Heterojunction fluorescent probe as well as preparation method and application thereof

Abstract

The invention provides a heterojunction fluorescent probe as well as a preparation method and application thereof. The heterojunction fluorescent probe comprises a Ti < 3 > C < 2 > T < x > MXene nanosheet and GQDs, wherein a heterojunction is formed between the Ti < 3 > C < 2 > T < x > MXene nanosheet and the GQDs. The 2D / 0D heterojunction fluorescent probe with the Schottky barrier can generate fluorescence response to H2S volatilization content change in the storage and decay process of fresh food, and the quality of the fresh food is determined according to TCTG fluorescence signal change.

Description

Technical Field

[0001] The present invention relates to the field of nondestructive food testing, and in particular to a heterojunction fluorescent probe and a preparation method and application thereof. Background Art

[0002] Hydrogen sulfide (H2S) is the third endogenous gas signal molecule after carbon monoxide (CO) and nitric oxide (NO), and is closely related to human physiology and disease. Abnormal concentrations of H2S can damage the respiratory, cardiac, ocular and other organ systems, and may lead to diseases such as atherosclerosis, Alzheimer's disease and Down syndrome. H2S can be produced during the decay of sulfur-rich organic foods such as fruits, vegetables and meats, and is characterized by a strong odor similar to rotten eggs. From a food safety perspective, monitoring the H2S content in food (especially fresh food) is crucial to assess freshness.

[0003] There are many methods for measuring H2S, including colorimetry, electrochemistry, gas / liquid chromatography, chemiluminescence detection, and fluorescence detection. Among them, fluorescence detection methods have attracted much attention due to their high sensitivity, high spatial resolution, real-time imaging, and non-destructive analysis capabilities. Currently, many fluorescent probes have been developed for the detection of H2S. However, these probes are limited by factors such as long response time, high limit of detection (LOD), narrow pH range, and practical application limitations. Therefore, it is urgent to develop new fluorescent probes that can overcome the above limitations.

[0004] Existing technologies and methods have some defects and shortcomings. They cannot perform visual non-destructive testing on the quality of fresh food during storage, logistics distribution, and trading. Existing methods are time-consuming and complicated, and cannot intuitively detect quality changes of fresh food. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a heterojunction fluorescent probe (based on Ti3C2TxMXene loaded with graphene quantum dots for detecting food quality) and a preparation method and application thereof.

[0006] According to the present invention, graphene quantum dots (GQDs) have a unique quasi-zero-dimensional (0D) structure, which gives them abundant edge defect positions. These positions can provide many charge catalytic active sites, thereby giving GQDs electrocatalytic, chemiluminescent and photoluminescent (PL) properties. In addition, GQDs also have photostability, excellent electron acceptance / donation properties and low toxicity, so they are expected to become materials for detecting volatile organic compounds (VOCs). MXene not only has an ultra-thin nanolayer structure and a naturally large specific surface area similar to graphene, but also has adjustable surface properties, excellent conductivity, hydrophilicity, and obvious thermal, mechanical, optical and chemical properties. Compared with traditional carbon-based nanomaterials, Ti3C2T X MXene nanosheets generally have higher surface chemical properties, thus providing abundant catalytic active sites. X The surface functional groups of MXene nanosheets can serve as anchoring sites to ensure stable binding to nanoparticles when mixed with other catalytic materials. In this case, the design and construction of 2D / 0D heterojunctions between MXene nanosheets and GQDs can merge the structural advantages of each component, resulting in a significant synergistic coupling effect. However, the optical properties of the interesting 2D / 0D nanocomposite system and its fluorescence detection performance for gas sensing have not been reported.

[0007] In a first aspect, the present invention provides a heterojunction fluorescent probe with a Schottky barrier for visual nondestructive detection of fresh food quality changes. The heterojunction fluorescent probe comprises Ti3C2T X MXene nanosheets and GQDs, the Ti3C2T x A heterojunction is formed between the MXene nanosheets and the GQDs. The 2D / 0D heterojunction fluorescent probe with a Schottky barrier provided by the present invention can generate a fluorescent response to the change in the content of H2S volatilization during the storage and corruption of fresh food, and determine the quality of the fresh food according to the change in the fluorescence signal of TCTG.

[0008] Preferably, the Ti3C2T X MXene nanosheets are single-layer Ti3C2T x MXene nanosheets.

