A micropore surface charge density measurement method based on ion current rectification effect

Abstract

The application provides a micropore surface charge density measurement method based on ion current rectification effect, which is based on ion current rectification effect (ICR), ion electroosmotic flow (EOF) in a micropore is driven by applying a voltage, and a rectification phenomenon of ion current will be formed under a concentration gradient. Since the ion solution in the high and low concentration liquid pools under positive and negative polarity voltages cannot fill the entire micropore, the ion current rectification ratio cannot be represented by the ratio of bulk solution conductivity. However, according to the ion concentration at different positions in the micropore, the resistance ratio under different polarity voltages can be used to effectively characterize the ion current rectification. The ion current rectification ratio can also be calculated through the current-voltage curve. Thus, the relationship between the micropore surface charge density and the ion current rectification ratio is established. The surface charge density is accurately predicted by measuring the ion current rectification ratio of the micropore.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of micro-nano technology, and particularly relates to a micropore surface charge density measurement method based on ion current rectification effect. BACKGROUND

[0002] Micropores have wide applications in the fields of material separation, sensing, and energy conversion. The surface charge density of micropores is one of the key parameters affecting their performance, which directly affects the selective separation efficiency, sensing sensitivity, and energy conversion efficiency of micropores by regulating the transport behavior of ions and molecules in the pore channel. The surface potential φ 0 is linearly related to the surface charge density σ , that is, σ = C dl φ 0, wherein C dl is the double-layer capacitance determined by the ion strength and ion valence. For example, in the field of biomolecule detection (such as DNA sequencing), the charge density affects the electrostatic interaction between the molecule and the pore wall, thereby regulating the capture speed and translocation signal of the molecule; in the field of ion sieving or seawater desalination, the charge density enhances the ion selective transport through the double-layer effect, achieving high-efficiency separation. Therefore, accurate prediction of the surface charge density of micropores is of great significance for optimizing their design, improving their performance, and promoting their practical applications.

[0003] The commonly used methods for measuring the surface charge density at present mainly include direct potential measurement using Kelvin force microscopy (KPFM), surface charge measurement using nanopore sensors, and zeta potential measurement using streaming potential and optical detection techniques. Kelvin probe force microscopy is a tool for imaging the nanoscale surface potential of various materials with sub-nanometer resolution. It can measure the contact potential difference (CPD) between the sample surface and the probe, and the voltage is V CPD ( φ tip - φ sample ) / e , wherein φ tip and φ sample are the functional functions of the tip and the sample, respectively, eis the elementary charge. This method can provide high-resolution surface potential distribution, but has obvious limitations, and requires high sample surface flatness and is difficult to measure directly in solution environment, limiting its application in complex practical systems. Nanopore sensors indirectly reflect the change of zeta potential by analyzing the relationship between ion current and voltage (I-V curve); the principle of optical detection technology for measuring zeta potential is to measure the mobility of charged particles in an electric field (electrophoretic mobility) to calculate the zeta potential. The relationship between electrophoretic mobility ( μ ) and zeta potential ( ζ ) is , where is the relative dielectric constant of the solution, is the vacuum dielectric constant, η is the viscosity of the solution, is a function related to the double-layer thickness κ -1 and the particle radius. Optical detection technology has high requirements for particle size and solution transparency, and it is difficult to achieve real-time dynamic monitoring. In summary, the existing surface charge density measurement methods generally face the challenges of complicated operation, dependence on high-precision instruments, and strict requirements for experimental conditions, especially in complex solution environments, making it difficult to achieve efficient and accurate measurement.

