A solution-interface measurement device based on nano-slit confinement effect and its preparation method and measurement method

Abstract

The present invention discloses a solution-interface measuring device based on the nano-slit confinement effect, a preparation method and a measuring method. The measuring device includes: a sample preparation layer, which includes a silicon substrate, on which two parallel electrodes spaced apart based on a MEMS process are formed, and a thiol self-assembly modification layer is formed on the upper surface of the electrode; a nano-groove is formed between the two electrodes, the entrance of the nano-groove is provided with an inclined introduction surface, and the surface of the inclined introduction surface is formed with a hydrophilic layer; an online monitoring layer, which includes a temperature control module, and the thermistor lattice of the temperature control module is arranged at the bottom of the silicon substrate; a fiber optic surface plasmon resonance sensor is also provided on the upper surface of the electrode, and a pH fiber optic probe is provided on the sidewall of the nano-groove; a signal processing layer, which includes an electrochemical impedance spectroscopy circuit board provided at the bottom of the online monitoring layer. The measuring device of the present invention can solve the problems of complex structure, easy clogging, weak interface signal and uneven solution introduction of traditional measuring devices.

Description

Technical Field

[0001] The present invention relates to the technical field of nanofluid measurement, and in particular to a solution-interface measurement device based on a nano-slit confinement effect, and a preparation method and a measurement method. Background Art

[0002] Accurately measuring the electrical double layer (EDL) characteristics at the electrode-solution interface is crucial for studying the nanoslit confinement effect. Currently, devices for measuring the EDL characteristics at the electrode-solution interface face numerous challenges, including complex structures that make fabrication difficult and costly, easy clogging of the nanoslits, uneven solution introduction that affects measurement repeatability, a lack of precise control over environmental parameters such as temperature and pressure, and weak interface signals that cannot simulate real-world application scenarios.

[0003] The present invention aims to provide a solution-interface measuring device based on the nano-slit confinement effect, as well as a preparation method and a measuring method, to solve the problems of the existing measuring devices such as complex structure, easy clogging of the nano-slit and uneven solution introduction. Summary of the Invention

[0004] The present invention aims to provide a solution-interface measurement device based on the nanoslit confinement effect, as well as a preparation and measurement method. The device exhibits a flattened, layered structure, making it easier to operate and conveniently handheld or integrated onto a measurement platform. This device addresses the challenges of conventional measurement devices, such as complex structures, easy clogging of the nanoslits, weak interface signals, and uneven solution introduction.

[0005] To this end, the present invention provides a solution-interface measurement device based on the nano-slit confinement effect, comprising: a sample preparation layer, comprising a silicon substrate, on which are formed two parallel and spaced electrodes, with a thiol self-assembly modification layer formed on the upper surfaces of the electrodes; a nano-groove formed between the two electrodes, with an inlet of the nano-groove provided with an inclined introduction surface, and a hydrophilic layer formed on the surface of the inclined introduction surface; an online monitoring layer, comprising a temperature control module, wherein a thermistor array of the temperature control module is arranged at the bottom of the silicon substrate; and further comprising an optical fiber surface plasmon resonance sensor arranged on the upper surfaces of the electrodes, and a pH optical fiber probe arranged on the sidewalls of the nano-groove; and a signal processing layer, comprising an electrochemical impedance spectroscopy circuit board arranged at the bottom of the online monitoring layer.

[0006] Preferably, the electrode is an aluminum electrode, the surface of the aluminum electrode is coated with a gold layer, and the thickness of the gold layer is 2 nm; the distance between the two electrodes is 40-60 nm, and the thickness of the electrode is 100-200 nm.

[0007] Preferably, the thickness of the thiol self-assembly modification layer is 1-2 nm.

[0008] Preferably, the nanogrooves have a depth of 100-200 nm and a length of 10-100 μm.

[0009] Preferably, the thickness of the hydrophilic layer is 5-10 nm, and the contact angle is ≤15°.

[0010] The present invention also provides a method for preparing the solution-interface measurement device based on the nano-slit confinement effect, the method comprising:

[0011] S1: Using mask lithography technology, a metal electrode pattern with a spacing of 50nm is produced on a silicon substrate. Photoresist is evenly coated on the silicon substrate, and the mask pattern is transferred to the photoresist using a photolithography method. After development, an aluminum mask electrode with a spacing of 50nm is formed. A gold layer is deposited on the surface of the exposed aluminum mask electrode to form two parallel electrodes.

[0012] S2: Immersing the electrode in a mixed solution of 11-mercaptoundecanoic acid and ethanol to form a thiol self-assembled modification layer on the electrode surface;

[0013] S3: Spin coating the surface of the inclined introduction layer in the nanogroove inlet area with a polyethylene glycol solution to form a hydrophilic layer;

[0014] S4: Attach the fiber optic surface plasmon resonance sensor parallel to the electrode surface, with the optical path of the fiber optic surface plasmon resonance sensor perpendicular to the length of the nanogroove, forming a "cross" layout;

[0015] Multiple pH fiber optic probes were embedded into the sidewalls of the nanogrooves at intervals of 15 μm, with the ends of the pH fiber optic probes flush with the electrode surface;

[0016] The temperature control module is mounted on the bottom of the silicon substrate, and the thermistors of the temperature control module are arranged in a dot matrix;

[0017] S5: Install the signal processing layer at the bottom of the online monitoring layer.

[0018] Preferably, a gold layer is deposited on the surface of the exposed aluminum mask electrode by magnetron sputtering, with the deposition power controlled at 150-251 W and the gas pressure at 1-5 mTorr.

[0019] Preferably, the electrode is immersed in a mixed solution of 11-mercaptoundecanoic acid and ethanol, wherein the molar concentration of 11-mercaptoundecanoic acid in the mixed solution is 0.8 mmol / L-1.2 mmol / L; and reacted at room temperature for 15-20 hours to form a dense thiol self-assembled modification layer on the electrode surface.

