Monodisperse shell-core structure MSNs (at) Au composite material as well as preparation method and application thereof

Abstract

The invention discloses a monodisperse shell-core structure MSNs (at) Au composite material and a preparation method and application thereof.The preparation method comprises the following steps that (1) distilled water and a chloroauric acid solution are mixed for condensation reflux, a sodium citrate solution is added after heating and boiling, heating reaction continues to be conducted, after the reaction is completed, cooling is conducted to the room temperature, and a colloidal gold solution is obtained; and (2) adding hexadecyl trimethyl ammonium bromide into deionized water, mixing and stirring, adding absolute ethyl alcohol after the solution becomes transparent, continuously stirring, then adding a colloidal gold solution, then adding ammonia water, dropwise adding tetraethyl orthosilicate, and after the reaction is completed, carrying out centrifugal precipitation, drying and calcining to obtain MSNs (at) Au. The prepared MSNs (at) Au composite material avoids agglomeration of colloidal gold in the electrocatalytic reaction process, so that the adsorption capacity of BPA molecules and the catalytic efficiency of electrochemical reaction are improved, the MSNs (at) Au composite material shows high sensitivity and good selectivity in BPA detection when used as a sensor, and BPA can be rapidly and accurately detected in a low concentration range.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical detection materials, and in particular to a monodisperse core-shell structure MSNs@Au composite material and a preparation method and application thereof. Background Art

[0002] Bisphenol A (BPA), a key raw material for the synthesis of polymer materials such as polycarbonate and epoxy resin, is widely used in everyday consumer products such as food containers and beverage bottles. However, as its use expands, its health risks are becoming increasingly apparent. As an endocrine disruptor (EDC), long-term exposure to BPA can affect the reproductive, immune, and nervous systems, and is also associated with metabolic diseases such as obesity and diabetes. Therefore, BPA detection has become a research priority in the fields of environmental monitoring and food safety.

[0003] Traditional BPA detection methods, such as GC-MS, HPLC, and spectroscopy, while highly sensitive and accurate, suffer from complex sample pretreatment, expensive instrumentation, and lengthy analysis times, making them difficult to meet the demands of real-time, on-site detection. In contrast, electrochemical sensors, due to their ease of operation, low cost, high sensitivity, and rapid detection, have become a research hotspot. These sensors, which reflect substance concentrations by monitoring electrochemical signals such as current and potential, have widespread applications in the environmental, food, and biomedical fields.

[0004] In the research of electrochemical sensors, nanomaterials have become key materials for improving sensor performance due to their unique physical and chemical properties. Nanomaterials have a large specific surface area, excellent electrical conductivity, catalytic properties and good dispersibility, which can significantly improve the sensitivity and response speed of the sensor. Mesoporous silica (MSNs), as a nanomaterial with an ordered pore structure and a high specific surface area, is widely used in fields such as drug delivery and catalytic reactions. In recent years, MSNs have also been introduced into the construction of electrochemical sensors. Studies have shown that they can provide abundant reaction sites and enhance the catalytic performance of electrodes. However, due to the poor electrical conductivity of MSNs, their application in electrochemical sensors is limited. How to use MSNs as a matrix material to design a composite material to improve its conductivity, and then apply it to the electrochemical detection process of BPA to improve detection sensitivity and selectivity, is the focus of current research. Summary of the Invention

[0005] The purpose of the present invention is to provide a monodisperse core-shell structure MSNs@Au composite material and its preparation method and application, in order to solve the problem that the above-mentioned MSNs have poor electrical conductivity and cannot be directly used in the electrochemical sensor detection of BPA. The present invention coats colloidal gold inside mesoporous silica to form a mesoporous silica (MSNs@Au) nanocomposite material coated with colloidal gold. This structure not only retains the high specific surface area and ordered pore structure of mesoporous silica, but also retains the electrical conductivity and electrocatalytic properties of colloidal gold, while avoiding the agglomeration of colloidal gold during the electrocatalytic reaction, thereby improving the adsorption capacity of BPA molecules and the catalytic efficiency of the electrochemical reaction. The high electrical conductivity of colloidal gold enables the MSNs@Au composite material to exhibit excellent performance in electrochemical sensors.

[0006] To achieve the above objectives, the present invention provides a method for preparing a monodisperse core-shell structured MSNs@Au composite material, comprising the following steps:

[0007] (1) Synthesis of colloidal gold

[0008] Distilled water and chloroauric acid solution were mixed and condensed under reflux, heated to a boil under stirring, and then sodium citrate solution was added, and the heating reaction was continued. After the reaction was completed, the mixture was cooled to room temperature to obtain a colloidal gold solution;

[0009] (2) Synthesis of MSNs@Au

[0010] Hexadecyltrimethylammonium bromide was added to deionized water and stirred. After the solution became transparent, anhydrous ethanol was added and continued to stir. Then, colloidal gold solution was added and mixed evenly. Then, ammonia water and tetraethyl orthosilicate were added dropwise. After the reaction was complete, MSNs@Au was obtained after centrifugal precipitation, drying and calcination.

[0011] Preferably, in step (1), the mass percentage of chloroauric acid in the chloroauric acid solution is 0.8-1.2%, and the mass percentage of sodium citrate in the sodium citrate solution is 0.8-1.2%.

[0012] Preferably, in step (1), the volume ratio of distilled water, chloroauric acid solution and citric acid solution is 100:(0.8-1.2):(1.5-3).

[0013] Preferably, in step (2), the mass volume ratio of hexadecyltrimethylammonium bromide and tetraethyl orthosilicate is 200-320 mg:1 mL.

