Preparation method of saffron red-based long-wave carbon dots and application thereof in anti-fake fluorescent ink

Abstract

The present application relates to a kind of saffron red base long wave carbon dots preparation method and its application in anti-counterfeit fluorescent ink, purpose is to solve carbon dots in anti-counterfeit ink encryption mode single, in MnO4 ‑ The detection range is narrow, and the detection limit is high in the detection technology, and the technical scheme is as follows: ultrasonic dissolution of safflower red T and oxalic acid in deionized water at room temperature; high-pressure reactor high-temperature heating reaction, natural cooling to room temperature, filtering, then dialysis membrane dialysis to obtain carbon dots aqueous solution, freeze-drying to obtain carbon dots powder (O-CDs), safflower red base long wave carbon dots and application in metal ion detection and fluorescent anti-counterfeit ink.The present application uses safflower T containing conjugated system as precursor, and successfully prepares carbon dots powder (O-CDs) by doping oxalic acid, which has good biocompatibility, wavelength independence, high stability, low biological toxicity and other advantages, and can be successfully applied to label-free detection and double anti-counterfeiting of MnO4 ‑ .

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of carbon nanomaterials, and particularly relates to a preparation method of crocein-based long-wave carbon dots and application thereof in anti-counterfeiting fluorescent ink. BACKGROUND

[0002] In recent years, counterfeiting has become a growing global social problem, and the general public and many enterprises have suffered from the harm of counterfeiting. Therefore, it is essential to use high-tech solutions to prevent and stop counterfeiting. Using fluorescent anti-counterfeiting security ink is an important anti-counterfeiting means. Organic dyes, conjugated polymer dots, semiconductor quantum dots and rare earth doped luminescent nanomaterials are commonly used materials for preparing fluorescent anti-counterfeiting security ink, but they all have certain limitations, such as the limitations of poor light stability and small Stokes shift of organic dyes, and the complex preparation process and high price of polymer dots.

[0003] So far, as a new type of carbon-based fluorescent nanomaterial, carbon quantum dots have been widely used as high-quality new fluorescent ink in data encryption and storage due to their good biocompatibility, environmental friendliness, low cost and excellent anti-photobleaching properties. The luminescent ink prepared by carbon quantum dots can be packaged in an inkjet printer or injected into a fountain pen, a gel pen or a brush pen, and can be printed or written on paper, textiles, leather, glass and the like without fluorescent agents, so as to realize encryption under sunlight and decryption under ultraviolet light. Moreover, the water solubility of carbon quantum dots is excellent, and the anti-counterfeiting ink prepared by carbon quantum dots has smooth ink flow and does not cause blockage. Therefore, as a fluorescent anti-counterfeiting material with excellent performance, carbon quantum dots have achieved considerable results in recent years.

[0004] However, the current reports on CDs in anti-counterfeiting applications mainly focus on single-encryption anti-counterfeiting technologies such as anti-counterfeiting labels and luminescent inks that are invisible under sunlight but visible under ultraviolet light, and there are still some challenges in developing multi-encryption technologies and realizing advanced anti-counterfeiting of CDs. Moreover, most of the existing fluorescent anti-counterfeiting inks based on CDs are mainly short-wavelength blue-green fluorescence, and it is of great significance to develop a long-wavelength CDs and apply it in fluorescent anti-counterfeiting ink.

[0005] Permanganate (MnO4 - ) is widely used in water treatment and in-situ chemical oxidation of contaminated soil and groundwater due to its stability, low cost and halogen-free characteristics, but excessive use of MnO4 - pollutes the water body greatly. In addition, excessive intake of MnO4 - by the human body may cause diseases such as depression, irritability, neurological disorders and even genetic mutations, so it is necessary to reduce the use of MnO4 -Studies have shown that fluorescence detection strategies represented by CDs are widely used due to their low toxicity, low cost, high biocompatibility and rapid detection. Therefore, it is necessary to develop a CDs-based sensing platform to quickly and sensitively detect MnO4. - It is particularly urgent. And based on MnO4 - To enhance or quench the fluorescence intensity of CDs, a MnO4 - The regulated anti-counterfeiting fluorescent ink can achieve multiple anti-counterfeiting encryption, which is also of great significance in the anti-counterfeiting field.

