A paper-based chip for detecting cadmium ions by LIBS and a preparation method and application thereof

Abstract

The application relates to the technical field of substance detection, in particular to a paper-based chip for LIBS detection of cadmium ions and a preparation method and application thereof. The preparation method comprises the following steps: 1) mixing a zinc salt solution and a sodium sulfide solution and carrying out reaction to obtain a ZnS nanoparticle solution; 2) mixing the ZnS nanoparticle solution, polyvinylpyrrolidone and an acid solution to obtain a ZnSNPs modification solution; and 3) mixing the ZnSNPs modification solution with a filter paper sheet and oscillating, adding an alcohol solution, cleaning and drying. The paper-based chip can efficiently enrich heavy metal elements cadmium in water to carry out LIBS detection. Through the use of the LIBS technology and the paper-based chip, high-sensitivity, rapid and efficient detection of heavy metal Cd in water can be realized.

Description

Technical Field

[0001] This invention relates to the field of material detection technology, and in particular to a paper-based chip for detecting cadmium ions using LIBS, its preparation method, and its application. Background Technology

[0002] Heavy metal pollution not only damages the environment but also impacts ecosystems through the food chain. Cadmium (Cd) is a typical toxic element, making the detection of excessive Cd levels in water bodies (such as ambient water and drinking water) crucial. Laser-induced breakdown spectroscopy (LIBS) is an elemental analysis technique. Its basic principle is to focus an ultrashort pulse laser on the sample surface, achieving a sufficiently high energy density to form a plasma. Atoms in the plasma are excited and emit characteristic spectra, which can be analyzed by a spectrometer to determine the sample's composition and content. LIBS technology, with its unique advantages, has shown strong application potential in multiple fields. LIBS has been applied in various fields; however, because harmful heavy metals in the environment are generally at trace levels, the detection limit of LIBS is often at the sub-ppm level, making it difficult for LIBS to directly detect trace heavy metals. Paper-based chips are paper-based detection devices based on microfluidic technology. They offer advantages such as being environmentally friendly, low-cost, easy to transport and store, and are used in clinical diagnostics, environmental monitoring, and food safety. Paper-based chips are microfluidic chips that use paper (such as filter paper, chromatography paper, and various cellulose membranes) as the chip fabrication material and biochemical analysis platform. They offer advantages such as fast detection speed, ease of operation, portability, and low cost, and are often a research hotspot in basic scientific research, biochemical detection, and other fields, promoting the development of low-cost analytical techniques. In recent years, nanomaterials, as multifunctional nanomaterials, have been widely used in medicine, sensors, and catalysis. Among them, biosensors based on metal nanoparticles have also been applied to heavy metal detection. The principle is mainly based on utilizing the specific binding of heavy metal ions to certain nanomaterials, thereby changing the physical and chemical properties (color development, fluorescence, catalytic activity, thermal effects, etc.) of the nanomaterials. Finally, changes in the physicochemical properties of the nanomaterials are collected by colorimetry, ultraviolet-visible spectroscopy, local plasmon resonance, and fluorescence spectroscopy, thus indirectly reflecting the content of heavy metal elements in the analyte.

[0003] Currently, many detection techniques (such as atomic absorption spectrometry, atomic fluorescence spectrometry, and inductively coupled plasma atomic emission spectrometry) are applied to the detection of the heavy metal element Cd. Although these methods can achieve highly sensitive detection of heavy metal elements, they are often only usable in the laboratory, requiring professional operation. They are also subject to drawbacks such as sample matrix effects, background interference, or interference from scattered light on the fluorescence signal, resulting in time-consuming, labor-intensive, and costly detection methods, making them difficult to apply to actual in-situ detection of heavy metals in the environment. To rapidly detect trace amounts of the heavy metal element Cd in water, a novel, rapid, and efficient method for detecting heavy metal elements is urgently needed. 3+ and Mn 2+ in Water Using Laser-Induced Breakdown Spectroscopy Combined with FilterPaper Modified with Gold Nanoclusters. Biosensors, 2024, 14 (6), 267. This document introduces a paper-based Cr-based composite material modified with gold nanoclusters using LIBS technology. 3+ and Mn 2+ While current literature demonstrates some detection capabilities for heavy metals such as Cr and Mn, it cannot analyze and detect Cd in water.

