Graphene-based polyaniline supported AgAu bimetallic composite catalyst and preparation and application thereof

Abstract

The invention provides a graphene-based polyaniline supported AgAu bimetallic composite catalyst as well as preparation and application thereof, and belongs to the technical field of testing or analyzing materials by means of measuring chemical or physical properties of the materials. The catalyst comprises a polyaniline-reduced graphene oxide composite sphere carrier with open pore channels, and AgAu bimetallic nanoparticles loaded on the surface and inside of the composite sphere carrier, the composite sphere carrier takes reduced graphene oxide which is spatially folded and curled under the coordination action of Fe < 3 + > as a framework, and polyaniline adheres to and grows on the surface of the framework; the AgAu bimetallic nanoparticles are formed through a replacement reaction, wherein the center of the AgAu bimetallic nanoparticles takes Ag as a main element, and the outer layer of the AgAu bimetallic nanoparticles is enriched with Au. The catalyst shows extremely low detection limit, wide linear range and high sensitivity to DA, inhibits non-specific response of AA and UA at the same time, and realizes excellent anti-interference performance.

Description

Technical Field

[0001] This invention relates to a graphene-based polyaniline-supported AgAu bimetallic composite catalyst, its preparation and application, and belongs to the technical field of testing or analyzing materials by measuring their chemical or physical properties. Background Technology

[0002] Dopamine (DA), an important catecholamine neurotransmitter, plays a crucial regulatory role in the human central nervous system, cardiovascular system, and endocrine system. The concentration of DA in normal human body fluids is extremely low (approximately 0.01 μM-1 μM in serum and 0.42 μmol / day-2.61 μmol / day in urine), and its abnormal fluctuations are closely related to various neurological diseases such as Parkinson's disease, schizophrenia, and pituitary tumors. Therefore, achieving highly sensitive detection of DA has significant clinical implications. Electrochemical sensing technology has become an important tool for biomolecular detection due to its ease of operation, rapid response, and low cost. However, in actual biological samples such as blood or urine, DA often coexists with high concentrations of ascorbic acid (AA) and uric acid (UA). All three are electrochemically active, and their oxidation potentials on conventional electrodes are similar, leading to signal overlap and severely affecting the selectivity and sensitivity of sensors. Therefore, developing electrochemical sensors capable of highly sensitive and selective detection of DA while effectively suppressing interference from AA and UA has become an urgent problem to be solved in the field of bioanalysis.

[0003] To address this issue, constructing high-performance nanocomposite catalytic materials to modify electrode interfaces has become an important strategy for improving detection performance. Among numerous candidate materials, composites of reduced graphene oxide (rGO) and conductive polymer polyaniline (PANI) have attracted significant attention. rGO possesses high specific surface area and excellent conductivity, while PANI offers advantages such as good environmental stability, tunable redox activity, and ease of synthesis. The combination of the two can produce a significant synergistic enhancement effect: rGO can effectively prevent the aggregation of PANI chains, improving the structural stability of the composite material; the introduction of PANI inhibits the recombination of rGO sheets and enhances interfacial electronic coupling through π–π interactions and hydrogen bonding, thereby improving the overall conductivity and catalytic activity of the composite material. Furthermore, noble metal nanoparticles (such as Au, Ag, Pt, and Pb) are widely used to modify electrodes due to their excellent catalytic activity and good biocompatibility, aiming to reduce overpotential and increase reaction rates. In particular, bimetallic systems, by regulating the electronic structure and synergistic effects between the two metals, typically exhibit superior catalytic performance and resistance to poisoning compared to single metals. However, simply combining the above-mentioned advantageous components is still insufficient to completely solve the problem of severe interference in complex biological samples. Summary of the Invention

[0004] This invention provides a graphene-based polyaniline-supported AgAu bimetallic composite catalyst, its preparation and application, which can effectively solve the above-mentioned problems.

[0005] This invention provides a graphene-based polyaniline-supported AgAu bimetallic composite catalyst, the catalyst comprising a polyaniline-reduced graphene oxide composite spherical support with open channels, and AgAu bimetallic nanoparticles loaded on the surface and inside of the composite spherical support; The composite spherical carrier is in Fe 3+ Reduced graphene oxide, which undergoes spatial folding and curling under coordination, forms the framework, and polyaniline is attached and grown on the surface of the framework. The AgAu bimetallic nanoparticles were formed through a substitution reaction, resulting in Ag-dominant nanoparticles with an outer layer enriched with Au.

[0006] In some embodiments, the AgAu bimetallic nanoparticles have a particle size of 30 nm to 60 nm.

