A micro-nano plastic detection method based on photothermal effect

Abstract

The application discloses a micro-nano plastic detection method based on a photothermal effect, and relates to the field of micro-nano optics. As one of the four new pollutants stipulated by the state, the micro-nano plastic currently urgently needs an efficient detection method. The application utilizes the resonance absorption of gold nanoparticles to 785nm laser, forms a strong photothermal trap in the solution through the photothermal effect, so that the micro-nano plastic can be efficiently enriched and captured. The enriched micro-nano plastic can be detected through the surface enhanced Raman spectroscopy (SERS) technology, so that the detection of low-concentration micro-nano plastic is realized. The application solves the problem that the existing means cannot effectively enrich and detect the micro-nano plastic in a large range, provides a new detection means for the monitoring of the micro-nano plastic in the water environment and the detection of the micro-nano plastic in the food industry, and has a wide application prospect.

Description

Technical Field

[0001] This invention is a method for enriching and detecting micro- and nano-plastic particles by manipulating the formation of a metal nanopile using the laser photothermal effect. This method can use lasers to enrich micro- and nano-plastic particles on a gold nanopile, thus providing a new means for the detection of micro- and nano-plastic particles in water. This invention has broad application prospects. Background Technology

[0002] Surface-enhanced Raman spectroscopy (SERS) is a non-destructive testing technique that uses photons as probes. It directly correlates with the vibrational spectra of molecular structures, providing a fingerprint-like authentication of substances. Even minute changes in a substance's structure are highly sensitively reflected in the Raman spectrum. Since the surface morphology of the substrate on which molecules are adsorbed is a crucial factor in whether the SERS effect occurs and the strength of the SERS signal, the molecular carrier is of paramount importance. Research on SERS substrates has always been a hot topic in this field. Metal nanoparticles can enhance the scattering and absorption of incident light at specific wavelengths, localizing the light field energy to the surface of the metal nanoparticles and increasing the surrounding electric field strength. This significantly improves the spectral signal intensity of the detected molecules in the surrounding area, leading to their wide application in the SERS field due to their unique optical properties.

[0003] Micro- and nano-plastics mainly refer to plastic particles with diameters at the nanometer and micrometer scales. These substances are primarily distributed in the ocean and biological tissues, posing a significant environmental hazard. Therefore, we need a method to detect micro- and nano-plastics in the environment. Currently, traditional methods for manipulating small particles mainly use optical tweezers, which are primarily designed for micrometer-scale particles. There is no effective method for nanometer-scale particles. Therefore, the method proposed in this invention, which utilizes the laser photothermal effect to enrich micro- and nano-plastics and combines it with SERS for detection, will be more practical. Summary of the Invention

[0004] To address the problems existing in current technologies, a method combining laser photothermal effect and SERS for the detection of micro- and nano-plastic particles is proposed. This method solves the current difficulties in large-scale manipulation of nanoplastics and the inability to detect low-abundance nanoplastics in water. Furthermore, compared to traditional SERS detection methods, this technique significantly reduces the size of detectable micro- and nano-plastics.

[0005] On one hand, a method for detecting nanoplastics based on photothermal effect is characterized by the following: the device includes a light manipulation-micro Raman system and a SERS-enhanced substrate module, which realizes light manipulation and SERS detection through the same optical path. The optical path includes a Raman detection module and a microscopic imaging module. The Raman detection module illuminates the SERS-enhanced substrate module (sample cell) with light emitted from a laser. The scattered light collected by the microscope objective is then introduced into the Raman detection module using a dichroic filter. The light of the image of the analyte collected by the microscope objective is then introduced into the microscopic imaging module using a dichroic filter, thereby realizing Raman spectral measurement and microscopic imaging of the analyte. The microscopic imaging module is used to record the motion state of the analyte particles caused by the photothermal effect. The SERS-enhanced substrate module consists of a stack of metal nanoparticles, a solution of analyte particles, and a microfluidic device. The power of the laser is 0-500mW.

