A CdSe@ZnS quantum dot and preparation method thereof

Abstract

The present invention relates to the technical field of nanomaterials, and provides a CdSe@ZnS quantum dot and a preparation method thereof. The method comprises: dissolving oil-soluble CdSe quantum dots in a non-polar organic solvent to obtain a seed solution; adding a zinc ion aqueous solution to a chiral ligand molecule aqueous solution for mixing, using sodium hydroxide to adjust the pH of the mixed aqueous solution until the white flocs disappear, and then adding a sulfur ion aqueous solution in an equal molar ratio to the zinc ion aqueous solution, mixing evenly, and obtaining a shell growth aqueous solution; then, adding the shell growth aqueous solution to the seed solution to form a two-phase interface, stirring for 6 to 24 hours at a temperature of 25°C to 45°C to form CdSe@ZnS quantum dots. The CdSe@ZnS quantum dots prepared by the present invention not only have excellent chirality and fluorescence properties, the fluorescence quantum yield can reach 67.2%, the chiral asymmetry factor can reach 0.01, but also have good water solubility and biocompatibility.

Description

Technical Field

[0001] The invention relates to the technical field of nanomaterials, and in particular to a CdSe@ZnS quantum dot and a preparation method thereof. Background Art

[0002] Chirality is a basic property of nature. Amino acids and sugar molecules in living organisms have special chiral configurations. Using chiral quantum dots as fluorescent markers, we can study the mechanism of action of chiral substances in organisms through the affinity differences of chiral quantum dots with different configurations in the body, which is very important for understanding the laws of chiral action and material metabolism pathways of living organisms.

[0003] Common preparation methods for chiral quantum dots include direct synthesis of chiral quantum dots in aqueous solution with the aid of chiral water-soluble ligands, and obtaining chiral quantum dots by ligand exchange of oil-soluble quantum dots with chiral molecules. However, although chiral quantum dots synthesized in aqueous phase have good biocompatibility, there are still problems of uneven size distribution and poor optical properties of quantum dots. The broad fluorescence emission and chiral spectrum, as well as weak fluorescence emission intensity, hinder subsequent research. Although chiral quantum dots obtained by ligand exchange have uniform size distribution and detailed chiral characteristic spectra, the ligand exchange process will inevitably cause too many defects on the surface of quantum dots, resulting in low fluorescence quantum yield.

[0004] Therefore, there is an urgent need to develop a water-soluble quantum dot with both high fluorescence intensity and strong chiral signal to meet the application requirements of actual biological imaging. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a water-soluble quantum dot having both high fluorescence intensity and strong chiral signal to meet the application requirements of actual biological imaging.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing CdSe@ZnS quantum dots, comprising:

[0008] S1, dissolving oil-soluble CdSe quantum dots in a non-polar organic solvent to obtain a seed solution;

[0009] S2, adding a zinc ion aqueous solution to the chiral ligand molecule aqueous solution to mix, adjusting the pH of the mixed aqueous solution with sodium hydroxide until the white flocs disappear, and then adding a sulfide ion aqueous solution in an equal molar ratio to the zinc ion aqueous solution, mixing evenly, to obtain a shell growth aqueous solution;

[0010] S3, adding the shell growth aqueous solution to the seed solution, stirring for 6 to 24 hours at a temperature of 25° C. to 45° C. to form CdSe@ZnS quantum dots.

[0011] In a second aspect, the present invention provides a CdSe@ZnS quantum dot, wherein the CdSe@ZnS quantum dot is prepared by the preparation method of the CdSe@ZnS quantum dot described in the first aspect.