[0020] Preferably, the thickness of the hydrophilic layer is 5-10 nm, and the contact angle is ≤15°.

[0021] The present invention also provides a measurement method of the solution-interface measurement device based on the nano-slit confinement effect, the method comprising:

[0022] S1: Select the target electrolyte solution KCl solution and ensure that the solution is free of bubbles and impurities;

[0023] The temperature of the measuring device was adjusted to 32°C ± 0.5°C, and the pressure outside the nanoslit was adjusted to 105 kPa ± 30 Pa;

[0024] Using the capillary effect, KCl solution was filled from bottom to top within 15 seconds with a uniformity deviation of less than 5%. The solution-electrode interface was allowed to reach equilibrium for 1-2 minutes. The local pH value at the solution-electrode interface was measured using a pH fiber optic probe.

[0025] S2: Apply a sinusoidal AC excitation signal with a frequency range of 10 3 -10 6 Hz, amplitude 5-10mV;

[0026] Impedance spectra were recorded using an EIS circuit, with 30–50 data points collected per decade.

[0027] The fiber optic surface plasmon resonance sensor was activated to monitor the electrode surface plasmon resonance signal at an 8Hz sampling rate. The real-time charge density was calculated based on the change in reflected light intensity with an accuracy of 0.2-0.3mC / m².

[0028] ±0.8 V linear sweep voltage was applied synchronously at a rate of 15 mV / s, and the current response curve was recorded;

[0029] S3: Input EIS impedance spectra, SPR charge density series, and IV curves into a simplified neural network algorithm; algorithm structure: 5-7 layers of convolutional network and 3-4 layers of fully connected network, input synthetic data training set with less than 8% noise;

[0030] Output electrode polarization impedance Rp, solution resistance Rs, and double-layer impedance ZEDL; use SPR data to correct polarization effects;

[0031] Inversion model calculations: Debye length, Zeta potential, ion mobility;

[0032] S4: Drain the solution, rinse the nanogrooves with deionized water, and blow dry with nitrogen; check the integrity of the electrode and thiol self-assembly modification layer, and re-modify if necessary.

[0033] Compared with the existing technology, the advantages and positive effects of the present invention are: the measuring device of the present invention has an overall flat layered structure, is more convenient to operate, and can be conveniently held or integrated into a measuring platform. The measuring device of the present invention can solve the problems of traditional measuring devices such as complex structure, easy clogging, weak interface signal, and uneven solution introduction. Specifically:

[0034] First, the present invention forms embedded trench electrodes on a silicon substrate 11, creating a three-dimensional structure. Specifically, aluminum electrodes are embedded within parallel trenches etched into the silicon substrate. The trenches are 100–200 nm deep, with the top surface of the electrodes flush with the top surface of the silicon substrate, forming a "grooved slit." The cross-sectional shape resembles a "[" character, with vertical electrode sidewalls and the bottom exposed to the silicon substrate. The electrodes of the present invention are embedded within the trenches of the silicon substrate, creating a stable and reliable structure that avoids the mechanical instability of conventional suspended electrodes while also forming nano-grooves with precise dimensions (accuracy ±8 nm).

[0035] Second, the two parallel electrodes (spacing ≤50nm) of the present invention are spaced apart to form a narrow, open channel (10–100μm long), resembling an "ultra-narrow gap formed by two parallel metal sheets," creating an open nanogroove. The open nature of the nanogroove avoids the dead corners and clogging issues of traditional closed nanogrooves. The nanogroove of the present invention is easy to clean, maintain, and reuse. Conventional measurement devices often use closed channels (such as PDMS microfluidics) that require an external pump to introduce solutions. However, the open structure of the nanogroove of the present invention allows for self-filling of solutions.

[0036] The opening of the nano-groove of the present invention is formed with an inclined introduction surface, and the inclined introduction surface is coated with a hydrophilic layer, which can reduce the flow resistance of the solution, thereby making it easier to introduce and fill the solution.

[0037] Third, the optical path of the fiber-optic surface plasmon resonance sensor is perpendicular to the length of the nanogroove, forming a "cross" layout, which improves the sensitivity and strength of the interface signal. Multiple pH fiber-optic probes are embedded in the sidewalls of the nanogroove at 15μm intervals. The ends of the pH fiber-optic probes are flush with the surface of the parallel aluminum electrodes, preventing protrusions from interfering with the flow field and improving measurement accuracy and sensitivity. The temperature control module's thermistors are arranged in a dot matrix, eliminating the nanogroove's space.

[0038] Other features and advantages of the present invention will become more apparent after reading the detailed description of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is one of the structural schematic diagrams of an embodiment of the sample preparation layer of the present invention;

[0040] Figure 2This is the second structural diagram of an embodiment of the sample preparation layer of the present invention;

[0041] Figure 3 yes Figure 2 Enlarged view of part A;

[0042] Figure 4 It is a structural diagram of an embodiment of the online monitoring layer of the present invention;

[0043] Figure 5 is a schematic structural diagram of an embodiment of a signal processing layer of the present invention;

[0044] Figure 6 It is a structural schematic diagram of an embodiment of a solution-interface measurement device based on the nano-slit confinement effect of the present invention. DETAILED DESCRIPTION

[0045] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0046] like Figures 1-6 As shown, the present invention provides a solution-interface measurement device based on the nano-slit confinement effect, and the measurement device includes a sample preparation layer, an online monitoring layer, and a signal processing layer arranged in sequence from top to bottom.

[0047] The sample preparation layer includes a silicon substrate 11, on which are formed two parallel and spaced electrodes 12. The upper surface of the silicon substrate 11 is flush with the upper surface of the electrode 12, and a thiol self-assembly modification layer 13 is formed on the upper surface of the electrode 12; a nano-groove 13 is formed between the two electrodes 12, and the entrance of the nano-groove 13 is provided with an inclined introduction surface 14, and a hydrophilic layer is formed on the surface of the inclined introduction surface 14.

