A reusable raman-enhancing substrate, method of manufacture, and method of cleaning

Abstract

The application belongs to the technical field of Raman spectrum detection, and particularly relates to a reusable Raman enhancement substrate, a preparation method and a cleaning method. The application prepares molybdenum dioxide nanoparticles by using molybdenum acetylacetonate as raw material through a hydrothermal reaction, disperses the molybdenum dioxide nanoparticles in water to form a molybdenum dioxide water dispersion, and drops the molybdenum dioxide water dispersion on a substrate to prepare a molybdenum dioxide substrate through drying. The molybdenum dioxide substrate prepared by the application has excellent Raman enhancement effect, and has excellent photo-thermal conversion efficiency and thermal conductivity. The molybdenum dioxide substrate can reach a surface temperature of 200-400 DEG C under the radiation of near-infrared laser or a xenon lamp, realizes the thermal decomposition removal of small molecules, achieves the purpose of cleaning and reusing the molybdenum dioxide substrate, and the MoO2 substrate still has excellent Raman enhancement effect and maintains the stability of the structure after 5 cycle tests.

Description

Technical Field

[0001] This invention belongs to the field of Raman spectroscopy detection technology, specifically relating to a reusable Raman enhancement substrate, its preparation method, and its cleaning method. Background Technology

[0002] Surface-enhanced Raman spectroscopy (SERS), as a convenient, sensitive, and non-destructive analytical technique, can provide vibrational fingerprint information of molecular structures, and has broad application prospects in food safety, environmental pollutant monitoring, life sciences, chemical and biosensing. Currently, SERS enhancement mainly employs two mechanisms: electromagnetic enhancement (EM) and chemical enhancement (CM). The electromagnetic mechanism is based on the localized surface plasmon resonance (LSPR) effect excited by incident light on a rough metal surface. This amplifies the local magnetic field around the metal, improving the radiation efficiency of the probe molecule's oscillating dipole source. Electromagnetic enhancement can generally increase the signal intensity of the analyte by 10%. 5 ~10 6 The chemical enhancement is the chemical interaction between the substrate and the probe molecules.

[0003] Noble metals are often used as active substrates for SERS due to their strong LSPR effect. For example, Au nanoparticles are a commonly used SERS substrate because of their very strong LSPR effect. However, the high cost of manufacturing gold nanomaterials, along with problems such as strong spectral background, poor biocompatibility, and low reproducibility, severely limit their application in SERS. Ag nanoparticles are another widely studied SERS substrate material. Although their price is much lower than Au, they are easily sulfided by sulfur-containing compounds in the environment or oxidized by laser irradiation in Raman spectroscopy. In recent years, the discovery of some novel LSPR-active metal oxides (such as oxygen-vacancy-rich unstable stoichiometric semiconductor oxides, such as WO3) has led to the development of new SERS substrates. 2.83 Nanorods, TiO 2-x Nanosheets, MoO 3-x Nanoparticles (such as those used in Raman spectroscopy) exhibit LSPR effects due to oxygen vacancies in their crystal lattices, enriching the variety of Raman-enhanced substrates to some extent. However, a common phenomenon with these substrates is that the analyte remains on the substrate surface after detection. Furthermore, the inherent instability of the substrate structure, such as MoO₂, further exacerbates this issue. 3-x After high-temperature treatment or acid / alkali soaking, the oxygen vacancies will be destroyed, and the sample will even be oxidized by oxygen in the air after being left at room temperature for a period of time. The valence state of the sample changes, and such samples are unstable, that is, it is difficult to maintain the stability of the structure. Due to the residue of the test substance on the substrate surface and the instability of the substrate structure itself, the substrate is difficult to reuse.

[0004] Currently, there are two main methods for achieving reusable Raman-enhanced substrates:

[0005] (1) Photodegradation: A substrate is formed by combining noble metals with semiconductors that have photocatalytic properties. The substrate is then self-cleaned by eliminating dye molecules adsorbed on the substrate surface through photocatalysis. However, traditional semiconductor catalysts generally have a small light absorption cross section and a narrow spectral response range, and the number of photons that can be captured and utilized is very limited, which greatly hinders the degradation efficiency of efficient photocatalytic systems. Therefore, the photocatalytic degradation time is generally long, and the catalyst is easily affected by temperature, pH value, surface defects, etc. during the catalytic process, which leads to a decrease or deactivation of catalytic activity and thus affects subsequent detection experiments.

[0006] (2) Solvent cleaning: The tested substrate is dispersed in acidic ethanol and ultrasonically treated. The sample is collected by centrifugation. The above steps are repeated several times until the dye molecules are completely removed. This method requires the use of hydrochloric acid during the cleaning process for some probe molecules. Hydrochloric acid is a controlled substance that is easily used to produce toxic substances and has a certain degree of corrosiveness, posing a certain risk during the experimental operation. After collecting the sample, a new substrate needs to be prepared for detection. Furthermore, using acidic ethanol for cleaning requires ensuring the structural stability of the substrate sample during the cleaning process, which limits the choice of substrate. Additionally, the acidic waste liquid generated during the cleaning process will cause a certain degree of environmental pollution.

[0007] Therefore, in order to address the problems existing in the current Raman-enhanced substrates, it is necessary to develop a highly sensitive, highly stable, low-cost, and versatile recyclable substrate. Summary of the Invention

[0008] To address the problems existing in the prior art, the present invention aims to provide a reusable Raman-enhanced substrate, its preparation method, and its cleaning method. The nano-MoO2 prepared by the present invention is in the form of flower-shaped or dumbbell-shaped nanospheres, exhibiting excellent photothermal conversion efficiency and thermal radiation stability. The Raman-enhanced substrate prepared with the nano-MoO2 of the present invention can reach a surface temperature of 200–400°C under near-infrared laser or xenon lamp radiation. This temperature exceeds the decomposition temperature of most small molecules, achieving the effect of substrate surface cleaning and enabling substrate reuse. Furthermore, the substrate exhibits good structural stability at this temperature, and still demonstrates excellent Raman enhancement effects after multiple cycle tests.

