A nitrogen-doped carbon quantum dot fluorescent probe and its preparation method and application

Abstract

This invention discloses a nitrogen-doped carbon quantum dot fluorescent probe, its preparation method, and its application. Nitrogen-doped carbon quantum dots with a particle size of 4.76 ± 0.3 nm, a fluorescence emission spectrum of 400-550 nm, and a quantum yield of 73.77% were synthesized using a one-step hydrothermal method with 2-aminoterephthalic acid. The product was characterized using high-magnification transmission electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and thermogravimetric analysis. The nitrogen-doped carbon quantum dots provided by this invention exhibit stable fluorescence emission properties, and the fluorescence intensity changes can be used to detect K+ ions. + and Fe 3+ Detection of ions; for K + and Fe 3+ The linear detection ranges for the ions are 1–10 and 5–85 μmol / L, respectively, with detection limits of 0.5 and 0.8 μmol / L, respectively. The nitrogen-doped carbon quantum dot preparation method provided by this invention is simple, low-cost, environmentally friendly, and exhibits strong and stable fluorescence luminescence properties, showing great application potential.

Description

Technical Field

[0001] This invention relates to the field of carbon quantum dot fluorescent probe technology, specifically to a nitrogen-doped carbon quantum dot fluorescent probe, its preparation method, and its application. Background Technology

[0002] Traditional semiconductor quantum dots often contain metal ions such as lead and cadmium. Due to the varying degrees of toxicity of metals to organisms and their significant environmental impact, their application in biological systems is difficult. Carbon quantum dots (CQDs) are a novel type of zero-dimensional carbon nanomaterial that possesses excellent fluorescence properties similar to semiconductor quantum dots. However, their preparation raw materials are typically metal-free organic compounds, making them widely available, inexpensive, low-toxicity, and environmentally friendly. Furthermore, the abundant hydrophilic groups (hydroxyl, carboxyl, etc.) on the surface of carbon quantum dots ensure their good water solubility. Therefore, carbon quantum dots are widely used in fields such as bioimaging, photocatalysis, optoelectronic devices, and fluorescent probes.

[0003] Potassium (K) + Potassium (K) is one of the most abundant elements in human cells. It regulates the appropriate osmotic pressure and acid-base balance of body fluids, participates in the metabolism of sugars and proteins within cells, maintains nerve health and a normal heartbeat, and assists in normal muscle contraction. A normal human body contains approximately 175 grams of potassium, 98% of which is stored as potassium ions in the cellular fluid; serum contains 3.5–5.5 mmol / L of potassium. When the potassium level in human serum reaches a certain level... + When the concentration of potassium ions is below 3.5 mmol / L, symptoms such as tachycardia and arrhythmia, nausea and vomiting, diarrhea, and muscle aches may occur; while excessively high concentrations of potassium ions may cause other symptoms. + Concentrations can cause the heart to beat too slowly or too fast; concentrations exceeding 7 mmol / L can even cause cardiac arrest. Therefore, establishing a sensitive and effective detection method for K is crucial. + Ionic methods are essential.

[0004] Currently, K + Methods for detecting ions mainly include atomic absorption spectrometry, spectrophotometry, and ion chromatography. These methods generally suffer from drawbacks such as complex instrument operation, long detection times, and high costs, limiting their application. Compared to these methods, fluorescence analysis has become a research hotspot due to its advantages of high sensitivity, strong selectivity, and ease of use. In recent years, although methods utilizing carbon quantum dots as fluorescent probes for the detection of Fe have emerged... 3+ Cu 2+ Co 2+ Sn 2+ Methods involving metal ions, but currently only applicable to the detection of K. + Fluorescent probes for detecting K ions are rarely reported. Therefore, developing a probe capable of detecting K ions is crucial. + Fluorescent probes for ions are of great significance. Summary of the Invention

[0005] The purpose of this invention is to address the limitations of existing technologies that can be used to detect K. + To address the shortcomings of nitrogen-doped carbon quantum dot fluorescent probes, such as the lack of ion-based carbon quantum dot fluorescent probes, this application provides a nitrogen-doped carbon quantum dot fluorescent probe, its preparation method, and its application. This quantum dot fluorescent probe exhibits high fluorescence intensity and strong fluorescence response to K+. + Ions exhibit strong fluorescence enhancement response, significant specificity, good stability, and high sensitivity, and are effective against K+. + The detection limit for ions is as low as 0.5 μmol / L.

