CN105236383A - Wavelength adjustable carbon quantum dots, preparation method and applications thereof - Google Patents

Abstract

The invention belongs to the technical field of nanometer materials, in particular to a carbon quantum dot with adjustable wavelength and its preparation method and application. The invention adopts a one-pot method (reaction kettle) to synthesize, the method is simple, green and environment-friendly, the raw materials used are cheap, the reaction temperature is 140-200 degrees Celsius, and the industrialized production prospect is great. Synthesized carbon quantum dots, the core has a graphitized lattice structure, the shell is a layer of amorphous carbon and contains a large number of hydrophilic functional groups, and has good solubility and stability in polar solvents; diameter distribution Between 1.5-4 nanometers; the fluorescence red shift of carbon quantum dots is produced by the change of surface functional groups. As a new type of luminescent material, it has low production cost, low biological toxicity, high luminous efficiency and good stability, and has good application prospects in optoelectronic devices and biotechnology.

Description

Carbon quantum dots with tunable wavelength and its preparation method and application

technical field

The invention belongs to the technical field of nanometer materials, and in particular relates to a carbon quantum dot and its preparation method and application.

Background technique

In recent years, fluorescent semiconductor quantum dots such as CdSe, ZnS, and CdSe-related core-shell nanoparticles have attracted widespread interest due to their unique optical properties and huge biomedical application prospects. Its luminescent mechanism is due to the transition of excitons between the valence and conduction bands. Semiconductor quantum dots have been used many times in fluorescence imaging experiments, and have been successfully applied in tumor vasculature, tumor-specific diaphragm antigens, and labeled lymph nodes. However, such quantum dots all contain heavy metal Cd, which is quite toxic even when used in extremely low concentrations, thus bringing huge health and environmental hazards to humans, thus limiting the application prospects of semiconductor quantum dots. especially for clinical applications. Therefore, it is necessary to find a new quantum dot with better optical properties and low toxicity to replace the above-mentioned semiconductor quantum dots. Since carbon quantum dots were first discovered in 2004, they have rapidly grown into a new star in the field of nanomaterials. This is a new class of carbon nanomaterials with a particle size of less than 10 nanometers, and has excellent properties such as strong luminescence stability, biological inertness, and good biocompatibility that other semiconductor quantum dots do not have, and is considered to be a The best substitute for other semiconductor quantum dots. What needs to be mentioned in particular is that carbon nanoparticles have very low toxicity, even at a concentration of mg/mL level, the toxicity is still very small, and carbon atoms are the main skeleton of organic matter, which makes the surface group modification of carbon easier. The selection is wider. These outstanding advantages make carbon nanoparticles have wider application prospects in biomarkers, biorecognition, and bioimaging. Through several years of development, many synthesis methods of carbon quantum dots have been reported, including hydrothermal method, microwave digestion method, laser ablation method, calcination method, and acid hydrolysis method. The particle size can be adjusted within a certain range. However, the luminescence mechanism of carbon nanoparticles is not very clear, and the phenomenon that the emission wavelength in the fluorescence spectrum is red-shifted with the increase of the excitation wavelength has not been explained. Most of the synthesized carbon quantum dots emit blue and green light, which is almost Few emit light in red light or near-infrared, and the corresponding quantum yields are all lower than 5%. As we all know, near-infrared light has a better penetration ability of biological tissues, and has great application prospects and significance in in vivo bio-nanotechnology. Currently, the reported emission of carbon dots is mainly concentrated in the blue and green light regions, which is a bottleneck limitation. Its biological applications in biology, especially small animal imaging. Therefore, it is necessary to prepare fluorescent carbon dots with higher quantum yield in the red light region. Another aspect is the multicolor marking properties of carbon dots. Most of the reported carbon dots can achieve multi-color labeling by changing the excitation wavelength, but they have not been able to achieve blue, green, yellow and red four-color labeling under single-wavelength excitation. This brings more opportunities for the application of carbon dots.

The application of quantum dots in biomedicine requires that quantum dots must have good water solubility, good luminescent properties, suitable particle size, good biocompatibility and bio-crosslinking.

Contents of the invention

The object of the present invention is to provide a carbon quantum dot (abbreviated as carbon dot) with low production cost, low biological toxicity, high luminous efficiency, good biocompatibility, and strong fluorescence with adjustable wavelength (color) and its preparation method and application.

