Double-beam Raman enhanced micro-plastic trace detection method based on bubble deposition principle and application of double-beam Raman enhanced micro-plastic trace detection method

Abstract

The invention relates to the field of nanoscience and nanotechnology, in particular to a double-beam Raman-enhanced trace detection method based on a shrinkage surface bubble deposition principle and application of the double-beam Raman-enhanced trace detection method based on the shrinkage surface bubble deposition principle. Laser heating is conducted, light bubbles are generated on the surface of the solution, laser heating is stopped when the bubbles are increased to a certain diameter, and in the bubble deposition process, precious metal nanoparticles and to-be-measured object particles are jointly deposited on the surface of the substrate; measuring an intrinsic Raman signal by using a double-beam confocal light path as a Raman detection light source; and comparing the measured intrinsic Raman signal with a standard Raman spectrum, and carrying out qualitative analysis on the to-be-measured object. According to the invention, Raman detection is carried out by simultaneously using two laser sources with different wavelengths as confocal light paths, so that the resolution and sensitivity of Raman spectrum are remarkably improved, fluorescence interference can be effectively reduced, and high-precision detection of particles to be detected is realized.

Description

Technical Field

[0001] The present invention relates to the field of nanoscience and nanotechnology, and particularly to a trace detection method and application of dual-beam Raman enhancement based on the principle of shrinkage surface bubble deposition. Background Art

[0002] Although the specific size ranges of "microplastics" and "nanoplastics" have not been clearly unified, microplastics are generally defined as particles with diameters between 1 and 5000 micrometers, while nanoplastics refer to tiny particles smaller than 1 micrometer. These plastic particles are widely present in the environment, and they have been detected in the open ocean, the Great Lakes, and rivers. Over time, plastic products gradually degrade into smaller particles in the natural environment, and this phenomenon has also been confirmed under laboratory weathering conditions. For example, a disposable polystyrene (PS) coffee cup lid can decompose into nanoplastic particles in a weathering chamber in just 2 months. Facing such a large and widespread plastic waste, we first need to observe and identify the plastic materials. Currently, the detection technology of nanoplastics mainly relies on pyrolysis coupled with gas chromatography-mass spectrometry (Pyr-GC / MS). This technology requires a large amount of concentration of lake water through steps such as ultrafiltration to detect trace nanoplastics. Although this method can achieve quantitative analysis, it cannot provide information on the size and morphology of nanoplastics. Raman spectroscopy combined with scanning electron microscopy (SEM) has been used to study the process of nanoplastics released from recycled polyvinyl chloride (PVC) powder, but these observations are not from natural water bodies. In addition, Raman spectroscopy technology has been used to capture and identify engineered plastic particles in lake water, but subsequent optical microscopy observations cannot provide sufficient resolution to reveal the morphological characteristics of nanoplastics. As previously studies have pointed out, the toxicity of microplastics and nanoplastics to organisms is closely related to their particle size and morphology, and the toxic effects are usually inversely proportional to the particle size. For example, under laboratory conditions, the negative impact of nanoscale polystyrene particles on the growth and reproduction of organisms is significantly higher than that of micron-scale particles. In addition, although no microplastics were found in the brains of fish observed in the laboratory, nanoparticles can penetrate the blood-brain barrier and accumulate in the brains of fish, resulting in behavioral disorders and oxidative DNA damage. Therefore, it is particularly important to achieve direct visualization of nanoplastics in the natural environment.

[0003] Before detection, it is necessary to collect water bodies first. It can be noted that microplastic pollution is more likely to appear in the following types of water quality: ① Polluted waters: Waters affected by industrial wastewater, urban sewage, and agricultural runoff are more likely to have microplastic pollution.

[0004] ② Waters with poor fluidity: In waters with poor fluidity, such as stagnant pools and lakes, microplastic particles are more likely to deposit and accumulate.

[0005] ③ Waters with higher temperatures: In waters with higher temperatures, plastics are more likely to decompose into microplastics. Summary of the Invention

[0006] One of the objectives of the present invention is to provide a dual-beam Raman-enhanced trace detection method for microplastics based on the principle of bubble deposition, which generates surface bubbles by optically heating plasmonic nanoparticles and enriches suspended microplastics to the surface by means of Marangoni flow, and uses a dual-beam Raman detection optical path to enhance the Raman signal.