[0014] Preferably, in step (2), the amount of colloidal gold solution added is 4 to 12 mL.

[0015] Preferably, in step (2), the calcination temperature is 500-600° C. and the calcination time is 5-8 hours.

[0016] The second aspect of the present invention provides a monodisperse core-shell structure MSNs@Au composite material, which is prepared by the above-mentioned preparation method.

[0017] Preferably, the monodisperse core-shell structure MSNs@Au composite material includes colloidal gold and mesoporous silica, and the colloidal gold is coated inside the mesoporous silica.

[0018] The third aspect of the present invention provides the application of the monodisperse core-shell structure MSNs@Au composite material, and the application of the monodisperse core-shell structure MSNs@Au composite material in the electrochemical detection of bisphenol A.

[0019] Preferably, in the electrochemical detection process of bisphenol A, the detection range of bisphenol A of the monodisperse core-shell structure MSNs@Au composite material is 0.01-40 μM, and the detection limit is 3.3 nM (S / N=3).

[0020] Therefore, the present invention adopts the above-mentioned monodisperse core-shell structure MSNs@Au composite material and its preparation method and application, which have the following beneficial effects:

[0021] (1) The present invention prepares an electrochemical sensor based on a nanocomposite material of mesoporous silica coated with colloidal gold, which achieves high-sensitivity detection of BPA. The MSNs@Au sensor has the advantages of simple operation, low cost, and fast response, and has broad application prospects.

[0022] (2) In the present invention, the MSNs@Au composite material is modified on the surface of a glassy carbon electrode (GCE) to construct a sensor. The sensor has excellent electrochemical performance in BPA detection, with a detection range of 0.01-40 μM and a detection limit of 3.3 nM (S / N=3). In addition, the linear range of the portable electrochemical sensor is 0.5-60 μM, showing good sensitivity and a wide linear range.

[0023] (3) The prepared MSNs@Au sensor also exhibited good performance in terms of selectivity, reproducibility, and stability. Through spike recovery experiments, the sensor's recoveries in real samples ranged from 96.37% to 116.37%, with RSDs ranging from 2.28% to 9.89%, demonstrating its reliability and practicality in complex samples.

[0024] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the preparation and application of MSNs@Au-240 / GCE sensor for BPA detection;

[0026] Figure 2Figures 1 and 2 are morphological characterizations of the composite materials of Example 1, Example 2, and Comparative Example 1, including (a) SEM image of MSNs; (b) SEM image of Au / Me-SiO2; (c) SEM image of MSNs@Au-240; (d) TEM image of MSNs; (e) TEM image of Au / Me-SiO2; (f) TEM image of MSNs@Au-240; (gh) EDS line scan spectrum of MSNs@Au-240; (il) elemental composition and distribution analysis of MSNs@Au-240;

[0027] Figure 3 N2 adsorption-desorption characterization diagrams of the composite materials of Example 1, Example 2, and Comparative Example 1, including (a) N2 adsorption-desorption isotherms and pore size distribution diagrams of MSNs; (b) N2 adsorption-desorption isotherms and pore size distribution diagrams of Au / Me-SiO2; (c) N2 adsorption-desorption isotherms and pore size distribution diagrams of MSNs@Au-240;

[0028] Figure 4 XRD and FTIR characterizations of the composite materials of Example 1, Example 2, and Comparative Example 1, including (a) XRD patterns of MSNs, Au / Me-SiO2, and MSNs@Au-240; (b) FTIR patterns of MSNs, Au / Me-SiO2, and MSNs@Au-240;

[0029] Figure 5 Electrochemical characterization of different modified electrodes in potassium ferrocyanide solution, including (a) CV curves of GCE, MSNs / GCE, Au / GCE, Au / Me-SiO2 / GCE, MSNs@Au-240 / SPEC, MSNs@Au / GCE, and MSNs@Au-240 / GCE; (b) EIS curves of the corresponding modified electrodes;

[0030] Figure 6 Characterization of the electrochemical behavior of bisphenol A on different modified electrodes, including (a) DPV curves of MSNs@Au in PBS without and with 40 μM BPA; (b) CV curves of GCE, MSNs / GCE, Au / GCE, Au / Me-SiO2 / GCE, MSNs@Au-240 / SPEC, MSNs@Au / GCE, and MSNs@Au-240 / GCE in PBS with 0.1 mM BPA;

[0031] Figure 7 Effect of pH value on electrochemical behavior, including (a) DPV curves of MSNs@Au in PBS with different pH values ​​containing 50 μM BPA; (b) relationship between peak current and pH; (c) relationship between peak potential and pH;

[0032] Figure 8 The effect of CV scan rate on electrochemical behavior, including (a) CV curves of MSNs@Au at different scan rates in PBS containing 20 μM BPA; (b) the relationship between peak current and scan rate; (c) the relationship between peak potential and the natural logarithm of scan rate;

[0033] Figure 9 To optimize the colloidal gold content, (a) the colloidal gold content in MSNs@Au synthesized with different colloidal gold addition amounts; (b) the relationship between the oxidation peak current of 40 μM BPA and the amount of colloidal gold added based on DPV measurement;

[0034] Figure 10 Optimization of colloidal gold particle size, including (a) the average particle size of colloidal gold generated at different sodium citrate addition amounts; (b) the relationship between the electrochemical response value of BPA based on DPV and the amount of sodium citrate added;

[0035] Figure 11 Optimization of the pore size of MSNs, including (a) the average pore size of MSNs@Au generated with different CTAB addition amounts; (b) the response value of MSNs@Au generated with different CTAB addition amounts to detect BPA;

