A method for cyclic detection of mercury ions based on sulfur-doped carbon dots, a microfluidic chip thereof and application thereof

Abstract

The application discloses a method for cyclic detection of mercury ions based on sulfur-doped carbon dots, a micro-fluidic chip and application thereof, and is characterized by comprising the following steps: after a to-be-detected sample containing Hg 2+ is fully mixed with a sulfur-doped carbon dot ethanol solution, the fluorescence intensity value F of the mixed solution is measured, the mixed solution is filtered through a filter membrane to adsorb Hg 2+ in the mixed solution, the sulfur-doped carbon dot ethanol solution is mixed again with a new to-be-detected sample containing Hg 2+ to realize cyclic utilization, the concentration of Hg 2+ in each to-be-detected solution is calculated according to the linear relationship between the concentration of Hg 2+ and the fluorescence intensity ratio F0 / F, and the micro-fluidic chip for cyclic detection of mercury ions based on sulfur-doped carbon dots is also provided. The application has the advantages that the mercury ions can be detected repeatedly with high sensitivity, and the chip has the characteristics of strong adaptability, good fluidity and high light transmittance.

Description

Technical Field

[0001] This invention relates to a method for detecting mercury ions, and more particularly to a method for detecting mercury ions based on sulfur-doped carbon dots in a cyclic manner, its microfluidic chip, and its application. Background Technology

[0002] In aquatic environments, mercury readily transforms into methylmercury and accumulates in aquatic products. It can then enter the human body through fish, shellfish, and other seafood, potentially causing health risks such as damage to the nervous system. Therefore, effective monitoring and control of mercury content in aquatic products has become an important research direction in the fields of food safety and environmental protection.

[0003] Currently, various rapid detection methods, such as fluorescence, electrochemical, and colorimetric methods, have been developed for the detection of heavy metal ions. Among them, electrochemical methods are widely accepted for heavy metal ion detection due to their reliability, high sensitivity, and rapid response. However, electrochemical methods typically rely on complex electrode preparation processes and stable electrochemical testing systems, placing high demands on electrode materials, surface modification, and the testing environment. Furthermore, the detection process often requires sophisticated instruments and external power supplies, hindering the miniaturization and integration of equipment. In addition, electrochemical detection is highly dependent on sample pretreatment and operational procedures in practical applications, making it difficult to ensure the stability and repeatability of results in complex environments. Therefore, there is an urgent need for an efficient, stable, and portable rapid detection method.

[0004] Microfluidic chips, with their advantages of low cost, low reagent consumption, and portability, have demonstrated significant importance in the detection of heavy metals and food safety. However, most existing microfluidic detection platforms focus on single-use applications, and research on achieving cyclic detection or reuse within the same chip system has not been reported, limiting their further application in continuous monitoring and resource conservation. Meanwhile, carbon dots (CDs), as environmentally friendly and easily surface-modified fluorescent nanomaterials, possess excellent photostability and tunable fluorescence response characteristics, and have been used in various analytical detection fields. Furthermore, carbon dots can achieve reversible modulation of fluorescence signals through surface functionalization, providing a new technical approach for constructing microfluidic detection systems with cyclic detection capabilities. Currently, there are no publicly available methods or applications for the cyclic detection of mercury ions based on sulfur-doped carbon dots, either domestically or internationally. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for the cyclic detection of mercury ions based on sulfur-doped carbon dots that enables highly sensitive and repeatable detection of mercury ions, as well as its microfluidic chip and application. The chip has the characteristics of strong adaptability, good fluidity and high light transmittance.

