A carbon dot-based method for detecting formaldehyde content in food

Abstract

The present application relates to a kind of carbon point-based formaldehyde content detection method in food, specifically includes the following steps: S1, preparation of carbon point o-PD-CDs;S2, the sample to be measured is handled, and the solution to be measured is obtained;S3, the solution to be measured is mixed with carbon point o-PD-CDs, and the detection solution is obtained;The pH value of detection solution is adjusted with B-R buffer solution, after the adjusted detection solution is incubated at room temperature, it is irradiated under the fluorescence of excitation wavelength 380nm, the fluorescence emission spectrum of 450nm~650nm is collected, and the fluorescence intensity at the emission center 552nm is recorded, to obtain the fluorescence quenching value of detection solution;S4, the formaldehyde content standard curve determined in advance is used to calculate the formaldehyde content of the sample to be measured.The detection method has the characteristics of high selectivity and high sensitivity, and can be used for the detection of formaldehyde content in actual food, and the recovery rate is 98.10~107.86%.

Description

Technical Field

[0001] This invention relates to a method for detecting formaldehyde content, specifically a method for detecting formaldehyde content in food based on carbon dots. Background Technology

[0002] Formaldehyde is a colorless, irritating, and highly water-soluble substance. 35-40% of formaldehyde is used as formalin to kill bacteria and prevent bacterial growth. Foods processed with formaldehyde solutions, such as dried bean curd, beans, vermicelli, and frozen fish and shrimp, can usually be stored at room temperature for extended periods without spoiling. However, formaldehyde has been identified by the World Health Organization as a carcinogenic and teratogenic substance that is toxic to humans. It has been reported that ingesting formaldehyde or exposure to environments containing excessive amounts of formaldehyde may cause respiratory and digestive problems. Furthermore, due to its high electrophilicity, formaldehyde exhibits strong reactivity with nucleophilic DNA and important protein molecules that cause cellular dysfunction. Nevertheless, the practice of soaking food in formaldehyde solutions to extend its shelf life still exists. In addition, formaldehyde is widely used as a chemical raw material in wood processing, textiles, and construction. Therefore, establishing an efficient and accurate method for quantifying formaldehyde is of great practical significance for health.

[0003] Existing methods for formaldehyde determination include high performance liquid chromatography (HPLC), gas chromatography (GC), gas chromatography-mass spectrometry, spectrophotometry, and colorimetry. These methods have drawbacks such as complex sample preparation processes and long measurement times.

[0004] In recent years, carbon-based nanomaterials have also been studied for the detection of formaldehyde. Carbon dots (CDs), a type of carbon nanomaterial, are discrete quasi-spherical carbon nanoparticles with a particle size of less than 10 nm. They possess characteristics such as high solubility, low toxicity, good biocompatibility, and controllable fluorescence. Currently, carbon dots have been successfully used to fabricate fluorescent probes for the detection of small organic molecules such as thiram and amines. However, the preparation process of carbon dots (CDs) into fluorescent probes is complex and costly, and their use in formaldehyde detection suffers from drawbacks such as poor selectivity and low sensitivity. Summary of the Invention

[0005] The purpose of this invention is to provide a method for detecting formaldehyde content in food based on carbon dots, so as to solve the problem of low sensitivity in formaldehyde detection using carbon-based nanomaterials.

