CN109097033B - Switch type fluorescent carbon dot and preparation method and application thereof - Google Patents

Abstract

The invention provides a switch type fluorescent carbon dot and a preparation method and application thereof, wherein the fluorescent carbon dot is an N, S co-doped fluorescent carbon dot (N, S-CDs), and the preparation method comprises the following steps: (1) weighing glucose, adding 50-95% sulfuric acid, uniformly stirring, and then dropwise adding ethylenediamine; (2) washing the product formed in the step (1) with ultrapure water, filtering, and removing insoluble substances to obtain a supernatant; (3) and (4) freeze-drying the supernatant to obtain yellow powder, namely the switch-type fluorescent carbon dots. N, S-CDs and N, S-CDs/Cr (VI) respectively have good selectivity and sensitivity to Cr (VI) and AA based on the inner filtering effect, Cr (VI) and AA can be identified and continuously determined without labels, the linear range for detecting Cr (VI) and AA is wide, and the detection limit is low. The N, S-CDs can be used for detecting Cr (VI) in water and AA in food. Based on the specific recognition of Cr (VI) AND AA by the system, an AND logic gate at a molecular level can be constructed. In addition, the prepared N, S-CDs have good biocompatibility and can be used for multichannel cell imaging and the determination of Cr (VI) and AA in living cells.

Description

Switch type fluorescent carbon dot and preparation method and application thereof

Technical Field

The invention relates to a fluorescent carbon dot, in particular to a switch type N and S co-doped fluorescent carbon dot, a preparation method thereof and application of the carbon dot in detecting Cr (VI) and ascorbic acid.

Background

Carbon Dots (CDs) are a novel Carbon-based nanomaterial discovered in 2014, and have many excellent characteristics, such as excellent optical properties, good water solubility, low toxicity, low price, and excellent biocompatibility. Based on these advantages, CDs are widely used in many fields, such as cellular imaging technology, environmental monitoring, drug delivery, and targeted imaging. Chromium compounds are widely present in many industries such as welding, metal surface treatment and leather tanning. Ring (C)Chromium (Cr) in the environment exists mainly in two valence states, namely Cr (iii) and Cr (vi). Cr (VI) can cause respiratory and digestive diseases, anemia and cancer in humans. Cr (VI) is usually Cr₂O₇ ^2-The form exists, the solubility is good and the toxicity is high. The us epa is reviewing the health impact data for cr (vi) and may set limits on the amount of cr (vi) in future drinking water. Therefore, the measurement of Cr (VI) is very important.

Ascorbic Acid (AA) is a water-soluble natural organic compound with antioxidant properties and is an important vitamin widely found in fresh fruits, vegetables and many living organisms. As a highly active substance, it is involved in many metabolic processes. In recent years, AA has attracted attention as one of the members protecting free radical damage in vivo, such as its anti-aging, resuscitation after severe burns and anti-cancer effects. Therefore, highly selective, highly sensitive and highly accurate AA assay methods are necessary.

CN201610054676.9 discloses a N, P, S co-doped fluorescent carbon dot which can be used for detecting Cr (VI) and MnO₄ ^-And AA, but the invention uses biological fungi (saccharomycetes, or escherichia coli, or staphylococcus aureus or aspergillus niger) as a carbon source, adopts a hydrothermal synthesis method, has a reaction temperature of 160-240 ℃, and requires dialysis on a product for not less than 3 days. The reactants used in the invention are easy to obtain, the synthesis reaction temperature is high, the preparation period is long, and when Cr (VI) and MnO are contained₄ ^-When coexisting, Cr (VI) detection requires MnO disposal₄ ^-。

CN201711455408.8 discloses a carbon spot capable of detecting Cr (VI) and a preparation method thereof, wherein reactants are placed in a high-pressure reaction kettle and reacted in an oven at the temperature of 150-250 ℃ for 5-50 hours, and the target carbon spot is obtained after macroporous resin adsorption, size exclusion gel or dialysis purification. The reaction conditions of the invention are high temperature and high pressure, the reaction time is long, and the post-treatment is complicated.

