CN115932010A - Method for batch preparation of potential type all-solid-state ion selective microelectrode and application - Google Patents
Method for batch preparation of potential type all-solid-state ion selective microelectrode and application Download PDFInfo
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Abstract
The invention relates to a microelectrode, in particular to a method for preparing a potential all-solid-state ion selective microelectrode in batches and application thereof. And (2) synthesizing a nanowire-shaped transduction layer on the surface of one bundle of treated carbon fibers in situ by adopting a chemical water bath method, assembling the grown carbon fibers into an ion selective microelectrode, and adsorbing an ion selective membrane, namely constructing the all-solid-state ion selective microelectrode in batches. The all-solid-state ion selective microelectrode constructed by the method has the advantages of simplicity and convenience in manufacturing, high sensitivity, low cost, easiness in miniaturization and the like, and can realize detection of ion flux of plant root systems. The detection of various ion fluxes of various plants can be realized by changing the types of the ionophores in the ion selective membrane and the root systems of the plants.
Description
Technical Field
The invention relates to a microelectrode, in particular to a method for preparing a potential all-solid-state ion selective microelectrode in batches and application thereof.
Background
Heavy metals are non-biodegradable pollutants, which pose certain threats to living beings and certain hazards to the environment. The migration and biocompatibility of heavy metal ions in the soil environment, a plant growth system, can easily enter a food chain to threaten human health. Therefore, the research on the migration mechanism of the heavy metal ions in the plant root system is very important for evaluating the transfer rule of the heavy metal ions in the food chain. At present, methods for measuring heavy metal ions mainly include atomic fluorescence spectrometry, atomic absorption spectrometry, inductively coupled plasma emission spectrometry, laser-induced breakdown spectrometry, X-ray fluorescence spectrometry and the like, and although the methods can provide accurate test data, instruments and devices required by the methods are large in size and high in operation cost, and the methods are not suitable for detecting heavy metal ions in micro-regions of plant root systems.
The potential microelectrode sensor is an ideal tool for detecting the change of ion flux in a tiny environment, is not influenced by the detection volume, and can realize the detection of the ion flux on the surface of a plant root system. Meanwhile, the potential microelectrode is combined with a non-damage detection platform to realize the visual detection of the ion flux of the plant root system. At present, microelectrodes are mainly classified into liquid film ion selective microelectrodes and all-solid-state ion selective microelectrodes. The all-solid-state ion selective microelectrode simplifies the use of the internal filling liquid of the liquid film ion selective microelectrode and solves the problem of leakage of the internal filling liquid. Therefore, all-solid-state ion-selective microelectrodes have gained widespread attention. At present, the structure of the all-solid-state ion selective microelectrode mainly comprises a capillary glass tube, a conducting wire, an electrode substrate, a transduction layer and a polymer ion selective membrane. The commonly used electrode substrate mainly comprises carbon fiber, gold, platinum and carbon materials, and the transduction layer mainly comprises conductive polymers, carbon materials, oxides, sulfides and other materials. The current preparation method of all-solid-state ion-selective microelectrodes comprises: (1) the preparation method of the carbon fiber microelectrode comprises the following steps: fixing a carbon fiber electrode on a lead, placing the lead into a glass tube, sealing the rear end with epoxy resin glue, sealing the tip of the front end with an alcohol lamp by using a flame melting method, controlling the length of the carbon fiber tip exposed out of the glass tube within 100 micrometers, and loading a transduction layer on the surface of the carbon fiber. When the conductive polymer is used as a transfer layer, the common method is an electrodeposition method, wherein the transfer layer is deposited on the surface of the carbon fiber for the microelectrodes one by one, and finally the polymer film is dipped on the surface of the carbon fiber. On one hand, the method needs to seal the front end of the glass tube by using an alcohol lamp under the condition of high temperature and control the length of the carbon fiber, and the operation is difficult to control; in addition, the transduction layer is deposited on the surface of the carbon fiber by using an electrodeposition method, and only one microelectrode can be deposited in the process at a time, so that the batch preparation of the electrode is difficult to realize; finally, the polymer film is loaded on the electrode in a dipping mode, and the polymer film is thin and is not