[0004] Therefore, it is of important research value and application significance to explore a new method that is simple to operate, has low equipment requirements, is highly adaptable, and can comprehensively, accurately and truly reflect the surface charge density. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a micropore surface charge density measurement method based on the ion current rectification effect (Ionic Current Rectification, ICR). The method can quickly and accurately calculate the surface charge density of the micropore by measuring the ion current rectification ratio of the micropore under the concentration gradient and combining the theoretical model. The method is simple, does not require professional instruments, has low experimental condition requirements and low cost; the measurement result is accurate and suitable for predicting the surface charge density of micropores with a pore size of 200-1000 nm. The present application is realized by the following technical solutions:

[0006] A micropore surface charge density measurement method based on the ion current rectification effect, which utilizes a micropore surface charge density measurement system based on the ion current rectification effect. The measurement system comprises two liquid pools with the same structure, electrodes arranged in each liquid pool, and a liquid pool fixing seat for fixing the liquid pool and the micropore membrane. The two liquid pools contain salt solutions respectively, and the micropore membrane has micropores. The liquid pool is made of transparent material. The measurement method comprises the following steps:

[0007] (1) The micropore membrane to be tested is placed between two liquid pools, and the solution environment is divided into left and right liquid pool regions. Material exchange can only occur through the micropore to be tested between the two liquid pools.

[0008] (2) Different concentrations of salt solutions (such as 50, 100, 200, 500, 800, and 1000 mmol / L KCl solutions) are prepared. The same volume of salt solutions with different concentrations is added to two identical liquid pools, and the height of the left and right liquid pools is ensured to be the same by visual observation. The two liquid pools are labeled as the low-concentration side and the high-concentration side according to the concentration of the salt solution. The two electrodes are inserted into the two liquid pools, and then a voltage is applied to the electrodes U , and the ion current in the micropore is measured.

[0009] (3) The concentration of the salt solution in the low-concentration side liquid pool is kept constant, and the concentration of the salt solution in the other liquid pool and the size of the voltage U are changed continuously, so as to obtain the current-voltage relationship curve of the micropore under the concentration gradient.

[0010] (4) The ion current rectification ratio is calculated from the current-voltage relationship curve.

[0011] (5) The surface charge density is predicted by measuring the ion current rectification ratio of the micropore.

[0012] In step (4), the ion current rectification ratio is calculated as follows:

[0013] The ion rectification ratio in the micropore to be tested is represented by formula (i):

[0014]

[0015]

[0016]

[0017]

[0018] In formulas (i), (ii), (iii), (iv), and (v), I is the total current (A), R is the total resistance (Ω), R ac is the contact resistance (Ω), R p is the pore resistance (Ω), C i is the ion concentration (mol / L), D i is the ion diffusion coefficient (m 2 / s),z i is the ion valence (dimensionless constant), R is the universal gas constant (J / mol / K), F is the Faraday constant (C / mol), T is the temperature (K), κ is the conductivity of the solution (S / m). The subscripts +, -, and i represent the positive voltage, negative voltage, and ion species, respectively.

[0019] The ion concentration in the micropore to be measured under different conditions is calculated using formulas (vi) and (vii):

[0020]

[0021]

[0022] In formulas (vi) and (vii), C H is the concentration of the high-concentration solution (mmol / L); C L is the concentration of the low-concentration solution (mmol / L); α H is the chemical activity coefficient of the high-concentration solution (dimensionless constant), α L is the chemical activity coefficient of the low-concentration solution (dimensionless constant), x is the axial position in the micropore (m), L is the length of the micropore (m), V is the magnitude of the applied voltage (V), σ is the surface charge density (C / m 2 ).

[0023] According to the present application, in step (1), the pore size of the micropore is 200-1000 nm, and the length of the micropore is 2-12 μm.

[0024] According to the present application, in step (1), the liquid pool is a liquid storage pool loaded with a salt solution, and the material is preferably an inert non-conductive material, such as poly chlorotrifluoroethylene (PCTFE).

[0025] According to the present application, preferably, in steps (2) and (3), the salt solution is an aqueous solution of a salt; the salt is potassium chloride or sodium chloride; the concentration of the low-concentration salt solution is 50 mmol / L; and the concentration of the high-concentration salt solution is 100-1000 mmol / L, so as to form a concentration ratio of 1:2, 1:4, 1:10, 1:16, and 1:20, thereby forming a concentration gradient.

