Preparation method and application of flower-shaped Ag / ZnO hybrid

Abstract

The application discloses a preparation method of flower-shaped Ag / ZnO hybrid and application thereof, and the preparation method comprises the following steps: step one, using silver nitrate as a silver source, malonic acid as a guiding agent, and ascorbic acid as a reducing agent to prepare flower-shaped Ag particles; and step two, using the flower-shaped Ag particles as a main body to introduce ZnO on the surface of the flower-shaped Ag particles to prepare flower-shaped Ag / ZnO hybrid. In the application, the flower-shaped Ag particles are prepared by using malonic acid as the guiding agent, and the preparation method is simple and effective. The flower-shaped Ag / ZnO hybrid prepared in the application has high SERS activity and excellent sensitivity, electromagnetic enhancement and chemical enhancement are generated by the enhancement effect of Ag and ZnO, and thus a qualitative and semi-quantitative basis is provided for the detection of illegal additives in food.

Description

TECHNICAL FIELD

[0001] The application relates to the field of surface enhanced Raman scattering technology, and particularly relates to a preparation method of flower-shaped Ag / ZnO hybrid and application thereof. BACKGROUND

[0002] The existing food additive detection also needs large equipment and complex sample processing technology, cannot guarantee the detection sensitivity and uniformity, and has the problems of interference and low precision; therefore, the rapid development puts forward higher and higher requirements for food safety monitoring technology, and the market urgently needs a high-sensitivity, rapid and convenient food additive real-time detection method. Surface enhanced Raman spectroscopy (SERS) has the advantages of providing the "fingerprint" vibration information of the structure and conformation of the target molecule, thereby realizing the high sensitivity and specificity of effective identification of the target molecule, and has become one of the most widely used analysis technologies at present; the nano structure of gold, silver and the like used in the SERS technology can improve the sensitivity of the traditional Raman spectrum and realize the trace detection of chemical molecules. Due to its advantages, it is widely used in food safety, environmental analysis, biomedical research, public safety and the like. Meanwhile, the SERS technology can use a portable Raman spectrometer without large equipment, thereby providing a convenient condition for rapid on-site inspection in food detection; the SERS substrate is composed of a metal surface with nano roughness, and the preparation technology of the metal nano material is particularly important for the SERS substrate; a SERS substrate with high sensitivity, good uniformity and time stability has important value and significance for the practical application of the SERS technology; with the dependence on the research of the SERS spectroscopy, researchers have extended the preparation of the SERS active substrate to non-IB group materials, including metal oxides (semiconductors, peroxometal, silver halide and the like), and various gold and silver decorated metal oxide composite materials can also be used as the SERS active substrate due to the electromagnetic field enhancement effect of the noble metal nanoparticles and the charge transfer mechanism of the metal oxide.

[0003] Therefore, the preparation of the new composite nano material of the noble metal and the metal oxide semiconductor will provide a new method for the detection of the food additive. SUMMARY

[0004] The application provides a preparation method of flower-shaped Ag / ZnO hybrid and application thereof, and the flower-shaped Ag / ZnO hybrid is used as a SERS active substrate and has high SERS activity and excellent sensitivity.

[0005] Technical scheme: A preparation method of flower-shaped Ag / ZnO hybrid, characterized by comprising the following steps,

[0006] Step one, flower-shaped Ag particles are prepared by taking silver nitrate as a silver source, malonic acid as a directing agent and ascorbic acid as a reducing agent;

[0007] Step two, with flower-like Ag particles as the main body, introduce ZnO on its surface, to prepare flower-like Ag / ZnO hybrid.

[0008] Further, the flower-like Ag particle preparation method is as follows:

[0009] Step 1, the ultrapure water is placed in an ice water bath, silver nitrate solution is added to the ultrapure water;

[0010] Step 2, under the condition of stirring, malonic acid solution is added to the above reaction solution, and stirring is uniform;

[0011] Step 3, ascorbic acid solution is quickly added to the above reaction solution, stirring is carried out until the reaction is completed, and the reaction product is obtained after centrifugation;

[0012] Step 4, the reaction product obtained in step three is washed with water and anhydrous ethanol several times, and then vacuum dried to obtain flower-like Ag particles.

[0013] Further, in the flower-like Ag particle preparation method, the molar ratio of silver nitrate, malonic acid and ascorbic acid is (80-120): (0.8-1.2): (80-120).

