CN114062336B - Method for detecting pesticide weed control intensity based on nitrogen-doped carbon quantum dot fluorescence on-off-on mode - Google Patents

Abstract

The invention discloses a method for detecting pesticide weed killer based on a nitrogen-doped fluorescent carbon quantum dot fluorescence on-off-on mode, which is convenient for synthesis, has good and stable fluorescence characteristic, and comprises the following steps of ³⁺ Can quench the fluorescence, and the weed killer can be combined with Fe ³⁺ The specific combination enables quenched fluorescence to be recovered within 1-2 min, so that the method can rapidly and specifically detect the herbicide strength, and can be used for detecting the herbicide strength in fruits, vegetables and water samples.

Description

A fluorescent "on-off-on" mode based on nitrogen-doped carbon quantum dots for the detection of pesticides and herbicides strong method

technical field

The invention belongs to the technical field of organic matter detection, and in particular relates to a method for detecting the pesticide herbicide using a carbon quantum dot fluorescence "on-off-on" method.

Background technique

Herbicide, also known as 3-amino-1,2,4-triazole, is a non-selective chemical herbicide. Due to its strong solubility in water (solubility in water at 25°C is 280g/L), leaching may occur under certain conditions, such as sandy soils with low organic carbon content and high water table, resulting in ground and The surface water is polluted, and its volatility is relatively poor (boiling point is 245°C). This characteristic can easily cause herbicide to accumulate in the water body, causing serious pollution of the water body, and polluting plant foods (fruits, vegetable). Excessive exposure to diaphan may cause alveolar damage in humans, and even cause thyroid and liver tumors, thus causing potential harm to the environment and human health. Therefore, it is of great significance to establish a highly selective, convenient and quick method for detecting the pesticide herbicide.

As a new type of nanomaterial, carbon quantum dots have attracted widespread attention since they were first discovered in 2004 due to their high chemical stability, good electrical conductivity and luminescence, and good biocompatibility. Carbon quantum dots are usually a collection of sp ² /sp ³ /sp ² -sp ³ hybrid carbonaceous entities with diameters less than 10 nm, and have specific quantum confinement and edge effects. Carbon quantum dots have a single-layer or multi-layer graphene structure, so they usually have a graphene lattice and often have a large number of oxygen-containing functional groups on the surface, and are now generally defined as a class with carbon (mainly sp ² ) nuclei and surface passivation Core-shell nanomaterials with functional groups. At present, the application of various dopants and the research progress on the surface functionalization of carbon quantum dots have improved the fluorescence properties of carbon quantum dots, improved the chemical stability of carbon quantum dots, and made carbon quantum dots have a broader application prospect. .

Contents of the invention

The problem to be solved by the present invention is to provide a method for sensitively and quickly detecting the pesticide herbicide using the carbon quantum dot fluorescence "on-off-on" method.

The technical solution adopted to solve the above technical problems consists of the following steps:

1. Add nitrogen-doped fluorescent carbon quantum dot aqueous solution and Fe ³⁺ solution to the centrifuge tube in turn, and then use ultrapure water to make up the volume, so that the concentration of nitrogen-doped fluorescent carbon quantum dots in the obtained mixture A is 0.6-1.0 The concentration of μg/mL and Fe ³⁺ is 0.015-0.030 mmol/L, and the fluorescence intensity F ₀ of the obtained mixture A at 430 nm is recorded at an excitation wavelength of 340 nm.

2. Add the nitrogen-doped fluorescent carbon quantum dot aqueous solution and the Fe ³⁺ solution to the centrifuge tube in turn, and add the dibasin standard solution, and then use ultrapure water to make the nitrogen-doped fluorescent carbon in the obtained mixed solution B The concentration of quantum dots and Fe ³⁺ is the same as in step 1. After the mixed solution B is shaken for 1 to 2 minutes, under the excitation wavelength of 340nm, record the fluorescence intensity F of the mixed solution B added with different concentrations of dichlorpyr standard solution at 430nm, to FF ₀ is the ordinate, and the added concentration of herbicide is the abscissa, and the standard curve of the fluorescence intensity changing with the concentration of herbicide is drawn.