[0006] The objective of this invention is achieved as follows: A method for detecting formaldehyde content in food based on carbon dots includes the following steps: S1, the preparation of carbon dot o-PD-CDs includes the following steps: S1-1. Mix o-phenylenediamine (o-PD) with N,N-dimethylformamide (DMF) and sonicate until completely dissolved to obtain a mixed solution; S1-2. Transfer the mixed solution to a three-necked flask and place it in a microwave catalytic reactor for reflux reaction. After the reaction is completed, carbon dots o-PD-CDs are obtained. S1-3. After cooling the carbon dot o-PD-CDs to room temperature, store them in a refrigerator away from light for later use. S2. Preparation of the test solution: The dried food to be tested is crushed into powder, and then the powder is placed in a container containing ultrapure water. After ultrasonic treatment, it is centrifuged and the supernatant is taken. The supernatant is filtered once with filter paper and once with filter membrane. The filtrate is the test solution. The test solution is stored in a refrigerator in the dark for later use. S3. Preparation of the detection solution: The test solution is mixed with carbon dots o-PD-CDs to prepare the detection solution; S4. Measure the fluorescence quenching value of the test solution: Adjust the pH value of the test solution with BR buffer, incubate the adjusted test solution at room temperature, and then irradiate it under the fluorescence of the fluorescence spectrometer with an excitation wavelength of 380nm. Collect the fluorescence emission spectrum of the test solution in the range of 450nm~650nm, and record the fluorescence intensity at the emission center at 552nm to obtain the fluorescence quenching value of the test solution. S5. Formaldehyde content detection: Based on the fluorescence quenching value of the test solution and the pre-determined formaldehyde content standard curve and linear equation, the formaldehyde content of the sample to be tested is calculated. Furthermore, the formaldehyde concentration in the test solution in step S3 is in the range of 0~0.8 mg / L.

[0007] Furthermore, the concentration of carbon dots o-PD-CDs is 50 µL / mL to 70 µL / mL.

[0008] Furthermore, the concentration of the test solution is 200 mg / mL to 400 mg / mL.

[0009] The detection method of this invention uses carbon dots o-PD-CDs as fluorescent probes. Because the surface of these carbon dots is rich in amino groups, they can react with formaldehyde in a Schiff base reaction to generate corresponding imines, thereby quenching the fluorescence of the carbon dots o-PD-CDs. The resulting fluorescence intensity change shows a good linear relationship with the formaldehyde concentration in the range of 0-0.8 mg / L, thus accurately determining the formaldehyde concentration. Furthermore, at higher concentrations of formaldehyde, the carbon dots o-PD-CDs, as fluorescent probes, can produce obvious Schiff base precipitation, causing the solution to become turbid. Based on this phenomenon, visual semi-quantitative detection of formaldehyde in the range of 0.5-150 mg / mL can be achieved, thus providing a new approach for formaldehyde detection. Attached Figure Description

[0010] Figure 1 These are characterization diagrams of carbon dots o-PD-CDs; Figure A shows the emission spectra of carbon dots o-PD-CDs under different excitation wavelengths; Figure B shows the excitation spectrum (dashed line) and emission spectrum (solid line) of carbon dots o-PD-CDs, and the inset in Figure B is a comparison photograph of the aqueous solution of carbon dots o-PD-CDs under sunlight (left) and ultraviolet light (right); Figure C is an HRTEM image of carbon dots o-PD-CDs; Figure D is a histogram of the size distribution of carbon dots o-PD-CDs.

[0011] Figure 2 Figure A shows the optimized detection conditions; Figure B shows the fluorescence spectra of carbon dot o-PD-CDs solutions with different concentrations; Figure C shows the fluorescence intensity as a function of carbon dot o-PD-CDs concentration; Figure D shows the F0-F variation as a function of incubation time; and Figure D shows the F0-F variation as a function of pH value.

[0012] Figure 3 These are the formaldehyde detection results; Figure A shows the fluorescence spectra of carbon dots o-PD-CDs after adding different concentrations of formaldehyde; Figure B shows the linear relationship between F0-F and formaldehyde concentration; Figure C shows the corresponding ultraviolet light photographs after adding different concentrations of formaldehyde to the system.

[0013] Figure 4 These are photos taken under sunlight after different concentrations of formaldehyde were added to the testing system.

[0014] Figure 5 The diagram shows the detection principle; Figure A shows the fluorescence lifetime of carbon dot o-PD-CDs and carbon dot o-PD-CDs in the presence of formaldehyde; Figure B shows the change in fluorescence intensity of carbon dot o-PD-CDs aqueous solution with incubation time.