[0026] According to the present application, preferably, in step (2), the types of salt solutions are the same.

[0027] According to the application, preferably, in step (2), the electrodes are both Ag / AgCl electrodes.

[0028] According to the application, preferably, in step (2), the electrodes are applied with a voltage U is -2.0 V~2.0 V.

[0029] According to the application, in step (4), in formula (ii), (vi), (vii), the pore length L is the thickness of the microporous membrane to be measured, and the activity coefficients corresponding to different salt solution concentrations can be obtained by consulting relevant information.

[0030] According to the application, in step (4), in formula (vi), (vii), C H and C L are the concentrations of the salt solutions in the two liquid pools obtained in the experimental solution preparation stage.

[0031] According to the application, in step (4), in formula (i), the ICR ratio can be obtained from the current-voltage curve of the micropore at different concentration gradients determined in step (3), or simulated using a finite element simulation method.

[0032] According to the application, in step (4), in formula (i), the ICR ratio can be represented by the ratio of the resistances under different polar voltages. By substituting formula (ii), (v) into formula (i), the relationship between the ion concentration in the micropore and the ICR ratio can be obtained.

[0033] According to the application, in step (4), in formula (vi), (vii), a preset surface charge density value is set, and the ion concentration in the micropore can be represented by the surface charge density of the micropore, the pore length, the applied voltage, the concentrations of the solutions in the two liquid pools, and the activity coefficients. By substituting them into formula (i), (ii), (v) and solving, the ICR ratio of the micropore can be obtained. By comparing the ICR ratios obtained in various ways, the preset surface charge density value is adjusted so that the error is less than 5%. The size of the preset surface charge density is the predicted surface charge density of the micropore.

[0034] Based on the experimental ICR ratio and the established concentration distribution equation, the application proposes a method for measuring the surface charge density. The ICR ratio obtained by experimental measurement, the pore size, the applied voltage, and the solution concentration are used as input parameters, and the surface charge density of the micropore is predicted by coupling equations.

[0035] The principle of the measuring method of the application is as follows: the measuring principle of the application is based on ion current rectification effect (ICR), and the ion electroosmotic flow (EOF) in the micropore is driven by applying a voltage, and the rectification phenomenon of ion current is formed under the concentration gradient. Because the aqueous solution in the high and low concentration liquid pool under the positive and negative voltage cannot fill the entire micropore, the ion current rectification ratio cannot be represented by the ratio of the bulk solution conductivity. But according to the ion concentration at different positions in the micropore, the resistance ratio under different polarity voltages can be used to effectively characterize the ion current rectification. The ion current rectification ratio can also be calculated through the current-voltage curve. Thus, the relationship between the surface charge density of the micropore and the ion current rectification ratio is established. Therefore, the surface charge density can be accurately predicted by measuring the ion current rectification ratio of the micropore.

[0036] The technical features and beneficial effects of the application are as follows:

[0037] 1. The method of the application is simple to operate, has low equipment requirements and strong adaptability, and is suitable for various micropores and complex solution environments, and can accurately measure the surface charge density of micropores with a pore size range of 200 nm to 1000 nm.

[0038] 2. The surface charge density predicted by the surface charge density measurement method proposed in the application has an error of less than 5% compared with the laboratory measurement and finite element simulation results, and is highly consistent, thereby realizing accurate prediction of the surface charge density of the micropore. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The schematic diagram of the measurement system structure used for measuring the pore size and pore density of the porous membrane in Example 1 is shown in the figure.

[0040] Wherein: 1-electrode, 2-liquid pool, 3-microporous membrane, 4-liquid pool fixing seat; 401-seat body, 402-positioning screw.

[0041] Figure 2 The current-voltage curve in the micropore under different concentration gradients of potassium chloride solution in Example 2 is shown in the figure.

[0042] Figure 3 The ion concentration distribution curve in the micropore predicted by using the formula in Example 2 is shown in the figure.