[0007] This invention also provides a method for preparing the graphene-based polyaniline-supported AgAu bimetallic composite catalyst as described above, comprising the following steps: (1) Preparation of Fe-graphene oxide framework: FeCl3 solution and graphene oxide dispersion were mixed, the pH of the system was adjusted to 6.8-7.2, and the reaction was carried out under heating conditions. The Fe-graphene oxide framework that underwent spatial folding and curling was separated and collected. (2) In-situ polymerization and Ag loading: The Fe-graphene oxide skeleton obtained in step (1) was dispersed in an aqueous phase, FeCl3 and aniline monomer were added, and after stirring, phosphoric acid was added to allow the aniline monomer to partially polymerize into a PANI layer and grow on the surface of the Fe-graphene oxide skeleton; then silver acetate solution was added to carry out a reduction reaction, and silver acetate was reduced to Ag nanoparticles. At the same time, the aniline monomer partially polymerized into a PANI layer, allowing the Ag nanoparticles to attach to the surface and interior of the PANI layer; then phosphoric acid solution containing ammonium persulfate was added to carry out a rapid oxidation reaction, and the product was separated and collected. (3) Removal of metal ions and reduction: The product obtained in step (2) is dispersed in a phosphoric acid solution containing ascorbic acid for reduction treatment to remove Fe from the system. 3+ The graphene oxide was then reduced, and the product was separated and collected. (4) Constructing the AgAu core-shell structure: Disperse the product obtained in step (3) in water, add chloroauric acid solution and let it stand to react. Use the displacement reaction to grow an Au coating layer in situ on the surface of Ag particles. After washing and drying, the product is obtained.

[0008] In some embodiments, in step (1), the heating conditions are 55-65°C and the stirring reaction time is 10-14 hours.

[0009] In some embodiments, in step (2), the phosphoric acid solution containing ammonium persulfate is introduced into the reaction system in a one-time rapid addition after the ammonium persulfate has completely dissolved.

[0010] In some embodiments, in step (4), the settling time is 22h-26h.

[0011] In some embodiments, the amount of silver acetate solution and chloroauric acid solution added is such that the molar ratio of Ag to Au is 14-16:1.

[0012] The present invention provides a method for preparing a modified electrode based on the above-mentioned graphene-based polyaniline-supported AgAu bimetallic composite catalyst, comprising the following steps: using Nafion as a binder, loading the graphene-based polyaniline-supported AgAu bimetallic composite catalyst onto a glassy carbon electrode.

[0013] This invention provides a modified electrode based on a graphene-based polyaniline-supported AgAu bimetallic composite catalyst prepared according to the above method.

[0014] This invention provides an electrochemical testing method for a capacitive electrode based on a graphene-based polyaniline-supported AgAu bimetallic composite catalyst, wherein the capacitive electrode is used as the working electrode, a graphite electrode as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode. Differential pulse voltammetry (DPV) is used for measurement, with a potential range of -0.1V to 0.9V, a scan amplitude of 45mV to 55mV, and a pulse width of 45ms to 55ms. All tests are performed in phosphate buffer solution.

[0015] This invention provides an application of the above-mentioned graphene-based polyaniline-supported AgAu bimetallic composite catalyst in the preparation of a dopamine electrochemical sensor.

[0016] The beneficial effects of this invention are: The catalyst of this invention has synergistic advantages in morphology. This invention constructs an open spherical structure, which allows the electrolyte and analyte to diffuse freely to the internal active surface, while retaining a large number of open channels by avoiding the disruption of interfacial balance by a large amount of oxidant. Compared with the two-dimensional (2D) structure, its catalytic activity is significantly improved (DA oxidation peak current is increased to about 1.54 times).

[0017] The catalyst of this invention exhibits anti-interference effects. In this invention, the core-shell structure formed by the AgAu bimetallic compound optimizes the d-band electronic structure, resulting in a significantly narrower oxidation response potential range for DA (0.11V–0.34V) and a smaller full width at half maximum (FWHM) compared to single-metal Ag or Au. Furthermore, the detection of DA remains unaffected even when coexisting with UA and AA.

[0018] The catalyst of this invention has excellent sensing performance: the detection limit of the catalyst for DA is as low as 0.001 μM, and it has a wide linear response range (0.001 μM-200 μM), which fully meets the requirements for accurate determination of DA content in human body fluids. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 Scanning electron microscope (SEM) images (A) and magnified views (B, C, and D) of the internal pores of the AgAu (OSPANI-rGO / AgAu) catalyst supported on an open-sphere (OS) carrier PANI-rGO. Image C is a magnified view of the red area in image B, and image D is a magnified view of the red area in image C.

[0021] Figure 2 The image shows the elemental surface scan (AD) image and EDS linear scan (E) of AgAu nanoparticles in the OSPANI-rGO / AgAu catalyst.

[0022] Figure 3 The DPV response diagrams of the electrodes modified with OSPANI-rGO (A), OSPANI-rGO / Ag (B), OSPANI-rGO / Au (C) and OSPANI-rGO / AgAu (D) catalysts in 0.1M PBS (pH 6.8) solution containing 200 μM DA, 1 mM UA and 1 mM AA are shown.

