Flexible surface-enhanced raman scattering chip based on non-noble metal and method of making and use thereof

Abstract

The present application belongs to the technical field of spectral analysis, and particularly relates to a flexible surface-enhanced Raman scattering chip based on non-noble metal and a preparation method and use thereof. The present application loads non-noble metal Raman active material onto the surface of nylon filter membrane material to construct a flexible surface-enhanced Raman scattering chip. The chip combines the advantages of non-noble metal material, promotes the charge transfer between the substrate and the target molecule by constructing a heterojunction, further enhances the Raman signal of the target molecule, and thus reduces the detection limit. Meanwhile, the chip also has strong time stability and specificity and strong mechanical stability, is simple to prepare, has lower cost, is convenient for transportation and storage, and can sensitively detect malachite green illegally added on the surface of freshwater fish.

Description

Technical Field

[0001] This invention belongs to the field of spectroscopic analysis technology, and specifically relates to a flexible surface-enhanced Raman scattering chip based on non-precious metals, its fabrication method, and its applications. Background Technology

[0002] Surface-enhanced Raman scattering (SERS) is a spectroscopic analysis method based on Raman scattering technology. This scattered light was first observed by the Indian physicist C.V. Raman in 1928 [see: (a) Song, G.; Gong, W.; Cong, S.; Zhao, Z. Angew. Chem. 2021, 133, 5565-5571.]. Surface-enhanced Raman scattering (SERS) is a promising analytical technique with unique advantages such as fast response, high sensitivity, and high spectral resolution. It has been widely applied in environmental pollutant analysis, biological tissue imaging, surface science, and trace species detection [see: (b) Liu, J.; Zheng, T.; Tian, ​​Y. Angew. Chem. Int. Ed. 2019, 58, 7757-7761. (c) Su, Y.; Yuan, B.; Jiang, Y.; Wu, P.; Huang, X.; Zhu, J.-J.; Jiang, L.-P. Chem. Sci. 2022, 13, 6573-6582.]. Commonly used substrate materials are mainly precious metals such as gold and silver. However, these substrate materials have weak selectivity for target molecules, poor oxidation stability, and are also very expensive. With the development of detection technologies, the development of novel substrate materials has become an urgent problem to be solved. In recent years, with the development of new synthetic techniques, novel Raman-enhanced substrate materials, such as graphene, metal-organic frameworks, and semiconductor metal oxides, have been proposed and utilized. These materials have been studied and successfully used as suitable alternatives to noble metals for monitoring various target substances [see: (d) Yilmaz, M.; Babur, E.; Ozdemir, M.; Gieseking, RL; Dede, Y.; Tamer, U.; Schatz, GC; Facchetti, A.;

[0003] Usta, H.; Demirel, G. Nat. Mater. 2017, 16, 918-924. (e) Wang, X.; Shi, W.; Jin, Z.; Huang, W.; Lin, J.; Ma, G.; Li, S.; Guo, L. Chem. Int. Ed. 2017, 56, 9851-9855. (f) Yin, D.; Wang, M.-L.; Wang, Y.-Z.; Hu, X.; Liu, B.; Liu, H.; Ma, L.; Gao, G.-GJ Mater. Chem. C 2019, 7, 9856-9864.]. Compared with noble metals, non-metallic SERS substrates such as semiconductor materials have higher selectivity and uniformity, as well as better stability and biocompatibility. Although some strategies have been applied to improve the SERS reaction of this material, the charge transfer process is a short-range pathway, and the relatively low enhancement effect and poor charge separation efficiency remain a major obstacle to the practical application of semiconductor substrates. [See: (g) Ling, X.; Fang, W.; Lee, Y.-H.; Araujo, PT; Zhang, X.; Rodriguez-Nieva, JF; Lin, Y.; Zhang, J.; Kong, J.; Lett.2014,14,3033-3040.(h)Li,C.;Li,S.;Qu,A.;Kuang,H.;Xu,L.;Xu,C.Adv.Funct.Mater.2020,30,2001451.(i ) Wen, S.; Su, Y.; Dai, C.; Jia, J.; Fan, G.-C.; Jiang, L.-P.; Song, R.; Zhu, J.-J. Anal. Chem. 2019, 91, 12298-12306.]. Among these, constructing non-noble metal heterostructure-like SERS substrates can effectively promote charge transfer processes and enhance Raman enhancement [see: (j) Li, J.; Xu, X.; Huang, B.; Lou, Z.; Li, B. ACS Appl. Mater. Interfaces 2021, 13, 10047-10053.]. Furthermore, the composition of heterostructure materials is diverse, allowing for highly controlled nanostructure and morphology, providing new insights for the design of high-performance Raman substrates [see: (k) Tan, X.; Wang, L.; Cheng, C.; Yan, X.; Shen, B.; Zhang, J. Chem. Commun. 2016, 52, 2893-2896.].

