Tunable fluorescent dandelion-derived carbon dots and applications thereof

Abstract

The application discloses taraxacum-derived carbon dots with tunable fluorescence and application thereof, and two kinds of carbon dots R-CDs and B-CDs with fluorescent colors can be obtained by high-temperature tuning with taraxacum as a carbon source, thereby creating conditions for double-channel fluorescence detection. The R-CDs can detect the percentage content of water in various organic solvents, and the test paper prepared can be repeatedly used for multiple times. The B-CDs are a multi-mode probe with fluorescence / colorimetric / absorption / RGB identification, and can simultaneously analyze and detect DNP in multiple ways. When a certain concentration of DNP is added into the B-CDs probe solution, a relatively significant fluorescence quenching phenomenon occurs, and the color of the solution becomes yellow. The specific detection of DNP is distinguished from other interfering components (metal ions, biological molecules and aromatic nitro compounds), and the detection method can be verified with each other, thereby improving the accuracy of detection. Meanwhile, the double-channel and multi-modal target detection is realized.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial synthesis and detection technology, specifically involving the synthesis of biomass-derived carbon dots and their application in fluorescence / colorimetric dual-mode analysis and mobile phone integrated detection technology. Background Technology

[0002] Since the 1990s, the unique physical and chemical properties of carbon nanomaterials have attracted widespread research interest. In recent decades, researchers have studied various types of carbon nanomaterials, including graphene, C... 60Carbon dots (CDs), as an emerging carbon nanomaterial, are generally defined as small carbon nanoparticles with a size of approximately 10 nm. Accidentally obtained from the purification of carbon nanotubes, they have been widely applied in biosensors, environmental monitoring, drug delivery, medical imaging, and optoelectronic devices due to their ease of preparation and surface modification, good water dispersibility and photostability, low cytotoxicity, and excellent biocompatibility [He, C.; Xu, P.; Zhang, X.; Long, W. The synthetic strategies, photoluminescence mechanisms and promising applications of carbondots: Current state and future perspective. Carbon, 2022, 186: 91-127.]. It is noteworthy that with the depletion of Earth's resources and ecological damage, current research focuses on developing high-value-added conversions and applications of renewable resources, which is conducive to maintaining sustainable development in harmony with human resources, natural resources, and the environment. However, the synthesis of carbon dots often requires high energy consumption and the use of hazardous chemicals, which not only increases production costs but also violates the fundamental concept of sustainability. Biomass waste, rich in ash, protein, and lignin, is a renewable, environmentally friendly, abundant, and harmless natural organic carbon source. It can effectively replace chemical reagents, fully meeting the needs of environmental protection and sustainable development. Currently, carbon dots have been synthesized from biomass waste such as avocado peel, pulp, ginger, yew, wheat straw, and clover [Fang, M.; Wang, B.; Qu, X.; Li, S.; Huang, J.; Li, J.; Lu, S.; Zhou, N. State-of-the-art of biomass-derived carbon dots: Preparation, properties, and applications. Chin. Chem. Lett., 2023: 108423.]. However, most biomass carbon dots (CDs) exhibit low fluorescence quantum yields, and their fluorescence is mainly concentrated in the blue region. These shortcomings limit the widespread application of biomass-derived carbon dots. In order to find a better source of biomass, we developed a simple solvothermal method using wild dandelion collected outdoors as raw material to prepare high-temperature tunable fluorescent carbon dots with good cost-effectiveness and high fluorescence quantum efficiency as multifunctional probes, which can realize the rapid detection of water percentage in organic solvents and 2,4-dinitrophenol (DNP) in solution.

[0003] Water is one of the basic substances for human survival and the most abundant component in the human body. However, under certain conditions, such as in high-purity organic solvents, anhydrous organic synthesis, pharmaceuticals, and food processing, the presence of water can affect the progress and yield of chemical reactions and reduce reaction products. In these cases, water is also considered a contaminant [Wang, B.; Yuan, X.; Lv, X.; Mei, Y.; Peng, H.; Li, L.; Guo, Y.; Du, J.; Zheng, B.; Xiao, D. Carbon dots-based room-temperature phosphorescent test strip: visual and convenient water detection in organic solvents. Dyes Pigments, 2021, 189:109226.]. Water contamination in organic solvents can also lead to hydrolysis and the formation of unwanted oxidation products, which can damage the organic solvent during storage [Moniruzzaman, M.; Kim, J. N-doped carbon dots with tunable emission for multifaceted application: solvatochromism, moisture sensing, pHsensing, and solid state multicolor lighting. Sens. Actuators B Chem., 2019, 295: 12-21.]. Therefore, detecting water in organic solvents is an essential and crucial step in various fields such as organic synthesis, biopharmaceuticals, and food processing.

[0004] In addition, many nitroaromatic compounds, such as 2,4-dinitrophenol (DNP), a common nitroaromatic compound, are toxic and explosive materials and are also used as raw materials for the synthesis of azo dyes, sulfur dyes and organic pigments [Mondal, T.; Kapuria, A.; Miah, M.; Saha, S. Solubility tuning of alkyl amine functionalized carbon quantum dots for selective detection of nitroexplosive. Carbon, 2023, 209: 117972.]. Furthermore, it is listed as an organic carcinogen and mutagen, exhibiting high toxicity to living organisms [Yuan, X.; Tu, Y.; Chen, W.; Xu, Z.; Wei, Y.; Qin, K.; Zhang, Q.; Xiang, Y.; Zhang, H.; Ji, X. Facile synthesis of carbon dots derived from ampicillin sodium for live / dead microbe differentiation, bioimaging and high selectivity detection of 2,4-dinitrophenol and Hg (II). Dyes Pigments, 2020,175: 108187.]. Because it is listed as a significant pollutant by international environmental authorities and readily infiltrates soil and groundwater, easily remaining in industrial wastewater and causing environmental pollution, the development of convenient and efficient detection methods is urgently needed. Therefore, rapid, highly selective, and sensitive determination of DNP is of great importance. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the application of tunable fluorescence dandelion-derived carbon dots, their fluorescence / colorimetric dual-mode analysis, and mobile phone integrated detection technology.

