A porous hollow nanocage material SPR fiber isopropanol breath detection sensor

Abstract

The application discloses a kind of porous hollow nanocage material's SPR optical fiber isopropanol breath detection sensor, it is related to optical fiber gas sensing technical field, including optical fiber body, gold film deposited on the surface of optical fiber and the gas sensitive layer coated on the surface of gold film, gas sensitive layer is the Co3O4 porous hollow nanocage material obtained by low-temperature pyrolysis of ZIF-67, the Co3O4 porous hollow nanocage is uniformly loaded on the surface of gold film of optical fiber by dip coating method, and forms SPR sensitive layer.The application solves the problems of high working temperature, low sensitivity and poor selectivity of existing isopropanol sensor, and the key points are as follows: after ultrasonic coordination of 2-methylimidazole and cobalt nitrate in methanol, ZIF-67 precursor is obtained by drying, then Co3O4 porous hollow nanocage is obtained by pyrolysis at a temperature increasing rate of 2°C / min to 300°C, and is coated on the surface of gold film of optical fiber.The application can produce obvious SPR response to isopropanol vapor as low as 50ppb at room temperature, and is mainly used for non-invasive breath detection of metabolic diseases such as diabetes.

Description

Technical Field

[0001] This invention relates to the field of fiber optic gas sensing technology, and in particular to an SPR fiber optic isopropanol breath detection sensor made of porous hollow nanocage material. Background Technology

[0002] Breath analysis, as a non-invasive diagnostic method, reflects the body's metabolic state by detecting changes in the types and concentrations of volatile organic compounds (VOCs) in exhaled breath. Studies have shown that isopropanol (IPA) is an important breath biomarker produced during ketone body metabolism in diabetic patients, and its breath concentration is correlated with blood glucose levels. Therefore, developing a highly sensitive and selective isopropanol breath detection sensor is of great significance for the early screening and non-invasive monitoring of diabetes.

[0003] Currently, the detection of isopropanol gas mainly relies on metal oxide semiconductor sensors, with commonly used sensing materials including SnO2, ZnO, and Co3O4. Among them, Co3O4, as a typical p-type semiconductor metal oxide, has abundant Co. 2 + / Co 3 Co3O4 gas-sensitive materials, with their redox pairs, high oxygen vacancy concentration, and excellent catalytic activity, are widely used in VOC gas detection. However, traditional Co3O4 gas-sensitive materials typically exist in the form of solid particles or dense thin films, resulting in limited specific surface area and insufficient exposure of active sites, leading to low sensor response sensitivity. Furthermore, to overcome the material's activation energy barrier, traditional Co3O4 resistive sensors usually need to operate at high temperatures ranging from 200°C to 350°C, resulting in high power consumption, slow start-up, safety hazards, and difficulties in integration with flexible wearable devices.

[0004] In recent years, the method of preparing Co3O4 porous hollow nanocages via pyrolysis using zeolitic imidazolate framework-67 (ZIF-67) as a sacrificial template has attracted attention. ZIF-67 is composed of Co... 2+ With Co 2- Methylimidazole coordination forms a rhombic dodecahedral morphology and abundant microporous structure. After low-temperature pyrolysis, it can be transformed into porous hollow Co3O4 nanocages that retain the precursor morphology, significantly increasing the specific surface area and exposing more active sites. However, existing gas sensors using ZIF-67-derived Co3O4 as the sensing material mostly employ resistive sensing mechanisms, typically operating at temperatures above 300°C, and there is limited research on room-temperature detection of isopropanol.

[0005] Fiber optic surface plasmon resonance (SPR) sensors, using optical signals as the carrier, offer advantages such as resistance to electromagnetic interference, intrinsic safety, remote transmission capability, and ease of miniaturization. However, existing SPR fiber optic gas sensors often employ noble metal nanoparticles or polymer films as the sensitive layer, which still exhibit insufficient selectivity and sensitivity for small-molecule VOCs such as isopropanol, making it difficult to achieve room-temperature detection of low concentrations of isopropanol at the ppb level. Furthermore, traditional electrical gas sensors suffer from poor stability under electromagnetic interference environments, making it difficult to meet the reliable detection requirements of complex exhaled breath samples.

