A color-changing visual sensing method for heavy metal ions based on hybrid nanoprobes

Abstract

The present invention discloses a color change visual sensing method for heavy metal ions based on a hybrid nanoprobe. The method comprises: mixing a heavy metal ion standard solution with a water-soluble CdSe / CdS quantum dot having an emission center of 550nm and a water-soluble CdSe / CdS quantum dot having an emission center of 620nm; photographing the fluorescence color of the above solution under the excitation of a 365nm light source, and recording the standard color of different heavy metal ion concentrations; mixing the sample to be detected with the water-soluble CdSe / CdS quantum dot having an emission center of 550nm and the water-soluble CdSe / CdS quantum dot having an emission center of 620nm successively, and comparing the color obtained under the excitation of a 365nm light source with the calibrated color to obtain the concentration of heavy metal ions in the sample to be detected. The method of the present invention combines two detection strategies of ratio fluorescence change and visual color change, improves the detection sensitivity, selectivity and stability of heavy metal ions, and is simple to operate, and is suitable for rapid detection of heavy metal ions in complex water samples.

Description

Technical Field

[0001] The invention relates to the technical field of heavy metal detection, in particular to a color change visual sensing method for heavy metal ions based on a hybrid nanoprobe. Background Art

[0002] With the discharge of industrial wastewater, urban sewage and agricultural fertilization, heavy metal ions are now widely present in natural water bodies. Although some heavy metals are essential trace elements for organisms, excessive heavy metal ions pose a serious threat to the environment and human health. For example, when the copper ion concentration reaches 4.0-6.0 mg / L, it will cause gastrointestinal discomfort symptoms. Therefore, it is crucial to develop a highly sensitive and highly selective rapid detection method for heavy metal ions.

[0003] At present, the detection methods of heavy metal ions have been greatly developed, and common techniques include ultraviolet-visible spectroscopy (UV-Vis), atomic absorption spectroscopy (AAS), chemiluminescence and colorimetry. At the same time, organic fluorescent dyes are also used in the detection of heavy metal ions, but they have disadvantages such as photobleaching, low fluorescence quantum yield, and wide emission band, resulting in insufficient sensitivity and susceptibility to interference. Therefore, researchers turned to quantum dots (QDs) as an alternative for detecting heavy metal ions.

[0004] Quantum dots have excellent optical properties such as wide absorption, narrow emission, strong fluorescence, high quantum yield, long life and good stability. Compared with organic fluorescent dyes, QDs show higher sensitivity and reliability in heavy metal ion detection. In addition, QDs have strong resistance to photobleaching and narrow emission band, which can effectively reduce background noise and improve signal resolution. Through surface modification, quantum dots can also enhance the selectivity and sensitivity to heavy metal ions.

[0005] Despite this, most fluorescence sensors still rely on a single fluorescence response mode, which is easily affected by environmental interference, changes in incident light intensity, and background noise, affecting the accuracy and reliability of the detection results. Therefore, a new hybrid nanoprobe is proposed that combines ratiometric fluorescence and visual detection methods to achieve continuous color changes when the concentration of heavy metal ions changes, providing an effective solution for high-sensitivity detection of heavy metal ions. Summary of the invention

[0006] In order to solve the problems of poor selectivity, low sensitivity and insufficient detection limit in traditional visual detection technology, the present invention provides a color change visual sensing method for heavy metal ions based on hybrid nanoprobes. The method combines the two detection strategies of ratiometric fluorescence change and visual color change, improves the detection sensitivity, selectivity and stability of heavy metal ions, and is easy to operate, which is suitable for rapid detection of heavy metal ions in complex water samples.

[0007] To achieve the above objectives, the present invention provides the following technical solutions:

[0008] A color change visual sensing method for heavy metal ions based on a hybrid nanoprobe, comprising:

[0009] (1) Accurately prepare heavy metal ion standard solutions of different concentrations;

[0010] (2) mixing a heavy metal ion standard solution and water-soluble CdSe / CdS quantum dots with an emission center of 550 nm to obtain a mixed solution; and then adding water-soluble CdSe / CdS quantum dots with an emission center of 620 nm to the mixed solution;

[0011] (3) photographing the fluorescence color of the above solution under the excitation of a 365 nm light source, and recording the standard color of different heavy metal ion concentrations;

[0012] (4) The sample to be tested is mixed evenly with water-soluble CdSe / CdS quantum dots with an emission center of 550nm and water-soluble CdSe / CdS quantum dots with an emission center of 620nm, and the color obtained under the excitation of a 365nm light source is compared with the calibrated color to obtain the concentration of heavy metal ions in the sample to be tested.

