A method for batch production of potential-type all-solid-state ion-selective microelectrode and application

Abstract

The present application relates to microelectrode, specifically to a method for batch production of potential type full solid-state ion selective microelectrode and application. A bundle of treated carbon fibers is used to in-situ synthesize nanowire-like transduction layer by chemical water bath method, and then the grown carbon fibers are assembled into ion selective microelectrode and adsorbed ion selective membrane, that is, the full solid-state ion selective microelectrode is constructed in batch. The full solid-state ion selective microelectrode constructed by the method has the advantages of simple production, high sensitivity, low cost and easy miniaturization, and can realize the detection of plant root ion flux. By changing the type of ion carrier in the ion selective membrane and the plant root, the detection of various ion fluxes of various plants can be realized.

Description

Technical Field

[0001] This invention relates to microelectrodes, specifically a method and application for the mass production of potential-type all-solid-state ion-selective microelectrodes. Background Technology

[0002] Heavy metals are non-biodegradable pollutants that pose threats not only to organisms but also to the environment. The migration and biocompatibility of heavy metal ions within the soil-plant growth system mean they can easily enter the food chain, posing a threat to human health. Therefore, studying the migration mechanisms of heavy metal ions in plant roots is crucial for assessing their transfer patterns in the food chain. Currently, methods for determining heavy metal ions mainly include atomic fluorescence spectrometry, atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry, laser-induced breakdown spectroscopy, and X-ray fluorescence spectrometry. While these methods provide accurate data, the large size and high operating costs of the instruments required make them unsuitable for detecting heavy metal ions in micro-regions of plant roots.

[0003] Potentiometric microelectrode sensors are ideal tools for detecting changes in ion flux in minute environments. Unaffected by the detection volume, they can detect ion flux on the surface of plant roots. Furthermore, combining potentiometric microelectrodes with non-destructive testing platforms enables visualized detection of ion flux in plant roots. Currently, microelectrodes are mainly divided into liquid-film ion-selective microelectrodes and all-solid-state ion-selective microelectrodes. All-solid-state ion-selective microelectrodes simplify the use of internal filling in liquid-film ion-selective microelectrodes, solving the problem of leakage. Therefore, all-solid-state ion-selective microelectrodes have received widespread attention. Currently, the structure of all-solid-state ion-selective microelectrodes mainly includes a capillary glass tube, a wire, an electrode substrate, a transconducting layer, and a polymer ion-selective membrane. Commonly used electrode substrates are mainly carbon fiber, gold, platinum, and carbon materials, while transconducting layers are mainly conductive polymers, carbon materials, oxides, and sulfides. The current preparation methods of all-solid-state ion-selective microelectrodes include: (1) Preparation method of carbon fiber microelectrodes: First, fix the carbon fiber electrode on the wire and then put it into the glass tube. Then, seal the rear end with epoxy resin and seal the front end with flame melting under an alcohol lamp. At the same time, control the length of the carbon fiber tip protruding from the glass tube to within 100 micrometers. Then, load the transconducting layer on the surface of the carbon fiber. When the conductive polymer is used as the transconducting layer, the commonly used method is electrodeposition. The transconducting layer is deposited on the carbon fiber surface one by one for the microelectrodes. Finally, the polymer film is dipped on the carbon fiber surface. This method requires sealing the front end of the glass tube under high temperature conditions with an alcohol lamp and controlling the length of the carbon fiber, which is difficult to control. In addition, the transconducting layer is deposited on the carbon fiber surface by electrodeposition. This process can only deposit one microelectrode at a time, so it is difficult to achieve batch preparation of electrodes. Finally, the polymer film is loaded on the electrode by dipping. The polymer film is thin, which is not conducive to the long-term use of the electrode. If carbon materials are used as the transconducting layer, they can be grown on the surface of carbon fibers by electrodeposition, high-temperature carbonization and chemical vapor deposition. However, the electrodeposition method is difficult to mass-produce, and the transconducting layer materials synthesized by this method mostly exhibit the morphology of nanoparticles or nanosheets. The contact area between this morphology and the polymer film is relatively small, resulting in fewer active sites for capacitance, thus limiting the improvement of electrode stability. However, the high-temperature carbonization and chemical vapor deposition methods are relatively complex to operate and require high temperature and high pressure, making the synthesis conditions of the transconducting layer harsh and complex. (2) Preparation method of gold wire microelectrode: Gold wire is used as the electrode substrate. The gold wire is fused with a glass tube by flame melting, and then the surface of the microelectrode is polished to prepare a gold microelectrode (diameter of 14 μm). The conductive layer is modified by electrodeposition of PEDOT-PSS, and then a polymer ion-selective polymer film is dipped onto the surface of the microelectrode to prepare an all-solid-state ion-selective microelectrode. Similarly, the preparation method of this microelectrode also has the problems of difficulty in mass production and service life.(3) Fabrication of carbon material microelectrodes: Disordered mesoporous carbon / carbon nanotubes / graphene were used as the filling material for the microelectrodes. Utilizing their large specific surface area and double-layer capacitance, the use of the transconductance layer was simplified. A micro-injection pump was used to pressurize and draw the membrane solution into the tip of the microelectrode, thus constructing an all-solid-state ion-selective microelectrode. The fabrication of this electrode requires filling the glass tube tip with carbon material, and the membrane solution needs to be adsorbed using a micro-injection pump, making the operation relatively cumbersome.

