In-situ electrochemical etching silk-screen printing silver electrode, preparation method thereof and EC-SERS platform

Abstract

The invention belongs to the technical field of detection, and particularly relates to an in-situ electrochemical etching silk-screen printing silver electrode, a preparation method thereof and an EC-SERS platform. On the basis of a pesticide protonation-EC-SERS combined strategy, an independently prepared SPE-Ag electrode is used as an enhanced substrate, a mobile phone is coupled to regulate and control a portable electrochemical workstation to apply potential, an EC-SERS rapid detection platform is established, the EC-SERS rapid detection platform is successfully used for rapid and sensitive detection of the residues of the neonicotinoid pesticide imidacloprid, the detection limit is as low as 1.5 nM, and the EC-SERS rapid detection platform can be used for rapid and sensitive detection of the residues of the neonicotinoid pesticide imidacloprid. According to the present invention, the problem that the on-site real-time application of the EC-SERS technology is limited by the equipment size, the cost and the operation complexity is solved, the portable and low-threshold on-site detection platform is provided, the detection cost is significantly reduced while the sensitivity of the traditional EC-SERS is maintained by the platform, the operation threshold is substantially reduced, and the detection efficiency is improved. And a method with a better application prospect is hopefully provided for on-site real-time detection of pesticide residues.

Description

Technical Field

[0001] This invention belongs to the field of detection technology, specifically to in-situ electrochemical etching screen-printed silver electrodes, their preparation methods, and the EC-SERS platform. Background Technology

[0002] In modern agricultural production, neonicotinoid pesticides are widely used due to their highly effective neurotoxicity against pests, with imidacloprid (IMI) being a typical example. Pesticide residues on fruits and vegetables pose a serious threat to food safety and human health. Developing efficient, sensitive, and convenient methods for pesticide residue detection has become an important research direction in the field of food safety. Traditional detection techniques mainly include gas chromatography (GC), high-performance liquid chromatography (HPLC), liquid chromatography (LC), liquid chromatography-tandem mass spectrometry (LC-MS / MS), immunoassay, and various biosensing methods. These methods have high accuracy and reliability, but generally suffer from drawbacks such as expensive equipment, complex operation, long detection cycles, and cumbersome sample pretreatment. Surface-enhanced Raman spectroscopy (SERS) possesses advantages such as molecular fingerprint recognition, fast detection speed, and ultra-high sensitivity, and is widely used in pesticide residue detection. However, SERS technology still faces challenges in practical applications, including insufficient interaction between pesticide molecules and the substrate and poor signal repeatability. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides an in-situ electrochemically etched screen-printed silver electrode, its preparation method, and an EC-SERS platform. This invention employs a screen printing method, first depositing carbon ink on a substrate to form a working electrode and a counter electrode, then depositing silver chloride paste to form a reference electrode, obtaining SPE-C. Next, Ag ink is deposited on the working electrode of SPE-C to obtain SPE-Ag ink. Finally, hydrochloric acid solution is deposited on the SPE-Ag ink, undergoing an oxidation-reduction process to obtain the SPE-Ag electrode. After connecting the SPE-Ag electrode to an electrochemical workstation, a reverse potential is applied through the workstation. The electrostatic adsorption of protonated imidacloprid by the SPE-Ag electrode adsorbs onto the surface of the working electrode, enhancing the SERS intensity of imidacloprid detection on the Raman spectrometer. This overcomes the problems of insufficient interaction between pesticide molecules and the substrate and poor signal repeatability in existing technologies.

[0004] Based on the above technical objectives, the present invention adopts the following technical solution: This invention protects a method for preparing in-situ electrochemical etching screen-printed silver electrodes, characterized by comprising the following steps: Using screen printing, conductive carbon ink is first deposited on the substrate to form working electrode and counter electrode patterns. After drying, silver chloride paste is deposited on the substrate using screen printing to form reference electrode patterns. After drying, a surface electrode-C composed of working electrode, reference electrode and counter electrode is obtained, denoted as SPE-C.

[0005] Ag ink was deposited on the working electrode of SPE-C using screen printing. After drying, silver-modified SPE was obtained, denoted as SPE-Ag ink.

[0006] Electrolyte hydrochloric acid solution was deposited on the working electrode, reference electrode, and counter electrode of SPE-Ag ink. Electrochemical roughening treatment was performed using a multi-potential stepping mode, first oxidation and then reduction, repeated at least twice, so that the metallic Ag on the SPE-Agink surface was transformed into dense, uniform, and interstitial silver nanoparticles, thereby endowing the electrode with local surface plasmon resonance (LSPR) activity and forming a large number of SERS active hot spots to enhance the Raman signal, resulting in an in-situ electrochemically etched screen-printed silver electrode, denoted as SPE-Ag electrode.

