Method for simultaneous detection and adsorption of iron ions based on chitosan-modified fluorescent carbon quantum dots

Abstract

The application provides a method for simultaneously detecting and adsorbing iron ions based on chitosan modified fluorescent carbon quantum dots, and belongs to the technical field of food safety detection.The preparation method of the chitosan modified carbon quantum dots comprises the following steps: reacting a nitrogen source, a carbon source, chitosan and a solvent to obtain the chitosan modified carbon quantum dots.The method can be used to quickly, sensitively, accurately, stably and selectively detect the content of iron ions, and can also adsorb the iron ions.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of food safety detection, and particularly relates to a method for simultaneously detecting and adsorbing iron ions based on chitosan-modified fluorescent carbon quantum dots. BACKGROUND

[0002] Iron ions, as a kind of metal ions widely used in nature, are essential for maintaining life activities of organisms. However, the excessive presence of iron ions can cause oxidative stress, cell damage and related health risks of chronic diseases. In the food industry, the addition and detection of iron become increasingly frequent, but there are still hidden safety hazards of excessive iron content and failure to detect and remove in time. At present, the detection methods of iron ions include electrochemical inductively coupled plasma mass spectrometry, atomic absorption spectrometry, colorimetric method and fluorescence spectrometry, etc. Although these methods have high sensitivity, they often require sample pretreatment or use multiple reagents, and have certain limitations due to high requirements for instruments and technology.

[0003] In terms of iron ion removal methods, traditional Fe 3+ Most removal methods rely on chemically synthesized adsorption materials. Although these methods have certain removal effects, they often have problems such as poor selectivity, greater environmental impact and poor biocompatibility. For example, although the Prussian blue staining method can show the content of trivalent iron in tissues, it is only suitable for detecting the content of iron ions tightly or loosely combined with proteins, and is not suitable for completely detecting free iron ions. Although the fluorescent probe technology is commonly used in the dynamic detection of iron content in living cells, it also has detection limitations such as complex pretreatment process, high requirements for instruments and detection personnel, etc.

[0004] In view of these defects of the prior art, it is particularly important to develop a rapid and effective method for detecting and removing iron ions to meet the needs of instant monitoring and preventing health risks. SUMMARY

[0005] The present application aims to at least partially solve at least one of the technical problems existing in the prior art. To this end, the present application proposes chitosan-modified carbon quantum dots, a reagent for simultaneously detecting and adsorbing iron ions, a method for simultaneously detecting and adsorbing iron ions and applications thereof. The method of the present application can simultaneously achieve the detection and adsorption of iron ions in the sample to be detected, has strong accuracy and stability of the detection results, high sensitivity, simple operation, and the material is easy to obtain and low in cost, and is suitable for wide application.

[0006] In a first aspect of the present application, a chitosan-modified carbon quantum dot is proposed. According to an embodiment of the present application, the preparation method of the chitosan-modified carbon quantum dot comprises: reacting a nitrogen source, a carbon source, chitosan and a solvent to obtain the chitosan-modified carbon quantum dot.

[0007] The chitosan-modified carbon quantum dots according to the present application can form carbon quantum dots (CQDs) by using aminotrimethyl phosphonic acid as a nitrogen source and citric acid as a carbon source, and the carbon quantum dots contain amino groups and phosphorus / oxygen functional groups which can be combined with Fe 3+ Further, by modifying the carbon quantum dots with chitosan, the chitosan-modified CQDs can form stable interactions with iron ions through the surface functional groups, and the adsorption characteristics of chitosan can achieve effective adsorption of iron ions. Moreover, the use of chitosan-modified carbon quantum dots can improve the specificity of iron ion detection, and thus is suitable for detecting samples with complex components.

[0008] In addition, the surface of the CQDs is rich in hydrophilic functional groups such as carboxyl and hydroxyl groups, which are easily attracted and aggregated in solution through hydrogen bonding. Moreover, the size and shape of the CQDs are different, resulting in uneven steric hindrance effects, and the particles are easily entangled and collided. This leads to poor dispersibility. When using conventional CQDs for fluorescence detection, the fluorescence signal is unstable within a short period of time (e.g., 1 min), and there is obvious precipitation at the bottom of the solution after standing. Aggregation and precipitation can affect the absorption and scattering of light, thereby affecting the intensity of the fluorescence signal. The addition of chitosan can significantly improve the dispersibility and stability of the CQDs, which means that the CQDs can be uniformly distributed in the solution during the detection process, increasing the contact with iron ions and thus improving the sensitivity of the detection. As a result, the detection limit is reduced to as low as 0.0049 μg / mL. Moreover, the CQDs solution with good stability and dispersibility can ensure the consistency of the concentration and distribution of the CQDs in each experiment, which helps to improve the reproducibility of the experimental results, reduces the error, and makes the detection results more accurate. Thus, the present application provides a low-cost and environmentally friendly method for high-sensitivity and selective detection of iron ions.

[0009] According to an embodiment of the present application, the temperature of the reaction is 150-250°C, and the time is 3-7h.

[0010] According to an embodiment of the present application, the carbon source includes aminotrimethyl phosphonic acid.