[0006] Safranine red T is a common biological dye with high safety and excellent luminescent properties, and is widely found in nature. Research both domestically and internationally has revealed that few methods exist for synthesizing carbon materials from saffron red. Therefore, we used saffron red as a carbon source and, by doping it with other raw materials, synthesized long-wavelength carbon dots for use in fluorescent anti-counterfeiting inks. Summary of the Invention

[0007] The purpose of the present invention is to solve the above problems and provide a preparation method and application of crocus red-based long-wavelength carbon dots.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0009] A method for preparing crocus red-based long-wavelength carbon dots comprises the following steps:

[0010] Step 1) dissolving Safranin T and oxalic acid in deionized water by ultrasonication at room temperature;

[0011] Step 2) placing the solution obtained in step 1) in a high-pressure reactor for high-temperature heating reaction;

[0012] Step 3) After the reaction is completed, the mixture is cooled to room temperature and filtered, and then dialyzed through a dialysis membrane to obtain a carbon dot aqueous solution;

[0013] Step 4) The carbon dot aqueous solution is frozen and dried to obtain saffron red-based long-wavelength carbon dot (O-CDs) powder.

[0014] Furthermore, in the step 1), the mass ratio of saffron red T to oxalic acid is 5:1.

[0015] Furthermore, in step 1), the mass ratio of deionized water to oxalic acid is 20:1, and the ultrasonic dissolution time is 3-7 minutes.

[0016] Furthermore, the heating temperature of the high temperature heating reaction in step 2) is 180-220° C., and the heating time is 6-8 hours.

[0017] Furthermore, the pore size of the filter membrane used for filtration in step 3) is 0.22 μm.

[0018] Furthermore, the dialysis in step 3) is performed using a 500-1000 Da dialysis membrane for 2-3 days.

[0019] The saffron-based long-wavelength carbon dots prepared by the above method are deposited on MnO4 - Applications in ion detection.

[0020] Application of saffron red-based long-wavelength carbon dots prepared by the above method in fluorescent anti-counterfeiting ink.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention has simple operation steps, and carbon dots with long-wave emission can be obtained by a simple one-step hydrothermal method;

[0023] 2. The present invention successfully prepared crocus red-based long-wavelength carbon dots (O-CDs) by using crocus T, which contains a large conjugated system, as a precursor and doping it with oxalic acid. The O-CDs have the advantages of good biocompatibility, wavelength independence, high stability, and low biotoxicity.

[0024] 3. The long-wavelength carbon dots synthesized by the present invention can be successfully applied to MnO4 - The label-free detection of MnO4 - Compared with the sensor, O-CDs have an ultra-wide detection range and a long emission wavelength. In addition, a smartphone colorimetric monitoring system for MnO4 was built using O-CDs. - Sensing platform;

[0025] 4. The O-CDs prepared by the present invention have good light stability and chemical stability. The fluorescent ink prepared based on O-CDs can respond to the concentration change of O-CDs and can be further stabilized by adding MnO4. - After that, the orange fluorescence of the fluorescent ink weakened, which corresponds to the detection of MnO4 by O-CDs. - , MnO4 - The fluorescence of O-CDs was quenched, and single and double anti-counterfeiting technologies were developed based on this, proving that O-CDs have certain application potential in the anti-counterfeiting field. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 (A) is a TEM image of O-CDs of the present invention;

[0027] Figure 1 (B) is the particle size distribution diagram of O-CDs of the present invention;

[0028] Figure 2(A) is the infrared spectrum of the O-CDs of the present invention;

[0029] Figure 2 (B) is the full XPS spectrum of O-CDs of the present invention;

[0030] Figure 2 (C) is the high-resolution C1s spectrum of the O-CDs of the present invention;

[0031] Figure 2 (D) is the N1s spectrum of O-CDs of the present invention;

[0032] Figure 2 (E) is the O1s high-resolution elemental spectrum of the O-CDs of the present invention;

[0033] Figure 2 (F) is the XRD spectrum of O-CDs of the present invention;