[0004] Therefore, there is a need to find a simple and rapid method for preparing microelectrodes in batches. At the same time, the microelectrodes should have the advantages of fast response speed, low detection limit, good stability and long-term use to meet the needs of practical applications. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing potentiometric all-solid-state ion-selective microelectrodes in batches and to apply them to the real-time detection of ion flux in plant roots.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for mass-producing potentiometric all-solid-state ion-selective microelectrodes involves using a chemical bath method to synthesize a transconducting layer in situ on the surface of a bundle of treated carbon fibers. Then, the deposited carbon fibers are used to assemble ion-selective microelectrodes and adsorb ion-selective membranes, thus mass-producing solid-state ion-selective microelectrodes.

[0008] The treated carbon fiber is a carbon fiber substrate that has been ultrasonically cleaned with a mixed solution of concentrated sulfuric acid and concentrated nitric acid to remove impurities; wherein the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 1:3 to 1:1. The concentrated sulfuric acid has a mass concentration of 98%, and the concentrated nitric acid has a mass concentration of 68%.

[0009] The in-situ synthesized transconducting layer on the carbon fiber surface is a metal sulfide obtained by chemical water bath method. A bundle of treated carbon fibers is immersed in a precursor solution, and nanowire-shaped basic carbonates are grown in situ on the carbon fiber surface intermediate through the reaction of metal ions with urea at 90-120 °C. Then, in an aqueous solution of sodium sulfide, the nanowire-shaped transconducting layer is synthesized in situ on the carbon fiber surface through ion exchange at 90-120 °C.

[0010] The transconducting layer is a metal sulfide; wherein the metal sulfide is a monometallic sulfide (nickel-based sulfide and cobalt-based sulfide) or a bimetallic sulfide (NiCo2S4 or CoNi2S4).

[0011] Further, a transduction layer was prepared using NiCo2S4 nanowires as an example:

[0012] The NiCo2S4 nanowires are grown on the surface of carbon fibers using a chemical bath method. A precursor solution is formed by dissolving a nickel source, a cobalt source, and urea in an aqueous solution, allowing for the growth of an intermediate on the carbon fiber surface. Then, a sulfur source is used to vulcanize the solution at a specific temperature, forming the NiCo2S4 nanowires grown on the carbon fiber surface. The molar concentration of the nickel source in the solvent is 0.025-0.5 mol / L. -1 The molar concentration of the cobalt source in the solvent is 0.5-0.1 mol L. -1 The molar concentration of the sulfur source in the solvent is 0.1-0.2 mol L. -1 .

[0013] The specific temperature at which the NiCo2S4 nanowires are grown on the carbon fiber surface through sulfurization is 90-120 ℃.

[0014] The nickel source is one of nickel nitrate, nickel chloride, and nickel acetate; the cobalt source is one of cobalt nitrate, cobalt chloride, and cobalt acetate; and the sulfur source is one of thioacetamide, thiourea, or sodium sulfide.