[0006] The technical solution adopted by this invention to solve the above-mentioned technical problem is as follows: a method for cyclic detection of mercury ions based on sulfur-doped carbon dots, comprising the following steps: [The method involves] reacting sulfur-doped carbon dots with sulfur-doped carbon dots to detect mercury ions. 2+ The sample to be tested was thoroughly mixed with a sulfur-doped carbon dot ethanol solution with a concentration of 100–300 mg / L at a volume ratio of 1:(8–10). The fluorescence intensity value F of the mixed solution was measured. The mixed solution was then filtered through a filter membrane to adsorb Hg from the mixed solution. 2+ And allow the sulfur-doped carbon dots to pass through, then react the sulfur-doped carbon dot ethanol solution again with new Hg-containing... 2+ The test samples are thoroughly mixed at a volume ratio of 1:(8-10) to achieve recycling, based on Hg 2+ The linear relationship between concentration and fluorescence intensity ratio F0 / F was used to calculate the Hg concentration in each test solution. 2+ The concentration of F0 is the initial fluorescence intensity value of the sulfur-doped carbon dot ethanol solution.

[0007] Further, the preparation method of the sulfur-doped carbon dots is as follows: o-phenylenediamine, trimesic acid and 4-aminothiophenol are dissolved in 8-12 mL of ultrapure water at a mass ratio of (1-3):(0.8-1.2):(1-3), 100 μL-300 μL of concentrated sulfuric acid is added, and the mixture is placed in a polytetrafluoroethylene-lined tube. After ultrasonic treatment, it is placed in a reaction vessel and reacted at 180℃-220℃ for 6-12 h. After cooling, it is dialyzed and freeze-dried to obtain a blue-black powder product, which is the sulfur-doped carbon dots.

[0008] Furthermore, the ultrasound treatment is performed at 30–50 Hz for 1–3 minutes; the dialysis uses a dialysis bag with a capacity of 1000–2000 Da, and the dialysis time is 24–36 hours.

[0009] Furthermore, the sulfur-doped carbon dot ethanol solution is prepared by dissolving sulfur-doped carbon dots in ethanol to a concentration of 100–300 mg / L.

[0010] Furthermore, the filter membrane is prepared by immersing a 0.2–0.25 μm nylon filter membrane in a 0.5–2 mM NaHCO3 solution for 5–20 minutes.

[0011] This invention also provides a microfluidic chip for the cyclic detection of mercury ions based on sulfur-doped carbon dots, comprising a microfluidic plate body, wherein the microfluidic plate body is provided with a sample injection port for supplying a sulfur-doped carbon dot ethanol solution and a solution containing Hg. 2+ The sample solution is mixed via a zigzag mixing channel; a first observation window is used to monitor the fluorescence intensity of the mixed solution; and a channel is used to adsorb Hg from the mixed solution. 2+The system includes a filter membrane through which sulfur-doped carbon dots pass, a second observation window for monitoring the fluorescence intensity of the mixed solution after adsorption through the filter membrane, and a circulation outlet and inlet for recycling the sulfur-doped carbon dots. The sample injection port and the circulation inlet are respectively connected to the inlet of the bent mixing channel. The first observation window is located at the outlet of the bent mixing channel, which is connected to the circulation outlet via the filter membrane. The second observation window is located at the outlet of the filter membrane. The circulation outlet and the circulation inlet are connected via a peristaltic pump. The sulfur-doped carbon dot ethanol solution and the sample solution pass through the mixing channel and then flow into the first observation window. At this point, the CDs solution is at Hg... 2+ Under the given conditions, it is a blue solution, which is then filtered through a membrane to remove Hg. 2+ After filtration, the sulfur-doped carbon dot ethanol solution changes from blue to red. The solution then flows back through the circulation outlet to the circulation inlet of the microfluidic chip via a peristaltic pump, completing one cycle.

[0012] Furthermore, both the upper and lower membranes of the microfluidic plate body are polymer membranes formed from cyclic olefin copolymers (COC).

[0013] Furthermore, the filter membrane is prepared by immersing a 0.2–0.25 μm nylon filter membrane in a 0.5–2 mM NaHCO3 solution for 5–20 minutes.

