Two-dimensional covalent organic framework humidity / pressure dual-mode sensor and preparation method and application thereof

Abstract

The invention particularly relates to a two-dimensional covalent organic framework humidity / pressure dual-mode sensor and a preparation method and application thereof, and belongs to the technical field of dual-mode sensors. The sensor sequentially comprises a substrate, a gold interdigital electrode arranged on the substrate and a 2D COF film arranged on the gold interdigital electrode from bottom to top, the 2D COF thin film is obtained through liquid-liquid interface synthesis. The invention further provides application of the two-dimensional covalent organic framework humidity / pressure dual-mode sensor in a wearable respiratory system and a pulse health monitoring system. The sensitivity of the device reaches 80875% per% RH in the environment with the relative humidity as high as 98%, the output signal of the device is microampere (muA)-level real-time current which is remarkably higher than that of a traditional nanoampere (nA)-level signal, the signal-to-noise ratio is effectively increased, and errors of a measurement system are reduced.

Description

Technical Field

[0001] This invention belongs to the field of dual-mode sensor technology, specifically relating to a two-dimensional covalent organic framework humidity / pressure dual-mode sensor, its preparation method, and its applications. Background Technology

[0002] Covalent organic frameworks (COFs), as a new generation of ordered porous materials, have shown great potential in the field of sensing due to their well-structured nanochannels (with pore sizes typically ranging from 0.8 to 4.7 nm) and excellent thermal stability (thermal decomposition temperatures generally exceeding 400°C). The inner surfaces of the pores in these materials can be precisely chemically modified, providing an ideal molecular recognition platform for achieving efficient humidity monitoring. Early studies mainly utilized the optical response characteristics of COFs, such as solvent-induced colorimetric changes (Nat. Commun. 2023.14. 578 A sweat-responsive covalent organic framework film for material-based liveness detection and sweat pore analysis) or fluorescence intensity decay (Angew. Chem. Int. Ed. 2025, 64, e202414472. Interfacially Fabricated Covalent Organic Framework Membranes for Film-based Fluorescence Humidity Sensors and Moisture Driven Actuators). Although these methods provide intuitive responses, they are easily affected by lighting conditions in practical applications and it is difficult to establish a stable quantitative detection relationship.

[0003] In contrast, resistive detection strategies offer advantages such as stable signal output, ease of integration, and quantitative analysis. Of particular note is the unique interlayer electron transport properties of two-dimensional COF materials with large π-conjugated systems, which provide a material foundation for the development of high-performance resistive sensors (ACS Nano 2024, 18, 728 - 737 Smart Home SleepRespiratory Monitoring System Based on a Breath-Responsive Covalent Organic Framework). Currently, commercially available humidity sensing elements primarily utilize metal oxides (such as zinc oxide-based devices, whose full-range response time typically exceeds 60 seconds) or polymer materials. While the fabrication processes are mature, significant limitations remain in detection range (common products are 20-90% RH), response speed, and environmental adaptability.

[0004] In the development of COF materials, powdered COFs have severely limited their device development due to high interparticle contact resistance and difficulty in forming a uniform and dense sensing layer (J. Mater. Chem. A, 2017, 5, 21820–21827 A porous, crystalline truxene-based covalent organic framework and its application in humidity sensing). This bottleneck has been effectively solved with breakthroughs in two-dimensional COF thin film technology. Among them, imine-bonded two-dimensional COF materials prepared by interfacial synthesis (Angew. Chem. Int. Ed. 2020, 59, 602–6036 Highly Crystalline and Semiconducting Imine-Based Two-Dimensional Polymers Enabled by Interfacial Synthesis) have attracted widespread attention due to their excellent crystallinity and conductivity. By introducing specific structural units, the electrical properties of the materials can be further optimized.