3. According to the method of step 2, when adding the herbicide sample to be tested, the fluorescence intensity at 430nm under the excitation wavelength of 340nm can be calculated according to the linear equation of the standard curve in step 2. Strong concentration of grass.

The synthesis method of the above-mentioned nitrogen-doped fluorescent carbon quantum dots is as follows: citric acid and urea are added into ultrapure water at a mass ratio of 1:1, mixed evenly, then added to a Teflon autoclave, and the Teflon autoclave is placed Put it into an oven, keep it at 180°C for 1 hour, and then cool it down to room temperature naturally to obtain a crude solution of nitrogen-doped fluorescent carbon quantum dots. The solution obtained from the reaction is added to a 1kw dialysis bag, and the dialysate is ultrapure water. Afterwards, the dialysate was collected and freeze-dried for 12-16 hours to obtain blue nitrogen-doped fluorescent carbon quantum dot powder, which was stored in a refrigerator at 4°C.

The above-mentioned Fe ³⁺ solution is an analytically pure FeCl ₃ aqueous solution.

The above-mentioned herbicide standard solution is the aqueous solution of herbicide.

The above-mentioned herbicidal samples to be tested are fruit and vegetable or water samples. Wherein, when the herbicide samples to be tested are fruits and vegetables, before the detection, the fruits and vegetables are added to the mixed solution of dichloromethane and acetic acid aqueous solution with a volume concentration of 1% in a volume ratio of 1:1, preferably the amount of fruits and vegetables in the mixed solution is controlled to 20-30g/100mL, pulverized and homogeneous, centrifuged, discarded the lower dichloromethane layer, took the supernatant and filtered it with a 0.22μm microfiltration membrane, and the obtained filtrate was used as the dichloromethane sample to be tested.

The beneficial effects of the present invention are as follows:

The nitrogen-doped fluorescent carbon quantum dot of the present invention is synthesized by a one-step hydrothermal method, which is convenient to synthesize, has good fluorescence characteristics and water stability, and Fe ³⁺ can quench its fluorescence, and dioxadon can specifically combine with Fe ³⁺ The quenched fluorescence recovers within 1-2 minutes, so the method can quickly and specifically detect the herbicide, and can be used to detect the herbicide in fruits, vegetables and water samples.

Description of drawings

Fig. 1 is an ultraviolet-visible absorption spectrum diagram of nitrogen-doped fluorescent carbon quantum dots.

Fig. 2 is a graph of fluorescence spectra of nitrogen-doped fluorescent carbon quantum dots at different excitation wavelengths.

Fig. 3 is a transmission electron microscope and a high-resolution transmission electron microscope image of nitrogen-doped fluorescent carbon quantum dots.

Fig. 4 is a particle size distribution diagram of nitrogen-doped fluorescent carbon quantum dots.

Fig. 5 is an X-ray diffraction pattern of nitrogen-doped fluorescent carbon quantum dots.

Fig. 6 is the X-ray photoelectron spectrum of nitrogen-doped fluorescent carbon quantum dots.

Figure 7 is the Fourier infrared spectrum of nitrogen-doped fluorescent carbon quantum dots.

Fig. 8 is a fluorescence spectrum diagram of a mixed solution of Fe ³⁺ and nitrogen-doped fluorescent carbon quantum dots in the presence of different concentrations of dimethadone.

Fig. 9 is a linear relationship diagram of the fluorescence intensity at 430nm of a mixed solution of Fe ³⁺ and nitrogen-doped fluorescent carbon quantum dots as a function of the concentration of herbicide.

Figure 10 shows the anti-interference performance of the mixed solution of Fe ³⁺ and nitrogen-doped fluorescent carbon quantum dots on the recognition of herbicide.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments.

