A method for detecting dopamine by using an in-situ synthesized iron-nickel alloy / nitrogen-doped carbon nanotube modified electrode

Abstract

The present invention discloses a method for detecting dopamine by using an in-situ synthesized iron-nickel alloy@nitrogen-carbon nanotube modified electrode, belonging to the fields of energy materials and electrochemistry. In the present invention, a composite material of iron-nickel alloy@nitrogen-carbon nanotubes is in-situ catalytically generated by simultaneously introducing iron and nickel bimetals, and it is further prepared into a DA sensor for detecting DA, which can achieve ultrasensitive detection of DA, and at the same time has an ultra-wide detection range (covering pM, nM, and μM concentrations) and excellent anti-interference performance.

Description

Technical Field

[0001] The present invention relates to the fields of energy materials and electrochemistry, and particularly to a method for detecting dopamine by in-situ synthesizing an iron-nickel alloy / nitrogen-carbon nanotube modified electrode. Background Art

[0002] Dopamine (DA) is an important component of neurotransmitters and plays an important role in the human central nervous system, kidneys, and metabolic processes. Imbalances in DA concentration can lead to various neurological diseases such as Parkinson's disease, schizophrenia, Alzheimer's disease, attention deficit hyperactivity disorder, and drug addiction. In addition, abnormal DA levels in blood or urine are used to reflect the occurrence of diseases such as neuroendocrine tumors, pheochromocytomas, and paragangliomas. Therefore, the ability to simply, rapidly, and accurately detect DA concentration is of great significance for disease management, monitoring, treatment planning, and medical diagnosis.

[0003] So far, some traditional methods for detecting and analyzing DA mainly include high-performance liquid chromatography (HPLC), chemiluminescence, spectrophotometry, colorimetry, surface-enhanced Raman spectroscopy, etc., which have disadvantages such as high cost, complex operation, low sensitivity, and long detection cycle, and are difficult to popularize in practical applications. Electrochemical detection has become a better choice for DA detection due to its advantages such as simple operation, high sensitivity, fast detection speed, and low cost.

[0004] To solve these problems, researchers have prepared various materials for modifying electrodes to improve the sensitivity and anti-interference ability of DA, including carbon-based materials, metals and their oxides, and conductive polymers, etc. However, these materials either have a complex and expensive synthesis process or cannot achieve ideal sensitivity and detection limits. In addition, in the detection of actual samples, there are still some problems. On the one hand, in addition to DA, human body fluids may contain proteins, fats, glucose, inorganic salts, and other biomolecules, etc. These substances will cause greater interference to the detection of DA due to their much higher concentrations than DA; especially uric acid (UA) and ascorbic acid (AA) have oxidation potentials closer to that of DA, making it difficult to distinguish the oxidation peak of DA. On the other hand, the content of DA in human body fluids is low. The DA concentration in urine and cerebrospinal fluid is 5 nM, and the DA level in human blood is less than 0.13 nM. Therefore, it is crucial to design and prepare an electrochemical method for DA with good selectivity and high sensitivity. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for detecting dopamine by in-situ synthesizing an iron-nickel alloy / nitrogen-carbon nanotube modified electrode.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] 1. A method for in-situ synthesis of an iron-nickel alloy / nitrogen carbon tube modified electrode for detecting dopamine, comprising the following steps:

[0008] (1) a certain amount of sodium chloride, glucose and melamine are dissolved in deionized water, a certain amount of FeCl3·6H2O and C4H6O4Ni·4H2O are gradually added to the mixed solution during continuous stirring, and then the mixture is stirred under heating until the water evaporates to obtain a dry block solid;

[0009] (2) transferring the dried solid block obtained in step (1) to an oven for further drying, and then ball-milling the solid block to obtain a pink powder sample;

[0010] (3) calcining the pink powder sample obtained in step (2) in a N2 atmosphere to obtain a black powder sample;

[0011] (4) The black powder sample obtained in step (3) is acid-washed, water-washed, and freeze-dried to obtain a Fe / Ni / N-CNT composite material;

[0012] (5) polishing and cleaning the glassy carbon electrode, then placing it in ethanol and deionized water for ultrasonic treatment, and finally drying it at room temperature to obtain a glassy carbon electrode to be modified;

