Electrochemical synthesis method of gold and silver core-shell nanoflowers and their application in SERS detection of thiram

Abstract

The invention discloses an electrochemical synthesis method of gold-silver core-shell nanoflowers, comprising adding an indium tin oxide carrier substrate to a tetrachloroauric acid solution, performing electrochemical deposition at a constant voltage of 0.3-0.7V to deposit gold nanoflowers on the indium tin oxide carrier substrate, wherein the deposition time is 25-125s; the gold nanoflowers are working electrodes, and electrochemical deposition is performed at a constant voltage of ‑0.7-‑0.5V in a silver nitrate solution to obtain gold-silver core-shell nanoflowers, wherein the deposition time is 25-125s. The preparation method has a short preparation time, and the prepared gold-silver shell nanoflowers can detect the concentration of thiram with high sensitivity, strong stability, and fast detection speed. The invention also discloses gold-silver core-shell nanoflowers prepared by the preparation method of gold-silver core-shell nanoflowers, and applications in detecting the concentration of thiram.

Description

Technical Field

[0001] The invention belongs to the field of compound detection, and specifically relates to an electrochemical synthesis method of gold-silver core-shell nanoflowers and SERS detection of thiram using the same. Background Art

[0002] Thiram, as a dithiocarbamate fungicide, has been widely used in seeds, fruits and vegetables. The improper disposal and abuse of thiram has posed a serious threat to human health and environmental sustainability. Trace ingestion or inhalation of thiram by the human body can also cause headaches, nausea, fatigue and dizziness. In addition, as a mutagen, thiram may also cause changes at the chromosomal level. Therefore, the development of reliable, simple and ultra-trace thiram sensing detection methods is crucial to ensure food safety activities.

[0003] Due to the potential health risks of thiram, many detection methods have been established, such as gas chromatography, high performance liquid chromatography, gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry. Although these analytical techniques have good sensitivity, they still have disadvantages such as inability to monitor in real time, complex operation, direct interaction with samples, and cumbersome and complicated sampling process. Compared with the above methods, the fingerprint spectrum shown by Raman spectroscopy makes Raman technology have better selectivity when applied to detection, but when traditional Raman technology analyzes the analyte, the signal is often weak, and there are certain limitations in practical applications. In recent years, surface enhanced Raman scattering (SERS) has aroused great interest in pesticide detection research due to its high sensitivity, short time, non-destructiveness and reliable molecular structure-based fingerprint monitoring. In previous studies, a variety of SERS substrate synthesis methods have emerged, such as template-assisted manufacturing, nanolithography, interface self-assembly technology and electrochemistry. Among the reported methods, electrochemical deposition provides a simple, easy and fast method for preparing SERS substrates.

[0004] Electrochemical techniques have been used to fabricate nanostructures and use them as SERS substrates. Therefore, new SERS substrates can be designed through different electrochemical deposition strategies, that is, by precisely electrochemically depositing precious metal materials in tunable anodized aluminum oxide and silicon dioxide nanochannels, and then removing the template material, many metal nanostructures with different sizes and morphologies can be designed. In addition, the combination of electrochemical deposition and nanolithography has also been used to form narrow gaps between adjacent nanostructures or "hot spot" areas, thereby significantly improving the enhancement factor. However, the complex preparation process and long preparation time limit their widespread use in SERS measurements, especially in the field of food analysis.

[0005] Direct deposition of metal nanostructures on conductive materials such as indium tin oxide (ITO) has been reported, but is usually limited to single-component nanoparticles. These single-component materials have relatively low SERS enhancement effects and poor signals. Inspired by the high performance of bimetallic nanostructures, bimetallic SERS substrates with high enhancement factors are designed through simple direct electrochemical steps, which can meet the requirements of practical applications. Summary of the invention

[0006] The present invention provides an electrochemical synthesis method of gold-silver core-shell nanoflowers. The preparation method has a short preparation time, and the prepared gold-silver shell nanoflowers can detect the concentration of thiram with higher sensitivity, stronger stability and faster detection speed.

[0007] An electrochemical synthesis method of gold and silver core-shell nanoflowers, comprising:

[0008] (1) adding an indium tin oxide carrier substrate to a tetrachloroauric acid solution, and performing electrochemical deposition at a constant voltage of 0.3-0.7 V to deposit gold nanoflowers on the indium tin oxide carrier substrate, wherein the deposition time is 25-125 s;

[0009] (2) Using the gold nanoflower obtained in step (1) as a working electrode, electrochemical deposition is performed in a silver nitrate solution at a constant voltage of -0.7 to -0.5 V to obtain gold-silver core-shell nanoflowers, wherein the deposition time is 25 to 125 seconds.