[0014] Further, in the flower-like Ag particle preparation method, the molar ratio of silver nitrate, malonic acid and ascorbic acid is 100:1:100.

[0015] Further, with flower-like Ag particles as the main body, introduce ZnO on its surface, to prepare flower-like Ag / ZnO hybrid, the specific method is as follows:

[0016] S1, zinc acetate and triethylamine are added to ethanol to obtain solution A;

[0017] S2, flower-like Ag particles are added to ethanol and ultrasonically treated to obtain solution B;

[0018] S3, solution B obtained in S2 is added to solution A and mixed uniformly to obtain solution C;

[0019] S4, the pH of solution C is adjusted to 10-11 with ammonia water, and ultrasonic treatment is continued for 2h, and the reaction product is obtained after centrifugation;

[0020] S5, the reaction product obtained in step S4 is centrifuged with water and anhydrous ethanol, and repeatedly washed until the centrifugal supernatant is neutral, and vacuum drying is carried out to obtain flower-like Ag / ZnO hybrid.

[0021] Further, in the method for preparing flower-like Ag / ZnO hybrid, the mass ratio of zinc acetate, triethylamine and flower-like Ag particles is (2-4):(4-8):(0.8-1.2).

[0022] Further, in the method for preparing the flower-shaped Ag / ZnO hybrid, the mass ratio of zinc acetate, triethylamine and flower-shaped Ag particles is 3:6:1.

[0023] The flower-shaped Ag / ZnO hybrid prepared by the method is used as a SERS substrate for detecting R6G and melamine in food.

[0024] Advantages:

[0025] 1) In the present application, the flower-shaped Ag particles are prepared by using malonic acid as a directing agent, and the preparation method is simple and effective.

[0026] 2) The flower-shaped Ag / ZnO hybrid prepared by the method has high SERS activity and excellent sensitivity, and the enhancement effect of Ag and ZnO produces electromagnetic enhancement and chemical enhancement, thereby providing a qualitative and semi-quantitative basis for the detection of illegal additives in food. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The preparation method flow chart of the flower-shaped Ag particles in the present application is shown in the figure;

[0028] Figure 2 The preparation method flow chart of the flower-shaped Ag / ZnO hybrid in the present application is shown in the figure;

[0029] Figure 3 The scanning electron microscope and transmission electron microscope pictures of the flower-shaped Ag particles and the flower-shaped Ag / ZnO hybrid prepared by the method are shown in the figures;

[0030] Among them, Figure 3 (a) is the scanning electron microscope picture of the flower-shaped Ag particles, Figure 3 (b) is the transmission electron microscope picture of the flower-shaped Ag particles; Figure 3 (c) is the scanning electron microscope picture of the flower-shaped Ag / ZnO hybrid, Figure 3 (d) is the transmission electron microscope picture of the flower-shaped Ag / ZnO hybrid;

[0031] Figure 4 The EDS spectrum and EDS mapping image of the flower-shaped Ag particles and the flower-shaped Ag / ZnO hybrid prepared by the method are shown in the figures;

[0032] Among them, Figure 4 (a) is the EDS spectrum of the flower-shaped Ag particles, Figure 4 (c) is the EDS mapping image of the flower-shaped Ag particles; Figure 4 (b) is the EDS spectrum of the flower-shaped Ag / ZnO hybrid, Figure 4 (d) is the EDS mapping image of the flower-shaped Ag / ZnO hybrid;

[0033] Figure 5 XRD patterns of the flower-like Ag particles and flower-like Ag / ZnO hybrids prepared in the present application.

[0034] Figure 6 SERS spectra of R6G and encoding using the flower-like Ag particles and flower-like Ag / ZnO hybrids prepared in the present application as substrates;

[0035] Figure 7 Concentration-dependent SERS spectra of R6G on the flower-like Ag particles and flower-like Ag / ZnO hybrids, and linear relationship between Raman intensity and R6G concentration / flower-like Ag particles and flower-like Ag / ZnO hybrids;

[0036] wherein, Figure 7 (a) SERS spectra of R6G at different concentrations using the flower-like Ag particles as substrates; Figure 7 (b) SERS spectra of R6G at different concentrations using the flower-like Ag / ZnO (b) hybrids as substrates; Figure 7 (c) Linear relationship between Raman intensity and R6G concentration / flower-like Ag particles; Figure 7 (d) Linear relationship between Raman intensity and R6G concentration / Ag / ZnO hybrids;