[0015] A carbon fiber with a nanowire transduction layer grown on its surface is fixed to the tip of a copper wire. Then, it is placed in a drawn glass tube to fix the carbon nanotube loaded with copper wire. Then, the polymer is adsorbed using capillary action to adsorb the ion-selective membrane. Finally, the rear end of the glass tube is sealed to obtain an all-solid-state ion-selective microelectrode.

[0016] The polymer ion-selective membrane comprises an ion carrier, an ion exchanger, a polymer substrate material, and a plasticizer, wherein the ion carrier may be lead ion, copper ion, cadmium ion, sodium ion, calcium ion, potassium ion, chloride ion, or ammonium ion.

[0017] A potential-type all-solid-state ion-selective microelectrode is prepared by the method described above, which can produce carbon fibers with a transconductance layer on the surface in batches, and then assembled in batches to obtain the all-solid-state ion-selective microelectrode.

[0018] An application of an all-solid-state ion-selective microelectrode for detecting changes in ion flux on the surface of plant roots.

[0019] The plant root system may be rice root, wheat root, Arabidopsis root, mulberry root, cotton seedling, oat seedling, pea root or reed root.

[0020] The preparation principle and implementation method of this invention:

[0021] This invention employs a chemical bath method to mass-produce ion-electron transduction layers on the surface of a carbon fiber electrode substrate. After growth, the carbon fiber electrode substrate is bonded to conductive copper wires using graphene conductive adhesive, and then slowly placed into a drawn capillary glass tube (the tip size of the glass tube is less than 20 micrometers). The rear end is fixed with epoxy resin, followed by the adsorption of an ion-selective polymer film. Finally, the rear end of the capillary is further sealed with epoxy resin, thus forming a microelectrode. This microelectrode construction method greatly simplifies the electrode preparation steps and enables the mass production of all-solid-state ion-selective microelectrodes.

[0022] Among them, microelectrodes were prepared by in-situ growth of nanowire NiCo2S4 as an ion-electron transduction layer on the surface of carbon fiber electrode substrate, which improved the stability of microelectrodes. In addition, the constructed potential-type ion-selective microelectrodes can be used for real-time detection of ion flux in plant roots.

[0023] The advantages of this invention are:

[0024] 1. The method for preparing the all-solid-state ion-selective microelectrode of the present invention simplifies the electrode preparation process and enables mass production.

[0025] 2. The present invention utilizes a potential-type microelectrode sensor, which has the advantages of fast response speed, high sensitivity and good stability, and can realize sensitive detection of ion flux in plant roots.

[0026] 3. This invention employs redox-type NiCo2S4 nanowires grown in situ on the surface of carbon fibers as an ion-electron transduction layer. The NiCo2S4 nanowire structure increases the contact area between the transduction layer and the ion-selective membrane, providing more redox sites and generating greater capacitance, which is beneficial for ion-electron transduction and improves the stability of the microelectrode. Furthermore, the ion-selective membrane of the ion-selective microelectrode prepared by this invention has a thickness of 50-60 micrometers, which can increase its service life.

[0027] 4. This invention can realize the detection of ion flux on the surface of various plant roots. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the fabrication process of the potential-type microelectrode sensor provided in an embodiment of the present invention.

[0029] Figure 2 Scanning electron microscope (SEM) images of carbon fiber microelectrodes provided for embodiments of the present invention (A), intermediates grown on the surface of carbon fibers (B), and NiCo2S4 grown in situ on the surface of carbon fibers (C).

[0030] Figure 3A photograph (left) and an optical microscope image (right) of the potential-type microelectrode sensor provided in the embodiments of the present invention.

[0031] Figure 4 Cyclic voltammetry curves (A) and electrochemical impedance spectroscopy (B) of carbon fibers and NiCo2S4-based carbon fibers provided in embodiments of the present invention.

[0032] Figure 5 The chronopotential curves (dashed lines) of the carbon fiber microelectrode and the chronopotential curves (solid lines) of the carbon fiber microelectrode based on NiCo2S4 provided for embodiments of the present invention.

[0033] Figure 6 The all-solid-state ion-selective microelectrode and liquid film microelectrode provided in the embodiments of the present invention are in the presence of lead nitrate at 10 -4 -10 -9 The real-time potential change response diagram (A) and calibration curve diagram (B) measured in the soil background solution of M are shown. In diagrams A and B, a is the all-solid-state lead ion selective electrode and b is the lead ion liquid membrane microelectrode.