beneficial to long-term use of the electrode. If a carbon material is used as a transduction layer, the carbon material can grow on the surface of carbon fiber by an electrodeposition method, high-temperature carbonization and a chemical vapor deposition method, batch preparation is difficult to realize by the electrodeposition method, and the transduction layer synthesized by the method mostly presents the morphology of nano particles or nano sheets, the contact area of the morphology and a polymer film is relatively small, active sites for generating capacitance are few, and the improvement of the stability of an electrode is limited. However, the high temperature carbonization and chemical vapor deposition methods are complicated to operate, require high temperature and high pressure, and are complicated and harsh in terms of the formation of the transduction layer. (2) the preparation method of the gold wire microelectrode comprises the following steps: adopting a gold wire as an electrode substrate, fusing the gold wire and a glass tube by using a flame fusion method, and then polishing the surface of the microelectrode to prepare a gold microelectrode (the diameter is 14 mu m); the conductive layer is modified by electrodepositing PEDOT-PSS, and then the surface of the microelectrode is dipped and coated by a polymer ion selective polymer film to prepare the all-solid-state ion selective microelectrode. The preparation method of the microelectrode also has the problems of difficult batch production and long service life. (3) preparation of carbon material microelectrode: the disordered mesoporous carbon/carbon nano tube/graphene is used as a filling material of the microelectrode, the use of a transfer layer is simplified by utilizing the characteristics of large specific surface area and double electric layer capacitance, and a micro-micro injection pump is adopted to pressurize and suck a film solution to the tip of the microelectrode, so that the all-solid-state ion selective microelectrode is constructed. The preparation of the electrode needs to fill the carbon material to the tip of the glass tube, and the membrane solution of the electrode needs to be adsorbed by a micro-injection pump, so that the operation is troublesome.
Therefore, a method for preparing a microelectrode which can be prepared in batch, is simple and quick is needed, and the microelectrode has the advantages of high response speed, low detection limit, good stability and long-term use, so as to meet the requirements of practical application.
Disclosure of Invention
The invention aims to provide a preparation method capable of preparing a potential all-solid-state ion selective microelectrode in batches and application of the potential all-solid-state ion selective microelectrode to real-time detection of plant root system ion flux.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for preparing potential type all-solid-state ion selective microelectrode in batch mode includes synthesizing a transfer layer on surface of a bundle of treated carbon fibers in situ by chemical water bath method, assembling ion selective microelectrode by deposited carbon fibers and adsorbing ion selective membrane, namely constructing solid-state ion selective microelectrode in batch mode.
The treated carbon fiber is a carbon fiber substrate, and is subjected to ultrasonic cleaning by using 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 1:3-1:1. the mass concentration of the concentrated sulfuric acid is 98%, and the mass concentration of the concentrated nitric acid is 68%.
The in-situ synthesis of the transition conducting layer on the surface of the carbon fiber as the metal sulfide is realized by immersing a bundle of treated carbon fibers in a precursor solution by a chemical water bath method, reacting metal ions with urea at 90-120 ℃ to grow nano linear basic carbonate on an intermediate on the surface of the carbon fiber in situ, and then carrying out ion exchange at 90-120 ℃ in a sodium sulfide aqueous solution to synthesize the nano linear transition conducting layer on the surface of the carbon fiber in situ.
The conducting layer is metal sulfide; wherein the metal sulfide is monometallic sulfide (nickel-based sulfide and cobalt-based sulfide) or bimetallic sulfide (NiCo) 2 S 4 Or CoNi 2 S 4 )。
Further using NiCo 2 S 4 Preparation of the transduction layer by taking the nanowire as an example:
the NiCo 2 S 4 The nano-wire grows on the surface of the carbon fiber, a chemical water bath method is adopted to dissolve a nickel source, a cobalt source and urea into a water solution to form a precursor solution, the growth of an intermediate on the surface of the carbon fiber is realized, and then a sulfur source is adopted to form NiCo through vulcanization at a specific temperature 2 S 4 The nanowires are grown on the surface of the carbon fibers. Wherein the molar concentration of the nickel source in the solvent is 0.025-0.5mol L -1 The molar concentration of the cobalt source in the solvent is 0.5-0.1mol L -1 The molar concentration of the sulfur source in the solvent is 0.1-0.2mol L -1 。
Said sulfidation forming NiCo 2 S 4 The specific temperature of the nanowire growth on the carbon fiber surface is 90-120 ℃.
