CN114951683B - Synthesis method of gold nanocluster and detection method of hexavalent chromium ions thereof - Google Patents

Abstract

The invention provides a synthesis method of gold nanoclusters AuNCs, which comprises the following synthesis steps: adding histidine and polylysine into chloroauric acid solution to obtain a reaction mixed solution; the mixed solution obtained in the step (A) is stirred by a stirrer, the synthesized solution is filtered by a filter membrane, the obtained solution is transferred to an ultrafiltration tube, and then a weapon is centrifuged in a centrifuge to obtain supernatant; and thirdly, freeze-drying the supernatant obtained in the step II to obtain gold nanocluster AuNCs solid, and re-dissolving the gold nanocluster AuNCs by using phosphate buffer solution PBS to obtain gold nanocluster AuNCs solution. The method solves the problems of high cost and long time consumption of synthesizing gold nanoclusters AuNCs in the prior art; the gold nanocluster fluorescent probe constructed by the invention detects Cr ⁶⁺ The method has the advantages of simple and quick operation, low cost, no need of complex large-scale instrument, strong practicability and Cr ⁶⁺ Has wide application prospect in the field of rapid detection.

Description

Synthesis method of gold nanocluster and detection method of hexavalent chromium ion

technical field

The invention belongs to the technical field of nanomaterials, and in particular relates to a synthesis method of gold nanoclusters and a detection method of hexavalent chromium ions.

Background technique

With the development of modern industry, chromium and its compounds are used in many industrial processes, such as metal processing, electroplating and leather tanning, among which, some manufacturers even use leather waste to produce edible capsule shells. A large amount of chromium leaks into the human living environment through these industrial processes, seriously endangering human life safety. Generally speaking, the two main valence states of chromium in nature are Cr ³⁺ and Cr ⁶⁺ , of which Cr ³⁺ is an essential element in human nutrition, while Cr ⁶⁺ is a highly toxic substance with non-biodegradability And carcinogenicity, even people exposed to low concentrations of Cr ⁶⁺ may cause hemolysis, renal failure, liver failure, etc., leading to the occurrence of cancer. Therefore, it is of great significance to establish an accurate and feasible detection method for hexavalent chromium ion for environmental monitoring and human health maintenance.

At present, the traditional methods for detecting chromium ions mainly include inductively coupled plasma mass spectrometry (ICP-MS), ion chromatography (IC), atomic absorption spectroscopy (AAS) and so on. Although these methods based on large-scale equipment have high sensitivity, superior accuracy and stability, they have disadvantages such as high detection cost, complicated and time-consuming pretreatment process, and high requirements for technicians to operate. Among them, ICP-MS and AAS methods can only detect the total amount of chromium, but cannot quantify Cr ⁶⁺ . Therefore, there is still a need to develop a simple, rapid, and highly sensitive method for the detection of Cr ⁶⁺ .