[0048] The electrode 12 is an aluminum electrode, and the surface of the aluminum electrode is coated with a gold layer with a thickness of 2 nm.

[0049] The present invention gold-plated the surface of the aluminum electrode, which has the advantages of enhancing electrode performance, adapting to surface functional modification, reducing material cost and preparation difficulty, etc., as follows:

[0050] Enhanced electrode performance: The gold layer improves electrode performance, enabling better measurement performance. Gold-plated electrodes provide more stable operation and ensure accurate measurements during electrochemical impedance spectroscopy (EIS), surface charge density monitoring (SPR), and voltammetry (IV) testing.

[0051] Compatible with surface functionalization: The gold-plated layer facilitates subsequent surface functionalization. The thiol self-assembled modification layer is anchored to the gold-plated electrode surface via Au-S bonds, providing carboxyl (-COOH) functional groups. This allows the surface charge density to be controlled by adjusting the solution pH, enabling the electrode to function better under different experimental conditions.

[0052] Reduced cost and difficulty: Compared to other solutions, the method of fabricating aluminum electrodes on a silicon substrate and then plating them with gold is widely available and inexpensive, and the aluminum electrode preparation process is relatively simple. While maintaining measurement accuracy, it significantly reduces material cost and preparation difficulty, improving the overall cost-effectiveness of the device.

[0053] The distance between the two electrodes 12 is 40-60 nm, which has the advantages of precise control of the electric field and adaptability to nanoscale applications. Specifically:

[0054] Precise control of the electric field: An electrode spacing of 40-60nm produces a relatively uniform electric field of appropriate strength between the electrodes. This facilitates precise electric field manipulation of substances or particles between the electrodes. For example, in nanoelectronic devices, the trajectory and behavior of electrons can be precisely controlled, improving device performance and stability.

[0055] Adaptable to nanoscale applications: The 40-60nm electrode spacing matches the scale of many nanomaterials and nanostructures. For example, in nanosensors, nanoscale analytes react or interact between electrodes, helping to improve sensor sensitivity and resolution, enabling the detection of extremely small amounts of substances or weak signal changes.

[0056] The thickness of the electrode 12 is 100-200 nm, which has the advantages of ensuring structural stability, optimizing electrical performance, and facilitating integration. Specifically:

[0057] Ensuring structural stability: Electrode thicknesses of 100-200nm provide sufficient mechanical strength and stability, making them less susceptible to deformation or damage in various environments and operating conditions. In some miniaturized electronic devices or nanodevices, they can withstand process stresses during manufacturing and external forces during use.

[0058] Optimizing electrical performance: An electrode thickness of 100-200nm ensures good electrical conductivity and charge transfer capabilities. Sufficient thickness reduces electrode resistance, lowers energy loss during charge transfer, and improves electrode conductivity, thereby enhancing the electrical performance and efficiency of the entire device.

[0059] Facilitates integration: The electrode thickness of 100-200nm is in line with the integration trend of nanodevices, making it easy to integrate with other nanoscale components or structures to form complex nanosystems or circuits, which helps to achieve miniaturization and high performance of the equipment.

[0060] The thickness of the thiol self-assembled modification layer 13 is 1-2 nm, and it has the advantages of precise control of molecular scale, good electron transfer performance, effective barrier and protection, and adaptability to nanostructures. Specifically:

[0061] Precise molecular-scale control: This thickness is within the molecular scale range, enabling precise control of the interaction between the modified layer, the electrode surface, and external substances. This allows the thiol molecules in the modified layer to adsorb onto the electrode surface in a specific orientation and arrangement, forming a compact and ordered monolayer, thereby achieving precise control of the electrode surface properties.

[0062] Good electron transfer performance: This thickness ensures effective electronic coupling between the thiol molecules and the electrode, facilitating electron transfer between the electrode and the modified layer, while not increasing the resistance to electron transfer due to excessive thickness. For example, in electrochemical sensors, this helps improve the sensor's response speed and sensitivity to target substances.

[0063] Effective barrier and protection: The 1-2 nm thiol self-assembled modified layer 13 acts as an effective barrier, preventing the electrode surface from being corroded by impurities, oxygen, or moisture in the external environment, thereby protecting the electrode. Furthermore, it selectively allows molecules of certain sizes and properties to pass through, functionalizing the electrode surface and improving its selectivity and anti-interference capabilities.

[0064] Adaptation to nanostructures: The thickness of 1-2nm matches the size of nanoscale electrodes and other nanomaterials. In the construction of nanodevices, it is conducive to achieving good interface bonding and collaborative work between the various components, which helps to improve the performance and stability of the entire nanosystem.

[0065] The depth of the nano-grooves 13 is 100-200 nm, which has the following advantages:

[0066] Accommodation and positioning: This depth can provide suitable accommodation space for some nanoscale substances or structures, such as precise positioning and fixation of nanoparticles, biological molecules, etc., which is conducive to achieving specific functions. For example, in nanosensors, the target detection object can be confined to a specific area to improve the accuracy of detection.

[0067] Enhanced interaction: This depth can increase the interaction area between the nano-grooves 13 and the internal substances. For example, in applications such as surface-enhanced Raman scattering, it can enhance the interaction between light and matter, increase signal intensity, and thus improve detection sensitivity.

[0068] The length of the nano-grooves 13 is 10–100 μm, which has the following advantages:

[0069] Material transport and distribution: This length range is conducive to the transport and distribution of materials within the nano-grooves 13. For example, in microfluidics applications, sufficient length allows analytes in the fluid to have enough time to diffuse and react within the grooves, facilitating their manipulation and analysis.

