A method for detecting copper ion concentration based on hydrogel coating of PMPCF-MZI and fluorescence colorimetric dual sensing

Abstract

This invention discloses a method for detecting copper ion concentration based on a hydrogel-coated PMPCF-MZI sensor and a fluorescence colorimetric dual-sensor. The detection device consists of a broadband light source, a single-mode optical fiber, a polarization controller, a flow cell, a PMPCF-MZI sensor, and a spectrometer. In the fiber optic detection path, light emitted from the broadband light source passes through the polarization controller and is input to the hydrogel-coated PMPCF-MZI, transforming into interference peaks of specific wavelengths. These peaks are displayed on the spectrometer. The hydrogel's volume and refractive index change after adsorbing copper ions, manifesting as a shift in the interference spectrum on the spectrometer. By comparing the relationship between different copper ion concentrations and the interference spectrum shift, rapid, accurate, and trace detection of copper ions in the aquatic environment is achieved. In the fluorescence detection path, the fluorescent detection solution is mixed with the test solution and irradiated with an ultraviolet lamp, inducing a change in fluorescence intensity, achieving visual qualitative detection. This invention employs a dual-system collaborative design, combining advantages such as simple structure, low detection limit, fast response time, easy operation, and high visualization. It has significant practical value and promising application prospects for rapid copper ion detection in the future.

Description

Technical Field

[0001] This invention relates to the fields of fiber optic sensing technology and fluorescence sensing technology, and in particular to a method for detecting copper ion concentration based on a Mach-Zehnder interferometer (MZI) and fluorescence colorimetric dual sensing, using hydrogel-coated polarization-maintaining photonic crystal fiber (PMPCF). Background Technology

[0002] With the continuous expansion of modern industrial and agricultural production and the disorderly discharge of various heavy metal pollutants, heavy metal ion pollution in water, soil, and atmosphere is becoming increasingly serious, posing a core bottleneck to ecological restoration and public health security. These pollutants are not only non-degradable, bioaccumulative, and highly toxic, but they can also enter the human body through various pathways such as drinking water, crop accumulation, and atmospheric deposition. Long-term accumulation can induce serious diseases such as liver and kidney damage, immune dysfunction, and even gene mutations. Crucially, heavy metal ions exist in the natural environment primarily at trace levels, and changes in their form and concentration are difficult to detect through conventional sensory means. Once visible pollution symptoms appear, irreversible damage to the ecosystem and human health has often already occurred. Therefore, developing heavy metal ion trace detection technologies with high sensitivity, high selectivity, and rapid response capabilities is not only a core prerequisite for pollution source control and dynamic environmental quality monitoring, but also an urgent need to safeguard human health and ecological security.

[0003] Copper, as a typical heavy metal element, is associated with excessive copper ions (Cu). 2+ Cu is widely found in industrial wastewater, soil, and drinking water environments. 2+ It can enter the human body through the digestive tract, skin contact, and other routes, thereby causing a series of gastrointestinal irritation symptoms. At the same time, it can also cause cumulative damage to organs such as the liver and kidneys, and interfere with the normal function of the central nervous system.

[0004] Currently, mature methods for detecting copper ions include spectrophotometry, inductively coupled plasma mass spectrometry, atomic absorption spectrometry, and atomic fluorescence spectrometry. These methods have been well-developed and are mature enough for heavy metal detection. However, these methods require sophisticated and expensive instruments and involve complex sample pretreatment processes. Moreover, the equipment is primarily laboratory-grade, and its bulkiness, portability, and inability to be used for on-site testing significantly limit the widespread adoption of these technologies.

[0005] After years of development, fiber optic MZI sensing technology is now emerging as a new type of photochemical sensor. Compared with traditional electronic sensors, fiber optic sensors have advantages such as compact structure, light weight and low cost, resistance to electromagnetic interference and corrosion, easy multiplexing and remote sensing, and large transmission capacity, and are widely used in fields such as physical parameters, chemical and biological sensing.

[0006] Hydrogels are novel biomaterials with unique physical and chemical properties, possessing a three-dimensional network composed of hydrophilic polymer chains. Their excellent swelling properties, biocompatibility, and functionalization have led to extensive exploration and their application in removing heavy metals from water. This invention combines a three-dimensional network hydrogel with traditional fiber optic detection technology to achieve not only the specific detection of copper ions but also high sensitivity, strong specificity, and a low detection limit.

