CN102702558A - Fluorescent sensor based on cellulose nanometer micro-fiber (TOCN) film serving as substrate and application thereof - Google Patents

Abstract

The invention relates to a fluorescent chemical sensor for ultra-trace detection of nitroaromatic explosives, which uses a cellulose nanofiber (TOCN) film as a carrier to chemically graft a fluorescent conjugated polymer. The preparation method of this sensor is to first use 2,2,6,6-tetramethylpiperidine oxide oxidized cellulose method to prepare TOCN film with carboxyl group at the C-6 position, and use the chemical bond of amine compound with bromophenyl group at the end Combined to the surface of the film, the prepared fluorescent conjugated polymer is introduced into the surface of the film through the "grafting to" technology, which realizes the ultra-sensitization of the film sensor, solves the stability and permeability problems of the film sensor, and is easy to diffuse the pore fraction Up to 97.4%. The fluorescent sensing film prepared by the present invention has the advantages of high mechanical properties, good flexibility, easy to carry, green and renewable, etc., can detect nitroaromatic explosives very conveniently, and can also visually detect nitroaromatic explosives under ultraviolet light thing.

Description

Fluorescence sensor based on cellulose nanofiber film as substrate and its application

technical field

The invention relates to a high-sensitivity fluorescent conjugated polymer chemical sensor, in particular to a preparation method for a fluorescent conjugated polymer film sensitive to nitroaromatic explosives.

Background technique

Since entering the 21st century, reliable and accurate detection of explosives has become one of the important issues of international concern. The ultra-trace detection of chemical explosives plays an important role in maintaining national security, preventing and controlling environmental pollution and forensic science. Due to the increasing threat of international terrorism, finding new methods for detecting explosives with high sensitivity and high selectivity has become a research hotspot at home and abroad.

In recent years, the application of fluorescent conjugated polymers to detect ultra-trace nitroaromatic explosives has received great attention. One of the important reasons is that when an electron-rich fluorescent conjugated polymer interacts with an electron-deficient substance, the light-induced charge transfer promotes the fluorescence quenching effect of the electron-rich donor, and the generated delocalized excitons are transmitted along the polymer chain, thereby Amplification leading to "superquenching". According to this principle, it can be applied to the rapid, accurate and ultra-high sensitivity detection of nitroaromatic explosives.

However, for fluorescent conjugated polymer sensing materials based on fluorescence quenching detection of nitroarenes, most fluorescent conjugated polymers are used under solid-state thin films, but when used in the solid state, the interaction between fluorescent chromophores occurs The self-quenching of fluorescence caused by π-π stacking will have an adverse effect on the sensitivity of explosive detection. Too low fluorescence intensity is easily interfered by the detection instrument itself and the background doping signal of the detection object during detection, which affects the accuracy of detection. .

Since fluorescent conjugated polymers were used as sensing materials, scholars at home and abroad have done some research work on inhibiting the self-quenching of material fluorescence and improving the rapid diffusion of explosive vapor molecules in films. Swager's research group mainly synthesized conjugated polymers such as poly(p-phenylene acetylene) containing pterene groups [J.Am.Chem.Soc.1998, 120, 5321-5322]. They introduced the three-dimensional pterene structure into the main chain of the polymer to isolate the main chain and avoid the π-π stacking between the chains, thereby inhibiting the self-quenching of fluorescence; they also increased the free volume fraction of the polymer film to form "molecular pores". ", which is conducive to the penetration and diffusion of the measured molecules on the membrane, and improves the response sensitivity.

In terms of visual detection of explosives, Zhang Zhongping’s research group soaked ordinary medium-speed filter paper in the prepared dual-emission quantum dot ratio fluorescent probe solution, and the TNT indicator test paper obtained by physically adsorbing quantum dots was irradiated by 365nm ultraviolet light. , capable of detecting surface TNT residues [J.Am.Chem.Soc.2011, 133, 8424-8427].