[0007] Preferably, the oxidation conditions are: oxidation at 1.05V~1.26V for 5s~30s.

[0008] Preferably, the reduction conditions are: reduction at -1.72V to -1.34V for 5s to 30s.

[0009] Preferably, the concentration of the hydrochloric acid solution is 0.1 mol / L to 0.6 mol / L.

[0010] Preferably, the working electrode is a circular electrode, and the counter electrode is arranged in concentric arcs around the working electrode, with the working electrode located between the reference electrode and the counter electrode.

[0011] This invention also protects an in-situ electrochemical etching screen-printed silver electrode, which is prepared using the above-described method.

[0012] This invention also protects an EC-SERS platform, which is prepared by the above-mentioned in-situ electrochemical etching screen-printed silver electrode.

[0013] Preferably, the EC-SERS platform includes a mobile phone-controlled portable electrochemical workstation, an in-situ electrochemically etched screen-printed silver electrode, and a Raman detector. The mobile phone-controlled portable electrochemical workstation is connected to the mobile phone via Bluetooth. The in-situ electrochemically etched screen-printed silver electrode is detachably connected to the mobile phone-controlled portable electrochemical workstation. The light source of the Raman detector is located above the in-situ electrochemically etched screen-printed silver electrode.

[0014] This invention also protects the application of the EC-SERS platform in the preparation of an imidacloprid detector. The application method is as follows: protonated imidacloprid solutions of different concentrations are drop-coated onto the working electrode of an in-situ electrochemically etched screen-printed silver electrode. A reverse potential is applied by a portable electrochemical workstation controlled by a mobile phone. Utilizing the electrostatic adsorption effect of the SPE-Ag electrode, the surface of the SPE-Ag electrode is negatively charged and can adsorb the protonated and positively charged imidacloprid. The protonated imidacloprid is adsorbed onto the surface of the working electrode. The SERS intensity of imidacloprid is detected on a Raman detector, and then a standard curve of imidacloprid concentration versus SERS intensity is plotted.

[0015] Among them, the protonated imidacloprid solution is obtained by dissolving imidacloprid in hydrochloric acid solution.

[0016] When detecting unknown concentrations of imidacloprid, repeat the above steps and calculate the concentration of unknown imidacloprid based on the standard curve and the detected SERS intensity.

[0017] When a positive potential is applied, the surface of the SPE-Ag electrode becomes positively charged, which can desorb the positively charged protonated imidacloprid. The detection effect of protonated imidacloprid can be improved by adjusting the potential using an electrochemical workstation.

[0018] Preferably, the limit of detection for imidacloprid is 1.5 nM.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention employs screen printing technology to prepare low-cost SPE-Ag electrodes. First, silver-modified SPE is prepared using screen printing. Then, the surface of the silver-modified SPE is roughened. The surface roughening process involves depositing an electrolyte hydrochloric acid solution onto the working electrode, reference electrode, and counter electrode of the silver-modified SPE. Electrochemical treatment is then performed using a multi-potential stepping mode, first oxidation, then reduction, repeating the oxidation-reduction cycle to obtain a structurally uniform and signal-stable Raman-active substrate, i.e., the SPE-Ag electrode. The purpose of the oxidation and reduction process of SPE-Ag ink is to transform the metallic Ag on the SPE-Ag ink surface into dense, uniform, and interstitial silver nanoparticles through electrochemical roughening, thereby endowing the electrode with localized surface plasmon resonance (LSPR) activity and forming numerous SERS active hot spots to enhance the Raman signal. Simultaneously, it ensures the uniformity and stability of the substrate signal. Without this process, the SPE-Ag ink maintains a partially overlapping layered structure, lacking silver nanoparticles and SERS active hot spots, thus failing to enhance the Raman signal.

[0020] 2. This invention uses an SPE-Ag electrode for the detection of imidacloprid. During detection, the lone pair electrons of the pyridine nitrogen atom in the imidacloprid molecule can combine with H⁺ in the detection solution to form a protonated pyridine nitrogen structure, giving the imidacloprid a positive charge. An electrochemical workstation is used to apply a reverse potential, driving the charged imidacloprid to be directionally adsorbed onto the Raman active site on the surface of the SPE-Ag electrode for EC-SERS detection. This method can meet the signal enhancement requirements of EC-SERS detection and exhibits good repeatability.

