Preparation method of xylan-based carbon dots with high fluorescence quantum yield

Abstract

The invention discloses a preparation method of xylan-based carbon dots with high fluorescence quantum yield, which comprises the following steps: dissolving xylan extracted from corncob and 3, 4-diaminobenzoic acid as raw materials in ultrapure water according to a certain proportion, uniformly mixing, transferring into a hydrothermal reaction kettle, putting into a muffle furnace for reaction, cooling to room temperature after the reaction is finished, and drying to obtain the xylan-based carbon dots with high fluorescence quantum yield. Performing separation and purification through centrifugation and dialysis, and finally performing freeze drying to obtain the xylan carbon dots. The xylan carbon dots prepared by the invention are dispersed in water and show blue fluorescence under a 365 nm ultraviolet lamp, and the fluorescence quantum yield is up to 60.01%. The xylan carbon dot provided by the invention has excellent fluorescence performance, solves the bottleneck problem that the carbon dot with high fluorescence quantum yield is difficult to obtain by taking xylan as a precursor, and is simple in preparation method and low in cost. The prepared xylan carbon dots have a wide application prospect in the fields of biomarkers, cell imaging, analysis and detection and the like due to high fluorescence quantum yield, and meanwhile, high-valued utilization of agricultural and forestry byproducts is realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of utilization of agricultural and forestry biomass resources, and relates to a preparation of a luminescent carbon nanomaterial, in particular to a preparation method of a xylan-based carbon dot with high fluorescence quantum yield. BACKGROUND

[0002] Agricultural and forestry by-products composed of cellulose, hemicellulose and lignin are a kind of renewable resources. Under the impetus of the concept of sustainable development, the conversion of agricultural and forestry by-products into carbon dots has become a research hotspot at present. Carbon dots have the advantages of high stability, low toxicity, good biocompatibility and excellent fluorescence performance, and have potential application prospects in the detection field. Xylan is the main component of hemicellulose, and becomes an ideal precursor for preparing carbon dots due to its thermochemical sensitivity. However, xylan lacks continuous conjugated double bonds and has a rich branched structure, which limits the sp 2 The formation of conjugated domains, thereby affecting the electronic delocalization effect and radiation transition process of xylan-based carbon dots, resulting in a low fluorescence quantum yield. In addition, xylans extracted from different sources have significant differences in chemical structure, such as molecular chain length, sugar unit type, branch number, etc. These differences will affect the degradation, reaction and carbonization behavior in the hydrothermal process, resulting in different performances of the obtained carbon dots, however, this aspect has not been deeply studied.

[0003] Carbon dots with low quantum yield have weak fluorescence intensity due to their low photoluminescence efficiency. Therefore, when using the same number of carbon dots to construct detection probes, their signal-to-noise ratio is poor, and the change range of fluorescence signal when responding to the target is usually narrow, resulting in low detection sensitivity and accuracy. For example, in our previous work, xylan was used as a carbon source to synthesize carbon dots with a fluorescence quantum yield of 23.04%, which was further compounded with rhodamine B to construct a ratiometric fluorescent probe for Vibrio parahaemolyticus detection. The research results show that the detection limit of the ratiometric fluorescent probe for Vibrio parahaemolyticus is 1.15 CFU / mL, and the recovery rates of seawater samples and commercially available clams are between 80%~102% (standard deviation RSD 13.8%~28.3%) and 92%~120% (16.3%~27.6%) respectively (Liu et al., 2018). Industrial Crops & Products, 2025, 228, 120871. It is worth noting that when the fluorescence signal response is weak, although the fluorescence spectrophotometer can detect such a small difference, the naked eye cannot identify it, which limits its application in rapid and on-site analysis. The patent uses xylan extracted from the agricultural and forestry by-products corncob as raw material, introduces 3, 4-diamino benzoic acid as a nitrogen dopant, and prepares xylan-based carbon dots with high fluorescence quantum yield (60.01%). Further, a ratio fluorescent probe is assembled by a similar method for Vibrio parahaemolyticus detection. It is worth noting that due to the improvement of the fluorescence quantum yield of the carbon dots, the ratio fluorescent probe has a low detection limit (0.54 CFU / mL), a high recovery rate (86%~105% and 90%~111%) and a small standard deviation (9.2%~16.3% and 9.5%~12.7%), and realizes the visual detection of Vibrio parahaemolyticus by the naked eye. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide a preparation method of xylan-based carbon dots with high fluorescence quantum yield, to broaden the high-value utilization way of xylan, and to provide a new method for preparing carbon dots with high fluorescence quantum yield.