[0005] However, current research on sensing based on 2D COF thin films exhibits a significant technological gap: almost all studies focus on single humidity sensing functions, completely neglecting their application potential in pressure sensing. Furthermore, no research has successfully achieved dual-mode signal decoupling and monitoring of humidity and pressure on a single COF sensing element. Moreover, the performance parameters of single COF humidity sensors remain unsatisfactory: they still suffer from narrow detection ranges, failing to cover the broader environments required for human health monitoring; their sensitivity remains 1-2 orders of magnitude lower than commercial polymer sensors; and, due to insufficient precision in thin film microstructure control and uneven distribution of functional groups, most devices exhibit poor long-term cycling stability. Therefore, developing devices capable of simultaneously responding to humidity changes and physical pressure, achieving independent, high-sensitivity detection of humidity and pressure signals on a single COF sensing element, is crucial for next-generation multifunctional, high-performance electronic devices for human health monitoring. Summary of the Invention

[0006] The purpose of this invention is to provide a two-dimensional covalent organic framework (COF) humidity / pressure dual-mode sensor, its preparation method, and its applications. This invention utilizes molecular design, selecting monomers containing alkoxy chains of specific lengths, and employing a liquid-liquid interface polymerization method to synthesize an ultrathin, continuous 2D COF film, which is then integrated with a flexible electrode system. Its sensing mechanism lies in two aspects: firstly, the hydrophilic functional groups of the alkoxy chains act as sensitive sites, achieving humidity sensing through reversible adsorption / desorption of water molecules; secondly, the alkoxy chains themselves act as flexible spacers, causing minute, recoverable deformation of the COF layered structure under pressure, thereby altering the degree of π-π stacking between layers and the charge transport resistance, achieving pressure sensing. This synergistic effect enables a single device to be used simultaneously for real-time, non-invasive monitoring of human respiration (humidity) and pulse (pressure).

[0007] To achieve the above objectives, the present invention adopts the following technical solution: This invention first provides a two-dimensional covalent organic framework humidity / pressure dual-mode sensor, which includes, from bottom to top: a substrate, a gold interdigitated electrode disposed on the substrate, and a 2D COF thin film disposed on the gold interdigitated electrode; The 2D COF film is synthesized through a liquid-liquid interface.

[0008] Preferably, the substrate is a PI (polyimide) substrate.

[0009] Preferably, the substrate thickness is 500 μm, the 2D COF film thickness is 7-8 nm, the gold (Au) interdigitated electrode thickness is 60 nm, and the channel length is 500 μm.

[0010] This invention also provides a method for fabricating a two-dimensional covalent organic framework humidity / pressure dual-mode sensor, comprising: Step 1: Inject an aqueous solution of the first monomer into the reaction vessel, and then inject an organic solution of the second monomer onto the liquid surface to form an immiscible liquid-liquid interface. Using acetic acid as a catalyst, a 2D COF film is formed at the interface. The first monomer is TAPB, and the second monomer is OH TPA, 2CO TPA, 3CO TPA, 4CO TPA, or 5CO TPA. Step 2: Deposit gold (Au) interdigitated electrodes on the substrate surface using a mask to form a bottom contact structure. Then, transfer the 2D COF thin film prepared in Step 1 onto the substrate on which the gold interdigitated electrodes are deposited to obtain a two-dimensional covalent organic framework humidity / pressure dual-mode sensor.

[0011] Preferably, the molar ratio of the first monomer and the second monomer in step one is 2:3.

[0012] Preferably, the reaction temperature in step one is room temperature, and the reaction time is 72 hours.

[0013] The present invention also provides the application of the above-mentioned two-dimensional covalent organic framework humidity / pressure dual-mode sensor in wearable respiratory systems.

[0014] This invention also provides the application of the above-mentioned two-dimensional covalent organic framework humidity / pressure dual-mode sensor in a pulse health monitoring system.

[0015] Beneficial effects of the present invention 1) This invention uses TAPB as the first monomer and OH TPA, 2CO TPA, 3CO TPA, 4CO TPA or 5CO TPA as the second monomer. By changing the length of the alkoxy chain of the linker side chain, the hydrophilicity, flexibility and structural stability of COF are precisely controlled, so that it has excellent water molecule adsorption capacity, sensitive pressure deformation capacity and long-term structural stability.

[0016] 2) This invention utilizes the liquid-liquid interface to confine the reaction to a strictly two-dimensional plane, resulting in relatively uniform reactant concentration, diffusion rate, and reaction rate, thus generating a thin film with uniform thickness and good crystallinity. The film exhibits preferential oriented growth (π-π stacking direction perpendicular to the interface), and this ordered structure facilitates rapid and selective molecular transport within the channels. Furthermore, the generated film possesses sufficient mechanical strength, allowing for convenient and complete transfer from the reaction interface to various target substrates (such as silicon wafers, copper meshes, porous alumina, etc.) via methods such as lifting or "scooping" with a supporting substrate, facilitating subsequent characterization and device fabrication.

