Wearable flexible electrochemical sensor and method for detecting kaempferol in plants

Abstract

The present invention provides a wearable flexible electrochemical sensor and method for detecting kaempferol in plants, comprising a flexible substrate, a curved three-electrode system and a material layer; the curved three-electrode is prepared on the surface of the flexible substrate; the curved three-electrode system comprises a working electrode, a counter electrode and a reference electrode; the working electrode, the counter electrode and the reference electrode are all in a serpentine shape and arranged side by side; the material layer is arranged in the area of ​​the working electrode; the material layer comprises a semiconductor material and a signal enhancement material. The sensor can detect kaempferol in plants in real time and in vivo, with reliable detection results, high sensitivity and low testing cost, providing a more accurate basis for judging the normal growth and development of plants.

Description

Technical Field

[0001] The present invention belongs to the field of sensor technology, and in particular relates to a wearable flexible electrochemical sensor and method for detecting kaempferol in plants. Background Art

[0002] Kaempferol, a flavonoid, is a naturally occurring polyphenol antioxidant found in plants. It is widely found in various fruits and vegetables, such as tea, broccoli, witch hazelnuts, and grapefruit. Kaempferol has many important physiological and biochemical functions in plants, including regulating growth and development, enhancing disease resistance, promoting photosynthesis, and increasing antioxidant capacity. Kaempferol also possesses pharmacological properties, including anti-inflammatory, antioxidant, anti-cancer, and anti-cardiovascular effects. Kaempferol also has many beneficial properties for human health. It can enhance the body's antioxidant capacity and prevent the production of free radicals and cellular damage. Therefore, understanding the changes in kaempferol in plants is crucial for understanding their physiological state.

[0003] Various analytical methods have been applied to the detection of kaempferol, including capillary electrophoresis, thin-layer chromatography, liquid chromatography-tandem mass spectrometry, and high-performance liquid chromatography. However, these methods suffer from technical complexity, high cost, lengthy sample pretreatment times, and low selectivity and sensitivity. Furthermore, these methods require the collection and pretreatment of plant samples, making in-situ, live plant monitoring impossible.

[0004] Compared with other analytical techniques, electrochemical methods have the advantages of simple operation, fast response time, time saving, high sensitivity, good selectivity and low cost, and can meet the needs of in-situ dynamic detection of kaempferol. However, traditional sensors based on rigid electrodes (such as glassy carbon electrodes, gold electrodes, etc.) cannot achieve effective adhesion to the plant surface, reducing the reliability and accuracy of the test results. On the other hand, it is difficult to fix it on the plant surface for long-term detection. For example, in outdoor environments such as wind, rain, and lightning, it is easy to cause deformation of plant samples, resulting in additional damage to the plants by the rigid electrodes.

[0005] Therefore, existing electrochemical rigid sensors have the disadvantages of being unable to perform long-term, live, and real-time detection of plant physiology and being destructive to plant samples. Traditional rigid sensors are difficult to meet the needs of long-term, on-site, live, and continuous monitoring of plant physiology. Summary of the Invention

[0006] In response to the above technical problems, the present invention provides a wearable flexible electrochemical sensor for detecting kaempferol in plants, as well as a preparation method and a detection method thereof. The sensor can detect kaempferol in plants in vivo and in real time. The detection results are reliable, highly sensitive, and the testing cost is low, providing a more accurate judgment basis for the normal growth and development of plants.

[0007] The present invention achieves the above technical objectives through the following technical means.

[0008] A wearable flexible electrochemical sensor for detecting kaempferol in plants, comprising a flexible substrate, a curved three-electrode system, and a material layer;

[0009] A curved three-electrode system is prepared on the surface of the flexible substrate; the curved three-electrode system includes a working electrode, a counter electrode, and a reference electrode; the working electrode, the counter electrode, and the reference electrode are all serpentine and arranged side by side;

[0010] The material layer is arranged in the region of the working electrode; the material layer includes a semiconductor material and a signal enhancement material.

[0011] In the above solution, the bending angle of each arc of the working electrode, the counter electrode and the reference electrode is 0 to 45°, and the width of the electrode is 1 to 4 mm.

