A method for detecting mercury ions by using o-phenylenediamine derivative carbon quantum dots as a fluorescent probe

Abstract

The present application relates to a kind of with o-phenylenediamine derivative carbon quantum dots as fluorescent probe detection mercury ion method, belong to analytical detection technical field.The present application with o-phenylenediamine derivative carbon quantum dots as fluorescent probe detection mercury ion method, specifically is first with taurine and o-phenylenediamine preparation carbon quantum dots solution yCQDs;Then carbon quantum dots solution and buffer solution form yCQDs fluorescent probe system;Directly use yCQDs fluorescent probe for Hg 2+ The fluorescence detection of the method not only saves the use of noble metal, but also has good selectivity and high sensitivity;In actual samples such as tap water, lake water and bottled drinking water, Hg 2+ It has good detection capacity.

Description

TECHNICAL FIELD

[0001] The application relates to a method for detecting mercury ions by using o-phenylenediamine derivative carbon quantum dots as a fluorescent probe, and belongs to the technical field of analysis and detection. BACKGROUND

[0002] The detection methods for different heavy metal ions in the prior art include electrochemical method, photoelectrochemical method, chemiluminescence method, surface-enhanced Raman spectroscopy method, colorimetric method and fluorescence spectroscopy method. Although these methods can be used for detecting low-concentration heavy metal ions, they usually need to bear high probe cost and complex process.

[0003] As a new fluorescent material, carbon quantum dots can be specifically surface-modified according to application requirements, and the properties thereof give it a very broad application prospect. In addition, the low cost, good hydrophilicity and good biocompatibility of the carbon quantum dots are also worth attention. The fluorescent method using carbon quantum dots as a sensor has the advantages of simple preparation of probes, environmental protection, high sensitivity and visualization, and is constantly bringing surprises to researchers in the field of heavy metal ion detection.

[0004] O-phenylenediamine (OPD) has unique aromatic amine properties and is an important precursor for synthesizing a large number of heterocyclic compounds or polymers.

[0005] Hg 2+ The fluorescent sensor is usually based on the catalytic effect of noble metal nanoparticles on the oxidation process of OPD and the inhibition or promotion effect of Hg 2+ on the catalytic performance to realize the detection of Hg 2+ , but these sensors often need to use noble metals, and the operation is complex and the cost is high. SUMMARY

[0006] In view of the above technical problems, the application provides a method for detecting mercury ions by using o-phenylenediamine derivative carbon quantum dots as a fluorescent probe, which specifically prepares nitrogen-sulfur co-doped yellow light-emitting carbon quantum dots yCQDs by a hydrothermal method, and uses the yCQDs as a fluorescent probe for direct fluorescence detection of Hg 2+ ; the method not only saves the use of high-cost noble metals, but also has the advantages of good selectivity and high sensitivity; and the method has good detection capability for Hg 2+ in actual samples such as tap water, lake water and bottled drinking water.

[0007] The application aims to provide a method for detecting mercury ions by using o-phenylenediamine derivative carbon quantum dots as a fluorescent probe, and the method comprises the following steps:

[0008] (1) Preparation of yCQDs fluorescent probe system

[0009] Dissolve taurine and o-phenylenediamine in water and adjust the pH of the solution to neutral, and then transfer to a high-pressure reactor for hydrothermal reaction to obtain a crude product; purify the crude product by silica gel column chromatography to obtain a carbon quantum dot solution yCQDs; mix the carbon quantum dot solution with a buffer solution uniformly to obtain a yCQDs fluorescent probe system;

[0010] (2) Quantitative relationship model construction

[0011] Take the yCQDs fluorescent probe system prepared in step (1) and a series of known concentrations of mercury ion solutions to obtain standard samples by oscillating uniformly, incubate at room temperature overnight, and then measure the fluorescence intensity of each standard sample under 418 nm excitation; take the fluorescence intensity as the vertical coordinate and the mercury ion concentration as the horizontal coordinate to establish a quantitative relationship model;

[0012] (3) Mercury ion content determination in a sample to be tested

[0013] Take the yCQDs fluorescent probe system prepared in step (1) and the sample to be tested, mix them uniformly, incubate at room temperature overnight, then measure the fluorescence intensity of the mixed solution under 418 nm excitation, and calculate the content of mercury ions in the sample to be tested according to the quantitative relationship model established in step (2).

[0014] In one embodiment, the reagent used for adjusting the pH of the solution in step (1) is a freshly prepared sodium hydroxide solution with a concentration of 0.1-0.2 mol / L.