[0010] Gold nanoparticles are evenly and independently dispersed on the smoky tin oxide glass slide substrate as round spots, and the shape of the gold nanoparticles is flower-like. The flower-like gold nanostructure is composed of sharp crystal 3D edges of different sizes gathered together.

[0011] After silver plating, the average size of the nanoflowers further increased, the sharp edges of the gold nanoflowers were extended, and many holes appeared between the edges, which are considered to be potential target trap locations. These 3D edges act as SERS "hotspot" areas, indicating their potential for high SERS enhancement performance.

[0012] The smaller spacing between adjacent extended branches of the assembled gold-silver core-shell nanoflowers leads to denser localized surface plasmon resonance "hot spots" and higher enhancement effects, making the surface enhanced Raman scattering of gold-silver core-shell nanoflowers produce higher SERS enhancement factors than gold nanoflowers. SERS signals were collected at 65 different locations. At 1361 cm -1 The surface enhanced Raman scattering signal recorded at remained stable with a relative standard deviation of 14.63%, indicating that the gold and silver core-shell nanoflower substrate is reliable and sensitive in quantitative analysis experiments.

[0013] The concentration of the tetrachloroauric acid solution is 20-30 mmol·L -1 The deposition time of step (1) is 50-100 s, the constant voltage is 0.3-0.7 V, and the concentration of the silver nitrate solution is 8-12 mmol·L -1 The deposition time of step (2) is 50-100 s, and the constant voltage is -0.7 to -0.5 V.

[0014] The electromagnetic field response before and after the silver layer was examined by commercial electronic solver simulation, and it was found that the diameter of the gold nanoparticle core was 35.0-45.0nm, the thickness of the silver layer was 15.0-25.0nm, and the electromagnetic field intensity near the nanoparticle increased significantly. This increase in electromagnetic field intensity is attributed to the charge density oscillation of free electrons or the increase in plasma frequency in the hybrid bimetallic structure.

[0015] Before adding the tetrachloroauric acid solution to the indium tin oxide carrier substrate, ultrasonic cleaning is performed in sequence using sodium hydroxide ethanol, acetone and distilled water.

[0016] The ultrasonic cleaning time is 10-60 minutes.

[0017] The indium tin oxide carrier substrate is a three-electrode system, wherein the working electrode is an indium tin oxide glass slide or gold nanoflower, the reference electrode is an Ag / AgCl electrode, and the counter electrode is a platinum wire.

[0018] Gold-silver core-shell nanoflowers are prepared by the preparation method of the gold-silver core-shell nanoflowers. The surface of the gold nanoflowers is coated with a silver nanoshell layer. The average size of the gold nanoflowers is 4.91±0.59 μm. The average size of the gold-silver core-shell nanoflowers after silver plating is 6.55±0.83 μm. The sharp edges of the gold nanoflowers are extended, and many holes appear between the edges. The presence of these holes can prompt the target to enter and form a SERS "hotspot" area with the 3D edges, indicating that the gold-silver core-shell nanoflowers have the potential for high SERS enhancement performance.

[0019] The application of the gold-silver core-shell nanoflower in detecting the content of thiram includes:

[0020] The gold-silver core-shell nanoflowers were placed in a concentration of 1×10 -7 -1×10 -3 mol·L -1 The SERS intensity of the thiram solution is measured by collecting the spectrum through a Raman spectroscopic microscope, and the SERS intensity is substituted into the thiram content-SERS intensity standard curve to obtain the thiram content.

[0021] When the SERS substrate, that is, the gold-silver core-shell nanoflower, is immersed in thiram, thiram is adsorbed on the surface of the gold-silver core-shell nanoflower in the form of Ag-S bonds. The SERS signal depends largely on the proximity of the probe near the SERS substrate and the interaction between them, so this partially covalent and partially electrostatic Ag-S bond helps to amplify the Raman scattering excellently.

[0022] The thiram content-SERS intensity standard curve is:

[0023] I=804.22C+5824.94,R 2 =0.996, where I is the SERS intensity and C is the logarithm of the thiram concentration.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The present invention synthesizes gold-silver core-shell nanoflowers by an electrochemical method, and the synthesis time is short. The synthesized gold-silver core-shell nanoflowers have long 3D crystal edges and multiple holes between the edges, which serve as target trap positions and become SERS hotspots, thereby achieving an ultra-low detection limit and a wide linear dynamic range. Therefore, the gold-silver core-shell nanoflowers prepared by the electrochemical method provided by the present invention can ensure the rapid and simple determination of thiram residues in complex food matrices.

