阅读说明：本技术 一种碳纳米管/氧化亚铜/金纳米颗粒/碳纤维丝电极、电化学传感器及制备与应用 (Carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode, electrochemical sensor, preparation and application ) 是由 龙拥兵 巫彬芳 徐海涛 栗云鹏 施玉峰 周华 汤新宇 姚志杰 邓海东 兰玉彬 于 2021-08-04 设计创作，主要内容包括：本发明属于电化学传感器技术领域,具体涉及一种碳纳米管/氧化亚铜/金纳米颗粒/碳纤维丝电极、电化学传感器及制备与应用。本发明采用导电银胶将碳纤维单丝和铜丝粘结,然后用毛细玻璃管封装,得到碳纤维丝电极；将上述电极、对电极和参比电极插入氯金酸溶液中进行电沉积,得到金纳米颗粒/碳纤维丝电极；将上述电极、对电极和参比电极插入到硝酸铜溶液中进行沉积,得到氧化铜/金纳米颗粒/碳纤维丝电极；将上述电极、对电极和参比电极插入到碳纳米管悬浮液中进行电沉积,得到碳纳米管/氧化亚铜/金纳米颗粒/碳纤维丝电极,该电极应用于制备电化学传感器,具有低检测限、高测试灵敏度、稳定性好、抗干扰能力强等特点。(The invention belongs to the technical field of electrochemical sensors, and particularly relates to a carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode, an electrochemical sensor, and preparation and application thereof. According to the invention, a carbon fiber monofilament and a copper wire are bonded by conductive silver adhesive, and then packaged by a capillary glass tube to obtain a carbon fiber wire electrode; inserting the electrode, the counter electrode and the reference electrode into a chloroauric acid solution for electrodeposition to obtain a gold nanoparticle/carbon fiber wire electrode; inserting the electrode, the counter electrode and the reference electrode into a copper nitrate solution for deposition to obtain a copper oxide/gold nanoparticle/carbon fiber wire electrode; the electrode, the counter electrode and the reference electrode are inserted into the carbon nano tube suspension for electrodeposition to obtain the carbon nano tube/cuprous oxide/gold nano particle/carbon fiber wire electrode, and the electrode is applied to the preparation of an electrochemical sensor and has the characteristics of low detection limit, high test sensitivity, good stability, strong anti-interference capability and the like.)

1. A carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode is characterized by being prepared by the following method:

bonding the carbon fiber single wire and the copper wire by adopting conductive silver adhesive, and then packaging by using a capillary glass tube to obtain a carbon fiber wire electrode; inserting the carbon fiber wire electrode, the counter electrode and the reference electrode into a chloroauric acid solution, performing primary electrodeposition by adopting a current time method, and cleaning and drying to obtain a gold nanoparticle/carbon fiber wire electrode; inserting the gold nanoparticle/carbon fiber wire electrode, the counter electrode and the reference electrode into a copper nitrate solution, performing secondary electrodeposition by adopting a current time method, and cleaning and drying to obtain a copper oxide/gold nanoparticle/carbon fiber wire electrode; and inserting the copper oxide/gold nanoparticle/carbon fiber wire electrode, the counter electrode and the reference electrode into the carbon nanotube suspension, performing third electrodeposition by adopting a current time method, and cleaning and drying to obtain the carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode.

2. The carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode of claim 1, wherein:

the concentration of the chloroauric acid solution is 1-5% (w/w).

3. The carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode of claim 1, wherein:

the initial potential of the first electrodeposition is-0.2 to-1.0V, and the deposition time is 10 to 100 s.

4. The carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode of claim 1, wherein:

the solvent of the copper nitrate solution is N, N-dimethylformamide, and the solute comprises copper nitrate, 1, 3, 5-benzenetricarboxylic acid and triethylamine hydrochloride, wherein the mass percentages of the copper nitrate, the 1, 3, 5-benzenetricarboxylic acid and the triethylamine hydrochloride are respectively 0.1-1% (w/w), 0.1-1% (w/w) and 0.05-5% (w/w).

5. The carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode of claim 1, wherein:

the initial potential of the second electrodeposition is-1.0 to-1.5V, and the deposition time is 50 to 200 s.

6. The carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode of claim 1, wherein:

in the carbon nano tube suspension, the concentration of the carbon nano tube is 0.5-2 mg/mL, and the length of the carbon nano tube is 10-20 nm.

7. The carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode of claim 1, wherein:

the initial potential of the third electrodeposition is-1.5 to-2.0V, and the deposition time is 100 to 1000 s.