With the rapid development of nanotechnology, new nanomaterials have become a hot topic in various research fields due to their special physical and chemical properties, among which gold nanoclusters (AuNCs) are characterized by adjustable fluorescence, good hydrophilicity, high biocompatibility, It has attracted much attention due to its simple synthetic route and other advantages. AuNCs are a special kind of fluorescent nanoparticles, which are generally composed of several to hundreds of gold atoms, with a size below 3nm, and are relatively stable molecular-like aggregates. Using the physical and chemical properties of AuNCs, researchers have successfully used them as fluorescent probes for the analysis and detection of Cr ⁶⁺ . Sun et al. (Sun, Zhang & Jin, Journal of Materials Chemistry C, 2013, 1(1), 138-143.) prepared 11-mercaptoundecanoic acid-modified gold nanoclusters that could respond specifically to Cr ³⁺ , and then used Ascorbic acid reduces Cr ⁶⁺ to Cr ³⁺ , which can detect Cr ⁶⁺ indirectly. However, Zhang et al. (Zhang, Liu, Wang, Yun, Li, Liu, et al. 2013, Analytica Chimica Acta, 770, 140-146.) prepared glutathione-modified gold nanoclusters for direct detection of hexavalent chromium. Although these two studies can detect Cr ⁶⁺ and Cr ³⁺ sensitively, EDTA needs to be added to cover Cr ³⁺ during the detection process, and the complexation time between EDTA and Cr ³⁺ is very long, so it is impossible to quickly detect Cr ⁶⁺ detection. Yin et al. (Yin, Coonrod, Heck, Lejarza & Wong, ACS Applied Materials & Interfaces, 2019, 11(19), 17491-17500.) synthesized microcapsules of glutathione-modified AuNCs, and Shellaiah et al. (Shelliah, Simon, Thirumalaivasan ,Sun,Ko&Wu,Microchimica Acta,2019,186(12),788.) synthesized cysteamine-modified gold-copper nanoclusters, although these two methods can directly detect Cr ⁶⁺ without the interference of Cr ³⁺ , However, these two fluorescent probes have the disadvantage of complex and time-consuming synthetic routes, which are not conducive to large-scale synthesis in practical applications. According to relevant literature, the method of detecting hexavalent chromium ions using histidine and polylysine-modified gold nanocluster fluorescent probes has not been reported yet.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the above-mentioned prior art and provide a method for utilizing histidine and polylysine-modified gold nanoclusters. The method is carried out at normal temperature, the synthesis process is simple, and the prepared The gold nanoclusters can be used as fluorescent probes for rapid and quantitative direct detection of hexavalent chromium ions.

The synthesis method of the gold nanocluster of the present invention is special in that it comprises the following steps:

(1) Histidine and polylysine are added in the chloroauric acid solution to obtain a reaction mixed solution;

(2) After stirring the mixed solution in step (1) with a stirrer, filter the synthesized solution with a filter membrane, transfer the obtained solution to an ultrafiltration tube, and centrifuge in a centrifuge to obtain a supernatant;

(3) Freeze-dry the supernatant obtained in step (2) to obtain the gold nanocluster AuNCs solid, and redissolve the gold nanocluster AuNCs with phosphate buffer solution PBS by weighing to obtain the gold nanocluster AuNCs solution.

Preferably, the histidine in step (1) is one of D-histidine, L-histidine and DL-histidine, the content of histidine is 0.1-5 mmol, and the content of polylysine is 0.01-1 mmol, the molecular weight of polylysine is 1,000-300,000, and the content of the chloroauric acid is 0.01-1 mmol.

Preferably, the stirring speed of the agitator in step (1) is 400-1200rpm, the stirring time is 0.5-3h, the specification of the filter membrane is 0.22μm, the molecular weight of the ultrafiltration tube is 3KD-100KD, and the centrifuge The rotation speed is 8000~15000rpm, and the centrifugation time is 10~30min;

Preferably, the pH of the phosphate buffer solution PBS in step (3) is 7-9, and the color of the gold nanocluster AuNCs solution is light yellow.

Preferably, the particle size of the gold nanocluster AuNCs is 1.4-2.5nm, the excitation wavelength of the gold nanocluster AuNCs is 370nm, and the emission wavelength is 480nm, and the emission wavelength increases with the increase of the excitation wavelength.

Another object of the present invention is to provide the application of the above-mentioned gold nanocluster as a fluorescent probe in the determination of hexavalent chromium ions. The special feature is that the specific steps are as follows:

(1) Prepare Cr ⁶⁺ standard solution with phosphate buffer solution PBS solution;

(2) Mix the gold nanocluster AuNCs with the Cr ⁶⁺ standard solution, and measure the fluorescence emission spectrum intensity diagram of the solution at the excitation wavelength of 370nm after the reaction;

(3) Take the Cr ⁶⁺ concentration as the abscissa, and the fluorescence quenching efficiency {QE=(FL ₀ -FL)/FL ₀ } as the ordinate, where FL and FL ₀ represent AuNCs in the presence and absence of Cr ⁶⁺ , respectively Fluorescence intensity; Obtain the linear relationship diagram between the fluorescence quenching efficiency and the Cr concentration of the AuNCs fluorescent probe solution with different concentrations of Cr ⁶⁺ , and establish ^a standard curve;