[0034] Figure 3 (A) is the UV-visible absorption spectrum and fluorescence spectrum of the O-CDs of the present invention;

[0035] Figure 3 (B) is the excitation emission 3D spectrum of O-CDs of the present invention;

[0036] Figure 3 (C) is a graph showing the effect of KCl salt concentration on the fluorescence intensity of O-CDs according to the present invention;

[0037] Figure 3 (D) is a graph showing the effect of pH value on the fluorescence intensity of O-CDs;

[0038] Figure 3 (E) is a graph showing the effect of xenon lamp irradiation time on the fluorescence intensity of O-CDs;

[0039] Figure 4 (A) for different MnO 4- Fluorescence spectra of O-CDs with different concentrations;

[0040] Figure 4 (B) is the ΔF of the present invention and MnO4 - Nonlinear fitting plot of concentration;

[0041] Figure 4 (C) is the ΔF and MnO4 of the present invention - Linear fitting plot of concentration;

[0042] Figure 4 (D) is a graph showing the effect of different metal ions on the fluorescence intensity of O-CDs according to the present invention;

[0043] Figure 5(A) is the fluorescence spectrum of O-CDs of the present invention and MnO4 - UV-visible absorption spectrum of ;

[0044] Figure 5 (B) The present invention contains and does not contain MnO4 - Fluorescence lifetime curve of O-CDs solution;

[0045] Figure 6 The smartphone imaging colorimetric detection of MnO4 - Schematic diagram;

[0046] Figure 7 The following are photos of the words "1902 Shanxi University" being handwritten on filter paper using a brush using 0.1, 0.25, and 0.5 mg / mL LO-CDs solutions under sunlight and 2254 nm UV light, respectively;

[0047] Figure 8 These are photos of writing text using different concentrations of O-CDs on non-fluorescent paper;

[0048] Figure 9 Photos showing text written on stone paper using different concentrations of O-CDs;

[0049] Figure 10 In order to write Chinese and English poems by hand on filter paper and non-fluorescent paper using 0.5 mg / m3 LO-CDs solution under sunlight and 254 nm UV light, and to write poems by hand on filter paper and non-fluorescent paper using a pen, and to write poems by hand on filter paper and non-fluorescent paper, and to write poems by hand on filter paper and non-fluorescent paper, respectively. - Related photos after solution;

[0050] Figure 11 In order to write Chinese and English poems by hand using 0.5 mg / mL O-CDs solution on filter paper and non-fluorescent paper with a pen under sunlight and 254 nm UV light, and to add 5 uL of 0.1 mol / L MnO4 to 0.5 mg / mL O-CDs solution, the 100 μg / mL O-CDs solution was used to write Chinese and English poems by hand using a pen on filter paper and non-fluorescent paper. - Related photos of handwritten poems in the post-configuration solution;

[0051] Figure 12 These are fluorescence photos of writing written on non-fluorescent paper, stone paper and filter paper using 0.5 mg / ml O-CDs solution under 254 nm ultraviolet light at different times.

[0052] Among them: O-CDs are saffron-based long-wavelength carbon dots. DETAILED DESCRIPTION

[0053] The present invention will be further described below with reference to the accompanying drawings and examples.

[0054] Example 1

[0055] Preparation of O-CDs powder

[0056] A preparation method of saffron red-based long-wave carbon dots, comprising the following steps:

[0057] Step 1) 25 mg of saffron red T and 5 mg of oxalic acid are ultrasonically dissolved in 20 mL of deionized water at room temperature for 3 min to dissolve the precursors;

[0058] Step 2) 50 mL of the solution obtained in step 1) is placed in a Teflon-lined, sealed into a stainless steel high-pressure hydrothermal reactor, and the high-pressure reactor is heated at 200℃ for 8 h;

[0059] Step 3) After the reaction is completed, the solution is naturally cooled to room temperature, filtered with a filter membrane with an average pore size of 0.22 μm, and then dialyzed with a 1000 Da dialysis membrane for 3 days to obtain a carbon dot aqueous solution;

[0060] Step 4) The carbon dot aqueous solution is frozen and dried to obtain saffron red-based long-wave carbon dot (O-CDs) powder. With cresol purple solution as a reference solution, the quantum yield of the O-CDs is 5.13%.