[0021] 3. Compared with existing technologies, this invention prepares an SPE-Ag electrode using screen printing combined with electrochemical roughening technology. By applying a directional potential with an electrochemical workstation, it achieves efficient enrichment and sensitive detection of imidacloprid. Experimental results show that by applying an optimal potential of -1.0V to drive the protonated imidacloprid to be directionally adsorbed onto the active site of the SPE-Ag electrode, the limit of detection (LOD) is as low as 1.5 nM, while the LOD of the traditional SERS detection method is 13.5 μM. Furthermore, the SPE-Ag electrode designed in this invention maintains the high sensitivity of EC-SERS while enabling mass production of the electrode, significantly reducing detection costs and operational barriers, and achieving portability. This opens up a promising path for rapid on-site detection of pesticide residues.

[0022] 4. The EC-SERS method can sensitively and accurately quantify imidacloprid in actual samples, showing broad application prospects in on-site monitoring of pesticide residues in fruits and vegetables. It has important practical significance for promoting rapid food safety control and ensuring the quality of agricultural products. However, in practical applications, the EC-SERS method still faces challenges such as complex electrode preparation processes, large equipment size, and harsh experimental conditions. Based on this, this invention provides a "pesticide protonation-EC-SERS" combined strategy. Using a self-prepared SPE-Ag electrode as the reinforcing substrate, it couples a portable electrochemical workstation with a mobile phone to control the applied potential. The mobile phone-controlled portable electrochemical workstation is small in size and easy to operate, establishing a portable, low-cost, fast, and low-operation-barrier electrochemical surface-enhanced Raman spectroscopy rapid detection platform, which has been successfully used for rapid and sensitive detection of neonicotinoid pesticide imidacloprid residues. After introducing the protonation strategy of pesticide molecules, the potential is applied by the portable electrochemical workstation through a mobile phone program setting, realizing the directional adsorption and enrichment of IMI pesticide molecules on the surface of the SPE-Ag electrode, significantly enhancing the SERS signal. The present invention also systematically evaluated the sensitivity, repeatability, selectivity and applicability of the platform in actual fruit and vegetable samples, with a overlap rate of 96.22%~104.12% (compared with HPLC-MS) and an RSD of 2.11%~7.54%. Attached Figure Description

[0023] The samples in the accompanying drawings of this invention are all samples prepared in Example 1.

[0024] Figure 1 This is a schematic diagram illustrating the principle of the in-situ electrochemical etching screen-printed silver electrode preparation method and the EC-SERS platform for detecting imidacloprid provided by the present invention.

[0025] Figure 2 Figures show the characterization results of the SPE-Ag electrode; Figure a is a schematic diagram of the preparation of the SPE-Ag electrode; Figures b to e are SEM images of SPE-C, silver-modified SPE, SPE-Ag2O, and SPE-Ag electrodes, respectively, with insets in Figures b to e showing the corresponding electrode photographs; Figure f is the EDS mapping diagram of C and Ag elements in the SPE-Ag electrode; Figure g is the XRD diffraction pattern of silver-modified SPE, SPE-Ag2O, and SPE-Ag electrodes; Figure h is the particle size distribution curve of silver nanoparticles in the SPE-Ag electrode.

[0026] Figure 3 ECSERS spectra of imidacloprid at different applied potentials.

[0027] Figure 4 Figure 1 shows the quantitative detection process of IMI; Figure 2a shows the EC-SERS spectra obtained at different IMI concentrations between 0.01 μM and 15 μM; Figure 3b shows the linear fitting curve of IMI in Figure 3a; Figure 4c shows the SERS spectra obtained at different IMI concentrations between 50 μM and 100 μM; and Figure 5d shows the linear fitting curve of IMI in Figure 4c.

[0028] Figure 5 In the image, a shows the physical image of the imidacloprid detection using the EC-SERS platform; b shows the physical image of the mobile phone-controlled portable electrochemical workstation connected to the SPE-Ag electrode; c shows the back view of the mobile phone-controlled portable electrochemical workstation; and d shows the front view of the mobile phone-controlled portable electrochemical workstation. Detailed Implementation

[0029] The technical solutions of the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention and not all embodiments. 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.

[0030] In this invention, the solute for the carbon ink is low-resistance conductive carbon ink (JC-2110), composed of 48 wt% carbon black, 25 wt% polyester resin, 26 wt% ester solvent, and 1 wt% co-solvent, purchased from Shenzhen Jieyongcheng Technology Co., Ltd., China. The silver chloride paste (Ag / AgCl, Elec-H230) is composed of 60 wt% silver, 10 wt% resin, and 30 wt% dibutyltin diacetate, purchased from Taobao Mall. The solute for the silver ink is silver ink (Ag, NY-120), provided by Shenzhen Yilai Technology Co., Ltd., China, composed of 57 wt% silver, 7 wt% polyester resin, and 36 wt% ethyl butoxyethyl acetate.