[0012] The preparation method of CdSe@ZnS quantum dots provided in the embodiment of the present invention is to dissolve oil-soluble CdSe quantum dots in a non-polar organic solvent to obtain a seed solution; add a zinc ion aqueous solution to a chiral ligand molecule aqueous solution for mixing, use sodium hydroxide to adjust the pH of the mixed aqueous solution until the white flocs disappear, and then add a sulfur ion aqueous solution in an equal molar ratio to the zinc ion aqueous solution, mix evenly, and obtain a shell growth aqueous solution; then, add the shell growth aqueous solution to the seed solution to form a two-phase interface, and stir for 6 to 24 hours at a temperature of 25°C to 45°C to form CdSe@ZnS quantum dots. The present invention can realize ligand exchange and shell growth at the two-phase interface at the same time, effectively reduce the generation of CdSe surface defect states, thereby obtaining water-soluble core-shell quantum dots (i.e., CdSe@ZnS quantum dots) with high brightness; and the chiral ligand-mediated shell growth can realize the chiral ligand-induced shell atomic arrangement, thereby making the CdSe@ZnS quantum dots have obvious chiral signals. The fluorescence quantum yield of the chiral CdSe@ZnS quantum dots prepared by the method provided in the embodiment of the present invention can reach 67.2%, and the chiral asymmetry factor can reach 0.01, while the fluorescence quantum yield of the chiral quantum dots prepared by the traditional method is not higher than 40%, and the chiral asymmetry factor is not higher than 10. -3 ~10 -5 In addition, the chiral CdSe@ZnS quantum dots prepared by the present invention not only have excellent chirality and fluorescence properties, but also have good water solubility and biocompatibility due to aqueous synthesis, that is, the chiral quantum dots obtained have broad application prospects in biological imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0014] Figure 1 is a physical image and a transmission electron microscope image of the seed solution in Example 1 of the present invention;

[0015] Figure 2 The physical image and transmission electron microscope image of CdSe@ZnS quantum dots prepared in Example 1 of the present invention are shown;

[0016] Figure 3 It is the fluorescence spectrum comparison result of the seed solution prepared in Example 1 of the present invention and the CdSe@ZnS quantum dots prepared in Examples 1 to 3;

[0017] Figure 4 It is the circular dichroism spectrum comparison result of the seed solution prepared in Example 1 of the present invention and the CdSe@ZnS quantum dots prepared in Examples 1 to 3;

[0018] Figure 5 The fluorescence spectra and circular dichroism spectra of the CdSe@ZnS quantum dots prepared in Example 1 of the present invention and Comparative Example 1 are compared;

[0019] Figure 6 It is the comparison result of fluorescence spectrum and circular dichroism spectrum between the CdSe@ZnS quantum dots prepared in Example 1 of the present invention and the CdSe quantum dots and CdSe@ZnS quantum dots prepared in Comparative Example 2. DETAILED DESCRIPTION

[0020] 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, but the embodiments of the present invention are not limited thereto.

[0021] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The experimental reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the amounts of the experimental reagents, unless otherwise specified, are all the amounts of reagents used in conventional experimental operations; the experimental methods, unless otherwise specified, are all conventional methods.

[0022] The embodiment of the present invention utilizes the two-phase interface formed by oil-soluble CdSe quantum dot seeds and water-soluble shell growth aqueous solution, and under the action of stirring, ligand exchange and shell growth are simultaneously performed at the interface, effectively avoiding the problem of severe decrease in quantum yield due to excessive surface defects of quantum dots; at the same time, the preparation method of the present invention can directly prepare water-soluble chiral CdSe quantum dots, and significantly improve the fluorescence quantum yield of the quantum dots, and the obtained chiral quantum dots have obvious chiral characteristic peaks through circular dichroism spectroscopy testing, have great application potential in chiral substance interactions, polarization imaging and biological analysis systems, and have huge application prospects in the field of biological imaging.

[0023] In a first aspect, this embodiment provides a method for preparing CdSe@ZnS quantum dots, comprising the following steps:

[0024] S1. Dissolving oil-soluble CdSe quantum dots in a non-polar organic solvent to obtain a seed solution.