[0061] In step 1), the mass ratio of saffron red T and oxalic acid can also be any other combination of 5:1, and the mass ratio of deionized water to oxalic acid can also be any other combination of 20:1. The ultrasonic dissolution time can also be any value between 3-7 min;

[0062] In step 2), the high-temperature heating reaction temperature can also be any value between 180-220℃, and the reaction time can also be any value between 6-8 h;

[0063] In step 3), the molecular weight cut-off of the dialysis membrane can also be any value between 500-1000 Da, and the dialysis time can also be any value between 2-3 d.

[0064] Structure characterization of O-CDs

[0065] As shown in Figure 1 , the TEM image and size distribution diagram of the O-CDs prepared in Example 1, the O-CDs have a quasi-spherical structure and a uniform dispersed morphology, and the average diameter is 1.87±0.27 nm.

[0066] The infrared spectrum (FTIR) characterization of the O-CDs prepared in this example is shown in Figure 2 (A). The carbon dots have O-H / N-H, Ar-N-H, C=O / C=N, C=C and C-O groups on the surface, corresponding to 3432 cm -1 , 3189 cm-1 , 1637cm -1 , 1531cm -1 and 1130cm -1 The absorption peak at

[0067] XPS full spectrum ( Figure 2 B) Three peaks appear at 284.8eV, 399.2eV, and 532.1eV, corresponding to the three components of C1s, N1s, and O1s, respectively. The contents of C, N, and O are 79.0%, 12.3%, and 8.7%, respectively.

[0068] like Figure 2 As shown in (C), the C1s spectrum can be divided into three peaks at 284.8 eV, 285.7 eV, and 288.8 eV, which are CC / C=C, CN / CO, and C=O functional groups, respectively;

[0069] N1s spectrum ( Figure 2 D) shows three peaks, indicating that the nitrogen element exists in the form of pyridinic N, amino N and pyrrolic N, corresponding to the peaks at 398.9 eV, 399.4 eV and 400.7 eV respectively;

[0070] The O element exists in the form of C=O (531.9 eV) and CO (532.7 eV) (Figure E). XPS and FTI show that the surface of O-CDs has a rich variety of surface functional groups. Different surface functional groups give the material different properties. For example, hydrophilic functional groups such as -OH and -NH2 give O-CDs excellent water solubility.

[0071] At the same time, the XRD results ( Figure 2 The broad diffraction peaks at 25° and 45° in F) confirm the presence of amorphous carbon structure.

[0072] The UV-visible absorption spectrum, excitation spectrum and emission spectrum of the O-CDs prepared in Example 1 are as follows: Figure 3 As shown in (A), O-CDs have absorption peaks at 248 and 276 nm in the UV spectrum, which are attributed to π-π* transitions and n-π* transitions. The optimal excitation and emission wavelengths of O-CDs are 525 and 590 nm, respectively.

[0073] Figure 3 (B) shows that O-CDs have no excitation wavelength dependence, and the emission wavelength is independent of the excitation wavelength;

[0074] In addition, at different salt ion concentrations ( Figure 3 C) and pH value ( Figure 3D) conditions, the fluorescence intensity of O-CDs remained stable, which proves that O-CDs have good application prospects in complex systems and biological systems. At the same time, the xenon lamp continuous irradiation experiment showed that O-CDs have excellent anti-photobleaching properties ( Figure 3 E).

