A heterojunction fluorescent probe and a preparation method and application thereof

Abstract

The application provides a heterojunction fluorescent probe and a preparation method and application thereof. X The heterojunction fluorescent probe comprises Ti3C2T x MXene nanosheets and GQDs, and a heterojunction is formed between the Ti3C2T x MXene nanosheets and the GQDs. The 2D / 0D heterojunction fluorescent probe with a Schottky barrier provided by the application can produce a fluorescent response to the content change of H2S volatilization in the storage and corruption process of fresh food, and the quality of the fresh food can be determined according to the fluorescent signal change of TCTG.

Description

Technical Field

[0001] This invention relates to the field of non-destructive testing of food, specifically to a heterojunction fluorescent probe, its preparation method, and its application. Background Technology

[0002] Hydrogen sulfide (H2S) is the third endogenous gaseous signaling molecule after carbon monoxide (CO) and nitric oxide (NO), and it is closely related to human physiology and disease. Abnormal concentrations of H2S can damage 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 for assessing freshness.

[0003] Currently, there are various methods for measuring H2S, including colorimetric methods, electrochemical methods, gas / liquid chromatography, chemiluminescence detection, and fluorescence detection. Among these, fluorescence detection methods have attracted much attention due to their high sensitivity, high spatial resolution, real-time imaging, and non-destructive analytical capabilities. Many fluorescent probes for H2S detection have been developed. However, these probes are limited by factors such as long response times, high limits of detection (LOD), narrow pH ranges, and practical application limitations. Therefore, there is an urgent need to develop novel fluorescent probes that can overcome these limitations.

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

[0005] To address the aforementioned technical problems, this invention provides a heterojunction fluorescent probe (based on Ti3C2TXMXene loaded graphene quantum dots for detecting food quality), its preparation method, and its application.

[0006] According to the present invention, graphene quantum dots (GQDs) possess a unique quasi-zero-dimensional (0D) structure, endowing them with abundant edge defect sites. These sites can provide numerous charge-catalyzed active sites, thereby endowing GQDs with electrocatalytic, chemiluminescent, and photoluminescent (PL) properties. Furthermore, GQDs also exhibit photostability, excellent electron acceptor / donor properties, and low toxicity, thus holding promise as materials for detecting volatile organic compounds (VOCs). MXene not only possesses an ultrathin nanolayer structure and a naturally large specific surface area similar to graphene, but also exhibits tunable surface properties, excellent conductivity, hydrophilicity, and significant thermal, mechanical, optical, and chemical properties. Compared with traditional carbon-based nanomaterials, Ti3C2T… X MXene nanosheets typically possess superior surface chemistry, thus providing abundant catalytic active sites. Furthermore, Ti3C2T... X The surface functional groups of MXene nanosheets can serve as anchoring sites, ensuring stable binding with nanoparticles when mixed with other catalytic materials. In this context, designing and constructing 2D / 0D heterojunctions between MXene nanosheets and GQDs can integrate the structural advantages of each component, resulting in a significant synergistic coupling effect. However, the optical properties of this intriguing 2D / 0D nanocomposite system and its fluorescence detection performance for gas sensing have not yet been reported.

[0007] In a first aspect, the present invention provides a heterojunction fluorescent probe with a Schottky barrier for visually and non-destructively detecting changes in the quality of fresh food. This 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 this invention can generate a fluorescence response to the change in H2S volatilization content during the storage and spoilage of fresh food, and determine the quality of fresh food based on the change in TCTG fluorescence signal.

[0008] Preferably, the Ti3C2T X MXene nanosheets are monolayer Ti3C2T x MXene nanosheets.

[0009] According to the present invention, through (monolayer) Ti3C2T xThe design and construction of a 2D / 0D heterojunction between MXene nanosheets and GQDs can integrate the structural advantages of each component, potentially leading to significant synergistic coupling effects and facilitating the sensing response to H2S. These results highlight the effectiveness of the proposed heterojunction fluorescent probe TCTG in sensing H2S generated during the spoilage of fresh food. Heterojunction fluorescent probes provide a rapid, reliable, and sensitive method to ensure food safety and reduce associated health and economic burdens.

