A method for preparing a flexible self-adhesive electrode of sandwich structure and application thereof

Abstract

The application discloses a preparation method of a sandwich-structured flexible self-adhesion electrode and application thereof. The preparation method comprises the following steps: preparing a nanofiber membrane on the surface of a substrate by using a handheld electrostatic spinning device; spraying a dispersion liquid of conductive nanomaterial on the surface of the nanofiber membrane and drying, then connecting a wire to obtain an electrode in a first state; and preparing a nanofiber membrane on the surface of the electrode in the first state again by using the handheld electrostatic spinning device to obtain the sandwich-structured flexible self-adhesion electrode. The sandwich-structured flexible self-adhesion electrode prepared by the application has excellent conductive stability; the measured object is regarded as a dielectric layer, and the electrode is prepared on the upper and lower surfaces of the dielectric layer to jointly form a capacitive sensor; the sensor has excellent capacitive monitoring stability and can in-situ monitor a plant tissue capacitive signal, and meanwhile, the health state of the plant is not affected.

Description

Technical Field

[0001] This invention belongs to the field of biosensor technology, and particularly relates to a method for preparing a flexible self-adhesive electrode with a sandwich structure and its application. Background Technology

[0002] Plants inevitably encounter various adverse factors during their growth, such as drought, pests and diseases, and soil salinization. These factors can affect plant health, and in severe cases, may lead to reduced crop yields, thus impacting the entire agricultural and forestry production process. Timely monitoring of crop health and these adverse factors, and taking corresponding measures, can prevent plant damage and increase crop yields, which is of great significance to agricultural and forestry production. Currently, there are two main direct methods for monitoring plant health or the degree of stress: one is to judge by the plant's appearance, and the other is to measure changes in the concentration of certain characteristic products in the plant, such as changes in the content of abscisic acid and reactive oxygen species. However, the appearance observation method has a certain lag, and the characteristic product measurement method cannot achieve in-situ monitoring. Therefore, researchers use plant electrical signals, such as capacitance signals, to reflect plant health.

[0003] The monitoring of plant capacitance signals is mostly achieved through direct monitoring by inserting needle electrodes into the sample or by directly monitoring the sample after sampling using rigid electrodes clamped under external force. Since the sampling and electrode insertion processes in these methods are external stimuli for the plant, they become potential interference factors. Therefore, the monitoring accuracy of these methods needs improvement. Furthermore, direct monitoring with needle electrodes inevitably causes damage to the monitored object, making sustainable monitoring impossible in the long run. While rigid electrode monitoring does not cause significant damage to the plant, rigid electrodes cannot perfectly adapt to the curved surfaces of the measured object, thus affecting the stability and accuracy of monitoring. Therefore, to improve the accuracy of plant tissue capacitance monitoring and reduce the impact of electrodes on plant health during monitoring, it is necessary to conduct in-depth research on in-situ sensing methods and devices for plant tissue capacitance.

[0004] To achieve in-situ real-time sensing of capacitance signals in plant tissues, researchers have used flexible wearable sensing devices for monitoring. Researchers have fabricated electrodes on flexible substrates using methods such as magnetron sputtering, evaporation, and laser induction, and then conformally attached them to leaf surfaces for capacitance monitoring. Other researchers have directly synthesized conductive polymer electrodes on leaf surfaces, achieving the monitoring of multiple signals including capacitance and impedance. However, these methods can affect leaf physiological activities during monitoring. Therefore, further research is needed on the fabrication methods of sensing devices to ensure that the plant's health is not affected during the monitoring of physiological signals such as capacitance. Summary of the Invention

[0005] To address the problem that existing flexible wearable sensing devices can easily affect plant health when monitoring signals such as capacitance, this invention provides a flexible self-adhesive electrode with a sandwich structure. The capacitance sensor prepared using this method has excellent capacitance monitoring stability and has no significant impact on plant health during the monitoring of capacitance signals in plant tissues.

[0006] The technical solution provided by this invention is as follows:

[0007] I. A method for fabricating a flexible self-adhesive electrode with a sandwich structure

[0008] Includes the following steps:

[0009] Step S1: Nanofiber membranes are prepared on the upper and lower surfaces of the object to be tested using a handheld electrospinning device; the specific method is as follows:

[0010] (1-1) Select a suitable polymer and dissolve it in an organic solvent. Stir it magnetically at room temperature to fully dissolve it and obtain a polymer solution.