[0036] Figure 12 To optimize the quality of electroactive materials, (a) DPV curves of MSNs@Au-240 modified electrode dispersions with different volumes; (b) relationship between MSNs@Au-240 dispersion volume and peak current;

[0037] Figure 13 The establishment of the standard curve for the MSNs@Au-240 sensor to detect bisphenol A, including (a) DPV curves of the MSNs@Au-240 sensor for different concentrations of BPA; (b) the linear relationship between the oxidation peak current of MSNs@Au-240 and BPA concentration;

[0038] Figure 14 The reproducibility, stability, selectivity and anti-interference performance of the sensor, including (a) the stability of the sensing electrode material; (b) the reproducibility of the sensing electrode material; (c) the selectivity of the sensing electrode material; (d) the anti-interference performance of the sensing electrode material;

[0039] Figure 15 For actual sample detection, (a) DPV curve of MSNs@Au-240 detecting BPA in river water; (b) DPV curve of MSNs@Au-240 detecting BPA in fresh milk; (c) DPV curve of MSNs@Au-240 detecting BPA in orange juice;

[0040] Figure 16For the application of portable sensors, (a) DPV curves of MSNs@Au-240 / SPCE sensor for different concentrations of BPA; (b) linear relationship between the oxidation peak current of MSNs@Au-240 / SPCE and BPA concentration. DETAILED DESCRIPTION

[0041] The present invention will be further described below. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and specific operation process, but the present invention is not limited to this embodiment.

[0042] Example 1

[0043] like Figure 1 As shown, the preparation method of the monodisperse core-shell structure MSNs@Au composite material includes the following steps:

[0044] (1) Synthesis of colloidal gold: First, all items that come into contact with colloidal gold are decontaminated with aqua regia and oven-dried. Next, 100 mL of distilled water and 1 mL of 1% chloroauric acid solution are added to a three-necked flask. The mixture is condensed and refluxed. After heating to boiling with stirring, 2 mL of 1% sodium citrate solution is added. After boiling for 15 minutes, the mixture is turned off and cooled to room temperature to synthesize the colloidal gold solution.

[0045] Preparation of 1% chloroauric acid solution: Accurately weigh 1.0 g HAuCl4·3H2O, dissolve in ultrapure water and dilute to 100 mL, store in a sealed container away from light (prepare for immediate use).

[0046] Preparation process of 1% sodium citrate solution: weigh 1.14g Na3C6H5O7·2H2O (converted as dihydrate), dissolve it in ultrapure water to 100mL, and store it in a sealed container at room temperature.

[0047] (2) Synthesis of MSNs@Au: Using the template method, 55 mL of deionized water was added to a round-bottom flask at 35 °C, and 160 mg of hexadecyltrimethylammonium bromide (CTAB) was added and stirred. After the solution was mixed and became transparent, 26 mL of anhydrous ethanol was added. After 5 minutes, 8 mL of colloidal gold solution was added and stirred. 1 mL of ammonia was added, and then 1 mL of TEOS was added dropwise to the above mixed solution to allow the reaction to complete. After the mixed solution was mixed and reacted for 3 hours, the precipitate was collected by centrifugation, dried in an oven at 60 °C overnight, and then calcined in a muffle furnace at 550 °C for 6 hours to obtain the material MSNs@Au.

[0048] Example 2

[0049] This example differs from Example 1 in the amount of CTAB added. In this example, 200 mg, 240 mg, 280 mg, and 320 mg of CTAB were added to the round-bottom flask. The resulting products were labeled MSNs@Au-200, MSNs@Au-240, MSNs@Au-280, and MSNs@Au-320, respectively. The amount of template used is a key factor influencing the pore size of the material. In this example, the effect of varying the CTAB dosage on the pore structure of the MSNs was investigated.

[0050] Example 3

[0051] This example is based on Example 2 and examines the effects of different amounts of colloidal gold added on the material. The amounts of colloidal gold solution added in this example are 4 mL, 6 mL, 10 mL, 12 mL, and 14 mL, respectively.

[0052] Example 4

[0053] This example is based on Example 2 and examines the effect of different colloidal gold particle sizes on the material. In this example, the added amounts of sodium citrate solution are 1 mL, 1.5 mL, 2.5 mL, and 3 mL, respectively.

[0054] Comparative Example 1

[0055] The preparation method of the Au / Me-SiO2 composite material comprises the following steps:

[0056] (1) Using the template method, 55 mL of deionized water was added to a round-bottom flask at 35 °C, and 160 mg of CTAB was added and stirred. After the solution was mixed and became transparent, 26 mL of anhydrous ethanol was added. After 5 minutes, 1 mL of ammonia was added, and then 1 mL of TEOS was added dropwise to the above mixed solution to complete the reaction. After the mixed solution was mixed and reacted for 3 hours, the precipitate was collected by centrifugation, dried in an oven at 60 °C overnight, and then calcined in a muffle furnace at 550 °C for 6 hours to obtain the material MSNs.

[0057] (2) 0.1 g of MSNs and 8 mL of anhydrous ethanol were placed in a centrifuge tube and sonicated for 15 min. The solution was then heated in a 25°C water bath with stirring, and 0.2 mL of 3-aminopropyltriethoxysilane (APTES) was slowly added and allowed to react for 6 h. Finally, the mixture was centrifuged, washed with anhydrous ethanol, and dried at 60°C to obtain NH2-MSNs.