[0006] Furthermore, the Raman detection system mainly includes: a laser, an incident optical fiber, a plano-convex lens system, a dichroic filter, a 60x microscope objective, a SERS-enhanced substrate enhancement module, an aperture, a plane mirror, a plano-convex lens, a detector, a collecting optical fiber, a spectrometer, and a computer. The laser emitted by the laser passes through the incident optical fiber and reaches the collimating plano-convex lens system. The outgoing light is reflected by the dichroic filter and then vertically focused by the microscope objective onto the SERS-enhanced substrate enhancement module. Inside the SERS-enhanced substrate module, the analyte particles are injected into a gold nanoparticle stack solution through a microfluidic device to achieve photothermal enrichment of microplastic particles and SERS detection. The excited Raman scattered beam passes through the microscope objective and the dichroic filter, and after passing through the focusing plano-convex lens, it is collected by the collecting optical fiber and transmitted to the spectrometer. After being dispersed by the spectrometer and converted into an electrical signal by the CCD, it is transmitted to the computer for display and storage, thus realizing the detection of the SERS signal.

[0007] Furthermore, the microscopic imaging system mainly includes: an LED array white light source, the light emitted by the LED array white light source passing sequentially through an aperture, a plane mirror, a microfluidic module, a 60x microscope objective, a dichroic filter, and a plano-convex lens before reaching the imaging CCD.

[0008] Furthermore, the numerical aperture of the collecting optical fiber is matched with the numerical aperture of the spectrometer slit.

[0009] Furthermore, the plano-convex lens and the dichroic filter are mounted in a cage-type right-angle adjustable reflective mounting base.

[0010] Furthermore, the microscopic imaging optical path is characterized by transmission illumination, and the aperture can effectively adjust the size of the illumination spot.

[0011] Furthermore, the average particle size of the metal nanosol is 50 nm.

[0012] Furthermore, it also includes a method for enriching and detecting microplastic particles based on photothermal effects. This method uses the laser photothermal effect to manipulate the formation of a strong photothermal trap of gold nanoparticles, thereby enriching and detecting micro- and nano-plastic particles.

[0013] Compared with the prior art, this technical solution has the following advantages:

[0014] (1) This method can manipulate micro- and nano-plastic particles in gold nanoparticle stacks over a wide range, and can gather a large number of particles in a short time. Compared with traditional methods, it has a significant enhancement effect on the SERS signal of the test object.

[0015] (2) This system uses only one laser beam to manipulate the formation of a gold nanopile with a strong photothermal trap to capture micro-nanoplastics and excite SERS signals.

[0016] Inventive Principles

[0017] This invention utilizes gold nanoparticles as a sol-gel to aggregate under laser control, forming a cluster of gold nanoparticles of a certain diameter as a strong photothermal trap. This strong photothermal trap allows for the enrichment of various micro / nano-plastics. Based on this principle, the aggregation of polystyrene particles with a diameter of 80 nm was achieved. Furthermore, since gold nanoparticles can serve as the substrate material for surface-enhanced Raman spectroscopy (SERS), and the laser used in the experiment can act as the excitation light for SERS, this invention not only achieves the aggregation of micro / nano-plastic particles but also yields the surface-enhanced Raman spectra of the aggregated nanoparticles. Ultimately, we have achieved the simultaneous enrichment and detection of nanoparticles using this invention. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a method for detecting micro / nano plastics based on the photothermal effect.

[0019] Figure 2 This is a schematic diagram of a microfluidic device for a method of detecting micro / nanoplastics based on the photothermal effect.

[0020] Figure 3 This image shows the results of enriching gold sol particles using a micro / nano plastic detection method based on the photothermal effect.

[0021] Figure 4 This is a graph showing the change in SERS intensity over time after enrichment of polystyrene microplastic particles, based on a photothermal effect-based micro / nanoplastics detection method.