[0011] According to an embodiment of the present application, the carbon source includes at least one of citric acid and sodium citrate.

[0012] According to an embodiment of the present application, the solvent includes ultrapure water.

[0013] According to an embodiment of the present application, in the mixed solution of the carbon source, the nitrogen source, and the chitosan, the concentration of the aminotrimethyl phosphonic acid is 0.02-0.06 g / mL, and / or the concentration of the citric acid is 0.03-0.07 g / mL, and / or the concentration of the chitosan is 0.03-0.07 g / mL.

[0014] According to an embodiment of the present application, the nitrogen source, the carbon source, the chitosan and the solvent are subjected to ultrasonic treatment before the reaction.

[0015] According to an embodiment of the present application, the ultrasonic treatment is performed for 10-50 minutes.

[0016] According to an embodiment of the present application, after the reaction, the reaction solution is subjected to the following steps: centrifugal treatment of the reaction solution to collect supernatant; dialysis treatment of the supernatant to collect effluent; and drying treatment of the effluent to obtain the chitosan-modified carbon quantum dots.

[0017] According to an embodiment of the present application, the centrifugal treatment comprises centrifuging the reaction solution at a speed of 10000-14000 rpm for 5-15 minutes.

[0018] According to an embodiment of the present application, the dialysis treatment has a molecular weight cut-off of 400-600 Da.

[0019] According to an embodiment of the present application, the drying treatment comprises oven drying.

[0020] In another aspect of the present application, the present application provides a reagent for simultaneously detecting and adsorbing iron ions. According to an embodiment of the present application, the reagent comprises the chitosan-modified carbon quantum dots having amino and phosphorus / oxygen functional groups.

[0021] It is understood by those skilled in the art that the features and advantages described above for the chitosan-modified carbon quantum dots also apply to the reagent for simultaneously detecting and adsorbing iron ions, which will not be repeated here.

[0022] According to an embodiment of the present application, the chitosan-modified carbon quantum dots are selected from the chitosan-modified carbon quantum dots described above.

[0023] According to an embodiment of the present application, the reagent further comprises a Tris-HCl buffer.

[0024] In another aspect of the present application, the present application provides the use of the chitosan-modified carbon quantum dots described above or the reagent for simultaneously detecting and adsorbing iron ions described above in simultaneously detecting and adsorbing iron ions.

[0025] It is understood by those skilled in the art that the features and advantages described above for the chitosan-modified carbon quantum dots also apply to the use, which will not be repeated here.

[0026] In another aspect of the present application, the present application provides a method for simultaneously detecting and adsorbing iron ions, according to an embodiment of the present application, the method comprises: contacting the aforementioned chitosan-modified carbon quantum dots or the aforementioned reagent for simultaneously detecting and adsorbing iron ions with a sample to be detected.

[0027] It can be understood by those skilled in the art that the features and advantages described above for the chitosan-modified carbon quantum dots also apply to the method, which will not be repeated here.

[0028] According to an embodiment of the present application, the fluorescence intensity value of the obtained mixture after the contacting is determined, and based on the fluorescence intensity value, the content of iron ions in the sample to be detected is determined.

[0029] According to an embodiment of the present application, the fluorescence intensity value is determined at 420-460 nm under excitation at a wavelength of 340-370 nm.

[0030] According to an embodiment of the present application, the obtained mixture after the contacting is centrifuged, and the precipitate is collected, so as to obtain carbon quantum dots adsorbed with iron ions.

[0031] According to an embodiment of the present application, the obtained mixture after the determination of the fluorescence intensity value is centrifuged, and the precipitate is collected, so as to obtain carbon quantum dots adsorbed with iron ions.

[0032] According to an embodiment of the present application, the method comprises: reacting the chitosan-modified carbon quantum dots or the reagent for simultaneously detecting and adsorbing iron ions, the sample to be detected and a buffer solution to obtain a mixture.

[0033] According to an embodiment of the present application, the temperature of the reaction is 25-45°C.

[0034] According to an embodiment of the present application, the pH of the reaction is 3.0-5.5.

[0035] According to an embodiment of the present application, the time of the reaction is 0-2 min.

[0036] Additional aspects and advantages of the present application will be partially given in the following description, partially will become obvious from the following description, or will be understood by the practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0037] The above and / or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description of embodiments, taken in conjunction with the accompanying drawings, in which:

[0038] Figure 1 The synthesis of CQDs in Example 1 of the present application and its principle diagram for detecting Fe 3+ ;

[0039] Figure 2The figure is the stability and dispersibility investigation result of CQDs in the embodiment 1 of the present application, wherein (A) is the comparison figure of each group at different time; (B) is the comparison figure of each group at different time;

[0040] Figure 3A The figure is the transmission electron microscope investigation result of CQDs in the embodiment 1 of the present application; Figure 3B The figure is the infrared investigation result of CQDs in the embodiment 1 of the present application;

[0041] Figure 4 The figure is the X-ray photoelectron spectroscopy investigation result of CQDs in the embodiment 1 of the present application, wherein (A) is the XPS spectrum of carbon element; (B) is the XPS spectrum of oxygen element; (C) is the XPS spectrum of nitrogen element; (D) is the XPS spectrum of CQDs;