[0007] Another objective of the present invention is to provide an application of the dual-beam Raman-enhanced trace detection method for microplastics based on the principle of bubble deposition.

[0008] The technical solution adopted by the present invention to achieve the first objective is as follows: A dual-beam Raman-enhanced trace detection method for microplastics based on the principle of bubble deposition, comprising the following steps: (1) Drop a solution containing analyte particles and noble metal nanoparticles on the surface of a substrate and irradiate the solution with a laser to generate photothermal bubbles on the surface of the solution. When the bubbles increase to a certain diameter, stop laser heating and let the bubbles gradually shrink until they completely disappear. During the bubble deposition process, the noble metal nanoparticles and the analyte particles are co-deposited on the surface of the substrate; (2) Use a dual-beam confocal optical path as the Raman detection light source to measure the intrinsic Raman signal; (3) Compare the intrinsic Raman signal measured in step (2) with the standard Raman spectrum for qualitative analysis of the analyte.

[0009] Preferably, in step (1), the noble metal nanoparticles are gold nanoparticles or silver nanoparticles, and the concentration of the noble metal nanoparticles in the solution is 0.01 - 0.05 mg / mL.

[0010] Preferably, in step (1), the solution also contains sodium citrate, and the concentration of sodium citrate is 0.01 - 0.03 mol / L.

[0011] Preferably, in step (1), the substrate is a silicon substrate or a glass substrate.

[0012] Preferably, in step (1), when the bubble diameter increases to 40 - 60 μm, stop laser heating.

[0013] Preferably, in step (1), the laser used is a pulsed laser with a wavelength of 520 - 540 nm, a repetition frequency of 20 kHz, and a current of 10200 - 10500 mA.

[0014] Preferably, in step (1), a charge-coupled device is used to observe the formation and deposition of bubbles.

[0015] Preferably, in step (2), a confocal optical path of pulsed lasers with wavelengths of 520 - 540 nm and 633 - 638 nm is used as the Raman detection light source to measure the intrinsic Raman signal.

[0016] Preferably, in step (2), the integration time for Raman detection is 120 - 480 s.

[0017] The present invention develops a dual - beam Raman - enhanced trace detection technology for microplastics based on the Marangoni effect of optothermal bubbles, which is used to detect various microplastic particles in water. The trace detection method of the present invention first utilizes the Marangoni flow induced by the shrinkage of optothermal bubbles, and then uses a dual - beam Raman detection optical path to enhance the Raman signal. Surface bubbles are generated by optically heating plasmonic nanoparticles, and the suspended analyte particles are enriched onto the surface by means of Marangoni flow, and then detected by a dual - beam Raman light source. During the surface - enhanced bubble deposition process, the analyte particles are co - deposited with noble metal nanoparticles, forming a surface - enhanced Raman spectroscopy (SERS) effect, which can be used for the direct chemical identification of analyte particles. The present invention utilizes the principle of shrinkage surface bubble deposition to mix noble metal nanoparticles with environmental water samples. Under laser excitation, the noble metal nanoparticles generate bubbles, and the suspended particles in water are greatly concentrated through thermo - fluid flow and deposited on the substrate for detection.

[0018] The technical solution adopted by the present invention to achieve the second object is: an application of the above - mentioned dual - beam Raman - enhanced microplastic trace detection method based on the bubble deposition principle, applying the trace detection method to the detection of microplastics in water.

[0019] Advantages of the present invention: The trace detection method of the present invention first utilizes the Marangoni flow induced by the shrinkage of optothermal bubbles, and then uses a dual - beam Raman detection optical path to enhance the Raman signal. Surface bubbles are generated by optically heating plasmonic nanoparticles, and the suspended analyte particles are enriched onto the surface by means of Marangoni flow, and then detected by a dual - beam Raman light source.