[0006] Dandelion-derived red / blue emitting carbon dot R-CDs / B-CDs are prepared by the following method:

[0007] 1) Take 10–80 g of dandelion, soak it in 50–400 mL of ethanol for 12–48 h, and heat it under reflux at 40–100 ℃ for 0.5–3 h. Filter it through a filter membrane and set it aside for later use.

[0008] 2) Add 0.1–3 mL of the above dandelion extract to a beaker, then add 7–10 mL of ethanol and stir thoroughly at room temperature to ensure homogeneity;

[0009] 3) The dandelion-derived red light emitting carbon dots (R-CDs) were subjected to isothermal treatment at 100–160 ℃ for 2–10 h and then cooled to room temperature.

[0010] Alternatively, the dandelion-derived blue light emitting carbon dots (B-CDs) can be obtained by isothermal treatment at 180–220 °C for 2–10 h and then cooling to room temperature.

[0011] The extract obtained in step 1) is filtered through a 0.22 μm filter membrane;

[0012] Step 1) The amount of dandelion used was 50 g, the amount of ethanol was 250 mL, the soaking time was 24 h, the reflux temperature was 50 ℃, and the time was 1 h;

[0013] Step 2) The mixing is 2 mL of dandelion extract and 8 mL of ethanol; Step 3) The isothermal treatment is performed at 120 °C for 2 h to obtain dandelion-derived red light emitting carbon dots R-CDs.

[0014] Alternatively, the mixing described in step 2) is a mixture of 0.4 mL of dandelion extract and 9.6 mL of ethanol; the isothermal treatment described in step 3) is a isothermal treatment at 200 °C for 6 h to produce dandelion-derived blue light emitting carbon dots B-CDs.

[0015] The dandelion-derived red-emitting carbon dots (R-CDs) and blue-emitting carbon dots (B-CDs) prepared in step 3) were filtered through a 0.22 μm filter membrane and dialyzed through a 1000 Da dialysis bag.

[0016] The application of the dandelion-derived red-emitting carbon dots (R-CDs) in the preparation of a sensor for detecting water content.

[0017] The water content mentioned refers to the water content in the organic solvent.

[0018] The application of the dandelion-derived blue light-emitting carbon dots B-CDs in the sensing analysis of DNP detection;

[0019] In the aforementioned application, ethylenediaminetetraacetic acid was added when detecting DNP in water.

[0020] The aforementioned sensing analysis includes: fluorescence sensing analysis, colorimetric sensing analysis, and test strip sensing analysis.

[0021] A method for detecting H2O and DNP using dandelion-derived, high-temperature tunable fluorescent carbon dots R-CDs / B-CDs includes:

[0022] 1) Construction of standard curves: R-CDs were mixed with equal volumes of organic solvents (ethanol, acetone, and acetonitrile) as blank groups, and their fluorescence intensity value I0 was measured. R-CDs were mixed with the above organic solvents with different water contents, and the fluorescence intensity value I at 673 nm was measured. The corresponding relative fluorescence intensity value I / I0 was calculated, and a standard curve corresponding to the relative fluorescence intensity value I / I0 and the water percentage was established. Under 365 nm UV light irradiation, 10 μL of ethanol solutions with different water contents were added to R-CDs test paper, photographed, and the color was extracted using Color Grab software. The B / R value was calculated, and a standard curve corresponding to the water percentage in the ethanol solution was established. B-CDs were mixed with water at a volume ratio of 1:2, and their fluorescence intensity value I0 and absorbance value A0 were measured as fluorescence and absorption blank groups, respectively. B-CDs were mixed with DNP aqueous solutions of different known concentrations, and the fluorescence intensity (I) at 425–482 nm and the absorbance (A) at 356 nm were measured. The corresponding relative fluorescence intensity (I / I0) and absorbance difference (ΔA) were calculated, and standard curves were established corresponding to the relative fluorescence intensity (I / I0) and absorbance difference (ΔA) and the DNP concentration in the aqueous solution. Under 365 nm UV light, 10 μL of DNP aqueous solutions of different known concentrations were added to B-CDs test strips, photographed, and the color was measured using Color Grab software. The B / G value was calculated, and a standard curve was established corresponding to the DNP concentration in the aqueous solution. B-CDs were mixed with ethanol solutions of different DNP concentrations at a volume ratio of 1:2, photographed under natural light, and the color was measured using Color Grab software. The G / B value was calculated, and a standard curve was established corresponding to the DNP concentration in the ethanol solution.

[0023] 2) R-CDs fluorescence detection of water content: Mix equal volumes of R-CDs with organic solutions (ethanol, acetone and acetonitrile) containing water to be tested, measure the fluorescence intensity value I and calculate the relative fluorescence intensity value I / I0. The water content in the organic solution to be tested is obtained according to the above standard curve.

[0024] 3) Detection of water content in ethanol using R-CDs test strip fluorescence: Take 10 μL of the ethanol solution with the water content to be tested and drop it onto the R-CDs test strip. Irradiate it under a 365 nm ultraviolet lamp, take a picture and use Color Grab software to extract the color. Calculate the B / R value in the three primary colors RGB and obtain the water content of the ethanol solution to be tested according to the above standard curve.

[0025] 4) B-CDs fluorescence detection of DNP in water: B-CDs and DNP aqueous solution of the concentration to be tested are mixed at a volume ratio of 1:2. The fluorescence intensity value I is measured and the relative fluorescence intensity value I / I0 is calculated. The concentration of DNP in the aqueous solution to be tested is obtained according to the above standard curve.

