Preparation method of SERS substrate based on elastic contraction, SERS substrate and detection method thereof

Abstract

The present invention discloses a preparation method of a SERS substrate based on elastic contraction, a SERS substrate and a detection method thereof. The present invention uses elastic PDMS as a substrate, and the PDMS is first biaxially stretched before assembly. After saturated self-assembly of silver nanoparticles is performed on the stretched PDMS surface, the tension is released, and the substrate is contracted to form a biaxial pleated structure to further shorten the distance between the silver particles, thereby forming an effective hot spot. The substrate does not need to be stretched again to adjust the hot spot during use. In addition to the contraction property, PDMS also has good flexibility and transparency. The PDMS-based SERS substrate prepared by the present invention can be directly attached to the surface of a solid object to be detected in any shape for rapid, in-situ detection.

Description

Technical Field

[0001] The invention relates to the technical field of Raman spectroscopy, and in particular to a preparation method of a SERS substrate based on elastic contraction, a SERS substrate and a detection method thereof. Background Art

[0002] At present, the construction of "hot spot" structures such as nanoscale gaps between gold and silver nanostructures is the main means to obtain highly sensitive SERS substrates. Although gold and silver colloids are simple to prepare, they are prone to agglomeration, resulting in poor stability and repeatability. Gold and silver thin film SERS substrates overcome this problem. The preparation methods of thin film substrates mainly include self-assembly, photolithography, electron beam etching, nanoimprinting, etc. Among them, photolithography, electron beam etching, and nanoimprinting can prepare SERS substrates with high uniformity and high repeatability, but photolithography and nanoimprinting require expensive nanostructure templates and complex preparation processes. The electron beam etching instrument is expensive and has a long preparation cycle. In comparison, the self-assembly method is simple to operate and has low cost.

[0003] On the other hand, traditional thin-film SERS substrates use hard materials such as silicon and glass as substrates. When detecting solid targets, the molecules to be detected need to be dissolved and extracted. The steps are cumbersome and the operation is complicated, the detection reliability is reduced, and it cannot be used for the detection of precious items such as antiques and cultural relics.

[0004] During the self-assembly process of silver nanoparticles on the substrate surface, due to the electrostatic repulsion or steric hindrance of the colloidal particle surface stabilizer, the particle spacing is difficult to further reduce after reaching saturated assembly, thus affecting the construction of efficient hotspot structures.

[0005] Therefore, this issue remains to be resolved. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a preparation method of a SERS substrate based on elastic contraction, a SERS substrate and a detection method thereof, so as to solve the technical problems mentioned in the background technology. In view of this problem, the present invention uses elastic PDMS as a substrate, and first biaxially stretches the PDMS before assembly. After saturated self-assembly of silver nanoparticles on the stretched PDMS surface, the tension is released, and the substrate shrinks and forms a biaxial pleated structure to further shorten the distance between the silver particles, thereby forming an effective hot spot. The substrate does not need to be stretched again to regulate the hot spot during use. In addition to the contraction characteristics, PDMS also has good flexibility and transparency. The PDMS-based SERS substrate prepared by the present invention can be directly attached to the surface of a solid object to be detected of any shape for rapid, in-situ detection.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A method for preparing a SERS substrate based on elastic contraction, the method comprising the following steps:

[0009] Step S1, preparing silver nanoparticles;

[0010] Step S2, preparing a PDMS substrate, wherein the PDMS substrate is obtained by mixing and curing a PDMS prepolymer and a curing agent;

[0011] Step S3, preparing an Ag / PDMS substrate, which comprises: firstly biaxially stretching the PDMS substrate obtained in step S2, and then, after stretching, performing saturated self-assembly of silver nanoparticles on the surface of the PDMS substrate based on the silver nanoparticles obtained in step S1, and finally releasing the surface tension of the PDMS substrate to generate wrinkles on its surface and shorten the distance between the silver particles to form a hot spot structure.

[0012] Furthermore, the step S1 includes:

[0013] Step S101, mixing 1 mL of 1% silver nitrate solution with 99 mL of deionized water, and heating to boiling at 100° C. while stirring;

[0014] Step S102, adding 1 mL of 1% trisodium citrate solution by mass, and keeping boiling for 30 minutes under stirring;

[0015] Step S103, after cooling, centrifugally wash with deionized water for 3 times at a speed of 6000 rpm.

[0016] Furthermore, the step S2 includes:

[0017] Step S201, PDMS prepolymer and curing agent are mixed evenly at a mass ratio of 10:1, and placed in a culture dish;

[0018] Step S202, after vacuuming for 30 minutes, curing at 60°C for 6 hours to obtain a PDMS elastic film with a thickness of about 0.5 mm;

[0019] Step S203, cutting the PDMS elastic film obtained in step S202 into small pieces of 1 cm×1 cm.