[0070] Integration and compatibility: This length is compatible with the sizes of many micro-nano devices, making it easy to integrate with other micro-nano structures on the same chip or device, realizing the integration of multiple functions and facilitating the construction of complex micro-nano systems.

[0071] The width of the nano-groove 13 is equal to the distance between the two electrodes 12, which has the following advantages:

[0072] Electric field uniformity: The uniformity of the width and electrode spacing helps generate a uniform electric field between the electrodes, resulting in a more stable and uniform electric field distribution within the nano-grooves 13. This is crucial for manipulating charged particles within the nano-grooves 13 or influencing chemical reactions therein, improving the consistency and repeatability of these processes.

[0073] Precise control: A width that matches the electrode spacing enables precise control of the environment within the nano-groove 13. For example, in electrically driven nanodevices, the movement of ions or electrons within the nano-groove 13 can be precisely controlled, enabling precise control of specific processes and improving device performance and reliability.

[0074] The angle between the inclined introduction surface 14 and the bottom surface of the nano-groove 13 is an acute angle, which can reduce the flow resistance of the solution, thereby making it easier to introduce and fill the solution.

[0075] The thickness of the hydrophilic layer is 5-10nm, and the contact angle is ≤15°, which includes the following advantages:

[0076] Good hydrophilicity and wettability: A smaller contact angle means that liquids can spread quickly on the surface of the hydrophilic layer, allowing the material surface to be quickly wetted by the liquid, which helps improve the interaction efficiency between the material and the liquid. A hydrophilic layer thickness of 5-10nm ensures that the hydrophilic layer has sufficient functional groups to interact with water molecules, while not affecting other material properties such as mechanical properties and light transmittance due to excessive layer thickness.

[0077] Improve antifouling performance: Since the hydrophilic layer can form a continuous water film on its surface, it can prevent dirt, bacteria and other substances from directly contacting the surface of the material, thereby reducing the attachment of dirt and bacteria, and making the material have better self-cleaning and antifouling properties.

[0078] Improved surface stability: The presence of a hydrophilic layer can reduce the free energy of the material surface, making the surface more stable. This helps to resist the effects of external environmental factors (such as temperature, humidity, and chemicals) on the material surface, reduce surface aging and corrosion, and extend the service life of the material.

[0079] The online monitoring layer includes a monitoring base plate 21 , which is mounted on the bottom of the silicon substrate 11 . The monitoring base plate 21 is provided with a temperature control module 22 , a pressure sensor 23 and an air pump 24 . The thermistor array of the temperature control module 22 is arranged on the monitoring base plate 21 .

[0080] The online monitoring layer also includes a fiber optic surface plasmon resonance sensor 25, which is arranged on the upper surface of one of the electrodes 12. The optical path direction of the fiber optic surface plasmon resonance sensor 25 is perpendicular to the length direction of the nano-groove 13, forming a "cross" layout, which includes the following advantages:

[0081] Improved Detection Sensitivity: The optical path of the fiber optic surface plasmon resonance sensor 25 is oriented perpendicular to the length of the nano-grooves 13, forming a "cross" shape. This allows the light to interact with the material within the nano-grooves 13 for a longer path. If the substance to be detected is present in the nano-grooves 13, the light has more opportunities to interact with it, enabling more sensitive detection of changes in the material, thereby improving the detection sensitivity of the fiber optic surface plasmon resonance sensor.

[0082] Facilitates signal collection and analysis: This layout allows the fiber-optic surface plasmon resonance sensor 25 to more easily detect changes in optical signals caused by changes in the material within the nano-grooves 13. The vertical optical path allows light to strike the nano-grooves 13 and the surface of the electrode 12 at a specific angle. The reflected or transmitted light signals are more easily collected and transmitted by the optical fiber, facilitating subsequent analysis and processing, and contributing to the acquisition of stable and accurate detection signals.

[0083] Efficient Space Utilization: The cross-shaped layout effectively integrates the fiber surface plasmon resonance sensor 25 with the nanogrooves 13 within a limited space. Placing the sensor on the top surface of electrode 12 saves space, while the vertical layout fully utilizes the planar space, facilitating miniaturization and integration of the entire device. This makes the device more compact and facilitates installation and operation in practical applications.

[0084] Avoiding Mutual Interference: The vertical layout helps minimize interference between the optical path of the fiber surface plasmon resonance sensor 25 and other physical processes within the nanogroove 13 (such as electric field effects and material transport). The optical path is independent of the length of the nanogroove 13, preventing it from being affected by factors such as material flow or electric field distribution within the nanogroove 13. This ensures the accuracy and stability of optical detection, allowing the sensor to more purely detect changes related to optical properties without interference from other irrelevant factors.

[0085] The online monitoring layer also includes multiple pH fiber optic probes 26, which are symmetrically arranged on the side walls of the two nano-grooves 13. The distance between two adjacent pH fiber optic probes 26 is 15 μm, and the ends of the pH fiber optic probes 26 are flush with the parallel aluminum electrode surfaces to avoid protrusions interfering with the flow field.

[0086] This application uses a fiber-optic surface plasmon resonance sensor 25 for charge monitoring. Electrode 12 is connected to the sensing area of ​​the fiber-optic surface plasmon resonance sensor 25. When incident light propagates through the fiber and strikes the surface of electrode 12, surface plasmon resonance is triggered, causing a change in the intensity of the reflected light. By monitoring this change in reflected light intensity, the surface charge density is calculated using a calibration curve. By optimizing the fiber surface modification and signal processing algorithms, the charge density resolution can reach 0.2-0.3 mC / m².