[0009] According to the present invention, by (single layer) Ti3C2T xThe design and construction of 2D / 0D heterojunctions between MXene nanosheets and GQDs can combine the structural advantages of each component, which may produce a significant synergistic coupling effect and facilitate the sensing response to H2S. These results emphasize that the heterojunction fluorescent probe TCTG proposed in this study can effectively sense H2S generated during the spoilage of fresh food. Heterojunction fluorescent probes provide a rapid, reliable and sensitive method to ensure food safety and reduce the associated health and economic burdens. Provide a rapid, reliable and sensitive method to ensure food safety and reduce the associated health and economic burdens.

[0010] Preferably, the GQDs are uniformly distributed in the Ti3C2T x The surface of MXene nanosheets.

[0011] Further preferably, the Ti3C2T x The weight ratio of the MXene nanosheets to the GQDs is 20:80-80:20, preferably 25:75-75:25.

[0012] In a second aspect, the present invention provides a method for preparing the heterojunction fluorescent probe, comprising Ti3C2T x MXene nanosheets and GQDs are used as raw materials and prepared by a hydrothermal method; preferably, the following steps are included.

[0013] 1) Ti3C2T x MXene nanosheets, GQDs and water were mixed and stirred to obtain a suspension.

[0014] 2) subjecting the suspension to hydrothermal treatment to obtain a hydrothermal reaction product, centrifuging and washing the hydrothermal reaction product, and then freeze-drying it.

[0015] Preferably, in step 1), the Ti3C2T x The ratio of MXene nanosheets to GQDs is 20mg:80mg ~80mg:20mg; preferably, the Ti3C2T x The ratio of MXene nanosheets, GQDs and water is 20 mg:80 mg:30 mL ~80 mg:20 mg:30 mL.

[0016] Preferably, in step 1), the stirring time is more than 25 minutes.

[0017] Preferably, in step 2), the temperature of the hydrothermal treatment is 90-120°C, preferably 100-110°C, and the time of the hydrothermal treatment is 3-6h, preferably 4-5h; and / or, the washing adopts 75%-95% ethanol; and / or, the temperature of the freeze-drying is -50--70°C, preferably -60--65°C, and the time is 20-30h, preferably 24-28h.

[0018] In the present invention, a heterojunction fluorescent probe is prepared by a hydrothermal method, using Ti3C2Tx MXene nanosheets and GQDs as raw materials. At the same time, the preparation conditions of the probe are optimized by optimizing the ratio of the nanosheets to GQDs, stirring time, hydrothermal treatment temperature and time, which significantly improves the performance and stability of the fluorescent probe, making it have higher sensitivity and reliability in application detection.

[0019] The present invention also studies GQDs and Ti3C2T x The preparation of MXene nanosheets was optimized by optimizing the preparation conditions of high-quality GQDs, rationally controlling the molar ratio of citric acid to urea, the pH value of the precursor solution, and the temperature of the heat treatment. x The reaction conditions in the preparation process of MXene nanosheets are precisely controlled, such as centrifugal speed, ultrasonic treatment power and time, which further improves the comprehensive performance of the heterojunction fluorescent probe, significantly improves the performance and stability of the fluorescent probe, and enables it to have better application effects.

[0020] Preferably, the preparation method of the GQDs comprises: mixing citric acid, urea and water and adjusting the pH to obtain a precursor solution; heat-treating the precursor solution and dialyzing the reaction liquid.

[0021] Further preferably, the molar ratio of citric acid to urea is 1:10-10:10, preferably 6:10; and / or the pH of the precursor solution is 4.5-9.5, preferably 4.5; and / or the temperature of the heat treatment is 140-220°C, preferably 200°C.

[0022] Preferably, the Ti3C2T x The preparation method of MXene nanosheets comprises: mixing Ti3AlC2, HCl and LiF to obtain a mixed solution, centrifuging and washing the mixed solution to obtain a multilayer Ti3C2T X , the multilayer Ti3C2T X The samples were sonicated in deionized water and then centrifuged at high speed, and the supernatant was freeze-dried.

[0023] Preferably, the mass volume ratio of the Ti3AlC2, HCl and LiF is 1~3g:30~50mL:1~3g, preferably 2g:40mL:2g; and / or the centrifugal speed is 3000~4000rpm, preferably 3500 rpm; and / or the washing is deionized water washing to a pH value ≥6; and / or the power of the ultrasonic treatment is 180~250W, preferably 200 W; and / or the ultrasonic time is 20~35min, preferably 30 min; and / or the high-speed centrifugal speed is 3000~4000rpm, preferably 3500rpm, and the time is 20~35min, preferably 30 min.

