Dynamic controllable hydrogel SERS (Surface Enhanced Raman Scattering) substrate based on specific effect of salt ions as well as preparation method and application of dynamic controllable hydrogel SERS substrate

Abstract

The invention provides a dynamic controllable hydrogel SERS (Surface Enhanced Raman Scattering) substrate based on a salt ion specific effect as well as a preparation method and application thereof.The method comprises the following steps: firstly, preparing hydrogel formed by wrapping triangular silver nanoparticles with PVA (Polyvinyl Alcohol), and then sequentially carrying out etching and salting-out treatment on the hydrogel, so as to obtain the dynamic controllable hydrogel SERS substrate based on the salt ion specific effect. The Raman signal intensity of the SERS substrate can be enhanced by means of the synergistic effect between the two, so that the sensitivity of the SERS substrate in spectrum detection is improved, and the hydrogel SERS substrate which can be applied to glucose and methamphetamine detection is finally prepared. The SERS substrate prepared by the preparation method provided by the invention not only retains all advantages of the existing hydrogel SERS substrate, but also realizes dual dynamic regulation and control of the morphology and the distance of the plasma nanostructure in the SERS substrate.

Description

Technical Field

[0001] The invention relates to the technical field of surface enhanced Raman substrate preparation, and in particular to a dynamically controllable hydrogel SERS substrate based on salt ion specific effect, and a preparation method and application thereof. Background Art

[0002] Surface enhanced Raman scattering (SERS) has the advantages of high sensitivity, mild detection conditions and strong chemical fingerprint resolution. It has become a very important detection technology in analytical science and is widely used in many fields such as food safety, bioanalysis, medical diagnosis, environmental testing and forensic science. One of the key elements in the application of SERS technology is the construction of SERS active substrates. Traditional rigid SERS substrates have the main disadvantages of being fragile, difficult to bend and inconvenient to carry, which limits their practical application. The design and development of flexible SERS substrates is a hot spot in the current practical application of SERS research. Flexible SERS substrates usually integrate plasma nanostructures with flexible substrates. Their SERS enhancement performance is mainly provided by precious metal nanostructures. The composition, morphology and size of the nanostructures are the key elements of SERS performance. Among them, hydrogels are a type of cross-linked polymer gel with a three-dimensional network structure. They have the characteristics of high chemical stability, biocompatibility, high water content and adjustable pore size. As a water-based soft material, they are also widely used in the development of SERS substrates.

[0003] At present, there are two main ways to prepare SERS hydrogel substrates: 1) dispersing metal nanoparticles in a hydrogel precursor solution and then gelling; 2) in situ growth of metal nanoparticles in a hydrogel material. By regulating the hydrogel network structure and optimizing the pores, the aggregation state or spacing of nanoparticles can be regulated, thereby macro-regulating the LSPR optical properties of the composite hydrogel and affecting its SERS enhancement performance. The hydrogel SERS substrate has the following advantages: 1) The three-dimensional porous structure of the hydrogel provides a protective barrier to prevent silver nanoparticles from aggregating or inactivating in a complex environment. 2) The porous structure of the hydrogel allows nanoparticles to effectively exchange with the substances to be detected in the environment. 3) The hydrogel is composed of a three-dimensional network structure with polymer network micropores, which can isolate the interference of biomacromolecules larger than the micropores and effectively shorten or eliminate the sample pretreatment procedure. It can be seen that the combination of hydrogel and metal nanoparticles can circumvent many key issues that promote the practical application of SERS, such as poor reproducibility and reliability, complex and time-consuming sample pretreatment, difficult operation, high cost, and low long-term storage stability.