[0013] The present invention uses water-soluble CdSe / CdS quantum dots with emission centers of 550nm and 620nm as hybrid nanoprobes. Among them, the water-soluble CdSe / CdS quantum dots with an emission center of 550nm are used as detection probes, and the water-soluble CdSe / CdS quantum dots with an emission center of 620nm are used as colorimetric warning probes. The hybrid nanoprobe system of the present invention avoids the errors and interferences caused by the single fluorescence response visual detection technology.

[0014] Preferably, the heavy metal ions are one or more of copper ions, mercury ions, silver ions, gold ions and lead ions.

[0015] Preferably, the water-soluble CdSe / CdS quantum dots are water-soluble quantum dots whose surfaces are modified by thiol groups.

[0016] More preferably, the water-soluble CdSe / CdS quantum dots are first transferred from the oil phase to the water phase through 1,2-propylenediamine as a mediator, and then ligand exchange is performed on the surface of the quantum dots with 1,2-propylenediamine through thioglycolic acid (TGA) dissolved in the water phase. By mediating the transition of quantum dots from the oil phase to the water phase and then ligand exchange, the quantum dots can be stably present in the water phase and can efficiently bind to heavy metal ions. After the surface modification of the quantum dots, the selectivity and sensitivity of the probe to heavy metal ions can be enhanced.

[0017] Preferably, the heavy metal ion standard solution is prepared using HEPES buffer with a pH of 7.4.

[0018] Preferably, the mixing ratio of water-soluble CdSe / CdS quantum dots with an emission center of 550 nm and water-soluble CdSe / CdS quantum dots with an emission center of 620 nm is 2:1.

[0019] The detection principle of the present invention is: heavy metal ions quench the fluorescence of the detection probe, and the green fluorescence intensity decreases as the heavy metal ion concentration increases, while the colorimetric warning probe (water-soluble CdSe / CdS quantum dots with an emission center of 620nm) introduced each time maintains the same fluorescence intensity. This causes the ratio of the two fluorescence intensities to change linearly with the increase of the heavy metal ion concentration, thereby producing obvious fluorescence ratio changes and color changes, and finally the heavy metal ion concentration is determined by the change of this fluorescence signal.

[0020] The beneficial effects of the present invention are:

[0021] (1) High sensitivity and low detection limit: The color change visual sensing strategy based on hybrid nanoprobes provided by the present invention combines the two detection methods of fluorescence ratio change and visual color change, significantly improving the visual detection sensitivity of heavy metal ions. The detection limit of this method can reach the nanometer level (nM level), which is far lower than the relevant environmental protection standards. It can achieve effective detection in the case of light water pollution, providing strong technical support for early pollution monitoring.

[0022] (2) Excellent selectivity and anti-interference ability: The probe of the present invention can still maintain high selectivity for the target heavy metal ions under the interference of various metal ions. Even in the presence of interfering ions (such as Ca²⁺, Mg²⁺, Na⁺, etc.) in common water bodies, it can still show good anti-interference performance. This enables the detection method to effectively avoid the influence of environmental factors in practical applications, especially in complex water samples, thereby ensuring the accuracy and reliability of the detection results.

[0023] (3) Simple operation and intuitive detection signals: Compared with traditional single fluorescent probe technology, the hybrid nanoprobe of the present invention not only provides more intuitive detection signals (such as color change), but also simplifies the detection process and reduces the dependence on complex instruments and equipment. Users can easily achieve qualitative and quantitative detection of heavy metal ions by visually observing color changes or fluorescence ratio changes, which greatly improves the convenience and operability of detection and is suitable for rapid on-site detection.

[0024] (4) Excellent environmental adaptability and wide applicability: The present invention exhibits excellent detection performance under laboratory conditions and also has strong adaptability in complex practical environments. In particular, it can accurately and quickly detect the concentration of heavy metal ions in different types of water bodies such as lake water and tap water, greatly improving the efficiency of environmental pollution monitoring and water quality analysis. At the same time, the method has good economy and ease of operation, providing users with an efficient and low-cost heavy metal ion detection tool.

[0025] (5) Stability and long-term application advantages: Due to the good optical stability and anti-photobleaching properties of quantum dots, the probe of the present invention can maintain relatively stable performance during long-term use, avoiding the reduction in sensitivity of traditional fluorescent probes due to photobleaching during use, and ensuring the long-term reliability of detection.

