A fiber sensor, its fabrication method and application

Abstract

This invention discloses a fiber sensor, its preparation method, and its application, belonging to the field of electrochemical sensor technology. The invention provides a flexible electrode for continuous monitoring of plant hormones, comprising a flexible conductive substrate and a fiber functional layer disposed on the end face of the flexible conductive substrate; the flexible conductive substrate includes a conductive inner core and an insulating outer layer surrounding the conductive inner core, the conductive inner core being a liquid metal gel, and the insulating outer layer comprising a polymer; the tensile stress of the flexible conductive substrate is 1~10 kPa, the plastic deformation range is 1~10 times, and the resistance change during plastic deformation is less than or equal to 4%. The fiber sensor provided by this invention, composed of the flexible electrode, can match the plastic deformation of plant growth, has low tensile stress, and maintains stable resistance during deformation, making it suitable for long-term stable monitoring of plant hormones, offering advantages of non-destructive, long-term, and stable monitoring.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical sensor technology, and more specifically, relates to a fiber sensor, its preparation method, and its application. Background Technology

[0002] Plants are fundamental to maintaining the stability of terrestrial ecosystems and biodiversity, providing habitats for most terrestrial species and playing a vital role in supplying human food and biomass resources. They are also considered a key component of closed life support systems in deep space exploration and space agriculture. However, climate change, extreme weather, and environmental pollution are expected to threaten the survival of numerous plant species. Endogenous hormones (such as abscisic acid, indoles, and phenolic hormones) are key signaling molecules in plant responses to stresses such as drought, salt stress, pathogen infection, and radiation. They regulate physiological processes such as stomatal opening and closing, root architecture, and leaf senescence, and are important indicators of plant stress responses and survival strategies. Continuous in-situ monitoring of these hormones throughout the entire growth cycle could not only capture the earliest biochemical stress responses but also establish characteristic "hormonal fingerprints" under different stresses, providing precise data for crop stress-resistant breeding and ecological protection.

[0003] Currently, plant hormone detection mainly relies on analytical techniques such as high-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS), which require shearing, grinding, and multi-step extraction and purification before sample injection. This process is complex, time-consuming, and highly destructive, making real-time, continuous monitoring under in vivo conditions impossible and difficult to match the dynamic changes during plant growth. With the development of flexible electronics and wearable sensing, researchers are attempting to deploy flexible devices on plant surfaces to monitor physical signals non-invasively. LeeChengkuo et al. reported a fully organic transparent plant "electronic skin" that fabricated an ultrathin transparent leaf-attached device by micro-patterning PEDOT:PSS on a stretchable PDMS substrate. This device can continuously monitor leaf strain and temperature, and combined with digital twins, enables visualized phenotypic analysis. However, these devices only attach to the epidermis, acquiring physical quantities such as surface deformation and temperature, without direct contact with the internal liquid environment, and therefore cannot directly monitor the concentration of endogenous hormones in the mesophyll or vascular tissues.

[0004] To obtain internal chemical information from plants, some studies have employed rigid probes or microneedle electrochemical sensors to penetrate tissues. Li Hongji et al. used vertical graphene as a carrier, introduced core-shell Au@SnO2 as abscisic acid active sites, grew an Au@SnO2-VG composite layer on tantalum wire, and constructed a microneedle electrode array that can achieve [the following results] within 10 [units of measurement missing]. -2 ~10 2Quantitative detection of abscisic acid (ABA) in cucumbers within the μM range demonstrates the feasibility of in vivo hormone detection. However, these microneedles, based on rigid matrices such as tantalum wires, inherently lack tensile strength and flexibility, making them suitable only for short-term or localized static detection. With the irreversible elongation of plant tissues, continuous mechanical stress and interfacial slippage occur between the rigid probe and the expanding tissue, easily leading to micro-damage and even tissue remodeling, altering local hormone levels and causing measurement bias; furthermore, current work mainly focuses on detection within approximately 10 μM. 3 The s-scale testing has not yet verified the ability to conduct long-term continuous monitoring throughout the complete growth cycle and its long-term biocompatibility.

[0005] Furthermore, research such as "plant electron injection" utilizes the high conductivity and fluidity of liquid metals, injecting them into stems and other parts of the plant to construct electronic units such as resistors, capacitors, and inductors, as well as functional structures such as electrodes and antennas, in situ within the plant. This allows for monitoring internal physical changes and enabling communication. While this technology offers advantages in endowing plants with electronic functions and device morphology freedom, liquid metals, being fluid media, are prone to changes in geometry and electrical parameters under natural wind, rain, or severe deformation conditions, resulting in insufficient long-term signal stability and repeatability. Additionally, selective interfaces for endogenous hormones have not yet been constructed, and effective decoupling of hormone signals from mechanical and electromagnetic interference remains unresolved. Recent advancements in wearable or hydrogel strain sensors based on PEDOT:PSS, conductive hydrogels, and carbon-based composite materials can monitor the growth deformation of bamboo, grasses, and other plants at strains of 100%–400% or even higher, exhibiting good cyclic stability. However, their mechanism is based on "resistance changing with strain," essentially characterizing only growth deformation rather than internal chemical signals.

[0006] In summary, the main problems with existing technologies are:

[0007] 1. Laboratory methods such as chromatography / mass spectrometry require in vitro sampling and complex pretreatment, which cannot achieve real-time and continuous monitoring of endogenous hormones in living plants; 2. Although plant electronic skin and flexible strain sensors can monitor growth strain and surface temperature over long periods with low damage, they are limited to surface physical signals and have difficulty obtaining information on hormones inside the plant. 3. Metal microneedle electrochemical sensors can penetrate into plants to detect hormones, but the devices are rigid and lack tensile compliance, making it difficult to adapt to the irreversible elongation growth characteristics of plants (3 to 10 times). Long-term implantation can easily generate cumulative stress and mechanical damage at the needle-tissue interface, thereby interfering with the hormone being tested. 4. Although liquid metal injection and other injectable conductive media have a certain degree of flexibility and deformation adaptability, they lack selective interface construction for hormones. Their fluidity leads to easy fluctuations in electrical parameters, making it difficult to ensure signal stability and resistance to environmental disturbances.

[0008] This creates a core technological contradiction: on the one hand, the sensor needs to be mechanically compatible with plant tissue throughout the entire growth cycle, possess good biocompatibility, be able to "grow" synchronously with the irreversible elongation of the plant, and achieve stretching under the least possible stress; on the other hand, the baseline electrical parameters of the device, such as resistance, are required to remain as constant as possible under large-scale deformation, so that the output signal is mainly driven by changes in endogenous hormone concentration, and is not overwhelmed by deformation, temperature, and environmental disturbances. Existing flexible / wearable devices focus on deformation signals, while existing rigid microneedles focus on transient chemical detection. There is currently no technology that simultaneously meets the four requirements of "matching plastic deformation to plant growth," "low tensile stress," "maintaining stable resistance during deformation," and "high sensitivity and high selectivity for plant hormones." Summary of the Invention

[0009] 1. The problem to be solved Addressing the practical need for in-situ, dynamic, and precise detection of endogenous hormones in living plants, existing sensing technologies all have inherent defects, making it difficult to achieve a synergistic unity between mechanical adaptability and biochemical detection performance. As a whole, they cannot meet the application requirements of non-destructive, long-term, and stable monitoring of living plants. This invention provides a fiber sensor that can match the plastic deformation of plant growth, has low tensile stress, and maintains stable resistance during deformation, which can be used for long-term stable monitoring of plant hormones, as well as its preparation method and application.