[0004] Traditional Raman substrate preparation methods often employ rigid supports to load Raman-active materials, which is disadvantageous for collecting target molecules from surfaces with unique morphologies. Furthermore, these rigid substrates are not ideal for carrying, transporting, and storing [see: (l) Zeng, F.; Duan, W.; Zhu, B.; Mu, T.; Zhu, L.; Guo, J.; Ma, X. Anal. Chem. 2019, 91, 1064-1070.]. Flexible Raman chips facilitate the collection of molecules from surfaces with unique morphologies and can be further coupled with handheld devices for rapid on-site detection. However, to date, there are no reported methods or applications for fabricating flexible SERS chips based on non-precious metals. Summary of the Invention

[0005] This invention addresses the aforementioned technical problems in the prior art by providing a method for preparing and using a flexible surface-enhanced Raman scattering chip based on non-precious metals, and achieves highly sensitive detection of malachite green illegally added to the surface of freshwater fish.

[0006] The technical solution of the present invention is as follows:

[0007] A flexible surface-enhanced Raman scattering chip based on non-precious metals, comprising a flexible support material and a Raman-active material;

[0008] The Raman-active material is a tungsten oxide / carbon nitride heterojunction material;

[0009] The tungsten oxide / carbon nitride heterojunction material is uniformly distributed on the surface of the flexible support material.

[0010] Preferably, the flexible support material is a nylon filter membrane.

[0011] Preferably, the nylon filter membrane has a diameter of 50 mm and a pore size of 0.22 micrometers.

[0012] The method for preparing the non-precious metal-based flexible surface-enhanced Raman scattering chip is as follows: tungsten oxide / carbon nitride heterojunction material is dispersed in anhydrous ethanol, filtered through a nylon filter membrane, and the tungsten oxide / carbon nitride heterojunction material is loaded onto the surface of the nylon filter membrane.

[0013] Preferably, the fabrication method of the non-noble metal flexible surface-enhanced Raman scattering chip is as follows:

[0014] Step 1. Disperse 20 mg of tungsten oxide / carbon nitride heterojunction material in 20 mL of anhydrous ethanol to obtain an ethanol dispersion of the material;

[0015] Step 2. Connect the vacuum pump to the Buchner funnel, place a nylon filter membrane in the center of the Buchner funnel with the front side facing up, and turn on the vacuum pump;

[0016] Step 3. Drop the ethanol dispersion of tungsten oxide / carbon nitride heterojunction material onto the surface of a nylon filter membrane, and filter under vacuum to load the tungsten oxide / carbon nitride heterojunction material onto the surface of the nylon filter membrane;

[0017] Step 4. After the filtration process is complete, remove the filter membrane and dry it.

[0018] Preferably, the dried filter membrane loaded with tungsten oxide / carbon nitride material is cut into 5mm×5mm squares with scissors, or cut into other shapes as needed to prepare a flexible surface-enhanced Raman scattering chip.

[0019] The synthesis method of the tungsten oxide / carbon nitride heterojunction material is as follows:

[0020] Step A. Calcine dicyandiamide at 500–550°C for 2–4 hours, then cool.

[0021] Step B. Calcine the product obtained in Step 1 at 500-550℃ for 2-4 hours, then cool to obtain carbon nitride nanosheets;

[0022] Step C. First, disperse tungsten hexachloride in ethanol, add the carbon nitride nanosheets obtained in step B, stir, and heat at 160-180℃ for 10 hours to obtain the precipitate, which is the tungsten oxide / carbon nitride heterojunction material.

