Multicolor fluorescent sulfur quantum dot as well as preparation method and application thereof

Abstract

The invention discloses a multicolor fluorescent sulfur quantum dot as well as a preparation method and application thereof, and relates to the field of fluorescent quantum dots. The method comprises the following steps: mixing sodium thiosulfate, hexadecyl trimethyl ammonium bromide and sulfydryl-containing amino acid or a derivative thereof in water, and reacting the mixture in a continuous heating and stirring state; and filtering and dialyzing the obtained product to obtain pure fluorescent sulfur quantum dots. According to the method, the yellow fluorescent sulfur quantum dots are prepared for the first time, the yellow fluorescent sulfur quantum dots are also SQDs with the longest emission wavelength at present, and due to the fact that long-wavelength fluorescence has higher tissue penetrating power, the sulfur quantum dots can be better applied to tissue imaging. According to the method, sulfur powder and sodium hydroxide used as raw materials in a previous method are abandoned for the first time, sodium thiosulfate and amino acid are used as substitutes in a breakthrough mode, pure green synthesis of the quantum dots is successfully achieved, the safety and stability of the synthesis process are guaranteed, and a solid foundation is laid for industrial production of the sulfur quantum dots.

Description

Technical Field

[0001] The present invention relates to the field of fluorescent quantum dots, and in particular to multicolor fluorescent sulfur quantum dots and a preparation method and application thereof. Background Art

[0002] As a luminescent material, quantum dots can provide color-adjustable narrow emission fluorescence, and therefore can be used as both a labeled fluorescent group and a phosphor. In addition, quantum dots have a broader UV absorption, adjustable photoluminescence (PL), and good optical and chemical stability. In the future, they can be widely used in photovoltaics, optoelectronics, and LED lighting. Because metal quantum dots are composed of a large amount of heavy metal elements, they are highly toxic and have poor biocompatibility, causing great harm to the environment. This has severely restricted their development in fields such as biomedicine and industrial lighting. As people continue to explore and find environmentally friendly quantum dots, non-metallic quantum dots have emerged.

[0003] Sulfur quantum dots (SQDs), a rising star in the non-metallic quantum dot family, have advantages such as high biocompatibility, simple synthesis process, and low price, and have gradually gained a place in the field of fluorescence. Currently, SQDs have been initially applied to research in fields such as analytical detection and cell imaging. However, the current sulfur quantum dots still have the following problems:

[0004] 1. The luminescence color of SQDs is concentrated in the blue light region, and the luminescence color is single, which greatly limits its practical application;

[0005] 2. As far as current synthesis methods are concerned, most syntheses require high concentrations of sodium hydroxide or high temperatures to etch sulfur powder, which increases the difficulty of SQDs synthesis and also greatly limits the subsequent purification and application;

[0006] 3. Sulfur powder used as raw material is difficult to preserve due to its flammable nature, and there are safety hazards in the experiment. Summary of the Invention

[0007] In order to overcome the shortcomings and deficiencies in the existing sulfur quantum dot technology, the first object of the present invention is to provide a method for preparing multicolor fluorescent sulfur quantum dots. The present invention uses sodium thiosulfate instead of sulfur powder as a sulfur source to prepare fluorescent SQDs, solving the problems of excessive alkalinity in the preparation process of SQDs, difficulty in preserving sulfur powder, and single luminescent color of SQDs. In some specific implementations, the present invention uses sodium thiosulfate as a substrate, glutathione or cysteine ​​or acetylcysteine ​​as an etchant, and continuously heats and stirs under the protection of a surfactant to obtain blue fluorescent sulfur quantum dots (B-SQDs), green fluorescent sulfur quantum dots (G-SQDs), and yellow fluorescent sulfur quantum dots (Y-SQDs). The addition of three different thiol reagents causes SQDs to produce different surface states. It is precisely the existence of this difference that allows us to accurately prepare SQDs with adjustable fluorescence color. Among them, yellow fluorescent SQDs are the longest emission wavelength fluorescence prepared for the first time in the field of sulfur quantum dots. The present invention successfully further solves the problem of single luminescent color and no long-wavelength fluorescence of SQDs.