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; the sulfur source is one of thioacetamide, thiourea or sodium sulfide;
and fixing one carbon fiber with the nanowire transfer layer grown on the surface at the tip end of the copper wire, placing the carbon fiber into a drawn glass tube to fix the carbon nanotube loaded with the copper wire, adsorbing the ion selective membrane by using the capillary display adsorption polymer, and finally sealing the rear end of the glass tube to obtain the all-solid-state ion selective microelectrode.
The polymer ion selective membrane comprises an ion carrier, an ion exchanger, a polymer substrate material and a plasticizer, wherein the ion carrier can be lead ions, copper ions, cadmium ions, sodium ions, calcium ions, potassium ions, chloride ions or ammonium ions.
The potential type all-solid-state ion selective microelectrode is prepared by the method, carbon fibers with a transfer layer on the surface can be prepared in batches, and the all-solid-state ion selective microelectrode is obtained by batch assembly.
The application of the all-solid-state ion selective microelectrode is to detect the change of ion flux on the surface of a plant root system.
The plant root system can be rice root, wheat root, arabidopsis root, mulberry root, cotton seedling, oat seedling, pea root or reed root.
The preparation principle and the implementation mode of the invention are as follows:
the invention adopts a chemical water bath method to grow ion-electron transfer layers on the surface of a carbon fiber electrode substrate in a large scale, after the growth is finished, the carbon fiber electrode substrate is adhered with a conductive copper wire by using a graphene conductive adhesive, then the carbon fiber electrode substrate is slowly placed into a drawn capillary glass tube (the size of the tip of the glass tube is less than 20 micrometers), the rear end of the drawn capillary glass tube is fixed by using an epoxy resin adhesive, then an ion selective polymer film is adsorbed, and finally the rear end of the capillary tube is further sealed by using the epoxy resin adhesive, so that the microelectrode is formed. The construction method of the microelectrode greatly simplifies the preparation steps of the electrode and can realize the batch preparation of the all-solid-state ion selective microelectrode.
Wherein, the nano-wire NiCo is used as the nano-wire 2 S 4 The potential type ion selective microelectrode is used as an ion-electron transfer layer to grow on the surface of a carbon fiber electrode substrate in situ to prepare the microelectrode, so that the stability of the microelectrode is improved, and in addition, the constructed potential type ion selective microelectrode can be used for real-time detection of the ion flux of a plant root system.
The invention has the advantages that:
1. the preparation method of the all-solid-state ion selective microelectrode simplifies the preparation process of the electrode and can realize mass preparation.
2. The invention has the advantages of high response speed, high sensitivity and good stability through the potential microelectrode sensor, and can realize the sensitive detection of the ion flux of the plant root system.
3. The invention adopts redox NiCo 2 S 4 The nano-wire is grown on the surface of the carbon fiber in situ to serve as an ion-electron transfer layer based on NiCo 2 S 4 The nanowire structure increases the contact area between the transduction layer and the ion selective membrane, can provide more redox sites, generates larger capacitance, is beneficial to realizing ion-electron transduction, and improves the stability of the microelectrode. In addition, the film thickness of the ion selective membrane of the ion selective microelectrode prepared by the invention is 50-60 micrometers, so that the service life of the ion selective microelectrode can be prolonged.
4. The invention can realize the ion flux detection of the surfaces of various plant roots.
Drawings
FIG. 1 is a schematic diagram of a process for manufacturing an potentiometric microelectrode sensor according to an embodiment of the present invention.
FIG. 2 is a scanning electron micrograph (FIG. A) of a carbon fiber microelectrode, and a scanning electron micrograph (FIG. B) of NiCo grown on the surface of a carbon fiber as an intermediate, according to an embodiment of the present invention 2 S 4 Scanning electron micrograph of in situ grown carbon fiber surface (fig. C).
FIG. 3 is a photograph of a potential microelectrode sensor according to an embodiment of the present invention taken in real life (left) and an optical microscope (right).
FIG. 4 shows a carbon fiber and NiCo-based carbon fiber according to an embodiment of the present invention 2 S 4 The cyclic voltammogram of carbon fiber (panel a) and the electrochemical impedance test panel (panel B).
FIG. 5 is a chronopotentiometric curve (dotted line) of a carbon fiber microelectrode and a microelectrode based on NiCo according to an embodiment of the present invention 2 S 4 Chronopotentiometric curve (solid line) of the carbon fiber microelectrode of (1).