[0020] The dual - beam Raman measurement technology of the present invention uses two laser sources with different wavelengths simultaneously as a confocal optical path for Raman detection, significantly improving the resolution and sensitivity of the Raman spectrum, effectively reducing fluorescence interference, and achieving high - precision detection of analyte particles. Combining the principle of shrinkage surface bubble deposition, dual - beam Raman measurement can directly visualize and identify analyte particles in complex water samples, providing a powerful tool for environmental monitoring. Description of the Drawings

[0021] Figure 1 It is a schematic diagram of the mechanism of using the Marangoni flow induced by the shrinkage of optothermal bubbles; Figure 2Schematic diagram of the dual-beam Raman detection of the present invention; Figure 3 Structural schematic diagram of the dual-beam Raman detection of the present invention; Figure 4 Schematic diagram of the optothermal bubble under the microscope in the detection method of the present invention; Figure 5 Raman signal detection graph of Example 2; Figure 6 Raman signal detection graph of Example 3; Figure 7 Raman signal detection graph of Example 4; Figure 8 Raman signal detection graph of Example 5; Figure 9 Raman signal detection graph of Comparative Example 1; Figure 10 Raman signal detection graph of Comparative Example 2. Detailed implementation manners

[0022] The present invention has developed a dual-beam Raman enhanced trace detection technology for microplastics based on the Marangoni effect of optothermal bubbles, which is used to detect nanoplastics in various water bodies, especially in lakes.

[0023] The core of this technology lies in utilizing the Marangoni flow induced by the shrinkage of optothermal bubbles (see Figure 1 ), and then using a dual-beam Raman detection optical path to enhance the Raman signal. Surface bubbles are generated by optically heating plasmonic nanoparticles, and the suspended nanoplastics are enriched on the bubble surface by means of Marangoni flow. During the surface-enhanced bubble deposition process, the microplastic particles are co-deposited with the noble metal nanoparticles, forming a surface-enhanced Raman spectroscopy (SERS) effect, which can be used for the direct chemical identification of trace nanoplastics.

[0024] In the embodiments of the present invention, the principle of shrinkage surface bubble deposition is utilized to mix noble metal nanoparticles with environmental water samples. Under laser excitation, the noble metal nanoparticles generate bubbles (see Figure 4 ), and the suspended particles in the water are greatly concentrated through thermal fluid flow, and the suspended particles are deposited on the substrate surface for observation and characterization. In the embodiments of the present invention, a dual-beam Raman measurement technology is adopted to replace the traditional Raman spectroscopy measurement, significantly improving the identification ability of the chemical properties of nanoplastics. The dual-beam Raman measurement technology uses two different wavelength laser sources as a confocal optical path at the same time (see Figure 2), significantly improving the resolution and sensitivity of Raman spectroscopy. This technique can not only effectively reduce fluorescence interference, but also achieve high-precision detection of nanoplastics by optimizing the optical path and detector configuration. Combining the principle of shrinkage surface bubble deposition, dual-beam Raman measurement can directly visualize and identify nanoplastics in complex water samples, providing a powerful tool for environmental monitoring. This method has been successfully applied to water samples collected from different locations, providing an efficient and reliable solution for the detection and analysis of nanoplastics.