The preparation methods of the carbon dots have the problems of high reaction temperature, long reaction time and complex post-treatment.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention aims to provide the switch-type fluorescent carbon dot and the preparation method thereof, the preparation method of the fluorescent carbon dot has the advantages of easily available raw materials, no need of high temperature and high pressure in reaction, short reaction time, simple post-treatment and easy realization of batch production; the prepared carbon has good point water solubility and biocompatibility, and can be used for cell imaging and the determination of environment and intracellular Cr (VI) and AA.

The invention provides a preparation method of a switch type fluorescent carbon dot, which comprises the following steps:

(1) weighing glucose, adding 50-95% sulfuric acid (volume percentage content), uniformly stirring, and then dropwise adding ethylenediamine;

(2) washing the product formed in the step (1) with ultrapure water, filtering, and removing insoluble substances to obtain a supernatant;

(3) and (4) freeze-drying the supernatant to obtain yellow powder, namely the switch type fluorescent carbon dots N, S-CDs.

The mass ratio of the glucose to 50-95% of sulfuric acid to ethylenediamine is 1: 6-20: 5-18.

The N, S-CDs prepared by the invention can be applied to the determination of Cr (VI) and AA.

The N, S-CDs prepared by the invention have lower cytotoxicity and excellent cell compatibility, can be used as a cell imaging reagent, and can be used for intracellular determination of Cr (VI) and AA.

The specific recognition AND the internal filtering effect of the N, S-CDs prepared by the invention on Cr (VI) AND AA can be used for constructing an 'AND' logic gate at a molecular level.

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

1. according to the invention, glucose, ethylenediamine and concentrated sulfuric acid (respectively used as C, N and S sources) are mixed, N and S co-doped carbon dots are prepared by a simple one-step acid-base neutralization reaction, insoluble substances are removed by filtration after the reaction, and a solvent is removed by freeze drying, so that the target product N, S-CDs is obtained. The method has the advantages of easily available raw materials, simple and quick preparation method and post-treatment, and easy realization of batch production.

2. Establishing a Cr (VI) determination method by significantly quenching the fluorescence of the N, S-CDs through Cr (VI) based on the inner filtering effect between Cr (VI) and the N, S-CDs; meanwhile, AA can recover the fluorescence of N, S-CDs quenched by Cr (VI), and a label-free fluorescent nano probe for detecting Cr (VI) and AA is established on the basis, the probe system has excellent selectivity and sensitivity to Cr (VI) and AA, the linear range of Cr (VI) is determined to be 0.065-198 mu mol/L (3.38-10296 mu g/L), and the detection limit is 0.56 nmol/L; the linear range of AA is 6.6-892 mu mol/L (1.16-157 mg/L), and the detection limit is 76 nmol/L.

3. Based on the specific recognition AND the internal filtering effect of the system on Cr (VI) AND AA, an 'AND' logic gate at a molecular level can be constructed. And the prepared N, S-CDs have lower cytotoxicity and excellent cell compatibility, can show red, green and blue fluorescence in cells, and can be used as a reagent for cell imaging and intracellular determination of Cr (VI) and AA.

Drawings

FIG. 1 is a graph showing the spectral properties of N, S-CDs. Wherein: a. visible-ultraviolet absorption spectrum, fluorescence excitation and emission spectrum of N, S-CDs in aqueous solution. The inset of a is a picture of the N, S-CDs aqueous solution under the irradiation of visible light (left) and 365nm ultraviolet light (right); b. emission spectra of N, S-CDs obtained at different excitation wavelengths.