8. The method for preparing the carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode according to any one of claims 1 to 7, comprising the steps of:

(1) ultrasonically cleaning carbon fiber yarns by adopting ethanol and water in sequence, and separating a plurality of bundles of carbon fiber yarns to obtain a single carbon fiber yarn; bonding single carbon fiber wires and copper wires by using conductive silver adhesive, and penetrating a bonding body of the carbon fiber wires and the copper wires into a capillary glass tube after the conductive silver adhesive is completely dried, wherein one end of the capillary glass tube is exposed out of the carbon fiber wires, and the other end of the capillary glass tube is exposed out of the copper wires; sealing and cleaning two open ends of the capillary glass tube to obtain a carbon fiber wire electrode;

(2) forming a three-electrode system by taking a carbon fiber wire electrode as a working electrode, a platinum wire electrode as a counter electrode and an Ag/AgCl electrode as a reference electrode, inserting the three-electrode system into a chloroauric acid solution, and performing primary electrodeposition by adopting a current time method under the condition of keeping the solution stirred; taking out the electrode after electrodeposition, cleaning and drying to obtain a gold nanoparticle/carbon fiber wire electrode;

(3) taking the gold nanoparticle/carbon fiber wire electrode prepared in the step (2) as a working electrode, a platinum wire electrode as a counter electrode and an Ag/AgCl electrode as a reference electrode to form a three-electrode system, inserting the three-electrode system into a copper nitrate solution, and carrying out secondary electrodeposition by adopting a current time method under the condition of keeping the solution stirred; taking out the electrode after electrodeposition, cleaning and drying to obtain a copper oxide/gold nanoparticle/carbon fiber wire electrode;

(4) taking the copper oxide/nano-particle/carbon fiber wire electrode prepared in the step (3) as a working electrode, a platinum wire electrode as a counter electrode and an Ag/AgCl electrode as a reference electrode to form a three-electrode system, inserting the three-electrode system into the carbon nano tube suspension, and performing third electrodeposition by adopting a current time method under the condition of keeping the solution stirred; and taking out the electrode after electrodeposition, and cleaning and drying to obtain the carbon nano tube/cuprous oxide/gold nano particles/carbon fiber wire electrode.

9. The application of the carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode as claimed in any one of claims 1 to 7 in preparation of indole-3-acetic acid electrochemical sensor.

10. An electrochemical sensor, characterized in that the carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode of any one of claims 1 to 7 is used as a working electrode.

Technical Field

The invention belongs to the technical field of electrochemical sensors, and particularly relates to a carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode, an electrochemical sensor, and preparation and application thereof.

Background

During the growth and development of plants, the content of phytohormones is small, but the phytohormones play a significant role in regulating the growth and apoptosis of plants. Indole-3-acetic acid is an endogenous auxin synthesized by plants, and participates in the regulation and control of various physiological processes, including the growth, flowering, withering and the like of the plants. The concentration information of the indole-3-acetic acid is collected, and the method has important significance for guiding the yield improvement and quality control of crops. Therefore, in agricultural production application, a new indole-3-acetic acid sensor needs to be designed to realize real-time detection of indole-3-acetic acid in plants.

At present, the conventional detection method for indole-3-acetic acid mainly comprises the following steps: mass spectrometry, liquid chromatography, fluorescence spectrometry, capillary electrophoresis, radioimmunoassay, and the like. However, most of the above detection methods adopt an ex vivo sampling method, and indole-3-acetic acid in a plant body cannot be detected in real time. In addition, the in vitro sampling method for detecting indole-3-acetic acid mostly adopts large-scale expensive instruments, corresponding pretreatment needs to be carried out before the instrument is installed, the pretreatment process is complex and time-consuming, and the change condition of the information of the object to be detected cannot be quickly obtained. Furthermore, the complex pretreatment procedure also requires that the test operator should have skilled laboratory skills.

Nowadays, more and more research efforts are based on developing methods for the immediate and rapid detection of plant hormone information in order to obtain in real time the hormonal response of plants under the influence of external environmental conditions. The electrochemical sensor method has the advantages of short response time, high accuracy, low pretreatment requirement, simple and convenient operation, low cost and the like, and can be used as one of the preferred methods for rapidly detecting the indole-3-acetic acid.

Disclosure of Invention

In order to solve the defects and shortcomings of the prior art, the invention mainly aims to provide a carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode.

The invention also aims to provide the preparation method of the carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode, which has the advantages of simple process, strong controllability and low manufacturing cost.

The invention further aims to provide application of the carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode.

The fourth purpose of the invention is to provide an electrochemical sensor, which adopts the carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode as a working electrode, has the characteristics of low detection limit, high test sensitivity, good stability and strong anti-interference capability, and is suitable for wide application and popularization of the sensor.

The fifth purpose of the invention is to provide the application of the electrochemical sensor in detecting indole-3-acetic acid in plants.

The purpose of the invention is realized by the following technical scheme:

a carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode is prepared by the following method:

bonding the carbon fiber single wire and the copper wire by adopting conductive silver adhesive, and then packaging by using a capillary glass tube to obtain a carbon fiber wire electrode; inserting the carbon fiber wire electrode, the counter electrode and the reference electrode into a chloroauric acid solution, performing primary electrodeposition by adopting a current time method, and cleaning and drying to obtain a gold nanoparticle/carbon fiber wire electrode; inserting the gold nanoparticle/carbon fiber wire electrode, the counter electrode and the reference electrode into a copper nitrate solution, performing secondary electrodeposition by adopting a current time method, and cleaning and drying to obtain a copper oxide/gold nanoparticle/carbon fiber wire electrode; inserting the copper oxide/gold nanoparticle/carbon fiber wire electrode, the counter electrode and the reference electrode into the carbon nanotube suspension, performing third electrodeposition by adopting a current time method, and cleaning and drying to obtain a carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode;