[0012] Furthermore, the bending angle of each arc of the working electrode, the counter electrode and the reference electrode is 30°, and the width of the electrode is 3 mm.

[0013] In the above scheme, the flexible substrate is polydimethylsiloxane (PDMS); the curved three-electrode system is formed by laser-induced graphene (LIG) printing of flexible polyimide (PI) tape; the semiconductor material is gold nanoparticles; and the signal enhancement material is a graphene-carbon nanotube mixture and dopamine (DA).

[0014] In the above solution, the material layer further includes an electrolyte.

[0015] A method for preparing a wearable flexible electrochemical sensor for detecting kaempferol in plants comprises the following steps:

[0016] Preparation of patterned PI tape: A flexible polyimide PI tape is printed with laser-induced graphene (LIG) to form a patterned PI tape, wherein the pattern formed on the PI tape has the same shape as the curved three-electrode system;

[0017] Curing: Covering the patterned PI tape with a flexible polydimethylsiloxane (PDMS) substrate, vacuum-freeing the film to remove air bubbles, and heat-treating the film at 90°C to 110°C for 8 to 13 hours until fully cured. The PI film is then peeled off to form a curved three-electrode system, i.e., a flexible and stretchable LIG / PDMS electrode.

[0018] Encapsulation: PDMS was applied to the middle curved area of ​​the curved three-electrode system and heated at 90°C to 110°C for 8h to 13h for insulation encapsulation.

[0019] Construction of the reference electrode: Evenly apply Ag / AgCl silver paste to the exposed reference electrode area and heat until solidified to complete the construction of the Ag / AgCl reference electrode;

[0020] Impurity removal: The LIG / PDMS electrode was activated in 0.01 mol / L phosphate buffer (pH 7.2-7.4) using a constant potential method for 200-350 s to remove impurities on the electrode surface.

[0021] Electrode modification: Gold nanoparticles (Au NPs) were electrochemically deposited on the surface of the working electrode using the time-current method, and dopamine was polymerized on the surface of the working electrode using the cyclic voltammetry method. Single-walled carbon nanotubes and hexagonal boron nitride were mixed, and a drop of the mixture was applied to the sensing area of ​​the working electrode and allowed to dry naturally.

[0022] In the above scheme, the heat treatment condition is: heating at 100°C for 10 hours until completely solidified.

[0023] In the above scheme, the modification steps are specifically as follows: preparing a 1 mg / L HAuCl4 solution, using the time current method to electrochemically deposit gold nanoparticles Au NPs on the surface of the working electrode, with a deposition time of 900 to 1300 s, then preparing a 5 mM dopamine solution, and using cyclic voltammetry under the conditions of -0.6 V to 0.6 V, 80 mv / s, 80 to 90 times, to polymerize dopamine on the surface of the working electrode; mixing 0.5 to 1.5 mg / ml single-walled carbon nanotubes and 1 mg / ml hexagonal boron nitride in a volume ratio of 1:1, taking 30 to 40 μL of the mixed solution droplet and applying it to the sensing area of ​​the working electrode and drying it naturally.

[0024] In the above scheme, a 1 mg / L HAuCl4 solution was prepared, and the deposition time was 1000 s; the cyclic voltammetry conditions were: -0.6 V to 0.6 V, 80 mv / s, 90 times; 1 mg / ml single-walled carbon nanotubes and 1 mg / ml hexagonal boron nitride were mixed in a volume ratio of 1:1, and 40 μL of the mixture was dropwise applied to the sensing area of ​​the working electrode and allowed to dry naturally.

