A D-amino acid modified fluorescent carbon quantum dot aqueous solution and preparation method thereof

Abstract

The present invention provides a D-type amino acid modified fluorescent carbon quantum dot aqueous solution and preparation method thereof, the preparation method includes: weighing D-histidine and levofloxacin solid, mixing, moving to a polytetrafluoroethylene reactor after mixing, heating in a blast drying oven and reacting for a period of time; after the reaction is completed, cooling to room temperature to obtain a carbon quantum dot reaction crude liquid, centrifuging the carbon quantum dot reaction crude liquid and passing through a filter membrane; after passing through the filter membrane, transferring to a cellulose dialysis bag, dialyzing in deionized water, adjusting the pH after dialysis to obtain carbon quantum dots; vacuum freeze-drying the carbon quantum dots, and dissolving with ultrapure water to obtain a D-type amino acid modified fluorescent carbon quantum dot aqueous solution. The synthesis technology provided by the present invention has simple process, only two small molecule substances are needed for the synthesis precursor, and the cost is low, which is suitable for large-scale batch production.

Description

Technical Field

[0001] The present invention relates to the field of nanotechnology, and in particular to a D-amino acid modified fluorescent carbon quantum dot aqueous solution and a preparation method thereof. Background Art

[0002] Carbon quantum dots (CQDs) are a new type of carbon nanomaterial with a size range between macroscopic bulk and microscopic atoms, with an average particle size of less than 10 nm. Their surface atoms account for a significant proportion, resulting in a significant quantum effect. CQDs offer advantages such as small size, simple synthesis, a wide range of raw materials, and good biocompatibility. Researchers typically use a bottom-up synthesis method to prepare CQDs, including hydrothermal, pyrolysis, and microwave-assisted methods. The hydrothermal method is widely used due to its ease of preparation, simple operation, and low cost. Recent studies have shown that the particle size and surface characteristics of CQDs have a significant impact on their properties. Smaller CQDs have a larger specific surface area and more surface luminescence sites. Consequently, smaller CQDs exhibit stronger luminescence than larger ones, further demonstrating that their luminescence is surface-dependent. Furthermore, CQDs with a high number of oxygen-containing groups (such as hydroxyl and carboxyl groups) on their surface exhibit good water solubility and are amenable to further functionalization. Therefore, fluorescent carbon quantum dots have unique physical and chemical properties and have broad application prospects in biomedicine and analysis fields.

[0003] The numerous properties of carbon quantum dots (CQDs) depend primarily on the raw materials used for synthesis, the internal structure of the nanomaterials, and their surface activity, with surface activity being the primary factor determining their performance. Functionalization of CQDs, achieved through surface modification, is the best approach for improving their performance. Their use as fluorescent probes in the biomedical field requires rapid visualization while achieving excellent sensitivity and selectivity to avoid interference from complex dynamic environments. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art and to provide an aqueous solution of fluorescent carbon quantum dots modified with D-amino acids and a preparation method thereof.

[0005] To achieve the above-mentioned object of the invention, on the one hand, the present invention provides a method for preparing an aqueous solution of D-amino acid-modified fluorescent carbon quantum dots, comprising:

[0006] Weigh D-histidine and levofloxacin solids, mix them evenly, transfer them to a polytetrafluoroethylene reactor, heat them in a forced air drying oven, and react for a period of time;

[0007] After the reaction is completed, the mixture is cooled to room temperature to obtain a crude carbon quantum dot reaction solution, which is then centrifuged and passed through a filter membrane;

[0008] After passing through the filter membrane, the solution was transferred to a cellulose dialysis bag and dialyzed in deionized water. After dialysis, the pH was adjusted to obtain carbon quantum dots.

[0009] The carbon quantum dots are vacuum freeze-dried and dissolved in ultrapure water to obtain an aqueous solution of fluorescent carbon quantum dots modified with D-amino acids.

[0010] In one embodiment, the fluorescent carbon quantum dot aqueous solution is subjected to rotary evaporation and vacuum drying to obtain fluorescent carbon quantum dot solid powder.

[0011] In one embodiment, the average particle size of the fluorescent carbon quantum dot solid powder is 1.10 nm.

[0012] In one embodiment, the mixture is heated to 200° C. in a forced air drying oven and reacted for 12 hours.

[0013] In one embodiment, the filter is a 0.22 μM filter.

[0014] In one embodiment, the dialysis bag is a 100-500D cellulose dialysis bag, and the dialysis time is 24 hours.

[0015] In one embodiment, the pH is adjusted to 7.4 with 1 M NaOH after dialysis to obtain the carbon quantum dots.

