A fluorescent probe for monitoring formaldehyde, preparation method and use and a portable sensor

Abstract

The application discloses a fluorescent probe for monitoring formaldehyde, a preparation method and application and a portable sensor. The fluorescent probe for monitoring formaldehyde has a structural formula as shown in formula (I): wherein R1 is selected from any one of C1-C2 hydrocarbon groups, phenyl groups and substituted phenyl groups; the substituted phenyl groups are preferably selected from alkyl-substituted phenyl groups, and more preferably selected from C1-C3 alkyl-substituted phenyl groups; R2 is selected from any one of oxygen atoms and sulfur atoms; R3 is selected from any one of cyano groups and carboxyl groups; and A is selected from any one of groups shown in formula (II) and groups shown in formula (III). The fluorescent probe has strong fluorescence emission performance in both solution and solid states, can be used for real-time monitoring of formaldehyde, has high sensitivity and selectivity, and the preparation method of the fluorescent probe is simple in process, convenient to operate, easy to control and low in cost.

Description

Technical Field

[0001] This invention relates to the field of fine chemical technology, specifically to a fluorescent probe for monitoring formaldehyde, its preparation method, its uses, and a portable sensor. Background Technology

[0002] Formaldehyde is a reactive carbonyl compound that plays a significant role in construction, furniture, textiles, and industrial chemicals. However, as a common indoor pollutant, gaseous formaldehyde is continuously released from formaldehyde-based products. Inhalation of formaldehyde (at concentrations above 0.1 mg / m³) can lead to airborne transmission. 3 Formaldehyde can cause headaches, sore throat, and difficulty breathing. Furthermore, long-term exposure to formaldehyde may lead to cancer. Therefore, developing a simple and sensitive method for detecting gaseous formaldehyde is essential.

[0003] Conventional methods for gaseous formaldehyde detection, such as high-performance liquid chromatography (HPLC), spectrophotometry, and gas chromatography (GC), suffer from high costs and complex operations, significantly hindering their application. Other methods for gaseous formaldehyde detection (such as piezoelectric methods, potentiometry, and electrochemical methods) offer simplified detection of gaseous formaldehyde, but their long-term stability and selectivity still need improvement. In contrast, fluorescent probes offer significant advantages, including low cost, ease of use, simple operation, and high selectivity.

[0004] Fluorescence analysis is a detection method that determines the content of a target analyte by detecting changes in its fluorescence signal through the interaction of a fluorescent probe. This method exhibits excellent selectivity, enables real-time online detection, and allows for non-invasive detection of biological samples. Although formaldehyde fluorescent probes have received considerable attention from researchers and have been extensively studied, the variety of probes remains limited, and they suffer from drawbacks such as complex molecular structures, numerous preparation steps, and slow response speeds. These limitations fail to meet the application requirements for formaldehyde testing and evaluation in materials, environments, and complex systems. Therefore, there is an urgent need to develop formaldehyde fluorescent probes with simpler structures, easier preparation, and faster response speeds. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention provides a fluorescent probe for monitoring formaldehyde, its preparation method and uses, and a portable sensor.

[0006] One objective of this invention is to provide a fluorescent probe for monitoring formaldehyde, the structure of which is shown in formula (I):

[0007]

[0008] Wherein, R1 is selected from any one of C1-C2 hydrocarbon groups, phenyl groups, and substituted phenyl groups; the substituted phenyl group is preferably selected from alkyl-substituted phenyl groups, more preferably from C1-C3 alkyl-substituted phenyl groups; R2 is selected from any one of oxygen atoms and sulfur atoms; R3 is selected from any one of cyano (-CN) and carboxyl (-COOH); A is selected from any one of the groups shown in formula (II) and formula (III) below:

[0009] (amino); (allylamino group); the curve marks the substitution sites (the same applies below).

[0010] In a preferred embodiment of the present invention,

[0011] R1 is selected from any one of the hydrocarbon groups from C1 to C2; and / or, R2 is selected from any one of the oxygen atom and sulfur atom; and / or, R3 is selected from any one of the cyano group and carboxyl group; and / or, A is selected from the group shown in formula (III).