[0058] (3) 0.09 g of NH2-MSNs was dispersed in 30 mL of water, and 100 μL of 0.1 g / mL HAuCl4·3H2O was added. After magnetic stirring at room temperature for 2 h, 20 μL of 10 nM NaBH4 solution was added dropwise. Finally, the precipitate was collected by centrifugation and dried in an oven at 60 °C overnight to obtain the Au / Me-SiO2 composite material.

[0059] The NaBH4 solution was prepared as follows: 3.78 mg NaBH4 was accurately weighed, dissolved in pre-cooled ultrapure water and the volume was adjusted to 1 L, and used immediately after preparation (operated in an ice bath to avoid decomposition).

[0060] Test Example 1

[0061] The micromorphology and internal structure of MSNs@Au were characterized by SEM and TEM. The lattice structure of MSNs@Au and the distribution of Au nanoparticles were further observed by HRTEM. The crystal structure of MSNs@Au was analyzed by XRD to confirm its crystalline phase composition. The presence of functional groups on the surface of MSNs@Au and their chemical environment were explored by FTIR. N2 adsorption-desorption was used to determine the specific surface area and pore size distribution of MSNs@Au. In addition, EDS was used to analyze the elemental composition and spatial distribution of MSNs@Au in detail to verify the coating of Au nanoparticles inside the mesoporous silica. The test results are as follows:

[0062] The morphological characteristics of the three nanocomposites were analyzed by SEM, TEM and EDS. SEM analysis ( Figure 2 (ac)) shows that the average diameter of mesoporous silica is about 200nm. After loading with gold nanoparticles, it still forms monodisperse nanospheres with uniform size. The two methods of composite gold nanoparticles do not significantly change the morphology of mesoporous silica. TEM further reveals the difference in microstructure: Au / Me-SiO2( Figure 2 e) The gold particles loaded on the surface are locally aggregated, while MSNs@Au-240( Figure 2 f) The gold particles are completely coated in the center of the mesoporous spheres without any structural defects. Figure 2 As shown in (il), the distribution of silicon (Si), oxygen (O) and gold (Au) is highly consistent, indicating that the gold nanoparticles are uniformly embedded in the silica skeleton. EDS line scan image ( Figure 2 gh) further showed that the Au signal intensity trended consistently with the Si and O signals, confirming the uniform distribution of the gold nanoparticles within the silica matrix. The coating structure of the present invention significantly enhances the material's catalytic activity, stability, and electrochemical reaction efficiency by inhibiting gold particle aggregation and providing a stable support. In summary, the unique core-shell structure and uniform gold distribution of MSNs@Au-240 enable high sensitivity and excellent stability in BPA detection.

[0063] The pore properties of MSNs, Au / Me-SiO2, and MSNs@Au materials were studied using N2 adsorption-desorption isotherms and pore size distribution diagrams. Figure 3 The N2 adsorption-desorption isotherm results of (ac) show that the materials before and after the MSNs loading and coating with nano-gold are all type IV isotherms, and an adsorption hysteresis loop appears at 0.4-1.0, indicating that MSNs, Au / Me-SiO2, and MSNs@Au have abundant mesopores. MSNs have a large specific surface area (1471.30m 2 / g), with a pore size of 2.67nm, showing its typical mesoporous structure and large surface active sites, which are very suitable for molecular adsorption and electrochemical sensing applications. However, the specific surface area of ​​Au / Me-SiO2 material is significantly reduced to 528.19m 2 / g, which indicates that when gold particles are loaded on the surface of mesoporous silica, the specific surface area is reduced, which may be due to the agglomeration of gold particles partially blocking the pores and reducing the effective surface area of ​​the material. 2 / g, pore size 2.86nm), the gold particles are encapsulated within the mesoporous silica, resulting in a still large specific surface area and a slightly increased pore size. This indicates that the encapsulated structure of the monodisperse gold particles effectively prevents the gold particles from blocking the pores, allowing the gold particles to maintain a relatively uniform dispersion state while retaining the excellent pore structure and high specific surface area of ​​the mesoporous silica. Compared to Au / Me-SiO2, the gold particle loading method of MSNs@Au-240 is more optimized, avoiding the agglomeration of gold particles and enhancing the stability and catalytic activity of the material.

[0064] Table 1 Specific surface area and average pore size of MSNs, Au / Me-SiO2, and MSNs@Au-240

[0065] <![CDATA[Specific surface area (m 2 / g)]]> Average pore size (nm) MSNs 1471.30 2.67 <![CDATA[Au / Me-SiO2]]> 528.19 3.76 MSNs@Au-240 1530.11 2.86

[0066] Figure 4The XRD patterns of a show that MSNs, Au / Me-SiO2, and MSNs@Au-240 exhibit typical diffraction peaks of silicon dioxide, while multiple diffraction peaks at 38.18°, 44.39°, 64.58°, 77.55°, 81.72°, 98.13°, 110.80°, 115.26°, and 135.42° correspond to the (111), (200), (220), (311), (222), (400), (331), (420), and (422) crystal planes of Au. Characteristic peaks associated with gold particles appear in Au / Me-SiO2 and MSNs@Au-240. The appearance of these characteristic peaks verifies the loading and coating of gold particles. Especially in MSNs@Au-240, due to the SiO2 coating, the diffraction peak intensity of gold is very low, but the coating of gold particles does not affect the overall structure of the material, and the gold is well dispersed, providing stable catalytic sites for electrochemical reactions.