[0016] On the other hand, the present invention provides an aqueous solution of D-amino acid-modified fluorescent carbon quantum dots prepared according to the above preparation method.

[0017] In one embodiment, the fluorescent carbon quantum dot aqueous solution is dark blue-green and clear, and when the ultraviolet-visible absorption spectrum of the fluorescent carbon quantum dot aqueous solution is scanned, the maximum absorption peak position of the fluorescent carbon quantum dot aqueous solution is at 306 nm.

[0018] The advantages and beneficial effects of the present invention over the prior art are:

[0019] (1) During the preparation of the aqueous solution of D-amino acid-modified fluorescent carbon quantum dots, no other reagents are required except for the addition of precursors D-histidine and levofloxacin. The precursors D-histidine and levofloxacin can be treated by a simple one-step hydrothermal method to obtain an aqueous solution of D-amino acid-modified fluorescent carbon quantum dots. The preparation process of the method of the present invention is simple, low in cost, and blue-green and environmentally friendly. In addition, the prepared D-amino acid-modified fluorescent carbon quantum dot solid powder has a regular morphology, uniform particle size, good water solubility, high solution stability, easy storage, and is convenient for large-scale batch production. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1This is a photo of an aqueous solution of fluorescent carbon quantum dots modified with D-amino acids under 365nm ultraviolet light.

[0021] Figure 2 This is the UV-visible absorption spectrum of the aqueous solution of fluorescent carbon quantum dots modified with D-amino acids.

[0022] Figure 3 These are the fluorescence excitation spectrum and fluorescence emission spectrum of the aqueous solution of fluorescent carbon quantum dots modified with D-amino acids.

[0023] Figure 4 This is a transmission electron microscopy image of an aqueous solution of fluorescent carbon quantum dots modified with D-amino acids.

[0024] Figure 5 This is the X-ray photoelectron spectrum of fluorescent carbon quantum dot solid powder modified with D-amino acid.

[0025] Figure 6 This is the infrared spectrum of the fluorescent carbon quantum dot solid powder modified with D-amino acid.

[0026] Figure 7 This is the result graph of the relative fluorescence quantum yield of the aqueous solution of fluorescent carbon quantum dots modified with D-amino acids. DETAILED DESCRIPTION

[0027] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] Example 1

[0029] (1) Accurately weigh 1.0000 g of D-histidine and 1.0000 g of levofloxacin solid, place in a 10 mL beaker, mix well, transfer to a polytetrafluoroethylene reactor, heat to 200°C in a forced air drying oven, and react for 12 h;

[0030] (2) Cooling the obtained carbon quantum dot crude solution to room temperature, centrifuging the obtained carbon quantum dot reaction crude solution and passing it through a 0.22 μM filter membrane;

[0031] (3) The filtrate obtained in step 2) was dialyzed in deionized water using a 100-500D cellulose dialysis bag for 24 hours, with the dialysis solution replaced every 4 hours;

[0032] (4) The pH was then adjusted to 7.4 with 1 M NaOH;

[0033] (5) The obtained carbon quantum dots were freeze-dried in vacuum and dissolved in ultrapure water to obtain a 2.0 mg / mL aqueous solution of D-amino acid-modified fluorescent carbon quantum dots. A photo of the solution under 365 nm ultraviolet light showed blue-green fluorescence, indicating its potential for imaging and sensing. Figure 1 .

[0034] Example 2

[0035] (1) Accurately weigh 1.0000 g of D-histidine and 1.0000 g of levofloxacin solid, place in a 10 mL beaker, mix well, transfer to a polytetrafluoroethylene reactor, heat to 200°C in a forced air drying oven, and react for 12 h;

[0036] (2) Cooling the obtained carbon quantum dot crude solution to room temperature, centrifuging the obtained carbon quantum dot reaction crude solution and passing it through a 0.22 μM filter membrane;

[0037] (3) The filtrate obtained in step 2) was dialyzed in deionized water using a 100-500D cellulose dialysis bag for 24 hours, with the dialysis solution replaced every 4 hours;

[0038] (4) The pH was then adjusted to 7.4 with 1 M NaOH;

[0039] (5) The obtained carbon quantum dots were freeze-dried in vacuum and dissolved in ultrapure water to obtain a 2.0 mg / mL aqueous solution of D-amino acid-modified fluorescent carbon quantum dots. A small amount of the solution was diluted to a dilute solution and its UV-visible absorption spectrum was scanned. The characteristic absorption peaks of the D-amino acid-modified fluorescent carbon quantum dots aqueous solution were at 306 nm and 395 nm (see Figure 2 ); At the same time, scanning its excitation spectrum and emission spectrum, the spectrum shows that the optimal emission wavelengths of carbon quantum dots aqueous solution are 370nm and 495nm (see Figure 3 ).

