A visual method for detecting nanoplastics in water

Abstract

The present invention discloses a method for visually detecting nanoplastics in water. The method comprises the following steps: preparing Au-MUA, preparing NPs test solution, quantitatively detecting NPs by Au-MUA, detecting NPs of different particle sizes, and calculating the concentration of NPs. The present invention provides a method for visually detecting nanoplastics in water, synthesizing Au-MUA recognition units in a convenient way, which has the characteristics of both NPs quantitative analysis and particle size screening, is easy to operate, has low cost, and can be completed within tens of seconds. It can realize on-site visual detection of emerging pollutants NPs in the environment, and is a new method and technology urgently needed for environmental pollutant monitoring, ecological risk assessment and governance.

Description

Technical Field

[0001] The invention belongs to the technical field of water pollution, and in particular relates to a method for visually detecting nano plastics in water. Background Art

[0002] Plastic products are widely used around the world. Studies have shown that about 10% of the annual production of plastics is abandoned into the environment. These discarded plastics release countless micro / nanoplastics (M / NPs) through physical, chemical and biological decomposition in water or soil. This type of new pollutant exists in the environment for a long time and is easy to enrich organic / inorganic pollutants, causing serious harm to the ecosystem. In addition, it is transmitted through the food chain and eventually transferred to the human body indirectly, threatening human health. In particular, nano-sized plastic particles (<1μm, NPs) are more harmful to the environment and humans than microplastics (1μm-5mm, MPs) due to their small size, high bioavailability and ability to penetrate cell membranes. At present, the commonly used NPs analysis techniques are mainly mass spectrometry and vibrational spectroscopy. These analysis techniques play their respective advantages in detecting NPs and provide a reliable basis for environmental monitoring, ecological risk assessment and other projects. However, the above analytical techniques cannot overcome the shortcomings of dependence on large or expensive instruments, complex operation, time-consuming sample pretreatment and difficulty in on-site detection. This is inconsistent with the current situation that NPs are widely distributed in the global environment and there is an urgent need for efficient, convenient and accurate on-site monitoring or detection of NPs analytical techniques.

[0003] The present invention uses gold nanoparticles (Au-MUA) functionalized with mercaptoundecanoic acid (MUA) as the detection unit, and for the first time develops a new method for visual detection of NPs that inhibits pH-induced Au-MUA aggregation. The experimental results reveal that nanosized NPs (≤100nm) combine with the MUA alkyl chain on the surface of Au NPs by hydrophilic and hydrophobic interactions, overcoming the Au-MUA aggregation phenomenon induced by the reduction of electrostatic repulsion after the protonation of the MUA terminal carboxyl group at low pH, and maintaining the original wine red color. This method combines the characteristics of NPs quantitative analysis and particle size screening, is easy to operate, low cost, and the detection can be completed within tens of seconds, which can realize on-site visual monitoring of emerging and widely distributed NPs pollutants in the environment. Summary of the invention

[0004] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0005] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0006] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for visually detecting nanoplastics in water.

[0007] In order to solve the above technical problems, the present invention provides the following technical solution: a method for visually detecting nanoplastics in water, which comprises the following steps:

[0008] Preparation of Au-MUA: MUA ethanol solution was added to Au NPs and allowed to stand overnight in the dark at room temperature to obtain MUA-modified Au NPs, which were labeled as Au-MUA;

[0009] Au-MUA quantitative detection of NPs: Take Au-MUA and centrifuge it, collect the precipitate, add a mixed solution of ethanol and water, add Au-MUA and NPs, mix well and let stand, adjust the pH and observe the solution color or measure the UV-Vis absorption spectrum;

[0010] Prepare NPs test solution: dilute NPs stock solution with Au-MUA;

[0011] Quantitative detection: The mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, diluted with water in a 1:1 ratio, placed in UV-Vis to record the absorption spectrum, and the maximum absorption peaks of NPs with different concentrations were compared to quantitatively analyze the NPs;

[0012] Detection of NPs of different particle sizes: The mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, diluted with water, placed in UV-Vis to record the absorption spectrum, and the maximum absorption peaks of NPs of different particle sizes were compared to analyze the particle size of NPs;

[0013] Calculate the concentration of NPs: transfer the mixed solution of Au-MUA, NPs and HCl into a quartz cuvette, dilute with water, place it in UV-Vis to record the absorption spectrum, repeat each sample 5 times and take the average value to quantify the concentration of NPs by measuring the difference between the absorption peak and the absorption peak of the blank sample.

