TWI776149B - Method of producing a flexible substrate for sers detection - Google Patents

Abstract

The present invention provides a method of producing a flexible substrate for SERS detection, comprising: providing a substrate; subjecting the substrate to a nitrogen atmospheric treatment to make a surface of the substrate hydrophilic; subjecting the substrate to a thermal evaporation to deposit a first metal nanoparticle and a second metal nanoparticle onto the substrate; and bending the substrate to a predetermined angle, wherein the predetermined angle is 5^o ~20^o .

Description

Method for preparing flexible substrate for SERS detection

The present invention relates to a method for preparing a flexible substrate; more particularly, the present invention relates to a method for preparing a flexible substrate for SERS detection.

Since 1974, Fleischmann et al. obtained the first Raman spectrum of pyridine adsorbed on the surface of silver electrode after roughening the surface of silver electrode. Since then, the first page of Surface Enhanced Raman Scattering (SERS) has been opened. Subsequent studies by many teams have found that the Raman signal enhancement is not only due to the increased surface area due to the rough structure, but also because of the nanostructure of precious metals (such as gold, silver, etc.), which significantly enhances the Raman scattering signal. In 1997, Kneipp, Nie and other research teams were the first to verify that SERS technology has the ability to detect a single small molecule. In addition to studying how to design appropriate nanostructures to enhance Raman signals, scientists also pursue higher spatial resolution to provide richer information. In 2000, the Raman images of BCB (BrilliantCresyl Blue) molecules measured by the so-called Tip Enhanced Raman spectroscopy (TERS) were also verified for the first time, and were subsequently used in many fields of research, such as DNA , carbon nanotubes, etc. Looking back on the discovery of the SERS phenomenon in 1974 to the present, this research and application field has developed rapidly and continued to grow in recent years.

Compared with traditional Raman spectroscopy, surface-enhanced Raman scattering (SERS) spectroscopy has the characteristics of micro-measurement and surface-specificity. In addition, because the Raman signal of water molecules is extremely weak and will not interfere with the Raman signal of the analyte, SERS spectroscopy is also very suitable for measuring biomolecules in aqueous solutions. In addition, SERS spectroscopy is only sensitive to molecules within a few nanometers of the metal surface, so it is suitable as a tool for studying surface science.

Surface-enhanced Raman scattering has the advantages of high sensitivity and rapidity in the existing sensing technology. Molecules are adsorbed on the surface to enhance their vibration characteristics, and can be analyzed numerically on the spectrum. Surface-enhanced Raman scattering technology can show its advantages in the sensing of trace substances, such as biochemical threat detection, biopharmaceutical diagnosis, genetic analysis and acid-base detection. Compared with ordinary Raman scattering, SERS exhibits very prominent sensitivity characteristics, and its advantages can be applied to the detection of low-concentration chemicals. The molecular structure fingerprint displayed on the SERS spectrum has a considerable resolving power, and can simultaneously and rapidly distinguish multiple chemical components without destroying the detected objects.

There are two main mechanisms of SERS. The first is the electromagnetic field effect caused by the roughness of the metal surface, and the second is the chemical effect caused by the charge transfer of the molecules adsorbed on the metal surface. The main SERS mechanistic contribution comes from the electromagnetic effect, which is produced by the localized field resonance in the nanostructure, also known as the localized surface plasmon resonance (LSPR) effect. Rough metal surfaces with periodic nanostructures and irregular discontinuous metal films can enhance LSPR. The excitation of surface plasmon resonance is affected by the nanoscale metal structure, including the size, shape and the gap distance between the metal; plasmonic nanomaterials are fabricated by the following methods, such as colloidal metal particles, electron beam micro Film technology, electron gun or thermal evaporation process technology on glass or silicon and other material substrates.