[0025] The oil-soluble CdSe quantum dots are bare core CdSe quantum dot materials with oleic acid ligands on the surface. The CdSe quantum dots can be obtained by referring to the existing very mature synthesis technology of CdSe quantum dots with oleic acid on the surface.

[0026] Before dissolving the oil-soluble CdSe quantum dots in a non-polar organic solvent, the CdSe quantum dots are first precipitated and washed at least three times with acetone to remove excess oil-soluble ligands on the surface of the CdSe quantum dots.

[0027] S2. Add zinc ion aqueous solution to the chiral ligand molecule aqueous solution and mix them, use sodium hydroxide to adjust the pH of the mixed aqueous solution until the white flocs disappear, then add sulfur ion aqueous solution in an equal molar ratio to the zinc ion aqueous solution, mix them evenly, and obtain a shell growth aqueous solution.

[0028] After adding the zinc ion aqueous solution to the chiral ligand molecule aqueous solution for mixing, the pH of the mixed aqueous solution is adjusted with sodium hydroxide until the white flocs disappear, thereby ensuring the normal progress of the subsequent synthesis steps.

[0029] S3, adding the shell growth aqueous solution to the seed solution, stirring for 6 to 24 hours at a temperature of 25° C. to 45° C. to form CdSe@ZnS quantum dots.

[0030] In some embodiments, in step S1, the non-polar organic solvent is chloroform.

[0031] In some embodiments, in step S1, the mass volume ratio of the oil-soluble CdSe quantum dots to the non-polar organic solvent is 10 mg:1.75 mL. That is, 10 mg of oil-soluble CdSe quantum dots are dissolved in 1.75 mL of non-polar organic solvent. It can be understood that in practical applications, this mass volume ratio can be proportionally expanded or reduced. For example, 100 mg of oil-soluble CdSe quantum dots are dissolved in 17.5 mL of non-polar organic solvent; 1000 mg of oil-soluble CdSe quantum dots are dissolved in 175 mL of non-polar organic solvent.

[0032] In some embodiments, in step S2, the chiral ligand molecule aqueous solution is a chiral histidine molecule aqueous solution.

[0033] In a preferred embodiment, when the chiral ligand molecule aqueous solution is a chiral histidine molecule aqueous solution, the fluorescence performance and chiral performance of the CdSe@ZnS quantum dots synthesized by the chiral histidine molecule are the best. However, the CdSe@ZnS quantum dots obtained by using other chiral ligands have weak fluorescence signals or poor chiral performance.

[0034] In some embodiments, in step S2, the concentration of the chiral ligand molecule aqueous solution is 100 mM to 400 mM.

[0035] In some embodiments, when the chiral ligand molecule aqueous solution is a chiral histidine molecule aqueous solution, the modification concentration reaches saturation when its concentration is 250 mM, and the prepared chiral CdSe@ZnS quantum dots have optimal optical properties.

[0036] In some embodiments, the chiral histidine molecule aqueous solution is a chiral L-histidine aqueous solution or a chiral D-histidine aqueous solution.

[0037] In some embodiments, in step S2, the zinc ion aqueous solution is a zinc chloride aqueous solution; the sulfide ion aqueous solution is at least one of a sodium sulfide aqueous solution, a thioacetamide aqueous solution or a thiourea aqueous solution.

[0038] In some embodiments, in step S2, the concentrations of the zinc ion aqueous solution and the sulfide ion aqueous solution are both 0.22 mM. In practical applications, the concentrations of the zinc ion aqueous solution and the sulfide ion aqueous solution can be slightly changed according to the amount of CdSe quantum dots added in the reaction system. The concentrations of the zinc ion aqueous solution and the sulfide ion aqueous solution and the amount of CdSe quantum dots added will affect the shell thickness and play a regulatory role in the synthesis of the material.

[0039] In some embodiments, in step S3, the molar concentration ratio of the shell growth aqueous solution to the seed solution is 5 to 50. As the concentration of the shell growth aqueous solution increases, the quantum dot shell gradually thickens and reaches saturation.