[0009] Based on the above objectives, the technical solution adopted by the present invention is as follows:

[0010] In a first aspect, the present invention provides a method for preparing a reusable Raman-enhanced substrate, comprising the following steps:

[0011] S1: Preparation of nano-MoO2

[0012] Molybdenum acetylacetonate was dissolved in an aqueous ethanol solution to form a precursor solution; the precursor solution was subjected to a hydrothermal reaction, and the precipitate was collected by centrifugation after the reaction, and then washed and dried to obtain nano-MoO2.

[0013] S2: Fabrication of reusable Raman-enhanced substrates

[0014] The nano-MoO2 obtained in step S1 is prepared into a MoO2 aqueous dispersion of 1-5 mg / mL. The MoO2 aqueous dispersion is dropped onto a substrate and dried to obtain a MoO2 substrate, which is the reusable Raman-enhanced substrate.

[0015] The molybdenum dioxide nanospheres prepared by the method of this invention are flower-shaped or dumbbell-shaped nanospheres with a rough surface full of sharp protrusions. These rough-surfaced nanospheres are composed of numerous small nanosheets, each approximately 10–20 nm in size, which stack to form flower-shaped or dumbbell-shaped nanospheres. The rough surface and abundant porosity are advantageous features of the SERS substrate structure, as the sharp protrusions and nanoscale gaps significantly enhance the local electromagnetic field strength and provide numerous active "hot spots." The molybdenum dioxide substrate prepared by the method of this invention exhibits a strong Raman enhancement effect, and its surface temperature can reach 200–400 °C under near-infrared laser or xenon lamp radiation. This allows for the thermal decomposition and removal of small organic molecules for surface purification. Furthermore, the molybdenum dioxide substrate maintains its structural stability after high-temperature treatment, laser irradiation, or acid / alkali immersion, and can be reused.

[0016] Experiments have shown that within the concentration range of the nano-MoO2 aqueous dispersion of this invention, a layer of nano-molybdenum dioxide can be spread evenly on the substrate, which can meet the requirements of Raman detection.

[0017] Preferably, the ethanol content in the aqueous ethanol solution in step S1 is 18% to 80% (v / v).

[0018] Preferably, the concentration of molybdenum acetylacetonate in the precursor solution is 2–6 mg / mL.

[0019] Experiments revealed that variations in the concentration of molybdenum acetylacetonate in the precursor solution within the aforementioned range had little impact on the morphology of molybdenum dioxide and the performance of the final molybdenum dioxide substrate. However, the ethanol content in the aqueous ethanol solution significantly affected the morphology of the nano-molybdenum dioxide. Only when the ethanol-to-water ratio was appropriate could nano-flower-like or dumbbell-shaped spherical molybdenum dioxide be obtained. Molybdenum dioxide substrates prepared from these nano-flower-like or dumbbell-shaped spherical molybdenum dioxide exhibited superior detection sensitivity.

[0020] Preferably, the temperature of the hydrothermal reaction in step S1 is 180–200°C, and the reaction time is 12–16 h.

[0021] Preferably, in step S1, molybdenum acetylacetonate is dissolved in an aqueous ethanol solution under stirring to form a precursor solution, wherein the stirring speed is 500-600 r / min and the stirring time is 24-48 h.

[0022] Preferably, the cleaning in step S1 includes the following steps: the precipitate collected by centrifugation is washed with anhydrous ethanol at 8000-15000 r / min for 5-10 min, and washed at least 3 times; then it is washed with water at 8000-15000 r / min for 10-15 min, and washed at least 3 times.

[0023] Preferably, the substrate is a cover glass or a silicon wafer.

[0024] Secondly, the present invention provides a reusable Raman-enhanced substrate prepared by the above method.

[0025] Thirdly, the present invention provides a method for cleaning and reusing a Raman-enhanced substrate, comprising the following steps:

[0026] The Raman-enhanced substrate was irradiated with near-infrared laser or xenon lamp until its surface temperature reached 200–400°C. Thermogravimetric analysis showed that molybdenum dioxide exhibited good thermal stability up to 700°C. Therefore, by controlling the laser irradiation power and irradiation time, the surface temperature of the molybdenum dioxide substrate could be controlled within 700°C. This maintained the structural stability of molybdenum dioxide while achieving the thermal decomposition and removal of compounds on the surface of the molybdenum dioxide substrate, thus enabling the reuse of the molybdenum dioxide substrate.

[0027] Preferably, a near-infrared laser with a wavelength of 808 nm and a laser power density of 0.75–2 W / cm² is selected. 2 The irradiation time is 5 to 20 minutes.

[0028] Preferably, the Raman-enhanced substrate is placed in an Ar / N2 atmosphere or air for near-infrared laser irradiation or xenon lamp irradiation.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] This invention prepares molybdenum dioxide nanoparticles via hydrothermal reaction using molybdenum acetylacetonate as a raw material. The prepared molybdenum dioxide nanoparticles are in the form of nanoflower-like spheres or dumbbell-shaped spheres, exhibiting excellent chemical, thermal, and radiation stability. The region near the Fermi level is composed of Mo 3d orbitals, and the large number of free electrons in the d orbitals gives them metallic properties. The high free electron density causes MoO2 to exhibit a localized surface plasmon resonance (LSPR) effect similar to that of metallic materials. Molybdenum dioxide exhibits more metallic properties than semiconductor properties.

[0031] The LSPR effect of nano-MoO2 in this invention is generated by its inherent free electrons, rather than by oxygen vacancies in the crystal lattice as in semiconductor oxides (e.g., TiO2). 2-x MoO 3-x Compared to semiconductor oxides, the MoO2 nanospheres prepared by this invention have superior stability and higher application value.

[0032] Furthermore, in the nano-MoO2 of this invention, the vibrating electrons convert kinetic energy into heat energy due to damping, resulting in a local increase in heat. This heat conduction raises the temperature of the metal material and diffuses it to the surroundings. Therefore, MoO2 also has excellent photothermal conversion efficiency. Under the radiation of near-infrared laser or xenon lamp, the surface temperature of the molybdenum dioxide substrate can reach 200-400°C, which exceeds the decomposition temperature of most small molecules. Experiments have shown that after about 10 minutes of laser radiation, the adsorbed molecules on the surface are completely removed. After 5 cycles of testing, the MoO2 substrate still has excellent Raman enhancement effect and can maintain structural stability.