[0037] Figure 8 Signal intensity stability of the flower-like Ag / ZnO substrate for R6G (50.0 ng mL -1 ) and characteristic peak intensity stability at 1359 cm -1 ;

[0038] wherein, Fig. 8(a) is signal intensity stability of the flower-like Ag / ZnO substrate for R6G (50.0 ng mL -1 ), and Fig. 8(b) is characteristic peak intensity stability at 1359 cm -1 ;

[0039] Figure 9 Raman spectrum of melamine and SERS spectrum of melamine;

[0040] wherein, Figure 9 (a) Raman spectrum of melamine, Figure 9 (b) SERS spectrum of melamine;

[0041] Figure 10 Concentration-dependent SERS spectra of melamine on the flower-like Ag particles and flower-like Ag / ZnO hybrids, and linear relationship between melamine concentration and flower-like Ag particles and flower-like Ag / ZnO hybrids;

[0042] wherein, Figure 10 (a) SERS spectra of different concentrations of melamine with flower-like Ag particles as substrate; Figure 10 (b) SERS spectra of different concentrations of melamine with flower-like Ag / ZnO hybrid as substrate; Figure 10 (c) Linear relationship between concentration of melamine and flower-like Ag particles; Figure 10 (d) Linear relationship between concentration of melamine and flower-like Ag / ZnO hybrid. DETAILED DESCRIPTION

[0043] The technical solutions of the present application will be described in detail below with reference to the accompanying drawings, but the protection scope of the present application is not limited to the examples.

[0044] In the examples of the present application, melamine and malonic acid are purchased from Tianjin Guangfu Fine Chemical Research Institute (Tianjin, China); ammonium hydroxide is purchased from Shanghai Maikelin Biochemical Technology Co., Ltd. (Shanghai, China); triethylamine and ethanol are purchased from Tianjin Fuyu Fine Chemical Co., Ltd. (Tianjin, China); zinc acetate and rhodamine 6G are purchased from Aladdin Reagent (Shanghai) Co., Ltd. (Shanghai, China). Silver nitrate is purchased from Tianjin Chemical Reagent Factory No. 1 (Tianjin, China). Ascorbic acid is sourced from Tianjin Damao Chemical Reagent Factory (Tianjin, China), and the reagents described in the experiment are used directly without further treatment. High-purity water (ultrapure water) is obtained from a Milli-Q water system.

[0045] In the examples, energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM) and scanning electron microscopy (SEM) are used to analyze the morphology and size of the prepared samples (SEM, Hitachi S-8010, Kyoto; TEM, Tecnai G20, Philips), and X-ray diffraction analysis is used to analyze the prepared samples (XRD, PANalytical B.V. X'Pert3 Powder). In the examples, the solvents of silver nitrate solution, malonic acid solution, ascorbic acid solution, and ethanol are ultrapure water.

[0046] The present application provides a preparation method of a flower-like Ag / ZnO hybrid, as shown in Figure 1 which comprises the following steps:

[0047] Step 1: flower-like Ag particles are prepared using silver nitrate as a silver source, malonic acid as a directing agent, and ascorbic acid as a reducing agent;

[0048] Step 2: flower-like Ag / ZnO hybrid is prepared by introducing ZnO on the surface of the flower-like Ag particles.

[0049] Example 1:

[0050] Flower-like Ag particles were prepared using silver nitrate as silver source, malonic acid as directing agent and ascorbic acid as reducing agent. The specific steps are as follows:

[0051] Step 1, 10.0 ml ultrapure water was placed in an ice water bath, 1.0 ml silver nitrate solution (concentration of 1.0 mol L -1 ) was added to the ultrapure water;

[0052] Step 2, under stirring, malonic acid solution (0.1 ml, 0.1 mol L -1 ) was added to the above reaction solution, and then stirring was continued for 10 min;

[0053] Step 3, ascorbic acid solution (1.0 ml, 1.0 mol L -1 ) was quickly added to the above reaction solution as a reducing agent, the solution immediately turned into silver gray, then stirring was continued for 15 min, the reaction was ended, and the reaction product was obtained after centrifugation;

[0054] Step 4, the reaction product obtained in step 3 was first washed with ultrapure water by centrifugation for three times, then washed with anhydrous ethanol by centrifugation for three times, the centrifugation condition was 8000 rpm, 10 min; then vacuum drying was carried out to obtain flower-like Ag particles.