FIG. 2N, S-CDs composition, morphology characterization. Wherein: a. x-ray photoelectron spectroscopy (XPS) full scan spectra; b. an N1s spectrum; c. a C1s spectrum; d. S2S spectrum; e. an O1s spectrum; f. fourier infrared absorption spectrum; g. transmission electron microscopy, inset is size distribution (lower left) and high resolution transmission electron microscopy (upper right, lattice parameter 0.22nm) for N, S-CDs; h. an atomic force microscope; i. dynamic light scattering images.

FIG. 3N, S-CDs selectivity and determination of Cr (VI). Wherein: a. selectivity of N, S-CDs to metal ions; b. selectivity of N, S-CDs for anions; c. selectivity of N, S-CDs for amino acids; d. interference experiments with metal ions at 10 times the cr (vi) concentration; e. the fluorescence spectrum of Cr (VI) added into the aqueous solution of N, S-CDs is shown as F₀Linear relationship of/F to different concentrations of Cr (VI).

FIG. 4 fluorescence recovery and determination of AA for the N, S-CDs/Cr (VI) system. Wherein: a. adding fluorescence spectra of different reducing agents into the N, S-CDs/Cr (VI) solution; b. n, S-CDs/Cr (VI) solutionFluorescence spectrum of AA added to the solution, inset: f₀-linear relationship of F to AA concentration; c. fluorescence intensity cycle plot of N, S-CDs after addition of Cr (VI) and AA.

FIG. 5N, application of S-CDs to construct "AND" molecular logic gates. Wherein: (a) logic schemes AND (b) input AND output tables of "AND" logic gates.

FIG. 6N, cytotoxicity evaluation of S-CDs and multichannel fluorescence imaging. Wherein: a. relative survival of SMMC 7721 cells incubated at 37 ℃ for 48 hours in different concentrations of N, S-CDs; b. confocal laser images of SMMC 7721 cells (250. mu.g/mL N, S-CDs, 2 hours incubation at 37 ℃), b1, b2, b3 and b4 at λ_ex/λ_emCell images taken at 543/650 + -25, 488/500 + -25, 405/422 + -25 and 515/570 + -25 nm, b5 is a brightfield image, b6 is a combined image of b1, b2, b3, b4 and b5, respectively.

FIG. 7 intracellular determination of Cr (VI) and AA for S-CDs. Wherein: (a) cytograms of different concentrations of N, S-CDs (concentrations of N, S-CDs of a1, a2, a3 and a4, 100, 200, 300 and 400. mu.g/mL, respectively); (b) cell images of 250. mu.g/mL N, S-CDs with Cr (VI) added at different concentrations (Cr (VI) concentrations of b1, b2, b3 and b4 of 0, 0.57, 2.1 and 4.3. mu. mol/L, respectively); (c) cell images at different times after 400. mu.g/mL N, S-CDs + 5. mu. mol/L Cr (VI) (times of c1, c2, c3, c4 and c5 were 0,1, 2, 3 and 4 minutes, respectively); (d) cell images at different times after 400. mu.g/mL N, S-CDs + 5. mu. mol/L Cr (VI) + 290. mu. mol/L AA (times for d1, d2, d3, d4 and d5 were 0,1, 2, 3 and 4 minutes, respectively).

Detailed Description

The invention is further illustrated by the following figures and examples, wherein the preparation conditions are only illustrated as typical and not limiting. All characterization and application used the carbon dots N, S-CDs prepared in example 1.

Example 1

(1) 0.4g of glucose is weighed, 4.0mL of 70% concentrated sulfuric acid is added, stirring is carried out uniformly, and then 6.0mL of ethylenediamine is added dropwise.

(2) Adding ultrapure water to wash the product, and filtering to remove insoluble substances to obtain a supernatant.

(3) And (4) freeze-drying the supernatant to obtain yellow powder, namely the prepared carbon dots N, S-CDs.

Example 2

(1) 0.4g of glucose is weighed, 2.7mL of 50% concentrated sulfuric acid is added, stirring is carried out uniformly, and then 3.0mL of ethylenediamine is added dropwise.

