A microplastic adsorption detection technology based on a microfluidic chip

Abstract

The application discloses a detection technology based on micro-plastic adsorption of a micro-fluidic chip, which forms a detection area by fixing micro-plastic particles in a chip channel in situ through a sodium alginate and calcium chloride system, and deducts background interference synchronously by using a parallel reference channel, and then pumps a solution containing a target adsorbate into the chip at a controllable flow rate, and simultaneously, real-time in-situ optical monitoring of the adsorption process is carried out by using a fluorescence technology, finally, the adsorption kinetics parameters and the adsorption isotherm are quantitatively calculated by analyzing the signal and time curve and the concentration gradient experiment, and the determination of the maximum adsorption capacity is realized; the micro-plastic is fixed, dynamic adsorption, real-time monitoring and data processing are integrated on the micro-fluidic chip platform, the problems that the traditional method cannot realize real-time observation, the background interference is large and the operation is complicated are effectively solved, and efficient quantitative analysis of the adsorption behavior of the micro-plastic is realized.

Description

Technical Field

[0001] This invention relates to the field of environmental pollutant detection technology, and in particular to a detection technology based on microfluidic chips for the adsorption of microplastics. Background Technology

[0002] As a global environmental pollutant, microplastics are considered a key pathway for environmental and health risks due to their strong adsorption of toxic and harmful substances such as heavy metals or persistent organic pollutants. Currently, the conventional methods for assessing the adsorption behavior of microplastics mainly include batch adsorption experiments, which involve mixing a certain amount of microplastic particles with a target pollutant solution in a container, separating the two phases after a specific time, and measuring the change in pollutant concentration in the solution by means of spectroscopy or chromatography, thereby indirectly calculating the adsorption amount.

[0003] First, batch experiments, being an "endpoint method," can only provide macroscopic data after adsorption equilibrium, failing to provide real-time, in-situ observation of the dynamic adsorption process. Therefore, it is difficult to accurately obtain key kinetic parameters such as adsorption rate and initial diffusion. Second, in both batch and column experiments, microplastic particles are in a suspended or aggregated state. Their contact interface with the contaminant is unstable and difficult to characterize precisely, leading to poor reproducibility of experimental results and the inability to exclude interference from interparticle interactions or mass transfer limitations on the adsorption process. Third, the detection signal of traditional methods usually originates from a holistic measurement of changes in contaminant concentration in the solution, resulting in significant background interference and limited sensitivity. The signal-to-noise ratio is insufficient, especially when dealing with low-concentration contaminants or studying initial adsorption behavior.

[0004] Therefore, in response to the problems mentioned above, this invention proposes a detection technology for the adsorption of microplastics based on microfluidic chips. Summary of the Invention

[0005] To overcome the limitations of existing technologies in providing in-situ, real-time visual monitoring of microplastic adsorption behavior and addressing the issue of significant background interference, this invention proposes a microplastic adsorption detection technology based on a microfluidic chip. This method forms a stable detection zone by fixing microplastic particles in situ within the chip channel, eliminates background interference through a dual-channel design, and integrates real-time optical monitoring technology, thereby enabling dynamic tracking and multi-parameter quantitative analysis of the microplastic adsorption process.

[0006] The technical solution of this invention is: a detection technology for the adsorption of microplastics based on microfluidic chips, comprising the following steps:

[0007] S1. A microfluidic chip made of transparent polymer material is provided. The chip includes at least one main detection channel and a reference channel parallel or perpendicular to it. The inner surface of the main detection channel is subjected to plasma treatment (preferably at a power of 50-100W for 30-90 seconds), and then an ethanol solution containing an aminosilane coupling agent with a concentration of 0.5% to 2.0% (w / v) is injected for incubation (preferably 30-60 minutes at a temperature of 25-60°C) to form an amino-functionalized layer on the inner wall of the channel. Then, the microplastic particles to be tested are uniformly dispersed in an aqueous solution of sodium alginate with a concentration of 0.5% to 2.0% (w / v) to form a microplastic suspension with a mass concentration of 0.01% to 0.1%. The microplastic suspension is then injected into the amino-functionalized main detection channel at a flow rate of 1-10 μL / min, and a microplastic suspension with a concentration of 1.0% to 5.0% is injected into the channel at the same flow rate. A (w / v) calcium chloride solution is used for a cross-linking reaction for 5-15 minutes, allowing the microplastic particles to initially adhere to the inner wall of the channel through electrostatic interaction. Then, calcium chloride solution is injected into the channel to cross-link and solidify the sodium alginate adhering to the microplastic particles and the inner wall of the channel, thereby fixing the microplastic particles in situ in a designated area of ​​the main detection channel, forming a "microplastic immobilization detection area".