[0015] In one embodiment, the incubation at room temperature overnight is incubation at 20-30°C overnight.

[0016] In one embodiment, the pH value adjusted to neutral in step (1) is 6.5-7.5.

[0017] In one embodiment, when the absorbance value of the carbon quantum dot solution yCQDs at 420 nm in the ultraviolet-visible absorption spectrum is 0.200, the corresponding concentration is defined as 1 unit, and the concentration of the carbon quantum dot solution yCQDs in the mixed solution of the yCQDs fluorescent probe system and the sample to be tested in step (3) is 0.1-0.5 units; the volume ratio of the yCQDs fluorescent probe system to the sample to be tested is 9:1.

[0018] In one embodiment, the buffer solution in step (1) is a phosphate buffer solution; the pH value of the buffer solution is 6.0-8.0, the concentration is 0.1-0.2 mol / L, and the volume accounts for 50-90% of the total volume of the yCQDs fluorescent probe system; the pH value of the buffer solution is preferably 6.0.

[0019] In one embodiment, the purification of the crude product by silica gel column chromatography in step (1) means that the crude product is purified by silica gel column chromatography twice, with the eluents being ethanol and ethyl acetate respectively.

[0020] In one embodiment, the temperature of the hydrothermal reaction in step (1) is 180~200℃ and the time is 8~12h.

[0021] In one embodiment, the mass ratio of taurine and o-phenylenediamine in step (1) is 1:1~2.

[0022] Another object of the present invention is to provide an application of the above method in the detection of mercury ions.

[0023] Beneficial effects of the present invention

[0024] (1) In this invention, nitrogen- and sulfur co-doped fluorescent carbon quantum dots (yCQDs) were prepared by hydrothermal method using o-phenylenediamine (OPD) and taurine as precursors. yCQDs have a high susceptibility to Hg. 2+ It exhibited sensitive recognition capabilities; the abundant functional groups on the surface of yCQDs can interact with Hg. 2+ Through multiple interactions, a complex is formed and the absorption of excitation light by the system is suppressed, thereby significantly quenching the fluorescence of yCQDs through a static quenching mechanism.

[0025] (2) The detection method established in this invention has the advantages of both good selectivity and high sensitivity. It can effectively detect Hg in actual samples such as tap water, lake water and commercially available bottled drinking water. 2+ It has good detection capability; the fluorescence intensity of the detection system is similar to that of Hg. 2+ Concentration at 1.00 × 10 -7 -3.00×10 -6 Linear correlation was observed in the range of mol / L (R0). 2 =0.9962), detection limit is 2.78×10 -8 mol / L. Attached Figure Description

[0026] Figure 1 This invention is based on yCQDs for detecting Hg. 2+ A schematic diagram of the principle;

[0027] Figure 2 The following are spectra of yCQDs prepared in Example 1 of this invention: (A) HRTEM image of yCQDs; (B) Particle size distribution statistics of yCQDs; (C) Three-dimensional fluorescence spectrum of yCQDs; (D) UV-Vis absorption spectrum and normalized excitation spectrum (λ) of yCQDs. em =575 nm) and emission spectrum (λex=418 nm);

[0028] Figure 3 The FT-IR spectrum and XPS full spectrum of yCQDs prepared in Example 1 of this invention; (A) FT-IR spectrum of yCQDs; (B) XPS full spectrum of yCQDs;

[0029] Figure 4 XPS fine spectra of yCQDs prepared in Example 1 of the present invention; (A) C 1s fine spectrum of yCQDs; (B) N 1s fine spectrum of yCQDs; (C) O 1s fine spectrum of yCQDs; (D) S 2p fine spectrum of yCQDs;

[0030] Figure 5 Fluorescence emission, absorption, and attenuation diagrams for two systems: yCQDs and yCQDs coexisting with mercury; (A) yCQDs, yCQDs+Hg 2+ The fluorescence emission spectrum; (B) yCQDs (1), yCQDs+Hg 2+ (2) Photographs under fluorescent light (above) and ultraviolet light (below); (C) yCQDs, yCQDs+Hg 2+ UV-Vis absorption spectrum; (D) yCQDs,yCQDs+Hg 2+ Fluorescence decay diagram;