[0014] This invention also provides a method for cyclically detecting mercury ions using the above-mentioned microfluidic chip, comprising the following steps: [The method involves] placing a Hg-containing... 2+ The sample solution to be tested is injected into the sample injection port of the microfluidic chip. A 100–300 mg / L sulfur-doped carbon dot ethanol solution is injected into the circulation inlet or initial carbon dot injection port of the microfluidic chip. After thorough mixing in the zigzag mixing channel, the solution flows through the first observation window to record the fluorescence intensity value F. After filtration through a filter membrane, the filtrate enters the circulation outlet and is returned to the microfluidic chip through the circulation inlet at a flow rate of 3–4 mL / s via a peristaltic pump, achieving cyclic detection and utilization. The solution is then processed by Hg... 2+ The linear relationship between concentration and fluorescence intensity ratio F0 / F was used to calculate the Hg concentration in the sample solution. 2+ The concentration of F0 is the initial fluorescence intensity value of the sulfur-doped carbon dot ethanol solution.

[0015] Furthermore, the mixing volume ratio of the sample solution to be tested to the sulfur-doped carbon dot ethanol solution is 1:(8-10), and the sulfur-doped carbon dot ethanol solution is prepared by dissolving sulfur-doped carbon dots in ethanol to a concentration of 100-300 mg / L.

[0016] Compared with existing technologies, the advantages of this invention are: a method for cyclic detection of mercury ions based on sulfur-doped carbon dots, its microfluidic chip, and its application; the fluorescence signal of the carbon dots is related to the detection of mercury ions by Hg. 2+ It exhibits significant response characteristics, displaying an "on-off" detection mode, enabling rapid identification and quantitative detection of mercury ions. Simultaneously, this invention incorporates a NaHCO3 filter membrane through a microfluidic chip structure design; after filtration through the membrane, the mixed solution adsorbs Hg from the solution. 2+ And allow the sulfur-doped carbon dot solution to pass through, so that it reacts with Hg 2+ The carbon dot system, after processing, can achieve fluorescence recovery and reflux within the microfluidic channel, thus enabling cyclic detection within the same chip platform. This overcomes the limitations of existing detection methods, which are mostly single-use and difficult to reuse. Furthermore, the microfluidic chip is integrated and portable, and the detection process is less affected by external environmental factors, effectively improving the stability and reliability of the detection. It also allows for rapid detection of mercury ions without relying on large, specialized instruments, making it suitable for on-site rapid detection needs. Attached Figure Description

[0017] Figure 1 For a specific embodiment, the cyclic detection of Hg using sulfur-doped carbon dots is described. 2+ Analytical diagram of the reaction mechanism; Figure 2 This is a design diagram of a microfluidic chip based on carbon dot fluorescence for cyclic detection of mercury ions, as shown in Specific Embodiment 2. Figure 3 This is a specific embodiment of the microfluidic chip components, where A is a microfluidic chip component and B is the principle of the filter membrane. Figure 4 In specific embodiment three, the microfluidic chip was used to detect Hg in a sulfur-doped carbon dot ethanol solution at different flow rates. 2+ The fluorescence ratio before and after (F0 / F), and the fluorescence ratio after recovery through the filter membrane (recovered F0 / F), where F0 is the initial fluorescence intensity of the sulfur-doped carbon dot ethanol solution, and F is the fluorescence intensity after the addition of Hg. 2+ Fluorescence intensity of the sulfur-doped carbon dot ethanol solution; Figure 5 To optimize the NaHCO3 soaking solution concentration of the filter membrane in Specific Embodiment 3, where A is a NaHCO3 concentration of 0.5 nM, B is a NaHCO3 concentration of 1.0 nM, C is a NaHCO3 concentration of 1.5 nM, and D is a NaHCO3 concentration of 2.0 nM; Figure 6 In the specific embodiment four, Hg is configured 2+The fluorescence color change of sulfur-doped carbon dots in ethanol solution at the first observation window of the microfluidic chip at concentrations of 0, 1.0, 5.0, 10.0, 20.0, and 40.0 nM; Figure 7 In the specific embodiment four, a microfluidic chip was used to detect the fluorescence ratio of biological samples with different concentrations of Hg. 2+ The linear relationship is shown below, where A is the large yellow croaker sample, B is the Litopenaeus vannamei sample, and C is the razor clam sample. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0019] Specific Embodiment 1: A method for cyclic detection of mercury ions based on sulfur-doped carbon dots, comprising the following steps: Containing Hg 2+ The sample to be tested was thoroughly mixed with a 200 mg / L sulfur-doped carbon dot ethanol solution at a volume ratio of 1:(8-10). The fluorescence intensity value F of the mixed solution was measured. The mixed solution was then filtered through a filter membrane to adsorb Hg from the mixed solution. 2+ And allow the sulfur-doped carbon dots to pass through, then react the sulfur-doped carbon dot ethanol solution again with new Hg-containing... 2+ The test samples are thoroughly mixed at a volume ratio of 1:(8-10) to achieve recycling, based on Hg 2+ The linear relationship between concentration and fluorescence intensity ratio F0 / F was used to calculate the Hg concentration in each test solution. 2+ The concentration of F0 is the initial fluorescence intensity value of the sulfur-doped carbon dot ethanol solution.