[0013] (6) dispersing the iron-nickel alloy / nitrogen carbon tube powder prepared in step (4) in deionized water to obtain a dispersion with a mass volume fraction of 10 mg / ml, then taking 5 μL of the dispersion and applying it on the surface of the glassy carbon electrode prepared in step (5), and drying it to obtain a Fe / Ni / N-CNT / GCE biosensor;

[0014] (7) In dopamine standard solutions of different concentrations, a conventional three-electrode system was used, with Fe / Ni / N-CNT / GCE as the working electrode, platinum wire as the counter electrode, and saturated calomel electrode as the reference electrode. The voltammetric response signal was recorded and a current-concentration standard curve was drawn. When the sample was tested, the sample response signal was compared with the standard curve to obtain the DA concentration of the corresponding sample.

[0015] Preferably, in step (1), the mass ratio of glucose to melamine is 1-3:10-20.

[0016] Preferably, in step (1), the mass ratio of FeCl3·6H2O to C4H6O4Ni·4H2O is 1-2:2-1. Preferably, in step (1), the heating temperature is 60°C.

[0017] Preferably, in step (2) of the present invention, the drying is performed at 60° C. for 24 hours.

[0018] Preferably, in step (2), the ball milling is carried out at a speed of 400 rpm / min for 4 hours.

[0019] Preferably, in step (3), the calcination is carried out as follows: first, heat to 300 °C and hold for 2 hours; then raise the temperature to 500 °C and hold for 2 hours; then raise the temperature to 800 °C and hold for 4 hours; finally, let the temperature drop to room temperature.

[0020] Preferably, in step (4), the pickling is carried out by stirring in 0.1 M hydrochloric acid for 10 min.

[0021] Preferably, in step (5), the frequency of the ultrasonic treatment is 40 KHZ, the input power is 80 W, and the treatment time is 5 minutes.

[0022] The beneficial effects of the present invention are as follows:

[0023] By simultaneously introducing iron and nickel bimetals to in-situ catalyze the formation of iron-nickel alloy / nitrogen-doped carbon nanotube composites and further preparing them into DA sensors for detecting DA, the present invention can achieve ultrasensitive detection of DA, and at the same time has an ultra-wide detection range (covering pM, nM, and μM concentrations) and excellent anti-interference performance. The Fe / Ni / N-CNT prepared by the present invention has a uniform morphology, a uniform distribution of iron-nickel alloy, and a low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] To make the objectives, technical solutions, and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration:

[0025] Figure 1 For Figure 1 : XRD pattern of Fe / Ni / N-CNT;

[0026] Figure 2 SEM images of Fe / Ni / N-CNT at different magnifications;

[0027] Figure 3 HR-TEM image of Fe / Ni / N-CNT;

[0028] Figure 4 XPS spectrum of Fe / Ni / N-CNT;

[0029] Figure 5 EDS spectrum of Fe / Ni / N-CNT;

[0030] Figure 6 For the Raman spectrum of Fe / Ni / N-CNT in the wavelength range of 700 - 2200 cm -1 interval;

[0031] Figure 7DPV curves of different comparison materials tested with the same concentration of DA under the same conditions;

[0032] Figure 8 DPV curves and corresponding fitting curves of different DA concentrations measured for Fe / Ni / N-CNT / GCE;

[0033] Figure 9 DPV curves of DA detection in the presence of UA and AA were measured for Fe / Ni / N-CNT / GCE;

[0034] Figure 10 The anti-interference property of Fe / Ni / N-CNT / GCE;

[0035] Figure 11 (c, d) reproducibility of the same Fe / Ni / N-CNT / GCE electrode and different Fe / Ni / NN-CNT / GCE electrodes for DA detection;

[0036] Figure 12 is the amperometric response of Fe / Ni / N-CNT / GCE biosensor to DA;

[0037] Figure 13 (a) CV curves of Fe / Ni / N-CNT / GCE at different scan rates (scan rate: 20-120 mV / s); (b) relationship between DA oxidation peak current and reduction peak current and scan rate; (c) relationship between DA oxidation peak potential and reduction peak potential and scan rate;

[0038] Figure 14 This is the stability test diagram of Fe / Ni / N-CNT / GCE. DETAILED DESCRIPTION