[0026] (2) The label-free gold-silver core-shell nanoflowers provided by the present invention have the advantages of short material synthesis time and high sensitivity, and can be used for SERS quantitative analysis of thiram residues in samples. The strong adsorption of thiram on the gold-silver core-shell nanoflower substrate provides a basis for establishing a label-free SERS detection platform. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a scanning electron microscope image of the gold nanoflower prepared in Example 1, wherein: Figure 1 (a) is a scanning electron microscope image of gold nanoparticles magnified to 20 μm. Figure 1 (b) is a scanning electron microscope image of gold nanoparticles magnified to 5 μm. Figure 1 (c) is a scanning electron microscope image of gold nanoparticles magnified to 300 nm;

[0028] Figure 2 This is the size distribution diagram of the gold nanoflowers and gold-silver core-shell nanoflowers prepared in Example 1;

[0029] Figure 3 The scanning electron microscope image and atomic force microscope analysis image of the gold-silver core-shell nanoflower prepared in Example 1 are shown in FIG. Figure 3 (a) is a scanning electron microscope image. Figure 3(b) is an atomic force microscope analysis image;

[0030] Figure 4 SERS signal collection diagram of different areas of gold and silver core-shell nanoflowers. Figure 4 (a) SERS spectra of 65 different regions, Figure 4 (b) is 1361cm -1 The corresponding SERS intensity map at ;

[0031] Figure 5 The SERS spectra of the gold-silver core-shell nanoflowers prepared in Example 1 at different thiram contents;

[0032] Figure 6 The logarithm of the thiram content in Example 1 and its corresponding 1378 cm -1 SERS intensity relationship diagram at ;

[0033] Figure 7 This is a scanning electron microscope image of the gold-silver core-shell nanoflowers prepared in Example 2. DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with specific embodiments.

[0035] Example 1

[0036] (1) Cleaning the electrode: pre-clean the fumed tin oxide glass slide substrate with sodium hydroxide ethanol, acetone and distilled water for 10 minutes in sequence;

[0037] (2) Preparation of gold nanoflowers: 24.3 mmol·L gold nanoparticles were electrochemically deposited on a pre-cleaned tin oxide glass slide using an amperometric method at a constant applied voltage of 0.5 V. -1 of tetrachloroauric acid solution, with a deposition time of 75 seconds, and successfully synthesized gold nanoflowers, such as Figure 1 As shown in (a), the average size of the synthesized gold nanoflowers is 4.91±0.59 μm, and the gold nanoparticles are evenly and independently dispersed on the tin oxide glass slide in the form of round spots, showing a complex morphological structure. Figure 1 As shown in (b) and (c), in the enlarged top view, the general shape of the gold nanoparticles is flower-like. Further enlargement of the flower-like gold nanostructure shows that sharp crystalline 3D edges of different sizes are clustered together;

[0038] (3) Preparation of gold-silver core-shell nanoflowers: Using gold nanoflowers as working electrodes, the silver shell was controlled to deposit on the gold structure to form a bimetallic core-shell heterostructure. -1 The silver nitrate solution was neutralized and electrochemically deposited under a voltage of -0.6 V to form gold-silver core-shell nanoflowers, such as Figure 3As shown in (a) and (b), the gold-silver core-shell nanoflowers uniformly dispersed on the oxidized tin glass slide maintain the shape of the gold nanoflowers. After the silver layer is coated, the sharp edges of the gold nanoflowers are extended, and many holes appear between the edges. These holes are considered to be potential target trap locations. These 3D edges act as SERS "hotspot" areas, indicating that the gold-silver core-shell nanoflowers have the potential to have high SERS enhancement performance. After rinsing and drying, as shown in Figure 2 As shown, the size of the gold-silver core-shell nanoflowers obtained after coating with silver is obviously larger than that of the gold nanoflowers;

[0039] (4) Drawing of working curve: The gold and silver core-shell nanoflowers were immersed in different concentrations of thiram, the specific concentration was 10 -3 M, 10 -4 M, 10 -5 M, 10 -6 M and 10 -7 M. Use 638nm laser excitation with a power of 50mW, a collection time of 5s, and a total of 3 times to monitor the surface enhanced Raman scattering signal at different spot positions, such as Figure 5 As shown, the SERS spectra of thiram are at 437, 562, 932, 1144, 1378 and 1519 cm -1 There is a characteristic peak at 1378cm -1 The high-intensity peak at 1382 cm corresponds to CN stretching and CH3 symmetric deformation and was selected as the experimental peak for designing the Fumei dual sensing strategy. -1 The SERS intensity increased linearly with the increase of thiram content; the intensity of different concentrations of thiram at 1378 cm -1 The intensity corresponding to the Raman shift at the position (SERS Intensity) is used as the ordinate, and the logarithm of the concentration of thiram (lg (C Thiram / mol / L)) as the horizontal axis, draw a standard curve as shown in Figure 6 The calculated detection limit is 7.09×10-8mol·L -1 The method has a wide linear range and the detection sensitivity complies with the national standard (GB 2763-2021) method (GB 2763-2021, National Food Safety Standard-Maximum Residue Limits of Pesticides in Food). Figure 4 (a) and (b) show that at 1361 cm -1 The recorded SERS signal remained stable, and the relative standard deviation (RSD) obtained was 14.63%, which showed that the prepared gold-silver core-shell nanoflower substrate was reliable and sensitive in quantitative analysis experiments.