[0043] Figure 4 The comparison diagram of the surface charge density prediction and the finite element simulation in Example 2 is shown in the figure.

[0044] Figure 5 The current-voltage curve in the micropore under different concentration gradients of sodium chloride solution in Example 3 is shown in the figure.

[0045] Figure 6 The comparison diagram of the surface charge density prediction and the finite element simulation in Example 3 is shown in the figure.

[0046] Figure 7 This is a comparison chart of the predicted ion concentration distribution in a micron-sized pore under different pore lengths in Example 3 and the finite element simulation.

[0047] Figure 8 This is a comparison chart of the predicted ion concentration distribution in the micron-sized pores and the finite element simulation under different concentration gradient conditions in Example 3.

[0048] Figure 9 The image shows a comparison between the predicted ion concentration distribution within the micron-sized pores and the finite element simulation under different surface charge density conditions in Example 3.

[0049] Figure 10 This is a comparison chart of the predicted ion concentration distribution in the micron-sized pores and the finite element simulation under different applied voltage conditions in Example 3. Detailed Implementation

[0050] The present invention will be further described below with reference to specific embodiments, but is not limited thereto.

[0051] Furthermore, unless otherwise specified, the experimental methods described in the following embodiments are all conventional methods; and unless otherwise specified, the reagents, materials and equipment are all commercially available.

[0052] Example 1: A measurement system for surface charge density of micron-sized pores based on ion current rectification effect.

[0053] like Figure 1 As shown, the experiment includes two identical liquid pools 2, electrodes 1 respectively disposed in each liquid pool 2, and a liquid pool fixing base 4. The liquid pool fixing base 4 includes a base body 401 and a positioning screw 402. The positioning screw 402 passes through one side of the base body 401 and contacts one of the liquid pools 2. A microporous membrane 3 is placed between the two liquid pools 2, separating them into two liquid pool regions, each containing a salt solution. The microporous membrane 3 has micropores. The liquid pools 2 are made of a transparent material. During the experiment, the microporous membrane 3 to be tested is placed between the two liquid pools 2. Then, the positioning screw 402 is rotated to fix the two liquid pools, ensuring the microporous membrane is fixed between them. Salt solutions of different concentrations but the same volume are added to the two liquid pools using a dropper. The electrodes are then inserted into the two liquid pools, completing the experimental system.

[0054] Example 2: A method for measuring the surface charge density of micron-sized pores based on the ion current rectification effect.

[0055] The experimental system used is as follows Figure 1As shown, the microporous membrane to be tested is fixed in the middle of the liquid cell 2, and the solution environment is divided into two liquid cell areas, and only material exchange can be carried out between the two liquid cells through the micropore 3. Different concentrations of KCl solution are added to the two liquid cells respectively, and the liquid level of the left and right liquid cells is ensured to be level by visual method, and the liquid level is higher than the micropore. The Ag / AgCl electrode 1 is immersed in the left and right two liquid cells respectively, and the experimental measurement system is obtained.

[0056] The microporous membrane to be tested in the example is PET material, and the micropore diameter is 475 nm. The micropore length is 12 μm. The micropores on the membrane are made by needle punching + track etching method.

[0057] The measurement method includes the following steps:

[0058] (1) After carefully washing the measurement system with deionized water, the microporous membrane is fixed between the two liquid cells. KCl solutions with concentrations of 50 mmol / L and 1000 mmol / L are prepared respectively. First, 50 mmol / L KCl solution is injected into one side of the liquid cell until the liquid cell is completely filled, and the side is marked as the low concentration solution, and the volume of the injected solution is recorded. Subsequently, the same volume of 1000 mmol / L KCl solution is injected into the other side of the liquid cell, which is marked as the high concentration solution, and the salt solution height in the two liquid cells is ensured to be consistent to eliminate the experimental error that may be caused by the difference in liquid level height. The Ag / AgCl electrode is immersed in the salt solution on both sides, and then a voltage is applied to the electrode U . The voltage is changed in the range of -2 V~2 V U . The corresponding current at each voltage is recorded to obtain the current-voltage curve of the micropore. As shown in Figure 2 . The ion current rectification ratio ICR ratio of the micropore is calculated by the formula I + / I - . The precise prediction of the surface charge density can be realized by the relationship between the rectification ratio and the surface charge density. As shown in Figure 4 , the predicted surface charge density of the example is in good agreement with the simulation result.

