Nitric oxide sensor based on radical ligand metal organic framework material and preparation method thereof

Abstract

The application discloses a nitric oxide sensor based on a free radical ligand metal organic framework material and a preparation method thereof. + The TTF ligand in the metal organic framework crystal structure is oxidized into TTF by iodization, free radicals are obtained, and metal organic framework materials with Cd, Co and Zn as metal centers are prepared. Based on the metal organic framework material, a nitric oxide sensor is further prepared, and the experimental detection limit of the sensor for NO reaches 3 ppb.

Description

Technical Field

[0001] This invention relates to the field of gas sensor technology, and in particular to a nitric oxide sensor based on free radical ligand metal-organic framework materials and its preparation method. Background Technology

[0002] Nitric oxide, besides being a common air pollutant with quantitative detection significance, is also an important biomarker. It is crucial not only in cellular physiological processes but also as a vital non-invasive marker for respiratory diseases. Exhaled nitric oxide concentration (FeNO) is widely used as a clinical diagnostic method for asthma and is also an important indicator for the diagnosis of chronic obstructive pulmonary disease (COPD) and the respiratory effects of environmental exposure. Therefore, the development of a real-time sensing platform for FeNO detection has attracted considerable interest.

[0003] Currently, sensors based on chemiluminescence and electrochemical detection technologies have demonstrated their promise and practicality in real-time FeNO detection. However, their requirement for complex experimental equipment and stringent testing environments hinders their integration and portability. Chemielectric sensors, which respond to the concentration of the analyte via channel current signals, are simple, economical, and easy to integrate; however, their high detection limit restricts their application in clinical FeNO testing (requiring a limit of less than 25 ppb).

[0004] Metal-organic frameworks (MOFs) possess tunable metal (cluster) centers, ligand compositions, and pore structures, which are beneficial for gas adsorption and multi-site reactions. The emergence and development of conductive MOFs have further promoted the feasibility study of MOFs for use in chemiluminescence sensors. However, due to the lack of suitable reaction site design and regulation, although the detection limit of MOFs for NO is significantly lower than that of two-dimensional materials, it still cannot meet the requirements for FeNO detection. In addition, due to similar sensing mechanisms, interfering gases in exhaled breath, such as volatile organic compounds, can also interfere with the FeNO test signal. Summary of the Invention

[0005] Purpose of the invention: The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a nitric oxide sensor based on free radical ligand metal-organic framework materials and its preparation method.

[0006] To achieve the above technical objectives, this invention proposes a nitric oxide sensor based on a free radical ligand metal-organic framework material. The nitric oxide sensor comprises a free radical ligand metal-organic framework material, wherein the free radical ligand metal-organic framework material is formed by oxidizing the tetrathiofulvalene tetraphenylcarboxylic acid (TTF) ligand in the metal-organic framework crystal structure to TTF· via iodination. + Free radicals, specific preparation methods include:

[0007] A100: dissolving cadmium nitrate tetrahydrate, cobalt nitrate hexahydrate and zinc nitrate hexahydrate in a first solvent respectively, and performing ultrasonic dissolution to obtain a metal salt solution;

[0008] A200: dissolving a tetrathiafulvalene tetracarboxylic acid TTF ligand in a second solvent and performing ultrasonic dissolution to obtain a ligand solution;

[0009] A300: mixing the metal salt solution and the ligand solution, carrying out a heating reaction, and then naturally cooling to room temperature;

[0010] A400: rinsing with a rinsing solution to obtain three metal-organic framework materials respectively corresponding to different metals;

[0011] A500: respectively soaking the three metal-organic framework materials in an organic solvent containing elemental iodine for a certain period of time, to obtain iodinated metal-organic framework materials Cd2[TTF](I3)x, Co2[TTF](I3)x and Zn2[TTF](I3)x respectively, wherein 0<x<0.5, and x is I3 in the iodinated metal-organic framework material - ion content.

[0012] wherein, in step A100, the first solvent is a mixed solvent containing ethanol and deionized water, the volume ratio of ethanol to deionized water ranges from 1:0.8 to 1:1.2, preferably, the volume ratio of ethanol to deionized water is 1:1, by which a material with good morphology can be obtained.