[0022] Figure 5 This study investigates the effect of different concentrations of polystyrene particles on the SERS signal intensity in a micro / nano-plastic detection method based on the photothermal effect.

[0023] Figure 6This image shows the results of a long-term detection method for low-concentration micro-nano plastics based on the photothermal effect.

[0024] Figure 1 In the diagram, 1 is a 785nm semiconductor laser, 2 is a spectrometer, 3 is the laser incident fiber, 4 is the spectrometer incident fiber, 5 is the first spherical convex lens, 6 is the first plane mirror, 7 is the collimating lens, 8 is the beam expander lens group, 9 is the first dichroic filter, 10 is the second dichroic filter, 11 is the second plane mirror, 12 is the imaging CCD, 13 is the second spherical convex lens, 14 is the third dichroic filter, 15 is the 60x microscope objective, 16 is the sample cell composed of a glass slide, gasket, cover glass, etc., 17 is the third plane mirror, 18 is the aperture, 19 is the third spherical convex lens, and 20 is the LED array white light source.

[0025] Figure 2 The diagram in the middle shows a microfluidic device. The two channels on the left are the input terminals, into which gold sol particle solution and analyte particle solution are injected, respectively. The solutions are collected in the elliptical sample cell through the tubing for aggregation or SERS detection. Detailed Implementation Plan

[0026] The technical solution adopted in this invention includes the following steps:

[0027] (1) Nanoparticle enrichment and detection system

[0028] The system mainly includes a Raman detection optical path and a microscopic imaging optical path, which are coupled together by a dichroic filter. The microscopic imaging optical path is a vertical optical path, which plays an important role in enriching the particles to be tested using the photothermal effect in this invention.

[0029] The microscopic imaging optical path is a transmission illumination.

[0030] The power of the laser ranges from 0 to 500 mW.

[0031] The focal length of the microscope objective is 6mm to 8mm.

[0032] The size of the beam waist after the laser passes through the microscope objective is 10-20 μm.

[0033] (2) Before Raman spectroscopy acquisition, gold nanosol is injected into the sample cell through a channel of the microfluidic device.

[0034] In this process, gold nanoparticles are focused to a suitable size using a laser to form a strong photothermal trap. Then, a polystyrene particle solution is injected into the sample cell of the microfluidic device through another channel for enrichment or detection.

[0035] (3) Place the microfluidic sample cell on the three-dimensional adjustable stage and adjust the laser focus to focus on the bottom of the sample cell.

[0036] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0037] The technical solution of the present invention is achieved through the following means: a method for enrichment and detection of microplastic particles based on photothermal effect, comprising the following steps:

[0038] (1) Nanoparticle enrichment and detection system

[0039] like Figure 1 1-11 and 14-16 together form the Raman detection module. The excitation light travels from the incident fiber 3 to the collimating lens 7, and after passing through the beam expanding lens group 8, it reaches the second plane mirror 11. The reflected light is reflected by the second dichroic filter 10 and reaches the third dichroic filter 14. After being reflected by this element, it is incident on the 60x microscope objective 15. The light is magnified by the objective and finally focused into the sample cell of the sample stage 16, where it reacts with the mixture of the test solution and gold paste to excite the Raman spectrum. The light is collected by the 60x microscope objective 15 and reaches the third dichroic filter 14 again. After reflection, it passes through the second dichroic filter 10 and the first dichroic filter 9 in sequence, and is reflected by the first plane mirror 6. It is then focused by the first spherical convex lens 5 and input into the incident fiber 4 of the spectrometer, and finally detected by the spectrometer 2, realizing the detection and storage of the Raman signal.

[0040] like Figure 1 12 to 20 together form a microscopic imaging module. The microscopic imaging optical path is a transmission illumination. The microscopic imaging module includes: an LED array white light source. The light emitted by the LED array white light source passes sequentially through the third spherical convex lens 19, the aperture 18, the third plane mirror 17, the sample stage 16, the microscope objective, the third dichroic filter 14, and the second spherical convex lens 13 before finally reaching the imaging CCD.