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

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

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

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

[0014] 2) The suspension is subjected to hydrothermal treatment to obtain a hydrothermal reaction product. The hydrothermal reaction product is centrifuged and washed, and then freeze-dried.

[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 25 minutes or more.

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

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

[0019] This invention also includes GQDs and Ti3C2T x The preparation of MXene nanosheets was optimized by improving the preparation conditions for high-quality GQDs, rationally controlling the molar ratio of citric acid to urea, the pH of the precursor solution, and the heat treatment temperature. Simultaneously, the preparation conditions for Ti3C2T were improved. x The reaction conditions during the preparation of MXene nanosheets are precisely controlled, such as centrifugation speed, ultrasonic treatment power and time, which further improves the overall performance of the heterojunction fluorescent probe, significantly enhances the performance and stability of the fluorescent probe, and makes it more effective in application.

[0020] Preferably, the preparation method of the GQDs includes: mixing citric acid, urea and water and adjusting the pH to obtain a precursor solution; subjecting the precursor solution to heat treatment; and dialysis treatment of the reaction liquid.

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

[0022] Preferably, the Ti3C2T x The preparation method of MXene nanosheets includes: mixing Ti3AlC2, HCl and LiF to obtain a mixture, centrifuging and washing the mixture to obtain multilayer Ti3C2T X The multilayer Ti3C2T X The solution is ultrasonically treated in deionized water, then centrifuged at high speed, and the supernatant is freeze-dried.

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

[0024] This invention uses 2D monolayer Ti3C2T X A novel heterojunction fluorescent probe was developed using MXene nanosheets as anchoring site donors and 0D GQDs as functionalized fluorescent substances. This probe exhibits a fluorescent response to changes in H2S volatilization during the storage and spoilage of fresh food, based on the Ti3C2T... X Changes in the fluorescence signal of @GQDs (TCTG) determine the quality of fresh food.

[0025] This invention provides GQDs, a single-layer Ti3C2T X This invention relates to the preparation of TCTG heterojunctions, the evaluation of TCTG's response performance to H2S, the response mechanism of TCTG to H2S, and its practical application in different fresh food storage processes. The invention also presents the novel heterojunction TCTG fluorescent probe, demonstrating excellent comprehensive performance in H2S response sensitivity, stability, specificity, selectivity, and anti-interference capabilities, as well as its practical application in different fresh food storage processes.

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

[0027] The technical solution proposed in this invention is based on 2D monolayer Ti3C2T x Highly uniform 0D GQDs were prepared by loading MXene nanosheets under optimized synthesis conditions. A heterojunction nanocomposite system was constructed via a hydrothermal method. Currently, the optical properties of 2D / 0D nanocomposite systems and their fluorescence detection performance for gas sensing have not been reported. This invention utilizes Ti3C2T… x Unique electronic properties and GQDs for Ti3C2T x Functional modifications were made to achieve a highly efficient fluorescence response to H2S. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[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 at different precursor solution pH and synthesis temperature according to the embodiments of the present invention.

[0031] Figure 3 Transmission electron microscopy (TEM) images and size distribution of GQDs prepared by citric acid / urea (6:10), pH=4.5, and synthesis temperature 200℃, as provided in this embodiment of the invention.

[0032] Figure 4 Ti3AlC2 and multilayer Ti3C2T provided in the embodiments of the present invention x Scanning electron microscopy, monolayer Ti3C2T x And TCTG transmission electron microscopy.

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

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

[0035] Figure 7 In this embodiment of the invention, TCTG was obtained after H2S (0-500 μM) titration for 20 s. (50%) Changes in fluorescence spectra and linear correlation.