[0013] in the metal salt solution, the mass ratio of cadmium nitrate tetrahydrate to the mixed solvent ranges from 1:50 to 5:1000, the mass ratio of cobalt nitrate hexahydrate to the mixed solvent ranges from 1:50 to 5:1000, and the mass ratio of zinc nitrate hexahydrate to the mixed solvent ranges from 1:50 to 5:1000; preferably, the mass ratio of cadmium nitrate tetrahydrate to the mixed solvent ranges from 1:50 to 1:80, the mass ratio of cobalt nitrate hexahydrate to the mixed solvent ranges from 1:50 to 1:80, and the mass ratio of zinc nitrate hexahydrate to the mixed solvent ranges from 1:50 to 1:80.

[0014] in step A200, the second solvent is a mixed solution containing N,N-dimethylformamide and ethanol, the volume ratio of N,N-dimethylformamide to ethanol ranges from 5:1 to 2.5:1, preferably, when the volume ratio is 3:1, crystals with good morphology can be obtained; the mass ratio of the tetrathiafulvalene tetracarboxylic acid TTF ligand to the mixed solvent ranges from 1:100 to 1:200; the volume ratio of the metal salt solution to the ligand solution ranges from 10:1 to 1:1.

[0015] When heating in step A300, first heat at 60°C for 6 hours, then raise the temperature to 80°C and heat for 24 hours, and let it cool naturally to room temperature after the reaction is complete.

[0016] In step A400, the rinsing solution is N,N-dimethylformamide and ethanol, and the washing is performed sequentially with N,N-dimethylformamide and ethanol.

[0017] In step A500, the metal-organic framework material is soaked in a cyclohexane solution of 0.05-0.1M iodine for 24-48 hours, and then rinsed with cyclohexane.

[0018] The present invention further proposes a method for fabricating the above-mentioned nitric oxide sensor, wherein the nitric oxide sensor comprises a substrate silicon wafer with an oxide layer, titanium interdigitated electrodes, free radical ligand metal-organic framework material, and aluminum-silicon alloy wire; wherein, the titanium interdigitated electrodes are vapor-deposited on the substrate silicon wafer; the free radical ligand metal-organic framework material is dispersed on the interdigitated electrodes by a drop-coating method to form the nitric oxide sensor, and the aluminum-silicon alloy wire is used to connect the interdigitated electrodes and external circuitry.

[0019] The oxide layer has a thickness of 200-300 nm; the substrate silicon wafer is a square with a side length of 1-2 cm; the interdigitated electrode parameters are 5-10 interdigitated electrode pairs, interdigitated electrode width of 2-4 μm, and interdigitated electrode spacing of 1-2 μm; the aluminum-silicon alloy wire length is 1.5-2 cm.

[0020] The free radical ligand metal-organic framework materials prepared by the above method are also within the scope of protection of this invention.

[0021] In one specific embodiment, a method for preparing a nitric oxide sensor based on a free radical ligand metal-organic framework material is described by the following steps:

[0022] S100: A silicon wafer containing an oxide layer is fabricated into a silicon wafer with titanium interdigitated electrodes. The specific steps include: masking the interdigitated electrode pattern on the silicon wafer containing a 275nm oxide layer using ultraviolet lithography; sequentially depositing the adhesion layer of metallic titanium and the electrode layer of metallic gold on the silicon wafer using electron beam evaporation; immersing the silicon wafer in acetone and ultrasonically removing the metal outside the masked electrode area; rinsing the silicon wafer containing the interdigitated electrodes with acetone and isopropanol and drying it with high-purity nitrogen gas to obtain the silicon wafer with interdigitated electrodes.

[0023] S200: A free radical ligand metal-organic framework material is dispersed on an interdigitated electrode using a drop-coating method to obtain a uniformly coated free radical ligand metal-organic framework material-based micro / nano device. The specific steps include: placing the interdigitated electrode silicon wafer obtained in step S100 in a plasma generator for oxygen plasma cleaning, and then placing it on a heating stage for heating; dispersing the free radical ligand metal-organic framework material in ethanol and ultrasonically treating it; then using a pipette to take a quantitative amount of the ethanol dispersion containing the free radical ligand metal-organic framework material and drop-coating it onto the interdigitated electrode; after heating to evaporate the ethanol, a uniformly coated free radical ligand metal-organic framework material-based micro / nano device is obtained.

[0024] S300: Connect the source and drain electrodes of the micro / nano device from step S200 to an external circuit via aluminum-silicon alloy wires to fabricate a nitric oxide sensor based on free radical ligand metal-organic framework material.