[0010] 2. Technical Solution To solve the above problems, the technical solution adopted in this application is as follows: The first aspect of the present invention provides a flexible electrode, comprising a flexible conductive substrate and a fiber functional layer disposed on an end face of the flexible conductive substrate; The flexible conductive substrate includes a conductive inner core and an insulating outer layer wrapped around the conductive inner core. The conductive inner core is a liquid metal gel, and the insulating outer layer includes a polymer. The thickness of the insulating outer layer is 50~200μm; the tensile stress of the flexible conductive substrate is 1~10kPa, the plastic deformation range is 1~10 times, and the resistance change during plastic deformation is less than or equal to 4%; The fiber functional layer is selected from one of the sensing layer, the reference functional layer, and the counter electrode functional layer.

[0011] It should be noted that liquid metal has good deformability. Under stretching, the connectivity increases due to the driving force of the polymer chains, which increases its electrical conductivity. Therefore, although stretching leads to an increase in the length of the liquid metal gel, the increased conductivity ultimately ensures that its resistance remains relatively stable under stretching, thus guaranteeing the accuracy of sensing data during plant growth.

[0012] As a preferred embodiment of any technical solution in the first aspect of the present invention, the liquid metal gel comprises polyvinyl alcohol (PVA) and liquid metal, wherein the mass ratio of polyethylene to liquid metal is 1:(55.56 ~250).

[0013] As a preferred embodiment of any technical solution in the first aspect of the present invention, the liquid metal includes one or more of gallium (Ga), gallium-indium alloy (EGaIn), and gallium-indium-tin alloy (EGaInSn).

[0014] As a preferred embodiment of any technical solution in the first aspect of the present invention, the polymer is polyvinyl alcohol (PVA).

[0015] As a preferred embodiment of any technical solution in the first aspect of the present invention, the fiber functional layer is in contact with the liquid metal gel on the end face of the flexible conductive substrate.

[0016] As a preferred embodiment of any technical solution in the first aspect of the present invention, the area of ​​the fiber functional layer projected onto the end face of the flexible conductive substrate accounts for 2-9%.

[0017] As a preferred embodiment of any technical solution in the first aspect of the present invention, the thickness of the fiber functional layer is 0.4~1mm.

[0018] As a preferred embodiment of any technical solution in the first aspect of the present invention, the sensing layer is a plant hormone selective electrochemical sensitive layer.

[0019] Further preferably, the sensing layer is prepared by modifying the surface of carbon nanotube fibers with a molecularly imprinted polymer using plant hormones as a template.

[0020] Further preferably, the sensing layer includes one or more of salicylic acid (SA) sensing layer, abscisic acid (ABA) sensing layer, and jasmonic acid (JA) sensing layer.

[0021] A second aspect of the present invention provides a method for preparing a flexible electrode for continuous monitoring of plant hormones, comprising the following steps: (1) Prepare polymer precursor solution, crosslinking agent solution and liquid metal; (2) The polymer precursor solution is mixed with liquid metal to form a homogenate, and a crosslinking agent solution is added to the homogenate. The mixture is stirred at 15~35℃ and 200~800 rpm for 1~10 min to crosslink and obtain liquid metal gel. (3) The polymer precursor solution and the crosslinking agent solution are mixed and crosslinked in situ to form an insulating outer layer, so that the insulating outer layer covers the liquid metal gel in step (2), and then the liquid metal gel is frozen at -80~-20℃ for 1~20min to obtain a flexible conductive matrix with a conductive inner core and an insulating outer layer wrapped around the conductive inner core (i.e., a core-shell structure). (4) Prepare the fiber functional layer and fix the fiber functional layer to the end face of the conductive core of the flexible conductive substrate.

[0022] It should be noted that during the freezing process in step (3), the liquid metal in the liquid metal gel undergoes a phase change and hardens, thereby providing the hardness of a flexible conductive substrate that can be implanted into plants.

[0023] As a preferred embodiment of any technical solution in the second aspect of the present invention, in step (1), the polymer precursor solution is a mixed solution of polyvinyl alcohol, glycerol and water, wherein the concentration of polyvinyl alcohol is 4~9wt%, the concentration of glycerol is 2~10wt%, and the remainder is water.

[0024] It should be noted that if the concentration of polyvinyl alcohol in the polymer precursor solution is too low, it will be difficult to form; if it is too high, the tensile stress of the flexible conductive matrix will exceed 10 kPa, which will not meet the requirements for low stress application.

[0025] As a preferred embodiment of any technical solution in the second aspect of the present invention, in step (1), the crosslinking agent solution is a 2-10 wt% sodium tetraborate solution.

[0026] As a preferred embodiment of any technical solution in the second aspect of the present invention, in step (1), the crosslinking agent solution is a 4wt% sodium tetraborate solution.

[0027] It should be noted that the crosslinking between sodium tetraborate and PVA is a dynamic covalent crosslinking. If other crosslinking agents are used, different crosslinking methods will be formed: if no additional crosslinking agent is added, PVA itself forms hydrogen bonds through freeze-thaw cycles, or if glutaraldehyde is used as a crosslinking agent to form a permanent covalent crosslinking with PVA, the crosslinked products cannot simultaneously meet the requirements of low tensile stress, plastic deformation, and high deformation (up to 10 times the original length).

[0028] As a preferred embodiment of any technical solution in the second aspect of the present invention, in step (1), the liquid metal includes one or more of gallium (Ga), gallium-indium alloy (EGaIn), and gallium-indium-tin alloy (EGaInSn).

[0029] As a preferred embodiment of any technical solution in the second aspect of the present invention, in step (2), the polymer precursor solution and the liquid metal are in a mass ratio of 1:(5~10).

[0030] It should be noted that if the proportion of polymer precursor in the polymer precursor solution to liquid metal is too high, the liquid metal gel will be liquid with poor stability and difficult to form; if the proportion of liquid metal is too high, the resistance will change too much during stretching, making it impossible to maintain resistance stability and failing to meet the application requirements.

[0031] As a preferred embodiment of any technical solution in the second aspect of the present invention, in step (2), the mass ratio of the crosslinking agent solution to the homogenizing liquid is 1:(10~40).

[0032] As a preferred embodiment of any technical solution in the second aspect of the present invention, in step (2), the mixing is performed by homogenizing and shearing for 5 to 15 minutes at a temperature of 15 to 35°C.

[0033] As a preferred embodiment of any technical solution in the second aspect of the present invention, in step (3), the mass ratio of the polymer precursor solution to the crosslinking agent solution is (1~4):1.

[0034] As a preferred embodiment of any technical solution in the second aspect of the present invention, in step (4), the fiber functional layer is selected from one of the sensing layer, the reference functional layer, and the counter electrode functional layer.

[0035] As a preferred embodiment of any technical solution in the second aspect of the present invention, the sensing layer is a plant hormone selective electrochemical sensitive layer.

[0036] Further preferably, the sensing layer is prepared by modifying the surface of carbon nanotube fibers with a molecularly imprinted polymer using plant hormones as a template.

[0037] Further preferably, the sensing layer includes one or more of salicylic acid (SA) sensing layer, abscisic acid (ABA) sensing layer, and jasmonic acid (JA) sensing layer.

[0038] As a preferred embodiment of any technical solution in the second aspect of the present invention, the area of ​​the fiber functional layer projected onto the end face of the flexible conductive substrate accounts for 2-9%.

[0039] It should be noted that if the projected area of ​​the fiber functional layer (sensing layer) on the end face of the flexible conductive substrate is too small, the effective electrochemical active area is too small, which is not conducive to high-sensitivity detection; if the projected area of ​​the fiber functional layer (sensing layer) on the end face of the flexible conductive substrate is too large, the stretchability of the electrode will be limited in order to ensure sensing performance.