[0036] Figure 8 This invention provides examples of TCTG levels with and without H2S at different pH values. (50%) Fluorescence changes.

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

[0038] Figure 10Other analytes are included in the embodiments of the present invention. TCTG Fluorescence intensity before and after H2S introduction.

[0039] Figure 11 These are images of eggs, pork, and fish at 25°C under sunlight and 365nm ultraviolet light in their fresh (0h) and spoiled (48h) states, as shown in this embodiment of the invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0041] Example 1

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

[0043] 1) Highly uniform graphene quantum dots (GQDs) were prepared by optimizing the synthesis conditions. The specific preparation process is as follows:

[0044] First, citric acid and urea of ​​different masses were weighed according to a molar ratio of 6:10, and dissolved in 10 mL of deionized water (total mass of citric acid and urea: 1.35 g). Then, the precursor solution (adjusted to pH 4.5) was transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene and heated in a high-temperature vacuum oven at 200°C for 12 h. Subsequently, the resulting yellow-brown liquid was placed in a dialysis bag (molecular weight cutoff: 100-500 Da) and dialyzed for 24 h, with water changed every 12 h. In this example, the pH of the solution was adjusted using NaOH (10 mol / L) or HCl (9 mol / L). The optimal citric acid / urea ratio, precursor solution pH, and synthesis temperature yielded the best fluorescence intensity for the GQDs prepared in this example. The fluorescence intensity of GQDs prepared with different citric acid / urea ratios is shown below. Figure 1 As shown. The fluorescence intensity of GQDs prepared at different precursor solution pH and synthesis temperature is as follows. Figure 2 As shown (the control group had a pH of 3). Transmission electron microscopy (TEM) images and size distributions of GQDs prepared with citric acid / urea (6:10), pH=4.5, and a synthesis temperature of 200℃ are shown below. Figure 3 As shown.

[0045] 2) Single-layer Ti3C2T XPreparation of MXene nanosheets and TCTG. The specific preparation process is as follows:

[0046] First, at a reaction temperature of 35°C, Ti3AlC2 (2g) was gradually added to a mixed solution consisting of 9M HCl (40 mL) and LiF (2g). After 24 h, the product was separated by centrifugation at 3500 rpm and continuously washed with deionized water until the pH value was ≥6, yielding expanded and viscous multilayer Ti3C2T. X To obtain a single-layer Ti3C2T X MXene nanosheets, multilayer Ti3C2T X The sample was dispersed in deionized water and then sonicated at 200 W for 30 min. The dispersion was then centrifuged at 3500 rpm for 30 min. Subsequently, the supernatant was collected and freeze-dried to obtain a gray powder, namely a monolayer Ti3C2T. X MXene nanosheets.

[0047] 3) Ti3C2T X @GQD's 2D / 0D heterojunction (TCTG) was prepared via a hydrothermal method. 100 mg of Ti3C2T at different weight percentages (25%, 50%, 75%) was used. X The mixture of GQDs and TCTG was added separately to 30 mL of deionized water and stirred vigorously for 30 min at room temperature to form a homogeneous suspension. The mixture was then transferred to an autoclave containing 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, it was freeze-dried at -60 °C for 24 h to obtain TCTG. （25%、50%、75%） powder.

[0048] Figure 4 Ti3AlC2 and multilayer Ti3C2T provided in the embodiments of the present invention x Scanning electron microscopy, monolayer Ti3C2T x And TCTG transmission electron microscopy. Ti3AlC2, as one of the MAX phase materials, has a unique layered hexagonal structure. Multilayer Ti3C2T x Exhibiting a layered structure, the thin, sheet-like nanosheets exhibit an accordion-like shape due to the stacking of layers. This characteristic appearance is a result of a chemical etching process, in which the selective removal of the Al layer from Ti3AlC2 leads to the formation of independent layers and a textured titanium carbide surface. Monolayer Ti3C2T x The nanosheets appeared extremely thin and almost transparent under a first-ever electron microscope due to a further exfoliation process. TEM images from TCTG showed GQD uniformly distributed within the monolayer Ti3C2T. x On the surface, GQD can be observed as a unique black dot-like structure.

