Preparation method of ionic liquid modified nanogold cluster material and application thereof in detection of heavy metal ion cadmium

Abstract

The application belongs to the technical field of heavy metal ion detection, and specifically discloses a preparation method of an ionic liquid modified nanometer gold cluster material and application of the material in detection of heavy metal ion cadmium. The application synthesizes nanometer gold clusters emitting red fluorescence by taking bovine serum albumin as a stabilizer and a reducing agent, and synthesizes an ionic liquid modified nanometer gold cluster composite material by utilizing electrostatic interaction between an imidazole ionic liquid and the BSA. Due to unique coordination between cadmium ions and the imidazole ionic liquid, the cadmium ions can effectively enhance the fluorescence intensity of the ionic liquid modified nanometer gold cluster composite material, and can be applied to detection of cadmium ions in actual samples, thereby providing a new idea for convenient detection of cadmium ions in complex substrates.

Description

Technical Field

[0001] This invention belongs to the field of heavy metal ion detection technology, specifically relating to a method for preparing ionic liquid-modified gold nanoclusters and its application in the detection of heavy metal ions cadmium. Background Technology

[0002] Heavy metals have wide applications in industry and agriculture. However, heavy metal ion pollution poses a serious threat to human health and ecosystems. Among various heavy metal ions, cadmium is one of the most toxic and harmful, widely used in nickel-cadmium batteries, plastic colorants, and cigarettes. Unlike many other heavy metals, cadmium does not participate in biological processes and is not an essential element for the human body. Therefore, even at extremely low concentrations, cadmium can have adverse effects on organisms through bioaccumulation. Cadmium easily accumulates in human organs, damaging organs such as the kidneys and liver. Long-term exposure to cadmium can damage blood vessels and systems, and even increase the risk of cancer. Therefore, establishing a sensitive cadmium ion concentration monitoring system is crucial. 2+ Quantitative detection methods are crucial. (Cd) 2+ The determination of Cd is mostly carried out using traditional methods such as atomic absorption spectrometry (AAS), atomic emission spectrometry (AES), and inductively coupled plasma mass spectrometry (ICP-MS). However, due to the special operation, expensive instruments, and long analysis time, these methods cannot meet the needs of rapid detection of Cd. 2+ The demand for [specific technology / technology] limits its application in real-time, on-site detection. Therefore, establishing an economical, convenient, and sensitive Cd [detection system / detection method] is crucial. 2+ The detection method is of great significance to environmental protection and human health.

[0003] Fluorescence spectroscopy offers advantages such as high sensitivity, ease of use, and cost-effectiveness. Fluorescent probes, used for specific analytes including metal ions, inorganic anions, and biologically important small molecules, have attracted significant interest due to the high sensitivity, convenience, and rapid response of optical detection methods. However, the presence of other heavy metal ions in food and the environment, such as Zn, has also contributed to this interest. 2+ High abundance of Cd 2+ Sensors require strict metal ion specificity. Ionic liquids, as a green and environmentally friendly functional material, have advantages such as highly tunable structure, negligible vapor pressure, and good thermal stability. They can act as functional modifiers and good solvents. In particular, based on the designability of ionic liquids, the properties of materials such as gold nanoparticles and quantum dots can be controlled. The resulting composite materials have great potential in the field of analytical detection, such as the detection of pesticides, metal ions, and antibiotics. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by designing and synthesizing an ionic liquid-modified gold nanocluster composite material as a fluorescent probe for the detection of cadmium ions. This method utilizes the electrostatic interaction between imidazole ionic liquids and BSA to synthesize an ionic liquid-modified gold nanocluster composite material, achieving specific detection of cadmium ions in food. Due to the unique coordination interaction between cadmium ions and imidazole ionic liquids, cadmium ions can effectively enhance the fluorescence intensity of the ionic liquid-modified gold nanocluster composite material, enabling its use in detecting cadmium ions in real samples. The probe designed and synthesized using this method possesses advantages such as high sensitivity and good specificity, and can be applied to the detection of cadmium ions in real samples, providing a new approach for the convenient detection of cadmium ions in complex matrices.