When the molecules adsorbed on the metal surface undergo a small change in orientation, they will be reflected in the Raman spectrum, which can be used as a tool for online monitoring of certain chemical reactions. However, the advantages of SERS sometimes become its own challenges. Since the state of molecules adsorbed on the metal surface is a factor that affects whether the SERS effect occurs and the signal strength, how to make the molecules to be tested can be stably adsorbed is a difficult problem. In addition, not all molecules have strong Raman scattering intensity, and most biological samples have very weak Raman signals, so substrate designs with higher enhancement factors are required. The analysis of Raman signals in complex organisms or mixtures is also a big problem, which usually has to be handled by some sample pretreatment or substrate modification actions. Hence, the importance of changing the substrate design or modification arises.

Compared with the flexible SERS substrate, the traditional rigid SERS substrate has the advantages of light weight, easy portability and efficient collection of analytes, and can be used for the development of SERS substrates with high transparency and repeatability. Therefore, how to prepare a flexible substrate to obtain high detection sensitivity, high stability and high reusability is a major challenge for the application of this technology.

The contents disclosed in the above background description paragraphs are only for enhancing understanding of the background of the present invention. Therefore, the above contents do not constitute prior art that hinders the present invention, and should be well known to those skilled in the art.

In the present invention, an Au-Ag nanoparticle array is prepared on the surface of a flexible modified polydimethylsiloxane (PDMS) substrate, which is applied to surface enhanced Raman scattering (SERS). The PDMS substrate is modified by nitrogen (N ₂ ) plasma treatment to form a surface with a hydrophilic layer. Compared with the non-plasma surface treatment, the contact angle of the plasma-treated PDMS substrate was reduced from 115.4 ^o to 32 ^o , which turned into a PDMS substrate with a hydrophilic surface. The uniformly arranged Au-Ag nanoparticle arrays were further prepared on the plasma-treated PDMS substrate by thermal evaporation method, and the surface structure was observed by scanning microscope (SEM). The results show that the Au-Ag@PDMS-N ₂ substrate has a uniform and narrow intergranular gap (about 2 nm), with high sensitivity and reproducibility for adenine (10 ^-4 M). In particular, the SERS intensity of the 2Au-6Ag@PDMS-N ₂ substrate at a bending angle of 5 ^° increased by about 4 times, indicating that the curved SERS substrate can effectively tune the distance between Au-Ag nanoparticles. Therefore, the flexible and ultra-sensitive SERS substrates prepared by evaporating Au-Ag nanoparticle arrays on the plasma surface-treated PDMS substrates have great application potential in the detection of biomolecules and environmental pollutants.

Therefore, the present invention adopts the thermal evaporation deposition method to deposit the Au-Ag nanoparticle array on the surface of the modified PDMS substrate. Through atmospheric plasma treatment, the surface of the PDMS substrate is modified and a hydrophilic surface is formed, which improves the adhesion of metal nanoparticles on the substrate surface. Uniform Au-Ag nanoparticle arrays were further deposited on atmospheric plasma-treated PDMS substrates, and the nanoparticle-structure spacing could also be manipulated. The flexible and ultra-sensitive SERS substrates prepared in this experiment can be used to detect biomolecules and environmental pollutants.

Specifically, the present invention provides a method for preparing a flexible substrate for SERS detection, comprising: providing a substrate; treating the substrate with nitrogen atmospheric pressure plasma to make the surface of the substrate hydrophilic; sequentially depositing the first metal nanoparticle and the second metal nanoparticle on the substrate; and folding the substrate to a bending angle, wherein the bending angle of the substrate is 5 ^{° ˜20°} .

In certain embodiments, the substrate is a silicon-based substrate or a glass substrate.

In certain embodiments, the silicon substrate is a PDMS substrate.

In some embodiments, the thickness ratio of the first metal nanoparticle to the second metal nanoparticle is 1:1˜4:1.

In certain embodiments, the first metal nanoparticle and the second metal nanoparticle are gold, silver, copper or iron.

In some embodiments, when the substrate is bent at an angle of 5 ^° , the SER strength is 4 times higher than when the substrate is not bent.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. The technical features, objects and advantages of the present invention will be readily understood from these descriptions and drawings and the scope of the claims. At the same time, in order to make the above-mentioned features and advantages of the present invention more obvious and easy to understand, the following embodiments are given and described in detail with the accompanying drawings.