[0033] In summary, the molybdenum dioxide substrate prepared by this invention not only has a strong Raman enhancement effect, but also excellent structural stability. It can achieve the surface purification effect of molybdenum dioxide substrate through short-term laser irradiation, thus realizing the reuse of molybdenum dioxide substrate. Attached Figure Description

[0034] Figure 1 This is a flowchart illustrating the preparation process of nanoflower-shaped MoO2 in Example 1.

[0035] Figure 2 Electron microscopy images and sample characterization of the nanoflower-like spherical MoO2 prepared in Example 1;

[0036] Figure 3 Stability testing of the nano-MoO2 prepared in Example 1;

[0037] Figure 4 This is a schematic diagram of Raman enhancement of the nano-MoO2 substrate prepared in Example 2;

[0038] Figure 5 Raman signals of different probe molecules on blank and MoO2 substrates in Example 2;

[0039] Figure 6 The thermogravimetric curves of nano MoO2 in N2, the thermogravimetric curves of dye molecules in air, and the temperature change curves of MoO2 and blank substrate under different laser power densities are shown in Example 3.

[0040] Figure 7 Example 3: Raman signal changes of dye molecules during the light-erasable process;

[0041] Figure 8 The variation of the R6G Raman signal during the optical-erasable cycle in Example 4;

[0042] Figure 9 The changes in R6G / RhB / MB / CV Raman signals during the optical-erasable cycle in Example 5;

[0043] Figure 10 Electron microscopy images and sample characterization of MoO2 after photo-wipeable cycle in Example 5;

[0044] Figure 11 The images show the morphology of samples with different ratios and the Raman signal of R6G in Example 6.

[0045] Figure 12 The images show the morphology of samples with different precursor amounts and the Raman signal of R6G in Example 7.

[0046] Figure 13 In Example 8, the laser power density was 0.75 W / cm². 2 The changes in the R6G Raman signal during the photo-erasable process;

[0047] Figure 14 Example 9: Laser power density is 1 W / cm² 2 The changes in the R6G Raman signal during the photo-erasable process;

[0048] Figure 15 Example 10: Laser power density is 2 W / cm² 2 The changes in the R6G Raman signal during the photo-erasable process;

[0049] Figure 16 The image shows a scanning electron microscope (SEM) image of the product in Comparative Example 1 and a schematic diagram of the Raman detection effect.

[0050] Figure 17 The image shows a scanning electron microscope (SEM) image of 2MoO2 and a schematic diagram of the Raman detection effect, which is a comparative example.

[0051] Figure 18 For Comparative Example 3, the laser power density is 0.5 W / cm². 2 The changes in the R6G Raman signal during the photo-erasable process;

[0052] Figure 19 10 μL of 10 μL was added to the blank substrate for Comparative Example 4. -4 Schematic diagram of the M R6G / RhB / MB / CV dye molecule before and after light irradiation. Detailed Implementation

[0053] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Unless otherwise specified, the experimental methods used in the embodiments are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available.

[0054] Example 1

[0055] This embodiment provides a method for preparing nanoflower-like spherical MoO2, the preparation process of which is as follows: Figure 1 As shown, it includes the following steps:

[0056] Weigh 0.1g of molybdenum acetylacetonate and grind it in a mortar for 10-20 minutes. After grinding, add 41mL of deionized water and 9mL of anhydrous ethanol in sequence, with the ratio of deionized water to anhydrous ethanol controlled at about 4:1. Stir for 24-48 hours at a speed of 500-600 r / min. Transfer the dissolved precursor liquid to a 100mL polytetrafluoroethylene reactor for hydrothermal reaction at a temperature of 180℃ for 12-16 hours.

[0057] The products after the hydrothermal reaction were washed by centrifugation with anhydrous ethanol and deionized water, respectively. First, the products were washed three times with anhydrous ethanol, with a centrifugation speed of 8000-15000 r / min each time and a washing time of 5-10 min. Then, the products were washed three times with deionized water, with a centrifugation speed of 8000-15000 r / min each time and a washing time of 10-15 min.

[0058] The cleaned sample was dried in a vacuum oven at 60–80°C for 3–8 hours to obtain nano-MoO2.

[0059] The performance of nano-MoO2 prepared by the above method was tested, such as... Figure 2 and Figure 3 As shown, where, Figure 2 a is a scanning electron microscope image of MoO2. Figure 2 Image b is a transmission electron microscope (TEM) image of MoO2. The fabricated nano-MoO2 sample exhibits a flower-like nanosphere morphology, with a rough surface filled with sharp protrusions. High-magnification scanning electron microscope (SEM) images further reveal that these rough-surfaced nanospheres are composed of numerous small nanosheets, approximately 10–20 nm in size, which stack together to form the flower-like nanospheres. The rough surface and abundant porosity are advantageous features of the SERS substrate structure, as the sharp protrusions and nanoscale gaps significantly enhance the local electromagnetic field intensity and provide numerous active "hot spots." Figure 2c is the XRD image of MoO2. The diffraction pattern of the nanospheres shows six narrow and sharp peaks at 26.3°, 37.1°, 41.6°, 53.9°, 60.9° and 67.0°, which correspond to the (110), (101), (111), (211), (301) and (002) crystal planes of MoO2 (PDF#32-0671), respectively. These characteristic diffraction peaks reflect the high crystallinity of the product. Figure 2 d represents the Raman spectrum of MoO2. The Raman spectra of MoO2 are shown at 121, 196, 220, 354, 488, 564, and 728 cm⁻¹. -1 Typical characteristic peaks are present at these locations. Specifically, the peaks at 564 and 728 cm⁻¹ are... -1 The characteristic peaks at 121, 196, 220, 354, and 488 cm⁻¹ can be attributed to the O-Mo bond vibration mode of MoO₂, while those at 121, 196, 220, 354, and 488 cm⁻¹ can be attributed to the O-Mo bond vibration mode of MoO₂. -1 The characteristic peak at that point can be attributed to the phonon vibration mode of MoO2.