[0025] A detection method for a wearable flexible electrochemical sensor for detecting kaempferol in plants comprises the following steps:

[0026] Prepare a standard curve for kaempferol;

[0027] Covering the working electrode region of the curved three-electrode system with electrolyte;

[0028] Microneedles are used to create micro-cavities on the surface of the fruit of the plant to be tested to release plant juice to the electrode surface, and the wearable flexible electrochemical sensor for detecting kaempferol in plants is attached to the surface of the plant to be tested; then, the kaempferol information in the fruit is collected through the sensor electrode surface and converted into a current signal. Then, a handheld electrochemical workstation is used to convert the current signal into a digital signal and send it to the smart terminal through a wireless transmission module.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention can achieve accurate, minimally invasive, in vivo, and real-time detection and analysis of kaempferol in plants. Compared with traditional rigid electrochemical sensors, flexible electrodes can adapt to the irregular surfaces of plants and can still maintain stable, highly sensitive, and highly specific electrochemical perception under deformation states such as bending and stretching. This method is more accurate in detection, has low production costs, a simple production process, a high tolerance for working environments, and can be applied to field detection. It can be combined with wearable smart agricultural application scenarios to provide technical support for unmanned, intelligent, real-time, and dynamic detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic structural diagram of a wearable flexible electrochemical sensor for detecting kaempferol in plants according to one embodiment of the present invention.

[0032] Figure 2 Schematic diagram of various bending angles of a motor according to an embodiment of the present invention.

[0033] Figure 3 Schematic diagram of the sensor manufacturing process according to one embodiment of the present invention.

[0034] Figure 4 Schematic diagram of materials on an electrode according to one embodiment of the present invention.

[0035] In the figure: 1. Flexible substrate; 2. Curved three-electrode system; 3. Material layer; 4. Working electrode; 5. Counter electrode; 6. Reference electrode. DETAILED DESCRIPTION

[0036] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0037] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "front", "back", "left", "right", "up", "down", "axial", "radial", "vertical", "horizontal", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined.

[0038] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediary; or internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0039] Figure 1 The figure shows a preferred embodiment of the wearable flexible electrochemical sensor for detecting kaempferol in plants, which includes a flexible substrate 1, a curved three-electrode system 2, and a material layer 3;

[0040] A curved three-electrode system 2 is prepared on the surface of the flexible substrate 1; the curved three-electrode system 2 includes a working electrode 4, a counter electrode 5, and a reference electrode 6; the working electrode 4, the counter electrode 5, and the reference electrode 6 are all serpentine and arranged side by side;

[0041] The material layer 3 is disposed in the region of the working electrode 4 ; the material layer 3 includes a semiconductor material and a signal enhancement material.

[0042] In one embodiment of the present invention, the bending angle of each arc of the working electrode 4 , the counter electrode 5 and the reference electrode 6 is 0-45°, and the width of the electrode is 1-4 mm.

[0043] Preferably, the bending angle of each arc of the working electrode 4, the counter electrode 5 and the reference electrode 6 is 30°, and the width of the electrode is 3 mm.

[0044] In one embodiment of the present invention, the flexible substrate 1 is polydimethylsiloxane (PDMS); the curved three-electrode system 2 is a flexible polyimide (PI) tape formed by laser-induced graphene (LIG) printing.

[0045] In one embodiment of the present invention, the semiconductor material is gold nanoparticles; and the signal enhancement material is a graphene-carbon nanotube mixture and dopamine DA.

[0046] In one embodiment of the present invention, the material layer 3 further includes an electrolyte.

[0047] A method for preparing a wearable flexible electrochemical sensor for detecting kaempferol in plants comprises the following steps:

[0048] Preparation of patterned PI tape: A flexible polyimide PI tape is printed by laser-induced graphene LIG to form a patterned PI tape, wherein the pattern formed on the PI tape has the same shape as the curved three-electrode system 2;

[0049] Curing: Covering the patterned PI tape with a flexible polydimethylsiloxane (PDMS) substrate 1, vacuum-degassing the substrate to remove air bubbles, and then heat-treating the substrate at 90°C to 110°C for 8 to 13 hours until fully cured. The PI film is then peeled off to obtain a curved three-electrode system 2, i.e., a flexible and stretchable LIG / PDMS electrode.

[0050] Encapsulation: PDMS was applied to the middle curved region of the curved three-electrode system 2 and heated at 90°C to 110°C for 8h to 13h for insulation encapsulation.

