Carbon dot fluorescent test paper for rapid detection of Cu < 2 + > and colorimetric method
By combining nitrogen-doped carbon dot fluorescent test paper prepared by the microchannel method with a colorimetric card, the complexity and cost issues of existing copper ion detection methods have been solved, achieving low-cost, low-toxicity, and high-efficiency visual detection of copper ions.
Patent Information
- Application Number
- CN202410438306.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-04-12
- Publication Date
- 2025-10-21
AI Technical Summary
Existing methods for detecting copper ions are complex to operate, have long detection cycles, are costly, and cannot achieve on-site visual detection. Traditional carbon dot preparation methods are energy-intensive and time-consuming.
Nitrogen-doped carbon dots (N-CDs) were prepared using a microchannel method, attached to cellulose test paper, and combined with a colorimetric card. The fluorescence intensity was captured and analyzed using a smartphone through the fluorescence quenching reaction between the carbon dots and copper ions, enabling rapid and visual detection.
It achieves low-cost, low-toxicity, and high-efficiency copper ion detection, simplifies the detection process, reduces equipment requirements, and enables on-site, real-time quantitative analysis.
Smart Images
Figure CN120820524A_ABST
Abstract
Description
Technical Field
[0001] The present application belongs to the field of nanomaterials and ion detection technology, and in particular relates to the preparation of fluorescent carbon dots and their use as a fluorescent test paper and colorimetric card for convenient and visual detection of copper ions in aqueous solutions. Background Art
[0002] Copper ions are essential metal ions for the human body, supporting various bodily functions and playing a crucial role in the natural environment. Excessive or insufficient copper ion levels can have serious impacts on both humans and the ecological environment. Existing copper ion detection methods, such as electrochemical methods, atomic absorption spectroscopy, and inductive coupling methods, suffer from complex procedures, long detection cycles, and high costs. Furthermore, they lack on-site visualization. Therefore, a new, efficient, and convenient ion detection method has been developed, which holds significant research and application value.
[0003] Carbon dots (Cdots) are newly developed fluorescent nanomaterials of the 21st century. They possess excellent fluorescence, stability, low toxicity, and ease of preparation. In recent years, they have been widely used in fields such as ion detection and luminescent materials. Due to their unique structure, Cdots can bind to metal ions to produce a quenching reaction, which in turn reduces fluorescence intensity. The ratio of the decrease in fluorescence intensity can be used to intuitively determine the concentration of copper ions, enabling visual detection of copper ions and possessing significant application value. Traditional methods such as hydrothermal and microwave thermal methods are energy-intensive and time-consuming. However, the microchannel method for preparing Cdots offers advantages such as higher production efficiency, enhanced process safety, and a smaller instrument footprint. Attaching Cdot solutions to test strips maximizes their feasibility for ion detection. Combined with a colorimetric card, the added copper ion concentration can be intuitively determined. This not only enhances the application value of Cdots but also truly realizes the commercialization of Cdot test strips, providing a new, efficient, and convenient visual instant detection technology for ion detection. Summary of the Invention
[0004] To solve the above problems, the present application provides a carbon dot fluorescent test paper with high efficiency and accurate visualization and a preparation method thereof.
[0005] The main purpose of the present invention is to provide a new visual, accurate and efficient detection method for current copper ion detection, that is, carbon dot fluorescent test paper is used in conjunction with a colorimetric card to achieve on-site instant detection.
[0006] The carbon dots of the present invention are prepared by the following method:
[0007] i) 0.44 g of citric acid and 0.91 mL of diethylenetriamine were mixed and added to 20 mL of ultrapure water, and sonicated for 20 minutes until the citric acid was completely dissolved;
[0008] ii) The solution was placed in a microchannel reactor for carbonization at 200° C. and 3.80 MPa, and the solution was dialyzed for 24 h using a dialysis bag (MWCO=500 Da) to obtain the final light yellow N-CDs.
[0009] Application of carbon dots N-CDs as fluorescent probes in copper ion detection:
[0010] In a first aspect, the present application provides a method for quantitatively detecting copper ions in an aqueous solution with a fluorescent test paper, the fluorescent test paper specifically comprising:
[0011] i) using cellulose test paper as a carrier to carry the carbon dot aqueous solution;
[0012] ii) Through carbon dots and different concentrations of Cu 2+ The fluorescence quenching reaction of Cu was accurately detected by using a smartphone to capture the color. The fluorescence intensity was measured by Image J. 2+ Perform quantitative detection.