[0020] Furthermore, the step S3 includes:

[0021] Step S301, biaxially stretching the PDMS substrate obtained in step S2 to a certain deformation amount, and then treating it with oxygen plasma for 3 minutes to form a hard layer on the PDMS surface;

[0022] Step S302, adding 1% PDDA solution to the PDMS surface to make the PDMS surface positively charged, and after 30 minutes, washing away the unabsorbed PDDA molecules on the PDMS surface with deionized water;

[0023] Step S303, dropping the Ag glue prepared in step S1 on the surface of the PDMS substrate, and allowing the self-assembly of the silver nanoparticles to reach saturation;

[0024] Step S304: releasing the tension to shrink the elastic substrate to obtain the SERS substrate.

[0025] Furthermore, the biaxial stretching to a certain deformation amount is specifically biaxial stretching of 30%.

[0026] Furthermore, the self-assembly of the silver nanoparticles reached saturation, and the self-assembly time was 120 minutes.

[0027] A SERS substrate based on elastic contraction is prepared by any one of the above-mentioned preparation methods.

[0028] A detection method based on a SERS substrate comprises: preparing a SERS substrate by any of the above-mentioned preparation methods, placing the SERS substrate on the surface of an object to be detected, and performing in-situ detection.

[0029] The beneficial effects of the present invention are:

[0030] 1. The present invention utilizes the elastic deformation recovery ability of the elastic film, and its preparation process is simple and low-cost. The obtained SERS substrate is flexible and transparent, can realize in-situ detection, is easy to use, and has a wide range of applications.

[0031] 2. The present invention performs self-assembly on the surface of an elastic substrate that has been "stretched", and generates a hard layer on the surface through oxygen plasma treatment (so that a wrinkle structure is generated when it shrinks), and then shortens the distance between Ag by shrinking and generating a wrinkle structure, thereby improving the sensitivity of the substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the process of preparing Ag / PDMS substrate by elastic contraction provided in Example 1

[0033] Figure 2 This is a morphology diagram of the Ag / PDMS substrate obtained in Example 1 when the self-assembly time is 60 min, wherein: Figure 2 a represents the morphology of the Ag / PDMS substrate obtained without stretching. Figure 2b represents the morphology of the g / PDMS substrate obtained under 30% biaxial stretching;

[0034] Figure 3 This is a morphology image of the Ag / PDMS substrate obtained in Example 1 under the condition of biaxial stretching of 30% and self-assembly time of 120 min;

[0035] Figure 4 Schematic diagram of the change of SERS activity of the Ag / PDMS substrate prepared under unstretched and 30% biaxially stretched conditions with assembly time in Example 1;

[0036] Figure 5 is the Raman spectrum of the Ag / PDMS substrate prepared in Example 1 with a biaxial stretch of 30% and an assembly time of 120 min, wherein: Figure 5 a represents the Raman spectra of crystal violet measured at 10 different positions on the Ag / PDMS substrate, Figure 5 b represents the Raman imaging of the substrate within the range of 0.5 mm × 0.5 mm;

[0037] Figure 6 The schematic diagram of the detection effect of the Ag / PDMS substrate prepared by biaxial stretching of 30% and assembly time of 120 min provided in Example 1, wherein: Figure 6 a means containing 10 -3 -10 -8 SERS spectrum of milk containing M tricyclazole on the surface of Ag / PDMS substrate, Figure 6 b represents tricyclazole 1083cm -1 The linear relationship between the Raman peak intensity and the logarithm of its concentration;

[0038] Figure 7 The schematic diagram of the peak intensity and SERS spectrum of the Ag / PDMS substrate prepared by biaxial stretching of 30% and assembly time of 120 min provided in Example 1, wherein: Figure 7 a represents the crystal violet 1162 cm-1 measured when the Ag / PDMS substrate was bent inward and outward at 10° and 20°. -1 The peak strength of Figure 7 b represents the in situ detection of 10 on the leaf surface using the Ag / PDMS substrate -3 -10 -7 SERS spectrum obtained from M tricyclazole. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] Example 1

[0041] See also Figure 1-Figure 7 This embodiment provides a method for preparing a SERS substrate based on elastic contraction, the formula used in the method includes: silver nitrate, trisodium citrate, polydiallyldimethylammonium chloride (PDDA), polydimethylsiloxane (PDMS) prepolymer and curing agent. The preparation process of the method is as follows: Figure 1 As shown, it specifically includes:

[0042] Step 1: Preparation of silver nanoparticles

[0043] Specifically, in this embodiment, step 1 specifically includes:

[0044] Mix 1 mL of 1% silver nitrate solution with 99 mL of deionized water, heat to 100°C while stirring, and add 1 mL of 1% trisodium citrate solution;

[0045] Keep boiling for 30 minutes under stirring; after cooling, wash with deionized water by centrifugation for 3 times at a speed of 6000 rpm.