[0040] Example 3

[0041] (1) Accurately weigh 1.0000 g of D-histidine and 1.0000 g of levofloxacin solid, place in a 10 mL beaker, mix well, transfer to a polytetrafluoroethylene reactor, heat to 200°C in a forced air drying oven, and react for 12 h;

[0042] (2) Cooling the obtained carbon quantum dot crude solution to room temperature, centrifuging the obtained carbon quantum dot reaction crude solution and passing it through a 0.22 μM filter membrane;

[0043] (3) The filtrate obtained in step 2) was dialyzed in deionized water using a 100-500D cellulose dialysis bag for 24 hours, with the dialysis solution replaced every 4 hours;

[0044] (4) The pH was then adjusted to 7.4 with 1 M NaOH;

[0045] (5) The obtained carbon quantum dots were freeze-dried in vacuum and dissolved in ultrapure water to obtain a 2.0 mg / mL aqueous solution of D-amino acid-modified fluorescent carbon quantum dots. The obtained aqueous solution was drop-coated on a copper mesh for transmission electron microscopy. The D-amino acid-modified fluorescent carbon quantum dots aqueous solution was a regular monodisperse spherical shape with an average particle size of 1.10 nm (see Figure 4 ), which is smaller than most carbon quantum dots and has a larger specific surface area, and has great research potential.

[0046] Example 4

[0047] (1) Accurately weigh 1.0000 g of D-histidine and 1.0000 g of levofloxacin solid, place in a 10 mL beaker, mix well, transfer to a polytetrafluoroethylene reactor, heat to 200°C in a forced air drying oven, and react for 12 h;

[0048] (2) Cooling the obtained carbon quantum dot crude solution to room temperature, centrifuging the obtained carbon quantum dot reaction crude solution and passing it through a 0.22 μM filter membrane;

[0049] (3) The filtrate obtained in step 2) was dialyzed in deionized water using a 100-500D cellulose dialysis bag for 24 hours, with the dialysis solution replaced every 4 hours;

[0050] (4) The pH was then adjusted to 7.4 with 1 M NaOH;

[0051] (5) The obtained carbon quantum dots were freeze-dried in vacuum and dissolved in ultrapure water to obtain a 2.0 mg / mL aqueous solution of fluorescent carbon quantum dots modified with D-amino acids. After rotary evaporation and vacuum drying, a solid powder of fluorescent carbon quantum dots modified with D-amino acids was obtained. The obtained powder was subjected to X-ray photoelectron spectroscopy. The spectrum showed that the surface of the carbon quantum dots contained a large amount of C, O, N, and F elements (see Figure 5 ), indicating that the surface of D-amino acid modified fluorescent carbon quantum dots contains multiple elements, which provides elemental support for studying their specific surface properties.

[0052] Example 5

[0053] (1) Accurately weigh 1.0000 g of D-histidine and 1.0000 g of levofloxacin solid, place in a 10 mL beaker, mix well, transfer to a polytetrafluoroethylene reactor, heat to 200°C in a forced air drying oven, and react for 12 h;

[0054] (2) Cooling the obtained carbon quantum dot crude solution to room temperature, centrifuging the obtained carbon quantum dot reaction crude solution and passing it through a 0.22 μM filter membrane;

[0055] (3) The filtrate obtained in step 2) was dialyzed in deionized water using a 100-500D cellulose dialysis bag for 24 hours, with the dialysis solution replaced every 4 hours;

[0056] (4) The pH was then adjusted to 7.4 with 1 M NaOH;

[0057] (5) The obtained carbon quantum dots were freeze-dried in vacuum and dissolved in ultrapure water to obtain a 2.0 mg / mL aqueous solution of D-amino acid-modified fluorescent carbon quantum dots. After rotary evaporation and vacuum drying, a solid powder of D-amino acid-modified fluorescent carbon quantum dots was obtained. The obtained powder was subjected to Fourier transform infrared (FTIR) spectroscopy, which further indicated the presence of oxygen-containing groups (CO, -COOH, C=O) and -NH2 as well as CC (see Figure 6 ), providing a structural basis for studying the relationship between the structure of D-amino acid modified fluorescent carbon quantum dots and their fluorescence properties and antibacterial properties.