[0026] 5) Fluorescent detection of DNP in water using B-CDs test strips: Add 10 μL of DNP aqueous solution of the desired concentration to B-CDs test strips, take a picture under 365 nm ultraviolet light, and use Color Grab software to extract the color. Calculate the B / G value and obtain the concentration of DNP in the aqueous solution according to the above standard curve.

[0027] 6) B-CDs were used for colorimetric visualization to detect DNP in water and ethanol respectively: B-CDs were mixed with an aqueous solution of DNP of the desired concentration at a volume ratio of 1:2, and the absorbance value A was measured and the absorbance difference ΔA was calculated. The concentration of DNP in the aqueous solution was obtained according to the above standard curve. B-CDs were mixed with an ethanol solution of DNP of the desired concentration at a volume ratio of 1:2, and the mixture was photographed and the color was measured using Color Grab software. The G / B value was calculated and the concentration of DNP in the ethanol solution was obtained according to the above standard curve.

[0028] In step 1) where the fluorescence change depends on the R-CDs solution, the applicable water percentage ranges for the organic solutions with different known water percentages and in the test solution in step 2) are 10–75% for ethanol solution, 10–65% for acetone solution, and 10–70% for acetonitrile solution; the applicable DNP concentration ranges for the DNP aqueous solutions with different known concentrations in step 1) and in the test aqueous solution in step 3) where the fluorescence change depends on the B-CDs solution are both 0.1–10 μM and 10–1000 μM.

[0029] The applicable concentration range of DNP in the DNP aqueous solution in step 1) and the test aqueous solution in step 4) depending on the change in absorbance of the solution is 3–100 μM; the applicable concentration range of DNP in the DNP ethanol solution of different known concentrations in step 1) and the test ethanol solution in step 5) depending on the change in color of the solution is 3–100 μM and 100–400 μM; the applicable water percentage of the ethanol solution in the ethanol solution of different water percentages in step 1) depending on the change in fluorescence of the R-CDs test paper and the test solution in step 6) is 0.5–20%; the applicable concentration range of DNP in the DNP aqueous solution of different known concentrations in step 1) and the test aqueous solution in step 6) depending on the change in fluorescence of the B-CDs test paper is 3–100 μM and 100–500 μM.

[0030] The optimal response time for the R-CDs and B-CDs solutions to detect water and DNP is 1 min. Invention Details:

[0032] The purpose of this invention is to provide a biomass-derived carbon dot and its synthesis method.

[0033] Another objective of this invention is to develop a method for a multichannel probe by modulating fluorescence through changing the synthesis temperature, and a method for detecting a variety of target analytes.

[0034] When synthesized at temperatures of 120–160 °C, the prepared R-CDs emit red light and exhibit a sensitive response to water molecules in organic solvents. When the synthesis temperature is changed to 180–220 °C, the prepared B-CDs emit blue light, serving as a multi-mode probe capable of simultaneous analysis and detection of DNP using multiple methods (fluorescence / visualization / absorption / mobile app recognition). Adding a certain concentration of DNP to the B-CD probe solution results in significant fluorescence quenching, and the solution color changes from colorless to yellow. Therefore, B-CDs can achieve specific detection of DNP, distinguishing it from other interfering components (metal ions, biomolecules, and aromatic nitro compounds), and the detection method can be cross-validated using both fluorescence and colorimetric modes, improving the accuracy and reliability of the detection. The relative fluorescence intensity I0 / I (I0 and I represent the emission intensity of B-CDs in blank samples and when different concentrations of target analytes are added, respectively), absorbance difference ΔA (ΔA=A-A0, where A and A0 represent the absorbance signal values ​​of B-CDs in blank samples and when different concentrations of target analytes are added, respectively), and the fixed ratio of smartphone RGB recognition all exhibit a good linear relationship with the concentration of DNP. Quantitative analysis of samples with unknown concentrations can be achieved through this linear relationship equation.

[0035] The present invention has the following beneficial effects:

[0036] 1. This invention uses ethanol extract of dandelion as a precursor. After temperature tuning and optimization, dandelion-derived carbon dots R-CDs (red light) / B-CDs (blue light) with different fluorescence emission and stable properties can be obtained.

[0037] 2. This invention utilizes the self-quenching of R-CDs in an aqueous medium and the static (SQE) and dynamic quenching (DQE) mechanisms with water to significantly quench the fluorescence of R-CDs, thereby achieving sensitive sensing of trace amounts of water molecules in organic solvents.

[0038] 3. By utilizing static quenching and fluorescence resonance energy transfer (FRET) between B-CDs and DNPs, the fluorescence, colorimetric, and RGB signal intensity of B-CDs can be altered for smartphone recognition. DNPs significantly reduce the fluorescence intensity of B-CDs while significantly enhancing the absorbance value and the signal at a fixed RGB ratio. This phenomenon of fluorescence quenching accompanied by colorimetric enhancement can be used for colorimetric and multi-mode fluorescence detection of DNPs.

[0039] 4. The dual-channel, multi-mode detection method for water molecules and DNPs in organic solvents constructed in this invention exhibits excellent performance with high selectivity and sensitivity. For fluorescence detection of the percentage of water molecules in ethanol, acetone, and acetonitrile solvents, the detection limits are as low as 0.197%, 0.259%, and 0.187%, respectively; the detection limit for water molecules in ethanol solvent using test strips is as low as 0.341%. For fluorescence, colorimetric, and test strip detection of DNPs in aqueous solutions, the detection limits are as low as 0.068 μM, 2.52 μM, and 2.29 μM, respectively. Furthermore, for the detection of DNPs in ethanol solutions, the detection limit obtained by using RGB color recognition of the solution is as low as 1.21 μM. These results demonstrate significant advantages over previous analytical methods, and are simple to operate, have a fast response, and are low in cost, making them suitable for large-scale application. Attached Figure Description

[0040] Figure 1 A schematic diagram of the synthesis of R-CDs / B-CDs and the principle of the dual-channel multi-mode detection platform.