[0014] As a preferred embodiment of the method for visually detecting nanoplastics in water according to the present invention, Au-MUA is used to quantitatively detect NPs, and after the addition of Au-MUA, a pH adjustment step is also included, wherein the pH adjuster is HCl.

[0015] As a preferred embodiment of the method for visually detecting nanoplastics in water bodies described in the present invention, Au-MUA quantitatively detects NPs and also includes Au-MUA concentration adjustment, wherein the Au-MUA concentration is adjusted to concentrate the Au-MUA obtained in the preparation of Au-MUA by one time.

[0016] As a preferred embodiment of the method for visually detecting nanoplastics in water according to the present invention, the amount of HCl used in the pH adjustment step is such that the pH of the solution after adding HCl is ≤4.

[0017] As a preferred embodiment of the method for visually detecting nanoplastics in water according to the present invention, the concentration of HCl in the NPs quantitatively detected by Au-MUA is 5 to 100 mM.

[0018] As a preferred embodiment of the method for visually detecting nanoplastics in water according to the present invention, wherein: Au-MUA is used to quantitatively detect NPs, and the concentration of Au-MUA is 1 times that of the product obtained by preparing Au-MUA.

[0019] As a preferred embodiment of the method for visually detecting nanoplastics in water according to the present invention, the concentration of HCl is 100 mM.

[0020] As a preferred embodiment of the method for visually detecting nanoplastics in water according to the present invention, Au-MUA is used to quantitatively detect NPs, and the volume ratio of Au-MUA:HCl is 100-300 μL: 1-4 μL.

[0021] As a preferred embodiment of the method for visually detecting nanoplastics in water according to the present invention, Au-MUA is used to quantitatively detect NPs, and the volume ratio is Au-MUA:HCl=100 μL:1 μL.

[0022] As a preferred embodiment of the method for visually detecting nanoplastics in water according to the present invention, wherein: Au-MUA quantitatively detects NPs, and the pH after adding HCl is 2.81.

[0023] Beneficial effects of the invention: The invention provides a method for visually detecting nanoplastics in water bodies, synthesizes Au-MUA recognition units in a convenient way, has the characteristics of NPs quantitative analysis and particle size screening, is easy to operate, low cost, and detection can be completed within tens of seconds. It can realize on-site visual detection of emerging pollutants NPs in the environment, and is a new method and technology urgently needed for environmental pollutant monitoring, ecological risk assessment and governance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0025] Figure 1 A schematic diagram of a visual detection method of nanoplastics in water provided by an embodiment of the present invention;

[0026] Figure 2 The UV-Vis spectra of Au NPs before and after MUA functionalization in the embodiment of the present invention (a), and the transmission electron microscopy image and particle size distribution diagram of Au-MUA (b);

[0027] Figure 3 UV-Vis spectra of various ingredients in the embodiments of the present invention;

[0028] In the figure, a is the UV-Vis spectrum of the reversibility of Au-MUA under acidic and alkaline conditions in Example 1, b is the UV-Vis spectrum of the sensing performance of Au-MUA to 50nm NPs, c is the UV-Vis spectrum of the sensing performance of Au NPs without MUA to 50nm NPs, and d is the UV-Vis spectrum of the sensing performance of Au-MUA to NPs of different particle sizes;

[0029] Figure 4 UV-Vis spectra under different solvent conditions in Example 1;

[0030] In the figure, a is the UV-Vis spectra of the sensing performance of Au-MUA to 50nm NPs in a mixed solution of ethanol and water with 10% and 0% ethanol (ultrapure water) content; b and c are the UV-Vis spectra of the sensing performance of Au-MUA to 50nm and 500nm NPs in a mixed solution of ethanol and water with different ethanol contents; d is a comparison of the sensing performance of Au-MUA to 50nm NPs dispersed in different organic solvents and water;

[0031] Figure 5 Schematic diagram of the Au-MUA inhibition phenomenon of different concentrations of NPs on pH-induced aggregation in Example 1;

[0032] In the figure, a is a photo of Au-MUA under different concentrations of NPs; b is the UV-Vis spectrum of Au-MUA under different concentrations of NPs; c is the linear relationship between the different concentrations of NPs and the shift value of the absorption peak of the UV-Vis spectrum;