[0004] Some hydrogel SERS sensing applications have also been disclosed in the prior art. For example, CN 202311793429 discloses a flexible sensing patch based on agarose to achieve in situ accurate identification and SERS detection of skin wound bacteria. CN202211565178.1, CN202211192639.5, CN202310503683.1 and CN202310502538.1 disclose a number of hydrogel SERS substrates and their applications, including uniform dispersion of nanoprobes in hydrogels to improve the poor repeatability of SERS detection and avoid complex loops. The interference of other impurities in the environment on SERS detection, including the cross-linking method of sodium alginate hydrogel does not require the use of "oil phase", avoiding the interference of organic reagents on the SERS detection target; including the loading of silver nanoparticles (AgNPs) modified with glucose oxidase (GOX) as SERS nanoprobes in droplet hydrogel microspheres to obtain SERS sensors, and the principle that gluconic acid (the reaction product of glucose and GOX) etches AgNPs to reduce its Raman enhancement effect, thus realizing the rapid indirect detection of glucose. Although hydrogel SERS substrates have unique potential in practical applications due to their advantages, there are still some shortcomings such as insufficient sensitivity or limited effect of regulating SERS enhancement strategies, that is, the reported regulation methods such as external cations entering the hydrogel to cause nanoparticle aggregation or external temperature causing hydrogel shrinkage are difficult to achieve continuous dynamic changes in SERS signals. Such macro-regulation is difficult to achieve repeated preparation of hydrogels and leads to poor reproducibility of hydrogel SERS results between batches, and cannot effectively capture the most effective SERS enhancement, thus restricting the development of hydrogel SERS substrates. In view of the dynamic regulation of nanoparticles inside hydrogels, patent CN202311186330.X discloses a microfluidic chip loaded with a dynamically controllable hydrogel SERS substrate and its preparation method. This patent is aimed at the quantitative detection of trace cancer markers, and provides a hydrogel-based dynamically controllable suspended substrate, which uses nucleic acid self-assembly technology to make it have target affinity, providing an effective solution for detecting trace targets in complex environments. Among them, the reported hot spot controllability is still achieved by changing the external temperature of the hydrogel to adjust the distance between nanoparticles. In summary, there is no continuous dynamic regulation and universal method for the signal enhancement strategy of the hydrogel SERS substrate.

[0005] In view of this, it is necessary to design an improved dynamically controllable hydrogel SERS substrate based on the salt ion specific effect, its preparation method and application to solve the above problems. Summary of the invention

[0006] The purpose of the present invention is to provide a dynamically controllable hydrogel SERS substrate based on the salt ion specific effect, and a preparation method and application thereof.

[0007] To achieve the above-mentioned object of the invention, the present invention provides a method for preparing a dynamically controllable hydrogel SERS substrate based on the salt ion specific effect, comprising the following steps:

[0008] S1. Add sodium citrate solution to silver nitrate solution, mix well, add sodium borohydride solution prepared in ice water dropwise to the mixed solution, stir well; irradiate with sodium lamp to carry out photoinduced reaction, and obtain blue triangular plate-shaped silver sol after irradiation for 14-16 hours;

[0009] S2. Concentrate the triangular plate-shaped silver sol obtained in step S1, mix it evenly with the PVA sol and pour it into a mold. After freezing it at a temperature below -20°C for 9-12 hours, take it out and thaw it at room temperature for 2-4 hours. Repeat the freezing-thawing steps several times to obtain a SERS hydrogel. Finally, immerse the SERS hydrogel in an etching solution and a salting-out solution in turn for etching and salting-out treatment to obtain a hydrogel SERS substrate.

[0010] Preferably, in step S2, the etching solution can form a slightly soluble compound with silver ions, the anion of which is Cl - ,I - Br - At least one of .

[0011] Preferably, the etching solution is Cl - The solution has a concentration of 1×10 -3 mol / L to 1mol / L, soaking time is 0-60min.

[0012] Preferably, in step S2, the salting-out solution is at least one of sulfate, carbonate, potassium ion and sodium ion.

[0013] Preferably, the salting-out solution is Na 2 SO 4 The solution has a concentration of 3 mol / L and a soaking time of 0-60 min.

[0014] Preferably, in step S1, the concentration of the silver nitrate solution is 1×10 -4 mol / L, the concentration of the sodium citrate solution is 0.1 mol / L, and the concentration of the sodium borohydride solution prepared with ice water is 8×10 -3 mol / L.

[0015] Preferably, in step S1, after adding ice water to prepare a fresh sodium borohydride solution, the molar ratio of silver nitrate, sodium citrate and sodium borohydride is 1:10:0.8.

[0016] Preferably, in step S1, the mixing process of the silver nitrate solution and the sodium citrate solution is carried out under magnetic stirring conditions, with a rotation speed of 600 rpm and a stirring time of 10-15 min.