[0060] Figure 3 a is the LSPR absorption spectrum of MoO2, showing a distinct absorption peak near 800 nm. This absorption peak is a typical characteristic of localized surface plasmon resonance. Figure 3 b~ Figure 3 Figure d shows the chemical, thermal, and radiation stability test results of MoO2. After high-temperature treatment, laser irradiation, and acid-base immersion, the local surface plasmon resonance absorption peak (LSPR) of MoO2 nanospheres did not change significantly, demonstrating high stability.

[0061] Example 2

[0062] This embodiment provides a method for preparing a reusable Raman-enhanced substrate using molybdenum dioxide nanoparticles prepared in Example 1. The preparation method includes the following steps:

[0063] Weigh a certain amount of the nano-MoO2 prepared in Example 1 and mix it with deionized water to prepare a MoO2 aqueous dispersion with a concentration of 1-5 mg / mL. Use a pipette to drop 10-50 μL of the MoO2 dispersion onto a substrate. The substrate can be a coverslip, silicon wafer, or other commonly used substrates. Then, dry the substrate in an oven at 60°C to obtain a MoO2 substrate.

[0064] In this embodiment, Rhodamine 6G (R6G), Rhodamine B (RhB), methylene blue (MB), and crystal violet (CV) were selected as probe molecules to analyze the performance of the Raman-enhanced substrate (MoO2 substrate) prepared in this embodiment.

[0065] Weigh out a certain amount of each of the four probe molecules and prepare them to a concentration of 10. -3 The mother liquor of M was diluted sequentially to obtain a concentration of 10. -410 -5 10 -6 10 -7 Four probe molecules of M were used for detection. 50–100 μL of each of the four different dyes were added dropwise to the prepared MoO2 substrate using a pipette. The concentrations of the dye molecules were 10-1. -4 ~10 -7 M, then dried in an oven at 60℃. After drying, the sample was subjected to Raman spectroscopy using a 532nm laser.

[0066] A schematic diagram of Raman enhancement on a MoO2 substrate is shown below. Figure 4 As shown, incident light excites a localized surface plasmon resonance (LSPR) effect on a metal surface, causing the electromagnetic field to concentrate on the metal surface and resulting in a surface enhancement effect. When the sample interacts with this surface enhancement effect, a strong Raman scattering signal can be generated, thereby enabling very high-sensitivity detection of the sample.

[0067] Figure 5 a, Figure 5 b、 Figure 5 c. Figure 5 d represents the Raman signals of different probe molecules on a blank substrate and a MoO2 substrate, respectively. Figure 5 As can be seen, the probe molecules were not detected on the blank substrate, but were detected at a concentration of 10 on the MoO2 substrate. -7 The probe molecule M indicates that the MoO2 substrate prepared in this invention has a Raman enhancement effect.

[0068] Example 3

[0069] In this embodiment, the R6G concentration detected in Example 2 is 10. -4 Taking a MoO2 substrate as an example, the cleaning and reuse method of the Raman-enhanced substrate of the present invention is described. The cleaning method of the present invention is based on "light-wipeable" removal of adsorbed molecules on the substrate surface, and includes the following steps:

[0070] The R6G concentration after testing in Example 2 was 10. -4 The MoO2 substrate of M was irradiated with an 808 nm near-infrared laser at a power density of 1.5 W / cm². 2 The substrates were irradiated in an Ar / N2 atmosphere, and the detection was performed every 2.5 minutes. The substrates were tested for irradiation time of 0, 2.5, 5, 7.5, and 10 minutes to observe the changes in the R6G signal. The experiment found that the R6G signal of the probe molecules disappeared after about 10 minutes of laser irradiation, indicating that the probe molecules adsorbed on the surface of the MoO2 substrate had been removed.

[0071] Figure 6Figure a shows the temperature change curves of the MoO2 substrate and the blank substrate under different laser power densities. As shown in the figure, under near-infrared laser radiation, the temperature change of the blank substrate is not significant, while the surface temperature of the MoO2 substrate gradually increases with the increase of laser power density, reaching a maximum at a laser power of 2 W / cm². 2 At this time, the surface temperature of molybdenum dioxide can reach 400℃, and its surface temperature can be further increased with the increase of laser power density. Figure 6 b is the thermogravimetric curve of MoO2 in N2. Under N2 atmosphere, MoO2 can remain stable between 300 and 700 °C. Figure 6 c. Figure 6 d、 Figure 6 e Figure 6 f represents the thermogravimetric curves of four dye molecules, R6G, RhB, MB, and CV, in air. The dyes begin to decompose at around 200℃.

[0072] comprehensive Figure 6 a~ Figure 6 As shown in f, under near-infrared laser radiation, the temperature change of the blank substrate is not significant, while the surface temperature of MoO2 can reach 400℃, which exceeds the decomposition temperature of most dye molecules. Furthermore, under N2 atmosphere, MoO2 can maintain structural stability between 300 and 700℃. In summary, we propose a photo-erasable method for achieving reusable MoO2 substrates.

[0073] Figure 7 a represents the change in the R6G Raman signal during irradiation. Figure 7 b represents the R6G concentration at R1614 cm⁻¹ during irradiation. -1 R2774 cm -1 R31360 cm -1 R41651 cm -1 The intensity change was observed, and the R6G signal disappeared after approximately 7.5 minutes. Existing methods for achieving substrate recyclability, involving substrate cleaning and photocatalytic degradation, generally require considerable time; for example, photocatalytic degradation typically takes over 2 hours. Therefore, compared to existing technologies, the Raman-enhanced substrate of this invention can achieve self-cleaning of its surface in a short time.

