Ginkgo biloba flower-derived porous carbon / thionine ratio-type electrochemical sensor and its application

Abstract

The application discloses a Jindalai flower carbon material, a preparation method thereof, a Jindalai flower carbon material / thionine ratio type electrode, and application of the Jindalai flower carbon material / thionine ratio type electrode in simultaneous detection of ascorbic acid and uric acid.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, specifically relating to a porous carbon / thionine ratio electrochemical sensor derived from azalea and its application. Background Technology

[0002] Ascorbic acid (AA) is a polyhydroxy compound with the chemical formula C6H8O6. It plays a crucial role in a series of important metabolic activities in the human body, primarily promoting peptide synthesis, the hydrolysis of proline and lysine, and the synthesis of adrenaline. AA deficiency can lead to various diseases and disorders, such as Parkinson's disease and cardiovascular disease, while excessive AA intake can cause urinary tract stones, diarrhea, and stomach cramps. Therefore, accurate measurement of AA is vital for human health. Uric acid (UA), with the chemical formula C5H4N4O3, is slightly soluble in water and readily forms crystals. It is an important small biomolecule in the human body. Uric acid is a trioxypurine, the final product of purine metabolism, and its alcohol form is weakly acidic. Uric acid is an antioxidant with neuroprotective effects. Gout, hyperuricemia-related arthritis, diabetes, high cholesterol, leukemia, and various other diseases can be diagnosed by measuring uric acid levels. Therefore, uric acid levels in body fluids can effectively reflect the body's metabolic and immune function.

[0003] Therefore, the detection of amino acids (AA) and amino acids (UA) in human physiological fluids is crucial. Currently, there are many methods for detecting biomolecules AA and UA, such as chromatography, chemiluminescence, and electrochemical methods. The first two methods often require time and significant analytical resources, or complex preparation processes and expensive reagents, thus limiting their widespread application. However, electrochemical sensors are simple and quick to operate, highly sensitive, and low-cost, making them the primary choice for biomolecule detection. Although there are reports on the detection of AA and UA, the overlapping oxidation peaks of both on conventional electrodes, slow electron transfer, excessive overpotential, and electrode oxidation product contamination prevent direct detection using bare electrodes, posing challenges to the electrochemical detection of AA and UA. To address this issue, modifying electrodes with biomass carbon-based materials can increase the electroactive specific surface area, reduce charge transfer resistance, and significantly enhance electrochemical performance.

[0004] In recent years, the preparation of multifunctional electrochemical sensing electrode materials using biomass waste as a carbon source has become a hot trend. For example, Wang et al. prepared layered mesoporous-macroporous carbon network aerogels (CNs-HMCNAs) using biomass apples as raw materials. This biomass carbon material has a unique mesoporous-macroporous structure, a large specific surface area, and many defect sites. When modified with this material, a glassy carbon electrode (CNs-HMCNAs / GCE) was used to detect amino acids (AA) using an amperometric method. Compared with CNTs / GCE or bare GCE, CNs-HMCNAs / GCE showed higher sensitivity for AA and a lower detection limit of 0.22 μM (S / N=3), demonstrating superior analytical performance. Biomass-derived carbon materials have advantages such as unique structure, wide applicability, high sustainability, and renewability. Therefore, the synthesis of multifunctional carbon materials using biomass as a carbon precursor can be used as electrode materials for electrochemical sensors. The preparation of biomass carbon materials involves pretreatment such as screening, washing, and drying, followed by high-temperature calcination. Common methods include hydrothermal carbonization, high-temperature pyrolysis, and activation. Biomass carbon materials possess excellent electrical conductivity and structural stability, as well as the ability to achieve high-voltage charging and discharging, and are often used as electrode materials for supercapacitors.

[0005] Rhododendron amurense, also known as azalea or xiong'an rhododendron, scientific name Rhododendron dauricum L. It grows on hillsides, grasslands, and thickets, and is widely distributed and easy to collect. The azalea flower also has medicinal uses; every part of it is valuable. Its leaves, known as "Chaoyao" in Traditional Chinese Medicine, can treat chronic bronchitis, coughs, asthma, high blood pressure, arthritis, urinary difficulties, alopecia, and stomach cramps. The leaves or leafy branches are called "Mongolian medicine," used to treat indigestion, diarrhea due to cold, dry cough, lung disease, kidney deficiency, edema, weakness, and spermatorrhea. Thionium (Thi) is a positively charged phenothiazine dye with excellent electrochemical activity and can also be used as an electrode modification material. Summary of the Invention

[0006] The purpose of this invention is to provide a high-performance porous carbon / thione ratio electrochemical sensor derived from azalea and its applications.

