Jackfruit nucleus carbon quantum dot fluorescent probe as well as preparation method and application thereof

Abstract

The invention discloses a jackfruit nucleus carbon quantum dot fluorescent probe, a preparation method thereof and an application of the jackfruit nucleus carbon quantum dot fluorescent probe in rapid detection of enoxacin. Green and environment-friendly waste jackfruit nucleus is selected as a carbon source, and JNW CDs with good luminescence stability and high solubility are synthesized through a one-step hydrothermal method after citric acid hydrolysis modification; the method is used for rapidly detecting the content of enoxacin in an actual sample, resource recycling can be achieved while the residual level of enoxacin in food is monitored, and environmental pollution is reduced.

Description

Technical Field

[0001] The invention relates to fluorescent carbon dots, and in particular to a jackfruit core carbon quantum dot fluorescent probe and a preparation method and application thereof. Background Art

[0002] Enoxacin (ENX) is a third-generation quinolone antibiotic. As a well-tolerated oral antibiotic, ENX has broad-spectrum antibacterial activity and strong bactericidal effects in vitro. It has shown significant therapeutic effects on infections caused by Gram-negative and Gram-positive bacteria and is widely used in the clinical treatment of infectious diseases. Due to their excellent bactericidal properties, quinolone antibiotics have been widely used in animal husbandry, especially in the prevention and treatment of diseases in edible animals such as chickens and cattle. This has led to antibiotic residues in food. Antibiotic residues in food may cause pathogens to develop resistance to clinical drugs, thereby threatening human health.

[133] . Since enoxacin can only be partially metabolized after use, its residues and metabolites are directly discharged into the environment and can therefore be detected in water. Previous studies have shown that residual drugs in water can lead to the production of antibiotic-resistant bacteria and genes, increase the risk of antibiotic resistance in pathogens, and exhibit significant ecotoxicity. Due to the negative impact of antibiotics on human health, people are increasingly concerned about the presence of residual antibiotics in the food supply. Melo et al. found that enoxacin promotes the production of tumor-suppressive miRNAs by binding to the biosynthetic proteins TARRNA and TRBP; Ostrov et al. found that enoxacin can be used as a new small molecule inhibitor to inhibit bone resorption by osteoclasts; Xu's team reported that enoxacin has the potential to become an anti-tumor drug for prostate cancer. Enoxacin has been widely studied in terms of its pharmacological effects, but there are relatively few reports on its application in the field of fluorescence analysis and detection.

[0003] Several methods have been reported for detecting antibiotics, such as gas chromatography, high-performance liquid chromatography, and voltammetry. However, these methods require sample preparation and expensive instrumentation, resulting in high processing costs, lengthy detection times, and complex operations. Given these challenges, developing new methods for the determination of enoxacin remains of practical significance. Compared with traditional methods, fluorescent probes offer higher sensitivity, lower cost, and easier operation. Furthermore, there are currently no reports on the use of carbon dots prepared from fruit pits, such as jackfruit, as fluorescent probes for the detection of enoxacin. Summary of the Invention

[0004] The present invention aims to provide a jackfruit core carbon quantum dot fluorescent probe. The probe uses discarded jackfruit core as a carbon source, adds citric acid for hydrolysis and modification, and then synthesizes green fluorescent carbon dots JNWCDs through a one-step hydrothermal method for the analysis and detection of enoxacin in food or water.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned fluorescent probe, which is as follows:

[0006] (1) Drying and grinding jackfruit cores to obtain a powdered carbon source;

[0007] (2) taking citric acid at a ratio of 7 g:5 mL and heating and dissolving it in ultrapure water to obtain a citric acid solution, then adding the jackfruit powder in the sampling step (1) to the citric acid solution at a mass ratio of jackfruit core powder to citric acid in the range of 1:1-1:11, and hydrolyzing the jackfruit core powder at 110° C. with continuous magnetic stirring using a magnetic stirrer to obtain a hydrolyzate;

[0008] (3) adding NaOH to adjust the pH value of the hydrolyzate to 6.0;

[0009] (4) adding the solution treated in step (3) to the organic solvent and ultrasonically treating for 5 min to ensure uniform mixing;

[0010] (5) gradually adding NaOH again to adjust the pH value of the solution in step (4) to 6.0;

[0011] (6) placing the solution from step (5) in a muffle furnace and heating at a constant temperature for 2 to 12 hours;

[0012] (7) After cooling to room temperature, centrifugation was performed at 4,000 rpm for 20 min, and the supernatant was filtered through a 0.22 μm filter membrane to obtain crude JNW CDs of jackfruit core-based carbon dots with green fluorescence;

[0013] (8) Purification: The crude JNWCDs were submitted to silica gel column chromatography and then eluted with isocratic dichloromethane and methanol in a ratio of 10:1. Thin layer chromatography was used to collect the green fluorescent elution and concentrate it under vacuum to obtain purified jackfruit core-based JNW CDs.