[0031] Figure 6 For oxOPD on the yCQDs surface, Hg is introduced 2+ Electrostatic potential energy diagrams of the molecular surface before and after the introduction of Hg; (A) Electrostatic potential energy diagram of the molecular surface of oxOPD; (B) Electrostatic potential energy diagram of the molecular surface of oxOPD before and after the introduction of Hg. 2+ After that, oxOPD+Hg 2+ Electrostatic potential energy diagram of the molecular surface of the system;

[0032] Figure 7 Different Hg values ​​in Embodiment 2 of the present invention 2+ Fluorescence emission spectra of yCQDs under different concentration conditions; (A) with different concentrations of Hg added. 2+ Fluorescence emission spectra of yCQDs; (B) Hg 2+ Concentration in the range of 0-1.00×10 -5 Within the mol / L range, the fluorescence intensity of yCQDs is related to Hg 2+ Concentration relationship (inset plot is 1.00 × 10⁻⁶) -7 -3.00×10 -6 Fluorescence intensity and Hg within the M range 2+ (Linear fitting results of concentration);

[0033] Figure 8The fluorescence intensity graph of yCQDs itself under different pH conditions in Example 3 of the present application and the quenching rate graph caused by adding Hg 2+ The fluorescence emission peak (575 nm) intensity of yCQDs; (B) the fluorescence quenching rate of yCQDs after adding 1.00×10 -6 M Hg 2+ The fluorescence quenching rate caused by adding Hg

[0034] Figure 9 The fluorescence emission spectrum graph of yCQDs under different incubation times or different incubation temperatures in Example 4 of the present application; (A) the fluorescence quenching rate of yCQDs after adding 1.00×10 -4 mol / L Hg 2+ The change of the fluorescence peak intensity of yCQDs within 52 min; (B) the fluorescence quenching rate of yCQDs after adding 1.00×10 -5 mol / L Hg 2+ The fluorescence emission spectrum of yCQDs under different incubation times; (C) the fluorescence quenching rate of yCQDs after adding Hg 2+ The fluorescence emission spectrum of yCQDs after incubation at room temperature or in a water bath for the same time;

[0035] Figure 10 The data graph of the selectivity and anti-interference ability of yCQDs in Example 5 of the present application; (A) the Hg 2+ selectivity of yCQDs, the fluorescence quenching rate of yCQDs in the presence of different metal cations in the system; (B) the anti-interference ability of yCQDs for Hg 2+ sensing, the fluorescence quenching rate of yCQDs in the presence of Hg 2+ and other metal cations in the system;

[0036] Figure 11 The standard curve graph in the determination of actual samples in Example 6 of the present application; (A) in the tap water sample, the relationship between the fluorescence intensity of the yCQDs system and the added Hg 2+ concentration (the interpolation graph is the linear fitting result in the range of 7.00×10 -8 -3.00×10 -6 mol / L); (B) in the river water sample, the relationship between the fluorescence intensity of the yCQDs system and the added Hg 2+ concentration (the interpolation graph is the linear fitting result in the range of 1.00×10 -7 -3.00×10 -6 mol / L); (C) in the bottled water sample, the relationship between the fluorescence intensity of the yCQDs system and the added Hg 2+ concentration (the interpolation graph is the linear fitting result in the range of 1.00×10 -7 -3.00×10 -6 mol / L). DETAILED DESCRIPTION

[0037] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention.

[0038] Example 1: Preparation of carbon quantum dots yCQDs

[0039] 0.05 g taurine and 0.05 g o-phenylenediamine were sonicated and dissolved in 20 mL deionized water. The pH of the solution was adjusted to 7.0 using 0.1 mol / L NaOH. The solution was then transferred to a stainless steel autoclave and reacted at 200 °C for 8 h to obtain the crude product. The crude product was subjected to two silica gel column chromatography processes to obtain purified yCQDs. The eluents used for the two silica gel column chromatography processes were ethanol and ethyl acetate, respectively.

[0040] Characterization of carbon quantum dots yCQDs

[0041] The purified yCQDs were diluted until the absorbance at 420 nm of their UV-Vis absorption spectrum was 0.200. At this point, the concentration of yCQDs was defined as 1 unit, and the yCQDs were stored at 4 °C for later use.