In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

The advantages and features of the present invention and the methods for achieving the same will be better understood by being described in more detail with reference to the exemplary embodiments and the accompanying drawings. However, the present invention may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough, complete and complete to convey the scope of the invention to those of ordinary skill in the art, and the invention will only be the scope of the appended claims defined. In the drawings, the sizes and relative sizes of elements are shown exaggerated for clarity. Throughout the specification, some of the different reference numerals may be the same element. As used hereinafter, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be more understandable that terms such as those defined in commonly used dictionaries should be construed as having meanings consistent with the meanings in the relevant art, and should not be construed in an overly formal meaning unless explicitly defined herein.

The singular forms "a," "at least one," and "the" as used herein may also include plural referents unless the context clearly dictates otherwise. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The exemplary embodiments will be described in detail below with reference to the drawings. These embodiments, however, may be embodied in different forms and should not be construed as limiting the scope of the claims of the present invention. These embodiments are provided so that the disclosure of the present invention will be complete and clear, and those skilled in the art will be able to understand the scope of the present invention through these embodiments.

The specific technical solutions of the present invention will be further clearly and completely described below with reference to specific embodiments. "Experimental Procedure" Nitrogen Atmospheric Pressure Plasma Treatment of Substrates

First, PDMS (Polydimethylsiloxane; polydimethylsiloxane) monomer and curing agent (mass ratio of monomer to curing agent is 10:1; curing agent (184B) was purchased from Weijida Enterprise Co., Ltd., batch number H047141042) A PDMS solution was prepared, and the bubbles inside the solution were removed by vacuuming in a vacuum ball. The PDMS solution was poured into an 88 mm petri dish and cured in a circulating oven at 80 °C for 3 h to obtain a PDMS substrate with a thickness of about 1 mm. After that, the PDMS substrate was surface-modified by nitrogen atmospheric pressure plasma treatment (AP plasma jet from Taiwan Fengtian Electronics Co., Ltd.) with a power of 1.6 kw and a time of 10 seconds. Among them, it should be noted that the substrate material of the present invention is not limited to PMDS, and any substrate of silicon material or glass material can be used in the present invention. Preparation of Au-Ag@PDMS-N ₂ SERS Substrates

Au-Ag@PDMS-N ₂ SERS substrates were prepared by spin thermal evaporation at 10 rpm on PDMS substrates treated with nitrogen plasma under high vacuum (3.3×10 ^-6 torr). A first layer of silver (Ag) nanoparticles with different thicknesses (2, 4, 6, and 8 nm), abbreviated as 2Ag, 4Ag, 6Ag, and 8Ag, were deposited on the plasma-treated PDMS substrate surface, respectively. Next, a 2 nm gold (Au) nanoparticle layer was further deposited on the surface of the above Ag nanoparticle layer to obtain an Au-Ag@PDMS-N ₂ SERS substrate for the detection of biomolecules and environmental pollutants, abbreviated respectively. are 2Au-2Ag@PDMS-N ₂ , 2Au-4Ag@PDMS-N ₂ , 2Au-6Ag@PDMS-N ₂ and 2Au-8Ag@PDMS-N ₂ . Thermal evaporation is mainly a coating technology in which the material source to be evaporated is heated and sublimated by resistance or electron beam to evaporate the material atoms to the surface of the substrate and adhere to the vapor deposition. Among them, it should be noted that since the specific absorption band of the localized surface plasmon resonance (LSPR) effect of silver nanoparticles is the longest, it is suitable for deposition on substrates, and gold nanoparticles are the least likely to be oxidized, so they are deposited on silver nanoparticles. on the nanoparticles as a passivation layer. The metal particles on the substrate of the present invention are not limited to gold or silver particles, and metal particles such as copper and iron can also be used in the present invention. Morphological features and SERS detection