[0014] Furthermore, the mass ratio of citric acid to jackfruit powder in step (2) is 7:1.

[0015] Furthermore, the organic solvent in step (4) includes EtOH, MeOH, ACE, DMF, n-ProH, and DMSO.

[0016] Furthermore, the organic solvent in step (4) is n-propanol.

[0017] Furthermore, the temperature of step (6) is 170°C.

[0018] Furthermore, the heating time in step (6) is 6 hours.

[0019] Another object of the present invention is to apply the jackfruit core carbon quantum dot fluorescent probe prepared by the above method in the rapid detection of enoxacin, and the probe solution of the fluorescent probe is used as a detection reagent to prepare a detection kit.

[0020] Furthermore, the specific steps of using the jackfruit core carbon quantum dot fluorescent probe to detect enoxacin include:

[0021] 1) Mix the enoxacin solution with the JNW CDs solution to obtain at least two mixed solutions with different enoxacin concentrations. ex is 450nm and λ em The fluorescence intensity of JNW CDs was measured at 530 nm (slit: 1.2 nm, 1.2 nm);

[0022] 2) mixing the sample to be tested with the JNWCDs solution to obtain a mixed solution of the sample to be tested, and measuring the fluorescence intensity of the mixed solution of the sample to be tested;

[0023] 3) Calculate the concentration of enoxacin in the mixed solution of the test sample according to the linear relationship between the fluorescence quenching efficiency (F0-F) / F0 and the concentration of enoxacin in the mixed solution in step 1); the linear relationship is to obtain the linear relationship between the fluorescence quenching efficiency (F0-F) / F0 and the concentration of enoxacin in the mixed solution:

[0024] The linear equation for enoxacin concentration in the range of 0 to 15 μM is (F0-F) / F0=0.015*X+0.0146(R1 2 =0.9903), based on a 3-fold signal-to-noise ratio, the detection limit was 8.62 nM;

[0025] When the concentration of enoxacin was in the range of 15-150 μM, the linear equation was (F0-F) / F0=0.041*X+0.1931(R2 2 =0.9918), and the limit of detection (LOD) was 37.59 nM.

[0026] Furthermore, in the step 2), the reaction time of JNWCDs and enoxacin is 5 min.

[0027] The working principle of the present invention is as follows: the present invention first uses jackfruit core as a carbon source, adopts n-propanol as a solvent, adds citric acid for hydrolysis modification, and then synthesizes jackfruit core-based carbon dots JNWCDs with green fluorescence through a "one-step hydrothermal method". When it is used to detect enoxacin, it shows a good linear relationship before and after with an enoxacin concentration of 15 μM as the node. When the enoxacin concentration is in the range of 0-15 μM, the linear equation is (F0-F) / F0=0.015*X+0.0146(R1 2=0.9903), based on a 3-fold signal-to-noise ratio, the detection limit was 8.62 nM; when the enoxacin concentration was in the range of 15-150 μM, the linear equation was (F0-F) / F0=0.041*X+0.1931(R2 2 =0.9918), with a limit of detection (LOD) of 37.59 nM. UV-Vis and fluorescence lifetime measurements revealed that the fluorescence decay lifetime of JNW CDs was approximately 6.02 ns, and 6.05 ns after binding to enoxacin, which is essentially consistent. Further investigation into the fluorescence quenching mechanism of enoxacin on JNW CDs revealed that the Em peaks in the JNW CDs fluorescence spectrum and the UV absorption peaks of enoxacin did not overlap, and there was no significant change in the fluorescence decay lifetime before and after quenching. The SV equation further confirmed that the linear slope decreased with increasing temperature, indicating that the fluorescence quenching mechanism of JNW CDs and enoxacin is SQ static quenching. JNW CDs were used to detect enoxacin in four different real samples, with spiked recoveries ranging from 96.7% to 103.6%, demonstrating that the JNW CDs fluorescent probe can be used for the detection of enoxacin.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) A biomass probe JNW CDs was prepared for detecting enoxacin concentration;

[0030] (2) While implementing the monitoring of the residue level of enoxacin in food, it can also achieve the recycling of resources and reduce environmental pollution.