[0040] As a preferred embodiment of any technical solution in the second aspect of the present invention, the thickness of the fiber functional layer is 0.4~1mm.

[0041] As a preferred embodiment of any technical solution in the second aspect of the present invention, the sensing layer is a plant hormone selective electrochemical sensitive layer.

[0042] As a preferred embodiment of any technical solution in the second aspect of the present invention, the sensing layer is prepared by modifying the surface of carbon nanotube fibers with a molecularly imprinted polymer using plant hormones as a template.

[0043] Further preferably, the sensing layer includes one or more of salicylic acid (SA) sensing layer, abscisic acid (ABA) sensing layer, and jasmonic acid (JA) sensing layer.

[0044] The flexible electrode for continuous monitoring of plant hormones provided by any of the technical solutions of the first aspect of the present invention can be prepared by the preparation method provided by any of the technical solutions of the second aspect of the present invention.

[0045] A third aspect of the present invention provides a fiber sensor for continuous monitoring of plant hormones, comprising: It includes a working electrode and a counter electrode, wherein the working electrode and the counter electrode are electrically connected; Alternatively, it may include a working electrode, a counter electrode, and a reference electrode, wherein the working electrode, the counter electrode, and the reference electrode are electrically connected; Wherein, the working electrode is a flexible electrode provided by any technical solution of the first aspect of the present invention or a flexible electrode prepared by any technical solution of the second aspect of the present invention, and the fiber functional layer of the flexible electrode is a sensing layer. The counter electrode is a flexible electrode provided by any technical solution of the first aspect of the present invention or a flexible electrode prepared by any technical solution of the second aspect of the present invention, and the fiber functional layer of the flexible electrode is the counter electrode functional layer. The reference electrode is a flexible electrode provided by any technical solution of the first aspect of the present invention or a flexible electrode prepared by any technical solution of the second aspect of the present invention, wherein the fiber functional layer of the flexible electrode is the reference functional layer.

[0046] Working electrode, counter electrode, and reference electrode are all types of flexible electrodes, differing only in their fiber functional layers. A flexible electrode with a fiber functional layer as the sensing layer is the working electrode; a flexible electrode with a fiber functional layer as the counter electrode is the counter electrode; and a flexible electrode with a fiber functional layer as the reference electrode is the reference electrode. The term "electrical connection" refers to an electrical connection formed at one end of the non-fiber functional layer.

[0047] 3. Beneficial effects Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The flexible electrode for continuous monitoring of plant hormones provided by the present invention uses liquid metal gel as the conductive inner core and polymer as the insulating outer layer to form a flexible conductive matrix with a core-skin structure and good flexibility. It has low tensile stress, undergoes irreversible plastic deformation when stretched, and has a large deformation range, which can meet the requirements of elongation with plant growth and has minimal additional load on plant tissue. Furthermore, by using liquid metal gel as a conductive core, the resistance remains highly stable during the large-scale deformation that occurs as the plant grows. This ensures that the output signal is primarily driven by changes in endogenous hormone concentration, rather than being overwhelmed by deformation, temperature, and environmental disturbances. This provides excellent anti-interference capabilities and guarantees the accuracy of sensing data during plant growth.

[0048] Using polyvinyl alcohol as the insulating outer layer for implantation into plant tissues has no significant impact on plant growth and demonstrates good biocompatibility.

[0049] (2) The method for preparing a flexible electrode for continuous monitoring of plant hormones provided by the present invention can prepare a flexible electrode with large plastic deformation, small tensile stress and stable resistance during deformation by adjusting the concentration of polymer precursor solution, the ratio of polymer precursor solution to liquid metal and the selection of crosslinking agent.

[0050] (3) The fiber sensor for continuous monitoring of plant hormones provided by the present invention uses the flexible electrode provided by the present invention as the working electrode, counter electrode or reference electrode, and has the advantages of non-destructive, long-term and stable monitoring when continuously monitoring endogenous hormones in living plants. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the salicylic acid sensor in Example 1, where: a is an assembly diagram of the working electrode and the counter electrode, and b is a schematic diagram of the liquid metal gel in the initial state and the stretched state. Figure 2 The diagram shows the end face structure of the salicylic acid sensor in Example 1, where: a is a schematic diagram of the end face structure, b is the SEM-EDS image of interface i, c is the SEM-EDS image of interface ii, and d is the SEM-EDS image of interface iii. Figure 3 The following are structural diagrams of the salicylic acid sensor before and after stretching in Example 1, where: a is the optical image, CT image and EDS image of the initial state, b is the optical image, CT image and EDS image after stretching to 1000%, and c is the FTIR spectrum under different tensile strains. Figure 4 The graphs show the mechanical and electrical performance results of the salicylic acid sensor in Example 1, where: a is its stress-strain curve during uniaxial tension, b is its strain-hysteresis diagram during uniaxial tension, c is its resistance change during uniaxial tension until fracture, d is a comparison graph of its maximum tensile stress and maximum strain with the existing system, e is a comparison graph of its tensile hysteresis with the existing system, and f is a comparison graph of its tensile resistance stability with the existing system. Figure 5The following are the sensing performance results of the salicylic acid sensor in Example 1 and the abscisic acid sensor in Example 2, wherein: a is a schematic diagram of the principle of the salicylic acid sensor, b is the differential pulse voltammetry curve of the salicylic acid sensor for detecting salicylic acid, c is the selectivity diagram of the salicylic acid sensor for salicylic acid, d is a schematic diagram of the principle of the abscisic acid sensor, e is the differential pulse voltammetry curve of the abscisic acid sensor for detecting abscisic acid, and f is the selectivity diagram of the abscisic acid sensor for abscisic acid. Figure 6 The data represent the continuous monitoring and regeneration performance of the salicylic acid sensor in Example 1 and the abscisic acid sensor in Example 2, where: a is the electrochemical procedure and regeneration cycle diagram of the salicylic acid sensor for continuous monitoring of salicylic acid, and b is the electrochemical procedure and regeneration cycle diagram of the abscisic acid sensor for continuous monitoring of abscisic acid. Figure 7 The results show the effect of the salicylic acid sensor on the proliferation of L929 cells in Example 1, where: a is a representative fluorescence image stained with Calcein and propidium iodide (PI), and b is the cell viability result measured by the CCK-8 assay; Figure 8 This is a schematic diagram of the sensing system of the fiber sensor of the present invention, wherein: a is an exploded view of the layer structure of the flexible printed circuit board (FPCB), b is a schematic diagram of the working principle of the FPCB, and c is an optical photograph of the packaged chip (FPCB) attached to the test blade. Figure 9 The figures show the long-term in vivo monitoring curves of the salicylic acid sensor in Example 1 and the abscisic acid sensor in Example 2, where: a) is the monitoring signal curve of the salicylic acid sensor over 30 days; b) is the fitting graph of the results of the salicylic acid sensor and LC-MS / MS detection of the same sample on day 1; c) is the fitting graph of the results of the salicylic acid sensor and LC-MS / MS detection of the same sample on day 30; d) is the monitoring signal curve of the abscisic acid sensor over 30 days; e) is the fitting graph of the results of the abscisic acid sensor and LC-MS / MS detection of the same sample on day 1; and c) is the fitting graph of the results of the abscisic acid sensor and LC-MS / MS detection of the same sample on day 30. Figure 10 The effects of implanting different sensors on the content of endogenous signal molecules in plants were investigated, where: a) changes in salicylic acid content in leaf veins and leaves, b) changes in abscisic acid content in leaf veins and leaves, and c) changes in reactive oxygen species content in leaf veins and leaves. Figure 11 The physiological state of the plant after implantation of the fiber sensor of the present invention is shown in the figure, where: a is the change of the maximum photochemical quantum efficiency of photosystem II over time, b is the change of stomatal conductance over time, c is the change of net primary productivity over time, and d is the change of intercellular carbon dioxide concentration over time. Figure 12To illustrate the biocompatibility and electrochemical sensing performance of different sensors, the following images are presented: a) Schematic diagram of the sensor implanted in plant tissue on day 1; b) Schematic diagram of the non-growing sensor group after 30 days; c) Optical microscope image (left) of the leaf vein cross-section at the implantation site of the non-growing sensor group and the corresponding trypan blue stained image (right); d) Schematic diagram of the growing fiber sensor group after 30 days; e) Optical images of the leaves of the growing fiber sensor group on day 1 (left) and day 30 (right); f) Optical microscope image (left) of the leaf vein cross-section at the implantation site of the growing fiber sensor group and the cross-sectional optical microscope image (right) after trypan blue stained image. Figure 13 To illustrate the effect of different polyvinyl alcohol concentrations, where: a) are optical images of polyvinyl alcohol precursors at different concentrations and the metal gels prepared therefrom; b) are optical images of metal gels prepared from polyvinyl alcohol precursors at different concentrations at 10 mm / min. -1 Stress-strain curves at tensile rates; Figure 14 The effect of different mass ratios of PVA precursor solution to liquid metal is shown, where: a) is the optical image of liquid metal gel obtained with different mass ratios of PVA precursor solution to liquid metal, and b) is the electromechanical coupling curve of liquid metal gel obtained with different mass ratios of PVA precursor solution to liquid metal. Figure 15 To illustrate the effect of different crosslinking agent methods, where: a) is an optical image of liquid metal gels prepared with different crosslinking agent methods, and b) is an image of liquid metal gels prepared with different crosslinking methods at a stretching rate of 10 mm / min. -1 The stress-strain curves are shown below, where c represents the stress-strain curves of liquid metal gels prepared by different crosslinking methods at a strain of 50% and a stretching rate of 10 mm / min. -1 The stress-strain curve of a single cycle is shown below. Figure 15 d is a hysteresis statistics diagram of liquid metal gels prepared by different crosslinking methods under 50% strain. Detailed Implementation