Adenine (Adenine), Rhodamine 6G (Rhodamine 6G) and Malachite Green (Malachite Green; MG) were purchased from Sigma-Aldrich and used for SERS detection without further purification. A 10 μL solution of the analyte was dropped onto the Au-Ag-PDMS-SERS substrate for SERS measurement. The Raman spectra of the 632.8 nm He-Ne laser and the 0.1 mw laser beam were recorded with a commercial Raman spectrometer (HR800, Horiba) and measured with a 50× objective lens (detection range 400-2000 cm ^-1 ). Static contact angle measurements were performed at 25 °C with a contact angle goniometer (DSA 100, Krüss GmbH, Hamburg, Germany). The morphological features of the Au-Ag@PDMS SERS substrate were investigated by scanning electron microscopy (SEM). Scanning electron microscopy images were performed with JEOL-JSM 6701F. "Results and Discussion" Water Contact Angle

The PDMS substrate surface was modified by nitrogen atmospheric pressure plasma treatment and detected by water contact angle analysis, as shown in Figure 1. The water contact angle of the untreated PDMS substrate surface was 115 ^o . After nitrogen plasma treatment, the water contact angle decreased from 115 ^o to 32 ^o , indicating that the surface of the PDMS substrate was modified and a hydrophilic surface layer was formed. . In addition, for further thermal evaporation processing, the aging of the plasma-treated PDMS substrate was also investigated. In the atmospheric environment, the surface contact angle increased from 32 ^o to 63 ^o with the increase of storage time from 1 to 9 minutes. This result indicates that the number of oxygen functional groups on the surface of PDMS substrates treated by surface plasmon reduction decreases with the storage time. Therefore, the plasma-treated PDMS substrate must be thermally evaporated within at most 10 minutes, preferably within 5 minutes, and most preferably within 1 minute, in order to avoid the reduction of oxygen functional groups. X- ray diffraction

In this example, the preparation process of the Au-Ag@PDMS-N ₂ substrate was studied by X-ray diffraction analysis, as shown in FIG. 2 . The untreated PDMS substrate obtained typical diffraction peaks at 2θ= ^12.1o . The diffraction peaks at 2θ = 38.1 ^o , 44.2 ^o , 64.4 ^o and 77.5 ^o when depositing the Ag nanoparticle layer on the plasma-treated PDMS substrate are represented by (111) on the Ag@PDMS-N ₂ substrate, respectively , (200), (220) and (311) planes (see Figure 2). After further deposition of the Au nanoparticle layer on the Ag@PDMS- _N2 substrate, the diffraction peaks of the Au-Ag@PDMS- _N2 substrate were compared with those of the Ag@PDMS- _N2 substrate on the X-ray diffraction pattern similar, indicating that the formation of Au and Ag nanoparticle layers has similar lattice parameters. Scanning Electron Microscope ( SEM)

In this example, the surface morphology of the Au-Ag@PDMS substrate before nitrogen plasma treatment was investigated by scanning electron microscopy (SEM). Figure 3 shows gold (Au) nanoparticle layers of 2 nm thickness deposited on Ag@PDMS substrates with different thicknesses of silver (2, 4, 6, and 8 nm), respectively. The results showed that the surface flatness of the Au-Ag@PDMS substrate increased with the increase of the thickness of the Ag nanoparticle layer, indicating that the increase of the thickness of the Ag nanoparticle layer would promote the uniform deposition of the Au nanoparticle layer. Au-Ag nanoparticle layer was deposited on the flexible PDMS substrate, and relatively uniform Au-Ag nanoparticle can be obtained on its surface. After nitrogen atmospheric pressure plasma treatment, the surface morphology of the Au-Ag@PDMS _- N substrate was investigated, as shown in Figure 4. When the PDMS substrate was treated by surface plasmonization, the surface morphology of the Au-Ag nanoparticle layer had a more independent surface structure of nanoparticle arrays. This is because the hydrophilicity of the surface layer is affected by the nitrogen plasma treatment of the PDMS substrate, resulting in a hydrophilic glass-like surface, thereby obtaining separated nanoparticle arrays. On the other hand, as the thickness of the Ag nanoparticle layer increases, the particle morphology of the Au-Ag nanoparticle array increases. However, some nanoparticle aggregation appeared on the 2Au-8Ag@PDMS-N ₂ substrate, indicating that the thickness of the Ag nanoparticle layer affects the arrangement and distribution of nanoparticles on the surface. As a result, uniformly arranged Au-Ag nanoparticles were obtained on the 2Au-6Ag@PDMS-N ₂ substrate, forming a high hot spot effect on the surface of PDMS, which is a preferred embodiment. Therefore, nitrogen plasma-treated PDMS substrates can obtain Au-Ag nanoparticle arrays with narrow gaps and improve the Raman enhancement effect. Surface-enhanced Raman scattering ( SERS)