[0012] In a preferred embodiment of the present invention,

[0013] R1 is selected from methyl; and / or, R2 is selected from oxygen atom; and / or, R3 is selected from either cyano or carboxyl, preferably cyano; and / or, A is selected from the group shown in formula (III).

[0014] A second objective of this invention is to provide a method for preparing a fluorescent probe according to one of the objectives of this invention, comprising the step of reacting a compound shown in formula (IV) and a compound shown in formula (V) in a reaction medium in the presence of a catalyst and an alkaline additive;

[0015]

[0016] In the formula, R1 is selected from any one of C1-C2 hydrocarbon groups, phenyl groups, and substituted phenyl groups; the substituted phenyl group is preferably selected from alkyl-substituted phenyl groups, more preferably from C1-C3 alkyl-substituted phenyl groups; R2 is selected from any one of oxygen atoms and sulfur atoms; R3 is selected from any one of cyano groups and carboxyl groups; A is selected from any one of the groups shown in formula (II) and formula (III); preferably,

[0017] R1 is selected from any one of the hydrocarbon groups from C1 to C2; and / or, R2 is selected from any one of the oxygen atom and sulfur atom; and / or, R3 is selected from any one of the cyano group and carboxyl group; and / or, A is selected from the group shown in formula (III).

[0018] In this invention, the compounds shown in formula (IV) and formula (V) can be commercially available or prepared using methods disclosed in the art in the prior art; preferably,

[0019] When A is selected from the group shown in formula (III), the preparation method of the compound shown in formula (IV) includes:

[0020] Will (Where R1 is selected from any one of C1-C2 hydrocarbon groups, phenyl groups, and substituted phenyl groups; the substituted phenyl group is preferably selected from alkyl-substituted phenyl groups, more preferably from C1-C3 alkyl-substituted phenyl groups.) The mixture is stirred with ammonia in methanol at 0-10°C for 5-60 min. After heating to 15-35°C, o-ditert-ol propylene borate is added and stirring continues for 5-24 h. The solvent is removed under reduced pressure, and the crude product is purified by column chromatography to obtain the compound of formula (IV) when A is selected from the group shown in formula (III).

[0021] Among them, ammonia and The preferred molar ratio is (5-20):1; 0.1-ditert-ol propylene borate and... The preferred molar ratio is (1-3):1. In this invention, It can be obtained from commercially available sources or prepared using publicly disclosed preparation methods in the art.

[0022] In a preferred embodiment of the present invention,

[0023] The reaction medium is selected from at least one organic solvent, preferably from at least one of tetrahydrofuran and 1,4-dioxane; and / or

[0024] The catalyst is selected from at least one of divalent copper compounds and Pd(0) compounds, preferably a combination of divalent copper compounds and Pd(0) compounds; the divalent copper compound is preferably copper acetate monohydrate; and / or, the Pd(0) compound is preferably tetrakis(triphenylphosphine)palladium; and / or,

[0025] The alkaline additive is selected from at least one organic amine, preferably from at least one of triethylamine, pyridine, and N,N-diisopropylethylamine (DIPEA).

[0026] In a preferred embodiment of the present invention,

[0027] The molar ratio of the compound shown in formula (IV), the compound shown in formula (V), the catalyst, and the basic additive is 1:(0.5–5):(0.1–3):(0.1–5), preferably 1:(2–3):(0.1–3):(1–3); and / or,

[0028] The mass ratio of the reaction medium to the compound shown in formula (IV) is (5-20):1, preferably (10-20):1.

[0029] In a preferred embodiment of the present invention,

[0030] The reaction time is 4 to 48 hours, preferably 10 to 30 hours; preferably, the reaction is carried out under reflux conditions; more preferably, the temperature of the reflux reaction is within 20°C above or below the boiling point of the reaction medium used in the reaction, and more preferably within 20°C above the boiling point of the reaction medium used in the reaction.

[0031] The present invention can adopt the following specific technical solutions:

[0032] The compounds shown in formula (IV) and (V) were dissolved in 1,4-dioxane, with divalent copper compounds and / or Pd(0) compounds as catalysts, and the mixture was refluxed for 4–48 h under the action of alkaline additives. After the reaction was completed, the fluorescent probe with the structure shown in formula (I) was obtained by column chromatography.