[0011] (1-2) Draw the above solution into a plastic syringe with a stainless steel flat-head needle at the front end of the syringe, and then insert the syringe into a handheld electrospinning device.

[0012] (1-3) With the handheld electrospinning instrument aligned with the surface of the object to be tested, the syringe is slowly pushed to spin nanofiber membranes on the surface of the object to be tested.

[0013] The high molecular polymers used include polylactic acid and polyvinylidene fluoride.

[0014] Organic solvents used include acetone, chloroform, and hexafluoroisopropanol.

[0015] Step S2: Spray a conductive nanomaterial dispersion (such as an aqueous dispersion of carbon nanotubes) onto the surface of the nanofiber membrane obtained in step S1. After spraying, dry it at room temperature, and then connect wires (such as conductive tape, copper wire, etc.) to obtain the electrode in the first state; the specific method is as follows:

[0016] (2-1) A certain concentration of conductive nanomaterial dispersion was loaded into an air pump spray gun and then sprayed onto the surface of a nanofiber membrane for a certain period of time (10 s). After spraying, the membrane was dried at room temperature to obtain a composite membrane.

[0017] (2-2) Connect wires (conductive tape, copper wire, etc.) to the surface of the composite film to obtain the electrode in the first state.

[0018] Step S3: The electrode surface in the first state obtained in step S2 is used again to prepare a nanofiber membrane using a handheld electrospinning device, in the same way as in step S1, so as to obtain a flexible self-adhesive electrode with a sandwich structure.

[0019] In step S3, a nanofiber membrane is prepared again on the electrode surface in the first state. By controlling the time of the second electrospinning, the thickness of the nanofiber membrane can be controlled, thereby obtaining flexible self-adhesive electrodes with sandwich structures of different stability.

[0020] In step S3, the electrospinning time is 30 s.

[0021] II. Application of flexible self-adhesive electrodes with sandwich structure

[0022] The object under test is regarded as a dielectric layer, and flexible self-adhesive electrodes with a sandwich structure are prepared on its upper and lower surfaces respectively to form a capacitive sensor.

[0023] Application of flexible self-adhesive electrodes in monitoring capacitance signals in plant leaves.

[0024] In this invention, pothos leaves are used as the dielectric layer. After electrodes are fabricated on their upper and lower surfaces, they can be combined to form a parallel plate capacitive sensor, thereby enabling the monitoring of the capacitive signal of the pothos leaves. Since the nanofiber membrane prepared by electrospinning technology carries a certain amount of charge on its surface, the nanofiber membrane can achieve good contact with the leaves through electrostatic interaction without the aid of external force or adhesive.

[0025] Because the conductive nanomaterials used in this invention are hydrophilic and the electrode morphology is porous, some water molecules can be adsorbed onto the electrode surface or enter the electrode interior during monitoring, reaching the dielectric layer. Since the dielectric constant of water molecules is approximately 80, much larger than that of the main components of the leaf (excluding water), the capacitance value monitored by the first-state electrode will be too high under high relative humidity conditions. After preparing a hydrophobic nanofiber membrane on the surface of the first-state electrode using electrospinning, the diffusion of water molecules into the dielectric layer is hindered, reducing the monitoring error. Therefore, the accuracy and stability of capacitance signal monitoring for the sandwich-structured flexible self-adhesive electrode are improved.

[0026] In this invention, a parallel-plate capacitance sensor is constructed by combining a blade and flexible self-adhesive electrodes in a sandwich structure on its upper and lower surfaces. This sensor can then measure the capacitance of the blade. The capacitance value of this sensor is primarily related to the dielectric constant of the blade. The dielectric constant of the blade is mainly related to its components and content. Among the various main components of the blade, water accounts for more than 80%, far exceeding other components such as cellulose and protein. Of these components, water has a dielectric constant of approximately 80, significantly higher than the dielectric constants of the other components. Therefore, the blade capacitance is mainly related to its water content. The higher the water content of the blade, the greater the capacitance value.