[0059] (2) Theoretical prediction of surface charge density:

[0060] The ion rectification ratio in the micropore to be tested is represented by formula (i):

[0061]

[0062]

[0063]

[0064]

[0065] in formula (i), (ii), (iii), (iv), (v), I is the total current (A), R is the total resistance (Ω), R ac is the contact resistance (Ω), R p is the pore resistance (Ω), C i is the ion concentration (mol / L), D i is the ion diffusion coefficient (m 2 / s), z i is the ion valence (dimensionless constant), R is the universal gas constant (J / mol / K), F is the Faraday constant (C / mol), T is the temperature (K), κ is the conductivity of the solution (S / m). The subscripts +, -, and i represent the positive voltage, negative voltage, and ion species, respectively.

[0066] Current I It can be measured in the laboratory by an electrochemical workstation and a picoammeter, or obtained by finite element simulation method.

[0067] Resistance R It can be calculated by formula (ii).

[0068] Ion concentration C It can be calculated by formula (vi), (vii).

[0069] The ion diffusion coefficient and the solution activity coefficient can be obtained by looking up the table.

[0070] The ion concentration in the micron-sized pore under different conditions is calculated by formula (vi), (vii):

[0071]

[0072]

[0073] in formula (vi), (vii), C H is the concentration of the high-concentration solution (mmol / L); C L is the concentration of the low-concentration solution (mmol / L); α H is the chemical activity coefficient of the high-concentration solution (dimensionless constant),α L the chemical activity coefficient (dimensionless constant) for the low concentration solution, x the axial position in the micropore (m), L the micropore length (m), V the applied voltage (V), σ the surface charge density (C / m 2 ).

[0074] The micropore length used in this example is 12 μm, the micropore diameter is 475 nm, the low concentration side salt solution is 50 mmol / L KCl solution, and the high concentration side salt solution is 1000 mmol / L KCl solution.

[0075] Table 1

[0076]

[0077] Note: The activity coefficients of salt solutions with different concentrations can be obtained by looking up the book Electrolyte solution; the ion diffusion coefficients corresponding to different ions can be obtained by querying the website aqion (https: / / www.aqion.de / ).

[0078] It is assumed in advance that the surface charge density of the micropore to be measured is -0.025 C / m 2 .

[0079] In formula (vi) and (vii), C H 、C L respectively represent the concentrations of the KCl salt solution prepared in advance, and the values are 1000 mmol / L and 50 mmol / L respectively; α H , α L The activity coefficients 0.604 and 0.816 corresponding to the KCl solutions with concentrations of 1000 mmol / L and 50 mmol / L respectively can be obtained by querying Electrolyte solution; the micropore length L is 12 μm, which can be determined by measuring the thickness of the micropore film; the applied voltage V is set to 2 V and -2 V; σ is the preset value of the surface charge density of the micropore, which is -0.025 C / m 2 ; x represents the axial position in the micropore, which ranges from 0 to 12 μm; C + , C -These represent the ion concentrations within the micron-sized pores under positive and negative voltages, respectively.

[0080] Will C H 、C L 、α H 、α L , L, V, σ, x Substituting into formulas (vi) and (vii), the ion concentration along the micron-pore axis under positive and negative voltages can be obtained. C + , C - Distribution, such as Figure 3 As shown.