FIG. 6 shows an example of an all-solid-state ion-selective microelectrode and a liquid film microelectrode with lead nitrate of 10 -4 -10 -9 M, a real-time potential change response graph (graph A) and a calibration graph (graph B) measured in a soil background solution, wherein in the graphs A and B, a is an all-solid-state lead ion selective electrode, and B is a lead ion liquid film microelectrode.
FIG. 7 is a photograph of a non-invasive detection system (FIG. A), an optical micrograph of an all-solid-state ion-selective microelectrode detected plant root system (FIG. B), and a comparison chart of an all-solid-state ion-selective electrode and a liquid membrane microelectrode detected ion flux of the plant root system (FIG. C), which are provided by the embodiments of the present invention.
Detailed Description
The following examples are presented to further illustrate embodiments of the present invention, and it should be understood that the embodiments described herein are for purposes of illustration and explanation only and are not intended to limit the invention.
The invention adopts a chemical water bath method to grow ion-electron transfer layers on the surface of the carbon fiber electrode substrate in a large scale, and the method does not need high temperature and high pressure, has mild preparation conditions and is easy to operate. And then adhering the grown carbon fiber electrode substrate with a conductive copper wire by using a graphene conductive adhesive, slowly putting the carbon fiber electrode substrate into a drawn capillary glass tube, fixing the rear end of the carbon fiber electrode substrate by using an epoxy resin adhesive, and adsorbing an ion selective polymer film to form the microelectrode, wherein the distance between the tip of the carbon fiber and the tip of the capillary glass tube is not more than 20 micrometers. The method is simple and easy to operate, can realize the mass preparation of the microelectrode, enables the thickness of the membrane to be about 50-60 microns by adsorbing the ion selective membrane, and can prolong the service life of the electrode. Meanwhile, the microelectrode has the advantages of high mass transfer rate, high current density, high response speed and the like, and can be used for detecting the ion flux of the plant root system microcell.
The reagents used in the following examples were purchased from pilot scale, wherein the nickel salt, cobalt salt, urea and sulfur source were analytically pure.
Example 1
The construction of the all-solid-state ion selective carbon fiber microelectrode is based on the in-situ generation of nanowire NiCo on the surface of carbon fiber by a chemical water bath method 2 S 4 As an ion-electron transfer layer, the carbon fiber microelectrode is prepared and adsorbs a polymer film ion selective film, thus realizing the mass preparation.
As can be seen from fig. 1, the schematic flow chart of the preparation process of the all-solid-state ion selective microelectrode firstly adopts a simple and mild water bath method to synthesize a nanowire-shaped transduction layer on the surface of carbon fiber, and then the nanowire-shaped transduction layer is assembled by an electrode to adsorb an ion selective membrane, so that the preparation process of the microelectrode is optimized, the preparation steps of the electrode are simplified, and the batch preparation of the microelectrode is realized.
The specific preparation steps of the all-solid-state ion selective microelectrode are as follows, as shown in figure 1:
a. treatment of the substrate: based on carbon fibers with the diameter of 7 micrometers as a substrate, before conducting the growth of a transduction layer, the carbon fiber substrate is prepared by mixing a solution of concentrated sulfuric acid with the mass concentration of 98% and concentrated nitric acid with the mass concentration of 68%, wherein the volume ratio is 3: and 1, performing ultrasonic treatment for 2h, cleaning the surface to remove impurities, and forming a rough structure on the surface of the carbon fiber to be beneficial to the growth of a transfer layer.
Fig. 2A shows a scanning electron microscope image of the surface of the carbon fiber after cleaning, specifically, the surface of the carbon fiber after cleaning has a stripe pattern, which is beneficial to the growth of the transfer layer.
b. Loaded NiCo 2 S 4 Preparation of carbon fiber of nanowire:
firstly, a hydroxyl nickel cobalt carbonate nanowire grown on the surface of a carbon fiber as a precursor is specifically prepared by the following steps: 118.85mg of nickel chloride, 237.931mg of cobalt chloride and 210.21mg of urea were weighed out and dissolved in 100mL of ultrapure water, respectively, and the solution was sonicated until completely dissolved to form a pink transparent solution. Then the solution was transferred to an erlenmeyer flask, followed by placing a bundle of cleaned carbon fibers of about 10cm in length and reacting at 90 ℃ for 6h (see fig. 2B);
secondly, the hydroxyl nickel carbonate sulfide cobalt nanowire is prepared by the following specific steps: 1.20g of sodium sulfide was weighed out and dissolved in 50mL of ultrapure water, and the solution was sonicated until completely dissolved to form a clear solution. The solution was then transferred to an erlenmeyer flask, and the carbon fiber with the precursor grown therein was placed in the erlenmeyer flask and the reaction was continued for 6h at 90 ℃ (see fig. 2C).