[0034] Figure 7 Photograph (A) of the non-destructive detection system provided in the embodiments of the present invention, optical micrograph (B) of the detection of plant roots by the all-solid-state ion-selective microelectrode, and comparison graph (C) of the ion flux of the all-solid-state ion-selective electrode and the liquid membrane microelectrode in detecting plant roots. Detailed Implementation

[0035] The following examples further illustrate specific embodiments of the present invention. It should be noted that the specific embodiments described herein are merely for illustration and explanation and are not intended to limit the scope of the present invention.

[0036] This invention employs a chemical bath method to grow ion-electron transduction layers on the surface of a carbon fiber electrode substrate in large quantities. This method does not require high temperature and pressure, and the preparation conditions are mild and easy to operate. The grown carbon fiber electrode substrate is then bonded to conductive copper wire using graphene conductive adhesive, and then slowly placed into a drawn capillary glass tube. The distance between the tip of the carbon fiber and the tip of the capillary glass tube is no more than 20 micrometers. The rear end is fixed with epoxy resin adhesive, and then an ion-selective polymer film is adsorbed, thus forming a microelectrode. This method is simple, easy to operate, and can achieve large-scale preparation of microelectrodes. By using an ion-selective film, the film thickness is maintained at approximately 50-60 micrometers, which can improve the lifespan of the electrode. Furthermore, utilizing the advantages of high mass transfer rate, high current density, and fast response speed of microelectrodes, they can be used for the detection of ion flux in micro-regions of plant roots.

[0037] All reagents used in the following examples were purchased on a trial basis. Among them, nickel salt, cobalt salt, urea and sulfur source were all of analytical grade.

[0038] Example 1

[0039] The construction of all-solid-state ion-selective carbon fiber microelectrodes is based on the in-situ generation of nanowire-shaped NiCo2S4 on the surface of carbon fibers as an ion-electron transduction layer by chemical bath method, and then the carbon fiber microelectrodes are prepared and adsorbed onto polymer membrane ion-selective membranes, realizing large-scale preparation.

[0040] Depend on Figure 1 As can be seen in the schematic diagram of the preparation process of the all-solid-state ion-selective microelectrode, a nanowire transconducting layer was first synthesized on the carbon fiber surface using a simple and mild water bath method. Then, the electrode was assembled to adsorb the ion-selective membrane. This optimized the preparation process of the microelectrode, simplified the preparation steps, and enabled the mass production of microelectrodes.

[0041] The specific fabrication steps of an all-solid-state ion-selective microelectrode are as follows: Figure 1 As shown:

[0042] a. Substrate treatment: Based on carbon fibers with a diameter of 7 micrometers as the substrate, before the growth of the transduction layer, the carbon fiber substrate was ultrasonically cleaned for 2 hours with a mixed solution of 98% concentrated sulfuric acid and 68% concentrated nitric acid at a volume ratio of 3:1 to remove impurities and form a rough structure on the carbon fiber surface, which is conducive to the growth of the transduction layer.

[0043] Depend on Figure 2 A in the image shows a scanning electron microscope image of the carbon fiber surface after cleaning. Specifically, the carbon fiber surface shows striped patterns after cleaning, which is beneficial for the growth of the transduction layer.

[0044] b. Preparation of carbon fibers loaded with NiCo2S4 nanowires:

[0045] First, the preparation method for growing nickel-cobalt hydroxycarbonate nanowires on the surface of carbon fibers as a precursor is as follows: 118.85 mg of nickel chloride, 237.931 mg of cobalt chloride, and 210.21 mg of urea were weighed and dissolved in 100 mL of ultrapure water, and sonicated until completely dissolved to form a pink and transparent solution. Then, the above solution was transferred to an Erlenmeyer flask, and a bundle of cleaned carbon fibers approximately 10 cm in length was placed inside. The reaction was carried out at 90 ℃ for 6 h (see...). Figure 2 (B)

[0046] Secondly, the preparation method for nickel-cobalt sulfide hydroxycarbonate nanowires is as follows: 1.20 g of sodium sulfide was dissolved in 50 mL of ultrapure water and sonicated until completely dissolved to form a transparent solution. Then, the solution was transferred to an Erlenmeyer flask, and carbon fibers with the precursor grown were placed into the flask. The reaction was continued at 90 °C for 6 h (see [link to relevant documentation]). Figure 2 ).