[0058] Example 6

[0059] (1) Accurately weigh 1.0000 g of D-histidine and 1.0000 g of levofloxacin solid, place in a 10 mL beaker, mix well, transfer to a polytetrafluoroethylene reactor, heat to 200°C in a forced air drying oven, and react for 12 h;

[0060] (2) Cooling the obtained carbon quantum dot crude solution to room temperature, centrifuging the obtained carbon quantum dot reaction crude solution and passing it through a 0.22 μM filter membrane;

[0061] (3) The filtrate obtained in step 2) was dialyzed in deionized water using a 100-500D cellulose dialysis bag for 24 hours, with the dialysis solution replaced every 4 hours;

[0062] (4) The pH was then adjusted to 7.4 with 1 M NaOH;

[0063] (5) The obtained carbon quantum dots were vacuum freeze-dried and dissolved in ultrapure water to obtain a 2.0 mg / mL aqueous solution of D-amino acid-modified fluorescent carbon quantum dots. Quinine sulfate dissolved in 0.1 M H2SO4 was used as a reference (360 nm as the excitation wavelength, absorbance at 360 nm, QY = 0.54), and the emission spectra of the D-amino acid-modified fluorescent carbon quantum dots and quinine sulfate under 360 nm excitation and the corresponding concentrations were measured respectively. The absorbance value at 360 nm in the corresponding absorption spectrum at the same concentration was plotted as the X-axis and the area integral of the emission spectrum was plotted as the Y-axis. The slope of the curve was calculated, and the relative fluorescence quantum yield was calculated according to the equation:

[0064] Φ x =ΦST (m x / m ST )(η x 2 / η ST 2 )

[0065] In the formula, “Φ x ” represents the fluorescence quantum yield of D-amino acid modified fluorescent carbon quantum dots, “Φ ST ” represents the fluorescence quantum yield of quinine sulfate, “m x ” and “m ST " represents the slope of the curve obtained by plotting the area integral of the emission spectra of D-amino acid modified fluorescent carbon quantum dots and quinine sulfate against the absorbance value, "η x ” and “η ST " represent the refractive index of D-amino acid modified fluorescent carbon quantum dots dissolved in ultrapure water and the refractive index of quinine sulfate dissolved in dilute sulfuric acid (wherein the refractive index of D-amino acid modified fluorescent carbon quantum dots dissolved in ultrapure water is 1.33, and the refractive index of quinine sulfate dissolved in dilute sulfuric acid is 1.33). The results are as follows Figure 7 As shown, the calculated relative fluorescence quantum yield of the D-amino acid modified fluorescent carbon quantum dots is 23.79%, indicating that it has stable fluorescence properties.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing an aqueous solution of fluorescent carbon quantum dots modified with D-amino acids, comprising: Weigh D-histidine and levofloxacin solids, mix them evenly, transfer them to a polytetrafluoroethylene reactor, heat them to 200°C in a forced air drying oven, and react for 12 h; After the reaction is completed, the mixture is cooled to room temperature to obtain a crude carbon quantum dot reaction solution, which is then centrifuged and passed through a filter membrane; After passing through the filter membrane, the solution was transferred to a cellulose dialysis bag and dialyzed in deionized water. After dialysis, the pH was adjusted to 7.4 with 1 M NaOH to obtain carbon quantum dots. The carbon quantum dots are vacuum freeze-dried and dissolved in ultrapure water to obtain a D-amino acid-modified fluorescent carbon quantum dot aqueous solution, wherein the fluorescent carbon quantum dot aqueous solution is dark blue-green and clear. When the ultraviolet-visible absorption spectrum of the fluorescent carbon quantum dot aqueous solution is scanned, the maximum absorption peak position of the fluorescent carbon quantum dot aqueous solution is at 306 nm. After rotary evaporation and vacuum drying of the fluorescent carbon quantum dot aqueous solution, fluorescent carbon quantum dot solid powder is obtained, and the average particle size of the fluorescent carbon quantum dot solid powder is 1.10 nm.

2. The method for preparing the D-amino acid modified fluorescent carbon quantum dot aqueous solution according to claim 1, wherein The filter membrane is 0.22 μM.

3. The method for preparing the D-amino acid modified fluorescent carbon quantum dot aqueous solution according to claim 1, wherein The dialysis bag is a 100-500D cellulose dialysis bag, and the dialysis time is 24 hours.

4. An aqueous solution of D-amino acid-modified fluorescent carbon quantum dots prepared according to the preparation method of any one of claims 1 to 3.

5. The D-amino acid modified fluorescent carbon quantum dot aqueous solution according to claim 4, characterized in that, The fluorescent carbon quantum dot aqueous solution is dark blue-green and clear. When the ultraviolet-visible absorption spectrum of the fluorescent carbon quantum dot aqueous solution is scanned, the maximum absorption peak position of the fluorescent carbon quantum dot aqueous solution is at 306 nm.

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