the counter electrode is preferably a platinum wire;

the reference electrode is preferably an Ag/AgCl electrode;

the concentration of the chloroauric acid solution is preferably 1-5% (w/w);

the initial potential of the first electrodeposition is preferably-0.2 to-1.0V, and the deposition time is preferably 10 to 100 s;

the solvent of the copper nitrate solution is N, N-dimethylformamide, and the solute comprises copper nitrate, 1, 3, 5-benzenetricarboxylic acid and triethylamine hydrochloride, wherein the concentrations of the copper nitrate, the 1, 3, 5-benzenetricarboxylic acid and the triethylamine hydrochloride are 0.1-1%, 0.1-1% and 0.05-5% (w/w), respectively;

the initial potential of the second electrodeposition is preferably-1.0 to-1.5V, and the deposition time is preferably 50 to 200 s;

in the carbon nanotube suspension, the concentration of the carbon nanotubes is preferably 0.5-2 mg/mL, and the length of the carbon nanotubes is preferably 10-20 nm;

the initial potential of the third electrodeposition is preferably-1.5 to-2.0V, and the deposition time is preferably 100 to 1000 s;

the preparation method of the carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode preferably comprises the following steps:

(1) ultrasonically cleaning carbon fiber yarns by adopting ethanol and water in sequence, and separating a plurality of bundles of carbon fiber yarns to obtain a single carbon fiber yarn; bonding single carbon fiber wires and copper wires by using conductive silver adhesive, and penetrating a bonding body of the carbon fiber wires and the copper wires into a capillary glass tube after the conductive silver adhesive is completely dried, wherein one end of the capillary glass tube is exposed out of the carbon fiber wires, and the other end of the capillary glass tube is exposed out of the copper wires; sealing and cleaning two open ends of the capillary glass tube to obtain a carbon fiber wire electrode;

(2) taking the carbon fiber wire electrode prepared in the step (1) as a working electrode, a platinum wire electrode as a counter electrode and an Ag/AgCl electrode as a reference electrode to form a three-electrode system, inserting the three-electrode system into a chloroauric acid solution, and performing primary electrodeposition by adopting a current time method under the condition of keeping the solution stirred; taking out the electrode after electrodeposition, cleaning and drying to obtain a gold nanoparticle/carbon fiber wire electrode;

(3) taking the gold nanoparticle/carbon fiber wire electrode prepared in the step (2) as a working electrode, a platinum wire electrode as a counter electrode and an Ag/AgCl electrode as a reference electrode to form a three-electrode system, inserting the three-electrode system into a copper nitrate solution, and carrying out secondary electrodeposition by adopting a current time method under the condition of keeping the solution stirred; taking out the electrode after electrodeposition, cleaning and drying to obtain a copper oxide/gold nanoparticle/carbon fiber wire electrode;

(4) taking the copper oxide/nano-particle/carbon fiber wire electrode prepared in the step (3) as a working electrode, a platinum wire electrode as a counter electrode and an Ag/AgCl electrode as a reference electrode to form a three-electrode system, inserting the three-electrode system into the carbon nano tube suspension, and carrying out third electrodeposition by adopting a current time method under the condition of keeping the solution stirred, wherein in the voltage deposition process, the copper oxide is reduced into cuprous oxide; taking out the electrode after electrodeposition, cleaning and drying to obtain a carbon nano tube/cuprous oxide/gold nano particle/carbon fiber wire electrode;

the length of the single carbon fiber yarn in the step (1) is preferably 4-6 cm;

the length of the carbon fiber filaments exposed out of one end of the capillary glass tube in the step (1) is preferably 0.5-2 cm, and the length of the copper wires exposed out of the other end of the capillary glass tube is preferably 0.8-1.2 cm;

the sealing in the step (1) is preferably performed by adopting a mass ratio of 1: 1, sealing the epoxy resin and the ethylenediamine;

the cleaning in the step (1) is preferably acetone cleaning to remove excess sealing agent (such as epoxy resin and ethylene diamine) on the carbon fiber filaments;

the washing and drying described in the steps (2), (3) and (4) are preferably carried out by the following method:

taking out the electrode after electrodeposition, washing with deionized water, and drying with nitrogen;

the carbon nano tube/cuprous oxide/gold nano particle/carbon fiber wire electrode is applied to the preparation of the indole-3-acetic acid electrochemical sensor;

an electrochemical sensor adopts the carbon nano tube/cuprous oxide/gold nano particles/carbon fiber wire electrode as a working electrode;

the electrochemical sensor preferably adopts a platinum wire as a counter electrode and Ag/AgCl as a reference electrode;

the detection substance of the electrochemical sensor is preferably indole-3-acetic acid;

the electrochemical sensor preferably further comprises an insulating housing;

the insulating shell consists of a substrate and a cover, the substrate is provided with three parallel grooves, and the reference electrode, the working electrode and the counter electrode are sequentially arranged in the three parallel grooves; one end of the substrate is provided with a protruding part, the protruding part is exposed out of the top end of the electrode arranged in the parallel groove by 0.5-2 cm, and the protruding part is used for inserting plant organs; the cover and the base are fastened through a buckle;

the bottom surface of the convex part is preferably hollowed;

the electrochemical sensor is applied to the detection of indole-3-acetic acid in plants;

the principle of the invention is as follows:

in the present invention, the electrode modifier is used as an electrode modifierThe carbon nano tube has the advantages of high electron mobility, high electrocatalytic activity and pollution resistance; cuprous oxide (Cu)₂O) the nano-particles have larger specific surface area and good electro-catalysis performance, and are suitable for nano-catalysts for fixing catalytic sites; the gold nanoparticles have the advantages of high conductivity, excellent electrocatalytic activity, catalytic selectivity and high stability; the three are used together, so that the electrochemical detection performance of the carbon fiber wire electrode can be greatly optimized; the carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode prepared by the method has the characteristics of low detection limit, high sensitivity and good stability.