[0007] The azalea carbon material is prepared by the following method:

[0008] 1) Take the petals of azalea flowers, wash and dry them, and grind them into powder;

[0009] 2) Take the powder prepared in step 1), add water and KOH solution, mix well, filter, retain the filtrate, and dry;

[0010] 3) Carbonize at 750~850°C for 2~4 hours under N2 atmosphere to obtain black granular carbon material;

[0011] 4) Add the carbon material described in step 3) to an acidic solution to remove impurities and neutralize unreacted KOH, then heat and stir in a water bath at 55-65°C for 10-15 hours.

[0012] 5) Centrifuge, remove the supernatant, dry the obtained solid material, grind it to obtain azalea carbon material;

[0013] The mixing described in step 2) involves ultrasonic vibration for 2-4 hours;

[0014] The carbonization described in step 3) is carried out at a temperature of 800℃ for 3 hours.

[0015] Step 4) The acidic solution is a hydrochloric acid solution, heated in a water bath at 60°C and stirred for 12 hours.

[0016] The azalea carbon material / anthine ratio electrode is prepared by the following method:

[0017] 1) Take the azalea carbon material obtained in step 5) above, dissolve it in dimethylformamide, mix well, and obtain a mixture;

[0018] 2) Grind, polish, and clean the glassy carbon electrode until it is clean and smooth, and dry it with nitrogen gas; take the mixture described in step 1), drop it onto the treated glassy carbon electrode, and dry it to obtain the azalea carbon material / glassy carbon electrode KACM / GCE.

[0019] 3) Dissolve thionine in hot water to prepare a Thi solution; immerse the azalea carbon material / glassy carbon electrode obtained in step 2) in the Thi solution, rinse after immersion for 5-50 minutes, and dry to obtain azalea carbon material / thionine ratio electrode.

[0020] The mixing described in step 1) involves ultrasonic oscillation for 2.5 to 3.5 hours.

[0021] Step 3) The soaking time is 15 minutes, and the Thi solution has a concentration of 1.0 mg / mL. -1 .

[0022] Application of azalea carbon material / thion ratio electrode in the simultaneous detection of ascorbic acid and uric acid;

[0023] The simultaneous detection of ascorbic acid and uric acid uses a three-electrode system with the aforementioned azalea carbon material / thionine ratio type electrode as the working electrode, Ag / AgCl as the reference electrode, and a platinum wire electrode as the counter electrode, and is performed by an electrochemical method.

[0024] The electrochemical methods mentioned are cyclic voltammetry, chronoamperometry, chronopotentialometry, open-circuit potential, cyclic voltammetry, linear sweep voltammetry, differential pulse voltammetry, conventional pulse voltammetry, square wave voltammetry, or AC impedance voltammetry.

[0025] This invention provides a rhododendron flower carbon material, which is prepared by the following method: Rhododendron flower petals are taken, washed, dried, and ground into powder; water and KOH solution are added, mixed, filtered, and the filtrate is retained and dried; carbonized at 750-850°C for 2-4 hours under a N2 atmosphere to obtain black granular carbon material; an acidic solution is added to remove impurities and neutralize unreacted KOH; the mixture is heated and stirred in a water bath at 55-65°C for 10-15 hours; centrifuged, the supernatant is removed, the resulting solid is dried, and ground to obtain the rhododendron flower carbon material; a rhododendron flower carbon material / sulfuron ratio type electrode is prepared by the following method: Rhododendron flower carbon material is taken, dissolved in dimethylformamide, and mixed to obtain a mixed solution; a glassy carbon electrode is ground, polished, and cleaned until clean and smooth, and dried with nitrogen; the mixed solution obtained in step 1) is drop-coated onto... After treatment, the glassy carbon electrode is dried to obtain a rhododendron carbon material / glassy carbon electrode KACM / GCE. Thionium is dissolved in hot water to prepare a Thi solution. The rhododendron carbon material / glassy carbon electrode is immersed in the Thi solution, rinsed, and dried to obtain a rhododendron carbon material / thionium ratiometric electrode. The rhododendron carbon material / thionium ratiometric electrode is used for the simultaneous detection of ascorbic acid and uric acid. Its advantages are: this invention uses rhododendron as raw material, activates and carbonizes to prepare porous carbon material KACM, which has better electrochemical performance than unactivated carbon material ACM and bare GCE. Modifying it onto a glassy carbon electrode and directly assembling thionium (Thi) molecules constructs a ratiometric electrochemical sensor for the simultaneous detection of AA and UA. Using Thi as a reference can reduce the detection error of AA and UA. This sensing platform has a wide linear range and low detection limit for the detection of AA and UA, and has been successfully applied to the detection of AA and UA in human urine. Attached Figure Description