The wavelength-tunable carbon quantum dots provided by the present invention have a graphitized lattice structure in the inner core and a layer of amorphous carbon in the outer shell containing a large number of hydrophilic functional groups, which are very strong in common polar solvents. Good solubility and stability; the diameter distribution is between 1.5-4 nanometers; the fluorescence red shift of carbon quantum dots is produced by the change of surface functional groups.

The preparation method of the wavelength-tunable carbon quantum dot provided by the present invention, the specific steps are as follows:

(1) One-pot preparation of mixed solutions containing various fluorescent carbon dots

Measure 5ml of ethanol into a 50ml centrifuge tube, then weigh a certain amount of urea (0.1-0.2g) and a certain amount of p-phenylenediamine (0.1-0.3g) into the centrifuge tube, shake until completely Dissolve, then add a certain amount of deionized water (20-45 ml), mix evenly, and transfer the mixture to a high-pressure reactor; first preheat the high-temperature oven to a certain temperature (140-200 degrees Celsius), and then react The kettle is put into an oven, reacted for several hours (6-18 hours), after the reaction is completed, turn off the oven, and cool to room temperature naturally;

(2) Separate the mixed solution and purify carbon dot samples with different fluorescent colors

Rotate the mixed solution obtained in step (1) until 3-5 ml of liquid remains, add 6-8 grams of silica gel (100-200 mesh), stir evenly, rotate again to dryness, and store; at the same time, use Pack the column by dry method (300-400 mesh silica gel); wait until the column is equipped, evenly disperse the spin-dried mixture on the silica gel column, and then add 9-11 grams (preferably 10 grams) of Na ₂ CO ₃ on it; Use a mixture of ethanol and ethyl acetate (volume ratio (18-25): 1, preferably 20: 1) as the eluent for separation; during the separation process, irradiate the outflowing solution with an ultraviolet lamp, The solution components that emit the same fluorescence are collected together, subjected to rotary evaporation, and dispersed in water again, finally obtaining a variety of aqueous solutions of carbon quantum dots that emit different fluorescence.

The present invention collects eight kinds of carbon dots with different luminescent colors, and their fluorescence peak positions are respectively: 440, 458, 517, 553, 566, 580, 594, and 625 nanometers, and the quantum yields are respectively: 21.23%, 13.18%, 8.53%, 19.64%, 27.5%, and 35.14%. , 29.62%, 23.81%. These eight types of carbon dots have similar particle diameters, about 2.5 nm, but different functional groups on the surface lead to different fluorescent properties.

In the process of preparing eight kinds of fluorescent carbon dots, the present invention adopts a one-pot method (reactor), the synthesis method is simple, green and environmentally friendly, the raw materials used are cheap, and the reaction temperature is 140-200 degrees Celsius, which has great industrial production prospect. At the same time, no toxic reagents (water, urea and p-phenylenediamine) are used in the reaction process, which is completely green chemistry. In the purification process, it only needs to be carried out at normal temperature, and only need to use cheaper organic reagents (ethanol and ethyl acetate). Although the amount used is relatively large, these reagents can be further used after simple distillation, which can be very convenient. Greatly reduce the cost of the production process.

The carbon dots with adjustable fluorescence prepared by the present invention have no difference in morphology, and the difference is mainly reflected in the surface functional groups. With the red shift of the fluorescence, the oxygen-containing functional groups on the surface of the carbon dots increase, that is, the degree of oxidation increases. Because these carbon dots contain a large number of hydrophilic functional groups, they can have good solubility in the water system, and the fluorescence will basically not change in the range of pH 3-12, and the fluorescence in the solution system with high ionic strength The strength does not attenuate basically, and these test conditions have proved that it is very promising in the application of the biological field. In addition, these carbon dots can be dissolved in organic solvents such as ethanol and ethyl acetate, and have a high quantum yield. These phenomena further indicate that the carbon dots prepared by this method can also have a wide range of application prospects in optoelectronic devices, catalysis and other fields. .

The preparation method proposed by the invention is not only green chemical, but also has low cost and convenient operation.

The eight kinds of fluorescent carbon dots obtained according to the above preparation method are all composed of graphitized core region and surface amorphous carbon in morphology. The average radius of its nanoparticles is about 2.5 nanometers. These nanoparticles contain a large number of hydrophilic functional groups in the surface area, including -NH, -OH, -COOH, etc., which can ensure their better water solubility. at the same time. The content of these oxygen-containing functional groups, especially carboxyl groups, increases as the fluorescence red shifts.