[0041] This invention achieves the enrichment and detection of microplastic particles through photothermal effects using a single optical path. This optical path includes a Raman detection module and a microscopic imaging module. The Raman detection module illuminates the sample cell of the SERS-enhanced substrate module (i.e., the microfluidic device) with light emitted from a laser. The scattered light (generated by the laser illuminating the SERS-enhanced substrate module) collected by the microscope objective is reflected into the Raman detection module using a dichroic filter. The light of the image of the test object (the image of the particles illuminated by the LED array white light source) collected by the microscope objective is transmitted into the microscopic imaging module through a dichroic filter, thereby realizing Raman spectral measurement and microscopic imaging of the test object. The microscopic imaging module is used to record the motion state of the microplastic particles caused by the photothermal effect.

[0042] Specifically, to determine the response of the particle aggregates to the 785nm laser, a 785nm semiconductor laser was selected as the laser source.

[0043] The first plane mirror 6 and the second plane mirror 11 are installed in a cage-type right-angle adjustable reflective mounting base. The purpose is to ensure the coaxiality of the laser beam and to adjust the angle between the laser and the vertical direction so that it is perpendicularly incident into the sample cell. Only when the laser beam is perpendicularly incident on the test object from top to bottom will a significant SERS enhancement effect be formed.

[0044] The numerical aperture of the optical fiber 4 is matched with the numerical aperture of the spectrometer slit.

[0045] Among them, the aperture 18 can effectively adjust the size of the illumination spot.

[0046] (2) Preparation of gold nanosol and a solution of a certain concentration for testing

[0047] Preparation of gold nanoparticle sol: The gold sol was prepared according to the traditional Frens method, with a concentration of 5.8 × 10⁻⁶. -3 A mol / L trisodium citrate solution was used as a reducing agent and slowly added to a boiling 1% (v / v) chloroauric acid solution, with continuous stirring and heating for 1 hour. The particle size of the gold nanoparticles obtained from the reaction can be controlled by adjusting the temperature and the amount of trisodium citrate added. The preferred average particle size of the gold nanoparticles is 50 nm.

[0048] Preparation of the test solution: The test solution was selected as a polystyrene particle solution.

[0049] (3) SERS detection of the test solution

[0050] The detection process using polystyrene as an example: First, the gold nanoparticle sol prepared in the previous step is injected into the sample cell through a channel of a microfluidic device, as shown in the example. Figure 2 As shown. Maintaining the laser beam propagation direction perpendicular to the auxiliary substrate surface, the laser focus is concentrated inside the sample cell. Studies have found that a significant SERS enhancement effect is only achieved when the laser beam is incident perpendicularly to the analyte from top to bottom. After 10-15 minutes, gold nanoparticles aggregate near the laser focus, forming a strong optical thermal trap, as shown... Figure 3As shown. The diameter of the photothermal trap can be controlled by the laser irradiation time, typically 8-100 μm. A pre-prepared polystyrene particle solution of a certain concentration is injected into the sample cell through another channel of the microfluidic device. By observing the particle movement direction captured by the CCD, which is towards the photothermal trap formed in the previous step, it can be inferred that the polystyrene particles are enriched towards the center. At this time, we can collect the scattered light excited by the polystyrene particles through the Raman detection module, and the results are as follows. Figure 4 As shown in the figure. From the graph, we can see that as time changes, the 998cm corresponding to the polystyrene particles... -1 The intensity of the SERS peak gradually increases, indicating that polystyrene particles gradually aggregate towards the laser focus (gold nanoparticle stack) over time.

[0051] To investigate the changes in SERS signal intensity caused by the enrichment of polystyrene particles at different concentrations based on the photothermal effect, several groups of 80nm polystyrene solutions (blank control, 0.05 μg / ml, 0.1 μg / ml, 0.5 μg / ml, 1 μg / ml, and 5 μg / ml) were used as examples to explore the influence on SERS signal intensity. Figure 5 As shown, by continuously adding, enriching, and detecting a polystyrene solution in a microfluidic system, the minimum detectable concentration can be continuously reduced. Figure 6 As shown, after 100 minutes of controlled enrichment, the detection of 0.005 μg / ml of 80 nm polystyrene plastic can be achieved.

