A fluorescent probe based on red light carbon quantum dots and its application in detecting ethanol concentration in ethanol-water system

Abstract

A fluorescent probe based on red light carbon quantum dots and its application in detecting ethanol concentration in ethanol-water system belong to the field of fluorescent probe technology. The present invention uses p-phenylenediamine as a carbon source and citric acid as a reducing agent, and adopts a one-step hydrothermal method to prepare carbon quantum dots, whose emission peak is located in the red light region and can be stored stably for a long time. The carbon quantum dots can quickly, simply and efficiently identify and detect the ethanol concentration in the ethanol-water system. By increasing the ethanol content, the emission peak of the carbon quantum dots blue-shifts and the fluorescence intensity gradually increases. The results show that when the concentration of ethanol is in the range of 20%-80%, there is a good linear relationship between the luminescence intensity of the carbon quantum dots and the concentration of ethanol. At the same time, the carbon quantum dots can also be used to detect low concentrations of ethanol in water, with a detection limit of 1.5%, and can be used for fluorescent detection of ethanol concentration and visual detection of ethanol concentration.

Description

Technical Field

[0001] The invention belongs to the technical field of fluorescent probes, and in particular relates to a fluorescent probe based on red light carbon quantum dots and an application thereof in detecting ethanol concentration in an ethanol-water system. Background Art

[0002] Ethanol is an essential medicine in medical institutions and home medicine cabinets. It is one of the most commonly used external preparations. Ethanol of different concentrations has completely different functions. For example, 95% ethanol can be used as fuel, 70%-75% ethanol can be used for sterilization, 40%-50% ethanol can be used to prevent bedsores, and 25%-50% ethanol can be used for physical fever reduction. In addition, ethanol is also an important component of drinking wine. Studies have shown that in China, there are tens of thousands of traffic accidents caused by drunk driving every year; moreover, more than 50% of traffic fatalities are related to drunk driving. Therefore, the detection of ethanol is of great significance and necessity. The development of new, highly sensitive ethanol-responsive fluorescent probes has important scientific significance and application needs.

[0003] As a new type of zero-dimensional carbon-based nanomaterial, carbon quantum dots (CDs) have attracted widespread attention in the scientific community in recent years. Compared with traditional semiconductor quantum dots and organic fluorescent dyes, carbon quantum dots have many excellent properties. Their superior optical properties, low toxicity, good biocompatibility and strong chemical inertness have led to their widespread use in many fields such as recognition sensing, bioimaging, drug delivery, solar cell development, etc. [1-5] However, there are some problems in the practical application of carbon quantum dots that cannot be ignored. For example, most reported carbon quantum dots often show blue fluorescence, which greatly limits the application and development of carbon quantum dots. Therefore, it is urgent to optimize the preparation process of carbon quantum dots so as to adopt a green and convenient preparation method to develop carbon quantum dots with red luminescence.

[0004] The present invention uses p-phenylenediamine (PPD) as a carbon source and citric acid (CA) as a reducing agent to synthesize carbon quantum dots with red luminescence characteristics, and uses Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM) to characterize its structure and morphology. The carbon quantum dots can quickly and efficiently produce fluorescence recognition for different concentrations of ethanol in an ethanol-water solution, and can quantitatively detect the concentration of ethanol in two different concentration ranges. Summary of the invention

[0005] The present invention provides a fluorescent probe based on red light carbon quantum dots that can quickly, simply and efficiently identify the concentration of ethanol and its application in detecting the concentration of ethanol in an ethanol-water system. The fluorescent probe can be used in the fluorescent detection of ethanol concentration and the visual detection of ethanol concentration in the ethanol-water system. The fluorescent probe is directly prepared by a one-step hydrothermal method under high temperature and high pressure conditions using p-phenylenediamine (PPD) as a carbon source and citric acid (CA) as a reducing agent. The optimal excitation wavelength of the fluorescent probe is 500nm and the emission wavelength is 620nm. Under the irradiation of an ultraviolet lamp (365nm), the fluorescent probe emits red light. Furthermore, we use the fluorescent probe to detect the concentration of ethanol in an ethanol-water system: by increasing the concentration of ethanol, the emission peak of the fluorescent probe blue-shifts and the fluorescence intensity gradually increases. The results show that when the concentration of ethanol is in the range of 20%-80%, there is a good linear response (R 2 =0.997), the linear equation is: F = 2.79413 [Ethanol] + 14.30169. Moreover, when the ethanol concentration is reduced, it can also detect ethanol in a lower concentration range (R 2 =0.999); when the ethanol concentration is 0-20%, its linear response equation is F=3.07887[Ethanol]+42.09551, and its detection limit for ethanol is 1.5%.