[0017] 3) Superior Sensitivity and Measurement Range: The device of this invention achieves a sensitivity of 80875% per %RH in environments with relative humidity up to 98%, one of the highest reported values ​​among similar COF sensors. Its output signal is a real-time current in the microampere (μA) range, significantly higher than traditional nanoampere (nA) signals, effectively improving the signal-to-noise ratio and reducing measurement system errors.

[0018] 4) Ultrafast response and recovery dynamics: The sensor of this invention possesses excellent dynamic response characteristics, with response and recovery times of 0.06 seconds and 0.24 seconds, respectively. This is due to the rapid capture of water molecules by densely distributed hydrophilic sites on the material surface and the rapid desorption of water molecules by the nanoscale ultrathin structure, thereby significantly reducing sensing hysteresis.

[0019] 5) Precise physiological signal monitoring capability: The device of this invention can accurately and in real time track changes in physiological signals caused by human activity, including rapid respiratory rate fluctuations of 13 to 45 breaths / minute before and after exercise, resting pulse of about 74 beats / minute and exercise pulse of 155 beats / minute. All monitoring data are within the normal physiological index range of adults, demonstrating its high fidelity in dynamic health monitoring.

[0020] 6) Wide temperature range operation stability: Within a wide temperature range of 25℃ to 75℃, the humidity response of the device of the present invention can still maintain a good linear relationship with the relative humidity, indicating that its sensing performance is minimally affected by ambient temperature fluctuations, ensuring reliability and accuracy under different operating environments.

[0021] 7) Excellent selectivity and anti-interference: The device of this invention shows no response to respiratory components and common gases in the environment (such as carbon dioxide, oxygen, nitrogen, and argon) as well as small polar organic molecules (such as methanol, ethanol, and acetone), exhibiting excellent selectivity. This characteristic ensures that interfering gases can be effectively eliminated and a pure humidity signal can be obtained when monitoring respiration in complex environments.

[0022] 8) Excellent mechanical and cyclic durability: After 1,000 repeated bending tests and 1,000 continuous response cycle tests, the sensing performance curve of the device did not show significant changes, and the current response value decay was negligible, proving that it has excellent mechanical robustness and long-term working stability as a wearable device in practical applications.

[0023] 9) The two-dimensional covalent organic framework humidity / pressure dual-mode sensor of this invention demonstrates outstanding application potential in the field of wearable health monitoring. By integrating it into everyday wearable devices (such as masks and wristbands), real-time and accurate tracking of key physiological signals can be achieved. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the 2D COF thin film structure of the present invention; Figure 2 This is a reaction flow diagram and a schematic diagram of the device structure for the 2D COF thin film of the present invention; Figure 3 This invention is a 2D COF TAPB-4CO TPA Microscopic photographs and large-format photographs; Figure 4 The monomers TAPB, 4CO TPA, and 2D COF of this invention are TAPB-4CO TPA Infrared spectrum and X-ray photoelectron spectrum; Figure 5 This is the X-ray diffraction pattern of the 2D COF thin film of the present invention; Figure 6 The current response curve of the 2D COF film humidity sensor of the present invention is shown. Figure 7 The above is the response / recovery time curve of the 2D COF film humidity sensor of the present invention; Figure 8 This invention is a 2D COF TAPB-4CO TPA Membrane operating temperature, selectivity, flexible sensing, and cycle stability curves; Figure 9 This invention is a 2D COF TAPB-4CO TPA Application curves for membrane respiration monitoring; Figure 10 This invention is a 2D COF TAPB-4CO TPA Membrane non-contact sensing curve; Figure 11 This invention is a 2D COF TAPB-4CO TPA Application curves of membrane pulse monitoring. Detailed Implementation

[0025] The present invention first provides a two-dimensional covalent organic framework humidity / pressure dual-mode sensor, which includes, from bottom to top: a substrate, a gold interdigitated electrode disposed on the substrate, and a 2D COF thin film disposed on the gold interdigitated electrode; the 2D COF thin film is obtained by liquid-liquid interface synthesis.