Example 1

1. Add 2g of citric acid and 2g of urea into 20mL of ultra-pure water, mix well and add into a Teflon high-pressure reactor, put the Teflon high-pressure reactor into an oven, and perform hydrothermal synthesis at 180°C for 1 hour to obtain deep turquoise The green fluorescent carbon quantum dot solution was dialyzed with a 1kw dialysis bag for 12 hours and then freeze-dried to obtain blue nitrogen-doped fluorescent carbon quantum dot powder. As can be seen from Figure 1, an absorption peak is observed at 238nm in the UV-Vis absorption spectrum of the resulting nitrogen-doped fluorescent carbon quantum dots, which is due to the π-π* transition of the C=C bond of the oxidized aromatic structure, and the π-π* transition at 332nm The absorption bands are due to surface carboxyl groups, amino groups, and other groups that passivate surface traps. When the excitation wavelength changes from 310nm to 370nm, the fluorescence intensity of nitrogen-doped fluorescent carbon quantum dots reaches a maximum at 340nm, and then further decreases, but the emission peak is at 430nm, which hardly changes with the excitation wavelength (see Figure 2 ), exhibiting an excitation-independent photoluminescence signature, which is the same as that reported for carbon quantum dots. As can be seen from Figure 3, the obtained nitrogen-doped fluorescent carbon quantum dots are spherical particles with good dispersion, the particle size range is between 4 and 13nm, and the average particle size is 8nm (see Figure 4), and the high-resolution image shows It has a lattice spacing of 0.32 nm, which also confirms the X-ray diffraction pattern of nitrogen-doped fluorescent carbon quantum dots ( FIG. 5 ). As shown in Figure 5, there are two peaks at 11.7° and 27.3°, corresponding to the lattice spacing of 0.75nm and 0.32nm, respectively, and the weaker peak at 2θ=11.7° is due to the lattice spacing of graphite oxide , indicating that nitrogen-doped fluorescent carbon quantum dots were partially oxidized during the synthesis process; the sharp high-intensity reflection at 2θ=27.3° is closer to the lattice spacing of graphene 0.34nm, which indicates that the generated nitrogen-doped fluorescent carbon quantum dots The dots have a graphene structure and demonstrate the successful synthesis of nitrogen-doped fluorescent carbon quantum dots. X-ray photoelectron spectroscopy was used to analyze the elemental composition and chemical bond types in the synthesized nitrogen-doped fluorescent carbon quantum dots. As shown in Figure 6, there are three main peaks at 284.6, 399.0, and 531.6 eV corresponding to C1s, N1s, and O1s, respectively, indicating that nitrogen atoms were successfully incorporated into the framework of carbon quantum dots by hydrothermal treatment. According to the peak intensities of carbon, nitrogen and oxygen, the doping concentration of nitrogen is about 12.1%. ^The high-resolution spectrum of C1s exhibits three main peaks, among which the strongest peak at 284.6eV corresponds to the sp conjugated two-dimensional framework structure of carbon atoms, while the other two peaks at 288.19eV and 286.10eV are attributed to In C=O bond and CO/CN bond. The high-resolution spectrum of N1s shows that the hybridization mode of nitrogen element is mainly pyrrole nitrogen and graphitic nitrogen. In addition, the functional groups of nitrogen- ^doped carbon quantum dots were characterized by Fourier transform infrared spectroscopy (see ^Figure 7), ^and the spectra showed that there were four ^strong The peaks represent the stretching vibration of -OH, the stretching vibration of C=O, the stretching vibration of NH, and the bending vibration of COC, indicating that there are a large number of amino groups, hydroxyl groups and carboxyl groups on the surface of nitrogen-doped fluorescent carbon quantum dots, which makes nitrogen-doped Heterocarbon quantum dots have the potential to become fluorescent probes with good hydrophilicity.

Add the above-mentioned nitrogen-doped fluorescent carbon quantum dot powder into ultrapure water to prepare a 3 μg/mL nitrogen-doped fluorescent carbon quantum dot solution; add 100 μL 3 μg/mL fluorescent carbon quantum dot solution and 100 μL 0.1 mmol/L _FeCl3 aqueous solution Add it into a 1.5mL centrifuge tube, then adjust the total volume to 400μL with ultrapure water, and record the fluorescence intensity F ₀ at 430nm at an excitation wavelength of 340nm.