[0020] The preparation method of sulfur-doped carbon dots is as follows: o-phenylenediamine, trimesic acid, and 4-aminobenzenethiophenol are dissolved in 8–12 mL of ultrapure water at a mass ratio of 3:1:2. 100 μL–300 μL of concentrated sulfuric acid is added, and the mixture is placed in a polytetrafluoroethylene-lined tube. After sonication at 40 Hz for 1–3 min, the mixture is placed in a reaction vessel and reacted at 180℃–220℃ for 6–12 h. After cooling, the mixture is dialyzed through a 1000–2000 Da dialysis bag for 24–36 h and then freeze-dried to obtain a blue-black powder product, which is the sulfur-doped carbon dots. The sulfur-doped carbon dots are dissolved in an ethanol solution to a concentration of 200 mg / L to obtain a sulfur-doped carbon dot ethanol solution. The preparation method of the filter membrane is as follows: A 0.22 μm nylon filter membrane is immersed in a 50 mL centrifuge tube containing 0.5–2.0 mM NaHCO3. After shaking for 10 min, the filter membrane is removed for use.

[0021] Figure 1 Cyclic detection of Hg using sulfur-doped carbon dots in molecular simulation 2+In the process, the sulfur-doped carbon dots in the ethanol system initially exist in a macromolecular aggregate state, and upon the addition of Hg... 2+ Subsequently, the sulfur-doped carbon dots began to dissociate into small molecules and dispersed, while after the addition of NaHCO3, Hg... 2+ The sulfur-doped carbon dots detach from the sulfur-doped carbon dots, which gradually return to an aggregated state. The final state is that the sulfur-doped carbon dots change from dispersed small molecules to a locally aggregated state, thus achieving cyclic detection.

[0022] Specific Embodiment 2: A microfluidic chip for cyclic detection of mercury ions based on sulfur-doped carbon dots in Specific Embodiment 1.

[0023] like Figure 2 and Figure 3 As shown, it includes a microfluidic plate body, within which a sample injection port is provided for supplying a sulfur-doped carbon dot solution and a solution containing Hg. 2+ The sample solution is mixed via a zigzag mixing channel; a first observation window is used to monitor the fluorescence intensity of the mixed solution; and a channel is used to adsorb Hg from the mixed solution. 2+ The filter membrane through which sulfur-doped carbon dots pass is used to monitor the fluorescence intensity of the mixed solution after adsorption by the filter membrane. The filter membrane also has a second observation window for recycling sulfur-doped carbon dots and a circulation outlet and circulation inlet. The sample injection port and circulation inlet are connected to the inlet of the bent mixing channel. A first observation window is set at the outlet of the bent mixing channel. The outlet of the bent mixing channel is connected to the circulation outlet through the filter membrane. A second observation window is set at the outlet of the filter membrane. The circulation outlet is connected to the circulation inlet through a peristaltic pump.

[0024] The upper and lower membranes of the aforementioned microfluidic plate are both polymer membranes formed from cyclic olefin copolymers (COC). The filter membrane is prepared by immersing a 0.22 μm nylon filter membrane in a 0.5–2 mM NaHCO3 solution for 5–20 min. The volume ratio of the sample solution to the sulfur-doped carbon dot ethanol solution is 1:9. The sulfur-doped carbon dot ethanol solution is prepared by dissolving sulfur-doped carbon dots in ethanol to a concentration of 200 mg / L.