[0046] Step 2: Preparation of PDMS substrate

[0047] Specifically, in this embodiment, step 2 specifically includes:

[0048] The PDMS prepolymer and curing agent were mixed evenly in a mass ratio of 10:1, poured into a culture dish, vacuumed for 30 minutes, and cured at 60°C for 6 hours to obtain a PDMS elastic film with a thickness of about 0.5 mm, which was then cut into small pieces of 1 cm×1 cm.

[0049] Step 3: Preparation of Ag / PDMS substrate

[0050] Specifically, in this embodiment, step 3 specifically includes:

[0051] The PDMS film prepared in step 2 is “bidirectionally” stretched to a certain deformation amount; oxygen plasma treatment is used for 3 minutes to generate an extremely thin hard layer on the surface of the PDMS;

[0052] 1% PDDA solution was added dropwise to make the PDMS surface positively charged; after 30 min, the unabsorbed PDDA molecules on the PDMS surface were washed away with deionized water;

[0053] The Ag glue prepared in step 1 is added dropwise. The surface of the Ag glue is negatively charged due to the adsorption of citrate, and is assembled onto the surface of the PDMS substrate through the electrostatic adsorption force between the Ag glue and PDDA.

[0054] After 120 min of self-assembly of Ag nanoparticles, the assembly reached saturation due to the electrostatic repulsion between Ag particles. Further extension of the time did not increase the number of Ag particles on the PDMS surface, that is, hot spots could not be formed by forming a dense distribution of Ag particles.

[0055] When the tension is released, the elastic substrate contracts and a bidirectional wrinkled structure is generated due to the presence of the hard layer on the surface. Therefore, the distance between the Ag particles is shortened, which is conducive to obtaining a highly sensitive Ag / PDMS Raman active substrate.

[0056] Through the above steps, the SERS substrate based on elastic contraction can be prepared. In addition to the contraction property, the PDMS substrate also has good flexibility and transparency. The PDMS-based SERS substrate prepared by the method of this embodiment can be directly attached to the surface of a solid object to be detected in any shape for rapid, in-situ detection.

[0057] Specifically, in this embodiment, the PDMS film prepared in step 2 is “bidirectionally” stretched to a certain deformation amount, and the specific deformation amount is bidirectional stretching of 30%.

[0058] Specifically, in this embodiment, in order to verify the advancement and correctness of the method of this embodiment, multiple groups of experiments and tests were conducted, and the specific results are as follows:

[0059] Figure 2 The morphology of Ag / PDMS substrate obtained by self-assembling Ag nanoparticles on the surface of unstretched and biaxially stretched 30% PDMS, the self-assembly time was 60min. Figure 2 It can be seen that the shrinkage of the PDMS substrate generates a wrinkled structure on the PDMS surface, which can significantly reduce the distance between the Ag nanoparticles.

[0060] Figure 3 The Ag / PDMS morphology was prepared by extending the self-assembly time of Ag nanoparticles to 120 min. Figure 3 It can be seen that extending the assembly time can further increase the density of Ag nanoparticles, but then it reaches saturation.

[0061] Figure 4The SERS activity of Ag / PDMS substrate prepared under unstretched and biaxially stretched conditions of 30% with crystal violet as the probe molecule varies with assembly time. It can be seen that at different assembly times, the elastic contraction of the PDMS substrate can significantly improve the sensitivity of the substrate. Among them, when the assembly time is 120 minutes, the contraction of the PDMS substrate enhances the Raman signal of crystal violet by about 13 times. The enhancement factor of the substrate is calculated to be 2.06×10 6 .

[0062] Figure 5 It shows that the Ag / PDMS substrate prepared under the conditions of 30% biaxial stretching and 120 min assembly time has good uniformity, and its relative standard deviation is only 5.62%.

[0063] Figure 6 a indicates that the Ag / PDMS substrate prepared under the conditions of 30% biaxial stretching and 120 min assembly time can easily detect 10 -7 M's tricyclazole; Figure 6 b represents tricyclazole 1083cm -1 There is a good linear relationship between the peak intensity and the logarithm of the tricyclazole concentration, thus indicating that the substrate has application prospects in quantitative detection.