[0025] Embodiments of the present invention further explore the principles of the Marangoni effect and dual-beam Raman signal measurement. The Marangoni effect refers to the flow phenomenon caused by the liquid surface tension gradient. This effect usually occurs at the liquid interface. When the surface tension of the liquid changes due to temperature or concentration differences, a surface tension gradient will be generated, driving the liquid to flow. In the detection of microplastics, the Marangoni effect can be used to enhance the manipulation and separation of microplastics in microfluidic systems. For example, by introducing a temperature or chemical concentration gradient in the microfluidic channel, Marangoni convection can be utilized to drive the movement of microplastic particles, thereby achieving their enrichment or separation. (See Figure 1Raman spectroscopy is essentially inelastic scattering of light at the molecular level. The vibrational energy levels of a molecule are excited by incident light (with frequency ω_0), that is, from the ground state to the excited state (which is extremely unstable), and then return to a lower energy state by emitting scattered photons (with frequency ω_R). The difference between ω_0 and ω_R corresponds to the vibrational energy levels of the molecule. The frequency shift of the scattered light relative to the incident light (ω_0 ± ω_R) is represented by the frequency of the vibrational peaks shown in the Raman spectrum. Therefore, Raman scattering has great advantages in studying molecular vibrations and rotations. As a non-destructive, fast, and highly sensitive detection method for non-polar functional groups, Raman spectroscopy can perform accurate qualitative and quantitative analysis on microplastics mainly composed of non-polar covalent bonds. Through Raman spectroscopy, the chemical composition of microplastics can be identified, thereby understanding their sources and degradation processes. Different types of plastics, such as Polyethylene (PE), Polypropylene (PP), Polyethylene terephthalate (PET), etc., have unique spectral characteristics in the Raman spectrum. By comparing and analyzing these characteristic spectra, the pollution path of micro- and nano-plastics can be traced, and their environmental impacts can be evaluated. Usually, the content of microplastics in environmental media is low. For easy detection, the sample pretreatment process in the existing technology often includes concentration and enrichment, and technical means of enhancing Raman are used to increase the Raman signal response value of micro- and nano-plastics. Surface-enhanced Raman spectroscopy (SERS) is a commonly used method to enhance the Raman spectrum signal by concentrating electromagnetic energy through metal nanostructures. The enhancement principle is divided into electromagnetic enhancement and chemical enhancement. First, the incident light drives the conduction band electrons on the metal surface. When the light frequency matches the oscillation frequency of the electrons, local surface plasmon resonance (LSPR) will occur, resulting in the formation of an optical electric field on the surface of the metal nanostructure. This optical electric field is much stronger than the incident optical electric field, and can provide an enhancement factor (EF) of about 10^6~10^8. The core of the dual-beam Raman measurement system is to use two lasers with different wavelengths to excite the sample respectively to generate Raman scattered light. By optimizing the optical path and detector configuration, the system can simultaneously or separately collect Raman spectra at two wavelengths. This method can effectively reduce fluorescence interference and improve the intensity and resolution of Raman signals. The present invention adopts a symmetric Czerny-Turner optical device, and the optical path of each laser is independent. The Raman spectrum is introduced into a single linear charge-coupled device (CCD) detector through an optical fiber (see Figure 3). In the present invention, the laser wavelengths used are 532 nm and 638 nm, which cover different Raman shift ranges and can meet the detection requirements of various samples. By using a single high-sensitivity CCD detector and optimizing the optical path design and laser configuration, the Raman spectra at two wavelengths can be simultaneously collected.

[0026] Example 1 A dual-beam Raman-enhanced trace detection method for microplastics based on the principle of bubble deposition, comprising the following steps: The lake water sample is composed of 80 μl of Ag NPs suspension (60 nm, 0.05 mg / ml, dissolved in 2 mM sodium citrate. Adding sodium citrate makes the bubbles more stable and less likely to burst, and at the same time makes the imaging more obvious.). The solution is dropped on the surface of a silicon substrate (a glass substrate can also be used instead in other embodiments) and placed on a glass slide. A 20x objective lens with an aperture of 0.42 is used to direct a 532 nm pulsed laser at a repetition rate of 20 kHz and a current of 10250 mA towards the sample (the inventors have verified that good results can be obtained when the laser with a wavelength of 520 - 540, a repetition rate of 20 kHz, and a current of 10200 - 10500 mA is used), generating bubbles with a stable rate for easy control and observation. The laser irradiates for about 10 s to generate photothermal surface bubbles on the silicon substrate (as Figure 4 shown). After the bubbles are formed on the surface of the silicon substrate, the size of the bubbles is adjusted by controlling the turning on and off of the laser. After the surface bubbles are generated, before cutting off the laser, the growth of the bubbles is monitored using a charge-coupled device (CCD camera), allowing the bubble diameter to increase to about 40 μm (the inventors have verified that good results can be obtained when the laser heating is stopped when the bubble diameter increases to 40 - 60 μm). Then the laser is stopped, and the bubbles start to shrink. After the bubbles shrink and finally disappear, the suspended particles are deposited on the silicon substrate, and Raman mapping of the deposited sample is performed using a dual-beam confocal optical path.

[0027] Due to the co-deposition of microplastics and silver nanoparticles, the SERS effect is activated. Due to the light absorption of the metal nanostructure on the surface, the spatially localized laser beam can heat the focal region, thereby generating steam bubbles. The temperature gradient around the bubbles leads to Marangoni flow. This flow near the bubbles attracts the NPs in the suspension to the vapor-liquid interface to capture the NPs. The flow finally pushes the NPs towards the three-phase contact line (TPCL), thereby depositing on the surface and finally accumulating into a high-density aggregation point (as Figure 1 shown).

