CN110423611B

CN110423611B - Red fluorescent carbon dot and preparation method thereof, fluorescent sensor and construction method and application thereof

Info

Publication number: CN110423611B
Application number: CN201910721022.XA
Authority: CN
Inventors: 杜甫佑; 程珍芳; 阮贵华; 赵晨曦
Original assignee: Changsha University
Current assignee: Changsha University
Priority date: 2019-08-06
Filing date: 2019-08-06
Publication date: 2022-02-18
Anticipated expiration: 2039-08-06
Also published as: CN110423611A

Abstract

The invention discloses a red fluorescent carbon dot for detecting alachlor concentration based on fluorescence quenching, wherein the red fluorescent carbon dot is spherical, the diameter of the red fluorescent carbon dot is 3.25-5.75nm, and the mass content of C, N, O in the red fluorescent carbon dot is 75-75.2%, 21-21.1% and 3.5-3.7% respectively. The red fluorescent carbon dot has the advantages of high quantum yield, excellent stability and optical properties, good repeatability, high sensitivity, accurate and reliable detection result and high selectivity on alachlor, and can be applied to the detection of the concentration of the alachlor herbicide in the environment (soil and environmental water) by combining with the alachlor quenching standard curve. The invention also provides a preparation method of the red fluorescent carbon dot, a fluorescent sensor and a construction method thereof, and application of the fluorescent sensor in detecting the concentration of alachlor in an environmental sample.

Description

Red fluorescent carbon dot and preparation method thereof, fluorescent sensor and construction method and application thereof

Technical Field

The invention belongs to the technical field of fluorescence sensing, and particularly relates to a red fluorescence carbon dot nano material, a preparation method thereof, a fluorescence sensor for detecting the concentration of alachlor based on fluorescence quenching, a construction method thereof, and application of the fluorescence sensor in detecting the concentration of alachlor in an environmental sample.

Background

Alachlor, also known as 2-chloro-N- (methoxymethyl) -N- (2, 6-diethylphenyl) acetamide, is one of the most widely used chloracetanilide herbicides for controlling broadleaf weeds pre-emergence. It is a mixed herbicide suitable for soil before planting and weed control in the planting process of corn, potato, peanut and soybean. However, the use of large amounts of alachlor can contaminate soil, water and other vegetation, and can also adversely affect hosts and other organisms such as birds, beneficial insects, fish and other non-target plants. In addition, it can also produce other deleterious environmental effects, for example, the application of alachlor in soil reduces the total digestible nutrient content; alachlor is highly soluble and will dissolve in ecological water and enter drinking water systems, and although its acute toxicity is very low, its carcinogenicity still poses a certain threat to human body, fish and other organisms.

To date, the development of alachlor detection technology has focused mainly on gas chromatography or gas chromatography-mass spectrometry. Despite their high sensitivity and specificity, these methods are costly, time consuming (requiring tedious sample pretreatment), inaccurate for detection of markers in complex systems, poor selectivity, and high requirements for the expertise of the detector. Therefore, there is a need to develop a simple and rapid alachlor assay with high sensitivity and selectivity.

However, the carbon dots are mostly applied to biological directions such as metal ion sensors and cell imaging, and no precedent for detecting alachlor by using the carbon dots as a fluorescence sensor exists.

Disclosure of Invention

The invention aims to solve the technical problems, overcome the defects and defects in the background technology, and provide a red fluorescent carbon dot nano material which has high sensitivity and high selectivity and can simply and quickly determine the concentration of alachlor, a preparation method thereof, a fluorescent sensor for detecting the concentration of alachlor based on fluorescence quenching, a construction method thereof and application of the fluorescent sensor for detecting the concentration of alachlor in an environmental sample.

In order to solve the technical problems, the technical scheme provided by the invention is as follows:

a red fluorescent carbon dot (N-CQDs) for detecting the concentration of alachlor based on fluorescence quenching is spherical, the diameter of the red fluorescent carbon dot is distributed between 3.25 and 5.75nm, the average diameter of the red fluorescent carbon dot is about 4.5nm (the red fluorescent carbon dot is uniformly dispersed in a solvent), and the mass content of C, N, O in the red fluorescent carbon dot is respectively 75 to 75.2 percent, 21 to 21.1 percent and 3.5 to 3.7 percent.