The eight kinds of fluorescent carbon dots prepared by the present invention have higher quantum yields in aqueous solution, among which the red light can reach 23.81%, which is also the highest reported so far. In other organic solvents, such as ethanol or ethyl acetate, the quantum yield can be as high as 50%. These carbon dots exhibit excitation-independent emission, and the position of the fluorescence peak can be tuned from 440 to 625 nm. Under the condition of ultraviolet light irradiation for one hour, these carbon dots still showed basically negligible fluorescence attenuation, confirming that these carbon dots have very strong fluorescence stability.

The eight fluorescent carbon dots prepared by the invention have very low toxicity. The half-lethal concentration for human cervical cancer cells is 1.8-2.0 mg/ml, which is more than 3 orders of magnitude higher than the corresponding toxicity of semiconductor quantum dots (CdSe and CdTe) reported so far. Therefore, even if the concentration of carbon dots prepared by this method is relatively high, it still does not affect the growth and morphology of cells. In addition, a large number of organic functional groups contained on the surface can provide a basis for the further functionalization of carbon dots and the application expansion of carbon dots.

The carbon dots obtained in the present invention can be used for cell imaging in vitro. When it is cultured with cells for a period of time, under the excitation of a single wavelength of 405 nm, it can be found that the carbon dots are mainly concentrated in the cytoplasm, and emit four obvious fluorescences of blue, green, yellow and red, so the nanoparticles can be used to label cells. In order to observe the growth process of cells, it can also be used for multi-color labeling.

The carbon dots prepared by the invention can be successfully used for small animal imaging due to the higher quantum yield in the red light region. After intravenous injection and subcutaneous injection, the fluorescence of red fluorescent carbon dots can penetrate the skin and tissue of nude mice, which further proves the low biological toxicity of our prepared carbon dots.

Description of drawings

Fig. 1 is the photograph of the solution of eight kinds of samples of embodiment 1 under ultraviolet light.

FIG. 2 is the fluorescence spectra of eight samples in Example 1.

3 is a transmission electron micrograph of four representative carbon dots (blue, green, yellow, and red) in Example 1.

4 is an optical imaging photo of four representative carbon dots in Example 1 in vitro and an optical imaging photo of red carbon dots in vivo.

detailed description

In order to better understand the content of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings.

Example 1

(1) Prepare a mixed solution containing various fluorescent carbon dots

First measure 5 ml of ethanol and put it into a 50 ml centrifuge tube, then weigh 0.2 g of urea and 0.2 g of unoxidized p-phenylenediamine and quickly add them to the centrifuge tube, shake until completely dissolved, and form a reddish-brown solution . Then add 45 ml of deionized water, mix well, transfer the mixture to a high-pressure reactor (150 ml), and seal it for storage. First preheat the high-temperature oven to 160 degrees Celsius, then put the reactor into the oven to react for 10 hours, after the reaction is completed, turn off the oven, open the oven, and cool down to room temperature naturally;

(2) Purify the mixed solution containing various fluorescent carbon dots

Rotate the mixture obtained in step (1) (water bath, 65 degrees Celsius) until 3-5 ml of liquid remains, add 6-8 grams of silica gel (100-200 mesh), stir well, and then rotate to dryness again, store . At the same time, use the dry method to pack the column (300-400 mesh silica gel), and wait for the column to be equipped (the column height is 12 cm, and the plane is uniform), and the spin-dried mixture is evenly dispersed on the silica gel column through the addition funnel, and the The surface of the mixture was tapped evenly, and then about 10 grams of Na ₂ CO 3 (for buffering) was added on top of it through an addition funnel. Finally, use dichloromethane as the eluent to wash away the yellow impurities, then use ethyl acetate as the eluent to separate the blue and green fluorescent carbon dots, and finally use a mixture of ethanol and ethyl acetate (volume ratio 20:1) as the eluent to separate the yellow and red fluorescent carbon dots. During the separation process, the solution was irradiated with ultraviolet lamps. When the solutions emitted the same fluorescence and the intensity was close, we collected them together, concentrated them by rotary evaporation, and dispersed them into water again. Finally, we obtained a variety of fluorescent substances emitting different fluorescence. Aqueous solution of carbon quantum dots. It should be noted that when the fluorescence of the solution is in transition, we need to slow down the dripping speed of the solution and increase the number of fluorescent color detections, so as to better separate the relatively pure fluorescent carbon dots with a single color.