[0004] Currently, there is an urgent need to provide a new type of paper-based chip for detecting cadmium ions in water using LIBS. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a paper-based chip for LIBS detection of cadmium ions, its preparation method, and its application. This invention achieves this by in-situ synthesis of zinc sulfide nanoparticles (ZnS nanaparticles, ZnSNPs) on a paper-based chip, which can detect cadmium ions containing Cd. 2+ By using LIBS technology and combining it with a paper-based chip modified with ZnSNPs for specific and efficient adsorption of the solution, it is possible to achieve rapid and efficient detection of heavy metal Cd in water with high sensitivity.

[0006] In a first aspect, the present invention provides a method for preparing a paper-based chip for LIBS detection of cadmium ions, comprising:

[0007] 1) A zinc salt solution and a sodium sulfide solution were mixed and reacted to obtain a ZnS nanoparticle solution.

[0008] 2) The ZnS nanoparticle solution, polyvinylpyrrolidone, and acid solution are mixed to obtain a ZnSNPs modified solution.

[0009] 3) Mix the ZnSNPs-modified solution with filter paper and shake, add an alcohol solution, wash, and dry. This invention utilizes LIBS technology combined with a ZnSNPs-modified paper-based chip to achieve the detection of the heavy metal Cd in water. Through process optimization, ZnSNPs are synthesized in situ on the paper-based chip, resulting in a paper-based chip capable of detecting Cd-containing substances. 2+ The solution was used for specific and efficient adsorption of Cd, and the LIBS signal of Cd in the paper-based chip was collected using a LIBS instrument. The relationship between the Cd LIBS signal and Cd was analyzed. 2+ The quantitative relationship model established based on the concentration of Cd in water can effectively achieve the analysis of Cd concentration in water. 2+ Detection and analysis.

[0010] According to the present invention, a paper-based chip for detecting cadmium ions using LIBS prepared according to the present invention is capable of specifically adsorbing Cd. 2+ The (ZnSNPs in-situ modified) fast paper-based sensor chip, with its porous structure and large specific surface area, can more efficiently and specifically adsorb the heavy metal element Cd in water, and also improves the LIBS signal of the analyte Cd, thus improving the sensitivity of Cd detection. 2+ This invention enables efficient and rapid detection of the heavy metal Cd in water, achieving highly efficient and specific enrichment and better LIBS detection of Cd in water. Furthermore, the nanoparticle-modified paper substrate of this invention is simple to prepare, inexpensive, and easy to promote and use. The ZnSNPs-modified paper substrate chip prepared by this invention exhibits excellent performance in efficiently and specifically adsorbing Cd and detecting it using LIBS. The principle behind this is likely that the ZnSNPs-modified paper substrate chip itself possesses a porous structure and a large specific surface area, which can effectively adsorb the heavy metal Cd. 2+ Meanwhile, Cd 2+ and S 2- There are stronger chemical bonding energies between them, making Cd 2+ With Zn 2+ Substitution or displacement reactions occur between them. Moreover, the nanomaterials increase the density of particles in the plasma phase during ablation, which can further improve the LIBS signal of the analyte Cd and enhance the sensitivity of Cd detection.

[0011] Preferably, in step 1), the zinc salt solution is a zinc nitrate solution with a concentration of 8-12 mM, preferably 10-11 mM; and / or, the sodium sulfide solution has a concentration of 10-14 mM, preferably 12-13 mM.

