Carbon nanodots with red light anti-stokes luminescence properties, and preparation method and application thereof

Abstract

The application provides carbon nanodots with red anti-Stokes luminescence characteristics and a preparation method and application thereof, relates to the field of carbon nanomaterials, and the carbon nanodots are prepared by using o-phenylenediamine as raw material, mainly have a main emission peak in a red light-near infrared region, and have anti-Stokes emission characteristics in a protic solvent. The anti-Stokes luminescence of the carbon nanodots with red anti-Stokes luminescence characteristics is derived from phonon-assisted single-photon absorption, can be excited by a continuous laser light source, and the anti-Stokes luminescence intensity increases with the increase of temperature. The carbon nanodots with red anti-Stokes luminescence characteristics can be applied to anti-Stokes fluorescence imaging and optoelectronic devices as anti-Stokes imaging reagents.

Description

Technical Field

[0001] This invention relates to the field of carbon nanomaterials, specifically to carbon nanodots with red light anti-Stokes luminescence properties, their preparation methods, and applications. Background Technology

[0002] Anti-Stokes biofluorescence imaging, due to its unique luminescent properties, can largely avoid the influence of background fluorescence (Stokes luminescence), improve penetration depth, and reduce phototoxicity, making it significant in in vivo fluorescence imaging. Therefore, the development of fluorescence imaging reagents with anti-Stokes luminescence properties is of great importance for the clinical advancement of biofluorescence imaging.

[0003] Carbon nanodots (CDs) are inexpensive to prepare, have low toxicity, easily tunable luminescence, and good biocompatibility, giving them unique advantages in fluorescence imaging. Current research on carbon nanodots largely focuses on Stokes luminescence. Most reported anti-Stokes luminescence of carbon nanodots is achieved through multiphoton absorption, requiring expensive femtosecond lasers as the light source, which severely limits the application of carbon nanodots in in vivo anti-Stokes fluorescence imaging. Therefore, there is an urgent need to investigate carbon nanodots that exhibit anti-Stokes luminescence properties under continuous laser excitation. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a carbon nanodot with red light anti-Stokes luminescence properties, its preparation method and application, wherein the main emission peak of the carbon nanodot is located in the red light-near infrared region, and exhibits red light anti-Stokes luminescence under continuous laser excitation.

[0005] In a first aspect, the present invention provides a carbon nanodot with red light anti-Stokes luminescence properties, which is prepared by solvothermal reaction using o-phenylenediamine as a raw material; the main emission peak of the carbon nanodot is located in the red light-near infrared region, and it can exhibit both red light anti-Stokes luminescence and Stokes luminescence under continuous laser excitation.

[0006] Preferably, the mass-to-volume ratio of o-phenylenediamine to solvent is 1:60 g / mL, and the solvent is an inorganic acidic solvent or a hydroxyl-rich solvent.

[0007] Preferably, the solvent is selected from, but not limited to, one or more of sulfuric acid, phosphoric acid, polyphosphoric acid, and ethanol.

[0008] Preferably, the raw material is o-phenylenediamine or a mixture of o-phenylenediamine and amino acids in a molar ratio of 1:1.

[0009] Preferably, the temperature of the solvothermal reaction is 160~220 °C, and the reaction time is 4~10 h.

[0010] Preferably, the main absorption peak of the carbon nanodots is located at 550~660 nm.

[0011] Preferably, the anti-Stokes emission peak differs in different solvents:

[0012] In acidic solutions and water, the anti-Stokes emission peak is located around 630–640 nm;

[0013] In ethanol solution, the anti-Stokes emission peaks are located near 600 nm and 640 nm.

[0014] In acidic films, the anti-Stokes emission peak is located near 630 nm.

[0015] Preferably, the Stokes emission peak of the carbon nanodots is located at 600~750 nm.