In the present invention, the concentration of the electrodeposition solution and parameters such as electrodeposition conditions are critical to the performance of the electrode, and for example, the deposition of gold nanoparticles in the present invention is not as much as possible. The carbon fiber filament has small volume, large resistance and small background current, and is easy to observe the oxidation current generated by the oxidation of a very small amount of auxin, so that the sensitive test of the auxin with trace concentration (as low as hundred pg/mL) can be realized; if the gold nanoparticles are deposited too much, the background current is increased, and the test of trace auxin is not facilitated. In addition, the cuprous oxide-gold nanoparticles and the carbon fiber wires form a composite structure, so that the conductivity of the gold nanoparticles can be cooperatively controlled, and the catalytic selectivity of the cuprous oxide can assist in providing the anti-interference capability of the electrode.

The indole-3-acetic acid sensor constructed by the invention has small volume and easy carrying, and can be applied to plant organs, such as: fruits, stems and the like, and has good application value when detecting the indole-3-acetic acid in real time.

Compared with the prior art, the invention has the following advantages and effects:

(1) the invention adopts the electrochemical deposition technology based on the current time method to carry out step-by-step multiple modification on the electrode, and finally obtains the carbon nano tube/cuprous oxide/gold nano particle/carbon fiber wire electrode. The carbon nano tube has high electron mobility, good catalytic activity on indole-3-acetic acid and good anti-pollution capacity; the cuprous oxide nanoparticles have a large specific surface area and good electrocatalytic performance; the gold nanoparticles have high conductivity, excellent electrocatalytic activity, catalytic selectivity and high stability; the three nano materials are sequentially deposited on the surface of the carbon fiber wire, so that the electrochemical detection performance of the carbon fiber wire electrode can be greatly promoted.

(2) The preparation method of the carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode provided by the invention has the advantage of easiness in operation, and the prepared carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode can be used for efficiently detecting indole-3-acetic acid and has the characteristics of low detection limit, high sensitivity and good stability.

(3) The electrochemical sensor provided by the invention can be applied to detecting the concentration content of indole-3-acetic acid in a plant body, has stable and reliable performance, small volume and convenient carrying, can realize the rapid and instant detection of the indole-3-acetic acid in the plant body, and has high sensitivity and wide detection range (in an effect embodiment, the sensitivity is 6.2 nA/(mu g/mL), and the detection range is 100 pg/mL-10 mu g/mL).

Drawings

Fig. 1 is an SEM morphology and EDX energy spectrum of the carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode in example 1, wherein, a: SEM morphology, b: EDX energy spectrum.

Fig. 2 is a differential pulse voltammogram of carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrodes prepared in example 2 using different carbon nanotube deposition times (100s, 300s, 500s, 700s, 1000s) in PBS solution with pH 7 and indole-3-acetic acid concentration of 300 ng/mL.

FIG. 3 is a layout view of a sensor housing.

Fig. 4 is a schematic diagram of the combination of the sensor housings.

FIG. 5 is a schematic diagram of an electrochemical sensor having a working electrode, a counter electrode, and a reference electrode mounted to a sensor housing.

FIG. 6 is a graph showing the test results of the stepwise increase of the response current of the electrochemical sensor using the current time method according to the concentration of the standard indole-3-acetic acid solution in the effect example.

FIG. 7 is a graph showing the relationship between the concentration of indole-3-acetic acid standard solution and the response current of an electrochemical sensor in effect example.

FIG. 8 is a differential pulse voltammogram of a standard solution of indole-3-acetic acid (concentration 300ng/mL) tested by an electrochemical sensor under different pH conditions in the effect examples.

FIG. 9 is a comparison of differential pulse voltammograms measured using an electrochemical sensor after 300ng/mL interferents (salicylic acid, citric acid, malic acid, glucose, vitamin C, respectively) were added to 300ng/mL indole-3-acetic acid.

FIG. 10 is a graph showing a current-time curve obtained by adding an indole-3-acetic acid standard solution to a juice of a stem of a cabbage in sequence and using an electrochemical sensor according to a spiking recovery method.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited thereto.

Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. Reagents, methods and apparatus used in the present invention are conventional in the art unless otherwise indicated.