[0031] (3) JNW CDs can be used as fluorescent probes to specifically detect enoxacin with high sensitivity, good selectivity, accuracy, and stability, providing a relatively rapid, sensitive, and effective method for the detection of enoxacin residues in the environment and food. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Prepare processes for JNWCDs;

[0033] Figure 2 The effect of citric acid ratio on the fluorescence quantum yield of JNWCDs;

[0034] Figure 3 is the effect of solvent on the fluorescence quantum yield of JNW CDs;

[0035] Figure 4 is the effect of temperature on the fluorescence quantum yield of JNW CDs;

[0036] Figure 5 is the effect of time on the fluorescence quantum yield of JNW CDs;

[0037] Figure 6 TEM, HR-TEM images and particle size distribution of JNWCDs;

[0038] Figure 7 XRD pattern of JNWCDs;

[0039] Figure 8 FTIR pattern of JNWCDs and its substrate, and Zeta potential pattern of different sample materials;

[0040] Figure 9 XPS full spectrum and high resolution XPS spectrum of C1s, N1s and O1s of JNWCDs;

[0041] Figure 10 UV-Vis spectrum and PL spectrum of JNWCDs;

[0042] Figure 11 Fluorescence spectrum of JNWCDs under different excitation;

[0043] Figure 12 Fluorescence lifetime decay curve of JNWCDs;

[0044] Figure 13 Fluorescence intensity change of JNWCDs under different pH conditions;

[0045] Figure 14 Fluorescence intensity change of JNWCDs in different salt concentration solutions;

[0046] Figure 15 Fluorescence intensity change of JNWCDs under different H2O2 concentration conditions;

[0047] Figure 16 Effect of natural light and ultraviolet light irradiation time on fluorescence intensity of JNWCDs;

[0048] Figure 17 Fluorescence quenching efficiency of small molecules and antibiotics (a), vitamins, amino acids and metal ions (b) on JNWCDs

[0049] Figure 18 Effect of pH value on fluorescence quenching efficiency of JNWCDs for detecting enoxacin;

[0050] Figure 19 Effect of reaction time on fluorescence quenching efficiency;

[0051] Figure 20Fluorescence spectra of JNW CDs and different concentrations of enoxacin (0-150 μM) (ad), UV illumination (b), linearity (0-15 μM, 15-150 μM) of JNW CDs and enoxacin (c);

[0052] Figure 21 Fluorescence lifetime of JNW CDs (a), UV absorption spectra of JNW CDs, enoxacin, and JNW CDs plus enoxacin (b), SV equation of JNW CDs (c). DETAILED DESCRIPTION

[0053] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following invention, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present invention.

[0054] Example 1: Preparation of Jackfruit Core-Based JNW CDs

[0055] Jackfruit seeds were dried at 80°C, finely ground, and sieved through a 60-mesh sieve to prepare a powdered carbon source. Subsequently, citric acid was added for hydrolysis, and jackfruit seed-based carbon dots (JNW CDs) were synthesized via a one-step hydrothermal method. The experimental steps were as follows: 7 g of citric acid was dissolved in 5 mL of ultrapure water and heated to 100°C until completely dissolved. Then, 1 g of jackfruit seed powder was added to the citric acid solution and hydrolyzed at 110°C for 8 h with continuous magnetic stirring. The pH of the mixture was then adjusted to 6.0 by adding 3 M NaOH. The treated solution was added to 5.0 mL of n-propanol and sonicated for 5 min to ensure uniform mixing. Subsequently, 3 M NaOH was gradually added to adjust the pH of the mixture to 6.0. The mixture was then heated in a muffle furnace at 170°C for 6 h. After cooling to room temperature, centrifuge at 4,000 rpm for 20 min, and filter the supernatant with a 0.22 μm filter membrane for subsequent purification to obtain jackfruit core-based carbon dots JNWCDs with green fluorescence. Figure 1 .

[0056] The crude JNW CDs were subjected to silica gel column chromatography and then eluted with isocratic dichloromethane and methanol in a ratio of 10:1. Thin layer chromatography was used to collect the green fluorescent elution and concentrate it under vacuum to obtain the purified jackfruit core-based JNW CDs.

[0057] Structural characterization and optical properties of JNWCDs prepared by the above method

[0058] (1) TEM characterization of JNWCDs

[0059] The morphology of JNW CDs was investigated by TEM, e.g. Figure 6 The JNW CDs prepared in this experiment exhibited excellent dispersion, no obvious aggregation, and a uniform particle size distribution. The particle size distribution plot showed an average particle size of 2.497 nm and a nearly spherical shape. HR-TEM images revealed a lattice spacing of approximately 0.234 nm. These results indicate that the JNW CDs possess a graphite-like crystal structure.

[0060] (2) XRD characterization of JNWCDs

[0061] X-ray powder diffraction technique is used to characterize the crystal structure of carbon dots, such as Figure 7 As shown in the figure, the results show that JNW CDs has only one obvious diffraction peak, and θ = 22.30°, indicating that JNW CDs is not an ordered crystal structure, but a disordered structure, which meets the requirements of the amorphous carbon.

[104] .