[0023] Figure 4 The DPV response curves of the OSPANI-rGO-based modified electrodes in 0.1M PBS (pH 6.8) solution containing 200 μM DA are shown.

[0024] Figure 5 The DPV response curves of AgAu-modified electrodes based on different supports in 0.1M PBS (pH 6.8) solution containing 200 μM DA are shown.

[0025] Figure 6 The DPV response of the OSPANI-rGO / Ag modified electrode to different concentrations of DA in 0.1M PBS (pH 6.8) and its standard curve.

[0026] Figure 7 The DPV response of the OSPANI-rGO / Au modified electrode to different concentrations of DA in 0.1M PBS (pH 6.8) is shown in (A) and its standard curve is shown in (B).

[0027] Figure 8 The DPV response of the OSPANI-rGO / AgAu modified electrode to different concentrations of DA in 0.1M PBS (pH 6.8) is shown in (A) and its standard curve is shown in (B). Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0029] Example 1: Preparation of OSPANI-rGO / AgAu: Add 2 mL of 0.1 M FeCl3 solution and 25 mL of 2 mg / mL graphene oxide dispersion to 50 mL of pure water, adjust the pH to 7, and stir at 60°C for 12 hours; under these conditions, graphene oxide in Fe... 3+ Under the influence of the reaction, spatial folding and curling occur. After the reaction, a microporous hybrid membrane with a pore size of 220 nm is used to remove the iron oxide solid suspension precipitated during the reaction. The Fe-graphene oxide framework in the filtrate is collected by high-speed centrifugation, washed with pure water, then collected by centrifugation again, and the product is dispersed in 50 mL of pure water.

[0030] To the above Fe-graphene oxide solution, add 200 μL of 0.1 M FeCl3 solution and 150 μL of aniline monomer, stir well, then add 2 mL of concentrated phosphoric acid and continue stirring for 30 minutes. At this point, the oily aniline monomer adheres to the surface of the Fe-graphene oxide framework and forms a bond with the Fe... 3+Under oxidation, PANI partially polymerizes and grows on the surface of the Fe-graphene oxide framework. Next, 400 μL of 8 g / L silver acetate solution is added and stirred for 1 hour. During this process, silver acetate is reduced to Ag nanoparticles by aniline, while aniline partially polymerizes to PANI, allowing Ag particles to successfully attach to the surface and interior of the PANI layer. Then, 0.3 g of ammonium persulfate is added to 5 mL of 10% phosphoric acid solution, completely dissolved, and then rapidly added to the above solution. The reaction is stirred for 1 to 1.5 hours. The rapid addition of a large amount of oxidant directly oxidizes the aniline attached to the Fe-graphene oxide surface, avoiding changes in the dielectric constant of the solution due to the addition of a large amount of oxidant, thus preventing disruption of the adhesion balance of oily aniline at the Fe-graphene oxide interface and the potential blockage of the numerous open channels to be formed. After the reaction, the product is separated by filtration and washed sequentially with water and ethanol.

[0031] The obtained powder was dispersed in 50 mL of a 5% phosphoric acid solution containing 100 mM ascorbic acid, and stirred for 24 hours to remove Fe from the system. 3+ The graphene oxide was then reduced. After filtration, the product was washed with water and ethanol, then dispersed in 30 mL of pure water, and 54 μL of 24.2 mM chloroauric acid was added. The mixture was allowed to stand for 24 hours. During this process, chloroauric acid underwent a displacement reaction with Ag and was reduced to Au. The standing conditions allowed the newly generated Au to form a nanofilm layer that coated the surface of the Ag particles, forming an AgAu bimetallic structure with a core-shell structure, thus completing the construction of a multi-synergistic catalytic system. Finally, the product was filtered, washed with water and ethanol, and air-dried to obtain OSPANI-rGO / AgAu powder.

[0032] Calculations show that the Ag:Au feed ratio (molar ratio) is approximately 14.7:1.

[0033] Comparative Example 1: Preparation of OSPANI-rGO vector 2 mL of 0.1 M FeCl3 solution and 25 mL of 2 mg / mL graphene oxide dispersion were added to 50 mL of pure water, and the pH was adjusted to 7. The mixture was stirred at 60°C for 12 hours. After the reaction was completed, the precipitated iron oxide solids were removed using a microporous hybrid membrane with a pore size of 220 nm. The Fe-graphene oxide product in the filtrate was collected by high-speed centrifugation, washed with pure water, and then collected again by centrifugation. The product was then dispersed in 50 mL of pure water.