[0074] Example 4

[0075] The purpose of this embodiment is to analyze the stability of the reusability of the MoO2 substrate prepared in Example 2. The specific experimental methods are as follows:

[0076] Add 10 μL of 10 μL of liquid to the MoO2 substrate using a pipette. -4The dye molecules of M were then dried in an oven at 60°C. Raman spectroscopy was performed on the substrate with the dye molecules adsorbed on its surface, using a 532nm laser. The concentration of R6G after detection was 10... -4 The substrate of M was irradiated with an 808nm near-infrared laser for 10 minutes, with a laser power density of 1.5W / cm². 2 After irradiation in an Ar / N2 atmosphere, Raman detection was performed using a 532nm laser, and no R6G signal was observed.

[0077] Using a pipette, add another 10 μL of 10 μL of liquid to the laser-irradiated MoO2 substrate. -4 The dye molecules of M were then dried in an oven at 60°C and Raman detected using a 532nm laser. The R6G signal was observed, and the concentration of the detected R6G was set to 10. -4 The M substrate was irradiated with an 808nm near-infrared laser for 10 minutes, with a laser power density of 1.5W / cm². 2 The sample was irradiated in an Ar / N2 atmosphere. After irradiation, Raman spectroscopy was performed using a 532nm laser, and no R6G signal was observed. The above cycle was repeated 5 times.

[0078] Figure 8 'a' represents the change in the R6G Raman signal during 5 cycles. Figure 8 b represents the R6G level at 614 cm during the 5th cycle. -1 774cm -1 1360cm -1 1651cm -1 Changes in intensity at the location. Figure 8 c represents the photo-erasable cycle process. In each detection cycle, the SERS spectrum of R6G was very similar. After five consecutive detection and decomposition cycles, the SERS spectra of R6G were observed at 614, 778, 1360, and 1651 cm⁻¹. -1 The intensity of the corresponding peak does not change much, indicating that the substrate has excellent reusability.

[0079] Example 5

[0080] The purpose of this embodiment is to analyze the detection sensitivity of a molybdenum dioxide substrate purified by laser irradiation. The specific experimental method is as follows:

[0081] Add 10 μL of 10 μL of liquid to the MoO2 substrate using a pipette. -4 The R6G dye molecules were then dried in an oven at 60°C. Raman spectroscopy was performed on the substrate with the dye molecules adsorbed on its surface using a 532nm laser. The R6G concentration after detection was 10... -4The M substrate was irradiated with an 808nm near-infrared laser for 10 minutes, with a laser power density of 1.5W / cm². 2 Irradiate in an Ar / N2 atmosphere and repeat the above cycle 5 times.

[0082] Use a pipette to add 50 μL of 10 to the MoO2 substrate that has undergone the above 5 cycles. -4 The R6G dye molecules of M were then dried in an oven at 60°C. Raman detection was performed on the substrate with the probe molecules adsorbed on its surface using a 532nm laser. The concentration of the R6G / RhB / MB / CV after detection was 10. -4 The M substrate was irradiated with an 808nm near-infrared laser for 10 minutes, with a laser power density of 1.5W / cm². 2 After irradiation in an Ar / N2 atmosphere, Raman detection was performed using a 532nm laser, and no R6G signal was observed.

[0083] Continue adding 50 μL of 10 to the MoO2 substrate using a pipette. -5 The R6G dye molecules were then dried in an oven at 60°C. Raman spectroscopy was performed on the substrate with the probe molecules adsorbed on its surface, using a 532nm laser. The concentration of R6G after detection was 10... -5 The M substrate was irradiated with an 808nm near-infrared laser for 10 minutes, with a laser power density of 1.5W / cm². 2 After irradiation in an Ar / N2 atmosphere, Raman detection was performed using a 532nm laser, and no R6G signal was observed.

[0084] Continue adding 50 μL of 10 to the MoO2 substrate using a pipette. -6 The R6G dye molecules were then dried in an oven at 60°C. Raman spectroscopy was performed on the substrate with the probe molecules adsorbed on its surface, using a 532nm laser. The concentration of R6G after detection was 10... -6 The M substrate was irradiated with an 808nm near-infrared laser for 10 minutes, with a laser power density of 1.5W / cm². 2 After irradiation in an Ar / N2 atmosphere, Raman detection was performed using a 532nm laser, and no R6G signal was observed.

[0085] Continue adding 50 μL of 10 to the MoO2 substrate using a pipette. -7 The R6G dye molecules were then dried in an oven at 60°C. Raman spectroscopy was performed on the substrate with the probe molecules adsorbed on its surface, using a 532nm laser. The concentration of R6G after detection was 10... -7The M substrate was irradiated with an 808nm near-infrared laser for 10 minutes, with a laser power density of 1.5W / cm². 2 After irradiation in an Ar / N2 atmosphere, Raman detection was performed using a 532nm laser, and no R6G signal was observed.

[0086] Following the method described above, R6G was replaced with dye molecules RhB, MB, and CV, respectively. During the aforementioned cyclic experiment, the changes in the Raman signals of R6G, RhB, MB, and CV were as follows: Figure 9 a, Figure 9 b、 Figure 9 c and Figure 9 As shown in d, the R6G / RhB / MB / CV signal disappeared after laser irradiation. However, with the addition of a low concentration of R6G / RhB / MB / CV dye, the R6G / RhB / MB / CV signal could still be detected, with a minimum detectable count of 10. -7 M, thus it can be seen that the molybdenum dioxide substrate of the present invention still retains 10% of the detection properties for dye molecules and other analytes after multiple cleanings. -7 The detection sensitivity of M.

[0087] Figure 10 a is a scanning electron microscope image of MoO2 after 5 cycles of detection. Figure 10 b is a transmission electron microscope image of MoO2 after 5 cycles of detection. Figure 10 c represents the XRD pattern of MoO2 after 5 cycles of detection. Figure 10 d represents the Raman signal of MoO2 after 5 cycles of detection. For example... Figure 10 As shown, the sample morphology did not change significantly, and the sharp protrusions on the surface remained. After cycling, the XRD and Raman spectra of the MoO2 substrate did not change significantly, further confirming the stability of the molybdenum dioxide substrate.