[0039] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0040] Example 1

[0041] Preparation of FeNi / N-CNT nanocomposites

[0042] (1) 15 g of sodium chloride, 0.4 g of glucose and 5 g of melamine were dissolved in 50 ml of deionized water, and then 1 g of FeCl3·6H2O and 1 g of C4H6O4Ni·4H2O were gradually added to the mixed solution during continuous stirring, and then the mixture was continuously stirred at 60°C until the water evaporated to obtain a dry block solid;

[0043] (2) Transfer the dried lumpy solid obtained in step (1) to an oven at 60 °C and continue drying for 24 hours. Then, mill the lumpy solid in a ball mill at a speed of 400 rpm / min for 4 hours to obtain a pink powder sample.

[0044] (3) Heat the pink powder sample obtained in step (2) to 300 °C in an N2 atmosphere and hold for 2 hours. Then, increase the temperature to 500 °C and hold for 2 hours. Finally, increase the temperature to 800 °C and hold for 4 hours. After the temperature drops to room temperature, a black powder sample is obtained; the heating rate is 2 °C / min.

[0045] (4) Stir the black powder sample obtained in step (3) in 0.1 M hydrochloric acid for 10 min, then wash it three times with deionized water and collect the sample by centrifugation. Finally, freeze-dry it to obtain an iron-nickel alloy / nitrogen-doped carbon nanotube nanocomposite (Fe / Ni / N-CNT).

[0046] Preparation of Fe / Ni / N-CNT / GCE Sensor

[0047] (1) First, polish a glassy carbon electrode (diameter: 3.0 mm) with 0.05 mm alumina powder, then clean it with deionized water. Subsequently, place the rinsed glassy carbon electrode in ethanol and deionized water successively and ultrasonically treat it (frequency: 40 KHZ; input power: 80 W) for 5 minutes. Finally, place it at room temperature for drying to obtain a glassy carbon electrode to be modified (GCE).

[0048] (2) Take 10 mg of the FeNi / N-CNT powder prepared in step 1 and disperse it in 1 ml of deionized water to obtain a concentration of 10 mg / ml. Subsequently, take 5 μl of the above dispersion and gently drop-coat it on the surface of the GCE, and dry it naturally in the air to obtain an Fe / Ni / N-CNT / GCE biosensor.

[0049] The electrochemical detection of DA and the electrochemical performance test of the material are both carried out on a CHI 660E electrochemical workstation, and a three-electrode system is used for testing. Among them, Fe / Ni / N-CNT / GCE is used as the working electrode, a saturated calomel electrode (SCE) and a platinum (Pt) wire electrode are used as the reference electrode and the counter electrode respectively. The parameter range is as follows: 0.01 M PBS is used as the electrolyte; the scanning range is -0.2 - 0.6; the pulse width = 0.06 s; the sampling width = 0.02 s.

[0050] From Figure 1It can be seen that the Fe / Ni / N-CNT prepared in Example 1 has a broad peak at 26.6°, corresponding to the (002) plane of graphite carbon (C-PDF#99-0057); diffraction peaks appear at 43.49°, 50.67° and 74.54°, corresponding to the (111), (102) and (220) crystal planes of the Fe / Ni alloy (Fe / Ni-PDF#47-1417).

[0051] Figure 2 It shows that Fe / Ni / N-CNTs have a uniformly distributed tubular structure. From Figure 1 , it can be seen from b that Fe / Ni / N-CNTs exhibit a high degree of curvature, which may be due to the anisotropy of Fe and Ni during the catalytic process. At the same time, it can also show that the tubular ports of Fe / Ni / N-CNTs are open, indicating that the metal catalyst at the top of the carbon nanotubes has been removed during the pickling process.

[0052] Figure 3 It shows that the in-situ catalytically generated iron-nickel alloy is uniformly embedded in the carbon nanotubes, with a size of about 6-8 nm.

[0053] Figure 4 It shows that the elements C, N, O, Fe, and Ni coexist in Fe / Ni / N-CNT.

[0054] Figure 5 It shows the respective proportions of the elements C, N, Fe, and Ni, which are 93.5%, 3.3%, 1.9%, and 1.2% respectively. It can be found that the proportions of Fe and Ni elements are not very different, indicating that the Fe and Ni elements are relatively evenly distributed during the formation of the alloy.

