Nano composite material, preparation method thereof and detection method of nano composite material on metal ions

Abstract

The invention relates to the technical field of metal ion detection, in particular to a nano composite material, a preparation method of the nano composite material and a metal ion detection method of the nano composite material, and the method comprises the following steps: S1, obtaining pure CdTe quantum dots; s2, obtaining a quantum dot (at) ZIF-8; s3, firstly synthesizing gold nanorods by adopting a seed growth method, then dispersing the gold nanorods in a Tris buffer solution to prepare a suspension, then adding a thiol solution to obtain a mixed solution, and then oscillating the mixed solution to form Janus gold nanorods; and S4, firstly dispersing the quantum dot (at) ZIF-8 microspheres in methanol, then adding Janus gold nanorods, carrying out ultrasonic treatment, then adding 1-ethyl-3-dimethylaminopropyl carbodiimide and N-hydroxysuccinimide, stirring at room temperature, then carrying out centrifugation to remove uncombined Janus gold nanorods, and carrying out vacuum drying to obtain the quantum dot (at) ZIF-8 microspheres. And resuspending the compound in a phosphate buffer solution containing sodium thiosulfate, and oscillating to obtain the nano composite material. According to the invention, wide-linearity, accurate, rapid and high-interference-resistance metal ion detection can be synchronously realized.

Description

Technical Field

[0001] This application relates to the technical field of metal ion detection, and in particular to nanocomposite materials, their preparation methods, and methods for detecting metal ions. Background Technology

[0002] With the acceleration of industrialization, heavy metal ions (such as Hg²⁺, Cr) are increasingly prevalent. 6 Pollution of water bodies and organisms by metal ions (such as ⁺) is becoming increasingly prominent. Their high toxicity, bioaccumulation, and carcinogenicity pose a serious threat to the ecological environment and human health. Traditional methods for metal ion detection, such as atomic absorption spectrometry and inductively coupled plasma mass spectrometry, while possessing high accuracy, often require expensive large-scale instruments, complex sample pretreatment processes, and long detection times, making them unsuitable for rapid on-site detection and real-time monitoring. Furthermore, some existing fluorescent probe detection methods suffer from insufficient sensitivity, poor selectivity, and unsatisfactory stability.

[0003] A search revealed Chinese Patent Publication No. CN108535227B, which discloses the application of CdTe QDs@ZIF-8 nanocomposite materials in the detection of chromium ions. This method involves dispersing the CdTe QDs@ZIF-8 nanocomposite materials in a HEPE buffer solution and adding different concentrations of chromium ions. 6 Standard samples containing ⁺ and Cr³⁺ ions were chemically stabilized, and fluorescence intensity was detected using a fluorescence spectrometer to plot a standard curve of F / F0 versus chromium ion concentration. CdTe QDs@ZIF-8 nanocomposite materials were dispersed in HEPEs buffer solution, and different analyte samples containing chromium ions were added. After chemical stabilization, fluorescence intensity was detected using a fluorescence spectrometer, and the Cr content in the analyte samples was determined using the standard curve. 6 The content of ⁺, and the differentiation of Cr based on fluorescence intensity. 6 ⁺ and Cr³⁺.

[0004] The aforementioned technologies suffer from the following drawbacks: They rely on a single fluorescence detection mode, which is susceptible to significant interference from ambient light or matrix background in the low concentration range below 1 μM, for example, with recovery rates fluctuating up to 13% in tap water samples. Furthermore, in the high concentration range above 40 μM, they face limitations due to fluorescence quenching saturation, thus failing to meet the requirement for wide linearity detection. Moreover, the uneven distribution of quantum dot size hinders the precise synergistic regulation of plasmon resonance and fluorescence, significantly reducing signal response accuracy. Simultaneously, these technologies rely on complex buffer systems such as HEPEs, severely limiting their applicability in the field and preventing rapid initial screening during sudden pollution events, especially when metal ion concentrations exceed 100 μM, easily triggering false positives. Additionally, in electroplating wastewater containing high concentrations of chloride or sulfate ions, or in special scenarios where quantum dots are adsorbed by proteins in blood samples, leading to aggregation, these drawbacks exacerbate interference and amplify detection errors, thus requiring improvement. Summary of the Invention

[0005] To simultaneously achieve wide linearity, high accuracy, high speed, and high interference immunity in metal ion detection, this application provides nanocomposite materials, their preparation methods, and their methods for detecting metal ions.

[0006] Firstly, the method for preparing the nanocomposite material provided in this application adopts the following technical solution: The method for preparing the nanocomposite material includes the following steps: S1. First, tellurium powder and sodium borohydride are reacted under nitrogen protection to generate sodium telluride solution. Then, cadmium chloride solution is added dropwise to sodium telluride solution. The pH of the system is then adjusted to 8.8-9.0 and refluxed. Afterward, pure CdTe quantum dots are obtained by dialysis purification. S2. First, 2-methylimidazole was dissolved in methanol to prepare solution A. Then, zinc nitrate hexahydrate and CdTe quantum dots were dissolved together in methanol to prepare solution B. Then, solution A and solution B were mixed and ultrasonically dispersed. After that, the dispersed solution was subjected to hydrothermal reaction and centrifuged, washed and dried in sequence to obtain quantum dots @ZIF-8. S3. First, gold nanorods were synthesized using the seed growth method. Then, they were dispersed in Tris buffer and prepared into a suspension. Then, thiol solution was added to obtain a mixture. The mixture was then shaken so that one end of the gold nanorod adsorbed p-mercaptobenzoic acid to expose the carboxyl group, and the other end adsorbed 6-mercapto-1-hexanol to expose the thiol group, thus forming Janus gold nanorods. S4. First, quantum dot @ZIF-8 microspheres were dispersed in methanol, then Janus gold nanorods were added and sonicated. Subsequently, 1-ethyl-3-dimethylaminopropylcarbodiimide and N-hydroxysuccinimide were added to activate the carboxyl groups, and the mixture was stirred at room temperature to allow the Janus gold nanorods to be anchored to the ZIF-8 surface through the coordination orientation of the carboxyl group -Zn²⁺. After centrifugation, the unbound Janus gold nanorods were removed. Then, the composite of quantum dot @ZIF-8 and Janus gold nanorods separated by centrifugation was resuspended in phosphate buffer containing sodium thiosulfate and shaken to obtain the nanocomposite material.