[0006] To achieve the above-mentioned objectives, the present invention employs the following technical solution:

[0007] A method for preparing a nitrogen-doped carbon quantum dot fluorescent probe includes the following steps:

[0008] Step 1: Add 2-aminoterephthalic acid (2-ATA) to deionized water and ultrasonically treat it at room temperature using an ultrasonic cleaner to obtain a mixture.

[0009] Step 2: Transfer the mixture obtained in Step 1 into the lining of a high-pressure reactor, seal it, place it in a heating device, raise the temperature from room temperature to 140-200℃, and maintain it for 7-11 hours;

[0010] Step 3: Stop heating and allow the high-pressure reactor to cool naturally to room temperature to obtain a yellow mixture.

[0011] Step 4: Transfer 9.5 mL of the yellow mixture after reaction to a 10 mL centrifuge tube, and place multiple centrifuge tubes symmetrically into a centrifuge for centrifugation; after centrifugation, remove the centrifuge tubes, remove 8 mL of the supernatant, add 8 mL of deionized water, press the tubes against a vortex mixer to mix, and then centrifuge again. Repeat the centrifugation operation 8 times.

[0012] Step 5: Disperse the product after centrifugation and washing in step 4 in deionized water, and treat it with an ultrasonic cleaner at room temperature. After ultrasonic treatment, let it stand for 24 hours, take the supernatant, and dialyze it with a dialysis bag. Take out the product from the dialysis bag and dry it in a vacuum drying oven at 60℃ for 7 days to obtain nitrogen-doped carbon quantum dots.

[0013] Furthermore, in the first step, the amount of 2-ATA used is 0.12-0.20g by mass-to-volume ratio, and the volume of deionized water is 15mL; the ultrasonic cleaner used has a power of 280W, a frequency of 40KHz, and an ultrasonic treatment time of 30 minutes.

[0014] Furthermore, in the second step, the heating device is an oven, and the heating rate is 3℃ / min.

[0015] Furthermore, in the fourth step, the high-speed centrifuge operates at 12,000-15,000 rpm, with each centrifugation lasting 5-10 minutes; the vortex mixer operates at 2,800 r / min, with a mixing time of 1 minute.

[0016] Furthermore, in the fifth step, the volume ratio of the product after centrifugal washing to deionized water is 2:7, the ultrasonic cleaner used has a power of 280W and a frequency of 40KHz, and the ultrasonic treatment time is 30 minutes; the molecular weight cutoff of the dialysis bag is 500-1000Da, and the dialysis time is 48 hours.

[0017] A nitrogen-doped carbon quantum dot fluorescent probe prepared by any of the above preparation methods, wherein the particle size of the nitrogen-doped carbon quantum dot fluorescent probe is 4.76±0.3nm, the optimal excitation wavelength is 354nm, the fluorescence emission spectrum is in the range of 400-550nm, and the fluorescence quantum yield is 73.77%.

[0018] Furthermore, the strongest peak of the fluorescence emission spectrum is at 448 nm.

[0019] This application also discloses nitrogen-doped carbon quantum dot fluorescent probes in K... + Applications in ion detection, for K + The fluorescence linear detection range of the ion is 1-10 μmol / L, and it is effective for K+. + The fluorescence detection limit for ions is 0.5 μmol / L.

[0020] This application also discloses nitrogen-doped carbon quantum dot fluorescent probes in Fe... 3+ Applications in ion detection, for Fe 3+ The fluorescence linear detection range of the ion is 5-85 μmol / L, for Fe 3+ The fluorescence detection limit for ions is 0.8 μmol / L.

[0021] The technical principles involved in this application are explained as follows: Carbon quantum dots have excellent photoluminescence properties. Their fluorescence emission mechanism is generally considered to include quantum size effect, carbon core state, surface state, molecular state, cross-linking enhanced emission effect, and other effects. The surface of nitrogen-doped carbon quantum dots contains a large number of functional groups such as hydroxyl, carboxyl, and amino groups. These functional groups can interact with metal ions, such as forming complexes, inducing quantum dot aggregation, and inducing electron transfer. These interactions can lead to a decrease or enhancement in the fluorescence emission performance of nitrogen-doped carbon quantum dots.