Reagents and manufacturers used in the examples of the invention:

PBS buffer (pH 7.4, guangdong reagent science and technology ltd); indole-3-acetic acid (99.8%, Guangdong reagent science, Inc.); carboxylated carbon nanotubes (length 10-20 nm, Hangzhou Xiifeng nanotechnology Co., Ltd.); chloroauric acid (99%, hangzhou xiaofeng nanotechnology limited); copper nitrate (99.0%, guangdong reagent science and technology ltd); potassium ferrocyanide (99.5%, guangdong reagent science and technology ltd); absolute ethanol (99.7%, shanghai Lingfeng Chemicals Co., Ltd.); triethylamine hydrochloride (99.9%, guangdong reagent science and technology ltd); 1, 3, 5-benzenetricarboxylic acid (99.5%, Guangdong reagent science and technology Co., Ltd.).

The instruments and models involved in the embodiments of the present invention are as follows: an electrochemical workstation: CHI760C, shanghai chenhua instruments ltd.

Example 1

(1) Preparing a carbon fiber wire electrode: ultrasonically cleaning carbon fiber yarns by adopting ethanol and water in sequence, separating a plurality of clean carbon fiber yarns under a microscope to obtain a single carbon fiber yarn, and cutting the single carbon fiber yarn to be 5cm long for later use; bonding a single carbon fiber wire (the diameter is about 7 mu m) and a copper wire (the diameter is about 0.4mm) which are 5cm long by using conductive silver adhesive, and penetrating a bonding body of the carbon fiber wire and the copper wire into a capillary glass tube (the inner diameter is 0.5mm) after the conductive silver adhesive is completely dried, wherein the carbon fiber wire is exposed at one end of the capillary glass tube, the copper wire is exposed at the other end of the capillary glass tube, and the two open ends of the capillary glass tube are respectively subjected to mass ratio of 1: 1, sealing the openings with epoxy resin and ethylenediamine, cleaning with acetone to remove the epoxy resin and ethylenediamine adhered on the carbon fiber wires and the copper wires, and finally cutting the exposed carbon fiber wires into 0.5cm in length and cutting the copper wires into 1cm in length to obtain carbon fiber wire electrodes;

(2) taking the carbon fiber wire electrode prepared in the step (1) as a working electrode, a platinum wire electrode as a counter electrode and an Ag/AgCl electrode as a reference electrode to form a three-electrode system, inserting the three-electrode system into a chloroauric acid solution with the concentration of 2.5% (w/w), selecting a current time method to perform electrodeposition (the initial potential is-0.2V and the deposition time is 50s) under the condition of keeping the solution stirring, taking out the electrode after electrodeposition, washing the surface of the electrode with deionized water, and drying with nitrogen to obtain a gold nanoparticle/carbon fiber wire electrode;

(3) taking the gold nanoparticle/carbon fiber wire electrode prepared in the step (2) as a working electrode, a platinum wire electrode as a counter electrode, and an Ag/AgCl electrode as a reference electrode to form a three-electrode system, inserting the three-electrode system into a copper nitrate solution (N, N-dimethylformamide is taken as a solvent, 1.0% (w/w) of copper nitrate, 1.0% (w/w) of 1, 3, 5-benzenetricarboxylic acid and 0.5% (w/w) of triethylamine hydrochloride), carrying out electrodeposition (initial potential is 1.2V, deposition time is 100s) by selecting a current time method under the condition of keeping the solution in a stirring state, taking out the electrode after electrodeposition, washing the surface of the electrode with deionized water, and drying with nitrogen to obtain a copper oxide/gold nanoparticle/carbon fiber wire electrode;

(4) taking the copper oxide/gold nanoparticle/carbon fiber wire electrode prepared in the step (3) as a working electrode, a platinum wire electrode as a counter electrode and an Ag/AgCl electrode as a reference electrode to form a three-electrode system, inserting the three-electrode system into a carbon nanotube suspension with the concentration of 1mg/ml, and carrying out electrodeposition (initial potential of-1.8V, and electrodeposition time is respectively set to be 100s, 300s, 500s, 700s and 1000s) by selecting a current time method under the condition of keeping the solution stirring; and taking out the electrode after electrodeposition, washing with deionized water, and drying with nitrogen to obtain the carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode with different carbon nanotube deposition times.

Example 2

(1) Preparing a carbon fiber wire electrode: ultrasonically cleaning carbon fiber yarns by adopting ethanol and water in sequence, separating a plurality of clean carbon fiber yarns under a microscope to obtain a single carbon fiber yarn, and cutting the single carbon fiber yarn to be 5cm long for later use; bonding a single carbon fiber wire (the diameter is about 7 mu m) and a copper wire (the diameter is about 0.4mm) which are 5cm long by using conductive silver adhesive, and penetrating a bonding body of the carbon fiber wire and the copper wire into a capillary glass tube (the inner diameter is 0.5mm) after the conductive silver adhesive is completely dried, wherein the carbon fiber wire is exposed at one end of the capillary glass tube, the copper wire is exposed at the other end of the capillary glass tube, and the two open ends of the capillary glass tube are respectively subjected to mass ratio of 1: 1, sealing the openings with epoxy resin and ethylenediamine, cleaning with acetone to remove the epoxy resin and ethylenediamine adhered on the carbon fiber wires and the copper wires, and finally cutting the exposed carbon fiber wires into 1cm in length and cutting the copper wires into 1cm in length to obtain carbon fiber wire electrodes;