The fluorescence of carbon dots prepared by this method can be adjusted from blue to red, and the reaction wavelength is from 440 to 625 nm. In order to study the influence of raw material ratio and reaction conditions on the formation of carbon dots, we selected four of them as the most representative The characteristic carbon dots (blue-green-yellow-red) were characterized in detail. The order in which carbon dots come out during separation is from small to large according to the polarity of the functional groups on the surface of the nanoparticles. Specifically, the change of the fluorescence of carbon dots from blue to red is due to the increase in the polarity of the surface functional groups of carbon dots. The specific structural characterization shows that the size distribution of carbon dots with different luminescent colors is similar, mainly concentrated at about 2.5 nanometers (as shown in Figure 3), but their surface oxygen content (oxidation degree) increases with the carbon In addition, it also contains a large number of other functional groups including -NH, -OH, -COOH, etc., ensuring that these carbon dots can be dissolved in most polar solvents. The quantum yields of blue, green, yellow, and red carbon dots in aqueous solution were accurately measured by an integrating sphere, and the values were 21, 9, 35, and 24%, respectively. Therefore, these materials have broad application prospects in optical devices and biological fields.

Example 2

The preparation method is the same as in Example 1, but the reaction temperature is changed to 180°C, and other conditions remain unchanged. The emission wavelengths of the four fluorescent carbon dots finally obtained are 434, 512, 564, and 609 nanometers. The specific values calculated by the integrating sphere The quantum yields are: 33, 12, 18, 6%, respectively.

Example 3

The preparation method is the same as in Example 1, but the reaction temperature is changed to 140 degrees Celsius, and other conditions remain unchanged. The emission wavelengths of the four fluorescent carbon dots that are finally obtained are 452, 525, 571, and 630 nanometers. The specific values calculated by the integrating sphere The quantum yields were: 11, 8, 5, 2%. From the results, the temperature has a significant effect on both the emission wavelength and the quantum yield, especially on the quantum yield, which may be because the temperature plays a key role in the formation of carbon dots.

Example 4

The preparation method is the same as in Example 1, but the ratio of raw materials, that is, the ratio of urea and p-phenylenediamine, is changed to 0:1. At this time, the emission wavelengths obtained are 0, 0, 589 and 610 nm, and the corresponding quantum yields are: 0, 0, 7 and 28%. It can be seen that when the raw material urea is not used, the blue light and green light do not exist, and the change of the raw material will significantly affect the emission wavelength and quantum yield. Therefore, it is necessary to study the effect of raw material ratio on the luminescence properties.

Example 5

The preparation method is the same as in Example 1, but the ratio of raw materials, that is, the ratio of urea and p-phenylenediamine, is changed to 1:10. At this time, the emission wavelengths obtained are 445, 518, 580 and 608 nanometers, and the corresponding quantum yields are: 3, 4, 15, and 23%. It can be seen that when the proportion of raw material urea is very low, although blue light and green light can also be detected, the corresponding quantum yield is very low. It can also be seen from this that urea is also critical to the formation of blue and green carbon dots.

Example 6

The preparation method is the same as in Example 1, but the ratio of raw materials, that is, the ratio of urea to p-phenylenediamine, is changed to 3:10. At this time, the emission wavelengths obtained are 443, 514, 585 and 612 nanometers, and the corresponding quantum yields are: 10, 5, 21 and 25%. It can be seen that when the proportion of raw material urea increases, the quantum yield of blue light and green light will also increase, and the fluorescence wavelength of the carbon dots of yellow light and red light has a certain red shift phenomenon.

Example 7

The preparation method is the same as in Example 1, but the ratio of raw materials, that is, the ratio of urea and p-phenylenediamine, is changed to 3:5. At this time, the emission wavelengths obtained are 443, 516, 587 and 618 nanometers, and the corresponding quantum yields are: 14, 8, 28 and 20%. It can be seen that when the proportion of raw material urea continues to increase, the quantum yields of blue light, yellow light and red light will also continue to rise, and the fluorescence wavelengths of the carbon dots of yellow light and red light also have a certain red shift phenomenon.