[0022] Compared with the prior art, the beneficial effects of the present invention include:

[0023] 1. This invention uses only 2-aminoterephthalic acid as a raw material and prepares it via a hydrothermal method. The raw material is inexpensive, the preparation operation is simple, and the reaction time is short.

[0024] 2. The obtained product exhibits good environmental stability, stable fluorescence properties, and high selectivity and sensitivity, making it suitable not only for detecting Fe 3+ Fluorescent probes for ions can also be used to detect K + Fluorescent probes for ions hold promise for applications in biological detection and industrial production;

[0025] 3. Currently used for detecting K + Fluorescent probes for K+ ions are rarely reported. The nitrogen-doped carbon quantum dots disclosed in this application can achieve fluorescence probes for K+ ions. + Highly sensitive detection of ions, with a detection limit as low as 0.5 μmol / L;

[0026] 4. Currently, Fe 3+ Most ion fluorescent probes have relatively high detection limits (>5 μmol / L). The nitrogen-doped carbon quantum dot fluorescent probe disclosed in this application has a detection limit for Fe. 3+ The fluorescence detection limit of ions can be as low as 0.8 μmol / L, and it has higher detection sensitivity. Attached Figure Description

[0027] Figure 1 These are high-power transmission electron microscope (HRTEM) images and electron diffraction (SAED) images of the nitrogen-doped carbon quantum dot fluorescent probe of this application, where (a) and (b) are HRTEM images of the obtained quantum dots; (c) is an electron diffraction image; and the inset in (a) is a particle size distribution bar chart.

[0028] Figure 2 The images show the X-ray diffraction (XRD) and photoelectron (XPS) patterns of the nitrogen-doped carbon quantum dot fluorescent probe of this application, where (a) is the XRD pattern; (bd) are the X-ray photoelectron (XPS) patterns; (b) is the C1s pattern; (c) is the O1s pattern; (d) is the N1s pattern; (e) is the Fourier transform infrared (FTIR) spectrum; and (f) is the thermogravimetric (TGA) curve.

[0029] Figure 3 The images show the spectra of the nitrogen-doped carbon quantum dot fluorescent probe of this application, where (a) is the UV-Vis spectrum, excitation spectrum (Ex), and fluorescence emission spectrum (Em) of the nitrogen-doped carbon quantum dot fluorescent probe, (b) is the fluorescence spectrum of the nitrogen-doped carbon quantum dot fluorescent probe at different excitation wavelengths, (c) is the fluorescence spectrum of the nitrogen-doped carbon quantum dot fluorescent probe at different experimental temperatures, and (d) is the fluorescence spectrum of the nitrogen-doped carbon quantum dot fluorescent probe at different solution acidities.

[0030] Figure 4 This is a bar graph showing the fluorescence intensity of the nitrogen-doped carbon quantum dot solution at 448 nm after adding different metal ions to the solution.

[0031] Figure 5 Different concentrations of K were added to the nitrogen-doped carbon quantum dot solution of this application. + Fluorescence spectra and fluorescence intensity linearity plots of ions, where (a) shows the fluorescence intensity of nitrogen-doped quantum dot solutions with different concentrations of K+. + Fluorescence spectra of ions, (b) showing the fluorescence spectrum of ions with added K. + The fluorescence intensity of the ion solution at 448 nm varies with K + Linear graph of ion concentration changes;

[0032] Figure 6 Different concentrations of Fe were added to the nitrogen-doped quantum dot solution of this application. 2+ Fluorescence spectra and fluorescence intensity linearity plots of the ions, where (a) shows the fluorescence intensity of the quantum dot solution with different concentrations of Fe. 2+ Fluorescence spectra of ions, (b) showing the fluorescence spectrum of Fe ions. 2+ The fluorescence intensity of the ion solution at 448 nm varies with K + Linear graph of ion concentration changes. Detailed Implementation

[0033] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0035] Example 1

[0036] A hydrothermal method for preparing, characterizing, and testing the performance of a nitrogen-doped carbon quantum dot fluorescent probe includes the following steps:

[0037] Step 1: Weigh 0.1354g of 2-aminoterephthalic acid (2-ATA), transfer it to an Erlenmeyer flask, add 15ml of deionized water, and ultrasonically treat it for 30 minutes at room temperature using an ultrasonic cleaner with a power of 280W and a frequency of 40KHz to obtain a mixture.