[0005] To achieve the above-mentioned purpose, the technical solutions adopted by the present application are as follows: The present application provides a preparation method of xylan-based carbon dots with high fluorescence quantum yield, comprising the following steps: a. Weigh the xylan and disperse it in deionized water, weigh the 3, 4-diamino benzoic acid and dissolve it in deionized water, mix and stir them uniformly to obtain a mixed solution; b. Transfer the mixed solution to a hydrothermal reaction kettle and perform hydrothermal reaction. After the reaction is completed, the hydrothermal reaction kettle is cooled to room temperature in the natural environment to obtain a brown carbon dot solid-liquid mixture.

[0006] c. Centrifugal purification is performed on the obtained carbon dot solid-liquid mixture to obtain supernatant and precipitate, respectively.

[0007] d. Dialysis is performed on the supernatant at room temperature to obtain xylan-based carbon dots with high fluorescence quantum yield.

[0008] Further, in step a, the xylan is extracted from corncob.

[0009] Further, in step a, the mass-to-volume ratio of xylan to deionized water is 0.05 g / mL~0.1 g / mL.

[0010] Further, in step a, the mass-to-volume ratio of 3, 4-diamino benzoic acid to deionized water is 0.025 g / mL~0.1 g / mL.

[0011] Further, in step a, the mass ratio of xylan to 3, 4-diaminobenzoic acid is 4:1~1:1.

[0012] Further, in step a, when the mass ratio of xylan to 3, 4-diaminobenzoic acid is 4:1~2:1, the quantum yield of the carbon dots prepared is 8.51%~16.91%; when the mass ratio is 2:1~4:3, the quantum yield of the carbon dots prepared is 16.91%~42.72%; and when the mass ratio is 4:3~1:1, the quantum yield of the carbon dots prepared is 42.72%~60.01%.

[0013] Further, in step b, the hydrothermal reaction temperature is 180~220 ℃, and the hydrothermal reaction time is 2~16 h.

[0014] Further, in step b, the hydrothermal reaction temperature is 220 ℃, and the hydrothermal reaction time is 12 h.

[0015] Further, in step c, the centrifugal speed is 10000-14000 revolutions / minute.

[0016] Further, in step d, the molecular weight of the dialysis bag is 100~500 Da, and the dialysis time is 3~7 days.

[0017] The application also provides a series of high-fluorescent quantum yield xylan-based carbon dots prepared by the above preparation method.

[0018] The application also provides application of the above high-fluorescent quantum yield xylan-based carbon dots in analysis and detection.

[0019] Compared with the prior art, the application has the following advantages: (1) xylan and 3, 4-diaminobenzoic acid are used as carbon source and nitrogen source respectively to synthesize carbon dots, the carbon source is extracted from corncob, is cheap and easy to obtain, and is abundant in source; (2) one-step hydrothermal method is adopted for preparation, the process is simple, the requirement for equipment is low, and it is suitable for large-scale production; (3) the carbon dots prepared are uniformly distributed, have high fluorescent quantum yield, and show significant advantages in analysis and detection applications. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a fluorescence quantum yield diagram of the xylan-based carbon dots prepared in Example 1 and Comparative Examples 3~5.

[0021] Figure 2 It is a fluorescence emission spectrum diagram of the xylan-based carbon dots prepared in Example 1.