[0026] (6) Environmental protection and safety: The quantum dots used in the present invention have undergone surface functionalization treatment and have good biocompatibility and low environmental toxicity. They are suitable for widespread application in environmental monitoring and water quality testing, conform to the concept of green environmental protection, and avoid the environmental safety issues of using toxic chemical reagents in traditional detection methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the fluorescence spectrum of water-soluble CdSe / CdS quantum dots.

[0028] Figure 2 The fluorescence spectrum of the fluorescence response changes with the copper ion concentration

[0029] Figure 3 The quantitative relationship between copper ion concentration and fluorescence intensity under single emission detection conditions. Inset (a) shows the results of single emission detection under 365 nm laser excitation, while inset (b) shows the visual effect caused by the change in fluorescence intensity ratio after the introduction of the colorimetric warning probe.

[0030] Figure 4 The fluorescence intensity response characteristics of the fluorescent probe under different metal ion backgrounds.

[0031] Figure 5 Fluorescence spectra of green (a) and red (b) fluorescent quantum dots under different pH conditions. DETAILED DESCRIPTION

[0032] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0033] Unless otherwise defined, technical or scientific terms used in the present disclosure shall have the common meanings understood by one of ordinary skill in the art to which the present invention belongs.

[0034] Example 1 Preparation of hybrid nanoprobes

[0035] The hybrid nanoprobe described in the present invention is based on CdSe / CdS quantum dots. The quantum dots are surface modified and functionalized to improve their water phase dispersibility and stability, thereby enabling high-sensitivity heavy metal ion detection in complex water samples.

[0036] (1) The specific preparation method of CdSe QDs is as follows:

[0037] S1: Preparation of Cd precursor: 0.5 mmol CdO was dissolved in a mixture of 8 mL ODE, 1 mL OA and 1 g TOPO, and heated to 300 °C with stirring under nitrogen to remove water and oxygen from the solution;

[0038] S2: Preparation of Se precursor: Se was mixed with 1 mL TOP at a certain ratio of Se to Cd and ultrasonicated so that Se was completely dissolved in TOP; Se:Cd=1:0.5-0.8;

[0039] S3: Rapidly inject the Se precursor into the Cd precursor, and react for 3 seconds to obtain green fluorescent quantum dots, and react for 5 minutes to obtain red fluorescent quantum dots.

[0040] (2) CdSe QDs are then shell modified to obtain CdSe / CdS QDs. The process is as follows:

[0041] S1: Prepare S precursor and Cd precursor separately:

[0042] S precursor: 0.5 mmol S and 3 ml ODE were mixed in beaker A, ultrasonically treated for 30 min, and then vacuum dried at 120 °C for 1 h.

[0043] Cd precursor: 0.5 mmol CdO, 0.4 ml OA and 4 ml ODE were mixed in beaker B, ultrasonically treated for 30 min, and then vacuum dried at 120 °C for 1 h.

[0044] S2: Take 0.4 ml of OLA and 3 ml of ODE, mix them, heat and stir them to 160°C, and slowly add 2 ml of CdSeQDs dissolved in toluene until the toluene is completely evaporated.

[0045] S3: After the toluene is completely evaporated, 1.5 ml of S-ODE is added dropwise. The temperature is raised to 180°C for 10-20 minutes, and then 1.5 ml of Cd precursor is added dropwise. After 15-20 minutes of reaction, the reaction is stopped and the mixture is quickly cooled to room temperature to obtain CdSe / CdS QDs.

[0046] (3) Functionalization of quantum dots and water phase transfer:

[0047] By using 1,2-propylenediamine as a mediator, the synthesized oil phase quantum dots are transferred to the aqueous phase. Then, thioglycolic acid (TGA) dissolved in the aqueous phase undergoes ligand exchange with 1,2-propylenediamine on the surface of the quantum dots. Finally, the surface of the quantum dots is water-soluble quantum dots modified with thiol groups, which further improves the stability of the quantum dots in the aqueous phase and the selectivity for heavy metal ions.

[0048] Finally, two quantum dots with different emission peaks are obtained:

[0049] (1) Water-soluble CdSe / CdS quantum dots with a green emission center of 550 nm are used as fluorescence detection probes for heavy metal ions.

[0050] (2) Water-soluble CdSe / CdS quantum dots with a red emission center of 620 nm are used as colorimetric early warning probes.

[0051] Figure 1 The fluorescence spectra of water-soluble CdSe / CdS quantum dots are shown. a is the fluorescence spectrum of water-soluble CdSe / CdS quantum dots with an emission center of 550 nm, b is the fluorescence spectrum of water-soluble CdSe / CdS quantum dots with an emission center of 620 nm, and c is the fluorescence spectrum of the mixture of the two. The illustrations show the corresponding visual color effects.