[0042] Figure 2 Image A is a high-resolution transmission electron microscope (HRTEM) image of yCQDs, showing that they are approximately spherical with high crystallinity and an interplanar spacing of approximately 0.33 nm. Statistical analysis of the HRTEM images indicates that their particle size is mainly distributed in the range of 2.51-5.16 nm, with an average particle size of 3.40 nm; three-dimensional fluorescence spectroscopy (…). Figure 2 C) indicates that the fluorescence emission peak of yCQDs is independent of the excitation wavelength and is stable around 575 nm, with the corresponding optimal excitation wavelength being 418 nm. This may be due to the relatively simple fluorophores on the surface of yCQDs. The UV-Vis absorption spectrum of yCQDs shows a characteristic absorption peak around 420 nm. Figure 2 D).

[0043] Based on this, it can be preliminarily inferred that the photoluminescence mechanism of yCQDs belongs to molecular photoluminescence, and its main fluorophore should be 2,3-diaminophenazine (oxOPD), an oxidation product of o-phenylenediamine. When rhodamine B (RB), with a quantum yield (QY) of 31% in water, is used as a reference, the QY of yCQDs is measured to be 4.2% by a relative method.

[0044] The structure and surface functional group information of yCQDs were analyzed using Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The FT-IR spectra of yCQDs... Figure 3 A) It can be determined that the location is at 3385cm. -1and 3201cm -1 The broad absorption band originates from the stretching vibrations of the OH and NH bonds, 1627 cm⁻¹ -1 and 1528cm -1 The nearby absorption band indicates the presence of unsaturated C=C bonds and aromatic rings, 1385 cm⁻¹ -1 The absorption peak at 1225 cm⁻¹ is caused by the stretching vibration of the CN bond. Absorption peaks attributable to the stretching vibrations of the S=O and CS bonds are visible at 1225 cm⁻¹. -1 With 1048cm -1 Therefore, based on the above analysis, it can be concluded that nitrogen and sulfur elements were successfully doped into yCQDs, and the surface of yCQDs contains amino and sulfonic acid groups.

[0045] Furthermore, in the XPS full spectrum ( Figure 3 In B), four peaks are visible at 532.40, 399.39, 285.13 and 168.28 eV, which are attributed to O 1s, N 1s, C 1s and S 2p, respectively, and the atomic ratio of these four elements is approximately 19.48:12.76:64.04:3.72.

[0046] C 1s fine spectrum ( Figure 4 The four peaks at 284.80, 285.65, 286.70, and 288.98 eV in A) correspond to the aromatic rings CC / C=C, CS / CO, CN, and C=O, respectively; N 1s fine spectrum ( Figure 4 The peaks at 399.15 and 400.25 eV in B) indicate the presence of CN and NH, respectively. Figure 4 The C-O 1s fine spectrum shows peaks at 532.14 and 532.98 eV, which are attributed to COH and O=CO, respectively; the S 2p fine spectrum ( Figure 4 The two peaks at 168.27 and 169.74 eV in D) correspond to the S 2p of the sulfone bridge -CS(O)2-C-. 3 / 2 and S 2p 1 / 2 The spin-orbit splitting double peaks indicate the presence of CS and S=O in the sample, while the peak at 166.58 eV can be attributed to SO. The surface functional group information of yCQDs obtained by XPS is consistent with the characterization results of FT-IR, both indicating successful doping of nitrogen and sulfur elements and the presence of amino and sulfonic acid groups.

[0047] Example 2

[0048] A method for detecting mercury ions in water based on yCQDs fluorescent probes, the method comprising the following steps:

[0049] Mix 0.30 mL of yCQDs solution (concentration of 1 unit) and 2.40 mL of phosphate buffer solution (0.1 mol / L, pH=6.0) and shake well. Then add 0.30 mL of Hg at different concentrations (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 70, 100 μmol / L). 2+ The solution and the blank control group were prepared by adding an equal amount of deionized water and shaking them thoroughly. After incubating at room temperature overnight, the fluorescence spectra of each sample were measured under 418 nm excitation.

[0050] Figure 7 The results show that the linear interval for Example 2 is 1.00 × 10⁻⁶. -7 -3.00×10 -6 mol / L, based on 3s b The detection limit (LOD) calculated by / S is 4.50 × 10⁻⁶. -8 mol / L, where s b S is the standard deviation of the blank sample, and S is the slope of the linear fitting equation.