[0026] Figure 1 Flowcharts for the preparation of KACM and the Thi / KACM / GCE ratio electrode;

[0027] Figure 2 (A) SEM plot of ACM, (B) SEM plot of KACM, (C) XRD plot of ACM, (D) XRD plot of KACM;

[0028] Figure 3 (A) N2 adsorption-desorption isotherm of ACM, (B) N2 adsorption-desorption isotherm of KACM (the inset is a pore size distribution diagram).

[0029] Figure 4 Raman spectra of KACM;

[0030] Figure 5(A) XPS plot of KACM, (B) High-resolution spectrum of C1s, (C) High-resolution spectrum of N1s, (D) High-resolution spectrum of O1s.

[0031] Figure 6 (A) Cyclic voltammograms of the three working electrodes in a mixed solution of 5 mM K3Fe(CN)6 and 0.1 M KCl; (B) Cyclic voltammograms of the three working electrodes in a mixed solution of 5 mM [Fe(CN)6]. 3- / 4- EIS diagram of a mixed solution of 0.1 M KCl;

[0032] Figure 7 (A) CV diagram of the three electrodes in N2-saturated PBS, (B) CV diagram of the three electrodes in the simultaneous presence of 1 mM AA and UA.

[0033] Figure 8 (A) Scan rate is 10 ~ 110 mV s -1 At that time, the CV diagram of Thi / KACM / GCE in N2-saturated PBS, (B) the relationship between peak current and scan rate;

[0034] Figure 9 (A) CV curves of Thi / KACM / GCE in N2-saturated PBS (0.1 M, pH=6) containing 1 mM AA and UA at different soaking times; (B) Line graph of Thi oxidation peak current versus soaking time.

[0035] Figure 10 (A) CV plots of Thi / KACM / GCE against 1 mM AA and UA in N2-saturated PBS at different pH values; (B) Line plots of oxidation peak current values ​​of Thi, AA and UA versus pH.

[0036] Figure 11 (A) DPV plot of Thi / KACM / GCE simultaneously measuring different concentrations of AA and UA in PBS, (B) Peak current ratio of AA, UA and Thi and concentration relationship plot, (C) DPV plot of KACM / GCE simultaneously measuring different concentrations of AA and UA in PBS, (D) Peak current and concentration relationship plot.

[0037] Figure 12 Figure showing the anti-interference test results of Thi / KACM / GCE. Detailed Implementation

[0038] Example 1: Preparation of carbon materials from azalea flowers

[0039] After washing and drying the collected azalea petals, grind them into powder using a ball mill. Accurately weigh 1 g of azalea powder and 2 g of KOH, mix them together in a beaker containing 30 mL of distilled water, and sonicate for 3 hours (to ensure uniform mixing). Then filter through filter paper, and dry the filter material above the filter paper in a drying oven at 80°C. Place the dried azalea material in a tube furnace and carbonize it at 800°C for 3 hours under a N2 atmosphere to obtain black granular carbon material. Grind the black granular carbon material into powder using a mortar and pestle, add it to a hydrochloric acid solution to remove metallic impurities and unreacted KOH, and simultaneously heat in a water bath at 60°C with stirring for 12 hours. After the reaction is complete, the mixture is placed in a centrifuge tube and an appropriate amount of distilled water is added. The mixture is centrifuged at 8000 rpm to remove the supernatant. The mixture is centrifuged multiple times until neutral. It is then dried in a drying oven and ground again to obtain activated azalea carbon material KACM. The preparation process is as follows: Figure 1 .