[0087] The temperature control of this application uses a thermistor heating element, which is combined with a temperature control module 22 to maintain a temperature control accuracy of ±0.5°C. Pressure control uses a pressure sensor 23 and an air pump 24. Through a feedback control algorithm, the air pressure outside the nano-groove 13 is regulated with an accuracy of ±20-±30Pa. Micro-area pH sensing uses a fluorescence ratio optical fiber sensor. Multiple pH optical fiber probes 26 are embedded on both sides of the nano-groove 13 at intervals of 15μm. The sensor surface is modified with a pH-sensitive fluorescent dye (such as BCECF). The local pH value is inverted through the dual-channel fluorescence intensity ratio (490nm / 535nm), with a spatial resolution of 15μm.

[0088] The signal processing layer includes a processing base plate 31 , which is mounted on the bottom of the monitoring base plate 21 . An electrochemical impedance spectroscopy circuit board 32 is provided on the processing base plate 31 .

[0089] The electrochemical impedance spectroscopy circuit board 32 uses a constant potential instrument and a lock-in amplifier to build a measurement circuit, and the frequency range is set to 10 3 -10 6 Hz. A filter circuit was introduced to suppress high-frequency noise and reduce electrode polarization effects. During EIS measurements, a ±0.8V linear sweep voltage was applied at a scan rate of 15mV / s, and the current response was simultaneously recorded to obtain the voltammetric characteristic curve.

[0090] Optimized impedance decomposition algorithm: uses a neural network structure, including 5-7 convolutional layers and 3-4 fully connected layers. The input is the EIS impedance spectrum (real / imaginary parts vary with frequency), SPR charge density series and IV curve, and the output is the electrode polarization impedance (Rp), solution resistance (Rs) and double electric layer impedance (ZEDL). COMSOL Multiphysics simulation is used to generate the ion concentration between 10 -5 -10 -3 M. A synthetic data set with a temperature range of 28-35°C was used for training, and a certain amount of noise was added. The network parameters were optimized through the back propagation algorithm to make the impedance component separation error less than 8%-10%.

[0091] The measuring device of the present invention has a flat layered structure as a whole, which is more convenient to operate and can be easily held or integrated into a measuring platform. The measuring device of the present invention can solve the problems of traditional measuring devices such as complex structure, easy clogging, weak interface signal, and uneven solution introduction. Specifically:

[0092] First, the present invention forms an embedded trench electrode 12 on a silicon substrate 11, creating a three-dimensional structure. Specifically, an aluminum electrode is embedded within parallel trenches etched into the silicon substrate 11. The trenches are 100–200 nm deep, and the top surface of the electrode 12 is flush with the top surface of the silicon substrate 11, forming a "grooved slit." The cross-sectional shape resembles a "[" character, with the electrode 12's sidewalls perpendicular and the silicon substrate 11 at its base. The electrode 12 of the present invention is embedded within the trench formed in the silicon substrate 11, creating a stable and reliable structure that avoids the mechanical instability of conventional suspended electrodes while forming a precisely dimensioned nano-groove 13 (accuracy ±8 nm).

[0093] Second, the two parallel electrodes 12 (spacing ≤50nm) of the present invention are spaced apart to form a narrow, open channel (10–100μm long), resembling an "ultra-narrow gap formed by two parallel metal sheets," forming an open nanogroove 13. The open nature of the nanogroove 13 of the present invention avoids the dead corners and clogging issues of traditional closed nanogrooves. The nanogroove 13 of the present invention is easy to clean, maintain, and reuse. Conventional measurement devices often use closed channels (such as PDMS microfluidics) that require an external pump to introduce solutions. However, the open structure of the nanogroove 13 of the present invention allows for self-filling of solutions.

[0094] The opening of the nano-groove 13 of the present invention is formed with an inclined introduction surface 14 , and the inclined introduction surface 14 is coated with a hydrophilic layer, which can reduce the flow resistance of the solution, thereby making it easier to introduce and fill the solution.

[0095] Third, the optical path of the fiber-optic surface plasmon resonance sensor 25 is perpendicular to the length of the nano-groove 13, forming a "cross" layout, which improves the sensitivity and strength of the interface signal. Multiple pH fiber-optic probes 26 are embedded in the sidewalls of the nano-groove 13 at 15μm intervals. The ends of the pH fiber-optic probes 26 are flush with the surface of the parallel aluminum electrodes, preventing protrusions from interfering with the flow field and improving measurement accuracy and sensitivity. The thermistors in the temperature control module 22 are arranged in a dot matrix, not occupying the space in the nano-groove 13.

[0096] The electrochemical impedance spectroscopy (EIS) circuit boards in the online monitoring layer and the signal processing layer work in tandem. The online monitoring layer is responsible for real-time collection of key data from the measurement device, such as temperature, pressure, solution pH, and electrode surface plasmon resonance signals. This data is crucial for accurate analysis of solution-interface characteristics. The EIS circuit board in the signal processing layer is primarily used for performing electrochemical impedance spectroscopy (EIS) scans, recording impedance spectrum data, and comprehensively processing and analyzing the various collected data.

[0097] During the actual measurement process, the data collected by the online monitoring layer is transmitted to the signal processing layer for subsequent processing along with the impedance spectrum data obtained by the electrochemical impedance spectroscopy circuit board. For example, the charge density data monitored by the fiber optic surface plasmon resonance sensor, the pH value data measured by the pH fiber probe, and the impedance spectrum data obtained by the EIS scan are input into a simplified neural network algorithm for data fusion and parameter inversion. This results in key parameters such as electrode polarization impedance, solution resistance, and double-layer impedance, as well as important indicators reflecting solution-interface characteristics such as Debye length, zeta potential, and ion mobility.

[0098] In the measuring device of the present invention, the optical fiber mainly functions through the optical fiber surface plasmon resonance sensor and the pH optical fiber probe to achieve monitoring of multiple key parameters.