[0028] During the deposition of surface bubbles, silver nanoparticles co-deposit with microplastic particles, triggering the surface-enhanced Raman scattering (SERS) effect, enhancing the Raman signal by 6-8 orders of magnitude, and enabling the identification of the chemical composition of trace amounts of nanoplastics. Without the co-deposition of silver nanoparticles, the Raman signal of nanoplastics would be difficult to detect. Therefore, silver nanoparticles play a dual role in this process: on the one hand, they contribute to the formation of plasmonic surface bubbles, enabling the collection, concentration, and deposition of nanoplastics; on the other hand, they facilitate the realization of the surface-enhanced Raman scattering (SERS) effect.

[0029] During the Raman mapping process, the dual-beam Raman detection technique significantly improves the resolution and sensitivity of Raman spectra by using two laser sources with different wavelengths. As Figure 2 shown, the specific settings are as follows: Dual-channel optical path design: An M-type Czerny-Turner optical path with symmetric distribution is adopted, and the two channels correspond to 638 nm and 532 nm excitations respectively. This design allows for the simultaneous acquisition of two Raman spectra, covering different Raman shift ranges at the same integration time. The shorter the wavelength, the wider the Raman shift range: When using a laser with a shorter wavelength (such as 532 nm) for excitation, the coverage range of the Raman spectrum is usually wider, capable of detecting higher wavenumber Raman shifts. For example, the Raman spectrum excited by a 532 nm laser can cover a range from a few hundred to several thousand wavenumbers. As Figure 3 shown, the longer the wavelength, the narrower the Raman shift range: When using a laser with a longer wavelength (such as 785 nm or 638 nm) for excitation, the coverage range of the Raman spectrum is relatively narrow, but it can reduce fluorescence interference. In the actual process, the Raman signal peaks of microplastics are dispersed, and the Raman shifts corresponding to different peaks vary greatly. It is difficult to achieve the purpose of detecting and identifying microplastic components using a single beam. Dual-beam and single-beam optical elements: Collimating mirror and focusing mirror: The focal length of the collimating mirror in the ultraviolet channel is 110 mm, and the focal length in the visible light channel is 51 mm. Grating: A holographic grating with 2400 lines / mm is used in the ultraviolet channel, and a grating with 1200 lines / mm is used in the visible light channel. Slit: The slit width of both channels is 16 μm to balance the resolution and light throughput. Detector: A highly sensitive back-illuminated CCD detector with a size of 2048×64 pixels and a pixel size of 14 μm is used. The dual-pixel merging technique further improves the sensitivity and signal-to-noise ratio of the detector.

[0030] Example 2 A dual-beam Raman enhanced trace detection method for microplastics based on the principle of bubble deposition, comprising the following steps: Prepare a polystyrene solution with a concentration of 0.1 mol / L. After diluting it 1000 times, take 50 μl and mix it evenly with 80 μl of Ag NPs suspension (60 nm, 0.05 mg / ml, dissolved in 2 mM sodium citrate). Drop the mixed solution onto the surface of a silicon substrate. Shoot a 532 nm pulsed laser at the sample with a repetition frequency of 20 kHz and a current of 10250 mA. Laser irradiate for about 10 s to generate photothermal surface bubbles on the silicon substrate. Use a charge-coupled device (CCD camera) to monitor the growth of the bubbles. Let the bubble diameter grow to about 40 μm, then stop laser heating, and then the bubbles start to shrink. After the bubbles shrink and finally disappear, the suspended particles are deposited on the silicon substrate, and Raman mapping of the deposited sample is performed with a dual-beam confocal optical path.

[0031] As Figure 5 shown is the Raman signal detection graph obtained in this embodiment. It can be seen from the graph that characteristic peaks appear at 1000 cm -1 and 1600 cm -1 . By comparing with the standard Raman spectrum, it is confirmed that these two characteristic peaks are both characteristic peaks of polystyrene, verifying the effectiveness of the method of the present invention.