[0033] Figure 6UV-Vis spectra of 50 nm NPs detected by Au-MUA with different volumes in Examples 2 and 3;

[0034] Figure 7 The relationship between the UV-Vis spectrum absorption peak shift values ​​of Au-MUA and HCl of different concentrations in Examples 4, 5 and 6. DETAILED DESCRIPTION

[0035] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0036] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0037] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0038] Example 1

[0039] A method for visually detecting nanoplastics in water comprises the following steps:

[0040] (1) Preparation of Au-MUA: 10 μL of MUA ethanol solution was added to 10 mL of 15 nm Au NPs to make the final MUA concentration 10 μM. The mixture was left to stand overnight in the dark at room temperature to obtain MUA-modified Au NPs, which were labeled as Au-MUA.

[0041] (2) Quantitative detection of NPs by Au-MUA: Take 1 mL of functionalized Au-MUA and centrifuge it, collect the precipitate, and add 0.5 mL of a mixed solution of ethanol and water with a concentration of 20% to concentrate the Au-MUA by about 1 time. During the detection, take 200 μL of concentrated Au-MUA, add 10 μL of NPs stock solution of different concentrations and shake evenly, then add 2 μL of 100 mM HCl to adjust the pH (the resulting pH is 2.81), and quickly mix the above mixed solution and let it stand for 30 seconds. The results can be obtained by observing the color of the solution or measuring the absorption spectrum with UV-Vis.

[0042] (3) Au-MUA detection of NPs of different particle sizes: Take 1mL of functionalized Au-MUA and centrifuge it, collect the precipitate, add 0.5mL of a mixed solution of ethanol and water with a concentration of 20% ethanol, and concentrate Au-MUA by 1 times. During the detection, take 200μL of treated Au-MUA, add 10μL of NPs of different particle sizes and shake evenly, then add 2μL of 100mM HCl to adjust the pH, and quickly mix the above mixed solution and let it stand for 30s. The results can be obtained by observing the color of the solution or measuring the absorption spectrum with UV-Vis.

[0043] (4) Preparation of NPs test solution: dilute the NPs stock solution with Au-MUA solution in a 1.5 mL centrifuge tube;

[0044] (5) Quantitative detection of NPs: The mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, ultrapure water was added at a ratio of 1:1, and the absorption spectrum was recorded by UV-Vis. The maximum absorption peaks of NPs with different concentrations were compared to quantitatively analyze the NPs.

[0045] (6) Detection of NPs of different particle sizes: The mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, ultrapure water was added at a ratio of 1:1, and the absorption spectrum was recorded using UV-Vis. The maximum absorption peaks of NPs of different particle sizes were compared to estimate the particle size of NPs.

[0046] (7) Calculation of NPs concentration: Under optimal conditions, the mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, ultrapure water was added at a ratio of 1:1, and the absorption spectrum was recorded by UV-Vis. Each sample was repeated 5 times and the average value was taken to quantify the concentration of NPs by measuring the difference between the absorption peak and the absorption peak of the blank sample.

[0047] Example 2

[0048] A method for visually detecting nanoplastics in water comprises the following steps:

[0049] (1) Preparation of Au-MUA: 10 μL of MUA ethanol solution was added to 10 mL of 15 nm Au NPs to make the final MUA concentration 10 μM. The mixture was left to stand overnight in the dark at room temperature to obtain MUA-modified Au NPs, which were labeled as Au-MUA.

[0050] (2) Quantitative detection of NPs by Au-MUA: Take 1 mL of functionalized Au-MUA and centrifuge it, collect the precipitate, and add 0.5 mL of a mixed solution of ethanol and water with a concentration of 20% to concentrate the Au-MUA by about 1 time. During the detection, take 100 μL of concentrated Au-MUA, add 10 μL of NPs stock solution of different concentrations and shake evenly, then add 1 μL of 100 mM HCl to adjust the pH (the resulting pH is 2.81), and quickly mix the above mixed solution and let it stand for 30 seconds. The results can be obtained by observing the color of the solution or measuring the absorption spectrum with UV-Vis.

[0051] (3) Au-MUA detection of NPs of different particle sizes: Take 1mL of functionalized Au-MUA and centrifuge it, collect the precipitate, add 0.5mL of a mixed solution of ethanol and water with a concentration of 20% ethanol, and concentrate Au-MUA by 1 times. During the detection, take 100μL of treated Au-MUA, add 10μL of NPs of different particle sizes and shake evenly, then add 1μL of 100mM HCl to adjust the pH, and quickly mix the above mixed solution and let it stand for 30s. The results can be obtained by observing the color of the solution or measuring the absorption spectrum with UV-Vis.