[0008] The reference channel undergoes the same processing but without fixing the microplastic particles, serving as a background reference.

[0009] S2, a solution containing the target adsorbate at a known concentration is used as the adsorption phase and pumped into the main detection channel and the reference channel at a constant and controllable flow rate (preferably between 0.5 μL / min and 20 μL / min). When the adsorption phase flows through the "microplastic immobilization detection zone" of the main detection channel, the target adsorbate is adsorbed on the surface of the microplastic particles.

[0010] S3. During the injection of the adsorbate phase and subsequent cleaning, an inverted fluorescence microscope equipped with a high-speed CCD or CMOS camera is used to optically monitor the "microplastic immobilization detection area". If the target adsorbate itself has fluorescence, its signal change is directly monitored. If the target adsorbate has no inherent optical signal, probe molecules that specifically bind to the target adsorbate and are fluorescently labeled are added to the adsorbate phase in advance or injected subsequently. The adsorption status of the adsorbate is indirectly reflected by monitoring the spatial distribution and temporal change of the fluorescence signal intensity, while the background signal of the corresponding area of ​​the reference channel is monitored simultaneously.

[0011] S4. Subtract the background signal of the reference channel at the corresponding time point from the optical signal intensity of the main detection channel collected in step S3 to obtain the net optical signal value. The net optical signal value is positively correlated with the amount of target adsorbate adsorbed in the "microplastic immobilization detection area". By analyzing the change curve of the net optical signal value with time, combined with the adsorption phase flow rate, concentration and theoretical volume of the microplastic immobilization area, the adsorption kinetic parameters of the microplastic on the target adsorbate are calculated, including the adsorption rate constant and the equilibrium adsorption amount. By changing the concentration of the injected adsorption phase, repeat steps S2-S4, draw the adsorption isotherm, and then determine the adsorption model and the maximum adsorption capacity.

[0012] Preferably, in step S1, the microplastic particles include one or more of polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyethylene terephthalate, or polyamide, with a particle size ranging from 0.1 μm to 100 μm.

[0013] Preferably, in step S1, after injecting the calcium chloride solution, the channel is rinsed with deionized water at a flow rate of 5-20 μL / min for 1-5 minutes to remove uncrosslinked sodium alginate and excess ions, thereby ensuring the stability of the immobilized structure and the cleanliness of the detection background.

[0014] Preferably, in step S2, the target adsorbent is an organic pollutant (such as polycyclic aromatic hydrocarbons, antibiotics, pesticides) or a heavy metal ion (such as... , , The adsorbent phase contains proteins, antibiotics, or nanoparticles, and also includes pH buffers (such as PBS, Tris-HCl) and electrolytes (such as...). To maintain stable ionic strength (preferably 0.01-0.1M) and pH value, and to simulate different environmental water conditions.

[0015] Preferably, in step S3, optical monitoring specifically involves: during fluorescence monitoring, the target adsorbate is a substance with inherent fluorescence or a polycyclic aromatic hydrocarbon pollutant, and the fluorescently labeled probe molecule is a fluorescently labeled antibody, aptamer, or molecularly imprinted polymer microsphere, preferably FITC, Cy3, or Cy5.

[0016] Preferably, when using fluorescently labeled probe molecules for indirect monitoring, after the adsorption phase is injected in step S2 and adsorption equilibrium is reached, pure buffer solution without target adsorbent and probe molecules needs to be pumped into the chip channel to wash away unbound free probe molecules in the channel, and then fluorescence signal is collected again. At this time, the stable fluorescence signal collected specifically corresponds to the target adsorbent and probe molecule complex that has been adsorbed on the microplastic surface.

[0017] Preferably, in step S3, the optical monitoring is surface-enhanced Raman scattering (SERS) monitoring, wherein the "microplastic immobilization detection zone" of the main detection channel is modified with gold nanorods or silver nanoparticles as a SERS enhancement substrate before or after the immobilization of microplastic particles, and the adsorption amount is quantified by monitoring the intensity change of the characteristic Raman peak of the target adsorbent in the hot spot region of the SERS substrate.