[0024] The present invention uses a 2D single-layer Ti3C2T X MXene nanosheets are used as anchoring site donors and 0D GQDs are used as the fluorescent material for functional detection to obtain a new type of heterojunction fluorescent probe. This probe can produce fluorescence response to the change in the content of H2S volatilization during the storage and corruption of fresh food. X The change of fluorescence signal of @GQDs (TCTG) determines the quality of fresh food.

[0025] The present invention provides GQDs, a single layer Ti3C2T X The preparation of TCTG heterojunction, the evaluation of TCTG response performance to H2S, the response mechanism of TCTG to H2S and the practical application in different fresh food storage processes, the heterojunction TCTG fluorescent probe prepared by the present invention, through the heterojunction fluorescent probe to H2S response sensitivity, stability, specific selectivity and anti-interference, and the practical application of the fluorescent probe in different fresh food storage processes, the new heterojunction fluorescent probe prepared by the present invention has a good comprehensive effect.

[0026] In a third aspect, the present invention provides the use of the heterojunction fluorescent probe or the heterojunction fluorescent probe obtained by the preparation method in monitoring the quality of fresh food, preferably in real-time monitoring of quality changes of eggs, pork, and fish.

[0027] The technical solution proposed in this invention is based on a 2D single-layer Ti3C2T x MXene nanosheets are loaded with highly uniform 0D GQDs prepared by optimizing the synthesis conditions. A heterojunction nanocomposite system is constructed by a hydrothermal method. Currently, the optical properties of the 2D / 0D nanocomposite system and its fluorescence detection performance for gas sensing have not been reported. x Unique electronic properties and GQDs on Ti3C2T x Functional modification of the nanostructured carbon nanotubes enables efficient fluorescence response to H2S. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 The fluorescence intensity of GQDs prepared with different citric acid / urea ratios provided in the embodiments of the present invention.

[0030] Figure 2 The fluorescence intensity of GQDs prepared with different precursor solution pH and synthesis temperature provided in the embodiments of the present invention.

[0031] Figure 3 Transmission electron microscope scanning image and size distribution of GQDs prepared by citric acid / urea (6:10), pH=4.5, and synthesis temperature of 200°C provided in an embodiment of the present invention.

[0032] Figure 4 Ti3AlC2 and multilayer Ti3C2T provided in the embodiment of the present invention x Scanning electron microscopy, single layer Ti3C2T x and TCTG transmission electron microscopy.

[0033] Figure 5 In the embodiment of the present invention, H2S, GQDs, TCTG (25–75%) The transient reaction kinetic curves between .

[0034] Figure 6 TCTG in the embodiment of the present invention (50%) Long-term stability of the fluorescent probe over 20 days.

[0035] Figure 7 TCTG after 20 s of H2S (0-500 μM) titration in the present invention (50%) Changes in fluorescence spectra and their linear correlation.

[0036] Figure 8 TCTG in the presence (20 & 200 μM) and absence of H2S at different pH values ​​in the present invention (50%) fluorescence changes.

[0037] Fig. 9 TCTG is the probe in the embodiment of the present invention (50%) Fluorescence spectra and UV absorption spectra after the introduction of other analytes and H2S.

[0038] Fig.10In the embodiments of the present invention, other analytes are contained TCTG Fluorescence intensity before and after the introduction of H2S.

[0039] Fig.11 These are images of the fresh (0h) and corrupt (48h) states of eggs, pork, and fish under sunlight and 365nm ultraviolet light at 25°C in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] Example 1

[0042] The present invention provides a 2D / 0D heterojunction fluorescent probe and a preparation method and practical application thereof, which is prepared as follows.

[0043] 1) Prepare graphene quantum dots GQDs with highly uniform size by optimizing the synthesis conditions. The specific preparation process is as follows: First, weigh different masses of citric acid and urea according to a molar ratio of 6:10, and dissolve them (the total mass of citric acid and urea is 1.35 g) in 10 mL of deionized water. Then transfer the precursor solution (adjust pH = 4.5) to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene and heat it at 200°C in a high-temperature vacuum oven for 12 hours. The yellow-brown liquid obtained by the reaction is then placed in a dialysis bag (molecular weight cutoff: 100-500Da) and dialyzed for 24 hours, changing the water every 12 hours. In the embodiment, NaOH (10 mol / L) or HCl (9 mol / L) is used to adjust the pH value of the solution. The fluorescence intensity of GQDs prepared at the preferred citric acid / urea ratio / precursor solution pH / synthesis temperature in this embodiment is the best. The fluorescence intensity of GQDs prepared with different citric acid / urea ratios is as shown in the figure. Figure 1 The fluorescence intensity of GQDs prepared at different precursor solution pH and synthesis temperature is shown in Figure 2 The transmission electron microscopy image and size distribution of GQDs prepared by citric acid / urea (6:10), pH=4.5, and synthesis temperature of 200℃ are shown in Figure 2 (pH of the control group is 3). Figure 3 shown.

