A method for in-situ detection of grafting density of polymer brush coating based on nanopore ion current

Abstract

The application discloses a method for in-situ detection of grafting density of polymer brush coating based on nanopore ion current, which comprises the following steps: establishing a quantitative relationship model between ion current in a nanopore and grafting density of the polymer brush in a solid-state nanopore sensor; placing the same solid-state nanopore sensor in an electrolyte solution, applying a driving voltage to both ends of the nanopore, and measuring actual ion current value through the nanopore; comparing the measured actual ion current value with the quantitative relationship model, and inversely obtaining the grafting density of the polymer brush coating. The application directly measures ion current under the working state of the nanopore, does not need to perform any form of disassembly, drying or transfer operation on the sample, realizes in-situ real-time dynamic monitoring of the grafting density of the polymer brush in a real liquid environment, and can truly reflect the grafting density of the coating under the working state.

Description

Technical Field

[0001] This invention belongs to the field of nanopore modification technology, specifically relating to an in-situ detection method for the grafting density of polymer brush coatings based on nanopore ion current. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] With the development of micro- and nanofabrication technologies, nanopores with controllable sizes and shapes can be easily fabricated on various thin films. Utilizing advanced precision current detection techniques, nanopores provide a direct platform for studying ion and fluid transport within confined spaces, finding wide application in fields such as biosensing and energy conversion. However, in practical applications, the adhesion of organic or inorganic nanoparticles or molecules in solution to the pore walls can cause blockage, leading to performance degradation or failure. Surface engineering techniques, such as surface deposition, self-assembly, or chemical grafting, can be used to modify the nanopore walls with nano-inorganic coatings, polymer brush coatings, functionalized molecules, etc., to endow nanopores with more properties.

[0004] The performance of solid nanopores can be further improved by modifying the inner wall with functionalized coatings. Among them, polymer brush coatings have attracted widespread attention due to their excellent anti-fouling, anti-adhesion, and intelligent response (such as pH response and electric field response). In particular, charged polymer brush coatings can introduce controllable space charge into the pore wall, effectively regulating ion transport behavior within the nanopore, thereby improving the detection sensitivity, selectivity, and stability of nanopore sensors. The grafting density of the polymer brush coating (i.e., the number of polymer chains grafted onto the nanopore wall per unit area) is one of the key parameters for the final functional performance of the coating. Grafting density directly affects the coating's ability to regulate ion transport; therefore, accurate characterization of grafting density is of great significance for performance optimization of polymer brush coatings, process control, and long-term stable operation of nanopore sensors. Patent CN109400827A uses an ellipsometry to test the thickness of the molecular brush and calculates it using a formula based on the molecular weight of the polymer brush. However, existing grafting density characterization methods have significant limitations: (1) Ellipsometry and atomic force microscopy: These methods usually require measurement in a dry, non-working environment and cannot reflect the swelling state of the polymer brush in a real liquid environment. They are non-in-situ measurements.

[0005] (2) Dynamic light scattering method and thermogravimetric analysis: suitable for characterizing coatings on the surface of spherical particles, but difficult to apply to the confined space of the inner wall of nanopores.

[0006] (3) Fluorescent labeling method: The polymer chain needs to be chemically labeled, which may change the intrinsic properties of the coating and cannot achieve real-time online monitoring.

[0007] (4) Advanced characterization methods such as neutron reflection method and surface force meter: The equipment is expensive, the operation is complicated, and the detection cycle is long, making it difficult to carry out in-situ, online, and low-cost detection in the micro-nano confined space of nanopores.

[0008] In summary, there is currently a lack of a method for in-situ, real-time, simple, and low-cost detection of the grafting density of polymer brush coatings on the inner wall of nanopores in a working fluid environment. This has become a bottleneck in the development and application of nanopore coating technology. Therefore, developing a method for in-situ, real-time, and simple detection of polymer brush grafting density within nanopores is of significant practical importance for optimizing coating performance and ensuring the long-term stable operation of nanopore sensors. Summary of the Invention

[0009] The present invention aims to overcome the above-mentioned shortcomings of the prior art and provide an in-situ detection method for the grafting density of polymer brush coating based on nanopore ion current, so as to solve the problem that the prior art cannot perform in-situ, real-time and simple detection of the grafting density of polymer brush coating on the inner wall of nanopore.