[0033] A third objective of this invention is to provide an indazole compound as a fluorescent probe for monitoring formaldehyde, wherein the structural formula of the indazole compound is:

[0034]

[0035] Wherein, R1 is selected from any one of C1-C2 hydrocarbon groups, phenyl groups, and substituted phenyl groups; the substituted phenyl group is preferably selected from alkyl-substituted phenyl groups, more preferably from C1-C3 alkyl-substituted phenyl groups; and / or, R2 is selected from any one of oxygen atoms and sulfur atoms; and / or, R3 is selected from any one of cyano groups and carboxyl groups; A is selected from any one of the groups shown in formula (II) and formula (III) below:

[0036]

[0037] In a preferred embodiment of the present invention,

[0038] R1 is selected from any one of the hydrocarbon groups from C1 to C2; and / or, R2 is selected from any one of the oxygen atom and sulfur atom; and / or, R3 is selected from any one of the cyano group and carboxyl group; and / or, A is selected from the group shown in formula (III).

[0039] In a preferred embodiment of the present invention,

[0040] R1 is selected from methyl; and / or, R2 is selected from oxygen atom; and / or, R3 is selected from either cyano or carboxyl, preferably cyano; and / or, A is selected from the group shown in formula (III).

[0041] In a preferred embodiment of the present invention,

[0042] When the indazole compound is used to monitor formaldehyde, it is first prepared to a concentration of 1×10⁻⁶. -3 ~1×10 -5 A mol / L solution was prepared and its fluorescence spectrum was measured. Then, the formaldehyde test solution was added, and its fluorescence spectrum was measured again. The changes in fluorescence spectra before and after the addition of the formaldehyde test solution were compared. The presence of formaldehyde in the test solution was determined by the changes in fluorescence spectra before and after the addition of the formaldehyde test solution. Preferably,

[0043] Concentration of 1×10 -3 ~1×10 -5 The medium in the solution of an indazole compound at a concentration of mol / L is a mixture of dimethyl sulfoxide and water, wherein the volume ratio of dimethyl sulfoxide to water in the mixture is preferably (0.2–5):1; and / or,

[0044] After adding the formaldehyde test solution, react at 20–50°C for 5–60 minutes before testing.

[0045] A fourth objective of this invention is to provide a portable formaldehyde sensor, obtained by loading a fluorescent probe obtained by the preparation method of one objective of this invention onto a solid matrix; preferably, the solid matrix is ​​at least one of paper and board, more preferably at least one of paper test paper, filter paper, and thin-layer chromatography; more preferably, the portable formaldehyde sensor is a formaldehyde test strip. The formaldehyde test strip enables simple and sensitive detection of gaseous formaldehyde.

[0046] The fluorescent probe for monitoring formaldehyde of the present invention contains a novel indazole fluorophore in its structure, exhibiting aggregation-induced emission properties. Compared to fluorophores with aggregation-induced quenching properties, the novel indazole fluorophore of the present invention still emits strong fluorescence in the aggregated state. Its reaction mechanism with formaldehyde is as follows (here, only the fluorescent probe is used as an example). (For example, at that time):

[0047]

[0048] The formaldehyde fluorescent probe of the present invention has strong fluorescence emission performance in both solution and solid states, and can be used for real-time monitoring of formaldehyde. It has high sensitivity and selectivity. Furthermore, the preparation method of the fluorescent probe provided by the present invention is simple, easy to operate, easy to control, and low in cost. Attached Figure Description

[0049] Figure 1 The mass spectrum of the fluorescent probe shown in I-1 (see Example 1 for details) is shown below. Figure 1The test data for the mass spectrum are as follows: Mass spectrometry (ESI-MS, m / z): calcd.for[C 16 H 12 N5O+H] + 290.1042; found 290.1042. Figure 1 The molecular weight detected by medium mass spectrometry is consistent with the theoretical molecular weight, proving the accuracy of the synthesized molecular structure.