[0031] In this invention, scanning electron microscopy (SEM; Thermo Fisher Scientific Verios G4 UC) combined with energy dispersive X-ray spectroscopy (EDS) was used to analyze the morphological characteristics of the electrode materials. The crystal structure of the nanomaterials was analyzed using X-ray diffraction (XRD; SmartLab 9kW, Rigaku), while the elemental composition and chemical state were determined using X-ray photoelectron spectroscopy (XPS; Axis Supra, Kratos).

[0032] Electrochemical roughening experiments were conducted using an electrochemical workstation (CHI760C, CH Instruments). EC-SERS measurements were performed using a Finder Insight Pro Raman spectrometer (FI785E, Zolix Analytical Instruments Co., Ltd.) equipped with a 785nm laser, while SERS imaging was performed using a LabRAM HR evolution Raman spectrometer (Horiba), also equipped with a 785nm laser. During SERS detection, a self-made portable sensor was used, consisting of a self-developed Android application (APP) and a handheld detector, to apply different constant electrode potentials.

[0033] The technical solution of the present invention will be studied using the following embodiments. The specific research methods and results are shown below: Example 1 A method for preparing an in-situ electrochemical etching screen-printed silver electrode, such as... Figure 1 As shown, it includes the following steps: S1, Preparation of SPE-C: SPE-C was prepared in the laboratory by manual screen printing using three key components: carbon ink, silver chloride paste and PET substrate. The shape and size properties of SPE were designed using computer-aided design software (CAD). The printing template contained an array of 20 identical electrode cavities. The template was made of nylon mesh with a mesh size of 200 mesh, a wire diameter of 48 μm and a thickness of 82 μm.

[0034] A printing stencil with working and counter electrode patterns is fixed on the screen printing equipment platform. A PET substrate is placed below the stencil. Carbon ink is applied to the stencil, and a squeegee is used to evenly press the carbon ink through the mesh of the screen to form the working and counter electrode patterns. The working and counter electrodes obtained by screen printing are dried at 45°C for 15 minutes. After completing the above steps, the stencil with the reference electrode pattern is replaced, and the reference electrode is printed using silver chloride paste. After drying at 45°C for 15 minutes, SPEs composed of carbon working / counter electrodes and silver chloride reference electrodes are prepared, denoted as SPE-C. Twenty SPEs-C can be obtained per printing.

[0035] S2. Preparation of Silver-Modified SPE (SPE-Ag ink): A printing stencil containing only a circular working electrode area is mounted on the screen printing machine platform. The previously printed SPEs-C is precisely aligned with the stencil. Ag ink is evenly coated onto the stencil using a squeegee and printed. After drying at 45°C for 25 minutes, silver-modified SPE is obtained, denoted as SPE-Ag ink. Each batch can produce 20 SPE-Ag ink units. This SPE-Ag ink has a 4mm diameter circular working electrode and consists of a three-layer structure: a silver ink top layer, a carbon ink intermediate layer, and a PET substrate bottom layer.

[0036] Preparation of S3 and SPE-Ag electrodes: To form a nanostructure with high efficiency in surface-enhanced Raman scattering (SERS), the surface of silver-modified SPE was electrochemically roughened using a redox cycle method. Specifically, 50 μL of 0.4 M hydrochloric acid solution was uniformly deposited onto the surface of the silver-modified SPE, ensuring complete coverage of the area containing the three electrodes. Electrochemical treatment was then performed in the hydrochloric acid aqueous solution using a multi-potential stepping mode: first, oxidation was performed at 1.05 V for 15 s to obtain SPE-Ag₂O, followed by reduction at -1.34 V for 15 s. This two-step procedure was repeated twice to obtain the SPE-Ag electrode. With the electrochemical roughening treatment of the silver-modified SPE surface, the circular working electrode exhibited a significant color change: it changed from metallic silver-white to black under the oxidation potential, and then returned to white after applying the reduction potential. After rinsing with deionized water, the formed nanostructured SPE-Ag electrode finally yielded an effective electrode suitable for EC-SERS.