[0051] according to Figure 5 A and 5C, comparing yCQDs and yCQDs+Hg 2+ Hg 2+ As can be seen from the process of Hg's involvement, 2+ The presence of [a specific substance] causes a decrease in the intensity of the absorption peak at 420 nm and quenches the fluorescence of the system, while the absorption values ​​in the bands below 362 nm and above 483 nm both increase. Furthermore, quantum chemical calculations were used to analyze the surface electrostatic potential distribution of oxOPD. Figure 6 The results showed that Hg 2+ It tends to bind to oxOPD via electrostatic interactions, using heterocyclic nitrogen atoms as binding sites. Meanwhile, given the strong binding tendency of Hg-S, Hg... 2+ There is also the possibility of bonding with sulfur-containing functional groups on the yCQDs surface. The result of the above interactions is Hg 2+ The complex formed by the binding of yCQDs suppressed the absorption of light at a wavelength of 420 nm, thus exhibiting fluorescence quenching. (Fluorescence decay diagram) Figure 5 D) indicates the addition of Hg 2+ The fluorescence lifetimes of the two systems were basically the same, i.e., the fluorescence lifetimes of the heavy metal ion Hg were similar. 2+ The introduction of Hg did not affect the radiative transition process of the fluorophore. 2+ The fluorescence quenching mechanism of yCQDs can also be determined to be static quenching.

[0052] Example 3

[0053] The sample preparation and detection method refer to Example 2, except that the pH value of the phosphate buffer system is adjusted to 3.0-12.0; and other conditions and parameters are the same as in Example 2.

[0054] The results are shown in Figure 8 , Figure 8 A shows that the relative fluorescence intensity of yCQDs is the highest when the pH of the system is 8.0, and the system will be acidic or alkaline, which will cause the relative fluorescence intensity of yCQDs to decay, and the acidic environment has a stronger inhibitory effect on the fluorescence of yCQDs; the influence of pH on the quenching effect of Hg 2+ is shown in Figure 8 B, and the environment of pH 6.0 is more conducive to the quenching of the fluorescence of yCQDs by Hg 2+ .

[0055] Example 4

[0056] The sample preparation and detection method refer to Example 2, except that the concentration of Hg 2+ is adjusted to 1.00×10 -4 mol / L and 1.00×10 -5 mol / L, and the influence of the reaction time or temperature of the system on the detection effect of mercury ions is investigated.

[0057] The results are shown in Figure 9 , Figure 9 A shows that 1.00×10 -4 mol / L Hg 2+ can almost completely quench the fluorescence of yCQDs in 30 min and keep stable; in the same time, 1.00×10 -5 mol / L Hg 2+ only produces a fluorescence quenching rate of about 63%; but after incubation overnight, 1.00×10 -5 mol / L Hg 2+ is also enough to keep the fluorescence of yCQDs stably almost completely quenched Figure 9 B).

[0058] The influence of incubation temperature on incubation time is shown in Figure 9 C, and from the figure it can be seen that increasing the incubation temperature does not promote the interaction between yCQDs and 1.00×10 -5 mol / L Hg 2+ , and the sample incubated at room temperature (20℃) for the same time produces a higher fluorescence quenching degree. This phenomenon also confirms that Hg 2+The fluorescence quenching mechanism of yCQDs should be static quenching, because higher incubation temperature reduces the stability of the complex, thereby weakening the degree of static quenching. To ensure that each concentration sample is fully incubated, longer incubation time is still required, so the sample processing temperature and time are incubated at room temperature overnight.

[0059] Example 5 Selectivity and anti-interference ability of yCQDs

[0060] A series of metal cations (Ag + , Ba 2+ , Ca 2+ , Co 2+ , Cr 3+ , Cu 2+ , Fe 2+ , Fe 3+ , K + , Mg 2+ , Mn 2+ , Na + , Pb 2+ , Zn 2+ ) were selected as interference substances for experiments.

[0061] The concentration of all metal cations in the experiment was 1.00 x 10 -5 mol / L; the sample preparation method was as described in Example 2, and different interference substance solutions were used to replace the Hg 2+ solution in the selectivity experiment; in the anti-interference experiment, different interference substances were added simultaneously with Hg 2+ .

[0062] The results are shown in Figure 10 , and Figure 10 it can be seen that among the selected ions in A, only Hg 2+ can significantly quench the fluorescence of yCQDs at the same concentration. As shown in Figure 10 B, when other ions at the same concentration as Hg 2+ are present in the detection system, the Hg 2+ detection ability of yCQDs is basically not affected.

[0063] The above experimental results show that yCQDs have excellent selectivity for Hg 2+ , and good anti-interference ability for Hg 2+ recognition ability.