[0025] Figure 2 The specific dimensions of the microfluidic chip are as follows: the microfluidic chip is 140.0 mm long, 80.0 mm wide, and 10.0 mm high; the mixing channel is 50.0 mm long, and 0.2 mm deep and wide; the first observation window (large observation window) is 15.0 mm wide and 31.3 mm long; the filter channel has a diameter of 25.0 mm; the second observation window (small observation window) is 14.6 mm long and has a circulation port diameter of 5.0 mm.

[0026] Figure 3The components of the microfluidic chip are: a microfluidic plate body, a sample injection port, an initial carbon dot injection port, a bent mixing channel, two observation windows, a filter membrane, and a circulation outlet and circulation inlet. Figure 3 The principle of filtration membrane is based on sulfur doping with carbon dots and Hg. 2+ After the mixed solution passes through the filter membrane, Hg 2+ The sulfur-doped carbon dots are adsorbed by the membrane, while the sulfur-doped carbon dots can pass through the filter membrane normally, and the fluorescence color changes from blue to red.

[0027] Specific Implementation Example 3: Optimization of conditions for cyclic detection of mercury ions using a microfluidic chip based on Specific Implementation Example 2.

[0028] Depend on Figure 4 It can be seen that when the peristaltic pump flow rate of the microfluidic chip is controlled at 4 mL / s, the sulfur-doped carbon dots affect Hg. 2+ It has a good fluorescence quenching effect (F0 / F), and the fluorescence intensity after quenching can be restored to the original F0 fluorescence intensity (recovery).

[0029] Depend on Figure 5 As shown in section A, when the filter membrane is immersed in a 0.5 mM NaHCO3 solution, the sulfur-doped carbon dots in the microfluidic chip can be recycled up to 5 times in ethanol solution. By the 6th time, the fluorescence loss is 21.21%. Figure 5 As shown in section B, when the concentration of NaHCO3 in the soaking solution is 1.0 mM, the sulfur-doped carbon dots in the microfluidic chip can be recycled up to 7 times, and by the 7th time, the fluorescence loss is only 7.95%. Figure 5 As shown in section C, when the concentration of NaHCO3 in the soaking solution is 1.5 mM, the sulfur-doped carbon dots in the microfluidic chip can be recycled up to 5 times in ethanol solution. By the 6th recycling, the fluorescence loss is 23.64%. Figure 5 As shown in D, when the concentration of NaHCO3 in the soaking solution is 2.0 mM, the sulfur-doped carbon dots in the microfluidic chip can be recycled up to 3 times. By the 4th time, the fluorescence loss is 19.38%. Therefore, when the filter membrane is soaked in 1.0 mM NaHCO3 solution, the microfluidic cycle can be up to 7 times.

[0030] Specific Embodiment Four: The method for cyclically detecting mercury ions in actual samples using the microfluidic chip of Specific Embodiment Two under optimal conditions. The specific steps are as follows: Step 1, Sample Pretreatment: Sample pretreatment: Take 2 g of biological sample into a 50 mL PTFE-lined tube, add 8 mL of concentrated nitric acid, 1 mL of concentrated sulfuric acid, and 1 mL of concentrated hydrochloric acid, and soak overnight. Then add 2 mL of hydrogen peroxide, tighten the cap, ensuring the volume does not exceed one-third of the liner tube, place it in a reaction vessel, and heat at 120-140℃ for 3 h, then cool to room temperature. Wash with ultrapure water, filter the supernatant and washings through a 0.45 μm filter membrane, collect the filtrate in a 100 mL volumetric flask, adjust the pH to 7, and make up to volume for later use.