[0047] Depend on Figure 2 Image B shows a scanning electron microscope image of a precursor of nickel-cobalt hydroxycarbonate nanowires grown on the surface of carbon fibers, specifically a precursor nanowire grown uniformly on the surface of carbon fibers.

[0048] Depend on Figure 2 As can be seen in C, this is a scanning electron microscope image of NiCo2S4 nanowires grown on the surface of carbon fibers, specifically, NiCo2S4 nanowires are uniformly grown on the surface of carbon fibers.

[0049] b. Preparation of ion-selective polymer membranes:

[0050] Weigh out 1.57 wt% lead ion carrier, 0.48 wt% sodium tetrakis(3,5-bis(trifluoromethyl))borate (NaTFPB), 33.05 wt% polyvinyl chloride (PVC), and 66.9 wt% o-nitrophenyl octyl ether (…). o 1.00% tetrabis(4-chlorophenyl)borate was dissolved in 1.5 mL of tetrahydrofuran (THF), stirred for 4-5 h, and then transferred to a desiccator for storage until use.

[0051] c. Fabrication of all-solid-state ion-selective microelectrodes:

[0052] Carbon fibers with grown NiCo2S4 nanowires were fixed to the tip of a copper wire using graphene conductive adhesive. After the graphene conductive adhesive dried, it was gently inserted into the rear end of a drawn glass tube, ensuring the distance between the carbon fiber tip and the glass tube tip did not exceed 20 micrometers. Then, epoxy resin was used to fix the rear end of the glass tube and the copper wire. Finally, the prepared microelectrode was gently placed into a polymer membrane solution to adsorb ion-selective membranes, and then dried overnight in a constant temperature and humidity drying oven for later use. Figure 3 The image shows a photograph (left) and an optical microscope image (right) of the all-solid-state ion-selective microelectrode.

[0053] Example 2

[0054] Based on the all-solid-state carbon fiber ion-selective microelectrode obtained in the above embodiments, the transconducting layer can also be CoNi2S4. Firstly, hydroxyl nickel-cobalt carbonate nanowires are grown on the carbon fiber surface as a precursor. The specific preparation method is as follows: 237.7 mg of nickel chloride, 118.97 mg of cobalt chloride, and 210.21 mg of urea are weighed and dissolved in 100 mL of ultrapure water, and sonicated until completely dissolved to form a pink transparent solution. Then, the above solution is transferred to an Erlenmeyer flask, and a bundle of cleaned carbon fibers approximately 10 cm in length is placed inside. The reaction is carried out at 90 ℃ for 6 h.

[0055] Secondly, the preparation method for nickel-cobalt sulfide hydroxycarbonate nanowires is as follows: 1.20 g of sodium sulfide was weighed and dissolved in 50 mL of ultrapure water, and sonicated until completely dissolved to form a transparent solution. Then, the solution was transferred to an Erlenmeyer flask, and carbon fibers with the precursor grown were placed into the flask. The reaction was continued at 90 °C for 6 h.

[0056] Example 3

[0057] Based on the all-solid-state carbon fiber ion-selective microelectrode obtained in the above embodiments, the transconducting layer can also be a metal sulfide (nickel-based sulfide and cobalt-based sulfide). First, hydroxyl nickel-cobalt carbonate nanowires are grown on the carbon fiber surface as a precursor. The specific preparation method is as follows: 237.7 mg of nickel chloride or 237.97 mg of cobalt chloride and 210.21 mg of urea are weighed and dissolved in 100 mL of ultrapure water, and sonicated until completely dissolved to form a pink transparent solution. Then, the above solution is transferred to an Erlenmeyer flask, and a bundle of cleaned carbon fibers approximately 10 cm in length is placed inside. The reaction is carried out at 90 ℃ for 6 h.

[0058] Secondly, the preparation method for nickel-cobalt sulfide hydroxycarbonate nanowires is as follows: 1.20 g of sodium sulfide was weighed and dissolved in 50 mL of ultrapure water, and sonicated until completely dissolved to form a transparent solution. Then, the solution was transferred to an Erlenmeyer flask, and carbon fibers with the precursor grown were placed into the flask. The reaction was continued at 90 °C for 6 h.