[0007] Optionally, in step S3, the thiol solution is prepared by mixing p-mercaptobenzoic acid and 6-mercapto-1-hexanol in a 1:2 molar ratio, so that p-mercaptobenzoic acid is adsorbed at one end of the gold nanorod to expose the carboxyl group and form a directional anchoring site, and 6-mercapto-1-hexanol is adsorbed at the other end to expose the thiol group and form Hg²⁺ trapping sites, thereby constructing an asymmetric bifunctional Janus structure.

[0008] Optionally, in step S4, the sodium thiosulfate concentration in the phosphate buffer is 5 mmol / L, and the shaking treatment time is 2 hours, so that sodium thiosulfate molecules diffuse into the ZIF-8 channels to form a reversible competitive ligand library.

[0009] Secondly, the nanocomposite material provided in this application adopts the following technical solution: the nanocomposite material is prepared by the above-mentioned preparation method.

[0010] Thirdly, the method for detecting metal ions using nanocomposite materials provided in this application adopts the following technical solution: The method for detecting metal ions using nanocomposite materials employs the aforementioned nanocomposite materials and includes the following steps: S1. The filtered and purified water sample to be tested is added to the suspension of the nanocomposite material and vortexed to mix, resulting in a mixture with an initial color of red. Then, the initial fluorescence intensity of the mixture under ultraviolet light is recorded. S2. After the reaction, record the color change of the mixture again, and measure the RGB value and real-time fluorescence intensity of the mixture. S3. Calculate the fluorescence quenching rate based on the initial fluorescence intensity and the real-time fluorescence intensity. Input the RGB values ​​into the color space conversion model to calculate the color difference. S4. When the color difference is greater than 5, it is judged as a positive signal, and the Hg²⁺ concentration is calculated in combination with the Hg²⁺ concentration standard curve; When the color difference is between 2 and 5 but the fluorescence quenching rate is greater than 15%, it is judged to be a low concentration of Hg²⁺. When the hue is blue but the fluorescence quenching rate is less than 15%, interfering ions are detected and a false positive alarm is triggered.

[0011] Optionally, in step S2, the p-thiol benzoic acid of Janus gold nanorods forms Hg-S coordination bonds through the specific binding of its thiol group with Hg²⁺, inducing head-to-head end self-assembly of Janus gold nanorods. Due to self-assembly, the longitudinal surface plasmon resonance absorption peak of Janus gold nanorods will undergo a blue shift, causing the color of the mixture to change from red to blue.

[0012] Optionally, in step S4, when the Hg²⁺ concentration exceeds 10 nmol / L, the excess Hg²⁺ competes with the sodium thiosulfate pre-loaded in the ZIF-8 channels for ligand binding. After the sodium thiosulfate binds with Hg²⁺, a complex is formed. The complex strips the Hg²⁺ bound to the surface of the Janus gold nanorods. By stripping and depolymerizing, the end self-assembled structure of the Janus gold nanorods is destroyed, causing a red shift in the longitudinal surface plasmon resonance absorption peak of the Janus gold nanorods, which restores the color of the mixture from blue to red.

[0013] Optionally, in step S4, after the end self-assembled structure of the Janus gold nanorod is destroyed, the 6-mercapto-1-hexanol modified end of the Janus gold nanorod captures part of Hg²⁺ through free thiol groups, and reduces Hg²⁺ to Hg under the catalysis of the Janus gold nanorod surface. 0 Hg 0 Diffusion into the Janus gold nanorod lattice forms a gold-mercury alloy with gold atoms, leading to an increase in the aspect ratio of the Janus gold nanorods and a further redshift of the longitudinal surface plasmon resonance absorption peak of the Janus gold nanorods.

[0014] Optionally, after the gold-mercury alloy is formed, it will continuously consume Hg²⁺, thereby reducing the concentration of Hg²⁺ in the mixture and forming an inverse concentration gradient difference inside and outside the ZIF-8 channel. This drives the free Hg²⁺ to migrate directionally from inside the ZIF-8 channel to outside the channel, resulting in further quenching of the quantum dot fluorescence.

[0015] Optionally, the method for generating the Hg²⁺ concentration standard curve in step S4 is as follows: using a Hg²⁺ standard solution with a concentration range of 0.01 nmol / L-500 mmol / L, obtaining fluorescence quenching rate data under the same detection conditions, and obtaining the quantitative relationship between fluorescence quenching rate and Hg²⁺ concentration through piecewise function fitting to generate the Hg²⁺ concentration standard curve.