[0025] The nitric oxide sensor based on free radical ligand metal-organic framework materials prepared in this invention is applied in nitric oxide detection. This sensor differs from traditional metal-organic framework-based chemiluminescence sensors by innovatively using free radical ligands as the active center, highlighting for the first time the regulatory role of ligands in sensing, and representing a significant breakthrough in sensing mechanism and performance.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) Based on the chemical properties of tetrathiofulvalene tetraphenylcarboxylic acid (TTF), this invention provides an iodine oxidation method to achieve the generation regulation of free radical ligands in metal-organic framework materials, thereby improving the sensitivity, detection limit, specificity and response / recovery time of nitric oxide sensors based on free radical ligand metal-organic framework materials to the level of FeNO detection.

[0028] (2) The nitrogen monoxide sensor based on free radical ligand metal-organic framework material achieves a detection limit of 3 ppb for NO. Thanks to the innovative sensing mechanism, this detection limit is reduced by four orders of magnitude compared with the detection limit of common volatile organic compounds in exhaled air, and can effectively shield the signal interference of other gases (such as acetone and ethanol) in exhaled air.

[0029] (3) By regulating the batch synthesis of a series of metal-organic framework materials with different metal centers, a sensor array can be formed to realize pattern recognition of exhaled gas components.

[0030] (4) Metal-organic framework materials and their sensors are easy to synthesize and prepare, have low unit cost, and belong to the category of room temperature sensors, making them suitable for large-scale production and use. Attached Figure Description

[0031] Figure 1The images show powder XRD patterns of the three metal centers in the free radical ligand metal-organic framework material in the examples.

[0032] Figure 2 The electron paramagnetic resonance (EPR) spectrum centered on Cd in the free radical ligand metal-organic framework material in the examples is shown.

[0033] Figure 3 This is a schematic diagram of the nitric oxide sensor structure based on free radical ligand metal-organic framework material in an embodiment of the present invention;

[0034] Figure 4 The response-recovery curves of nitric oxide sensors fabricated with three typical metal centers in free radical ligand metal-organic framework materials to different concentrations of nitric oxide at room temperature are shown. In the figure, a represents the metal center with Cd, b represents the metal center with Zn, and c represents the metal center with Co. The unit is ppb.

[0035] Figure 5 Response calibration curves of nitric oxide sensors fabricated for three typical metal centers in free radical ligand metal-organic framework materials to different concentrations of nitric oxide at room temperature;

[0036] Figure 6 Comparison of the detection limits of nitric oxide, ethanol and acetone by nitric oxide sensors fabricated from free radical ligand metal-organic framework materials at room temperature;

[0037] Figure 7 Stability of a nitric oxide sensor fabricated from a Co-centered radical ligand metal-organic framework material during long-term testing;

[0038] Figure 8 Principal component analysis of the response of an array of free radical ligand metal-organic framework materials to NO and volatile organic compounds. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0040] Example 1: Preparation of metal-organic framework materials based on free radical ligands.

[0041] Metal-organic framework materials based on free radical ligands were prepared according to the following steps:

[0042] (1) Dissolve 6 mg of cadmium nitrate tetrahydrate, cobalt nitrate hexahydrate or zinc nitrate hexahydrate in 1.25 mL of a mixed solution containing 0.625 mL of ethanol and 0.625 mL of deionized water, respectively, and sonicate for 15 minutes to dissolve, to obtain three metal salt solutions: cadmium nitrate solution, cobalt nitrate solution and zinc nitrate solution.

[0043] (2) Dissolve 3 mg of tetrathiofulvalene tetraphenylcarboxylic acid TTF ligand in 0.12 mL of a mixed solution containing N,N-dimethylformamide (0.09 mL) and ethanol (0.03 mL), and sonicate for 15 minutes to dissolve, thus obtaining the ligand solution;

[0044] (3) Mix the metal salt solutions (cadmium nitrate solution, cobalt nitrate solution and zinc nitrate solution) with the ligand solution respectively, heat the mixture and then allow it to cool naturally to room temperature; specifically, mix the metal salt solution and the ligand solution, shake well, put it into a 15mL hard pressure-resistant glass tube, place it in a constant temperature oven, heat it at 60℃ for 6 hours, then raise the temperature to 80℃ and heat it for 24 hours. After the reaction is completed, allow it to cool naturally to room temperature and filter to obtain a solid sample;

[0045] (4) Rinse three times with N,N-dimethylformamide and then rinse three times with ethanol to obtain pure metal-organic framework materials, and obtain metal-organic framework materials of three different metals respectively.