[0052] (4) Preparation of NPs test solution: dilute the NPs stock solution with Au-MUA solution in a 1.5 mL centrifuge tube;

[0053] (5) Quantitative detection of NPs: The mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, ultrapure water was added at a ratio of 1:1, and the absorption spectrum was recorded by UV-Vis. The maximum absorption peaks of NPs with different concentrations were compared to quantitatively analyze the NPs.

[0054] (6) Detection of NPs of different particle sizes: The mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, ultrapure water was added at a ratio of 1:1, and the absorption spectrum was recorded using UV-Vis. The maximum absorption peaks of NPs of different particle sizes were compared to estimate the particle size of NPs.

[0055] (7) Calculation of NPs concentration: Under optimal conditions, the mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, ultrapure water was added at a ratio of 1:1, and the absorption spectrum was recorded by UV-Vis. Each sample was repeated 5 times and the average value was taken to quantify the concentration of NPs by measuring the difference between the absorption peak and the absorption peak of the blank sample.

[0056] Example 3

[0057] A method for visually detecting nanoplastics in water comprises the following steps:

[0058] (1) Preparation of Au-MUA: 10 μL of MUA ethanol solution was added to 10 mL of 15 nm Au NPs to make the final MUA concentration 10 μM. The mixture was left to stand overnight in the dark at room temperature to obtain MUA-modified Au NPs, which were labeled as Au-MUA.

[0059] (2) Quantitative detection of NPs by Au-MUA: Take 1 mL of functionalized Au-MUA and centrifuge it, collect the precipitate, and add 0.5 mL of a mixed solution of ethanol and water with a concentration of 20% to concentrate the Au-MUA by about 1 time. During the detection, take 300 μL of concentrated Au-MUA, add 10 μL of NPs stock solution of different concentrations and shake evenly, then add 3 μL of 100 mM HCl to adjust the pH (the resulting pH is 2.81), and quickly mix the above mixed solution and let it stand for 30 seconds. The results can be obtained by observing the color of the solution or measuring the absorption spectrum with UV-Vis.

[0060] (3) Au-MUA detection of NPs of different particle sizes: Take 1mL of functionalized Au-MUA and centrifuge it, collect the precipitate, add 0.5mL of a mixed solution of ethanol and water with a concentration of 20% ethanol, and concentrate Au-MUA by 1 times. During the detection, take 300μL of treated Au-MUA, add 10μL of NPs of different particle sizes and shake evenly, then add 3μL of 100mM HCl to adjust the pH, and quickly mix the above mixed solution and let it stand for 30s. The results can be obtained by observing the color of the solution or measuring the absorption spectrum with UV-Vis.

[0061] (4) Preparation of NPs test solution: dilute the NPs stock solution with Au-MUA solution in a 1.5 mL centrifuge tube;

[0062] (5) Quantitative detection of NPs: The mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, ultrapure water was added at a ratio of 1:1, and the absorption spectrum was recorded by UV-Vis. The maximum absorption peaks of NPs with different concentrations were compared to quantitatively analyze the NPs.

[0063] (6) Detection of NPs of different particle sizes: The mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, ultrapure water was added at a ratio of 1:1, and the absorption spectrum was recorded using UV-Vis. The maximum absorption peaks of NPs of different particle sizes were compared to estimate the particle size of NPs.

[0064] (7) Calculation of NPs concentration: Under optimal conditions, the mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, ultrapure water was added at a ratio of 1:1, and the absorption spectrum was recorded by UV-Vis. Each sample was repeated 5 times and the average value was taken to quantify the concentration of NPs by measuring the difference between the absorption peak and the absorption peak of the blank sample.

[0065] Example 4

[0066] A method for visually detecting nanoplastics in water comprises the following steps:

[0067] (1) Preparation of Au-MUA: 10 μL of MUA ethanol solution was added to 10 mL of 15 nm Au NPs to make the final MUA concentration 10 μM. The mixture was left to stand overnight in the dark at room temperature to obtain MUA-modified Au NPs, which were labeled as Au-MUA.