[0062] (3) FT-IR characterization of JNWCDs

[0063] Analyze the surface structure of JNWCDs and use FTIR to identify the functional groups on JNW CDs

[105] .from Figure 8 It can be seen that 3571.9cm -1 The strong peak at is the characteristic stretching vibration of OH or NH (ν N-H / ν O-H ). 2973.8cm -1 and 2572.5cm -1 The weak peak at corresponds to the stretching vibration of CH (ν C-H ) and OH stretching vibration of carboxylic acid (ν O-H The water solubility of JNWCDs is due to the presence of surface functional groups. -1 The moderate absorption peak at C-＝O ), 1635.6cm -1 The weak absorption peak at 1473.6 cm -1 The moderate intensity absorption peak at reveals the stretching vibration of C=C bond (ν C＝C ), further confirming the graphitic characteristics of JNW CDs. In addition, at 1242.1 cm -1 and 1068.5cm -1 The deformation vibration of CO bond (δ C-O ) and the stretching vibration of the CN bond (ν C-O ). 634.6cm -1The absorption peaks at 240 nm and 280 nm correspond to the deformation vibration of C=C-H (δ C＝C-H ), which demonstrates the chemical diversity of the surface of JNW CDs. The multiple functional groups and high carbonization level of the synthesized JNW CDs potentially improve the solubility of carbon dots in aqueous solution.

[0064] In the aqueous phase system, the standard of nanoparticle dispersion stability is usually the Zeta potential of ±30 mV

[102] When the Zeta potential is more than or less than 30 mV, the dispersion system tends to be stable. By analyzing the Zeta potential diagram, it can be determined that the JNW CDs system has good stability.

[0065] (4) XPS characterization of JNW CDs, the XPS of this study shows the elemental composition of carbon dots. The full spectrum is fitted by peaks, showing three significant spectra Figure 9 ). The C, O, and N peaks in the full scan spectrum indicate that the prepared JNW CDs contain these three elements

[104] . In the C1s high-resolution spectrum Figure 9 a), the peaks at 284.80 eV, 286.62 eV, and 288.97 eV are attributed to C=C, C-O / C-OH, and HO-C=O bonds, respectively, among which the C=C bond at 284.80 eV is the main peak, revealing that the carbon dots are mainly sp 2 hybrid graphite structure with a graphitized core, which is consistent with the results reported in the literature. The O1s spectrum Figure 9 c) has two peaks at 532.24 eV and 533.75 eV, corresponding to O-H / O-C and O=C bonds, respectively. The N1s peak Figure 9 d) has peaks at 400.25 eV and 401.98 eV, corresponding to N-C=O and N-H bonds.

[0066] The XPS results are consistent with the FT-IR analysis, showing that the JNW CDs contain a large number of hydroxyl and carboxyl groups on the surface, exhibiting good water solubility, which is very important for analyzing the surface chemical properties of carbon dots, and can provide important information about the elemental composition, chemical state, and molecular structure, providing valuable reference for the elemental composition and bonding properties of the studied CDs.

[0067] (5) UV-visible absorption, fluorescence excitation, and emission spectra of JNW CDs

[0068] Through the optical property study of JNW CDs, it is found that the carbon dots have the characteristics of wide UV-visible absorption spectrum, optimal fluorescence excitation and emission spectrum, etc. Figure 10 The data show that JNW CDs exhibit significant absorption at 240 nm, which is also attributed to the sp 2The figure also shows the optimal excitation and emission spectra of JNWCDs, with the optimal excitation and emission wavelengths located at 450nm and 530nm, respectively.

[0069] (6) JNWCDs excitation wavelength

[0070] In order to further explore the optical properties of the synthesized JNWCDs, namely the fluorescence emission characteristics of JNWCDs under different excitation wavelengths, the variation of the emission wavelength with the excitation wavelength was studied. The results are shown in Figure 11 In the experiment, the excitation wavelength was gradually increased from 380 nm to 490 nm, and measurements were performed every 10 nm.

[0071] The results show that the fluorescence intensity of JNWCDs first increases and then decreases. Notably, the main emission peak of the JNWCDs solution remains constant at approximately 530 nm throughout the entire test range, demonstrating that the fluorescence emission of JNWCDs is highly independent of the excitation wavelength.

[0072] (7) JNWCDs fluorescence lifetime

[0073] Under 450nm excitation, the fluorescence lifetime of JNWCDs solution was measured by TCSPC method, and the obtained fluorescence lifetime data were fitted and plotted (as shown in Figure 2). Figure 12 ), and the final measured lifetime value was 6.02ns. In addition, there are literature studies reporting that fluorescence quenching can affect the fluorescence lifetime of carbon dots. The specific influencing mechanism may include various physical and chemical processes such as FRET and electron transfer.

[113] In practical applications, it is necessary to select appropriate carbon dots and quenchers according to specific circumstances to achieve the best fluorescence lifetime and fluorescence intensity. Based on this, the mechanism of this study will be verified in the subsequent fluorescence quenching mechanism.