[0034] In the above Fe-graphene oxide solution, 200 μL of 0.1 M FeCl3 solution and 150 μL of aniline monomer were added, stirred until homogeneous, and then 2 mL of concentrated phosphoric acid was added. Stirring was continued for 1.5 hours. Next, 0.3 g of ammonium persulfate was added to 5 mL of 10% phosphoric acid solution. After complete dissolution, the solution was quickly added back to the above solution, and the reaction was stirred for 1 to 1.5 hours. After the reaction was complete, the product was separated by filtration and washed sequentially with water and ethanol. The obtained powder was dispersed in 50 mL of 5% phosphoric acid solution containing 100 mM ascorbic acid and stirred for 24 hours. Finally, the product was filtered, washed with water and ethanol, and air-dried to obtain OSPANI-rGO powder with an open-pore spherical structure.

[0035] Comparative Example 2: Preparation of OSPANI-rGO / Ag: 2 mL of 0.1 M FeCl3 solution and 25 mL of 2 mg / mL graphene oxide dispersion were added to 50 mL of pure water, and the pH was adjusted to 7. The mixture was stirred at 60°C for 12 hours. After the reaction was completed, the precipitated iron oxide solids were removed using a microporous hybrid membrane with a pore size of 220 nm. The Fe-graphene oxide product in the filtrate was collected by high-speed centrifugation, washed with pure water, and then collected again by centrifugation. The product was then dispersed in 50 mL of pure water.

[0036] In the above Fe-graphene oxide solution, 200 μL of 0.1 M FeCl3 solution and 150 μL of aniline monomer were added, stirred until homogeneous, and then 2 mL of concentrated phosphoric acid was added, with stirring continuing for 30 minutes. Next, 400 μL of 8 g / L silver acetate solution was added, and stirring was carried out for 1 hour. Then, 0.3 g of ammonium persulfate was added to 5 mL of 10% phosphoric acid solution, and after complete dissolution, it was quickly added to the above solution, and the reaction was stirred for 1 to 1.5 hours. After the reaction was completed, the product was separated by filtration and washed sequentially with water and ethanol. The obtained powder was dispersed in 50 mL of 5% phosphoric acid solution containing 100 mM ascorbic acid and stirred for 24 hours. Finally, the product was filtered, washed with water and ethanol, and air-dried to obtain OSPANI-rGO / Ag powder.

[0037] Comparative Example 3: Preparation of OSPANI-rGO / Au: 2 mL of 0.1 M FeCl3 solution and 25 mL of 2 mg / mL graphene oxide dispersion were added to 50 mL of pure water, and the pH was adjusted to 7. The mixture was stirred at 60°C for 12 hours. After the reaction was completed, the precipitated iron oxide solids were removed using a microporous hybrid membrane with a pore size of 220 nm. The Fe-graphene oxide product in the filtrate was collected by high-speed centrifugation, washed with pure water, and then collected again by centrifugation. The product was then dispersed in 50 mL of pure water.

[0038] To the above Fe-graphene oxide solution, add 200 μL of 0.1 M FeCl3 solution and 150 μL of aniline monomer, stir until homogeneous, then add 2 mL of concentrated phosphoric acid and continue stirring for 30 minutes. Next, add 432 μL of 24.2 mM chloroauric acid solution and stir for 1 hour. Then, take 0.3 g of ammonium persulfate, add it to 5 mL of 10% phosphoric acid solution, and after complete dissolution, quickly add it to the above solution, stirring for 1 to 1.5 hours. After the reaction is complete, separate the product by filtration and wash with water and ethanol sequentially. Disperse the obtained powder in 50 mL of 5% phosphoric acid solution containing 100 mM ascorbic acid and stir for 24 hours. Finally, filter and wash the product with water and ethanol, and air dry to obtain OSPANI-rGO / Au powder.

[0039] Comparative Example 4: Preparation of PANI / AgAu: Add 200 μL of 0.1 M FeCl3 solution and 200 μL of aniline monomer to 50 mL of pure water, stir well, then add 2 mL of concentrated phosphoric acid and continue stirring for 30 minutes. Next, add 400 μL of 8 g / L silver acetate solution and stir for 1 hour. Then, take 0.3 g of ammonium persulfate, add it to 5 mL of 10% phosphoric acid solution, and after it is completely dissolved, slowly add it dropwise to the above solution, stirring the reaction for 1 to 1.5 hours. After the reaction is complete, separate the product by filtration and wash it with water and ethanol successively. Disperse the obtained powder in 50 mL of 5% phosphoric acid solution containing 100 mM ascorbic acid and stir for 24 hours. After filtration, wash the product with water and ethanol, then disperse it in 30 mL of pure water, add 54 μL of 24.2 mM chloroauric acid solution, and let it stand for 24 hours. Finally, filter and wash the product with water and ethanol, and air dry to obtain PANI / AgAu powder.