[0010] The above-mentioned objectives are achieved by the present invention through the following technical solution: In a first aspect, the present invention provides a method for in-situ detection of graft density of polymer brush coating based on nanopore ion current, comprising the following steps: (1) Establish a quantitative relationship model between the ion current inside the nanopore and the polymer brush grafting density in the solid-state nanopore sensor; (2) The nanopore sensor without polymer brush modification and the nanopore sensor with polymer brush coating were placed under the same experimental conditions as when the quantitative relationship model was established. A driving voltage was applied to both ends of the nanopore, and the actual ion current value through the nanopore was measured respectively. (3) Compare the actual ion current value measured in step (2) with the quantitative relationship model described in step (1) to obtain the grafting density of the polymer brush coating.

[0011] Preferably, in step (1), the quantitative relationship model uses grafting density σ s As variables, they are constructed using the following methods: (1a) A two-dimensional axisymmetric nanopore model was constructed using COMSOL Multiphysics software. The solid membrane has cylindrical liquid pools on both sides, and the liquid pools and nanopores are filled with electrolyte solution. The inner wall of the nanopore is modified with a zwitterionic polymer brush coating. The space charge density ρ is defined within the space of the polymer brush coating. fix , ρ_ fix =e×Z×σ s / t, where e is the elementary charge, Z is the valence of the dissociable groups on each polymer chain, and σ s Where t is the grafting density and t is the coating thickness; (1b) with multiple discrete grafting densities σ s Using the values ​​as input, the coupled Poisson-Nernst-Planck equation and Navier-Stokes equation are solved, and the corresponding theoretical ion current values ​​are calculated to obtain the current-grafting density calibration curve.

[0012] Preferably, the pore size D of the nanopore is 5 nm to 30 nm, more preferably 10 nm.

[0013] Preferably, the pore length L of the nanopore is 25 nm to 100 nm, preferably 100 nm.

[0014] Preferably, the applied voltage V is 0.25 V to 1 V, preferably 0.5 V.

[0015] Preferably, the electrolyte solution is a KCl, LiCl, KF, or NaCl solution; more preferably, the solution type is LiCl.

[0016] The solution concentration is from 50 mM to 150 mM; preferably, the concentration is 50 mM.

[0017] Preferably, the polymer brush coating is a positively charged polymer brush coating or a negatively charged polymer brush. The positively charged polymer brush includes polymethacryloyloxyethyltrimethylammonium chloride (PMETAC or PMETA), quaternized poly(dimethylaminoethyl methacrylate) (Q-PDMAEMA), quaternary ammonium salt polyionic liquid brushes (PILs Brushes), and cationic-zwitterionic copolymer brushes (PSBMA-co-DMC).

[0018] Preferably, when the pore diameter D=10 nm, pore length L=100 nm, applied voltage V=0.5 V, electrolyte is LiCl, and concentration is 50 mM, the ion current and grafting density exhibit the optimal strictly monotonically increasing relationship, with the largest rate of change and the highest detection sensitivity.

[0019] In step (2), the measured current inside the nanopore without polymer brush modification is I0, and the current inside the nanopore with polymer brush modification is I... measured In step (3), I0 and I measured To calculate the rate of change of current, use the formula (I measured-I0) / I0×100% is shown; the calculated value is compared with the value on the current-grafting density calibration curve to obtain the grafting density range of the current change rate value calculated by the model. The following processing is performed in Excel: take the line segment between the two endpoints of the grafting density on the current-grafting density calibration curve and perform two-point interpolation to obtain the function expression of the line segment, which is y=ax+b, where x is the change rate, y is the grafting density in the nanopore, and a and b are the values ​​obtained by linear fitting.