[0059] Example 4

[0060] The carbon fiber microelectrode loaded with NiCo2S4 nanowires obtained in the above embodiments was tested for its excellent electrochemical performance using cyclic voltammetry (CV), and its performance was compared with that of a carbon fiber microelectrode without a transconductance layer. Specifically, the two microelectrodes were subjected to 10... -1 Cyclic voltammetry was performed in a MgCl electrolyte solution using a three-electrode system. The specific parameters were as follows: potential window of -0.8–0.65 V, scan rate of 100 mV / s. -1 .

[0061] Fabrication of carbon fiber microelectrodes without a transconducting layer:

[0062] The cleaned carbon fibers are fixed to copper wires with graphene conductive adhesive, and then placed into a drawn capillary glass tube. The rear end is fixed with epoxy resin but not sealed. Then, a carbon fiber microelectrode adsorbing polymer membrane ion-selective membrane is prepared. Finally, the rear end is sealed to obtain a carbon fiber ion-selective microelectrode without a transconducting layer.

[0063] Depend on Figure 4As can be seen from the cyclic voltammetry test curve of A, the carbon fiber microelectrode loaded with NiCo2S4 nanowires has a larger current response than the carbon fiber microelectrode, indicating that the transconducting layer has a large capacitance that can effectively realize ion-electron transduction.

[0064] Example 4

[0065] The carbon fiber microelectrode loaded with NiCo2S4 nanowires obtained in the above embodiments was further validated for its excellent electrochemical performance by electrochemical impedance spectroscopy (EIS), and its performance was compared with that of a carbon fiber microelectrode without a transconductance layer. Specifically, the two microelectrodes were subjected to electrochemical impedance spectroscopy (EIS) at 10... -1 Electrochemical impedance spectroscopy was performed in a KCl electrolyte solution using a three-electrode system. Specific parameters were as follows: frequency 0.01-10 Hz. 5 Hz, amplitude is 10 mV.

[0066] like Figure 4 As shown in B, the slope of the impedance diagram of the all-solid-state ion-selective microelectrode loaded with the NiCo2S4 transconductance layer is close to 90°, indicating that it has good diffusion resistance.

[0067] Example 5

[0068] Based on the all-solid-state ion-selective microelectrode based on NiCo2S4 nanowires obtained in the above embodiments, its short-term stability was characterized by chronopotential testing, and its performance was compared with that of an all-solid-state ion-selective carbon fiber electrode without a transconductance layer. Specifically, the all-solid-state ion-selective microelectrode based on NiCo2S4 nanowires in Example 1 and the comparison electrode (all-solid-state ion-selective microelectrode without a transconductance layer) set above were first compared using lead ions as a model. The activated microelectrode was then subjected to 10... -5 Chronopotential testing was performed in a lead nitrate solution (M) using a three-electrode system. Specific parameters are as follows: Applied current: + 10 pA, each time for 60 s.

[0069] Depend on Figure 5 It is evident that the introduction of the transconducting layer NiCo2S4 significantly reduces the voltage drop of the all-solid-state ion-selective microelectrode and substantially improves the electrode's stability.

[0070] Example 6

[0071] a. Preparation of lead ion-selective liquid membrane: 3.92 mg lead ion carrier, 1.2 mg NaTFPB, and 2.5 mg ETH500 were dissolved in 2 mL o- Stir in NPOE for about 6 hours, then place in a desiccator for later use.

[0072] b. Preparation of lead-ion selective liquid film microelectrode: First, quickly dip the drawn glass tube into a reagent bottle containing a lead-ion selective liquid film, ensuring the tip is fully filled. Then, fix the glass tube containing the lead-ion selective liquid film on a holder, adjusting the tip position to be close to the microscope's field of view, and locate the tip within the field of view. Next, take a glass microelectrode, fill a syringe with electrolyte, and inject electrolyte from the rear end, producing a liquid column of ~10 mm. Mount the glass microelectrode on the holder of the electrode pressure adjustment device and fix it to the microscope stage. Under the microscope, adjust the tip of the proportional microelectrode to be aligned horizontally with the tip of the capillary glass tube containing the lead-ion selective liquid film. By adjusting the three-way valve and the syringe, fill the capillary glass tube with the lead-ion selective liquid film to a distance of 50-60 micrometers from the tip, thus obtaining the lead-ion liquid film microelectrode.