[0074] (8) Stability of JNWCDs

[0075] ① pH stability of JNWCDs

[0076] Figure 13 The fluorescence intensity variation of JNWCDs at different pH values ​​is shown. The fluorescence intensity variation of CDs at different pH values ​​may be related to the protonation or deprotonation of surface groups in acidic or alkaline solutions.

[114] Specifically, the fluorescence intensity of JNWCDs gradually increased within the pH range of 2.2 to 7.0, while fluctuating significantly between 6.0 and 12.0. These results indicate that CDs can be used over a wide pH range without significant changes in fluorescence intensity.

[0077] ②Ionic strength stability of JNWCDs

[0078] like Figure 14 The fluorescence intensity of JNWCDs decreased slightly in solutions with varying salt concentrations, indicating that the fluorescence properties of JNWCDs are relatively stable under different salt concentrations. As the NaCl concentration increases, the fluorescence intensity remains high, confirming the salt tolerance of JNWCDs. Therefore, the properties of JNWCDs are relatively stable under different salt concentrations, which helps them maintain a certain performance in practical applications.

[0079] ③ Antioxidant stability of JNWCDs

[0080] like Figure 15 , showing the change in fluorescence intensity of JNWCDs under different H2O2 concentrations. If the fluorescence intensity fluctuates with the increase of H2O2 concentration, but the fluctuation is not large and can be almost ignored, it indicates that JNWCDs have a certain stability to H2O2 and have good antioxidant capacity.

[115] This antioxidant capacity means that JNWCDs can maintain relatively stable fluorescence properties when affected by external oxidants. Figure 15 The results showed that the JNWCDs had good antioxidant capacity.

[0081] ④Stability of JNWCDs under natural light and ultraviolet light

[0082] Figure 16 , showing the change in fluorescence intensity of JNWCDs after 60 minutes of irradiation under natural light. The experimental results show that JNWCDs exhibit good stability under natural light irradiation, and the fluorescence intensity does not change significantly, which indicates that carbon dots have good stability under natural light conditions. In addition, there is no obvious decreasing trend in the fluorescence intensity of JNWCDs after 60 minutes of irradiation under ultraviolet light, indicating that JNWCDs have a certain resistance to ultraviolet light and are not easily quenched by ultraviolet light. As mentioned above, CDs show good luminescence and stability

[116] .

[0083] Taken together, these results demonstrate that JNWCDs have good photostability and can resist the effects of natural light and ultraviolet light on their fluorescence properties to a certain extent, which has positive significance for their stability and durability in practical applications.

[0084] Example 2: Optimization of JNWCDs preparation conditions

[0085] (1) Optimization of ratio

[0086] In the experiment, the reaction time was set to 8h, n-propanol (n-PrOH) was used as the reaction solvent, the reaction temperature was 170℃, and the mass ratio of jackfruit seeds to citric acid (CA) was changed in the range of 1:1-1:11. The quantum yield was measured as the inspection standard. Figure 2 As shown in the figure, QY first increases and then decreases with the change of reaction ratio. When the ratio of jackfruit core to CA is 1:7, the QY value is the largest, the quantum yield reaches the maximum value, the effect is the best, and the fluorescence intensity is the highest. As the ratio is subsequently increased, it is found that QY gradually decreases, indicating that excessive CA dosage cannot improve the quantum yield of the synthetic material, but will lead to a decrease in optical properties.

[0087] (2) Optimization of solvent types

[0088] The optimal ratio of jackfruit core to CA was 1:7. Other reaction conditions were the same as (1). Six different solutions were selected for the experiment, including ethanol (EtOH), methanol (MeOH), N,N-dimethylformamide (DMF), acetone (ACE), n-propanol (n-PrOH) and dimethyl sulfoxide (DMSO) to prepare optimized CDs. The results are shown in Figure 1. Figure 3 As shown in the figure, n-PrOH has the highest QY value among the six solvents, and the quantum yield reaches the maximum and the effect is the best.

[0089] (3) Preparation temperature optimization

[0090] n-PrOH was used as the optimal reaction solvent. Other reaction conditions were the same as (2). The reaction temperature was changed to 150℃-200℃. The quantum yield was measured as the evaluation standard. Figure 4 As shown in the figure, the fluorescence quantum yield of CDs shows an increasing trend with increasing temperature. When heated to 170°C, QY reaches its highest value. Then, as the temperature increases, the QY value gradually decreases. This result shows that reaction temperature is an important control parameter in the preparation of CDs. When the temperature is too low, the reaction rate may be slow, resulting in low quantum yield. However, when the temperature is too high, the nanostructure of the material will be destroyed, thereby reducing the quantum yield. Therefore, in the preparation of CDs, 170°C is the optimal reaction temperature for achieving high quantum yield. The preparation process of carbon dots usually requires high temperature conditions to promote the decomposition of precursors and the formation of carbon structures.