[0099] Surface charge density monitoring: The optical path of the fiber-optic surface plasmon resonance sensor is perpendicular to the length of the nanogrooves, forming a "cross" pattern. When incident light propagates through the fiber and strikes the surface of the electrode connected to it, it triggers surface plasmon resonance, causing a change in the intensity of the reflected light. By monitoring this change in reflected light intensity, the surface charge density can be calculated using a calibration curve with a resolution of up to 0.2-0.3 mC / m², enabling real-time monitoring of the electrode surface charge density.

[0100] Micro-area pH measurement: Multiple pH fiber optic probes are embedded in the sidewalls of the nanogrooves at 15 μm intervals, with their ends flush with the surfaces of the parallel aluminum electrodes. These pH fiber optic probes are surface-modified with a pH-sensitive fluorescent dye, such as BCECF. By monitoring the ratio of fluorescence intensities at 490 nm and 535 nm, the local pH value is inverted using the fluorescence ratio method with a spatial resolution of 15 μm, enabling precise measurement of the local pH value at the solution-electrode interface.

[0101] The present invention also provides a method for preparing a solution-interface measuring device based on the nano-slit confinement effect, comprising:

[0102] S1: Using masked photolithography, a metal electrode pattern with a spacing of 50 nm is fabricated on a silicon substrate 11. Photoresist is evenly coated on the silicon substrate 11, and the mask pattern is transferred to the photoresist using photolithography. After development, an aluminum metal mask with a spacing of 50 nm is formed. Next, a gold layer with a thickness of 2 nm is deposited on the exposed electrode areas using magnetron sputtering. The deposition power is controlled between 150-251 W and the pressure is maintained at 1-5 mTorr, forming parallel electrodes 12 with a spacing of 50 nm and a thickness of 100-200 nm.

[0103] S2: Immerse the electrode in a mixed solution of 11-mercaptoundecanoic acid and ethanol, where the molar concentration of 11-mercaptoundecanoic acid is 0.8 mmol / L to 1.2 mmol / L. The reaction is allowed to react at room temperature for 15-20 hours, forming a dense thiol self-assembled layer 13 on the surface of electrode 12. The thickness of thiol self-assembled layer 13 is 1-2 nm. This layer is anchored to the surface of electrode 12 via Au-S bonds, providing carboxyl (-COOH) functional groups. The surface charge density can be controlled by adjusting the pH of the solution.

[0104] S3: Spin-coat the inclined inlet surface 14 at the entrance of the nano-groove 13 with a polyethylene glycol solution to form a 5-10 nm thick hydrophilic layer with a contact angle of ≤15°. Leveraging the capillary effect, the solution fills the nano-groove 13 within 15 seconds with a uniformity deviation of <5%.

[0105] S4: Mount the monitoring base plate 21 on the bottom of the silicon substrate 11. Attach the fiber optic surface plasmon resonance sensor 25 parallel to the surface of the electrode 12, with the optical path of the fiber optic surface plasmon resonance sensor 25 perpendicular to the length of the nanogrooves 13, forming a "cross" layout.

[0106] A plurality of pH fiber optic probes 26 are embedded into the sidewalls of the nano-grooves 13 at intervals of 15 μm. The ends of the pH fiber optic probes 26 are flush with the surfaces of the parallel electrodes 12 to avoid protrusions interfering with the flow field.

[0107] S5: Install the signal processing layer at the bottom of the online monitoring layer.

[0108] The preparation method of the solution-interface measurement device based on the nano-slit confinement effect of the present invention has the following advantages:

[0109] First, optimizing electrode preparation and material selection: Aluminum electrodes are fabricated on silicon substrates and then plated with gold, replacing traditional processes. Compared to other approaches, silicon substrates are widely available and inexpensive, and the aluminum electrode preparation process is relatively simple. Subsequent gold plating not only enhances electrode performance but also allows for better integration with surface functionalization. While maintaining measurement accuracy, this significantly reduces material cost and preparation difficulty, improving the overall cost-effectiveness of the device.

[0110] Second, optimize monitoring solutions to improve practicality: Fiber-optic surface plasmon resonance sensors are low-cost, compact, and easy to install. Micro-area environmental control uses low-cost devices like thermistors and standard pressure sensors, and their temperature and pressure control accuracy can meet the needs of some experiments.

[0111] Third, efficient algorithms reduce resource requirements: The simplified neural network structure reduces the demand for computing resources, shortens training time, and can still effectively separate impedance components under specific experimental conditions to achieve multi-parameter measurement.

[0112] The present invention also provides a measurement method of a solution-interface measurement device based on the nano-slit confinement effect, comprising:

[0113] S1: Sample and device preparation, including the following steps:

[0114] S 1.1: Select the target electrolyte solution, KCl solution, concentration 10 -4 M, make sure there are no bubbles and impurities.

[0115] Adjust the solution pH (by acid-base titration) according to the experimental requirements to match the charge characteristics of the thiol self-assembled modification layer. The solution pH should be adjusted to match the charge characteristics of the thiol self-assembled modification layer. For example, if the thiol self-assembled modification layer is negatively charged (such as the carboxylic acid end), the solution pH should be higher than its pKa (such as pH>5) to ensure that the thiol self-assembled modification layer is ionized (-COO - ); If the thiol self-assembled modification layer is positively charged (such as the amino terminus), the pH should be lower than its pKa (such as pH < 9).

[0116] S1.2: Temperature / pressure setting: Set the target temperature using a thermistor heating element, such as 32°C ± 0.5°C. Use a small air pump to adjust the air pressure outside the slit, such as 105 kPa ± 30 Pa. Temperature fluctuations must be less than ± 0.5°C, and pressure fluctuations must be less than ± 30 Pa to avoid affecting capillary filling and measurement repeatability.

[0117] S1.3: Activate the hydrophilic layer and confirm that the PEG hydrophilic coating at the slit entrance is intact and the contact angle is ≤15°.