[0040] In some embodiments, in step S3, the shell growth aqueous solution is added to the seed solution and stirred for 12 hours at a temperature of 25° C. to form CdSe@ZnS quantum dots.

[0041] As the temperature increases, the reaction rate can be accelerated, but when the temperature exceeds 45°C, the shell material will self-nucleate to form new quantum dots, which is not conducive to the growth of the chiral core-shell structure. At room temperature (25°C), the growth of core-shell quantum dots is slow and requires long-term stirring. As the stirring time increases, the reaction is more thorough. Generally, stirring for 12 hours at room temperature is conducive to the growth of the chiral CdSe@ZnS core-shell structure, and the obtained chiral CdSe@ZnS quantum dots have good fluorescence properties and chiral properties.

[0042] In a second aspect, an embodiment of the present invention further provides a CdSe@ZnS quantum dot, which is prepared by the preparation method of the CdSe@ZnS quantum dot described in the first aspect. The obtained CdSe@ZnS quantum dot is water-soluble, has a good chiral optical signal, and the fluorescence quantum yield is significantly higher than the shell material regrown after ligand exchange.

[0043] The present invention has been tested for many times, and some test results are now cited as references to further describe the invention in detail, and the following is a detailed description in conjunction with specific embodiments.

[0044] Example 1 Synthesis of CdSe@ZnS quantum dots mediated by chiral L-histidine at the two-phase interface

[0045] Chiral L-histidine-mediated CdSe@ZnS quantum dots were prepared via interfacial synthesis, in which oleic acid-capped CdSe quantum dots dissolved in chloroform and shell growth aqueous solution reacted at the two-phase interface to obtain water-soluble chiral CdSe@ZnS core-shell quantum dots.

[0046] The specific preparation method is as follows:

[0047] Step S1, dissolve 10 mg of CdSe nanocrystal powder in 1.75 mL of chloroform, stir and mix evenly to obtain a seed solution. The actual image and transmission electron microscope image of the seed solution are as follows: Figure 1 shown.

[0048] Step S2, prepare a chiral L-histidine aqueous solution with a concentration of 250mM, add 1mL of a 0.22mmol zinc chloride solution to 1mL of a 100mM chiral histidine aqueous solution, and use 1M NaOH to adjust the pH value of the system until the solution is clear without white flocs. Then, add 1mL of a 0.22mmol thiourea solution under vigorous stirring, stir and mix evenly, and obtain a shell growth aqueous solution.

[0049] Step S3, pour the shell growth aqueous solution prepared in step S2 directly into the seed solution containing the oleic acid-terminated CdSe core to form a two-phase interface (the upper layer is the water phase and the lower layer is the oil phase). Then, stir at a temperature of 25°C. During the stirring process, it can be observed that the quantum dots gradually transfer from the lower oil phase to the upper water phase under vigorous stirring. After continuous stirring for 12 hours, take out the supernatant containing the chiral quantum dots (i.e., CdSe@ZnS quantum dots) aqueous solution, add 1.2 equivalents of ethanol to precipitate the quantum dots from the aqueous solution, and remove the excess unreacted ligands and raw materials by centrifugal precipitation of the quantum dot material. Repeat the precipitation twice to remove excess ligands and redisperse in deionized water. Finally, the obtained CdSe@ZnS quantum dots are stored at 4 degrees Celsius for subsequent testing.

[0050] Figure 2 The following are the physical pictures and transmission electron microscope pictures of CdSe@ZnS quantum dots prepared in Example 1. Figure 1 and Figure 2 It can be seen that the ZnS shell layer was successfully epitaxially grown on the surface of CdSe quantum dots to obtain CdSe@ZnS quantum dots. The obtained chiral CdSe@ZnS quantum dots were transferred from the lower oil phase to the upper water phase, and the fluorescence brightness was significantly enhanced.