[0042] Figure 5 The figure is the physical property investigation result of CQDs in the embodiment 1 of the present application, wherein (A) is the particle size investigation result figure; (B) is the zeta potential investigation result figure; 50

[0043] Figure 6 The figure is the fluorescence intensity of CQDs under different excitation in the embodiment 1 of the present application, wherein (A) is the fluorescence intensity without Fe 3+ ; (B) is the fluorescence intensity with Fe 3+ ;

[0044] Figure 7 The figure is the fluorescence spectrum investigation result figure of different components in the embodiment 2 of the present application;

[0045] Figure 8 The figure is the optimization investigation result figure of CQDs for detecting Fe 3+ by the fluorescence spectrometer in the embodiment 3 of the present application, wherein (A) is the temperature optimization investigation result figure; (B) is the pH optimization investigation result figure; (C) is the time optimization investigation result figure;

[0046] Figure 9 The figure is the investigation result figure of CQDs for detecting Fe 3+ in the embodiment 4 of the present application; wherein (A) is the fluorescence intensity investigation result figure of CQDs for detecting different concentration of Fe 3+ ; (B) is the standard curve figure obtained by fitting calculation of (A); (C) is the fluorescence intensity investigation result figure of CQDs before modification for detecting different concentration of Fe 3+ ; (D) is the standard curve figure obtained by fitting calculation of (C);

[0047] Figure 10 The figure is the fluorescence spectrum investigation result figure of CQDs for detecting different samples in the embodiment 5 of the present application. ​DETAILED DESCRIPTION

[0048] Embodiments of the present application are described in detail below. The embodiments described below are examples for explaining the present application and are not to be understood as limiting the present application.

[0049] It should be noted that the terms "first", "second" are used only for descriptive purposes and are not to be construed as indicating or implying relative importance or a specific order of limiting the technical features indicated. Thus, features limited by "first", "second" can explicitly or implicitly include one or more of the features. Further, in the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specified.

[0050] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges or values should be construed to be roughly about the ranges or values. For ranges, the endpoints are included, unless otherwise indicated, and each intervening value between the endpoints is included. For ranges, the endpoints are included, unless otherwise indicated, and each intervening value between the endpoints is included. For single point values, the value is included, unless otherwise indicated, and each intervening point value between the endpoints is included.

[0051] In this document, the terms "comprises" or "comprising" are open-ended, that is, they mean including, but not limited to, the indicated features.

[0052] In this document, the terms "optionally", "optional" or "optional" generally mean that the subsequently described event or circumstance can or can not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.

[0053] In this document, the term "CQDs" is chitosan-modified carbon quantum dots obtained by the method of the present application.

[0054] In this document, the term "pre-modification CQDs" is carbon quantum dots obtained by the preparation of the present application without chitosan.

[0055] Chitosan-modified carbon quantum dots

[0056] In a first aspect, the present application provides a chitosan-modified carbon quantum dot. According to an embodiment of the present application, a preparation method of the chitosan-modified carbon quantum dot comprises: reacting a nitrogen source, a carbon source, chitosan and a solvent to obtain the chitosan-modified carbon quantum dot. The present application synthesizes the chitosan-modified carbon quantum dot, wherein aminotrimethyl phosphonic acid is used as the nitrogen source and citric acid is used as the carbon source to participate in the formation of the CQDs. The inventor surprisingly finds that the chitosan can play a role in detecting and adsorbing iron ions after being added, and the dispersion and stability of the CQDs can be significantly improved after the chitosan is added, and the agglomeration phenomenon is reduced to maintain the suspended state in the solution. Because the surface of the CQDs is rich in hydrophilic functional groups such as carboxyl and hydroxyl groups, the CQDs are easy to attract and agglomerate with each other in the solution through hydrogen bonding, and the size and shape of the CQDs are different, which causes the space steric hindrance effect to be unbalanced, and the particles are easy to collide and entangle with each other, resulting in poor dispersion. When the conventional CQDs are used for fluorescence detection, the fluorescence signal is unstable and there is obvious precipitation at the bottom of the solution after the solution is left to stand for a short time (such as 1 min), and the agglomeration and precipitation can affect the absorption and scattering of light, thereby affecting the intensity of the fluorescence signal. The dispersion and stability of the CQDs can be significantly improved after the chitosan is added, which means that the CQDs can be uniformly distributed in the solution during the detection process, the contact with the iron ions is increased, and the detection sensitivity is improved, thereby reducing the detection limit, and the detection limit can be as low as 0.0049 μg / mL. Moreover, the CQDs solution with good stability and dispersion can ensure that the concentration and distribution of the CQDs are consistent in each experiment, which helps to improve the reproducibility of the experimental results, reduces the error, and makes the detection result more accurate. Thus, a low-cost and environmentally friendly new method for high-sensitivity and selective detection of iron ions is provided.