[0040] Unactivated azalea carbon material was used as a control group. 1g of azalea powder was accurately weighed, and activation with KOH was not performed. The remaining steps were the same as described above to obtain unactivated azalea carbon material, i.e., ACM.

[0041] Example 2: Preparation of a rhododendron carbon material / sulfide ratio electrode

[0042] Take a certain amount of KACM and ACM and dissolve them in N , N A mixture of carbon material and DMF was obtained by ultrasonic oscillation for 3 hours in a dimethylformamide (DMF) solution. Thionium was dissolved in hot water to prepare a 1.0 mg / mL solution. -1 Thi solution. Before modifying the electrode, the glassy carbon electrode must be polished. The process is as follows: the glassy carbon electrode is polished sequentially on a polishing cloth using alumina polishing powders with diameters of 1.0 μm, 0.3 μm, and 50 nm. After rinsing with distilled water, it is ultrasonically cleaned in nitric acid solution, anhydrous ethanol, and distilled water respectively until the mirror surface is clean and smooth. Finally, it is dried with high-purity nitrogen gas. The preparation of the ratio type electrode is as follows. Figure 1 A certain amount of the mixture was drop-coated onto a clean glassy carbon electrode and dried in an infrared lamp drying oven to obtain KACM / GCE and ACM / GCE. The prepared KACM / GCE was then immersed in 1.0 mg / mL water. -1 Soak the thion-modified azalea carbon material electrode Thi / KACM / GCE in Thi solution for 15 minutes (5-50 minutes is acceptable), then rinse off the poorly adsorbed Thi with water and air dry.

[0043] Example 3 Characterization methods for carbon materials KACM and ACM

[0044] The morphology of carbon materials was characterized by SEM, the degree of graphitization of carbon materials was detected by XRD, the specific surface area and pore properties of carbon materials were studied by N2 adsorption-desorption curves, the elemental composition and content of carbon materials were characterized by XPS, and the degree of defects of carbon materials were characterized by Raman spectroscopy.

[0045] First, the morphology and microstructure of the two carbon materials were characterized using SEM. Figure 2 In materials A and B, ACM exhibits a smooth surface and a three-dimensional (3D) mesoporous structure. In contrast, KACM's SEM image shows a rougher surface with numerous cross-linked carbon nanoparticles forming a branched nanostructure, thus increasing KACM's specific surface area. X-ray diffraction was used to further characterize the structures of both materials. Figure 2 As shown in C and D, both ACM and KACM show two diffraction peaks at 23° and 44°, which are attributed to the (002) crystal plane of graphitic carbon and the (101) crystal plane of disordered carbon, respectively.

[0046] The N2 adsorption-desorption isotherms further characterized the pore structure of the two carbon materials. Figure 3 A represents the N2 adsorption-desorption isotherm of ACM. The figure shows that ACM exhibits a Type IV isotherm with an H4 hysteresis loop, indicating the presence of mesoporous structures. The specific surface area of ​​ACM, calculated using the BET method, is 417.386 m². 2 g -1 According to the pore size distribution diagram in the illustration, the ACM pore size is mainly distributed at 2 nm, 3 nm, and 5 nm, with a pore volume of 0.197 cm³. 3 g -1 . Figure 3 B is the N2 adsorption-desorption isotherm of KACM, where KACM is under a relative pressure. P / P A significant hysteresis loop exists in the range of 0.4 to 1.0, with a BET surface area of ​​788.922 m². 2 g -1 The pore sizes are mainly distributed between 2 nm and 3 nm, and the pore volume is 0.362 cm³. 3 g -1 Therefore, compared with ACM, KACM has a larger BET specific surface area and larger pore volume, and has a hierarchical structure of micropores and mesopores, which is more conducive to improving electrochemical reactions and enhancing electrochemical performance.