[0081] In equation (v), F The Faraday constant is 96485.33289 C / mol; R The universal gas constant is 8.31451 J / mol / K; Z i It is an ionic oxidation state; C i This refers to the ion concentration. D i The ion diffusion coefficient is... D K+ 1.96×10 -9 m 2 / s, D Cl﹣ 2.03×10 -9 m 2 / s, this value can be obtained from the Aqion website (https: / / www.aqion.de / ); κ Let be the conductivity of the solution.

[0082] Will C + , C - Substituting into formula (v), the solution conductivity at each axial position within the micron-hole under positive and negative voltages can be obtained. κ + , κ - .

[0083] In equation (ii), d The pore diameter is 475 nm, which can be calculated during the micron-pore preparation process; L The pores are micron-sized and 12 μm in length.

[0084] Will κ + , κ- Substitute equation (ii) into equation (i), the micropore resistance under positive and negative voltage can be obtained R + 、 R - The whole micropore corresponds to R + and R - are 2939555 Ω and 34461874 Ω respectively.

[0085] In equation (i), the current rectification ratio ICR ratio can be calculated by the current ratio in the micropore under positive and negative voltage I + / I - The current I + 、 I - The kitheley picoammeter and the electrochemical workstation can be used to measure the current under positive and negative voltage respectively. Or use the finite element simulation method to obtain Figure 2 The measured current-voltage curve is shown. The ICR ratio obtained by experiment and finite element simulation method is 11.00974 and 11.02297 respectively.

[0086] Substitute R + 、 R - into equation (i), the micropore current rectification ratio ICR ratio can be calculated, which is 11.72350. Compare the ICR ratio obtained by different methods, and continuously adjust the preset surface charge density value until the error of the surface charge density value calculated by two methods is less than 5%, which can be considered as the predicted surface charge density. The final predicted surface charge density value of this example is-0.023 C / m 2 .

[0087] Example 3, simulation of multiple condition factors

[0088] As shown in Figures 5-10 , this embodiment carries out simulation of multiple condition factors

[0089] 3.1 Different salt solutions: under the same conditions, sodium chloride solution is used to carry out experiment and simulation, and the results are shown in Figure 5 and Figure 6 , it is verified that the micropore surface charge density measurement method proposed by the application is also applicable to sodium chloride solution.

[0090] 3.2 Different pore length: Under the same conditions, experiments and simulation were performed using micropores with different pore lengths, and the results are shown in FIG. 3.2, which shows that as the pore length of the micropore gradually increases, the fitting degree of the ion concentration prediction formula in the micropore proposed by the present application and the simulation results gradually decreases. The error gradually increases only in the range of 8 μm~12 μm of the axial range of the micropore. Figure 7

[0091] 3.3 Different concentrations: Under the same conditions, experiments and simulation were performed using salt solutions with different concentrations, and the results are shown in FIG. 3.3, which shows that as the concentration gradually increases, the error of the concentration fitting curve in the range of 8 μm~12 μm of the micropore gradually increases. Figure 8

[0092] 3.4 Different surface charge densities and voltages: As shown in FIG. 3.4 and FIG. 3.5, the error of the ion concentration distribution in the micropore obtained by the inventors under different surface charge densities and different voltages does not change significantly. Figure 9 Figure 10

[0093] Therefore, it can be considered that the prediction formula of the ion concentration distribution in the micropore proposed by the present application can be applied to a larger range of voltages U and surface charge densities σ .