[0052] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0053] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0054] Concentration, amount, and other numerical data may be presented in range format herein. It should be understood that such range format is used solely for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges encompassed within the range, as if each value and subrange were explicitly stated. For example, a range of values ​​from about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as "less than about 4.5," which should be interpreted to include all the values ​​and ranges described above. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0055] The present invention will be further described below with reference to specific embodiments.

[0056] Raw material information used in the examples Carbon nanotube (CNT) layer: Chengdu Jiacai Technology Co., Ltd., diameter 80μm; Polyvinyl alcohol (PVA): Shanghai Maclean Biochemical Technology Co., Ltd., PVA 1799 type (polyvinyl alcohol with a degree of polymerization of 1700 and a degree of alcoholysis of 99%); Gallium-indium alloy (EGaIn): Dongguan Dingguan Metal Technology Co., Ltd. (Ga 80%, In 20%).

[0057] Preparation of fiber functional layer 1. Preparation of salicylic acid sensing layer First, the carbon nanotube (CNT) layer is immersed in a polymerization solution prepared by dissolving 2.5 mM salicylic acid, 6.25 mM 3-aminophenylboronic acid and 18.25 mM pyrrole in deionized water. Subsequently, cyclic voltammetry (CV) deposition was performed (potential range 0–1 V, 9 scans, scan rate 50 mV·s). -1 Electrochemical synthesis of imprinted polymers on CNT layers; Next, the obtained CNT layer was immersed in a methanol / acetic acid mixed solution (volume ratio 3:7) for 2 hours to extract the template molecules. Finally, it was immersed in deionized water and dried overnight at room temperature to obtain a salicylic acid sensing layer with a thickness of 500 μm.

[0058] 2. Preparation of abscisic acid sensing layer Prussian blue nanoparticles (PBNPs) were deposited onto carbon nanotube (CNT) layers using cyclic voltammetry (CV). The deposition process was carried out in an aqueous solution containing 0.1 M HCl, 0.1 M KCl, 3 mM FeCl3, and 3 mM K3[Fe(CN)6] (scan cycles: 20, potential range: -0.2 V to 0.6 V, scan rate: 50 mV·s). -1 ); Subsequently, the CNT-PBNPs composite layer was rinsed with deionized water and then immersed in a solution containing 0.1 M HCl and 0.1 M KCl for repeated CV scans (potential range: -0.2 V to 0.6 V, scan rate: 50 mV·s). -1 ), until a stable response is obtained; The obtained CNT-PBNPs composite layer was immersed in a polymerization solution containing 2.5 mM abscisic acid, 6.25 mM 3-aminophenylboronic acid, and 18.75 mM pyrrole, and the deposition was performed using CV deposition (potential range: 0–1 V, scan cycles: 10, scan rate: 50 mV·s). -1 Molecularly imprinted polymers (MIPs) were synthesized on CNT-PBNP layers. The template molecules were extracted by immersing them in a methanol / acetic acid mixture (volume ratio 3:7) for 1 hour, followed by PBNP activation by applying a constant potential polarization of 1 V for 600 seconds in 0.5 M HCl solution. Finally, a CV scan was performed in 0.1 M KCl solution (potential range: -0.2 V to 0.6 V, scan rate: 50 mV·s). -1 The stabilization process was completed to obtain an abscisic acid sensing layer with a thickness of 500 μm.

[0059] 3. Preparation of silver / silver chloride layer First, Ag nanoparticles were coated onto the CNT layer in a solution containing 0.25 M AgNO3, 0.75 M Na2S2O3 and 0.5 M NaHSO3 by a multicurrent step electrodeposition method. The deposition program was: -0.01 mA for 150 seconds, -0.02 mA for 50 seconds, -0.05 mA for 50 seconds, -0.08 mA for 50 seconds, and -0.1 mA for 350 seconds. Subsequently, the Ag-deposited CNT layer was immersed in a 0.1 M FeCl3 solution for 30 seconds for chlorination treatment; Finally, 4 μL of PVB solution (prepared by dissolving 79.1 mg PVB and 50 mg NaCl in 1 mL of methanol) was dropped onto the chlorinated CNT layer to prepare an Ag / AgCl reference layer with a thickness of 500 μm.

[0060] Example 1 1. Preparation of salicylic acid sensing electrode (working electrode) (1) Prepare sufficient polymer precursor solution, crosslinking agent solution and liquid metal; Polymer precursor solution: PVA and glycerol were added to deionized water and stirred continuously at 1000 rpm for 2 hours at 90°C until PVA was completely dissolved, to obtain a PVA precursor solution, wherein the concentration of polyvinyl alcohol was 7 wt% and the concentration of glycerol was 4 wt%. Crosslinking agent solution: Prepare a 4% sodium tetraborate solution; Liquid metal: Gallium-indium alloy (EGaIn).

[0061] (2) Take a certain amount of the PVA precursor solution from step (1) and mix it with liquid metal at a mass ratio of 1:9. Use a handheld homogenizer (Huxi, HR-6B) to fully shear at 25°C for 10 minutes to form a homogenate. Add a crosslinking agent solution (the mass ratio of the crosslinking agent solution to the homogenate is 1:20) to the homogenate and stir at 25°C and 500 rpm for 10 minutes to crosslink and obtain a liquid metal gel. The mass ratio of polyvinyl alcohol to liquid metal in the liquid metal gel is 1:128.57.