(4) Select different inorganic interfering substances, the inorganic interfering substances include Cr ⁶⁺ or do not contain Cr ⁶⁺ , and obtain the fluorescence intensity according to the detection method in step (2) and step (3);

(5) After the actual sample is pretreated, add Cr ⁶⁺ to prepare a sample solution with a spiked concentration of Cr ⁶⁺ ; obtain the fluorescence intensity according to the detection method in step (2) and step (3), and compare it with the standard curve to determine the test solution The content of Cr ⁶⁺ in the sample was calculated, and the standard addition recovery and relative standard deviation were calculated; in order to verify the reliability of the fluorescence method, the commonly used traditional ion chromatography method was also used to detect the Cr ⁶⁺ concentration in the actual sample, and the results were compared with Fluorescence was compared.

Preferably, in step (1), the pH of the PBS solution is 7-9.

Preferably, the volume ratio of gold nanocluster AuNCs to Cr ⁶⁺ standard solution in step (2) is 1:1, and the reaction time is 1-5 min.

Preferably, in step (2) and step (3), the gold nanocluster fluorescence method to detect Cr ⁶⁺ further includes: histidine and polylysine are coated around the gold core, so that the gold nanocluster AuNCs has many oxygen-containing and Nitrogen groups, these groups combine with Cr ⁶⁺ to cause energy resonance transfer between gold nanoclusters AuNCs and Cr ⁶⁺ , and make gold nanoclusters AuNCs aggregate, thereby quenching the fluorescence of gold nanoclusters AuNCs; through gold nanoclusters The change value of the cluster AuNCs fluorescence intensity signal realizes the quantitative detection of Cr ⁶⁺ .

Preferably, step (5) also includes pretreatment of the analyte, the step of pretreatment of the analyte, specifically: agricultural products: take 1-10 g of agricultural products, grind them into slurry or powder, add 100 mL of phosphate buffer solution PBS, pH=7~9, then ultrasonic treatment for 30min; capsule sample: take 1g capsule shell and dissolve in 100mL phosphate buffer solution PBS, pH=7~9, heat until dissolved, then cool to room temperature; leather sample: take 1g leather and cut into Small pieces were dissolved in 100mL phosphate buffered saline solution PBS (pH=7~9), then shaken for 3h under nitrogen atmosphere; soil sample: take 1g of soil and dissolved in 100mL phosphate buffered saline solution PBS (pH=7~9), then Ultrasonic treatment for 30 minutes; water samples: boil the water samples, then cool to room temperature; then centrifuge all the sample solutions at a speed of 13,000 rpm for 30 minutes, and filter the obtained supernatant with a 0.45 μm filter membrane to obtain the actual sample solution after treatment.

Compared with prior art, beneficial effect of the present invention:

(1) The gold nanocluster AuNCs prepared by the present invention is used as a fluorescent probe to detect Cr ⁶⁺ , which is simple, fast, selective, and sensitive, and can reach the detection level of the Cr ⁶⁺ limit specified in the national standard or pharmacopoeia. The sanitation standard for drinking water GB5749-2022 stipulates that the hexavalent chromium limit is 0.05 mg/L; the national food safety standard GB2762-2017 stipulates that the chromium limit in grains and their products is 1 mg/kg, and the chromium limit in vegetables and their products The value is 0.5mg/kg; the 2010 edition of "Chinese Pharmacopoeia" stipulates that the chromium content in medicinal capsules and gelatin raw materials used should not exceed 2mg/kg; the European Union stipulated in the reach regulations in May 2015 that the limit value of hexavalent chromium in leather is 3mg /kg, while the detection limit of Cr ⁶⁺ in this method is 7.2μg/L.

(2) The reagents used in the gold nanocluster AuNCs fluorescent probe prepared by the present invention are histidine, polylysine and chloroauric acid, which have no toxic and side effects and are environmentally friendly reagents. The synthesis method of the probe has the advantages of simple synthesis, low cost It is relatively low, fast and convenient, and only needs to be reacted at room temperature, and no toxic pollutants are produced during the synthesis process.