[0007] Fluorescent sensors offer advantages such as high sensitivity, high selectivity, ease of operation, strong visualization, low sample consumption, and easy functionalization, making them suitable for trace substance detection in various fields. This invention combines the targeted recognition characteristics of fluorescence colorimetry with the high-sensitivity optical response of hydrogel-coated MZI, enabling precise and interference-resistant detection of copper ions. It also features both visual screening and online monitoring capabilities, making it suitable for complex water sample analysis in various scenarios. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a copper ion concentration detection method based on a fiber optic Mach-Zehnder interferometer (PMPCF-MZI) with hydrogel-coated polarization-maintaining photonic crystal fiber and fluorescence colorimetric dual sensing. The detection capability of the fiber optic sensor is obtained by modifying the PMPCF-MZI with a three-dimensional network hydrogel that specifically binds to copper ions; the detection capability of the fluorescence sensor is obtained by formulating a fluorescent detection solution from a composite material that specifically binds to copper ions.

[0009] The fabrication steps of the aforementioned fiber optic sensor are as follows: Preparation of S1, PMPCF-MZI (5); S2. Preparation of a composite fluorescent probe (52) consisting of GSH-stabilized gold nanoclusters embedded in ZIF-8; S3, Preparation and modification of three-dimensional network hydrogels (53) that can specifically bind to copper ions;

[0010] In step S1, the PMPCF-MZI (5) is formed by splicing single-mode fiber 1 (51), PMPCF (54), and single-mode fiber 2 (55) in sequence.

[0011] Preferably, the length of the PMPCF is 3-4 cm.

[0012] The preparation of the composite fluorescent probe (52) in step S2 is obtained by assembling the prepared GSH-Au NCs with zinc nitrate and 2-methylimidazole under specific conditions. Specifically, GSH aqueous solution is mixed with HAuCl4 solution, stirred at room temperature, and then ultrapure water is added. The mixture is heated and stirred at 70°C for 24 hours to obtain GSH-Au NCs. Its aqueous solution is mixed with Zn(NO3)2·6H2O solution, pH is adjusted to 5.0, the precipitate is centrifuged and resuspended in methanol, and the suspension is added to the mixture of Zn(NO3)2·6H2O and 2-methylimidazole. The mixture is reacted at 37°C overnight, centrifuged and dried, and then redispersed in PBS buffer with a pH of 7.2-7.4 to obtain the target probe.

[0013] The preparation of the three-dimensional network hydrogel (53) that specifically binds to copper ions in step S3 is achieved by dispersing a composite fluorescent probe (52) in sodium alginate and crosslinking with calcium chloride. Specifically, the sodium alginate solution is thoroughly mixed with the composite fluorescent probe (52), and then the sodium alginate is crosslinked with calcium chloride. 2+ Cross-linking and curing occur under the action of the agent, resulting in a uniform three-dimensional network hydrogel of GSH-Au NCs@ZIF-8 composite (53).

[0014] Preferably, the sodium alginate solution has a mass-volume concentration of 2%, and the CaCl2 solution has a molar concentration of 300 mM.

[0015] Preferably, the volume ratio of the composite fluorescent probe (52) to the sodium alginate solution is 1:1.

[0016] The modification of the three-dimensional network hydrogel (53) that specifically binds to copper ions in step S3 is achieved by immersing the optical fiber in a mixture of sodium alginate and composite fluorescent probe (52) for coating, followed by cross-linking and curing with CaCl2 solution. Specifically, PMPCF-MZI (5) is first cleaned with a mixture of concentrated sulfuric acid and hydrogen peroxide (volume ratio 3:1), then rinsed with deionized water and anhydrous ethanol, and dried under a nitrogen atmosphere. After that, the dried PMPCF-MZI (5) is immersed in a mixture of composite fluorescent probe (52) and sodium alginate for coating. After coating, the optical fiber is immersed in CaCl2 solution and left to stand for 10 minutes to allow the sodium alginate to be in the CaCl2 solution. 2+ Cross-linking and curing occur under the action of [a process described in the original text], ultimately forming a stable hydrogel coating on the surface of the optical fiber. After removal, the fiber is dried in a drying oven at 50°C for 1 hour to form a film. Then, the hydrogel-modified optical fiber is rinsed sequentially with deionized water and anhydrous ethanol to remove excess molecules, and then dried under a nitrogen atmosphere.

[0017] The PMPCF-MZI sensor is connected to the copper ion detection platform. Specifically, the broadband light source (1) is connected to the left end of the polarization controller (3) through the single-mode fiber (2). The polarization controller (3) is connected to the PMPCF-MZI sensor (5). The PMPCF-MZI sensor (5) is fixed in the flow cell (4) and connected to the spectrometer (6) on the right end. The broadband light source (1) is used to provide the light source, the polarization controller (3) is used to obtain a larger fringe contrast, the flow cell (4) is used to add the solution of the ion to be tested, and the spectrometer (6) is used to monitor and record the spectral changes. When the hydrogel (53) modified on the surface of PMPCF-MZI (5) adsorbs copper ions, the volume and refractive index change, which is reflected in the drift of the interference spectrum on the spectrometer (6). By comparing the relationship between different copper ion concentrations and the drift of the interference spectrum, the concentration of copper ions in the water environment can be detected.