As can be seen from fig. 2B, a scanning electron microscope picture of the hydroxy nickel carbonate cobalt nanowire precursor is grown on the surface of the carbon fiber, specifically, the precursor nanowire is uniformly grown on the surface of the carbon fiber.
As can be seen in FIG. 2C, niCo is grown on the surface of the carbon fiber 2 S 4 Scanning electron microscope picture of nanowire, specifically, niCo is uniformly grown on the surface of carbon fiber 2 S 4 A nanowire.
b. Preparation of ion-selective polymer membranes:
1.57wt% of lead ionophore, 0.48wt% of sodium tetrakis (3, 5-bis (trifluoromethyl) borate (NaTFPB), 33.05wt% of polyvinyl chloride (PVC), 66.9wt% of o-nitrophenyl octyl ether (o-NPOE), 1.00% of tetrakis (4-chlorophenyl) borate were weighed out and dissolved in 1.5mL of Tetrahydrofuran (THF), stirred for 4-5h, and then transferred to a desiccator for storage.
c. Preparing an all-solid-state ion selective microelectrode:
will grow with NiCo 2 S 4 The carbon fiber of the nanowire is fixed at the tip of the copper wire by using the graphene conductive adhesive, the graphene conductive adhesive is put into the drawn glass tube from the rear end of the drawn glass tube after being dried, so that the distance between the tip of the carbon fiber and the tip of the glass tube is not more than 20 micrometers, and then the carbon fiber is fixed by using the rear end of the epoxy resin adhesive glass tube and the copper wire. And finally, lightly putting the prepared microelectrode into a polymer film solution to adsorb an ion selective film, and then putting the microelectrode into a constant-temperature constant-humidity drying box to dry overnight for later use. FIG. 3 shows a photograph of a real object (left) and a photograph of an optical microscope (right) of the all-solid ion-selective microelectrode.
Example 2
The all-solid-state carbon fiber ion selective microelectrode obtained on the basis of the embodiment can also be provided with a transduction layer of CoNi 2 S 4 . Firstly, hydroxyl nickel carbonate cobalt nanowires are grown on the surface of carbon fibers as a precursor, and the specific preparation method comprises the following steps: 237.7mg of nickel chloride, 118.97mg of cobalt chloride and 210.21mg of urea were weighed out and dissolved in 100mL of ultrapure water, respectively, and the solution was sonicated until completely dissolved to form a pink transparent solution. Then transferring the solution into a conical flask, then putting a bundle of cleaned carbon fibers with the length of about 10cm into the conical flask, and reacting for 6 hours at 90 ℃;
secondly, the hydroxyl nickel carbonate sulfide cobalt nanowire is prepared by the following specific steps: 1.20g of sodium sulfide was weighed out and dissolved in 50mL of ultrapure water, and the solution was sonicated until completely dissolved to form a clear solution. And then transferring the solution into an erlenmeyer flask, putting the carbon fiber with the precursor into the erlenmeyer flask, and continuing to react for 6 hours at 90 ℃.
Example 3
Based on the all-solid-state carbon fiber ion-selective microelectrode obtained in the above embodiment, the transduction layer may also be a metal sulfide (nickel-based sulfide and cobalt-based sulfide). Firstly, hydroxyl nickel carbonate cobalt nanowires are grown on the surface of carbon fibers as a precursor, and the specific preparation method comprises the following steps: 237.7mg of nickel chloride or 237.97mg of cobalt chloride and 210.21mg of urea were weighed out and dissolved in 100mL of ultrapure water, respectively, and the solution was sonicated until completely dissolved to form a pink transparent solution. Then transferring the solution into a conical flask, then putting a bundle of cleaned carbon fibers with the length of about 10cm into the conical flask, and reacting for 6 hours at 90 ℃;
secondly, the hydroxyl nickel carbonate sulfide cobalt nanowire is prepared by the following specific steps: 1.20g of sodium sulfide was weighed out and dissolved in 50mL of ultrapure water, and the solution was sonicated until completely dissolved to form a clear solution. And then transferring the solution into a conical flask, putting the carbon fiber with the precursor in the conical flask, and continuously reacting for 6 hours at 90 ℃.