[0062] (3) Take a certain amount of the polymer precursor solution from step (1) and mix it with the crosslinking agent solution at a mass ratio of 2:1, and mix this mixture at 200 g / m 2 The amount of liquid metal gel is poured into the inner surface of a semi-circular polytetrafluoroethylene mold (1 mm in diameter and 5 mm in length) and crosslinked in situ to form an insulating outer layer (200 μm thick). Then, the liquid metal gel from step (2) is laid on the surface of the insulating outer layer. Finally, a mixture of the polymer precursor solution and the crosslinking agent solution is covered on the surface of the liquid metal gel and crosslinked in situ to form the liquid metal gel. The liquid metal gel is then encapsulated and frozen at -20°C for 10 min to assist in demolding and stabilize the structure, thereby obtaining a flexible conductive substrate with a skin-core structure. The "skin" is the insulating outer layer obtained by in situ crosslinking of PVA and sodium tetraborate, and the "core" is the liquid metal gel. It should be noted that after freezing at -20°C, the liquid metal undergoes a phase change and hardens. Therefore, the flexible conductive substrate can have a certain degree of hardness to be implanted into plant tissue.

[0063] The tensile stress of the flexible conductive substrate is 3.2 kPa, and the change in resistance is less than or equal to 4% under 10 times plastic deformation. Figure 4 ).

[0064] (4) Cut the salicylic acid sensing layer into a circular piece with a diameter of 0.158 mm, and use the self-adhesive properties of the liquid metal gel to adhere to the end face of one end of the flexible conductive substrate in step (3) to form a flexible electrode (i.e. the working electrode of the salicylic acid sensor).

[0065] The salicylic acid sensing layer is in contact with its core liquid metal gel (the salicylic acid sensing layer accounts for 5% of the orthogonal projection area on the end face of the flexible conductive substrate), and its structure is as follows: Figure 1 a, Figure 2 As shown in a.

[0066] The other end face of the flexible conductive substrate is used to connect the wire, forming an electrical connection with the counter electrode or reference electrode.

[0067] 2. Preparation of silver / silver chloride electrode (in this embodiment, the silver / silver chloride electrode serves as both the counter electrode and the reference electrode) The silver / silver chloride electrode is prepared according to the method in "1. Preparation of salicylic acid sensing electrode (working electrode)". The difference between preparing the silver / silver chloride electrode and "1. Preparation of salicylic acid sensing electrode (working electrode)" is that the salicylic acid sensing layer is replaced with the silver / silver chloride layer in the corresponding step (4).

[0068] 3. Fabrication of salicylic acid sensor The salicylic acid sensing electrode (working electrode) and the silver / silver chloride electrode (combining the counter electrode and reference electrode) are assembled into a fiber sensor; in this embodiment, it is a salicylic acid sensor. A schematic diagram of the salicylic acid sensor is shown below. Figure 1 As shown: Figure 1 a is an assembly structure diagram of a salicylic acid sensing electrode and a silver / silver chloride electrode. The self-healing properties of PVA gel in the insulating outer layer are used to combine two flexible electrodes with a semi-circular cross section into a fiber sensor with a circular cross section. like Figure 1 As shown in b, the core of the flexible electrode contains two types of cross-linking: dynamic covalent cross-linking composed of PVA and sodium tetraborate, and hydrogen bonding cross-linking between liquid metal and PVA. During the stretching process, the dynamic covalent cross-linking points with lower bond energy preferentially break and continuously recombine due to tensile stress, causing continuous slippage of PVA segments, manifested as macroscopic plastic deformation. The slippage of PVA segments further drives the gradual fusion between the liquid metals, increasing connectivity and conductivity, compensating for the resistance changes caused by morphological changes, and thus maintaining resistance stability during the stretching process. In this process, hydrogen bonds act as stabilizing anchors, maintaining the structural integrity of the fiber sensor throughout.

[0069] Example 2 The only difference between this embodiment and embodiment 1 is that the sensing layer used in step (4) of “1. Preparation of salicylic acid sensing electrode (working electrode)” is different. In this embodiment, the exfoliated acid sensing layer is used to replace the “salicylic acid sensing layer”.

[0070] The fiber sensor prepared in this embodiment is an abscisic acid sensor.

[0071] Example 3 The only difference between this embodiment and Embodiment 1 is that: ① The polymer precursor solution in step (1) is different. In this embodiment, the concentration of polyvinyl alcohol in the polymer precursor solution is 9 wt%, and the concentration of glycerol is 2 wt%; ② The mass ratio of PVA precursor solution to liquid metal in step (2) is different. In this embodiment, the mass ratio of PVA precursor solution to liquid metal is 1:5; ③ The mass ratio of the crosslinking agent solution (4% sodium tetraborate solution) to the homogenate in step (2) is different. In this embodiment, the mass ratio of the crosslinking agent solution (4% sodium tetraborate solution) to the homogenate is 1:12. The flexible conductive substrate prepared in this embodiment has a tensile stress of 8 kPa, a maximum stretchability of 500%, and a resistance change of 3% under this plastic deformation.

[0072] Experimental Example 1 To investigate the structure of the salicylic acid sensor prepared in Example 1, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) was performed on the end face of the salicylic acid sensor in Example 1 with the fiber functional layer (salicylic acid sensing layer and silver / silver chloride layer). The results are as follows: Figure 2 As shown: Figure 2 a is a schematic diagram of the salicylic acid sensor end face. Figure 2 b is the SEM-EDS image of interface i (scale bar is 100 μm), in which the liquid metal Ga is concentrated inside the semi-circle, and its outer layer elements are C and O, which proves that the flexible conductive substrate has a core-skin structure with liquid metal gel as the "core" and PVA gel as the "skin". Figure 2 c is the SEM-EDS image of interface ii (scale bar is 100 μm). The results show that there is an insulating PVA gel between the flexible electrode with the salicylic acid sensing layer and the flexible electrode with the silver / silver chloride layer, and electrical isolation is formed between the two electrodes. Figure 2 d is the SEM-EDS image of interface iii (scale bar 20 μm). There is a C-containing region in the middle of the liquid Ga metal, corresponding to... Figure 2 The black dots in 'a' represent carbon elements in the fiber functional layer (the salicylic acid sensing layer and the silver / silver chloride layer). Overall, Figure 2The structure of the salicylic acid sensor in Example 1 is clearly shown, and its relationship with... Figure 1 The illustration in Figure 1 To.

[0073] Experimental Example 2 To investigate the structural changes of the salicylic acid sensor in Example 1 before and after stretching, it was characterized by microcomputed tomography (CT), energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). The results are as follows: Figure 3 As shown: Figure 3 a represents the optical image, CT image, and EDS image of the salicylic acid sensor in its initial state. Figure 3 b shows the optical image, CT image, and EDS image of the salicylic acid sensor after it has been stretched to 1000%. (Comparison) Figure 3 a and Figure 3 As shown in b, after stretching 10 times, the liquid metal gradually connects into a continuous body from the small spheres that are close to each other (the silver part in the CT image and the yellow part in the EDS), indicating that the conductivity gradually increases and the electrical conductivity increases, which compensates for the resistance change caused by the shape change and thus maintains the resistance stability during the stretching process.

[0074] Figure 3 c shows the FTIR spectra of the salicylic acid sensor under different tensile strains. The results show that as the stretching increases, the absorbance intensity of the first type of crosslinking point, namely the dynamic covalent bond (boronate bond BOC) between sodium tetraborate and PVA, decreases (top figure), indicating that it gradually breaks. This shows that the first type of crosslinking point mainly plays the role of energy dissipation. The bottom figure shows that the hydroxyl peak (hydrogen bond between liquid metal and PVA) shifts, but the absorbance intensity remains unchanged, indicating that the hydrogen bond between PVA and liquid metal remains stable during stretching, which can maintain the stability of the flexible electrode structure.