[0067] Figure 4 The FTIR spectrum of b further proves the surface chemical characteristics of MSNs@Au-240. For MSNs, the -1 The stretching vibration peak of the silicon-oxygen bond (Si-O-Si) is at 476 cm -1 and 3452cm -1 The Si-O bending vibration peak and OH vibration peak are located at the bottom, indicating that the surface contains abundant hydroxyl functional groups, which are conducive to the adsorption of BPA. Au itself usually does not have obvious absorption peaks in the infrared region, and the spectrum may be flat. However, since the solvent is water, a wide range of OH stretching vibration peaks (3245cm -1 ) and HOH bending vibration peak (1629cm -1 The Au / Me-SiO2 pattern shows that after colloidal gold is loaded onto the mesoporous surface, some hydroxyl groups may bind to or be shielded by the gold particles, resulting in a decrease in the OH peak intensity. The FTIR spectrum of MSNs@Au-240 reveals that after gold is encapsulated within the mesoporous surface, the pores become less open, with some hydroxyl groups consumed or shielded, similarly leading to a decrease in the OH peak intensity. This interaction between the gold particles and the SiO2 surface provides a theoretical basis for the catalytic properties of gold.

[0068] In summary, the MSNs@Au-240 material possesses excellent structural properties and a well-defined pore structure, and the gold particle coating prevents agglomeration. These properties make MSNs@Au-240 an ideal electrochemical sensor modification material, particularly for the high-sensitivity detection of BPA. Comprehensive characterization using surface area, pore structure, XRD, and FTIR analysis confirmed the unique advantages of MSNs@Au-240 in electrochemical sensing applications.

[0069] Test Example 2

[0070] Establishment of electrochemical sensing method for detection of bisphenol A:

[0071] First, BPA was dissolved in anhydrous ethanol to prepare a 20 mM BPA solution, which was then diluted to the desired concentration using phosphate buffered saline (PBS). In the electrochemical test, a three-electrode system was used, with GCE as the working electrode, Ag / AgCl electrode as the reference electrode, and platinum electrode as the counter electrode. CV and EIS were used to characterize the electrochemical performance of the different modified electrodes. 3- / 4- CV measurements were performed in 0.1 M PBS (pH 7.0) with a voltage sweep range of -0.2 to 0.6 V and in 0.1 M KCl in 0.1 M PBS containing BPA over a voltage range of 0.2 to 0.8 V, both at a scan rate of 50 mV / s. Furthermore, DPV measurements in BPA solutions were performed over a voltage range of 0.2 to 0.7 V with an amplitude of 50 mV.

[0072] like Figure 5 As shown in a, CV was used to analyze the GCE with different modified materials in the presence of 5.0 mM [Fe(CN)6] 3- / 4- The redox behavior of MSNs@Au-240 / GCE was characterized in 0.1M KCl solution. The experimental results showed that MSNs@Au-240 / GCE exhibited the highest redox peak current (103.2μA) and the smallest peak potential difference (ΔE pa =0.114V), the peak current is 39.2μA higher than that of the unmodified electrode. This shows that the MSNs@Au-240 modified layer can effectively promote the electron transfer dynamics. The main reason for the performance improvement is the adsorption enrichment effect of the mesoporous structure and the catalytic activity of gold nanoparticles. Among them, the high specific surface area of ​​mesoporous silica (MSNs) provides a uniformly dispersed carrier for gold nanoparticles (AuNPs), thereby significantly improving the conductivity of the electrode and the density of active sites. The interface performance of the charge transfer characteristics was further verified by EIS ( Figure 5 b) The Nyquist plot of MSNs@Au-240 / GCE exhibits the smallest semicircle diameter, indicating the lowest charge transfer resistance and significantly reduced interfacial electron transport resistance. This result is consistent with the CV analysis and further verifies the synergistic effect of the MSNs@Au-240 composite: the three-dimensional pore structure of mesoporous silica promotes electrolyte diffusion, while the high conductivity of gold nanoparticles accelerates redox reactions on the electrode surface.

[0073] Figure 6Figure a shows the DPV curves of MSNs@Au-240 in 0.1 M PBS (pH = 7) solution without and with 40 μM BPA. The black curve represents the blank PBS solution, where almost no obvious oxidation peak signal is observed, indicating that no significant oxidation reaction occurs on the electrode surface in the absence of BPA. In contrast, the red curve corresponds to the solution containing 40 μM BPA, where a significant oxidation peak appears at approximately 0.55 V, indicating that the MSNs@Au-240-modified GCE exhibits an excellent electrochemical response to BPA. This result confirms the feasibility of the MSNs@Au-240-modified electrode for the electrochemical detection of BPA.

[0074] Figure 6 b shows the CV curves of different modified electrodes detecting 0.1 mM BPA in 0.1 M PBS (pH = 7). The experimental results show that MSNs@Au-240 / GCE exhibits the highest oxidation peak current (12.0 μA), which is significantly better than other modified electrodes (such as GCE, MSNs / GCE, Au / GCE, Au / Me-SiO2 / GCE, etc.), and exceeds the unmodified electrode by 7.2 μA. This phenomenon further confirms the superior performance of the MSNs@Au-240 modified layer. The results show that MSNs@Au-240 / GCE exhibits excellent electrochemical performance in BPA detection. Its high sensitivity, good catalytic activity, and stable electrochemical response make it an ideal candidate material for constructing efficient electrochemical sensors.