[0049] The TCTG prepared in the examples was evaluated for its H2S response sensitivity, stability, specific selectivity, and anti-interference properties. Details are as follows. TCTG (50%) The fluorescence intensity changed rapidly after 2 seconds, while TCTG (25%和75%) H2S and GQD show changes after 4s, 4s, and 9s respectively, and finally reach stable values ​​after 3s, 6s, 9s, and 12s. H2S, GQDs, and TCTG... (25–75%) The transient reaction kinetic curves between them are as follows: Figure 5 As shown.

[0050] After introducing 50 μM H2S, the probe exhibited high long-term stability, with minimal response change over 20 days (5.43%–5.32%). The small error range highlights the reliability and repeatability of the probe measurements. TCTG (50%) The long-term stability of the fluorescent probe over 20 days is as follows: Figure 6 As shown.

[0051] Figure 7 TCTG after titration with H2S (0-500 μM) for 20 s (50%) Changes in fluorescence spectra (left panel), with an inset showing the color change of the fluorescent probe under ultraviolet light; and TCTG. (50%) The fluorescence intensity shows a linear correlation with H2S (0-500 μM) (right side). As the H2S concentration increases from 0 to 500 μM, the fluorescence peak at λem=440 nm under 360 nm excitation decreases, and the fluorescence color changes from bright blue to light blue. The probe's fluorescence intensity exhibits a strong linear correlation with H2S concentration, as shown in the right side. Figure 7 As shown. The Pearson R value for the linear relationship is 0.9968, and the LOD calculated based on fluorescence intensity is 41.82 ppb.

[0052] Figure 8 TCTG in the presence (20 μM and 200 μM) and absence of H2S at different pH values (50%) The fluorescence change. In the absence of H2S, the probe TCTG... (50%) No fluorescence change was observed within the pH range of 1–13, indicating excellent stability under different pH conditions. Probe TCTG (50%) After being exposed to H2S (200 μM) for 60 s, it exhibited a significant and stable fluorescence quenching phenomenon in the pH range of 4 to 13, and showed good selectivity for H2S in the pH range of 5 to 10.

[0053] Figure 9 For probe TCTG (50%)Fluorescence and UV absorption spectra after the introduction of other analytes and H2S. TCTG was evaluated in the presence of various competing analytes. (50%) Absorption and fluorescence spectra of [the gas], including VOCs (formaldehyde, methane, ethanol, acetone, and H2S) and inorganic gases (NO, H2, NH3, and SO2). [The data is then] directed to TCTG. (50%) The addition of H2S or other analytes (all at 10 ppm) to the solution resulted in a significant decrease in fluorescence intensity at λem440 nm only in H2S-treated solutions. Furthermore, Figure 9 The illustrations show that, among the selected competing analytes (10 ppm each), only H₂S caused a significant decrease in UV absorption at 330 nm. Further investigation of TCTG is needed. (50%) The anti-interference properties are achieved by introducing H2S into TCTG containing various analytes. (50%) Competition experiments were conducted in solution. TCTG (50%) The fluorescence intensity of H2S is not affected by other interfering analytes.

[0054] To further study TCTG (50%) The anti-interference properties are achieved by introducing H2S into TCTG containing various analytes. (50%) Competition experiments were conducted in solution. TCTG (50%) The fluorescence intensity of H2S is not affected by other interfering analytes. Figure 10 The fluorescence intensity of TCTG containing other analytes before and after the introduction of H2S.

[0055] This embodiment demonstrates the practical application of TCTG in the storage of fresh food. The specific steps are as follows.