[0020] In a second aspect, the present invention provides a detection apparatus for the method described in the first aspect, comprising: A solid film having a nanopore formed thereon, wherein the inner wall surface of the nanopore is grafted with a charged polymer brush coating. Two liquid pools are located on both sides of the solid membrane; Positive and negative electrodes are respectively disposed in the two liquid pools; The current detection unit is connected to the positive and negative electrodes; The computer terminal is connected to the current detection unit. The computer terminal is configured with a current acquisition program and a data processing unit. The data processing unit stores a pre-constructed quantitative relationship model between ion current and grafting density.

[0021] Preferably, the quantitative relationship model between ion current and grafting density stored in the data processing unit is pre-constructed according to the method described in the first aspect.

[0022] Thirdly, the present invention provides the application of the in-situ detection method for grafting density of polymer brush coating based on nanopore ion current as described in the first aspect and / or the detection device as described in the second aspect in the detection of grafting density of zwitterionic polymer brush coating on the inner wall of nanopores.

[0023] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows: (1) In-situ, real-time online detection: This invention directly measures the ion current in the working state of the nanopore without any disassembly, drying or transfer of the sample. It realizes in-situ real-time dynamic monitoring of the polymer brush grafting density in a real liquid environment, which can truly reflect the grafting density of the coating in the working state.

[0024] (2) Non-invasive and unmarked: The entire detection process involves only the excitation and acquisition of electrical signals. There is no need to use fluorescent or radioactive markers, nor is it necessary to rely on physical contact with the coating such as atomic force microscopes or surface force meters. It is a non-destructive test that ensures the integrity of the coating properties.

[0025] (3) Simple operation and low cost: The hardware required for this method is only a conventional voltage source and a picoammeter (or electrochemical workstation), and the equipment cost is far lower than that of high-end characterization methods such as neutron reflectometers and surface force meters. The data processing flow is simple and easy to program for automation.

[0026] (4) High detection sensitivity and strong regularity: Simulation results show that under optimized detection conditions (such as pore size D=10nm, pore length L=100 nm, applied voltage V=0.5 V, LiCl concentration 50 mM), the ion current response to the change in graft density shows a strict monotonically increasing relationship. Moreover, at a graft density of 0.6 grafts / nm², the current change rate can reach 233.64%, and the current change rate at adjacent graft densities can reach more than 27%, which significantly improves the ability to distinguish graft density and the detection accuracy.

[0027] (5) Clear scope of application and clear operation window: Through system simulation research, this invention reveals the influence of parameters such as pore size, pore length, solution concentration, electrolyte type and applied voltage on the current-grafting density relationship, and provides a clear window of optimal operation parameters, ensuring the stability, reliability and repeatability of the method. Attached Figure Description

[0028] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0029] Figure 1 A two-dimensional axisymmetric nanopore model, as shown in the figure, was constructed using COMSOL Multiphysics software.

[0030] Figure 2 : Schematic diagram of the device structure used to implement the detection method of the present invention.

[0031] The diagram is labeled as follows: 1-Power supply, 2-Current detection unit, 3-Computer terminal, 4-AgCl electrode, 5-Liquid pool, 6-Polymer brush coating, 7-Solid film, 8-Nanopore.

[0032] Figure 3 : Flowchart of the method of the present invention.

[0033] Figure 4 : Curves showing the relationship between ion current and grafting density for different nanopore sizes.

[0034] The horizontal axis in the figure represents the grafting density σ. s (roots / nm²), with the ordinate representing the relative change rate of ion current (I0). b I0) / I0, where I bI0 and I0 represent the ion currents with and without brushes, respectively. The five curves represent the variations when the pore size is D = 10 nm, D = 14 nm, D = 18 nm, D = 22 nm, and D = 30 nm, respectively.

[0035] Figure 5 The graph shows the relationship between the relative rate of change of ion current and grafting density under different pore lengths, with an optimal pore size D = 10 nm. The horizontal axis represents the grafting density σ. s The vertical axis represents the relative rate of change of current. The three curves represent L=25 nm, L=50 nm, and L=100 nm, respectively.