[0047] The comparison of the characterization results of KACM and ACM shows that KACM is more suitable as an electrode material for electrochemical sensors than ACM, therefore a more accurate characterization of KACM is necessary. The molecular structure of KACM was characterized using Raman spectroscopy. Figure 4The Raman spectrum from KACM shows the position at 1340 cm⁻¹. -1 D-band at 1584 cm -1 The G-band is related to the degree of defects in the crystal structure, i.e., amorphous carbon, while the G-band is related to the ordered structure in the carbon lattice, i.e., graphitic carbon. According to the literature, the relative intensity ratio of the D-band to the G-band ( I D / I G The value is proportional to the number of defect sites in the material. The KACM is calculated... I D / I G It is 2.89, which is greater than the previously reported ratio of carbon fiber ( I D / I G =1.511) and carbon nanotubes ( I D / I G =0.999), indicating that the prepared KACM has a large number of defect sites, which is beneficial to the electrochemical reaction.

[0048] The surface composition of KACM was studied using XPS. Figure 5 A shows the XPS full spectrum from KACM, revealing three characteristic peaks at approximately 533 eV, 400 eV, and 284 eV, corresponding to the characteristic peaks of O 1s, C 1s, and N 1s, respectively. The atomic percentages of C, N, and O are 74.33%, 2.19%, and 23.48%, respectively. Further analysis of C, N, and O elements was conducted. Figure 5 B is the high-resolution spectrum of C1s. The C1s spectrum can be fitted to the C in the C=C double bond at 284.4 eV, the C in the COC bond at 284.8 eV, the C in the C-OH at 285.6 eV, and the C in the C=O double bond at 286.3 eV. Figure 5 C represents the high-resolution spectrum of N1s, which can be fitted to pyridine nitrogen, pyrrole nitrogen, graphitic nitrogen, and oxidized nitrogen at 398.4, 400.1, 401.1, and 402.2 eV, respectively. Figure 5 D represents the high-resolution spectrum of O1s. The O1s spectrum can be fitted to the O in C=O at 532.2 eV and the O in COC at 533.3 eV. The presence of N atoms in KACM carbon materials may facilitate the generation of more defect sites, thereby improving electrochemical electrocatalytic performance.

[0049] Example 4 Electrochemical Methods and Experimental Parameters

[0050] The electrochemical methods used in this embodiment are: cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse voltammetry. The electrochemical experiments were conducted on a CHI660E electrochemical workstation using a three-electrode system: bare GCE (3 mm diameter), KACM / GCE, ACM / GCE, and Thi / KAPC / GCE as working electrodes; Ag / AgCl as the reference electrode; and a platinum wire electrode as the counter electrode. Unless otherwise specified, the electrolyte was a 0.1 M PBS phosphate buffer solution with a pH of 6, prepared from 0.1 M NaOH, Na₂HPO₄, and NaH₂PO₄.

[0051] CV tests were performed in the range of −0.2 to +0.6 V at a scan rate of 10 mV / s. -1 EIS testing was performed with an oscillation voltage of −0.1V, a frequency range of 0.01Hz to 100kHz, and an AC amplitude of ±10mV; DPV testing was performed with a potential range of −0.4V to +0.8V, a potential increment of 4mV, and an amplitude of 50mV. Unless otherwise specified, the scan rate for both CV and LSV methods was 10mV s. -1 .

[0052] Cyclic voltammetry was used to evaluate the electrochemical performance of the modified electrode. Figure 6 A shows the CV plots of the three working electrodes in a mixed solution of 5 mM K3Fe(CN)6 and 0.1 M KCl. Compared with the bare GCE and ACM / GCE, KACM / GCE showed a higher redox current and a smaller redox potential difference. The heterogeneous electron transfer rate of KACM / GCE (0.00423 cm·s⁻¹) was calculated according to the Nicholson equation. -1 (Higher than ACM / GCE (0.00246 cm·s)) -1 ) and naked GCE (0.00214 cm·s) -1 The heterogeneous electron transfer rate indicates that activated KACM increases the electron transfer rate. Calculations based on the Randles-Sevcik equation show that the electrochemical active areas of KACM / GCE, ACM / GCE, and bare GCE are 0.102, 0.095, and 0.07 cm², respectively. 2 The electrochemical active area of ​​KACM / GCE is higher than that of KACM / GCE and GCE. The faster electron transfer rate and higher electrochemical active area of ​​KACM / GCE can be attributed to the large BET specific surface area, hierarchical porous structure, and abundant defect sites of KACM, which are beneficial for enhancing electrochemical performance.