[0023] Preferably, the specific method of step A is as follows: the calcination conditions of the dicyandiamide are 2.5℃·min. -1 The temperature was increased from 20°C to 550°C and held at this temperature for 240 minutes. After the reaction was completed, the temperature was allowed to cool naturally to room temperature.

[0024] The specific method of step B is as follows: the product obtained in step 1 is ground and then calcined again; the calcination conditions are: 2℃·min -1 The temperature was increased from 20°C to 500°C and held at this temperature for 120 minutes. After the reaction was completed, the temperature was naturally cooled to room temperature to obtain the product.

[0025] The specific method of step C is as follows: First, disperse the tungsten hexachloride precursor solution in ethanol, add the carbon nitride nanosheets prepared in step B, stir at room temperature for 45 minutes to obtain a uniform suspension; then seal the suspension in a stainless steel autoclave with a Teflon liner and heat at 160°C for 10 hours; after the reaction is completed, cool the mixture to room temperature; collect the final precipitate by centrifugation, treat it three times with water and ethanol, and use it after vacuum drying at 60°C for 12 hours.

[0026] Preferably, in step C, the mass ratio of the tungsten hexachloride precursor solution to the carbon nitride nanosheets is 1:1; 50 mg of the tungsten hexachloride precursor solution is added to every 30 mL of ethanol.

[0027] The flexible surface-enhanced Raman scattering chip based on non-precious metals can be used to detect malachite green.

[0028] Preferably, the flexible surface-enhanced Raman scattering chip based on non-precious metals can be used to detect residual malachite green on the surface of freshwater fish.

[0029] A method for detecting malachite green using a flexible surface-enhanced Raman scattering chip made of non-precious metals:

[0030] The surface-enhanced Raman scattering chip was immersed in malachite green molecular solutions of different concentrations, dried, and then the Raman signal of the malachite green molecules was obtained by Raman instrument testing. A linear fitting curve between the Raman signal and the concentration of the malachite green molecular solution was obtained.

[0031] The surface-enhanced Raman scattering chip is brought into full contact with the analyte, and after drying, the Raman signal of the analyte molecules is obtained by using a Raman instrument. The signal is then input into the linear fitting curve to calculate the concentration of malachite green molecules in the analyte.

[0032] Preferably, the Raman signal is obtained using a confocal Raman spectrometer, with a 633nm laser as the excitation source, a 20× objective lens, a laser power of 1.7 milliwatts, and 10 acquisitions.

[0033] Preferably, the Raman spectral characteristic peak obtained from the Raman signal reading is 1176 cm⁻¹. -1 and 1617cm -1 The data intensity value at that location.

[0034] Compared with the prior art, the advantages of the present invention are as follows:

[0035] This invention constructs a flexible surface-enhanced Raman scattering (SERS) chip by loading non-precious metal Raman-active materials onto the surface of a nylon filter membrane. This chip combines the advantages of non-precious metal materials, promoting charge transfer between the substrate and target molecules through the construction of heterojunctions, further enhancing the Raman signal of the target molecules, thereby lowering the detection limit. Simultaneously, the chip also exhibits strong temporal stability, specificity, and mechanical stability. It is simple to prepare, lower in cost, and convenient for transportation and storage. This invention can achieve highly sensitive detection of malachite green illegally added to the surface of freshwater fish. Attached Figure Description

[0036] Figure 1 This is a schematic diagram illustrating the construction of the flexible surface-enhanced Raman scattering chip used in this invention.

[0037] Figure 2 This is a schematic diagram illustrating the synthesis of the tungsten oxide / carbon nitride heterojunction material used in this invention.

[0038] Figure 3 The images show the characterization of the tungsten oxide / carbon nitride heterojunction material used in this invention. In the images, a is the X-ray powder diffraction pattern of the sample; b, c, and d are the scanning electron microscope (SEM), transmission electron microscope (TEM), and elemental distribution maps of the sample, respectively; e is the solid-state ultraviolet characterization of the sample; and f is the electron paramagnetic resonance (EPR) characterization of the sample.

