A method for preparing carbon dots by frying bread crumbs

Abstract

The invention discloses a method for preparing carbon dots by frying bread crumbs, and belongs to the field of biomass carbon dot preparation. The invention includes steps such as preparation of carbon dots, extraction of carbon dots, and purification of carbon dots. The invention uses bread crumbs as raw materials, and can quickly produce carbon dots inside bread crumbs within a few minutes by frying, greatly shortening the synthesis time of carbon dots. At the same time, the carbon dots are derived from food, greatly increasing its biosafety. The invention specifically analyzes the carbon dots extracted from bread crumbs fried at 180°C for 5min, and finds that it has good dispersibility in water, uniform particle size distribution, and an average particle size of 2.67±0.48nm. It also contains a large amount of C and O elements, and the molecular mass is concentrated in 700-1000, which is smaller than other carbon dots. At the same time, the method used in the invention is simple to prepare carbon dots, the extractant can be recycled, the extraction result is stable, and different carbon dots can be extracted according to different frying conditions, which can be applied to a variety of purposes.

Description

Technical Field

[0001] The invention belongs to the technical field of biomass carbon point preparation, and particularly relates to a method for preparing carbon points by using fried bread crumbs. Background Art

[0002] Nanoparticles are widely used in sterilization, detection and food processing and preservation due to their small size (1-100nm), large specific surface area and unique physical and chemical properties compared to raw materials. Nowadays, there are many methods for synthesizing carbon dots, the most commonly used of which are hydrothermal method and microwave method. However, most of the raw materials are chemical reagents and even contain toxicity, so they may not be suitable for fluorescence imaging. With the progress of research, people have found that carbon dots can also be produced in food during thermal processing, and they are named food-derived carbon dots.

[0003] Food-derived carbon dots can be divided into three categories based on their sources. The first category is food-derived carbon dots in meat products. Since meat contains a large amount of protein, this type of carbon dots has a high N content and a relatively high fluorescence quantum yield. The second category is food-derived carbon dots in carbohydrates. Due to their low protein content, the fluorescence quantum yield of this type of carbon dots is generally low. The third category is food-derived carbon dots in beverages, which are mainly produced by high-temperature thermal processing during high-temperature sterilization.

[0004] At present, the preparation of food-derived carbon dots mainly relies on the baking method. For example, the carbon dots extracted from roast duck in the literature need to be cut into 2×2×2cm cubes before baking, and baked at 170℃ for 60min. The molecular weight of the obtained carbon dots is concentrated at 1040, and the fluorescence quantum yield is 4.4%; while the preparation of carbon dots from beef needs to be baked at 280℃ for 30min, and the molecular weight of the obtained carbon dots is concentrated at 1057; the preparation of carbon dots from salmon needs to be baked at 200℃ for 50min, and the molecular weight of the carbon dots is concentrated at 1056. From the existing literature, the baking method takes a long time, and most of them use meat as raw material. The raw materials need to be cut into pieces to ensure that all parts are heated evenly during the baking process, so as to ensure the preparation of uniform carbon dots. At the same time, the molecular weight of the food-derived carbon dots obtained by baking exceeds 1000, and the molecular weight has not changed significantly compared with the conventional hydrothermal synthesis of carbon dots. However, large molecular carbon dots are not easy to pass through the human blood-brain barrier and are not easily absorbed by the human body. Therefore, there is a need for a method that can be quickly prepared, with cheap and easily available raw materials, and can obtain small molecular weight carbon dots. Summary of the invention

[0005] The present invention provides a method for extracting carbon dots from fried bread crumbs, which solves the problems of rare raw materials and environmental pollution in existing carbon dot preparation methods. The carbon dots only require short frying to prepare, which greatly reduces the preparation time and is low in cost.