[0057] According to an embodiment of the present application, the temperature of the reaction is 150-250 ℃, for example, can be 150 ℃, 160 ℃, 170 ℃, 180 ℃, 190 ℃, 200 ℃, 210 ℃, 220 ℃, 230 ℃, 240 ℃, 250 ℃; the time is 3-7 h, for example, can be 3 h, 4 h, 5 h, 6 h, 7 h. Thus, the reaction is sufficient to form the carbon quantum dots.

[0058] According to an embodiment of the present application, the carbon source comprises aminotrimethyl phosphonic acid. Thus, the aminotrimethyl phosphonic acid participates in the formation of the carbon quantum dots as a nitrogen source, and can play the role of the nitrogen source and the phosphorus source.

[0059] According to an embodiment of the present application, the carbon source comprises at least one of citric acid and sodium citrate. Thus, the carbon source participates in the formation of the carbon quantum dots as a carbon source, and can adjust the fluorescence properties of the carbon quantum dots.

[0060] According to an embodiment of the present application, the solvent comprises ultrapure water. Thus, the reaction is provided with a necessary environment.

[0061] According to an embodiment of the present application, the concentration of the aminotrimethyl phosphonic acid in the mixture of the carbon source, the nitrogen source and the chitosan is 0.02-0.06 g / mL, and / or the concentration of the citric acid is 0.03-0.07 g / mL, and / or the concentration of the chitosan is 0.03-0.07 g / mL. Thus, the carbon quantum dots capable of detecting and adsorbing iron ions are synthesized.

[0062] For example, the concentration of the aminotrimethyl phosphonic acid can be 0.02 g / mL, 0.03 g / mL, 0.04 g / mL, 0.05 g / mL or 0.06 g / mL; the concentration of the citric acid can be 0.03 g / mL, 0.04 g / mL, 0.05 g / mL, 0.06 g / mL or 0.07 g / mL; and the concentration of the chitosan can be 0.03 g / mL, 0.04 g / mL, 0.05 g / mL, 0.06 g / mL or 0.07 g / mL.

[0063] According to an embodiment of the present application, the nitrogen source, the carbon source, the chitosan and the solvent are subjected to ultrasonic treatment before the reaction. Thus, the reaction efficiency is improved and the uniform distribution of the reactants is ensured.

[0064] According to an embodiment of the present application, the ultrasonic treatment is performed for 10-50 min. Thus, the reaction efficiency is further improved and the uniform distribution of the reactants is ensured.

[0065] According to an embodiment of the present application, after the reaction, the obtained reaction solution is subjected to the following steps: the reaction solution is subjected to centrifugal treatment to collect supernatant; the supernatant is subjected to dialysis treatment to collect effluent; and the effluent is subjected to drying treatment to obtain the chitosan-modified carbon quantum dots. Thus, the chitosan-modified carbon quantum dots are purified, and the subsequent detection and adsorption of iron ions are not affected by impurities.

[0066] According to an embodiment of the present application, the centrifugal treatment includes centrifuging the reaction solution at a speed of 10000-14000 rpm for 5-15 min. Thus, the chitosan-modified carbon quantum dots with high purity are separated.

[0067] According to an embodiment of the present application, the dialysis treatment has a molecular weight cut-off of 400-600 Da; for example, the molecular weight cut-off can be 400 Da, 500 Da or 600 Da. Thus, small molecular impurities that are not needed are removed, while the carbon quantum dots are retained, and carbon quantum dots with high purity are obtained.

[0068] According to an embodiment of the present application, the drying treatment includes oven drying. Thus, the water is removed, which helps to maintain the chemical stability of the chitosan-modified carbon quantum dots and facilitates storage and transportation.

[0069] Reagent for simultaneously detecting and adsorbing iron ions

[0070] In another aspect of the present application, the present application provides a reagent for simultaneously detecting and adsorbing iron ions. According to an embodiment of the present application, the reagent comprises chitosan-modified carbon quantum dots having amino and phosphorus / oxygen functional groups.

[0071] It is understood by those skilled in the art that the features and advantages described above for the chitosan-modified carbon quantum dots also apply to the reagent for simultaneously detecting and adsorbing iron ions, which will not be repeated here.

[0072] According to an embodiment of the present application, the chitosan-modified carbon quantum dots are selected from the aforementioned chitosan-modified carbon quantum dots.

[0073] According to an embodiment of the present application, the reagent further comprises a Tris-HCl buffer. Thereby, a stable reaction environment is provided, which helps to improve the accuracy and repeatability of the experiment. Illustratively, a purchased Tris-HCl buffer is added to HCl to reach the desired pH, and the pH value of the Tris-HCl buffer is 3-4.

[0074] Application

[0075] In another aspect of the present application, the present application provides an application of the aforementioned chitosan-modified carbon quantum dots or the aforementioned reagent for simultaneously detecting and adsorbing iron ions in simultaneously detecting and adsorbing iron ions. Using the method of the present application, not only can the content of iron ions be detected quickly, sensitively, accurately, stably and with high selectivity, but also iron ions can be adsorbed.

[0076] It is understood by those skilled in the art that the features and advantages described above for the chitosan-modified carbon quantum dots also apply to the application, which will not be repeated here.