[0012] Further preferably, in step 1), the volume ratio of the zinc nitrate solution to the sodium sulfide solution is 4~7:3~6, preferably 5~6:4~5. By optimizing the concentration and ratio of zinc nitrate and sodium sulfide, ZnS nanoparticles are better generated, ultimately achieving a better modification effect. This contributes to improving the material properties of subsequent paper chips and enhancing the resistance to heavy metal ions Cd²⁺. + Adsorption capacity.

[0013] Further preferred, in step 1), the reaction temperature can be room temperature; preferably, the reaction temperature is 25±2℃, the reaction time is 10±2min, and the stirring speed is 200±5 r / min.

[0014] Preferably, in step 2), the ratio of the ZnS nanoparticle solution, the polyvinylpyrrolidone, and the acid solution is 6~10mL:0.3~0.8g:0.05~0.2mL, and more preferably 8~9mL:0.4~0.5g:0.08~0.1mL.

[0015] Further preferably, in step 2), the acid solution is hydrochloric acid, and the concentration of the hydrochloric acid is 0.05~0.15M, preferably 0.1~0.12M.

[0016] In this invention, adjusting the ratio and concentration of the prepared ZnS nanoparticle solution, polyvinylpyrrolidone, and hydrochloric acid can enhance adsorption performance, improve LIBS sensitivity, and optimize detection results. Especially under preferred conditions, it can further improve the uniformity of nanoparticle distribution on the paper substrate and facilitate the detection of Cd²⁺. + The improved specific adsorption effect, with further optimized ratios, can enhance the adsorption of Cd²⁺ in water. + This improves the detection effect, further ensuring detection sensitivity and accuracy, while reducing possible background interference and the influence of other metal ions. Combined with the optimized hydrochloric acid concentration, it can ensure the stability of ZnS particles, avoid particle aggregation and precipitation, and further improve the stability and sensitivity of the LIBS signal.

[0017] Preferably, in step 3), the shaking time is 8-12 min, preferably 10-11 min; and / or, the size of the filter paper is 0.5-1.5 cm × 0.5-1.5 cm, preferably 1-1.2 cm × 1-1.2 cm; and / or, the alcohol solution is an ethanol solution, and the volume of the ethanol solution is preferably 2-3 mL.

[0018] Further preferably, in step 3), the cleaning is performed by washing with deionized water 2-3 times; and / or, the drying temperature is 35-40℃, preferably 37-38℃. In this invention, the drying temperature is higher than room temperature but not too high. Too low or too high a temperature will affect the effect. For example, a temperature exceeding 50℃ will cause the paper base to scorch. The drying temperature selected in this invention is preferably 37-38℃ for the best effect.

[0019] Secondly, the LIBS paper-based chip for detecting cadmium ions provided by this invention is prepared by the aforementioned method for preparing a LIBS paper-based chip for detecting cadmium ions. The LIBS paper-based chip for detecting cadmium ions prepared by this invention can specifically enrich cadmium ions in water, and its combination with LIBS technology enables highly sensitive and rapid detection of the heavy metal Cd in water.

[0020] Thirdly, the present invention provides a LIBS paper-based chip for detecting cadmium ions prepared by the above-described method, or the application of the above-described LIBS paper-based chip for detecting cadmium ions, particularly in the application of LIBS for detecting Cd in water. 2+ Applications in the specific adsorption detection of [the substance].

[0021] In this invention, ZnSNPs are synthesized in situ on a paper substrate to target ZnSNPs containing Cd. 2+ The water body was subjected to specific and efficient adsorption, and the LIBS signal of Cd was collected using a LIBS instrument. The relationship between the Cd LIBS signal and Cd was then analyzed. 2+ A quantitative relationship model was established for the concentration of Cd in water to achieve this. 2+ Detection and analysis.

[0022] Further optimization yielded the following quantitative relationship model: Y = aX + b; where Y is the LIBS signal intensity at 226.56 nm, and X is the Cd... 2+ Concentrations, a is 51.5±0.2, and b is 1869.6±0.2. The paper-based chip for LIBS detection of cadmium ions prepared in this invention specifically enriches cadmium ions in water and uses LIBS technology to excite the spectral signal of the metal ion Cd. Through the established quantitative model between the LIBS signal and Cd concentration, it is possible to achieve more sensitive, rapid, and efficient detection of the heavy metal Cd in water.