(2) Adding ultrapure water to wash the product, and filtering to remove insoluble substances to obtain a supernatant.

(3) And (4) freeze-drying the supernatant to obtain yellow powder, namely the prepared carbon dots N, S-CDs.

Example 3

(1) 0.4g of glucose is weighed, 4.4mL of 95% concentrated sulfuric acid is added, stirring is carried out uniformly, and then 8.4mL of ethylenediamine is added dropwise.

(2) Adding ultrapure water to wash the product, and filtering to remove insoluble substances to obtain a supernatant.

(3) And (4) freeze-drying the supernatant to obtain yellow powder, namely the prepared carbon dots N, S-CDs.

Example 4

(1) 0.4g of glucose is weighed, 3.0mL of 80% concentrated sulfuric acid is added, stirring is carried out uniformly, and then 5.0mL of ethylenediamine is added dropwise.

(2) Adding ultrapure water to wash the product, and filtering to remove insoluble substances to obtain a supernatant.

(3) And (4) freeze-drying the supernatant to obtain yellow powder, namely the prepared carbon dots N, S-CDs.

Example 5

(1) 0.4g of glucose is weighed, 5.5mL of 60% concentrated sulfuric acid is added, stirring is carried out uniformly, and then 7.0mL of ethylenediamine is added dropwise.

(2) Adding ultrapure water to wash the product, and filtering to remove insoluble substances to obtain a supernatant.

(3) And (4) freeze-drying the supernatant to obtain yellow powder, namely the prepared carbon dots N, S-CDs.

The N, S-CDs prepared in examples 1-5 have small particles and are uniformly dispersed in water, and can be used for Cr (VI) and AA determination.

Example 6 characterization of N, S-CDs

FIG. 1 is a graph showing the absorption spectrum and fluorescence spectrum of N, S-CDs. In fig. 1 a, absorption peaks at 280 and 333nm for the prepared N, S-CDs absorption curves are due to C ═ C bond pi → pi transition and C ═ O bond N → pi transition, respectively, and fluorescence excitation and emission wavelengths are 372nm and 465nm, respectively. The inset in fig. 1 a illustrates that aqueous solutions of N, S-CDs are yellow transparent under visible light and exhibit blue fluorescence under 365nm ultraviolet light. In b of FIG. 1, when the fluorescence excitation wavelength is shifted from 280nm to 440nm, the fluorescence emission wavelength of N, S-CDs is red-shifted from 465nm to 495nm, while the fluorescence intensity increases to a maximum at 380nm and decreases to a minimum at 495nm, indicating that the fluorescence of the carbon spot has excitation wavelength dependence. Further, the quantum yield of the carbon dots was calculated to be 5.1% using the five-dot method.

FIG. 2 is an X-ray photoelectron spectrum, Fourier infrared spectrum, transmission electron microscope, atomic force microscope, and dynamic light scattering diagram. The elemental analysis shows that the elemental composition of the prepared N, S-CDs is C₂H₁₁N₂SO₄. The X-ray photoelectron spectroscopy (XPS) full spectrum scan (a in fig. 2) shows five peaks at 527, 396, 280, 227 and 164eV, which should be attributed to O1S, N1S, C1S, S2S and S2p, respectively. The high resolution O1S XPS spectrum (b in fig. 2) decomposed into five peaks at 531.78, 531.17, 530.66, 530.17 and 529.66eV, which correspond to O/S-O, C-OH/C-O, C-O-C, O ═ C-O and SO of pyridine₄ ^2-. N1s (c in FIG. 2) has four peaks at 400.70, 399.86, 398.92 and 398.08eV, corresponding to the pyridine and pyrrole nitrogens, e.g., -NH-of pyridine₂N-OH and-CN/N- (C). The C1S spectrum (d in fig. 2) shows five peaks at 286.5, 285.5, 285.0, 284.5 and 283.5eV, which are attributed to C-O/C ═ O, C-N/C-O-C, C-C/C-H, C ═ C and C-S groups. The S2p3/2 spectrum (e in fig. 2) exhibits three peaks at 168.65, 167.71 and 166.78, indicating that sulfur is predominantly present as thiophenesulfur and-C-SOx (x ═ 2, 3, 4), which are due to SO respectively₄ ^2-，N-S(O)/SO₃ ^2-And N-S (O)/S₂O₃ ^2-A group. All results show that N and S are successfully doped in the prepared N, S-CDs.