[0036] Figure 6 The graph shows the relationship between the relative change rate of ion current and grafting density under different electrolyte types, with an optimal pore size D = 10 nm. The graph compares four electrolytes: KCl, KF, NaCl, and LiCl.

[0037] Figure 7 The graph shows the relationship between the relative change rate of ion current and grafting density under different electrolyte concentrations when the preferred pore size D = 10 nm. The graph compares three concentrations: 50 mM, 100 mM, and 150 mM.

[0038] Figure 8 The graph shows the relative change rate of ion current with grafting density under different applied voltage conditions when the preferred pore size D = 10 nm. The graph shows the comparison at 0.25 V, 0.5 V and 1 V.

[0039] Figure 9 Ion current-grafting density calibration curve under optimal conditions (D=10 nm, L=100 nm, V=0.5 V, LiCl 50 mM). Detailed Implementation

[0040] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0041] In some embodiments of the present invention, an in-situ detection method for the grafting density of polymer brush coatings based on nanopore ion current is provided, such as... Figure 3 As shown, it includes the following steps: Step 1: Establish a quantitative relationship model between ion current and grafting density: (1a) Determine the geometric parameters of the nanopore, including the pore diameter D and the pore length L.

[0042] (1b) The grafting density of the polymer brush coating is determined to be in the range of 0.1 to 0.6 grafts / nm. 2 This grafting density range is the most common based on conventional polymer brush grafting techniques. In this method, the grafting density set in the simulation is within this range, and the grafting density within this range can be calculated by inversion using this model.

[0043] (1c) Determine the thickness t of the polymer brush coating. For planar substrates, the thickness is most often determined by ellipsometry, while patterned polymer brushes can also be measured using AFM, but the tip compression effect must be noted; for spherical particles, the swelling thickness is determined by dynamic light scattering (DLS), or the dry thickness is estimated using thermogravimetric analysis (TGA) combined with a formula. Since the coating thickness affects the fluid transport within the nanopores, and thus the current value within the pores, determining the actual coating thickness within the nanopores to be tested is crucial for setting the thickness of the grafting density region in subsequent simulations and for the accuracy of the grafting density obtained from inversion calculations.

[0044] (1d) Determine the charge properties of the polymer brush coating, including the valence Z of the dissociable groups on each polymer chain.

[0045] (1e) Under predetermined exogenous parameter conditions, construct the ion current I inside the nanopore and the polymer brush grafting density σ. s A quantitative relationship model between them; The method for constructing the quantitative relationship model is as follows: Assume the polymer brush coating is an ion-permeable porous medium; each polymer brush chain is continuously and uniformly grafted onto the pore wall and carries the same charge density; the polymer coating has the same thickness at different axial positions on the nanopore wall, and its deformation is not considered. Define the space charge density ρ within the coating space. fix The space charge density and the grafting density σ s The following relationship must be satisfied: Where e is the elementary charge; With the grafting density σ s As a variable, multiple discrete values ​​(e.g., 0.1 grafts / nm² to 0.6 grafts / nm²) are taken within a pre-defined range of graft density variation. These values ​​are substituted into the space charge density formula, and the theoretical ion current value I corresponding to each graft density value is obtained by solving the coupled Poisson-Nernst-Planck equation and Navier-Stokes equation, thereby establishing the ion current-graft density relationship model.

[0046] Step 2: Analyze the sample to be tested. (2a) A thin film with a single nanopore and a charged polymer brush coating on the pore wall is placed in an electrolyte solution, so that the nanopore is connected to two liquid pools located on both sides of the solid film.

[0047] (2b) A driving voltage is applied across the nanopore by means of a positive electrode and a negative electrode located in the two liquid pools. This driving voltage is the same as the applied voltage V used when establishing the quantitative relationship model.

[0048] (2c) The actual ion current value I through the nanopore is measured and recorded by the signal detection unit. measured .

[0049] Step 3: Inversion to obtain grafting density: The actual ion current value I obtained in step (2c) measured Compare with the quantitative relationship model established in step 3 to determine the relationship with I. measured The corresponding grafting density value σ s_measured In-situ detection of the grafting density of the polymer brush coating was completed.