[0015] Figure 6 This is a response signal diagram of formaldehyde and interfering substances using carbon dot o-PD-CDs as fluorescent probes. Detailed Implementation

[0016] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings. Reagents and operations not mentioned in the embodiments can be performed according to conventional practices in the art.

[0017] The reagents used were o-phenylenediamine (o-PD) and N,N-dimethylformamide (DMF), and the water used was ultrapure water.

[0018] The instruments used included: F-7000 fluorescence spectrophotometer, XH-MC-1 laboratory microwave catalytic reactor, RE-2000 rotary evaporator, XGQ-3000 vacuum drying oven, and Thermo Fisher Talos F200s transmission electron microscope.

[0019] 1. Preparation of carbon dot o-PD-CDs: 1 g of o-phenylenediamine (o-PD) was mixed with 20 mL of N,N-dimethylformamide (DMF) and sonicated until completely dissolved to obtain a mixed solution. This solution was transferred to a 50 mL three-necked flask and placed in a laboratory microwave catalytic reactor. The mixture was refluxed at 200 W and 150 °C for 40 min to obtain carbon dot o-PD-CDs. After cooling to room temperature, the carbon dot o-PD-CDs were stored in a refrigerator at 0–4 °C in the dark for future use as a fluorescent probe for detecting formaldehyde content in food.

[0020] 2. Characterization of carbon dots o-PD-CDs: The prepared carbon dots were characterized optically and morphologically, such as... Figure 1 As shown in (A), the fluorescence spectrum of the carbon dot o-PD-CDs indicates that the carbon dot exhibits excitation-independent emission, with a maximum emission wavelength of 552 nm and a maximum excitation wavelength of 380 nm in aqueous solution. Figure 1 (B)). For example Figure 1 As shown in (C), the morphology of carbon dots o-PD-CDs was characterized by HRTEM. The results showed that the carbon dots were uniformly dispersed in aqueous solution, forming spherical particles with an average particle size of approximately 2.5 nm. Figure 1 (D)).

[0021] 3. Optimization of detection conditions: In order to improve the sensing performance of carbon dot o-PD-CDs for formaldehyde detection, the following optimizations were made to the amount of fluorescent probe, incubation time and pH value of the reaction.

[0022] First, optimize the amount of fluorescent probe used. Figure 2 (A) shows the fluorescence spectra of carbon dot o-PD-CDs at different concentrations. The fluorescence intensity gradually increases with increasing concentration of the carbon dot o-PD-CDs, reaching its maximum and stabilizing when the concentration of the fluorescent probe reaches 60 µL / mL (see Figure 1). Figure 2 (B) Therefore, the concentration range of carbon dot o-PD-CDs is selected as 50µL / mL~70µL / mL, and the optimal concentration is 6070µL / mL.

[0023] Secondly, the optimal incubation time for the reaction system was investigated. The results showed that after 40 min, the difference between the fluorescence intensity (F0) of the blank carbon dot o-PD-CDs solution and the fluorescence intensity (F) of the carbon dot o-PD-CDs solution after adding formaldehyde tended to stabilize, indicating that the system had reacted completely at this point (see...). Figure 2 (C)).

[0024] Finally, the effect of the pH value of the reaction system on the sensing performance was investigated. The pH value of the reaction system was adjusted using BR buffer solutions with different pH values. The results showed that the sensing performance was optimal at pH = 6.8 (see...). Figure 2 (D)).

[0025] 4. Formaldehyde Detection Performance of Carbon Dot o-PD-CDs: This example investigated the formaldehyde detection performance of carbon dot o-PD-CDs. For example... Figure 3 As shown in (A), the fluorescence spectra of carbon dot o-PD-CDs after adding different concentrations of formaldehyde show that at the emission wavelength of 552 nm, the fluorescence intensity gradually decreases with increasing formaldehyde concentration. Using the difference in fluorescence intensity (F0-F) as the quantitative basis, it conforms to the linear equation F0-F = 216.5118[formaldehyde] + 0.2555, R = 0.9969, within the range of 0–0.8 mg / L. Figure 3 (B)), LOD is 5.2µg / L.