[0017] In particular, the hydrogel SERS substrate prepared by the preparation method proposed in the present invention can be applied to the detection of glucose and methamphetamine.

[0018] The beneficial effects of the present invention are:

[0019] 1. The preparation method of the dynamic controllable hydrogel SERS substrate based on the salt ion specific effect provided by the present invention, the method first prepares a composite hydrogel wrapped with triangular plate-shaped silver nanoparticles formed by PVA as a matrix, and then sequentially etches and salts out the hydrogel (Hofmeister effect), so that the Raman signal intensity of the SERS substrate can be enhanced by the synergistic effect between the two, thereby improving the sensitivity of the SERS substrate in spectral detection, and finally preparing a hydrogel SERS substrate that can be applied to glucose and methamphetamine detection. The SERS substrate prepared by the preparation method proposed by the present invention not only retains all the advantages of the existing hydrogel SERS substrate, but also realizes the dual dynamic regulation of the morphology and distance of the plasma nanostructure in the SERS substrate, and the preparation method is simple to operate, easy to implement, and has good experimental reproducibility.

[0020] 2. The preparation method of the dynamically controllable hydrogel SERS substrate based on the salt ion specific effect provided by the present invention, by using triangular plate-shaped silver nanoparticles as plasma nanostructures in SERS hydrogel, can utilize its unique sharp corners and edge effects to achieve SERS enhancement of composite hydrogel materials. In addition, since the morphology of triangular plate-shaped silver nanoparticles can change under the etching action of specific ions, nanoparticles with specific localized plasma characteristics can be obtained by selecting specific etching conditions (solution type, concentration, etching time), and then further affecting the ion-polymer chain-water interaction in the hydrogel under the action of salting out, so that the network structure of the hydrogel shrinks. This effect can realize dynamic regulation of the network structure by selecting specific anions and cations (solution type, concentration, immersion time), and can also obtain stronger mechanical properties. The shrinkage of the hydrogel volume during the salting out process will cause the distance between the silver nanoparticles in the hydrogel to change, so that the "hot spot" domain of the SERS substrate increases. Under the combined action of the above two factors, the Raman signal of the hydrogel SERS substrate is effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a characterization diagram of the triangular plate-shaped silver nanoparticle sol prepared in Example 1 of the present invention;

[0022] Figure 2Optical photographs of the color changes of the SERS hydrogel substrate prepared in Example 1 of the present invention in different concentrations and different types of solutions;

[0023] Figure 3 The UV-visible absorption spectra of the SERS hydrogel prepared in Example 1 of the present invention after being immersed in KCl solutions of different concentrations for 5 minutes;

[0024] Figure 4 The SERS hydrogel prepared in Example 1 of the present invention was exposed to 3 mol / L Na 2 SO 4 SERS spectra measured with R6G as the probe molecule after immersion in the solution for different time periods;

[0025] Figure 5 The Raman detection results of the SERS hydrogel prepared in Example 1 of the present invention for different concentrations of R6G during the preparation process;

[0026] Figure 6 The indirect SERS detection of glucose using the SERS hydrogel substrate prepared in Example 1 of the present invention and the 1604 cm -1 The linear relationship between the characteristic peak intensity at and the logarithmic value of glucose concentration;

[0027] Figure 7 In order to utilize the direct SERS detection of methamphetamine in Example 2 of the present invention and the 995 cm -1 The linear relationship between the characteristic peak intensity at and the logarithmic value of methamphetamine concentration;

[0028] Figure 8 The comparison results of the enhancement effect of the SERS hydrogel substrate prepared in Comparative Example 1 of the present invention on the probe R6G are shown;

[0029] Fig. 9 The Raman detection results of R6G with different concentrations during the preparation process of the SERS hydrogel prepared in Comparative Example 2 of the present invention are shown. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the scheme of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0032] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0033] The method for preparing a dynamically controllable hydrogel SERS substrate based on the salt ion specific effect provided by the present invention comprises the following steps:

[0034] S1. Preparation of triangular plate-shaped silver (AgNPrs) sol: add sodium citrate solution to silver nitrate solution, mix well, add sodium borohydride solution prepared with ice water dropwise to the mixed solution, stir well; irradiate with sodium lamp for light-induced reaction, and obtain blue plate-shaped silver sol after irradiation for 14-16 hours. The side length of triangular plate silver nanoparticles in the plate-shaped silver sol is about 100 nm;

[0035] S2. Preparation of hydrogel SERS substrate: Concentrate the triangular plate-shaped silver sol prepared in step S1, mix it evenly with PVA sol and pour it into a mold, freeze it at a temperature below -20°C for 9-12 hours, take it out, thaw it at room temperature for 2-4 hours, and repeat the freezing-thawing steps 3-5 times to obtain a SERS hydrogel; finally, immerse the SERS hydrogel in an etching solution and a salting-out solution in turn to obtain a hydrogel SERS substrate.