[0018] Preferably, the microfluidic chip is made of polydimethylsiloxane, polymethyl methacrylate, or cyclic olefin copolymer, and the inlets of the main detection channel and the reference channel are respectively connected to independent injection pumps or pressure controllers for synchronous control of flow rate.

[0019] Preferably, during steps S2 and S3, the microfluidic chip is arranged on an integrated temperature control module to conduct the adsorption experiment at a constant temperature between 5°C and 50°C (preferably 15°C, 25°C, and 35°C) to study the effect of temperature on the adsorption behavior of microplastics.

[0020] Preferably, in step S4, the adsorption kinetic parameters are calculated based on a pseudo-first-order or pseudo-second-order adsorption kinetic model; the adsorption isotherms are plotted based on the Langmuir adsorption isotherm.

[0021] The beneficial effects of this invention are:

[0022] 1. This invention, with the assistance of a sodium alginate and calcium chloride system, fixes microplastic particles in situ within the main detection channel of a microfluidic chip to form a stable "microplastic immobilization detection area." Parallel or vertical reference channels are set up for synchronous background signal monitoring and subtraction, thereby eliminating optical interference caused by particle movement, interface instability, and chip material and solution background in traditional suspension or accumulation systems. This enables accurate acquisition of the interaction signal between the adsorption sites on the microplastic surface and the target pollutant.

[0023] 2. This invention utilizes microfluidic technology to control fluid velocity and composition, combined with the in-situ monitoring capability of a high-speed optical imaging system for immobilized detection areas, to achieve visualized tracking of the entire process of pollutant adsorption. It can capture the complete signal evolution curve from initial rapid adsorption to final equilibrium, overcoming the limitation of traditional batch "endpoint method" which can only obtain static equilibrium data.

[0024] 3. This invention integrates microplastic immobilization, controllable adsorption, in-situ optical detection, and multi-model data analysis into a microfluidic chip platform. It can complete a comprehensive quantitative analysis of adsorption kinetics, adsorption isotherms, and the influence of environmental factors through a single or series of experiments, which greatly simplifies the operation process and improves experimental throughput and data consistency. Attached Figure Description

[0025] Figure 1 The diagram shown illustrates the workflow of this invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Please see Figure 1 This invention provides an embodiment of a detection technique for microplastic adsorption based on a microfluidic chip:

[0028] S1. A microfluidic chip was fabricated using polydimethylsiloxane with good light transmittance through soft photolithography. The chip design includes two parallel channels, namely the main detection channel and the reference channel, both of which are identical in size (200 μm wide, 100 μm high, and 2 cm long). The inner surface of the chip channel was treated with an oxygen plasma treatment machine at 80 W power for 60 seconds to activate the surface and generate hydroxyl groups. The chip was then immediately bonded to a pre-treated glass substrate to form a closed channel. Then, a 1.0% (v / v) solution of 3-aminopropyltrimethoxysilane ethanol was injected into the main detection channel and the reference channel at a flow rate of 2 μL / min using a precision injection pump. The channel was then incubated in a 60°C oven for 40 minutes. After incubation, the channel was rinsed with anhydrous ethanol for 5 minutes and then cured at 110°C for 15 minutes, thereby forming a strong amino-functionalized layer on the inner wall of both channels.

[0029] Prepare the microplastic sample to be tested, taking pristine polystyrene microspheres with a particle size of 5.0 ± 1.5 μm as an example. Disperse them ultrasonically in a 1.0% (w / v) sodium alginate aqueous solution to prepare a 0.05% (w / v) homogeneous suspension. Inject this suspension separately into the main detection channel using a syringe pump at a flow rate of 5 μL / min, and incubate at room temperature for 10 minutes. During this process, the negatively charged sodium alginate molecules bind to the positively charged aminated channel wall through electrostatic interactions. Simultaneously, the sodium alginate network also encapsulates and carries the PS microspheres to attach together. Then, inject 2.0% (w / v) calcium chloride solution at the same flow rate. ( ) solution, for 5 minutes. Specific ionic cross-linking occurs with the guluronic acid units in sodium alginate, rapidly forming a three-dimensional network structure. This fixes the PS microspheres on the bottom surface of the channel, creating a dense and uniform single-layer or multi-layer microsphere immobilization area approximately 3 mm long (about 15% of the channel length), which is the "microplastic immobilization detection area." Finally, 0.01 M sodium nitrate (… The background electrolyte solution (pH=7.0, used for subsequent experiments) was used to flush the channel for 3 minutes at a flow rate of 10 μL / min to thoroughly remove uncrosslinked polymers and free ions. The reference channel underwent the same amination and flushing process, but without the injection of microplastic suspension and calcium chloride, and was only flushed with the background electrolyte solution to ensure that its optical background was highly consistent with that of the main channel, except for the lack of microplastic target material.