[0005] This invention synthesizes red fluorescent gold nanoclusters using bovine serum albumin (BSA) as a stabilizer and reducing agent, and further synthesizes gold nanoclusters with [C... 16 Imidazole ionic liquids, represented by M2Im]Br ionic liquids, are mixed with BSA-Au NCs by simple stirring. [C 16 The M2Im]Br ionic liquid can electrostatically interact with BSA on the surface of BSA-AuNCs, thereby modifying the surface of BSA-AuNCs and obtaining [C 16 The M2Im]Br@BSA-Au NCs composite material was used as a fluorescent probe for rapid and sensitive quantitative detection of cadmium ions. Its detection limit was 5.09 × 10⁻⁶. -9 M is far below the limit of 0.5 mg / L (food) set by the World Health Organization (WHO) and the International Organization for Standardization (ISO). Despite interference from other heavy metal ions in complex matrices, this probe exhibits selective specificity for cadmium ions among 15 heavy metal ions and 12 other interfering ions. Furthermore, the constructed sensor can also be used for the detection of cadmium ions in various real-world samples.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for detecting cadmium ions using an ionic liquid-modified gold nanocluster composite material as a fluorescent probe involves mixing the ionic liquid-modified gold nanocluster composite material with a sample solution and reacting for a certain period of time (preferably 5 ± 0.5 min after mixing). The fluorescence emission spectrum of the probe is then measured. If the fluorescence intensity at 620 ± 5 nm increases after the addition of the sample solution, the sample solution is considered to contain cadmium ions; otherwise, the sample solution is considered not to contain cadmium ions.

[0008] The imidazole ionic liquid was mixed with gold nanoclusters synthesized using bovine serum albumin as a stabilizer and reducing agent to obtain the ionic liquid-modified gold nanocluster composite material.

[0009] The preparation method of the ionic liquid modified gold nanocluster composite material includes: (1) mixing HAuCl4 solution and bovine serum albumin solution, adjusting the pH range to 11-12, stirring vigorously, and synthesizing a gold nanocluster solution that emits red fluorescence; (2) mixing imidazole ionic liquid solution with gold nanocluster solution, stirring, and the two undergo electrostatic interaction to obtain the ionic liquid modified gold nanocluster composite material.

[0010] In step (1), the ratio of HAuCl4 to bovine serum albumin is 1 mmol: 5 g. Preferably, the volume ratio of HAuCl4 solution to bovine serum albumin solution is 1:1. More preferably, the concentration of HAuCl4 solution is 10 mM.

[0011] In step (1), NaOH solution is added to adjust the pH range, and the concentration of NaOH solution is 1.0M.

[0012] In step (1), the stirring time is 24 hours and the stirring temperature is 37°C.

[0013] In step (2), the molar ratio of the imidazole ionic liquid to the gold nanoparticles is 2:1. Preferably, the volume ratio of the imidazole ionic liquid solution to the gold nanoparticle cluster solution is 1:1. More preferably, the concentration of the imidazole ionic liquid solution is 10 mM.

[0014] The structural formula of the imidazole ionic liquid is as follows:

[0015] R is an alkyl group with 12-16 carbon atoms, preferably a straight-chain alkyl group with 12-16 carbon atoms; X is Br, Cl or I.

[0016] Preferably, the chemical formula of the imidazole ionic liquid is [C 16 M2Im]Br, its structural formula is as follows:

[0017]

[0018] The detection limit of the ionic liquid-modified gold nanocluster composite material as a fluorescent probe is 5.09 × 10⁻⁶. -9 M.

[0019] In step (2), the stirring time is 30 minutes.

[0020] Furthermore, a method for detecting cadmium ions using an ionic liquid-modified gold nanocluster composite material as a fluorescent probe includes the following steps: S1. Plotting a standard fitting curve for cadmium ions: The ionic liquid-modified gold nanocluster composite material is mixed with a series of cadmium ion solutions of different concentrations, the volume is adjusted, and the mixture is shaken (e.g., at a rotation speed of 300-400 r / min) or left to stand for 5 min. The fluorescence emission spectrum of the probe is then measured. The fluorescence intensity difference of 620±5 nm before and after the addition of cadmium ions is used as the ordinate, and the cadmium ion concentration is used as the abscissa for linear calibration to obtain the standard fitting curve for fluorescence detection.

[0021] S2 involves mixing the ionic liquid-modified gold nanocluster composite material with the sample solution, adjusting the volume, shaking (e.g., at a speed of 300-400 r / min) or letting it stand for 5 min, and then measuring the fluorescence emission spectrum of the probe. The cadmium ion concentration in the sample solution is calculated using the fitted curve from S1.

[0022] The concentration of cadmium ions in the sample solution to be tested was 1.0 × 10⁻⁶. -8 –1.0×10 -6 M.