[0008] The optimization of the synthesis method of the present invention improves the problems of extreme synthesis conditions, strong alkalinity, and single luminescent color of SQDs, and develops a mild and green synthesis method. Subsequently, the G-SQDs prepared by this method were successfully applied to Fe 3+ This shows that this method has great significance for the future application of SQDs in light-emitting components and biomedicine.

[0009] The second object of the present invention is to provide multicolor fluorescent sulfur quantum dots obtained by the above preparation method.

[0010] The third object of the present invention is to provide applications of the multicolor fluorescent sulfur quantum dots.

[0011] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0012] The method for preparing multicolor fluorescent sulfur quantum dots comprises mixing sodium thiosulfate, hexadecyltrimethylammonium bromide and sulfhydryl-containing amino acids or their derivatives in water, and reacting the mixture under continuous heating and stirring; the obtained product is filtered and dialyzed to obtain fluorescent sulfur quantum dots.

[0013] Furthermore, the sulfhydryl-containing amino acid or its derivative is any one of glutathione, cysteine, and acetylcysteine;

[0014] When the sulfhydryl-containing amino acid or its derivative is glutathione, blue fluorescent sulfur quantum dots are obtained;

[0015] When the thiol-containing amino acid or its derivative is cysteine, green fluorescent sulfur quantum dots are obtained;

[0016] When the sulfhydryl-containing amino acid or its derivative is acetylcysteine, yellow fluorescent sulfur quantum dots are obtained.

[0017] Furthermore, when the thiol-containing amino acid or its derivative is glutathione, the ratio of sodium thiosulfate, hexadecyltrimethylammonium bromide, thiol-containing amino acid and water is 0.05-0.6g: 0.08-0.8g: 0.01-0.05g: 5-30ml; preferably 0.05-0.15g: 0.5-0.7g: 0.01-0.03g: 15-25ml; more preferably 0.1g: 0.6g: 0.02g: 20ml.

[0018] Furthermore, when the thiol-containing amino acid or its derivative is cysteine, the ratio of sodium thiosulfate, hexadecyltrimethylammonium bromide, thiol-containing amino acid and water is 0.03-0.5g: 0.05-0.5g: 0.01-0.05g: 5-30ml; preferably 0.07-0.09g: 0.3-0.5g: 0.01-0.03g: 15-25ml; more preferably 0.08g: 0.4g: 0.02g: 20ml.

[0019] Furthermore, when the thiol-containing amino acid or its derivative is acetylcysteine, the ratio of sodium thiosulfate, hexadecyltrimethylammonium bromide, thiol-containing amino acid and water is 0.05-0.6g: 0.08-0.8g: 0.01-0.06g: 5-30ml; preferably 0.1-0.2g: 0.6-0.6g: 0.02-0.04g: 15-25ml; more preferably 0.15g: 0.7g: 0.03g: 20ml.

[0020] Furthermore, the reaction conditions are: temperature 40-80°C, time 10-15h; preferably temperature 65-75°C, time 11-13h; more preferably in an oil bath, temperature 70°C, time 12h.

[0021] Furthermore, the filtration is 0.22 μm microporous membrane filtration.

[0022] Furthermore, the molecular weight of the dialysis bag used in the dialysis is 500-3000 Da, preferably 500 Da.

[0023] Multicolor fluorescent sulfur quantum dots are obtained by the above preparation method.

[0024] Yellow fluorescent sulfur quantum dots are obtained by the above preparation method.

[0025] The application of the above-mentioned multicolor fluorescent sulfur quantum dots in the detection of metal ions.

[0026] Furthermore, the metal is at least one of iron, zinc, copper and mercury.

[0027] Furthermore, the detection is a quantitative detection.