[0075] Example 2 O-CDs in MnO4 - Application in detection

[0076] O-CDs prepared in Example 1 to MnO4 - Label-free detection of Figure 4 The titration results are shown in Figure 4 As shown in A, as MnO4 - As the concentration increased, the fluorescence intensity of O-CDs gradually decreased;

[0077] According to the change of fluorescence intensity and MNO4 - The concentration was fitted with the Boltzmann equation, and the results were as follows Figure 4 As shown in B, the fitting equation is Y = 518.651-932.572 / ((1+exp(X-69.105) / 248.935))(R2=0.9985). At the same time, we found that MnO4 - The fluorescence intensity changes with the concentration of MnO4 in the range of 0.5-400μM. - The linear equation was Y = 0.854X-4.629, the correlation coefficient R2 = 0.9925, and the limit of detection (LOD) was 0.23 μM (n = 11). - Compared with sensors, O-CDs have an ultra-wide detection range and a long emission wavelength ( Figure 4 C);

[0078] Figure 4 D is the selectivity of the O-CDs sensing platform to different ions. The results show that only MnO4 - It can significantly quench the fluorescence intensity of O-CDs, while other ions do not cause fluorescence quenching, indicating that O-CDs has a great influence on the fluorescence intensity of MnO4 - The detection has good selectivity and anti-interference ability.

[0079] O-CDs prepared in Example 1 to MnO4 - The response mechanism is as follows Figure 5 As shown, the UV-visible absorption spectrum and fluorescence lifetime of MnO4 - The fluorescence quenching mechanism of O-CDs. Figure 5 As shown in A, MnO4 -The UV-Vis absorption spectrum of O-CDs has a large area overlap with the excitation spectrum of O-CDs, and the emission spectrum of O-CDs has a large area overlap with the excitation spectrum of O-CDs Figure 5 B shows that the addition of MnO4 - The fluorescence lifetime before and after has no obvious change, indicating that the mechanism of fluorescence quenching may be the inner filter effect.

[0080] The O-CDs prepared in Example 1 have a linear relationship with the concentration of MnO4 - The smart phone measurement platform as shown in Figure 6 , after adding different concentrations of MnO4 - , the color of the solution of O-CDs gradually changes, and a series of visible images can be captured by the smart phone camera. Then through the color recognition APP on the phone, the RGB value of the corresponding color can be obtained. The obtained RGB value is input into the smart phone software (WPS Office) to confirm the linear relationship between R2 / (G+B) value and MnO4 - concentration. It is found that with the gradual addition of MnO4 - , the color of the solution gradually changes from pink to light pink, and R2 / (G+B) changes linearly with the change of MnO4 - concentration, the linear regression equation is Y=-0.497X+294.923, R2=0.9898, and the LOD is 1.58 μM (n=3).

[0081] Example 3 Single anti-counterfeiting application of O-CDs in fluorescent anti-counterfeiting ink

[0082] The application of O-CDs prepared in Example 1 in anti-counterfeiting is as shown in Figure 7 , Figure 8 , Figure 9 The fluorescent ink made of O-CDs is applied to anti-counterfeiting writing, and the specific operation is that the fluorescent ink prepared by 0.1 mg / mL, 0.25 mg / mL and 0.5 mg / mL O-CDs solution is used to write on filter paper, non-fluorescent paper and stone paper with a fine brush pen.

[0083] As shown in Figure 7 , Figure 8 , Figure 9 The "1902 Shanxi University" written on the three kinds of paper with O-CDs ink is light pink under sunlight, and all emits orange fluorescence under 254 nm ultraviolet light, which corresponds to the fluorescence color of the carbon dots, and the phenomenon responds to the change of concentration, and the orange fluorescence becomes brighter with the increase of O-CDs concentration. The results show that the O-CDs can be used as fluorescent anti-counterfeiting ink, which is light pink under sunlight and orange fluorescence under ultraviolet light, realizing single information anti-counterfeiting.

[0084] Example 4: Dual Anti-Counterfeiting Application of O-CDs in Fluorescent Anti-Counterfeiting Ink

[0085] This example is based on the O-CDs to MnO4 - A label-free detection method was designed to respond to MnO4 - Detection of anti-counterfeiting mode. Figure 10 As shown, Chinese and English poems were written on filter paper and non-fluorescent paper using 0.5 mg / mL O-CDs solution, and then irradiated under 254 nm UV light, which showed orange fluorescence. However, when sprayed with 0.1 mol / L MnO4 - After solution, the orange fluorescence of the fluorescent ink was masked, which corresponds to the detection of MnO4 by O-CDs. - .