[0022] Figure 3This is a transmission electron microscope (TEM) image of the xylan-based carbon dots prepared in Example 1.

[0023] Figure 4 The ratio of the fluorescence intensity at 435 nm to that at 578 nm to the signal intensity of the ratioic fluorescent probe assembled from xylan-based carbon dots prepared in Example 1 is given by F. 435 nm / F 587 nm Standard curve of Vibrio parahaemolyticus concentration. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to specific embodiments and accompanying drawings. The described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1 1.0 g of xylan extracted from corn cob was weighed and dispersed in 10 mL of deionized water (the mass-to-volume ratio of xylan to deionized water was 0.1 g / mL). 1.0 g of 3,4-diaminobenzoic acid was weighed and dissolved in 10 mL of deionized water (the mass-to-volume ratio of 3,4-diaminobenzoic acid to deionized water was 0.1 g / mL, and the mass ratio of xylan to 3,4-diaminobenzoic acid was 1:1). The two solutions were mixed thoroughly. The mixture was transferred to a hydrothermal reactor and reacted at 220 °C for 12 h. After the reaction was complete, the hydrothermal reactor was cooled to room temperature under natural conditions to obtain a brown carbon dot solid-liquid mixture. The obtained carbon dot solid-liquid mixture was centrifuged at 10,000 rpm to purify it, obtaining a supernatant and a precipitate. The supernatant was dialyzed for 7 days in a dialysis bag with a molecular weight of 100 Da at room temperature to obtain xylan-based carbon dots with high fluorescence quantum yield.

[0026] The fluorescence quantum yield of the xylan-based carbon dots prepared in this embodiment was 60.01% ( Figure 1 ), Figure 2 The emission spectra of the xylan-based carbon dots prepared in this embodiment under different excitations are shown, indicating that the xylan-based carbon dots exhibit a certain degree of excitation dependence. Transmission electron microscopy (TEM) images are shown below. Figure 3 As shown, the xylan-based carbon dots prepared in this embodiment are evenly distributed.

[0027] Example 2 0.5 g of xylan extracted from corn cob was weighed and dispersed in 10 mL of deionized water (the mass-to-volume ratio of xylan to deionized water was 0.05 g / mL). 0.5 g of 3,4-diaminobenzoic acid was weighed and dissolved in 10 mL of deionized water (the mass-to-volume ratio of 3,4-diaminobenzoic acid to deionized water was 0.05 g / mL, and the mass ratio of xylan to 3,4-diaminobenzoic acid was 1:1). The two solutions were mixed thoroughly. The mixture was transferred to a hydrothermal reactor and reacted at 220 °C for 12 h. After the reaction, the hydrothermal reactor was cooled to room temperature under natural conditions to obtain a brown carbon dot solid-liquid mixture. The obtained carbon dot solid-liquid mixture was centrifuged at 12000 rpm to obtain a supernatant and precipitate. The supernatant was dialyzed for 5 days at room temperature using a dialysis bag with a molecular weight of 500 Da to obtain xylan-based carbon dots with a fluorescence quantum yield of 32.72%.

[0028] Example 3 1.0 g of xylan extracted from corn cob was weighed and dispersed in 10 mL of deionized water (the mass-to-volume ratio of xylan to deionized water was 0.1 g / mL). 1.0 g of 3,4-diaminobenzoic acid was weighed and dissolved in 10 mL of deionized water (the mass-to-volume ratio of 3,4-diaminobenzoic acid to deionized water was 0.1 g / mL, and the mass ratio of xylan to 3,4-diaminobenzoic acid was 1:1). The two solutions were mixed thoroughly. The mixture was transferred to a hydrothermal reactor and reacted at 180 °C for 12 h. After the reaction, the hydrothermal reactor was cooled to room temperature under natural conditions to obtain a brown carbon dot solid-liquid mixture. The obtained carbon dot solid-liquid mixture was centrifuged at 10,000 rpm to obtain a supernatant and precipitate. The supernatant was dialyzed for 7 days at room temperature using a dialysis bag with a molecular weight of 100 Da to obtain xylan-based carbon dots with a fluorescence quantum yield of 49.91%.