[0006] like Figure 1 As shown, the fluorescent probe based on red light carbon quantum dots described in the present invention is prepared by the following method: weigh 0.01-0.03g of p-phenylenediamine and dissolve it in 10mL of water. After it is fully dissolved, add 8-15mL of 1mM citric acid aqueous solution, and then stir at room temperature for 8-15min; then transfer it to a high-pressure reactor with a polytetrafluoroethylene liner, and react at 170-190°C for 8-15h, thereby obtaining the fluorescent probe solution based on red light carbon quantum dots described in the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 : Schematic diagram of the synthetic route for preparing fluorescent probe solution using p-phenylenediamine and citric acid as raw materials.

[0008] Figure 2 : Fourier transform infrared (FT-IR) absorption spectrum of the fluorescent probe solution (p-phenylenediamine-carbon quantum dots) prepared in Example 1.

[0009] Figure 3 : Transmission electron microscopy (TEM) image and particle size distribution diagram (inset) of red light carbon quantum dots in the fluorescent probe solution prepared in Example 1.

[0010] Figure 4: Fluorescence spectra of the fluorescent probe solution in ethanol-water solutions of different concentrations (0-100%) under excitation of a 500nm light source.

[0011] Figure 5 : The dotted line graph (a) and linear relationship graph (b) of the fluorescence intensity of the fluorescent probe solution changing with the ethanol concentration (0-100%) under the excitation of 500nm light source.

[0012] Figure 6 : Fluorescence images of the fluorescent probe solution in different ethanol-water solutions (ethanol concentration is 0-100%) under ultraviolet light (365nm).

[0013] Figure 7 : Fluorescence spectrum of the fluorescent probe solution in low concentration ethanol-water solution (0-20%) under 500nm light source excitation.

[0014] Figure 8 : Linear relationship diagram of the fluorescence intensity of the fluorescent probe solution changing with the ethanol concentration (0-20%) under 500nm light source excitation.

[0015] Fig. 9 : Fluorescence images of the fluorescent probe solution in different ethanol-water solutions (ethanol concentration is 0-20%) under ultraviolet light (365nm).

[0016] The present invention uses Fourier transform infrared spectroscopy to characterize the surface functional groups of carbon quantum dots. Figure 2 As shown, 3330cm -1 The absorption peak at is the stretching vibration peak of OH [6] , 1628cm -1 and 1514cm -1 The absorption peaks at are the stretching vibration peaks of C=O and C=N. [7] , 1388cm -1 The absorption peak at corresponds to the stretching vibration peak of CN [8] Therefore, these results indicate that the surface of carbon quantum dots contains free carboxyl and amino groups. Further, transmission electron microscopy (TEM) was used to characterize the morphology of carbon quantum dots. Figure 3 It can be observed that the obtained carbon quantum dots are spherical and have good monodispersity in aqueous solution. After statistical analysis of about 200 dispersed particles, it was found that the average particle size of the obtained carbon quantum dots is concentrated at ~3.21nm. The above results show that we used p-phenylenediamine and citric acid as raw materials and used a simple and easy-to-operate one-step hydrothermal method to successfully synthesize a fluorescent probe based on red light carbon quantum dots with an emission center of 620nm.

[0017] like Figure 4As shown in the figure, when carbon quantum dots are mixed with ethanol-water solutions of different concentrations (0-100%), as the concentration of ethanol increases, the emission peak of the carbon quantum dots blue-shifts and the fluorescence intensity gradually increases; when the concentration of ethanol is in the range of 20%-80%, the luminescence intensity of the carbon quantum dots has a good linear relationship with the concentration of ethanol (such as Figure 5 As shown in (b), R 2 =0.997), its linear response equation is: F = 2.79413 [Ethanol] + 14.30169. In addition, if Figure 8 As shown, the carbon quantum dots can also detect ethanol more sensitively in a lower concentration range: when the ethanol concentration is 0-20%, its linear response equation is F=3.07887[Ethanol]+42.09551, and the minimum detection limit of ethanol is 1.5%, where F represents the fluorescence intensity of the fluorescent probe, and [Ethanol] represents the concentration of ethanol. DETAILED DESCRIPTION

[0018] The following examples further illustrate the content of the present invention, but the present invention is not limited to these examples. The p-phenylenediamine and citric acid used in the present invention were purchased from Shanghai Aladdin Reagent Co., Ltd., and anhydrous ethanol was purchased from Shandong Yuwang Hetianxia New Materials Co., Ltd. Deionized ultrapure water was used throughout the experiment.