[0075] BPA molecules contain two phenolic hydroxyl groups, and their electrochemical behavior is significantly affected by the pH value of the solution. Under appropriate pH conditions, the hydrogen ions in the phenolic hydroxyl groups can be deprotonated to form anions, thereby promoting their migration in the electric field. In order to study the effect of pH on the electrochemical behavior of BPA, this test example used DPV to systematically study the electrochemical performance of 50μM BPA solution in the pH range of 5.0 to 9.0. Figure 7 As shown in a, with the increase of pH value, the oxidation peak current of BPA gradually increases, indicating that protons are involved in the reaction process between the MSNs@Au electrode surface and BPA molecules. However, when the pH value increases further, the oxidation peak current of BPA begins to decrease. This may be because the MSNs@Au electrode surface is negatively charged, and an electrostatic repulsion is generated between it and the deprotonated BPA anions, thereby inhibiting the adsorption and oxidation reaction of BPA on the electrode surface. The experimental results show that when the pH value is 7.0, the oxidation peak current of BPA reaches its maximum value. At this time, the pH value of the solution is lower than the pK4 value of BPA (9.73), and BPA mainly exists in molecular form, which is easy to adsorb on the electrode surface, thereby showing the best electrochemical response. Therefore, PBS buffer solution with pH = 7.0 was selected as the optimal condition for subsequent experiments. In addition, Figure 7 b and c show the relationship between the BPA oxidation peak current and oxidation peak potential and the change of pH value. As the pH value increases, the BPA oxidation peak potential (E pa ) gradually moves in the negative direction. Linear regression analysis of pH value and oxidation peak potential showed that within the pH range of 5.0 to 9.0, there was a good linear relationship between oxidation peak potential and pH value, and the linear regression equation was E pa =-0.048V+0.8083, with a correlation coefficient of 0.992. Each unit change in pH value resulted in a shift of the BPA oxidation peak potential by approximately 48 mV, and this slope was close to the theoretical Nernst slope (59 mV / pH), indicating that the BPA oxidation reaction on the MSNs@Au electrode involves equal proton and electron transfer processes.

[0076] In order to further explore the oxidation reaction mechanism of BPA on the MSNs@Au modified electrode, the electrochemical behavior of 20 μM BPA was systematically studied by CV at different scan rates. Figure 8 a shows the CV curves of MSNs@Au in 0.1MPBS solution containing 20μM BPA at a scan rate ranging from 10mV / s to 100mV / s. Figure 8 As shown in Figure b, with the increase of scan rate, the oxidation peak current of BPA gradually increases, and when the scan rate increases from 10mV / s to 100mV / s, the oxidation peak current and the scan rate show a good linear relationship. This phenomenon shows that the oxidation process of BPA on the surface of MSNs@Au electrode is a typical adsorption-controlled process, which further confirms the effectiveness of MSNs@Au material in BPA pre-enrichment and quantitative detection. In addition, Figure 8 c shows the E of BPA pa The relationship between the change of the logarithm of the scanning rate. The experimental results show that the oxidation peak potential shifts positively with the increase of the scanning rate, and its linear regression equation is E pa (V) = 0.02178mv + 0.4297(R 2 =0.995). For a completely irreversible electrode process controlled by adsorption, E pa It can be described by the following formula:

[0077]

[0078] Among them, E θis the formal redox potential, K is the standard rate constant of the reaction, n is the number of electrons transferred, R is the gas constant (8.314 J / (mol·K)), α is the electron transfer coefficient, T is the Kelvin temperature (298K), v is the scan rate, and F is the Faraday constant (96500°C / mol). Typically, for irreversible reactions, α is set to 0.5. Based on the above formula, the number of electrons transferred during BPA oxidation is calculated to be approximately 2, indicating that the BPA oxidation reaction involves the transfer of two electrons.

[0079] It is worth noting that at low scan rates, anionic impurities may adsorb and accumulate on the electrode surface, leading to the formation of oxides. Due to the longer potential retention time, the oxide coverage increases. At high scan rates, however, the increased background current may interfere with the experimental results. For these reasons, the present invention selects 50 mV / s as the optimal scan rate to balance the effects of reaction sensitivity and background interference.

[0080] Test Example 3

[0081] Investigate the influence of composite material synthesis conditions on electrochemical behavior.

[0082] (1) Optimization of colloidal gold content

[0083] Gold nanoparticles (AuNPs) have important applications in electrochemical sensors due to their excellent electrical conductivity and catalytic activity. To optimize the performance of MSNs@Au composites, this study investigated the effect of different colloidal gold addition amounts on the material's catalytic performance. Figure 9 a shows the content of colloidal gold in MSNs@Au synthesized with different amounts of colloidal gold solution (measured by ICP-MS). Figure 9 b shows the oxidation peak current response of these materials to 40 μM BPA.

[0084] Experimental results show that the peak current for the oxidation of BPA by MSNs@Au gradually increases with increasing colloidal gold loading, reaching a maximum at 8 mL of colloidal gold. This phenomenon is primarily attributed to the high catalytic activity and electrical conductivity of gold nanoparticles. The appropriate amount of gold nanoparticles uniformly dispersed within the mesoporous silica provides abundant active sites and forms an efficient conductive network, significantly enhancing the electrode's ability to oxidize BPA. Furthermore, the surface plasmon resonance effect of the gold nanoparticles further enhances the local electric field strength, promoting the adsorption and oxidation of BPA molecules.

[0085] However, when the amount of colloidal gold added exceeded 8 mL, the oxidation peak current began to decrease. This may be due to the partial agglomeration of the excess gold nanoparticles, which reduced the effective active sites and may have a certain impact on the mesoporous structure, reducing the material's mass transfer efficiency. Therefore, in this experimental example, MSNs@Au synthesized with an addition of 8 mL of colloidal gold was selected for subsequent experiments. The material synthesized under these conditions achieved an optimal balance between catalytic activity, conductivity, and structural stability, providing an ideal platform for the high-sensitivity detection of BPA.