[0023] The beneficial effects of this invention are at least as follows: This invention is the first to realize the detection of Cd in water using a paper-based chip modified with ZnSNPs and LIBS technology. 2+ Enrichment was carried out, thereby achieving the extraction of Cd from water. 2+ This invention provides a highly efficient and rapid detection method applicable to the detection of excessive levels of the heavy metal Cd in water. 2+The detection linear range is 0~100μg / L, and the sensitivity is 1.10μg / L. The recovery rate for actual samples is between 95% and 115%. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 This is a laser-induced breakdown spectroscopy instrument device in an embodiment of the present invention.

[0026] Figure 2 This is a schematic diagram of the fabrication process of a paper-based chip modified with ZnSNPs, provided in an embodiment of the present invention.

[0027] Figure 3 The adsorption results of some conventional metal ions by the ZnSNPs modified paper-based chip provided in Example 1 of this invention are shown.

[0028] Figure 4 The ZnSNPs-modified paper-based chip provided in Embodiment 1 of this invention is used to detect Cd in water. 2+ LIBS spectrum for adsorption detection.

[0029] Figure 5 The ZnSNPs-modified paper-based chip provided in Embodiment 1 of this invention is effective against Cd in water. 2+ A quantitative model for detection in the concentration range (0~100 μg / L) was established.

[0030] Figure 6 The ZnSNPs-modified paper-based chip provided in Embodiment 2 of this invention is effective against Cd in water. 2+ The optimal enrichment time for detection.

[0031] Figure 7 The ZnSNPs-modified paper-based chip provided in Embodiment 2 of this invention has a high sensitivity to Cd in water. 2+ Determine the optimal pH conditions for the solution.

[0032] In the figure, 1-signal delay generator; 2-laser; 3-plasma; 4-3D detection platform; 5-paper-based chip; 6-optical fiber; 7-spectrometer; 8-focusing lens; 9-mirror; 10-reaction vessel; 11-zinc ion; 12-sulfur ion; 13-filter paper; 14-ZnSNPs-modified nanopaper substrate; 15-cadmium ion; 16-adsorbed Cd 2+ Nanopaper-based; 17-laser-induced breakdown spectroscopy instrument. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0034] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0035] Unless otherwise specified, the techniques or conditions described in the literature of this invention shall be followed, or the product instructions shall be followed. Devices, instruments, reagents, etc., whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels. All experimental reagents and raw materials involved are commercially available, and all reagents are analytical grade products. In the following examples, zinc nitrate (Zn(NO3)2) (purchased from Maclean, model: 228737-100g), sodium sulfide (Na2S standard solution, 0.1M, purchased from Guangzhou Hewei Pharmaceutical Technology Co., Ltd.) and Cd... 2+ Standard solutions and other conventional metal ion standard solutions (initial concentration 1000 ppm, purchased from the National Standard Material Platform), ethanol (purchased from Beijing Jintonglete Chemical Products Co., Ltd.), polyvinylpyrrolidone (purchased from Maclean's, reagent number: 81440-250G), and hydrochloric acid (purchased from Maclean's, reagent number: 1.09063, 2M). In the following examples, the main experimental equipment involved was a self-built, research-grade LISB instrument.