[0055] The preparation method of flower-like silver in the application is low in cost and environmentally friendly. Malonic acid is used as a directing agent and ascorbic acid is used as a reducing agent to synthesize flower-like silver. Silver nitrate is used as a silver source, then malonic acid is added to the clear and transparent silver nitrate solution in an ice water bath, and the mixed solution is still clear and transparent. However, after ascorbic acid is added to the solution, the color of the mixed solution immediately becomes deep (turns into silver gray), and a large amount of product is formed. The silver particles produced in the solution are very sensitive to the presence of acid. Malonic acid is a carbon atom between two carboxyl groups. The results show that the number of carbon atoms between the carboxyl groups of the directing agent has an effect on Ag, and malonic acid hinders its effect. After ascorbic acid is added, a certain amount of flaky Ag structure is formed in the mixed solution. With the increase of reaction time, the flaky Ag structure forms flower-like silver particles through self-assembly.

[0056] Example 2:

[0057] Flower-like Ag / ZnO hybrid was prepared by introducing ZnO on the surface of flower-like Ag particles; the specific steps are as follows:

[0058] S1, zinc acetate (0.6 g) and triethylamine (1.6 ml) were added to ethanol (28.0 ml) to obtain solution A;

[0059] S2, flower-like Ag particles (0.2 g) were added to 20 ml ethanol, and ultrasonic treatment was carried out for 30 min to obtain solution B;

[0060] S3, the solution B obtained in S2 is added to 8 ml of solution A, mixed uniformly to obtain solution C;

[0061] In solution C, the mass ratio of zinc acetate, triethylamine, and flower-shaped Ag particles is 3:6:1.

[0062] S4, the pH of solution C is adjusted to 10-11 with ammonia water, and the reaction mixture is obtained after 2h of continuous ultrasonic treatment, and the reaction product is obtained by suction filtration;

[0063] S5, the reaction product obtained in step S4 is centrifuged with ultrapure water and anhydrous ethanol, and repeatedly washed until the supernatant is neutral after centrifugation, and the flower-shaped Ag / ZnO hybrid is obtained by vacuum oven drying.

[0064] The prepared sample is subjected to SERS detection, and the detection method is:

[0065] 1. 10.0 mg of the prepared sample (the prepared sample refers to flower-shaped Ag particles or flower-shaped Ag / ZnO hybrid) is mixed with 1.0 ml of target molecules (the target molecules refer to rhodamine 6G or melamine) and added to a centrifuge tube; the mixture of the sample and the target molecules is dropped onto a glass sheet for SERS detection.

[0066] 2. SERS analysis is performed by Renishaw inVia microconfocal Raman spectroscopy: 532 nm laser is selected as the light source; the exposure time is 10 s; the selected wavelength range is 400 cm -1 to 1800 cm -1 ; the incident laser power remains unchanged, and a 20x objective is used to collect data; each spectrum is averaged by scanning 5 times to obtain the average value,

[0067] I. The properties of the prepared sample are characterized by SEM, TEM, XRD and EDS to analyze the sample amount, structure and element analysis, and the results are as follows:

[0068] (1) The morphology and size of the flower-shaped Ag particles and the flower-shaped Ag / ZnO hybrid are analyzed by scanning electron microscopy SEM and transmission electron microscopy TEM. The results are shown in Figure 3 as shown in Figure 3 (a), the initial structure of the flower-shaped Ag particles is uniform, and the surface is composed of irregular sheet structures. Although the scanning electron microscope image of the flower-shaped Ag / ZnO hybrid is slightly different from that of the flower-shaped Ag particles, the morphology of the flower-shaped Ag / ZnO hybrid is still clear. According to Figure 3 (b) and 3(d), although there is no difference between the flower-shaped Ag particles and the flower-shaped Ag / ZnO hybrid, there is a slight difference in the sheet structure.