[0036] As an embodiment of the present invention, in step S1, the concentration of the silver nitrate solution is 1×10 -4 mol / L, the concentration of sodium citrate solution is 0.1mol / L; the concentration of sodium borohydride solution prepared in ice water is 8×10 -3 mol / L, and its specific preparation method is as follows: weigh the required mass of sodium borohydride, add it into ice water under stirring, and after it is fully dissolved, the sodium borohydride solution is obtained.

[0037] Furthermore, after adding the newly prepared sodium borohydride solution, the molar ratio of silver nitrate, sodium citrate and sodium borohydride is 1:10:0.8. In the above technical scheme, by adjusting the amount of each raw material added and the reaction conditions (sodium lamp irradiation), silver nanoparticles are obtained, and their morphology is mainly a triangular plate. It should be noted that in other embodiments, other methods can also be used to prepare triangular plate-shaped silver sols. The specific preparation method can be selected according to actual needs and is not limited to this.

[0038] As an embodiment of the present invention, in step S1, the mixing process of the silver nitrate solution and the sodium citrate solution is carried out under magnetic stirring conditions, with a rotation speed of 600 rpm and a stirring time of 10-15 min.

[0039] As an embodiment of the present invention, in step S2, the salting-out solution is at least one of sulfate, carbonate, potassium ion, sodium ion, etc., preferably Na with a concentration of 3 mol / L. 2 SO 4 Solution, when the salting solution is Na 2 SO 4 When the solution is used, the soaking time is 0-60 minutes.

[0040] As an embodiment of the present invention, in step S2, the etching solution can form a slightly soluble compound with silver ions, and its anion is Cl - ,I - Br - At least one of the following, preferably Cl - The solution has a concentration of 1×10 -3 mol / L to 1mol / L, soaking time is 3-5min.

[0041] In particular, the hydrogel SERS substrate prepared by the preparation method proposed in the present invention can be used for the detection of glucose in the fields of medicine and food, and can also be used for the detection of methamphetamine in forensic science. After integration, it can be used for wearable hydrogel patch sensors for indicators such as glucose and drugs in sweat.

[0042] The preparation method and application of the dynamically controllable hydrogel SERS substrate based on the salt ion specific effect proposed by the present invention are further described below in conjunction with specific embodiments:

[0043] Example 1

[0044] This embodiment prepares a dynamically controllable hydrogel SERS substrate based on the salt ion specific effect, which specifically includes the following steps:

[0045] S1, add 99mL of concentration 1×10 -4 mol / L silver nitrate solution, add 1 mL of 0.1 mol / L sodium citrate solution and stir vigorously for 10 min; add 1.0 mL of 8×10 -3 mol / L ice water to prepare a sodium borohydride solution, so that the molar ratio of silver nitrate, sodium citrate and sodium borohydride is 1:10:0.8. The addition of sodium borohydride immediately turns the solution yellow. After stirring for 2 minutes, a high-pressure sodium lamp (manufacturer: Shanghai Yaming Lighting Co., Ltd., model NG70W) is used as a light source for photoinduction. After irradiation for 14 hours, a blue triangular plate-shaped silver sol can be obtained. Centrifuge at a speed of 9500 rpm for 5 minutes, concentrate it to 10 mL, and set aside.