[0029] Example 4 1.0 g of xylan extracted from corn cob was weighed and dispersed in 10 mL of deionized water (the mass-to-volume ratio of xylan to deionized water was 0.1 g / mL). 0.75 g of 3,4-diaminobenzoic acid was weighed and dissolved in 10 mL of deionized water (the mass-to-volume ratio of 3,4-diaminobenzoic acid to deionized water was 0.075 g / mL, and the mass ratio of xylan to 3,4-diaminobenzoic acid was 4:3). The two solutions were mixed thoroughly. The mixture was transferred to a hydrothermal reactor and reacted at 220 °C for 12 h. After the reaction, the hydrothermal reactor was cooled to room temperature under natural conditions to obtain a brown carbon dot solid-liquid mixture. The obtained carbon dot solid-liquid mixture was centrifuged at 14,000 rpm to purify it, obtaining a supernatant and a precipitate. The supernatant was dialyzed for 3 days at room temperature using a dialysis bag with a molecular weight of 500 Da to obtain xylan-based carbon dots with a fluorescence quantum yield of 42.72%.

[0030] Example 5 1.0 g of xylan extracted from corn cob was weighed and dispersed in 10 mL of deionized water (the mass-to-volume ratio of xylan to deionized water was 0.1 g / mL). 1.0 g of 3,4-diaminobenzoic acid was weighed and dissolved in 10 mL of deionized water (the mass-to-volume ratio of 3,4-diaminobenzoic acid to deionized water was 0.1 g / mL, and the mass ratio of xylan to 3,4-diaminobenzoic acid was 1:1). The two solutions were mixed thoroughly. The mixture was transferred to a hydrothermal reactor and reacted at 220℃ for 8 h. After the reaction was complete, the hydrothermal reactor was cooled to room temperature under natural conditions to obtain a brown carbon dot solid-liquid mixture. The obtained carbon dot solid-liquid mixture was centrifuged at 12000 rpm to purify it, obtaining a supernatant and a precipitate. The supernatant was dialyzed for 5 days at room temperature using a dialysis bag with a molecular weight of 100 Da to obtain xylan-based carbon dots with a fluorescence quantum yield of 54.03%.

[0031] Based on the examples, by changing the temperature and time of the hydrothermal reaction, and by changing the amount of 3,4-diaminobenzoic acid and xylan added, a series of carbon dots were prepared. The quantum yield of these carbon dots and the corresponding preparation conditions are shown in Table 1.

[0032] Table 1. Fluorescence quantum yield of xylan-based carbon dots prepared under different conditions

[0033] Based on the examples, by changing the types of xylan and dopant during the hydrothermal reaction, a series of carbon dots were obtained. The quantum yields of these carbon dots were much lower than those of the carbon dots obtained by reacting corn cob xylan with 3,4-diaminobenzoic acid, as shown in Comparative Examples 1 to 7 below: Comparative Example 1 1.0 g of xylan extracted from corn cob was weighed and dispersed in 10 mL of deionized water (the mass-to-volume ratio of xylan to deionized water was 0.1 g / mL). The mixture was transferred to a hydrothermal reactor and reacted at 220 °C for 12 h. After the reaction was completed, the hydrothermal reactor was cooled to room temperature under natural conditions to obtain a brown carbon dot solid-liquid mixture. The obtained carbon dot solid-liquid mixture was purified by centrifugation at 12,000 rpm to obtain a supernatant and precipitate. The supernatant was dialyzed for 7 days at room temperature using a dialysis bag with a molecular weight of 500 Da to obtain xylan-based carbon dots with a fluorescence quantum yield of 7.83%.

[0034] As shown in Table 1, the carbon dot fluorescence quantum yield obtained from xylan extracted from corn cobs of a single component is low, and dopants need to be added for co-carbonization to improve the fluorescence quantum yield.