[0053] Electrochemical impedance spectroscopy is used to analyze and study the electrochemical sensing mechanism, diffusion coefficient, and solution resistance (Ro) at the electrode / electrolyte interface. s ) and charge transfer resistance (Rct )wait. Figure 6 B represents KACM / GCE, ACM / GCE, and bare GCE at 5 mM [Fe(CN)6]. 3- / 4- EIS plots of KACM / GCE, ACM / GCE, and bare GCE were obtained by software fitting. ct The impedances are 39.95, 106.9, and 116.2 Ω, respectively. Compared with ACM / GCE and GCE, KACM / GCE has a lower electron transfer impedance and a faster electron transfer rate, which is consistent with the results obtained from cyclic voltammetry.

[0054] The electrocatalytic performance of three electrode pairs for simultaneous detection of AA and UA was studied using cyclic voltammetry. Figure 7 A shows the CV diagrams of three electrodes—KACM / GCE, ACM / GCE, and bare GCE—in N2-saturated PBS without AA and UA. No redox peaks were observed in any of the three electrodes, and the background current of KACM / GCE was greater than that of ACM / GCE and bare GCE, possibly due to the larger electrochemical active area of ​​KACM / GCE. Figure 7 B shows the CV curves of the three electrodes with 1 mM AA and UA simultaneously. The curves show that all three electrodes produced oxidation peaks for AA and UA. Compared with ACM / GCE and bare GCE, KACM / GCE has a higher current response to 1 mM AA and UA. The oxidation peak potential of KACM / GCE for AA is about 0.2 V, and the peak potential for UA is about 0.56 V. The potential difference between the two oxidation peaks is about 360 mV, which can be well distinguished.

[0055] The data above lead to the conclusion that, compared with ACM / GCE and bare GCE, KACM / GCE exhibits a higher heterogeneous electron transfer rate, a higher electrochemical active area, a smaller charge transfer resistance, and a better response to both AA and UA, while also being able to distinguish their oxidation peaks. Therefore, Thi was assembled on KACM / GCE to construct a Thi / KACM / GCE ratiometric electrochemical sensor for the simultaneous detection of AA and UA.

[0056] Example 5: Effects of Thi / KACM / GCE on AA and UA

[0057] I. Dynamics Research

[0058] The effect of scan rate on the redox process of Thi / KACM / GCE was investigated using cyclic voltammetry. Figure 8 A represents the scan rate range of Thi / KACM / GCE in PBS, from 10 to 110 mV / s. -1In the CV plot, the peak current increases with increasing scan rate, and both the oxidation peak current and the reduction peak current increase linearly with scan rate, as shown below. Figure 8 B, the corresponding linear regression equation, Thi oxidation peak: y = 0.124x + 2.72 (R 2 =0.993), Thi reduction peak: y = -0.215x- 4.61 (R 2 =0.991), AA: y = 0.254ⅹ+ 9.24 (R 2 =0.986), UA: y = 0.426ⅹ+ 8.31 (R 2 =0.99). This indicates that the electrochemical behavior of AA and UA on Thi / KACM / GCE is a surface-controlled adsorption process.

[0059] II. Effect of Immersion Time of Thi / KACM / GCE in Thi Solution

[0060] The effect of immersion time in Thi / KACM / GCE solution on Thi solution was studied using cyclic voltammetry. Figure 9 A. Soaking in Thi solution for different times did not significantly affect the oxidation peak current of AA and UA, but it did affect the peak current response of Thi. Figure 9 B is a line graph showing the relationship between the peak current of the Thi oxidation process and the soaking time. As the soaking time increases from 5 minutes to 15 minutes, the increase in peak current is significant; however, from 15 minutes to 50 minutes, the increase is less pronounced. Considering the time cost of the experiment, a soaking time of 15 minutes is recommended.

[0061] III. The Effect of pH

[0062] The pH value of the electrolyte PBS also affects the electrochemical response of AA and UA. Figure 10 A used cyclic voltammetry to investigate the oxidation peak currents of 1 mM AA and UA in N2-saturated PBS at different pH values ​​using the Thi / KACM / GCE method. Figure 10 B is a line graph of oxidation peak current versus PBS pH value. As pH increases, the oxidation peak current values ​​of Thi, AA and UA all increase first and then decrease, reaching their maximum values ​​at pH = 6. Therefore, PBS with pH = 6 was selected as the substrate for the electrochemical reaction.