Based on a general technical concept, the invention also provides a preparation method of the red fluorescent carbon dot, which comprises the following steps:

(1) dispersing p-phenylenediamine in ethanol, and mixing to obtain a mixture;

(2) transferring the mixture obtained in the step (1) into a polytetrafluoroethylene microwave digestion tank for reaction, and cooling to obtain a dark red liquid;

(3) and (3) centrifuging the deep red liquid obtained in the step (2) to remove precipitates, filtering the obtained supernatant by using a 0.2-micron nylon membrane, dialyzing by using a dialysis bag with the molecular weight cut-off of 500Da to remove tiny impurities to obtain a deep red solution containing red fluorescent carbon dots, and freeze-drying to obtain solid red fluorescent carbon dots.

In the above preparation method, preferably, in the step (1), the concentration of p-phenylenediamine in the mixture is 0.02-0.1 mmol/mL; more preferably, the amount of the absolute ethyl alcohol is fixed to 50mL, and the amount of the p-phenylenediamine is 3 mmol.

Preferably, in the step (2), the power of the polytetrafluoroethylene microwave digestion tank is 500-800W, the reaction temperature is 160-220 ℃, and the reaction time is 1-10 min; more preferably, the power of the polytetrafluoroethylene microwave digestion tank is 800W, the reaction temperature is 220 ℃, and the reaction time is 10 min.

Preferably, in the step (3), the centrifugation rotation speed is 8000-10000rpm, the centrifugation time is 10-20min, and the dialysis time is 24-48 h; more preferably, the centrifugation speed is 10000rpm, the centrifugation time is 10min, and the dialysis time is 48 h.

The p-phenylenediamine participates in the reaction in a molecular form, and is carbonized in an ethanol solvent at the high temperature of a polytetrafluoroethylene microwave digestion tank to finally obtain the p-phenylenediamine carbon dots.

Based on a general technical concept, the invention also provides a fluorescence sensor for detecting the concentration of alachlor based on fluorescence quenching, which comprises the red fluorescent carbon dot and an alachlor quenching standard curve, wherein the alachlor quenching standard curve is obtained by mixing the red fluorescent carbon dot with alachlor solutions with different concentrations, and then measuring and drawing fluorescence intensity.

Based on a general technical concept, the invention also provides a construction method of the fluorescence sensor for detecting the concentration of alachlor based on fluorescence quenching, which comprises the following steps: diluting the obtained red fluorescent carbon dots with ethanol to obtain red fluorescent carbon dot solutions, mixing the red fluorescent carbon dot solutions with alachlor solutions with different concentrations to obtain different mixed solutions, detecting the fluorescence intensity of the mixed solutions, immediately recording the fluorescence intensity of the different mixed solutions at the emission wavelength of 603nm when the mixed solutions are excited at the excitation wavelength of 510nm, and then drawing an alachlor quenching standard curve by taking the different concentrations of the alachlor solutions as abscissa and the detected fluorescence intensity value as ordinate to complete the construction of the fluorescence sensor.

After the red fluorescent carbon dot solution and the alachlor solution are mixed, no new ultraviolet absorption peak appears, and the Ksv value is found to be reduced along with the temperature rise according to the determination of the Stern-Volmer equation, which indicates that the fluorescence quenching of the alachlor to the carbon dots belongs to the static quenching process. Therefore, electrostatic interaction exists between alachlor and the surface of the red fluorescent carbon dot, and further fluorescence quenching of the carbon dot can be caused.

The red fluorescent carbon dot has good stability, and the optimal excitation wavelength and the optimal emission wavelength are 510nm and 603nm respectively, so that the fluorescence intensity value of the carbon dot with the emission position of 603nm obtained when the carbon dot is excited at 510nm is selectively recorded. As the concentration of the alachlor is increased, the fluorescence intensity value of the carbon dot is reduced, and the linearity is good in the range of the concentration of the alachlor solution between 5nmol/L and 25 mu mol/L, so that quantitative analysis is carried out on the alachlor by researching the fluorescence quenching degree of the carbon dot.

In the above construction method, preferably, the concentration of the red fluorescent carbon dot solution is 0.2 mg/mL; the alachlor solution is an aqueous solution or an ethanol solution containing alachlor; the volume ratio of the red fluorescent carbon dot solution to the alachlor solution is 1: 1; the different mixed solutions contain alachlor at concentrations of 0.005 mu mol/L, 0.05 mu mol/L, 0.1 mu mol/L, 0.25 mu mol/L, 0.5 mu mol/L, 2.5 mu mol/L, 5 mu mol/L, 10 mu mol/L, 20 mu mol/L and 25 mu mol/L respectively.