[0041] Figure 2 Fluorescence spectra of R-CDs obtained at (a) different reaction temperatures, (c) different reaction times, and (e) different precursor-to-anhydrous ethanol solution volume ratios, and corresponding line graphs showing fluorescence intensity changes at different reaction temperatures (b), different reaction times (d), and different precursor-to-anhydrous ethanol solution volume ratios (f) (Inset: corresponding photographs under a 365 nm UV lamp).

[0042] Figure 3 Fluorescence spectra of B-CDs obtained at (a) different reaction times and (c) different volume ratios of precursor to anhydrous ethanol, and corresponding line graphs showing the changes in fluorescence intensity at different reaction temperatures (b) and reaction times (d) (inset: corresponding photographs under a 365 nm UV lamp).

[0043] Figure 4 (a) UV-Vis absorption and fluorescence spectra of R-CDs (Inset: Corresponding images under sunlight and 365 nm UV lamp). (b) 3D spectra of R-CDs. (c) Emission spectra of R-CDs under various excitations (340–390 nm) (Inset: CIE 1931 (x, y) chromaticity diagram of R-CDs). (d) UV-Vis absorption and fluorescence spectra of B-CDs (Inset: Corresponding images under sunlight and 365 nm UV lamp). (e) 3D spectra of B-CDs. (f) Emission spectra of B-CDs under various excitations (340–390 nm) (Inset: CIE 1931 (x, y) chromaticity diagram of B-CDs).

[0044] Figure 5 (a) Fluorescence spectra of R-CDs at different UV irradiation times and AFC-CDs at different (b) UV irradiation times, (c) pH and (d) NaCl salt concentrations (inset: corresponding radar plots).

[0045] Figure 6 The fluorescence response of R-CDs to water (a), the fluorescence response of B-CDs to DNP (b), and the absorbance response of B-CDs to DNP (c) as a function of reaction time.

[0046] Figure 7 (a) Fluorescence spectra of R-CDs after adding various organic solvents and water. (b) Corresponding radial plots. (c) Corresponding photographs taken under UV light.

[0047] Figure 8 The fluorescence spectra of a series of R-CDs with different water percentages in (a) ethanol, (b) acetone and (c) acetonitrile are presented, along with the corresponding linear relationships between the water percentage in (d) ethanol, (e) and (f) acetonitrile and I0 / I, and the corresponding photographs of R-CDs with different water percentages in (g) ethanol, (h) acetone and (i) acetonitrile.

[0048] Figure 9 (a) Selectivity of R-CDs test paper for various organic solvents and water. (b) Repeatable use of R-CDs test paper for humidity sensing. (c) Effect of ethanol solutions with different water percentages on fluorescence quenching of R-CDs test paper.

[0049] Figure 10 Linear relationship between different water percentages in ethanol and B / R ratio.

[0050] Figure 11 FL spectra (a) of B-CDs with 200 μM of various metal ions, biomolecules, and aromatic compounds (including nitro explosives) added, and corresponding UV-lit responses to metal ions (b), biomolecules (c), and aromatic compounds (d), respectively.

[0051] Figure 12 The I0 / I responses of B-CDs to different (a) metal ions (200 μM, blue), (b) biomolecules (200 μM, green), and (c) aromatic compounds (200 μM, yellow) (before and after the introduction of DNP). (d) Fluorescence spectra of B-CDs and the B-CDs + DNP system before and after the introduction of EDTA.

[0052] Figure 13(a) Fluorescence spectra of B-CDs at a series of concentration gradients of DNP (0.1–1000 μM). (b) Scatter plot of fluorescence intensity changes of B-CDs with varying DNP concentration (inset: corresponding photographs under UV light). (c) Linear fit between I0 / I and DNP concentration. (d) Linear fit between emission wavelength of B-CDs and DNP concentration.

[0053] Figure 14 (a) Selectivity of B-CDs test strips for various analytes (metal ions, biomolecules, and aromatic compounds). (b) Effect of aqueous solutions with different DNP concentrations on fluorescence quenching of B-CDs test strips.

[0054] Figure 15 Linear fitting between the color ratio B / G and DNP concentration of B-CDs test strips.

[0055] Figure 16 Photographs of the UV-Vis absorption spectra of B-CDs for various analytes (metal ions, biomolecules, and aromatic compounds) in water (a) and the responses of B-CDs to various metal ions (b), biomolecules (c), and aromatic compounds (including nitro explosives) (d) with 200 μM added.

[0056] Figure 17 (a) Effect of aqueous solutions with different DNP concentrations on the UV spectra of B-CDs. (b) Linear fit between ΔA and DNP concentration in aqueous solution (inset: corresponding photograph under fluorescent light). (c) Linear fit between color ratio G / B and DNP concentration in ethanol (inset: corresponding photograph under fluorescent light). Detailed Implementation

[0057] Example 1: Preparation of R-CDs / B-CDs

[0058] After washing the collected dandelions, dry them to remove surface moisture. Weigh 50 g of dandelion, grind it in a mortar and pestle, add 250 mL of ethanol, and soak at room temperature for 24 h, then reflux at 50 ℃ for 1 h. After soaking, filter through a 0.22 μm filter membrane to obtain the dandelion extract for later use. Figure 1 ).

[0059] To obtain R-CDs / B-CDs with high luminescence efficiency, dandelion extract was used as a precursor, and several important conditions (synthesis temperature, synthesis time, precursor solution concentration, etc.) were optimized during the synthesis process. First, the synthesis temperature was investigated, such as... Figure 2As shown in (a) and (b), CDs synthesized below 160 °C are located in the red light emission region, while CDs synthesized above 160 °C are located in the blue light emission region. Among them, the red CDs synthesized at 120 °C have the highest fluorescence intensity, and the blue CDs synthesized at 200 °C have the highest fluorescence intensity. Therefore, 120 °C was chosen as the condition for synthesizing R-CDs, and 200 °C was chosen as the condition for synthesizing B-CDs.