[0035] Comparative Example 2 1.0 g of 3,4-diaminobenzoic acid was weighed and dispersed in 10 mL of deionized water (the mass-to-volume ratio of 3,4-diaminobenzoic acid to deionized water was 0.1 g / mL). The mixture was transferred to a hydrothermal reactor and reacted at 220 °C for 12 h. After the reaction was completed, the hydrothermal reactor was cooled to room temperature under natural conditions to obtain a brown carbon dot solid-liquid mixture. The obtained carbon dot solid-liquid mixture was centrifuged at 12,000 rpm to purify it, obtaining a supernatant and a precipitate. The supernatant was dialyzed for 7 days at room temperature using a dialysis bag with a molecular weight of 500 Da to obtain 3,4-diaminobenzoic acid carbon dots with a fluorescence quantum yield of 0.44%.

[0036] Compared with the data in Table 1, the carbon dot fluorescence yield obtained by the single component 3,4-diaminobenzoic acid is the lowest, and xylan co-carbonization is required to improve the fluorescence quantum yield.

[0037] Comparative Example 3 1.0 g of xylan extracted from corn cob was weighed and dispersed in 10 mL of deionized water (the mass-to-volume ratio of xylan to deionized water was 0.1 g / mL). 1.0 g of citric acid was weighed and dissolved in 10 mL of deionized water (the mass-to-volume ratio of citric acid to deionized water was 0.1 g / mL, and the mass ratio of xylan to citric acid was 1:1). The two solutions were mixed thoroughly. The mixture was transferred to a hydrothermal reactor and reacted at 220 °C for 12 h. After the reaction was completed, the hydrothermal reactor was cooled to room temperature under natural conditions to obtain a brown carbon dot solid-liquid mixture. The obtained carbon dot solid-liquid mixture was centrifuged at 10,000 rpm to purify it, obtaining a supernatant and a precipitate. The supernatant was dialyzed for 5 days at room temperature using a dialysis bag with a molecular weight of 500 Da to obtain xylan-based carbon dots with a fluorescence quantum yield of 13.58%.

[0038] Compared to carbon dots obtained from xylan extracted from corn cobs alone, co-carbonization with citric acid failed to significantly improve the fluorescence properties of the carbon dots, indicating that introducing citric acid as an auxiliary precursor is not an effective strategy for optimizing the photoluminescence properties of xylan-based carbon dots. However, the fluorescence quantum yield of carbon dots obtained by co-carbonization of 3,4-diaminobenzoic acid as an auxiliary precursor with xylan extracted from beech was significantly improved. This may be attributed to the presence of both amino and carboxyl functional groups in 3,4-diaminobenzoic acid, which simultaneously introduces nitrogen doping and provides carboxyl groups during carbon dot synthesis. Furthermore, the benzene ring structure in the 3,4-diaminobenzoic acid molecule helps to synergistically form a more stable sp24-p-xylan precursor. 2 Conjugated structures are beneficial for enhancing electron delocalization and reducing nonradiative transitions.

[0039] Comparative Example 4 1.0 g of xylan extracted from sugarcane bagasse was weighed and dispersed in 10 mL of deionized water (the mass-to-volume ratio of xylan to deionized water was 0.1 g / mL). 1.0 g of 3,4-diaminobenzoic acid was weighed and dissolved in 10 mL of deionized water (the mass-to-volume ratio of 3,4-diaminobenzoic acid to deionized water was 0.1 g / mL, and the mass ratio of xylan to 3,4-diaminobenzoic acid was 1:1). The two solutions were mixed thoroughly. The mixture was transferred to a hydrothermal reactor and reacted at 220℃ for 12 h. After the reaction, the hydrothermal reactor was cooled to room temperature under natural conditions to obtain a brown carbon dot solid-liquid mixture. The obtained carbon dot solid-liquid mixture was centrifuged at 12000 rpm to obtain a supernatant and precipitate. The supernatant was dialyzed for 7 days at room temperature using a dialysis bag with a molecular weight of 500 Da to obtain xylan-based carbon dots with a fluorescence quantum yield of 7.82%.