[0063] IV. Thi / KACM / GCE for the detection of AA and UA

[0064] Under optimal experimental conditions, Thi / KACM / GCE simultaneously measured the oxidation currents of different concentrations of AA and UA in N2-saturated PBS using the DPV method, such as... Figure 11As the concentrations of A, AA, and UA increased from 0.05 mM to 9 mM, the oxidation peak current also increased. Figure 11 B shows that in the range of 0.05 ~ 9 mM, the ratio of AA to Thi peak current and the AA concentration are linearly related: I AA / I Thi =0.089 C AA + 0.446 (R) 2 =0.997), the detection limit was 6.4 μM (S / N=3); the peak current ratio of UA and Thi also showed a linear relationship with the UA concentration: I UA / I Thi = 0.137 C UA + 0.2 (R) 2 =0.997), and the detection limit was 10 μM (S / N=3).

[0065] Under optimal experimental conditions, the current response of unmodified KACM / GCE in PBS with different concentrations of AA and UA was detected using the DPV method. Figure 11 C. As the concentrations of AA and UA increase, the oxidation peak current also increases. Figure 11 D shows the relationship between the peak currents of AA and UA and their concentrations. For AA concentrations of 0.075 ~ 6 mM (R... 2 =0.995) and at 6 ~ 9 mM (R 2 =0.992) indicates a linear correlation, with a detection limit of 24.8 μM (S / N=3); when the UA concentration is 0.075 ~ 9 mM, the linear equation is I UA = 3.46 C UA +3.46 (R) 2 =0.990), and the detection limit was 22.3 μM (S / N=3). The detection limits for AA and UA were higher than those determined by Thi / KACM / GCE, indicating that Thi / KACM / GCE performs better in detecting AA and UA than KACM / GCE without Thi modification. Furthermore, the ratiometric Thi / KACM / GCE exhibits higher accuracy and smaller error in the linear equation for AA and UA.

[0066] The ratiometric Thi / KACM / GCE electrode for detecting AA and UA prepared in this study was compared with other reported electrodes for detecting AA and UA, as shown in Table 1. The results show that the Thi / KACM / GCE electrode has a wide linear range for the detection of AA and UA, and can achieve simultaneous detection of AA and UA.

[0067] Table 1 Comparison of different modified electrodes for electrochemical determination of AA and UA

[0068]

[0069] Note: PG / GCE is a pristine graphene-modified glassy carbon electrode; GO / TmPO4 / GCE is a thulium phosphate and graphene oxide nanocomposite material-modified glassy carbon electrode; GQDs / IL-SPCE is a graphene quantum dot and ionic liquid-modified screen-printed carbon electrode.

[0070] V. Reproducibility, stability, and anti-interference capability of Thi / KACM / GCE

[0071] The prepared electrode Thi / KACM / GCE was used to detect 1 mM AA and UA using the DPV method, and its Ig was recorded. AA / I Thi I UA / I Thi The value was measured 10 times in a cycle, and I was calculated. AA / I Thi The RSD is 2.37%, I UA / I Thi The RSD was 1.65%, indicating good electrode reproducibility. The stability of the Thi / KACM / GCE electrode was also investigated. The electrode was stored in a refrigerator, and after two weeks, the detected current response did not decrease significantly. Thi, AA, and UA maintained 99.1%, 97.7%, and 95.6% of the initial current response, respectively, indicating that Thi / KACM / GCE has good stability.

[0072] In actual samples, AA and UA may coexist with certain inorganic ions and organic compounds. Therefore, by adding citric acid (CA), dopamine (DA), glucose (Glu), and Na+... + and K + The anti-interference ability of the modified electrode Thi / KACM / GCE was tested. The current response of Thi / KACM / GCE to 50 mM AA and UA was measured using the DPV method in N2-saturated 0.1 M PBS (pH=6). Subsequently, three times the concentration of the anti-interference agent was added, and the results were as follows: Figure 12 (Bar chart CA, DA, Glu, Na) + and K + (These represent the addition of corresponding substances to AA and UA, respectively). The results show that the percentage change in peak current is between 96.7% and 100.3%, none of which exceeds 5% of the original current value. Therefore, this electrode has strong anti-interference ability when detecting AA and UA.