[0013] In a second aspect, the colorimetric card of the present invention is prepared by the following method:
[0014] i) adding different concentrations of Cu to the carbon dot N-CDs fluorescent test paper according to claim 3; 2+ solution;
[0015] ii) Use a 365nm UV flashlight to illuminate the fluorescent test paper, photograph it with a smartphone, and analyze the color using Photoshop;
[0016] iii) According to the obtained RGB value and Cu 2+ The linear relationship between the concentration of Cu 2+ The colorimetric card under different concentrations can be used to measure the Cu 2+ Perform quantitative analysis.
[0017] Furthermore, the colorimetric card of the present invention is a colorimetric card for different concentrations of Cu 2+ A quenching reaction occurs with the fluorescent test paper. When using a 365nm ultraviolet flashlight, the irradiation angle and irradiation area must be fixed (forming an inscribed circle with the test paper). The smartphone's camera parameters and shooting angle must be fixed.
[0018] The present invention provides a method for detecting Cu in aqueous solution. 2+ Carbon dot fluorescence test paper and colorimetric card were prepared by using citric acid as carbon source and diethylenetriamine as nitrogen source. Nitrogen-doped carbon dots N-CDs were synthesized by an efficient and convenient microchannel method as a fluorescent marker for the detection of Cu 2+ The fluorescent probe has the characteristics of low cost, low toxicity and easy preparation. Cellulose test paper is used as a carrier to carry carbon dots. 2+The fluorescence quenching reaction occurs, which causes the color of the test paper to change significantly under the irradiation of the ultraviolet flashlight. It can be used with the corresponding color card to detect Cu 2+ It can realize rapid visual quantitative detection. It effectively solves the existing problems of time-consuming and labor-intensive ion detection in the industry and high costs. 2+ The detection provides an efficient and accurate visual instant detection technology.
[0019] The present invention has the following advantages:
[0020] 1. Carbon dots have the advantages of low cost, low toxicity and good selectivity, which can be used for Cu 2+ Conduct precise testing.
[0021] 2. Compared with traditional carbon dot preparation methods such as the hydrothermal method, the novel microchannel method for preparing carbon dots has the advantages of higher production efficiency, safer process, and smaller instrument size.
[0022] 3. It removes the limitation of aqueous solution on the application of carbon dots, thus getting rid of the use of large instruments, greatly simplifying the steps of ion detection, and reducing the detection cost.
[0023] 4. Fluorescent test paper has the advantages of easy preparation, low cost, and easy portability, and its synergy with carbon dots produces extremely high application value.
[0024] 5. The ion concentration can be intuitively judged by the color change of the test paper, realizing on-site visual instant detection. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.
[0026] Figure 1 This is the fluorescence spectrum of N-CDs in the present invention at an excitation wavelength of 330nm to 400nm.
[0027] Figure 2 The N-CDs and different concentrations of Cu in the present invention 2+ After the reaction, the maximum fluorescence intensity and Cu 2+ Linear relationship with concentration.
[0028] Figure 3 This is a fluorescence intensity diagram of N-CDs after reacting with different metal ions in the present invention.
[0029] Figure 4 is the UV-visible spectrum of N-CDs in the present invention.
[0030] Figure 5 This is the nanoparticle size distribution diagram of N-CDs in the present invention.
[0031] Figure 6 This is the Zeta potential distribution diagram of N-CDs in the present invention.
[0032] Figure 7 TEM electron microscope image of N-CDs in the present invention.
[0033] Figure 8 This is the particle size distribution diagram of N-CDs in the present invention.
[0034] Figure 9 This is the infrared spectrum image of N-CDs in the present invention.
[0035] Figure 10 This is the image of the fluorescent test paper of the present invention under the irradiation of an ultraviolet flashlight.
[0036] Figure 11 Add different concentrations of Cu to the fluorescent test paper 2+ The image is then taken under a UV flashlight.
[0037] Figure 12 is the fluorescence intensity of the test paper and Cu 2+ Linear relationship with concentration.
[0038] Figure 13 The RGB value of the test paper in the present invention and Cu 2+ Linear relationship with concentration.
[0039] Figure 14 It is the standard colorimetric card for fluorescent test paper in the present invention.
[0040] Figure 15 This is the image under a UV flashlight after adding a real water sample to the fluorescent test paper. DETAILED DESCRIPTION
[0041] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the present invention. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.