[0027] The beneficial effects of this invention are as follows:

[0028] This invention yields a flexible, self-adhesive electrode with high monitoring stability. The capacitive sensor composed of this electrode and a dielectric layer exhibits excellent capacitive monitoring stability. When monitoring the capacitance signal of pothos leaves, the electrode has no significant impact on the plant's health status. Attached Figure Description

[0029] Figure 1 Curves showing the rate of change of capacitance signal versus relative humidity for flexible self-adhesive electrodes with different sandwich structures (i.e., different times for the second electrospinning).

[0030] Figure 2 The graph shows the rate of change of the capacitance signal of the flexible self-adhesive electrode with sandwich structure and the electrode in the first state over time.

[0031] Figure 3 A graph showing the change in capacitance signal and rate of change of a sandwich-structured flexible self-adhesive electrode as a function of temperature.

[0032] Figure 4 A graph showing the change in capacitance signal and rate of change of a flexible self-adhesive electrode with a sandwich structure as a function of illuminance.

[0033] Figure 5 A graph showing the variation of capacitance signal and rate of change of a sandwich-structured flexible self-adhesive electrode with wind speed.

[0034] Figure 6 A graph showing the change in capacitance signal and rate of change of a flexible self-adhesive electrode with a sandwich structure as a function of electrode bending.

[0035] Figure 7 A graph showing the change in capacitance signal and rate of change over time for a flexible self-adhesive electrode with a sandwich structure.

[0036] Figure 8 A graph showing the change in capacitance rate over time for monitoring the flexible self-adhesive electrode with a sandwich structure in the leaves of a pothos plant.

[0037] Figure 9 The difference in nitrogen content between the area covered by the electrode on the blade surface and other areas during the monitoring of capacitive signals;

[0038] Figure 10 The difference in relative chlorophyll content between the electrode-covered area on the leaf surface and other areas during capacitance signal monitoring;

[0039] Figure 11 Peeling curve of flexible self-adhesive electrode with sandwich structure on blade surface;

[0040] Figure 12The difference in nitrogen content between the electrode-covered area and other areas on the blade surface during the monitoring of blade capacitance signals by a traditional non-self-adhesive flexible sensor;

[0041] Figure 13 The difference in relative chlorophyll content between the electrode-covered area and other areas on the leaf surface during the monitoring of leaf capacitance signals by a traditional non-self-adhesive flexible sensor;

[0042] Figure 14 The images show actual images of a blade after monitoring the blade capacitance signal using the sandwich-structured flexible self-adhesive electrode prepared according to the present invention and a traditional non-self-adhesive flexible wearable electrode; (a) is a blade after monitoring using the sandwich-structured flexible self-adhesive electrode, and (b) is a blade after monitoring using the traditional non-self-adhesive flexible wearable electrode. Detailed Implementation

[0043] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0044] Example 1

[0045] Step S1: Polylactic acid (PLA) nanofiber membranes were prepared on the upper and lower surfaces of a 3 mm thick silicone sheet using a handheld electrospinning device. The specific method is as follows:

[0046] 1) Add 1.5 g PLA to 10 mL of hexafluoroisopropanol and stir magnetically for 12 h at room temperature to obtain a PLA solution with a concentration of 15% w / v.

[0047] 2) Draw the above PLA solution into a 5 mL plastic syringe. The stainless steel flat-head needle at the tip of the syringe is model 20G with a diameter of 0.6 mm. Then, insert the syringe into the handheld electrospinning device.

[0048] 3) With the handheld electrospinning instrument aligned with the surface of a 3 mm thick silicone sheet, the syringe is slowly pushed and spun on the surface of the object to be tested for 30 seconds using a mold to obtain a circular PLA nanofiber membrane.

[0049] Step S2: A 50 mg / mL CNT aqueous dispersion was loaded into an air pump spray gun, and then CNTs were sprayed onto the surface of the PLA nanofiber membrane for 10 seconds. After spraying, the membrane was dried at room temperature to obtain a CNT@PLA membrane. Conductive tape was then attached to the surface of the CNT@PLA membrane to obtain a CNT@PLA electrode.

[0050] Step S3: PLA nanofiber membranes are prepared again on the CNT@PLA electrode surface obtained in step S2 using a handheld electrospinning device, following the same method as in step S1. The second spinning times are 10, 20, 30, 40, and 50 s, respectively, thus preparing five different flexible self-adhesive electrodes with sandwich structures. The silicone sheet and the electrodes on its upper and lower surfaces together form a capacitive sensor.