The spin coating method is a common method for preparing conjugated polymer sensing films, but there are some shortcomings in the preparation of films and processes by the traditional spin coating method that affect its practical application, such as the difficulty in controlling the thickness of the film, and the glass sheet used as the carrier , quartz sheets, etc. are not easy to carry, and there are also problems with chemical stability and thermal stability, especially when used in organic solutions, they are prone to cracking or being dissolved, polluting the system to be tested, etc.

Contents of the invention

The object of the present invention is to provide a kind of cellulose nanofiber (TOCN) film that is prepared by TEMPO (2,2,6,6-tetramethylpiperidine oxide) oxidation method based on green regeneration as matrix, then The invention discloses a preparation method of a fluorescent chemical sensing film capable of detecting trace amounts of nitroaromatic explosives of branched conjugated polymers. The method has simple process and mild reaction conditions. The prepared fluorescent sensing film is easy to carry, and can realize on-site, rapid and visual detection of nitroaromatic explosives under ultraviolet light.

The purpose of the present invention is achieved through the following technical solutions:

A method for preparing a high-sensitivity fluorescent sensor based on a cellulose nanofiber film as a substrate, the specific steps are as follows:

(1) Preparation of TOCN thin film

Ultrasonic defoaming of the TOCN aqueous suspension to obtain a casting solution, wherein the mass fraction of TOCN is 0.2% to 0.3%; the resulting casting solution is poured into a polytetrafluoroethylene mold, and after standing for 10min to 1h, put it in 30～ Put it in an oven at 70°C for 6-10 hours, and get a TOCN film after the solvent is completely evaporated.

(2) Preparation of bromophenyl TOCN film

Under the action of the condensing agent 1-(3-dimethylaminopropyl)-3-ethylcarbodiamine/N-hydroxysuccinimide, the carboxyl group at the C-6 position on the surface of the TOCN film and the bromine-containing The phenyl amine compound was reacted for 0.5-40 hours, washed repeatedly with distilled water and acetone, and vacuum-dried to prepare a TOCN film with Suzuki-reactive active sites.

(3) Preparation of fluorescent conjugated polymer (CP)

Under the protection of nitrogen, using tetrakis(triphenylphosphine)palladium ((PPh ₄ ) ₃ Pd) as a catalyst, the Suzuki-reactive monomers were reacted at reflux temperature for 12-56 hours. After the reaction is finished, the product is repeatedly washed with methanol and water, and dried in vacuum to prepare a fluorescent conjugated polymer.

(4) Preparation of fluorescent conjugated polymer film (TOCN-CP film)

Under nitrogen protection, the fluorescent conjugated polymer was dissolved in tetrahydrofuran, and 1-3 mol/L K ₂ CO ₃ aqueous solution was added, wherein the volume ratio of tetrahydrofuran to K ₂ CO ₃ aqueous solution was 3:2. Add catalyst (PPh ₄ ) ₃ Pd (2mol%) under the protection of N ₂ , and react at reflux temperature for 8-15 hours. After the reaction, wash with methanol, tetrahydrofuran, and water several times in sequence until no fluorescent substance appears in the solution, and after drying, a TOCN-CP film is obtained.

Beneficial effect

1 The TOCN film used in the present invention has the advantages of flexibility, light weight, low cost, renewability, and active carboxyl group at the C-6 position. The bromophenyl group at the end is chemically bonded to the C-6 position on the surface of the TOCN film, and the "grafting to" technology is used to introduce the fluorescent conjugated polymer to the surface of the TOCN film by forming a stable covalent bond, realizing the inhibition of conjugation The π-π stacking of polymer chains can also form channels between chains, which is conducive to the diffusion of quencher molecules. The fluorescent sensing film is insoluble in various solvents, does not pollute the system to be measured, and can be reused It overcomes the defects in the existing research from the design, solves some problems in the fluorescent sensing film prepared by physical spin coating and other methods, and further improves the response rate and detection sensitivity of the fluorescent sensing film.