[0046] (5) The three metal-organic framework materials were immersed in a 0.1M cyclohexane solution of elemental iodine for 48 hours and then rinsed three times with cyclohexane to obtain the iodinated metal-organic framework material Cd2[TTF](I3). x Co2[TTF](I3) x Zn2[TTF](I3) x , where x is 0.33.

[0047] Figure 1 The images show powder XRD patterns of the three metal centers. Powder X-ray diffraction (PXRD) of the samples before and after iodization shows similar peak positions, indicating that the isomorphic crystal structure of the metal-organic framework materials before and after iodization, and the structural stability of the free radical ligand metal-organic framework materials, are maintained after iodine oxidation treatment. Electron paramagnetic resonance (EPR) of the solid samples at 100 K further confirms the effectiveness of chemical doping. Figure 2 All EPR spectra (recorded under identical conditions) showed a set of axial g values ​​(g). x，y =2.007 and g z =2.011), this is TTF .+ Typical values ​​for free radicals. The EPR signal of free radical ligand metal-organic framework materials significantly increased after iodine oxidation treatment, directly verifying the TTF. .+ The concentration increased, while the initial Cd2[TTF] showed a very weak signal value in the EPR spectrum.

[0048] Example 2: Nitric oxide sensor based on free radical ligand metal-organic framework material.

[0049] This embodiment provides a nitric oxide sensor based on a radical ligand metal-organic framework (MOF) material, comprising a silicon substrate with a 275nm silicon oxide layer, titanium interdigitated electrodes, the radical ligand MOF material, and an aluminum-silicon alloy wire. The titanium interdigitated electrodes are adhered to the silicon substrate, the radical ligand MOF material is dispersed on the interdigitated electrodes using a drop-coating method, and the aluminum-silicon alloy wire connects the interdigitated electrodes to an external circuit, which includes a power supply and a digital source meter. The silicon substrate is a square with a side length of 2cm; the interdigitated electrode parameters are: 9 pairs of interdigitated electrodes, an interdigital width of 2μm, and a distance of 2μm between adjacent interdigitated electrodes; the aluminum-silicon alloy wire has a length of 1.5-2cm.

[0050] The specific preparation method is as follows:

[0051] S100: A silicon wafer containing an oxide layer is fabricated into a silicon wafer with attached interdigitated electrodes. Specifically, this involves: uniformly spin-coating photoresist onto the silicon wafer containing a 275nm oxide layer using a spin coater. The spin coater speed is 600 rpm for 6 seconds in the first stage and 3000 rpm for 30 seconds in the second stage. The silicon wafer with photoresist is then placed on a heating stage and heated at 170°C for 10 minutes. An interdigitated electrode pattern is then masked onto the silicon wafer using ultraviolet lithography. Subsequently, 50nm of titanium and 100nm of gold are sequentially deposited onto the silicon wafer using electron beam evaporation. The interdigitated electrodes connect the metal-organic framework material and the external circuitry; titanium serves as the adhesive layer, and gold as the electrode material.

[0052] The silicon wafer coated with titanium gold was immersed in acetone and ultrasonically removed the metal layer outside the interdigitated electrode area. The silicon wafer with interdigitated electrodes was then rinsed with acetone and isopropanol, and then dried with high-purity nitrogen to obtain a silicon wafer with interdigitated electrodes attached.

[0053] S200: A uniformly coated metal-organic framework (MOF) based micro / nano devices are obtained by dispersing free radical ligand metal-organic framework materials onto interdigitated electrodes using a drop-coating method. Specifically, this includes:

[0054] The silicon wafer with interdigitated electrodes obtained in step S100 was placed in a plasma generator and cleaned with oxygen plasma for 10 minutes, and then placed on a heating stage at 45°C for later use. 5 mg of free radical ligand metal-organic framework material was dispersed in 1 mL of ethanol and sonicated for 5 minutes. Then, 4 μL of the ethanol dispersion containing the metal-organic framework material was pipetted onto the interdigitated electrodes. After the ethanol evaporated, a uniformly distributed metal-organic framework material-based micro / nano device was obtained. The free radical ligand metal-organic framework material was prepared and synthesized using the above-described method for preparing free radical ligand metal-organic framework materials.