[0037] Example 2 A method for preparing an in-situ electrochemically etched screen-printed silver electrode includes the following steps: S1, Preparation of SPE-C: SPE-C was prepared in the laboratory by manual screen printing using three key components: carbon ink, silver chloride paste and PET substrate. The shape and size properties of SPE were designed using computer-aided design software (CAD). The printing template contained an array of 20 identical electrode cavities. The template was made of nylon mesh with a mesh size of 200 mesh, a wire diameter of 48 μm and a thickness of 82 μm.

[0038] A printing stencil with working and counter electrode patterns is fixed on the screen printing equipment platform. A PET substrate is placed below the stencil. Carbon ink is applied to the stencil, and a squeegee is used to evenly press the carbon ink through the mesh of the screen to form the working and counter electrode patterns. The working and counter electrodes obtained by screen printing are dried at 45°C for 15 minutes. After completing the above steps, the stencil with the reference electrode pattern is replaced, and the reference electrode is printed using silver chloride paste. After drying at 45°C for 15 minutes, SPEs composed of carbon working / counter electrodes and silver chloride reference electrodes are prepared, denoted as SPE-C. Twenty SPEs-C can be obtained per printing.

[0039] S2. Preparation of Silver-Modified SPE (SPE-Ag ink): A printing stencil containing only a circular working electrode area is mounted on the screen printing machine platform. The previously printed SPEs-C is precisely aligned with the stencil. Ag ink is evenly coated onto the stencil using a squeegee and printed. After drying at 45°C for 25 minutes, silver-modified SPE is obtained, denoted as SPE-Ag ink. Each batch can produce 20 SPE-Ag ink units. This SPE-Ag ink has a 4mm diameter circular working electrode and consists of a three-layer structure: a silver ink top layer, a carbon ink intermediate layer, and a PET substrate bottom layer.

[0040] Preparation of S3 and SPE-Ag electrodes: To form a nanostructure with high efficiency in surface-enhanced Raman scattering (SERS), an electrochemical roughening treatment was performed on the surface of silver-modified SPE using a redox cycle method. Specifically, 50 μL of 0.1 M hydrochloric acid solution was uniformly deposited onto the surface of the silver-modified SPE, ensuring complete coverage of the area containing the three electrodes. Electrochemical treatment was then performed in the hydrochloric acid aqueous solution using a multi-potential stepping mode: first, oxidation was performed at 1.10 V for 30 s to obtain SPE-Ag₂O, followed by reduction at -1.72 V for 30 s. This two-step procedure was repeated twice to obtain the SPE-Ag electrode. With the electrochemical roughening treatment of the silver-modified SPE surface, the circular working electrode exhibited a significant color change: it changed from metallic silver-white to black under the oxidation potential, and then returned to white after applying the reduction potential. After rinsing with deionized water, the formed nanostructured SPE-Ag electrode finally yielded an effective electrode suitable for EC-SERS.

[0041] Example 3 A method for preparing an in-situ electrochemically etched screen-printed silver electrode includes the following steps: S1, Preparation of SPE-C: SPE-C was prepared in the laboratory by manual screen printing using three key components: carbon ink, silver chloride paste and PET substrate. The shape and size properties of SPE were designed using computer-aided design software (CAD). The printing template contained an array of 20 identical electrode cavities. The template was made of nylon mesh with a mesh size of 200 mesh, a wire diameter of 48 μm and a thickness of 82 μm.

[0042] A printing stencil with working and counter electrode patterns is fixed on the screen printing equipment platform. A PET substrate is placed below the stencil. Carbon ink is applied to the stencil, and a squeegee is used to evenly press the carbon ink through the mesh of the screen to form the working and counter electrode patterns. The working and counter electrodes obtained by screen printing are dried at 45°C for 15 minutes. After completing the above steps, the stencil with the reference electrode pattern is replaced, and the reference electrode is printed using silver chloride paste. After drying at 45°C for 15 minutes, SPEs composed of carbon working / counter electrodes and silver chloride reference electrodes are prepared, denoted as SPE-C. Twenty SPEs-C can be obtained per printing.

[0043] S2. Preparation of Silver-Modified SPE (SPE-Ag ink): A printing stencil containing only a circular working electrode area is mounted on the screen printing machine platform. The previously printed SPEs-C is precisely aligned with the stencil. Ag ink is evenly coated onto the stencil using a squeegee and printed. After drying at 45°C for 25 minutes, silver-modified SPE is obtained, denoted as SPE-Ag ink. Each batch can produce 20 SPE-Ag ink units. This SPE-Ag ink has a 4mm diameter circular working electrode and consists of a three-layer structure: a silver ink top layer, a carbon ink intermediate layer, and a PET substrate bottom layer.