The invention also provides an application of the fluorescent sensor, which is based on a general technical concept and is used for detecting the concentration of alachlor in an environmental sample.

In the above application, preferably, the specific detection method comprises the following steps: diluting the red fluorescent carbon dots of the fluorescent sensor with ethanol to obtain a red fluorescent carbon dot solution, mixing the red fluorescent carbon dot solution with a sample to be detected containing alachlor in the same volume, detecting the fluorescence intensity of the red fluorescent carbon dot solution to obtain a corresponding fluorescence intensity value, and finding the concentration of the alachlor corresponding to the fluorescence intensity value in the alachlor quenching standard curve to obtain the concentration of the sample to be detected containing the alachlor;

more preferably, the sample to be detected containing alachlor is a water sample or a soil sample; when the sample to be detected containing alachlor is a soil sample, ultrasonically dissolving the soil sample by using ethanol, filtering by using a 0.2-micron organic phase filter head, and collecting filtrate to obtain a sample solution to be detected containing alachlor; when the sample to be detected containing alachlor is a water sample, the water sample is filtered by a 0.22 mu m membrane to remove impurities, and an EDTA solution (20 mu mol/L) is added before the fluorescence intensity is detected so as to eliminate the interference of other metal ions in the environment.

Compared with the prior art, the invention has the beneficial effects that:

1. the red fluorescent carbon dot has the advantages of high quantum yield, excellent stability and optical properties, good repeatability, high sensitivity, accurate and reliable detection result and high selectivity on alachlor, and can be applied to the detection of the concentration of the alachlor herbicide in the environment (soil and environmental water) by combining with the alachlor quenching standard curve.

2. The preparation method of the red fluorescent carbon dot, the construction method of the fluorescent sensor and the detection method of the alachlor concentration have the advantages of simple operation, low cost and environment-friendly reaction process, and can eliminate the interference of other metal ions in the environment.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a schematic diagram showing the synthesis of red fluorescent carbon dots and the process for detecting alachlor;

FIG. 2 is a UV-Vis spectrum of the red fluorescent carbon dots of the example after mixing with metolachlor (black) and metolachlor (red);

FIG. 3 is a graph of Excitation (EX) and Emission (EM) spectra of red fluorescent carbon dots dispersed in absolute ethanol in the example;

FIG. 4 is a fluorescence emission spectrum of a red fluorescent carbon dot under different excitations in the example;

FIG. 5 is a FT-IR spectrum of a red fluorescent carbon dot in the example;

FIG. 6 is a three-dimensional matrix diagram of the fluorescence spectrum of the red fluorescent carbon dots in the embodiment, wherein the excitation wavelength range is 220-900nm, and the emission wavelength range is 220-650 nm;

FIG. 7 is the photostability of the red fluorescent carbon dots of the examples after UV irradiation for 60 min;

FIG. 8 is a TEM image of red fluorescent carbon dots in the example;

FIG. 9 shows the results of the size distribution of red fluorescent carbon dots in the examples;

FIG. 10 is an EDs spectrum analysis of red fluorescent carbon dots in the examples;

FIG. 11 is the fluorescence spectra of the red fluorescent carbon dots in the examples after mixing with different concentrations of acetochlor (from top to bottom: 5nmol/L-25 μmol/L);

FIG. 12 is a standard curve for alachlor quenching prepared by mixing red fluorescent carbon dots with alachlor ethoxide of different concentrations in the examples;

FIG. 13 is the fluorescence spectra of the red fluorescent carbon dots in the examples mixed with different concentrations of alachlor (from top to bottom: 5nmol/L-25 μmol/L);

FIG. 14 is a standard curve for alachlor quenching prepared by mixing red fluorescent carbon dots with water-soluble alachlor of different concentrations in the examples;

FIG. 15 is a diagram showing the results of the specificity test of alachlor in the red fluorescent carbon dot test in the examples; wherein (A) is under an ultraviolet lamp; (B) under a fluorescent lamp;

FIG. 16 is the fluorescence intensity of the red fluorescent carbon dots mixed with various herbicides having a concentration of 500. mu. mol/L in the examples;

FIG. 17 is the relative fluorescence intensity ((F0-F)/F0X 100%) of red fluorescent carbon dots versus various herbicides in the absence (left) and presence (right) of alachlor (2. mu. mol/L) in the examples; wherein F0 represents the fluorescence intensity value of the carbon dot mixed solution in the absence of the herbicide, F is the fluorescence intensity value of the carbon dot mixed solution in the presence of the herbicide, and (F0-F)/F0X 100% is the relative fluorescence intensity of the carbon dot to the respective herbicides.