[0030] S2 simulates the contact adsorption process of pollutants with immobilized microplastics under flowing conditions, thereby studying the effect of PS microplastics on heavy metal lead ions ( Taking the adsorption of lead nitrate as an example, a series of lead nitrate solutions with different concentrations (e.g., 0.5, 1, 2, 5, 10 mg / L) were prepared. The solution was used as the adsorption phase, and all solutions were prepared using 0.01M solution. Used to maintain a constant ionic strength, and with dilute... Alternatively, adjust the pH to 6.0 ± 0.1 with NaOH. Place the chip on the stage of an inverted fluorescence microscope and connect two independent syringe pumps to drive the fluid in the main detection channel and the reference channel, respectively. Start the syringe pumps to deliver a specific concentration of [missing information - likely a specific chemical or ingredient] at a constant flow rate. The adsorbed phase is simultaneously pumped into two channels, and the stable flow of the fluid ensures the controllability and repeatability of mass transfer conditions. When the adsorbed phase flows through the immobilized PS region of the main channel, Ions adsorb onto the PS surface; while the reference channel contains no PS and is used only to record changes in background signals such as solution background and chip material fluorescence.

[0031] S3, targeting Due to its inherent lack of fluorescence, an indirect fluorescent labeling method is used to label the adsorbed phase (…). A fluorescent probe is pre-added to the solution. Taking cadmium reagent (a chelating agent with high selectivity for lead ions) as an example, its own fluorescence is weak, but it reacts with... The complex formed after complexation produces strong red fluorescence (emission peak at approximately 580 nm) under specific excitation light (excitation wavelength 365 nm). Monitoring is performed using an inverted fluorescence microscope equipped with a mercury lamp light source, corresponding filter set, and a high-speed CMOS camera. From the moment the adsorbed phase begins to be injected, continuous video recording or timed photography (e.g., 1 frame per second) is performed on the immobilized area of ​​the main detection channel and the corresponding area of ​​the reference channel. As adsorption progresses... The cadmium reagent probe adsorbs onto the PS surface and binds to it from the surrounding area, leading to a gradual increase in the fluorescence signal on the PS microsphere surface, while the free probe in solution... Due to the high flow rate, the complex generates very little signal contribution during the exposure time. Simultaneously, the camera acquires the signal from the reference channel, which mainly originates from the background fluorescence of the adsorbed phase solution flowing through that channel. The entire adsorption process continues until the fluorescence signal in the main channel reaches a stable plateau (e.g., for 30 minutes), indicating that the adsorption has reached dynamic equilibrium.

[0032] S4. Using image processing software, analyze the acquired sequence images. For each frame, select the immobilized area of ​​the main detection channel and the same area of ​​the reference channel, calculate their average fluorescence intensity (grayscale value), and subtract the intensity value of the reference channel at the same time from the intensity value of the main channel to obtain the net fluorescence intensity. This value directly reflects the amount of material fixed to the PS surface. The amount of the probe complex, i.e., the PS pair The amount of adsorption. Plot time (t) on the x-axis. Plot the adsorption kinetics curve with I_net as the ordinate. Assume that I_net is related to the adsorption amount ( It is directly proportional to, that is (where k is the proportionality coefficient), then the curve can be transformed into -t relationship. Using a quasi-second-order dynamic model (formula: ,in The rate constant is To balance the adsorption amount, the data is nonlinearly fitted, and the software can directly calculate... and Value. To obtain the adsorption isotherm, different initial concentrations were used ( )of Adsorbed phase, repeat steps S2-S4 to obtain a series of corresponding equilibrium adsorption amounts ( ).by The x-axis is... Plot isotherms on the ordinate. Use the Langmuir model (formula: ,in Approximately equal to Because of the small adsorption capacity, For maximum adsorption capacity, By fitting the affinity constant (where is the affinity constant), the affinity of PS microplastics to the desired value can be obtained. The theoretical maximum adsorption capacity ( ) and Langmuir constant. All data processing and model fitting were performed using plotting software, and the goodness of fit was reported ( To evaluate the applicability of the model.