[0088] Example 6

[0089] The purpose of this embodiment is to investigate the influence of different molybdenum dioxide preparation methods on the Raman enhancement properties of the prepared molybdenum dioxide substrate. The specific experimental methods are as follows:

[0090] Weigh 0.1g of molybdenum acetylacetonate and grind it in a mortar for 10–20 minutes. After grinding, add deionized water and anhydrous ethanol sequentially, varying the ratio of deionized water to anhydrous ethanol to 10mL:40mL, 20mL:30mL, 30mL:20mL, and 25mL:25mL. Stir for 24–48 hours at a speed of 500–600 rpm. Transfer the dissolved precursor solution to a 100mL polytetrafluoroethylene reactor for hydrothermal reaction at 180℃ for 12–16 hours to produce molybdenum dioxide.

[0091] A certain amount of molybdenum dioxide prepared by mixing the above four types of deionized water and ethanol in ratios of 10 mL:40 mL, 20 mL:30 mL, 30 mL:20 mL, and 25 mL:25 mL, respectively, was weighed out. MoO2 was then mixed with deionized water to prepare a MoO2 stock solution with a concentration of 5 mg / mL. 10 μL of the MoO2 dispersion was dropped onto a substrate using a pipette, and then dried in an oven at 60 °C to obtain four types of MoO2 substrates.

[0092] Using a pipette, 100 μL of 10-10-10 μL solution was added to each of the four prepared MoO2 substrates. -7 The R6G dye molecules of M were then dried in an oven at 60°C. After drying, the samples were subjected to Raman spectroscopy using a 532nm laser. Experiments showed that 10 M could be detected on molybdenum dioxide substrates prepared in all four formulations. -7 MR6G dye molecule.

[0093] The detected R6G concentration was 10. -7 The M substrate was irradiated with an 808nm laser for 10 minutes, with a laser power density of 1.5W / cm². 2 After irradiation in an Ar / N2 atmosphere, Raman spectroscopy was performed using a 532nm laser, but no R6G signal was observed. 100μL of 10... -7 The dye molecules of M were then dried in an oven at 60°C and Raman detected using a 532nm laser, and the signal of R6G was detected again.

[0094] Figure 11 a~ Figure 11 Images d show the morphology of molybdenum dioxide samples with four different ethanol-water ratios. Figure 11 e~ Figure 11f represents the Raman signal changes of molybdenum dioxide substrate samples under four different ratios. The morphology and aggregation state of MoO2 changed with the volume ratio of deionized water to ethanol. At a deionized water:ethanol ratio of 10 mL:40 mL, MoO2 aggregation was significant, and the morphology was irregular. As the ratio of deionized water to ethanol changed to 20 mL:30 mL and 30 mL:20 mL, the aggregation of MoO2 gradually weakened. When the ratio was 25 mL:25 mL, MoO2 dispersion was significant. In summary, the ratio of deionized water to ethanol has some influence on the morphology and aggregation state of MoO2, but within a certain range (ethanol content in the aqueous solution is 18%–80%), the effect on the Raman enhancement effect of the prepared molybdenum dioxide and the corresponding substrate is not significant.

[0095] Example 7

[0096] The purpose of this embodiment is to investigate the effect of the amount of molybdenum acetylacetonate on the prepared molybdenum dioxide and the molybdenum dioxide substrate. The specific experimental method is as follows:

[0097] Weigh 0.3g of molybdenum acetylacetonate and grind it in a mortar for 10-20 minutes. After grinding, add 41mL of deionized water and 9mL of anhydrous ethanol. The ratio of deionized water to anhydrous ethanol should be controlled at approximately 4:1. Stir for 24-48 hours at a speed of 500-600 rpm. Transfer the dissolved precursor solution to a 100mL polytetrafluoroethylene reactor for hydrothermal reaction at 180℃ for 12-16 hours to produce molybdenum dioxide.

[0098] Weigh a certain amount of the above MoO2 and prepare a MoO2 stock solution with a concentration of 1-5 mg / mL using deionized water. Use a pipette to drop 10-50 μL of the MoO2 dispersion onto the substrate, and then dry it in an oven at 60°C to obtain the MoO2 substrate.

[0099] 100 μL of 10- ... -7 The R6G dye molecules of M were then dried in an oven at 60°C. After drying, the samples were subjected to Raman spectroscopy using a 532nm laser, which detected 10... -7 M R6G dye molecule.

[0100] The detected R6G concentration was 10. -7 The M substrate was irradiated with an 808nm near-infrared laser for 10 minutes, with a laser power density of 1.5W / cm². 2After irradiation in an Ar / N2 atmosphere, Raman spectroscopy was performed using a 532nm laser, but no R6G signal was observed. 100μL of 10... -7 The dye molecules of M were then dried in an oven at 60°C and Raman detected using a 532nm laser, and the signal of R6G was observed again.

[0101] Figure 12 a shows the morphology of molybdenum dioxide obtained under different amounts of molybdenum acetylacetone. Figure 12 b represents the change in the R6G Raman signal on the molybdenum dioxide substrate. When the amount of molybdenum acetylacetonate is increased to 0.3g, the molybdenum dioxide changes from flower-shaped nanospheres to dumbbell-shaped nanostructures. After photo-erasable processing, low-concentration detection can still be achieved. That is, when the amount of molybdenum acetylacetonate is changed within a certain range (the concentration of molybdenum acetylacetonate in ethanol aqueous solution is 2-6 mg / mL), it does not affect the detection effect of the molybdenum dioxide substrate.

[0102] Example 8

[0103] A method for removing adsorbed molecules from a substrate surface using a "photo-wipeable" technique, comprising the following steps: [The method involves] applying a 10⁻⁶ R₆G solution after detection... -4 The substrate of M was irradiated with an 808nm near-infrared laser at a power density of 0.75W / cm². 2 The R6G signal was monitored every 10 minutes. After approximately 30 minutes of laser irradiation, the probe molecule signal disappeared, indicating that the adsorbed molecules on the surface had been removed.

[0104] Figure 13 The laser power density is 0.75 W / cm². 2 The changes in the R6G Raman signal during the photo-erasable process were observed. After irradiation for 30–40 minutes, the R6G Raman signal disappeared, indicating that the dye molecules were decomposed on the substrate surface. When the laser power density decreased, the time required for dye decomposition increased. This is because as the laser power density decreased, the surface temperature of the molybdenum dioxide substrate also decreased, correspondingly extending the time required for dye decomposition. Therefore, by increasing the laser irradiation power density, the thermal decomposition and removal time of the detectable material on the molybdenum dioxide substrate surface can be significantly shortened.