[0050] Figure 2 The image shows the 1H NMR spectrum of the fluorescent probe shown in I-1 (see Example 1 for details). Figure 2 The test data for the hydrogen NMR spectrum are as follows: 1 H NMR (400MHz, DMSO-d6, ppm) δ = 4.35 (s, 3H, NCH3-H), δ = 5.24 (s, 2H, NH2-H), δ = 6.88 (d, J = 8.0Hz, 1H, Ph-H), δ = 7.00 (s, 1H, Ph-H), δ=7.24 (d, J=4.0Hz, 1H, furan-H), δ=7.49 (d, J=8.0Hz, 1H, Ph-H), δ=7.68 (d, J=4.0Hz, 1H, furan-H), δ=8.20 (s, 1H, alkene-H). Figure 2 The data above most directly demonstrates the successful synthesis of the fluorescent probe shown in I-1.

[0051] Figure 3 The graph shows the changes in fluorescence properties of probe I-2 before and after reacting with formaldehyde in Application Example 2. Curve 1 is the fluorescence curve before reacting with formaldehyde, and curve 2 is the fluorescence curve after reacting with formaldehyde. Detailed Implementation

[0052] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0053] Unless otherwise specified, the raw materials used in the embodiments of the present invention are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0054] The detection instruments used in the embodiments of this invention are shown in Table 1:

[0055] Table 1

[0056]

[0057] Example 1

[0058] Synthesis of fluorescent probe I-1:

[0059]

[0060] In a dry Shrek tube, IV-1 (147 mg, 1 mmol, CAS No.: 50593-24-3), copper acetate monohydrate (300 mg, 1.5 mmol), V-1 (432 mg, 3 mmol, CAS No.: 3237-22-7), and pyridine (0.2 mL) were added separately and dissolved in 3 mL of 1,4-dioxane. Tetraphenylphosphine palladium (58.8 mg, 0.05 mmol) was then rapidly added. The mixture was stirred at 25 °C for 5 min under argon protection and refluxed at 120 °C for 24 h. After the reaction was complete, the reaction solution was cooled to room temperature and diluted with 20 mL of dichloromethane. The solution was then filtered. The organic phases were combined and rotary evaporated under reduced pressure. The mixture was separated by column chromatography (developing solvent: dichloromethane: petroleum ether = 1:1, 300-400 mesh silica gel). 112 mg of the fluorescent probe with the structure shown in Formula I-1 was obtained, with a yield of 39%.

[0061] Example 2

[0062] Synthesis of fluorescent probe I-2:

[0063]

[0064] 1-Methyl-1H-indazole-5-carboxaldehyde (806 mg, 5 mmol, CAS No.: 872607-89-1) was mixed with 25% ammonia solution (3.78 mL, ammonia content 50 mmol) in 50 mL of methanol and stirred at 0 °C for 30 min. After heating to 25 °C, o-tert-alkenyl propenyl borate (924 mg, 6 mmol) was added and stirring continued for 12 h. The solvent was removed under reduced pressure, and the crude product was purified by chromatographic column chromatography using ethanol / dichloromethane (v / v 1:10) to give solid compound IV-2 (660 mg, yield 38%).

[0065] In a dry Shrek tube, IV-2 (200 mg, 1 mmol), copper acetate monohydrate (300 mg, 1.5 mmol), V-1 (432 mg, 3 mmol, CAS No.: 3237-22-7), and pyridine (0.2 mL) were added separately and dissolved in 3 mL of 1,4-dioxane. Tetraphenylphosphine palladium (58.8 mg, 0.05 mmol) was then rapidly added. The mixture was stirred at 25 °C for 5 min under argon protection and refluxed at 120 °C for 24 h. After the reaction was complete, the reaction solution was cooled to room temperature and diluted with 20 mL of dichloromethane. The solution was then filtered. The organic phases were combined and rotary evaporated under reduced pressure. The mixture was separated by column chromatography (developing solvent: dichloromethane: petroleum ether = 1:1, 300-400 mesh silica gel). 132 mg of the fluorescent probe with the structure shown in Formula I-2 was obtained, with a yield of 38.7%.