[0040] Co-carbonation of xylan extracted from sugarcane bagasse with 3,4-diaminobenzoic acid failed to improve the fluorescence quantum yield of carbon dots, which may be attributed to the influence of the xylan's molecular weight (the molecular weight of sugarcane bagasse xylan is 6.3 × 10⁻⁶). 4 Da, the molecular weight of corn cob xylan is 1.4 × 10⁻⁶. 3 (Da). High molecular weight xylan undergoes random fragmentation during hydrothermal processes, forming fragments with a wide molecular weight distribution. This results in the coexistence of carbon dots of different sizes in the system, leading to the superposition of multiple emission peaks upon excitation, which affects optical uniformity. Furthermore, high molecular weight xylan is difficult to graphitize, affecting the formation of luminescent centers.

[0041] Comparative Example 5 1.0 g of xylan extracted from beech was weighed and dispersed in 10 mL of deionized water (the mass-to-volume ratio of xylan to deionized water was 0.1 g / mL). 1.0 g of 3,4-diaminobenzoic acid was weighed and dissolved in 10 mL of deionized water (the mass-to-volume ratio of 3,4-diaminobenzoic acid to deionized water was 0.1 g / mL, and the mass ratio of xylan to 3,4-diaminobenzoic acid was 1:1). The two solutions were mixed thoroughly. The mixture was transferred to a hydrothermal reactor and reacted at 220 °C for 12 h. After the reaction, the hydrothermal reactor was cooled to room temperature under natural conditions to obtain a brown carbon dot solid-liquid mixture. The obtained carbon dot solid-liquid mixture was centrifuged at 14,000 rpm to purify it, obtaining a supernatant and a precipitate. The supernatant was dialyzed for 7 days at room temperature using a dialysis bag with a molecular weight of 100 Da to obtain xylan-based carbon dots with a fluorescence quantum yield of 30.83%. Compared to bagasse xylan, beech xylan has a smaller molecular weight (3.5 × 10⁻⁶). 4 Da), thus enhancing the fluorescence quantum yield.

[0042] Comparative Example 6 Beech polysaccharide was degraded by sodium periodate oxidation (the molecular weight was reduced to 1.1 × 10⁻⁶). 41.0 g of beech xylan was dispersed in 10 mL of deionized water (the mass-to-volume ratio of xylan to deionized water was 0.1 g / mL). 1.0 g of 3,4-diaminobenzoic acid was dissolved in 10 mL of deionized water (the mass-to-volume ratio of 3,4-diaminobenzoic acid to deionized water was 0.1 g / mL, and the mass ratio of xylan to 3,4-diaminobenzoic acid was 1:1). The two solutions were mixed thoroughly. The mixture was transferred to a hydrothermal reactor and reacted at 220 °C for 12 h. After the reaction, the reactor was cooled to room temperature under natural conditions to obtain a brown carbon dot solid-liquid mixture. The resulting carbon dot solid-liquid mixture was centrifuged at 14,000 rpm to purify it, yielding a supernatant and precipitate. The supernatant was dialyzed for 5 days at room temperature using a dialysis bag with a molecular weight of 100 Da to obtain xylan-based carbon dots with a fluorescence quantum yield of 36.58%.

[0043] Compared with carbon dots obtained by co-carbonization of xylan extracted from beech and 3,4-diaminobenzoic acid, carbon dots obtained by co-carbonization of xylan extracted from beech and 3,4-diaminobenzoic acid have a higher fluorescence yield, but are still lower than xylan carbon dots obtained by co-carbonization of xylan extracted from corn cobs and 3,4-diaminobenzoic acid.