[0026] According to the present invention, the substrate is preferably a PI (polyimide) substrate.

[0027] According to the present invention, the substrate thickness is preferably 500 μm, the 2D COF film thickness is preferably 7-8 nm, the gold (Au) interdigitated electrode thickness is preferably 60 nm, and the channel length is preferably 500 μm.

[0028] This invention also provides a method for fabricating a two-dimensional covalent organic framework humidity / pressure dual-mode sensor, such as... Figure 2As shown, it includes: Step 1: Inject an aqueous solution of the first monomer into a reaction vessel, then inject an organic solution of the second monomer onto the liquid surface to form an immiscible liquid-liquid interface. The reaction is catalyzed by acetic acid. The preferred reaction time is room temperature and 72 hours. A 2D COF film is formed at the interface. The aqueous solution of the first monomer is obtained by dissolving the first monomer in a mixed solvent composed of 1,4-dioxane and ultrapure water. The preferred volume ratio of 1,4-dioxane to ultrapure water in the mixed solvent is 2:5. The organic solution of the second monomer is obtained by dissolving the second monomer in a solvent, preferably mesitylene. The first monomer is 1,3,5-tris(4-aminophenyl)benzene (TAPB), and the second monomer is selected from one of the following five aldehyde monomers: 2,5-dihydroxyterephthalaldehyde (OHTPA), 2,5-di(2-methoxyethoxy)terephthalaldehyde (2COTPA), 2,5-di[2-(2-methoxyethoxy)ethoxy]terephthalaldehyde (3COTPA). TPA), 2,5-bis[2-[2-(2-methoxyethoxy)ethoxy]ethoxy]terephthalaldehyde (4CO TPA) or 2,5-bis(3,6,9,12-tetraoxatridecane-1-yloxy)terephthalaldehyde (5CO TPA); the molar ratio of the first monomer and the second monomer is preferably 2:3, and the volume ratio of the catalyst to the solvent is preferably 1.1:18.

[0029] According to this invention, the prepared organic phase solution of the second monomer is slowly injected along the beaker wall onto the aqueous phase solution, forming a clear and stable liquid-liquid interface. The reaction system is then allowed to stand at room temperature for 72 hours. During this process, the monomers undergo pre-assembly and condensation reactions at the interface, ultimately growing into a complete and continuous two-dimensional COF film. After the reaction, the film is preferably washed with methanol solvent to remove residual monomers and solvent, finally obtaining a pure two-dimensional COF film. A schematic diagram of the reaction process of the first and second monomers in this invention is shown below. Figure 1 As shown.

[0030] Step 2: Using a mask-assisted thermal evaporation process, gold (Au) interdigitated electrodes are deposited on the surface of a flexible substrate to form a bottom contact structure. The 2D COF thin film prepared in Step 1 is then transferred onto the substrate where the gold interdigitated electrodes are deposited, resulting in a two-dimensional covalent organic framework humidity / pressure dual-mode sensor. The substrate is preferably 2 cm × 2 cm in size and 500 μm thick. According to the present invention, before use, the substrate preferably needs to be ultrasonically cleaned in acetone to remove surface organic contaminants. The cleaned substrate is then immersed in a saturated solution of potassium hydroxide in isopropanol and left to stand for 24 hours. After treatment, the substrate is rinsed with deionized water to remove residual alkali, thereby achieving hydrophilic treatment of the substrate.

[0031] Device structure parameters: The sensor prepared in this embodiment has a two-dimensional COF film thickness of about 7-8 nm, a gold interdigitated electrode thickness of about 60 nm, and an electrode channel length of 500 μm.

[0032] The present invention also provides the application of the above-mentioned two-dimensional covalent organic framework humidity / pressure dual-mode sensor in wearable respiratory systems.

[0033] This invention also provides the application of the above-mentioned two-dimensional covalent organic framework humidity / pressure dual-mode sensor in a pulse health monitoring system.

[0034] Specific applications are as follows: 1. Dynamic monitoring of respiratory pattern and intensity By integrating sensors into the mask, different breathing patterns can be clearly distinguished and exercise intensity can be fed back: Pattern recognition: In the resting state, the nasal breathing pattern is a stable signal with a low frequency (about 13 times / minute) and a small current response amplitude (about 2-3 μA); the mouth breathing frequency is about 13 times / minute, and the current response amplitude is significantly enhanced to 5-6 μA due to the greater humidity of the exhaled gas.