FIG. 18 is the relative fluorescence intensities of the red carbon dot for various metal ions in the examples (1- (F0-F)/F0X 100%) in the absence (left) and presence (right) of alachlor (400 nmol/L).

Detailed Description

In order to facilitate understanding of the invention, the invention will be described more fully and in detail with reference to the accompanying drawings and preferred embodiments, but the scope of the invention is not limited to the specific embodiments below.

Unless otherwise defined, all terms of art used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.

Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.

Example (b):

the red fluorescent carbon dot, the synthesis of the red fluorescent carbon dot and the process for detecting alachlor are shown in figure 1, and the preparation method of the red fluorescent carbon dot comprises the following steps:

324mg (3mmol) of p-phenylenediamine is weighed and dispersed in 50mL of ethanol, after the mixture is fully mixed, the mixture is transferred to a polytetrafluoroethylene microwave digestion tank and reacts for 10min under the conditions of 800W and 220 ℃, after the mixture is cooled to room temperature, a dark red liquid is obtained, then the mixture is centrifuged for about 10min at 10000rpm to remove precipitates, the obtained supernatant is collected and filtered by a 0.2 mu m nylon membrane, and then the mixture is dialyzed for about 48h at room temperature by a dialysis bag with the molecular weight cutoff of 500Da to remove tiny impurities. Finally, a dark red solution containing N-CQDs was obtained. Solid N-CQDs are finally obtained by drying the red fluorescent carbon dot solution in a freeze dryer. Before use, N-CQDs were dissolved in ethanol and water, respectively, to prepare a 5mg/mL solution of N-CQDs, and stored at room temperature.

The characterization of the red fluorescent carbon dots prepared in this example is shown in FIGS. 2-10. In the UV-Vis absorption spectrum of N-CQDs (FIG. 2), two absorption bands were observed at 240 and 285nm, which are C-C bonds and N- π - π transitions, respectively. As can be seen from FIG. 3, it can be seen that the maximum excitation and emission wavelengths of N-CQDs are 510 and 603nm, respectively. It is observed in fig. 4 that the emission spectrum can be divided into two regions, respectively called blue band (360nm to 480nm) which shows the classical excitation-dependent properties and red band (510nm to 750nm) which shows emission characteristics independent of the excitation. From FIG. 5, it can be seen that the peak value at 2920cm^-1There is a very small peak due to C-H stretching vibrations; at 1396cm^-1The spike in (a) is due to tensile vibration of the C-N bond; at 3308cm^-1There are two separate absorption peaks nearby, corresponding to two types of amino groups: primary amine (-NH2) and secondary amine (-NH-) in addition to other functional groups, including C-H (2910 cm)^-1)，V_CN(1627cm^-1)，V_C-C(1512cm^-1)，H-N(1263cm^-1). The 700-900nm luminescence characteristics shown in fig. 6 represent the characteristic of the synthetic carbon dots with significant down-conversion luminescence, while also having a weaker up-conversion luminescence. FIG. 7 shows that the fluorescence intensity of N-CQDs is stable over the duration of the illumination studied, indicating that N-CQDs have excellent photostability. As can be seen from FIGS. 8 and 9, the shapes of N-CQDs synthesized by the microwave digestion method are nearly spherical, and the size distribution results of N-CQDs indicate that the diameter distribution of N-CQDs is 3.255.75nm, average diameter of about 4.5nm, and uniform dispersion in a solvent. As can be seen in FIG. 10, N-CQDs have three typical peaks at 0.25, 0.4, 0.54 and 1.75; KeV corresponds to C1s, N2p, O1s, Si2p, C, N, O and Si at 75.15%, 21.09%, 3.66% and 0.1%, respectively, where Si is due to the substrate and is not all of the N-CQDs.