[0060] Given a fixed synthesis temperature, R-CDs were further optimized. Synthesis times (2 h, 4 h, 6 h, 8 h, and 10 h) were optimized. Figure 2 c, d) and the ratio of dandelion extract to ethanol (0.4:9.6, 0.7:9.3, 1:9, 2:8 and 3:7) Figure 2 Investigations were conducted in steps e and f, revealing that the synthesis time had no significant impact on the fluorescence intensity of R-CDs. Therefore, the shortest investigation time of 2 hours was chosen as the final synthesis time for R-CDs. Furthermore, the fluorescence intensity change tended to level off when the ratio of dandelion extract to ethanol reached 2:8, so a 2:8 ratio was ultimately selected for R-CD synthesis. In summary, the optimal conditions for R-CD synthesis were determined to be heating 2 mL of dandelion extract and 8 mL of ethanol at a constant temperature of 120 °C for 2 hours.

[0061] Similarly, for the synthesis of B-CDs, by optimizing the above key conditions, the optimal conditions for the synthesis of B-CDs were determined to be: 0.4 mL of dandelion extract and 9.6 mL of anhydrous ethanol heated at 200 °C for 6 h in an autoclave. Figure 3 After the R-CDs / B-CDs cooled naturally to room temperature, the solution was purified by centrifugation (6000 rpm, 10 min), filtration (0.22 μm filter membrane), and dialysis (MWCO: 1000 Da, 24 h). Finally, the purified R-CDs / B-CDs were aliquoted into centrifuge tubes, sealed, and stored in a refrigerator at 4 °C.

[0062] Example 2 Optical Characterization of R-CDs / B-CDs

[0063] To study their optical properties, the fluorescence and absorption spectra of R-CDs and B-CDs were first tested. Figure 4 Figure a shows the excitation, emission, and absorption spectra of R-CDs. The broad absorption peak at 211 nm in the absorption spectrum of R-CDs originates from aromatic sp... 2 π-π in the field (C=C, CC) *The transitions, with strong and weak absorption peaks at 400 nm and 650-675 nm, typically correspond to the Soret and q bands of chlorophyll-derived porphyrins, respectively. The optimal excitation wavelength is 610 nm, and the optimal emission wavelength is 673 nm. In the illustration, the R-CDs solution under natural light is dark green, while under UV light it exhibits bright red fluorescence. Figure 4 The three-dimensional mapping spectrum in b and 4c show that the emission wavelength of R-CDs is independent of the excitation wavelength of 570-630 nm, indicating that R-CDs are not excitation-dependent. Figure 4 (c) The illustration shows that the CIE chromaticity indicates that the fluorescence color of R-CDs under different excitations is in the red light range. Figure 4 (d) shows the excitation, emission, and absorption spectra of B-CDs. The prominent absorption band at 258 nm in the absorption spectrum of B-CDs is attributed to the typical π-π... * Transition. The optimal excitation wavelength is 350 nm, and the optimal emission wavelength is 423 nm. In the illustration, the B-CDs solution under natural light is light brown, while it shows bright blue fluorescence under ultraviolet light. Figure 4 The three-dimensional mapping map of e and Figure 4 The emission spectra under different excitations show that the emission wavelength of B-CDs depends on the excitation wavelength of 300–400 nm, with a slight redshift between 408–474 nm, indicating that B-CDs have obvious excitation dependence, which can be attributed to the heterogeneity of their surface functional groups. Figure 4 The illustration shows that the CIE chromaticity reveals that the fluorescence colors of B-CDs under different excitations are all within the blue light range.

[0064] Example 4: Stability Analysis of R-CDs / B-CDs

[0065] Considering the crucial importance of probe fluorescence stability for practical applications, the effects of pH, NaCl salt ionic strength, and UV irradiation duration on the fluorescence intensity of R-CDs / B-CDs were investigated. After continuous irradiation under a 365 nm UV lamp for 6 h, the fluorescence intensity of R-CDs showed no significant change. Figure 5 a) indicates that R-CDs have stable resistance to photobleaching. B-CDs were continuously irradiated under a 365 nm UV lamp for 6 h ( Figure 5 b) PBS buffer solution with a pH range of 2-12 ( Figure 5 c) and salt solutions with NaCl concentrations in the range of 0.2-1 M ( Figure 5 No significant changes in fluorescence intensity were observed in d), indicating that B-CDs possess excellent optical stability and environmental tolerance. To optimize the sensing performance of R-CDs / B-CDs for water and DNP, the response of incubation time to fluorescence intensity and absorbance was tested. When the fluorescence sensing performance of R-CDs for the solvent water was... Figure 6 a) Fluorescence of B-CDs to DNP ( Figure 6 b) and absorbance response ( Figure 6 c) When both fluorescence intensity and absorbance exceed 1 min, they tend to stabilize. Therefore, 1 min is considered the most suitable fluorescence / colorimetric response time.

[0066] Example 5: R-CDs as fluorescent probes for detecting percentage water content in organic solvents

[0067] R-CDs were used as fluorescent probes to analyze the percentage water content in organic solvents. When a certain amount of water molecules were added to the R-CD probe, a significant fluorescence quenching phenomenon occurred. The relative fluorescence intensity (I0 / I) of the R-CD probe exhibited a good linear relationship with the water content in the organic solvent, allowing for quantitative analysis of organic solvent samples with unknown water content using this linear equation.