[0055] Figure 6 It can further reflect the graphitization degree of Fe / Ni / N-CNT, which is usually represented by the ratio of the D peak to the G peak. It can be found that the I D / I G of Fe / Ni / N-CNT is 0.87, indicating that the material has a good graphitization degree.

[0056] Figure 7C-N materials without FeCl3·6H2O and C4H6O4Ni·4H2O were prepared by the same material preparation method, Fe / N-CNT catalyzed by adding only 2 g of FeCl3·6H2O, Ni / N-CNT catalyzed by adding only 2 g of C4H6O4Ni·4H2O, and the Fe / Ni / N-CNT material prepared in Example 1. Subsequently, the above four prepared catalytic materials were used to prepare DA sensors by the same method, and then 100 μM DA was detected under the same conditions (0.01 M PBS as the electrolyte; scanning range: -0.2 - 0.6; pulse width = 0.06 s; sampling width = 0.02 s). It can be found from the experimental results that compared with C-N, Fe / N-CNT, and Ni / N-CNT catalysts, Fe / Ni / N / N-CNT has a significantly enhanced peak current, indicating that Fe / Ni / N / N-CNT has superior oxidation performance for DA.

[0057] Figure 8 It shows that the detection concentration range of the Fe / Ni / N-CNT / GCE sensor for DA is: 1 pM - 400 μM, including three concentration orders of magnitude, and the detection range is wide. Secondly, according to Figure 8 , b, the linear relationship in the range of 1 - 100 pM is: I (μA) = 3.757×10 -3 C DA(pM) + 0.132 (R 2 = 0.922). Calculated according to the formula of the lowest detection limit (LOD) = 3σ / S (N = 3), LOD = 0.5 pM. Here, σ represents the standard error of the response current value, S represents the slope of the calibration curve, and S / N represents the signal-to-noise ratio.

[0058] Figure 9 It shows that when ascorbic acid and uric acid coexist, the sensor can obtain well-separated voltammetric peaks, and the corresponding separation peaks are 232 mV (from AA to DA), 164 mV (from DA to UA), and 396 mV (from AA to UA), respectively. Therefore, when detecting dopamine, it is easy to distinguish the interfering ascorbic acid and dopamine, showing good selectivity.

[0059] To test the anti-interference ability of Fe / Ni / N-CNT / GCE in detecting DA, we used Fe / Ni / N-CNT / GCE in 0.1 M PBS (pH 7.0) with DA, Ca 2+ , Fe 2+ , K + , Na + , NH4 + , glucose (Glucose), glutamic acid (Glutamic), as Figure 10As shown. It can be seen from the figure that only DA shows an obvious oxidation peak in the solution for Fe / Ni / N-CNT / GCE, indicating that this sensor can detect DA molecules, but cannot detect several other ions or molecules other than DA, and has good anti-interference ability.

[0060] Under the optimal conditions, the repeatability and reproducibility of the Fe / Ni / N-CNT / GCE biosensor for DA detection were studied. As Figure 11 , as shown in a and b, in a 100 μM DA solution, the same biosensor was used for 6 tests, and the RSD calculated from the 6 currents was 1.52%, indicating that the Fe / Ni / N-CNT / GCE biosensor has good reproducibility for DA detection. As Figure 11 , as shown in c and d, 6 biosensors with Fe / Ni / N-CNT / GCE were prepared according to the same procedure, and a 100 μM DA solution was detected under the same conditions. The RSD of the peak current numbers obtained from the 6 electrodes was calculated to be 4.73%. These results show that the Fe / Ni / N-CNT / GCE biosensor has good reproducibility for DA detection.

[0061] Figure 12 The results show that when the Fe / Ni / N-CNT / GCE biosensor detects DA, the oxidation current increases very fast and reaches equilibrium within 1.8 s, indicating that the DA diffusion process is relatively fast.