[0044] Preparation of S3 and SPE-Ag electrodes: To form a nanostructure with high efficiency in surface-enhanced Raman scattering (SERS), an electrochemical roughening treatment was performed on the surface of silver-modified SPE using a redox cycle method. Specifically, 50 μL of 0.6 M hydrochloric acid solution was uniformly deposited onto the surface of the silver-modified SPE, ensuring complete coverage of the area containing the three electrodes. Electrochemical treatment was then performed in the hydrochloric acid aqueous solution using a multi-potential stepping mode: first, oxidation was performed at 1.26 V for 5 s to obtain SPE-Ag₂O, followed by reduction at -1.50 V for 5 s. This two-step procedure was repeated twice to obtain the SPE-Ag electrode. With the electrochemical roughening treatment of the silver-modified SPE surface, the circular working electrode exhibited a significant color change: it changed from metallic silver-white to black under the oxidation potential, and then returned to white after applying the reduction potential. After rinsing with deionized water, the formed nanostructured SPE-Ag electrode finally yielded an effective electrode suitable for EC-SERS.

[0045] Examples 1 to 3 of this invention all yielded effective SPE-Ag electrodes suitable for EC-SERS. The SPE-Ag electrode from Example 1 is used as an example for further research. Specific research methods and results are shown below: Detection method: Electrochemical surface-enhanced Raman scattering (SPE-Ag) data acquisition: First, a standard solution of imidacloprid (IMI), i.e., protonated imidacloprid, was prepared in a background electrolyte of HCl solution (10 mM, pH=2). This solution was then diluted to obtain IMI gradient solutions of different concentrations. The prepared SPE-Ag electrode was inserted into the electrochemical interface of a self-made portable sensor. The self-made portable sensor is a mobile phone-controlled electrochemical portable workstation + Raman detector. The electrochemical portable workstation is disclosed in the paper entitled "Smartphone-based molecularly imprinted sensors for rapid detection of thiamethoxam residues and applications" (i.e., Figure 1 The black circuit board in the image shows an electrochemical portable workstation connected to a mobile phone via Bluetooth. An app is set up on the phone for parameter adjustment. 50 μL of IMI solution is added to the surface of the SPE-Ag electrode, ensuring complete coverage of the three-electrode area. A potential is applied to the SPE-Ag electrode using the electrochemical portable workstation for 480 s, and then EC-SERS spectra are acquired. Figure 5As shown. To determine the optimal potential for EC-SERS detection, the applied potential was adjusted from the open-circuit potential (OCP) in increments of -0.1V to -1.1V, with EC-SERS spectra of 10 μM IMI acquired at each step. Under the optimized potential conditions, EC-SERS spectra corresponding to different IMI concentrations were obtained. All EC-SERS measurements were performed at room temperature, and the total sample volume remained constant at 50 μL throughout the process.

[0046] IMI detection in actual samples: peas ( Pisumsativum L.) and scallions ( Allium fistulosum L.) Samples were purchased from the local market. Extracts were prepared according to Chinese national standard (GB23200.121-2021). Ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS / MS) was used to detect the sample extracts to validate the EC-SERS method. Positive samples (samples with imidacloprid detected on the surface by UPLC-MS / MS) were dried, redissolved in hydrochloric acid buffer (pH=2), and directly analyzed by EC-SERS. Negative samples (samples without imidacloprid detected by UPLC-MS / MS) were used as blank matrix for spiking experiments. The required concentration of IMI was added to the extract, and after drying, it was redissolved in hydrochloric acid buffer (pH=2) and then analyzed by EC-SERS to evaluate the method performance.

[0047] Results and Discussion: 1. Characterization of solid-state electrode (SPE-Ag electrode): Figure 2 Figure a illustrates the SPE-Ag electrode fabrication process, comprising three key stages: first, SPE-Ag ink is prepared using screen printing technology; second, oxidation is performed at a potential of 1.05V; and finally, reduction is carried out at a potential of -1.34V. The circular working electrode region was characterized using scanning electron microscopy (SEM), revealing its morphological characteristics. SEM images show that the SPE-C surface consists of irregularly interconnected particles, exhibiting a distinct porous structure, such as... Figure 2 As shown in Figure b. Subsequently, after the silver ink was screen-printed onto the circular area of ​​the working electrode, the surface of the silver-modified SPE exhibited a silvery-white metallic luster. SEM observation revealed that it displayed a partially overlapping layered structure, as shown in Figure b. Figure 2 As shown in Figure c, after the second oxidation process, the silver completely reacts and transforms into silver oxide. Visually, the original silvery-white area of ​​the working electrode turns black, while under SEM, it exhibits a tightly packed, blocky structure, as shown... Figure 2 As shown in Figure d, after the reduction reaction, the electrode regained its silvery-white luster but appeared slightly duller, and its morphology transformed into dense, uniform nanoparticles with gaps, such as... Figure 2As shown in Figure e. These silver nanoparticles have an average size of 139 nm, as... Figure 2 As shown in Figure h, the atoms are uniformly distributed on the surface of the circular region of the working electrode, forming a rough plane. When light of a specific wavelength is irradiated onto this rough plane, localized surface plasmon resonance (LSPR) can be induced. Utilizing this property, a large number of SERS active hotspots can be generated, ultimately yielding a promising SERS substrate. In energy dispersive spectroscopy imaging, after reduction, the distribution of C and Ag atoms on the working electrode is clearly visible, as shown in Figure h. Figure 2 As shown in Figure f, combined with the elemental analysis results, the successful synthesis of the SPE-Ag electrode was confirmed.