[0031] Step 2: Inject a 200 mg / L sulfur-doped carbon dot ethanol solution into the initial carbon dot injection port (or circulation inlet). Prepare Hg-containing solutions of 0, 1.0, 5.0, 10.0, 20.0, and 40.0 nM. 2+ The sample solution was sequentially injected into the other sample injection port, along with a sulfur-doped carbon dot ethanol solution containing Hg. 2+ After the sample solution is thoroughly mixed through the zigzag mixing channel, it flows through the first observation window, where it appears blue. The fluorescence intensity value F of the mixed solution is recorded. After filtration through a filter membrane, the solution changes from blue to red, and then returns to the microfluidic chip's circulation inlet at a rate of 4 mL / s via a peristaltic pump, enabling single-cycle sample detection. Different Hg levels are captured by imaging through the first observation window. 2+ Fluorescence images of mixed solutions at different concentrations of Hg were collected. 2+ The fluorescence intensity value F corresponding to the mixed solution of different concentrations was used to establish Hg. 2+ A standard curve of the concentration-to-fluorescence intensity ratio F0 / F was used to obtain the concentration of Hg in the sample. 2+ Quantitative detection of concentration, where F0 is the initial fluorescence intensity value of the sulfur-doped carbon dot ethanol solution.

[0032] Figure 6 For different Hg 2+ Fluorescence images captured by the first observation window in the microfluidic chip at a concentration of Hg 2+ The concentration range is 0-40.0 nM, and the fluorescence intensity value varies with Hg. 2+ As the concentration increases, the color changes from red to blue. When Hg... 2+ At a concentration of 20.0 nM, the fluorescence color turns blue.

[0033] The above method was used to determine the levels of Hg in large yellow croaker, Litopenaeus vannamei, and razor clams, and a standard curve was plotted. 2+ A standard curve was plotted with concentration on the x-axis and the fluorescence intensity ratio F0 / F on the y-axis. The results are as follows: Figure 7 As shown.

[0034] Depend on Figure 7 As can be seen from A, in the detection of large yellow croaker samples, Hg 2+It exhibits good linearity in the concentration range of 0-40.0 nM, with the linear equation being y = 1.0067 + 0.01053x, R0 2 = 0.9828, the detection limit is calculated to be 1.46 nM; from Figure 7 From B, we know that in the detection of Litopenaeus vannamei samples, the linear equation is y = 1.01235 + 0.01602x, R0 2 = 0.9874, the detection limit is calculated to be 1.28 nM; from Figure 7 From equation C, we know that in the detection of razor clam samples, the linear equation is y = 1.0532 + 0.01027x, R0 2 =0.9633, the detection limit is calculated to be 1.32 nM, where y is the fluorescence intensity ratio F0 / F, and x represents Hg. 2+ The concentration.

[0035] In summary, the detection method described in Specific Embodiment Four is used to cyclically detect Hg. 2+ It can perform up to 7 cycles of detection and has low detection limit and high sensitivity in real samples, indicating that the method is not only low in detection cost but also has good practicality in real samples.

[0036] The foregoing description is not intended to limit the invention, nor is the invention limited to the examples given. Any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the invention should also be considered within the protection scope of the invention.

Claims

1. A method for cyclic detection of mercury ions based on sulfur-doped carbon dots, characterized in that, Includes the following steps: Containing Hg 2 + The sample to be tested was thoroughly mixed with a sulfur-doped carbon dot ethanol solution with a concentration of 100–300 mg / L at a volume ratio of 1:(8–10). The fluorescence intensity value F of the mixed solution was measured. The mixed solution was then filtered through a filter membrane to adsorb Hg from the mixed solution. 2+ And allow the sulfur-doped carbon dots to pass through, then react the sulfur-doped carbon dot ethanol solution again with new Hg-containing... 2+ The test samples are thoroughly mixed at a volume ratio of 1:(8-10) to achieve recycling, based on Hg 2+ The linear relationship between concentration and fluorescence intensity ratio F0 / F was used to calculate the Hg concentration in each test solution. 2+ The concentration of F0 is the initial fluorescence intensity value of the sulfur-doped carbon dot ethanol solution.