[0055] S300: Using a wire bonding machine, the source and drain electrodes of the micro / nano device from step S200 are connected to the external circuit via aluminum-silicon alloy wires to fabricate a nitric oxide sensor based on a free radical ligand metal-organic framework material, such as... Figure 3 As shown.

[0056] The prepared nitric oxide sensor based on free radical ligand metal-organic framework material can be used to detect nitric oxide.

[0057] The working principle is as follows: When the nitric oxide sensor based on a free radical ligand metal-organic framework is placed in an inert carrier gas of nitrogen, the sensor's conductivity remains stable and unresponsive. When nitric oxide molecules are introduced, the free radical nitric oxide molecules and the free radical ligands in the metal-organic framework interact strongly, changing the electronic state / carrier concentration on the sensor surface and thus altering the sensor's conductivity. We define the sensor's response as:

[0058]

[0059] Where G1 is the conductivity of the sensor when nitric oxide is introduced, and G0 is the conductivity of the sensor in nitrogen gas.

[0060] This invention provides a method for synthesizing free radical ligand metal-organic framework materials, which enables the metal-organic framework to possess both a porous structure and highly reactive free radical ligands. Based on the synthesized free radical ligand metal-organic framework, specific detection of nitric oxide can be achieved, and the sensor exhibits high sensitivity, low detection limit, and excellent long-term stability.

[0061] This invention uses a silicon wafer with a 200-300nm oxide layer as the device substrate, on which vapor-deposited titanium interdigitated electrodes are attached. A free radical ligand metal-organic framework material is dispersed onto the interdigitated electrodes using a drop-coating method to form a sensor device. The free radical ligand TTF· is generated via iodine oxidation. + It exhibits a specific chemical reaction with nitric oxide, enabling the detection of nitric oxide concentrations as low as 3 ppb. Furthermore, the sensor device of this invention features a simple structure, low power consumption, and small size. More importantly, due to its different sensing mechanism, the nitric oxide sensor based on free radical ligand metal-organic framework materials has a detection limit for nitric oxide that is four orders of magnitude lower than that of common volatile organic compounds in exhaled breath, such as ethanol and acetone. It also demonstrates excellent long-term stability, meeting the requirements for chemielectric sensors in FeNO detection.

[0062] The fabricated device is encapsulated in a polydimethylsiloxane (PDMS) cavity to allow for the injection of a target gas at a specific concentration. Nitric oxide (NO) is detected by mixing high-purity nitrogen and 600 ppb nitric oxide at different volume ratios to generate NO gas of varying concentrations. For volatile organic compound (VOC) detection, dried nitrogen is vaporized by passing it through an ethanol and acetone solution, then mixed with pure nitrogen via a gas flow meter to prepare the target gas. The IT curve of the device is collected using an external circuit with a 1V bias. See [reference needed]. Figures 4-8 The performance evaluation is as follows:

[0063] When using the nitric oxide sensor based on free radical ligand metal-organic framework materials of the present invention for nitric oxide detection, such as Figure 4 As shown, the sensor response increases with increasing gas concentration, and the sensor's lowest detection limit for nitric oxide reaches 3 ppb. Figure 5 The calibration curves of the response of a nitric oxide sensor based on a radical ligand metal-organic framework (MOF) as a function of nitric oxide concentration are presented. All curves show excellent linearity within the test range, with the Co-centered MOF sensor exhibiting the highest relative response. Figure 6 The detection limits of a typical Co-centered radical ligand-based metal-organic framework (MOF) nitric oxide sensor for nitric oxide, ethanol, and acetone are shown. The detection limit for nitric oxide is 3 ppb, four orders of magnitude lower than that for ethanol and acetone, demonstrating excellent shielding against interfering gases in exhaled breath. Meanwhile, the detection lines of nitric oxide sensors with other metal centers are consistent, differing only in response intensity. Furthermore, principal component analysis was performed on arrays composed of radical ligand MOFs with three different metal centers, such as... Figure 8 As shown, the confidence intervals of the three gases can be clearly distinguished by principal component 1 and principal component 2, and they do not overlap, indicating the sensor's ability to distinguish between exhaled species. Furthermore, Figure 7 The results indicate that the nitric oxide sensor based on radical ligand metal-organic framework materials showed no significant fluctuations in relative response during long-term testing, and its long-term stability met the requirements of the FeNO testing environment. These results demonstrate the broad application prospects of the radical ligand metal-organic framework material nitric oxide sensor in nitric oxide detection, especially in FeNO detection.