[0068] (2) Quantitative detection of NPs by Au-MUA: Take 1 mL of functionalized Au-MUA and centrifuge it, collect the precipitate, and add 0.5 mL of a mixed solution of ethanol and water with a concentration of 20% to concentrate Au-MUA by 1 time. During the detection, take 200 μL of treated Au-MUA, add 10 μL of NPs stock solution of different concentrations and shake evenly, then add 1 μL of 100 mM HCl to adjust the pH (the resulting pH is 3.01), and quickly mix the above mixed solution and let it stand for 30 seconds. The results can be obtained by observing the color of the solution or measuring the absorption spectrum with UV-Vis.

[0069] (3) Au-MUA detection of NPs of different particle sizes: Take 1mL of functionalized Au-MUA and centrifuge it, collect the precipitate, add 0.5mL of a mixed solution of ethanol and water with a concentration of 20% ethanol, and concentrate Au-MUA by 1 times. During the detection, take 200μL of treated Au-MUA, add 10μL of NPs of different particle sizes and shake evenly, then add 1μL of 100mM HCl to adjust the pH (the resulting pH is 3.01), and quickly mix the above mixed solution and let it stand for 30s. The results can be obtained by observing the color of the solution or measuring the absorption spectrum with UV-Vis.

[0070] (4) Preparation of NPs test solution: dilute the NPs stock solution with Au-MUA solution in a 1.5 mL centrifuge tube;

[0071] (5) Quantitative detection of NPs: The mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, and 200 μL of ultrapure water was added. The absorption spectrum was recorded by UV-Vis, and the maximum absorption peaks of NPs with different concentrations were compared to quantitatively analyze the NPs.

[0072] (6) Detection of NPs of different particle sizes: The mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, and 200 μL of ultrapure water was added. The absorption spectrum was recorded by UV-Vis, and the maximum absorption peaks of NPs of different particle sizes were compared to analyze the particle size of NPs.

[0073] (7) Calculation of NPs concentration: Under optimal conditions, the mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, and 200 μL of ultrapure water was added. The absorption spectrum was recorded in UV-Vis. Each sample was repeated 5 times and the average value was taken to quantify the concentration of NPs by measuring the difference between the absorption peak and the absorption peak of the blank sample.

[0074] Example 5

[0075] A method for visually detecting nanoplastics in water comprises the following steps:

[0076] (1) Preparation of Au-MUA: 10 μL of MUA ethanol solution was added to 10 mL of 15 nm Au NPs to make the final MUA concentration 10 μM. The mixture was left to stand overnight in the dark at room temperature to obtain MUA-modified Au NPs, which were labeled as Au-MUA.

[0077] (2) Quantitative detection of NPs by Au-MUA: Take 1 mL of functionalized Au-MUA and centrifuge it, collect the precipitate, and add 0.5 mL of a mixed solution of ethanol and water with a concentration of 20% to concentrate Au-MUA by 1 time. During the detection, take 200 μL of treated Au-MUA, add 10 μL of NPs stock solution of different concentrations and shake evenly, then add 4 μL of 100 mM HCl to adjust the pH (the resulting pH is 2.55), and quickly mix the above mixed solution and let it stand for 30 seconds. The results can be obtained by observing the color of the solution or measuring the absorption spectrum with UV-Vis.

[0078] (3) Au-MUA detection of NPs of different particle sizes: Take 1mL of functionalized Au-MUA and centrifuge it, collect the precipitate, add 0.5mL of a mixed solution of ethanol and water with a concentration of 20% ethanol, and concentrate Au-MUA by 1 times. During the detection, take 200μL of treated Au-MUA, add 10μL of NPs of different particle sizes and shake evenly, then add 4μL of 100mM HCl to adjust the pH (the resulting pH is 2.55), and quickly mix the above mixed solution and let it stand for 30s. The results can be obtained by observing the color of the solution or measuring the absorption spectrum with UV-Vis.

[0079] (4) Preparation of NPs test solution: dilute the NPs stock solution with Au-MUA solution in a 1.5 mL centrifuge tube;

[0080] (5) Quantitative detection of NPs: The mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, and 200 μL of ultrapure water was added. The absorption spectrum was recorded by UV-Vis, and the maximum absorption peaks of NPs with different concentrations were compared to quantitatively analyze the NPs.