[0075] Experimental Example 3 To investigate the mechanical properties and resistance changes of the salicylic acid sensor in Example 1 during the tensile process, stress-strain, strain hysteresis, and resistance were tested during the tensile process. The results are as follows: Figure 4 As shown: Figure 4 Figure 4a shows the stress-strain curve during uniaxial tension, indicating that the salicylic acid sensor in Example 1 can be stretched under a relatively small tensile stress (3.2 kPa), allowing it to deform synchronously with the plant under the drive of weak plant growth forces, thereby effectively avoiding tissue damage and artificial hormone disturbance. Figure 4b, combined with the strain-hysteresis data, illustrates that the salicylic acid sensor in Example 1 undergoes plastic deformation during tension, with a small tendency to spring back (hysteresis is one of the characterization indicators of material plasticity; the greater the plasticity, the greater the hysteresis, and the smaller the tendency to spring back).

[0076] Figure 4 c represents the resistance change of the salicylic acid sensor during uniaxial stretching until fracture, where the ordinate is... R / R0 represents the relative resistance change. Compared to a conductor whose conductivity remains constant (Poiseuille's law describes that the resistance of a conductor with constant conductivity increases exponentially with increasing stretch, which is used here as a contrast), the flexible electrode of the salicylic acid sensor in Example 1 maintains a stable resistance due to the gradual increase in conductivity (caused by the more concentrated liquid metal), with a resistance change of only 4% at a strain of 1000%.

[0077] Figure 4 d~ Figure 4 e is a comparison graph of the performance of the salicylic acid sensor in Example 1 and the existing system, where Figure 4 d is a comparison diagram of the maximum tensile stress and maximum strain. Figure 4 e is a comparison chart of tensile hysteresis. Figure 4 f is a comparison chart of tensile resistance stability. The data corresponding to the existing system are derived from publicly available data statistics in scientific and technological literature. In the chart, the metals are stainless steel wire and titanium wire; the carbon materials are carbon fiber and oriented carbon nanotube fiber; the composite materials are liquid metal and PDMS composites, silver nanowires and styrene-ethylene-butene-styrene block copolymers (SEBS), etc.; the conductive polymers are poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS), polyaniline, etc. The results of the above comparison charts show that the fiber sensor provided by the present invention (the salicylic acid sensor in Example 1) has lower stress and irreversible plastic deformation under large deformation, and also has stable resistance.

[0078] Test Example 4 To investigate the sensing performance of the fiber sensor provided by this invention, the salicylic acid sensor in Example 1 and the abscisic acid sensor in Example 2 were tested, and the results are as follows: Figure 5 , Figure 6 As shown: Figure 5 a is a schematic diagram of the principle of the salicylic acid sensor. Salicylic acid is an electroactive molecule that can be directly used for monitoring. Figure 5 b shows the differential pulse voltammetry curve of the salicylic acid sensor used to detect salicylic acid. The results show that the current intensity increases with increasing salicylic acid concentration. Figure 5 The inset in Figure b shows the linear fitting curve of salicylic acid concentration versus current response. The horizontal axis represents the concentration of salicylic acid, and the vertical axis represents the current response. This inset indicates that the current response increases linearly with increasing concentration, with a linear response range of 0.1–100 μM. The slope characterizes the sensitivity of the salicylic acid sensor, which is 0.13 μA / μM. Figure 5The results show that the salicylic acid sensor in Example 1 has high sensitivity and good reliability. Figure 5 c is the selectivity diagram of the salicylic acid sensor for salicylic acid. The results show that in the presence of multiple interfering substances (SA is salicylic acid; ABA is abscisic acid; Glu is glucose; Arg is arginine; Ser is serine), the salicylic acid sensor in Example 1 basically does not respond to the interfering substances, showing high selectivity for salicylic acid.

[0079] Figure 5 d~ Figure 5 f represents a schematic diagram of the abscisic acid sensor in Example 2, a differential pulse voltammetry curve for detecting abscisic acid (the inset shows a linear fitting curve of abscisic acid concentration versus current response), and a selectivity graph for abscisic acid. Abscisic acid is a non-electroactive molecule, and an indirect detection principle is used. Figure 5 e indicates that the abscisic acid sensor in Example 2 has high sensitivity to abscisic acid (1.64 μA / dec, where dec means a 10-fold change in abscisic acid concentration) and good reliability (good linearity, with a linear response range of 0.1-1000 μM). Figure 5 f indicates that it has good selectivity for abscisic acid.

[0080] Overall, Figure 5 The results show that the fiber sensor provided by the present invention has good sensing performance for responding plant hormones, meeting the needs of in vivo monitoring.

[0081] Figure 6 The data represent the continuous monitoring and regeneration performance of the salicylic acid sensor in Example 1 and the abscisic acid sensor in Example 2, wherein... Figure 6 A salicylic acid sensor is used for the electrochemical program and regeneration cycle diagram of continuous salicylic acid monitoring. Figure 6 b shows the electrochemical program and regeneration cycle diagram for continuous monitoring of abscisic acid using the abscisic acid sensor. Both employ in-situ application of constant potential polarization for regeneration. Figure 6 The results show that the target molecules (salicylic acid or abscisic acid) are easily adsorbed on the sensing sites. By applying constant potential polarization to repel the adsorbed target molecules, the in-situ sensing sites are regenerated, enabling the fiber sensor of the present invention to achieve continuous monitoring of the target molecules.

[0082] Experimental Example 5 To investigate the biosafety of the fiber sensor provided by this invention, the effect of the salicylic acid sensor in Example 1 on the proliferation of L929 cells (L929 cells are the standard model for characterizing the cytotoxicity of the device) was studied. The results are as follows: Figure 7 As shown: Figure 7Image a shows a representative fluorescence image (scale bar 250 μm) of calcein and propidium iodide (PI) staining, where green represents calcein staining, indicating live cells, and red represents propidium iodide staining, indicating dead cells. Figure 7 b represents the cell viability results determined by the CCK-8 assay, and NS indicates that there was no significant difference after one-way ANOVA. n = 3. Figure 7 The results showed that the fiber sensor provided by the present invention did not affect cell proliferation and had no obvious cytotoxicity.

[0083] Experimental Example 6 To investigate the performance of the fiber sensor provided by this invention in actual plant hormone monitoring, the salicylic acid sensor in Example 1 and the abscisic acid sensor in Example 2 were compared according to... Figure 8 The installation connection was shown, and the plant was implanted into the plant to study its actual performance. The results are shown in Figure 1-2.

[0084] Figure 8 This is a schematic diagram of the sensing system of the fiber sensor of the present invention, wherein, Figure 8 a is an exploded view of the layer structure of a flexible printed circuit board (FPCB). Figure 8 c is an optical photograph of the packaged chip (FPCB) attached to the test blade. Figure 8 b is a schematic diagram illustrating the working principle of FPCB. For example... Figure 8 As shown in b, the growing fiber sensor (detecting salicylic acid / abscisic acid) outputs a signal to the signal output MCU. After being acquired by its ADC and processed by the Core, the signal is transmitted to the wireless control MCU via USART, and then wireless monitoring is achieved by the BLE module. The entire system is powered by a battery through LDO1 / LDO2 voltage regulation.