[0006] Therefore, how to combine the advantages of high specific surface area and high active sites of ZIF-67 derived Co3O4 porous hollow nanocages with the optical detection advantages of SPR fiber sensing to construct a breath detection sensor that can operate at room temperature and has high sensitivity and high selectivity for low concentrations of isopropanol is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] To address the shortcomings of existing isopropanol gas sensors, such as high operating temperature, high power consumption, low sensitivity, poor selectivity, and weak resistance to electromagnetic interference, the present invention aims to provide an SPR fiber optic isopropanol breath detection sensor based on ZIF-67 derived Co3O4 porous hollow nanocage material. This sensor can achieve highly sensitive and selective optical detection of low concentrations of isopropanol vapor at room temperature, and is suitable for non-invasive breath monitoring of metabolic diseases such as diabetes.

[0008] To achieve the above objectives, the present invention provides the following technical solution: an SPR fiber optic isopropanol breath detection sensor based on ZIF-67-derived Co3O4 porous hollow nanocage material, comprising an optical fiber body, a gold film deposited on the surface of the optical fiber body, and a gas-sensitive layer coated on the surface of the gold film. The gas-sensitive layer is a Co3O4 porous hollow nanocage material derived from ZIF-67 through low-temperature pyrolysis. The Co3O4 porous hollow nanocage is prepared by pyrolyzing a ZIF-67 precursor at a heating rate of 2°C / min to 300°C and then cooling it in a furnace. The Co3O4 porous hollow nanocage is uniformly loaded onto the surface of the optical fiber gold film by dip coating to form an SPR sensitive layer. The sensor uses the intensity change of the surface plasmon resonance peak as the isopropanol concentration detection signal, with a resonance peak wavelength of approximately 641 nm.

[0009] Preferably, the ZIF-67 precursor is prepared by dissolving 2-methylimidazole in methanol to obtain solution A, dissolving cobalt nitrate hexahydrate in methanol to obtain solution B, quickly pouring solution A into solution B, sonicating at room temperature for 1 hour, centrifuging to collect the precipitate, washing it three times with ethanol, and drying it at 60°C for 24 hours to obtain purple ZIF-67 nanocages.

[0010] Preferably, the molar ratio of 2-methylimidazole to cobalt nitrate hexahydrate is 4:1.

[0011] Preferably, the optical fiber body is a multimode silica optical fiber, and the gold film thickness is 40nm to 50nm.

[0012] Preferably, the sensor is manufactured as follows:

[0013] (1) Fiber pretreatment and gold film deposition: The coating layer of the multimode silica fiber is stripped off, and it is cleaned with anhydrous ethanol and deionized water in sequence and dried with nitrogen. The gold film with a thickness of 40nm to 50nm is deposited on the surface of the fiber by magnetron sputtering as the SPR excitation layer.

[0014] (2) Sensitive layer coating: The prepared Co3O4 porous hollow nanocage is dispersed in anhydrous ethanol to prepare a Co3O4 porous hollow nanocage impregnation dispersion with a concentration of 50 mg / mL. The nanocage is ultrasonically dispersed for 20 min to make the nanocage uniformly dispersed.

[0015] (3) The sensitive area of ​​the gold-plated optical fiber is immersed in the Co3O4 porous hollow nanocage dipping dispersion and coated by dip coating method to uniformly load the Co3O4 porous hollow nanocage on the gold film surface. The coating is applied 14 times, that is, a total of 14 layers of material are coated. After drying at room temperature, the SPR optical fiber isopropanol breath detection sensor of the present invention is obtained. The best performance (highest sensitivity) can be achieved when the number of material layers on the sensor surface reaches 14, that is, when the number of material layers on the sensor surface reaches 14. When the number of layers exceeds 14, the performance will decrease.

[0016] Preferably, the sensor detects isopropanol vapor, with a minimum detectable concentration of 500 ppb.