2. The fluorescent sensing film prepared by the present invention can conveniently detect solution-state and vapor-state nitroaromatic explosives by using the principle of fluorescence quenching, and can also visually detect solution-state and vapor-state nitroaromatic explosives under ultraviolet light .

Description of drawings

Accompanying drawing 1 the influence of 2,4-dinitrotoluene solutions of different concentrations on the fluorescence intensity of TOCN-CP film.

Accompanying drawing 2 changes in the fluorescence intensity of TOCN-CP film after exposure in 2,4-dinitrotoluene vapor for different time.

Accompanying drawing 3 TOCN-CP film quenching efficiency and 2,4-dinitrotoluene vapor exposure time relationship curve.

Accompanying drawing 4 is the visualization photograph of detecting 2,4-dinitrotoluene under the irradiation of ultraviolet light.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments.

Example 1

(1) Weigh 0.1g TEMPO and 1gNaBr into 500mL deionized water, stir fully at room temperature; after TEMPO and NaBr are completely dissolved, add 10g wet wood pulp cellulose (the mass fraction of cellulose is 20.15%) to the reaction system After the cellulose is dispersed evenly, add 20g of NaClO solution to the system, and control the pH value of the reaction system in the range of 10 to 10.5; pH value of the system, until the NaOH solution is no longer consumed, the reaction is over; filter in a sand core funnel, and wash 3 to 5 times to prepare oxidized cellulose; supernatant and centrifuge the prepared oxidized cellulose, and take the upper layer clear solution, the TOCN solution was obtained. Ultrasonic defoaming of the TOCN aqueous suspension to obtain a casting solution, wherein the mass fraction of TOCN is 0.2% to 0.3%; the resulting casting solution is poured into a polytetrafluoroethylene mold, and after standing for 10min to 1h, put it in 30 Place in an oven at ~70°C for 6-10 hours, and obtain a TOCN film after the solvent is completely evaporated.

(2) Put the TOCN film into the morpholine ethanesulfonic acid buffer solution with a pH of 4 to 7, add the condensing agent 1-(3-dimethylaminopropyl)-3-ethylcarbodiamine/N-hydroxy Succinimide, the molar ratio is 2:1. After 30min, add the DMF solution of p-bromoaniline. After reacting for 16 hours, wash with water and ethanol repeatedly, and vacuum-dry the obtained film to obtain a TOCN active film capable of Suzuki reaction.

(3) Dissolve 3,6-dibromocarbazole and 9,9-dihexylfluorene-2,7-diborate in tetrahydrofuran at a molar ratio of 1:1, and add 1 to 3 mol/L of K ₂ CO ₃ aqueous solution, wherein the volume ratio of tetrahydrofuran to K ₂ CO ₃ aqueous solution is 3:2. After passing nitrogen for a period of time, the catalyst (PPh ₄ ) ₃ Pd (2mol%) was added, and the reaction was carried out at reflux temperature for 36-56 hours. The reaction solution was washed several times with methanol and distilled water in that order. The washed solid is vacuum-dried in a vacuum oven at room temperature for 12-24 hours to obtain a fluorescent conjugated polymer.

(4) Under nitrogen protection, the fluorescent conjugated polymer was dissolved in tetrahydrofuran, and 1-3 mol/L K ₂ CO ₃ aqueous solution was added, wherein the volume ratio of tetrahydrofuran to K ₂ CO ₃ aqueous solution was 3:2. Add catalyst (PPh ₄ ) ₃ Pd (2mol%) under nitrogen protection, and react at reflux temperature for 8-15 hours. After the reaction, wash with methanol, tetrahydrofuran and water repeatedly until no fluorescent substance appears in the solution, and after drying, a TOCN-CP film is obtained.