[0077] Method for simultaneously detecting and adsorbing iron ions

[0078] In another aspect of the present application, the present application provides a method for simultaneously detecting and adsorbing iron ions. According to an embodiment of the present application, the method comprises: contacting the aforementioned chitosan-modified carbon quantum dots or the aforementioned reagent for simultaneously detecting and adsorbing iron ions with a sample to be tested. Using the method of the present application, not only can the content of iron ions be detected quickly, sensitively, accurately, stably and with high selectivity, but also iron ions can be adsorbed.

[0079] It is understood by those skilled in the art that the features and advantages described above for the chitosan-modified carbon quantum dots also apply to the method, which will not be repeated here.

[0080] It should be noted that the complex environmental sample needs to be simply pretreated before detection to remove floating impurities and insoluble substances, for example, filtered by a filter paper or filter membrane with a pore size of 0.22 μm, and the filtrate is collected. For solid samples, the Tris-HCl buffer solution can be used for dissolution in advance, and the pH value is adjusted to 3.5.

[0081] According to an embodiment of the present application, the fluorescence intensity value of the mixed solution obtained after the contacting is determined, and the iron ion content in the sample to be detected is determined based on the fluorescence intensity value. In this way, the iron ion content can be detected quickly, sensitively, accurately, stably and selectively.

[0082] According to an embodiment of the present application, the fluorescence intensity value is obtained by measuring at 420-460 nm under excitation at a wavelength of 340-370 nm. In this way, the sensitivity, selectivity, accuracy and stability of the detection are ensured.

[0083] According to an embodiment of the present application, the mixed solution obtained after the contacting is centrifuged, and the precipitate is collected to obtain carbon quantum dots adsorbed with iron ions. In this way, the carbon quantum dots adsorbed with iron ions are effectively separated from the mixed solution, which provides convenience for subsequent analysis, application and research.

[0084] According to an embodiment of the present application, the mixed solution after the determination of the fluorescence intensity value is centrifuged, and the precipitate is collected to obtain carbon quantum dots adsorbed with iron ions. In this way, the function of adsorbing iron ions can be achieved while detecting the concentration of iron ions, and the iron ions can be removed from the sample to be detected.

[0085] According to an embodiment of the present application, the method comprises: subjecting the chitosan-modified carbon quantum dots or the reagent for simultaneously detecting and adsorbing iron ions, the sample to be detected and the buffer solution to a standing treatment to obtain a mixed solution. In this way, the effective reaction between the carbon quantum dots and the iron ions in the sample to be detected is ensured.

[0086] According to an embodiment of the present application, the temperature of the reaction is 25-45℃. In this way, the sensitivity, selectivity, accuracy and stability of the reaction are further ensured.

[0087] According to an embodiment of the present application, the pH of the reaction is 3.0-5.5. In this way, the sensitivity, selectivity, accuracy and stability of the reaction are further ensured.

[0088] According to an embodiment of the present application, the time of the reaction is 0-2 min. In this way, the sensitivity, selectivity, accuracy and stability of the reaction are further ensured.

[0089] The schemes of the present application will be explained below with reference to examples. Those skilled in the art will understand that the examples below are only for illustration of the present application and should not be considered as limiting the scope of the present application. The specific techniques or conditions not mentioned in the examples are carried out according to the techniques or conditions described in the literature in the art or according to the product instructions. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be obtained commercially.

[0090] Example 1:

[0091] This example provides a preparation method of fluorescent carbon quantum dots based on chitosan modification, which is shown as Figure 1 The specific steps are as follows:

[0092] 0.4 g of aminotrimethyl phosphonic acid (ATMP), 0.5 g of citric acid and 0.5 g of chitosan were dissolved in 10 ml of ultrapure water, and after ultrasonic treatment for 30.0 min, the solution was transferred to a 50 ml polytetrafluoroethylene lined high-temperature reaction kettle, and heated at 200℃ for 5 h. After the temperature of the reaction dropped to room temperature, centrifugation was carried out at a speed of 12000.0 rpm for 10.0 min, and the supernatant was taken and repeated three times. Then the solution was filtered under a 0.22 μM filter membrane by a syringe, dialyzed in a dialysis bag (MW 500 Da) for 24 hours, and finally dried into powder in an oven, to obtain CQDs. The CQDs were dissolved in deionized water to obtain a CQDs solution with a concentration of 0.2 mg / mL.

[0093] The same method as above was used, except that no chitosan was added, to prepare an unmodified carbon quantum dot solution.

[0094] The inventors unexpectedly found that the unmodified carbon quantum dot solution became turbid after standing for 1 min, and obvious precipitation occurred after standing for 24 h. After adding chitosan, the stability and dispersibility of the carbon quantum dots were significantly improved, as shown in Figure 2 A and Figure 2As shown in Figure B, the unmodified CQDs solution became turbid after 24 hours of standing, exhibiting significant aggregation and a noticeable precipitate at the bottom. In contrast, the chitosan-modified CQDs solution remained clear with no visible change. This indicates that the addition of chitosan improved the stability and dispersibility of carbon quantum dots in solution, reduced aggregation, and maintained their suspension. This means that CQDs can be uniformly distributed in the solution during detection, increasing contact with iron ions and thus improving detection sensitivity. The stable and well-dispersed CQDs solution ensures consistent concentration and distribution of CQDs in each experiment, contributing to improved reproducibility. Aggregation and precipitation can lead to measurement errors because they can affect light absorption and scattering, thus influencing the intensity of the fluorescence signal. The uniform distribution of the modified CQDs reduces this error, resulting in more accurate detection results.