[0073] Example 7

[0074] Based on the all-solid-state ion-selective microelectrode based on NiCo2S4 nanowires obtained in the above embodiments, the activated microelectrode is used to detect lead ions in the solution. Specifically, the all-solid-state ion-selective microelectrode based on NiCo2S4 nanowires in Example 1 is first used to detect lead ions in the solution.

[0075] Specifically, a 16-channel potentiometer was used to measure the potential response of the microelectrode. An Ag / AgCl micro-reference electrode with a 0.1 M lithium acetate bridge was used as the reference electrode, and a prepared all-solid-state ion-selective microelectrode was used as the indicator electrode. The open-circuit potential of lead ion solutions of different concentrations in a soil background was measured using the 16-channel potentiometer, and the corresponding potential-time curves and correction (logarithm of activity versus potential) curves were plotted. (See [link to relevant documentation]). Figure 6 .

[0076] Depend on Figure 6 As can be seen from curve a, the all-solid-state ion-selective microelectrode based on NiCo2S4 nanowires exhibits a fast potential response and good potential stability. This electrode works at a lead nitrate concentration of 10... -4 - 10 -7 mol L -1 The simulated soil solution exhibited a linear Nernst response with a Nernst slope of 31.1 ± 0.3 mV / dec, and the detection limit for lead ions in the solution was 3.2. × 10 -8 mol L -1 The performance of liquid-contact microelectrodes was also compared, and the results showed that the Nernst response concentration range of this electrode was 10. -4 - 10 -7 mol L -1 The detection limit of the electrode is 3.2.× 10 -7 mol L -1 .Depend on Figure 6 As can be seen from curve b, the liquid film microelectrode also exhibits a relatively fast potential response speed. This electrode works in a lead nitrate concentration of 10... -4 - 10 -6 mol L -1 The sample exhibited a Nernst response under simulated soil solution conditions, with a Nernst slope of 27.4 ± 0.8 mV / dec and a detection limit of 3.2 for lead ions in solution. × 10 -7 mol L -1 Therefore, the detection limit of the all-solid-state ion-selective microelectrode constructed in this work is an order of magnitude lower than that of the liquid-contact ion-selective microelectrode, making it more suitable for detecting ion flux at low concentrations of heavy metal ions in plant roots.

[0077] Example 8

[0078] The all-solid-state ion-selective microelectrode based on NiCo2S4 nanowires obtained in the above embodiments is applied to a non-destructive detection system for detecting ion flux on the surface of rice plant roots. Specifically:

[0079] The constructed all-solid-state ion-selective microelectrode was used as the indicator electrode, and Ag / AgCl as the reference electrode. Before testing, the electrode was first calibrated for Nernst slope. Then, a blank test was performed in the test solution (containing 1 µM Pb(NO3)2, 0.1 mM KCl, 0.1 mM CaCl2, 0.1 mM MgSO4, 1.0 mM NaCl, and 0.15 mM MES) to reconfirm the electrode's usability. Subsequently, rice plant roots were placed in the test solution and equilibrated for 10 minutes. Then, the root cap and the all-solid-state ion-selective electrode were located under a microscope, their positions were adjusted, and the ion flux of the plant roots was detected by software control.

[0080] Depend on Figure 7 visible, Figure 7 In the image, A represents a photograph of rice roots taken using a non-destructive testing platform. Figure 7 B in the image is an optical microscope photograph of the plant root system, which tested the absorption and release of heavy metal ions at a distance of 1 cm from the tip of the rice plant. Figure 7 C in the figure represents the result of the ion flux of plant roots tested using a non-destructive testing platform. The results show that rice exhibits absorption of heavy metal ions at a distance of 1 cm from the root tip, and the absorption of heavy metal ions is greatest at a distance of 600 micrometers from the root tip.

[0081] In summary, the potentiometric ion-selective microelectrode of this invention employs a mild and simple method to construct a nanowire-like transduction layer, simplifying the microelectrode fabrication process and enabling mass production of microelectrodes. Based on the above results, the following conclusions can be drawn:

[0082] (1) The method for batch preparation of all-solid-state ion-selective microelectrodes proposed in this invention firstly uses a chemical water bath method to prepare nanowire-shaped transduction layer materials. This method does not require harsh synthesis conditions and the preparation process is simple and easy to operate. The carbon fiber substrate loaded with the transduction layer is assembled and adsorbed polymer film, which simplifies the electrode preparation process, realizes the batch preparation of microelectrodes, and saves time and cost.