(2) taking the carbon fiber wire electrode prepared in the step (1) as a working electrode, a platinum wire electrode as a counter electrode and an Ag/AgCl electrode as a reference electrode to form a three-electrode system, inserting the three-electrode system into a chloroauric acid solution with the concentration of 1.0% (w/w), selecting a current time method to perform electrodeposition (the initial potential is-0.5V, the deposition time is 100s) under the condition of keeping the solution stirring, taking out the electrode after electrodeposition, washing the surface of the electrode with deionized water, and drying with nitrogen to obtain a gold nanoparticle/carbon fiber wire electrode;

(3) taking the gold nanoparticle/carbon fiber wire electrode prepared in the step (2) as a working electrode, a platinum wire electrode as a counter electrode, and an Ag/AgCl electrode as a reference electrode to form a three-electrode system, inserting the three-electrode system into a copper nitrate solution (N, N-dimethylformamide is used as a solvent, 0.1% (w/w) of copper nitrate, 0.5% (w/w) of 1, 3, 5-benzenetricarboxylic acid and 0.05% (w/w) of triethylamine hydrochloride), carrying out electrodeposition (initial potential is-1.0V, deposition time is 200s) by selecting a current time method under the condition of keeping the solution in a stirring state, taking out the electrode after electrodeposition, washing the surface of the electrode with deionized water, and drying with nitrogen to obtain a copper oxide/gold nanoparticle/carbon fiber wire electrode;

(4) taking the copper oxide/gold nanoparticle/carbon fiber wire electrode prepared in the step (3) as a working electrode, a platinum wire electrode as a counter electrode and an Ag/AgCl electrode as a reference electrode to form a three-electrode system, inserting the three-electrode system into a carbon nanotube suspension liquid with the concentration of 2mg/mL, and carrying out electrodeposition (initial potential of-1.5V and electrodeposition time of 1000s) by selecting a current time method under the condition of keeping the solution stirring; and taking out the electrode after electrodeposition, washing with deionized water, and drying with nitrogen to obtain the carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode with different carbon nanotube deposition times.

Example 3

(1) Preparing a carbon fiber wire electrode: ultrasonically cleaning carbon fiber yarns by adopting ethanol and water in sequence, separating a plurality of clean carbon fiber yarns under a microscope to obtain a single carbon fiber yarn, and cutting the single carbon fiber yarn to be 5cm long for later use; bonding a single carbon fiber wire (the diameter is about 7 mu m) and a copper wire (the diameter is about 0.4mm) which are 5cm long by using conductive silver adhesive, and penetrating a bonding body of the carbon fiber wire and the copper wire into a capillary glass tube (the inner diameter is 0.5mm) after the conductive silver adhesive is completely dried, wherein the carbon fiber wire is exposed at one end of the capillary glass tube, the copper wire is exposed at the other end of the capillary glass tube, and the two open ends of the capillary glass tube are respectively subjected to mass ratio of 1: 1, sealing the openings with epoxy resin and ethylenediamine, cleaning with acetone to remove the epoxy resin and ethylenediamine adhered on the carbon fiber wires and the copper wires, and finally cutting the exposed carbon fiber wires into 2cm long pieces and cutting the copper wires into 1cm long pieces to obtain carbon fiber wire electrodes;

(2) taking the carbon fiber wire electrode prepared in the step (1) as a working electrode, a platinum wire electrode as a counter electrode and an Ag/AgCl electrode as a reference electrode to form a three-electrode system, inserting the three-electrode system into a chloroauric acid solution with the concentration of 5.0% (w/w), selecting a current time method to perform electrodeposition (the initial potential is-1.0V and the deposition time is 20s) under the condition of keeping the solution stirring, taking out the electrode after electrodeposition, washing the surface of the electrode with deionized water, and drying the electrode with nitrogen to obtain a gold nanoparticle/carbon fiber wire electrode;

(3) taking the gold nanoparticle/carbon fiber wire electrode prepared in the step (2) as a working electrode, a platinum wire electrode as a counter electrode, and an Ag/AgCl electrode as a reference electrode to form a three-electrode system, inserting the three-electrode system into a copper nitrate solution (N, N-dimethylformamide is taken as a solvent, 0.5% (w/w) of copper nitrate, 0.5% (w/w) of 1, 3, 5-benzenetricarboxylic acid and 0.25% (w/w) of triethylamine hydrochloride), carrying out electrodeposition (initial potential is-1.5V, deposition time is 50s) by selecting a current time method under the condition of keeping the solution in a stirring state, taking out the electrode after electrodeposition, washing the surface of the electrode with deionized water, and drying with nitrogen to obtain a copper oxide/gold nanoparticle/carbon fiber wire electrode;

(4) taking the copper oxide/gold nanoparticle/carbon fiber wire electrode prepared in the step (3) as a working electrode, a platinum wire electrode as a counter electrode and an Ag/AgCl electrode as a reference electrode to form a three-electrode system, inserting the three-electrode system into a carbon nanotube suspension liquid with the concentration of the carbon nanotube of 0.5mg/mL, and carrying out electrodeposition (initial potential of-2.0V and electrodeposition time of 100s) by selecting a current time method under the condition of keeping the solution stirring; and taking out the electrode after electrodeposition, washing with deionized water, and drying with nitrogen to obtain the carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode with different carbon nanotube deposition times.