Example 8

The preparation method is the same as in Example 1, but the ratio of raw materials, that is, the ratio of urea and p-phenylenediamine, is changed to 4:5. At this time, the emission wavelengths obtained are 441, 514, 570 and 624 nanometers, and the corresponding quantum yields are: 18, 11, 27 and 17%. It can be seen that when the proportion of raw material urea continues to rise, the quantum yields of blue light and green light will also continue to rise, but only the fluorescence wavelength of red carbon dots continues to have a certain red shift phenomenon, while blue, green and yellow three This color has a small amount of blue shift.

Example 9

The preparation method is the same as in Example 1, but the ratio of raw materials, that is, the ratio of urea and p-phenylenediamine, is changed to 5:6. At this time, the emission wavelengths obtained are 438, 518, 566 and 612 nanometers, and the corresponding quantum yields are: 32, 29, 23 and 9%. It can be seen that when the proportion of raw material urea continues to rise, the quantum yield of blue light and green light will continue to rise, but that of yellow light and red light will decrease. In terms of wavelength, blue light, green light, yellow light and red light all show a small amount of blue shift, but the blue shift of red light is relatively obvious. This shows that when the amount of urea exceeds that of p-phenylenediamine, the effect on the wavelength of red light is the greatest.

Example 10

The preparation method is the same as in Example 1, but the ratio of raw materials, that is, the ratio of urea and p-phenylenediamine, is changed to 2:3. At this time, the emission wavelengths obtained are 437, 514, 562 and 607 nanometers, and the corresponding quantum yields are: 44, 35, 27 and 6%. It can be seen that when the quality of raw material urea exceeds half of that of p-phenylenediamine, the quantum yield of blue light and green light will continue to rise, while the quantum yield of red light will continue to decrease. In terms of wavelength, blue light is basically not shifted, but green, yellow and red light are still slightly blue-shifted.

The above embodiments can be summarized as the following table:

Claims (5)

1. a preparation method for the carbon quantum dot of Wavelength tunable, is characterized in that concrete steps are as follows:

(1) mixing solutions of one kettle way preparation containing various fluorescent carbon point

Measure 5 milliliters of ethanol to put in the centrifuge tube of 50 milliliters, then weigh the urea of 0.1-0.2 gram and the Ursol D of 0.1-0.3 gram respectively, join in centrifuge tube, concussion until dissolve completely, then adds the deionized water of 20-45 milliliter, mixes; Mixed solution is transferred in autoclave; High temperature oven is preheated to 140-200 degree Celsius, then reactor is put into baking oven stoichiometric number 6-18 hour, react complete, naturally cool to room temperature;

(2) be separated mixing solutions, be purified into the carbon point sample that fluorescence color is different;

The mixed solution obtained in step (1) is revolved and steams to residual 3-5 milliliters of liquid, add 100-200 object 6-8 gram silica gel, stir, again revolve and steam to dry, preserve; Meanwhile, dry method equipment 300-400 object silicagel column is adopted; Then the mixture be spin-dried for is dispersed in above silicagel column, then adds the Na of 9-11 gram in the above ₂cO ₃; With the mixed solution of ethanol and ethyl acetate for eluent, be separated; In the process be separated, the solution flowed out with ultra violet lamp, collects the solution component launching identical fluorescence together, carries out revolving steaming, be again distributed in water, finally obtain the carbon quantum dot aqueous solution of the different fluorescence of multiple transmitting.

2. preparation method according to claim 1, it is characterized in that the carbon point of collection eight kinds of different glow colors, their fluorescence peak position is respectively: 440,458,517,553,566,580,594,625 nanometers, quantum yield is followed successively by: 21.23%, and 13.18%, 8.53%, 19.64%, 27.5%, 35.14%, 29.62%, 23.81%.

3. the carbon quantum dot of the Color tunable prepared by preparation method described in claim 1, its kernel has graphited crystalline network, shell is the unbodied carbon of one deck and containing a large amount of hydrophilic functional groups, has good solubleness and stability in polar solvent; Diameter Distribution is between 1.5-4 nanometer; The fluorescence red shift of carbon quantum dot is produced by the change of surface functional group.

4. the application of carbon quantum dot in cells in vitro imaging of Color tunable as claimed in claim 3.

5. application according to claim 4, wherein the red four kinds of carbon quantum dot of bluish-green Huang are used for multi-color marking in HeLa cell.