Example 4
Loaded NiCo obtained on the basis of the above examples 2 S 4 The carbon fiber microelectrode of the nanowire is verified to have good electrochemical performance through an electrical Cyclic Voltammetry (CV), and is compared with a carbon fiber microelectrode without a transfer layer in performance, and the method specifically comprises the following steps: two kinds of microelectrodes are arranged at 10 -1 And (3) in the M KCl electrolyte solution, adopting a three-electrode system to carry out cyclic voltammetry test. The parameters are as follows: the potential window is-0.8-0.65V, and the scanning rate is 100mV s -1 。
Preparing a carbon fiber microelectrode without a transduction layer:
fixing the cleaned carbon fiber on a copper wire by using a graphene conductive adhesive, then putting the copper wire into a drawn capillary glass tube, fixing the rear end of the drawn capillary glass tube by using an epoxy resin adhesive without sealing, then preparing a carbon fiber microelectrode adsorption polymer membrane ion selective membrane, and finally sealing the rear end to obtain the carbon fiber ion selective microelectrode without a transfer layer.
As can be seen from the cyclic voltammetry test curve of FIG. 4A, niCo is loaded 2 S 4 The carbon fiber microelectrode of the nanowire has larger current response than the carbon fiber microelectrode, which shows that the transduction layer has large capacitance and can effectively realize ion-electron transduction.
Example 4
Loaded NiCo obtained on the basis of the above examples 2 S 4 The carbon fiber microelectrode of the nanowire is further verified to have good electrochemical performance through an Electrochemical Impedance Spectroscopy (EIS), and is compared with the carbon fiber microelectrode without a transfer layer in performance, and the method specifically comprises the following steps: two kinds of microelectrodes are arranged at 10 -1 And in the M KCl electrolyte solution, a three-electrode system is adopted to test the electrochemical impedance. The parameters are as follows: frequency of 0.01-10 5 Hz, amplitude of 10mV.
As shown in FIG. 4B, loaded with NiCo 2 S 4 The slope of the all-solid-state ion-selective microfeature electrode impedance plot of the transduction layer is close to 90 deg., indicating that it has good diffusion resistance.
Example 5
NiCo-based products obtained on the basis of the above examples 2 S 4 The all-solid-state ion selective microelectrode electrode of the nanowire has short-term stability represented by a chronopotentiometry and is compared with an all-solid-state ion selective carbon fiber electrode without a transfer layer in performance, and the method specifically comprises the following steps: first of all, the catalyst of example 1 is based on NiCo 2 S 4 The all-solid-state ion selective microelectrode of the nanowire and the comparative electrode (the all-solid-state ion selective microelectrode without a transfer layer) arranged above are subjected to lead ion model activation, and the activated microelectrode is arranged at 10 -5 In M lead nitrate solution, a three-electrode system is adopted for timing potential test. The parameters are as follows: applying current: . + -. 10pA for 60s each.
As can be seen from FIG. 5, the transduction layer NiCo 2 S 4 The voltage drop of the all-solid-state ion selective microelectrode is obviously reduced, and the stability of the electrode is obviously improved.
Example 6
a. Preparation of lead ion selective liquid membrane: 3.92mg of lead ion carrier, 1.2mg of NaTFPB and 2.5 mg of ETH500 are dissolved in 2mL of o-NPOE, stirred for about 6 hours and put into a dryer for standby.
b. Preparing a lead ion selective liquid film microelectrode: firstly, quickly dipping a drawn brush pen glass tube in a reagent bottle filled with a lead ion selective liquid film to fill the tip. Then, the glass tube containing the lead ion-selective liquid film was fixed to a holder, and the tip was positioned so as to be close to the field of view of the microscope and the tip portion thereof was found in the field of view. Subsequently, a glass microelectrode was taken and the electrolyte was injected from the back end using an electrolyte fill syringe to create a-10 mm liquid column. The glass microelectrode is mounted on the holder of the electrode pressure regulating device and fixed on the microscope stage. The tip of the proportional microelectrode is adjusted under a microscope to be opposite to the tip of the capillary glass tube filled with the lead ion selective liquid film on the same horizontal plane. And filling the lead ion selective liquid film to the position of the distance between the tip of the capillary glass tube and the tip by 50-60 microns through regulating the three-way valve and the injector to obtain the lead ion liquid film microelectrode.