The fluorescent sensor for detecting the alachlor concentration based on fluorescence quenching is established by adopting the obtained red fluorescent carbon dots, and the construction method comprises the following steps:

by diluting N-CQDs with ethanol to 0.2mg/mL, at which concentration N-CQDs exhibit the strongest fluorescence intensity, and using 0.2mg/mL N-CQDs for the experiment, 2.0mL of different concentrations of alachlor solution (an aqueous or ethanol solution of alachlor) were added to 2.0mL of the above N-CQDs solution in a 10mL centrifuge tube to obtain different mixed solutions (containing alachlor at a concentration gradient of 0.005. mu. mol/L, 0.05. mu. mol/L, 0.1. mu. mol/L, 0.25. mu. mol/L, 0.5. mu. mol/L, 2.5. mu. mol/L, 5. mu. mol/L, 10. mu. mol/L, 20. mol/L, 25. mu. mol/L) and measuring the fluorescence intensity thereof, the fluorescence intensity of different concentrations of the quenched solution of alachlor was immediately recorded at 603nm upon excitation at 510nm, namely, the fluorescence intensity of different mixed solutions (such as the fluorescence intensity of the alachlor in figure 11, and the fluorescence intensity of the water-soluble alachlor in figure 13), and then, with different concentrations of the alachlor solution as abscissa and the detected fluorescence intensity value as ordinate, a alachlor quenching standard curve (such as the alachlor quenching standard curve in figure 12, and the water-soluble alachlor quenching standard curve in figure 14) is drawn by using spectral measurement, thus completing the construction of the fluorescence sensor.

The invention takes p-phenylenediamine as a carbon source and a nitrogen source, successfully prepares a double-emission carbon dot with red fluorescence by adopting a microwave digestion method, and an emission spectrum can be divided into two regions which are respectively called a blue band (360nm to 480nm) and a red band (510nm to 750 nm). The blue band shows classical excitation dependent properties and the red band shows emission characteristics independent of excitation with a relative fluorescence quantum yield of 28.26%. The N-CQDs show excellent selectivity and specificity to alachlor herbicides, ethanol and water are respectively adopted to dissolve alachlor, and two alachlor quenching standard curves for detecting the alachlor are obtained based on a fluorescence quenching mechanism. Under the optimal condition, the fluorescence quenching degree of the N-CQDs and the ethanol soluble and water soluble alachlor are in a linear relation in the range of 5nmol/L-25 mu mol/L, the detection limits are 0.2nmol/L and 0.5nmol/L respectively, and the recovery rates of the alachlor in the actual ethanol extraction sampling and water sample are 86.4% -116.9% and 86.5% -116.9% respectively. The method can be used for selectively detecting the alachlor herbicide in soil samples and water samples.

During the reaction, alachlor can reduce the fluorescence intensity of N-CQDs, so that the concentration of the alachlor can be analyzed by researching the fluorescence quenching degree of the N-CQDs. Through quantitative analysis, the linear equation for detecting alachlor is shown in table 1:

table 1 linear equation for alachlor detection

Wherein y is the fluorescence intensity; x is the concentration of alachlor, mu mol/L; r²The relative standard deviation is shown, the linear range is 0.005-25 mu mol/L, LOD is the detection limit, and the detection limits of ethanol and water-soluble alachlor in the actual sample are 0.2nmol/L and 0.5nmol/L respectively.

When the standard curve is measured, water and ethanol solution are respectively used as solvents to prepare a series of alachlor water or ethanol solution. Mixing with ethanol-soluble N-CQDs and measuring the change of fluorescence intensity.

The red fluorescent carbon dot prepared by the embodiment is used for detecting the alachlor herbicide in an environmental soil sample and a water sample, and the detection method comprises the following steps:

N-CQDs are diluted by 0.2mg/mL by ethanol, the fluorescence intensity of the N-CQDs is strongest under the concentration, 0.2mg/mLN-CQDs are used for the following experiments, 2.0mL of a sample solution to be detected containing alachlor is added into 2.0mL of the N-CQDs solution in a 10mL centrifugal tube, EDTA is added for reaction, the fluorescence intensity is detected to obtain a corresponding fluorescence intensity value, and the concentration of the alachlor corresponding to the fluorescence intensity value is found in the alachlor quenching standard curve, so that the concentration of the sample to be detected containing alachlor is obtained.

To evaluate the performance of N-CQDs as a sensor for alachlor in real samples, environmental soil samples, tap water, lake water and farmland water samples were selected as real samples.

Treatment of the soil sample before the actual sample measurement: the soil sample is ultrasonically dissolved for 10min by ethanol, then a 0.2-micron organic phase filter head is used, a 5mL syringe is used for filtration, and the filtrate is collected for later use.