[0035] Intensity Feedback: During exercise, the sensor can synchronously capture dramatic changes in breathing. For example, during running, the nasal breathing rate can increase sharply to approximately 45 breaths per minute, and the response waveform of a single respiratory cycle also changes accordingly. This provides precise data support for quantitatively assessing exercise intensity and monitoring the body's real-time status.

[0036] 2. Real-time sensing and recording of pulse waveforms By integrating sensors into a wristband worn on the inner wrist near the radial artery, continuous pulse monitoring is achieved. At rest, the device stably records a steady pulse of approximately 74 beats per minute with a clear, complete waveform and distinct characteristic points, consistent with the typical heart rate of a healthy adult. During exercise, the device can record rapid pulses up to 155 beats per minute, with results consistent with current commercially available fitness trackers, demonstrating excellent consistency. This design is suitable for daily cardiac health monitoring, and its high sensitivity provides reliable physiological data support for real-time assessment of the cardiovascular system.

[0037] The present invention will be further described in detail below through specific embodiments. All raw materials involved in the embodiments were purchased through commercial channels.

[0038] Example 1 2D COF TAPB-4CO TPA Thin film preparation First, weigh out 1.4 mg (4 × 10⁻⁶). -6 1,3,5-tris(4-aminophenyl)benzene (TAPB) was dissolved in 14 mL of a solvent consisting of 1,4-dioxane and ultrapure water at a volume ratio of 2:5. This solution was poured into the bottom of a 50 mL clean beaker to form a homogeneous static aqueous phase. Subsequently, 2.75 mg (6 × 10⁻⁶ mol) of TAPB was weighed out. -6 2,5-bis[2-[2-(2-methoxyethoxy)ethoxy]ethoxy]terephthalaldehyde (4CO TPA) was dissolved in 18 mL of mesitylene. This organic phase solution was slowly and steadily added along the inner wall of a beaker to the upper layer of the aqueous phase solution, eventually forming a clear and stable liquid-liquid interface. 1.1 mL of glacial acetic acid was added to the system as a catalyst, and the reaction was allowed to stand at room temperature for 3 days. After the reaction was complete, the generated 2DCOF... TAPB-4CO TPA The film was carefully separated from the interface and washed three times with methanol solvent to completely remove residual monomers and catalysts, finally obtaining pure COF film material.

[0039] Figure 3 This invention is a 2D COF TAPB-4CO TPA Morphology and macroscopic characterization of thin films; among which Figure 3 a) An atomic force microscopy (AFM) image of the thin film and the corresponding height profile. Measurements show that the film thickness is approximately 7.2 nm and the surface roughness is as low as 0.87 nm (approximately two atomic layers), confirming its ultrathin and uniform physical properties. Figure 3 b) is an optical microscope image of the thin film. The image shows that the film surface is continuous, smooth, and free of macroscopic defects; Figure 3 c) is a scanning electron microscope (SEM) image of the thin film. The image shows the film transferred intact and undamaged onto the TEM copper mesh support, demonstrating the film's excellent mechanical integrity and flexibility, which meets the requirements for subsequent device fabrication and transfer. Figure 3 d) is a photograph of the thin film transferred onto a silicon wafer with a diameter of approximately 5 cm. This demonstrates that the synthesis method of the present invention has the capability for large-scale wafer-level fabrication.

[0040] Figure 4 This invention is a 2D COF TAPB-4CO TPA Chemical structure analysis of thin films; among which Figure 4a)-4c) are Fourier transform infrared spectra. The characteristic stretching vibration peak of the imine bond (-C=N-) is visible in the spectra, while the characteristic peaks of the original amino group (-NH2) and aldehyde group (-C=O) are significantly weakened or disappeared, proving that the condensation reaction occurred and the imine bond was successfully formed; Figure 4 d) X-ray photoelectron spectroscopy. This demonstrates the formation of the imine nitrogen (-C=N-) chemical environment, which corroborates the infrared spectroscopy findings and jointly verifies the chemical composition and structure of the target COF material.