[0023] The sample to be tested is a food product, including beverages and grains, and its raw materials, diluents, or extracts obtained through simple pretreatment have a cadmium ion concentration of 1.0 × 10⁻⁶. -8 –1.0×10 -6 M.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] This invention successfully synthesized a functionalized ionic liquid-modified [C] 16 M2Im]Br@BSA-Au NCs composite material was used for the rapid and accurate quantitative detection of cadmium ions. When cadmium ions were added, [C 16 The red fluorescence of the M2Im]Br@BSA-Au NCs composite material exhibits a significant fluorescence enhancement effect, [C 16 The linear range of the M2Im]Br@BSA-Au NCs composite material for cadmium ions using fluorescence spectroscopy was 1.0 × 10⁻⁶. -8 –1.0×10 -6 M, with a detection limit of up to 5.09 × 10 -9 Furthermore, the designed and synthesized probe can selectively identify cadmium ions from 15 heavy metals and 12 other interfering ions (100 times higher than the concentration of cadmium ions), exhibiting good specificity. After simple pretreatment of actual samples, this probe can achieve quantitative detection of cadmium ions, providing a new approach for the sensitive and rapid detection of cadmium ions in complex matrices.

[0026] This invention provides a sensitive fluorescence platform for the determination of cadmium ions in food, offering high accuracy, high sensitivity, and good linearity. Compared to existing detection methods, it avoids the drawbacks of large equipment and long processing times, and does not require highly specialized expertise from operators. This strategy provides a sensitive fluorescence platform for the determination of cadmium ions in food. 2+ The detection provides a new method with broad application prospects in food safety monitoring. Attached Figure Description

[0027] Figure 1 This invention uses BSA-Au NCs and [C 16 The fluorescence emission spectrum of the M2Im]Br@BSA-AuNCs composite material is plotted with fluorescence intensity as the ordinate and wavelength as the abscissa (where insets a and b are BSA-AuNCs and [C...). 16 Fluorescence color image of M2Im]Br@BSA-Au NCs composite material at 365nm.

[0028] Figure 2 [C] was prepared for this invention. 16 Adding [C]Br@BSA-AuNCs to BSA-AuNCs composites 16 The concentration optimization plot of M2Im]Br, before and after the addition of cadmium ions [C 16 The fluorescence enhancement intensity (F1-F0) of the M2Im]Br@BSA-AuNCs composite material is used as the ordinate, and the fluorescence intensity before the addition of cadmium ions is used as the modulus. 16 The concentration of M2Im]Br is represented on the x-axis.

[0029] Figure 3 For the present invention BSA-Au NCs and [C 16 Transmission electron microscopy (TEM) images of the M2Im]Br@BSA-AuNCs composite material, where a is the TEM image of BSA-AuNCs and b is the image of [C 16 TEM image of the M2Im]Br@BSA-AuNCs composite material.

[0030] Figure 4 The present invention is based on [C] 16 A linear calibration curve of M2Im]Br@BSA-AuNCs composite material with fluorescence enhancement intensity (F1-F0) as the ordinate and cadmium ion concentration (10-1000 nM) as the abscissa.

[0031] Figure 5 The present invention is based on [C] 16 M2Im]Br@BSA-AuNCs composites were respectively added with Cd 2+ A bar chart is plotted with fluorescence intensity as the ordinate and the type of heavy metal as the abscissa.

[0032] Figure 6 For the present invention to be used in Cd 2+ After adding different interfering ions in the presence of [C] 16 A bar chart is plotted with fluorescence intensity of the M2Im]Br@BSA-AuNCs composite material as the ordinate and the types of interfering ions as the abscissa.

[0033] Figure 7 The results of spiked recovery of this invention in actual samples (rice, sea buckthorn juice, prickly pear juice, West Lake Longjing tea, Pu'er tea, baijiu, huangjiu, apple juice, grape juice and packaged drinking water) are presented. Detailed Implementation

[0034] To better understand the present invention, the following specific embodiments further illustrate the content of the present invention. However, the content of the present invention is not limited to the following embodiments, and the following content should not be construed as a limitation on the scope of protection of the present invention.

[0035] All chemical reagents and solvents used in the examples were of analytical grade.

[0036] In the following examples, the fluorescence spectroscopy measurement conditions were all: emission wavelength 500-700 nm, excitation wavelength 365 nm, and slit width 10 nm.