[0051] Example 2 Synthesis of CdSe@ZnS quantum dots mediated by chiral D-histidine at the two-phase interface

[0052] Example 2 Except that the chiral L-histidine aqueous solution used in Example 1 was replaced by a chiral D-histidine aqueous solution of the same concentration and volume, the remaining reagents and preparation process were the same as those in Example 1.

[0053] Example 3 Synthesis of CdSe@ZnS quantum dots mediated by racemic DL-histidine at the two-phase interface

[0054] Example 3 Except that the chiral L-histidine aqueous solution used in Example 1 was replaced by a racemic DL-histidine aqueous solution of the same concentration and volume, the other reagents and preparation process were the same as those in Example 1.

[0055] The seed solution (OA-CdSe), CdSe@ZnS quantum dots (L-His CdSe@ZnS) prepared in Example 1, the CdSe@ZnS quantum dots (D-His CdSe@ZnS) prepared in Example 2, and the CdSe@ZnS quantum dots (DL-His CdSe@ZnS) prepared in Example 3 were tested by fluorescence spectrum and circular dichroism spectrum, respectively. The fluorescence spectrum test results are shown in FIG. Figure 3 As shown, the circular dichroism spectrum test results are as follows Figure 4 shown.

[0056] Fluorescence spectra were measured on an Edinburgh FLS1000 photoluminescence spectrometer with an excitation wavelength of 365 nm. Circular dichroism spectra were measured on a BioLogic MOS-450 circular dichroism spectrometer with a scan speed of 100 nm / min. A quartz cuvette with a path length of 1 cm was used for the above measurements.

[0057] Depend on Figure 3 It can be seen that the fluorescence spectra of L-His CdSe@ZnS prepared in Example 1, D-His CdSe@ZnS prepared in Example 2, and DL-His CdSe@ZnS prepared in Example 3 overlap. It can be seen that based on the two-phase interface, there is no significant difference in the fluorescence properties of CdSe@ZnS quantum dots obtained by the synthesis method of CdSe@ZnS quantum dots mediated by chiral histidine of different configurations, and compared with the seed solution (OA-CdSe), the fluorescence intensity of L-His CdSe@ZnS, D-His CdSe@ZnS and DL-HisCdSe@ZnS is significantly enhanced.

[0058] Depend on Figure 4 It can be seen that the circular dichroism spectral curves of the seed solution (OA-CdSe) prepared in Example 1 and the DL-His CdSe@ZnS prepared in Example 3 overlap, and both are close to 0. That is, the CdSe@ZnS quantum dots obtained by the synthesis method of CdSe@ZnS quantum dots mediated by racemic DL-histidine have no chiral optical activity. The chiral spectra of L-His CdSe@ZnS prepared in Example 1 and D-His CdSe@ZnS prepared in Example 2 are mirror-symmetrical, and there is no obvious difference in signal intensity. Therefore, by using chiral L-histidine or chiral D-histidine as the chiral ligand molecule for preparing CdSe@ZnS quantum dots, CdSe@ZnS quantum dots with both excellent fluorescence properties and chiral activity can be obtained.

[0059] Example 4 Synthesis of CdSe@ZnS quantum dots mediated by chiral L-histidine based on two-phase interface: Step S1 is the same as that of Example 1 above.

[0060] Step S2, prepare a 100 mM chiral L-histidine aqueous solution, add 1 mL of 0.22 mmol zinc chloride solution to 1 mL of 100 mM chiral L-histidine aqueous solution, and use 1 M NaOH to adjust the pH value of the system until the solution is clear without white flocs. Then, add 1 mL of 0.22 mmol thiourea solution under vigorous stirring, stir and mix evenly, and obtain a shell growth aqueous solution.

[0061] Step S3 is the same as that in the above-mentioned embodiment 1.