[0006] In order to achieve the above objectives, the present invention is implemented by the following technical solutions:

[0007] The object of the present invention is to provide a simple and convenient method for preparing carbon dots, comprising the following steps:

[0008] 1. A method for preparing carbon dots by frying bread crumbs, wherein the method comprises the following steps:

[0009] (1) Preparation: Pour edible oil into a pot, heat it, add bread crumbs, and fry them to obtain fried bread crumbs;

[0010] (2) Extraction: washing the fried bread crumbs with petroleum ether, then mixing the washed fried bread crumbs with an ethanol-water solution, mixing evenly, collecting the filtrate by centrifugation, and drying to obtain a crude extract;

[0011] (3) Removal of impurities: re-dissolve the crude extract obtained above with a methanol-ethanol mixture, filter, collect the filtrate, dry to remove the solvent, re-dissolve with water, filter, dialyze the filtrate, collect the dialyzate and concentrate it again to obtain a concentrate;

[0012] (4) Chromatographic purification: The concentrated solution obtained above was further purified by preparative liquid chromatography, and the effluent with fluorescence at a wavelength of 360 nm was collected and subjected to vacuum rotary evaporation to obtain carbon dots.

[0013] Preferably, the frying temperature in step (1) is 100-220° C., and the oil temperature is maintained for 1-30 min.

[0014] Preferably, during frying in step (1), the mass volume ratio of bread crumbs to edible oil is 1 g:(3-5 ml).

[0015] Preferably, in step (1), the higher the frying temperature and the longer the frying time, the more conducive to improving the carbon dot yield and quantum yield.

[0016] Preferably, in the step (2), the volume ratio of petroleum ether to bread crumbs is (2-5 ml): 1 g, and the step is repeated 2-3 times.

[0017] Preferably, the ethanol volume concentration of the ethanol-water solution in step (2) is 10%-80%.

[0018] Preferably, in step (2), the stirring speed of the fried bread crumbs and the ethanol-water solution after mixing is 500-800 rpm, and the stirring time is 10-16 hours.

[0019] Preferably, in step (2), the ultrasonic power is 30-40 kHz and the ultrasonic time is 0.5-1 h.

[0020] Preferably, in step (3), the volume concentration of methanol in ethanol is 10%-20%.

[0021] Preferably, the specification of the dialysis bag used in step (3) is 3.5kDa-1kDa.

[0022] Preferably, in the step (2), the stationary phase of the preparative HPLC is a C18 column, the mobile phase is 20%-40% methanol, and the flow rate is 7-12 mL / min.

[0023] Beneficial effects:

[0024] (1) The present invention uses fried bread crumbs as raw materials, which are easily available and low in cost.

[0025] (2) The present invention adopts frying as the preparation method, which is simple to prepare and fast to produce. The carbon dots can be produced in only 5 minutes.

[0026] (3) The molecular weight of the carbon dots prepared by the present invention is small, concentrated between 700-1000, which is much smaller than that of most existing biomass carbon dots. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a high-resolution transmission electron microscopy image of the carbon dots extracted in Example 1 of the present invention.

[0028] Figure 2 The fluorescence emission spectrum and UV-visible absorption spectrum of the carbon dots extracted in Example 1 of the present invention.

[0029] Figure 3 This is the X-ray diffraction pattern (XRD) of the carbon dots extracted in Example 1 of the present invention.

[0030] Figure 4 This is the Fourier transform infrared spectrum (FT-IR) of the carbon dots extracted in Example 1 of the present invention.

[0031] Figure 5 This is the X-ray photoelectron spectrum (XPS) of the carbon dots extracted in Example 1 of the present invention.

[0032] Figure 6 This is the matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOFMS) of the carbon dots extracted in Example 1 of the present invention.

[0033] Figure 7 Effects of frying conditions on the yield and optical properties of carbon dots. DETAILED DESCRIPTION

[0034] In order to better understand the present invention, the present invention is further described below in conjunction with embodiments, but the scope of protection claimed by the present invention is not limited to the scope described in the embodiments.

[0035] Sources of raw materials for the embodiments of the present invention:

[0036] Sources of bread crumbs and cooking oil: local supermarket.

[0037] Ethanol and other reagents: Sinopharm Group.

[0038] Preparative liquid chromatography: Waters Technologies Inc. (Waters).

[0039] Those skilled in the art will appreciate that the present invention can theoretically be implemented by replacing the aforementioned materials with other brands.