[0016] In summary, this application includes the following beneficial technical effects: 1. This application improves the concentration detection defects of traditional fluorescent probes by synergistically combining plasma color shift and fluorescence quenching. In the low concentration range, this application relies on the fluorescence quenching of quantum dots to achieve high-sensitivity detection from 0.01 nmol / L to 10 nmol / L. In the high concentration range, this application uses sodium thiosulfate competitive ligands to trigger color reversal, achieving accurate quantification from 10 nmol / L to 500 mmol / L. This solves the fluorescence quenching saturation problem of traditional detection methods at concentrations above 40 μmol / L and significantly improves the detection linear range. 2. The sub-nanometer sieving function of the ZIF-8 channel in this application selectively shields interfering substances such as chloride ions, sulfate ions and serum proteins. The color difference is maintained at greater than 35 in electroplating wastewater containing 200 mmol / L chloride ions, and the false positive rate is less than 0.2%. The recovery rate is as high as 98.5% in a serum environment with 10 g / L albumin. Compared with traditional methods, the anti-interference ability is significantly improved, and the detection accuracy can be guaranteed without relying on complex buffer systems such as HEPES. 3. This application can complete RGB analysis via smartphone. Under ambient light conditions greater than 500 lux, the detection error is less than 1%, and the entire process from sample addition to result output can be completed within 5 minutes, greatly improving detection efficiency. In addition, the self-migration mechanism driven by gold amalgam will avoid secondary contamination of chemical reagents, making it suitable for rapid on-site handling of sudden pollution incidents. 4. Through the superposition of blue-shift and red-shift effects, and the synergy of static fluorescence quenching and competitive depolymerization reversal, this application maintains a significant signal response at a concentration of 0.01 nmol / L. At the same time, the reverse concentration gradient difference formed by the continuous consumption of Hg²⁺ by the gold amalgam will drive the directional migration of Hg²⁺, realizing dynamic signal amplification and compressing the detection limit to 0.01 nmol / L, further improving the sensitivity. Attached Figure Description

[0017] Figure 1 This is a flowchart of the preparation method of the nanocomposite material of this application; Figure 2 This is a flowchart of the method for detecting metal ions using nanocomposite materials in this application. Detailed Implementation

[0018] The following is in conjunction with the appendix Figure 1-2 This application will be described in further detail. Example 1

[0019] This application discloses a method for preparing nanocomposite materials. For example... Figure 1 As shown, the preparation method of the nanocomposite material includes the following steps: S1. First, tellurium powder and sodium borohydride are reacted under nitrogen protection to generate sodium telluride solution. Then, cadmium chloride solution is added dropwise to sodium telluride solution. The pH of the system is then adjusted to 8.8-9.0 and refluxed. Afterward, pure CdTe quantum dots are obtained by dialysis purification. S2. First, 2-methylimidazole was dissolved in methanol to prepare solution A. Then, zinc nitrate hexahydrate and CdTe quantum dots were dissolved together in methanol to prepare solution B. Then, solution A and solution B were mixed and ultrasonically dispersed. After that, the dispersed solution was subjected to hydrothermal reaction and centrifuged, washed and dried in sequence to obtain quantum dots @ZIF-8. S3. First, gold nanorods were synthesized using the seed growth method. Then, they were dispersed in Tris buffer and prepared into a suspension. Then, thiol solution was added to obtain a mixture. The mixture was then shaken so that one end of the gold nanorod adsorbed p-mercaptobenzoic acid to expose the carboxyl group, and the other end adsorbed 6-mercapto-1-hexanol to expose the thiol group, thus forming Janus gold nanorods. S4. First, quantum dot @ZIF-8 microspheres were dispersed in methanol, then Janus gold nanorods were added and sonicated. Subsequently, 1-ethyl-3-dimethylaminopropylcarbodiimide and N-hydroxysuccinimide were added to activate the carboxyl groups, and the mixture was stirred at room temperature to allow the Janus gold nanorods to be anchored to the ZIF-8 surface through the coordination orientation of the carboxyl group -Zn²⁺. After centrifugation, the unbound Janus gold nanorods were removed. Then, the composite of quantum dot @ZIF-8 and Janus gold nanorods separated by centrifugation was resuspended in phosphate buffer containing sodium thiosulfate and shaken to obtain the nanocomposite material.

[0020] Specifically, in step S1, tellurium powder and sodium borohydride are first reacted under nitrogen protection to generate a sodium telluride solution, wherein sodium borohydride is in 20% excess to ensure complete reduction of tellurium powder and suppress interference from hydrogen telluride byproducts. Then, cadmium chloride solution is slowly added dropwise to the sodium telluride solution at a rate of 0.5 mL / min, while stirring simultaneously to maintain a homogeneous reaction. After the addition is complete, the pH of the system is adjusted to a weakly alkaline environment of 8.8-9.0, and the system is refluxed at 90°C for 1.5 hours to promote the directional binding of Cd²⁺ and Te²⁻ to form uniformly sized CdTe quantum dot nuclei. The reaction solution is then purified for 24 hours through a dialysis membrane to completely remove unreacted Cd²⁺ and Te²⁻ and small molecule byproducts, resulting in pure CdTe quantum dots with excellent monodispersity and a fluorescence quantum yield of 70%.

[0021] In step S2, 2-methylimidazole was first dissolved in anhydrous methanol to prepare a 0.8 mol / L solution A. Zinc nitrate hexahydrate was then accurately weighed to achieve a molar ratio of 1:4 with 2-methylimidazole. Zinc nitrate hexahydrate and 0.5 μmol / L pure CdTe quantum dots were then dissolved together in anhydrous methanol to prepare solution B. Solution A and solution B were then mixed at a volume ratio of 1:1 and dispersed at 40 kHz ultrasonic power for 10 min to form a homogeneous precursor solution. The precursor solution was then transferred to a polytetrafluoroethylene-lined reactor and subjected to hydrothermal reaction at 100 °C for 6 hours, allowing Zn²⁺ and 2-methylimidazole to grow in a directional manner on the CdTe quantum dot surface to form a ZIF-8 framework. After the reaction, the precipitate was collected by centrifugation at 10000 r / min for 10 min and then washed three times with anhydrous methanol to remove unreacted monomers. Finally, the precipitate was vacuum dried at 60 °C for 12 h to obtain quantum dot@ZIF-8 core-shell microspheres.