[0041] Figure 5 This is the X-ray diffraction pattern of the 2D COF thin film of this invention. The sharp Bragg diffraction peaks appearing in the pattern indicate that the prepared COF thin film has a highly ordered crystalline structure, proving its good crystallinity.

[0042] Example 2 2D COF TAPB-OH TPA Thin film preparation The experimental conditions and procedures were the same as in Example 1, except that 1 mg of OH TPA monomer was dissolved in mesitylene solvent and reacted for 3 days under acetic acid catalysis to obtain 2D COF. TAPB-OH TPA film.

[0043] Example 3 2D COF TAPB-2CO TPA Thin film preparation The experimental conditions and procedures were the same as in Example 1, except that 1.7 mg of 2CO TPA monomer was dissolved in mesitylene solvent and reacted for 3 days under acetic acid catalysis to obtain 2D COF. TAPB-2CO TPA film.

[0044] Example 4 2D COF TAPB-3CO TPA Thin film preparation The experimental conditions and procedures were the same as in Example 1, except that 2.3 mg of 3CO TPA monomer was dissolved in mesitylene solvent and reacted for 3 days under acetic acid catalysis to obtain 2D COF. TAPB-3CO TPA film.

[0045] Example 5 2D COF TAPB-5CO TPA Thin film preparation The experimental conditions and procedures were the same as in Example 1, except that 3.3 mg of 5CO TPA monomer was dissolved in mesitylene solvent and reacted for 3 days under acetic acid catalysis to obtain 2D COF TAPB-5CO TPA film.

[0046] Example 6: Fabrication of a two-dimensional covalent organic framework humidity / pressure dual-mode sensor Substrate pretreatment: The polyimide substrate was ultrasonically cleaned in acetone to remove surface organic contaminants. The cleaned substrate was then immersed in a saturated solution of potassium hydroxide in isopropanol and allowed to stand for 24 hours. After treatment, the substrate was rinsed with deionized water to remove residual alkali, thus achieving hydrophilication of the substrate.

[0047] Electrode preparation: Interdigitated electrodes were fabricated using a thermal evaporation process. A patterned mask with a thickness of 0.1 mm was tightly coated onto a pretreated PI substrate, followed by the deposition of a 60 nm thick gold layer in a vacuum chamber to form the desired electrode structure.

[0048] Thin film transfer and device integration: The two-dimensional COF thin films synthesized in Examples 1-5 are transferred to the above-mentioned polarized substrate: the electrode substrate is inserted into the liquid surface below the film, and then the electrode substrate is slowly raised from below the liquid surface. Through capillary action and van der Waals forces, the floating film is accurately retrieved and attached to the device surface to complete the device integration.

[0049] Device performance testing Test system setup: The sensor devices were fixed in a sealed test chamber, and electrical signals were acquired using a Keithley 2612A source meter. During the test, a 3V DC bias voltage was applied to all devices, and the current response was recorded in real time.

[0050] Humidity response test: A series of relative humidity environments (2%, 11%, 33%, 43%, 57%, 75%, 85%, 98%) were precisely created at 25°C by introducing dry N2 gas or placing different saturated salt solutions (including LiCl, MgCl2, CuCl, K2CO3, NaBr, NaCl, KCl, and Cu2SO4) into a sealed cavity. At each humidity point, the device was exposed for 10 minutes, and electrical data were recorded after its response stabilized.

[0051] Figure 6 The figure shows the current response curve of the 2D COF film humidity sensor of the present invention; Figure 6 a) For 2DCOF TAPB-OH TPA , Figure 6 b) is a 2D COF TAPB-2CO TPA , Figure 6 c) is 2D COF TAPB-3CO TPA , Figure 6 d) is 2DCOF TAPB-4CO TPA , Figure 6 e) is 2D COF TAPB-5CO TPAAs can be seen, all devices exhibit significant humidity response characteristics, with current values ​​increasing from the pA level to the μA level as ambient humidity rises, spanning six orders of magnitude. This wide detection range and high current signal under high humidity conditions contribute to improved detection accuracy and equipment compatibility.