[0056] 500g of fish fillets and pork were washed with distilled water, while the eggs were homogenized. A TCTG fluorescent probe (0.1 mg / mL) was placed in a petri dish, and then packaged with the fish fillets, pork, and liquid eggs into a sealed food storage container. The container was then placed in a 25°C incubator, and the fluorescence intensity of the probe was recorded at different time points (0, 6, 12, 18, 24, 30, 36, 42, and 48 h), as well as images of the food's freshness and spoilage under daylight (sunlight) and 365 nm ultraviolet light irradiation.

[0057] Figure 11 Images of eggs, pork, and fish at 25°C under sunlight and 365nm ultraviolet light irradiation in their fresh (0h) and spoiled (48h) states, as well as in the headspace environment of the food preservation container, show the H2S concentration increasing at different time points due to spoilage of fresh food. （50%） The change in fluorescence intensity.

[0058] In the early stages of storage, three probes were used for TCTG. (50%) Both exhibited bright blue fluorescence: after 48 hours of storage at 25℃, the fluorescence of the probe was almost invisible in the fish group, while weak blue fluorescence was visible in both the egg and pork groups. Eggs produced a large amount of H2S within 24-48 hours at a rapid rate, while a significant increase in headspace concentration was not observed in pork until 36 hours later. Fish fillets, due to their high moisture content, enhanced the activity of putrefactive bacteria, and their loose tissue structure facilitated bacterial invasion and decomposition, resulting in the highest H2S production in the shortest time (12-30 hours). Pork, with its lower moisture content and more complex muscle tissue, exhibited slower microbial activity and slower H2S production. These results indicate that TCTG... (50%) It has a specific response to H2S and can be used as a convenient fluorescent probe for monitoring the quality of raw meat without the need for complex instruments.

[0059] The embodiments of the present invention also provide the following effect verification, which can be illustrated by the following examples.

[0060] Example 1: Quality inspectors monitor the quality changes of eggs, pork, and fish in real time from delivery to the point of sale. The quality inspection process for eggs, pork, and fish is as follows: 1) Before entering the cold chain delivery vehicle, 2-3 eggs and 500g of pork or fish are collected as samples and placed in a preservation box containing the TCTG heterojunction fluorescent probe prepared in the above example. 2) During the logistics and transaction stages, the fluorescent probe is irradiated with a 365nm ultraviolet lamp for random sampling at various times and locations. 3) The quality changes of eggs, pork, and fish are monitored in real time by observing changes in fluorescence intensity.

[0061] Example 2: Real-time monitoring of freshness changes in eggs, pork, and fish during the retail stage. The quality testing process for eggs, pork, and fish is as follows: 1) After eggs, pork, and fish are sold to supermarkets, markets, etc., each retail location is equipped with a 365nm ultraviolet lamp and a TCTG heterojunction fluorescence probe device for use by merchants and consumers. 2) The seller takes an appropriate amount of the batch of eggs, pork, and fish as a sample and places it in a sealed preservation box containing the TCTG heterojunction fluorescence probe for consumer testing. 3) Consumers use the provided 365nm ultraviolet lamp device to conduct the testing. The quality of eggs, pork, and fish is tested through this device, and consumers decide whether to purchase them.