[0026] In addition, such as Figure 4 As shown, when the formaldehyde concentration further increases to 0.5 mg / mL, the solution begins to become turbid. With increasing formaldehyde concentration, the turbidity gradually worsens, and a noticeable precipitate forms until it disappears at a concentration of 150 mg / mL. Therefore, this reaction system can also achieve visualized semi-quantitative detection of formaldehyde content in the range of 0.5–150 mg / mL.

[0027] Table 1. Comparison of linear range, sensitivity, and selectivity of different reported methods for formaldehyde detection

[0028] 5. Principle analysis of formaldehyde detection using carbon dot o-PD-CDs: In Figure 5(A) shows the fluorescence lifetime of carbon dots o-PD-CDs and carbon dots o-PD-CDs + formaldehyde. The fluorescence lifetime of carbon dots o-PD-CDs remained almost unchanged after the addition of formaldehyde, indicating a static quenching relationship between carbon dots o-PD-CDs and formaldehyde. Furthermore, due to the complexity and diversity of the reactions during microwave-assisted solvothermal synthesis of carbon dots, the resulting product has a complex composition. The main component of this carbon dot is likely oxidized o-PD, i.e., 2,3-diaminophenazine (DAP), which itself exhibits yellow fluorescence emission. Additionally, the carbon dot contains an incompletely oxidized o-phenylenediamine structure, which is easily oxidized under light. As the incubation time of carbon dots o-PD-CDs in water increases, their fluorescence intensity gradually increases. Figure 5 (B) This also confirms the above observations. Formaldehyde and primary amines can undergo a Schiff base reaction, thereby preventing the oxidation process of o-PD and causing fluorescence quenching of carbon dots, which is similar to the mechanism reported in the literature. On the other hand, the formation of Schiff base precipitation also leads to aggregation-induced quenching of carbon dots.

[0029] 6. Regarding the selectivity of DPA@Ag / Cu NCs: This embodiment investigated the selectivity of the constructed formaldehyde fluorescence sensor for formaldehyde, and for inorganic ions (Cl-) that may be present in food samples. - F - PO4 3- HPO4 2- H2PO4 - CO3 2- HCO3 - SO4 2- Cd 2+ Ca 2+ Fe 3+ Cr 3+ Al 3+ Zn 2+ Mg 2+ The test was conducted. During the experiment, the concentration of formaldehyde was 0.8 mg / L, and the Cl... - F - PO4 3- HPO4 2- H2PO4 - CO3 2- HCO3 - SO4 2- Cd 2+ Ca 2+ The concentration was 8 mg / L, Fe 3+ Cr 3+ Al 3+ Zn 2 + Mg 2+The concentration is 4 mg / L. For example... Figure 6 As shown, under optimal experimental conditions, the constructed formaldehyde sensor exhibits almost no response or a small response signal to the measured inorganic ions, indicating that the presence of these substances does not interfere with formaldehyde detection. Therefore, this sensor demonstrates good selectivity for formaldehyde and can be used for the detection of formaldehyde content in food samples.

[0030] 7. Preparation of test solutions: The dried bean curd sticks and vermicelli were pulverized separately. 10g of bean curd stick powder and 10g of vermicelli powder were weighed and placed separately into containers containing 50mL of ultrapure water. Each container and its contents were ultrasonically treated for 20min and then centrifuged at 10000 rpm for 10min. The supernatant was then collected, filtered once with filter paper, and then once with a 0.22µm filter membrane. Both filtrates were stored at 4℃ for later use, yielding the test solutions for the bean curd sticks and vermicelli.