[0040] Comparative Example 5: Preparation of Two-Dimensional PANI-rGO / AgAu Composite Catalyst (2DPANI-rGO / AgAu) Add 200 μL of 0.1 M FeCl3 solution and 25 mL of 2 mg / mL graphene oxide dispersion to 50 mL of pure water. Stir for 10 to 20 minutes, then add 150 μL of aniline monomer and 2 mL of concentrated phosphoric acid. Sonicate for 20 to 30 minutes. Next, add 400 μL of 8 g / L silver acetate solution and continue stirring for 1 hour. Then, take 0.3 g of ammonium persulfate, add it to 5 mL of 10% phosphoric acid solution, and after it is completely dissolved, slowly add it dropwise to the above solution, stirring for 1 to 1.5 hours. After the reaction is complete, separate the product by filtration and wash it with water and ethanol successively. Disperse the obtained powder in 50 mL of 5% phosphoric acid solution containing 100 mM ascorbic acid and stir for 24 hours. After filtration, wash the product with water and ethanol, then disperse it in 30 mL of pure water, add 54 μL of 24.2 mM chloroauric acid solution, and let it stand for 24 hours. Finally, the product was filtered and washed with water and ethanol, and then air-dried to obtain 2DPANI-rGO / AgAu powder.

[0041] Example 2: Preparation of modified electrode: A 5 mm diameter glassy carbon electrode was polished sequentially on a polishing pad using alumina slurries with particle sizes of 3 μm, 1 μm, 0.3 μm, and 0.05 μm. It was then rinsed with distilled water, followed by ultrasonic cleaning in anhydrous ethanol and distilled water, and air-dried at room temperature. 2 mg of the nanocatalyst powder prepared in Example 1 and Comparative Examples 1-6 was dispersed in 10 μL of 5% Nafion (perfluorosulfonic acid polymer ion exchange resin) ethanol solution in 0.5 mL of ethanol and ultrasonically treated for 30 min to form a homogeneous suspension. 10 μL of this suspension was drop-coated onto the cleaned glassy carbon electrode surface, air-dried at room temperature, and then the modified electrode was immersed in 0.1 M PBS solution containing 1 mM AA for storage.

[0042] Example 3 Electrochemical Test: Electrochemical measurements were performed using a three-electrode system: the catalyst-modified electrodes prepared in Example 2 were used as working electrodes, the graphite electrode as the counter electrode, and the saturated calomel electrode (SCE) as the reference electrode. Differential pulse voltammetry (DPV) was used for measurements, with a potential range of -0.1V to 0.9V (vs. SCE), a scan amplitude of 50mV, and a pulse width of 50ms. All experiments were conducted in 0.1M PBS phosphate buffer (pH 6.8).

[0043] Test Result Analysis Figure 1 This is a scanning electron microscope (SEM) image of the OSPANI-rGO / AgAu catalyst. Figure 1 As shown in Figure A, this catalyst exhibits an open-sphere (OS) structure with a diameter of tens of micrometers. In Fe... 3+Under the influence of these factors, graphene oxide undergoes spatial folding and curling, and synergistically forms a spherical composite carrier with abundant open channels with polyaniline. From Figure 1 SEM images of the internal pores (Figures B, C, and D) show that the loaded AgAu is in the form of spherical particles with a particle size between 30 nm and 60 nm. These particles are distributed on the surface of the PANI-rGO layer or partially embedded in the PANI-rGO layer, together forming a multi-synergistic catalytic system.

[0044] Figure 2 The images show elemental surface scan (SBS) images and EDS spectra of AgAu nanoparticles in the OSPANI-rGO / AgAu catalyst. The figures show that Au was successfully reduced and formed AgAu nanocomposite material through a displacement reaction. The AgAu nanoparticles exhibit an irregular morphology with a diameter of approximately 40-60 nm. In the AgAu nanoparticles, the Ag content at the particle center is significantly higher than that in the outer layer (…). Figure 2 B, 2D, and 2E), while Au content is low in the center of AgAu nanoparticles, mainly concentrated in the outer layer of the particles (B, 2D, and 2E). Figure 2 (C, 2D, and 2E), thus forming AgAu bimetallic nanoparticles with Ag as the main element at the center and Au enriched in the outer layer.

[0045] Figure 3The DPV response of the catalyst-modified electrodes OSPANI-rGO (A), OSPANI-rGO / Ag (B), OSPANI-rGO / Au (C), and OSPANI-rGO / AgAu (D) in 0.1M PBS (pH 6.8) solution containing 200 μM DA, 1 mM UA, and 1 mM AA is shown in the figure. As shown, 1 mM AA did not produce a significant response signal on any electrode; although the oxidation peak of UA partially overlapped with that of DA, it did not interfere with the accurate determination of the DA peak current. This indicates that the four catalyst-modified electrodes prepared using OSPANI-rGO as the support all exhibit good selectivity and anti-interference ability for the DPV determination of DA. Compared with the unloaded OSPANI-rGO, the oxidation current of DA by the metal-loaded OSPANI-rGO / Ag, OSPANI-rGO / Au, and OSPANI-rGO / AgAu all showed varying degrees of enhancement, indicating higher electrocatalytic activity. It is worth noting that, compared to the more significant enhancement of the UA signal to the DA signal observed by the OSPANI-rGO / Ag and OSPANI-rGO / Au electrodes, the OSPANI-rGO / AgAu electrode exhibits a smaller enhancement of the oxidation signal to UA, indicating that it has superior selectivity for the electrochemical response to DA, which is beneficial for the stable detection of DA in complex systems. Therefore, OSPANI-rGO / AgAu demonstrates excellent sensitivity, selectivity, and anti-interference performance in the electrochemical detection of DA.