[0036] In this embodiment of the invention, Figure 1 This is a schematic diagram of a laser-induced breakdown spectroscopy instrument, which includes a signal delay generator 1, a laser 2, a plasma 3, a 3D detection platform 4, a paper-based chip 5, an optical fiber 6, a spectrometer 7, a focusing lens 8, and a mirror 9. Figure 2The fabrication process of the ZnSNPs-modified paper-based chip provided in this embodiment of the invention involves first mixing and shaking a zinc nitrate solution and a sodium sulfide solution. After 2 minutes, PVP and hydrochloric acid solutions are added and mixed. Then, filter paper is placed in the above solution and shaken at room temperature for 10 minutes. Ethanol is added to terminate the reaction. Finally, the ZnSNPs-modified paper-based chip is removed, washed twice with deionized water, and dried at 37°C for later use. By synthesizing ZnSNPs in situ on the paper-based chip, the paper-based chip modified with these nanoparticles can specifically enrich cadmium ions in water. Finally, LIBS technology is used to excite the spectral signal of metal ion Cd, and a quantitative model between the LIBS signal and Cd concentration is established to achieve high-sensitivity, rapid, and efficient detection of heavy metal Cd in water. In the figure, reaction vessel 10 (centrifuge tube), zinc ions 11, sulfide ions 12, filter paper 13, ZnSNPs-modified nanopaper substrate 14, cadmium ions 15, and adsorbed Cd. 2+ 16. Nanopaper-based 17. Laser-induced breakdown spectroscopy instrument.

[0037] Example 1

[0038] This embodiment provides a ZnSNPs-modified paper-based chip and its preparation method, utilizing LIBS technology combined with the ZnSNPs-modified paper-based chip to detect Cd in water. 2+ Enrichment and efficient rapid detection were performed on the ZnSNPs-modified paper-based chip prepared in this embodiment, including specificity experiments, Cd adsorption detection, LIBS signal acquisition and quantitative relationship model establishment, and performance testing of actual samples.

[0039] (1) Fabrication of ZnSNPs modified paper-based chips

[0040] Take 5 mL of zinc nitrate solution (10 mM) and 4 mL of sodium sulfide solution (12 mM) and mix for 2 min. Then add 0.5 g of polyvinylpyrrolidone and add hydrochloric acid (0.1 mL, 0.1 M) dropwise. After mixing, place 50 filter paper sheets (1 cm × 1 cm) in the mixture and shake for 10 min. Then add 2 mL of ethanol solution to stop the reaction. Finally, remove the filter paper, wash it twice with deionized water, and dry it at 37 °C for later use to obtain the ZnSNPs modified paper substrate (chip).

[0041] (2) Specific detection

[0042] This embodiment verifies and proves the effect of ZnSNPs-modified paper substrate on Cd. 2+This invention demonstrates strong adsorption performance. The adsorption of various common metal ions by a ZnSNPs-modified paper substrate was compared, and other metal ions were prepared at a concentration of 0.2 mg / L. After shaking for 15 min, the paper substrate chip was removed and washed twice with deionized water. LIBS signals of characteristic peaks for adsorbed metal ions corresponding to different paper substrates were collected using LIBS technology. Data processing and comparative analysis were then performed. Figure 3 As shown in the bar chart, the detection results show that the signal for cadmium ions collected by LIBS is 1000, the signal for copper ions is 100, while the signals for other metal elements are basically 0. Based on the detection results, this invention concludes that the paper substrate modified with ZnSNPs has very high specific adsorption performance for insulators and can effectively detect insulators.

[0043] (3) Cd 2+ Establishment of a quantitative relationship model for detection

[0044] Prepare 5 mL of Cd solutions with different concentration gradients 2+ Solutions (0, 5, 10, 50, 100, 200, 500, 1000 μg / L) were prepared, and a pre-prepared ZnSNPs-modified paper-based chip was added to each solution. After shaking for 15 min, the paper-based chip was removed and washed twice with deionized water. Finally, the LIBS signal of Cd on the paper-based chip was detected. A Cd [structure / system] was established. 2+ A quantitative model of the relationship between concentration and its LIBS signal.

[0045] (4) Cd in pond water and river water 2+ Analysis and detection and recovery rate calculation

[0046] Pond water and river water were collected and their Cd concentrations were first determined using ICP-MS. The results showed that the Cd concentrations in the pond water and river water were 0.003 μg / L and 0.002 μg / L, respectively. Then, spiking experiments were performed on the samples (10 μg / L and 50 μg / L of Cd were added, respectively), and the concentration values ​​and recoveries were calculated using linear regression analysis.