[0031] 8. Based on fluorescence spectroscopy and spiking method: Two test solutions were mixed with carbon dot o-PD-CDs, with a concentration of 60 µL / mL in each mixture, to obtain two detection solutions. The formaldehyde concentration in the two detection solutions was 0–0.8 mg / L. The pH of the two detection solutions was adjusted to 6.8 using BR buffer. The two adjusted detection solutions were incubated at room temperature for 40 min. The incubated detection solutions were then irradiated with a fluorescence spectrometer at an excitation wavelength of 380 nm. The fluorescence emission spectra of the two detection solutions in the range of 450 nm–650 nm were collected, and the fluorescence intensity at the emission center of 552 nm was recorded to obtain the fluorescence quenching values ​​of the two detection solutions.

[0032] 9. Based on the pre-determined formaldehyde content standard curve, calculate the formaldehyde content of dried bean curd sticks and the formaldehyde content of vermicelli.

[0033] This example demonstrates the use of a 60 µL / mL carbon dot o-PD-CDs fluorescent probe for the detection of formaldehyde in actual food products (dried bean curd sticks and vermicelli). The experimental results are shown in Table 2. The formaldehyde recovery rate reached 98.10%–107.86%, indicating a good recovery rate.

[0034] Table 2. Carbon dot o-PD-CDs used for formaldehyde content detection in food.

[0035] In summary, this invention uses carbon dot o-PD-CDs as fluorescent probes to detect formaldehyde content in solutions and has been successfully applied to the detection of formaldehyde in actual food products. The formaldehyde detection method of this invention has the advantages of high selectivity and high sensitivity, and is simple to operate and easy to understand.

Claims

1. A method for detecting formaldehyde content in food based on carbon dots, characterized in that, Includes the following steps: S1, the preparation of carbon dot o-PD-CDs includes the following steps: S1-1. Mix o-phenylenediamine with N,N-dimethylformamide and sonicate until completely dissolved to obtain a mixed solution; S1-2. Transfer the mixed solution to a three-necked flask and place it in a microwave catalytic reactor. Reflux the mixture at 200W and 150℃ for 40 minutes. After the reaction is complete, carbon dots o-PD-CDs are obtained. S1-3. After cooling the carbon dot o-PD-CDs to room temperature, store them in a refrigerator away from light for later use. S2. Preparation of the test solution: The dried food to be tested is crushed into powder, and then the powder is placed in a container containing ultrapure water. After ultrasonic treatment, it is centrifuged and the supernatant is taken. The supernatant is filtered once with filter paper and once with filter membrane. The filtrate is the test solution. The test solution is stored in a refrigerator in the dark for later use. S3. Preparation of the detection solution: The test solution is mixed with carbon dots o-PD-CDs to prepare the detection solution; S4. Measure the fluorescence quenching value of the test solution: Adjust the pH value of the test solution with BR buffer, incubate the adjusted test solution at room temperature, and then irradiate it under the fluorescence of the fluorescence spectrometer with an excitation wavelength of 380nm. Collect the fluorescence emission spectrum of the test solution in the range of 450nm~650nm, and record the fluorescence intensity at the emission center at 552nm to obtain the fluorescence quenching value of the test solution. S5. Formaldehyde content detection: The formaldehyde content of the sample to be tested is calculated based on the fluorescence quenching value of the test solution and the pre-determined formaldehyde content standard curve and linear equation.

2. The method for detecting formaldehyde content in food based on carbon dots according to claim 1, characterized in that, The formaldehyde concentration in the test solution in step S3 is in the range of 0~0.8 mg / L.

3. The method for detecting formaldehyde content in food based on carbon dots according to claim 1, characterized in that, The concentration of carbon dots o-PD-CDs is 50µL / mL to 70µL / mL.

4. The method for detecting formaldehyde content in food based on carbon dots according to claim 1, characterized in that, The concentration of the test solution is 200 mg / mL to 400 mg / mL.

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