Treating the water sample before actual sample determination: prior to detection, all water samples were filtered using a membrane (0.22 μm) to remove impurities. Alachlor (0.1, 0.5, 1 and 10 mu mol/L) with different concentrations is respectively added into a water sample, and the recovery rate is determined by a sensing method using developed water as a solvent.

The results are shown in tables 2 and 3.

TABLE 2 carbon point for the detection and spiking recovery of acetochlor (n ═ 3)

TABLE 3 detection of carbon dots on metolachlor and recovery of water-soluble metolachlor by adding standard (n ═ 3)

The results show that the fluorescence intensity of N-CQDs is gradually reduced along with the increase of the concentration of alachlor, when the alachlor takes ethanol as a solvent, the linearity is good in the range of 5nmol/L-25 mu mol/L (y is 1377.5349-15.0517x), and the correlation coefficient R is²Is 0.990, and the detection limit LOD is 0.2 nmol/L; when water is used as the solvent, the linear relationship is better in the range of 5nmol/L-25 mu mol/L, (y is 579.438-4.203x), and the correlation coefficient (R)²) 0.992, LOD 0.5 nmol/L.

To evaluate the selectivity of N-CQDs, all experiments were performed at room temperature by testing other related analogs (including thiobencarb, diuron, dichlobenil, trifluralin, methylcarbinol, chlorpropham, prometryn, simazine, prometryn) in a similar manner, with the results shown in FIG. 15. FIG. 15 is a comparison of carbon dot solutions containing 500. mu. mol/L of each herbicide under UV and daylight lamps, from left to right, in order N-CQDs blank, N-CQDs with prometon, chlorphenamine, thiobencarb, dichlobenil, diuron, simazine, prometryn, methyl viologen, trifluralin, and alachlor. Under the daylight lamp, the color of the solution is changed from orange red to black gray after the alachlor and the carbon dots are mixed, and under the ultraviolet lamp, the color is changed from red to blue green, so that the N-CQDs have obvious selectivity and specificity to the alachlor.

To evaluate the selectivity of N-CQDs for the detection of metolachlor ethoxide, the fluorescent response of carbon dots with various other herbicides as potential interfering substances including thiobencarb, diuron, dichlobenil, trifluralin, methyl viologen, chlorpropham, prometryn, prometon, simazine were tested under the same conditions. As can be seen from FIG. 16, the fluorescence intensity of N-CQDs was reduced by about 80% in the presence of alachlor (at a concentration of 500. mu. mol/L), while the fluorescence intensity did not change significantly in the presence of other herbicides (each at a concentration of 500. mu. mol/L). These results indicate that alachlor can highly quench the fluorescence of N-CQDs compared to other herbicides, probably due to the carbonyl group in alachlor in combination with the amino group of N-CQDs, promoting a concerted interaction between them. In addition, the anti-interference test of alachlor detection is also carried out in the coexistence of other herbicides, and the result is shown in fig. 17. The relative fluorescence intensity in the presence of alachlor (2 μmol/L) ((F0-F)/F0 × 100%) was not affected by a 50-fold excess of interfering herbicide (100 μmol/L) compared to the blank sample, indicating negligible interference by the co-existing herbicide. The above results indicate that N-CQDs show excellent selectivity and specificity for alachlor herbicides.

To further evaluate the interference of N-CQDs by other ions in the environment, the fluorescence response of carbon dots was tested under the same conditions for various metal ions as potential interfering species, including Cr³⁺，Co²⁺，Fe³⁺，Co²⁺，Ni²⁺，Zn²⁺，Cd²⁺，Cu⁺，Cu²⁺，Pb²⁺，Ag⁺，Ba²⁺，Hg²⁺，Mg²⁺，Ca²⁺，K⁺And Na⁺. The results are shown in FIG. 18 and show that the interference of metal ions with respect to the alachlor content of aqueous solutions for the detection of N-CQDs is successfully masked by the addition of 20. mu. mol/LEDTA. As the addition amount of EDTA increased from 0.5. mu. mol/L to 50. mu. mol/L, the fluorescence intensity of N-CQDs tended to increase and decrease, and at a concentration of EDTA of 20. mu. mol/L, the fluorescence intensity remained the same as that of N-CQDs, so that the addition amount of EDTA was selected to be 20. mu. mol/L.