[0040] Example 1 Extraction of carbon dots from fried bread crumbs

[0041] A specific method for extracting carbon dots from fried bread crumbs comprises the following steps:

[0042] (1) Put bread crumbs into oil whose temperature has been stabilized at 180°C, with the mass volume ratio of bread crumbs to oil being 1:4 (g:ml), and adjust the power so that the oil temperature rises quickly and stabilizes at 180°C, and then take out after frying for 5 minutes;

[0043] (2) Put the fried bread crumbs into a beaker, and add petroleum ether with a boiling range of 60-90° C. to wash the fried bread crumbs at a mass volume ratio of 1:4 (g:ml), place it on a magnetic stirrer and stir for 2 minutes, discard the petroleum ether, and repeat the above operation at least twice until the discarded petroleum ether is clear and transparent, and remove the residual petroleum ether by blowing naturally in a fume hood;

[0044] (3) adding 50% ethanol at a mass volume ratio of 1:20 (g:ml) to the washed fried bread crumbs, stirring for 12 h in the dark, and ultrasonicating at 40 kHz for 0.5 h;

[0045] (4) centrifuging and filtering the bread crumbs and ethanol solution ultrasonically treated in step (3), and collecting the filtrate;

[0046] (5) The filtrate is subjected to vacuum rotary evaporation, and after evaporation to dryness, it is re-dissolved in a methanol-ethanol mixture with a volume ratio of 1:9, and filtered with a 0.22 μm filter membrane. The filtrate is further subjected to vacuum rotary evaporation. After the solvent is evaporated to dryness, it is re-dissolved in water to obtain a primary extract, and the evaporated 50% ethanol and the methanol-ethanol mixture are collected for reuse;

[0047] (6) placing the primary extract obtained in (5) under a 3.5 kDa dialysis bag for dialysis, collecting the dialysate and concentrating it again;

[0048] (7) The concentrated solution obtained in (6) was further purified by Waters preparative-grade fully automated high performance liquid chromatography, with the specific conditions being: using a C18 column as the stationary phase, 35% methanol as the mobile phase, 10 mL / min as the mobile phase flow rate, and collecting the portion with fluorescence at 360 nm, to obtain carbon dots with a quantum yield of 3.16%;

[0049] (8) The collected solution is subjected to vacuum rotary evaporation, then reconstituted with water and freeze-dried using a vacuum freeze dryer. After freeze-drying, it can be stored at -20°C for at least 6 months.

[0050] Example 2

[0051] (1) Bread crumbs were placed in oil at a temperature stabilized at 150°C, with the mass volume ratio of bread crumbs to cooking oil being 1:3 (g:ml). The oil temperature was quickly raised and stabilized at 150°C by adjusting the power, and the oil was removed after frying for 5 minutes.

[0052] (2) Put the fried bread crumbs into a beaker, and add petroleum ether with a boiling range of 60-90° C. at a mass-to-volume ratio of 1:3 (g:ml), place on a magnetic stirrer and stir for 2 min, discard the petroleum ether, and repeat the above operation at least twice until the discarded petroleum ether is clear and transparent, and remove the residual petroleum ether by natural dispersal in a fume hood;

[0053] (3) adding 50% ethanol at a mass volume ratio of 1:15 (g:ml) to the washed fried bread crumbs, stirring for 14 h in the dark, and ultrasonicating at 35 kHz for 1 h;

[0054] (4) centrifuging and filtering the bread crumbs and ethanol solution ultrasonically treated in step (3), and collecting the filtrate;

[0055] (5) subjecting the filtrate to vacuum rotary evaporation, evaporating to dryness, re-dissolving with a methanol-ethanol mixture having a volume ratio of 2:8, filtering with a 0.22 μm filter membrane, and continuing to subject the filtrate to vacuum rotary evaporation. After the solvent is evaporated to dryness, re-dissolving with water to obtain a primary extract, collecting the evaporated 50% ethanol and the methanol-ethanol mixture for reuse;

[0056] (6) placing the primary extract obtained in (5) under a 1 kDa dialysis bag for dialysis, collecting the dialysate and concentrating it again;

[0057] (7) The concentrated solution obtained in (6) was further purified using a Waters preparative-grade fully automatic high performance liquid chromatography. The specific conditions were: using a C18 column as the stationary phase, 30% methanol as the mobile phase, and a mobile phase flow rate of 7.5 mL / min. The portion with fluorescence at 360 nm was collected to obtain carbon dots with a quantum yield of 1.98%.