[0048] In addition, such as Figure 2 As shown in Figure g, the compositional changes of the working electrode during the redox cycle were examined by XRD analysis, further confirming the successful preparation of the SPE-Ag electrode. Both SPE-Ag ink and SPE-Ag electrodes exhibited characteristic diffraction peaks at 38.0° (111), 44.3° (200), 64.5° (220), and 77.3° (311), which are attributed to metallic silver (JCPDS No. 04-0783). SPE-Ag2O showed an additional diffraction peak at 32.1° (111), a peak characteristic of Ag2O (JCPDS No. 75-1532). Simultaneously, SPE-Ag2O retained Ag-related diffraction peaks. This phenomenon indicates that electrochemical oxidation mainly occurs at the surface layer. Furthermore, at 46.2°, SPE-Ag2O also exhibited a diffraction peak corresponding to the AgCl crystal (220) plane (JCPDS No. 31-1238). It is reasonable to speculate that this peak originates from Ag during the oxidation phase. + With Cl in HCl electrolyte - Caused by ionic reactions.

[0049] 2. Electrochemical adsorption and SERS detection of IMI on SPE-Ag electrode: like Figure 3 As shown in the results, the potential optimization results indicate that the SERS enhancement effect is significantly better than other potentials when a potential of -1.0V is applied: when the potential is below -1.0V (e.g., -1.1V), excessively high negative potentials can easily lead to H+ in the electrolyte. + Hydrogen gas is reduced and evolved on the SPE-Ag electrode surface, disrupting the adsorption environment of IMI and interfering with the "hot spot" structure. When the potential is higher than -1.0V (e.g., -0.9V to -0.4V), the reverse driving force is insufficient, making it impossible to efficiently enrich protonated IMI, thus weakening the signal enhancement effect. Notably, when a potential of -0.4V is applied, the characteristic peak of IMI is not observed in the detection spectrum. This is because -0.4V is an inhibitory potential, which has a repulsive effect on the positively charged protonated IMI, causing the IMI to move away from the active site and failing to generate a recognizable SERS signal.

[0050] 3. Quantitative detection of IMI: To establish a quantitative detection method, SERS and EC-SERS tests were performed on IMI solutions of different concentrations. Figure 4 As shown in Figure a, the EC-SERS signal intensity gradually increases with increasing IMI pesticide concentration, corresponding to a detection range limited to 0.01 μM–15 μM. It is noteworthy that at 643 cm⁻¹… -1 The SERS intensity at the location showed an excellent linear relationship with the IMI concentration (e.g., Figure 4 (As shown in Figure b). Furthermore, the calibration curve yields the equation: Y = 993.3X + 656.2, with a correlation coefficient R0. 2 Up to 0.9983. The calculated limit of detection (LOD) is 1.5 nM. For example... Figure 4 As shown in Figure c, within the concentration range of 50 μM to 100 μM, the IMI is at 643 cm⁻¹. -1 The intensity of the surface-enhanced Raman scattering characteristic peak at that location also exhibits a linear relationship. For example... Figure 4 As shown in plot d, the fitted standard curve equation is Y = 14.35x - 270.85, R0 2 =0.9951, detection limit is 13.5μM.

[0051] To evaluate the feasibility of EC-SERS in sample matrices, this invention applies EC-SERS to peas ( Pisumsativum L.) and scallions ( Allium fistulosum IMI in L. samples was directly quantitatively analyzed. In the spiked experiments, IMI was added to the negative sample extract and SERS was measured. As shown in Table 1, where S represents the spiked sample number, the recovery rate of IMI ranged from 90.65% to 103.04%, and the relative standard deviation (RSD) ranged from 2.11% to 7.54%. Subsequently, EC-SERS was performed on three pea and three scallion positive samples, and the results were compared with those of UPLC-MS / MS.