In the above examples, environmental soil and water samples were used as the subjects to confirm the high sensitivity and selectivity of the red fluorescent carbon dots prepared by the present invention for the detection of alachlor herbicide. However, the above description is only a preferred embodiment of the present invention, and not intended to limit the present invention in any way, and any person skilled in the art may make many alterations and modifications to the equivalent embodiment without departing from the scope of the present invention, and any simple modification, equivalent change and modification made to the above embodiment according to the technical spirit of the present invention may still fall within the scope of the present invention.

Claims

1. A fluorescence sensor for detecting alachlor concentration based on fluorescence quenching is characterized by comprising a red fluorescence carbon point and a alachlor quenching standard curve; the red fluorescent carbon dots are spherical, the diameters of the red fluorescent carbon dots are 3.25-5.75nm, and the mass content of C, N, O in the red fluorescent carbon dots is 75-75.2%, 21-21.1% and 3.5-3.7% respectively; the alachlor quenching standard curve is obtained by mixing the red fluorescent carbon dots with alachlor solutions with different concentrations, and then measuring and drawing fluorescence intensity.

2. The fluorescence sensor according to claim 1, wherein the method for preparing the red fluorescent carbon dot comprises the following steps:

(1) dispersing p-phenylenediamine in ethanol, and mixing to obtain a mixture;

3. The fluorescence sensor of claim 2, wherein in step (1), the concentration of p-phenylenediamine in the mixture is from 0.02 to 0.1 mmol/mL.

4. The fluorescence sensor according to claim 2, wherein in step (2), the power of the polytetrafluoroethylene microwave digestion tank is 500-800W, the reaction temperature is 160-220 ℃, and the reaction time is 1-10 min.

5. The fluorescence sensor according to claim 2, wherein in step (3), the centrifugation speed is 8000-10000rpm, the centrifugation time is 10-20min, and the dialysis time is 24-48 h.

6. A construction method of a fluorescence sensor for detecting alachlor concentration based on fluorescence quenching is characterized by comprising the following steps: diluting the red fluorescent carbon dots of the fluorescent sensor according to any one of claims 1 to 5 with ethanol to obtain a red fluorescent carbon dot solution, mixing the red fluorescent carbon dot solution with alachlor solutions with different concentrations to obtain different mixed solutions, detecting the fluorescence intensity of the mixed solutions, immediately recording the fluorescence intensity of the different mixed solutions at an emission wavelength of 603nm when the mixed solutions are excited at an excitation wavelength of 510nm, and then drawing an alachlor quenching standard curve by taking the different concentrations of the alachlor solutions as abscissa and the detected fluorescence intensity value as ordinate to complete the construction of the fluorescent sensor.

7. The construction method according to claim 6, wherein the concentration of the red fluorescent carbon dot solution is 0.2 mg/mL; the alachlor solution is an aqueous solution or an ethanol solution containing alachlor; the volume ratio of the red fluorescent carbon dot solution to the alachlor solution is 1: 1; the different mixed solutions contain alachlor at concentrations of 0.005 mu mol/L, 0.05 mu mol/L, 0.1 mu mol/L, 0.25 mu mol/L, 0.5 mu mol/L, 2.5 mu mol/L, 5 mu mol/L, 10 mu mol/L, 20 mu mol/L and 25 mu mol/L respectively.

8. Use of the fluorescence sensor according to any of claims 1 to 5 or the fluorescence sensor obtained by the construction method according to claim 6 or 7, wherein the fluorescence sensor is used for detecting the concentration of alachlor in an environmental sample.

9. The use according to claim 8, wherein the specific detection method comprises the steps of: diluting the red fluorescent carbon dots of the fluorescent sensor with ethanol to obtain a red fluorescent carbon dot solution, mixing the red fluorescent carbon dot solution with a sample to be detected containing alachlor in the same volume, detecting the fluorescence intensity of the red fluorescent carbon dot solution to obtain a corresponding fluorescence intensity value, and finding the concentration of the alachlor corresponding to the fluorescence intensity value in the alachlor quenching standard curve to obtain the concentration of the sample to be detected containing the alachlor;

the sample to be detected containing the alachlor is a water sample or a soil sample; when the sample to be detected containing alachlor is a soil sample, ultrasonically dissolving the soil sample by using ethanol, filtering by using a 0.2-micron organic phase filter head, and collecting filtrate to obtain a sample solution to be detected containing alachlor; when the sample to be detected containing alachlor is a water sample, filtering the water sample by using a 0.22 mu m membrane to remove impurities, and adding an EDTA solution before detecting the fluorescence intensity of the water sample.