[0046] The UV-visible absorption spectrum of triangular plate-shaped silver sol is shown in Figure 1 As shown in a, its UV-visible absorption spectrum has three absorption peaks at 331nm, 513nm and 740nm, which belong to the out-of-plane quadruple, in-plane quadruple and in-plane dipole resonance modes of silver nanoparticles, respectively, indicating that the blue plate-like silver sol was successfully prepared; TEM image is shown in Figure 1 As shown in b, it can be seen from the figure that the morphology of silver nanoparticles is mainly triangular;

[0047] S2. Heat 20 mL of 10% PVA solution in a water bath at 88°C for 3 h to dissolve and form a PVA polymer solution; take 10 mL of PVA polymer solution and mix it evenly with 10 mL of concentrated triangular plate-shaped silver sol, remove bubbles by ultrasonication for 5 min, pour it into a polytetrafluoroethylene mold (diameter × height = 1.6 cm × 3 cm), freeze it at -20°C for 9 h, take it out and thaw it for 2 h, repeat the freeze-thaw cycle three times, and obtain a blue SERS hydrogel containing triangular plate-shaped silver nanoparticles; finally, immerse the hydrogel in an etching solution and a salting-out solution in turn for etching and salting-out treatment, and obtain an enhanced hydrogel SERS substrate. The etching solution is 1×10 -2 mol / L chloride ion solution (specifically KCl solution), the immersion time is 5 min, and the salting-out solution is 3 mol / L Na 2 SO 4 Solution, soaking time is 15min. It should be noted that one cycle here refers to one freezing and thawing operation; in addition, the size of the mold used in the hydrogel preparation process can also be selected as needed, as long as it can meet the actual needs, and it is not limited to this here.

[0048] In the above process, the size and shape of the nanoparticles in the SERS hydrogel may change under the action of the etching solution, thereby affecting the SERS performance of the substrate. To explore the effect of different etching solutions on the morphology of the SERS hydrogel, the SERS hydrogel was immersed in 1×10 -1 , 1×10 -2 , 1×10 -3 mol / L SO 4 2- , CO 3 2- ,Ac - 、NO 3 - , Cl - ,I - Br - Ionic solution (such as Figure 2 The results show that the hydrogels have different concentrations of SO 4 2- , CO3 2- ,Ac - 、NO 3 - After being immersed in the solution, the color of the ball did not change significantly, and the blue color of the ball gradually faded with the increase of ion concentration. When the concentration of the solution increased to 1 mol / L, the ball 4 2- , CO 3 2- ion solution, the volume decreases, and SO 4 2- The phenomenon of the volume reduction of the small spheres in the ionic solution is more obvious, which is the manifestation of the shrinkage of the hydrogel network structure under the action of salt precipitation. - ,I - Br - When in ion solution, the color of the hydrogel changes significantly at different concentrations. This is due to the Cl - ,I - Br - After the ions enter the hydrogel grid, the silver triangular plate-shaped nanoparticles in the hydrogel are etched by the halogen ions, causing their shape and size to change significantly, and their LSPR optical properties also change. At the same concentration, the color change rate of the hydrogel is Cl - - <Br - Therefore, Cl was used in subsequent experiments. - The UV-visible absorption spectral properties of the hydrogel after being immersed in chloride ion solutions of different concentrations for 5 minutes are shown in Figure 2. Figure 3 As shown, with Cl - As the concentration increases, the UV-visible absorption spectrum of the hydrogel undergoes an obvious blue shift, and the height of the absorption peak gradually decreases. -3 mol / L, the UV-visible absorption peaks of the hydrogel obtained after immersion were almost the same as those of the untreated hydrogel, indicating that at this concentration, the chloride ion solution had little etching effect on the triangular plate-shaped silver nanoparticles in the hydrogel. The color of the hydrogel changed too quickly in the 1 mol / L chloride ion solution, indicating that the etching speed was too fast at this concentration, and it was difficult to capture the dynamic changes with etching time. Therefore, the concentration of 1×10 -2 mol / L chloride ion solution is used as the optimal etching solution. Experiments have shown that it has a more obvious etching effect on hydrogels and is highly controllable.

[0049] ​In the above process, the salting-out solution can cause the SERS hydrogel network structure to change and shrink in volume, and affect the spacing between nanoparticles in the hydrogel, thereby affecting the SERS performance of the substrate. 2 SO 4 ) on the SERS hydrogel. This implementation case investigated the SERS spectra of the hydrogel after immersion for 0, 10, 15, 20, 30, 45, and 60 min. Figure 4 As shown in the figure, 1506cm -1 The intensity of the Raman characteristic peak increases with the immersion time. After immersion for 15 minutes to within 60 minutes, the growth rate of the SERS spectrum intensity does not change much. This is because the salting-out effect affects the ion-polymer chain-water interaction in the hydrogel, causing the network structure of the hydrogel to shrink, leading to a smaller distance between the silver nanoparticles, effectively increasing the hot spot domain, and further enhancing the Raman signal.