[0018] Preferably, the wavelength of the broadband light source (1) is 1500-1620nm.

[0019] The working principle of the copper ion concentration detection sensor based on hydrogel-coated PMPCF-MZI prepared in this invention is as follows: When light emitted from the broadband light source (1) is injected from the single-mode fiber 1 (51) into the first collapsed part, part of the light will be coupled into the cladding of the PMPCF (54), which will excite the higher-order cladding mode of the PMPCF (54). The remaining light still propagates along the core of the PMPCF (54). At the second collapsed part, the stimulated higher-order cladding mode of the PMPCF (54) is recoupled into the core of the single-mode fiber 2 (55), thereby interfering with the core mode. The phase difference between the core mode and the stimulated higher-order cladding mode will change with the change of the external environment, which can be expressed as: In the formula The effective refractive index difference between the core and the m-th cladding mode. The wavelength of the input light. Given the length of the PCF, the output intensity of PMPCF-MZI(5) is: In the formula and These represent the light intensities propagating along the fiber core and cladding, respectively. Three-dimensional network hydrogels exhibit swelling properties, especially when Cu is present in the test solution. 2+The hydrogel (53) modified on the surface of PMPCF-MZI (5) expands after specifically adsorbing copper ions, resulting in changes in its volume and effective refractive index. As shown in equations (1) and (2), when the external refractive index changes, the interference spectrum of PMPCF-MZI (5) will also change accordingly. By studying different Cu... 2+ The relationship between concentration and interference spectrum drift can be used to indirectly detect Cu. 2+ .

[0020] The fabrication steps of the fluorescence sensor are as follows:

[0021] The composite fluorescent probe (52) was added to a pH-stable PBS buffer and dispersed thoroughly to obtain a uniform fluorescent detection solution (56). Then, an equal volume of the detection solution (56) was mixed with copper ion solutions of different concentration gradients, shaken and incubated at room temperature for 5 minutes. The samples were then irradiated with a UV lamp and fluorescence images of each sample were collected. When the fluorescent detection solution (56) containing GSH-Au NCs@ZIF-8 reacted fully with copper ions, it was reflected as a change in fluorescence intensity under a UV lamp. Finally, the presence or absence of brightness or differences in intensity of the fluorescence images were observed visually to achieve qualitative detection of copper ions.

[0022] The working principle of the copper ion concentration detection sensor based on fluorescence colorimetry prepared in this invention is as follows: GSH-Au NCs with aggregation-induced emission (AIE) effect are encapsulated in ZIF-8 to prepare a GSH-Au NCs@ZIF-8 composite material detection probe. The confinement effect of ZIF-8 can enhance the fluorescence performance and stability of GSH-Au NCs. During detection, the composite material enriches Cu based on the adsorption and complexation of ZIF-8. 2+ And Cu 2+ The strong binding force with imidazolium pyridine nitrogen disrupts the ZIF-8 structure, weakens the AIE effect, and triggers fluorescence quenching, thereby enabling the detection of copper ions.

[0023] In summary, this invention provides a method for specifically detecting Cu. 2+ A concentration-based PMPCF-MZI sensor and a fluorescence sensor, this fiber optic sensor is based on a three-dimensional network hydrogel for Cu 2+ The specific adsorption of Cu alters the effective refractive index, causing a shift in the interference spectrum of PMPCF-MZI, thus realizing Cu 2+ The detection method features simple structure, low detection limit, and fast response time; this fluorescence sensor is based on GSH-Au NCs@ZIF-8 composite material and Cu. 2+ The specific effect of Cu leads to changes in fluorescence intensity, thus realizing Cu 2+ The detection method has the advantages of being easy to operate, highly visualized, and stable.

[0024] The beneficial effects of this invention are: this invention combines the specific Cu adsorption of a three-dimensional network hydrogel. 2+ It combines the high sensitivity of PMPCF-MZI with the specific fluorescence response characteristics of GSH-Au NCs@ZIF-8 composite material, providing two efficient methods for detecting Cu. 2+ The scheme. Among them, the PMPCF-MZI sensor for Cu 2+ The detection limit is as low as 13.9 pM, the response time is 6 min, and the detection range is 10. -11 M-10 -4 M; The fluorescence sensor achieves detection of Cu using a specific fluorescent detection solution. 2+ This visual inspection method boasts high specificity, ease of operation, and good stability, making it adaptable to various inspection scenarios. This dual-system sensing inspection mode can be applied to Cu in real-world environments. 2+ With its rapid and accurate response, it enhances the reliability and applicability of testing, combining innovation and practical value, and has broad application prospects. Attached Figure Description

[0025] Figure 1 A schematic diagram of a copper ion concentration detection sensor based on hydrogel-coated PMPCF-MZI.