[0052] Table 1 Recovery and Validation Results of Electro-Driven Adsorption SERS As shown in Table 1, the concordance rates between EC-SERS and UPLC-MS / MS ranged from 96.22% to 104.12%. These results demonstrate that the EC-SERS detection method based on the SPE-Ag electrode exhibits excellent accuracy and reliability in analyzing IMI in real samples.

[0053] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for the preparation of in situ electrochemically etched screen-printed silver electrodes, characterized in that, The method comprises the following steps: A carbon ink is deposited on the substrate by screen printing to form a working electrode and a counter electrode pattern, and then a silver chloride paste is deposited on the substrate by screen printing to form a reference electrode pattern, and after drying, a surface electrode-C composed of the working electrode, the reference electrode and the counter electrode is obtained; An Ag ink is deposited on the working electrode of the surface electrode-C by screen printing, and after drying, a silver ink modified SPE is obtained; An electrolyte hydrochloric acid solution is deposited on the working electrode, the reference electrode and the counter electrode of the silver ink modified SPE, and then an electrochemical roughening treatment is performed in a multi-potential stepping mode, first oxidation and then reduction, repeated at least twice, so that the surface metal Ag of the silver ink modified SPE is converted into nano silver particles, and an in-situ electrochemically etched screen-printed silver electrode, denoted as SPE-Ag electrode, is obtained.

2. The method of claim 1, wherein the in-situ electrochemical etching of the screen printed silver electrode is performed by applying a voltage of 0.5 to 1.5 V for 1 to 10 minutes. The oxidation condition is: oxidation at 1.05V-1.26V for 5s-30s.

3. The method of claim 1, wherein the in-situ electrochemical etching of the screen printed silver electrode is performed by applying a voltage of 0.5 to 1.5 V for 1 to 10 minutes. The reduction condition is: reduction at-1.72V--1.34V for 5s-30s.

4. The method of claim 1, wherein the in-situ electrochemical etching of the screen printed silver electrode is performed by applying a voltage of 0.5 to 1.5 V for 1 to 10 minutes. The concentration of the hydrochloric acid solution is 0.1mol / L-0.6mol / L.

5. The method of claim 1, wherein the in-situ electrochemical etching of the screen printed silver electrode is performed by applying a voltage of 0.5 to 1.5 V for 1 to 10 minutes. The working electrode is a circular electrode, the counter electrode is in the form of a concentric circular arc surrounding the working electrode, and the working electrode is located between the reference electrode and the counter electrode.

6. An in-situ electrochemical etching screen printed silver electrode characterized by, The in-situ electrochemically etched screen-printed silver electrode is prepared by the preparation method of any one of claims 1-5.

7. An EC-SERS platform, characterized in that, The in-situ electrochemically etched screen-printed silver electrode is prepared by the preparation method of claim 6.

8. The EC-SERS platform of claim 7, wherein, The EC-SERS platform comprises a mobile phone controlled portable electrochemical workstation, an in-situ electrochemically etched screen-printed silver electrode and a Raman detector, the mobile phone controlled portable electrochemical workstation is connected with a mobile phone through Bluetooth, the in-situ electrochemically etched screen-printed silver electrode is detachably connected with the mobile phone controlled portable electrochemical workstation, and the light source of the Raman detector is located above the in-situ electrochemically etched screen-printed silver electrode.

9. Use of the EC-SERS platform of claim 7 in the preparation of a detector for imidacloprid, characterized in that, The application method is: different concentrations of protonated imidacloprid solution are dropped on the working electrode of the in-situ electrochemically etched screen-printed silver electrode, a reverse potential is applied to the mobile phone controlled portable electrochemical workstation through the mobile phone, protonated imidacloprid is adsorbed to the surface of the working electrode by the electrostatic adsorption of the SPE-Ag electrode, the SERS intensity of imidacloprid is detected on the Raman detector, and then a standard curve of the concentration of imidacloprid and the SERS intensity is drawn; The protonated imidacloprid solution is obtained by dissolving imidacloprid in a hydrochloric acid solution; When detecting an unknown concentration of imidacloprid, the above operation is repeated, and the concentration of the unknown imidacloprid is calculated according to the standard curve and the detected SERS intensity. 10.The use of the EC-SERS platform according to claim 9 in the preparation of a detector for imidacloprid, characterized in that, The minimum detection limit of imidacloprid is 1.5nM.

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