In order to detect the SERS-enhancing ability of the Au-Ag@PDMS substrate and Au-Ag@PDMS-N ₂ substrate, a small molecule adenine (Adenine 10 ^-4 M) was selected as the detection molecule (Fig. 5). The prominent characteristic peak of small molecule adenine is 732 cm ^-1 . In Figure 5(a), the 2Au-6Ag@PDMS substrate exhibits stronger SERS enhancement effect before nitrogen plasma treatment. Since the Au-Ag@PDMS-N2 substrate shows a uniform Au-Ag nanoparticle array on the nitrogen plasma-treated PDMS surface when the PDMS substrate is treated by nitrogen plasma, the Au-Ag@PDMS _{- N2} substrate has The SERS enhancement effect is more pronounced than that of the Au-Ag@PDMS substrate (as shown in Fig. 5(b)). The results show that the 2Au-6Ag@PDMS _- N substrate has the strongest SERS enhancement effect due to the narrow particle spacing of the Au-Ag nanoparticle array. Similarly, the SERS detection of rhodamine (R6G) and malachite green (MG) in Fig. 6(a) and Fig. 6(b) can also see the same SERS-enhancing effect. In addition, the integrated area of the characteristic peak at 732 cm ^-1 was used to compare the Ag nanoparticle layer thickness (Fig. 7). The results show that the SERS enhancement effect of the Au-Ag@PDMS _- N substrate is stronger than that of the Au-Ag@PDMS substrate. Among these SERS-active substrates, the 2Au-6Ag@PDMS-N ₂ substrate achieves the highest SERS enhancement effect through nitrogen plasma treatment of the PDMS substrate and control of the change in the gap between nanoparticles.

In addition, using adenine (Adenine 10 ^-4 M) as the detection molecule, the effect of substrate curvature on the SERS signal intensity was investigated on the 2Au-6Ag@PDMS-N ₂ substrate. 8 is a schematic diagram of the method of bending the PDMS substrate to a predetermined angle according to the present invention. The Au-Ag@PDMS substrate is first prepared and placed on a glass stage. Put more pieces of glass on the side, and then adjust it with a reverse clip and use a protractor to confirm that it is adjusted to the desired angle. The SERS spectra of the 2Au-6Ag@PDMS-N ₂ substrates with different bending angles (0 ^o , 5 ^o and 20 ^o ) are shown in Fig. 9. As the bending angle increases, the SERS intensity increases, and the Raman enhancement effect is the strongest for the 2Au-6Ag@PDMS _- N substrate at a bending angle of 5 ^o . The results show that the bending strain can effectively narrow the nanogap of the Au-Ag nanoparticle array and improve the SERS intensity. At the same time, with the increase of the bending angle from 5 ^o to 20 ^o , the SERS intensity decreased. It is speculated that some Au-Ag nanoparticles were clustered due to the close spacing of the particles due to the increase of the bending angle. Among them, the SERS intensity of the 2Au-6Ag@PDMS-N ₂ substrate at a bending angle of 5 ^° increased by about 4 times, indicating that the curved SERS substrate can effectively control the spacing between Au-Ag nanoparticle arrays. "in conclusion"