[0028] The present invention has the following advantages and effects compared to the prior art:

[0029] The novel sulfur quantum dot synthesis method provided by the present invention has the advantages of environmentally friendly and pollution-free raw materials, simple and easy-to-operate process, and large product quantities that are easy to obtain. It also has the following two innovative advantages:

[0030] (1) Using this method, yellow fluorescent sulfur quantum dots were prepared for the first time. These are also the SQDs with the longest emission wavelength currently available. Since long-wavelength fluorescence has higher tissue penetration, sulfur quantum dots will be better suited for tissue imaging.

[0031] (2) This method, for the first time, abandoned the sulfur powder and sodium hydroxide used as raw materials in the previous method, and used sodium thiosulfate and amino acids as substitutes, successfully realizing the pure green synthesis of quantum dots and ensuring the safety and stability of the synthesis process, laying a solid foundation for the industrial production of sulfur quantum dots.

[0032] (3) Compared with existing sulfur quantum dot synthesis technologies, the method established by this invention has the following major advantages: it can achieve green and efficient synthesis of blue, green, and yellow fluorescent sulfur quantum dots, solving the problem of previous methods that cannot produce long-wavelength fluorescent quantum dots, and enhancing the environmental friendliness of the synthesis method. This invention has opened up an unprecedented new approach for the industrial production and practical application of sulfur quantum dots. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 1 and 2 are transmission electron microscope (TEM) characterization images of three types of SQDs prepared in the present invention; wherein, A, A1, and A2 are Example 1, B, B1, and B2 are Example 2, and C, C1, and C2 are Example 3.

[0034] Figure 2 These are atomic force microscope (AFM) characterization images of three types of SQDs prepared in the present invention; wherein, A3 is Example 1, B3 is Example 2, and C3 is Example 3.

[0035] Figure 3 This is a particle size characterization diagram of three types of SQDs prepared in the present invention; among them, from top to bottom are Example 1, Example 2, and Example 3.

[0036] Figure 4 These are the fluorescence spectra of three types of SQDs; A is Example 1, B is Example 2, C is Example 3, and D is a photograph.

[0037] Figure 5 These are fluorescence spectra of three SQDs blank control group experiments; A is Example 1, B is Example 2, and C is Example 3.

[0038] Figure 6 G-SQDs add Fe 3+ ion; A is the fluorescence change of G-SQDs after adding different concentrations of Fe 3+ ion fluorescence changes, B is Fe 3+ Linear relationship between ion concentration and fluorescence quenching efficiency of G-SQDs. DETAILED DESCRIPTION

[0039] The present invention will be described in further detail below with reference to the embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0040] The experimental methods in the following examples are all conventional methods unless otherwise specified; the experimental materials used are all purchased from conventional biochemical reagent manufacturers unless otherwise specified.

[0041] Example 1

[0042] Preparation and characterization of blue fluorescent sulfur quantum dots (B-SQDs), and confirmation of the fluorescence source by blank experiments:

[0043] Step 1: Sodium thiosulfate (Na2S2O3 0.1 g), cetyltrimethylammonium bromide (CTAB 0.6 g), water (20 mL) and glutathione (GSH 0.02 g) were added to a 50 mL round-bottom flask equipped with a glass condenser, and the mixture was reacted in a 70°C oil bath under continuous stirring for 12 h. The product obtained by the reaction is called "B-SQDs".

[0044] Step 2: The obtained product was filtered using a 0.22 μm microporous filter membrane, added to a 500 Da pre-treated dialysis bag, and continuously stirred and dialyzed in 500 mL of ultrapure water. After purification for 24 hours, a pure B-SQDs sample was obtained.

[0045] Step 3: As a blank control experiment, CTAB (0.6 g), water (20 mL) and GSH (0.02 g) were added to a 50 mL round-bottom flask equipped with a glass condenser, and the mixture was reacted in an oil bath at 70°C for 12 h under continuous stirring.