[0040] (5) Determination of Thiram concentration in samples: Thiram with known concentrations of 0.12, 0.24, 0.60 and 2.40 ppm was added to the samples. The gold and silver core-shell nanoflowers were immersed in the samples to be tested without any pretreatment. The spectra were collected using a Raman spectroscopic microscope, and the concentration of Thiram in the samples to be tested was obtained based on the established standard curve. As shown in Table 1, it is shown that there is a very high consistency between the spiked concentration and the measured content. The recoveries of milk and juice samples are in the range of 91.76±6.825 and 109.40±28.370, respectively. The good recovery and relative standard deviation values ​​in the table also indicate that there is no potential matrix interference, so it has the reliability to analyze complex food matrices.

[0041] Table 1. Analysis of Thiram in untreated milk and juice samples using this method* (n=5)

[0042]

[0043] *Average ± standard deviation of five measurements

[0044] Example 2

[0045] (1): Same as (1)-(2) in Example 1;

[0046] (2) Preparation of gold nanoflowers: On a pre-cleaned tin oxide glass slide, 24.3 mmol·L of gold nanoflowers were electrochemically deposited at a constant applied voltage of 0.3 V using the galvanometer method. -1 of tetrachloroauric acid solution, with a deposition time of 75 seconds, and successfully synthesized gold nanoflowers;

[0047] (3): Preparation of gold-silver core-shell nanoflowers: Using gold nanoflowers as working electrodes, the silver shell is controlled to deposit on the gold structure to form a bimetallic core-shell heterostructure. -1 The silver nitrate solution was neutralized and electrochemically deposited under a voltage of -0.6 V to form gold-silver core-shell nanoflowers, such as Figure 7 As shown, the gold and silver core-shell nanoflowers uniformly dispersed on the oxidized tin glass slide maintained the shape of the gold nanoflowers;

[0048] (4)-(5): Same as (3)-(5) in Example 1;

[0049] Note: The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention; therefore, although this specification has described the present invention in detail with reference to the above embodiments, a person skilled in the art should understand that the present invention can still be modified or replaced by equivalents; and all technical solutions and improvements thereof that do not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. An electrochemical synthesis method of gold and silver core-shell nanoflowers, characterized in that: include: (1) adding an indium tin oxide carrier substrate to a tetrachloroauric acid solution, and performing electrochemical deposition at a constant voltage of 0.3-0.7 V to deposit gold nanoflowers on the indium tin oxide carrier substrate, wherein the deposition time is 25-125 s; (2) Using the gold nanoflower obtained in step (1) as a working electrode, electrochemical deposition is performed in a silver nitrate solution at a constant voltage of -0.7 to -0.5 V to obtain gold-silver core-shell nanoflowers, wherein the deposition time is 25 to 125 seconds.

2. The electrochemical synthesis method of gold and silver core-shell nanoflowers according to claim 1, characterized in that: The concentration of the tetrachloroauric acid solution is 20-30 mmol·L -1 The deposition time of step (1) is 50-100 s, the constant voltage is 0.3-0.7 V, and the concentration of the silver nitrate solution is 8-12 mmol·L -1 The deposition time of step (2) is 50-100 s, and the constant voltage is -0.7 to -0.5 V.

3. The electrochemical synthesis method of gold and silver core-shell nanoflowers according to claim 1, characterized in that: Before adding the tetrachloroauric acid solution to the indium tin oxide carrier substrate, ultrasonic cleaning is performed in sequence using sodium hydroxide ethanol, acetone and distilled water.

4. The electrochemical synthesis method of gold and silver core-shell nanoflowers according to claim 3, characterized in that: The ultrasonic cleaning time is 10-60 minutes.

5. The electrochemical synthesis method of gold and silver core-shell nanoflowers according to claim 1, characterized in that: The indium tin oxide carrier substrate is a three-electrode system, wherein the working electrode is a gold nanoflower, the reference electrode is an Ag / AgCl electrode, and the counter electrode is a platinum wire.

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