[0039] Figure 4 These are Raman performance test images of the flexible surface-enhanced Raman scattering chip used in this invention. Image a shows a comparison of Raman enhancement of malachite green molecules using tungsten oxide, carbon nitride, and a tungsten oxide / carbon nitride heterojunction as substrates, respectively; image b shows the Raman response of malachite green molecules under different laser excitation sources; images c and d show the detection signal response of malachite green molecules at different concentrations under optimal substrate materials and optimal laser excitation sources, along with corresponding scatter plots and linear fitting curves; image e shows the uniformity of the Raman response signal of the constructed substrate; and image f shows the stability characterization of the tungsten oxide / carbon nitride heterojunction material used in this invention.

[0040] Figure 5 This diagram illustrates the mechanical stability of the flexible surface-enhanced Raman scattering (SERS) chip used in this invention. A, b, and c represent schematic diagrams of the SERS chip in its normal state, signal hotspot maps of 10 randomly selected points in the corresponding state, and the corresponding characteristic peak intensities, respectively. D, e, and f represent schematic diagrams of the SERS chip in its tortuous state, signal hotspot maps of 10 randomly selected points in the corresponding state, and the corresponding characteristic peak intensities, respectively. G, h, and i represent schematic diagrams of the SERS chip in its bent state, signal hotspot maps of 10 randomly selected points in the corresponding state, and the corresponding characteristic peak intensities, respectively.

[0041] Figure 6 This is a schematic diagram illustrating the principle of using the flexible surface-enhanced Raman scattering chip of this invention to detect residual malachite green on the skin surface of fish. Detailed Implementation

[0042] Example 1. Construction of a flexible surface-enhanced Raman scattering chip

[0043] 20 mg of tungsten oxide / carbon nitride heterojunction material was dispersed in 20 mL of anhydrous ethanol and vortexed for 30 seconds to obtain an ethanol dispersion of the material. A vacuum pump was connected to a Buchner funnel, and a nylon filter membrane with a diameter of 50 mm and a pore size of 0.22 μm was placed in the center of the Buchner funnel with the front side facing up. The vacuum pump was turned on. The ethanol dispersion of the tungsten oxide / carbon nitride heterojunction material was dropped onto the surface of the nylon filter membrane. The ethanol was filtered out by vacuum, and the tungsten oxide / carbon nitride heterojunction material was loaded onto the surface of the nylon filter membrane. After the filtration process, the filter membrane was carefully removed, transferred to a petri dish, and placed in a vacuum oven to dry for later use. The dried filter membrane loaded with tungsten oxide / carbon nitride material was cut into 5 mm × 5 mm squares, or other shapes as needed, to prepare a flexible surface-enhanced Raman scattering chip. The surface-enhanced Raman scattering chip was immersed in molecular solutions of different concentrations. After 3 hours, it was removed, rinsed simply, dried, and the Raman signal of the molecules was obtained by testing with a Raman instrument.

[0044] Example 2. Synthesis of tungsten oxide / carbon nitride heterojunction for flexible surface-enhanced Raman scattering chip

[0045] Take 6.0 g of dicyandiamide, place it in a covered porcelain boat, transfer it to a muffle furnace, and heat at 2.5 °C·min. -1 The temperature was increased from 20°C to 550°C and maintained at this temperature for 240 minutes. After the reaction, the mixture was allowed to cool naturally to room temperature, yielding a pale yellow product. The obtained product was then ground and placed back into a covered porcelain boat, transferred to a muffle furnace, and heated at 2°C / min. -1 The temperature was increased from 20°C to 500°C and held at this temperature for 120 minutes. After the reaction, the mixture was allowed to cool naturally to room temperature to obtain the product. First, 50 mg of tungsten hexachloride precursor solution was sonicated for 5 minutes and dispersed in 30 mL of ethanol. Then, 50 mg of carbon nitride nanosheets were added, and the mixture was stirred at room temperature for 45 minutes to obtain a uniform suspension. The mixture was then sealed in a Teflon-lined stainless steel autoclave and heated at 160°C for 10 hours. After the reaction was complete, the mixture was cooled to room temperature. The final precipitate was collected by centrifugation, treated three times with water and ethanol, and then vacuum dried at 60°C for 12 hours before use.