[0064] All parts not covered in this invention are the same as or implemented using existing technology. The above description, in conjunction with specific embodiments, provides a further detailed explanation of the invention and should not be construed as limiting the specific implementation of the invention to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the invention, and all such modifications and substitutions should be considered within the scope of protection of this invention.

Claims

1. A nitric oxide sensor based on a free radical ligand metal-organic framework material, characterized in that, The said nitric oxide sensor comprises a radical ligand metal-organic framework material, wherein The said radical ligand metal-organic framework material is prepared by the following method: A100: dissolving cadmium nitrate tetrahydrate, cobalt nitrate hexahydrate and zinc nitrate hexahydrate in a first solvent respectively, and performing ultrasonic dissolution to obtain a metal salt solution; A200: dissolving a tetrathiafulvalene tetracarboxylic acid TTF ligand in a second solvent, and performing ultrasonic dissolution to obtain a ligand solution; A300: mixing the metal salt solution and the ligand solution, carrying out a heating reaction, and then naturally cooling to room temperature; A400: rinsing with a rinsing solution to obtain three kinds of metal-organic framework materials of different metals respectively; A500: respectively soaking the three kinds of metal-organic framework materials in an organic solution of elemental iodine for a certain period of time, to obtain iodinated metal-organic framework materials Cd2[TTF] (I3)x, Co2[TTF] (I3)x, Zn2[TTF] (I3)x respectively, wherein 0<x<0.5, the said nitric oxide sensor comprises a silicon substrate with an oxide layer, titanium-gold interdigitated electrodes, the radical ligand metal-organic framework material and an aluminum-silicon alloy wire; wherein the titanium-gold interdigitated electrodes are evaporated on the silicon substrate; the radical ligand metal-organic framework material is dispersed on the interdigitated electrodes by a drop-casting method to form the nitric oxide sensor, and the aluminum-silicon alloy wire is used to connect the interdigitated electrodes to an external circuit.

2. The nitric oxide sensor according to claim 1, characterized in that, In step A100, the first solvent is a mixed solvent containing ethanol and deionized water, and the volume ratio of ethanol to deionized water ranges from 1:0.8 to 1:1.

2.

3. The nitric oxide sensor according to claim 1, characterized in that, In the metal salt solution, the mass ratio of cadmium nitrate tetrahydrate to the mixed solvent ranges from 1:50 to 5:1000, the mass ratio of cobalt nitrate hexahydrate to the mixed solvent ranges from 1:50 to 5:1000, and the mass ratio of zinc nitrate hexahydrate to the mixed solvent ranges from 1:50 to 5:1000.

4. The nitric oxide sensor according to claim 1, characterized in that, In step A200, the second solvent is a mixed solution containing N,N-dimethylformamide and ethanol, the volume ratio of N,N-dimethylformamide to ethanol ranges from 5:1 to 2.5:1; the mass ratio of the tetrathiafulvalene tetracarboxylic acid TTF ligand to the mixed solvent ranges from 1:100 to 1:200; the volume ratio of the metal salt solution to the ligand solution ranges from 10:1 to 1:

1.

5. The nitric oxide sensor according to claim 1, characterized in that, In the heating step in step A300, heating is first performed at 60°C for 6 hours, then the temperature is raised to 80°C for heating for 24 hours, and after the reaction is completed, it is naturally cooled to room temperature.

6. The nitric oxide sensor according to claim 1, characterized in that, In step A400, the rinsing solutions are N,N-dimethylformamide and ethanol, and the product is washed with N,N-dimethylformamide and ethanol sequentially.

7. The nitric oxide sensor according to claim 1, characterized in that, In step A500, the metal-organic framework material is soaked in a cyclohexane solution of iodine with a concentration of 0.05-0.1M for 24-48 hours, and then rinsed with cyclohexane.

8. The nitric oxide sensor according to claim 1, characterized in that, The thickness of the oxide layer is 200-300nm; the substrate silicon wafer is a square with a side length of 1-2 cm; the parameters of the interdigitated electrodes are: the number of interdigitated electrode pairs is 5-10, the width of interdigitated fingers is 2-4μm, the gap between adjacent interdigitated fingers is 1-2μm; the length of the aluminum-silicon alloy wire is 1.5-2 cm.

Images