[0022] In step S3, gold nanorods with a diameter of 10 nm, a length of 45 nm, and an aspect ratio of 4.5 are first synthesized using a seed growth method, and then dispersed in pH 4.5. The gold nanorods were prepared by adding 8.3% Tris buffer to form a 1 nmol / L suspension. A thiol solution was then added to obtain a mixture, which was prepared by mixing p-mercaptobenzoic acid and 6-mercapto-1-hexanol in a 1:2 molar ratio, with p-mercaptobenzoic acid concentration of 0.1 mmol / L and 6-mercapto-1-hexanol concentration of 0.2 mmol / L. The mixture was then shaken at 35°C for 60 min. Through the covalent bonding between the thiol groups of p-mercaptobenzoic acid and the surface of the gold nanorods, p-mercaptobenzoic acid was selectively adsorbed at one end of the gold nanorods to expose the carboxyl groups and form directional anchoring sites, while 6-mercapto-1-hexanol was adsorbed at the other end to expose free thiol groups and construct Hg²⁺-specific trapping sites. This resulted in bifunctional Janus gold nanorods with a carboxyl-to-thiol functional group density ratio of 1:2, an Hg²⁺ binding capacity of 1.8 ± 0.2 μmol / mg, and spatial asymmetric properties.

[0023] In step S4, quantum dot@ZIF-8 microspheres were dispersed in methanol to form a uniform suspension, and then Janus gold nanorods were added. The mixture was then treated with ultrasonic power at 40 kHz for 10 min to ensure thorough mixing. Subsequently, 1-ethyl-3-dimethylaminopropylcarbodiimide and N-hydroxysuccinimide were added, and the pH of the system was adjusted to 6.0 to activate the carboxyl functional groups at the carboxyl ends of the Janus gold nanorods. The mixture was then stirred at room temperature for 12 h to allow the activated carboxyl groups to be directionally anchored to Zn²⁺ on the ZIF-8 surface through coordination bonds, forming a stable composite structure. Unbound Janus gold nanorods were then removed by centrifugation at 10000 r / min to ensure the purity of the composite. Finally, the precipitate was resuspended in phosphate buffer containing 5 mmol / L sodium thiosulfate and shaken at 25 °C for 2 h to allow sodium thiosulfate molecules to diffuse through the sub-nanopores of ZIF-8 into the internal cavity, forming a dynamically reversible competitive ligand library and realizing a signal reversal mechanism at high concentrations of Hg²⁺.

[0024] Existing technologies rely on single fluorescence detection and are limited by narrow linear range and matrix interference. Compared with existing technologies, this preparation method achieves the following beneficial effects through the asymmetric modification of Janus gold nanorods and the synergistic design of ZIF-8 channels: 1. One end of the Janus gold nanorod is oriented and anchored with a carboxyl group to ensure the stability of the composite material, while the other end achieves specific capture of Hg²⁺ through the long-chain hydrophobic effect of 6-mercapto-1-hexanol. At the same time, combined with the surface plasmon resonance effect of the Janus gold nanorod, a dual verification mode of colorimetric and fluorescence signals is realized, thereby increasing the detection recovery rate of tap water samples from 75%±13% to 95%±2% and completely overcoming the interference of ambient light. 2. Sodium thiosulfate preloaded in the ZIF-8 channels forms a reversible competitive ligand library. Signal reversal is triggered by ligand competition at high concentrations, which solves the fluorescence quenching saturation problem of traditional fluorescent probes at concentrations above 40 μmol / L and significantly improves the detection linear range. 3. The quantum dot@ZIF-8 core-shell structure can shield the adsorption of interfering substances such as chloride ions, sulfate ions and proteins. It can maintain a 95% anti-interference rate in electroplating wastewater and a 90% anti-interference rate in serum samples pretreated by ultrafiltration. It does not require complex buffer systems such as HEPES and meets the needs of rapid on-site detection. Example 2

[0025] This application discloses nanocomposite materials. The nanocomposite materials are prepared by the method of Example 1. Example 3

[0026] This application discloses a method for detecting metal ions using nanocomposite materials. For example... Figure 2As shown, the method for detecting metal ions using nanocomposite materials, employing the aforementioned nanocomposite materials, includes the following steps: S1. The filtered and purified water sample to be tested is added to the suspension of the nanocomposite material and vortexed to mix, resulting in a mixture with an initial color of red. Then, the initial fluorescence intensity of the mixture under ultraviolet light is recorded. S2. After the reaction, record the color change of the mixture again, and measure the RGB value and real-time fluorescence intensity of the mixture. S3. Calculate the fluorescence quenching rate based on the initial fluorescence intensity and the real-time fluorescence intensity. Input the RGB values ​​into the color space conversion model to calculate the color difference. S4. When the color difference is greater than 5, it is judged as a positive signal, and the Hg²⁺ concentration is calculated in combination with the Hg²⁺ concentration standard curve; When the color difference is between 2 and 5 but the fluorescence quenching rate is greater than 15%, it is judged to be a low concentration of Hg²⁺. When the hue is blue but the fluorescence quenching rate is less than 15%, interfering ions are detected and a false positive alarm is triggered.

[0027] Specifically, in step S1, the virus, dissolved organic matter, and colloidal particles in the water sample to be tested are first removed by ultrafiltration. Then, 100 μL of the filtered water sample is accurately measured and added to 5 mL of phosphate buffer suspension containing 50 mg of nanocomposite material. The mixture is then immediately vortexed at 1500 r / min for 60 s to form a uniformly dispersed red homogenate. At this point, the longitudinal surface plasmon resonance absorption peak of the Janus gold nanorods is located at 650 nm. Subsequently, using a 405 nm excitation light source, the initial fluorescence intensity of the homogenate at the emission wavelength of 610 nm is recorded by a fluorescence spectrophotometer under shielded ambient light conditions. The background fluorescence value of the gold nanorods is subtracted simultaneously and used as the benchmark value for subsequent fluorescence quenching rate calculation.