[0051] Construction of the reference electrode: Ag / AgCl silver paste is evenly applied to the exposed reference electrode 4 area and heated until solidified to complete the construction of the Ag / AgCl reference electrode;

[0052] Impurity removal: The LIG / PDMS electrode was activated in 0.01 mol / L phosphate buffer (pH 7.2-7.4) using a constant potential method for 200-350 s to remove impurities on the electrode surface.

[0053] Electrode modification: Gold nanoparticles (Au NPs) were electrochemically deposited on the surface of the working electrode 4 using the time-current method, and dopamine was polymerized on the surface of the working electrode 4 using the cyclic voltammetry method. Single-walled carbon nanotubes and hexagonal boron nitride were mixed, and a drop of the mixture was applied to the sensing area of ​​the working electrode 4 and allowed to dry naturally.

[0054] In the above scheme, the heat treatment condition is: heating at 100°C for 10 hours until completely solidified.

[0055] In the above scheme, the modification steps are specifically as follows: preparing a 1 mg / L HAuCl4 solution, using the time current method to electrochemically deposit gold nanoparticles Au NPs on the surface of the working electrode 4, the deposition time is 900 to 1300 s, then preparing a 5 mM dopamine solution, using cyclic voltammetry, the conditions are: -0.6 V to 0.6 V, 80 mv / s, 80 to 90 times, to polymerize dopamine on the surface of the working electrode 4; 0.5 to 1.5 mg / ml single-walled carbon nanotubes and 1 mg / ml hexagonal boron nitride are mixed in a volume ratio of 1:1, and 30 to 40 μL of the mixed solution is dropwise applied to the sensing area of ​​the working electrode 4 and allowed to dry naturally.

[0056] In the above scheme, a 1 mg / L HAuCl4 solution was prepared, and the deposition time was 1000 s; the cyclic voltammetry conditions were: -0.6 V to 0.6 V, 80 mv / s, 90 times; 1 mg / ml single-walled carbon nanotubes and 1 mg / ml hexagonal boron nitride were mixed in a volume ratio of 1:1, and 40 μL of the mixture was dropwise applied to the sensing area of ​​the working electrode 4 and allowed to dry naturally.

[0057] A detection method for a wearable flexible electrochemical sensor for detecting kaempferol in plants comprises the following steps:

[0058] Prepare a standard curve for kaempferol;

[0059] Covering the working electrode 4 area of ​​the curved three-electrode system 2 with electrolyte;

[0060] Microneedles are used to create micro-cavities on the surface of the fruit of the plant to be tested to release plant juice to the electrode surface, and the wearable flexible electrochemical sensor for detecting kaempferol in plants is attached to the surface of the plant to be tested; then, the kaempferol information in the fruit is collected through the sensor electrode surface and converted into a current signal. Then, a handheld electrochemical workstation is used to convert the current signal into a digital signal and send it to the smart terminal through a wireless transmission module.

[0061] Combine Figure 2-4 As shown, in one embodiment of the present invention, a wearable flexible electrochemical sensor is used to detect the kaempferol content in plant fruits in real time. The specific experimental steps are as follows:

[0062] (1) Stick the PI tape on a 6×6 cm 2 The glass plate was ultrasonically cleaned with ultrapure water and ethanol, then dried with a hair dryer. Laser writing was performed on the PI tape on the glass plate according to the drawn pattern, including the working electrode sensing area, the counter electrode sensing area, the reference electrode sensing area, the middle curved conductive portion, and the electrode connection area, to create the designed curved three-electrode system. The PI tape was then induced to form a flexible graphene electrode (LIG) with excellent conductivity.

[0063] In the present invention, the main factors affecting the conductivity of the curved electrode structure include the angle and width of the curved portion. Therefore, the present invention optimizes the designed electrode at several common angles. According to the angle, the electrodes are divided into the following different angles: 0°, 15°, 30°, and 45°, as follows Figure 2 shown.

[0064] Electrochemical sensors at these angles were tested using an electrochemical workstation using the time-current method (i / t). Three measurements were performed and the average value was calculated. The results showed that the electrode with a 30° bend angle had the highest current and the best conductivity, as shown in Table 1.