[0037] Example 1

[0038] A [C] 16 The synthesis method of M2Im]Br@BSA-Au NCs composite material is as follows:

[0039] (1) Synthesis of BSA-AuNCs:

[0040] Stock solutions of 50 mg / mL BSA and 10 mM HAuCl4 were prepared separately using double-distilled water. In a 50 mL round-bottom flask held at 37°C, 15 mL of HAuCl4 solution was added to 15 mL of BSA solution with constant stirring. After 2 min, 1.5 mL of 1.0 M NaOH solution was added to adjust the pH to 12, and the mixture was stirred vigorously at 37°C for 24 h. The color of the mixture gradually changed from pale yellow to brownish-yellow, indicating successful synthesis of BSA-Au NCs (concentration approximately 5 mM).

[0041] (2) [C 16 Synthesis of M2Im]Br@BSA-Au NCs composite material:

[0042] 15 mL of [C] at different concentrations (5 mM, 8 mM, 9 mM, 10 mM, 12 mM, 15 mM, 20 mM) was prepared. 16The M2Im]Br solution (prepared with double-distilled water) and 15 mL of the 5 mM BSA-AuNCs solution synthesized in step (1) were mixed in a 50 mL round-bottom flask and gently stirred for 30 min at room temperature to obtain a series of [C 16 M2Im]Br@BSA-Au NCs composite material.

[0043] First, the 100μL series [C] 16 The M2Im]Br@BSA-Au NCs composite material was mixed with 900 μL of deionized water, and a series of [C] were measured. 16 The original fluorescence intensity of the M2Im]Br@BSA-Au NCs composite was obtained to get F0, and then 100 μL of series [C 16 M2Im]Br@BSA-Au NCs composite material and 100 μL of 1 μM cadmium chloride solution were added to centrifuge tubes, then diluted to 1.0 mL with deionized water. After shaking (25℃, 350 r / min) for 5 min, a series of [C] samples were measured using a quartz dish. 16 The fluorescence emission spectrum of the M2Im]Br@BSA-AuNCs composite probe was obtained to obtain F1; the [C] before and after the addition of cadmium ions was compared with the fluorescence emission spectrum of the M2Im]Br@BSA-AuNCs composite probe. 16 The fluorescence enhancement intensity (F1-F0) of the M2Im]Br@BSA-AuNCs composite material is used as the ordinate, and the fluorescence intensity before the addition of cadmium ions is used as the modulus. 16 The concentration of M2Im]Br was used as the x-axis to obtain a concentration optimization graph. For example... Figure 2 As shown, when the added [C 16 When the concentration of the M2Im]Br solution is 10 mM, [C 16 M2Im]Br@BSA-Au NCs composites with Cd 2+ The fluorescence enhancement effect before and after the reaction was optimal; therefore, [C] was ultimately selected. 16 The specific concentration of M2Im]Br is 10 mM.

[0044] 10mM[C 16 Fluorescence spectroscopy was performed on the materials before and after M2Im]Br modification, such as... Figure 1 As shown, [C 16 The fluorescence intensity of the M2Im]Br@BSA-Au NCs composite material was increased compared to that of pure BSA-Au NCs, and both emitted bright red fluorescence. The obtained [C 16 M2Im]Br@BSA-Au NCs and BSA-Au NCs materials were characterized by transmission electron microscopy, such as Figure 3 As shown, the particle size of BSA-Au NCs is approximately 2-3 nm (the scale bar in the lower right corner is 50 nm), while after modification [C 16The particle size of the M2Im]Br@BSA-Au NCs composite material is approximately 50-200 nm (the scale bar in the lower right corner is 2.0 μm), indicating that the particle size of the modified composite material is significantly increased.

[0045] Example 2

[0046] [C 16 The M2Im]Br@BSA-Au NCs composite material was used as a fluorescent probe for rapid and sensitive detection of cadmium ions in real samples. The specific steps included:

[0047] (1) Preparation of fluorescent probes:

[0048] A stock solution of 50 mg / mL BSA and 10 mM HAuCl4 was prepared using double-distilled water. In a 50 mL round-bottom flask held at 37°C, 15 mL of HAuCl4 solution was added to 15 mL of BSA solution with constant stirring. After 2 minutes, 1.5 mL of 1.0 M NaOH solution was added to adjust the pH to 12, and the mixture was stirred vigorously at 37°C for 24 hours. The color of the mixture gradually changed from pale yellow to brownish-yellow, yielding a 5 mM BSA-Au NCs solution. Further, 15 mL of 10 mM [C]... 16 The [M2Im]Br solution and 15 mL of 5 mM BSA-AuNCs solution were mixed in a 50 mL round-bottom flask and gently stirred at room temperature for 30 min to obtain [C 16 The M2Im]Br@BSA-Au NCs composite material is used for subsequent fluorescent probe detection of cadmium ions.