Effect example 1

In this embodiment, the following experiment is performed by using the carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode prepared in the step (4) of the example 1 with the electrodeposition time of 500s, specifically:

firstly, detecting the shape of the micro-structure on the surface of the carbon nano tube/cuprous oxide/gold nano particle/carbon fiber wire electrode

SEM detection and EDX analysis were performed on the surface of the carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode prepared in example 1 according to a conventional method.

The surface microstructure morphology of the carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode prepared in example 1 is shown in fig. 1 a. As can be seen from fig. 1a, curved carbon nanotubes are deposited on the surface of the electrode, and a plurality of carbon nanotubes are entangled together to form a three-dimensional carbon nanotube network, which is favorable for the transmission of charges on the surface of the electrode and the improvement of the performance of the electrode; it was also observed that many nanoparticles were deposited on the electrode surface. The result of combining the EDX spectrum corresponding to the electrode surface structure (fig. 1b) shows that the element composition of the surface nanostructure is C, N, O, Cu and Au, which indicates that the electrode surface has been successfully deposited with the nanostructures such as cuprous oxide, gold nanoparticles, etc.

Secondly, an electrochemical sensor is prepared by using the carbon nanotube/cuprous oxide/gold nanoparticle/carbon fiber wire electrode prepared in the example 1 as a working electrode:

(1) preparing an indole-3-acetic acid electrochemical sensor: the indole-3-acetic acid electrochemical sensor comprises an insulating shell, wherein the insulating shell consists of a substrate and a cover, as shown in figure 3, the substrate is provided with three parallel grooves, and a reference electrode (Ag/AgCl), a working electrode (carbon nano tube/cuprous oxide/gold nano particles/carbon fiber wire electrode) and a counter electrode (platinum wire) are sequentially arranged in the three parallel grooves; one end of the substrate is provided with a protruding part which is exposed 0.5-2 cm from the top end of the electrode arranged in the parallel groove and used for inserting plant organs, the cover and the substrate are fastened through a buckle, the assembling relation is shown as figure 4, and a real object diagram of the electrochemical sensor for assembling the working electrode, the counter electrode and the reference electrode is shown as figure 5;

(2) the indole-3-acetic acid electrochemical sensor prepared in the step (1) is used for detecting the content of indole-3-acetic acid, and the indole-3-acetic acid is tested by a differential pulse voltammetry method and a calibration function relation is obtained:

preparing indole-3-acetic acid with different concentrations by taking a PBS (pH 7) solution as a solvent, and establishing a standard solution system;

and secondly, respectively detecting indole-3-acetic acid standard solutions with different concentrations by using the indole-3-acetic acid electrochemical sensor prepared in the step (1) by using a current-time method of an electrochemical workstation with 0.7V as a detection voltage to obtain corresponding current-time curves.

Thirdly, establishing a concentration-current function relation according to current-time curves of indole-3-acetic acid standard solutions with different concentrations, wherein the method comprises the following steps: and taking the indole-3-acetic acid concentration as an abscissa and the constant voltage response current of the indole-3-acetic acid as an ordinate, and fitting by using a function equation so as to establish a calibration function between the sensor response current and the indole-3-acetic acid concentration.

Using the electrochemical sensor of this example, the current time curves of different concentrations (100pg/mL to 10. mu.g/mL) of indole-3-acetic acid standard solutions were tested, as shown in FIG. 6. As can be seen from FIG. 6, as the concentration of the indole-3-acetic acid standard solution increases, the response current detected by the electrochemical sensor also increases, i.e., as the concentration of the indole-3-acetic acid increases, the time curve of the detected current tends to increase in a step-like manner. The result shows that the concentration of the indole-3-acetic acid can be reflected by the response current of the sensor, and a corresponding conversion relation exists between the two.

The concentration range of indole-3-acetic acid that can be measured by using the electrochemical sensor of this example is 100pg/mL to 10. mu.g/mL. Within the concentration range, a trend relation between the indole-3-acetic acid concentration of the electrochemical sensor and a sensor response current quantitative index can be established, and test data are shown in table 1. The data listed in table 1 were plotted on a graph showing the trend relationship between the indole-3-acetic acid standard solution concentration and the sensor response current, with the indole-3-acetic acid concentration as the abscissa and the quantitative index as the ordinate, respectively, as shown in fig. 7. Fitting the trend relation by adopting a piecewise linear fitting method to obtain a sensor calibration equation, wherein when the concentration of the indole-3-acetic acid is 100 pg/mL-1 mu g/mL, a calibration function is as follows: y is 0.0062X +1.71, R²0.931; when the concentration of the indole-3-acetic acid is 1 mu g/mL-10 mu g/mL, the calibration function is as follows: y is 0.0047X +3.54, R²0.989; the limit of detection of indole-3-acetic acid is: the LOD is 3 alpha/s is 40.73pg/mL, the sensitivity is 6.2 nA/(mu g/mL), and the detection range is 100 pg/mL-10 mu g/mL.