[0062] Example 5 The synthesis step S1 of CdSe@ZnS quantum dots mediated by chiral L-histidine based on the two-phase interface is the same as that of the above-mentioned Example 1.

[0063] Step S2, prepare a chiral L-histidine aqueous solution with a concentration of 150mM, add 1mL of a 0.22mmol zinc chloride solution to 1mL of a chiral L-histidine aqueous solution with a concentration of 150mM, and use 1M NaOH to adjust the pH value of the system until the solution is clear without white flocs. Then, add 1mL of a 0.22mmol thiourea solution under vigorous stirring, stir and mix evenly, and obtain a shell growth aqueous solution.

[0064] Step S3 is the same as that in the above-mentioned embodiment 1.

[0065] Example 6 The synthesis step S1 of CdSe@ZnS quantum dots mediated by chiral L-histidine based on the two-phase interface is the same as that of the above-mentioned Example 1.

[0066] Step S2, prepare a 200 mM chiral L-histidine aqueous solution, add 1 mL of 0.22 mmol zinc chloride solution to 1 mL of 200 mM chiral L-histidine aqueous solution, and use 1 M NaOH to adjust the pH value of the system until the solution is clear without white flocs. Then, add 1 mL of 0.22 mmol thiourea solution under vigorous stirring, stir and mix evenly, and obtain a shell growth aqueous solution.

[0067] Step S3 is the same as that in the above-mentioned embodiment 1.

[0068] Example 7 The synthesis step S1 of CdSe@ZnS quantum dots mediated by chiral L-histidine based on the two-phase interface is the same as that of the above-mentioned Example 1.

[0069] Step S2, prepare a chiral L-histidine aqueous solution with a concentration of 300mM, add 1mL of a 0.22mmol zinc chloride solution to 1mL of a 300mM chiral L-histidine aqueous solution, and use 1M NaOH to adjust the pH value of the system until the solution is clear without white flocs. Then, add 1mL of a 0.22mmol thiourea solution under vigorous stirring, stir and mix evenly, and obtain a shell growth aqueous solution.

[0070] Step S3 is the same as that in the above-mentioned embodiment 1.

[0071] Example 8 The synthesis step S1 of CdSe@ZnS quantum dots mediated by chiral L-histidine based on the two-phase interface is the same as that of the above-mentioned Example 1.

[0072] Step S2, prepare a chiral L-histidine aqueous solution with a concentration of 350mM, add 1mL of a 0.22mmol zinc chloride solution to 1mL of a 350mM chiral L-histidine aqueous solution, and use 1M NaOH to adjust the pH value of the system until the solution is clear without white flocs. Then, add 1mL of a 0.22mmol thiourea solution under vigorous stirring, stir and mix evenly, and obtain a shell growth aqueous solution.

[0073] Step S3 is the same as that in the above-mentioned embodiment 1.

[0074] Example 9 The synthesis step S1 of CdSe@ZnS quantum dots mediated by chiral L-histidine based on the two-phase interface is the same as that of the above-mentioned Example 1.

[0075] Step S2, prepare a 400 mM chiral L-histidine aqueous solution, add 1 mL of 0.22 mmol zinc chloride solution to 1 mL of 400 mM chiral L-histidine aqueous solution, and use 1 M NaOH to adjust the pH value of the system until the solution is clear without white flocs. Then, add 1 mL of 0.22 mmol thiourea solution under vigorous stirring, stir and mix evenly, and obtain a shell growth aqueous solution.

[0076] Step S3 is the same as that in the above-mentioned embodiment 1.

[0077] Comparative Example 1 Preparation of CdSe@ZnS quantum dots based on chiral L-histidine ligand exchange

[0078] Chiral L-histidine-capped CdSe@ZnS quantum dots were obtained by ligand exchange of oleic acid-capped CdSe@ZnS quantum dots with chiral L-histidine.