[0046] The differences in the aforementioned electrochemical responses are closely related to the structural characteristics of the AgAu bimetallic nanoparticles and their catalytic mechanisms for different molecules. The AgAu bimetallic nanoparticles prepared via a substitution reaction form bimetallic nanoparticles with Ag as the main element at the center and Au enriched in the outer layer. This structure exhibits differentiated electrocatalytic activities for DA and UA.

[0047] The oxidation peak potential of DA is relatively low (approximately 0.21V-0.26V). Its electro-oxidation process mainly involves the adsorption of molecules on the electrode surface, electron transfer, and desorption of intermediate products, without relying on the participation of oxygen-containing species on the surface. Single-metal Ag exhibits weak adsorption of DA, resulting in a slow electron transfer rate. However, intermediate products readily desorb from the electrode surface, releasing effective active sites, thus demonstrating a certain catalytic activity compared to pure supports. Single-metal Au exhibits strong adsorption of DA, which is beneficial for electron transfer. However, oxidation intermediates (such as ortho-quinones) are excessively adsorbed on the Au surface, easily occupying active sites and inhibiting sustained catalysis. When an AgAu bimetallic structure is formed, the outer layer of Au, enriched in DA, is affected by the electronic effects and lattice strain of the inner Ag, causing its d-band center to shift downwards. This results in the adsorption energy of DA on the outer Au surface falling between that of pure Ag and pure Au. As described by the Sabatier principle, this optimization ensures both effective adsorption of DA to promote electron transfer and rapid desorption of intermediate products, allowing for the regeneration of active sites and significantly enhancing the electrocatalytic activity for DA.

[0048] In comparison, UA exhibits a higher oxidation peak potential (approximately 0.34V-0.42V), and its electro-oxidation process involves multiple electron transfer steps and is highly sensitive to the participation of oxygen-containing species on the electrode surface. At potentials of 0.34V-0.42V, single-metal Ag readily forms surface oxides or adsorbs hydroxyl groups. These species can act as redox mediators, promoting UA conversion through an indirect oxidation mechanism. Therefore, OSPANI-rGO / Ag exhibits a high current for UA. The favorable response of single-metal Au to UA is mainly due to the direct adsorption and activation ability of its d-band electronic structure on the UA purine ring, i.e., catalysis is achieved through a direct oxidation mechanism. In the AgAu bimetallic structure, the outer layer of enriched Au covers the inner layer of Ag, shielding Ag's original ability to form oxygen-containing species on the surface and blocking the UA reaction pathway dependent on indirect oxidation. Simultaneously, the electronic effect of the inner Ag on the outer Au causes the d-band center of Au to shift downwards relative to pure Au, weakening the adsorption energy of UA on the surface, thus inhibiting the direct oxidation pathway that originally relied on strong adsorption activation. The combined effect leads to a significant reduction in the oxidation current of UA on the AgAu bimetallic surface.

[0049] In summary, AgAu bimetallic nanoparticles optimize the electrocatalytic performance of DA by modulating the surface electronic structure, but also weaken the key conditions for the effective oxidation of UA. This differentiated catalytic behavior enables OSPANI-rGO / AgAu to effectively achieve selective and interference-resistant detection of DA in DA and UA coexisting systems.

[0050] Figure 4The DPV response curves of OSPANI-rGO-based modified electrodes in 0.1M PBS (pH 6.8) solution containing 200 μM DA are shown. The results indicate that the oxidation potential of DA on the OSPANI-rGO-modified electrode ranges from 0.12 V to 0.50 V, with an oxidation peak potential at 0.27 V and a peak current of 3.94 μA. When OSPANI-rGO is loaded with Ag or Au single metals, the oxidation potential range of DA does not change significantly, but the oxidation peak potential shifts positively to 0.24 V–0.25 V, and the peak current increases to 1.45–1.55 times that of OSPANI-rGO. After loading with AgAu bimetal, the oxidation potential range of DA shifted significantly to 0.10V–0.36V, the oxidation peak potential shifted further to 0.21V, and the peak current increased to 7.82μA, which is 1.85 times that of OSPANI-rGO and significantly higher than that of OSPANI-rGO / Ag and OSPANI-rGO / Au electrodes. These results indicate that the OSPANI-rGO / AgAu modified electrode exhibits superior electrocatalytic performance for DA oxidation, demonstrating the synergistic enhancing effect of AgAu bimetal in the sensitive detection of DA.