Fourier infrared spectroscopy (FTIR) also demonstrated the presence of N and S, as shown in f of figure 2. IR (KBr) cm^-1：3462，γ_OH/NH；3181,γ_NH(elongation of amide bond)Vibration reduction); 3022 γ ═ y_C-H(C-H stretching vibration of double bond); 2930, gamma_C-H(asymmetric stretching vibration of methyl and methylene); 2863, gamma_C-H(symmetric stretching vibration of methylene and methyl); 2469 and gamma_NH(N-H stretching vibration in amine salt); 2130 and 2180, gamma_{C＝C＝O/C≡N}(telescopic vibration of triple bonds or cumulative double bonds); 1644, gamma_O＝C-N(stretching vibration of C ═ O of amide bond); 1540, delta_N-H(in-plane bending vibration of N-H in the secondary amide); 1456, delta_C-H(asymmetric bending vibration of methylene and methyl); 1385, delta_C-H(symmetric bending vibrations of methylene and methyl groups); 1343, delta_O-H(in-plane bending vibration of O-H); 1092, delta_C-O/C-N；975,δ_＝C-H(ii) a 644 and 606, SO₃ ^2-/SO₄ ^2-. From the FTIR and XPS spectra, S may be present as a sulfate, sulfite or thiosulfate salt.

And (4) characterizing the morphology and size distribution of the prepared N, S-CDs by a Transmission Electron Microscope (TEM). The g of the representative TEM image 2 shows that N, S-CDs are mainly round and uniformly distributed on the surface of the copper mesh, the particle size distribution is 2.2-5.8 nm, and the average particle size is 3.4 + -0.5 nm calculated by 100 particles. The high resolution TEM inset in FIG. 2 g illustrates that the N, S-CDs have lattice fringes of 0.22nm, confirming that the N, S-CDs have a crystalline structure, similar to the (100) plane of the graphitic structure. FIG. 2, h is an Atomic Force Microscope (AFM) image used to further characterize the morphology of N, S-CDs, confirming that the N, S-CDs particles are uniformly distributed with an average height of 0.5-2.5 nm. FIG. 2, i is a Dynamic Light Scattering (DLS) result, indicating that N, S-CDs have an average hydrodynamic particle size of 9.6. + -. 0.6nm, are highly dispersible in aqueous solution, and do not aggregate.

Example 7 determination of Cr (VI)

FIG. 3 shows the determination of Cr (VI) by N, S-CDs. In FIG. 3, a, b and c are the selectivities of N, S-CDs for 19 metal ions, 13 anions and 18 amino acids, respectively. In FIG. 3 a shows Fe³⁺And Cr (VI) can significantly quench the fluorescence of N, S-CDs. FIG. 3 d shows the anti-interference performance of the N, S-CDs/Cr (VI) system, with the coexisting metal ions (Mn) being 10 times the concentration of Cr (VI)²⁺,Cd²⁺,Al^{3 +},Zn²⁺,Ca²⁺,Na⁺,K⁺,Mg²⁺,Fe²⁺,Ag⁺,Ni²⁺,Co²⁺,Cu²⁺,Hg²⁺And Cr³⁺) Can not cause the fluorescence of N, S-CDs/Cr (VI) to be obviously changed. Reaction ratio of N, S-CDs to Cr (VI) Fe³⁺More sensitive, the selectivity of the prepared N, S-CDs to Cr (VI) is better than that of other metal ions. And Fe (OH) in aqueous solution₃Has a solubility product of 4X 10^-38When pH is 7, [ Fe ]³⁺]＝4×10^-17The determination of Cr (VI) is not affected.