[0050] The present invention will be further described below with reference to the embodiments.

[0051] Example 1 This embodiment describes the entire process of constructing a quantitative relationship model between ion current and graft density based on simulation data, and using this model to detect graft density.

[0052] Step 1: Constructing a nanopore model Built using COMSOL Multiphysics software, such as Figure 1 The diagram shows a two-dimensional axisymmetric nanopore model. The nanopore diameter is R = 5 nm, and the pore length is L = 50 nm. Theoretically, the solid membrane material only needs to satisfy the condition that the nanopore wall has no surface charge density; no other requirements are necessary. The solid membrane is flanked by cylindrical liquid pools with heights of 5 μm and diameters of 10 μm. The liquid pools and the nanopores are filled with a 100 mM KCl electrolyte solution with a dielectric constant of 78.54, and the system temperature is 298 K. The inner wall of the nanopore is modified with a positively charged polymer brush coating with a thickness of t = 2 nm.

[0053] The polymer brush coating is considered as an ion-permeable porous medium, and the space charge density is defined within the coating space: ρ_ fix =e×Z×σ s / t Where e is the elementary charge, Z is the valence of the dissociable groups on each polymer chain (take Z = +1), and σ s The grafting density of the polymer brush coating ranges from 0.1 grafts / nm² to 0.6 grafts / nm².

[0054] Step 2: Establish a quantitative relationship model In the COMSOL software, set the above geometric parameters, material parameters, and physical fields. The three physical fields are the electric field, the rarefied mass transport field, and the laminar flow field. Then, solve the coupled Poisson-Nernst-Planck equation and Navier-Stokes equation (Equations 1-4) in the COMSOL software.

[0055]

[0056] Among them, z i C i J i and D i These represent the charge number, concentration, ion flux, and diffusion coefficient of different ion species *i* in the solution system, respectively. *u* is the fluid velocity, and *ε* is the dielectric constant of the solution. *φ*, *N*, *F*, *R*, *T*, and *μ* represent the potential, number of ion species, Faraday constant, gas constant, temperature, pressure, and liquid viscosity, respectively. *q* is a region indicator factor; *q*=1 indicates the region is within the coating, and *q*=0 indicates the region is outside the coating. *γ* represents the friction coefficient of the polymer brush against the fluid, expressed by the following formula, where λ... 1 This indicates the softness of the coating.

[0057]

[0058] The boundary conditions for each physical field are set as follows: the boundary between the two liquid pools is set to a fixed concentration C=100 mM and a fixed potential (one end is set to V=0.5 V, and the other end is grounded); the inner wall of the nanopore (except for the coating area) is set as a wall surface with no slip and no surface charge density; the interface between the coating area and the solution area is an internal boundary with continuous flux.

[0059] The domain conditions are set as follows: Define a volumetric force 1 in the brush layer region, with the formula es.Er×(K). + -Cl - )×F_const-gamma×u and es.Ez×(K + -Cl -)×F_const-gamma×w, where gamma is the coefficient of friction of the polymer brush (refer to the paper "Concentration - Gradient Power Generation Coupled with Surface and SpaceCharges"), F_const (the definition in COMSOL software) is the Faraday constant, es.Er represents the radial electric field strength, es.Ez represents the axial electric field strength, u represents the radial fluid velocity, and w represents the axial fluid velocity. A volume force 2 is defined outside the brush layer, with the formula es.Er×(K + -Cl - )×F_const and es.Ez×(K + -Cl - The space charge density of the brush layer region is set to (K)×F_const. + -Cl - )×F_const+ρ_ fix The space charge density outside the brush layer is set to (K + -Cl - )×F_const. The initial conditions for the electrostatic field are: potential 0; for the rarefied mass transport field, system concentration 100 mM; and for the laminar flow field, velocity and pressure both 0. Then, mesh generation is performed.