[0079] The specific preparation method is as follows:

[0080] 200 μL of 1M tetramethylammonium hydroxide aqueous solution was added to 1mL of 200mM chiral L-histidine aqueous solution and mixed evenly to obtain a mixed solution. Next, the mixed solution was added to a chloroform solution containing oleic acid-capped CdSe@ZnS quantum dots (10mg oleic acid-capped CdSe@ZnS quantum dots were dissolved in 1.75mL chloroform solution) at a temperature of 65°C, and ligand exchange was performed with the aid of ultrasound (ultrasound time of 70s, ultrasonic power of 850W). During the ultrasound process, the quantum dots in the lower layer of chloroform will gradually transfer to the upper aqueous solution. After the ultrasound is over, the quantum dots in the upper aqueous solution are taken out and purified by adding 1.2 equivalents of ethanol. Repeat the reprecipitation twice to remove excess ligands and redisperse in deionized water. The obtained quantum dots were stored at 4°C for subsequent testing.

[0081] The fluorescence spectrum and circular dichroism spectrum of the CdSe@ZnS quantum dots (L-His CdSe@ZnS) prepared in Example 1 and the chiral L-histidine-terminated CdSe@ZnS quantum dots (L-His-(OA-CdSe@ZnS)) prepared in Comparative Example 1 were tested respectively. The test results are as follows: Figure 5 shown.

[0082] Depend on Figure 5 It can be seen that the CdSe@ZnS quantum dots (L-His CdSe@ZnS) prepared in Example 1 not only have obvious fluorescence signals, but also have obvious chiral signals (such as Figure 5 As shown on the right); while the chiral L-histidine-terminated CdSe@ZnS quantum dots (L-His-(OA-CdSe@ZnS)) prepared in Comparative Example 1 have obvious fluorescence signals, their chiral signals are very weak (as shown in FIG. Figure 5 shown on the left).

[0083] Comparative Example 2 Synthesis of CdSe@ZnS quantum dots mediated by chiral L-histidine in pure water

[0084] 10 mg of oleic acid-capped CdSe quantum dots were dissolved in 1.75 mL of chloroform solution to obtain a CdSe solution. Then, 1 mL of an aqueous solution containing 250 mM chiral L-histidine molecules was taken, the pH of the solution was adjusted to 11.0 by 1 M sodium hydroxide, and then transferred to the surface of the CdSe solution to form a two-phase interface (the upper layer is the aqueous phase and the lower layer is the oil phase). After vigorous stirring for 12 hours, chiral L-histidine-capped CdSe quantum dots can be obtained in the upper aqueous solution. Next, the upper aqueous solution was taken, 1.2 equivalents of ethanol were added, and the CdSe quantum dots in the upper aqueous solution were centrifuged and precipitated. The precipitation was repeated twice to remove excess ligands and redispersed in deionized water. The obtained chiral L-histidine-capped CdSe quantum dots were stored at 4 ° C for subsequent testing.

[0085] The entire solution of the chiral L-histidine-terminated CdSe quantum dots prepared above was used as a seed, and the shell growth aqueous solution prepared in step S2 of the above Example 1 was added. After vigorous stirring for 12 hours, the upper aqueous solution was taken out, and 1.2 equivalents of ethanol were added to precipitate the quantum dots therein, and the excess unreacted substances were removed. The obtained quantum dots were stored at 4°C for subsequent testing.

[0086] Fluorescence spectroscopy and circular dichroism spectroscopy were performed on the CdSe@ZnS quantum dots (L-His CdSe@ZnS) prepared in Example 1, the chiral L-histidine-terminated CdSe quantum dots (L-His CdSe) prepared in Comparative Example 2, and the CdSe@ZnS quantum dots (L-His CdSe@ZnS(Aqueous)), respectively. The test results are shown in FIG. Figure 6 shown.