[0016] Secondly, the present invention also provides a method for preparing carbon nanodots with red light anti-Stokes luminescence properties as described in any one of the above claims, comprising the following steps:

[0017] (1) Dissolve o-phenylenediamine in a polar solvent at a mass-to-volume ratio of 1:60 g / mL and carry out a solvothermal reaction;

[0018] (2) Add sodium hydroxide solution to the obtained reaction solution to adjust the pH to 6.0~7.0;

[0019] (3) After centrifuging the neutralized reaction solution at 8000 r / min for 5 minutes, discard the liquid and suspended matter, retain the precipitate, and wash and centrifuge repeatedly with deionized water to obtain red light-reflecting Stokes luminescent carbon nanodots.

[0020] The polar solvent is selected from one or more of sulfuric acid, phosphoric acid, polyphosphoric acid, and ethanol;

[0021] The temperature of the solvothermal reaction is 160~220 ℃, and the reaction time is 4~10 h.

[0022] Thirdly, the present invention also provides the application of carbon nanodots with red light anti-Stokes luminescence properties as described in any of the above-mentioned claims in anti-Stokes red light imaging reagents or in anti-Stokes red light imaging films.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] The carbon nanodots provided by this invention, which possess red-light anti-Stokes luminescence properties, can be excited by continuous laser to exhibit phonon-assisted anti-Stokes luminescence properties. They exhibit bimodal emission in the red-near-infrared region and can simultaneously achieve red-light anti-Stokes and Stokes emission. The intensity of anti-Stokes luminescence increases with increasing temperature, enabling temperature-dependent anti-Stokes fluorescence imaging and in vivo near-infrared anti-Stokes fluorescence imaging. Consequently, they can be used as near-infrared optical imaging reagents in anti-counterfeiting and in vivo fluorescence imaging. Attached Figure Description

[0025] Figure 1 This is a transmission electron microscope image of the anti-Stokes luminescent carbon nanodots in Example 1 of the present invention;

[0026] Figure 2 The absorption and emission spectra of the red-light-reflecting Stokes luminescent carbon nanodots in Example 1 of this invention;

[0027] Figure 3 The figure shows the results of anti-Stokes emission spectroscopy tests on the acid solution with anti-Stokes luminescent carbon nanodots in Example 1 of the present invention at different power. In the figure, (a) is the anti-Stokes emission spectrum under different excitation light power, and (b) is the curve of anti-Stokes emission intensity changing with temperature.

[0028] Figure 4 The carbon nanodots in Example 2 of this invention exhibit red light-reflecting Stokes luminescence absorption and emission spectra.

[0029] Figure 5 The emission spectrum of the red-light-reflecting Stokes-luminescent carbon nanodots in Example 3 of this invention under 655 nm laser excitation in acid solution;

[0030] Figure 6 The emission spectrum of the red-light-reflecting Stokes-luminescent carbon nanodots in Example 4 of this invention under 655 nm laser excitation in acid solution;

[0031] Figure 7 The emission spectra of the product in Example 5 of this invention under 655 nm laser excitation in acid solution and N,N'-dimethylformamide solution;

[0032] Figure 8 The emission spectra of the red-light-reflecting Stokes-luminescent carbon nanodots in Example 6 of this invention under 655 nm laser excitation in acid and ethanol solutions;

[0033] Figure 9The following are the emission spectra of the red LED device in Embodiment 1 of the present invention and the anti-Stokes red LED device using an anti-Stokes carbon nanodot doped film as the light conversion layer;

[0034] Figure 10 This is a temperature-varying reverse Stokes imaging image of the reverse Stokes carbon nanodot / polyacrylic acid mixture film in Example 1 of the present invention;

[0035] Figure 11 This is a near-infrared reverse Stokes imaging image of mice after gavage administration of reverse Stokes luminescent carbon nanodots as an imaging reagent in Example 1 of the present invention. Detailed Implementation

[0036] This invention provides a carbon nanodot with red light anti-Stokes luminescence properties, which has bimodal emission in the red and near-infrared regions. It is prepared by a solvothermal method using o-phenylenediamine as a raw material and achieves anti-Stokes luminescence through phonon-assisted single-photon excitation.

[0037] This invention provides a method for preparing the red-light-reflecting Stokes-luminescent carbon nanodots described in the above-mentioned technical solution, comprising the following steps:

[0038] The o-phenylenediamine or a mixture of o-phenylenediamine and amino acids is dissolved in an acidic or hydroxyl-rich solvent and subjected to a solvothermal reaction.