[0049] (2) Fluorescence detection of cadmium ions by the probe:

[0050] 100 μL of [C] prepared in step (1) 16 M2Im]Br@BSA-AuNCs composite material and 100 μL of cadmium chloride solutions of different concentrations (10 nM, 100 nM, 400 nM, 600 nM, 800 nM, 1000 nM) were added to a centrifuge tube, then diluted to 1.0 mL with deionized water. After shaking (25℃, 350 r / min) for 5 min, the concentrations of [C] at different cadmium ion concentrations were measured using a quartz dish. 16 The fluorescence emission spectrum of the M2Im]Br@BSA-Au NCs composite probe was obtained; a standard fitting curve for fluorescence detection was obtained by linear calibration with the fluorescence enhancement intensity at approximately 620 nm before and after the addition of cadmium ions as the ordinate and the cadmium ion concentration as the abscissa. The results are as follows: Figure 4 As shown. Within the range of 10.0-1000.0 nM [C 16 The reinforcing intensity (F1-F0) of the emission peak of the M2Im]Br@BSA-Au NCs composite material is related to the cadmium ion concentration at 1.0×10⁻⁶.-8 –1.0×10 -6 A linear relationship is observed within the range of M, and the linear correlation equation is fitted as F1-F0=0.3674C. Cd 2+ +629.2668(R 2 =0.998). Based on the 3σ / s principle (σ is the standard deviation obtained from the blank sample measurement, and s is the slope of the linear regression curve), the detection rate of Cd by this sensing method is calculated. 2+ The limit of detection (LOD) is 5.09 × 10⁻⁶. -9 M.

[0051] (3) Study on the selectivity of probe for cadmium ion detection

[0052] The 100 μL [C] prepared in step (1) 16 100 μL of 10-Br@BSA-Au NCs composite material was added separately. -6 M of Cd 2+ Or 100μL 10 -4 Various heavy metal ions and other interfering ions of M (in the following forms: HgSO4, Pb(NO3)2, AgNO3, CuCl2, ZnCl2, MgCl2, Al2(SO4)3, CrCl3, KCl, NiCl2, CaCl2, BaCl2, NaCl, MnCl2, oxalic acid, tartaric acid, citric acid, and citric acid-heavy metal complexes) were diluted to 1.0 mL with deionized water, shaken (25℃, 350 r / min) for 5 min, and then the fluorescence intensity was measured. A bar graph was plotted with fluorescence intensity (F1) as the ordinate and the types of interfering ions as the abscissa, demonstrating that the probe has excellent selectivity. Figure 5 As shown. It can be seen from... Figure 5 It is obvious that only Cd is visible. 2+ This enhances the fluorescence of the composite material, while weakening others. Keeping the probe solution volume constant at 100 μL, further [the experiment was conducted] in 100 μL of Cd [solution / treatment]. 2+ (10 -6 In the presence of M), 100 μL of different interfering ions (10 -4 M) Add the probe solution, dilute to 1.0 mL with deionized water, shake (25℃, 350 r / min) for 5 min, and then detect the fluorescence intensity. Plot a bar graph with fluorescence intensity (F1) as the ordinate and the types of interfering ions as the abscissa to demonstrate that the probe has a certain anti-interference ability. The results are as follows: Figure 6 As shown. From Figure 6 It can be seen that most ions are Cd 2+ The detection of Ag does not cause much of an impact. + It may be quite obvious, but its interference can be avoided by adding a metal masking agent later.