[0081] (6) Detection of NPs of different particle sizes: The mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, and 200 μL of ultrapure water was added. The absorption spectrum was recorded by UV-Vis, and the maximum absorption peaks of NPs of different particle sizes were compared to analyze the particle size of NPs.

[0082] (7) Calculation of NPs concentration: Under optimal conditions, the mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, and 200 μL of ultrapure water was added. The absorption spectrum was recorded in UV-Vis. Each sample was repeated 5 times and the average value was taken to quantify the concentration of NPs by measuring the difference between the absorption peak and the absorption peak of the blank sample.

[0083] Example 6

[0084] A method for visually detecting nanoplastics in water comprises the following steps:

[0085] (1) Preparation of Au-MUA: 10 μL of MUA ethanol solution was added to 10 mL of 15 nm Au NPs to make the final MUA concentration 10 μM. The mixture was left to stand overnight in the dark at room temperature to obtain MUA-modified Au NPs, which were labeled as Au-MUA.

[0086] (2) Quantitative detection of NPs by Au-MUA: Take 1 mL of functionalized Au-MUA and centrifuge it, collect the precipitate, and add 0.5 mL of a mixed solution of ethanol and water with a concentration of 20% to concentrate Au-MUA by 1 time. During the detection, take 200 μL of treated Au-MUA, add 10 μL of NPs stock solution of different concentrations and shake evenly, then add 2 μL of 5 mM HCl to adjust the pH (the resulting pH is 4.38), and quickly mix the mixed solution and let it stand for 30 seconds. The results can be obtained by observing the color of the solution or measuring the absorption spectrum with UV-Vis.

[0087] (3) Au-MUA detection of NPs of different particle sizes: Take 1mL of functionalized Au-MUA and centrifuge it, collect the precipitate, add 0.5mL of a mixed solution of ethanol and water with a concentration of 20% ethanol, and concentrate Au-MUA by 1 times. During the detection, take 200μL of treated Au-MUA, add 10μL of NPs of different particle sizes and shake evenly, then add 2μL of 5mM HCl to adjust the pH (the resulting pH is 4.38), and quickly mix the above mixed solution and let it stand for 30s. The results can be obtained by observing the color of the solution or measuring the absorption spectrum with UV-Vis.

[0088] (4) Preparation of NPs test solution: dilute the NPs stock solution with Au-MUA solution in a 1.5 mL centrifuge tube;

[0089] (5) Quantitative detection of NPs: The mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, and 200 μL of ultrapure water was added. The absorption spectrum was recorded by UV-Vis, and the maximum absorption peaks of NPs with different concentrations were compared to quantitatively analyze the NPs.

[0090] (6) Detection of NPs of different particle sizes: The mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, and 200 μL of ultrapure water was added. The absorption spectrum was recorded by UV-Vis, and the maximum absorption peaks of NPs of different particle sizes were compared to analyze the particle size of NPs.

[0091] (7) Calculation of NPs concentration: Under optimal conditions, the mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, and 200 μL of ultrapure water was added. The absorption spectrum was recorded in UV-Vis. Each sample was repeated 5 times and the average value was taken to quantify the concentration of NPs by measuring the difference between the absorption peak and the absorption peak of the blank sample.

[0092] In the above embodiments, it should be pointed out that compared with the 200 μL Au-MUA used in Example 1, which has a more moderate color, when the corresponding components in other embodiments are used, the color is too light at lower concentrations and too dark at higher concentrations, which is not convenient for the human eye and measuring instruments such as OD values.

[0093] The NPs in Example 1 are a high-concentration stock solution. It should be pointed out that in the subsequent process, there is a relationship of coordination between the amount of substance of Au-MUA and NPs. If the concentration of Au-MUA prepared in the first half of the second step changes, the volume used will also change accordingly. There is a corresponding relationship between the concentration and the volume, and based on the data in the subsequent drawings, the parameters selected in Example 1 are preferred.

[0094] Depend on Figure 2 It can be seen that the MUA of the present invention still maintains good stability after modifying Au NPs, and the particle size of Au-MUA is relatively uniform, about 15 nm;

[0095] Depend on Figure 6It can be obtained that the UV-Vis spectrum of Au-MUA is in the state of induced aggregation, Au-MUA (200 μL) + HCl is the blank value of adding HCl without adding 50 nm NPs to inhibit aggregation; 100 μL Au-MUA, 200 μL Au-MUA and 300 μL Au-MUA are the results of taking 100, 200 and 300 μL of Au-MUA to add HCl and 50 nm NPs to induce aggregation, respectively. The more the UV-Vis peak value deviates from the blank value, the better the analytical performance, and the higher the peak intensity, the easier it is to observe with the naked eye. Therefore, 200 μL Au-MUA has the best performance.