[0058] (8) The collected solution is subjected to vacuum rotary evaporation and then reconstituted with water and stored at 4°C for at least 6 months.

[0059] It should be noted that in the above extraction method of the present invention and Examples 1 and 2, the frying temperature and time can be further shortened or increased. The yield and quantum yield of the carbon dots extracted under various frying conditions are as follows: Figure 7 As shown, the obtained carbon dots can be stored for at least half a year at 4°C or -20°C.

[0060] Example 3 Characterization Results

[0061] The carbon dots obtained in Example 1 were observed using a high-resolution transmission electron microscope. Figure 1 It can be seen that the carbon dots obtained by this extraction method have good dispersibility in water, uniform particle size distribution, an average particle size of 2.67±0.48nm, and a clear lattice structure can be seen on the surface of the carbon dots through a high-resolution transmission electron microscope.

[0062] from Figure 2 It can be seen that the carbon dots obtained in Example 1 have an optimal emission wavelength of 397 nm at an optimal excitation wavelength of 320 nm, and have a broad absorption peak at 250-300 nm.

[0063] Figure 3 : is the XRD spectrum of the carbon dots obtained in Example 1, which is consistent with the common carbon dot spectrum, indicating that the carbon dots are amorphous.

[0064] Figure 4 This is the FT-IR spectrum of the carbon dots obtained in Example 1. It can be seen that the carbon dots contain a large number of hydroxyl groups, indicating that they may have antioxidant potential.

[0065] Figure 5 This is the XPS spectrum of the carbon dots obtained in Example 1. It can be seen that the carbon dots are composed of C, O, and N elements, of which C accounts for 57.85%, O accounts for 39.61%, and N accounts for 2.53%.

[0066] Figure 6 This is the mass spectrum of the carbon dots obtained in Example 1. It can be seen that the molecular weight of the generated carbon dots is concentrated between 700-1000, with the highest peak at 851.3, which is significantly lower than the molecular weight of existing carbon dots. At the same time, since its particle size is mainly concentrated between 2-3.5nm, it is easier to be absorbed by the human body and even pass through the blood-brain barrier.

Claims

1. A method for preparing carbon dots by frying bread crumbs, wherein the method comprises the following steps: (1) Preparation: Pour edible oil into a pot, heat it, add bread crumbs, and fry them to obtain fried bread crumbs; the mass volume ratio of bread crumbs to edible oil during frying is 1 g:4 mL; the frying temperature is 180° C., and the frying time is 5 min; (2) Extraction: The fried bread crumbs were washed with petroleum ether, and then 50% ethanol was added to the washed fried bread crumbs at a mass volume ratio of 1:20 g:mL, stirred in the dark for 12 h, and ultrasonicated at 40 kHz for 0.5 h. The ultrasonicated bread crumbs and ethanol solution were centrifuged and filtered, and the filtrate was collected; (3) Removal of impurities: re-dissolve the crude extract obtained above with a methanol-ethanol mixture, filter, collect the filtrate, dry to remove the solvent, re-dissolve with water, filter, dialyze the filtrate, collect the dialyzate and concentrate it again to obtain a concentrate; (4) Chromatographic purification: The concentrated solution obtained above was further purified by preparative liquid chromatography using a C18 column as the stationary phase, 35% methanol as the mobile phase, and a mobile phase flow rate of 10 mL / min. The effluent with fluorescence at a wavelength of 360 nm was collected and vacuum rotary evaporated to obtain carbon dots.

2. The method for preparing carbon dots by frying bread crumbs according to claim 1, characterized in that: In the step (3), the volume concentration of methanol in ethanol is 5%-25%.

3. The method for preparing carbon dots by frying bread crumbs according to claim 1, characterized in that: The specification of the dialysis bag in step (3) is 500-3.5 kDa.

4. The method for preparing carbon dots by frying bread crumbs according to claim 1, characterized in that: The carbon dots obtained in step (4) can be stored at 0°C-4°C or -18°C for a long time.

5. Use of the carbon dots prepared by the method for preparing carbon dots by using fried bread crumbs according to any one of claims 1 to 4 in the field of preparation of biological imaging equipment.

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