[0038] Step 2: Transfer the mixture obtained in Step 1 into the reactor liner, place the liner into the stainless steel reactor kit, cover it, and tighten the kit cover; place the reactor in an oven, adjust the oven heating rate, raise it from room temperature (20℃) to 140℃ within 40 minutes, and maintain it at 140℃ for hydrothermal reaction for 7 hours.

[0039] Step 3: Turn off the oven power and stop heating. Allow the high-pressure reactor to cool naturally to room temperature to obtain a yellow mixture.

[0040] Step 4: After cooling to room temperature in Step 3, transfer the resulting yellow mixture into several 10mL centrifuge tubes, filling each tube with 9.5mL. Place the tubes symmetrically in a centrifuge and centrifuge at 12000rpm for 10 minutes. After centrifugation, remove the tubes, discard 8mL of the supernatant, add 8mL of deionized water, cap the tubes, and press them against a vortex mixer at 2800rpm for 1 minute. Centrifuge again, repeating the above steps 8 times. After the last centrifugation, discard 7.5mL of the supernatant and retain 2mL of the lower mixture.

[0041] Step 5: Disperse 2 mL of the lower layer mixture after centrifugation and washing in step 4 into 7 mL of deionized water. Sonicate the mixture for 30 minutes at room temperature using an ultrasonic cleaner with a power of 280 W and a frequency of 40 kHz. After sonication, let it stand for 24 hours. Take 4 mL of the supernatant and transfer it to a dialysis bag (with a molecular weight cutoff of 500-1000 Da). Place the dialysis bag in 1 L of deionized water for dialysis for 72 hours, changing the deionized water every 8 hours. After dialysis, remove the product from the dialysis bag and dry it in a vacuum drying oven at 60 °C for 7 days. The dried product obtained is nitrogen-doped carbon quantum dots.

[0042] Step 6: Characterize the morphology of the dialysis product obtained in Step 5 (see attached diagram). Figure 1 The dried product obtained in step five was subjected to chemical structural characterization (see attached). Figure 2 );

[0043] Figure 1 The image shows a high-resolution transmission electron microscope (HRTEM) image of the product. The product is a nanoparticle with a uniform particle size distribution (4.76±0.3 nm) and approximately spherical shape. The core lattice parameters of the nanoparticles are 0.34 and 0.27 nm, and they have obvious electron diffraction patterns. Figure 2In Figure 'a', the X-ray diffraction (XRD) data of the product is shown. The spectrum contains three distinct diffraction peaks, indicating that the product contains crystalline components. The lattice spacings corresponding to two of the diffraction signals are 0.34 and 0.23 nm, which are basically consistent with the HRTEM observations and correspond to the (002) and (100) crystal planes formed by carbon hybridization, respectively. The lattice spacing corresponding to the other diffraction peak is 0.59 nm, which can be attributed to the (101) crystal plane of the graphite carbon structure. Therefore, the XRD results show that the product contains a crystalline graphene structure. Figure 2 The image shows the C1s, O1s, and N1s spectra of the product obtained from X-ray photoelectron spectroscopy (XPS). The figure reveals that the product surface contains structures such as CO, C=O, CN, and C=N, indicating that the nanoparticle surface not only contains oxygen-containing groups such as hydroxyl and carboxylic acid groups, but also nitrogen-containing functional groups such as amino and imino groups. Figure 2 In the figure, e represents the infrared spectrum (FTIR) of the product. It can be seen that in the range of 3000–3500 cm⁻¹... -1 The characteristic absorption peak at 1692 cm⁻¹ is due to the OH / NH stretching vibration. -1 The characteristic absorption peak at 1316 cm⁻¹ belongs to the C=O stretching vibration. -1 The corresponding stretching vibration of CN is 1115 cm. -1 The peak at this point can be attributed to the stretching vibration of C-OH or C=N; further confirmation indicates that the product contains hydroxyl, carboxyl, carbonyl, and amino groups. Based on this, it is inferred that the product is a nanoparticle composed of a crystalline graphene core and an organic shell, exhibiting the structural characteristics of nitrogen-doped carbon quanta; (Attached) Figure 2 Figure f shows the thermogravimetric analysis (TGA) results of the product. As can be seen from the figure, the product should contain about 56% organic shell and about 44% graphene core. Based on the above results, the product is nitrogen-doped carbon nanoparticles.