[0017] Preferably, the sensor operates at room temperature and requires no external heating device.

[0018] The technical effects and advantages of this invention are as follows:

[0019] 1. High-sensitivity detection at room temperature: This invention uses ZIF-67-derived Co3O4 porous hollow nanocages as the SPR sensitive layer, utilizing the high specific surface area and abundant Co provided by its porous hollow structure. 2+ / Co 3+ The active site, combined with the high sensitivity of SPR optical detection, enables a significant response to a low concentration of 50 ppb isopropanol vapor at room temperature. This eliminates the need for the high-temperature heating of 200°C to 350°C required by traditional Co3O4 resistive sensors, significantly reducing power consumption and improving safety in use.

[0020] 2. High selectivity: The sensor of this invention has excellent selectivity for isopropanol. It generates a significant SPR signal response in the presence of 50 ppb isopropanol vapor and a weak response signal in the presence of 50 ppb acetone vapor. This indicates that the sensor can selectively identify isopropanol in the presence of interfering gases such as acetone, which is beneficial for the accurate analysis of complex exhalation samples.

[0021] 3. Anti-electromagnetic interference: This invention adopts the fiber optic SPR optical detection principle, using optical signals as the detection carrier. It is inherently safe, unaffected by electromagnetic interference, and suitable for breath detection in complex clinical environments.

[0022] 4. Simple preparation process and low cost: This invention uses ZIF-67 as a sacrificial template and can prepare Co3O4 porous hollow nanocages through a two-step method of methanol room temperature coordination and low temperature pyrolysis. The raw materials are readily available, the process is controllable and has good reproducibility; the sensitive layer is loaded by dip coating, which is simple and easy to scale up.

[0023] 5. Non-invasive application: The sensor of this invention can be used for non-invasive breath detection of metabolic diseases such as diabetes. It reflects the body's metabolic state by detecting changes in the concentration of isopropanol in exhaled gas, and has clinical application prospects. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of the SPR fiber optic isopropanol breath detection sensor of the present invention;

[0025] Figure 2 This is a schematic diagram of the preparation process of ZIF-67 derived Co3O4 porous hollow nanocages in an embodiment of the present invention.

[0026] Figure 3 This is a graph showing the SPR time response of the sensor of the present invention to 500 ppb isopropanol vapor at room temperature.

[0027] Figure 4 This is a graph showing the SPR time response of the sensor of the present invention to 50 ppb acetone vapor at room temperature.

[0028] In the figure: 1. Optical fiber body; 2. Gold film; 3. Co3O4 porous hollow nanocage gas-sensitive layer. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0030] Example 1: Preparation of ZIF-67 precursor

[0031] 10.8 mmol (0.8868 g) of 2-methylimidazole was weighed and dissolved in 40 mL of methanol. The solution was stirred magnetically until completely dissolved to obtain solution A. 2.7 mmol (0.7858 g) of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) was weighed and dissolved in 40 mL of methanol. The solution was stirred magnetically until completely dissolved to obtain solution B. Solution A was quickly poured into solution B. The mixed solution was sonicated at room temperature for 1 h. After the reaction was completed, the resulting suspension was centrifuged to collect the purple precipitate. The precipitate was washed three times with anhydrous ethanol to remove unreacted raw materials and byproducts. The washed precipitate was dried in a 60°C drying oven for 24 h to obtain the purple ZIF-67 nanocage precursor.

[0032] In this embodiment, the molar ratio of 2-methylimidazole to cobalt nitrate hexahydrate is 4:1. This ratio is beneficial for forming a complete ZIF-67 rhombic dodecahedral morphology, ensuring the crystallinity and morphological uniformity of the precursor.

[0033] Example 2: Preparation of Co3O4 porous hollow nanocages

[0034] The ZIF-67 nanocage precursor prepared in Example 1 was placed in a ceramic crucible and then placed in a muffle furnace. The temperature was slowly increased to 300°C at a heating rate of 2°C / min and held at 300°C for pyrolysis. The mixture was then cooled to room temperature with the furnace to obtain black Co3O4 porous hollow nanocage powder.