The fluorescence titration experiment was used to investigate the relationship between the fluorescence intensity of N, S-CDs and the Cr (VI) concentration, as shown in e of FIG. 3. FIG. 3, e, shows that the fluorescence intensity of N, S-CDs decreases with increasing concentration of Cr (VI). The fluorescence intensity and the Cr (VI) concentration have good linear relation in the range of 0.065-198 mu mol/L (namely 3.38-10296 mu g/L), and the linear equation is that y is 0.0052x +0.9817(R is R²0.9957 and n 23). The quenching constant was estimated to be 5.2X 10²L/mol. Where F and F₀Is the fluorescence intensity of N, S-CDs at 465nm in the presence and absence of Cr (VI). The limit of detection (LOD) of the nanoprobe was calculated to be 0.56nmol/L based on three times the standard deviation divided by the quenching constant. SASO, GSO and WHO propose that the limit concentration of Cr in drinking water is 50 mug/L, which means that the constructed N, S-CDs fluorescent nanoprobe can well determine the content of Cr (VI) in tap water.

EXAMPLE 8 Ascorbic Acid (AA) assay

FIG. 4 shows the determination of Ascorbic Acid (AA) by N, S-CDs/Cr (VI). The prepared N, S-CDs can be used as a nano probe for detecting Cr (VI) through an 'On-Off' process. Using different reducing agents (KF, KCl, KBr, citric acid, glucose, KBH)₄，NaNO₃，Na₂SO₃，Na₂S₂O₃，Na₂S, glutathione, glycine, glutamic acid, cysteine and AA) restores the fluorescence of N, S-CDs quenched by cr (vi). FIG. 4 a shows that AA can significantly restore the fluorescence of the N, S-CDs/Cr (VI) system, and FIG. 4 b shows that the fluorescence intensity of the N, S-CDs/Cr (VI) system gradually increases with the increase of AA concentration. The inset of b in FIG. 4 shows that F₀A good linear relation exists between F and AA concentration, the linear range is 6.6-892 mu mol/L (namely: 1.16-157 mg/L), and the linear equation is that F is equal to F-F₀＝0.3372C_AA-4.6917(R²0.9824, n 15), LOD 76 nM. Finally, the number of fluorescence cycles of the prepared N, S-CDs between Cr (VI) and AA was studied, and c in FIG. 4 shows that the "On-Off-On" nanoprobe can achieve 12 cycles of Cr (VI) and AA measurements, and that the fluorescence intensity approximately recovers 73% of the initial fluorescence in each cycle.

Example 9 application of "AND" molecular logic Gate

FIG. 5 is a table of inputs and outputs of the constructed molecular logic gate. Since Cr (VI) can quench the fluorescence of N, S-CDs by the internal filtering effect, AND the addition of AA can weaken the internal filtering effect AND recover the fluorescence, an 'AND' molecular logic gate can be constructed. Cr (VI) and AA are used as input signals with the "On" and "Off" fluorescence states, and the fluorescence recovery at 465nm is shown as output signal in FIG. 5 (a). As shown in fig. 5 (b), the presence and absence of cr (vi) and AA are designated as "1" and "0", respectively. And the output strong/weak fluorescence is defined as "1/0". When Cr (VI) and AA are absent or only one of them is present, i.e., inputs are (0,0), (0,1) and (1,0), the outputs are both "0". Only cr (vi) and AA coexist, i.e. when the input is (1,1), the output is "1".