[0052] Table 1 presents the statistical results and response range of the 2D COF film humidity sensor of this invention. Among all samples, the TAPB-4CO TPA-based sensor exhibited the highest responsivity at 98% RH, with a sensitivity of 80875% per%RH. This superior performance is attributed to the abundant hydrophilic hydroxyl groups on its surface providing numerous water molecule adsorption sites, while the moderate side chain length effectively inhibits excessive swelling of the material while promoting moisture diffusion, thus maintaining the structural stability of the film. (The fitted sensitivity of the device in the low humidity region (2%–33% RH) and the high humidity region (33%–98% RH) is the slope of the responsivity-relative humidity curve. The sensitivity calculation formula is: S = ΔResponse / ΔRH. Where, ΔResponse = (IRH - I0) / I0, IRH is the current value at a certain humidity, I0 is the reference current value at the initial humidity (2% RH), and ΔRH is the corresponding change in relative humidity.) Table 1

[0053] Figure 7 The figure shows the response / recovery time curve of the 2D COF film humidity sensor of this invention; Figure 7 a) is 2DCOF TAPB-OH TPA , Figure 7 b) is a 2D COF TAPB-2CO TPA , Figure 7 c) is 2D COF TAPB-3CO TPA , Figure 7 d) is 2DCOF TAPB-4CO TPA , Figure 7 e) is 2D COF TAPB-5CO TPA As can be seen, all devices exhibit fast response and recovery characteristics. Among them, 2D COF TAPB-4CO TPA Its performance is particularly outstanding, with response and recovery times of 0.06 s and 0.24 s, respectively. This excellent kinetic performance is attributed to two factors: the abundant hydrophilic alkoxy groups on the material surface enable rapid capture and release of water molecules; and its nanoscale ultrathin and flat film structure not only greatly promotes the adsorption / desorption kinetics of water molecules but also ensures good contact with the electrode.

[0054] Figure 8 This invention is a 2D COF TAPB-4CO TPAThe membrane's operating temperature, selectivity, flexible sensing, and cycle stability curves are shown in the figure. Figure 8 a) is the operating temperature curve. The device exhibits good linear response in the range of 25–75℃, indicating that it can work stably under different ambient temperatures. Figure 8 b) is the selectivity curve. The sensor shows no obvious response to common gas molecules in the atmosphere and respiration, as well as weakly polar volatile organic compounds, demonstrating excellent selectivity and making it particularly suitable for complex gas environments. Figure 8 c) shows the flexible sensing curve. After 1000 bending cycle tests, the sensing performance curve of the device did not change significantly, proving its excellent mechanical flexibility and structural durability. Figure 8 d) is the cyclic stability curve. In 1000 consecutive humidity cycles, the sensor response remained consistent and no significant signal attenuation was observed, demonstrating excellent long-term operational reliability.

[0055] These combined advantages enable the sensor to adapt to complex real-world application environments and have broad application prospects in fields such as wearable respiratory monitoring.

[0056] To evaluate the performance of humidity sensors in real-world scenarios, a wearable respiratory monitoring experiment was conducted. Volunteers wore devices integrating 2D COF... TAPB-4CO TPA The humidity sensor-equipped mask monitors the current in real time during walking and running.

[0057] Figure 9 This invention is a 2D COF TAPB-4CO TPA Performance curves of thin-film sensors in real-time respiratory monitoring. Figure 9 a) and Figure 9 (b) These are the real-time monitoring curves of nasal breathing from the sensor. The data shows that the respiratory cycle is approximately 4.50 s / breath (about 13 breaths / minute) during walking, and increases to 1.33 s / breath (about 45 breaths / minute) during running. Figure 9 c) and Figure 9 d) shows the monitoring results for mouth breathing. During walking, the respiratory cycle was approximately 4.57 s / breath (about 13 breaths / minute), while during running it shortened to 1.32 s / breath (about 45 breaths / minute). Under the same exercise conditions, because mouth breathing typically carries a larger amount of water vapor, the electrical response signal intensity generated by mouth breathing is significantly higher than that of nasal breathing. Furthermore, as exercise intensity increases, the respiratory interval during running is significantly shorter than that during walking, consistent with the physiological law that respiratory rate increases with metabolic demand.

[0058] Figure 10The results demonstrate humidity monitoring data under non-contact conditions. The device exhibits a sensitive response to minute amounts of moisture on the fingertip as the fingertip is repeatedly brought close to (approximately 5 mm away) and moved away. These results fully demonstrate the reliability and application potential of this sensor in the field of sensitive, real-time signal monitoring for dynamic non-contact sensing.