TABLE 1 concentration of indole-3-acetic acid in solutions of different concentrations and the corresponding quantitative index

(3) Performance detection of sensor under different pH conditions

Detecting the performance change of the indole-3-acetic acid electrochemical sensor prepared in the step (1) under different pH conditions: the response current of indole-3-acetic acid standard solutions (concentration 300ng/mL) at different pH conditions (pH 4, 5, 6, 7, 8) was tested as a function of pH, and DPV tests were performed at different pH conditions (5 replicates for each pH condition were averaged) and the results are shown in fig. 8. As can be seen from fig. 8, in the tested indole-3-acetic acid electrochemical sensor, the current response of the electrode is sequentially reduced under the condition that the pH value of the solution is sequentially changed from 4 to 8, and the voltage corresponding to the peak current is also sequentially reduced. This shows that the pH of the test solution has an effect on the detection current response and calibration relationship of the electrode, and in the application of testing a sample, the actual pH of the sample to be tested should be considered to determine the calibration relationship.

(4) Specific detection of sensor under different interferents

Carrying out specificity detection by adopting the indole-3-acetic acid electrochemical sensor prepared in the step (1): in a standard solution of indole-3-acetic acid (PBS) with a concentration of 300ng/mL (pH 7), the same concentrations of the interfering substances, salicylic acid, citric acid, malic acid, glucose, vitamin C, were added to perform DPV tests (5 times of repeated tests for averaging), and the results are shown in fig. 9. As can be seen from FIG. 9, the response current of the prepared indole-3-acetic acid electrochemical sensor remained stable even if an interfering substance was added to the detection solution. The interference substances are common substances in plant body fluid and can not obviously influence the result of detecting the indole-3-acetic acid by the electrochemical sensor. Thus, the sensor is extremely tamper resistant.

(5) Application of auxin in plants (cabbage heart)

Taking the stem tips of a plurality of heart-shaped vegetables, preparing the stem tips into pulp by using a juicer, and testing the pH value of the homogenate of the stem tips of the heart-shaped vegetables to be 7 by using a digital handheld pH meter, so that the subsequent test can be carried out by adopting the calibration relation of an indole-3-acetic acid PBS standard solution with the pH value of 7. And (2) testing the indole-3-acetic acid content of the cabbage heart stem tip homogenate by adopting the indole-3-acetic acid electrochemical sensor prepared in the step (1), wherein the testing method is a current-time method, the testing starts from 0 second, after the curve is stabilized, indole-3-acetic acid is sequentially added into the homogenate every 10 seconds from 20 seconds, the concentration of 250ng/mL is increased every time, the indole-3-acetic acid is continuously added for 5 times, and the current-time curve is recorded, and the result is shown in figure 10.

TABLE 2 sample determination and results of labeling

Sample (I)	Standard addition (ng/mL)	Expectation value (ng/mL)	Measured value (ng/mL)	The recovery rate is high
					1	——	——	527.11	——
2	250	777.11	774.95	99.7
					3	500	1027.11	1003.22	97.7
4	750	1277.11	1272.58	99.6
					5	1000	1527.11	1542.74	101.0
6	1250	1777.11	1835.05	103.3

The standard adding recovery method can obtain the measured value of adding fixed-concentration indole-3-acetic acid each time, and the linear reverse deduction is carried out on the measured value of adding standard 5 times to obtain the content of indole-3-acetic acid in the stem tip serous fluid of the cabbage heart as 527.11 ng/mL. After the measured value of the pure cabbage stem tip serous fluid is obtained, the expected value of the sample under different adding concentrations is calculated, and the recovery rate under different adding concentrations is obtained. The specific data are shown in table 2, and the standard recovery rate of the sample of the serum of the stem tip of the obtained cabbage heart is between 97.7 and 103.3 percent. The test result of the standard recovery rate shows that the electrochemical sensor provided by the invention can truly reflect the concentration of indole-3-acetic acid in the Chinese flowering cabbage homogenate, so that the sensor can be used for detecting the indole-3-acetic acid in plants, and the test accuracy is high.

Effect example 2 Effect of different deposition times of carbon nanotubes on electrode Performance

The indole-3-acetic acid electrochemical sensor prepared in example 1 at different deposition times of carbon nanotubes was subjected to DPV test using a 300ng/mL indole-3-acetic acid PBS standard solution (PH 7), and the results are shown in fig. 2.

From fig. 2, the effect of the deposition time of the carbon nanotubes is: the deposition time is within the range of 100 s-1000 s, and the electrochemical response of the electrode to indole-3-acetic acid is gradually and remarkably enhanced along with the increase of the deposition time; after the time exceeds 500s, the deposition time of the carbon nano tube is continuously increased, and the response signal to the indole-3-acetic acid has no obvious change, so that the deposition time of the carbon nano tube is preferably 500s in practical application in consideration of the electrode performance and the deposition efficiency.

In conclusion, the indole-3-acetic acid electrochemical sensor prepared by using the carbon nano tube/cuprous oxide/gold nano particles/carbon fiber wire electrode as the working electrode, the platinum wire as the counter electrode and the Ag/AgCl as the reference electrode has high practical application value, strong anti-interference capability and specificity for indole-3-acetic acid determination. Meanwhile, in the actual measurement of the homogenized sample of the stem tip of the cabbage heart, the excellent recovery rate of 97.7-103.3% can be obtained, the actual error is within 5%, and the result of the actual sample detection of the indole-3-acetic acid sensor is extremely high in accuracy.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.