(3) The detection method of the present invention is simple, fast, and low in cost, does not require complex large-scale instruments, has strong practicability, and has broad application prospects in the field of rapid detection of Cr ⁶⁺ .

Description of drawings

Fig. 1A is the high-resolution transmission electron microscope picture of gold nanocluster AuNCs of the present invention; Fig. 1B is the particle size distribution figure of the high-resolution transmission electron microscope of AuNCs of the present invention;

Fig. 2 is the fluorescence intensity figure of the gold nanocluster AuNCs that adds different Cr ⁶⁺ contents in the present invention;

Fig. 3 is a linear relationship diagram between the fluorescence quenching efficiency and ^Cr content of gold nanocluster AuNCs of the present invention;

Figure 4A is a high-resolution transmission electron microscope image of gold nanocluster AuNCs after adding Cr ⁶⁺ in the present invention;

Fig. 4B is the particle size distribution diagram of the high-resolution transmission electron microscope of the gold nanocluster AuNCs after adding Cr ⁶⁺ in the present invention;

Fig. 5 is a selectivity diagram of adding different metal ions to the fluorescence method according to the present invention.

Detailed ways

The present invention will be described in further detail below in conjunction with accompanying drawing:

[Example 1]:

The preparation method of gold nanocluster AuNCs, concrete steps are as follows:

Add 1mmol D-histidine and 0.1mmol polylysine (molecular weight is about 5000) to 0.1mmol chloroauric acid solution, stir at 800rpm on the stirrer for 1h, then mix the synthesized light yellow solution with 0.22μm filter membrane, and the resulting solution was centrifuged at 10,000 rpm for 20 min in a 3KD ultrafiltration tube. Finally, the obtained supernatant was freeze-dried to obtain a solid gold nanocluster AuNCs, and by weighing, the gold nanocluster AuNCs was redissolved with a phosphate buffer solution PBS (pH=7) to obtain a particle size of 1.4-2.5nm and The high-resolution transmission electron microscope image and particle size distribution of the light yellow AuNCs fluorescent probe with relatively uniform dispersion are shown in Figure 1.

[Example 2]:

The preparation method of gold nanocluster AuNCs, concrete steps are as follows:

5mmolDL-histidine and 1mmol polylysine (molecular weight is about 5000) were added to 1mmol chloroauric acid solution, after stirring for 3h with the speed of 1200rpm on the stirrer, the light yellow solution synthesized was filtered with 0.22μm After membrane filtration, the obtained solution was centrifuged at 15,000 rpm for 10 min in a 3KD ultrafiltration tube. Finally, the obtained supernatant was freeze-dried to obtain the gold nanocluster AuNCs solid, and by weighing, the gold nanocluster AuNCs were redissolved with PBS (pH=7.5) to obtain light yellow gold nanocluster AuNCs fluorescent probes.

[Example 3]:

The preparation method of gold nanocluster AuNCs, concrete steps are as follows:

0.1mmol L-histidine and 0.01mmol polylysine (molecular weight is about 5000) are added in the 0.01mmol chloroauric acid solution, after stirring 0.5h with the rotating speed of 400rpm on the stirrer, the pale yellow solution of synthesis is used After filtering through a 0.22 μm filter membrane, the obtained solution was centrifuged at 8000 rpm for 30 min in a 3KD ultrafiltration tube. Finally, the obtained supernatant was freeze-dried to obtain solid AuNCs of gold nanoclusters. By weighing, the AuNCs were redissolved with PBS (pH=8) to obtain light yellow fluorescent probes of AuNCs.

[Example 4]:

The preparation method of AuNCs, concrete steps are as follows:

Add 1mmol D-histidine and 0.05mmol polylysine (molecular weight is about 30000) to 0.1mmol chloroauric acid solution, stir at a speed of 1200rpm on the stirrer for 2h, and then mix the synthesized light yellow solution with 0.22μm filter membrane, and the resulting solution was centrifuged at 1200 rpm for 15 min in a 10KD ultrafiltration tube. Finally, the obtained supernatant was lyophilized to obtain solid AuNCs, and the AuNCs were redissolved with PBS (pH=9) by weighing to obtain light yellow AuNCs fluorescent probes.