[0046] Example 3. Raman signal detection based on flexible surface-enhanced Raman scattering chip

[0047] Malachite green molecular solutions of different concentrations were prepared as target molecules. The pre-cut flexible surface-enhanced Raman scattering (SERS) chips were then immersed in these solutions for 3 hours. After 3 hours, the chips were removed, rinsed with deionized water to remove non-specifically adsorbed molecules, and then dried in an oven. A confocal Raman spectrometer was used with a 633 nm laser as the excitation source, a 20× objective lens, a laser power of 1.7 mW, and 10 acquisitions. Stability data were obtained by comparing the detection capabilities of flexible SERS chips prepared from materials with different storage times. Related analytical results are shown below. Figure 4 .like Figure 4 As shown in Figure a, compared to tungsten oxide and carbon nitride materials alone, the constructed tungsten oxide / carbon nitride heterojunction material has a more significant enhancement effect on malachite green molecules. As shown in Figure b, the 633nm laser can more effectively promote the enhancement effect. As shown in Figures c and d, the positions of the spectral characteristic peaks obtained by detection using this flexible chip are basically consistent. At lower detection concentrations, the Raman characteristic peak positions of malachite green molecules do not show significant shifts, indicating that the substrate does not affect the molecular structure of malachite green. As the concentration decreases, there are fewer malachite green molecules on the chip, thus the Raman information of malachite green molecules detected by the detector is relatively reduced, and the intensity of the obtained Raman characteristic peaks gradually decreases. This result shows a good linear correlation between the characteristic peak intensity and the concentration. At 10 -4 ~10 -9 Within the concentration range of mol / L, it is at 1176 cm⁻¹. -1 and 1617cm -1 The linear fitting equation for the characteristic peak intensity at a given location as a function of its concentration is y1 = 28046 + 8144 * logC. MG And y2 = 38314 + 10929 * logC MG This indicates that the flexible surface-enhanced Raman scattering chip constructed in Example 3 has high sensitivity to malachite green molecules. Figures e and d demonstrate the chip's good signal uniformity and excellent stability.

[0048] Example 4. Mechanical stability testing of flexible surface-enhanced Raman scattering chips

[0049] Malachite green molecular solutions of different concentrations were prepared as target molecules. The pre-cut flexible surface-enhanced Raman scattering (SERS) chip was then immersed in these solutions for 3 hours. After 3 hours, the chip was removed, rinsed with deionized water to remove non-specifically adsorbed molecules, and then dried in an oven. The flexible SERS chip was then bent and twisted. A confocal Raman spectrometer was used with a 633 nm laser as the excitation source, a 20× objective lens, a laser power of 10%, and 10 acquisitions. Finally, the mechanical stability data of the flexible SERS chip were obtained, and the relevant analysis results are shown below. Figure 5 .like Figure 5 As shown, after bending and twisting the flexible chip, the spectral data from ten randomly selected tests did not show significant differences from the spectral data under normal conditions, demonstrating the good mechanical stability of the flexible surface-enhanced Raman scattering chip.

[0050] Example 5. Detection of residual malachite green on fish skin surface based on flexible surface-enhanced Raman scattering chip

[0051] Malachite green molecular solutions of different concentrations were prepared as target molecules. Ten microliters of each solution were then dropped onto the surface of a fish. A pre-constructed flexible surface-enhanced Raman scattering (SERS) chip was then attached to the fish. After two hours, the chip was removed and dried in an oven. A confocal Raman spectrometer was used with a 633 nm laser as the excitation source, a 20× objective lens, a laser power of 10%, and 10 acquisitions. The data obtained from the flexible SERS chip's simulation of residual malachite green on the fish skin surface are shown in the diagram. Figure 6 .

[0052] Comparative Example 1

[0053] Similar to Example 3, except that the excitation laser of 633nm was changed to 488nm, the technical effect was that the Raman signal of the obtained malachite green was poor.

[0054] Comparative Example 2

[0055] Similar to Example 2, except that the first step calcination synthesis temperature of carbon nitride was changed from 550°C to 450°C, the resulting substrate showed a poor Raman enhancement signal for malachite green.