[0062] Verification has shown that the TCTG heterojunction fluorescent probe prepared in this invention can accurately simulate the quality of eggs, pork, and fish during cold chain transportation and trading. This invention effectively improves the ability to monitor the quality of eggs, pork, and fish during cold chain transportation and trading, ensuring the quality of eggs, pork, and fish, and providing convenience for quality inspectors to conduct rapid, real-time testing. This invention can accurately predict the quality of eggs, pork, and fish at the retail stage, providing consumers with quality information. This invention effectively avoids damage to egg, pork, and fish products, achieving non-destructive testing.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate 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; the Ti3C2T X MXene nanosheets are monolayer Ti3C2T x MXene nanosheets; the GQDs are uniformly distributed in the Ti3C2T x The surface of MXene nanosheets, the Ti3C2T x The weight ratio of MXene nanosheets to GQDs is 20:80 to 80:20; The method for preparing the heterojunction fluorescent probe includes: preparing Ti3C2T x MXene nanosheets, GQDs, and water were mixed and stirred to obtain a suspension. The suspension was subjected to hydrothermal treatment to obtain a hydrothermal reaction product. The hydrothermal reaction product was centrifuged and washed, and then freeze-dried. The preparation method of the GQDs includes: mixing citric acid, urea and water and adjusting the pH to obtain a precursor solution; subjecting the precursor solution to heat treatment; and subjecting the reaction liquid to dialysis treatment. The Ti3C2T x The preparation method of MXene nanosheets includes: mixing Ti3AlC2, HCl and LiF to obtain a mixture, centrifuging and washing the mixture to obtain multilayer Ti3C2T X The multilayer Ti3C2T X The solution is subjected to ultrasonic treatment in deionized water, followed by high-speed centrifugation, and the supernatant is freeze-dried. The mass-to-volume ratio of Ti3AlC2, HCl, and LiF is 1-3g: 30-50mL: 1-3g. The centrifugation speed is 3000-4000rpm. The washing is performed with deionized water until the pH value is ≥6. The ultrasonic treatment power is 180-250W. The ultrasonic treatment time is 20-35min. The high-speed centrifugation speed is 3000-4000rpm and the time is 20-35min.

2. The method for preparing the heterojunction fluorescent probe according to claim 1, characterized in that, include: 1) Ti3C2T x MXene nanosheets, GQDs and water were mixed and stirred to obtain a suspension. 2) The suspension is subjected to hydrothermal treatment to obtain a hydrothermal reaction product. The hydrothermal reaction product is centrifuged and washed, and then freeze-dried. In step 1), the Ti3C2T x The ratio of MXene nanosheets to GQDs is 20mg:80mg to 80mg:20mg; The preparation method of the GQDs includes: mixing citric acid, urea and water and adjusting the pH to obtain a precursor solution; subjecting the precursor solution to heat treatment; and subjecting the reaction liquid to dialysis treatment. The Ti3C2T x The preparation method of MXene nanosheets includes: mixing Ti3AlC2, HCl and LiF to obtain a mixture, centrifuging and washing the mixture to obtain multilayer Ti3C2T X The multilayer Ti3C2T X The solution is subjected to ultrasonic treatment in deionized water, followed by high-speed centrifugation, and the supernatant is freeze-dried. The mass-to-volume ratio of Ti3AlC2, HCl, and LiF is 1-3g: 30-50mL: 1-3g. The centrifugation speed is 3000-4000rpm. The washing is performed with deionized water until the pH value is ≥6. The ultrasonic treatment power is 180-250W. The ultrasonic treatment time is 20-35min. The high-speed centrifugation speed is 3000-4000rpm and the time is 20-35min.

3. The method for preparing a heterojunction fluorescent probe according to claim 2, characterized in that, In step 2), the hydrothermal treatment temperature is 90~120℃ and the hydrothermal treatment time is 3~6h; and / or, the washing uses 75%~95% ethanol; and / or, the freeze-drying temperature is -50~-70℃ and the time is 20~30h.

4. The method for preparing a heterojunction fluorescent probe according to claim 2, characterized in that, The molar ratio of citric acid to urea is 1:10 to 10:10; and / or the pH of the precursor solution is 4.5 to 9.

5.

5. The method for preparing a heterojunction fluorescent probe according to claim 2, characterized in that, The heat treatment temperature is 140~220℃.

6. The application of the heterojunction fluorescent probe according to claim 1 or the heterojunction fluorescent probe prepared by any one of claims 2-5 in monitoring the quality of fresh food.

7. The application according to claim 6, characterized in that, Applications in real-time monitoring of quality changes in eggs, pork, and fish.

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