[0044] Comparative Example 7 1.0 g of xylose (molecular weight 150.13) was weighed and dispersed in 10 mL of deionized water (molecular weight ratio of xylose to deionized water was 0.1 g / mL). 1.0 g of 3,4-diaminobenzoic acid was weighed and dissolved in 10 mL of deionized water (molecular weight ratio of 3,4-diaminobenzoic acid to deionized water was 0.1 g / mL, and the mass ratio of xylose to 3,4-diaminobenzoic acid was 1:1). The two solutions were mixed thoroughly. The mixture was transferred to a hydrothermal reactor and reacted at 220 °C for 12 h. After the reaction, the reactor was cooled to room temperature under natural conditions to obtain a brown carbon dot solid-liquid mixture. The resulting carbon dot solid-liquid mixture was centrifuged at 14,000 rpm to obtain a supernatant and precipitate. The supernatant was dialyzed for 5 days at room temperature using a dialysis bag with a molecular weight of 100 Da to obtain xylose-based carbon dots with a fluorescence quantum yield of 34.99%.

[0045] Although xylose has a lower molecular weight than xylan extracted from corn cobs, its fluorescence quantum yield was not further improved. Figure 1 The fluorescence quantum yield diagrams of xylan-based carbon dots prepared in Examples 1 and Comparative Examples 3-5 are shown. It can be seen that only the co-carbonization of xylan extracted from corn cobs and 3,4-diaminobenzoic acid can yield xylan carbon dots with high fluorescence quantum yield.

[0046] Comparative Example 8 To demonstrate the advantages of high quantum yield xylan carbon dots in detection, the carbon dot xylan carbon dots obtained in Example 1 were further assembled with a rhodamine B ratiometric fluorescent probe for the detection of Vibrio parahaemolyticus and actual sample testing. Seawater samples and commercially available clams were used as matrices for actual sample testing. Three concentrations of Vibrio parahaemolyticus were added to the samples for detection and recovery rate studies.

[0047] (1) Sample source Seawater samples were collected from the waters off Guangzhou, and the clams sold in the market were purchased from the local market.

[0048] (2) Determination of standard curve The bacterial suspension was serially diluted with sterile physiological saline to obtain values ​​from 5 to 5 × 10⁻⁶. 6 CFU / mL concentration gradient bacterial suspensions were prepared by mixing 0.5 mL of each concentration gradient bacterial suspension with 0.5 mL of ratiometric fluorescent probe and incubating with shaking at room temperature for 30 minutes. 200 μL of the mixture was then injected into a small quartz cuvette for fluorescence spectral data acquisition. Figure 4 The blue / orange fluorescence intensity ratio (F) is shown. 435nm / F 587nm Quantitative analysis of Vibrio parahaemolyticus concentration (linear range: 5 ~ 5 × 10⁻⁶) 6 (CFU / mL, detection limit is 0.54 CFU / mL).

[0049] (3) Spike recovery rate Seawater was centrifuged to remove sediment, and the supernatant was collected for later use. Commercially available clams were shelled, and 5 g of soft tissue was added to 10 mL of ultrapure water for homogenization. The mixture was then filtered through qualitative filter paper to remove suspended solids, yielding clam meat extract. 5 × 10⁻⁶ g of the extract was added to the seawater. 1 5 × 10 3 5 × 10 6 CFU / mL Vibrio parahaemolyticus was added to clam meat extract at a concentration of 1 × 10⁻⁶ CFU / mL. 2 1 × 10 4 5 × 10 6 CFU / mL of Vibrio parahaemolyticus was collected to obtain spiked samples. 0.5 mL of the spiked sample was mixed with 0.5 mL of a ratiometric fluorescent probe and incubated at room temperature with shaking for 30 min. 200 μL of the mixture was injected into a small quartz cuvette, and the fluorescence spectrum was measured (excitation wavelength 355 nm, emission spectrum data acquisition range 375-650 nm) to obtain the F... 435nm / F 587nmThe concentration of Vibrio parahaemolyticus was obtained using a standard curve. The recovery rate and standard deviation were calculated by repeating the test three times. The results are shown in Table 2.