[0044] Step 7: Prepare a 70 μg / mL aqueous solution from the product obtained in Step 5. Detect the UV absorption spectrum of this aqueous solution using UV-Vis absorption spectroscopy. Detect the fluorescence excitation spectrum and fluorescence generation spectrum of this nitrogen-doped carbon quantum dot aqueous solution using a fluorescence spectrophotometer.

[0045] Figure 3 Figure a shows the ultraviolet-visible spectrum (UV-vis), excitation spectrum (Ex), and fluorescence emission spectrum (Em) of the obtained product. It can be seen from the figure that the product can absorb light near 225 and 346 nm; the strongest peak of its excitation spectrum is at 354 nm, and the strongest peak of its fluorescence emission spectrum is near 448 nm. Figure 3The figures show the fluorescence spectra of the product aqueous solution under different fluorescence excitation wavelengths, ambient temperatures, and acid-base conditions, respectively. It can be seen from the figures that the fluorescence emission spectrum of the product is significantly affected by the excitation wavelength, with the optimal excitation wavelength being between 350-360 nm. Figure 3 (b) The fluorescence emission spectrum is within a certain temperature range (20-80℃). Figure 3 c) Remains stable under certain acidity conditions (pH = 5-8). Figure 3 (d). It can be seen that the obtained nitrogen-doped carbon nanoparticles have strong and stable fluorescence luminescence properties. Therefore, this product can be called nitrogen-doped carbon quantum dots.

[0046] Based on the above results, it can be inferred that the product is a nitrogen-doped carbon quantum dot with stable fluorescence luminescence properties.

[0047] Example 2

[0048] A nitrogen-doped carbon quantum dot fluorescent probe is used for the qualitative detection of metal ions, comprising the following steps:

[0049] Step 1: Prepare 100 mL of a 70 μg / mL aqueous solution of the nitrogen-doped carbon quantum dots obtained in Example 1, and dispense 4 mL portions of this aqueous solution; separately prepare 10 mmol / L Na... + Ag + Al 3+ Co 2+ Fe 3+ Ca 2+ Ni 2+ 、Zn 2+ Mn 4+ K + Cr 3+ Cd 2+ 10 mL of each ionic solution.

[0050] Step 2: Add 40 μL of the different metal ion solutions mentioned in Step 1 to the 4 mL nitrogen-doped carbon quantum dot aqueous solution described in Step 1, shake to mix evenly, let stand for 20 min, and then test its fluorescence spectrum.

[0051] Step 3: Based on the fluorescence spectra of the nitrogen-doped carbon quantum dot aqueous solution before and after the addition of metal ions, calculate F / F0-1 (F represents the fluorescence intensity of the nitrogen-doped carbon quantum dot solution at 448 nm after the addition of metal ions, and F0 represents the fluorescence intensity of the nitrogen-doped carbon quantum dot solution at 448 nm without metal ions); plot a bar chart of (F / F0-1) against different metal ions (see attached). Figure 4 (As shown).

[0052] exist Figure 4In the figure, F / F0 represents the ratio of the fluorescence intensity of the nitrogen-doped carbon quantum dot solution at 448 nm after the addition of metal ions to that of the nitrogen-doped carbon quantum dot solution without metal ions, and F / F0⁻¹ represents the degree of influence of metal ions on the fluorescence intensity of the nitrogen-doped carbon quantum dot solution. Since the percentage of the metal ion solution volume to the nitrogen-doped carbon quantum dot aqueous solution volume is no greater than 1%, the solution volume can be considered constant (the same applies below). Therefore, the concentration of nitrogen-doped carbon quantum dots in the test solution was 70 μg / mL, and the concentration of metal ions was 100 μmol / L; the fluorescence excitation wavelength was 354 nm, the temperature was 25℃, and the pH was 7-8. The figure shows that the addition of most metal ions leads to a decrease in the fluorescence intensity of the nitrogen-doped carbon quantum dot aqueous solution, indicating that these metal ions have a quenching effect on the fluorescence of the product. Among them, Fe... 3+ The ion quenching effect is the strongest, with a 71% decrease in fluorescence intensity; in contrast, K + The fluorescence intensity of the nitrogen-doped carbon quantum dot solution increased by 18% after the addition of ions, instead of decreasing.