[0047] Table 1 Cd 2+ Actual sample testing

[0048]

[0049] (5) Specificity analysis

[0050] To verify the effect of this invention on Cd 2+The ZnSNPs-modified paper-based chip provided in this embodiment exhibits highly specific adsorption performance for Cd, showing strong adsorption specificity (LIBS signal of 1000), while showing virtually no adsorption capacity or weak signals for other metal elements (LIBS signal of only 100 for copper ions, and almost 0 for other metal ions). The ZnSNPs-modified paper-based chip provided by this invention can achieve adsorption of Cd in water. 2+ Specific adsorption detection.

[0051] (6) Sensitivity analysis

[0052] from Figure 4 It can be seen that after the ZnSNPs-modified paper-based chip adsorbs different concentrations (0~1000 μg / L) of Cd, the LIBS spectrum changes with the adsorption of Cd. 2+ The signal at 226.56 nm increases with increasing Cd concentration. 2+ The effect increases with increasing concentration, and from Figure 5 It can also be seen that the LIBS signal strength is related to Cd 2+ A positive correlation is observed within a certain concentration range. To establish a better quantitative model and calculate the optimal limit of detection, such as... Figure 5 As shown, this invention establishes a corresponding quantitative relationship model (Y=51.5887X+1869.6045, R) for concentrations (0~100μg / L). 2 =0.9922), which enables more accurate quantitative detection, and the Cd concentration can be calculated. 2+ The detection limit was 1.10 μg / L.

[0053] (7) Analysis of test results

[0054] To verify the practicality of this method, this embodiment uses Cd to test actual samples (pond water and river water). 2+ Spikes were added to the water samples, and the spiked water samples were analyzed and tested. Table 1 shows the results of the actual sample spiked test and the calculation of the recovery rate. The recovery rate can be maintained between 95% and 115%.

[0055] Comparative Example 1

[0056] This comparative example provides a paper substrate modified with zinc sulfide nanoparticles for the detection of cobalt ions, and its preparation method is as follows:

[0057] (1) Preparation of zinc sulfide nanoparticle dispersion: Zinc salt and sodium sulfide with a molar ratio of 0.3:1 were dissolved in deionized water to obtain zinc salt solution and sodium sulfide solution respectively; the zinc salt solution was heated to 80°C, and then mercaptoacetic acid was added dropwise and stirred for 30 min. The volume ratio of mercaptoacetic acid to zinc salt solution was 0.05:1; then the sodium sulfide solution was added dropwise, and the mixture was stirred for 90 min and then cooled to obtain zinc sulfide nanoparticle dispersion.

[0058] (2) Preparation of test paper: The adsorption layer is fully immersed in the zinc sulfide nanoparticle dispersion obtained in step (1), and then the immersed adsorption layer is taken out and dried to obtain cobalt ion detection test paper. This comparative example provides a different preparation method, using mercaptoacetic acid as a stabilizer, which is different from the polyvinylpyrrolidone used in this invention. Its final detection specificity is poor. Comparative example 1 cannot achieve specific adsorption of Cd element, and cannot achieve accurate and efficient detection of Cd element using LIBS.