[0059] Stress response test: First, the two-dimensional COF film was allowed to fully adsorb water molecules in a high-humidity environment until equilibrium was reached. Then, it was placed in a constant humidity environment of 98%RH. Subsequently, external pressure was applied to the device, and changes in its current signal were monitored to evaluate its piezoresistive response characteristics under humid conditions.

[0060] To evaluate the performance of pressure sensors in real-world scenarios, the sensors were integrated into wristband devices or neck patches and tested by volunteers.

[0061] Figure 11 It displays the real-time monitoring results of human pulse signals. Among them... Figure 11 a) is the pulse wave of the radial artery at rest (approximately 74 beats per minute). Figure 11 b) The pulse wave of the radial artery at rest within 6.5 seconds (simultaneous presence of the percussion wave (P wave) and tension wave (T wave)). c) The pulse wave of the radial artery at exercise (fusion of the percussion wave (P wave) and tension wave (T wave), with the dicrotic wave (D wave) visible, approximately 155 beats per minute). Monitoring of the radial artery at rest shows that the sensor successfully captured a clear and stable pulse waveform. Each heartbeat cycle corresponds to two consecutive characteristic peaks, corresponding to the percussion wave (P wave) and tension wave (T wave) in the clinical pulse wave. The calculated pulse rate was approximately 74 beats per minute, within the normal resting heart rate range of a healthy adult. During exercise, the pulse rate increased to approximately 155 beats per minute, and the waveform showed significant fusion between different peaks, with the pulse morphology becoming sharper and stronger. A third characteristic peak, the dicrotic wave (D wave), further emerged in the waveform, providing the possibility for more in-depth pathological analysis. The above monitoring results are consistent with the frequency recorded by currently commercial fitness trackers, verifying the application potential of this sensor in real-time, non-invasive cardiovascular physiological monitoring.

Claims

1. A two-dimensional covalent organic framework humidity / pressure dual-mode sensor, characterized in that, The sensor, from bottom to top, comprises: a substrate, interdigitated gold electrodes disposed on the substrate, and a 2D COF thin film disposed on the interdigitated gold electrodes; The 2D COF film is synthesized through a liquid-liquid interface.

2. The two-dimensional covalent organic framework humidity / pressure dual-mode sensor according to claim 1, characterized in that, The substrate is a PI substrate.

3. The two-dimensional covalent organic framework humidity / pressure dual-mode sensor according to claim 1, characterized in that, The substrate has a thickness of 500 μm, the 2D COF film has a thickness of 7-8 nm, the gold interdigitated electrode has a thickness of 60 nm, and the channel length is 500 μm.

4. The method for fabricating a two-dimensional covalent organic framework humidity / pressure dual-mode sensor according to claim 1, characterized in that, include: Step 1: Inject an aqueous solution of the first monomer into the reaction vessel, and then inject an organic solution of the second monomer onto the liquid surface to form an immiscible liquid-liquid interface. Using acetic acid as a catalyst, a 2D COF film is formed at the interface. The first monomer is TAPB, and the second monomer is OH TPA, 2CO TPA, 3CO TPA, 4CO TPA, or 5CO TPA. Step 2: Deposit gold interdigitated electrodes on the substrate surface using a mask to form a bottom contact structure. Then transfer the 2D COF thin film prepared in Step 1 onto the substrate on which the gold interdigitated electrodes are deposited to obtain a two-dimensional covalent organic framework humidity / pressure dual-mode sensor.

5. The method for fabricating a two-dimensional covalent organic framework humidity / pressure dual-mode sensor according to claim 4, characterized in that, The molar ratio of the first monomer and the second monomer mentioned in step one is 2:

3.

6. The method for fabricating a two-dimensional covalent organic framework humidity / pressure dual-mode sensor according to claim 4, characterized in that, The reaction temperature in step one is room temperature, and the reaction time is 72 hours.

7. The application of the two-dimensional covalent organic framework humidity / pressure dual-mode sensor as described in claim 1 in a wearable respiratory system.

8. The application of the two-dimensional covalent organic framework humidity / pressure dual-mode sensor as described in claim 1 in a pulse health monitoring system.

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