[101] ,Although higher temperature can accelerate the formation of Cdots, it must be carefully controlled to prevent excessive ,temperature from causing excessive growth of Cdots or structural instability.

[0091] (4) Preparation time optimization

[0092] The optimal preparation temperature is 170 °C, and other reaction conditions are the same as (3). The reaction time is changed in the range of 2 h-12 h, and the quantum yield is used as the standard for investigation. The experimental results are shown in Table 2. Figure 5 The experimental data show that, in the reaction time interval of 2 h to 12 h, the quantum yield of CDs changes with the change of reaction time. When the reaction time is 6 h, the quantum yield reaches the maximum value, and the effect is the best. When the reaction time exceeds 6 h, the quantum yield will gradually decrease. The results show that the reaction time is also an important control parameter in the preparation of CDs. Within a certain range, increasing the reaction time can improve the quantum yield of CDs. When the reaction time is too long, not only the quantum yield of the synthesized material cannot be further improved, but also the amorphous carbon structure is destroyed, resulting in the decline of its optical properties. Therefore, 6 h is selected as the optimal reaction time for the preparation of CDs, which can obtain the highest quantum yield and the best optical properties.

[0093] Example 3: Specificity experiment of jackfruit kernel-based carbon dots JNWCDs

[0094] The selectivity experiment of enoxacin was selected from 53 kinds of interferents, which are 1 μg / L of metal ions and anions (Ag + , Fe 3+ , Cr 6+ , Pb 2+ , As 3+ , F - , Cl - , Br - , I - , NO 3- , NO 2- , SO4 2- ), 1 μM of amino acids and vitamins (Arg, Val, His, Lys, Cys, Lle, Ala, Gly, Gln, Asp, Met, Glu, Leu, Trp, Ser, VP, VC, VH, VK3, VB2, VB3) and antibiotics (ENR, CAP, FFL, CLB, RAC, SAL, DEX, CEC, CEV, CFX, CIP, ENX, CAZ, AZI, CFQ, SPEC, KAN, FLX, SAR, SPFX) and the like. The selectivity and anti-interference experiment was carried out: 30 μL of the above-mentioned antibiotic, metal ion, amino acid solution, small molecule, vitamin and 1 μL of JNW CDs solution were added to a 1.5 mL centrifuge tube, and then the volume was made to 1 mL with ultrapure water, vortexed for 5 min to ensure uniform mixing, and the optimal λ ex is 450 nm and λ emThe fluorescence intensity of JNW CDs was measured at 530 nm (slit: 1.2 nm, 1.2 nm). Each interfering compound was measured in triplicate. A pie chart comparing the effects of different interfering compounds on the fluorescence intensity of JNW CDs was plotted, with F / F0 as the ordinate (F0 and F represent the fluorescence intensity of the C-dots before and after the addition of each interfering compound).

[0095] The results are as follows Figure 17 As shown in the figure, when enoxacin is present, the fluorescence value is significantly reduced, while other common antibiotics, metal ions, small molecules, vitamins and amino acids basically have no effect on the fluorescence intensity value of the probe and can be ignored. Therefore, the JNW CDs fluorescent probe shows high specific recognition in detecting enoxacin.

[0096] Example 4: Study on the micro-detection analysis method of enoxacin using JNW CDs

[0097] (1) pH stability

[0098] The experimental results showed that pH value significantly affected the fluorescence intensity of CDs and the detection effect of enoxacin, which may be related to the protonation or deprotonation phenomenon of CDs surface groups under acidic or alkaline conditions. Figure 18 The results show that the fluorescence quenching efficiency of JNWCDs is stronger and the fluorescence response is wider in the pH range of 4.0-5.0 and 9.0-11.0.

[0099] (2) Determination of reaction time

[0100] Figure 19 The following curve shows the effect of reaction time on the fluorescence quenching efficiency of enoxacin detected by JNW CDs at room temperature. The experiment found that the fluorescence quenching value (F / F0) was relatively stable within the reaction time of 0-15 minutes between JNWCDs and enoxacin. Although the fluorescence intensity of the reaction between enoxacin and carbon dots fluctuated over time, it did not show significant changes overall. Based on this result, the optimal reaction time was determined to be 5 minutes.

[0101] (3) Standard curve of enoxacin

[0102] The fluorescence quenching effect of enoxacin on JNW CDs was further explored by measuring the changes in fluorescence intensity after the continuous addition of known concentrations of enoxacin from 0 to 150 μM. Figure 20 As shown in a, the fluorescence intensity of the JNW CDs solution decreases with the gradual increase of the concentration of enoxacin (0-150 μM), and the fluorescence intensity of the carbon dots and different concentrations of enoxacin under ultraviolet light (365 nm) is Figure 20b also clearly shows the fluorescence quenching effect of enoxacin on JNWCDs.