[0035] In this embodiment, the slow heating rate is conducive to the ordered pyrolysis of the ZIF-67 framework and the formation of the Co3O4 crystal phase, while preserving the polyhedral cage morphology of the ZIF-67 precursor, forming a porous hollow structure; the pyrolysis temperature of 300°C can ensure the complete oxidation and removal of the ZIF-67 organic ligands, and avoid the excessive growth of Co3O4 grains and the collapse of the pore structure, thereby obtaining a high specific surface area and abundant active sites.

[0036] Example 3: Fabrication of an SPR fiber optic isopropanol breath detection sensor

[0037] (1) Fiber pretreatment and gold film deposition: The coating layer of the multimode silica fiber is stripped off, and it is cleaned with anhydrous ethanol and deionized water in sequence and dried with nitrogen. A gold film with a thickness of 40nm to 50nm is deposited on the surface of the fiber by magnetron sputtering as the SPR excitation layer.

[0038] (2) Sensitive layer coating: Weigh the Co3O4 porous hollow nanocages prepared in Example 2, disperse them in anhydrous ethanol, prepare a dispersion with a concentration of 50 mg / mL, and ultrasonically disperse for 20 min to make the nanocages uniformly dispersed; immerse the sensitive area of ​​the gold-plated optical fiber in the dispersion, and use dip coating method to coat it so that the Co3O4 porous hollow nanocages are uniformly loaded on the surface of the gold film. The coating is done 14 times, that is, a total of 14 layers of material are coated. After drying at room temperature, the SPR optical fiber isopropanol breath detection sensor of the present invention is obtained. The material is coated 14 times, that is, the number of material layers on the sensor surface reaches 14 layers to achieve the best performance (highest sensitivity). When the number of layers exceeds 14, the performance will decrease.

[0039] Example 4: Isopropanol gas-sensing performance test:

[0040] The gas-sensing performance of the sensor of the present invention was tested using a static gas chamber testing system. The testing system included: a halogen tungsten lamp light source with a wavelength range of 360 nm to 2500 nm; a spectrometer with a detection wavelength range of 200 nm to 1100 nm; and a sealed gas chamber with a volume of 20 L. The test was conducted at room temperature of 25°C, and the monitoring wavelength was set to the position of the SPR resonance peak, which is approximately 641 nm.

[0041] During the test, a certain volume of liquid isopropanol was injected into the sealed gas chamber using a microsyringe. After it was completely evaporated, a set concentration of isopropanol gas was obtained. The sensor was placed in the gas chamber, and the change in SPR resonance peak intensity (Counts) over time was recorded.

[0042] The test results are attached. Figure 3 As shown, under a 500 ppb isopropanol vapor atmosphere, the sensor's SPR signal changes significantly over time. The initial signal is approximately 19,300 Counts, and during the response, the signal drops to approximately 19,220 Counts before rebounding, with a response amplitude of approximately 80 Counts. This indicates that the sensor has a significant response capability to a low concentration of 500 ppb isopropanol vapor.

[0043] Example 5: Selective Testing

[0044] To verify the sensor's selectivity for isopropanol, a comparative test was conducted by injecting 50 ppb of acetone vapor into the gas chamber under the same test conditions.

[0045] The test results are attached. Figure 4 As shown: Under a 50ppb acetone vapor atmosphere, the sensor's SPR signal fluctuated between 19215 counts and 19360 counts. The signal fluctuation amplitude was moderate and showed a clear, regular response trend, indicating that the sensor responds to acetone. (Comparison) Figure 3 and Figure 4It can be seen that the sensor of the present invention has a significantly stronger response to 500 ppb isopropanol than to 50 ppb acetone, demonstrating good selectivity for isopropanol, and can effectively identify isopropanol in the presence of interfering gases such as acetone in exhaled samples.