[0060] In this model, a freely partitioned triangular mesh is used. To account for the influence of the charged coating region on ion transport within the nanopores, the mesh size is set to 0.1 nm on the inner wall of the pores and the outer surface (3 μm wide) outside the pore boundaries. For other parts of the outer surface, the mesh size is set to 0.5 nm. This meshing method improves computational efficiency and reduces computational cost while maintaining computational accuracy.

[0061] Using a steady-state solver, with graft density σ s Using ions as variables, parametric scan calculations were performed at seven discrete points: 0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 ions / nm². The ion current through the orifice was obtained by integrating the total ion flux at the orifice cross-section using the formula I = F_const×∫ s Σ(z i ×J i The value is obtained by calculating )·ndS, where z i J i Let n and d represent the charge number and ion flux of different ion species i in the solution system, respectively. n is the normal vector at the cross section, d is the differential sign, and S is the area of ​​the cross section.

[0062] The theoretical current values ​​corresponding to each grafting density were compiled into a data table, which served as the benchmark calibration curve for subsequent testing (see...). Figure 4 ).

[0063] Step 3: Grafting density detection The nanopore sensor with a polymer brush coating was placed under the exact same experimental conditions as when the calibration curve was established (KCl 100 mM, driving voltage 0.5 V, temperature 298 K). First, the current I0 without polymer brush modification was measured. Then, the nanopore wall was modified with a positively charged polymer brush coating identical to the model settings, and the current I0 was measured again under the same conditions. measured Do (I) measured The current change rate is obtained by calculating (-I0) / I0×100%. The value of the current change rate is compared with the value on the calibration curve to find the two grafting density points between them. Then, an interpolation calculation is performed in Excel to obtain the expression for the line segment between the two points. Substituting the current change rate value into the expression, the grafting density is calculated.

[0064] Example 2 Figure 5 The variation of current change rate with grafting density under different aperture lengths is shown, and it can be seen that the monotonicity is optimal when L=100 nm. Figure 6 The study showed that the rate of change of current varies with grafting density under different electrolytes. It can be seen that the rate of change of current is the largest in LiCl solution, which has high resolution and is more suitable for current detection. Figure 7 The study demonstrates the change in current rate with grafting density at different concentrations. Similarly, the current rate of change is greatest at a concentration of 50 mM, making it suitable for current detection. Figure 8 The study demonstrates the variation of current change rate with graft density under different voltages. Although 0.25 V exhibits the largest current change rate at high graft densities, the current change rate is even greater at 0.5 V when the graft density is less than 0.3 grafts / nm². Considering that lower voltages result in lower current values, leading to larger detection errors, 0.5 V is considered the optimal voltage.

[0065] In summary, when D = 10 nm, L = 100 nm, V = 0.5 V, and the LiCl concentration is 50 mM, the current exhibits the optimal monotonic characteristics as a function of grafting density. Figure 9 As shown, the linear formula obtained through linear fitting is y = 0.00249x - 0.01836, R0 2 =0.98762, where x is the rate of change, and the calculated y value is the grafting density within the nanopore at this point, exhibiting good linearity. Under adjacent grafting densities (grafting density interval 0.1 grafts / nm), 2The difference in the relative rate of change of current was 42.8% (0~0.1 nm). 2 ), 52.3% (0.1~0.2 roots / nm) 2 ), 44.9% (0.2~0.3 roots / nm) 2 ), 36.1% (0.3~0.4 roots / nm) 2 ), 30.5% (0.4~0.5 roots / nm) 2 ), 27.1% (0.5~0.6 roots / nm) 2 This demonstrates that the method exhibits good sensitivity and resolution. The highest rate of change in total current occurs at adjacent graft densities (0.1 grafts / nm² interval), facilitating high-precision measurement and representing a preferred embodiment of the invention.

[0066] Example 3 Step 1: After completing the COMSOL model calculation according to Example 1 and obtaining the current-graft density calibration curves under different conditions, the following experimental operations were performed to detect the grafting density of the polymer brush coating in a single nanopore.