[0105] Example 9

[0106] A method for removing adsorbed molecules from a substrate surface using a "photo-wipeable" technique, comprising the following steps: [The method involves] applying a 10⁻⁶ R₆G solution after detection... -4 The substrate of M was irradiated with an 808nm laser with a laser power density of 1W / cm². 2The probe was irradiated in an Ar / N2 atmosphere, and the R6G signal was observed every 5 minutes. After approximately 20 minutes of laser irradiation, the probe molecule signal disappeared, indicating that the adsorbed molecules on the surface had been removed.

[0107] Figure 14 The laser power density is 1W / cm² 2 The changes in the R6G Raman signal during the photo-erasable process were observed. After 20 minutes of irradiation, the R6G Raman signal disappeared, indicating that the dye molecules were decomposed on the substrate surface. The time required for dye decomposition decreased with increasing laser power density because the surface temperature of the molybdenum dioxide substrate also increased with the increase in laser power density, correspondingly shortening the time required for dye decomposition.

[0108] Example 10

[0109] A method for removing adsorbed molecules from a substrate surface using a "photo-wipeable" technique, comprising the following steps: [The method involves] applying a 10⁻⁶ R₆G solution after detection... -4 The substrate of M is placed under an 808nm laser with a laser power density of 2W / cm². 2 The probe was irradiated in an Ar / N2 atmosphere, and the R6G signal was observed every 2.5 minutes. The signal disappeared after approximately 5 minutes of laser irradiation, indicating that the adsorbed molecules on the surface had been removed.

[0110] Figure 15 The laser power density is 2W / cm² 2 The changes in the R6G Raman signal during the photo-erasable process were observed. After 5 minutes of irradiation, the R6G Raman signal disappeared, indicating that the dye molecules were decomposed on the substrate surface. As the laser power density increased, the time required for dye decomposition gradually decreased. This is because as the laser power density increased, the surface temperature of the molybdenum dioxide substrate also increased, correspondingly shortening the time required for dye decomposition.

[0111] Comparative Example 1

[0112] A method for preparing a metal oxide surface-enhanced Raman spectroscopy substrate includes the following steps: weighing 0.1 g of molybdenum acetylacetonate, grinding it in a mortar for 10–20 minutes, adding 50 mL of deionized water after grinding, stirring for 24–48 h at a speed of 500–600 r / min, transferring the dissolved precursor liquid to a 100 mL polytetrafluoroethylene reactor for hydrothermal reaction at a temperature of 180 °C for 12–16 h.

[0113] Weigh a certain amount of the above product and prepare a mother liquor with a concentration of 1-5 mg / mL using deionized water. Use a pipette to drop 10-50 μL of the dispersion onto the substrate, and then dry it in an oven at 60°C to obtain the substrate.

[0114] Use a pipette to add 100 μL of 10 to the prepared substrate. -7 The R6G dye molecules of M were then dried in an oven at 60°C. After drying, the samples were Raman detected using a 532nm laser, with a detection limit below 10. -7 M.

[0115] Figure 16 a is a scanning electron microscope image of the product. Figure 16 b represents the SERS detection performance of the product. When only deionized water is used as the solvent, the sample morphology changes significantly, exhibiting sheet-like nanoribbons with sizes in the micrometer range. In this case, the substrate detection performance is greatly affected by the morphology, and the detection limit is below 10. -7 M, the Raman enhancement effect is not as good as that of nanoflower-like or dumbbell-shaped nanospheres of molybdenum dioxide.

[0116] Comparative Example 2

[0117] A method for preparing a metal oxide surface-enhanced Raman spectroscopy substrate includes the following steps: weighing 0.1 g of molybdenum acetylacetonate, grinding it in a mortar for 10–20 minutes, adding 50 mL of anhydrous ethanol after grinding, stirring for 24–48 h at a speed of 500–600 r / min, transferring the dissolved precursor liquid to a 100 mL polytetrafluoroethylene reactor for hydrothermal reaction at a temperature of 180 °C for 12–16 h.

[0118] Weigh a certain amount of the above MoO2 and prepare a MoO2 stock solution with a concentration of 1-5 mg / mL using deionized water. Use a pipette to drop 10-50 μL of the MoO2 dispersion onto the substrate, and then dry it in an oven at 60°C to obtain the MoO2 substrate.

[0119] 100 μL of 10- ... -7 The R6G dye molecules of M were then dried in an oven at 60°C. After drying, the samples were Raman detected using a 532nm laser, with a detection limit below 10. -7 M.

[0120] Figure 17 a is a scanning electron microscope image of MoO2. Figure 17b represents the SERS detection effect of MoO2. When only anhydrous ethanol is used as the solvent, the sample morphology changes significantly, exhibiting nanospheres with a size of approximately 5–10 μm. In this case, the detection effect of the substrate is greatly affected by the morphology, and the detection limit is below 10 μm. -7 M, the enhancement effect is not as good as that of nano-flower-shaped or dumbbell-shaped nano-spherical molybdenum dioxide.

[0121] Comparative Example 3

[0122] A method for removing adsorbed molecules from a substrate surface using a "photo-wipeable" technique, comprising the following steps: [The method involves] applying a 10⁻⁶ R₆G solution after detection... -4 A molybdenum dioxide substrate of M was irradiated with an 808 nm laser at a power density of 0.5 W / cm². 2 The R6G signal was monitored every 10 minutes. The probe molecule signal remained intact after approximately 60 minutes of laser irradiation.

[0123] Figure 18 The laser power density is 0.5 W / cm². 2 The changes in the R6G Raman signal during the photo-erasable process were observed. After 60 minutes of irradiation, the R6G Raman signal weakened but did not completely disappear, indicating that the dye molecules only partially decomposed on the substrate surface. Figure 6 As shown in figure a, when the laser power density is 0.5 W / cm² 2 At that time, the surface temperature of the molybdenum dioxide substrate was below 200℃ (near the lowest temperature at which dye molecules decompose). Figure 6 c~ Figure 6 f), correspondingly, only a portion of the dye molecules on the surface of the molybdenum dioxide substrate decompose.