[0039] Add sodium hydroxide solution to the resulting reaction solution to adjust it to a weakly acidic state;

[0040] After the neutralized reaction solution was centrifuged at high speed (8000 r / min, 5 minutes), the liquid and suspended matter were discarded, and the precipitate was retained and repeatedly washed and centrifuged with deionized water to obtain red-light reflective Stokes luminescent nanodots.

[0041] In this invention, the anti-Stokes luminescent carbon nanodots have a size distribution of 2-6 nm and a height of approximately 8 nm;

[0042] In this invention, the Stokes emission peak of the anti-Stokes luminescent carbon nanodots is located in the 600~750 nm spectral range;

[0043] In this invention, the anti-Stokes emission peaks of the carbon nanodots in solutions of different solvents are located around 600 nm and 630~640 nm.

[0044] In this invention, the reaction time is preferably 4 to 10 hours. The reaction is a high-temperature and high-pressure reaction; the reaction temperature during heating is preferably 160 to 220 °C.

[0045] In this invention, since the anti-Stokes luminescence mechanism of carbon nanodots is phonon-assisted single-photon excitation, the intensity of anti-Stokes luminescence increases with increasing temperature, enabling temperature-dependent anti-Stokes fluorescence imaging and in vivo near-infrared anti-Stokes fluorescence imaging. This allows it to be used as a near-infrared optical imaging reagent in anti-counterfeiting and in vivo imaging.

[0046] This invention provides an application of carbon nanodots as described in the above technical solution or prepared by the above technical solution in variable-temperature inverse Stokes fluorescence imaging and in vivo inverse Stokes fluorescence imaging, as well as potential applications in inverse Stokes optoelectronic devices, laser cooling, and other fields.

[0047] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, of the red-light-reflecting Stokes luminescent nanodots provided by the present invention, their preparation method, and their applications, should not be construed as limiting the scope of protection of the present invention.

[0048] Example 1

[0049] Carbon nanodots exhibiting red light-reflecting Stokes luminescence properties were prepared by solvothermal heating of o-phenylenediamine in polyphosphoric acid.

[0050] The specific preparation method of the carbon nanodots with the red light anti-Stokes luminescence property is as follows:

[0051] 5 mg of o-phenylenediamine was dissolved in 30 mL of a mixture of polyphosphoric acid and water (polyphosphoric acid to water volume ratio 1:1), and reacted in a reactor at 200 °C for 5 hours. After centrifugation, the mixture was washed twice with water to obtain a black powder, which is a carbon nanodot with red light-reflecting Stokes luminescence properties.

[0052] Combination Figure 1-3 Example 1:

[0053] The carbon nanodots exhibiting red light anti-Stokes luminescence properties from Example 1 were characterized by transmission electron microscopy (TEM). The results are as follows: Figure 1 As shown, clearly dispersed carbon nanoparticles can be observed.

[0054] Absorption and fluorescence emission spectra were analyzed in sulfuric acid and ethanol solutions of the carbon nanodots exhibiting red light-reflecting Stokes luminescence properties from Example 1. The results are as follows: Figure 2As shown, the main absorption peak of carbon nanodots is a double absorption in the range of 500-660 nm. The emission spectrum under 540 nm excitation is in the range of 550-800 nm. In acidic solution, an anti-Stokes emission peak of 630 nm can be obtained by excitation at 670 nm. In alcoholic solution, anti-Stokes emission peaks of 640 nm and 600 nm can be obtained by excitation at 655 nm.

[0055] The sulfuric acid solution of carbon nanodots exhibiting red-light anti-Stokes luminescence properties from Example 1 was subjected to anti-Stokes emission spectroscopy tests under laser excitation at different power levels. The results are as follows: Figure 3 As shown in (a), the anti-Stokes emission process is demonstrated to be a single-photon absorption process. Temperature-dependent fluorescence emission spectroscopy analysis was performed on the acidity of the red-light anti-Stokes luminescent carbon nanodots of Example 1, as shown... Figure 3 In (b), the intensity of the anti-Stokes emission peak in acidic solution increases with increasing temperature.