[Example 5]:

Application of AuNCs in Detection of Cr ⁶⁺

Detection of Cr ⁶⁺

Prepare 1g/LCr ⁶⁺ mother liquor with ultrapure water, then dilute with PBS (pH=7) solution to obtain different concentrations of Cr ⁶⁺ standard solutions (0.01, 0.04, 0.07, 0.1, 0.4, 0.7, 1, 4, 7, 10, 40, 70, 100 mg/L). Then 200 μL of 1 mg/mL AuNCs was directly mixed with 200 μL of Cr ⁶⁺ standard solution, and the fluorescence emission spectrum intensity of the solution at the excitation wavelength of 370 nm was measured after reacting for 2 minutes, as shown in Figure 2. Take the Cr ⁶⁺ concentration as the abscissa, and the fluorescence quenching efficiency {QE=(FL ₀ -FL)/FL ₀ } as the ordinate (where FL and FL ₀ represent the fluorescence intensity of AuNCs in the presence and absence of Cr ⁶⁺ , respectively ), ^the linear relationship diagram between the fluorescence quenching efficiency and the Cr concentration of the AuNCs fluorescent probe solution added with different concentrations of Cr ⁶⁺ is shown in Figure 3, and the linear relationship is QE=0.0462C _Cr ⁶⁺ +0.0002( R ² =0.991), the detection linear range is 10-10000 μg/L, and the detection limit is 7.2 μg/L.

Detection principle:

Please refer to Figure 1, the AuNCs fluorescent probe synthesized by histidine and polylysine is used to detect Cr ⁶⁺ . Since histidine and polylysine are coated around the gold core, AuNCs have many oxygen- and nitrogen-containing groups, which can combine with Cr ⁶⁺ to cause energy resonance transfer between AuNCs and Cr ⁶⁺ , and The AuNCs are aggregated, and the high-resolution transmission electron microscope image and particle size distribution of AuNCs after adding Cr ⁶⁺ are shown in Figure 4, so that the fluorescence of AuNCs is quenched. Quantitative detection of Cr ⁶⁺ was realized through the change value of the fluorescence intensity signal of AuNCs.

Optional experiment:

Use PBS (pH=7) to prepare 50 ^mg /L of different kinds of ^inorganic substances (K ₂ Cr ₂ O ₇ , CrCl ₃ , PbCl ₂ , CoCl ₂ , CdCl ₂ , Hg(NO ₃ ) ₂ , AlCl ₃ , FeCl ₃ , MnCl ₂ , Fe(NH ₄ ) ₂ (SO ₄ ) ₂ , BaCl ₂ , CaCl ₂ , NaCl, MgCl ₂ , InCl ₃ and GaCl ₃ ) as interfering substances, and then 200 μL of 1 mg/mL AuNCs was directly mixed with 200 μL of Cr ⁶⁺ -free or Cr ⁶⁺ -containing inorganic solution, and the fluorescence signal of the solution at an excitation wavelength of 370 nm was measured after reacting for 2 min. The resulting fluorescence quenching efficiency diagram of AuNCs is shown in Figure 5. The fluorescence quenching efficiency of AuNCs when Cr ⁶⁺ is added alone is much higher than that of adding other interferents without adding Cr ⁶⁺ . However, when Cr ⁶⁺ and other single interfering substances were added simultaneously in the system, the fluorescence quenching efficiency of AuNCs was significantly improved and reached a level similar to that of Cr ⁶⁺ added alone. This indicates that other inorganic substances have little interference to this method, indicating that the AuNCs-based fluorescence method has good selectivity for Cr ⁶⁺ .