[0050] The above examples show that etching and salting-out can affect the LSPR effect of nanoparticles in hydrogels and contribute to the SERS enhancement performance. The Raman detection results of the SERS substrate prepared in this example for different concentrations of R6G at various stages of preparation are shown in Figure 2. Figure 5 As shown in Figure 2, the Raman detection results of R6G after the substrate was etched are as follows: Figure 5 As shown in a, the lowest concentration of R6G is 1×10 -10 mol / L; the Raman detection results of R6G on the substrate after etching and salting-out treatment are as follows Figure 5 As shown in b, the lowest concentration of R6G is 1×10 -12 mol / L.

[0051] Furthermore, this example also explores the application of the hydrogel SERS substrate prepared in Example 1 in glucose analysis and detection. The detection process is based on the glucose oxidase method. Glucose is catalyzed by glucose oxidase to generate gluconic acid and hydrogen peroxide. Hydrogen peroxide reacts with the colorimetric probe 3,3',5,5'-tetramethylbenzidine (TMB) to generate a blue quinone oxidation product oxTMB. The SERS technology is used to detect the change of the specific Raman peak generated by oxTMB. The intensity of the peak is proportional to the glucose concentration, and the glucose concentration can be indirectly measured. The specific results are as follows: Figure 6 As shown in a, oxTMB with a strong SERS signal at 608 cm -1 、755cm -1 、1191cm -1 、1334cm -1 、1604cm -1The characteristic Raman peaks appeared at the same position and were linearly dependent on the glucose concentration. The lowest detectable glucose concentration was 1×10 -6 mol / L, take 1604cm -1 The linear relationship between the Raman characteristic peak and the glucose concentration is as follows: Figure 6 b. Experiments show that the hydrogel SERS substrate prepared by the method proposed in the present invention has a good effect in the indirect analysis and detection of glucose, with convenient operation and high sensitivity; the glucose concentration in human sweat is between 10-200 μM, and the linear range of glucose detection concentration in the present invention includes the concentration range of glucose detection in human sweat, indicating that the method proposed in the present invention is expected to be applied to the glucose content in human sweat, and is expected to provide new ideas for the application of wearable biomedical devices.

[0052] Example 2

[0053] This example explores the application of the hydrogel SERS substrate prepared in Example 1 in the detection of banned drugs (such as methamphetamine, MAMP), and the detection results are as follows: Figure 7 As shown in a, it can be seen from the figure that different concentrations of MAMP are all at 757cm -1 、995cm -1 、1216cm -1 、1598cm -1 Obvious Raman characteristic peaks appeared at the same positions, and the lowest detectable concentration was 0.01ppm. The appearance and concentration dependence of these characteristic peaks provided a reliable basis for the rapid and sensitive detection of trace MAMP samples; Figure 7 b shows 995cm -1 The Raman spectrum intensity of the MAMP molecule at the site shows a good linear relationship with the logarithm of the concentration. Based on the trace detection of glucose in Example 1, this embodiment also expands the application of the hydrogel SERS substrate in trace drug detection, and has important application potential in the fields of forensics, border control and public safety. In addition, taking sweat detection as an example, as a non-invasive analytical method, the hydrogel sensing material can use its inherent advantages to block the biological macromolecules in sweat from entering the hydrogel to cause interference with the spectral signal, and it is also expected to simultaneously realize the trace detection of multiple biomarkers in epidermal sweat, such as glucose, metabolic drugs, etc. As a non-invasive detection method, it is of great significance for health assessment and disease diagnosis.

[0054] Comparative Example 1

[0055] The only difference between Comparative Example 1 and Example 1 is that the SERS hydrogel is not subjected to etching and salting-out treatment, but is directly used as a SERS substrate. The other steps and experimental parameters are the same as those in Example 1 and will not be described again.