[0124] Comparative Example 4

[0125] A method for removing dye molecules using a light-erasable technique involves adding 10 μL of 10 μL of the solution to a blank substrate using a pipette. -4 M's R6G, RhB, MB, or CV dye molecules were then dried in an oven at 60°C. The concentration of the dried R6G, RhB, MB, or CV was 10. -4 The M substrate was irradiated with an 808nm near-infrared laser for 30 minutes, with a laser power density of 1.5W / cm². 2 When irradiated in an Ar / N2 atmosphere, the dye molecules do not decompose after irradiation.

[0126] Figure 19 a~ Figure 19 d represents the amount of 10 μL of solution added to the blank substrate before and after irradiation. -4A schematic diagram of the R6G / RhB / MB / CV dye molecule M shows no significant change before and after light irradiation, indicating that the R6G / RhB / MB / CV dye molecules do not decompose on a blank substrate. This is because the blank substrate has no thermal effect under laser irradiation, and the corresponding dye does not decompose. Only when molybdenum dioxide is present as a substrate does the temperature of the substrate surface rise under laser irradiation, causing the dye molecules to decompose.

[0127] The experimental results from Examples 1, 2, 6, 7, Comparative Example 1, and Comparative Example 2 show that only when the ratio of deionized water to ethanol is appropriate can nano-flower-like or dumbbell-shaped MoO2 nanospheres be obtained. The ratio of deionized water to ethanol and the amount of molybdenum acetylacetonate have a certain influence on the morphology of MoO2. Within a certain range, changing the ratio of deionized water to ethanol and the amount of molybdenum acetylacetonate has little effect on the detection and photo-erasable properties of the molybdenum dioxide substrate. However, when only deionized water or anhydrous ethanol is used as the solvent, the morphology of the prepared molybdenum dioxide sample changes significantly, the Raman enhancement effect of the prepared substrate is poor, and the detection sensitivity is lower than 10. -7 M.

[0128] The experimental results from Examples 2, 3, 4, 5, and Comparative Example 4 show that the detection limit of MoO2 for the four probe molecules is 10. -7 M, on a blank substrate, the detection limit of the probe molecules is less than 10. -7 Thermogravimetric analysis (TGA) of MoO2 in N2 showed that MoO2 did not decompose within a temperature range of 300–700 °C. Under different laser power densities, MoO2 could achieve temperature variations of 200–400 °C. Furthermore, MoO2 exhibited excellent chemical, thermal, and radiation stability, maintaining structural stability even after five cycles of testing. The four dye molecules R6G, RhB, MB, and CV began to decompose at approximately 200 °C. The substrate after testing was placed under an 808 nm near-infrared laser with a laser power density of 1.5 W / cm². 2 When irradiated in an Ar / N2 atmosphere, the probe molecule signal disappeared within 10 minutes, indicating that the adsorbed molecules on the surface had been removed and the substrate could be reused. However, on a blank substrate, the probe molecules remained after laser irradiation.

[0129] The experimental results from Examples 3, 4, 8, 9, 10, and Comparative Example 3 show that laser power density has a significant impact on degradation time. As the laser power density increases from 0.75 W / cm², the degradation time decreases. 2 Change to 2W / cm 2 The degradation time gradually shortens, but when the laser power density is below 0.75 W / cm², the degradation time becomes shorter. 2At this time, the surface temperature of the molybdenum dioxide substrate is lower than the minimum temperature at which dye molecules decompose, and the dye molecules on the substrate surface do not decompose completely.

Claims

1. A method for cleaning and reusing a Raman-enhancing substrate, comprising: Includes the following steps: The Raman-enhanced substrate is irradiated with a near-infrared laser or a xenon lamp until its surface temperature reaches 200-400°C, thereby decomposing and removing the compounds on the surface of the Raman-enhanced substrate, achieving the purpose of cleaning and reusing the surface of the Raman-enhanced substrate. The near-infrared laser wavelength is 808nm, the laser power density is 0.75-2W / cm 2 , and the irradiation time is 5-20min. The Raman-enhanced substrate is prepared by the following method, including the following steps: S1: Preparation of nano-MoO2 Molybdenum acetylacetonate was dissolved in an aqueous ethanol solution under stirring to form a precursor solution. The stirring speed was 500-600 r / min and the stirring time was 24-48 h. The precursor solution was subjected to a hydrothermal reaction, and the precipitate was collected by centrifugation after the reaction. Then, it was washed and dried to obtain nano-MoO2. S2: Fabrication of reusable Raman-enhanced substrates The nano-MoO2 obtained in step S1 is prepared into a MoO2 aqueous dispersion of 1-5 mg / mL. The MoO2 aqueous dispersion is dropped onto a substrate and dried to obtain a MoO2 substrate, which is the reusable Raman-enhanced substrate.

2. The method of claim 1, wherein the Raman-enhancing substrate is cleaned and reused. The Raman-enhanced substrate is placed in an Ar / N2 atmosphere or air for near-infrared laser irradiation or xenon lamp irradiation.

3. The method of claim 1, wherein the Raman-enhancing substrate is cleaned and reused. The ethanol content in the aqueous ethanol solution described in step S1 is 18% to 80% (v / v).

4. The method of claim 1, wherein the Raman-enhancing substrate is cleaned and reused. The hydrothermal reaction in step S1 is carried out at a temperature of 180–200°C for 12–16 hours.

5. The method of claim 1, wherein the Raman-enhancing substrate is cleaned and reused. The cleaning process described in step S1 includes the following steps: the precipitate collected by centrifugation is washed with anhydrous ethanol at 8000-15000 r / min for 5-10 min, and washed at least 3 times. Then, it is washed with water at 8000-15000 r / min for 10-15 min, and washed at least 3 times.

6. The method of claim 1, wherein the Raman-enhancing substrate is cleaned and reused. The substrate is a cover glass or a silicon wafer.

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