[0065] Table 1 Current values ​​corresponding to different angles

[0066]

[0067] The electrode widths of 1 mm, 2 mm, 3 mm, and 4 mm were compared in experiments, and it was found that the 3 mm electrode had the best conductivity. The corresponding currents of electrodes of different widths are shown in Table 2 below.

[0068] Table 2 Current values ​​corresponding to different widths

[0069]

[0070] (2) The patterned PI tape is covered with polydimethylsiloxane (PDMS), and air bubbles are removed by vacuum. The film is then heated at 90°C-110°C for 8-13 hours until fully cured. Under these heat treatment conditions, air bubbles in the PDMS are completely eliminated, and the electrode structure is very flexible, not prone to breakage, and exhibits no signs of aging. Gently peeling off the PI film yields a flexible and stretchable LIG / PDMS electrode.

[0071] (3) Apply an appropriate amount of polydimethylsiloxane (PDMS) to the middle curved area of ​​the electrode and perform the same heat treatment to achieve insulation encapsulation. Finally, apply a certain amount of Ag / AgCl silver paste evenly to the exposed reference electrode area and heat until solidified, completing the construction of the Ag / AgCl reference electrode.

[0072] (4) The LIG / PDMS electrode was then activated in 0.01 mol / L phosphate buffer solution with a pH of 7.2-7.4 using a constant potential method (-1.7 V) for 200-350 s to remove impurities on the electrode surface.

[0073] (5) A 1 mg / L HAuCl4 solution was prepared, and gold nanoparticles (Au NPs) were electrochemically deposited on the electrode surface using the time current method (-1 V) for 900-1300 s. Then, a 5 mM dopamine solution was prepared and polymerized on the electrode surface using the cyclic voltammetry method (-0.6 V to 0.6 V, 80 mv / s, 80-90 times) to form polydopamine (pDA). Finally, 0.5-1.5 mg / ml single-walled carbon nanotubes (SWCNTs) and 1 mg / ml hexagonal boron nitride (h-BN) were mixed in a volume ratio of 1:1, and 30-40 μL of the mixed solution SWCNT@h-BN was drop-coated on the sensing area of ​​the working electrode 4 and allowed to dry naturally to obtain a LIG / PDMS / AuNPs / pDA / SWCNT@h-BN sensor.

[0074] This modification method was first used for electrode modification, leveraging the superior conductivity and stability of gold nanoparticles to enhance electrode performance. Electropolymerization of dopamine further enhanced conductivity and improved catalytic activity. A mixture of single-arm carbon nanotubes and hexagonal boron nitride, leveraging the spatial structure of the carbon nanotubes, not only enhanced conductivity but also increased the electrode's surface area. The hexagonal boron nitride exhibited excellent electrocatalytic activity for kaempferol, demonstrating a rapid and sensitive reaction. Furthermore, the electrode's detection range and detection limit, compared to those of traditional electrochemical sensors, were significantly improved, as shown in Table 3.

[0075] Table 3 Comparison of detection effects of different sensors

[0076]

[0077] (6) Kaempferol-phosphate buffer (pH = 7.2-7.4) solutions with concentrations of 0, 25, 50, 100, 200, 500, and 800 nM were prepared, and differential pulse voltammetry was performed using the prepared LIG / PDMS / AuNPs / pDA / SWCNT@h-BN sensor (potential 0-0.6 V, potential increase 0.004 V, amplitude 0.05 V, pulse width 0.02 s, pulse period 0.5 s, rest time 2 s). A set of curves showing the relationship between concentration and peak current after background current deduction were obtained, and a standard curve for kaempferol was prepared.

[0078] (7) Preparation of electrolyte: Weigh appropriate amounts of KCl and KH2PO4 respectively and place them in a 50 mL beaker. Accurately pipette a certain amount of deionized water into the beaker. After complete dissolution, adjust the pH of the solution with 1 M hydrochloric acid or potassium hydroxide. Weigh a certain amount of gelatin and add it to the above salt solution. Heat and stir until completely dissolved. Transfer the above mixture to a 5-10 mL syringe and cool and age at room temperature overnight until a gel is formed. Finally, take an appropriate amount of gelatin electrolyte to cover the working sensing area.