[0056] The SERS hydrogel of Comparative Example 1 was used to detect R6G solutions of different concentrations. The results are as follows: Figure 8 As shown in Figure 2, the lowest concentration of R6G that can be detected by SERS hydrogel under this condition is 1×10 -5 mol / L.

[0057] Comparative Example 2

[0058] The difference between Comparative Example 2 and Example 1 is that the SERS hydrogel is first subjected to salting-out treatment, and then the SERS hydrogel is further subjected to etching treatment. The types, concentrations and treatment times of the etching solution and the salting-out solution are all Figure 2 and 3 The other steps and experimental parameters are the same as those in Example 1 and will not be described in detail here. The Raman detection results of the SERS substrate prepared in Comparative Example 2 for different concentrations of R6G at various stages of preparation are shown in FIG. Fig. 9 As shown in Figure 2, the Raman detection results of R6G after the substrate was etched are as follows: Fig. 9 As shown in a, the lowest concentration of R6G is 1×10 -8 mol / L; the Raman detection results of R6G on the substrate after etching and salting-out treatment are as follows Fig. 9 As shown in b, the lowest concentration of R6G is 1×10 -10 mol / L, the above results are significantly higher than the detection results of R6G by the SERS substrate in Comparative Example 1 when the substrate is not treated.

[0059] It can be seen that both etching and salting-out treatment are beneficial to improving the SERS enhancement effect of hydrogels, and the combined enhancement strategy of etching first and then salting-out is the best. This may be because before the hydrogel network structure is changed, the external etching solution ions interact more easily with the silver nanoparticles in the hydrogel, so etching first and then salting-out has a greater dynamic regulation range on the SERS performance of the hydrogel.

[0060] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a dynamically controllable hydrogel SERS substrate based on salt ion specific effect, characterized in that: The steps include: S1. Add sodium citrate solution to silver nitrate solution, mix well, add sodium borohydride solution prepared in ice water dropwise to the mixed solution, stir well; irradiate with sodium lamp to carry out photoinduced reaction, and obtain blue triangular plate-shaped silver nanoparticle sol after irradiation for 14-16 hours; S2. Concentrate the triangular plate-shaped silver nanoparticle sol obtained in step S1, mix it evenly with the PVA polymer aqueous solution and pour it into a mold, freeze it in an environment below -20°C for 9-12 hours, take it out, thaw it at room temperature for 2-4 hours, and repeat the freezing-thawing steps several times to obtain a SERS hydrogel; finally, immerse the SERS hydrogel in an etching solution and a salting-out solution in turn for etching and salting-out treatment, so as to obtain a hydrogel SERS substrate.

2. The preparation method according to claim 1, characterized in that: In step S2, the etching solution can form a slightly soluble compound with silver ions, the anion of which is Cl - ,I - Br - At least one of .

3. The preparation method according to claim 2, characterized in that: The etching solution is Cl - The solution has a concentration of 1×10 -3 mol / L to 1mol / L, soaking time is 0-60min.

4. The preparation method according to claim 1, characterized in that: In step S2, the salting-out solution is at least one of sulfate, carbonate, potassium ion and sodium ion.

5. The preparation method according to claim 4, characterized in that: The salting-out solution is a Na2SO4 solution with a concentration of 3 mol / L and a soaking time of 0-60 min.

6. The preparation method according to claim 1, characterized in that: In step S1, the concentration of the silver nitrate solution is 1×10 -4 mol / L, the concentration of the sodium citrate solution is 0.1 mol / L, and the concentration of the sodium borohydride solution prepared with ice water is 8×10 -3 mol / L.

7. The preparation method according to claim 1, characterized in that: In step S1, after adding ice water to prepare a new sodium borohydride solution, the molar ratio of silver nitrate, sodium citrate and sodium borohydride is 1:10:0.

8.

8. The preparation method according to claim 1, characterized in that: In step S1, the mixing process of the silver nitrate solution and the sodium citrate solution is carried out under magnetic stirring conditions, with a rotation speed of 600 rpm and a stirring time of 10-15 min.

9. A hydrogel SERS substrate prepared by the preparation method according to any one of claims 1 to 8.

10. Use of a hydrogel SERS substrate prepared by the preparation method described in any one of claims 1 to 8 or a hydrogel SERS substrate described in claim 9 in the detection of glucose and methamphetamine.

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