2. Add 100 μL of 3 μg/mL nitrogen-doped fluorescent carbon quantum dot solution, 100 μL of 0.1 mmol/L FeCl ₃ aqueous solution and 200 μL of 0.5, 1, 5, 10, 15, 20, 25 respectively into a 1.5 mL centrifuge tube , 30, 35, 40, 50, 60, 80, and 100 μg/mL of herbicide aqueous solutions, with a total volume of 400 μL. After the mixed solution was shaken for 1 min, at the excitation wavelength of 340 nm, it was recorded at 430 nm where different concentrations of herbicide were added. Fluorescence intensity F, with FF ₀ as the ordinate, and the concentration of phytoxadin as the abscissa, draw the standard curve of the fluorescence intensity changing with the concentration of phytoxadin.

It can be seen from Figure 8 that the fluorescence light intensity of the mixed solution system of Fe ³⁺ and nitrogen-doped fluorescent carbon quantum dots after adding different concentrations of dichlorpyr increases without red shift or blue shift , indicating that dichlorpyr can effectively restore the fluorescence of the mixed solution system of Fe ³⁺ and nitrogen-doped fluorescent carbon quantum dots. It can be seen from Fig. 9 that the fluorescence intensity of the system changes significantly with the increase of the concentration of webicide in the system, indicating that the mixed solution system of Fe ³⁺ and fluorescent carbon quantum dots has a high detection sensitivity to webicide. Construct a standard curve for the detection of herbicide, where when the concentration of herbicide is 0-40 μg/mL, the difference between the fluorescence intensity and the concentration of herbicide is linear, the correlation coefficient is 0.9996, and the linear equation is: y=19.77318x–2.9781 , where y is the fluorescence intensity difference (FF ₀ ), and x is the added concentration of dibasin. It can be seen from Figure 9 that the linear relationship between FF ₀ and the concentration of herbicide is very good. Utilize the formula of the minimum detection limit to calculate the minimum detection limit, the detection limit (LOD=3s/K, s is the standard deviation of the blank, K is the slope of the linear equation) is 0.183 μ g/mL (about 0.183 mg/kg), lower than The limit in fruit stipulated in the national standard is 0.5mg/kg.

3. Weigh 5g of the fruit to be tested in a 50mL centrifuge tube, add 10mL of dichloromethane and 10mL of acetic acid aqueous solution with a volume concentration of 1%, crush and homogenize, and centrifuge at 5000r/min for 15min, discard the lower dichloromethane layer , take 5 mL of the supernatant, filter it with a 0.22 μm microfiltration membrane, and the obtained filtrate is used as a sample of dibasin to be tested. According to the method of step 2, when adding the herbicide sample to be tested, under the excitation wavelength of 340nm, the fluorescence intensity at 430nm can be calculated according to the linear equation of the standard curve in step 2. concentration.

In order to prove the beneficial effects of the present invention, Fe3 ⁺ and nitrogen-doped fluorescent carbon quantum dot mixed solution system are tested for the selectivity of herbicide, and the test conditions are as follows:

Add 100 μL of 3 μg/mL nitrogen-doped fluorescent carbon quantum dot solution, 100 μL of 0.1 mmol/L FeCl ₃ aqueous solution, 200 μL of 20 μg/mL aqueous solution of dibasin or 200 μL of 1 mmol/L interfering ions into a 1.5 mL centrifuge tube ^{or _ _ _ _ _} _{_} ^{_ _} _{_} ^_ 200 μL of 100 μg/mL other pesticides (such as mancozeb, phoxim, cypermethrin, the amount of other pesticides is 5 times that of herbicide), the total volume is 400 μL, and the mixed solution is shaken for 1 min at an excitation wavelength of 340 nm, and recorded at Fluorescence intensity of different interfering ions and pesticides added at 430nm.

As shown in Figure 10, the fluorescence intensity of the mixed solution system of Fe ³⁺ and nitrogen-doped fluorescent carbon quantum dots is obviously restored when only dichlorpyr exists. All other pesticides and interfering ions do not react with the mixed solution system of Fe ³⁺ and nitrogen-doped fluorescent carbon quantum dots. These results show that other ions and other pesticides have little interference on the fluorescence value of the system, indicating that the mixed solution system of quenched Fe ³⁺ and nitrogen-doped fluorescent carbon quantum dots has a high selectivity for the detection of the target herbicide sex.