[0051] The capacitance signals of five sensors were measured at 70–90% relative humidity (temperature 25 ˚C, illuminance 5000 lux, wind speed 0, and bending degree 0), and the capacitance change rate was calculated (the capacitance change is the difference between the sensor's capacitance signal at any given time and the initial capacitance signal; the ratio of the capacitance change to the initial capacitance value is the capacitance change rate). Figure 1 As shown, within the relative humidity range of 70-90%, the capacitance change rate monitored by each electrode increases with increasing relative humidity. Furthermore, the capacitance change rate monitored by the electrode gradually decreases with increasing second spinning time. From 30 s onwards, the capacitance change rate at 90% relative humidity shows no significant change. Therefore, the preferred second spinning time is 30 s.

[0052] Example 2

[0053] The steps in Example 2 are the same as those in Example 1, except that:

[0054] In step S1, a nanofiber membrane is prepared on the surface of a 2 mm thick glass slide;

[0055] In step S3, the second spinning time is 30 s, and the temperature, humidity and illuminance are all indoor environments. The capacitance value is measured over 30 days, and the capacitance change rate at each time point relative to day 0 is calculated.

[0056] Example 3

[0057] The steps in Example 3 are the same as those in Example 1, except that:

[0058] In step S3, the second spinning time is 30 s, the relative humidity is 50%, and the temperature is 5~40 ˚C.

[0059] Example 4

[0060] The steps in Example 4 are the same as those in Example 1, except that:

[0061] In step S3, the second spinning time is 30 s, the relative humidity is 50%, and the illuminance is 0~10000 lux.

[0062] Example 5

[0063] The steps in Example 5 are the same as those in Example 1, except that:

[0064] In step S3, the second spinning time is 30 s, the relative humidity is 45~50%, and the wind speed is 0~10 m / s.

[0065] Example 6

[0066] The steps in Example 6 are the same as those in Example 1, except that:

[0067] In step S1, a nanofiber membrane is prepared on the surface of a 0.3 mm thick PET membrane;

[0068] In step S3, the second spinning time is 30 s, the relative humidity is 45~50%, and the degree of bending is 0~20%.

[0069] Example 7

[0070] The steps in Example 7 are the same as those in Example 1, except that:

[0071] In step S3, the second spinning time is 30 s, and the monitoring environment is room temperature.

[0072] like Figure 2 As shown, when the two electrodes are used for capacitance monitoring of the same dielectric layer (2 mm thick glass plate) at room temperature, the absolute value of the rate of change of the capacitance signal monitored by the sandwich structure electrode is always lower than that of the double-layer structure electrode. This indicates that the second electrospinning in this invention can improve the stability of capacitance signal monitoring of the electrode.

[0073] like Figure 3 , Figure 4 , Figure 5 , Figure 6 and Figure 7 As shown, the monitored capacitance signal and rate of change do not change much with temperature, illuminance, wind speed, electrode bending degree, and time, indicating that the flexible self-adhesive electrode with sandwich structure of the present invention has good monitoring stability.

[0074] Example 8

[0075] Application of flexible self-adhesive electrodes with sandwich structure in blade capacitance signal monitoring:

[0076] In this application, the fabrication steps of the sandwich-structured flexible self-adhesive electrode are the same as in Example 1, except that:

[0077] In step S1, a nanofiber membrane is prepared in the middle of the leaves of the pothos plant (avoiding the main vein);

[0078] In step S3, the second spinning time is 30 s, and the monitoring environment is room temperature.

[0079] The prepared capacitive sensor is connected to a handheld LCR meter using conductive tape. The handheld LCR recorder records the sensor's capacitance signal, calculates the capacitance change rate, and plots a curve showing the capacitance change rate as a function of external conditions.

[0080] The results are as follows Figure 8 As shown. When monitoring leaf capacitance, the capacitance value is related to the leaf dielectric constant, which in turn is related to the leaf water content. During the day, leaves undergo various physiological activities, resulting in water loss through stomata. At night, in the absence of light and low temperatures, the stomata gradually close, and the transpiration rate decreases. Therefore, plants lose more water through transpiration during the day than at night; that is, the relative water content of leaves is higher at night than during the day, hence the leaf capacitance is higher at night than during the day.

[0081] Example 9

[0082] The steps in Example 9 are the same as those in Example 8.