[0069] (2) In order to further study the composition of the flower-like Ag particles and the flower-like Ag / ZnO hybrid, the chemical composition of the prepared samples (flower-like Ag particles and flower-like Ag / ZnO hybrid) was analyzed by EDS spectroscopy. Figure 4 EDS spectra and EDS mapping images of the flower-like Ag particles and the flower-like Ag / ZnO hybrid. As shown in Figure 4 (a), the EDS spectrum of the flower-like Ag particles shows that it contains Ag and C elements. Compared with the EDS spectrum of the flower-like Ag particles, the EDS spectrum of the flower-like Ag / ZnO hybrid shows that it contains Ag, C, O and Zn elements, wherein the O and Zn elements are derived from zinc oxide, and due to the low content of zinc oxide, the contents of Zn and O elements are low, which is similar to the results of EDS mapping (4(c) and 4(d)). Figure 4

[0070] (3) The information of the flower-like Ag particles and the flower-like Ag / ZnO hybrid was obtained by XRD characterization. As shown in Figure 5 , the XRD curve clearly shows the high crystalline structure of the flower-like Ag particles. The five characteristic diffraction peaks of 38.27°, 44.43°, 64.67°, 77.52° and 81.66° appearing on the XRD curve of the flower-like Ag particles belong to the face-centered cubic (fcc) (111), (200), (220), (311) and (222) crystal planes, which are consistent with the data of JCPDS (No. 04-0783). The results show that the prepared flower-like Ag particles have no diffraction peaks of silver oxide, and are not oxidized. The reflection peak of flower-like silver at 38.27° is related to the Miller index (111) of bulk silver. The super-high intensity at 38.27° indicates that the (111) plane is more abundant, and the flower-like Ag particles tend to grow along the (111) direction. At the same time, the results obtained from the intensity ratio of (111) / (200) (4.05) are all higher than the standard file value 2.1, and the prepared sample is pure crystalline silver, so there is no other impurity peak in the XRD curve of the flower-like Ag particles. Compared with the XRD spectrum of the flower-like Ag particles, the flower-like Ag / ZnO hybrid has the same five diffraction peaks, which indicates that the zinc oxide introduced on the surface of Ag does not form a crystalline phase, or the content of the zinc oxide introduced on the surface of Ag is too low.

[0071] II. SERS activity of the flower-like Ag / ZnO hybrid as a substrate

[0072] ​In the experiment, R6G (Rhodamine 6G) was used as an analyte to study the SERS enhancement performance of the flower-like Ag / ZnO hybrid. On the one hand, R6G is a common probe molecule with a distinct spectrum. On the other hand, R6G is also an illegal additive in food. Raman experiments were carried out at a laser wavelength of 532 nm, with flower-like Ag particles and flower-like Ag / ZnO hybrids as substrates, and 5 μg mL -1 of R6G solution, and the SERS spectrum is shown in Figure 6 .

[0073] Compared with the SERS spectrum with flower-like Ag as the substrate, the SERS spectrum obtained by flower-like Ag / ZnO has better characteristic peaks. This indicates that the SERS spectrum of R6G with flower-like Ag / ZnO as the substrate has higher mass resolution. The vibration peak of R6G molecule at 610 cm -1 is related to the in-plane bending vibration of C-C-C ring and the out-of-plane bending of C-H bond. The vibration peak near 771 -1 cm originates from the C-H bond outside the plane bending vibration. The vibration peak at 1182 cm -1 is caused by the bending vibration of the in-plane C-H bond. In addition, the stretching vibration peak of the C-N bond belongs to 1308 cm -1 and 1573 cm -1 . An apparent characteristic peak near 1359 cm -1 is related to the deformation of symmetric methyl and xanthene ring C-H bending mode. The vibration peak of C-C bond in the plane symmetric stretching vibration is attached to 1507 cm -1 . The characteristic peak at 1647 cm -1 comes from the C=C bond stretching vibration. Then, the obtained R6G SERS spectrum is encoded. And the SERS spectrum peak is converted into a bar code. Like the characteristic peaks of SERS, each substance corresponds to its unique bar code. The bar code information is more intuitive than the SERS spectrum information, and has better development potential in food safety detection.