(5) Soak the TOCN-CP film in a certain concentration of 2,4-dinitrotoluene solution, take it out after a period of time, and immediately detect the change of its fluorescence intensity. Typical test results are shown in Figure 1.

Example 2

(1) Ultrasonic defoaming of the TOCN aqueous suspension to obtain a casting solution, wherein the mass fraction of TOCN is 0.2% to 0.3%; the resulting casting solution is poured into a mold made of polytetrafluoroethylene, and left to stand for 10min to 1h Finally, put it in an oven at 30-70°C for 6-10 hours, and get a TOCN film after the solvent is completely evaporated.

(2) Put the TOCN film into the morpholine ethanesulfonic acid buffer solution with a pH of 4 to 7, add the condensing agent 1-(3-dimethylaminopropyl)-3-ethylcarbodiamine/N-hydroxy The molar ratio of succinimide is 2:1. After 30 minutes, add the DMF solution of p-bromoaniline. After reacting for 16 hours, wash with water and ethanol repeatedly, and vacuum-dry the obtained film to obtain a TOCN active film capable of Suzuki reaction.

(3) Dissolve 3,6-dibromocarbazole and 9,9-dihexylfluorene-2,7-diborate in tetrahydrofuran at a molar ratio of 1:1, and add 1 to 3 mol/L of K ₂ CO ₃ aqueous solution, wherein the volume ratio of tetrahydrofuran to K ₂ CO ₃ aqueous solution is 3:2. After passing nitrogen for a period of time, the catalyst (PPh ₄ ) ₃ Pd (2mol%) was added, and the reaction was carried out at reflux temperature for 36-56 hours. The reaction solution was washed several times with methanol and distilled water in that order. The washed solid is vacuum-dried in a vacuum oven at room temperature for 12-24 hours to obtain a fluorescent conjugated polymer.

(4) Under nitrogen protection, the fluorescent conjugated polymer was dissolved in tetrahydrofuran, and 1-3 mol/L K ₂ CO ₃ aqueous solution was added, wherein the volume ratio of tetrahydrofuran to K ₂ CO ₃ aqueous solution was 3:2. Add catalyst (PPh ₄ ) ₃ Pd (2mol%) under nitrogen protection, and react at reflux temperature for 8-15 hours. After the reaction, wash with methanol, tetrahydrofuran and water repeatedly until no fluorescent substance appears in the solution, and after drying, a TOCN-CP film is obtained.

(5) Expose the TOCN-CP film to 2,4-dinitrotoluene vapor, take it out after a period of time, and immediately detect the change of its fluorescence intensity. Typical test results are shown in attached drawings 2 and 3.

Example 3

(1) Ultrasonic defoaming of the TOCN aqueous suspension to obtain a casting solution, wherein the mass fraction of TOCN is 0.2% to 0.3%; the resulting casting solution is poured into a mold made of polytetrafluoroethylene, and left to stand for 10min to 1h Finally, put it in an oven at 30-70°C for 6-10 hours, and get a TOCN film after the solvent is completely evaporated.

(2) Put the TOCN film into the morpholine ethanesulfonic acid buffer solution with a pH of 4 to 7, add the condensing agent 1-(3-dimethylaminopropyl)-3-ethylcarbodiamine/N-hydroxy The molar ratio of succinimide is 2:1. After 30 minutes, add the DMF solution of p-bromoaniline. After reacting for 16 hours, wash with water and ethanol repeatedly, and vacuum-dry the obtained film to obtain a TOCN active film capable of Suzuki reaction.

(3) Dissolve 3,6-dibromocarbazole and 9,9-dihexylfluorene-2,7-diborate in tetrahydrofuran at a molar ratio of 1:1, and add 1 to 3 mol/L of K ₂ CO ₃ aqueous solution, wherein the volume ratio of tetrahydrofuran to K ₂ CO ₃ aqueous solution is 3:2. After passing nitrogen for a period of time, the catalyst (PPh ₄ ) ₃ Pd (2mol%) was added, and the reaction was carried out at reflux temperature for 36-56 hours. The reaction solution was washed several times with methanol and distilled water in that order. The washed solid is vacuum-dried in a vacuum oven at room temperature for 12-24 hours to obtain a fluorescent conjugated polymer.