[0051] Figure 5 The DPV response curves of AgAu-modified electrodes based on different supports in 0.1M PBS (pH 6.8) solution containing 200 μM DA are shown. The results show that on the PANI / AgAu-modified electrode, the oxidation potential of DA ranges from 0.14 V to 0.40 V, with an oxidation peak potential of 0.24 V and a peak current of 3.96 μA. When the support is the two-dimensional complex 2DPANI-rGO (2DPANI-rGO / AgAu), the oxidation potential range of DA shifts significantly positively to 0.10 V–0.36 V, the oxidation peak potential is between 0.21 V and 0.22 V, and the peak current is increased by approximately 1.28 times compared to PANI / AgAu. When OSPANI-rGO was used as the support (OSPANI-rGO / AgAu), its oxidation potential range (0.10V–0.36V) and peak potential (0.21V) were similar to those of the 2DPANI-rGO / AgAu system, but the peak current significantly increased to 7.82 μA, which is 1.97 times and approximately 1.54 times that of PANI / AgAu and 2DPANI-rGO / AgAu, respectively. This comparison indicates that the OSPANI-rGO support can construct a more efficient multi-layered synergistic catalytic interface with AgAu bimetallic nanoparticles, thus exhibiting superior electrocatalytic performance in DA detection.

[0052] Figure 6The DPV response and standard curves of the OSPANI-rGO / Ag modified electrode in 0.1M PBS (pH 6.8) to different concentrations of DA are shown. The DA concentrations tested were 200, 150, 100, 50, 10, 5, 1, 0.5, 0.1, and 0.05 μM, respectively. Figure 6 As shown in Figure A, the oxidation potential range of DA at various concentrations on this electrode is 0.1V–0.6V, with an oxidation peak potential of approximately 0.24V; the electrochemical response signal of DA increases with increasing concentration, and its detection limit is 0.05μM. Figure 6 As shown in section B, the OSPANI-rGO / Ag electrode exhibits a bilinear response to DA in the concentration range of 0.05 μM–200 μM: in the high concentration region of 1 μM–200 μM, the linear equation is I = 0.029C + 0.519(R). 2 =0.99708); in the low concentration region of 0.05 μM–1 μM, the linear equation is I = 0.155C + 0.2651 (R = 0.99708). 2 =0.98544).

[0053] Figure 7 The DPV response and standard curve of the OSPANI-rGO / Au modified electrode in 0.1M PBS (pH 6.8) to different concentrations of DA are shown. The tested DA concentrations were 200, 150, 100, 50, 10, 5, 1, 0.5, 0.1, 0.05, 0.01, and 0.005 μM, respectively. Figure 7 As shown in Figure A, the oxidation potential range of DA at various concentrations on this electrode is 0.1V–0.6V, with the oxidation peak potential around 0.25V; the response signal increases with increasing DA concentration, and the detection limit is 0.005μM. According to... Figure 7 In the medium B, the OSPANI-rGO / Au electrode exhibits a bilinear response to DA in the concentration range of 0.005 μM–200 μM: in the high concentration range of 5 μM–200 μM, the linear equation is I = 0.019C + 2.215 (R 2 =0.99247); in the low concentration range of 0.005 μM–1 μM, the linear equation is I = 1.0282C + 0.3526 (R = 0.99247). 2 =0.991).