[0019] Embodiment 1:

[0020] Synthesis of fluorescent probe solution: Weigh 0.02g p-phenylenediamine and dissolve it in 10mL water. After fully dissolving, add 10mL citric acid (1mM), stir at room temperature for 10min, and transfer to a high-pressure reactor with a polytetrafluoroethylene liner. Then place the reactor in a constant temperature oven and react at 180℃ for 10h to obtain the fluorescent probe solution based on red light carbon quantum dots of the present invention ( Figure 1 ).

[0021] The results show that the emission wavelength of the fluorescent probe solution obtained in Example 1 is 620 nm. The structure and surface functional groups of the red light carbon quantum dots were characterized by Fourier transform infrared spectroscopy. Figure 2 As shown, 3330cm -1 The absorption peak at is the stretching vibration peak of OH [6] , 1628cm -1 and 1514cm -1 The absorption peaks at are the stretching vibration peaks of C=O and C=N. [7] , 1388cm -1 The absorption peak at corresponds to the stretching vibration peak of CN [8] Therefore, the surface of the red light carbon quantum dots contains free carboxyl and amino groups. Transmission electron microscopy was further used to characterize the morphology of the carbon quantum dots, such as Figure 3 As shown in Figure 2, the carbon quantum dots are spherical and well dispersed in aqueous solution. After statistical analysis of about 200 particles, it was found that the average particle size of the carbon quantum dots is concentrated around 3.21 nm (see Figure 3 illustration).

[0022] Embodiment 2:

[0023] Fluorescence response of the fluorescent probe solution to high concentration of ethanol in ethanol-water solution: prepare ethanol-water mixed solutions with different ethanol volume fractions (wherein the volume fraction of ethanol is 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%), then add 950 μL of ethanol-water mixed solutions with different concentrations and 50 μL of the red light carbon quantum dot-based fluorescent probe solution prepared in Example 1 to the cuvette, mix thoroughly and measure the fluorescence spectrum of the above solution. Figure 4 The experimental results show that as the ethanol concentration increases, the fluorescence intensity of the fluorescent probe solution gradually increases. At the same time, by drawing a graph showing the relationship between the fluorescence intensity of the fluorescent probe solution and the ethanol concentration ( Figure 5 ) It can be clearly seen that when the concentration of ethanol is in the range of 20%-80%, there is a good linear response relationship between the fluorescence intensity of the fluorescent probe solution and the concentration of ethanol (R 2 =0.997), and its linear response equation is: F=2.79413[Ethanol]+14.30169, where F represents the fluorescence intensity of the fluorescent probe and [Ethanol] represents the concentration of ethanol.

[0024] Embodiment 3:

[0025] Visual response of the fluorescent probe solution to high concentration of ethanol: When the ethanol-water mixed solution with different ethanol volume fractions configured in Example 2 is irradiated with ultraviolet light (365nm), the mixed solution of the fluorescent probe solution and the ethanol-water solution with different concentrations (0-100%) exhibits red light of obviously different intensities, and the visual response of the fluorescent probe solution in ethanol solutions with different concentrations under ultraviolet light can be obtained. Figure 6 As shown: the fluorescent probe solution emits red light under ultraviolet light, and as the ethanol concentration increases, the red light of the fluorescent probe solution increases.