[0094] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.​​​​

Claims

1. A method for measuring surface charge density of a micropore based on ion current rectification effect, characterized in that, The application discloses a measuring system for surface charge density of a micropore based on ion current rectification effect, and a measuring method thereof. The measuring system comprises two liquid pools with the same structure, electrodes arranged in the liquid pools respectively, and a liquid pool fixing base for fixing the liquid pools and a micropore membrane; the two liquid pools contain salt solutions respectively, and the micropore membrane has micropores; the measuring method comprises the following steps: (2) Different concentrations of salt solution were prepared; the same volume of salt solution with different concentrations was added to two identical liquid pools, ensuring that the heights of the left and right liquid pools were the same; according to the concentration of the salt solution, the two liquid pools were marked as the low-concentration side and the high-concentration side; two electrodes were inserted into the two liquid pools, and then a voltage was applied to the electrodes U , and the current in the micropore was measured; (3) keeping the concentration of the low concentration side constant, changing the concentration of the other solution and the voltage constantly U the size of the concentration gradient, and the current-voltage relationship curve of the micropore under the concentration gradient is obtained. (1) placing the micropore membrane to be measured between the two liquid pools, dividing the salt solution environment into left and right liquid pool regions, and allowing material exchange between the two liquid pools only through the micropore to be measured; (4) calculating the ion current rectification ratio through a current-voltage relationship curve; (5) realizing prediction of the surface charge density through the ion current rectification ratio of the micropore; In step (5), the ion concentration in the micropore to be measured is calculated according to the preset surface charge density, so as to calculate the solution conductivity; the resistance is calculated by means of the conductivity, and then the ion current rectification ratio of the micropore is obtained; the obtained rectification ratio is compared with the rectification ratio calculated through the current-voltage curve; 2. The method of claim 1, wherein the method is characterized by, According to the comparison result of the obtained rectification ratio and the rectification ratio calculated through the current-voltage curve, the preset surface charge density value is continuously adjusted until the error of the surface charge density values calculated by the two methods is less than 5%, and the predicted surface charge density is considered as the surface charge density of the micropore. In step (4), the ion current rectification ratio is calculated through the following manner: in formulae (i), (ii), (iii), (iv), I is the total current, A; R is the total resistance, Ω; R ac Rct is the contact resistance, Ω; R p Rb is the bulk resistance, Ω; d D is the micropore diameter, μm; L L is the micropore length, μm; In step (4), the ion concentration in the micropore to be measured under different conditions is calculated through formulas (vi) and (vii): σ is the conductivity of the solution, S / m; the subscripts +, - and i represent the positive voltage, negative voltage and ionic species, respectively; in formula (v), C i is the ion concentration, mol / L; D i is the ion diffusion coefficient, m 2 / s; z i is the ion valence, dimensionless constant; R is the universal gas constant, J / mol / K; F is the Faraday constant, C / mol; T is the temperature, K; the subscripts +, - and i represent positive voltage, negative voltage and ion species, respectively.

3. The method of claim 2, wherein the method is characterized by, In step (5), the surface charge density of the micropore to be measured is calculated in the following manner: In equations (vi) and (vii), C H The concentration of the high-concentration solution is expressed in mmol / L. C L The concentration of the low-concentration solution is expressed in mmol / L. α H is the chemical activity coefficient of a high-concentration solution, a dimensionless constant; α L is the chemical activity coefficient of a low-concentration solution, a dimensionless constant; x The axial position within the micrometer-sized aperture is in meters (m). L The pore length is in micrometers (m). V The applied voltage is expressed in V. The preset surface charge density is substituted into formulas (vi) and (vii) to calculate the ion concentration in the micropore to be measured. Surface charge density, C / m 2 .

4. The method of claim 3, wherein the method is characterized by, In step (1), the micropore diameter of the micropore to be measured is 200-1000 nm, and the micropore length is 2-12 microns. In step (2), the salt solution is selected from a sodium chloride solution or a potassium chloride solution.

5. The method of claim 1, wherein the method is characterized by: In step (2), the salt solution concentration includes 50, 100, 200, 500, 800 and 1000 mmol / L.

6. The method of claim 1, wherein the method is characterized by, The electrodes are all Ag / AgCl electrodes.

7. The method of claim 1, wherein the method is characterized by: ​ 8. The method of claim 1, wherein the method is characterized by, ​ 9. The method of claim 1, wherein the method is characterized by, In step (2), the voltage applied by the electrodes is between -2.0 and 2.0 V. U In step (2), the voltage applied by the electrodes is between -2.0 and 2.0 V.

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