(4) Dissolve the fluorescent conjugated polymer in tetrahydrofuran under nitrogen atmosphere, and add 1-3 mol/L K ₂ CO ₃ aqueous solution, wherein the volume ratio of tetrahydrofuran to K ₂ CO ₃ aqueous solution is 3:2. Add catalyst (PPh ₄ ) ₃ Pd (2mol%) under nitrogen protection, and react at reflux temperature for 8-15 hours. After the reaction, wash with methanol, tetrahydrofuran and water repeatedly until no fluorescent substance appears in the solution, and after drying, a TOCN-CP film is obtained.

(5) Expose the TOCN-CP film to 2,4-dinitrotoluene vapor, take it out after a period of time, and observe the color change under an ultraviolet lamp. The typical test results are shown in Figure 4.

Claims (5)

1. one kind is the highly sensitive fluorescent optical sensor of matrix based on Mierocrystalline cellulose nanometer fento film; But its characteristic is to introduce Suzuki reactive behavior site at the carboxyl with the reproducible TOCN film surface of snappiness and environmental protection C-6 position, then with the fluorescent conjugated polymer chemical graft to film surface.

2. as claimed in claim 1 is the preparation method of the highly sensitive fluorescent optical sensor of matrix based on Mierocrystalline cellulose nanometer fento film, and its characteristic may further comprise the steps:

(1) preparation TOCN film

The ultrasonic deaeration of TOCN aqeous suspension is got film-casting liquid, and wherein the massfraction of TOCN is 0.2%～0.3%; The film-casting liquid of gained is poured in the mould by tetrafluoroethylene system, leave standstill 10min～1h after, put into 30～70 ℃ of baking oven 6～10h, treat solvent after evaporating fully the TOCN film;

(2) preparation bromophenyl TOCN film

Under the effect of condensing agent 1-(3-dimethyl aminopropyl)-3-ethyl carbon diamines/N-maloyl imines; Carboxyl and the aminated compounds reaction 0.5～40h that contains bromophenyl with C-6 position on the TOCN film surface; Use zero(ppm) water and acetone repetitive scrubbing; After vacuum-drying, but process TOCN film with Suzuki reactive behavior site;

(3) preparation fluorescent conjugated polymer

Under the nitrogen protection, with tetrakis triphenylphosphine palladium ((PPh ₄) ₃Pd) be catalyzer, but the monomer of Suzuki reaction is reacted 12～56h under reflux temperature.After reaction finishes, use methyl alcohol, water repetitive scrubbing product, after vacuum-drying, process fluorescent conjugated polymer;

(4) preparation fluorescent conjugated polymer film (TOCN-CP film)

The fluorescent conjugated polymer of preparation is dissolved in the mixing solutions of THF and salt of wormwood, puts into there-necked flask, N with bromophenyl TOCN film ₂Protection adds (PPh down ₄) ₃Pd, reflux temperature use methyl alcohol after reacting 2～24h down, THF, water repetitive scrubbing, and no fluorescent substance occurs in solution, after the drying, gets the TOCN-CP film.

3. method according to claim 2 is characterized in that in the step (2) the brominated phenyl group of described amino-complex.

4. method according to claim 2 is characterized in that in the step (3), but the monomer of described Suzuki reaction is the boric acid or the boric acid ester of aryl or thiazolinyl, chlorine, bromine, iodo aromatic hydrocarbons or alkene.

5. method according to claim 2 is characterized in that in the step (3) the end group boronic acid containing of described fluorescent conjugated polymer, boric acid ester.

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