[0026] Embodiment 4:

[0027] Fluorescence response of fluorescent probe solution to low concentration of ethanol in ethanol-water solution: prepare ethanol-water mixed solutions with different ethanol volume fractions (the volume fractions of ethanol are 0%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%), then add 990 μL of ethanol-water solutions with different concentrations and 10 μL of fluorescent probe solution to the cuvette, mix thoroughly and measure the fluorescence spectra of the above solutions. Figure 7 The experimental results show that as the ethanol concentration increases, the fluorescence intensity of the fluorescent probe solution gradually increases. At the same time, by drawing a graph showing the relationship between the fluorescence intensity of the fluorescent probe solution and the ethanol concentration ( Figure 8 ) shows that when the concentration of ethanol is in the range of 0%-20%, the fluorescence intensity of the fluorescent probe solution and the concentration of ethanol have a good linear response (R 2 =0.999), the linear equation is: F=3.07887[Ethanol]+42.09551, the detection limit is 1.5%, F represents the fluorescence intensity of the fluorescent probe, and [Ethanol] represents the concentration of ethanol.

[0028] Embodiment 5:

[0029] Visual response of the fluorescent probe solution to low concentration ethanol: When the ethanol-water mixed solution with different ethanol volume fractions configured in Example 4 is irradiated with ultraviolet light (365nm), the fluorescent probe solution and the mixed solution of ethanol-water solution with different concentrations (0-20%) show red light with obviously different intensities, and the visual response of the fluorescent probe solution in ethanol solutions with different concentrations under ultraviolet light can be obtained. Fig. 9 As shown: the fluorescent probe solution emits red light under ultraviolet light, and as the ethanol concentration increases, the red light of the fluorescent probe solution increases.

[0030] In addition, it should be noted that the specific embodiments listed in this specification are only used to illustrate the contents of the present invention and do not limit the protection scope of the present invention in any way; relevant technical personnel in the field can make improvements or changes based on some of the above descriptions, but all these improvements and changes should fall within the protection scope of the claims of the present invention.

[0031] References

[0032] [1]Y.Lin,D.Knopp,Anal.Chem.89(2017),5637–5645

[0033] 2] J. Shangguan, J. Tang, Anal. Chem. 89 (2017), 7477–7484

[0034] [3]Q.Zheng,L.Wang,Nanotechnology 31(2020)175102

[0035] [4]W.Sun,L.Fan J.Phys.Chem.Lett.11(4)(2020)1357-1363

[0036] [5]H.Wang,G.Zou Nanoscale Research Letters 11(27)(2016)3-6

[0037] [6]Y.Ma,Q.Hu ACS Appl.Mater.Interfaces 9(2017)33011-33019

[0038] [7]S.Huang,Q.Xiao Sensors and Actuators B 234(2016)255–263

[0039] [8]H.Wang,S.Yao Sensors and Actuators B 250(2017)429–435。

Claims

1. An application of a fluorescent probe based on red light carbon quantum dots in fluorescent detection of ethanol concentration in an ethanol-water system, characterized in that: The fluorescent probe based on red light carbon quantum dots is prepared by the following method: Weigh 0.01-0.03 g of p-phenylenediamine and dissolve it in 10 mL of water. After it is fully dissolved, add 8-15 mL of 1 mM citric acid aqueous solution and stir at room temperature for 8-15 min. Then transfer it to a high-pressure reactor with a polytetrafluoroethylene liner and react at 170-190°C for 8-15 h to obtain a fluorescent probe solution based on red light carbon quantum dots. As the concentration of ethanol increases, the emission peak of the fluorescent probe solution blue-shifts and the fluorescence intensity gradually increases. When the concentration of ethanol is in the range of 20% to 80%, the linear response equation of the luminescence intensity of carbon quantum dots and the concentration of ethanol is F=2.79413[Ethanol]+14.30169, R 2 =0.997; when the ethanol concentration is 0~20%, the linear response equation is F=3.07887[Ethanol]+42.09551, R 2 = 0.999; the minimum detection limit for ethanol is 1.5%; F represents the fluorescence intensity of the fluorescent probe, and [Ethanol] represents the concentration of ethanol.

2. An application of a fluorescent probe based on red light carbon quantum dots in visual detection of ethanol concentration in an ethanol-water system, characterized in that: The fluorescent probe based on red light carbon quantum dots is prepared by the following method: Weigh 0.01-0.03 g of p-phenylenediamine and dissolve it in 10 mL of water. After it is fully dissolved, add 8-15 mL of 1 mM citric acid aqueous solution and stir at room temperature for 8-15 min. Then transfer it to a high-pressure reactor with a polytetrafluoroethylene liner and react at 170-190°C for 8-15 h to obtain a fluorescent probe solution based on red light carbon quantum dots.

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