Example 7
NiCo-based products obtained on the basis of the above examples 2 S 4 The all-solid-state ion selective microelectrode electrode of the nanowire detects the lead ions in the solution by the activated microelectrode, and specifically comprises the following steps: first of all, the catalyst of example 1 is based on NiCo 2 S 4 The all-solid-state ion selective microelectrode electrode of the nanowire is used for detecting lead ions in a solution.
The method comprises the following specific steps: a sixteen-channel potentiometer is adopted to perform potential response measurement on the microelectrode, an Ag/AgCl micro reference electrode connected with a 0.1M lithium acetate bridge is used as a reference electrode, and the prepared all-solid-state ion selective microelectrode is used as an indicating electrode. Open-circuit potential of lead ion solutions of different concentrations in a soil background were tested using a sixteen-channel potentiometer, and corresponding potential-time curves and calibration (log of activity versus potential) curves were plotted, see fig. 6.
As can be seen from the a-curve in FIG. 6, based on NiCo 2 S 4 The all-solid-state ion selective microelectrode of the nanowire has higher potential response speed and good potential stability, and the electrode has the lead nitrate concentration of 10 -4 -10 -7 mol L -1 The simulated soil solution has linear performance of the Stokes response, the Nernst slope is 31.1 +/-0.3 mV/dec, and the detection limit of lead ions in the solution is 3.2 multiplied by 10 -8 mol L -1 . Meanwhile, the performance of the liquid contact microelectrode is compared, and the result shows that the Nernst response concentration range of the electrode is 10 -4 -10 -7 mol L -1 The detection limit of the electrode is 3.2 multiplied by 10 -7 mol L -1 . As can be seen from the curve b in FIG. 6, the liquid film microelectrode also exhibited a faster potential response speed at a lead nitrate-containing concentration of 10 -4 - 10 -6 mol L -1 In the simulated soil solution background, the model shows the Nernst response and the Nernst slopeThe rate is 27.4 +/-0.8 mV/dec, and the detection limit of lead ions in the solution is 3.2 multiplied by 10 -7 mol L -1 . Therefore, the detection limit of the all-solid-state ion selective microelectrode constructed by the work is lower than that of the liquid contact type ion selective microelectrode by one order of magnitude, and the all-solid-state ion selective microelectrode is more suitable for detecting the ion flux of the heavy metal ions in the plant root system under low concentration.
Example 8
NiCo-based products obtained on the basis of the above examples 2 S 4 The all-solid-state ion selective microelectrode of the nanowire is applied to a non-damage detection system and used for detecting the ion flux on the surface of the root system of the rice plant. The method comprises the following specific steps:
the constructed all-solid-state ion selective microelectrode is used as an indicating electrode and Ag/AgCl is used as a reference electrode. The electrodes were first subjected to Nernst slope correction prior to testing and then in the test solution (containing 1. Mu.M Pb (NO) 3 ) 2 ,0.1mM KCl,0.1mM CaCl 2 ,0.1mM MgSO 4 1.0mM NaCl and 0.15mM MES) to determine the availability of the electrode again, then putting the rice plant root into the solution to be tested to balance for 10 minutes, then finding the root cap of the root and the all-solid-state ion selective electrode under a microscope, adjusting the position, and detecting the ion flux of the plant root system through software control.
As can be seen from fig. 7, fig. 7A is a photograph of a non-damaged detection platform for detecting a rice root system, and fig. 7B is a photograph of an optical microscope for detecting a plant root system, in which the absorption and release of heavy metal ions at a distance of 1cm from a rice tip are tested. Fig. 7C is a result of the ion flux of the plant root system measured by using the non-damage test platform, and the result shows that the rice shows the condition of absorbing heavy metal ions at a distance of 1cm from the tip of the rice, and the absorption capacity of the rice to the heavy metal ions is the maximum at a distance of 600 microns from the tip of the rice.