Example 10 cytotoxicity assessment and Multi-channel imaging

Fig. 6 is a graph of cytotoxicity evaluation and multi-channel laser confocal (LSCM) imaging. The toxicity of the prepared N, S-CDs on SMMC 7721 cells was evaluated by MTT assay for further biological applications. As shown in a in FIG. 6, even if SMMC 7721 cells were incubated with 800. mu.g/mL of N, S-CDs at 37 ℃ for 48 hours, the survival rate of the cells was still higher than 66%, indicating that the N, S-CDs were very low in cytotoxicity and useful for intracellular identification and cellular imaging. In FIG. 6 b shows that N, S-CDs in SMMC 7721 cells can exhibit red, green, blue and yellow fluorescence emissions when the excitation wavelengths are 543nm (b1), 488nm (b2), 405nm (b3) and 515nm (b4), indicating that N, S-CDs can be used as potential multi-color biomarker reagents.

Example 11 intracellular Cr (VI) and AA determination

The ability of nanoprobes to image cr (vi) and AA was measured in SMMC 7721 cells with an excitation wavelength of 488 nm. FIG. 7 (a) depicts that the fluorescence intensity increases with increasing N, S-CDs concentration. FIG. 7 (b) shows that the fluorescence intensity decreases with increasing Cr (VI) concentration, and the fluorescence almost completely disappears at a Cr (VI) concentration of 4.3. mu. mol/L. LSCM dynamic scan as shown in fig. 7 (c), as cr (vi) entered SMMC 7721 cell nutrient solution, green fluorescence gradually decreased over time until it was barely visible. However, when AA was added to SMMC 7721 cell nutrient solution, green emission was gradually increased with time (fig. 7 (d)), demonstrating that fluorescence emission of N, S-CDs/cr (vi) in cells can be restored by AA. The results show that N, S-CDs can be used as an excellent fluorescent nano probe to cyclically detect Cr (VI) and AA in living cells in an On-Off-On mode.

Claims (6)

1. The application of the switch type fluorescent carbon dot in Cr (VI) determination is characterized in that the preparation method of the switch type fluorescent carbon dot comprises the following steps:

(1) weighing glucose, adding 50-95% sulfuric acid, uniformly stirring, and then dropwise adding ethylenediamine;

(2) washing the product formed in the step (1) with ultrapure water, filtering, and removing insoluble substances to obtain a supernatant;

(3) and (4) freeze-drying the supernatant to obtain yellow powder, namely the switch-type fluorescent carbon dots.

2. The use according to claim 1, wherein the mass ratio of glucose, sulfuric acid and ethylenediamine is 1: 6-20: 5-18.

3. The application of the switch-type fluorescent carbon dot in ascorbic acid determination is characterized in that the preparation method of the switch-type fluorescent carbon dot comprises the following steps:

(1) weighing glucose, adding 50-95% sulfuric acid, uniformly stirring, and then dropwise adding ethylenediamine;

(2) washing the product formed in the step (1) with ultrapure water, filtering, and removing insoluble substances to obtain a supernatant;

(3) and (4) freeze-drying the supernatant to obtain yellow powder, namely the switch-type fluorescent carbon dots.

4. The use according to claim 3, wherein the mass ratio of glucose, sulfuric acid and ethylenediamine is 1: 6-20: 5-18.

5. The application of the switch type fluorescent carbon dot in an 'AND' molecular logic gate is characterized in that the preparation method of the switch type fluorescent carbon dot comprises the following steps:

(1) weighing glucose, adding 50-95% sulfuric acid, uniformly stirring, and then dropwise adding ethylenediamine;

(2) washing the product formed in the step (1) with ultrapure water, filtering, and removing insoluble substances to obtain a supernatant;

(3) and (4) freeze-drying the supernatant to obtain yellow powder, namely the switch-type fluorescent carbon dots.

6. The use according to claim 5, wherein the mass ratio of glucose, sulfuric acid and ethylenediamine is 1: 6-20: 5-18.

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