[0052] Example 2 Detection of copper ions

[0053] (1) Preparation of copper ion standard solution

[0054] Prepare copper ion standard solutions with a certain concentration range by dissolving copper chloride (CuCl2) in deionized water to prepare copper ion standard solutions of different concentrations (3 nM to 65.4 nM).

[0055] The standard copper ion concentration solutions were added to the water-soluble CdSe / CdS quantum dot solution with an emission center of 550nm, and then mixed with the water-soluble CdSe / CdS quantum dots with an emission center of 620nm. The mixture was evenly mixed and the fluorescence spectrum was scanned and recorded at room temperature using a PerkinElmer FL6500 fluorescence spectrometer under 365 nm excitation. The quantitative relationship between the copper ion concentration and the fluorescence intensity of the probe was measured (see Figure 2 ).

[0056] There is a relationship between the copper ion concentration and the fluorescent color of the solution, such as Figure 3 The insets (a) and (b) shown were recorded under 365nm light source excitation. Figure 3 The illustration (a) shows that the fluorescence intensity of the detection probe is quenched and enhanced as the copper ion concentration increases. Figure 3 The illustration (b) in the figure is a recorded image after adding the same amount of colorimetric warning probe based on the experimental steps shown in the illustration (a).

[0057] After filtering the sample to be tested twice with filter paper, follow the above steps without scanning. You only need to shoot and record the fluorescence color under the excitation of 365nm light source and compare it with the calibrated color to know the actual copper ion concentration in the water sample.

[0058] In addition, we explored the selectivity of the heavy metal ion detection probe. In order to comprehensively evaluate the performance of the probe, we selected Cd²⁺, Mg²⁺, K⁺, Na⁺, Fe³⁺, Ca²⁺, Mn²⁺, Zn²⁺ and Ba²⁺ as interfering ions. Figure 4 It shows that in the presence of other metal ions, the fluorescence intensity of the detection probe changes little and maintains good stability, while copper ions significantly cause fluorescence quenching. This shows that the synthesized probe has good selectivity and anti-interference, and can still clearly distinguish copper ions in a variety of ion backgrounds.

[0059] We evaluated the hybrid nanoprobe under pH values ​​of 4, 5, 6, 7, 8, 9, 10, and 11, aiming to explore the effect of different pH environments on the fluorescence response and to determine the pH conditions that are most conducive to the detection of copper ions by the fluorescent probe. Figure 5 The fluorescence response of the two quantum dots was shown to change with the pH value increasing from 4 to 11. The results showed that the fluorescence response showed a trend of first increasing and then decreasing, and a peak value appeared between pH 7 and 8.

[0060] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for realizing color change visual sensing of heavy metal ions based on hybrid nanoprobes, characterized in that: include: Accurately prepare standard solutions of heavy metal ions of different concentrations; the heavy metal ions are one or more of copper ions, mercury ions, silver ions, gold ions and lead ions; The heavy metal ion standard solution and the water-soluble CdSe / CdS quantum dots with an emission center of 550 nm are uniformly mixed to obtain a mixed solution; and then the water-soluble CdSe / CdS quantum dots with an emission center of 620 nm are added to the mixed solution; The fluorescence color of the above solution was photographed under the excitation of a 365nm light source, and the standard colors of different heavy metal ion concentrations were recorded; The sample to be tested is mixed evenly with water-soluble CdSe / CdS quantum dots with an emission center of 550nm and water-soluble CdSe / CdS quantum dots with an emission center of 620nm in turn, and the color obtained under the excitation of a 365nm light source is compared with the calibrated color to obtain the concentration of heavy metal ions in the sample to be tested.

2. The method according to claim 1, characterized in that The water-soluble CdSe / CdS quantum dots are water-soluble quantum dots whose surfaces are modified by thiol groups.

3. The method according to claim 2, characterized in that The water-soluble CdSe / CdS quantum dots are first transferred from the oil phase to the water phase through 1,2-propylenediamine as a medium, and then ligands are exchanged between the surface of the quantum dots and 1,2-propylenediamine by thioglycolic acid (TGA) dissolved in the water phase.

4. The method according to claim 1, characterized in that: The heavy metal ion standard solution is prepared using HEPES buffer with a pH of 7.

4.

5. The method according to claim 1, characterized in that The mixing ratio of water-soluble CdSe / CdS quantum dots with an emission center of 550 nm and water-soluble CdSe / CdS quantum dots with an emission center of 620 nm is 2:1.

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