[0085] Figure 9 These are the results of long-term in vivo monitoring using two types of fiber sensors. Figure 9 a represents the monitoring signal curve of the salicylic acid sensor in Example 1 over 30 days. Figure 9 d represents the monitoring signal curve of the abscisic acid sensor in Example 2 over 30 days, with values ​​collected at the same time each day for statistical analysis. Figure 9 a, Figure 9 b indicates that both fiber sensors can operate normally within 30 days, demonstrating that they can meet long-term monitoring requirements; Figure 9Figures b, c, e, and f show the fitting graphs of the results obtained from detecting the same sample using a fiber sensor and liquid chromatography-tandem mass spectrometry (LC-MS / MS). Specifically, the same leaf was simultaneously tested using the sensor and then LC-MS / MS, and the trends of both measurements were fitted. Higher linearity indicates a more consistent trend between the two measurements. It should be noted that because the detection principle of the fiber sensor differs from that of LC-MS / MS, the absolute values ​​and units of the obtained salicylic acid concentrations are not identical; however, their trends can be used for comparison. Figure 9 b is a comparison of the concentration of salicylic acid detected by the sensor and the concentration measured by LC-MS / MS in different leaves (with different salicylic acid concentrations) on the first day of monitoring. The results show that the linear fit between the two is highly correlated, indicating that the salicylic acid sensor has high accuracy in monitoring salicylic acid. Figure 9 c is a comparison chart of the 30th day of monitoring. Figure 9 e Figure 9 f are comparison graphs of abscisic acid concentration measured by the abscisic acid sensor and LC-MS / MS on the 1st and 30th days of monitoring, respectively. Both graphs show high linearity, which indicates that the fiber sensor provided by the present invention can accurately monitor plant hormone concentration in vivo over a long period of time.

[0086] Figure 10 To investigate the effects of implanted sensors on the content of endogenous signaling molecules in plants, a blank control group (without any sensor implanted), a non-growing probe group (implanted with titanium wire), and a growing fiber sensor group (implanted with the fiber sensor of this invention) were set up. After 30 days, the content of endogenous signaling molecules (salicylic acid, abscisic acid, and reactive oxygen species) in each group of plants was measured by LC-MS / MS to analyze the interference of implanted sensors on endogenous signaling molecules in different parts of the plant. The size of the implanted titanium wire was consistent with the size of the salicylic acid sensor implanted in Example 1.

[0087] Figure 10 a represents the change in salicylic acid content in leaf veins and leaves. Figure 10 b represents the changes in abscisic acid content in leaf veins and leaves. Figure 10 c represents the change in reactive oxygen species content in leaf veins and leaves. Values ​​in the figure are expressed as mean ± standard deviation, n=3. P-values ​​were calculated using one-way ANOVA. NS, P>0.05: no significant difference. P ≤ 0.05, P ≤ 0.01, P ≤ 0.001, P ≤ 0.0001. Comparison of results across groups revealed that the values ​​in the growing fiber sensor group were close to those in the control group, indicating that the implantation of the fiber sensor of this invention did not cause significant stress at the implantation site, did not significantly affect changes in hormone concentration at the implantation site, and did not induce reactive oxygen species expression. In contrast, the data in the non-growing probe group showed significant fluctuations compared to the control group, causing stress at the implantation site, resulting in large changes in hormone concentration at the implantation site, and inducing significant expression of reactive oxygen species.

[0088] Figure 11 To assess the physiological state of plants after implantation of the fiber sensor of this invention, a blank control group (without any sensor implanted) and a growing fiber sensor group (implanted with the salicylic acid sensor in Example 1) were set up. The maximum photochemical quantum efficiency (Fv / Fm) of photosystem II, stomatal conductance (Gs), net primary productivity (NPP), and intercellular carbon dioxide concentration (Ci) of each group of plants were tested within 30 days to evaluate the physiological state of each group of plants.

[0089] Figure 11 Figures a through d show the changes in Fv / Fm, Gs, NPP, and Ci over time, respectively. The results indicate that implanting the fiber sensor provided by this invention did not affect the normal physiological state of the plant.

[0090] Figure 12 To assess the biocompatibility and electrochemical sensing performance of different sensors, a non-growing sensor group (implanted with titanium wire) and a growing fiber sensor group (implanted with the abscisic acid sensor from Example 2) were set up. Changes in the sensors, their impact on leaf growth, and the electrochemical sensing performance of the sensors under different scenarios were observed over 30 days. The size of the implanted titanium wire was consistent with the size of the implanted salicylic acid sensor from Example 1.

[0091] Figure 12 a is a schematic diagram of the sensor implanted in plant tissue on day 1. Figure 12 b is a schematic diagram of the non-growth-type sensor group after 30 days. Figure 12 c shows an optical microscope image (left) of the leaf vein cross-section at the implantation site of the non-growth sensor group and the corresponding trypan blue stained image (right) (scale bar is 400 μm). In the figure, the black arrow indicates the position of the titanium wire probe, the brown arrow indicates the browning area, and the blue arrow indicates the dead tissue stained with trypan blue. The results show that implantation of the non-growth sensor for one month caused damage to the surrounding tissue (browning, cell apoptosis).

[0092] Figure 12 d is a schematic diagram of the fiber sensor group that has grown after 30 days. Figure 12e shows optical images of the leaf of the growth fiber sensor group on day 1 (left) and day 30 (right) (scale bar 1 cm). The inset shows a micro-computed tomographic image of the growth fiber sensor group in the leaf veins (scale bar 500 μm). Liquid metal has a higher X-ray absorption rate than plant tissue, so the growth fiber sensor can be distinguished from the surrounding tissue to observe its state in the leaf veins. The sensor side length of the growth fiber sensor group can be clearly observed in the figure, which shows that it can deform with the growth of the plant.

[0093] Figure 12 f shows an optical microscope image (left) of the leaf vein cross-section at the implantation site of the growth fiber sensor group and an optical microscope image (right) of the cross-section after trypan blue staining (scale bar: 400 μm). The black arrow in the figure indicates the location of the abscisic acid sensor. The results show that the implantation of the growth fiber sensor did not cause significant damage to the surrounding tissue.

[0094] Figure 12 g、 Figure 12 h represents the cyclic voltammetric curves of the non-growing sensor group and the growing fiber sensor group under static, simulated wind field and simulated rain conditions for monitoring 400 μM abscisic acid. The results show that the non-growing sensor group fails to sense under dynamic conditions, while the growing fiber sensor group performs stably. Figure 12 i represents the cyclic voltammetric curves of 400 μM abscisic acid monitored by the growing fiber sensor under different uniaxial tensile strains. The results show that the growing fiber sensor can also achieve stable sensing under different tensile amounts, exhibiting excellent sensing stability.

[0095] Comparative Example 1 This comparative study investigated the effect of polyvinyl alcohol concentration in the polymer precursor solution on the preparation of the fiber sensor.

[0096] The only difference between this comparative example and Example 1 is the concentration of polyvinyl alcohol in the polymer precursor solution prepared in step (1). This comparative example prepared polymer precursor solutions with polyvinyl alcohol concentrations of 3.5 wt% and 10 wt%, and used them to prepare two different groups of liquid metal gels.

[0097] The liquid metal gel prepared in this comparative example and the liquid metal gel in Example 1 were tested, and the results are as follows: Figure 13 As shown: When the polyvinyl alcohol concentration was 3.5 wt%, the prepared liquid metal gel did not form; when the polyvinyl alcohol concentration was 10 wt%, the maximum tensile stress of the prepared liquid metal gel exceeded 10 kPa (the mechanical properties of the conductive core reflect the overall mechanical properties of the flexible conductive substrate with a core-shell structure to a certain extent), which could not meet the requirements for low stress use.

[0098] Comparative Example 2 This comparative study investigates the effect of the mass ratio of PVA precursor solution to liquid metal on the fabrication of fiber sensors.