[0054] Figure 8 The DPV response and standard curve of the OSPANI-rGO / AgAu modified electrode in 0.1M PBS (pH 6.8) to different concentrations of DA are shown. The tested DA concentrations were 200, 150, 100, 50, 10, 5, 1, 0.5, 0.1, 0.05, 0.01, 0.005, and 0.001 μM, respectively. Figure 8As shown in Figure A, the oxidation potential range of DA at various concentrations on this electrode is 0.11V–0.34V, with an oxidation peak potential of approximately 0.20V. Compared to the wider oxidation potential range (0.1V–0.6V) and obvious signal tailing exhibited by the OSPANI-rGO / Ag and OSPANI-rGO / Au modified electrodes during DA detection, the oxidation response potential range of the OSPANI-rGO / AgAu modified electrode is significantly narrower, with a smaller half-width, which is beneficial for improving the selectivity and anti-interference ability of DA detection. The electrochemical response signal of DA increases with increasing concentration, and its detection limit is 0.001μM. Figure 8 As shown in section B, the OSPANI-rGO / AgAu electrode exhibits a bilinear response to DA in the concentration range of 0.001 μM–200 μM: in the high concentration range of 5 μM–200 μM, the linear equation is I = 0.0235C + 2.6866 (R 2 =0.99245); in the low concentration range of 0.001 μM–1 μM, the linear equation is I = 1.629C + 0.539 (R = 0.99245). 2 =0.99704). Compared to OSPANI-rGO / Ag and OSPANI-rGO / Au modified electrodes, the OSPANI-rGO / AgAu modified electrode exhibits a lower detection limit and a wider linear response range in DA detection. It is known that the concentration of DA in the extracellular fluid of healthy individuals is typically in the range of 0.01 μM–1 μM, and the normal concentration of DA in urine is 0.1 μM–2 μM. Therefore, the OSPANI-rGO / AgAu modified electrode constructed in this invention can meet the requirements for accurate determination of DA content in human body fluids in terms of both sensitivity and linear detection range, and the detection of DA is not interfered with by the coexistence of UA and AA.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A graphene-based polyaniline-supported AgAu bimetallic composite catalyst, characterized in that, The catalyst comprises a polyaniline-reduced graphene oxide composite sphere support with open channels, and AgAu bimetallic nanoparticles loaded on the surface and inside of the composite sphere support. The composite sphere carrier is made of reduced graphene oxide with spatial folding and curling under coordination action, and polyaniline is attached and grown on the surface of the skeleton. 3+ The reduced graphene oxide with spatial folding and curling under coordination action is used as a skeleton, and polyaniline is attached and grown on the surface of the skeleton. The AgAu bimetallic nanoparticles were formed through a substitution reaction, resulting in Ag-dominant nanoparticles with an outer layer enriched with Au.

2. The graphene-based polyaniline-supported AgAu bimetallic composite catalyst according to claim 1, characterized in that, The AgAu bimetallic nanoparticles have a particle size of 30nm-60nm.

3. A method for preparing the graphene-based polyaniline-supported AgAu bimetallic composite catalyst as described in claim 1 or 2, characterized in that, Includes the following steps: (1) Preparation of Fe-graphene oxide framework: FeCl3 solution and graphene oxide dispersion were mixed, the pH of the system was adjusted to 6.8-7.2, and the reaction was carried out under heating conditions. The Fe-graphene oxide framework that underwent spatial folding and curling was separated and collected. (2) In-situ polymerization and Ag loading: The Fe-graphene oxide skeleton obtained in step (1) was dispersed in an aqueous phase, FeCl3 and aniline monomer were added, and after stirring, phosphoric acid was added to allow the aniline monomer to partially polymerize into a PANI layer and grow on the surface of the Fe-graphene oxide skeleton; then silver acetate solution was added to carry out a reduction reaction, and silver acetate was reduced to Ag nanoparticles. At the same time, the aniline monomer partially polymerized into a PANI layer, allowing the Ag nanoparticles to attach to the surface and interior of the PANI layer; then phosphoric acid solution containing ammonium persulfate was added to carry out a rapid oxidation reaction, and the product was separated and collected. (3) Removal of metal ions and reduction: The product obtained in step (2) is dispersed in a phosphoric acid solution containing ascorbic acid for reduction treatment to remove Fe from the system. 3+ The graphene oxide was then reduced, and the product was separated and collected. (4) Constructing the AgAu core-shell structure: Disperse the product obtained in step (3) in water, add chloroauric acid solution and let it stand to react. Through the displacement reaction, Au is reduced and coated on the surface of Ag particles to form AgAu nanocomposite material with Ag as the core. After washing and drying, it is obtained.

4. The method according to claim 3, characterized in that, In step (1), the heating conditions are 55°C-65°C and the stirring reaction time is 10h-14h.

5. The method according to claim 3, characterized in that, In step (2), the phosphoric acid solution containing ammonium persulfate is introduced into the reaction system in a one-time rapid addition after the ammonium persulfate has completely dissolved.

6. The method according to claim 3, characterized in that, In step (4), the static reaction time is 22h-26h.

7. The method according to claim 3, characterized in that, The amount of silver acetate solution and chloroauric acid solution added is such that the molar ratio of Ag to Au is 14-16:

1.

8. A method for preparing a modified electrode of graphene-based polyaniline-supported AgAu bimetallic composite catalyst according to 1 or 2, characterized in that, Includes the following steps: Using Nafion as a binder, the graphene-based polyaniline-supported AgAu bimetallic composite catalyst was loaded onto a glassy carbon electrode.

9. A modified electrode, characterized in that, The modified electrode is prepared by using Nafion as a binder to support the graphene-based polyaniline-supported AgAu bimetallic composite catalyst as described in claim 1 or 2 on a glassy carbon electrode.

10. The application of a graphene-based polyaniline-supported AgAu bimetallic composite catalyst in the preparation of a dopamine electrochemical sensor, characterized in that, The graphene-based polyaniline-supported AgAu bimetallic composite catalyst is the composite catalyst as described in claim 1 or 2.

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