[0068] (1) Selectivity of fluorescence method for detecting solvent water

[0069] Since excellent selectivity and anti-interference ability are important indicators for evaluating the sensing performance of fluorescent probes, the selectivity of R-CDs for water molecule detection was studied. The selectivity of R-CDs for water was evaluated by measuring the FL spectra of R-CDs with 18 organic solvents (excluding water) including ethyl acetate (EtAC), petroleum ether (PE), Triton (TX-100), N,N-dimethylformamide (DMF), acetone (Ace), dimethyl sulfoxide (DMSO), dichloromethane (DCM), triethylene glycol (TEG), cyclohexane (CYH), toluene (Tol), methanol (MeOH), chloroform (TCM), tetrahydrofuran (THF), ethanol (EtOH), acetonitrile (ACN), isopropanol (IPA), tetraethyl orthosilicate (TEOS), and n-hexanol (n-HA)). Figure 7 a). The results showed that the presence of organic solvents did not cause significant fluorescence changes in R-CDs; only the addition of water resulted in a significant decrease in fluorescence intensity. The intensity-normalized radial plot more clearly demonstrated the degree of quenching of R-CDs by DNPs. Figure 7 b) Using the fluorescence intensity after adding ethanol as the standard, the quenching rate of R-CDs after adding water reached as high as 93.7%, which was also confirmed by corresponding photographs taken under ultraviolet light. Figure 7 c) This has been confirmed. In summary, R-CDs exhibit excellent selectivity for the solvent water.

[0070] (2) Sensitivity of fluorescence method for detecting water in organic solvents

[0071] Based on the excellent selectivity of R-CDs fluorescent probes for water, the sensitivity of R-CDs for detecting water content in EtOH, Ace, and ACN solvents was further investigated. Equal volumes of R-CDs were mixed with three organic solvents with different water contents, and after reacting for 1 min, the fluorescence response of R-CDs to different water contents in the organic solvents was monitored by fluorescence spectroscopy to verify its sensitivity. Figure 8 As can be seen from the ac, the fluorescence intensity of R-CDs at 673 nm gradually decreases with the increase of the organic solvent water content. Figure 8 The df graph more clearly shows the decreasing trend of fluorescence intensity, which is consistent with the decrease in fluorescence intensity of the sample under UV light in the inset. Calculations show a good linear relationship between the relative fluorescence intensity I / I0 in EtOH, Ace, and ACN solvents and the water percentage in the ranges of 10–75%, 10–65%, and 10–70%, respectively. Figure 8 Based on the formula 3σ / k (σ is the standard deviation of the detection method relative to the blank solution, and k is the slope of the linear equation of the detection method), the detection limits for water content in EtOH, Ace, and ACN solvents are calculated to be as low as 0.197%, 0.259%, and 0.187%, respectively. Therefore, R-CDs can be used as fluorescent probes for detecting water content in organic solvents based on different organic systems, enabling rapid, accurate, and real-time detection in organic solvents.

[0072] Example 6: R-CDs test paper as a fluorescent probe for detecting the water content in EtOH

[0073] The preparation method of R-CDs fluorescent test strips is as follows: Cut filter paper into small squares of the same size (1.5 cm × 1.5 cm), immerse them in R-CDs stock solution for 10 min, remove and air dry to obtain R-CDs test strips for the next experiment. When 10 μL of water-containing EtOH is added to the R-CDs test strip, a significant fluorescence quenching phenomenon occurs. The fixed color ratio B / R of the R-CDs test strip has a good linear relationship with the water content in EtOH, and quantitative analysis of EtOH samples with unknown water content can be performed through the linear relationship equation.

[0074] (1) Evaluation of the selectivity of R-CDs test paper to solvent water

[0075] The selectivity of R-CDs test strips to water was investigated. 10 μL of each of 19 other organic solvents, including water, was added to the R-CDs test strips, and the fluorescence changes were observed to evaluate the selectivity of the R-CDs test strips to water. Figure 9a). The results showed that the presence of organic solvents did not significantly attenuate the fluorescence of the R-CDs test strips; only the addition of water caused significant fluorescence quenching. This indicates that the test strip perfectly retains the function of R-CDs and exhibits rapid and specific selectivity to water. Notably, the R-CDs test strips, after being quenched by water, immediately regained their fluorescence upon drying and can be reused multiple times without altering their detection performance, making them both environmentally friendly and low-cost. Figure 9 b).

[0076] (2) Sensitivity assessment of R-CDs test strips for detecting water percentage in EtOH

[0077] Based on the selectivity of R-CDs test paper for water solvent, the sensitivity of R-CDs test paper for detecting the water percentage in EtOH solvent was further studied. 10 μL of EtOH with different water percentages were added to R-CDs test paper, and the phenomena were observed by photographing under a 365 nm UV lamp. Figure 9 As shown in Figure c, with the increase of water content in EtOH, the fluorescence intensity of the R-CDs test strip exhibits a noticeable fluorescence quenching that can be observed with the naked eye. Color sampling and calculation using the Color Grab mobile app show a good linear relationship between the B / R ratio in EtOH and the water content in the range of 0.5–20%. Figure 10 According to the formula 3σ / K, the detection limit of R-CDs test paper for water content in EtOH can be as low as 0.341%. Therefore, R-CDs test paper can also achieve accurate and real-time on-site determination of water content in ethanol.

[0078] Example 7: B-CDs as fluorescent probes for detecting DNP in water

[0079] Using B-CDs as fluorescent probes, DNP in water can be analyzed. When a certain concentration of DNP is added to the B-CDs probe solution, a significant fluorescence quenching phenomenon occurs. The relative fluorescence intensity (I0 / I) of the B-CDs fluorescent probe has a good linear relationship with DNP in water. The linear relationship equation can be used to quantitatively analyze samples with unknown concentrations of DNP.