[0032] Example 3 A dual-beam Raman enhanced trace detection method for microplastics based on the principle of bubble deposition, comprising the following steps: The lake water sample is composed of 80 μl of Ag NPs suspension (60 nm, 0.05 mg / ml, dissolved in 2 mM sodium citrate) and 50 μl of collected Lake A water. Drop the sample onto the surface of a silicon substrate. Shoot a 532 nm pulsed laser at the sample with a repetition frequency of 20 kHz and a current of 10250 mA. Laser irradiate for about 10 s to generate photothermal surface bubbles on the silicon substrate. Use a charge-coupled device (CCD camera) to monitor the growth of the bubbles. Let the bubble diameter grow to about 40 μm, then stop laser heating, and then the bubbles start to shrink. After the bubbles shrink and finally disappear, the suspended particles are deposited on the silicon substrate, and Raman mapping of the deposited sample is performed with a dual-beam confocal optical path.

[0033] As Figure 6 shown is the Raman signal detection graph obtained in this embodiment. It can be seen from the graph that characteristic peaks appear at 720 cm -1 , 800 cm -1 , 910 cm -1 , 1120 cm -1 and 1180 cm -1 . By comparing with the standard Raman spectrum, it can be seen that the characteristic peak at 720 cm -1 corresponds to PE, 800 cm-1 and 910 cm -1 and 1180 cm -1 The characteristic peaks at correspond to PP, and the characteristic peak at 1120 cm -1 corresponds to PET.

[0034] Example 4 The difference between this example and Example 3 is that silver nanoparticles are replaced by gold nanoparticles, and other schemes are the same.

[0035] As Figure 7 shown is the Raman signal detection diagram obtained in this example. It can be seen from the figure that at 1118 cm -1 and 1124 cm -1 1150 cm -1 nearby, characteristic peaks all appear. By comparing with the standard Raman spectrum, these three characteristic peaks correspond to PET. Compared with Figure 6 , no relevant characteristic peaks of PP and PE appear, indicating that when using gold nanoparticles for co-deposition, it is not as easy to excite photothermal signals as when using silver nanoparticles for co-deposition, and the Raman signal is more obvious.

[0036] Example 5 The difference between this example and Example 3 is that the lake water sample is Lake B water sample, and other schemes are the same.

[0037] As Figure 8 shown is the Raman signal detection diagram obtained in this example. It can be seen from the figure that at 725cm -1 , 805cm -1 , 912 cm -1 , 1118 cm -1 and 1183 cm -1 the characteristic peaks all appear. By comparing with the standard Raman spectrum, it can be seen that the characteristic peak at 725cm -1 corresponds to PE, and the characteristic peaks at 805 cm -1 , 912 cm -1 and 1183 cm -1 correspond to PP, and the characteristic peak at 1118 cm -1 corresponds to PET.

[0038] Comparative Example 1 The difference between this comparative example and Example 2 is that a single-beam light source with a laser wavelength of 532nm is used for Raman detection, and other schemes are the same.

[0039] Figure 9 As shown is the Raman signal detection diagram obtained in this comparative example. It can be seen from the figure that at 1000cm -1 and 1600 cm-1 No effective characteristic peaks appeared in any of the cases, further verifying that the use of a double-beam focusing optical path for Raman detection in the present invention improves the resolution and sensitivity of the Raman spectrum, can effectively reduce fluorescence interference, and enables high-precision detection of the particles to be measured.

[0040] Comparative Example 2 The difference between this comparative example and Comparative Example 1 is that a single-beam light source with a laser wavelength of 638 is used for Raman detection, and other schemes are the same.

[0041] Figure 10 The Raman signal detection graph obtained from this comparative example is shown. It can be seen from the graph that no effective characteristic peaks appear, proving that a single-beam light source with a wavelength of 638 nm alone cannot effectively perform Raman detection in the solution system of the present invention.

[0042] The trace detection method of the present application can provide information for qualitatively analyzing microplastics at low concentrations and is expected to become a powerful tool to supplement existing quantitative techniques (such as pyrolysis gas chromatography-mass spectrometry, Pyr-GC / MS) to address these challenges. In order to achieve quantitative analysis of the shrinkage surface bubble deposition principle, more fundamental hydrodynamic studies on its deposition process are needed to establish the relationship between the deposited particle density and the concentration of suspended particles in the solution.

[0043] The present invention has developed a rapid and convenient environmental nanoplastics detection technology, which complements existing GC / MS, Fourier transform infrared spectroscopy (FT-IR), and Raman spectroscopy technologies. Directly detecting the types of nanoplastics particles in non-concentrated water samples is crucial for environmental and toxicological research.