[0046] Example 2

[0047] Preparation and characterization of green fluorescent sulfur quantum dots (G-SQDs), and confirmation of the fluorescence source by blank experiments:

[0048] Step 1: Sodium thiosulfate (Na2S2O3 0.08 g), cetyltrimethylammonium bromide (CTAB 0.4 g), water (20 mL) and cysteine ​​(Cys 0.02 g) were added to a 50 mL round-bottom flask equipped with a glass condenser, and the mixture was reacted in an oil bath at 70°C under continuous stirring for 12 h. The product obtained by the reaction is called "G-SQDs".

[0049] Step 2: The obtained product was filtered using a 0.22 μm microporous filter membrane, added to a 500 Da pre-treated dialysis bag, and continuously stirred and dialyzed in 500 mL of ultrapure water. After purification for 24 hours, a pure G-SQDs sample was obtained.

[0050] Step 3: As a blank control experiment, CTAB (0.4 g), water (20 mL) and Cys (0.02 g) were added to a 50 mL round-bottom flask equipped with a glass condenser, and the mixture was reacted in a 70°C oil bath for 12 hours under continuous stirring.

[0051] Example 3

[0052] Preparation and characterization of yellow fluorescent sulfur quantum dots (Y-SQDs), and confirmation of the fluorescence source by blank experiments:

[0053] Step 1: Sodium thiosulfate (Na2S2O3 0.15 g), cetyltrimethylammonium bromide (CTAB 0.7 g), water (20 mL) and acetylcysteine ​​(NAC 0.03 g) were added to a 50 mL round-bottom flask equipped with a glass condenser. The mixture was reacted in an oil bath at 70°C under continuous stirring for 12 h. The product obtained by the reaction was called "Y-SQDs".

[0054] Step 2: The obtained product was filtered using a 0.22 μm microporous filter membrane, added to a 500 Da pre-treated dialysis bag, and continuously stirred and dialyzed in 500 mL of ultrapure water. After purification for 24 hours, a pure Y-SQDs sample was obtained.

[0055] Step 3: As a blank control experiment, CTAB (0.7 g), 20 mL of water and NAC (0.03 g) were added to a 50 mL round-bottom flask equipped with a glass condenser, and the mixture was reacted in an oil bath at 70° C. for 12 h under continuous stirring.

[0056] The SQDs aqueous solution prepared in Examples 1 to 3 was filtered using a 0.22 μm filter membrane and ultrasonicated for 30 minutes. 15 μL was added dropwise to a copper mesh and allowed to dry naturally. The morphology, size, and lattice spacing of the SQDs were observed using a high-magnification transmission electron microscope. The results are as follows: Figure 1As shown in the figure, the SQDs exhibit uniform particle size distribution and good dispersion, with no large agglomerates. Furthermore, the large number of SQDs in the field of view indicates a high concentration of the synthesized product and a considerable yield. Furthermore, the high-magnification transmission electron micrograph in the inset shows that the lattice spacing of all three SQDs is 0.21 nm, consistent with previously reported data for SQDs.

[0057] The prepared SQDs aqueous solution was filtered using a 0.22 μm filter membrane and ultrasonicated for 30 minutes. 15 μL was added dropwise to a mica sheet and allowed to dry naturally. The morphology, size, and lattice spacing of the SQDs were observed using an atomic force microscope. The results are as follows: Figure 2 As shown in the figure, it can be seen that the height of SQDs is about 1nm.

[0058] The prepared SQDs aqueous solution was filtered using a 0.22 μm filter membrane and ultrasonicated for 30 minutes. 100 μL was taken and diluted to 1 mL with ultrapure water, added to a specific cuvette, and placed in an instrument to monitor the quantum dot particle size. The results are as follows: Figure 3 As shown in the figure, it can be seen that when the surface of the nanoparticles is modified with different ligands, the particle size of the prepared SQDs is all concentrated around 4.5nm, and there is no obvious difference in particle size.