[0099] The only difference between this comparative example and Example 1 is the mass ratio of PVA precursor solution to liquid metal in step (2). In this comparative example, four different liquid metal gels were prepared according to the feeding ratios of PVA precursor solution to liquid metal of 1:1.8, 1:2.8, 1:4.5 and 1:28.5 respectively.

[0100] The liquid metal gel prepared in this comparative example and the liquid metal gel in Example 1 were tested, and the results are as follows: Figure 14 As shown: When the mass ratio of PVA precursor solution to liquid metal is 1:1.8, 1:2.8, and 1:4.5, the liquid metal gel is in a liquid state, which is difficult to shape and has poor stability. When the mass ratio of PVA precursor solution to liquid metal is 1:28.5, the resistance of the prepared liquid metal gel changes significantly during stretching, which cannot meet the requirements for use.

[0101] Comparative Example 3 This comparative study investigates the effect of the type of crosslinking agent on the preparation of the fiber sensor.

[0102] The only difference between this comparative example and Example 1 is the crosslinking agent prepared in step (1). This comparative example uses ① no additional crosslinking agent is introduced, and PVA forms hydrogen bonds through freeze-thaw cycles, and ② glutaraldehyde is used as a crosslinking agent to form permanent covalent bonds with PVA to prepare two different liquid metal gels.

[0103] The liquid metal gel prepared in this comparative example and the liquid metal gel in Example 1 were tested, and the results are as follows: Figure 15 As shown: Among them, 15a shows optical images of liquid metal gels prepared by different crosslinking agent methods. Figure 15 b represents liquid metal gels prepared using different crosslinking methods at a stretching rate of 10 mm / min. -1 The stress-strain curve under the following conditions Figure 15 c represents liquid metal gels prepared by different crosslinking methods at a strain of 50% and a stretching rate of 10 mm / min. -1 The stress-strain curve of a single cycle is shown below. Figure 15 d is a hysteresis statistics diagram of liquid metal gels prepared by different crosslinking methods under 50% strain.

[0104] Figure 15The results showed that changing the crosslinking agent and the crosslinking method resulted in significant changes to the mechanical properties of the prepared liquid metal gel. After changing to other crosslinking methods, the hysteresis decreased to below 60%. Figure 15 d) Plasticity decreases, maximum stress exceeds 20 kPa and tensile capacity is limited to 300% ( Figure 15 (b) Performance degrades, failing to meet usage requirements.

[0105] The above description provides an illustrative overview of the present invention and its embodiments. This description is not restrictive, and the embodiments shown are merely one example of the invention's implementation. Actual implementations are not limited to these examples. Therefore, if those skilled in the art are inspired by this description and design similar implementations and examples without departing from the spirit of the invention, such designs should fall within the scope of protection of the present invention.

Claims

1. A flexible electrode for continuous monitoring of plant hormones, characterized in that, It includes a flexible conductive substrate and a fiber functional layer disposed on the end face of the flexible conductive substrate; The flexible conductive substrate includes a conductive inner core and an insulating outer layer wrapped around the conductive inner core. The conductive inner core is a liquid metal gel, and the insulating outer layer includes a polymer. The thickness of the insulating outer layer is 50~200μm; the tensile stress of the flexible conductive substrate is 1~10kPa, the plastic deformation range is 1~10 times, and the resistance change during plastic deformation is less than or equal to 4%; The fiber functional layer is selected from one of the sensing layer, the reference functional layer, and the counter electrode functional layer.

2. The flexible electrode for continuous monitoring of plant hormones according to claim 1, characterized in that, The liquid metal gel comprises polyvinyl alcohol and liquid metal, wherein the mass ratio of polyvinyl alcohol to liquid metal is 1:(55.56~250).

3. The flexible electrode according to claim 2, characterized in that, The liquid metal includes one or more of gallium, gallium-indium alloy, and gallium-indium-tin alloy; The polymer includes polyvinyl alcohol.

4. The flexible electrode for continuous monitoring of plant hormones according to any one of claims 1 to 3, characterized in that, The fiber functional layer is in contact with the liquid metal gel at the end face of the flexible conductive substrate; The area of ​​the fiber functional layer projected onto the end face of the flexible conductive substrate accounts for 2-9%; The thickness of the fiber functional layer is 0.4~1mm.

5. A method for preparing a flexible electrode for continuous monitoring of plant hormones, characterized in that, Includes the following steps: (1) Prepare polymer precursor solution, crosslinking agent solution and liquid metal; (2) The polymer precursor solution is mixed with liquid metal to form a homogenate, and a crosslinking agent solution is added to the homogenate. The mixture is stirred at 15~35℃ and 200~800 rpm for 1~10 min to crosslink and obtain liquid metal gel. (3) The polymer precursor solution and the crosslinking agent solution are mixed and crosslinked in situ to form an insulating outer layer, so that the insulating outer layer covers the liquid metal gel in step (2), and then the liquid metal gel is frozen at -80~-20℃ for 1~20min to obtain a flexible conductive matrix with a conductive inner core and an insulating outer layer wrapped around the conductive inner core. (4) Prepare the fiber functional layer and fix the fiber functional layer to the end face of the conductive core of the flexible conductive substrate.

6. The method for preparing a flexible electrode for continuous monitoring of plant hormones according to claim 5, characterized in that, In step (1), the polymer precursor solution is a mixed solution of polyvinyl alcohol, glycerol and water, wherein the concentration of polyvinyl alcohol is 4~9wt%, the concentration of glycerol is 2~10wt%, and the remainder is water; The crosslinking agent solution is a 2-10 wt% sodium tetraborate solution; The liquid metal includes one or more of gallium, gallium-indium alloy, and gallium-indium-tin alloy.

7. The method for preparing a flexible electrode for continuous monitoring of plant hormones according to claim 5 or 6, characterized in that, In step (2), the polymer precursor solution and liquid metal are mixed at a mass ratio of 1:(5~10). In step (2), the mass ratio of the crosslinking agent solution to the homogenate is 1:(10~40).

8. The method for preparing a flexible electrode for continuous monitoring of plant hormones according to claim 5 or 7, characterized in that, In step (3), the mass ratio of the polymer precursor solution to the crosslinking agent solution is (1~4):

1.

9. The method for preparing a flexible electrode for continuous monitoring of plant hormones according to claim 8, characterized in that, In step (4), the fiber functional layer is selected from one of the sensing layer, the reference functional layer, and the counter electrode functional layer; The area of ​​the fiber functional layer projected onto the end face of the flexible conductive substrate accounts for 2-9%; The thickness of the fiber functional layer is 0.4~1mm.

10. A fiber sensor for continuous monitoring of plant hormones, characterized in that, It includes a working electrode and a counter electrode, wherein the working electrode and the counter electrode are electrically connected; Alternatively, it may include a working electrode, a counter electrode, and a reference electrode, wherein the working electrode, the counter electrode, and the reference electrode are electrically connected; Wherein, the working electrode is the flexible electrode according to any one of claims 1 to 4 or the flexible electrode prepared by the preparation method according to any one of claims 5 to 8, and the fiber functional layer of the flexible electrode is the sensing layer; The counter electrode is the flexible electrode according to any one of claims 1 to 4 or the flexible electrode prepared by the preparation method according to any one of claims 5 to 8, and the fiber functional layer of the flexible electrode is the counter electrode functional layer. The reference electrode is the flexible electrode according to any one of claims 1 to 4 or the flexible electrode prepared by the preparation method according to any one of claims 5 to 8, and the fiber functional layer of the flexible electrode is the reference functional layer.

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