[0087] Depend on Figure 6 It can be seen that the CdSe@ZnS quantum dots (L-His CdSe@ZnS) prepared in Example 1 not only have obvious fluorescence signals, but also have obvious chiral signals (such as Figure 6 The fluorescence signal of the chiral L-histidine-terminated CdSe quantum dots (L-His CdSe) prepared in Comparative Example 2 is significantly reduced, and the chiral signal is very weak; although the CdSe@ZnS quantum dots (L-His CdSe@ZnS (Aqueous)) have a more obvious fluorescence signal, its chiral signal is very weak.

[0088] In the embodiment of the present invention, oil-soluble CdSe quantum dots (oleic acid-capped CdSe quantum dots) washed with acetone for multiple times are used as seeds, and the seeds are dissolved in a non-polar organic solvent to obtain a seed solution; a zinc ion aqueous solution is added to a chiral ligand molecule aqueous solution, and the pH of the mixed aqueous solution is adjusted with sodium hydroxide until the white flocs disappear, and then a sulfur ion aqueous solution in an equal molar ratio to the zinc ion aqueous solution is added, and the mixture is stirred evenly to obtain a shell growth aqueous solution; then, the shell growth aqueous solution is transferred to the seed solution to form a two-phase interface; then, under the action of vigorous stirring, with the aid of the formed two-phase interface, ligand exchange and shell growth are simultaneously performed at the two-phase interface, so that not only the generation of CdSe surface defect states can be effectively reduced, and water-soluble core-shell quantum dots with high brightness can be obtained, but also the chiral ligand-mediated shell growth can realize the chiral ligand-induced shell atomic arrangement, so that the prepared CdSe@ZnS quantum dots can have obvious chiral signals.

[0089] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention.

Claims

1. A method for preparing CdSe@ZnS quantum dots, characterized in that: include: S1, dissolving oil-soluble CdSe quantum dots in a non-polar organic solvent to obtain a seed solution; S2, adding a zinc ion aqueous solution to the chiral ligand molecule aqueous solution to mix, adjusting the pH of the mixed aqueous solution with sodium hydroxide until the white flocs disappear, then adding a sulfide ion aqueous solution in an equal molar ratio to the zinc ion aqueous solution, mixing evenly, to obtain a shell growth aqueous solution; the chiral ligand molecule aqueous solution is a chiral histidine molecule aqueous solution; the concentration of the chiral ligand molecule aqueous solution is 100mM to 400mM; S3, adding the shell growth aqueous solution to the seed solution, stirring for 6 to 24 hours at a temperature of 25° C. to 45° C. to form CdSe@ZnS quantum dots.

2. The preparation method according to claim 1, characterized in that: In step S1, the non-polar organic solvent is chloroform; The mass volume ratio of the oil-soluble CdSe quantum dots to the non-polar organic solvent is 10 mg:1.75 mL.

3. The preparation method according to claim 1, characterized in that: The chiral histidine molecule aqueous solution is a chiral L-histidine aqueous solution or a chiral D-histidine aqueous solution.

4. The preparation method according to claim 1, characterized in that: In step S2, the zinc ion aqueous solution is a zinc chloride aqueous solution; The sulfide ion aqueous solution is at least one of a sodium sulfide aqueous solution, a thioacetamide aqueous solution or a thiourea aqueous solution.

5. The preparation method according to claim 1, characterized in that: In step S2, the concentrations of the zinc ion aqueous solution and the sulfur ion aqueous solution are both 0.22 mM.

6. The preparation method according to claim 1, characterized in that: In step S3, the molar concentration ratio of the shell growth aqueous solution to the seed solution is 5-50.

7. The preparation method according to claim 1, characterized in that: In step S3, the shell growth aqueous solution is added to the seed solution, and stirred for 12 hours at a temperature of 25° C. to form CdSe@ZnS quantum dots.

8. A CdSe@ZnS quantum dot, characterized in that: The CdSe@ZnS quantum dots are prepared by the method for preparing CdSe@ZnS quantum dots according to any one of claims 1 to 7.

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