[0103] Select the fluorescence spectrum ( Figure 20 d)F 530 The linear relationship between the two segments is obtained by linear fitting. Figure 20 c It can be seen that with 15 μM as the node, a good linear relationship is shown before and after. In the range of 0-15 μM concentration of enoxacin, the linear equation is (F0-F) / F0=0.015*X+0.0146(R1 2 =0.9903), based on a 3-fold signal-to-noise ratio, the detection limit was 8.62 nM. When the enoxacin concentration was in the range of 15-150 μM, the linear equation was (F0-F) / F0=0.041*X+0.1931(R2 2 =0.9918), and the limit of detection (LOD) was 37.59 nM. Therefore, the JNW CDs prepared in this experiment can be used as a fluorescent probe to detect the content of enoxacin in food.

[0104] Example 4: Detection of Enoxacin in Actual Samples

[0105] To further explore the practicality of the JNW CDs fluorescent probe, enoxacin was selected as the target analyte for testing in real samples. Water samples were collected from the Baoxiang River and the natural water bodies on the Kunming University campus, and pork and milk samples were purchased from local markets for enoxacin analysis. Three enoxacin concentration points (5μM, 10μM, and 25μM) were set in the experiment. Three replicate measurements were performed at each concentration point, and the average value was calculated to verify the sample analysis and ensure the accuracy and reliability of the experimental results.

[0106] To prepare deproteinized milk samples, 36% acetic acid was added to the milk to achieve fat removal. The milk was then centrifuged at 5000 rpm for 15 minutes to separate the precipitated protein. The clear supernatant was then filtered through a 0.22 μm filter and collected for subsequent experiments. Commercially available ground pork samples were used in the experiments. 5 g of the sample was placed in a centrifuge tube, homogenized with 2 g of MgSO₄ and 25 mL of acetonitrile, and then centrifuged at 5000 rpm for 15 minutes to obtain the supernatant. The supernatant was then filtered through a 0.22 μm pore size membrane. Water samples were filtered three times with qualitative filter paper to remove insoluble matter such as solid particles and impurities. The sample solution was then filtered through a 0.22 μm membrane to obtain a clean solution for later use.

[0107] All samples from the Baoxiang River, natural water bodies on campus, pork, and milk were pre-treated and filtered through a 0.22 μm filter before testing for enoxacin. 1 μL of JNW CDs solution (1 mg / mL) was diluted to 1 mL with ultrapure water, and the fluorescence value was measured as F0. The 1 μL JNW CDs solution was then diluted to 1 mL with the treated sample solution, and the fluorescence was measured as F. Simultaneously, a peak experiment was performed as follows: enoxacin target standard solutions (5 μM, 10 μM, and 25 μM) were added to the treated sample containing 1 μL of JNW CDs, and then the enoxacin spike experiment was performed.

[0108] The test results are shown in Table 1. The spiked amounts of the three samples were all 5 μM, 10 μM, and 15 μM. Fluorescence detection of enoxacin in Baoxiang River, natural water bodies on campus, pork, and milk showed spiked recoveries ranging from 96.7% to 103.6%, with RSDs (n=3) less than 3.5%, indicating that the results of ENX detection using JNW CDs are accurate and reliable, and are suitable for the detection of enoxacin in actual samples.

[0109] Table 1 Actual sample testing

[0110]

[0111] (2) Comparison with other methods

[0112] By consulting relevant literature reports and comparing the fluorescence analysis method for detecting enoxacin by JNW CDs established in this experiment with other methods and comparing their concentration detection range and detection limit, it can be considered that this analysis method has high accuracy as shown in Figure 2. In addition, there are few reports on the fluorescence analysis method for detecting enoxacin.

[0113] Table 2 Comparison of detection methods

[0114]

[0115] The enoxacin content in Baoxiang River, natural water bodies on campus, pork and milk was analyzed and detected, and the spiked recoveries were between 96.7% and 103.6%, indicating that the JNW CDs fluorescent probe can be used for the detection of enoxacin.

[0116] It should be understood that the above-described specific embodiments of the present invention are merely illustrative of the invention or explanation of the principles of the present invention, and do not constitute limitations of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included within the scope of protection of the present invention. In addition, the appended claims are intended to cover all variations and modifications that fall within the scope and metes and bounds of the appended claims, or equivalents of such scope and metes and bounds.

[0117] [1]He Y, Wang HF, YanX P. Exploring Mn-doped ZnS quantum dots for theroom-temperature phosphorescence detection of enoxacin in biological fluids[J]. Analytical chemistry, 2008, 80(10): 3832-3837.

[0118] [2] Mo Keting. Synthesis and application of doped carbon quantum dots based on aromatic compounds as carbon sources[D]. Guangxi Normal University, 2022.