[0083] When monitoring the capacitance signal, the relative chlorophyll content and nitrogen content in the electrode-covered area on the leaf surface and in the other areas of the same leaf are measured simultaneously, and the curves of nitrogen content and relative chlorophyll content in the two areas of the leaf change over time are plotted.

[0084] The results are as follows Figure 9 and Figure 10 As shown, during capacitance signal monitoring using the flexible self-adhesive electrode with a sandwich structure prepared according to the present invention, the nitrogen content and relative chlorophyll content in the electrode-covered area on the leaf surface showed no significant difference compared to the content in other areas of the same leaf.

[0085] like Figure 11 As shown, the peel strength of the nanofiber membrane when peeled from the surface of the pothos leaf is 1.13 ± 0.20 N / m, indicating that the nanofiber membrane prepared in this invention can self-adhere to the surface of the pothos leaf, thus eliminating the need for an adhesive.

[0086] like Figure 12 As shown, during the monitoring of blade capacitance using a traditional flexible wearable sensor, the nitrogen content in the electrode coverage area gradually decreased during the monitoring process, while the difference in nitrogen content between the two areas on the blade surface gradually increased.

[0087] like Figure 13 As shown, during the monitoring of leaf capacitance using a traditional flexible wearable sensor, the relative chlorophyll content in the electrode coverage area gradually decreased during the monitoring process, while the difference in relative chlorophyll content between the two areas on the leaf surface gradually increased.

[0088] like Figure 14 As shown, after the capacitance signal monitoring is completed, the color of the area covered by the flexible self-adhesive electrode with the sandwich structure is not significantly different from that of other areas of the same leaf, while the color of the leaf is significantly different from that of other areas of the same leaf in the area covered by the traditional flexible wearable electrode.

[0089] contrast Figure 12 -14. When using traditional flexible wearable electrodes, additional adhesives are required during capacitance signal monitoring, resulting in a significantly lower nitrogen content and relative chlorophyll content in the electrode-covered area compared to the rest of the leaf.

[0090] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for fabricating a flexible self-adhesive electrode with a sandwich structure for monitoring capacitance signals in plant leaves, characterized in that, Includes the following steps: Step S1: Prepare nanofiber membranes by electrospinning on the upper and lower surfaces of plant leaves using a handheld electrospinning device; Step S2: A conductive nanomaterial dispersion is uniformly sprayed onto the surface of the nanofiber membrane obtained in step S1. After drying at room temperature, a composite membrane is obtained on the upper and lower surfaces of the test object. Wires are connected to the upper and lower composite membrane surfaces respectively to obtain the electrode in the first state. Step S3: Use a handheld electrospinning device to electrospin on the upper and lower surfaces of the first state electrode to prepare a hydrophobic nanofiber membrane, thus obtaining a flexible self-adhesive electrode with a sandwich structure. The thickness of the nanofiber membrane is controlled by controlling the electrospinning time in step S3, thereby obtaining a flexible self-adhesive electrode with a sandwich structure that has different capacitance monitoring stability. In step S3, the electrospinning time is 30 s.

2. The method for preparing a flexible self-adhesive electrode with a sandwich structure for monitoring the capacitance signal of plant leaves according to claim 1, characterized in that, The electrospinning process in steps S1 and S3 is specifically as follows: The polymer was dissolved in an organic solvent and magnetically stirred at room temperature until completely dissolved to obtain a homogeneous polymer solution. The polymer solution was then drawn into a syringe and the syringe was inserted into a handheld electrospinning apparatus. The electrospinning apparatus is aligned with the surface of the object to be tested, and the syringe is slowly pushed to spin fibers evenly on the surface of the object to obtain a hydrophobic nanofiber membrane.

3. The method for preparing a flexible self-adhesive electrode with a sandwich structure for monitoring the capacitance signal of plant leaves according to claim 1, characterized in that: Step S2 specifically involves: loading an aqueous dispersion of conductive nanomaterials into an air pump spray gun, then uniformly spraying the conductive nanomaterial dispersion onto the surface of the nanofiber membrane, drying at room temperature after spraying, and connecting wires to the surface of the resulting composite membrane to obtain the electrode in the first state.

4. The method for preparing a flexible self-adhesive electrode with a sandwich structure for monitoring the capacitance signal of plant leaves according to claim 1, characterized in that: The conductive nanomaterial is a carbon nanotube or a metal nanowire.

Images