The Au-Ag@PDMS-N ₂ SERS substrate was successfully prepared by plasma treatment on the flexible PDMS substrate for surface modification and deposition of Au-Ag nanoparticle arrays. The surface of the PDMS substrate was modified by nitrogen atmospheric plasma treatment to prepare a hydrophilic glass-like surface layer. Surface plasma treatment reduces the contact angle of PDMS substrate from 115.4 ^o to 32 ^o , which proves that the surface of PDMS is hydrophilic. In addition, uniform Au-Ag nanoparticle arrays were evaporated on plasma-treated PDMS substrates for SERS detection. The Au-Ag@PDMS-N ₂ substrate has high sensitivity and Raman-enhanced properties due to the narrow-pitch nanoparticle arrays that can be obtained by plasma processing. In particular, the SERS intensity of the 2Au-6Ag@PDMS-N substrate at a bending angle of ₅ ^° increased by about 4 times, indicating that the curved SERS substrate can effectively tune the spacing between Au-Ag nanoparticle arrays. Therefore, the flexible and ultrasensitive SERS substrate of Au-Ag@PDMS-N ₂ will provide great potential for practical application.

All features disclosed in this specification can be combined in any way. Features disclosed in this specification may be replaced by features of the same, equivalent or similar purpose. Accordingly, unless expressly stated otherwise, a feature disclosed in this specification is one embodiment of a series of equivalent or similar features.

In addition, according to the contents disclosed in this specification, those skilled in the art can easily make appropriate changes and modifications for different usage methods and situations according to the basic features of the present invention without departing from the spirit and scope of the present invention. Therefore, other Embodiments are also included in the scope of the patent application.

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Through the detailed description and the accompanying drawings, only the accompanying drawings of the embodiments of the present invention will be more fully understood; therefore, the following drawings are only used to explain the embodiments of the present invention and do not limit the scope of the invention; (a) PDMS substrate before plasma treatment; (b) plasma treated PDMS substrate with storage time of 1 minute; (c) plasma treated PDMS substrate with storage time of 5 minutes; and (d) storage time is the contact angle image of the PDMS substrate treated by plasma for 9 minutes; FIG. 2 is the X-ray diffraction analysis diagram of the PDMS, Ag@PDMS-N ₂ and Au-Ag@PDMS-N ₂ substrates of the present invention; FIG. 3 is the present invention. Figure 4 (a) 2Au-2Ag@PDMS-N ₂ ; (b) 2Au-4Ag@PDMS-N ₂ ; (c) 2Au-6Ag@PDMS-N ₂ ; and (d) 2Au after nitrogen plasma treatment of the present invention -8 SEM images of Ag@PDMS-N ₂ substrate; Figure 5 shows (a) Au-Ag@PDMS SERS substrate before nitrogen plasma treatment and (b) Au-Ag@PDMS SERS after nitrogen plasma treatment of the present invention Substrate detection SERS spectrum of adenine (Adenine 10 ^-4 M); Figure 6 is the SERS spectrum of malachite green (R6G) detected by the Au-Ag@PDMS SERS substrate before and after nitrogen plasma treatment (a) of the present invention ; (b) SERS spectra of malachite green (MG) detected on Au ^- Ag@PDMS SERS substrates before and after nitrogen plasma treatment; The relationship diagram of the thickness of Ag nanoparticle layer on the @PDMS substrate and the Au-Ag@PDMS-N ₂ substrate; FIG. 8 is a schematic diagram of the method of bending the PDMS substrate to a desired angle of the present invention; and FIG. 9 is the 2Au of the present invention. -6Ag@PDMS-N ₂ was used as the substrate to measure the SERS spectra of the analyte adenine (Adenine 10 ^-4 M) at different bending angles (0 ^o , 5 ^o and 20 ^o ).

Claims (5)

A method for preparing a flexible substrate for SERS detection, comprising: providing a substrate; treating the substrate with nitrogen atmospheric pressure plasma to make the surface of the substrate hydrophilic; Nano metal particles and second nano metal particles are deposited on the substrate; and the substrate is folded to a bending angle; wherein, when the bending angle of the substrate is 5°, its SER intensity is when the substrate is not bent 4 times. The method of claim 1, wherein the substrate is a silicon substrate or a glass substrate. The method of claim 2, wherein the silicon substrate is a PDMS substrate. The method as recited in claim 1, wherein the deposition thickness ratio of the first metal nanoparticle and the second metal nanoparticle is 1:1˜4:1. The method of claim 1, wherein the first metal nanoparticle and the second metal nanoparticle are gold, silver, copper or iron.

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