[0064] Due to the good flexibility and transparency of PDMS, the Ag / PDMS substrate prepared by biaxial stretching of 30% and assembly time of 120 min can be attached to the surface of solid detection objects for in-situ detection. In the attached state, the substrate may bend. Figure 7 a shows that the Ag / PDMS substrate has good enhancement performance under different bending states. Figure 7 b is the in-situ detection result, which shows that the substrate provided by this embodiment can directly detect the surface of the leaves 10 -6 M of tricyclazole.

[0065] In summary, the method of this embodiment utilizes the elastic deformation recovery ability of the elastic film, and its preparation process is simple and low-cost. The obtained SERS substrate is flexible and transparent, can realize in-situ detection, is easy to use, and has a wide range of applications.

[0066] The method of this embodiment self-assembles the surface of the "stretched" elastic substrate and generates a hard layer on the surface through oxygen plasma treatment (so that a wrinkle structure is generated when it shrinks), and then shortens the distance between Ag by shrinking and generating a wrinkle structure, thereby improving the sensitivity of the substrate.

[0067] Example 2

[0068] This example is an Ag / PDMS substrate prepared by the method of Example 1.

[0069] Example 3

[0070] In this embodiment, the Ag / PDMS substrate is prepared by the method of Example 1, and the Ag / PDMS substrate is directly attached to the surface of the solid test object to achieve in-situ and rapid detection of the target molecule.

[0071] The matters not described in detail in the present invention are all known technologies to those skilled in the art.

[0072] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for preparing a SERS substrate based on elastic contraction, characterized in that: The method comprises the following steps: Step S1, preparing silver nanoparticles; Step S2, preparing a PDMS substrate, wherein the PDMS substrate is obtained by mixing and curing a PDMS prepolymer and a curing agent; Step S3, preparing an Ag / PDMS substrate, which comprises: firstly biaxially stretching the PDMS substrate obtained in step S2, and then, after stretching, saturated self-assembly of silver nanoparticles on the surface of the PDMS substrate based on the silver nanoparticles obtained in step S1, and finally releasing the surface tension of the PDMS substrate to generate wrinkles on the surface thereof, and shortening the distance between the silver particles to form a hot spot structure; The step S3 comprises: Step S301, biaxially stretching the PDMS substrate obtained in step S2 to a certain deformation amount, and then treating it with oxygen plasma for 3 minutes to form a hard layer on the PDMS surface; Step S302, adding 1% PDDA solution to the PDMS surface to make the PDMS surface positively charged, and after 30 minutes, washing away the unabsorbed PDDA molecules on the PDMS surface with deionized water; Step S303, dropping the Ag glue prepared in step S1 on the surface of the PDMS substrate, and allowing the self-assembly of the silver nanoparticles to reach saturation; Step S304: releasing the tension to shrink the PDMS substrate to obtain the SERS substrate.

2. The method for preparing a SERS substrate based on elastic contraction according to claim 1, characterized in that: The step S1 comprises: Step S101, mixing 1 mL of 1% silver nitrate solution with 99 mL of deionized water, and heating to boiling at 100° C. while stirring; Step S102, adding 1 mL of 1% trisodium citrate solution by mass, and keeping boiling for 30 minutes under stirring; Step S103, after cooling, centrifugally wash with deionized water for 3 times at a speed of 6000 rpm.

3. The method for preparing a SERS substrate based on elastic contraction according to claim 2, characterized in that: The step S2 comprises: Step S201, PDMS prepolymer and curing agent are mixed evenly at a mass ratio of 10:1, and placed in a culture dish; Step S202, after vacuuming for 30 minutes, curing at 60°C for 6 hours to obtain a PDMS elastic film with a thickness of about 0.5 mm; Step S203, cutting the PDMS elastic film obtained in step S202 into small pieces of 1 cm×1 cm.

4. The method for preparing a SERS substrate based on elastic contraction according to claim 3, characterized in that: The biaxial stretching is performed to a certain deformation amount, and specifically the biaxial stretching is performed by 30%.

5. The method for preparing a SERS substrate based on elastic contraction according to claim 4, characterized in that: The self-assembly of the silver nanoparticles reached saturation, and the self-assembly time was 120 min.

6. A SERS substrate based on elastic contraction, characterized in that: The SERS substrate based on elastic contraction is prepared by the preparation method described in any one of claims 1-5.

7. A detection method based on a SERS substrate, characterized in that: The detection method comprises: preparing a SERS substrate by the preparation method described in any one of claims 1 to 5, placing the SERS substrate on the surface of an object to be detected, and performing in-situ detection.

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