[0028] In step S2, after the homogenate reacts with Hg²⁺ for 5 min, the p-thiobenzoic acid modified end of the Janus gold nanorods forms Hg-S coordination bonds through the specific binding of its thiol group with Hg²⁺, inducing the Janus gold nanorods to self-assemble into a dimer structure in a head-to-head manner. This self-assembly causes the longitudinal surface plasmon resonance absorption peak of the Janus gold nanorods to shift from 650 nm to 520 nm, resulting in a change in the color of the homogenate from red to blue. Simultaneously, the RGB values ​​of the homogenate are collected using a smartphone camera under illumination conditions greater than 1000 lux, and the real-time fluorescence intensity of the homogenate at 610 nm is measured using a 405 nm excitation light source under shielded ambient light conditions. The background absorption value of the gold nanorods is subtracted simultaneously, and the phenomenon of increased half-width at half-maximum (WHM) of the longitudinal surface plasmon resonance peak of the Janus gold nanorods caused by self-assembly and the concentration-dependent fluorescence quenching effect are recorded.

[0029] In step S3, based on the recorded initial fluorescence intensity and real-time fluorescence intensity, the background fluorescence value of the phosphate buffer is first subtracted, and then the difference is obtained by subtracting the real-time fluorescence intensity from the initial fluorescence intensity. This difference is then divided by the initial fluorescence intensity and finally multiplied by 100% to calculate the fluorescence quenching rate, thus accurately reflecting the quenching effect of Hg²⁺ concentration on quantum dot fluorescence. Simultaneously, the measured RGB values ​​of the mixed solution are first input into the CIE LCh color space conversion model, then the RGB values ​​are converted to XYZ tristimulus values, and finally, the CIE LCh color space conversion rate is calculated through nonlinear transformation. The L, a, and b components of the Lab color space are then used to calculate lightness, chroma, and hue angle using a Cartesian to polar coordinate transformation formula. To address the difference in hue angle before and after the reaction, a ring-shaped continuity correction algorithm is used to eliminate cross-quadrant jump errors. Finally, the lightness difference, chroma difference, and hue difference processed by a sine function are input into the CIEDE2000 color difference formula. This formula dynamically corrects the perceptual differences in different color regions through lightness weighting functions, chroma weighting functions, hue weighting functions, and the rotation function RT, and finally outputs the comprehensive color difference. The color difference parameters are used to objectively characterize the color response intensity induced by the self-assembly of Janus gold nanorods.

[0030] In step S4, when the calculated color difference is greater than 5, it is judged as a positive signal, indicating that the Hg²⁺ concentration has exceeded the standard. At this time, the specific concentration value is calculated in conjunction with the pre-established Hg²⁺ concentration standard curve. When the color difference is between 2 and 5 but the fluorescence quenching rate is greater than 15%, it is judged as a low concentration of Hg²⁺. At this time, the quantum dot fluorescence quenching dominates the detection signal. When the hue is blue but the fluorescence quenching rate is less than 15%, it is judged that there are interfering ions, triggering a false positive alarm.

[0031] The method for generating the Hg²⁺ concentration standard curve in step S4 is as follows: using Hg²⁺ standard solutions with a concentration range of 0.01 nmol / L to 500 mmol / L, the fluorescence quenching rate data corresponding to each concentration point are measured under the same detection conditions. The quantitative relationship between fluorescence quenching rate and Hg²⁺ concentration is obtained by piecewise function fitting. Linear regression fitting is used for 0.01 nmol / L to 10 μmol / L, and S-type Boltzmann function fitting is used for 10 μmol / L to 500 mmol / L, thereby generating an Hg²⁺ concentration standard curve covering the range from trace to ultra-high concentration. This curve maintains a 95% recovery rate stability in complex matrices with chloride ion concentrations below 200 mmol / L and a 90% recovery rate stability in serum matrices with albumin concentrations below 10 g / L, and supports rapid on-site quantitative analysis.

[0032] Specifically, in step S4, when the Hg²⁺ concentration exceeds 10 nmol / L, the excess Hg²⁺ competes with the 5 mmol / L sodium thiosulfate pre-loaded in the ZIF-8 channels for ligand binding. The sodium thiosulfate directly forms a stable [Hg(S₂O₃)₂]²⁻ complex with Hg²⁺. This complex removes the Hg²⁺ bound to the surface of the Janus gold nanorods through steric hindrance. By removing and depolymerizing, it disrupts the end self-assembled structure of the Janus gold nanorods, causing the longitudinal surface plasmon resonance absorption peak of the Janus gold nanorods to redshift from 520 nm to 650 nm, thus restoring the color of the mixture from blue to red. At the same time, the complex remains at the entrance of the ZIF-8 channels, enhancing the quenching effect on the quantum dot fluorescence through energy transfer or electron transfer. Thus, the precise quantification of high-concentration Hg²⁺ is achieved through the synergistic effect of color difference and fluorescence signals.

[0033] When the end-self-assembled structure of Janus gold nanorods is disrupted, the 6-mercapto-1-hexanol modified ends of the Janus gold nanorods capture part of Hg²⁺ through free thiol groups. A redox reaction then occurs under the catalysis of defect sites on the Janus gold nanorod surface, where the thiol groups are oxidized to disulfide bonds and release electrons, thereby reducing Hg²⁺ to Hg. 0 Hg 0 Diffusion into the Janus gold nanorod lattice forms a gold-mercury alloy with gold atoms, leading to lattice expansion and axial elongation of the nanorods. This increases the aspect ratio of the Janus gold nanorods, causing the longitudinal surface plasmon resonance absorption peak of the Janus gold nanorods to redshift from 650 nm to 680 nm. This redshift effect is superimposed on the redshift effect dominated by depolymerization, thus enhancing the significant color difference of the mixed liquid as it recovers from blue to red.

[0034] After its formation, the gold-mercury alloy continuously consumes Hg²⁺ at a rate of 0.5 μmol / (L·min), significantly reducing the Hg²⁺ concentration in the mixture and creating an inverse concentration gradient inside and outside the ZIF-8 channels. This gradient drives free Hg²⁺ to migrate directionally from inside the ZIF-8 channels to outside, where it is continuously consumed by the gold-mercury alloy. Simultaneously, the Hg²⁺ retained in the channels combines with surface defects of the CdTe quantum dots, achieving static quenching. The Hg²⁺ retained in the channels also diffuses to the quantum dot surface, triggering Förster resonance energy transfer and achieving dynamic quenching. This dual quenching mechanism further quenches the fluorescence of the quantum dots, thereby achieving efficient amplification of the detection signal.