[0086] (2) Optimization of colloidal gold particle size

[0087] In order to explore the effect of colloidal gold particle size on the electrochemical detection performance of BPA, the colloidal gold particle size was regulated by adjusting the amount of sodium citrate added. Figure 10 As shown in Figure a, as the sodium citrate dosage increases from 1.0 mL to 3.0 mL, the colloidal gold particle size decreases significantly. This phenomenon stems from sodium citrate's dual role as a reducing agent and stabilizer. At high concentrations, gold ions are rapidly reduced, forming a large number of gold nanoparticles, whose growth is inhibited by steric hindrance. At low concentrations, the number of nuclei formed is reduced, the particle growth time is prolonged, and eventually large gold particles are formed.

[0088] Figure 10 Figure b further demonstrates the electrochemical response of MSNs@Au synthesized with colloidal gold of varying particle sizes to BPA detection. As the colloidal gold particle size decreases (i.e., the amount of citric acid added increases), the BPA oxidation peak current first increases and then decreases, reaching a maximum value at 2.0 mL of citric acid. This trend indicates that colloidal gold particle size significantly affects the electrocatalytic performance of MSNs@Au: smaller gold nanoparticles, due to their larger surface area, promote electron transfer and increase active sites, enhancing the BPA oxidation signal; whereas excessively small particle size may induce aggregation or weaken the overall electrochemical performance due to decreased electron transfer capacity.

[0089] Experiments show that the colloidal gold particle size is crucial to the BPA electrochemical detection performance of MSNs@Au. The optimization results show that when the amount of citric acid is 2.0 mL, the current response of the MSNs@Au modified electrode is optimal, showing the best electrocatalytic activity.

[0090] (3) MSNs aperture optimization

[0091] By adjusting the amount of template during the synthesis process, the effect of the pore size distribution of MSNs on the electrochemical sensor was explored. The amount of template is one of the key factors affecting the pore size of the material. First, the effect of CTAB on the pore structure of MSNs was studied by adjusting the amount of CTAB. Figure 11As shown in a, as the amount of CTAB added increased from 160 mg to 320 mg, the pore size of MSNs gradually increased. Because CTAB acts as a template, its concentration significantly affects the size of the mesoporous structure (high concentration corresponds to large pore size, low concentration forms small pore size). Then, the MSNs@Au modified electrodes synthesized with different CTAB dosages were used to detect BPA. Figure 11 Figure b shows that the oxidation peak current reaches its maximum when the CTAB dosage is 240 mg. This phenomenon may be attributed to the fact that MSNs within this pore size range provide a more suitable specific surface area and permeability, thereby optimizing the mass transfer process and electrocatalytic reaction efficiency of BPA. Larger pore sizes facilitate the rapid diffusion and adsorption of BPA molecules, while too small pore sizes may limit mass transfer efficiency and reduce the electrochemical response.

[0092] These results demonstrate that the amount of CTAB added directly affects the pore size of MSNs, which in turn influences the electrochemical detection performance of the MSNs@Au modified electrode. By optimizing the CTAB dosage, the pore size of MSNs can be regulated, thereby improving the electrode's sensitivity and detection efficiency. Therefore, MSNs@Au-240 synthesized with 240 mg of CTAB was selected for subsequent experiments to achieve optimal electrochemical performance.

[0093] Test Example 4

[0094] Optimize the quality of electroactive materials on the GCE surface.

[0095] The GCE electrode was modified by drop coating different volumes of MSNs@Au-240 dispersion, and the effect of material loading on the electrochemical response of BPA was studied using the DPV method. Figure 12 As shown, as the volume of the MSNs@Au-240 dispersion increases from 2 μL to 4 μL, the peak current for BPA oxidation gradually increases. This is attributed to the increased loading of the composite material on the electrode surface, which provides more active sites and enhances the electrochemical response. However, when the volume exceeds 4 μL, the current response begins to decrease. This is presumably because the excess material leads to an excessively thick film, hindering electron transfer and the diffusion of BPA molecules. These results indicate that the loading amount of conductive material on the electrode surface significantly affects the electrocatalytic performance of the sensor. To achieve optimal BPA detection performance, 4 μL of MSNs@Au-240 dispersion was used in subsequent experiments.

[0096] Test Example 5

[0097] Establishment of the standard curve for the detection of bisphenol A using the MSNs@Au-240 sensor:

[0098] Under the above optimal experimental conditions, different concentrations of BPA were detected on the MSNs@Au-240 / GCE sensor using DPV. Figure 13As shown in (a), the oxidation peak current gradually increases with the increase of BPA concentration. Figure 13 b shows the linear relationship between the peak current and concentration of BPA oxidation of the MSNs@Au-240 sensor in 0.1M PBS. The experimental results show that in the concentration range of 0.01 to 40μM, the peak current of BPA oxidation shows a good linear relationship with its concentration. The linear regression equation is Ip (μA) = 0.08054C (μM) + 0.3038, and the correlation coefficient R 2 =0.997, and the detection limit was 3.3 nM (S / N=3).

[0099] In order to evaluate the stability of the sensor, e.g. Figure 14 As shown in a, after 5 days of storage, the electrode retained 94.68% of the initial current response, indicating that the designed sensor has good stability. In addition, in order to test the reproducibility of MSNs@Au-240, this experiment used the same method to prepare 6 parallel modified electrodes. Figure 14 As shown in b, the RSD on the six electrodes is 1.84%, indicating that the sensor exhibits good reproducibility. In order to further verify the anti-interference and selectivity of the sensor, eight common potential interferents with different concentrations were selected for testing. Na + , Ca 2+ Mg 2+ , K + 、CO3 2- The DPV test was performed on 50 times the concentration of p-nitrophenol, sucrose and glucose. Figure 14 As shown in (cd), the effects of the eight interferents on the anodic oxidation current of BPA were all less than 5%, and the peaks of the interferents did not appear at the characteristic peaks of BPA. The results showed that the designed sensor had good anti-interference and selectivity.