[0059] The prepared SQDs aqueous solution was diluted 10 times with ultrapure water and filtered using a 0.22 μm filter membrane. 2 mL of SQDs solution was added to a cuvette and the fluorescence spectrum was monitored. The results were as follows: Figure 4 and Figure 5 As shown. Figure 4 It can be seen from the figure that the three SQDs produce obvious blue, green and yellow fluorescence, and the fluorescence effect is good. This shows that our strategy of changing the fluorescence color of SQDs by adjusting the surface thiol ligand is feasible. Figure 5 It was found that no fluorescence could be generated when sodium thiosulfate was not added, which once again verified that the fluorescent light source came from SQDs.

[0060] Example 4

[0061] Fe-based sulfur quantum dots 3+ Detection:

[0062] Step 1: Sodium thiosulfate (Na2S2O3 0.08 g), cetyltrimethylammonium bromide (CTAB 0.4 g), water (20 mL) and cysteine ​​(Cys 0.02 g) were added to a 50 mL round-bottom flask equipped with a glass condenser, and the mixture was reacted in an oil bath at 70°C under continuous stirring for 12 h. The product obtained by the reaction is called "G-SQDs".

[0063] Step 2: The obtained product was filtered using a 0.22 μm microporous filter membrane, added to a 500 Da pre-treated dialysis bag, and continuously stirred and dialyzed in 500 mL of ultrapure water. After purification for 24 hours, a pure G-SQDs sample was obtained.

[0064] Step 3: Add 200 μL of freshly prepared G-SQDs to 1.6 mL of water and mix well. Prepare aqueous solutions of 0.9 mM, 0.8 mM, 0.7 mM, 0.6 mM, 0.5 mM, 0.4 mM, and 0.3 mM concentrations of FeCl3, and take 200 μL of the solution to be tested at different concentrations and add them to 1.8 mL of SQDs solution. Vortex mix and then detect the fluorescence spectrum. By observing the quenching of SQDs fluorescence, the Fe 3+ Detection.

[0065] Figure 6 G-SQDs add Fe 3+ ion fluorescence changes. It can be seen from the figure that as Fe 3+ With the gradual addition of ions, the fluorescence intensity of SQDs decreases continuously, indicating that SQDs have good metal ion detection ability.

[0066] Example 5

[0067] Detection of Fe in Tangerine Peel Using Sulfur Quantum Dots 3+ content:

[0068] Step 1: Prepare Fe at concentrations of 40mM, 55mM, and 70mM respectively 3+ 1 mL of the standard solution was evenly sprayed on the surface of the tangerine peel and placed in a beaker to dry naturally. The treated tangerine peel was then placed in 100 mL of ultrapure water eluent and allowed to stand for 12 hours.

[0069] Step 2: Filter the solution with a 0.22 μm microporous filter membrane to obtain the spiked Fe 3+ Residual solution.

[0070] Step 3: Perform fluorescence detection on the spiked solution and use the fluorescence value at 540 nm to enter the linear fitting equation to calculate Fe 3+ The concentration was calculated and compared with the standard concentration (40μM, 55μM and 70μM) to obtain the recovery rate. The recovery rate was 84.38% to 117.72%. The above results show that the G-SQDs fluorescence sensor we developed can be preliminarily applied to the detection of Fe in tangerine peel. 3+ Content monitoring.

[0071] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the described embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing multicolor fluorescent sulfur quantum dots, characterized by: Sodium thiosulfate, hexadecyltrimethylammonium bromide and sulfhydryl-containing amino acid or its derivatives are mixed in water, and the mixture is reacted under continuous heating and stirring; the obtained product is filtered and dialyzed to obtain fluorescent sulfur quantum dots.

2. The method for preparing multicolor fluorescent sulfur quantum dots according to claim 1, wherein: The sulfhydryl-containing amino acid or its derivative is any one of glutathione, cysteine, and acetylcysteine; When the sulfhydryl-containing amino acid or its derivative is glutathione, blue fluorescent sulfur quantum dots are obtained; When the thiol-containing amino acid or its derivative is cysteine, green fluorescent sulfur quantum dots are obtained; When the sulfhydryl-containing amino acid or its derivative is acetylcysteine, yellow fluorescent sulfur quantum dots are obtained.