[0095] Next, the synthesized CQDs were analyzed. From Figure 3A The TEM images show that the synthesized CQDs are well dispersed, spherical, and well-combined. Figure 3B The infrared imaging results fully demonstrate the successful synthesis of CQDs. Simultaneously, X-ray photoelectron spectroscopy (XPS) was performed on the CQDs, and the results are as follows... Figure 4 As shown, this confirms that CQDs contain C, N, and O elements, providing strong evidence for their successful synthesis. Furthermore, as... Figure 5 As shown in Figure A, the D of CQDs before modification 50 With a particle size of 0.8 nm, the modified CQDs have a D... 50 The particle size is 1.2 nm, such as Figure 5 As shown in Figure B, the zeta potential of the unmodified CQDs was 5.0 ± 0.2 mV, while that of the modified CQDs was 17 ± 0.7 mV. This demonstrates the successful synthesis of the CQDs and the successful attachment of chitosan. Figure 6 As shown, with increasing excitation wavelength, the peak position of fluorescence intensity shifts towards longer wavelengths (redshift). This indicates that the wavelength of fluorescence emission also increases with increasing excitation wavelength. Figure 6 A represents the fluorescence intensity of the modified CQDs under different excitations, compared to... Figure 6 B added Fe 3+ The fluorescence intensity is significantly lower than Figure 6 A indicates that the modified CQDs affect Fe. 3+ There is a clear fluorescence quenching phenomenon.

[0096] Example 2:

[0097] In this embodiment, the CQDs solution prepared in Example 1 was subjected to iron ion detection and adsorption. The specific steps are as follows:

[0098] 20.0 μL of CQDs solution with a concentration of 0.2 mg / mL was added into 170.0 μL of Tris-HCl buffer with a pH value of 3.5, followed by 10.0 μL of Fe 3+ The standard solution (detection sample) was measured by a fluorescence spectrometer at an excitation wavelength of 355 nm for the fluorescence intensity value at 435 nm after 1.0 min of reaction at 35℃, and this experimental group was recorded as CQDs+Fe 3+ Meanwhile, the CQDs solution, Fe 3+ standard solution and chitosan solution (deionized water as solvent, respectively configured into a solution with a concentration of 0.2 mg / mL, 20 μL of solution was added into 180.0 μL of Tris-HCl buffer with a pH value of 3.5, and reacted for 1.0 min at 35℃) were subjected to fluorescence detection.

[0099] The results are shown in Figure 7 It can be seen that only the CQDs and CQDs+Fe 3+ two groups have obvious fluorescence changes, but the fluorescence intensity of the latter is less than that of the former. It is shown that the blue fluorescence of CQDs is inhibited after the addition of Fe 3+ , which shows the feasibility of the fluorescence method for detecting Fe 3+ .

[0100] Example 3:

[0101] Based on the iron ion detection and adsorption method of Example 2, the pH value, temperature and reaction time of the detection reaction were optimized, and the results are shown in Figure 8 .

[0102] As shown in Figure 8 A, when the temperature value is in the range of 25.0℃ to 30.0℃, the fluorescence intensity quenching difference of the reaction system at 435 nm increases with the increase of the reaction temperature, and when the temperature exceeds 35.0℃ and increases to 45.0℃, the fluorescence intensity quenching difference gradually decreases with the increase thereof, so 35.0℃ is selected as the optimal temperature of the detection system. Then the catalytic performance of the system in the pH range of 3.0 to 5.5 was explored, and the results are shown in Figure 8 B, when the pH value is in the range of 3.0 to 3.5, the fluorescence intensity quenching difference of the reaction system at 435 nm increases with the increase of the pH value of the buffer system, and when the pH value exceeds 3.5, the fluorescence intensity quenching difference gradually decreases with the increase thereof, so 3.5 is selected as the optimal pH value of the system. Finally, the reaction time of the reaction system was optimized, and the results are shown in Figure 8As shown in C, within 0.0 to 3.0 min, the fluorescence intensity difference of the reaction system at 435 nm increased with the increase of reaction time, and basically did not change after 1.0 min, so 1.0 min was selected as the optimal reaction time of the system. At the same time, it was found through comparison that the fluorescence intensity of the system added with Fe 3+ and without Fe 3+ appeared obvious difference, and the difference gradually increased with time, which further proved the feasibility of the system for detecting Fe 3+ .