[0100] Test Example 6

[0101] The MSNs@Au-240 sensor was tested on real samples. To verify the detection performance of the MSNs@Au-240 / GCE sensor in real samples, river water, fresh milk, and orange juice were selected as representative samples for analysis. All samples were collected locally and diluted 10-fold in PBS buffer (pH 7.0). As shown in Table 2, a standard spike-addition recovery experiment was performed to detect BPA in the three samples. The results showed that no endogenous BPA was detected in the real samples. The sensor's recoveries ranged from 96.37% to 116.37%, with RSDs of 2.28% to 9.89%. To further validate its performance, HPLC and electrochemical methods were used for comparative analysis. The spike-addition recoveries of the HPLC method ranged from 80.49% to 110.92%, which closely matched the sensor's recovery range and fell within the acceptable range. These results collectively confirm that the MSNs@Au-240 / GCE sensor exhibits excellent accuracy and reliability in complex matrices, highlighting its potential for effective quantitative analysis of BPA in real samples.

[0102] Table 2 Detection of BPA in actual samples by MSNs@Au-240 electrode

[0103]

[0104] Test Example 7

[0105] Applications of Portable Electrochemical Sensors:

[0106] In order to verify the practical application potential of MSNs@Au-240 materials in portable sensors, this experimental example modified it on the surface of screen printed electrode (SPCE), with carbon electrode as counter electrode and Ag / AgCl as reference electrode to construct MSNs@Au-240 / SPCE sensor. Figure 16 As shown in (a), the DPV response curves of the MSNs@Au-240 / SPCE sensor to different concentrations of BPA show that the oxidation peak current gradually increases with the increase of BPA concentration. Figure 16 b further shows the linear relationship between the oxidation peak current and BPA concentration. The linear regression equation is Ip (μA) = 0.06435C (μM) + 0.1374, and the correlation coefficient R 2=0.997, indicating that the sensor has a good linear response over the concentration range of 0.5-60 μM. Although the sensitivity of the MSNs@Au-240 / SPCE sensor is slightly lower than that of the MSNs@Au-240 / GCE, it still demonstrates excellent detection performance, sufficient for on-site detection. SPCE offers the advantages of portability, low cost, and high-throughput detection. Combined with the high catalytic activity and stability of the MSNs@Au-240 material, the MSNs@Au-240 / SPCE sensor has broad application prospects in rapid on-site detection in fields such as food safety and environmental monitoring.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a monodisperse core-shell structured MSNs@Au composite material, characterized by: The following steps are involved: (1) Synthesis of colloidal gold Distilled water and chloroauric acid solution were mixed and condensed under reflux, heated to a boil under stirring, and then sodium citrate solution was added, and the heating reaction was continued. After the reaction was completed, the mixture was cooled to room temperature to obtain a colloidal gold solution; (2) Synthesis of MSNs@Au Hexadecyltrimethylammonium bromide was added to deionized water and stirred. After the solution became transparent, anhydrous ethanol was added and continued to stir. Then, colloidal gold solution was added and mixed evenly. Then, ammonia water and tetraethyl orthosilicate were added dropwise. After the reaction was complete, MSNs@Au was obtained after centrifugal precipitation, drying and calcination.

2. The method for preparing the monodisperse core-shell structure MSNs@Au composite material according to claim 1, characterized in that: In step (1), the mass percentage of chloroauric acid in the chloroauric acid solution is 0.8-1.2%, and the mass percentage of sodium citrate in the sodium citrate solution is 0.8-1.2%.

3. The method for preparing the monodisperse core-shell structure MSNs@Au composite material according to claim 2, characterized in that: In step (1), the volume ratio of distilled water, chloroauric acid solution and citric acid solution is 100: (0.8~1.2): (1.5~3).

4. The method for preparing the monodisperse core-shell structure MSNs@Au composite material according to claim 1, characterized in that: In step (2), the mass volume ratio of hexadecyltrimethylammonium bromide and tetraethyl orthosilicate is 200-320 mg:1 mL.

5. The method for preparing the monodisperse core-shell structure MSNs@Au composite material according to claim 4, characterized in that: In step (2), the amount of colloidal gold solution added is 4-12 mL.

6. The method for preparing the monodisperse core-shell structure MSNs@Au composite material according to claim 1, characterized in that: In step (2), the calcination temperature is 500-600°C and the calcination time is 5-8 hours.

7. Monodisperse core-shell structure MSNs@Au composite material, characterized by: Prepared by the preparation method according to any one of claims 1 to 6.

8. The monodisperse core-shell structure MSNs@Au composite material according to claim 7, characterized in that: The monodisperse core-shell structure MSNs@Au composite material includes colloidal gold and mesoporous silica, and the colloidal gold is coated inside the mesoporous silica.

9. Use of the monodisperse core-shell structure MSNs@Au composite material according to any one of claims 7 to 8, characterized in that: Application of monodisperse core-shell structured MSNs@Au composites in electrochemical detection of bisphenol A.

10. The use of the monodisperse core-shell structured MSNs@Au composite material according to claim 9, characterized in that: In the electrochemical detection of bisphenol A, the detection range of bisphenol A of the monodisperse core-shell structure MSNs@Au composite material is 0.01~40μM, and the detection limit is 3.3nM.

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