In conclusion, the potentiometric ion-selective microelectrode adopts a mild and simple method to construct the nanowire transduction layer, simplifies the preparation process of the microelectrode, realizes the batch preparation of the microelectrode, and can draw the following conclusion according to the results:
(1) The method for preparing the all-solid-state ion selective microelectrode in batches firstly adopts a chemical water bath method to prepare the nanowire-shaped transduction layer material, does not need harsh synthesis conditions, has simple preparation process and easy operation, simplifies the electrode preparation process by assembling and adsorbing a polymer film on the carbon fiber substrate loaded with the transduction layer, realizes the batch preparation of the microelectrode, and saves time and cost.
(2) The introduction of the microelectrode transduction layer is beneficial to the transduction of ions and electrons, and the stability of the all-solid-state ion selective microelectrode is improved. The potential response test result shows that: the all-solid-state lead ion selective microelectrode has the advantages of high potential response speed, good Nernst response and low detection limit (3.2 multiplied by 10) -8 mol L -1 ) And the detection limit is lower by one order of magnitude than that of the liquid contact type ion selective microelectrode.
(3) The all-solid-state ion selective microelectrode constructed by the invention can realize the detection of various ions (sodium ions, potassium ions, calcium ions, copper ions and the like) only by changing the ionophore in the ion selective polymer film, and has certain universality. In addition, the all-solid-state ion selective microelectrode constructed by the invention can be used for real-time detection of ion flux on the surface of a plant root system (rice root, wheat root, arabidopsis thaliana root, mulberry root, cotton seedling, pea root, oat seedling or reed root and the like), and has certain wide applicability.
Claims (9)
1. A method for preparing potential type all-solid-state ion selective microelectrode in batch is characterized in that: and (2) synthesizing a nanowire-shaped transduction layer on the surface of one bundle of treated carbon fibers in situ by adopting a chemical water bath method, assembling the grown carbon fibers into an ion selective microelectrode, and adsorbing an ion selective membrane, namely constructing the all-solid-state ion selective microelectrode in batches.
2. The method for mass-producing a potentiometric all-solid-state ion-selective microelectrode according to claim 1, wherein: ultrasonically cleaning the treated carbon fiber serving as a substrate by using 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 3:1-1:1, the time is 1-4h.
3. The method for mass-producing a potentiometric all-solid-state ion-selective microelectrode according to claim 1, wherein: the nano-wire-shaped transduction layer is prepared by immersing a bundle of treated carbon fibers in a precursor solution containing active ingredients by a chemical water bath method, reacting metal ions with urea at 90-120 ℃ to grow nano-wire-shaped basic carbonate on the surface of the carbon fibers in situ to serve as an intermediate, and then carrying out ion exchange at 90-120 ℃ in an aqueous solution of sodium sulfide to synthesize the metal sulfide nano-wire-shaped transduction layer on the surface of the carbon fibers in situ.
4. The method for mass-producing a potentiometric all-solid-state ion-selective microelectrode according to claim 1, wherein: the conducting layer is a metal sulfide; wherein the single metal sulfide is single metal sulfide (nickel-based sulfide and cobalt-based sulfide) or bimetal sulfide (NiCo) 2 S 4 Or CoNi 2 S 4 )。
5. The method for mass-producing a potentiometric all-solid-state ion-selective microelectrode according to any of claims 1 to 4, characterized in that: and fixing one carbon fiber of the nanowire transfer layer growing on the surface at one end of the copper wire, then placing the copper wire into a drawn glass tube to fix the copper wire loaded with the carbon fiber, and then adsorbing the polymer ion selective membrane by utilizing the capillary phenomenon to obtain the all-solid-state ion selective microelectrode.
6. The method of claim 5, wherein the polymer-adsorbed ion-selective membrane comprises an ionophore, an ion exchanger, a polymer base material, and a plasticizer, wherein the ionophore includes lead ions, copper ions, cadmium ions, sodium ions, calcium ions, potassium ions, chloride ions, or ammonium ions.
7. A potential type all-solid-state ion selective microelectrode is characterized in that: the method of claim 1 is used for preparing carbon fiber with transfer layer on the surface, and the carbon fiber is assembled in batch to obtain the all-solid-state ion selective microelectrode.
8. Use of an electrode according to claim 7, wherein: the potential type all-solid-state ion selective microelectrode is applied to flux detection of ions in a plant root system.
9. Use of an electrode according to claim 8, characterized in that: the plant root system can be rice root, wheat root, arabidopsis root, mulberry root, cotton seedling, pea root, oat seedling or reed root, etc.
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