[0086] To eliminate the MnO4 - The masking effect caused by the color of the solution itself, configured with O-CDs+MnO4 - of solution and write. Figure 11 As shown, 5uL of 0.1mol / L MnO4 was added to 0.5mg / mL O-CDs solution. - Afterwards, Chinese and English poems were written on filter paper and non-fluorescent paper and irradiated under 254nm UV light. Compared with the results of direct writing with O-CDs, the results of using O-CDs+MnO4 - The fluorescence color of the writing in the solution is significantly weakened, and this result also corresponds to the detection of MnO4 by O-CDs. - Based on this, it is light pink under sunlight and orange under ultraviolet light. - The fluorescence is reduced or even eliminated after adjustment, which is a dual information anti-counterfeiting mode. The above results show that the O-CDs as fluorescent inks have good application potential in anti-counterfeiting.

[0087] To investigate the stability of O-CDs as anti-counterfeiting ink, the fluorescent color of the words "1902 Shanxi University" written on filter paper, non-fluorescent paper and stone paper with a 0.5 mg / mL O-CDs solution was investigated after 2 and 4 days of rest. Figure 12 As shown in the figure, there is no significant change in color development after 2 and 4 days, indicating that the O-CDs fluorescent ink prepared in Example 3 has good time stability.

[0088] (1) The O-CDs powder prepared in Example 1 was prepared into 0.1 mg / mL, 0.25 mg / mL, and 0.5 mg / mL CDs solutions to prepare fluorescent inks;

[0089] (2) Temperature is 25 DEG C, through surface tension meter, viscosity meter detects three different concentrations of solution surface tension and viscosity.

[0090] Adopt surface tension meter, viscosity meter to three kinds of sample detection, the results are shown in Table 1.Meet the standard of national standard QB / T2730.1-2013 inkjet printer ink, that is, surface tension is 25-60 mN / m, viscosity is 1-15 mPa·s, the results show that the O-CDs prepared by example 1 can also be used as inkjet printer ink, and has good application potential in the aspect of anti-counterfeiting.

[0091] Table 1 Fluorescent ink surface tension and viscosity detection

[0092]

[0093] The contents not described in detail in the specification of the present application belong to the prior art known to the person skilled in the art. Although the above describes the specific embodiments of the present application for the purpose of facilitating the understanding of the present application by the person skilled in the art, it should be clear that the present application is not limited to the scope of the specific embodiments, and for the person skilled in the art, it is obvious that all kinds of changes within the spirit and scope of the present application defined and determined by the appended claims are obvious, and all kinds of inventions utilizing the concept of the present application are included in the protection.

Claims

1. A saffron-based long-wavelength carbon dot on MnO4 - Application in ion detection, characterized in that, The preparation method of saffron red-based long-wavelength carbon dots comprises the following steps: Step 1) dissolving Safranin T and oxalic acid in deionized water by ultrasonication at room temperature; Step 2) placing the solution obtained in step 1) in a high-pressure reactor for high-temperature heating reaction at a temperature of 180-220° C. for 6-8 hours; Step 3) After the reaction is completed, the mixture is cooled to room temperature and filtered, and then dialyzed through a dialysis membrane to obtain a carbon dot aqueous solution; Step 4) Freezing and drying the carbon dot aqueous solution to obtain saffron red-based long-wavelength carbon dot powder.

2. The saffron-based long-wavelength carbon dots according to claim 1 are prepared in MnO4 - Application in ion detection, characterized in that, In the step 1), the mass ratio of saffron red T to oxalic acid is 5:

1.

3. The crocus red-based long-wavelength carbon dots according to claim 1 are prepared in MnO4 - Application in ion detection, characterized in that, In step 1), the mass ratio of deionized water to oxalic acid is 20:1, and the ultrasonic dissolution time is 3-7 minutes.

4. The crocus red-based long-wavelength carbon dots according to claim 1 in MnO4 - Application in ion detection, characterized in that, The pore size of the filter membrane used for filtration in step 3) is 0.22 μm.

5. The crocus red-based long-wavelength carbon dots according to claim 1 in MnO4 - Application in ion detection, characterized in that, The dialysis in step 3) is performed using a 500-1000 Da dialysis membrane for 2-3 days.

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