[0118] Utilizing the capillary effect, KCl solution fills the nanogrooves from bottom to top within 15 seconds with a uniformity deviation of less than 5%. Wait 1-2 minutes for the solution-electrode interface to reach equilibrium and stabilize the double layer. Equilibrium at the solution-electrode interface refers to the dynamic equilibrium of mass exchange and charge transfer between the solution and electrode in an electrochemical system. This 1-2 minute wait ensures that the local pH value at the solution-electrode interface, measured by the pH fiber optic probe, is accurate and reliable, as only in equilibrium can the measured value truly reflect the properties of the system.

[0119] The micro-area pH fiber optic sensor measures the local pH value at the solution-electrode interface (such as near the double layer), such as the BCECF fluorescent dye detecting the 490nm / 535nm ratio.

[0120] S2: Multi-parameter synchronous measurement, signal synchronization: EIS, SPR, and IV data must be strictly time-aligned and use a unified trigger signal; specifically, the following steps are included:

[0121] S2.1: Electrochemical impedance spectroscopy (EIS) scan;

[0122] Apply a sinusoidal AC excitation signal (frequency range 10 3 –10 6 Hz, amplitude 5-10mV).

[0123] Impedance spectra (real and imaginary parts) were recorded using an EIS circuit, with 30–50 data points collected per decade.

[0124] For electrochemical impedance spectroscopy (EIS) scanning, the frequency range is relatively narrow, and 30-50 data points are collected for each decade. This ensures the acquisition of key data and reflects the trend of impedance spectrum changes, while effectively shortening the measurement time and improving experimental efficiency without excessive loss of measurement accuracy. It is also possible to further improve data accuracy and reduce the error caused by the reduction of data points by taking the average value of multiple measurements.

[0125] S2.2: Surface charge density monitoring (SPR);

[0126] The optical fiber surface plasmon resonance sensor was started to monitor the surface plasmon resonance signal of the gold electrode at a sampling rate of 8 Hz.

[0127] The real-time charge density (accuracy 0.2–0.3 mC / m²) is calculated from the change in reflected light intensity.

[0128] S2.3: Volt-ampere characteristic (IV) test;

[0129] ±0.8 V linear sweep voltage (rate 15 mV / s) was applied synchronously, and the current response curve was recorded.

[0130] S3: Data processing and parameter inversion, specifically including the following steps:

[0131] S3.1: Data fusion;

[0132] The EIS impedance spectrum, SPR charge density series, and IV curve were input into the simplified neural network algorithm.

[0133] Algorithm structure: 5-7 layers of convolutional network and 3-4 layers of full connection, input noise <8% synthetic data training set.

[0134] S3.2: Impedance component separation;

[0135] Output electrode polarization impedance (Rp), solution resistance (Rs), and double electric layer impedance (ZEDL).

[0136] The polarization effect was corrected using the SPR data (formula: , α fitting coefficient), can make the measured impedance-related data more accurate and reduce the interference of polarization effect on the measurement results.

[0137] S3.3: Multi-parameter output;

[0138] Inversion model calculation: Debye length (λD, reflecting the thickness of the double layer).

[0139] Zeta potential (characterizes the interface potential).

[0140] Ion mobility (reflects the conductivity of the solution).

[0141] S4: Drain the solution, rinse the nanogrooves three times with deionized water, and blow dry with nitrogen. Check the integrity of the electrode and SAM layer, re-modify if necessary, and immerse in an ethanolic solution of 11-mercaptoundecanoic acid (MUA) for 15–20 hours.

[0142] The present invention achieves efficient collaborative measurement of nanoconfined interface parameters through "capillary filling solution → multi-sensor synchronous measurement → intelligent algorithm analysis", significantly improving measurement simplicity and measurement data reliability. Specifically:

[0143] First, the solution introduction method: This application coats the inclined introduction surface 14 at the entrance of the nano-grooves 13 with polyethylene glycol (PEG) to form a hydrophilic layer. This utilizes the capillary effect to introduce the solution, allowing the solution to fill the nano-grooves 13 from bottom to top along the inclined introduction surface 14 within 15 seconds with a uniformity deviation of less than 5%. This eliminates the need for complex external equipment, simplifies the operation process, and improves the uniformity of solution distribution. Traditional measurement devices, on the other hand, often use external pumps to drive the solution flow, which can easily lead to uneven solution introduction, affecting measurement repeatability and accuracy.

[0144] Second, simultaneous multi-parameter measurement: This application utilizes a fiber-optic surface plasmon resonance sensor 25 to monitor charge density in real time, simultaneously performing electrochemical impedance spectroscopy (EIS) scans and volt-ampere (IV) measurements. This allows the acquisition of multiple key parameters within the same timeframe, ensuring data synchronization and correlation, and more comprehensively and accurately reflecting solution-interface characteristics. Conventional methods often struggle to achieve simultaneous and precise multi-parameter measurement, or require multiple independent devices to measure different parameters separately, which is cumbersome and prone to errors.

[0145] Third, data processing and analysis: This application uses an impedance decomposition algorithm with a simplified neural network structure to process data. The algorithm inputs the EIS impedance spectrum, SPR charge density series, and IV curves, and outputs parameters such as electrode polarization impedance, solution resistance, and double-layer impedance. The SPR data is also used to correct for electrode polarization effects, and a multi-parameter inversion model is used to derive Debye length, Zeta potential, and ion mobility, improving data processing efficiency and accuracy and unlocking the potential value of the data. Traditional measurement device data processing methods are relatively simple and difficult to accurately extract key information from complex data.

[0146] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for a person skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to replace some of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions claimed to be protected by the present invention.