[0079] (8) Experimental Materials Pomelo was selected as the test object. Before the test, the surface of the crop was first cleaned with deionized water, then dried at room temperature and the pomelo skin was gently scratched. A flexible wearable sensor device equipped with a gelatin semi-solid electrolyte was then attached to the pomelo skin to be tested. Due to the intrinsic adhesion properties of the semi-solid electrolyte and PDMS, the prepared flexible wearable sensor device can self-adhere to the surface of the pomelo. A handheld electrochemical workstation was then connected to complete the construction of the flexible wearable sensing system. The real-time changes in the concentration of kaempferol in pomelo were detected by differential pulse voltammetry.

[0080] Mature grapefruit was selected, and the LIG / PDMS / AuNPs / pDA / SWCNT@h-BN sensor of the present invention was used to detect the kaempferol content using differential pulse voltammetry (DPV) according to the detection method of the present invention. A linear detection range of 0.5-800 nM and a detection limit of 0.5 nM were obtained.

[0081] Furthermore, in one embodiment of the present invention, the specific experimental steps are as follows:

[0082] (1) Stick the PI tape on a 6×6cm 2 The glass plate was ultrasonically cleaned with ultrapure water and ethanol, and then dried with a hair dryer. A curved three-electrode system with a 30° bend angle and a 3mm width was designed. Laser writing was performed on the PI tape on the glass plate according to the drawn pattern, including the working electrode sensing area, the counter electrode sensing area, the reference electrode sensing area, the middle curved conductive part, and the electrode connection area, to generate the designed curved three-electrode. The PI tape was induced to form a flexible graphene electrode (LIG) with good conductivity.

[0083] (2) Cover the patterned PI tape with PDMS, remove bubbles under vacuum, and then heat at 100°C for 10 h until fully cured. Gently peel off the PI film to obtain a flexible and stretchable LIG / PDMS electrode.

[0084] (3) Apply an appropriate amount of PDMS to the middle curved area of ​​the electrode and perform the same heat treatment to achieve insulation encapsulation. Finally, apply a certain amount of Ag / AgCl silver paste evenly to the exposed reference electrode area and heat until solidified, completing the construction of the Ag / AgCl reference electrode.

[0085] (4) The LIG / PDMS electrode was then activated in 0.01 mol / L, pH 7.2 phosphate buffer using a constant potential method (-1.7 V) for 350 s to remove impurities on the electrode surface.

[0086] (5) Prepare 1 mg / L HAuCl4 solution, and electrochemically deposit gold nanoparticles (Au NPs) on the electrode surface using the time current method (-1 V) for 1000 s; then prepare 5 mM dopamine solution, and polymerize it on the electrode surface using the cyclic voltammetry method (-0.6 V to 0.6 V, 80 mv / s, 90 times); finally, mix 1 mg / ml single-walled carbon nanotubes and 1 mg / ml hexagonal boron nitride in a volume ratio of 1:1, take 40 μL of the mixture and apply it to the sensing area of ​​the working electrode and let it dry naturally.

[0087] (6) Kaempferol-phosphate buffer (pH = 7.2) solutions with concentrations of 0, 25, 50, 100, 200, 500, and 800 nM were prepared, and differential pulse voltammetry was performed using the prepared LIG / PDMS / AuNPs / pDA / SWCNT@h-BN sensor (potential 0-0.6 V, potential increase 0.004 V, amplitude 0.05 V, pulse width 0.02 s, pulse period 0.5 s, rest time 2 s). A set of curves showing the relationship between concentration and peak current after background current deduction were obtained, and a standard curve for kaempferol was prepared.

[0088] (7) Preparation of electrolyte: Weigh 25 ml of 0.1 M KCl and KH2PO4 respectively and place them in a 50 ml beaker. Accurately pipette 10 ml of deionized water into the beaker and adjust the pH of the solution with 1 M hydrochloric acid or potassium hydroxide after it is completely dissolved. Weigh 10 ml of gelatin and add it to the above salt solution. Heat and stir until it is completely dissolved. Transfer the above mixture to an 8 ml syringe and cool and age at room temperature overnight until a gel is formed. Finally, take an appropriate amount of gelatin electrolyte to cover the working sensing area.

