-doped graphene composite material modified electrode loaded by Ag-CuS core-shell microspheres is characterized in that the nitrogen-doped graphene composite material loaded by the Ag-CuS core-shell microspheres in claim 6 is used as an electrode modified material.
8. The Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material modified electrode according to claim 7 is characterized by being prepared by the following method:
ultrasonically dispersing the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material in an organic solvent to obtain an electrode modification solution;
and dropwise adding the electrode modification solution on the surface of the glassy carbon electrode, and drying to obtain the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material modified electrode.
9. The application of the Ag-CuS core-shell microsphere-loaded nitrogen-doped graphene composite material modified electrode in detecting the tyrosine content in food according to claim 7 or 8.
10. The use according to claim 9, wherein the detection is performed using differential pulse voltammetry, the method comprising the steps of:
forming a three-electrode system by using the Ag-CuS core-shell microsphere loaded nitrogen-doped graphene composite material modified electrode as a working electrode, a platinum electrode as a counter electrode and a saturated calomel electrode as a reference electrode, and connecting the assembled three-electrode system with an electrochemical workstation to form an electrochemical detection device;
preparing a standard solution and an actual sample solution to be detected;
measuring the oxidation peak current value of tyrosine in different standard solutions by using a differential pulse voltammetry, obtaining a linear equation according to the relation between the oxidation peak current value of tyrosine and the concentration of the tyrosine, measuring the oxidation peak current value of tyrosine in an actual sample solution to be measured by using the differential pulse voltammetry, and converting the tyrosine concentration according to the obtained linear equation to obtain the tyrosine content in the actual sample to be measured;
wherein the linear equation in the range of 0.3-300 mu mol/L is as follows: i.e. ip=0.0183c+1.9233×10-7(R20.9927), the linear equation is in the range of 300-4000 mu mol/L: i.e. ip=0.00348c+3.640×10-6(R20.9898), the linear equation is as follows within the range of 4000-7000 mu mol/L: i.e. ip=0.01124c+2.581×10-5(R20.9855); c in the equation is tyrosine concentration, and the unit is mol/L; i.e. ipThe unit is A for the oxidation peak current value obtained by differential pulse voltammetry;
the detection conditions of the differential pulse voltammetry are as follows: the pH value of the detection base solution is 3.96, the enrichment time is 60s, the potential increment is 4mV, the amplitude is 50mV, the primary pulse width is 0.2s, the secondary pulse width is 0.05s, the sample measurement width is 0.0167s, and the pulse period is 0.5 s.
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