[0042] Example 1: Preparation of carbon dots N-CDs
[0043] Carbon dots (N-CDs) were prepared by mixing 0.44 g of citric acid as a carbon source and 0.91 mL of diethylenetriamine as a nitrogen source in 20 mL of ultrapure water. After being ultrasonicated, the mixture was carbonized in a microchannel reactor at 200°C and 3.80 MPa. The solution was then dialyzed for 24 hours using a dialysis bag with a molecular weight cutoff of 500 to obtain the final light yellow N-CDs, which exhibited a strong blue fluorescence effect under ultraviolet light. Under an excitation wavelength of 360 nm, the maximum fluorescence intensity was at an emission wavelength of 440 nm ( Figure 1 ).
[0044] Example 2: Carbon dot N-CDs on Cu 2+ Detection
[0045] After diluting the carbon dots 150 times, different concentrations of copper ions (0.1, 0.08, 0.06, 0.04, 0.02 mol / L) were added to the carbon dot solution and allowed to stand for three minutes until the reaction was complete. 2+ The fluorescence intensity of the carbon dot solution decreased significantly when Cu 2+ The higher the concentration, the more obvious the quenching effect. Using a fluorescence spectrophotometer to measure the fluorescence intensity, it can be observed that the fluorescence intensity gradually decreases with the increase of copper ion concentration, and there is a good linear relationship ( Figure 2 ), proving that the carbon dots can achieve quantitative and high-precision detection of copper ions.
[0046] Example 3: Carbon dots N-CDs on Cu 2+ Selectivity of detection
[0047] Quantitative detection of Cu using carbon dots N-CDs as a fluorescent probe 2+ , the selectivity of carbon dots to other metal ions must be considered. Take equal volumes and concentrations of Cu 2+ 、Fe 3+ 、Cd 2+ Mg 2+ , Ca 2+ 、Mn 2+ 、Zn 2+ 、Ba 2+ , Pb 2+ , K + 、Na + The carbon dots solution was mixed with the carbon dots solution in a volume ratio of 1:1, and the maximum fluorescence intensity of the carbon dots after adding each metal ion was recorded at an excitation wavelength of 365 nm and an emission wavelength of 440 nm. The other metal ions had almost no effect on the fluorescence intensity of the carbon dots, while the addition of Cu 2+ The fluorescence intensity dropped significantly after the experiment, which was obviously different from the blank control. However, the other metal ions were almost the same as the blank control data ( Figure 3 ), which proves that carbon dots have good selectivity for copper ions and can be used for Cu 2+Specific detection.
[0048] Example 4: Preparation of carbon dot N-CDs fluorescent test paper
[0049] Cellulose test paper was cut into squares with a side length of 22.20 mm and soaked in a carbon dot solution for 30 minutes to ensure that the carbon dots were evenly distributed on the test paper. The test paper was taken out and placed in a culture dish and dried in a 60°C oven until completely dry, thus obtaining a fluorescent test paper for detecting copper ions.
[0050] Example 5: Characterization and testing of carbon dot fluorescent test paper
[0051] It can be observed that N-CDs has an absorption peak at 350nm ( Figure 4 ), which is different from the maximum emission wavelength of its emission spectrum, proving that there is no obvious overlap between the absorption spectrum and fluorescence emission spectrum of the carbon dots. According to the nanoparticle size and Zeta potential, it can be seen that the obtained PDI is relatively large and there is a small amount of agglomeration ( Figure 5-Figure 6 ).
[0052] According to TEM test results, N-CDs are spherical nanoparticles with good dispersion ( Figure 7 ), and its particle size distribution range is relatively narrow (12-21nm), and its average particle size is about 16.55nm ( Figure 8 ), the narrow particle size distribution of N-CDs provides them with good fluorescence properties.
[0053] According to the FT-IR test results, N-CDs at 3308 cm -1 and 2383cm -1 The absorption peak at 1635 cm is consistent with the stretching vibration of OH and NH, indicating that N-CDs have good water solubility and contain amino groups on the surface. -1 The absorption peak at 1418 cm is related to the typical C=N stretching vibration. -1 The absorption peak at is a typical C=C stretching vibration ( Figure 9 ), which is due to the establishment of unsaturated aromatic ring structures during the microchannel processing. These functional groups prove that N-CDs have good water solubility and can be evenly distributed on the test paper.