[0083] (2) The introduction of the resulting microelectrode transduction layer facilitates ion-electron transduction and improves the stability of the all-solid-state ion-selective microelectrode. Potential response test results show that the all-solid-state lead ion-selective microelectrode exhibits a fast potential response speed, good Nernst response, and a low detection limit (3.2). × 10 -8 mol L -1 It has a detection limit that is an order of magnitude lower than that of liquid contact ion-selective microelectrodes.

[0084] (3) The all-solid-state ion-selective microelectrode constructed in this invention can detect a variety of ions (such as sodium ions, potassium ions, calcium ions, and copper ions) simply by changing the ion carrier in the ion-selective polymer membrane, thus possessing a certain degree of versatility. In addition, the all-solid-state ion-selective microelectrode constructed in this invention can be used for real-time detection of ion flux on the surface of plant roots (such as rice roots, wheat roots, Arabidopsis roots, mulberry roots, cotton seedlings, pea roots, oat seedlings, or reed roots), thus possessing a certain degree of wide applicability.

Claims

1. A method for batch fabrication of potential-mode all-solid-state ion-selective microelectrodes, characterized by: The nanowire transduction layer is in-situ synthesized on the surface of a bundle of treated carbon fibers with a diameter of 7 microns by a chemical water bath method, and then the grown carbon fibers are assembled into an ion-selective microelectrode and a polymer ion-selective membrane is adsorbed, that is, a batch of solid-state ion-selective microelectrodes are constructed; The nanowire transduction layer is in-situ synthesized on the surface of a bundle of treated carbon fibers with a diameter of 7 microns by a chemical water bath method, and then the grown carbon fibers are assembled into an ion-selective microelectrode and a polymer ion-selective membrane is adsorbed, that is, a batch of solid-state ion-selective microelectrodes are constructed; The nanowire transduction layer is in-situ synthesized on the surface of a bundle of treated carbon fibers with a diameter of 7 microns by a chemical water bath method, and then the grown carbon fibers are assembled into an ion-selective microelectrode and a polymer ion-selective membrane is adsorbed, that is, a batch of solid-state ion-selective microelectrodes are constructed; The nanowire transduction layer is in-situ synthesized on the surface of a bundle of treated carbon fibers with a diameter of 7 microns by a chemical water bath method, and then the grown carbon fibers are assembled into an ion-selective microelectrode and a polymer ion-selective membrane is adsorbed, that is, a batch of solid-state ion-selective microelectrodes are constructed; 2. The method of claim 1, wherein the method is capable of batch fabrication of potential-mode, all-solid-state, ion-selective microelectrodes, characterized in that: The treated carbon fibers are cleaned by ultrasonic cleaning with a mixed solution of concentrated sulfuric acid and concentrated nitric acid to remove impurities, wherein the volume ratio of the concentrated sulfuric acid to the concentrated nitric acid is 3:1-1:1, and the cleaning time is 1-4 hours.

3. The method of mass production of potential-type all-solid-state ion-selective microelectrodes according to claim 1, characterized in that The polymer ion-selective membrane comprises an ion carrier, an ion exchanger, a polymer base material and a plasticizer, wherein the ion carrier is an ion carrier containing lead ions, copper ions, cadmium ions, sodium ions, calcium ions, potassium ions, chloride ions or ammonium ions.

4. A potentiometric all-solid-state ion-selective microelectrode, characterized by: The method of claim 1 is used to prepare carbon fibers with nanowire transduction layers on the surface in batches, and the carbon fibers are assembled in batches to obtain solid-state ion-selective microelectrodes.

5. Use of the potential-type all-solid-state ion-selective microelectrode according to claim 4, characterized in that: The potential-type solid-state ion-selective microelectrode is used for detecting ions in plant root systems.

6. Use of the potential-type all-solid-state ion-selective microelectrode according to claim 5, characterized in that: The plant root systems are rice roots, wheat roots, Arabidopsis roots, mulberry roots, cotton seedlings, pea roots, oat seedlings or reed roots.

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