[0053] (4) Detection of cadmium ions in actual samples

[0054] Real samples were collected, consisting of rice, sea buckthorn juice, prickly pear juice, West Lake Longjing tea, Pu'er tea, Wuliangye liquor, Shaoxing rice wine, apple juice, grape juice, and packaged drinking water. Except for the packaged drinking water, all samples underwent simple pretreatment to obtain extracts. Cadmium ions (in cadmium chloride form) were added to both the packaged drinking water and the extracts to prepare solutions with different cadmium ion concentrations (10...). -6 5×10 -7 10 -8 The test solution of M) was determined by the recovery rate experiment. Among them: the original wine sample was diluted 1000 times for subsequent experiments, and the original sea buckthorn juice, prickly pear juice, apple juice and grape juice were diluted 10 times for subsequent experiments. Tea (0.5g) was soaked in 15.0mL of deionized water and ultrasonically treated for 30 minutes. The soaking solution was filtered through a 0.22uM filter membrane to remove insoluble impurities to obtain tea extract, which was diluted 1000 times for subsequent experiments. The purchased rice sample was first ground into powder. The rice powder (0.5g) was weighed and placed in a beaker, and then 10mL of HNO3 (5%) was added. The rice powder was soaked in HNO3 for 2h, ultrasonically treated for 15min, and centrifuged at 3000rpm for 10min. The supernatant was diluted to 25mL, and NaOH solution was gradually added to adjust the pH to 7. The resulting solution was used for subsequent experiments. The addition of 10% HNO3 was measured according to the method of step (2). -8 5.0×10 -7 10 -6 The fluorescence spectra of each test solution before and after the addition of cadmium ions in M ​​were obtained, and the recovery rate was calculated using the fitted curve from step (2). The results are as follows: Figure 7 As shown, the recoveries ranged from 91.7% to 110.7%, with relative standard deviations (RSD) of less than 1.2%.

Claims

1. A method for detecting cadmium ions using an ionic liquid-modified gold nanocluster composite material as a fluorescent probe, characterized in that, The ionic liquid-modified gold nanocluster composite material was mixed with the sample solution to be tested, and the fluorescence emission spectrum of the probe was measured. If the fluorescence intensity at 620±5nm increased after the addition of the sample solution to be tested, it was determined that the sample solution to be tested contained cadmium ions. Otherwise, the sample solution to be tested does not contain cadmium ions; The preparation method of the ionic liquid modified gold nanocluster composite material includes: (1) mixing HAuCl4 solution and bovine serum albumin solution, adjusting the pH range to 11-12, stirring vigorously, and synthesizing a gold nanocluster solution that emits red fluorescence; (2) mixing imidazole ionic liquid solution with gold nanocluster solution, stirring, and the two undergo electrostatic interaction to obtain the ionic liquid modified gold nanocluster composite material. The structural formula of the imidazole ionic liquid is as follows: R is an alkyl group with 12-16 carbon atoms; X is Br, Cl or I.

2. The method according to claim 1, characterized in that, The fluorescence emission spectrum of the probe was measured after mixing the ionic liquid-modified gold nanocluster composite material with the sample solution and reacting for 5 ± 0.5 min.

3. The method according to claim 1, characterized in that, The chemical formula of the imidazole ionic liquid is [C 16 M2Im]Br, its structural formula is as follows:

4. The method according to claim 1, characterized in that, In step (2), the molar ratio of the imidazole ionic liquid to the gold nanoclusters is 2:

1.

5. The method according to claim 4, characterized in that, In step (2), the volume ratio of the imidazole ionic liquid solution to the gold nanoparticle cluster solution is 1:

1.

6. The method according to claim 5, characterized in that, In step (2), the concentration of the imidazole ionic liquid solution is 10 mM.

7. The method according to claim 1, characterized in that, In step (1), the ratio of HAuCl4 to bovine serum albumin is 1 mmol: 5 g.

8. The method according to claim 7, characterized in that, In step (1), the volume ratio of the HAuCl4 solution to the bovine serum albumin solution is 1:

1.

9. The method according to claim 8, characterized in that, In step (1), the concentration of the HAuCl4 solution is 10 mM.

10. The method according to claim 3, characterized in that, The detection limit of the ionic liquid-modified gold nanocluster composite material as a fluorescent probe is 5.09 × 10⁻⁶. -9 M.

11. The method according to any one of claims 1-10, characterized in that, The steps include: S1. Plotting the standard fitting curve of cadmium ions: Mix the ionic liquid-modified gold nanocluster composite material with cadmium ion solutions of different concentrations, make up the volume, shake or let stand for 5 minutes, and then measure the fluorescence emission spectrum of the probe. The fluorescence intensity difference of 620±5nm before and after the addition of cadmium ions is used as the ordinate and the cadmium ion concentration is used as the abscissa for linear calibration to obtain the standard fitting curve of fluorescence detection. In S2, the ionic liquid-modified gold nanocluster composite material is mixed with the sample solution to be tested, the volume is adjusted, and the sample is shaken or left to stand for 5 minutes before the fluorescence emission spectrum of the probe is measured. The cadmium ion concentration in the sample solution to be tested is calculated using the fitted curve in S1.

12. The method according to claim 11, characterized in that, The sample to be tested is a food product, including beverages and grains, and its raw materials, diluents, or extracts obtained through simple pretreatment have a cadmium ion concentration of 1.0 × 10⁻⁶. -8 –1.0×10 -6 M.

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