[0059] Comparative Example 2

[0060] This comparative example provides a gold nanocomposite particle synthesized based on click chemistry as a labeling probe for a transverse chromatography test strip and a signal output probe for LIBS technology. It also incorporates immunological principles to achieve the detection of insulators. The preparation method is as follows: First, gold nanoparticles are prepared using conventional methods. Then, the nanoparticles are modified with Tz molecules and TCO-Ab, respectively. The modified nanoparticles are then subjected to a click reaction between TCO and Tz to obtain gold nanocomposite particles. These nanocomposite particles are used as the labeling probe and signal output probe for a transverse chromatography test strip, and further combined with immunological principles to detect Cd... 2+ The reaction proceeds, ultimately linking the LIBS signal of the gold nanocomposite particles aggregated at the T line of the test strip with Cd. 2+ To establish a quantitative model for Cd concentration, thereby achieving... 2+ The present invention provides a highly efficient and rapid detection method. While the comparative example combines a transverse chromatography strip with LIBS and uses gold nanocomposite particles as a probe, it can test for Cd using LIBS, but its cost is relatively high and the preparation process of the gold nanocomposite particles is relatively cumbersome. In contrast, the method provided by this invention, using ZnS nanoparticles as an enrichment probe, is simple to prepare, has lower cost, and is easy to promote.

[0061] Example 2

[0062] This embodiment uses the same method as Embodiment 1, the only difference being that the ZnSNPs-modified paper substrate is paired with Cd. 2+ The adsorption time for detection was adjusted to 15 minutes. Based on experimental analysis (e.g., ... Figure 6 As shown in the figure, enrichment saturation is reached in 15 minutes. The optimal adsorption and enrichment time of this invention is 15 minutes.

[0063] Example 3

[0064] This embodiment uses the same method as Embodiment 1, the only difference being that the ZnSNPs-modified paper substrate is paired with Cd. 2+ The pH of the enrichment solution should be adjusted to 6-8 (optimal). If the acidity is too strong, Cd... 2+ More active, which is not good for Cd 2+ Cd accumulates on the paper base, but if the alkalinity is too strong, it will... 2+ It easily forms Cd(OH)2 precipitate, which is also unfavorable for Cd. 2+ enrichment ( Figure 7 ).

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a paper-based chip for detecting cadmium ions by LIBS, characterized in that, The application relates to a paper-based chip for detecting cadmium ions by LIBS (Laser-induced breakdown spectroscopy). The paper-based chip comprises the following steps: 1) mixing and reacting a zinc salt solution and a sodium sulfide solution to obtain a ZnS nanoparticle solution; The zinc salt solution is a zinc nitrate solution with a concentration of 10-11 mM, and the concentration of the sodium sulfide solution is 12-13 mM; the volume ratio of the zinc nitrate solution to the sodium sulfide solution is 5-6:4-5; 2) mixing the ZnS nanoparticle solution, polyvinylpyrrolidone and hydrochloric acid to obtain a ZnSNPs modified solution; the ratio of the ZnS nanoparticle solution, the polyvinylpyrrolidone and the hydrochloric acid is 8-9 mL:0.4-0.5 g:0.08-0.1 mL; the concentration of the hydrochloric acid is 0.1-0.12 M; 2. The method of claim 1, wherein the paper-based chip for detecting cadmium ions by LIBS is prepared by the steps of: 3) mixing the ZnSNPs modified solution with filter paper pieces and oscillating, adding an alcohol solution, cleaning and drying at 37-38 DEG C.

3. The method for preparing a paper-based chip for LIBS detection of cadmium ions according to claim 1, characterized in that, In step 3), the oscillation time is 8-12 min, and the alcohol solution is an ethanol solution.

4. A paper-based chip for LIBS detection of cadmium ions, characterized by, In step 3), the cleaning is cleaning with deionized water for 2-3 times. The paper-based chip for detecting cadmium ions by LIBS is prepared by the preparation method of the paper-based chip for detecting cadmium ions by LIBS according to any one of claims 1-3.

5. The method for preparing the paper-based chip for detecting cadmium ions by LIBS according to any one of claims 1-3, the paper-based chip for detecting cadmium ions by LIBS prepared by the method or the paper-based chip for detecting cadmium ions by LIBS according to claim 4, characterized in that, Application in the specific adsorption detection of Cd 2+ in water body by LIBS.

6. Use according to claim 5, characterized in that, The quantitative relationship model used: Y = aX + b; in the formula, Y is the LIBS signal intensity at 226.56 nm, X is Cd 2+ concentration, a is 51.5±0.2, and b is 1869.6±0.2.

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