2. The method for cyclic detection of mercury ions based on sulfur-doped carbon dots according to claim 1, characterized in that, The preparation method of the sulfur-doped carbon dots is as follows: o-phenylenediamine, trimesic acid and 4-aminothiophenol are dissolved in 8-12 mL of ultrapure water at a mass ratio of (1-3):(0.8-1.2):(1-3), 100 μL-300 μL of concentrated sulfuric acid is added, and the mixture is placed in a polytetrafluoroethylene-lined tube. After ultrasonic treatment, the mixture is placed in a reaction vessel and reacted at 180℃-220℃ for 6-12 h. After cooling, the mixture is dialyzed and freeze-dried to obtain a blue-black powder product, which is the sulfur-doped carbon dots.

3. The method for cyclic detection of mercury ions based on sulfur-doped carbon dots according to claim 2, characterized in that, The ultrasound treatment is performed at 30–50 Hz for 1–3 minutes; the dialysis uses a dialysis bag with a capacity of 1000–2000 Da and the dialysis time is 24–36 hours.

4. The method for cyclic detection of mercury ions based on sulfur-doped carbon dots according to claim 1, characterized in that, The sulfur-doped carbon dot ethanol solution is prepared by dissolving sulfur-doped carbon dots in ethanol to a concentration of 100–300 mg / L.

5. The method for detecting mercury ions based on sulfur-doped carbon dots in a cyclic manner according to claim 1, characterized in that, The filter membrane is prepared by immersing a 0.2–0.25 μm nylon filter membrane in a 0.5–2 mM NaHCO3 solution for 5–20 min.

6. A microfluidic chip for cyclic detection of mercury ions based on sulfur-doped carbon dots, characterized in that, The system includes a microfluidic plate body, which has a sample injection port for supplying a sulfur-doped carbon dot ethanol solution and a solution containing Hg. 2+ The sample solution is mixed via a zigzag mixing channel; a first observation window is used to monitor the fluorescence intensity of the mixed solution; and a channel is used to adsorb Hg from the mixed solution. 2+ The system includes a filter membrane through which sulfur-doped carbon dots pass, a second observation window for monitoring the fluorescence intensity of the mixed solution after adsorption by the filter membrane, and a circulation outlet and a circulation inlet for recycling sulfur-doped carbon dots. The sample injection port and the circulation inlet are respectively connected to the inlet of the bent mixing channel. The first observation window is located at the outlet of the bent mixing channel. The outlet of the bent mixing channel is connected to the circulation outlet through the filter membrane. The second observation window is located at the outlet of the filter membrane. The circulation outlet and the circulation inlet are connected through a peristaltic pump.

7. The microfluidic chip according to claim 6, characterized in that, The upper and lower membranes of the microfluidic plate body are both polymer membranes formed by cyclic olefin copolymers.

8. The microfluidic chip according to claim 6, characterized in that, The filter membrane is prepared by immersing a 0.2–0.25 μm nylon filter membrane in a 0.5–2 mM NaHCO3 solution for 5–20 min.

9. A method for cyclically detecting mercury ions based on a microfluidic chip according to any one of claims 6 to 8, characterized in that, Includes the following steps: containing Hg 2+ The sample solution to be tested is injected into the sample injection port of the microfluidic chip. A 100–300 mg / L sulfur-doped carbon dot ethanol solution is injected into the circulation inlet or initial carbon dot injection port of the microfluidic chip. After thorough mixing in the zigzag mixing channel, the solution flows through the first observation window to record the fluorescence intensity value F. After filtration through a filter membrane, the filtrate enters the circulation outlet and is returned to the microfluidic chip through the circulation inlet at a flow rate of 3–4 mL / s via a peristaltic pump, achieving cyclic detection and utilization. The solution is then processed via Hg... 2+ The linear relationship between concentration and fluorescence intensity ratio F0 / F was used to calculate the Hg concentration in the sample solution. 2+ The concentration of F0 is the initial fluorescence intensity value of the sulfur-doped carbon dot ethanol solution.

10. The method for cyclically detecting mercury ions using a microfluidic chip according to claim 9, characterized in that, The volume ratio of the sample solution to be tested to the sulfur-doped carbon dot ethanol solution is 1:(8-10), and the sulfur-doped carbon dot ethanol solution is prepared by dissolving sulfur-doped carbon dots in ethanol to a concentration of 100-300 mg / L.

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