[0033] Comparative Example 1 provided by the present invention:

[0034] This embodiment follows the steps S1-S4 of the above embodiment to treat lead ions ( The adsorption kinetics and isotherms of the reagent were studied using PS microspheres for immobilization, and the adsorbed phase was a solution containing 10 μM cadmium. The solution was prepared with concentration gradients of 0.5, 1, 2, 5, and 10 mg / L, a flow rate of 5 μL / min, and a temperature of 25 °C.

[0035] The comparative method used the traditional batch method. First, 5 mg of the same PS microspheres and 10 mL of different initial concentrations were added to a 10 mL centrifuge tube. (same as above) The solution (without probe) was placed in a temperature-controlled shaker (25°C, 150 rpm) and shaken. At each preset time point (e.g., 1, 3, 5, 10, 20, 30, 60, 120 minutes), a centrifuge tube was removed, centrifuged, and the supernatant was collected. The remaining components were then analyzed using inductively coupled plasma mass spectrometry. Concentration, adsorption capacity is calculated by the difference. Equilibrium adsorption capacity The sample was taken after 24 hours of shaking.

[0036] Using the two methods described above, this invention easily obtains high temporal resolution data for the initial adsorption phase (high data point density in the first 30 seconds) through continuous monitoring, clearly capturing the rapid adsorption stage. In contrast, the comparative method, limited by the intervals of manual sampling, has sparse data points in the first few minutes, making it impossible to accurately describe the initial rate.

[0037] (1) The adsorption kinetic data of the same concentration of 5 mg / L were fitted using a pseudo-second-order model, and the results are shown in the table below:

[0038]

[0039] The table above shows the results obtained by the two methods. The close proximity verified the accuracy of the method of the present invention, and the present invention obtained... More accurate values ​​(smaller standard deviation) and higher R² indicate better data quality and a better model fit.

[0040] (2) According to the concentrations The isotherms were plotted and fitted using the Langmuir model. The results are shown in the table below:

[0041]

[0042] From the table above, we can see that the measurements obtained by both methods... There was no significant difference, but the present invention also exhibited a smaller error range and a higher goodness of fit.

[0043] This embodiment demonstrates that, for non-fluorescent target substances, the present invention successfully achieves real-time visual monitoring of the adsorption process by introducing a specific fluorescent probe. Compared with the cumbersome offline sampling and instrument detection of the batch method, the present invention can complete the full set of data acquisition from kinetics to isotherms in a single run, which significantly improves efficiency and provides higher data accuracy and reliability.

[0044] Comparative Example 2 is provided in this invention:

[0045] This embodiment studies the in-situ adsorption of the organic dye (Rhodamine B). The target adsorbate in this embodiment is Rhodamine B, which has strong autofluorescence. Step S1 is the same as before. In step S2, the adsorbate phase is Rhodamine B solution of different concentrations (1, 5, 10 mg / L), without the need for an external probe. Three different flow rates were used for the experiment: 2 μL / min (low), 10 μL / min (medium), and 30 μL / min (high). In step S3, fluorescence microscopy was used for direct monitoring (excitation 540 nm, emission 585 nm).

[0046] The comparative example is the same as in Example 1, but the target analyte is Rhodamine B, and the adsorption amount is calculated by measuring the UV-Vis absorbance of the supernatant at 554 nm.

[0047] In this experiment, the present invention can intuitively demonstrate the adsorption process. At the beginning of the experiment, the immobilized PS microsphere region is a dark field. As Rhodamine B solution flows in, the edges of the microspheres light up first, and the fluorescence signal gradually diffuses and intensifies towards the center of the microspheres. Finally, the entire microsphere region presents a uniform bright spot, vividly demonstrating the diffusion and adsorption process of pollutants from the solution to the particle surface. In contrast, the comparative model cannot obtain any visualization information.