[0103] Example 4:

[0104] 4.1 Establishment of standard curve and sample detection method

[0105] (1) Establishment of linear equation for detection

[0106] 20.0 μL of CQDs nanomaterial solution with a concentration of 0.2 mg / mL was added into 170.0 μL of Tris-HCl buffer with a pH value of 3.5, and then 10.0 μL of Fe 3+ standard solution with different concentrations was added. After reaction at 35℃ for 1.0 min, the fluorescence intensity value at 435 nm was measured under excitation wavelength of 355 nm by fluorescence spectrometer, which was recorded as fluorescence value F1:

[0107] The results are shown in Figure 9 , Figure 9 A is the fluorescence intensity graph of different iron ion concentrations, Figure 9 and B is the fitting calculation graph. As can be seen, the fluorescence intensity difference at 435 nm and the added Fe 3+ and without Fe 3+ concentration between 0 and 120 μg / mL has a good linear relationship, and the regression equation is ΔF = -4.83832C Fe 3+ + 1.07549, the correlation coefficient is 0.9938, and the detection limit is 0.0049 μg / mL.

[0108] (2) Pretreatment of sample to be detected

[0109] The protein powder with residual Fe 3+ was dissolved with Tris-HCl buffer (pH value of 3.5), filtered with pore size of 0.22 μm filter paper or filter membrane, and the filtrate was collected for detection.

[0110] (3) Detection of sample to be detected

[0111] Different concentrations of FeCl3 and 20.0 μL of 0.2 mg / mL CQDs solution were mixed in centrifuge tubes, and then Tris-HCl buffer with a pH of 3.5 was added and the volume was adjusted to 200.0 μL. After reacting at 35 °C for 1.0 min, the mixture was transferred to a fluorescence dish, and the fluorescence intensity at 435 nm was measured using a fluorescence spectrometer at an excitation wavelength of 355 nm. This value was recorded as the fluorescence value Fn.

[0112] (4) Calculate the Fe content in the sample to be tested. 3+ concentration

[0113] Substitute the fluorescence value Fn obtained in step (3) into the linear equation of fluorescence intensity ΔF = -4.83832C Fe 3+ +1.07549 indicates the presence of Fe in the sample being tested. 3+ Concentration C Fe 3+ The value is Fe 3+ Residual values.

[0114] 4.2 The method described in 4.1 is used, except that the unmodified CQDs are used for detection, and the results are as follows. Figure 9 As shown, Figure 9 C represents the fluorescence intensity of the CQDs solution before modification at different iron ion concentrations; Figure 9 D is the standard curve of iron ions detected in the unmodified CQDs solution, with the regression equation being ΔF = -4.55829C. Fe 3+ The correlation coefficient was +1.03755, the detection limit was 0.9648, and the detection limit was 0.0058 μg / mL. These results indicate that the unmodified CQDs exhibited low sensitivity in detecting iron ions. Furthermore, the correlation coefficient of the standard curve for iron ion detection using the unmodified CQDs solution was small, indicating poor volatility, stability, and accuracy. In contrast, the chitosan-modified carbon quantum dots of this application exhibited high sensitivity, low detection limit, low volatility, and high stability and accuracy.

[0115] Example 5:

[0116] In this embodiment, the inventors further investigated the effects of different interfering substances on Fe based on CQDs. 3+The detection method is as follows: the detection method is as described in Example 2, and the detection samples are as follows: CaCl2, FeCl3, CuSO4, KCl, AlCl3, MgCl2, MnCl2, NaCl, GeCl4, CoCl2, histidine, methionine, serine, tyrosine, and threonine. 2 mg of each sample was dissolved in 1 mL of deionized water to prepare a 2 mg / mL solution. 20.0 μL of the CQDs solution with a concentration of 0.2 mg / mL, 10 μL of the sample solution with a concentration of 2 mg / mL, and 170.0 μL of Tris-HCl buffer solution with a pH of 3.5 were mixed in a centrifuge tube, and then the volume was adjusted to 200.0 μL. After reaction at 35°C for 1.0 min, the mixture was transferred to a fluorescence dish, and the fluorescence intensity value at 435 nm was measured by a fluorescence spectrometer under an excitation wavelength of 355 nm.

[0117] The results are shown in Table 1, which show that the CQDs of the present application can be used to detect the selectivity of different samples in different environments. Figure 10

[0118] 1. Ca 2+ 2. Fe 3+ 3. Cu 2+ 4. K + 5. Al 3+ 6. Mg 2+ 7. Mn 2+ 8. Na + 9. Ge 4+ 10. Co 2+ 11. Histidine; 12. Methionine; 13. Serine; 14. Tyrosine; 15. Threonine.

[0119] The results show that the CQDs of the present application can specifically detect Fe 3+ , and other interfering substances have no effect on the method of the present application, which shows the anti-interference and high sensitivity of the present application.

[0120] Example 6:

[0121] In this example, the CQDs of the present application are used to detect actual samples

[0122] 6.1 Protein powder actual sample detection:

[0123] Protein powder pretreatment: 1.0 g of protein powder (soybean protein powder, pea protein powder, or microbial protein powder) was dissolved in 30.0 mL of ultrapure water, and after ultrasonic treatment for 30.0 min, the supernatant was taken after centrifugal filtration as the sample solution.