[0066] Example 3

[0067] Synthesis of fluorescent probe I-3:

[0068]

[0069] In a dry Shrek tube, IV-2 (200 mg, 1 mmol), copper acetate monohydrate (300 mg, 1.5 mmol), V-2 (480 mg, 3 mmol, CAS No.: 28162-32-5), and pyridine (0.2 mL) were added separately and dissolved in 3 mL of 1,4-dioxane. Tetraphenylphosphine palladium (58.8 mg, 0.05 mmol) was then rapidly added. The mixture was stirred at 25 °C for 5 min under argon protection and refluxed at 120 °C for 24 h. After the reaction was complete, the reaction solution was cooled to room temperature and diluted with 20 mL of dichloromethane. The solution was then filtered. The organic phases were combined and rotary evaporated under reduced pressure. Separation was performed by column chromatography (developing solvent: dichloromethane: petroleum ether = 1:1, 300-400 mesh silica gel). 154 mg of the fluorescent probe with the structure shown in Formula I-3 was obtained, with a yield of 43%.

[0070] Application Test Case 1

[0071] I-2 from Example 2 was dissolved in dimethyl sulfoxide (analytical grade) to prepare 1.0 × 10⁻⁶ ppm solution. -3 Prepare a stock solution of M (M represents mol / L); then prepare 1.0 × 10⁻⁶ mol / L. -2 Prepare an aqueous solution of formaldehyde (M); then prepare 3 mL of a test system solution with a dimethyl sulfoxide (DMSO) to water volume ratio of 1:1. Add 30 μL of the above stock solution to the 3 mL test system solution, and then add 60 μL of the above aqueous formaldehyde solution. React the resulting mixture at 37 °C for 20 min. After thoroughly mixing the mixture, transfer it to an optical quartz cuvette (10 × 10 mm) to test its fluorescence spectrum. Figure 3 The probe I-2 in this embodiment has a concentration of 1.0 × 10⁻⁶.-5 mol·L -1 The graph shows the changes in fluorescence spectra before and after adding formaldehyde aqueous solution (20 times the equivalent of I-2). Figure 3 As shown, I-2 showed almost no fluorescence signal without the addition of formaldehyde aqueous solution; however, when formaldehyde aqueous solution was added, the maximum emission peak appeared at about 630 nm with 500 nm as the excitation wavelength, demonstrating excellent responsiveness.

[0072] As can be seen from application test example 1, the fluorescent probe of the present invention has strong fluorescence emission performance and can be used for real-time monitoring of formaldehyde. Furthermore, A is preferably [missing information - likely a specific component or parameter]. The fluorescent probe, when A is in the fluorescent probe shown in formula (I) The fluorescence response at time A is better than that at time B. The fluorescence response effect, because A is When the fluorescent probe reacts with formaldehyde, it forms a Schiff base, which is unstable and prone to hydrolysis. This may result in unstable or weak fluorescence signals, potentially leading to errors when monitoring formaldehyde.

[0073] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

[0074] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0075] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0076] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values; such ranges or values ​​should be understood to include values ​​close to them. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In principle, various technical solutions can be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0077] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

[0078] Furthermore, any implementation described herein can be freely combined with one or more other implementations described herein, and the resulting technical solutions or technical ideas shall be regarded as part of the original disclosure or original record of the present invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art believe that the combination is obviously unreasonable.

Claims

1. A fluorescent probe for monitoring formaldehyde, the structural formula of which is shown in formula (I): （I）； in, R1 is selected from any of the C1~C2 hydrocarbon groups; R2 is selected from any of the oxygen atom and sulfur atom; R3 is selected from any of the cyano group and carboxyl group; A is selected from any of the groups shown in formula (II) and formula (III) below: (II)) (III)。 2. The fluorescent probe as described in claim 1, characterized in that: R1 is selected from any one of the hydrocarbon groups from C1 to C2; and / or, R2 is selected from any one of the oxygen atom and sulfur atom; and / or, R3 is selected from any one of the cyano group and carboxyl group; and / or, A is selected from the group shown in formula (III).

3. The fluorescent probe as described in claim 2, characterized in that: R1 is selected from methyl; and / or, R2 is selected from oxygen atom; and / or, R3 is selected from either cyano or carboxyl; and / or, A is selected from the group shown in formula (III).

4. The fluorescent probe as described in claim 3, characterized in that: R1 is selected from methyl; and / or, R2 is selected from oxygen atom; and / or, R3 is selected from cyano; and / or, A is selected from the group shown in formula (III).