[0073] Example 6 Analysis of AA and UA in actual samples

[0074] To demonstrate the feasibility of using Thi / KACM / GCE for ratiometric detection of AA and UA in real samples, the spiked recovery method was employed to determine the levels of AA and UA in human urine samples. Using the DPV method, a certain amount of urine sample was added to nitrogen-saturated 0.1 M PBS (pH=6), followed by repeated additions of known concentrations of AA and UA, with the Ig values ​​recorded each time. AA / I Thi I UA / I Thi The values ​​(all three times). According to Figure 11 The linear regression equation of B was used to calculate the detection concentrations of AA and UA, and the specific values ​​are shown in Table 2. The average recoveries of AA and UA were 99.7% and 100.2%, respectively, with RSDs ranging from 1.2% to 3.1%. Therefore, the ratiometric electrochemical sensor constructed with the modified electrode Thi / KACM / GCE showed good precision and accuracy in the detection of AA and UA.

[0075] This invention uses biomass azalea flowers as a carbon precursor, which is activated with KOH and then carbonized at high temperature to obtain carbon material KACM. Compared with unactivated ACM, KACM has more defect sites, larger specific surface area, and larger pore volume. Compared with ACM / GCE and bare GCE, the KACM / GCE electrode has a higher electron transfer rate, a larger electrochemical active area, and a smaller charge transfer impedance, which can enhance the electrocatalysis of AA and UA. Moreover, the oxidation peak potential difference between the two is as high as 360 mV, which can simultaneously and effectively detect AA and UA. Therefore, Thi is assembled on the KACM / GCE electrode to construct a ratiometric electrochemical sensing platform for AA and UA based on Thi / KACM / GCE. Compared with KACM / GCE without Thi modification, Thi / KACM / GCE uses Thi as a reference, which reduces error, and exhibits a wider linear range and lower detection limit for the detection of AA and UA. It also shows good selectivity and stability, and demonstrates good analytical performance for the simultaneous detection of AA and UA in human urine.

Claims

1. Azalea carbon material / anthine ratio type electrode, which is prepared by the following method: (1) Take azalea carbon material and dissolve it in N , N Mix the dimethylformamide solution thoroughly to obtain a mixed solution; (2) Grind, polish, and clean the glassy carbon electrode until it is clean and smooth, and dry it with nitrogen gas; take the mixture described in step (1), drop it onto the treated glassy carbon electrode, and dry it to obtain the azalea carbon material / glassy carbon electrode. (3) Dissolve thionine in hot water to prepare a Thi solution; immerse the azalea carbon material / glassy carbon electrode described in step (2) in the Thi solution, rinse after immersion for 5~50 min, and dry to obtain azalea carbon material / thionine ratio electrode. The aforementioned azalea carbon material is prepared by the following method: 1) Take the petals of azalea flowers, wash and dry them, and grind them into powder; 2) Take the powder prepared in step 1), add water and KOH solution, mix well, filter, retain the filtrate, and dry; 3) Carbonize the dried material obtained in step 2) at 750~850°C for 2~4 hours under N2 atmosphere to obtain black granular carbon material; 4) Add the carbon material described in step 3) to an acidic solution to remove impurities and neutralize unreacted KOH, then heat and stir in a water bath at 55-65°C for 10-15 hours. 5) Centrifuge, remove the supernatant, dry the obtained solid material, grind it to obtain azalea carbon material.

2. The azalea carbon material / sulfuron ratio type electrode according to claim 1, characterized in that: The mixing process described in step 2) involves ultrasonic vibration for 2-4 hours.

3. The azalea carbon material / sulfuron ratio type electrode according to claim 2, characterized in that: The carbonization process described in step 3) is carried out at a temperature of 800°C for 3 hours.

4. The azalea carbon material / sulfuron ratio type electrode according to claim 3, characterized in that: Step 4) The acidic solution is a hydrochloric acid solution, heated in a water bath at 60°C and stirred for 12 hours.

5. The azalea carbon material / sulfonium ratio type electrode according to claim 1, 2, 3 or 4, characterized in that: The mixing in step (1) involves ultrasonic oscillation for 2.5 to 3.5 hours.

6. The azalea carbon material / sulfonium ratio type electrode according to claim 5, characterized in that: The soaking time in step (3) is 15 minutes, and the Thi solution concentration is 1.0 mg·mL. -1 .

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