3. The method for preparing multicolor fluorescent sulfur quantum dots according to claim 2, wherein: When the thiol-containing amino acid or its derivative is glutathione, the ratio of sodium thiosulfate, hexadecyltrimethylammonium bromide, thiol-containing amino acid, and water is 0.05-0.6 g: 0.08-0.8 g: 0.01-0.05 g: 5-30 ml; When the thiol-containing amino acid or its derivative is cysteine, the ratio of sodium thiosulfate, hexadecyltrimethylammonium bromide, thiol-containing amino acid, and water is 0.03-0.5 g: 0.05-0.5 g: 0.01-0.05 g: 5-30 ml; When the thiol-containing amino acid or its derivative is acetylcysteine, the ratio of sodium thiosulfate, hexadecyltrimethylammonium bromide, thiol-containing amino acid and water is 0.05-0.6g: 0.08-0.8g: 0.01-0.06g: 5-30ml.

4. The method for preparing multicolor fluorescent sulfur quantum dots according to claim 2, wherein: When the thiol-containing amino acid or its derivative is glutathione, the ratio of sodium thiosulfate, cetyltrimethylammonium bromide, thiol-containing amino acid, and water is 0.05-0.15 g: 0.5-0.7 g: 0.01-0.03 g: 15-25 ml; When the thiol-containing amino acid or its derivative is cysteine, the ratio of sodium thiosulfate, hexadecyltrimethylammonium bromide, thiol-containing amino acid, and water is 0.07-0.09 g: 0.3-0.5 g: 0.01-0.03 g: 15-25 ml; When the thiol-containing amino acid or its derivative is acetylcysteine, the ratio of sodium thiosulfate, hexadecyltrimethylammonium bromide, thiol-containing amino acid, and water is 0.1-0.2 g: 0.6-0.6 g: 0.02-0.04 g: 15-25 ml; The reaction conditions are: temperature 40-80°C, time 10-15h.

5. The method for preparing multicolor fluorescent sulfur quantum dots according to claim 2, wherein: When the thiol-containing amino acid or its derivative is glutathione, the ratio of sodium thiosulfate, cetyltrimethylammonium bromide, thiol-containing amino acid and water is 0.1g:0.6g:0.02g:20ml; When the thiol-containing amino acid or its derivative is cysteine, the ratio of sodium thiosulfate, hexadecyltrimethylammonium bromide, thiol-containing amino acid, and water is 0.08g:0.4g:0.02g:20ml; When the thiol-containing amino acid or its derivative is acetylcysteine, the ratio of sodium thiosulfate, hexadecyltrimethylammonium bromide, thiol-containing amino acid, and water is 0.15 g: 0.7 g: 0.03 g: 20 ml; The reaction conditions are: temperature 65-75° C., time 11-13 h.

6. The method for preparing multicolor fluorescent sulfur quantum dots according to any one of claims 1 to 5, characterized in that: The reaction conditions are as follows: carried out in an oil bath at 70°C for 12 h; The filtration is carried out by 0.22 μm microporous membrane filtration; The molecular weight of the dialysis bag used in the dialysis is 500-3000Da.

7. Multicolor fluorescent sulfur quantum dots, characterized by: The method is obtained by the preparation method described in any one of claims 1 to 6.

8. A yellow fluorescent sulfur quantum dot, characterized in that: The preparation method is obtained by the preparation method described in any one of claims 2 to 6.

9. Use of the multicolor fluorescent sulfur quantum dots according to claim 7 or the yellow fluorescent sulfur quantum dots according to claim 8 in detecting metal ions.

10. The use according to claim 9, characterized in that: The metal is at least one of iron, zinc, copper and mercury; The detection is a quantitative detection.

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