5. A method for preparing a fluorescent probe as described in any one of claims 1 to 4, comprising the step of reacting a compound of formula (IV) and a compound of formula (V) in a reaction medium in the presence of a catalyst and an alkaline additive; (IV) (V) In the formula, R1 is selected from hydrocarbon groups of C1 to C2; R2 is selected from oxygen atom and sulfur atom; R3 is selected from cyano group and carboxyl group; A is selected from the group shown in formula (II) and the group shown in formula (III).

6. The method as described in claim 5, characterized in that: The reaction medium is selected from at least one of tetrahydrofuran and 1,4-dioxane; and / or, The catalyst is selected from at least one of divalent copper compounds and Pd(0) compounds; the divalent copper compound is copper acetate monohydrate; and / or, the Pd(0) compound is tetraphenylphosphine palladium; and / or, The alkaline additive is selected from at least one of triethylamine, pyridine, and N,N-diisopropylethylamine.

7. The method as described in claim 5, characterized in that: The molar ratio of the compound shown in formula (IV), the compound shown in formula (V), the catalyst, and the basic additive is 1:(0.5~5):(0.1~3):(0.1~5); and / or, The mass ratio of the reaction medium to the compound shown in formula (IV) is (5~20):

1.

8. The method as described in claim 7, characterized in that: The molar ratio of the compound shown in formula (IV), the compound shown in formula (V), the catalyst, and the basic additive is 1:(2~3):(0.1~3):(1~3); and / or, The mass ratio of the reaction medium to the compound shown in formula (IV) is (10~20):

1.

9. The method as described in claim 5, characterized in that: The reaction time is 4 to 48 hours.

10. The method as described in claim 9, characterized in that: The reaction time is 10-30 h.

11. The method as described in claim 10, characterized in that: The reaction was carried out under reflux conditions.

12. The use of an indazole compound as a fluorescent probe for monitoring formaldehyde, wherein the indazole compound has the following structural formula: （I）； in, R1 is selected from C1 to C2 hydrocarbon groups; and / or, R2 is selected from oxygen atoms and sulfur atoms; and / or, R3 is selected from cyano groups and carboxyl groups; A is selected from any one of the groups shown in formula (II) and formula (III) below: (II)) (III)。 13. The use as described in claim 12, characterized in that: R1 is selected from any one of the hydrocarbon groups from C1 to C2; and / or, R2 is selected from any one of the oxygen atom and sulfur atom; and / or, R3 is selected from any one of the cyano group and carboxyl group; and / or, A is selected from the group shown in formula (III).

14. The use as described in claim 13, characterized in that: R1 is selected from methyl; and / or, R2 is selected from oxygen atom; and / or, R3 is selected from either cyano or carboxyl; and / or, A is selected from the group shown in formula (III).

15. The use as described in claim 14, characterized in that: R1 is selected from methyl; and / or, R2 is selected from oxygen atom; and / or, R3 is selected from cyano; and / or, A is selected from the group shown in formula (III).

16. The use as described in any one of claims 12 to 15, characterized in that: When the indazole compound is used to monitor formaldehyde, it is first prepared to a concentration of 1×10⁻⁶. -3 ~1×10 -5 A mol / L solution was prepared and its fluorescence spectrum was measured. Then, the formaldehyde test solution was added and its fluorescence spectrum was measured again. The changes in fluorescence spectrum before and after the addition of formaldehyde test solution were compared.

17. The use as described in claim 16, characterized in that: Concentration of 1×10 -3 ~1×10 -5 The medium in a solution of indazole compounds at mol / L is a mixture of dimethyl sulfoxide and water; and / or, After adding the formaldehyde test solution, react at 20~50℃ for 5~60 min before testing.

18. The use as described in claim 17, characterized in that: In the mixture of dimethyl sulfoxide and water, the volume ratio of dimethyl sulfoxide to water is (0.2~5):

1.

19. A portable formaldehyde sensor, obtained by loading a fluorescent probe according to any one of claims 1 to 4 or a fluorescent probe obtained by any one of claims 5 to 11 onto a solid matrix.

20. The portable formaldehyde sensor as described in claim 19, characterized in that: The portable formaldehyde sensor is a formaldehyde test strip.

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