[0067] Step 2: Set up as follows Figure 2 The experimental setup shown includes a solid membrane 7 with a nanopore 8 formed on it. A polymer brush coating 6 is grafted onto the inner surface of the nanopore 8. Two liquid pools 5 are positioned on either side of the solid membrane 7, each containing an AgCl electrode 4. A Kethley 6487 current measuring instrument is used for the current detection unit 2, which is communicatively connected to a computer 3. The AgCl electrode 4 is clamped to the wires on both sides of the current detection unit 2 via clamps, and a power supply 2 is connected to one of the wires. The computer 3 is configured with a current acquisition program and a data processing unit to acquire and process the current signal. In this embodiment, the data processing unit stores a pre-constructed quantitative relationship model between ion current and grafting density.

[0068] Step 3: Optimize the film thickness, i.e., the nanopore length L = 100 nm as set in the model, and fabricate nanopores with a pore size D = 10 nm on the film using track etching technology. First, place the film in a... Figure 2 The two liquid pools in the experimental setup shown were clamped together, and the solution parameters (50 mM LiCl solution) and voltage (0.5 V) were the same as those in the model. The measured current inside the nanopore without polymer brush modification was I0, which was 0.0987 nA.

[0069] Step 4: Modify the pore walls of individual nanopores on the film with a zwitterionic polymer brush coating. In this example, polymethacryloyloxyethyltrimethylammonium chloride (PMETAC or PMETA) is used, consistent with the polymer brush type set in the model of Example 1.

[0070] In other embodiments, the zwitterionic polymer brush can also be a positively charged polymer brush such as quaternized poly(dimethylaminoethyl methacrylate) (Q-PDMAEMA), quaternary ammonium salt type polyionic liquid brush (PILs Brushes), or cationic-zwitterionic copolymer brush (PSBMA-co-DMC), or a negatively charged polymer brush.

[0071] Step 5: Place the single nanoporous film modified with a positively charged polymer brush between the two liquid pools of the experimental setup and clamp it tightly to prevent leakage from affecting the detection results.

[0072] Step 6: Clamp the AgCl electrode onto the two clamps of the Kethley 6487 and place it in the two-liquid pool. The solution in the two-liquid pool is consistent with the model settings, which is 50 mM LiCl solution (preferred condition).

[0073] Step 7: Set the voltage of Kethley6487 to 0.5 V on the computer, start the program to detect the actual via current, and save the current signal in Excel format.

[0074] Step 8: Measure the actual current I using a Kethley 6487. measured The measured current I measured =7.50 nA.

[0075] Step 9: Compare the I0 measured in Step 2 with the I measured in Step 7. measured To calculate the rate of change of current, use the formula (I measured The result is shown as -I0) / I0×100%. The calculated value is compared with the value on the current-grafting density calibration curve. Here, the calculated current change rate is 75%, and the calculated grafting density is 0.1 grafts / nm. 2 and 0.2 roots / nm 2 In Excel, the following processing is performed: On the calibration curve, take the line segment between these two grafting density points and perform two-point interpolation to obtain the function expression for this line segment, resulting in the expression y = 0.001914x + 0.018081. Substituting x = 75, the calculated y value is 0.161614, meaning the measurement shows a grafting density of 0.161614 grafts / nm. 2 .

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for in-situ detection of graft density of polymer brush coating based on nanopore ion current, characterized in that, Includes the following steps: (1) Establish a quantitative relationship model between the ion current inside the nanopore and the polymer brush grafting density in the solid-state nanopore sensor; (2) The nanopore sensor without polymer brush modification and the nanopore sensor with polymer brush coating were placed under the same experimental conditions as when the quantitative relationship model was established. A driving voltage was applied to both ends of the nanopore, and the actual ion current value through the nanopore was measured respectively. (3) Compare the actual ion current value measured in step (2) with the quantitative relationship model described in step (1) to obtain the grafting density of the polymer brush coating.