[0096] Depend on Figure 7 The UV-Vis spectrum absorption peak shift value can be referred to Figure 6 , which is the difference between the absorption peak of Au-MUA aggregation induced by adding HCl (Au-MUA+HCl) and the absorption peak of Au-MUA aggregation inhibited by adding 50nm NPs induced by HCl (200μL Au-MUA). The larger the difference, the better the result recognition. The addition of 5mM HCl at pH 4.38 is not enough to induce Au-MUA aggregation, and it is still wine red. Therefore, the peak shift value is larger than that of the blank control group Au-MUA+HCl, but this value is meaningless. When the HCl concentration is 12.5 to 200mM and the pH is 3.98 to 2.55, the peak shift value increases from small to small and then decreases, and reaches the optimal shift value when the HCl concentration is 100mM and the pH is 2.81.

[0097] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for visually detecting nanoplastics in water, characterized in that: The steps include: Preparation of mercaptoundecanoic acid functionalized gold nanoparticles (Au-MUA): MUA ethanol solution was added to Au NPs and allowed to stand overnight in the dark at room temperature to obtain MUA-modified Au NPs, which were labeled as Au-MUA; Au-MUA quantitative detection of NPs: Take Au-MUA and centrifuge it, collect the precipitate, add a mixed solution of ethanol and water, add Au-MUA and NPs, mix well and let stand, adjust the pH and observe the solution color or measure the UV-Vis absorption spectrum; Prepare NPs test solution: dilute NPs stock solution with Au-MUA; Quantitative detection: The mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, diluted with water in a 1:1 ratio, placed in UV-Vis to record the absorption spectrum, and the maximum absorption peaks of NPs with different concentrations were compared to quantitatively analyze the NPs; Detection of NPs of different particle sizes: The mixed solution of Au-MUA, NPs and HCl was transferred into a quartz cuvette, diluted with water, placed in UV-Vis to record the absorption spectrum, and the maximum absorption peaks of NPs of different particle sizes were compared to analyze the particle size of NPs; Calculate the concentration of NPs: transfer the mixed solution of Au-MUA, NPs and HCl into a quartz cuvette, dilute with water, place it in UV-Vis to record the absorption spectrum, repeat each sample 5 times and take the average value to quantify the concentration of NPs by measuring the difference between the absorption peak and the absorption peak of the blank sample.

2. The method for visually detecting nanoplastics in water according to claim 1, characterized in that: The Au-MUA quantitative detection of NPs further includes a pH adjustment step after the addition of Au-MUA, and the pH adjuster is HCl.

3. The method for visually detecting nanoplastics in water according to claim 1, characterized in that: The Au-MUA quantitative detection of NPs also includes Au-MUA concentration adjustment, and the Au-MUA concentration adjustment is to concentrate the Au-MUA obtained in the preparation of Au-MUA by one time.

4. The method for visually detecting nanoplastics in water according to claim 2, characterized in that: The amount of HCl used in the pH adjustment step is such that the pH of the solution after adding HCl is ≤4.

5. The method for visually detecting nanoplastics in water according to claim 2, characterized in that: In the Au-MUA quantitative detection NPs, the concentration of HCl is 5~100 mM.

6. The method for visually detecting nanoplastics in water according to claim 1, characterized in that: In the Au-MUA quantitative detection NPs, the concentration of the Au-MUA is 1 times that of the product obtained by the preparation of Au-MUA.

7. The method for visually detecting nanoplastics in water according to claim 5, characterized in that: The concentration of HCl is 100 mM.

8. The method for visually detecting nanoplastics in water according to claim 1 or 7, characterized in that: The Au-MUA quantitative detection NPs, according to volume, the Au-MUA: HCl = 100~300 μL: 1~4 μL.

9. The method for visually detecting nanoplastics in water according to claim 1, characterized in that: The Au-MUA quantitative detection NPs is carried out in the following ratio: Au-MUA:HCl=100 μL:1 μL by volume.

10. The method for visually detecting nanoplastics in water according to claim 1, characterized in that: The Au-MUA quantitative detection NPs had a pH of 2.81 after adding HCl.

Images