[0053] Example 3

[0054] A nitrogen-doped carbon quantum dot fluorescent probe for K + Quantitative detection of ions includes the following steps:

[0055] Step 1: Prepare 100 mL of a 70 μg / mL aqueous solution from the nitrogen-doped carbon quantum dots obtained in Example 1, and dispense 10 portions of this aqueous solution in 4 mL portions; separately prepare 1 mmol / L K... + 200 mL of ionic solution.

[0056] Step 2: Add 0, 4, 8, 12, 16, 20, 24, 32, 36, and 40 μL of the K from Step 1 to the 10 portions (4 mL) of nitrogen-doped carbon quantum dot aqueous solution described in Step 1, respectively. + The ionic solution was shaken to mix thoroughly, and its fluorescence spectrum was measured after standing for 20 minutes.

[0057] Step 3: Analyze the fluorescence spectra of the 10 samples obtained in Step 2 using a fluorescence spectrometer (as shown in the attached image). Figure 5 As shown in Figure a), the F / F0 ratio is calculated based on the fluorescence intensity at 448 nm in the spectrum. The F / F0 ratio is then compared with K... + Ion concentration plot, as shown in the attached figure. Figure 5 As shown in b.

[0058] Depend on Figure 5 It can be seen that the concentration of nitrogen-doped carbon quantum dots in the test solution was 70 μg / mL, the fluorescence excitation wavelength was 354 nm, the temperature was 25℃, and the pH was 7-8. The F / F0 ratio increased with K. +The ion concentration (in the range of 1-10 μmol / L) showed a linear increasing trend, with a linear regression equation of Y = 0.018X + 0.998 and a correlation coefficient R. 2 =0.993, detection limit is 0.5 μmol / L. Clearly, the nitrogen-doped carbon quantum dots prepared in Example 1 can be used as fluorescent probes for K+ in aqueous solutions. + Quantitative detection of ions.

[0059] Example 4

[0060] A nitrogen-doped carbon quantum dot fluorescent probe for Fe 3+ Quantitative detection of ions includes the following steps:

[0061] Step 1: Prepare 100 mL of a 70 μg / mL aqueous solution from the nitrogen-doped carbon quantum dots obtained in Example 1, and dispense 10 portions of this aqueous solution in 4 mL portions; separately prepare 2 mmol / L Fe... 3+ 200 mL of ionic solution and 10 mmol / L Fe 3+ 200 mL of ionic solution.

[0062] Step 2: Add 2 mmol / L Fe to each of the 10 4 mL nitrogen-doped carbon quantum dot aqueous solutions described in Step 1. 3+ Ionic solutions of 0, 10, 20, 30, and 40 μL, and 10 mmol / L Fe... 3+ Ionic solutions of 24, 26, 28, 30, and 34 μL were mixed thoroughly by shaking and allowed to stand for 20 min before their fluorescence spectra were measured.

[0063] Step 3: Use a fluorescence spectrometer to test the fluorescence spectra of the 10 samples obtained in Step 2 (see attached image). Figure 6 In section a), the F / F0 ratio is calculated based on the fluorescence intensity at 448 nm in the spectrum. Then, the F / F0 ratio is used to compare with K. + Plotting ion concentrations yields the attached... Figure 6 b.

[0064] Depend on Figure 6 It can be seen that the concentration of nitrogen-doped carbon quantum dots in the test solution was 70 μg / mL, the fluorescence excitation wavelength was 354 nm, the temperature was 25℃, and the pH was 7-8. The F / F0 ratio increased with Fe. 3+ The ion concentration (in the range of 5-85 μmol / L) showed a linear decreasing trend, with a linear regression equation of Y = -0.0074X + 1.0075 and a correlation coefficient R. 2 =0.999, detection limit is 0.8 μmol / L. Clearly, the nitrogen-doped carbon quantum dots prepared in Example 1 can be used as fluorescent probes for Fe in aqueous solutions. 3+ Quantitative detection of ions.

[0065] Synthesis conditions:

[0066] The experiment found that, under the premise that other experimental conditions remained unchanged, when the amount of 2-ATA varied in the range of 0.13-0.2g, the resulting products had essentially the same structure and properties.

[0067] The experiment found that, under the premise that other experimental conditions remain unchanged, when the hydrothermal reaction temperature varies within the range of 140-200℃, the resulting products have essentially the same structure and properties.

[0068] The experiment found that, under the premise that other experimental conditions remained unchanged, the products obtained had basically the same structure and properties when the hydrothermal reaction time varied between 7 and 11 hours.