[0044] 2) Single-layer Ti3C2T X Preparation of MXene nanosheets and TCTG. The specific preparation process is as follows: First, Ti3AlC2 (2 g) was gradually added to a mixed solution consisting of 9 M HCl (40 mL) and LiF (2 g) at a reaction temperature of 35 °C. After 24 h, the obtained product was separated by centrifugation at 3500 rpm and washed continuously with deionized water until the pH value was ≥6 to obtain expanded and sticky multilayer Ti3C2T X In order to obtain a single layer Ti3C2T X MXene nanosheets, multilayer Ti3C2T X The Ti3C2T monolayer was dispersed in deionized water and then ultrasonicated at 200 W for 30 min. The dispersion was centrifuged at 3500 rpm for 30 min. The supernatant was then collected and freeze-dried to obtain a gray powder, i.e., a monolayer Ti3C2T X MXene nanosheets.

[0045] 3) Ti3C2T X The 2D / 0D heterojunctions (TCTG) of @GQD were prepared by a hydrothermal method. 100 mg of Ti3C2T X The mixture of TCTG and GQDs was added to 30 mL of deionized water and stirred vigorously at room temperature for 30 min to form a uniform suspension. Subsequently, the mixed solution was transferred to an autoclave equipped with a polytetrafluoroethylene container and treated at 100 °C for 4 h. The hydrothermal reaction product was centrifuged and washed several times with 75% ethanol. Finally, TCTG was freeze-dried at -60 °C for 24 h to obtain （25%、50%、75%） powder.

[0046] Figure 4 Ti3AlC2 and multilayer Ti3C2T provided in the embodiment of the present invention x Scanning electron microscopy, single layer Ti3C2T x and TCTG transmission electron microscopy. Ti3AlC2, as one of the MAX phase materials, has a unique layered hexagonal structure. Multilayer Ti3C2T x Displaying a layered structure, the thin, flaky nanosheets exhibit an accordion-like morphology due to the stacking of the individual layers. This characteristic appearance is the result of a chemical etching process, where the selective removal of the Al layer from Ti3AlC2 leads to the formation of independent layers and a textured titanium carbide surface. x The nanosheets appear extremely thin and almost transparent under the first electron microscope due to the further exfoliation process. The TEM image of TCTG shows that GQDs are evenly distributed on the monolayer Ti3C2T x on the surface of the PDMS chip, where GQDs can be observed as unique black dot-like structures.

[0047] The TCTG prepared in the example was evaluated for its sensitivity, stability, selectivity and anti-interference to H2S. The details are as follows. (50%) The fluorescence intensity of TCTG changes rapidly after 2 seconds. (25%和75%) and GQDs changed after 4s, 4s and 9s, respectively, and finally reached stable values ​​after 3s, 6s, 9s and 12s. (25–75%) The transient reaction kinetic curve between Figure 5 shown.

[0048] After the introduction of 50 μM H2S, the probe showed high long-term stability, with little change in response (5.43%~5.32%) within 20 days. The small error range highlights the reliability and repeatability of the probe measurement. TCTG (50%) The long-term stability of the fluorescent probe within 20 days is shown in Figure 6 shown.

[0049] Figure 7 TCTG was titrated for 20 s after H2S (0-500 μM) (50%) Changes in fluorescence spectra (left), with the inset showing the color change of the fluorescent probe under UV light; and TCTG (50%) Linear correlation between fluorescence intensity and H2S (0-500 μM) (right amplitude). As the H2S concentration increases from 0 to 500 μM, the fluorescence peak at λem=440 nm decreases under 360 nm excitation, and the fluorescence color changes from bright blue to light blue. The fluorescence intensity of the probe shows a strong linear correlation with the H2S concentration. Figure 7 The Pearson R value of the linear relationship was 0.9968, and the LOD based on fluorescence intensity was calculated to be 41.82 ppb.