[0035] In summary, the principle of this detection method is based on the multi-level response mechanism of Hg²⁺ and nanocomposite materials, as detailed below: 1. When Hg²⁺ in the water sample comes into contact with the nanocomposite material, Hg²⁺ specifically binds to the free thiol groups at the modified ends of Janus gold nanorods to form high-bond-energy coordination bonds, inducing the self-assembly of Janus gold nanorods. This causes the longitudinal surface plasmon resonance absorption peak of the Janus gold nanorods to shift from 650 nm to 520 nm, and the solution color changes from red to blue. At the same time, Hg²⁺ migrates through the ZIF-8 channels into the interior of the ZIF-8 channels to quench the fluorescence of quantum dots. 2. When the Hg²⁺ concentration exceeds 10 nmol / L, the excess Hg²⁺ competes with the pre-loaded sodium thiosulfate to form a complex. The complex strips the Hg²⁺ from the surface of the Janus gold nanorods, and the self-assembled structure of the Janus gold nanorods will be depolymerized. This causes the longitudinal surface plasmon resonance absorption peak of the Janus gold nanorods to shift from 520 nm to 650 nm, and the solution color changes from blue to red. The complex is retained at the entrance of the ZIF-8 channel to enhance fluorescence quenching. 3. Hg²⁺ captured by Janus gold nanorods is reduced to Hg in situ. 0 The formation of a gold-mercury alloy causes the longitudinal surface plasmon resonance absorption peak of the Janus gold nanorods to redshift from 650 nm to 680 nm. This redshift effect, combined with the redshift effect dominated by depolymerization, significantly enhances the color difference. Simultaneously, the gold-mercury alloy continuously consumes Hg²⁺ to form an inverse concentration gradient, driving Hg²⁺ to migrate directionally from inside the ZIF-8 channels to outside the channels, thereby achieving dynamic signal amplification.

[0036] This detection method overcomes the linear range bottleneck of traditional fluorescence detection by synergistic triple signals of plasma color shift, fluorescence quenching, and competitive inversion, achieving a wide detection range from 0.01 nmol / L to 500 mmol / L. The ZIF-8 channel precision sieving mechanism significantly improves the anti-interference rate in complex matrices. The dual signal coupling of color difference and fluorescence supports rapid analysis by smartphones, completing the detection within 5 minutes with minimal ambient light error. This provides a highly sensitive and highly interference-resistant technical solution for on-site monitoring of heavy metal pollution. Example 4

[0037] The system was detected using Hg²⁺ standard solutions with concentrations ranging from 0.005 nmol / L to 15 nmol / L. Experimental data showed that within the range of 0.01 nmol / L to 10 nmol / L, the fluorescence quenching rate exhibited a good linear relationship with the Hg²⁺ concentration, with a linear correlation coefficient R² = 0.9985.

[0038] As shown in Table 1, at a concentration of 0.005 nmol / L, the fluorescence quenching rate still reached 12.3%, with a signal-to-noise ratio of 2.8; at a concentration of 0.008 nmol / L, the fluorescence quenching rate was 15.7%, with an S / N ratio of 3.2. Based on this, the limit of detection of the method was determined to be 0.008 nmol / L. At a concentration of 0.01 nmol / L, six parallel experiments showed a fluorescence quenching rate of 18.5% ± 1.2% and a color difference of 3.2 ± 0.3, demonstrating excellent low-concentration detection capability and repeatability. Table 1 As shown in Table 2, the CdTe QD@ZIF-8 material disclosed in Chinese Patent CN108535227B was used to detect Hg²⁺ at concentrations of 0.01–10 nmol / L under the same conditions. Experimental results show that at concentrations below 1 nmol / L, the fluorescence quenching rate is less than 5% and shows no significant linear relationship with concentration. At 0.01 nmol / L, the fluorescence quenching rate is only 3.2% ± 2.1%, with a signal-to-noise ratio < 1, making reliable detection impossible. The calculated limit of detection for this method is 0.5 nmol / L, significantly higher than that of this invention. Table 2 As can be seen from the above comparative data, the present invention has significant advantages in the detection of low concentration Hg²⁺, with a detection sensitivity that is about 62 times higher than that of the comparative example, and the detection repeatability in the low concentration region is far superior to that of the comparative example, which fully demonstrates the outstanding technical progress of this application in the detection of trace heavy metals. Example 5

[0039] As shown in Table 3, the detection concentration range of Hg²⁺ was extended to 0.01 nmol / L–500 mmol / L for validation. Within the range of 0.01 nmol / L–10 μmol / L, the fluorescence quenching rate maintained a linear relationship with concentration, with a linear correlation coefficient R² = 0.998. When the concentration exceeded 10 nmol / L, the signal reversal mechanism triggered by the sodium thiosulfate competitive ligand began to function; within the range of 10 nmol / L–500 mmol / L, the relationship between the color difference value and the Hg²⁺ concentration conformed to an sigmoid Boltzmann function fit. Table 3 The goodness of fit R² = 0.9943, indicating that even at an extremely high concentration of 500 mmol / L, the fluorescence quenching rate still reached 95.2%, and no fluorescence saturation was observed. In contrast, traditional fluorescent probes show obvious fluorescence saturation above 40 μmol / L.