[0044] The value of the shrinkage surface bubble deposition principle lies in its ability to effectively concentrate nanoplastics in water, thereby reducing the required water sample volume and significantly improving the sensitivity of downstream analysis. Combining our unique integrated optical path design and state-of-the-art analytical tools, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and double-beam Raman measurement technology, enables efficient detection and characterization of nanoplastics particles in the environment. The double-beam Raman measurement technology can simultaneously detect Raman spectra in different wavenumber ranges by combining two lasers with different wavelengths (532 nm and 638 nm). This technology not only expands the detection range and resolution of the Raman spectrum but also reduces fluorescence interference, making the chemical identification of nanoplastics more accurate. For example, ultraviolet Raman spectroscopy features high scattering intensity and low fluorescence interference, while visible light Raman spectroscopy is good at detecting low wavenumbers with high resolution. Through this double-beam Raman measurement technology, we can more comprehensively analyze the chemical composition of nanoplastics, thus providing more powerful support for environmental monitoring and toxicological research.

[0045] The present invention helps to show that nanoplastics are widely present in water bodies such as lakes, and can be identified and characterized by advanced methods such as the principle of shrinkage surface bubble deposition and dual-beam Raman measurement. The combination of these technologies not only improves the efficiency and accuracy of nanoplastics detection, but also provides new ideas and methods for solving the problem of nanoplastics pollution.

[0046] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A dual-beam Raman enhanced trace detection method for microplastics based on the principle of bubble deposition, characterized in that, It includes the following steps: (1) Drop a solution containing analyte particles and noble metal nanoparticles on the surface of a substrate and irradiate the solution with a laser to generate a photothermal bubble on the surface of the solution. When the bubble grows to a certain diameter, stop the laser heating and let the bubble gradually shrink until it completely disappears. During the bubble deposition process, the noble metal nanoparticles and the analyte particles are co-deposited on the surface of the substrate; (2) Use a double-beam confocal optical path as a Raman detection light source to measure the intrinsic Raman signal; (3) Compare the intrinsic Raman signal measured in step (2) with the standard Raman spectrum for qualitative analysis of the analyte.

2. The method for trace detection of microplastics with dual-beam Raman enhancement based on the principle of bubble deposition according to claim 1, characterized in that In step (1), the noble metal nanoparticles are gold nanoparticles or silver nanoparticles, and the concentration of the noble metal nanoparticles in the solution is 0.01 - 0.05 mg / mL.

3. The dual-beam Raman enhanced trace detection method for microplastics based on the principle of bubble deposition according to claim 1, characterized in that In step (1), the solution also contains sodium citrate, and the concentration of sodium citrate is 0.01 - 0.03 mol / L.

4. The trace detection method for microplastics with dual-beam Raman enhancement based on the principle of bubble deposition according to claim 1, wherein, In step (1), the substrate is a silicon substrate or a glass substrate.

5. The method for trace detection of microplastics with dual-beam Raman enhancement based on the principle of bubble deposition according to claim 1, characterized in that, In step (1), when the bubble diameter increases to 40 - 60 μm, stop the laser heating.

6. The dual-beam Raman enhanced trace detection method for microplastics based on the principle of bubble deposition according to claim 1, wherein, In step (1), the laser used is a pulsed laser with a wavelength of 520 - 540 nm, a repetition frequency of 20 kHz, and a current of 10200 - 10500 mA.

7. The method for trace detection of microplastics by dual-beam Raman enhancement based on the principle of bubble deposition according to claim 1, characterized in that, In step (1), a charge-coupled device is used to observe the formation and deposition of the bubble.

8. The method for trace detection of microplastics with dual-beam Raman enhancement based on the principle of bubble deposition according to claim 1, wherein In step (2), a confocal optical path of a pulsed laser with a wavelength of 520 - 540 nm and a pulsed laser with a wavelength of 633 - 638 nm is used as a Raman detection light source to measure the intrinsic Raman signal.

9. The method for trace detection of microplastics by dual-beam Raman enhancement based on the principle of bubble deposition according to claim 1, wherein In step (2), the integration time for Raman detection is 120 - 480 s.

10. Use of the method for trace detection of microplastics with dual-beam Raman enhancement based on the principle of bubble deposition according to any one of claims 1-9, characterized in that: Apply the trace detection method to the trace detection of microplastics in water.

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