[0052] This invention provides a method for detecting micro- and nano-plastics based on the photothermal effect. Using this method, polystyrene particles larger than 30 nm can be manipulated, enriched, and detected over a wide range. Compared to existing technologies, this device and method can achieve the enrichment of nanoscale particles, and the detection signal is significantly improved compared to traditional methods. This provides a new means for detecting microplastics, a marine pollutant, and has broad application prospects.

Claims

1. A method for detecting micro / nanoplastics based on photothermal effect, which utilizes laser irradiation of gold nanosol for a certain period of time to form a strong photothermal trap, followed by the addition of micro / nanoplastics solution for particle enrichment and SERS signal detection.

2. The method for detecting micro / nano plastics based on photothermal effect as described in claim 1, characterized in that, By using laser focusing to form a gold nanoparticle sol stack as a strong light heat trap and Raman-enhanced substrate, large-scale enrichment and detection of micro- and nano-plastics can be achieved.

3. A method for detecting micro / nano plastics based on photothermal effect, the specific steps of which are as follows: Step 1: Prepare a nanosol, which includes gold nanoparticles; Step 2, measurement of the analyte: The gold nanosol prepared in Step 1 is injected into the sample cell through a microfluidic device. After deposition and aggregation using a laser, a gold nanoparticle stack is formed. The solution of micro-nanoplastics particles of the analyte is injected into the sample cell through another channel of the microfluidic device and placed in the detection system. The laser beam is focused on the gold nanoparticle stack, and the particles of the analyte will move rapidly to the vicinity of the gold nanoparticle stack under the photothermal effect of the laser beam. Step 3: The scattered light emitted by the micro-nano plastic particles is collected by a microscope objective and then collected by a spectrometer via a Raman optical path to achieve the detection of micro-nano plastics.

4. The method for detecting micro / nano plastics based on photothermal effect as described in claim 3, characterized in that, The nanosol in step one is a gold nanosol with an average particle size of 50 nm.

5. The method for detecting micro / nano plastics based on photothermal effect as described in claim 3, characterized in that, The microfluidic device includes two input channels on one side and one output channel on the other side. One input channel is injected with a solution of gold nanoparticles, and the other input channel is injected with a solution of analyte particles. The two input channels converge and pass through an elliptical sample cell, where the analyte aggregates and SERS is detected.

6. The method for detecting micro / nano plastics based on photothermal effect as described in claim 3, characterized in that, The same laser beam, with a wavelength of 785 nm, is used to detect and manipulate the aggregation of nanoparticles in SERS. The excitation light is focused onto the bottom of the sample cell surface through a microscope objective.

7. The method for detecting micro / nano plastics based on photothermal effect as described in claim 6, characterized in that, A laser beam irradiates the metal nanosol in the sample cell of the microfluidic device to form a high-intensity optical heat trap with a diameter of 8-100 μm. The high-intensity optical heat trap is used to enrich and detect micro- and nano-plastics.

8. The method for detecting micro / nano plastics based on photothermal effect as described in claim 3, characterized in that, Micro-nanoplastics are polystyrene particles larger than 10 nm.

9. The method for detecting micro / nano plastics based on photothermal effect as described in claim 3, characterized in that, By continuously adding polystyrene solution in a microfluidic system, the minimum detection concentration can be continuously reduced. After 100 minutes of controlled enrichment, the detection of 80 nm polystyrene plastic at a concentration of 0.005 μg / mL can be achieved.

10. The method for detecting micro / nano plastics based on photothermal effect as described in claim 7, characterized in that, The laser beam irradiates the metal nanosol for 10-15 minutes to form a laser-gold nanoparticle stack photothermal trap.

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