[0040] As shown in Table 4, different concentrations of Hg²⁺ were detected using a conventional CdTe quantum dot fluorescent probe (excluding ZIF-8 coating and Janus gold nanorods). The experiment showed that the fluorescence quenching rate reached 98% at a concentration of 35 μmol / L. However, at concentrations above 40 μmol / L, the fluorescence intensity no longer changed with increasing concentration, exhibiting a clear saturation phenomenon, making accurate quantification in the high-concentration region impossible. Table 4 As can be seen from the comparison data in Tables 3 and 4, this application has successfully solved the problem of fluorescence quenching saturation of traditional fluorescent probes in high concentration regions by introducing a signal reversal mechanism triggered by sodium thiosulfate competitive ligands. This extends the detection linear range from 0-35 μmol / L in the comparative example to 0.01 nmol / L-500 mmol / L, demonstrating significant technological progress. Example 6

[0041] As shown in Table 5, 10 nmol / L Hg²⁺ was added to a simulated water sample containing a mixture of ions: 200 mmol / L Cl⁻, 100 mmol / L SO₄²⁻, 50 mmol / L CO₃²⁻, 5 mmol / L Ca²⁺, 5 mmol / L Mg²⁺, 1 mmol / L Fe³⁺, and 0.5 mmol / L Cu²⁺ for detection. The results showed that the color difference was 36.8±1.2, the fluorescence quenching rate was 86.7%±2.1%, and the false positive rate was 0.18%. In simulated serum samples containing 10 g / L bovine serum albumin, 5 g / L globulin, and 2 g / L fibrinogen, the recovery rate of 5 nmol / L Hg²⁺ reached 98.5%±1.8%, the fluorescence quenching rate was 82.3%±2.4%, and the color difference was 6.8±0.5. In actual electroplating wastewater samples containing 200 mmol / L Cl⁻, the recovery rate of 10 nmol / L Hg²⁺ was 96.8%±2.3%. Table 5 As shown in Table 6, using the method described in Chinese Patent CN108535227B, the detection of 10 nmol / L Hg²⁺ in a simulated water sample containing 200 mmol / L Cl⁻ yielded results showing a color difference of only 8.2, a fluorescence quenching rate of 45.3% ± 12.7%, and a false positive rate of 13.5%. In serum samples, due to quantum dot aggregation caused by protein adsorption, the recovery rate of 5 nmol / L Hg²⁺ was only 72.4% ± 15.3%. Table 6 As can be seen from the comparative data in Tables 5 and 6, the false positive rate of this application in a high-concentration chloride ion environment is only 0.18%, far lower than the 13.5% of the comparative example; the recovery rate in serum samples reaches 98.5%±1.8%, significantly better than the 72.4%±15.3% of the comparative example. This indicates that this application, through the precise sieving function of the ZIF-8 channels and the specific recognition mechanism of Janus gold nanorods, effectively eliminates the influence of various interfering substances in complex matrices and possesses excellent anti-interference performance. Example 7

[0042] As shown in Table 7, the nanocomposite materials were placed in buffer solutions with pH values ​​of 4, 5, 7, 9 and 10, and their properties were tested after being stored at 4°C for 30 days. The performance retention rate showed excellent stability. Table 7 Within a pH range of 5-9, the fluorescence intensity retention rate was above 95%, and the shift in the plasmon absorption peak position was less than 2 nm. Under extreme conditions of pH 4 and pH 10, the fluorescence intensity retention rates were 82.3% and 85.7%, respectively.

[0043] As shown in Table 8, a series of tests were conducted on a 10 nmol / L Hg²⁺ water sample, and the results showed that the method has excellent accuracy. Table 8 Ten parallel tests were performed on a 10 nmol / L Hg²⁺ water sample. The relative standard deviation of fluorescence quenching rate was 2.1%, and the relative standard deviation of color difference was 3.5%. In interval experiments conducted on different dates by different operators, the relative standard deviation of fluorescence quenching rate was 3.8%, and the relative standard deviation of color difference was 4.2%.

[0044] As shown in Table 9, the stability test results of traditional CdTe quantum dots under the same conditions are significantly lower than those of the materials in this application. Table 9 After being stored under the same conditions for 30 days, traditional CdTe quantum dots only retained 65.3% ± 8.7% of their fluorescence intensity in a pH 7 buffer solution. The retention rates dropped to 52.1% and 58.6% at pH 5 and pH 9, respectively, and the shift in the plasma absorption peak position was significantly greater than that of the material in this application.

[0045] The comparative data in Tables 7-9 fully demonstrate that the nanocomposite material formed by ZIF-8 coating and Janus gold nanorods in this application has significantly improved stability and repeatability, providing a reliable guarantee for practical applications. Example 8

[0046] As shown in Table 10, color difference analysis was performed using three smartphones from different brands (Huawei P40, Xiaomi 11, and iPhone 12) under ambient light conditions of 500-1500 lux. Table 10 Compared with the measurement results of a professional colorimeter, the average deviation is 0.82% and the maximum deviation is 1.35%. The entire testing process, from sample addition to result output, can be completed within 5 minutes.

[0047] As shown in Table 11, the accuracy of detection under different environmental conditions is evaluated. Table 11 Under outdoor natural light conditions (illuminance 800-1200 lux), the relative deviation of the 10 nmol / L Hg²⁺ water sample from the traditional laboratory method was 2.3%, and the test results of the two actual water samples also showed good consistency.

[0048] Table 12 shows a performance comparison of different detection methods. Table 12 As shown in Table 13, the field applicability test was conducted under the same conditions using the method in Chinese Patent CN108535227B. Table 13 As can be seen from the comparative data in Tables 10-13, the detection method of this application has significant advantages in terms of detection speed, equipment cost, ease of operation and environmental adaptability. In particular, in terms of ambient light interference, the detection error of this method is controlled within 3.5%, which is far lower than the 18.7%-30.8% of the comparative example, fully demonstrating its practical value in rapid on-site detection.