[0124] ​Before testing, the prepared sample solution was adjusted to pH 3.5. Then, 20.0 μL of CQDs solution with a concentration of 0.2 mg / mL was added to the above sample solution. At this time, different concentrations of FeCl3 were added to the above system by standard addition method, and after mixing uniformly, the fluorescence intensity value change at 435 nm was measured by fluorescence spectrometer under 355 nm excitation wavelength.

[0125] The results are shown in Table 1 and Table 2, and the recovery rate of the fluorescence method is 100.00% to 107.40%, and the relative standard deviation (R.S.D.) is less than 5.00%. This shows that the CQDs-based method has good feasibility and reproducibility in detecting Fe 3+ in actual samples.

[0126] Table 1. Protein powder detection results

[0127]

[0128] 6.2 Hemoglobin actual sample detection:

[0129] Hemoglobin pretreatment: 0.1 g of hemoglobin powder was dissolved in 30.0 mL of ultrapure water, and after ultrasonic treatment for 30.0 minutes, the supernatant was taken as the sample solution after centrifugal filtration.

[0130] Before testing, the prepared sample solution was adjusted to pH 3.5. Then, 20.0 μL of CQDs solution with a concentration of 0.2 mg / mL was added to the above sample solution. At this time, different concentrations of FeCl3 were added to the above system by standard addition method, and after mixing uniformly, the fluorescence intensity value change at 435 nm was measured by fluorescence spectrometer under 355 nm excitation wavelength.

[0131] Table 2. Hemoglobin detection results

[0132]

[0133] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples without contradiction.

[0134] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and that variations, modifications, substitutions and changes can be made by those skilled in the art without departing from the scope of the present application.

Claims

1. A chitosan-modified carbon quantum dot, characterized by, The preparation method of the chitosan-modified carbon quantum dots comprises: reacting a nitrogen source, a carbon source, chitosan and a solvent to obtain the chitosan-modified carbon quantum dots; the temperature of the reaction is 150-250℃, and the time is 3-7 hours; the nitrogen source comprises aminotrimethyl phosphonic acid; the carbon source comprises at least one of citric acid and sodium citrate; the solvent comprises ultrapure water; in the mixed solution of the carbon source, the nitrogen source and chitosan, the concentration of the aminotrimethyl phosphonic acid is 0.02-0.06 g / mL, the concentration of the citric acid is 0.03-0.07 g / mL, and the concentration of chitosan is 0.03-0.07 g / mL; before the reaction, the nitrogen source, the carbon source, chitosan and the solvent are subjected to ultrasonic treatment; the time of the ultrasonic treatment is 10-50 minutes; after the reaction, the obtained reaction solution is subjected to the following steps: the reaction solution is subjected to centrifugal treatment to collect supernatant; the supernatant is subjected to dialysis treatment to collect effluent; the effluent is subjected to drying treatment to obtain the chitosan-modified carbon quantum dots; the centrifugal treatment comprises centrifuging the reaction solution at a speed of 10000-14000 rpm for 5-15 minutes; the cut-off molecular weight of the dialysis treatment is 400-600 Da; the drying treatment comprises oven drying.

2. The chitosan-modified carbon quantum dots according to claim 1, characterized in that, The D of the chitosan-modified carbon quantum dots is 0.5~1.0 nm 50 The particle size is 1.0 nm~1.4 nm; The zeta potential of the chitosan-modified carbon quantum dots is 15 mV-20 mV.

3. A reagent for simultaneously detecting and adsorbing iron ions, characterized by comprising the compound according to claim 1 or 2. The reagent comprises the chitosan-modified carbon quantum dots, and the chitosan-modified carbon quantum dots have amino groups and phosphorus / oxygen functional groups; The chitosan-modified carbon quantum dots are selected from the chitosan-modified carbon quantum dots according to any one of claims 1-2; The reagent further comprises a Tris-HCl buffer.

4. Application of the chitosan-modified carbon quantum dots according to any one of claims 1-2 or the reagent for simultaneously detecting and adsorbing iron ions according to claim 3 in simultaneously detecting and adsorbing iron ions.

5. A method of simultaneously detecting and adsorbing iron ions, characterized by, The method comprises: contacting the chitosan-modified carbon quantum dots according to any one of claims 1-2 or the reagent for simultaneously detecting and adsorbing iron ions according to claim 3 with a sample to be tested; measuring the fluorescence intensity value of the obtained mixture after the contacting, and determining the content of iron ions in the sample to be tested based on the fluorescence intensity value; the fluorescence intensity value is measured at 420-460 nm under excitation at a wavelength of 340-370 nm.

6. The method of claim 5, wherein, centrifuging the mixture after the measurement of the fluorescence intensity value to collect precipitate, so as to obtain carbon quantum dots adsorbing iron ions.

7. The method of claim 6, wherein, centrifuging the mixture after the measurement of the fluorescence intensity value to collect precipitate, so as to obtain carbon quantum dots adsorbing iron ions.

8. The method of claim 5, wherein, The method comprises: reacting the chitosan-modified carbon quantum dots or the reagent for simultaneously detecting and adsorbing iron ions, a sample to be tested and a buffer solution to obtain a mixture; the temperature of the reaction is 25-45℃; the pH of the reaction is 3.0-5.5; the time of the reaction is 0-2 minutes.

Images