Feasibility experiment:

In order to verify the feasibility of this method to detect Cr ⁶⁺ in actual samples, the standard recovery experiment was carried out. Cabbage, rice, capsule shell, leather, soil and river water were selected as actual samples, and the samples were pretreated individually first. The pretreatment of each sample is as follows: Chinese cabbage: Grind 10 g of celery and cabbage into a slurry, add 100 mL of PBS (pH=7), and then sonicate for 30 minutes; rice flour: dissolve 1 g of rice flour in 100 mL of PBS (pH=7), then sonicate for 30 minutes; Shell: Dissolve 1g of capsule shell in 100mL PBS (pH=7) and heat until dissolved, then cool to room temperature; Leather: Cut 1g of leather into small pieces and dissolve in 100mL PBS (pH=7), then shake for 3h under nitrogen atmosphere; River water: the collected river water was heated to boiling point, and then cooled to room temperature; soil: 1 g of soil was dissolved in 100 mL of LPBS (pH=7), and then sonicated for 30 min. Then, all the sample solutions were centrifuged at a speed of 13000 rpm for 30 min, and the obtained supernatant was filtered through a 0.45 μm filter membrane to obtain the actual sample solution after treatment. After that, different contents of 1.0 g/L Cr ⁶⁺ were added to the actual sample solution to prepare sample solutions with different spiked concentrations (50, 300 and 3000 μg/L). Then 200 μL of 1 mg/mL AuNCs was directly mixed with 200 μL of spiked actual sample solutions with different Cr ⁶⁺ concentrations, and after 2 minutes of reaction, the fluorescence emission spectrum intensity graph of the solution at the excitation wavelength of 370 nm was measured, according to the standard curve linear equation QE=0.0462C _Cr ⁶⁺ +0.0002, the Cr ⁶⁺ concentration calculated by AuNCs fluorescence method can be obtained, and the standard addition recovery and relative standard deviation can be calculated. In addition, in order to verify the reliability of the fluorescence method, the commonly used traditional method (ion chromatography) was also used to detect the Cr6 ⁺ concentration in the actual sample, and the results were compared with the fluorescence method. The results are shown in Table 1:

Table 1

The recovery rate of AuNCs-based fluorescence method was 84.9%-102.9%, and the RSD value was 2.7%-5.8%. Compared with ion chromatography, it was found that the fluorescence method also had good precision and accuracy, indicating that the AuNCs-based fluorescence method can be used as an alternative method for the detection of Cr ⁶⁺ .

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the claims of the present invention shall fall within the scope of the claims of the present invention.

Claims (7)