2. The method for in-situ detection of graft density of polymer brush coating based on nanopore ion current according to claim 1, characterized in that, In step (1), the quantitative relationship model uses grafting density σ s As variables, they are constructed using the following methods: (1a) A two-dimensional axisymmetric nanopore model was constructed using COMSOL Multiphysics software. The solid membrane has cylindrical liquid pools on both sides, and the liquid pools and nanopores are filled with electrolyte solution. The inner wall of the nanopore is modified with a zwitterionic polymer brush coating. The space charge density ρ is defined within the space of the polymer brush coating. fix , ρ_ fix =e×Z×σ s / t, where e is the elementary charge, Z is the valence of the dissociable groups on each polymer chain, and σ s Where t is the grafting density and t is the coating thickness; (1b) with multiple discrete grafting densities σ s Using the values ​​as input, the coupled Poisson-Nernst-Planck equation and Navier-Stokes equation are solved, and the corresponding theoretical ion current values ​​are calculated to obtain the current-grafting density calibration curve.

3. The method for in-situ detection of graft density of polymer brush coating based on nanopore ion current according to claim 2, characterized in that, The pore size D of the nanopore is 5 nm to 30 nm, preferably 10 nm.

4. The method for in-situ detection of graft density of polymer brush coating based on nanopore ion current according to claim 2, characterized in that, The pore length L of the nanopore is from 25 nm to 100 nm, preferably 100 nm.

5. The method for in-situ detection of graft density of polymer brush coating based on nanopore ion current according to claim 2, characterized in that, The driving voltage V is from 0.25 V to 1 V, preferably 0.5 V.

6. The method for in-situ detection of graft density of polymer brush coating based on nanopore ion current according to claim 2, characterized in that, The electrolyte solution is a KCl, LiCl, KF, or NaCl solution; preferably, the solution type is LiCl. Furthermore, the solution concentration is from 50 mM to 150 mM; preferably, the concentration is 50 mM.

7. The method for in-situ detection of graft density of polymer brush coating based on nanopore ion current according to claim 2, characterized in that, The polymer brush coating is a positively charged polymer brush coating or a negatively charged polymer brush coating; the positively charged polymer brush includes polymethacryloyloxyethyltrimethylammonium chloride, quaternized polymethacrylate dimethylaminoethyl ester, quaternary ammonium salt type polyionic liquid brush, and cationic-zwitterionic copolymer brush.

8. The method for in-situ detection of graft density of polymer brush coating based on nanopore ion current according to claim 2, characterized in that, In step (2), the measured current inside the nanopore without polymer brush modification is I0, and the current inside the nanopore with polymer brush modification is I... measured In step (3), I0 and I measured To calculate the rate of change of current, use the formula (I measured -I0) / I0×100% is shown; the calculated value is compared with the value on the current-grafting density calibration curve to obtain the grafting density range of the current change rate value calculated by the model. The following processing is performed in Excel: take the line segment between the two endpoints of the grafting density on the current-grafting density calibration curve and perform two-point interpolation to obtain the function expression of the line segment, which is y=ax+b, where x is the change rate, and the calculated y value is the grafting density result in the nanopore at this time.

9. A device for in-situ detection of polymer brush coating graft density based on nanopore ion current, characterized in that, include: A solid film having a nanopore formed thereon, wherein the inner wall surface of the nanopore is grafted with a charged polymer brush coating; Two liquid pools are located on both sides of the solid membrane; Positive and negative electrodes are respectively disposed in the two liquid pools; The current detection unit is connected to the positive and negative electrodes; The computer terminal is communicatively connected to the current detection unit. The computer terminal is configured with a current acquisition program and a data processing unit. The data processing unit stores a pre-constructed quantitative relationship model between ion current and grafting density. The quantitative relationship model between ion current and grafting density stored in the data processing unit is pre-constructed according to the detection method described in any one of claims 1 to 8.

10. The application of the in-situ detection method for grafting density of polymer brush coating based on nanopore ion current as described in any one of claims 1 to 8 and / or the in-situ detection device for grafting density of polymer brush coating based on nanopore ion current as described in claim 9 in the detection of grafting density of zwitterionic polymer brush coating on the inner wall of nanopores.

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