[0089] (8) Experimental Materials Pomelo was selected as the test object. Before the test, the surface of the crop was first cleaned with deionized water, then dried at room temperature and the pomelo skin was gently scratched. A flexible wearable sensor device equipped with a gelatin semi-solid electrolyte was then attached to the pomelo skin to be tested. Due to the intrinsic adhesion properties of the semi-solid electrolyte and PDMS, the prepared flexible wearable sensor device can self-adhere to the surface of the pomelo. A handheld electrochemical workstation was then connected to complete the construction of the flexible wearable sensing system. The real-time changes in the concentration of kaempferol in pomelo were detected by differential pulse voltammetry.

[0090] The experimental results show that the kaempferol content in mature grapefruit was detected by the electrochemical method of the present invention. The results are shown in the following table.

[0091]

[0092] The present invention provides a method for accurate, targeted, minimally invasive, and real-time detection of kaempferol in plant fruits; a wearable flexible sensor system based on electrochemical detection technology; the detection target is kaempferol, and in one embodiment of the present invention, the kaempferol content in grapefruit is used as a specific research object; a flexible curved three-electrode sensor is modified by electrodeposition, drop coating, and other means to achieve highly sensitive detection of kaempferol, and this method is used for kaempferol detection for the first time; the detection target material is plant material, mainly fruits, vegetables, and the like; and the detection site is plant tissues such as stems, leaves, and fruits.

[0093] The flexible electrode of the present invention is prepared by laser printing a drawn pattern on a flexible polyimide (PI) tape, which is then transferred to polydimethylsiloxane (PDMS) and coated with Ag / AgCl silver paste. After encapsulation, a flexible, serpentine-shaped, three-electrode system 2 is prepared. Gold nanoparticles, a graphene-carbon nanotube mixture, and dopamine (DA) are modified on a working electrode 4 by methods such as electrodeposition and drop coating. An electrolyte is then applied to the modified working electrode 4. Microcavities are made on the surface of the fruit using a microneedle to release plant juice to the electrode surface. The flexible electrode is then attached to the plant surface. Differential pulse voltammetry is then used to record the real-time changes in kaempferol in the plant fruit. A handheld electrochemical workstation is used to convert the current signal into a digital signal and transmit it to a smartphone terminal via a wireless transmission system.

[0094] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0095] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A wearable flexible electrochemical sensor for detecting kaempferol in plants, characterized in that: It comprises a flexible substrate (1), a curved three-electrode system (2) and a material layer (3); A curved three-electrode system (2) is prepared on the surface of the flexible substrate (1); the curved three-electrode system (2) comprises a working electrode (4), a counter electrode (5) and a reference electrode (6); the working electrode (4), the counter electrode (5) and the reference electrode (6) are all in a serpentine curved shape and are arranged side by side; The material layer (3) is arranged in the region of the working electrode (4); the material layer (3) comprises a semiconductor material and a signal enhancement material; The bending angle of each arc of the working electrode (4), the counter electrode (5) and the reference electrode (6) is 0-45°, and the width of the electrode is 1-4 mm.

2. The wearable flexible electrochemical sensor for detecting kaempferol in plants according to claim 1, characterized in that: The bending angle of each arc of the working electrode (4), the counter electrode (5) and the reference electrode (6) is 30°, and the width of the electrode is 3 mm.

3. The wearable flexible electrochemical sensor for detecting kaempferol in plants according to claim 1, characterized in that: The flexible substrate (1) is polydimethylsiloxane (PDMS); the curved three-electrode system (2) is a flexible polyimide (PI) tape formed by laser-induced graphene (LIG) printing; the semiconductor material is gold nanoparticles; and the signal enhancement material is a graphene-carbon nanotube mixture and dopamine (DA).

4. The wearable flexible electrochemical sensor for detecting kaempferol in plants according to claim 1, characterized in that: The material layer (3) also includes an electrolyte.