[0056] Example 2

[0057] Carbon nanodots exhibiting red light-reflecting Stokes luminescence properties were prepared by solvothermal heating of o-phenylenediamine and cysteine ​​in sulfuric acid solvent.

[0058] The specific preparation method of the carbon nanodots with the red light anti-Stokes luminescence property is as follows:

[0059] 0.5 g of o-phenylenediamine and 0.125 g of cysteine ​​were dissolved in 30 mL of sulfuric acid solution (50%) and reacted in a reactor at 160 °C for 4 hours. After centrifugation, the mixture was washed twice with water to obtain a black powder, which is a carbon nanodot with red light-reflecting Stokes luminescence properties.

[0060] Combination Figure 4 Example 2:

[0061] Absorption and fluorescence emission spectra were analyzed in sulfuric acid and ethanol solutions of the carbon nanodots exhibiting red light anti-Stokes luminescence properties from Example 2. Figure 4 As shown, the absorption of carbon nanodots in acid and alcohol solutions is similar to that in Example 1. Under continuous laser excitation at 655 nm, carbon nanodots still exhibit significant anti-Stokes emission at 630 nm in acid solution, while in alcohol solution, the anti-Stokes emission peaks are located at 640 nm and 600 nm.

[0062] Example 3

[0063] Carbon nanodots exhibiting red light-reflecting Stokes luminescence properties were prepared by solvothermal heating of o-phenylenediamine and glutamic acid in a solvent of polyphosphoric acid and water (volume ratio 1:1).

[0064] The specific preparation method of the carbon nanodots with the red light anti-Stokes luminescence property is as follows:

[0065] 0.5 g of o-phenylenediamine and 0.125 g of glutamic acid were dissolved in 30 mL of polyphosphoric acid solution (50%) and reacted in a reactor at 220 °C for 10 hours. After centrifugation, the mixture was washed twice with water to obtain a black powder, which is a carbon nanodot with red light-reflecting Stokes luminescence properties.

[0066] Fluorescence emission spectroscopy analysis was performed on the sulfuric acid solution of the red-light-reflecting Stokes-luminescent carbon nanodots from Example 3, such as... Figure 5 As shown, carbon nanodots exhibit a distinct 625 nm anti-Stokes emission peak when excited at 655 nm in acid solution.

[0067] Example 4

[0068] Carbon nanodots exhibiting red light-reflecting Stokes luminescence properties were prepared by solvothermal heating of o-phenylenediamine and tryptophan in a solvent of polyphosphoric acid and water (volume ratio 1:1).

[0069] The specific preparation method of the carbon nanodots with the red light anti-Stokes luminescence property is as follows:

[0070] 0.5 g of o-phenylenediamine and 0.125 g of tryptophan were dissolved in 30 mL of polyphosphoric acid solution (50%) and reacted in a reactor at 220 °C for 10 hours. After centrifugation, the mixture was washed twice with water to obtain a black powder, which is a carbon nanodot with red light-reflecting Stokes luminescence properties.

[0071] Fluorescence emission spectroscopy analysis was performed on the sulfuric acid solution of the red-light-reflecting Stokes-luminescent carbon nanodots from Example 4, such as... Figure 6 As shown, carbon nanodots exhibit a distinct 625 nm anti-Stokes emission peak when excited at 655 nm in acid solution.

[0072] Example 5

[0073] An attempt was made to synthesize carbon nanodots using o-phenylenediamine as a raw material in N,N'-dimethylformamide solvent by solvothermal heating.

[0074] The specific preparation method of the above-mentioned carbon nanodots is as follows:

[0075] 0.5 g of o-phenylenediamine was dissolved in 30 mL of N,N'-dimethylformamide and reacted in a reactor at 160 °C for 6 hours. After centrifugation, the mixture was washed twice with water to obtain a black powder.

[0076] Fluorescence emission spectroscopy analysis was performed on sulfuric acid solution and N,N'-dimethylformamide solution of the product from Example 5, as follows: Figure 7 As shown, the carbon nanodots did not exhibit a significant anti-Stokes emission peak when excited at 655 nm in acid solution and N,N'-dimethylformamide, proving that this method did not yield the target red-light anti-Stokes carbon nanodots.