[0054] Example 6: Fluorescent test paper to Cu 2+ Detection
[0055] To ensure the accuracy of the experimental data, an inscribed circle was drawn in a square fluorescent test paper with a side length of 22.22 mm. 1 mL of Cu 2+ Add it dropwise at the center of the inscribed circle and wait for 3 minutes for the reaction to be complete before observing. The fluorescent test paper without Cu2+ has a strong blue fluorescence ( Figure 10 ), fluorescent carbon dots along with Cu 2+ As the concentration increases, the fluorescence quenching reaction becomes more obvious, and the blue fluorescence of the test paper decreases more significantly as can be observed with the naked eye ( Figure 11 ). Combined with Cu 2+ The linear relationship between the concentration and the fluorescence intensity of the carbon dot solution, Cu 2+ The linear relationship between the concentration and the fluorescence intensity of the test paper ( Figure 12 ), Cu 2+ The linear relationship between concentration and RGB value of test paper ( Figure 13 ), it can be observed that the slopes and intercepts of the three linear relationships are in multiples and have strong comparability. It can be concluded that the present invention has the characteristics of visual, efficient and accurate quantitative detection of Cu 2+ effect.
[0056] Example 7: Preparation of colorimetric card
[0057] Add different concentrations of Cu on the fluorescent test paper 2+ The solution was placed under a 365nm UV flashlight, photographed with a smartphone, and analyzed using Photoshop. The obtained RGB values were compared with the Cu 2+ The linear relationship of concentration, the different color cards generated correspond to different Cu 2+ Concentration, that is, the color card ( Figure 14 ), through the color change of fluorescent test paper, it can be combined with the color card to measure Cu 2+ Perform quantitative analysis.
[0058] Example 8: Real water sample test
[0059] The real water sample was taken from the laboratory tap water pipe, and it was dropped into the center of the circle inscribed on the fluorescent test paper. After standing for 3 minutes, it was placed under a 365nm fluorescent flashlight. It was observed that the color of the test paper hardly changed ( Figure 15 ).
Claims
1. Carbon dots N-CDs are prepared by the following method, characterized in that : i) mixing citric acid and diethylenetriamine, adding the mixture to ultrapure water, and sonicating until the citric acid is completely dissolved; ii) placing the solution in a microchannel reactor and carbonizing it under a certain temperature, pressure, and flow rate, and dialyzing the solution using a dialysis bag to obtain the final N-CDs.
2. The carbon dots N-CDs according to claim 1, characterized in that: The optimal molar ratio of the citric acid to the diethylenetriamine is 1:(4-5).
3. The microchannel reactor according to claim 1, wherein: The optimal temperature, pressure and flow rate ranges are 170-240° C., 0.5-4.0 MPa, and 5-40 mL / min.
4. The carbon dots N-CDs described in claim 1 are used as fluorescent probes to detect Cu 2+ Application in this area.
5. Carbon dot N-CDs fluorescent test paper was prepared by the following method: i) Cutting the cellulose test paper into squares and soaking it in the carbon dot solution to ensure that the carbon dots are evenly distributed on the test paper; ii) taking out the test paper and placing it in a culture dish, and drying it in an oven until it is completely dry, thereby obtaining a fluorescent test paper for detecting copper ions.
6. The N-CDs fluorescent test paper according to claim 6, characterized in that: According to Cu 2+ The fluorescence quenching reaction with N-CDs was visually observed as a color change of the test paper.
7. The colorimetric card is prepared by the following method: i) Different concentrations of Cu 2+ The fluorescent test paper uses a smartphone to pick up the color, and Photoshop is used to extract the RGB value of the image; ii) Generate different Cu according to RGB values 2+ The color card below is formed to form a color comparison card that can be used with fluorescent test paper.
8. The colorimetric card according to claim 5, characterized in that: Draw Cu 2+ The linear relationship with RGB values can be used to determine the different Cu 2+ RGB values under different concentrations, thus achieving instant and accurate detection.
9. The colorimetric card according to claim 6, characterized in that: The color picking process is carried out under a 365 nm fluorescent flashlight, which is consistent with the detection wavelength of the fluorescence spectrophotometer, and the irradiation angle and irradiation area are fixed during color picking.
10. The fluorescent test paper and colorimetric card according to claims 5-7, characterized in that: When using a smartphone to capture color, the camera parameters such as shutter time, aperture, and sensitivity must remain constant.