[0050] Figure 8 TCTG in the presence (20 μM and 200 μM) and absence of H2S at different pH values (50%) In the absence of H2S, the probe TCTG (50%) There was no fluorescence change in the pH range of 1 to 13, indicating that it has excellent stability under different pH conditions. (50%) After the action of H2S (200 μM) for 60 s, the fluorescence quenching phenomenon was obvious and stable in the pH range of 4-13, and it showed good selectivity for H2S in the pH range of 5-10.

[0051] Fig. 9 TCTG (50%)Fluorescence spectra and UV absorption spectra after the introduction of other analytes and H2S. (50%) Absorption and fluorescence spectra of TCTG, including VOCs (formaldehyde, methane, ethanol, acetone and H2S) and inorganic gases (NO, H2, NH3 and SO2). (50%) The addition of H2S or other analytes (all at 10 ppm) to the solution resulted in a significant decrease in the fluorescence intensity at λem440 nm only in the H2S-treated solution. Fig. 9 The inset shows that among the selected competing analytes (10 ppm each), only H2S caused a significant decrease in UV absorbance at 330 nm. (50%) The anti-interference properties of H2S were introduced into TCTG containing various analytes. (50%) Competition experiments were performed in solution. (50%) The fluorescence intensity of H2S was not affected by other interfering analytes.

[0052] To further study TCTG (50%) The anti-interference properties of H2S were introduced into TCTG containing various analytes. (50%) Competition experiments were performed in solution. (50%) The fluorescence intensity of H2S was not affected by other interfering analytes. Fig.10 is the fluorescence intensity of TCTG containing other analytes before and after the introduction of H2S.

[0053] This example provides a practical application of TCTG in the storage process of fresh food. The specific steps are as follows.

[0054] 500 g of fish fillets and pork were washed with distilled water, and eggs were homogenized and mixed. TCTG fluorescent probe (0.1 mg / mL) was placed in a culture dish and then placed in a well-sealed food preservation box together with fish fillets, pork and liquid eggs. Subsequently, the preservation box was placed in a 25°C constant temperature incubator, and the fluorescence intensity of the probe at different time points (0, 6, 12, 18, 24, 30, 36, 42 and 48 h) was recorded, as well as the freshness and corruption state images of the food during the day (daylight) and under 365 nm ultraviolet light.

[0055] Fig.11 The images of the fresh (0h) and spoiled (48h) states of eggs, pork, and fish under sunlight and 365nm ultraviolet light at 25°C in the embodiment of the present invention. As the fresh food spoils, the H2S concentration in the headspace of the food preservation box increases, the probe TCGC at different time points （50%） The change of fluorescence intensity.

[0056] At the beginning of storage, 3 sets of probes TCTG (50%) All exhibited bright blue fluorescence: after storage at 25°C for 48 hours, the fluorescence of the probe in the fish group was almost invisible, while weak blue fluorescence was visible in both the egg and pork groups. Eggs produce a large amount of H2S within 24-48 hours, and the speed is very fast, while a significant increase in headspace concentration was not observed in pork until 36 hours later. Fish fillets have high moisture content, which enhances the activity of spoilage bacteria, and their loose tissue structure is conducive to bacterial invasion and decomposition, producing the most H2S in the shortest time (12-30 hours). Pork has a lower moisture content and more complex muscle tissue, resulting in slower microbial activity and slower H2S production. These results indicate that TCTG (50%) It reacts specifically to H2S and can be used as a convenient fluorescent probe to monitor raw meat quality without the need for complex instruments.

[0057] The embodiments of the present invention also provide the following effect verification, which can be specifically explained by the following examples.

[0058] Example 1: Quality inspectors detect the quality changes of eggs, pork, and fish in real time from the start of distribution to the sales site. The quality inspection process of eggs, pork, and fish is as follows: 1) Before eggs, pork, and fish enter the cold chain delivery vehicle, collect 2-3 eggs, 500g pork or fish as samples and put them into a fresh-keeping box containing the TCTG heterojunction fluorescent probe prepared in the above embodiment. 2) Use 365nm ultraviolet light to irradiate the fluorescent probe during the logistics and transaction stages, and conduct random inspections at irregular intervals. 3) Monitor the quality changes of eggs, pork, and fish in real time through changes in fluorescence intensity.

[0059] Example 2: Consumers detect the freshness changes of eggs, pork, and fish in real time during the retail stage. The quality detection process of eggs, pork, and fish is as follows: 1) After eggs, pork, and fish are sold to supermarkets and other places, each retail site is equipped with a 365nm UV lamp and a TCTG heterojunction fluorescent probe device for merchants and consumers to use. 2) The seller takes an appropriate amount of samples of the batch of eggs, pork, and fish and puts them into a sealed fresh-keeping box with a TCTG heterojunction fluorescent probe for consumers to test. 3) Consumers use the equipped 365nm UV lamp device for testing. The quality of eggs, pork, and fish is tested by the device and consumers decide whether to buy them.