[0119] [3]Pecorelli I,Galarini R,Bibi R,et al.Simultaneous determination of13quinolones from feeds using accelerated solvent extraction and liquidchromatography[J].Analytica Chimica Acta,2003,483(1-2):81-89.

[0120] [4]WangW,Sang Q,Yang M,et al.Detection of several quinoloneantibiotic residues in water based on Ag-TiO2SERS strategy[J].Science of theTotal Environment,2020,702:134956.

Claims

1. A jackfruit core carbon quantum dot fluorescent probe, characterized in that The probe is green fluorescent carbon dots (JNW CDs), which are synthesized by a one-step hydrothermal method using discarded jackfruit kernels as a carbon source, modified with citric acid, and then transferred to an organic solvent.

2. A method for preparing the jackfruit core carbon quantum dot fluorescent probe according to claim 1, characterized in that, The following steps are involved: (1) Drying and grinding jackfruit cores to obtain a powdered carbon source; (2) taking citric acid at a ratio of 7 g:5 mL and heating to dissolve in ultrapure water to obtain a citric acid solution, then adding the jackfruit powder in the sampling step (1) to the citric acid solution at a mass ratio of jackfruit core powder to citric acid in the range of 1:1-1:11, and hydrolyzing with continuous stirring using a magnetic stirrer under high temperature conditions to obtain a hydrolyzate; (3) adding NaOH to adjust the pH value of the hydrolyzate to 6.0; (4) adding the solution treated in step (3) to the organic solvent and ultrasonically treating for 5 min to ensure uniform mixing; (5) gradually adding NaOH again to adjust the pH value of the solution in step (4) to 6.0; (6) placing the solution from step (5) in a muffle furnace and heating at a constant temperature for 2 to 12 hours; (7) After cooling to room temperature, centrifugation was performed at 4,000 rpm for 20 min, and the supernatant was filtered through a 0.22 μm filter membrane to obtain crude JNW CDs of jackfruit core-based carbon dots with green fluorescence; (8) Purification: The crude JNW CDs were submitted to silica gel column chromatography and then eluted with isocratic dichloromethane and methanol in a ratio of 10:

1. Thin layer chromatography was used to collect the green fluorescent elution and concentrate it under vacuum to obtain the purified jackfruit core-based JNW CDs.

3. A method for preparing a jackfruit core carbon quantum dot fluorescent probe according to claim 2, characterized in that, The mass ratio of citric acid to jackfruit powder in the step (2) is 7:

1.

4. A method for preparing a jackfruit core carbon quantum dot fluorescent probe according to claim 2, characterized in that, The organic solvent in step (4) includes EtOH, MeOH, ACE, DMF, n-ProH, and DMSO.

5. A method for preparing a jackfruit core carbon quantum dot fluorescent probe according to claim 4, characterized in that, The organic solvent in step (4) is n-ProH.

6. A method for preparing a jackfruit core carbon quantum dot fluorescent probe according to claim 2, characterized in that, The temperature of step (6) is 170° C. and the heating time is 6 hours.

7. Use of the jackfruit core carbon quantum dot fluorescent probe according to claim 1 or prepared by the preparation method according to any one of claims 2 to 7 in the rapid detection of enoxacin.

8. The use according to claim 1, characterized in that: A detection kit is prepared by using the probe solution of the fluorescent probe as a detection reagent.

9. The use according to claim 7 or 8, characterized in that The specific steps of using the jackfruit core carbon quantum dot fluorescent probe to detect enoxacin include: 1) Mix the enoxacin solution with the JNW CDs solution to obtain at least two mixed solutions with different enoxacin concentrations. ex is 450nm and λ em The fluorescence intensity of JNW CDs was measured at 530 nm; 2) mixing the sample to be tested with a certain amount of JNW CDs solution to obtain a mixed solution of the sample to be tested, and measuring the fluorescence intensity of the mixed solution of the sample to be tested; 3) Calculate the concentration of enoxacin in the mixed solution of the test sample according to the linear relationship between the fluorescence quenching efficiency (F0-F) / F0 and the concentration of enoxacin in the mixed solution in step 1); the linear relationship is to obtain the linear relationship between the fluorescence quenching efficiency (F0-F) / F0 and the concentration of enoxacin in the mixed solution: The linear equation for enoxacin concentration in the range of 0 to 15 μM is (F0-F) / F0=0.015*X+0.0146(R1 2 =0.9903), based on a 3-fold signal-to-noise ratio, the detection limit was 8.62 nM; When the concentration of enoxacin was in the range of 15-150 μM, the linear equation was (F0-F) / F0=0.041*X+0.1931(R2 2 =0.9918), and the limit of detection (LOD) was 37.59 nM.

10. The use according to claim 9, characterized in that The reaction time of JNW CDs and enoxacin in step 2) is 5 minutes.

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