[0064] Example 6

[0065] The actual samples were tap water, lake water and bottled drinking water. The tap water sample was collected from the laboratory of Jiangnan University, the lake water sample was from the campus lake of Jiangnan University, and the bottled drinking water sample was purchased from a local supermarket. The three samples were filtered through a 0.22 μm filter membrane before use.

[0066] For the detection of mercury ions in actual samples using the yCQDs system as a fluorescent probe, 0.30 mL of yCQDs solution (1 unit in concentration), 2.10 mL of phosphate buffer solution (0.1 mol / L, pH = 6.0) were mixed and shaken uniformly, then 0.30 mL of actual sample and 0.30 mL of Hg 2+ solution or deionized water of different concentrations were added, shaken again, and incubated at room temperature overnight; finally, the fluorescence spectra of each sample were measured under excitation at 418 nm.

[0067] The relationship between the fluorescence intensity of the system in different samples and the Hg 2+ spiked concentration is shown in Figure 11 ; the detection limits of Hg 2+ in the three actual samples were calculated to be 5.71 x 10 -8 mol / L, 4.22 x 10 -8 mol / L and 4.19 x 10 -8 mol / L, respectively.

[0068] After the detection curve was established, the Hg 2+ spiked recovery experiment in actual samples was carried out, and the results are shown in Table 1. The recovery rate was distributed in the range of 92-111%, and the relative standard deviation was in the range of 0.83-4.73%.

[0069] Table 1 Results of Hg 2+ spiked recovery experiment in actual samples

[0070]

[0071] The above examples describe the basic principles, main features and advantages of the present application, but those skilled in the art should understand that the present application is not limited by the above examples. Various changes and improvements can be made to the present application without departing from the spirit and scope of the present application, therefore the protection scope of the present application should be defined by the claims.

Claims

1. A method for detecting mercury ions using o-phenylenediamine-derived carbon quantum dots as fluorescent probes, characterized in that, The method includes the following steps: (1) Preparation of yCQDs fluorescent probe system Taurine and o-phenylenediamine were dissolved in water and the pH of the solution was adjusted to neutral. The solution was then transferred to a high-pressure reactor for hydrothermal reaction to obtain a crude product. The crude product was purified by silica gel column chromatography to obtain carbon quantum dot solution yCQDs. The carbon quantum dot solution and the buffer solution were mixed evenly to obtain the yCQDs fluorescent probe system. The hydrothermal reaction is carried out at a temperature of 180~200℃ for 8~12 hours. The pH of the solution is adjusted to a neutral value of 6.5-7.5; The mass ratio of taurine to o-phenylenediamine is 1:1~2; The purification of the crude product by silica gel column chromatography means that the crude product is purified by silica gel column chromatography twice, with the eluents being ethanol and ethyl acetate respectively. The buffer solution is a phosphate buffer solution; the pH value of the buffer solution is 6.0, the concentration is 0.1~0.2 mol / L, and the volume accounts for 50-90% of the total volume of the yCQDs fluorescent probe system. (2) Construction of quantitative relationship model The yCQDs fluorescent probe system prepared in step (1) was shaken with a series of mercury ion solutions of known concentrations to obtain standard samples. After incubating at room temperature overnight, the fluorescence intensity of each standard sample under 418 nm excitation was measured. A quantitative relationship model was established with the fluorescence intensity at 420 nm as the ordinate and the mercury ion concentration as the abscissa. The overnight incubation at room temperature refers to overnight incubation at 20~30℃. (3) Determination of mercury ion content in the sample to be tested The yCQDs fluorescent probe system prepared in step (1) was uniformly mixed with the sample to be tested and incubated at room temperature overnight. Then the fluorescence intensity of the mixture under 418 nm excitation was measured, and the content of mercury ions in the sample to be tested was calculated according to the quantitative relationship model constructed in step (2).

2. The method according to claim 1, characterized in that, The reagent used to adjust the pH of the solution in step (1) is a freshly prepared sodium hydroxide solution with a concentration of 0.1~0.2 mol / L.

3. The method according to claim 1, characterized in that, The concentration of the carbon quantum dot solution yCQDs with an absorbance of 0.200 at 420 nm in the UV-Vis absorption spectrum is defined as 1 unit. In step (3), the concentration of the carbon quantum dot solution yCQDs in the mixture of the yCQDs fluorescent probe system and the sample to be tested is 0.1-0.5 units; the volume ratio of the yCQDs fluorescent probe system to the sample to be tested is 9:

1.

4. The application of the method according to any one of claims 1 to 3 in the detection of mercury ions.

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