[0060] It has been verified that the TCTG heterojunction fluorescent probe prepared by the embodiment of the present invention can accurately simulate the quality of eggs, pork and fish during cold chain transportation and trading. The embodiment of the present invention can effectively improve the quality monitoring ability of eggs, pork and fish during cold chain transportation and trading, ensure the quality of eggs, pork and fish, and provide convenience for quality inspectors to conduct rapid and real-time detection. The embodiment of the present invention can accurately predict the quality of eggs, pork and fish at the shelf retail stage, and provide consumers with quality basis. The embodiment of the present invention can effectively avoid damage to eggs, pork and fish products and achieve non-destructive testing.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A heterojunction fluorescent probe, characterized in that: Including Ti3C2T X MXene nanosheets and GQDs, the Ti3C2T x A heterojunction is formed between the MXene nanosheets and the GQDs.

2. The heterojunction fluorescent probe according to claim 1, characterized in that: The Ti3C2T X MXene nanosheets are single-layer Ti3C2T x MXene nanosheets; preferably, the GQDs are uniformly distributed on the Ti3C2T x The surface of MXene nanosheets.

3. The heterojunction fluorescent probe according to claim 1 or 2, characterized in that: The Ti3C2T x The weight ratio of the MXene nanosheets to the GQDs is 20:80 to 80:

20.

4. The method for preparing the heterojunction fluorescent probe according to any one of claims 1 to 3, characterized in that: To contain Ti3C2T x MXene nanosheets and GQDs are used as raw materials and prepared by a hydrothermal method; preferably, the method comprises: 1) Ti3C2T x MXene nanosheets, GQDs and water were mixed and stirred to obtain a suspension; 2) subjecting the suspension to hydrothermal treatment to obtain a hydrothermal reaction product, centrifuging and washing the hydrothermal reaction product, and then freeze-drying it.

5. The method for preparing a heterojunction fluorescent probe according to claim 4, characterized in that: In step 1), the Ti3C2T x The ratio of MXene nanosheets to GQDs is 20 mg:80 mg to 80 mg:20 mg; and / or, the stirring time is more than 25 min.

6. The method for preparing a heterojunction fluorescent probe according to claim 4 or 5, characterized in that: In step 2), the temperature of the hydrothermal treatment is 90-120°C, and the time of the hydrothermal treatment is 3-6 hours; and / or, the washing adopts 75%-95% ethanol; and / or, the temperature of the freeze-drying is -50--70°C, and the time is 20-30 hours.

7. The method for preparing a heterojunction fluorescent probe according to any one of claims 4 to 6, characterized in that: The preparation method of the GQDs comprises: mixing citric acid, urea and water and adjusting the pH to obtain a precursor solution; heat-treating the precursor solution and dialyzing the reaction liquid.

8. The method for preparing a heterojunction fluorescent probe according to claim 7, characterized in that: The molar ratio of citric acid to urea is 1:10-10:10; and / or the pH of the precursor solution is 4.5-9.5; and / or the temperature of the heat treatment is 140-220°C.

9. The method for preparing a heterojunction fluorescent probe according to any one of claims 4 to 8, characterized in that: The Ti3C2T x The preparation method of MXene nanosheets comprises: mixing Ti3AlC2, HCl and LiF to obtain a mixed solution, centrifuging and washing the mixed solution to obtain a multilayer Ti3C2T X , the multilayer Ti3C2T X Ultrasonic treatment is performed in deionized water, followed by high-speed centrifugation, and the supernatant is freeze-dried; preferably, the mass volume ratio of the Ti3AlC2, HCl and LiF is 1~3g:30~50mL:1~3g; and / or the speed of the centrifugation is 3000~4000rpm; and / or the washing is deionized water washing to a pH value ≥6; and / or the power of the ultrasonic treatment is 180~250W; and / or the ultrasonic time is 20~35min; and / or the speed of the high-speed centrifugation is 3000~4000rpm, and the time is 20~35min.

10. Use of the heterojunction fluorescent probe according to any one of claims 1 to 3 or the heterojunction fluorescent probe obtained by the preparation method according to any one of claims 4 to 9 in monitoring the quality of fresh food, preferably in real-time monitoring of quality changes of eggs, pork and fish.

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