[0062] Through Figure 13 , it can be known from a that in 100 μM DA, the peak current increases with the increase of the scanning rate. Figure 13 , b shows the good linearity between I and v: I pa (μA) = 2.26v + 3.057 (R 2 = 0.997) and I pc (μA) = -1.705v + 6.987 (R 2 = 0.999), indicating that the reaction of the Fe / Ni / N-CNT / GCE biosensor when detecting DA is a diffusion-controlled process. In addition, as v increases, E pa and E pc shift positively. The electron transfer rate k of Fe / Ni / N-CNT / GCE can be calculated through the Laviron equation s = 5.212 s -1 , compared with some literature reports (title: rGO / ReO3 nano composite modifiedelectrode for the ultra-sensitive determination of dopamine and uric acid; ks = 0.14 s -1 ) compared, k s is larger, indicating that the electron transfer rate of DA on Fe / Ni / N-CNT / GCE is very fast.

[0063] From Figure 14 it can be seen that after the DA generates a response current, there is no obvious current drop after 4 ks, indicating that the Fe / Ni / N-CNT / GCE biosensor has good stability.

[0064] The above embodiments are only the optimal embodiments of the present invention. Referring to the same preparation method, when the mass ratio of glucose to melamine is in the range of 1-3:10-20, and the mass ratio of FeCl3·6H2O to C4H6O4Ni·4H2O is in the ranges of 1:2, 1:1 and 2:1, and the carbonization temperature of Fe / Ni / N-CNT / GCE is in the ranges of 700 °C, 800 °C, 900 °C and 1000 °C, the same or similar technical effects can be achieved.

[0065] The above-described embodiments are only preferred embodiments given to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention is subject to the claims.

Claims

1. A method for detecting dopamine by using an in-situ synthesized iron-nickel alloy / nitrogen-doped carbon nanotube modified electrode, characterized in that, The steps include: (1) dissolving a certain amount of sodium chloride, glucose and melamine in deionized water, gradually adding a certain amount of FeCl3·6H2O and C4H6O4Ni·4H2O to the mixed solution during continuous stirring, and then stirring under heating until the water evaporates to obtain a dry block solid; the mass ratio of the glucose to the melamine is 1~3:10~20; the mass ratio of the FeCl3·6H2O to the C4H6O4Ni·4H2O is 1~2:2~1; (2) transferring the dried solid block obtained in step (1) to an oven for further drying, and then ball-milling the solid block to obtain a pink powder sample; (3) The pink powder sample obtained in step (2) is calcined in a N2 atmosphere to obtain a black powder sample; the calcination is first heated to 300°C and maintained for 2 hours; then the temperature is increased to 500°C and maintained for 2 hours; then the temperature is increased to 800°C and maintained for 4 hours; and finally the temperature is lowered to room temperature; (4) The black powder sample obtained in step (3) is acid-washed, water-washed, and freeze-dried to obtain a Fe / Ni / N-CNT composite material; (5) polishing and cleaning the glassy carbon electrode, then placing it in ethanol and deionized water for ultrasonic treatment, and finally drying it at room temperature to obtain the glassy carbon electrode to be modified; (6) The Fe / Ni / N-CNT powder prepared in step (4) was dispersed in deionized water to obtain a dispersion with a mass volume fraction of 10 mg / ml. Then, 5 μl of the dispersion was dropwise applied to the surface of the glassy carbon electrode prepared in step (5) and dried to obtain a Fe / Ni / N-CNT / GCE biosensor. (7) In dopamine standard solutions of different concentrations, a conventional three-electrode system was used, with Fe / Ni / N-CNT / GCE as the working electrode, platinum wire as the counter electrode, and saturated calomel electrode as the reference electrode. The voltammetric response signal was recorded and a current-concentration standard curve was drawn. When the sample was tested, the sample response signal was compared with the standard curve to obtain the DA concentration of the corresponding sample.

2. The method according to claim 1, characterized in that, In step (1), the heating temperature is 60°C.

3. The method according to claim 1, characterized in that, In step (2), the drying is performed at 60° C. for 24 hours.

4. The method according to claim 1, characterized in that, In step (2), the ball milling is performed at a speed of 400 rpm / min for 4 hours.

5. The method according to claim 1, characterized in that, In step (4), the acid washing is carried out by stirring in 0.1 M hydrochloric acid for 10 min.

6. The method according to claim 1, characterized in that, In step (5), the frequency of the ultrasonic treatment is 40KHZ, the input power is 80 W, and the treatment time is 5 minutes.

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