Claims (7)

1. A method for detecting pesticide herbicide based on nitrogen-doped fluorescent carbon quantum dot fluorescence "on-off-on" mode, characterized in that: (1) Nitrogen-doped fluorescent carbon quantum dot aqueous solution and Fe ³⁺ solution are added in the centrifuge tube successively, then constant volume with ultrapure water, make the concentration of nitrogen-doped fluorescent carbon quantum dot in the obtained mixed solution A be 0.6～ 1.0 μg/mL, the concentration of Fe ³⁺ is 0.015 ~ 0.030mmol/L, under the excitation wavelength of 340nm, record the fluorescence intensity F ₀ of the obtained mixture A at 430nm; (2) Add nitrogen-doped fluorescent carbon quantum dot aqueous solution and Fe ³⁺ solution to the centrifuge tube successively, and add dichlorpyr standard solution, then use ultrapure water to constant volume, make the nitrogen-doped fluorescence in the obtained mixed solution B The concentration of carbon quantum dots and Fe ³⁺ is the same as in step (1). After the mixed solution B is shaken for 1 to 2 minutes, under the excitation wavelength of 340nm, record the fluorescence intensity of the obtained mixed solution B at 430nm by adding different concentrations of dichlorpyr standard solution F, with FF ₀ as the ordinate, and the addition concentration of herbicide as the abscissa, draw the standard curve that the fluorescence intensity varies with the concentration of herbicide; (3) according to the method test of step (2) when adding the herbicide to be tested sample, under the excitation wavelength of 340nm, the fluorescence intensity at 430nm, the linear equation of the standard curve in the contrast step (2) can calculate the to-be-tested herbicide The concentration of herbicide in the grass strength sample. 2. the method for detecting pesticide herbicide based on nitrogen-doped fluorescent carbon quantum dot fluorescence "on-off-open" mode according to claim 1, characterized in that the synthesis method of said nitrogen-doped fluorescent carbon quantum dot is : Add citric acid and urea into ultrapure water at a mass ratio of 1:1, mix well and then add the Teflon autoclave, put the Teflon autoclave in an oven, keep at 180°C for 1 hour, and then cool naturally to At room temperature, a crude solution of nitrogen-doped fluorescent carbon quantum dots was obtained, and the solution obtained from the reaction was added to a 1kw dialysis bag, the dialysate was ultrapure water, and the small molecule impurities were removed by dialysis for 8-12 hours, and then the dialysate was collected and freeze-dried for 12-16 hours to obtain blue The colored nitrogen-doped fluorescent carbon quantum dot powder was stored in a refrigerator at 4°C. 3. the method for detecting the pesticide herbicide based on nitrogen-doped fluorescent carbon quantum dot fluorescence "on-off-on" mode according to claim 1, characterized in that: the ^Fe solution is analytically pure FeCl _aqueous solution . 4. The method according to claim 1 based on the fluorescence "on-off-on" mode of nitrogen-doped fluorescent carbon quantum dots to detect the method of pesticide abicide, characterized in that: said abicide standard solution is a diazepam aqueous solution. 5. The method for detecting the pesticide herbicide based on nitrogen-doped fluorescent carbon quantum dot fluorescence "on-off-on" mode according to claim 1, characterized in that: the sample of herbicide to be tested is fruit, vegetable or water Sample. 6. The method for detecting the pesticide herbicide based on nitrogen-doped fluorescent carbon quantum dot fluorescence "on-off-on" mode according to claim 5, characterized in that: when the sample of herbicide to be tested is a fruit or vegetable, Before the test, add the fruits and vegetables to the mixture of dichloromethane and 1% acetic acid aqueous solution with a volume ratio of 1:1, crush and homogenize, then centrifuge, discard the lower dichloromethane layer, and take the supernatant with 0.22 μm Microfiltration membrane filtration, the obtained filtrate is used as the sample of dibasin to be tested. 7. The method for detecting the pesticide herbicide based on nitrogen-doped fluorescent carbon quantum dot fluorescence "on-off-on" mode according to claim 6, characterized in that: adding dichloromethane and 1% volume concentration of fruits and vegetables In the mixed solution whose volume ratio of acetic acid aqueous solution is 1:1, the amount of fruits and vegetables added in the mixed solution is controlled to be 20-30g/100mL.

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