Claims

1. A solution-interface measurement device based on nano-slit confinement effect, characterized in that: include: A sample preparation layer comprises a silicon substrate on which two parallel and spaced electrodes are formed, and a thiol self-assembly modification layer is formed on the upper surfaces of the electrodes; The electrodes are embedded in parallel grooves etched into the silicon substrate, and the top surfaces of the electrodes are flush with the top surface of the silicon substrate, forming a "groove-type slit"; A nano-groove is formed between the two electrodes, an inlet of the nano-groove is provided with an inclined introduction surface, and a hydrophilic layer is formed on the surface of the inclined introduction surface; An online monitoring layer includes a temperature control module having a thermistor array arranged at the bottom of the silicon substrate; a fiber optic surface plasmon resonance sensor disposed on the upper surface of the electrode; and a pH fiber optic probe disposed on the sidewall of the nano-groove; the optical path of the fiber optic surface plasmon resonance sensor is perpendicular to the length of the nano-groove, forming a "cross" layout, and the end of the pH fiber optic probe is flush with the electrode surface; The signal processing layer includes an electrochemical impedance spectroscopy circuit board arranged at the bottom of the online monitoring layer.

2. The solution-interface measurement device based on the nano-slit confinement effect according to claim 1, characterized in that: The electrode is an aluminum electrode, the surface of which is coated with a gold layer, and the thickness of the gold layer is 2 nm; The distance between the two electrodes is 40-60 nm, and the thickness of the electrodes is 100-200 nm.

3. The solution-interface measurement device based on the nano-slit confinement effect according to claim 1, characterized in that: The thickness of the thiol self-assembly modification layer is 1-2 nm.

4. The solution-interface measurement device based on the nano-slit confinement effect according to claim 1, characterized in that: The nanogrooves have a depth of 100-200 nm and a length of 10-100 μm.

5. The solution-interface measurement device based on the nano-slit confinement effect according to claim 1, characterized in that: The thickness of the hydrophilic layer is 5-10 nm, and the contact angle is ≤15°.

6. A method for preparing a solution-interface measurement device based on the nano-slit confinement effect according to any one of claims 1 to 5, characterized in that: The method comprises: S1: Using mask lithography technology, a metal electrode pattern with a spacing of 50nm is produced on a silicon substrate. Photoresist is evenly coated on the silicon substrate, and the mask pattern is transferred to the photoresist using a photolithography method. After development, an aluminum mask electrode with a spacing of 50nm is formed. A gold layer is deposited on the surface of the exposed aluminum mask electrode to form two parallel electrodes. S2: Immersing the electrode in a mixed solution of 11-mercaptoundecanoic acid and ethanol to form a thiol self-assembled modification layer on the electrode surface; S3: Spin coating the surface of the inclined introduction layer in the nanogroove inlet area with a polyethylene glycol solution to form a hydrophilic layer; S4: Attach the fiber optic surface plasmon resonance sensor parallel to the electrode surface, with the optical path of the fiber optic surface plasmon resonance sensor perpendicular to the length of the nanogroove, forming a "cross" layout; Multiple pH fiber optic probes were embedded into the sidewalls of the nanogrooves at intervals of 15 μm, with the ends of the pH fiber optic probes flush with the electrode surface; The temperature control module is mounted on the bottom of the silicon substrate, and the thermistors of the temperature control module are arranged in a dot matrix; S5: Install the signal processing layer at the bottom of the online monitoring layer.

7. The method for preparing a solution-interface measurement device based on the nano-slit confinement effect according to claim 6, wherein: A gold layer was deposited on the surface of the exposed aluminum mask electrode using a magnetron sputtering method with a deposition power of 150-251 W and a gas pressure of 1-5 mTorr.

8. The method for preparing a solution-interface measurement device based on the nano-slit confinement effect according to claim 6, wherein: The electrode is immersed in a mixed solution of 11-mercaptoundecanoic acid and ethanol, wherein the molar concentration of 11-mercaptoundecanoic acid in the mixed solution is 0.8 mmol / L-1.2 mmol / L; the mixture is reacted at room temperature for 15-20 hours to form a dense thiol self-assembled modification layer on the electrode surface.

9. The method for preparing a solution-interface measurement device based on the nano-slit confinement effect according to claim 6, wherein: The thickness of the hydrophilic layer is 5-10 nm, and the contact angle is ≤15°.

10. A measurement method for a solution-interface measurement device based on a nano-slit confinement effect according to any one of claims 1 to 5, characterized in that: The method comprises: S1: Select the target electrolyte solution KCl solution and ensure that the solution is free of bubbles and impurities; The temperature of the measuring device was adjusted to 32°C ± 0.5°C, and the pressure outside the nanoslit was adjusted to 105 kPa ± 30 Pa; Using the capillary effect, KCl solution was filled from bottom to top within 15 seconds with a uniformity deviation of less than 5%. The solution-electrode interface was allowed to reach equilibrium for 1-2 minutes. The local pH value at the solution-electrode interface was measured using a pH fiber optic probe. S2: Apply a sinusoidal AC excitation signal with a frequency range of 10 3 -10 6 Hz, amplitude 5-10mV; Impedance spectra were recorded using an EIS circuit, with 30–50 data points collected per decade. The fiber optic surface plasmon resonance sensor was activated to monitor the electrode surface plasmon resonance signal at an 8Hz sampling rate. The real-time charge density was calculated based on the change in reflected light intensity with an accuracy of 0.2-0.3mC / m². ±0.8 V linear sweep voltage was applied synchronously at a rate of 15 mV / s, and the current response curve was recorded; S3: Input EIS impedance spectra, SPR charge density series, and IV curves into a simplified neural network algorithm; algorithm structure: 5-7 layers of convolutional network and 3-4 layers of fully connected network, input synthetic data training set with less than 8% noise; Output electrode polarization impedance Rp, solution resistance Rs, and double-layer impedance ZEDL; use SPR data to correct polarization effects; Inversion model calculations: Debye length, Zeta potential, ion mobility; S4: drain the solution, rinse the nanogrooves with deionized water, and blow dry with nitrogen gas; Check the integrity of the electrode and thiol self-assembly modification layer and re-modify.

Images