[0048] In this experiment, the present invention directly investigated the effect of hydrodynamic conditions on adsorption by changing the flow rate. At high flow rates, the time to reach adsorption equilibrium was significantly shortened, but the final equilibrium adsorption amount remained unchanged, which is consistent with the external mass transfer control mechanism. The external mass transfer coefficient can be estimated by analyzing the kinetic curves at different flow rates. In the comparative example, under oscillating conditions, the mass transfer conditions are fuzzy and cannot be precisely quantified.

[0049] The adsorption kinetics data for a concentration of 10 mg / L at a medium flow rate of 10 μL / min are compared below, and the results are shown in the table below:

[0050]

[0051] This embodiment demonstrates the in-situ monitoring capability of the present invention for pollutants with inherent fluorescent properties. The present invention can not only provide quantitative data, but also provide spatially resolved adsorption images, thereby intuitively revealing the adsorption front and uniformity.

[0052] Comparative Example 3 is provided in this invention:

[0053] This embodiment studies sulfamethoxazole antibiotic, with the target being a non-fluorescent sulfamethoxazole antibiotic. First, sulfamethoxazole antibiotic is covalently coupled to bovine serum albumin (BSA), and then a fluorescently labeled specific antibody (Cy5-labeled) is prepared using BSA as the antigen. Step S1 is the same as before. In step S2, different concentrations of sulfamethoxazole antibiotic standard solutions are injected to allow for competitive adsorption on the PS surface. In step S3, the fluorescently labeled antibody (Cy5-Ab) is injected. The antibody binds to the sulfamethoxazole antibiotic adsorbed on the PS surface (if the sulfamethoxazole antibiotic is not adsorbed, the antibody does not bind to the PS). Unbound antibodies are eluted with buffer. Finally, the Cy5 fluorescence signal (excitation 650 nm, emission 670 nm) is monitored, and the signal intensity is inversely proportional to the amount of sulfamethoxazole antibiotic adsorbed. The chip is placed on a Peltier temperature control module, and the experiment is repeated at 15℃, 25℃, and 35℃.

[0054] The comparative study used high performance liquid chromatography (HPLC) to detect the SMX concentration, and the temperature effect study required multiple independent experiments to be conducted in constant temperature shaking ovens at different temperatures.

[0055]

[0056] The table above shows the results obtained by the two methods at 15℃, 25℃, and 35℃. The results showed a high degree of agreement, verifying the accuracy of the data from this invention. Furthermore, this invention can continuously complete the adsorption isotherm measurements at all three temperature points on the same chip, with a total time of only about 6.5 hours. The process is automated, and the data exhibits good inherent consistency. In contrast, the traditional batch method requires multiple lengthy experiments to be conducted independently in different isothermal devices, taking over 72 hours in total, resulting in low efficiency and cumbersome operation.

[0057] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A detection technique for microplastic adsorption based on a microfluidic chip, characterized in that, It includes the following steps: S1 provides a transparent polymer microfluidic chip, which includes at least a main detection channel and a reference channel parallel or perpendicular to it; the inner surface of the main detection channel is subjected to plasma treatment, and then an amino-functionalized layer is formed on the inner wall of the channel by incubation in a solution containing an aminosilane coupling agent; then the microplastic particles to be tested are uniformly dispersed in an aqueous solution containing sodium alginate to form a microplastic suspension; the microplastic suspension is then injected into the amino-functionalized main detection channel, so that the microplastic particles initially adhere to the inner wall of the channel through electrostatic interaction; then calcium chloride solution is injected into the channel, so that the sodium alginate attached to the microplastic particles and the inner wall of the channel crosslinks and solidifies, thereby fixing the microplastic particles in situ in a designated area of ​​the main detection channel to form a "microplastic immobilization detection area"; The reference channel undergoes the same processing but without fixing the microplastic particles, serving as a background reference. S2, a solution containing the target adsorbate at a known concentration is used as the adsorption phase and is simultaneously pumped into the main detection channel and the reference channel at a constant and controllable flow rate. When the adsorption phase flows through the "microplastic immobilization detection zone" of the main detection channel, the target adsorbate is adsorbed by the surface of the microplastic particles. S3. During the adsorption phase injection and subsequent cleaning process, an inverted fluorescence microscope equipped with a high-speed CCD or CMOS camera is used to optically monitor the "microplastic immobilization detection area". If the target adsorbent itself has fluorescence, its signal change is directly monitored. If the target adsorbent does not have an inherent optical signal, probe molecules that specifically bind to the target adsorbent and are fluorescently labeled are added to the adsorption phase in advance or injected subsequently. The adsorption status of the adsorbent is indirectly reflected by monitoring the spatial distribution and temporal changes of the fluorescence signal intensity, while the background signal of the corresponding area of ​​the reference channel is monitored simultaneously. S4. Subtract the background signal of the reference channel at the corresponding time point from the optical signal intensity of the main detection channel collected in step S3 to obtain the net optical signal value. The net optical signal value is positively correlated with the amount of target adsorbate adsorbed in the "microplastic immobilization detection area". By analyzing the change curve of the net optical signal value with time, combined with the adsorption phase flow rate, concentration and theoretical volume of the microplastic immobilization area, the adsorption kinetic parameters of the microplastic on the target adsorbate are calculated, including the adsorption rate constant and the equilibrium adsorption amount. By changing the concentration of the injected adsorption phase, steps S2-S4 are repeated to draw the adsorption isotherm, and then the adsorption model and the maximum adsorption capacity are determined.