[0046] Example 6: Application Case

[0047] This invention relates to a sensor for non-invasive breath detection of diabetes. During use, the subject exhales into a gas collection bag, which is then connected to the sensor's air chamber. Broadband light emitted from a light source is transmitted via optical fiber to the sensitive area of ​​a gold film, exciting surface plasmon resonance (SPR). When isopropanol molecules are adsorbed by the porous hollow nanocage of Co3O4, the refractive index of the gold film changes, leading to a change in the intensity of the SPR resonance peak. By real-time monitoring of the SPR resonance peak intensity at 641 nm using a spectrometer, isopropanol concentration information can be obtained, reflecting the subject's ketone body metabolism status and assisting in diabetes screening and monitoring.

[0048] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A porous hollow nanocage material SPR fiber optic isopropanol breath detection sensor, comprising an optical fiber body, a gold film deposited on the surface of the optical fiber body, and a gas-sensitive layer coated on the surface of the gold film, characterized in that: The gas-sensitive layer is a Co3O4 porous hollow nanocage material derived from the ZIF-67 precursor through low-temperature pyrolysis. The Co3O4 porous hollow nanocage is uniformly loaded onto the surface of the optical fiber gold film by dip coating to form an SPR sensitive layer. The sensor uses the intensity change of the surface plasmon resonance peak as the isopropanol concentration detection signal, and the resonance peak wavelength is about 641 nm.

2. The SPR fiber optic isopropanol breath detection sensor based on a porous hollow nanocage material according to claim 1, characterized in that: The ZIF-67 precursor was prepared by dissolving 2-methylimidazole in methanol to obtain solution A, dissolving cobalt nitrate hexahydrate in methanol to obtain solution B, quickly pouring solution A into solution B, sonicating at room temperature for 1 hour, centrifuging to collect the precipitate, washing it three times with ethanol, and drying it at 60°C for 24 hours to obtain purple ZIF-67 nanocages.

3. The SPR fiber optic isopropanol breath detection sensor based on a porous hollow nanocage material according to claim 2, characterized in that: The molar ratio of 2-methylimidazole to cobalt nitrate hexahydrate is 4:

1.

4. The SPR fiber optic isopropanol breath detection sensor based on a porous hollow nanocage material according to claim 1, characterized in that: The Co3O4 porous hollow nanocage was prepared by pyrolyzing the ZIF-67 precursor at a heating rate of 2°C / min to 300°C and then cooling it in the furnace.

5. The SPR fiber optic isopropanol breath detection sensor based on a porous hollow nanocage material according to claim 1, characterized in that: The optical fiber body is a multimode silica optical fiber, and the gold film thickness is 40nm to 50nm.

6. The SPR fiber optic isopropanol breath detection sensor based on a porous hollow nanocage material according to claim 5, characterized in that: The sensor is manufactured as follows: (1) Fiber pretreatment and gold film deposition: The coating layer of the multimode quartz fiber is stripped off, and it is cleaned with anhydrous ethanol and deionized water in sequence, and then dried with nitrogen. The gold film with a thickness of 40 nm to 50 nm was deposited on the surface of the optical fiber using magnetron sputtering as the SPR excitation layer; (2) Sensitive layer coating: The prepared Co3O4 porous hollow nanocage is dispersed in anhydrous ethanol to prepare a Co3O4 porous hollow nanocage impregnation dispersion with a concentration of 50 mg / mL. The nanocage is ultrasonically dispersed for 20 min to make the nanocage uniformly dispersed. (3) The sensitive area of ​​the gold-plated optical fiber is immersed in the Co3O4 porous hollow nanocage dipping dispersion and coated by dip coating method to make the Co3O4 porous hollow nanocage uniformly loaded on the gold film surface. The coating is applied 14 times, that is, a total of 14 layers of material are coated. After drying at room temperature, the SPR optical fiber isopropanol breath detection sensor of the present invention is obtained.

7. The SPR fiber optic isopropanol breath detection sensor based on a porous hollow nanocage material according to claim 6, characterized in that: The sensor detects isopropanol vapor, with a minimum detectable concentration of 50 ppb.

8. The SPR fiber optic isopropanol breath detection sensor based on a porous hollow nanocage material according to claim 7, characterized in that: The sensor operates at room temperature and requires no external heating device.

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