[0074] The semi-quantitative analysis of R6G was carried out with flower-like Ag and Ag / ZnO as the SERS substrate, as shown in Figure 7 (a), the SERS spectrum of R6G with flower-like Ag as the substrate was obtained at a concentration of 5.0 ng mL -1 ~ 50.0 μg mL -1 . With the decrease of R6G concentration, the intensity of the characteristic peak of SERS gradually weakens. At a R6G concentration of 5.0 ng mL, no significant SERS characteristic peak is obtained. Compared with flower-like Ag, the SERS characteristic peak of R6G can be detected by flower-like Ag / ZnO, and gradually weakens with the decrease of R6G concentration Figure 7(b)). When the concentration was 5.0 ng mL -1 , the characteristic peak of R6G still appeared. The concentration of R6G was continuously decreased, and when the concentration of R6G was reduced to 0.5 ng mL -1 , the intensity of the vibration peak was further weakened, and the information recognition was not accurate. Therefore, the minimum concentration of R6G detected by the flower-like Ag / ZnO was 0.5 ng mL -1 . Figure 7 (c) and 7(d) show the changes of the SERS intensity of the Raman peaks at 610 cm and 1507 cm with the R6G concentration of the flower-like Ag and Ag / ZnO, respectively. The concentration is related to the Raman signal, and the linear relationship obtained by using the flower-like Ag as the SERS substrate is not satisfactory. Compared with the flower-like Ag, the linear correlation of the flower-like Ag / ZnO as the substrate is better. It belongs to the enhancement effect of Ag and ZnO.

[0075] The signal intensity stability is an important parameter for characterizing the performance of the SERS substrate, and it is inseparable from the practicability of the SERS substrate. The signal intensity stability of the flower-like Ag / ZnO substrate for R6G (50.0 ng mL -1 ) was studied, and the results are shown in Figure 8 (a). At the same time, 9 random points were randomly selected to collect data. The SERS spectra obtained at the 9 points had no significant difference in shape and characteristic peak position. At the Raman shift of 1359 cm -1 , the relative standard deviation of the peak intensity was less than 12.0%, which indicated that the SERS substrate had good signal uniformity.

[0076] Three, SERS detection of melamine

[0077] The illegal addition of excessive melamine in food has potential risks to human health. Therefore, it is necessary to detect melamine in food. The Raman method was used to record the solid powder of melamine, and the results are shown in Figure 9 (a). In the Raman spectrum of melamine, two obvious characteristic peaks appeared, at 671 cm -1 and 983 cm -1 . Compared with the melamine powder, due to the interaction of melamine on the surface of the Ag / ZnO substrate, the vibration peak of melamine in the SERS spectrum shifted from 671 cm -1 to 698 cm -1 . Another typical neutral melamine peak attached to the SERS spectrum at 983 cm -1The above is called C-N-C bending vibration. The SERS spectra of melamine detected by flower-like Ag and flower-like Ag / ZnO as substrates were compared at the same concentration. The results show that the SERS signal intensity obtained by flower-like Ag / ZnO is higher at the same consistency. The SERS characteristic peaks of melamine are coded based on flower-like Ag / ZnO. After coding melamine, it is helpful for the detection, identification and comparison of excessive melamine in food. As shown in Figure 10 , the SERS signals of melamine at different concentrations (10 ng mL -1 - 50.0 μg mL -1 ) were recorded by flower-like Ag and Ag / ZnO. Compared with the results of flower-like Ag as substrate, the lowest concentration of melamine that can be detected by flower-like Ag / ZnO is 10 ng mL. The above sensitivity detection results show that the SERS signal decreases significantly as the concentration of melamine decreases. The peak value 698 cm -1 is selected to study the relationship between SERS intensity and melamine concentration. The reasonable linear response of flower-like Ag and flower-like Ag / ZnO is shown in Figure 10 (c) and 10 (d), respectively. The correlation coefficient of flower-like Ag is 0.90, and the correlation coefficient of flower-like Ag / ZnO is 0.95. The results show that the characteristic peak intensity of melamine is linearly related to the concentration, and the correlation coefficient is high. In other words, the flower-like Ag / ZnO substrate can be used for qualitative and semi-quantitative analysis of melamine in food medium.

[0078] Four, SERS mechanism of flower-like Ag / ZnO

[0079] The signal enhancement mechanism of flower-like Ag / ZnO includes electromagnetic enhancement and chemical enhancement. Electromagnetic enhancement is caused by the enhanced electric field generated by the surface plasmon of silver particles and the gap plasmon excited by the gap between adjacent particles, and chemical enhancement comes from the charge transfer process between ZnO, Ag and the target under laser excitation. In addition, the charge transfer process is enhanced by effectively injecting plasma-induced heat into the semiconductor. When Ag is in contact with zinc oxide, the charge distribution is reorganized to adjust the Fermi level, and a depletion layer is formed at the junction. When the energy level of the system matches the highest occupied and lowest unoccupied molecular orbital energy level of the target molecule, charge transfer occurs, resulting in chemical enhancement. Therefore, the excellent SERS performance is a combination of electromagnetic enhancement and chemical enhancement.