[0077] Example 6

[0078] Carbon nanodots were prepared by solvothermal heating in ethanol solvent using o-phenylenediamine as a raw material. The specific preparation method for the above-mentioned carbon nanodots is as follows:

[0079] 0.5 g of o-phenylenediamine was dissolved in 30 mL of ethanol and reacted in a reactor at 160 °C for 6 hours. After centrifugation, the mixture was washed twice with water to obtain a black powder, which was carbon nanoparticles.

[0080] Fluorescence emission spectroscopy analysis was performed on sulfuric acid and ethanol solutions of the carbon nanodots from Example 6, such as... Figure 8 As shown, carbon nanodots exhibit a distinct 625 nm anti-Stokes emission peak when excited at 655 nm in acid solution, but no anti-Stokes emission peak is observed in alcohol solution.

[0081] Example 7

[0082] Application of carbon nanodots with red light anti-Stokes luminescence properties as a light conversion film in anti-Stokes LEDs.

[0083] The carbon nanodots with red light anti-Stokes emission properties prepared in Example 1 were dispersed on a polyacrylic acid film and coated onto the surface of a red LED (emission wavelength: 660 nm) as a light conversion layer to obtain an LED with red light anti-Stokes emission. Figure 9 The emission spectra of a red LED and a red anti-Stokes emission LED fabricated using carbon nanodots as the anti-Stokes light conversion layer are shown. The results indicate that the carbon nanodot light conversion layer enables the LED device to exhibit anti-Stokes emission.

[0084] Example 8

[0085] The carbon nanodots with red light-reflecting Stokes luminescence properties prepared in Example 1 were mixed with polyacrylic acid and used to write the letter "JLU" on a glass slide. After drying, a carbon nanodot / polyacrylic acid mixture film was obtained. The letter was placed on a hot stage and imaged under a CMOS camera through a 650 nm short-pass filter under 655 nm laser excitation. The image is shown below. Figure 10As shown in the figure. The results show that reverse Stokes luminescence of the letters can be observed at room temperature, and the luminescence of the letters is enhanced with increasing temperature. This indicates that red light reverse Stokes luminescent carbon nanodots can be used for temperature-dependent reverse Stokes imaging, which has potential applications in the field of encryption and anti-counterfeiting.

[0086] Example 9

[0087] The carbon nanodots with red-light anti-Stokes luminescence properties prepared in Example 1 were used as fluorescence imaging reagents in in vivo anti-Stokes fluorescence imaging.

[0088] Red-light-reflecting Stokes-luminescent carbon nanodots were dissolved in dilute hydrochloric acid. One mL of this solution was administered to mice via gavage. The mice were then excited by a 671 nm continuous-wave laser, and the images were captured by a CMOS camera through a 650 nm short-pass filter. Figure 11 The image shown is a reverse Stokes imaging photograph of a mouse, compared to a mouse that did not receive carbon dot gavage. Figure 11 (Right), after carbon dots were administered via gavage ( Figure 11 The gastric luminescence can be clearly observed in the left image, indicating that red-light anti-Stokes luminescent carbon nanodots can be used as anti-Stokes imaging reagents for in vivo imaging.

[0089] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. The application of carbon nanodots with red-light anti-Stokes luminescence properties in temperature-dependent anti-Stokes fluorescence imaging, characterized in that, The carbon nanodots are prepared by a solvothermal reaction using o-phenylenediamine as a raw material and polyphosphoric acid as a solvent. The temperature of the solvothermal reaction is 160~220 °C and the reaction time is 4~10 h. The main emission peak of the carbon nanodots is located in the red-near-infrared region, and they can exhibit red-light anti-Stokes luminescence and Stokes luminescence under continuous laser excitation.

2. The application of carbon nanodots with red-light anti-Stokes luminescence properties according to claim 1 in temperature-dependent anti-Stokes fluorescence imaging, characterized in that, The Stokes emission peak of the carbon nanodots is located at 600~750 nm.

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