[0080] (1) Evaluation of selectivity and anti-interference of DNP detection by fluorescence method

[0081] The sensing performance was investigated under optimized conditions. Tests were conducted by adding 200 μM of 15 common metal ions (Ca) to a B-CDs solution at a volume ratio of 1:2 (B-CDs: analyte). 2+ Fe 2+ Ba 2+ Pb 2+ Cd 2+ Co2+ Zn 2+ Ni 2+ Fe 3 + Ag + Cr 3+ Mn 2+ Hg 2+ Cu 2+ and Mg 2+ The selectivity for DNP was evaluated by examining the fluorescence spectra of 18 biomolecules (Ser, Citn, Trp, DA, Cys, Phe, Met, Glu, GSH, AA, Lys, Leu, Ur, UA, Glc, Thr, Asp, and His) and 9 aromatic compounds (o-nitrophenol (2-NP), m-nitrophenol (3-NP), p-nitrophenol (4-NP), 2,4-dinitrophenol (DNP), nitrobenzene (NB), trinitrophenol (TNP), toluene (Tol), p-nitrotoluene (4-NT), and m-nitrotoluene (3-NT)). A significant decrease and slight redshift in the FL intensity of DNP were observed. Figure 11 a). In contrast, the effects of other samples on the fluorescence intensity of B-CDs were negligible, and the corresponding photographs under UV light confirmed the same conclusion. Figure 11 (bd). Subsequently, the anti-interference performance of B-CDs was evaluated by determining the ratio (B-CDs / DNP / other interfering substances) to 1:1:1 and measuring FL to ensure its practical application feasibility. (Except for interfering ions Hg) 2+ and Ag + The fluorescence intensity of B-CDs decreased sharply after the addition of DNP, which fully demonstrates that, in addition to Hg, 2+ Ag + The coexistence of other interfering substances will not hinder the monitoring of DNP. Figure 12 ac). Here, ethylenediaminetetraacetic acid (EDTA) is chosen as the masking agent, following the introduction of Hg. 2+ Ag + After adding 10 μL of saturated EDTA, the fluorescence decreased to normal levels, confirming that the probe's anti-interference ability is undeniable with the help of the masking agent. Figure 12 d). Furthermore, this masking agent will not disrupt the fluorescence of B-CDs and the B-CDs + DNP system, thus avoiding interference, and can be used with confidence.

[0082] (2) Sensitivity of DNP detection by fluorescence method

[0083] The sensitivity of B-CDs to DNP was investigated, and the fluorescence intensity (λ) of B-CDs was recorded in the presence of a series of DNP concentration gradients.em = 425-482 nm). When the concentration of DNP gradually increased from 0.1 μM to 1000 μM, a significant decay of the fluorescence spectrum of B-CDs was observed, accompanied by a regular red shift. Figure 13 a). Figure 13 b more clearly shows the trend of fluorescence quenching, which is consistent with the trend of fluorescence intensity change of the sample under UV light. Figure 13 (b. Illustration) Within the ranges of 0.1–10 μM and 10–1000 μM, the fluorescence quenching of B-CDs exhibited a linear relationship with increasing DNP concentration. Figure 13 c). Based on 3σ / k, the detection limit was as low as 0.068 μM. It is noteworthy that the fluorescence spectra of B-CDs exhibited a linear relationship of regular redshift under a series of DNP concentration gradients. Figure 13 d). This regular redshift sensing phenomenon provides a strong guarantee for the feasibility of detecting DNP using B-CDs fluorescent probes.

[0084] Example 8: B-CDs test strips as fluorescent probes for detecting DNP in water

[0085] B-CDs test strips were prepared using the same method as R-CDs test strips. When 10 μL of a certain concentration of DNP was added to the B-CDs test strip, a significant fluorescence quenching phenomenon occurred. The fixed colorimetric ratio B / G of the B-CDs test strip showed a good linear relationship with the water content in EtOH, allowing for quantitative analysis of samples with unknown DNP concentrations using this linear equation.

[0086] (1) Selectivity assessment of DNP detection by B-CDs test strips

[0087] The selectivity of B-CDs test strips for DNP was investigated by adding 10 μL of the above analytes to each B-CDs test strip and observing the fluorescence changes to evaluate the selectivity of B-CDs test strips for DNP. Figure 14 a) The results showed that other analytes did not cause significant quenching of the fluorescence of B-CDs test strips. Only the addition of DNP caused significant fluorescence quenching of B-CDs, indicating that the test strip has good selectivity for DNP.

[0088] (2) Sensitivity assessment of B-CDs test strips for detecting DNP

[0089] Based on the selectivity of B-CDs test strips for DNP, the sensitivity of B-CDs test strips for DNP detection was further studied. 10 μL of different concentrations of DNP were added to B-CDs test strips, and the results were observed and compared under a 365 nm UV lamp. Figure 14As shown in Figure b, with the increase of DNP concentration, a relatively obvious fluorescence quenching can be observed in the fluorescence intensity of the B-CDs test strip. Color Grab sampling and calculation revealed a good linear relationship between the B / G value and the concentration of DNP in the aqueous solution in the ranges of 3–100 μM and 100–500 μM. Figure 15 According to the formula 3σ / K, the detection limit of B-CDs test strips for DNP in aqueous solution is as low as 2.29 μM. Therefore, B-CDs test strips can also achieve accurate and real-time on-site determination of DNP.

[0090] Example 9: B-CDs as colorimetric probes for the detection of DNP in water and ethanol

[0091] In addition to fluorescence response, B-CDs also exhibit colorimetric response to DNP. To investigate the colorimetric selectivity of B-CDs for DNP, the aforementioned analytes were selected and mixed with B-CDs as substrates for observing absorbance signals and color changes. The absorbance difference ΔA of the B-CD colorimetric probes showed good linear relationships with the DNP concentration in water, and the color ratio G / B of the probes showed good linear relationships with the DNP concentration in ethanol. This linear equation allows for quantitative analysis of DNP samples with unknown concentrations.