5. A method for preparing a wearable flexible electrochemical sensor for detecting kaempferol in plants according to any one of claims 1 to 4, characterized in that: The following steps are involved: Preparing a patterned PI tape: printing a flexible polyimide PI tape by laser-induced graphene LIG printing to prepare a patterned PI tape, wherein the pattern formed on the PI tape has the same shape as the curved three-electrode system (2); Curing: Cover the patterned PI tape with a flexible substrate (1) made of polydimethylsiloxane (PDMS), remove bubbles by vacuum, heat at 90°C to 110°C for 8 h to 13 h until completely cured, peel off the PI film, and obtain a curved three-electrode system (2), i.e., a flexible and stretchable LIG / PDMS electrode; Packaging: PDMS is applied to the middle bending area of ​​the curved three-electrode system (2), and heated at 90°C to 110°C for 8 h to 13 h for insulation packaging; Construction of the reference electrode: Ag / AgCl silver paste is evenly coated on the exposed reference electrode (6) area, and heated until solidified to complete the construction of the Ag / AgCl reference electrode; Impurity removal: The LIG / PDMS electrode was activated in a 0.01 mol / L, pH=7.2-7.4 phosphate buffer using a constant potential method for 200-350 s to remove impurities on the electrode surface; Electrode modification: gold nanoparticles Au NPs are electrochemically deposited on the surface of the working electrode (4) using the time current method, and dopamine is polymerized on the surface of the working electrode (4) using the cyclic voltammetry method; single-walled carbon nanotubes and hexagonal boron nitride are mixed, and a drop of the mixed solution is applied to the sensing area of ​​the working electrode (4) and dried naturally.

6. The method for preparing a wearable flexible electrochemical sensor for detecting kaempferol in plants according to claim 5, characterized in that: The heat treatment conditions are: heating at 100°C for 10 hours until completely cured.

7. The method for preparing the wearable flexible electrochemical sensor for detecting kaempferol in plants according to claim 5, It is characterized in that The modification steps are specifically as follows: preparing a 1 mg / L HAuCl4 solution, using a time current method to electrochemically deposit gold nanoparticles Au NPs on the surface of the working electrode (4), the deposition time being 900 to 1300 seconds, then preparing a 5 mM dopamine solution, using a cyclic voltammetry method under the conditions of -0.6 V to 0.6 V, 80 mv / s, 80 to 90 times, to polymerize dopamine on the surface of the working electrode (4); mixing 0.5 to 1.5 mg / ml single-walled carbon nanotubes and 1 mg / ml hexagonal boron nitride in a volume ratio of 1:1, taking 30 to 40 μL of the mixed solution droplets and applying them to the sensing area of ​​the working electrode (4) and drying them naturally.

8. The method for preparing a wearable flexible electrochemical sensor for detecting kaempferol in plants according to claim 7, characterized in that: A 1 mg / L HAuCl4 solution was prepared, and the deposition time was 1000 s; the conditions of the cyclic voltammetry were: -0.6 V to 0.6 V, 80 mv / s, 90 times; 1 mg / ml single-walled carbon nanotubes and 1 mg / ml hexagonal boron nitride were mixed in a volume ratio of 1:1, and 40 μL of the mixed solution was dropwise applied to the sensing area of ​​the working electrode (4) and dried naturally.

9. A detection method of a wearable flexible electrochemical sensor for detecting kaempferol in plants according to any one of claims 1 to 4, characterized in that: The following steps are involved: Prepare a standard curve for kaempferol; Covering the working electrode (4) region of the curved three-electrode system (2) with electrolyte; Micro holes are made on the surface of the fruit of the plant to be tested by using a microneedle to release plant juice to the electrode surface, and the wearable flexible electrochemical sensor for detecting kaempferol in the plant is attached to the surface of the plant to be tested; then, the kaempferol information in the fruit is collected through the sensor electrode surface and converted into a current signal, and then a handheld electrochemical workstation is used to convert the current signal into a digital signal and send it to the smart terminal through a wireless transmission module.

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