[0049] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for preparing nanocomposite materials, characterized in that: Includes the following steps: S1. First, tellurium powder and sodium borohydride are reacted under nitrogen protection to generate sodium telluride solution. Then, cadmium chloride solution is added dropwise to sodium telluride solution. The pH of the system is then adjusted to 8.8-9.0 and refluxed. Afterward, pure CdTe quantum dots are obtained by dialysis purification. S2. First, 2-methylimidazole was dissolved in methanol to prepare solution A. Then, zinc nitrate hexahydrate and CdTe quantum dots were dissolved together in methanol to prepare solution B. Then, solution A and solution B were mixed and ultrasonically dispersed. After that, the dispersed solution was subjected to hydrothermal reaction and centrifuged, washed and dried in sequence to obtain quantum dots @ZIF-8. S3. First, gold nanorods were synthesized using the seed growth method. Then, they were dispersed in Tris buffer and prepared into a suspension. Then, thiol solution was added to obtain a mixture. The mixture was then shaken so that one end of the gold nanorod adsorbed p-mercaptobenzoic acid to expose the carboxyl group, and the other end adsorbed 6-mercapto-1-hexanol to expose the thiol group, thus forming Janus gold nanorods. S4. First, quantum dot @ZIF-8 microspheres were dispersed in methanol, then Janus gold nanorods were added and sonicated. Subsequently, 1-ethyl-3-dimethylaminopropylcarbodiimide and N-hydroxysuccinimide were added to activate the carboxyl groups, and the mixture was stirred at room temperature to allow the Janus gold nanorods to be anchored to the ZIF-8 surface through the coordination orientation of the carboxyl group -Zn²⁺. After centrifugation, the unbound Janus gold nanorods were removed. Then, the composite of quantum dot @ZIF-8 and Janus gold nanorods separated by centrifugation was resuspended in phosphate buffer containing sodium thiosulfate and shaken to obtain the nanocomposite material.

2. The preparation method according to claim 1, characterized in that: In step S3, the thiol solution is prepared by mixing p-mercaptobenzoic acid and 6-mercapto-1-hexanol in a 1:2 molar ratio, so that p-mercaptobenzoic acid is adsorbed at one end of the gold nanorod to expose the carboxyl group and form a directional anchoring site, and 6-mercapto-1-hexanol is adsorbed at the other end to expose the thiol group and form an Hg²⁺ trapping site, thereby constructing an asymmetric bifunctional Janus structure.

3. The preparation method according to claim 2, characterized in that: In step S4, the sodium thiosulfate concentration in the phosphate buffer is 5 mmol / L, and the shaking treatment time is 2 hours, so that sodium thiosulfate molecules diffuse into the ZIF-8 channels to form a reversible competitive ligand library.

4. A nanocomposite material, characterized in that: It is prepared by the preparation method described in claim 3.

5. A method for detecting metal ions using nanocomposite materials, characterized in that: The detection using the nanocomposite material described in claim 4 includes the following steps: S1. The filtered and purified water sample to be tested is added to the suspension of the nanocomposite material and vortexed to mix, resulting in a mixture with an initial color of red. Then, the initial fluorescence intensity of the mixture under ultraviolet light is recorded. S2. After the reaction, record the color change of the mixture again, and measure the RGB value and real-time fluorescence intensity of the mixture. S3. Calculate the fluorescence quenching rate based on the initial fluorescence intensity and the real-time fluorescence intensity. Input the RGB values ​​into the color space conversion model to calculate the color difference. S4. When the color difference is greater than 5, it is judged as a positive signal, and the Hg²⁺ concentration is calculated in combination with the Hg²⁺ concentration standard curve; When the color difference is between 2 and 5 but the fluorescence quenching rate is greater than 15%, it is judged to be a low concentration of Hg²⁺. When the hue is blue but the fluorescence quenching rate is less than 15%, interfering ions are detected and a false positive alarm is triggered.

6. The detection method according to claim 5, characterized in that: In step S2, the p-thiol benzoic acid of Janus gold nanorods forms Hg-S coordination bonds through the specific binding of its thiol group with Hg²⁺, inducing head-to-head end self-assembly of Janus gold nanorods. Due to self-assembly, the longitudinal surface plasmon resonance absorption peak of Janus gold nanorods will undergo a blue shift, causing the color of the mixed liquid to change from red to blue.

7. The detection method according to claim 6, characterized in that: In step S4, when the Hg²⁺ concentration exceeds 10 nmol / L, the excess Hg²⁺ competes with the sodium thiosulfate preloaded in the ZIF-8 channels for ligand binding. After the sodium thiosulfate binds with Hg²⁺, a complex is formed. The complex strips the Hg²⁺ bound to the surface of the Janus gold nanorods. This stripping and depolymerization disrupts the end self-assembled structure of the Janus gold nanorods, causing a red shift in the longitudinal surface plasmon resonance absorption peak of the Janus gold nanorods, which restores the color of the mixture from blue to red.

8. The detection method according to claim 7, characterized in that: In step S4, after the end self-assembly structure of the Janus gold nanorod is disrupted, the 6-mercapto-1-hexanol modified end of the Janus gold nanorod captures part of Hg²⁺ through free thiol groups, and reduces Hg²⁺ to Hg under the catalysis of the Janus gold nanorod surface. 0 Hg 0 Diffusion into the Janus gold nanorod lattice forms a gold-mercury alloy with gold atoms, leading to an increase in the aspect ratio of the Janus gold nanorods and a further redshift of the longitudinal surface plasmon resonance absorption peak of the Janus gold nanorods.

9. The detection method according to claim 8, characterized in that: After its formation, the gold-mercury alloy will continuously consume Hg²⁺, causing the concentration of Hg²⁺ in the mixture to decrease. This will create an inverse concentration gradient difference inside and outside the ZIF-8 channels, driving free Hg²⁺ to migrate directionally from inside the ZIF-8 channels to outside, resulting in further quenching of the quantum dot fluorescence.

10. The detection method according to claim 5, characterized in that: The method for generating the Hg²⁺ concentration standard curve in step S4 is as follows: using Hg²⁺ standard solutions with a concentration range of 0.01 nmol / L to 500 mmol / L, fluorescence quenching rate data are obtained under the same detection conditions, and the quantitative relationship between fluorescence quenching rate and Hg²⁺ concentration is obtained by fitting a piecewise function to generate the Hg²⁺ concentration standard curve.

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