[0050] Table 2. Recovery rates of Vibrio parahaemolyticus in seawater samples and commercially available clams.

[0051] The detection limit of this ratiometric fluorescent probe for Vibrio parahaemolyticus was 0.54 CFU / mL, and the recoveries for seawater samples and commercially available clams were (10~10). 6 The CFU / mL values ​​were 86%–105% (RSD 9.2%–16.3%) and 90%–111% (RSD 9.5%–12.7%), respectively. See Table 2 for details. Furthermore, xylan carbon dots with a fluorescence quantum yield of 23.04% were further combined with Rhodamine B to construct a ratiometric fluorescent probe. Its detection limit for Vibrio parahaemolyticus was 1.15 CFU / mL, and its recoveries for seawater samples and commercially available clams were 80%–102% (RSD 13.8%–28.3%) and 92%–120% (RSD 16.3%–27.6%), respectively. These results confirm that xylan with a high fluorescence quantum yield makes the spiked recovery rate for Vibrio parahaemolyticus closer to 100%, significantly reducing the standard deviation and thus improving the accuracy of the detection results.

[0052] In summary, compared with the prior art, the present invention has the following advantages: (1) Carbon dots were synthesized using xylan and 3,4-diaminobenzoic acid as carbon and nitrogen sources, respectively. The carbon source was extracted from corn cob, which is inexpensive, readily available and abundant. (2) It is prepared by a one-step hydrothermal method, which is simple in process, has low equipment requirements, and is suitable for large-scale production; (3) The carbon dots prepared are uniformly distributed and have a high fluorescence quantum yield, showing significant advantages in analytical detection applications.

[0053] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing xylan-based carbon dots with high fluorescence quantum yield, characterized in that, Includes the following steps: a. Weigh xylan and disperse it in deionized water, weigh 3,4-diaminobenzoic acid and dissolve it in deionized water, mix the two evenly to obtain a mixed solution; b. Transfer the mixed solution to a hydrothermal reactor for hydrothermal reaction. After the reaction is completed, cool the hydrothermal reactor to room temperature under natural conditions to obtain a brown carbon dot solid-liquid mixture. c. Centrifuge the carbon dot solid-liquid mixture to obtain the supernatant and precipitate; d. Dialyze the supernatant at room temperature to obtain xylan carbon dots with high fluorescence quantum yield.

2. The preparation method according to claim 1, characterized in that, In step a, the xylan is extracted from corn cobs.

3. The preparation method according to claim 1, characterized in that, In step a, the mass-to-volume ratio of xylan to deionized water is 0.05 g / mL to 0.1 g / mL.

4. The preparation method according to claim 1, characterized in that, In step a, the mass-to-volume ratio of 3,4-diaminobenzoic acid to deionized water is 0.025 g / mL to 0.1 g / mL.

5. The preparation method according to claim 1, characterized in that, In step a, when the mass ratio of xylan to 3,4-diaminobenzoic acid is 4:1 to 2:1, the quantum yield of the prepared carbon dots is 8.51% to 16.91%; when the mass ratio is 2:1 to 4:3, the quantum yield of the prepared carbon dots is 16.91% to 42.72%; and when the mass ratio is 4:3 to 1:1, the quantum yield of the prepared carbon dots is 42.72% to 60.01%.

6. The preparation method according to claim 1, characterized in that, In step b, the hydrothermal reaction temperature is 180~220 ℃, and the hydrothermal reaction time is 2~16 h.

7. The preparation method according to claim 1, characterized in that, In step c, the centrifugal speed is 10,000-14,000 rpm.

8. The preparation method according to claim 1, characterized in that, In step d, the molecular weight of the dialysis bag is 100~500 Da, and the dialysis time is 3~7 days.

9. High fluorescence quantum yield xylan-based carbon dots prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the high fluorescence quantum yield xylan-based carbon dots according to claim 9 in analytical detection.

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