[0056] Comparative Example 3

[0057] Similar to Example 2, only the hydrothermal synthesis temperature of the tungsten oxide / carbon nitride heterojunction was changed from 160°C to 180°C, and the material obtained was used as a Raman enhancement substrate, which showed poor Raman enhancement signal for malachite green molecules.

[0058] It should be noted that the above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Equivalent substitutions or alternatives made on the basis of the above shall all fall within the scope of protection of the present invention.

Claims

1. The application of a non-precious metal-based flexible surface-enhanced Raman scattering chip in the detection of malachite green, characterized in that, The non-precious metal-based flexible surface-enhanced Raman scattering chip includes a flexible support material and a Raman-active material. The Raman-active material is a tungsten oxide / carbon nitride heterojunction material; The tungsten oxide / carbon nitride heterojunction material is uniformly distributed on the surface of the flexible support material; the flexible support material is a nylon filter membrane. The synthesis method of the tungsten oxide / carbon nitride heterojunction material is as follows: Step A. Calcine dicyandiamide at 500-550 °C for 2-4 h, then cool. Step B. Calcine the product obtained in Step 1 at 500~550 °C for 2~4 h, then cool to obtain carbon nitride nanosheets; Step C. First, disperse the tungsten hexachloride precursor solution in ethanol, add the carbon nitride nanosheets obtained in step B, stir, and heat at 160~180°C for 10 hours to obtain the precipitate, which is the tungsten oxide / carbon nitride heterojunction material.

2. The application as described in claim 1, characterized in that, The specific method for step A is as follows: the calcination conditions for the dicyandiamide are 2.5 °C·min. −1 The temperature was increased from 20°C to 550°C and held at this temperature for 240 minutes. After the reaction was completed, the temperature was allowed to cool naturally to room temperature. The specific method of step B is as follows: the product obtained in step 1 is ground and then calcined again; the calcination conditions are: 2 °C·min −1 The temperature was increased from 20 °C to 500 °C and held at this temperature for 120 minutes. After the reaction was completed, the mixture was allowed to cool naturally to room temperature to obtain the product. The specific method of step C is as follows: First, disperse the tungsten hexachloride precursor solution in ethanol, add the carbon nitride nanosheets prepared in step B, stir at room temperature for 45 minutes to obtain a uniform suspension; then seal the suspension in a stainless steel autoclave with a Teflon liner and heat at 160°C for 10 hours; after the reaction is completed, cool the mixture to room temperature; collect the final precipitate by centrifugation, treat it three times with water and ethanol, and use it after vacuum drying at 60°C for 12 hours.

3. The application as described in claim 1, characterized in that, In step C, the mass ratio of the tungsten hexachloride precursor solution to the carbon nitride nanosheets is 1:1; 50 mg of the tungsten hexachloride precursor solution is added to every 30 mL of ethanol.

4. The application as described in claim 1, characterized in that, Tungsten oxide / carbon nitride heterojunction material is dispersed in anhydrous ethanol, filtered through a nylon filter membrane, and then loaded onto the surface of the nylon filter membrane.

5. The application as described in claim 4, characterized in that, Tungsten oxide / carbon nitride heterojunction material was dispersed in anhydrous ethanol, with 1 mg of tungsten oxide / carbon nitride heterojunction material dispersed in each milliliter of anhydrous ethanol.

6. The application as described in claim 1, characterized in that, The non-precious metal-based flexible surface-enhanced Raman scattering chip was applied to detect residual malachite green on the surface of freshwater fish.

7. The application as described in claim 1, characterized in that, The method for detecting malachite green using the non-precious metal flexible surface-enhanced Raman scattering chip is as follows: The surface-enhanced Raman scattering chip was immersed in malachite green molecular solutions of different concentrations, dried, and then the Raman signal of the malachite green molecules was obtained by Raman instrument testing. A linear fitting curve between the Raman signal and the concentration of the malachite green molecular solution was obtained. The surface-enhanced Raman scattering chip is brought into full contact with the analyte, and after drying, the Raman signal of the analyte molecules is obtained by using a Raman instrument. The signal is then input into the linear fitting curve to calculate the concentration of malachite green molecules in the analyte.

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