[0080] In summary, a flower-like Ag / ZnO substrate can quickly, universally and cheaply detect R6G and melamine. Compared with the Raman characteristic peaks of melamine powder, significant SERS characteristic peaks of melamine powder are obtained on flower-like Ag / ZnO. Coding avoids the interference of impurity peaks and reduces background noise. In the detection of melamine at 1.0 ng mL-1 ~50.0ug mL -1 The linear correlation coefficient obtained at 698cm -1 The linear correlation coefficient obtained at 698cm The excellent SERS enhancement of flower-like Ag / ZnO depends on the electromagnetic enhancement of Ag and the chemical enhancement of ZnO. It is demonstrated that flower-like Ag / ZnO can be used as a substrate for the detection of illegal adulterant melamine in food, and good results are achieved, which provides a new idea for the on-site detection of samples in complex matrix and the practical application of SERS in food safety, environmental monitoring, public health and other fields.

[0081] As mentioned above, although the application has been indicated and described with reference to specific preferred embodiments, it is by no means to be construed as a limitation of the application itself. Various changes in form and details can be made thereto without departing from the spirit and scope of the application as defined in the appended claims.

Claims

1. A method for preparing flower-like Ag / ZnO hybrid, characterized in that, The method comprises the following steps: Step 1, flower-shaped Ag particles are prepared by using silver nitrate as a silver source, malonic acid as a guiding agent and ascorbic acid as a reducing agent; Step 2, flower-shaped Ag / ZnO hybrid is prepared by introducing ZnO on the surface of the flower-shaped Ag particles; the specific method is as follows: S1, zinc acetate and triethylamine are added into ethanol to obtain solution A; S2, flower-shaped Ag particles are added into ethanol and ultrasonic treatment is performed to obtain solution B; S3, solution B obtained in S2 is added into solution A and mixed uniformly to obtain solution C; S4, the pH of solution C is adjusted to 10-11 by using ammonia water, and ultrasonic treatment is continuously performed for 2 hours; the reaction product is obtained after centrifugation; S5, the reaction product obtained in S4 is centrifuged with water and anhydrous ethanol, repeatedly washed until the supernatant is neutral, and dried in a vacuum oven to obtain flower-shaped Ag / ZnO hybrid.

2. The method for preparing a flower-like Ag / ZnO hybrid according to claim 1, characterized in that, The preparation method of the flower-shaped Ag particles is as follows: Step 1, ultrapure water is placed in an ice water bath, and silver nitrate solution is added into the ultrapure water; Step 2, malonic acid solution is added into the above reaction solution under stirring and stirring is uniformly performed; Step 3, ascorbic acid solution is quickly added into the above reaction solution, stirring is performed until the reaction is completed, and the reaction product is obtained after centrifugation; Step 4, the reaction product obtained in step 3 is centrifuged and washed with water and anhydrous ethanol several times, and then vacuum dried to obtain flower-shaped Ag particles.

3. The method for preparing a flower-like Ag / ZnO hybrid according to claim 2, characterized in that, In the preparation method of the flower-shaped Ag particles, the molar ratio of silver nitrate, malonic acid and ascorbic acid is (80-120):(0.8-1.2):(80-120).

4. The method for preparing a flower-like Ag / ZnO hybrid according to claim 3, characterized in that, In the preparation method of the flower-shaped Ag particles, the molar ratio of silver nitrate, malonic acid and ascorbic acid is 100:1:

100.

5. The method for preparing a flower-like Ag / ZnO hybrid according to claim 4, characterized in that, In the method for preparing the flower-shaped Ag / ZnO hybrid, the mass ratio of zinc acetate, triethylamine and flower-shaped Ag particles is (2-4):(4-8):(0.8-1.2).

6. The method for preparing a flower-like Ag / ZnO hybrid according to claim 5, characterized in that, In the method for preparing the flower-shaped Ag / ZnO hybrid, the mass ratio of zinc acetate, triethylamine and flower-shaped Ag particles is 3:6:

1.

7. The flower-shaped Ag / ZnO hybrid prepared by the preparation method according to any one of claims 1-6 is used as a SERS substrate.

8. The flower-shaped Ag / ZnO hybrid prepared by the preparation method according to any one of claims 1-6 is used as a SERS substrate for detecting R6G and melamine in food.

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