[0069] In summary, the method for preparing nitrogen-doped carbon quantum dot fluorescent probes disclosed in this invention is simple to operate, low in cost, and has relatively relaxed synthesis conditions. Furthermore, the product exhibits stable luminescence properties and is effective against K+. + and Fe 3+ Ion detection has a wide linear range and low detection limit, and has promising application prospects.

[0070] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for preparing a nitrogen-doped carbon quantum dot fluorescent probe, characterized in that, Includes the following steps: Step 1: Add 2-aminoterephthalic acid (2-ATA) to deionized water and ultrasonically treat it at room temperature using an ultrasonic cleaner to obtain a mixture; Step 2: Transfer the mixture obtained in Step 1 into the lining of a high-pressure reactor, seal it, place it in a heating device, raise the temperature from room temperature to 140-200℃, and maintain it for 7-11 hours; Step 3: Stop heating and allow the high-pressure reactor to cool naturally to room temperature to obtain a yellow mixture. Step 4: Transfer 9.5 mL of the yellow mixture after reaction to a 10 mL centrifuge tube, and place multiple centrifuge tubes symmetrically into a centrifuge for centrifugation; after centrifugation, remove the centrifuge tubes, remove 8 mL of the supernatant, add 8 mL of deionized water, press the tubes against a vortex mixer to mix, and then centrifuge again. Repeat the centrifugation operation 8 times. Step 5: Disperse the product after centrifugation and washing in step 4 in deionized water, and treat it with an ultrasonic cleaner at room temperature. After ultrasonic treatment, let it stand for 24 hours, take the supernatant, and dialyze it with a dialysis bag. Take out the product from the dialysis bag and dry it in a vacuum drying oven at 60℃ for 7 days to obtain nitrogen-doped carbon quantum dots.

2. The method for preparing a nitrogen-doped carbon quantum dot fluorescent probe according to claim 1, characterized in that: In the first step, the amount of 2-ATA used is 0.12-0.20g by mass-to-volume ratio, and the volume of deionized water is 15mL; the ultrasonic cleaner used has a power of 280W, a frequency of 40KHz, and an ultrasonic treatment time of 30 minutes.

3. The method for preparing a nitrogen-doped carbon quantum dot fluorescent probe according to claim 1, characterized in that: In the second step, the heating device is an oven, and the heating rate is 3℃ / min.

4. The method for preparing a nitrogen-doped carbon quantum dot fluorescent probe according to claim 1, characterized in that: In the fourth step, the high-speed centrifuge operates at 12,000-15,000 rpm, with each centrifugation lasting 5-10 minutes; the vortex mixer operates at 2,800 r / min, with a mixing time of 1 minute.

5. The method for preparing a nitrogen-doped carbon quantum dot fluorescent probe according to claim 1, characterized in that: In the fifth step, the volume ratio of the product after centrifugation and washing to deionized water is 2:

7. The ultrasonic cleaner used has a power of 280W and a frequency of 40KHz, and the ultrasonic treatment time is 30 minutes. The molecular weight cutoff of the dialysis bag is 500-1000Da, and the dialysis time is 48 hours.

6. A nitrogen-doped carbon quantum dot fluorescent probe prepared by any one of the preparation methods described in claims 1-5, characterized in that: The nitrogen-doped carbon quantum dot fluorescent probe has a quantum dot size of 4.76±0.3 nm, an optimal excitation wavelength of 354 nm, a fluorescence emission spectrum in the range of 400-550 nm, and a fluorescence quantum yield of 73.77%.

7. A nitrogen-doped carbon quantum dot fluorescent probe according to claim 6 in K + Its application in ion detection is characterized by: For K + The fluorescence linear detection range of the ion is 1-10 μmol / L, and it is effective for K+. + The fluorescence detection limit for ions is 0.5 μmol / L.

8. A nitrogen-doped carbon quantum dot fluorescent probe according to claim 6 in Fe 3+ Its application in ion detection is characterized by: For Fe 3+ The fluorescence linear detection range of the ion is 5-85 μmol / L, for Fe 3+ The fluorescence detection limit for ions is 0.8 μmol / L.

9. A nitrogen-doped carbon quantum dot fluorescent probe according to claim 6, characterized in that: The strongest peak in the fluorescence emission spectrum is at 448 nm.

Images