2. The detection technology for microplastic adsorption based on a microfluidic chip according to claim 1, characterized in that: In step S1, the microplastic particles include one or more of polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyethylene terephthalate, or polyamide, with a particle size ranging from 0.1 μm to 100 μm.

3. The detection technology for microplastic adsorption based on a microfluidic chip according to claim 1, characterized in that: In step S1, after injecting calcium chloride solution, the channel is rinsed with deionized water to remove uncrosslinked sodium alginate and excess ions.

4. The detection technology for microplastic adsorption based on a microfluidic chip according to claim 1, characterized in that: In step S2, the target adsorbent is an organic pollutant, heavy metal ion, protein, antibiotic or nanoparticle. The adsorbent phase also contains pH buffer salt and electrolyte to maintain stable ionic strength and pH value, simulating different environmental water conditions.

5. The detection technology for microplastic adsorption based on a microfluidic chip according to claim 1, characterized in that, In step S3, optical monitoring specifically involves the following: during fluorescence monitoring, the target adsorbate is a substance with inherent fluorescence or a polycyclic aromatic hydrocarbon pollutant, and the fluorescently labeled probe molecule is a fluorescently labeled antibody, aptamer, or molecularly imprinted polymer microsphere.

6. The detection technology for microplastic adsorption based on a microfluidic chip according to claim 5, characterized in that: When using fluorescently labeled probe molecules for indirect monitoring, after adsorption equilibrium is reached by injecting the adsorption phase in step S2, pure buffer solution without target adsorbent and probe molecules needs to be pumped into the chip channel to wash away unbound free probe molecules in the channel. Then, fluorescence signal acquisition is performed again. The stable fluorescence signal acquired at this time specifically corresponds to the target adsorbent and probe molecule complex that has been adsorbed on the microplastic surface.

7. The detection technology for microplastic adsorption based on a microfluidic chip according to claim 1, characterized in that: In step S3, the optical monitoring is surface-enhanced Raman scattering (SERS) monitoring. The "microplastic immobilization detection zone" of the main detection channel is modified with gold nanorods or silver nanoparticles as a SERS enhancement substrate before or after the immobilized microplastic particles. The adsorption amount is quantified by monitoring the intensity change of the characteristic Raman peak of the target adsorbent in the hot spot region of the SERS substrate.

8. The detection technology for microplastic adsorption based on a microfluidic chip according to claim 1, characterized in that: The microfluidic chip is made of polydimethylsiloxane, polymethyl methacrylate, or cyclic olefin copolymer. The inlets of the main detection channel and the reference channel are respectively connected to independent injection pumps or pressure controllers for synchronous control of flow rate.

9. The detection technology for microplastic adsorption based on a microfluidic chip according to claim 1, characterized in that: In steps S2 and S3, the microfluidic chip is arranged on an integrated temperature control module to conduct the adsorption experiment at a constant temperature between 5°C and 50°C, in order to study the effect of temperature on the adsorption behavior of microplastics.

10. The detection technology for microplastic adsorption based on a microfluidic chip according to claim 1, characterized in that: In step S4, the adsorption kinetic parameters are calculated based on a pseudo-first-order or pseudo-second-order adsorption kinetic model; the adsorption isotherms are plotted based on the Langmuir adsorption isotherm.

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