1. a synthetic method of the gold nano-cluster of the fluorescent probe that hexavalent chromium ion measures, is characterized in that, comprises the following steps: (1) Histidine and polylysine are added in the chloroauric acid solution, obtain reaction mixed solution; Step (1) described histidine is D-histidine, L-histidine, DL-histidine One, the content of histidine is 0.1～5mmol, the content of polylysine is 0.01～1mmol, the molecular weight of polylysine is 1000～300000, and the content of described chloroauric acid is 0.01～1mmol; step (1) stirring The stirring speed is 400-1200rpm, the stirring time is 0.5-3h, the filter membrane size is 0.22μm, the molecular weight of the ultrafiltration tube is 3KD-100KD, the centrifuge speed is 8000-15000rpm, and the centrifugation time is 10-30min; (2) After stirring the mixed solution in step (1) with a stirrer, filter the synthesized solution with a filter membrane, transfer the obtained solution to an ultrafiltration tube, and centrifuge in a centrifuge to obtain a supernatant; (3) Freeze-dry the supernatant obtained in step (2) to obtain the gold nanocluster AuNCs solid, and by weighing, use the phosphate buffer solution PBS to redissolve the gold nanocluster AuNCs to obtain the gold nanocluster AuNCs solution; the phosphate described in step (3) The pH of the buffer solution PBS is 7-9, and the color of the gold nanocluster AuNCs solution is light yellow. 2. the gold nanocluster that the synthetic method described in claim 1 makes is characterized in that, the particle diameter of described gold nanocluster AuNCs is 1.4～2.5nm, and the excitation wavelength of described gold nanocluster AuNCs is 370nm, and emission wavelength is 480nm, and the emission wavelength increases with the increase of the excitation wavelength. 3. an application of a gold nanocluster according to claim 1 as a fluorescent probe measured at hexavalent chromium ions, characterized in that, the specific steps are as follows: (1) Prepare Cr ⁶⁺ standard solution with phosphate buffer solution PBS solution; (2) Mix the gold nanocluster AuNCs with the Cr ⁶⁺ standard solution, and measure the fluorescence emission spectrum intensity diagram of the solution at the excitation wavelength of 370nm after the reaction; (3) Take the Cr ⁶⁺ concentration as the abscissa, and the fluorescence quenching efficiency {QE=(FL ₀ -FL)/FL ₀ } as the ordinate, where FL and FL ₀ represent AuNCs in the presence and absence of Cr ⁶⁺ , respectively Fluorescence intensity; Obtain the linear relationship diagram between the fluorescence quenching efficiency and the Cr concentration of the AuNCs fluorescent probe solution with different concentrations of Cr ⁶⁺ , and establish ^a standard curve; (4) Select different inorganic interfering substances, the inorganic interfering substances include Cr ⁶⁺ or do not contain Cr ⁶⁺ , and obtain the fluorescence intensity according to the detection method in step (2) and step (3); (5) After the actual sample is pretreated, add Cr ⁶⁺ to prepare a sample solution with a spiked concentration of Cr ⁶⁺ ; obtain the fluorescence intensity according to the detection method in step (2) and step (3), and compare it with the standard curve to determine the test solution The content of Cr ⁶⁺ in the sample was calculated, and the standard addition recovery and relative standard deviation were calculated; in order to verify the reliability of the fluorescence method, the commonly used traditional ion chromatography method was also used to detect the Cr ⁶⁺ concentration in the actual sample, and the results were compared with Fluorescence was compared. 4. The application of the gold nanocluster according to claim 3 as a fluorescent probe for the determination of hexavalent chromium ions, characterized in that, in step (1), the pH of the PBS solution is 7-9. 5. the gold nanocluster described in claim 3 is as the application of the fluorescent probe that measures at hexavalent chromium ion, it is characterized in that, step (2) described gold nanocluster AuNCs and Cr The volume ratio of ^standard solution is 1:1 , The reaction time is 1-5min. 6. the gold nanocluster described in claim 3 is as the application of the fluorescent probe in hexavalent chromium ion mensuration, it is characterized in that, in step (2) and step (3), described gold nanocluster fluorescence method detects ^Cr further comprising: Histidine and polylysine are coated around the gold core, making the gold nanocluster AuNCs have many oxygen- and nitrogen-containing groups, which combine with Cr ⁶⁺ to make the gold nanocluster AuNCs and Cr ⁶⁺ generate energy Resonance transfer, and the aggregation of gold nanocluster AuNCs, thereby quenching the fluorescence of gold nanocluster AuNCs; the quantitative detection of Cr ⁶⁺ is realized by the change value of the fluorescence intensity signal of gold nanocluster AuNCs. 7. The application of the gold nanocluster according to claim 3 as a fluorescent probe in the determination of hexavalent chromium ions, is characterized in that step (5) also includes the pretreatment of the analyte, the step of the pretreatment of the analyte, specifically For: agricultural products: take 1~10g of agricultural products, grind them into slurry or powder, add 100mL phosphate buffer solution PBS, pH=7~9, and then ultrasonicate for 30min; capsule samples: take 1g capsule shell and dissolve in 100mL phosphate buffer Solution PBS, pH = 7 ~ 9, heated to dissolve, then cooled to room temperature; leather sample: take 1g of leather cut into small pieces and dissolve in 100mL phosphate buffer solution PBS, pH = 7 ~ 9, and then vibrate under nitrogen atmosphere Shake for 3 hours; soil sample: take 1g of soil and dissolve it in 100mL phosphate buffer solution PBS (pH=7~9), and then sonicate for 30 minutes; water sample: take the water sample and boil it, then cool it to room temperature; Centrifuge at a rotating speed of 30 min, and filter the obtained supernatant with a 0.45 μm filter membrane to obtain the actual sample solution after treatment.

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