[0092] (1) Selectivity assessment of DNP detection by B-CDs colorimetric method

[0093] To investigate the colorimetric selectivity of B-CDs for DNP, the analyte was added to B-CDs at a volume ratio of 1:2 (B-CDs: analyte), and the absorbance signal and color change were observed to evaluate the selectivity of B-CDs for DNP. Figure 16 As shown in Figure a, the presence of other analytes did not significantly alter the absorbance signal of the B-CDs solution. Only the addition of DNP resulted in a significant increase in the absorbance signal value of B-CDs. Figure 16 (bd) The observed responses of B-CDs to metal ions, small biomolecules and aromatic compounds under fluorescent light are consistent, indicating that the probe has excellent colorimetric selectivity for DNP.

[0094] (2) Sensitivity of B-CDs colorimetric detection of DNP

[0095] Based on the good colorimetric selectivity of B-CDs for DNP, the sensitivity of B-CDs for DNP detection in water was further investigated. DNP aqueous solutions of different concentrations were mixed with B-CDs at a volume ratio (B-CDs: DNP = 1: 2), and the absorbance signals were observed. With increasing DNP concentration, a significant increase in the absorbance curve of B-CDs was observed. Figure 17a). Within the concentration range of 3–100 μM DNP, the absorbance signal of B-CDs increased linearly with increasing DNP concentration in the aqueous solution. Figure 17 b). Based on 3σ / k, the detection limit was as low as 2.52 μM.

[0096] DNP also functions as an acid-base indicator, commonly used to determine available phosphorus in soil, exhibiting a color change from colorless to yellow within a pH range of 2.0 to 4.7. To prevent slight dissociation of water from altering the chemical properties of DNP, high-concentration DNP solutions are typically prepared using ethanol for organic synthesis; therefore, quantitative detection of DNP concentration in ethanol is essential. DNP solutions prepared with ethanol of different concentrations were added to B-CDs solutions at a volume ratio of 1:2 (B-CDs:DNP), and the color changes were observed. Figure 17 As shown in Figure c, a significant color change from colorless to yellow was observed in the solution system as the DNP concentration increased. Analysis of photographs taken under fluorescent light and using a mobile app revealed a linear increase in the colorimetric signal G / B of B-CDs with increasing DNP concentration in ethanol. At lower DNP concentrations (3–100 μM), the linear relationship was Y = 0.0040X + 1.2435 (R0). 2 =0.996). At higher concentrations (100–400 μM), the linear relationship is Y = 0.0013X + 1.5189 (R² = 0.996). 2 =0.998). Based on 3σ / k, the detection limit was as low as 1.21 μM. Therefore, the concentration of DNP in ethanol solutions of unknown concentration can be analyzed by linear equations, enabling quantitative detection of DNP concentration.

[0097] In summary, this work simultaneously achieves dual-channel and multi-modal target detection with good selectivity and high sensitivity, enabling rapid and accurate real-time on-site measurement, and has broad application prospects.

Claims

1. Dandelion-derived red-emitting carbon dots (R-CDs) or blue-emitting carbon dots (B-CDs) are prepared by the following method: 1) Take 10–80 g of dandelion, soak it in 50–400 mL of ethanol for 12–48 h, and heat it under reflux at 40–100 ℃ for 0.5–3 h. Filter it through a filter membrane and set it aside for later use. 2) Add 0.1–3 mL of the above dandelion extract to a beaker, then add 7–10 mL of ethanol and stir thoroughly at room temperature to ensure homogeneity; 3) The dandelion-derived red light emitting carbon dots (R-CDs) were subjected to isothermal treatment at 100–160 ℃ for 2–10 h and then cooled to room temperature. Alternatively, dandelion-derived blue-emitting carbon dots (B-CDs) can be treated at 180–220 °C for 2–10 h and then cooled to room temperature.

2. The dandelion-derived red-emitting carbon dots (R-CDs) or blue-emitting carbon dots (B-CDs) according to claim 1, characterized in that: The membrane filtration described in step 1) is filtration through a 0.22 μm membrane.

3. The dandelion-derived red-emitting carbon dots (R-CDs) or blue-emitting carbon dots (B-CDs) according to claim 2, characterized in that: Step 1) The amount of dandelion used was 50 g, the amount of ethanol was 250 mL, the soaking time was 24 h, the reflux temperature was 50℃, and the time was 1 h.

4. The dandelion-derived red-emitting carbon dots (R-CDs) or blue-emitting carbon dots (B-CDs) according to claim 3, characterized in that: Step 2) involves mixing 2 mL of dandelion extract with 8 mL of ethanol; Step 3) involves isothermal treatment at 120 °C for 2 h to obtain dandelion-derived red light emitting carbon dots (R-CDs). Alternatively, step 2) involves mixing 0.4 mL of dandelion extract with 9.6 mL of ethanol; step 3) involves isothermal treatment at 200°C for 6 h to produce dandelion-derived blue light emitting carbon dots (B-CDs).

5. The dandelion-derived red-emitting carbon dots (R-CDs) or blue-emitting carbon dots (B-CDs) according to claim 4, characterized in that: The dandelion-derived red-emitting carbon dots (R-CDs) and blue-emitting carbon dots (B-CDs) prepared in step 3) were filtered through a 0.22 μm filter membrane and dialyzed through a 1000 Da dialysis bag.

6. The application of the dandelion-derived red-emitting carbon dots (R-CDs) as described in claim 1 in the sensing analysis of water content detection.

7. The application according to claim 6, characterized in that: The water content mentioned refers to the water content in the organic solvent.

8. The application of the dandelion-derived blue-emitting carbon dots B-CDs as described in claim 1 in the sensing analysis of DNP detection.

9. The application according to claim 8, characterized in that: Ethylenediaminetetraacetic acid was added when detecting DNP in water.

10. The application according to claim 6 or 8, characterized in that: The aforementioned sensing analysis includes: fluorescence sensing analysis, colorimetric sensing analysis, and test strip sensing analysis.

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