[0026] Figure 2 A schematic diagram of a copper ion concentration detection sensor based on fluorescence colorimetry.

[0027] Figure 3 Interference spectra of the PMPCF-MZI sensor in copper ion solutions of different concentrations.

[0028] Figure 4 PMPCF-MZI sensor interference peak intensity variation fitting curve.

[0029] Figure 5 PMPCF-MZI sensor time response diagram.

[0030] Figure 6 PMPCF-MZI sensor specific response diagram. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to specific embodiments:

[0032] Example 1: Preparation of PMPCF-MZI (5).

[0033] In this embodiment, see Figure 1PMPCF-MZI (5) was prepared by fusion collapse method. The specific method is as follows: First, the coating layers of single-mode fiber 1 (51), PMPCF (54) and single-mode fiber 2 (55) were stripped using a commercial fusion splicer, and then cleaned with deionized water and anhydrous ethanol in sequence. The end face to be fused was cut flat with a fiber cleaver, and then the fusion splicer was used to perform discharge fusion in sequence. The length of PMPCF is preferably 3cm to obtain PMPCF-MZI (5) structure.

[0034] Example 2: Preparation of composite fluorescent probe (52).

[0035] In this embodiment, the preparation of the composite fluorescent probe (52) involves the following steps: a) Mix 12.0 mL of GSH aqueous solution (10 mM) with 0.8 mL of HAuCl4 solution (100 mM), stir at room temperature for 5 min, add 27.2 mL of ultrapure water, heat and stir at 70 °C for 24 h, collect the product GSH-Au NCs, and store at 4 °C for later use. b) Mix 6.0 mL of GSH-Au NCs aqueous solution with 480 μL of Zn(NO3)2·6H2O (240 mM) solution, adjust the pH to 5.0, centrifuge to collect the precipitate and redisperse it in 2.0 mL of methanol; add the suspension to a mixture of 7.5 mL of Zn(NO3)2·6H2O (25 mM) and 7.5 mL of 2-methylimidazole (25 mM), react at 37°C overnight, centrifuge and dry, and redisperse in PBS buffer with a pH of 7.2-7.4 to obtain the target probe.

[0036] Example 3: Preparation and modification of a three-dimensional network hydrogel (53) that can specifically bind to copper ions.

[0037] In this embodiment, the preparation and modification of the three-dimensional network hydrogel (53) that can specifically bind to copper ions are carried out through the following steps: a) Mix an equal volume of the composite fluorescent probe (52) with a 2% sodium alginate solution to obtain a mixed solution; b) Clean the PMPCF-MZI (5) sequentially with deionized water and anhydrous ethanol, then immerse the optical fiber in a mixed solution of concentrated sulfuric acid and hydrogen peroxide in a volume ratio of 3:1 for 30 min to remove all impurities from the surface of the optical fiber. Finally, clean the optical fiber with deionized water and anhydrous ethanol and dry it under a nitrogen atmosphere. c) Immerse the thoroughly cleaned optical fiber in a mixture containing GSH-Au NCs@ZIF-8 probe and sodium alginate for coating. After coating, immerse the optical fiber in a CaCl2 solution (300mM) and let it stand for 10 minutes to allow the sodium alginate to settle. 2+Cross-linking and curing occur under the action of the agent, eventually forming a stable hydrogel coating on the surface of the optical fiber. After removal, the fiber is dried in a drying oven at 50°C for 1 hour, eventually forming a stable hydrogel coating on the surface of the optical fiber (53). Then, the optical fiber is rinsed with deionized water and anhydrous ethanol to remove excess molecules and dried under a nitrogen atmosphere.

[0038] Example 4: Construction of the detection platform.

[0039] In this embodiment, see Figure 1 The detection platform is a single-mode optical fiber (2) connecting a broadband light source (1), a polarization controller (3), a PMPCF-MZI sensor (5) placed in a flow cell (4), and a spectrometer (6). The broadband light source (1) has a wavelength range of 1500-1620nm and is used to provide light. The polarization controller (3) is used to obtain a greater stripe contrast. The flow cell (4) is used to add the solution of the ions to be tested. The spectrometer (6) is used to monitor and record the spectral changes. When the hydrogel (53) modified on the surface of PMPCF-MZI (5) adsorbs copper ions, its volume and refractive index change, which is reflected in the drift of the interference spectrum on the spectrometer (6). By comparing the relationship between different copper ion concentrations and the drift of the interference spectrum, the concentration of copper ions in the water environment can be detected.

[0040] Example 5: Cu 2+ Concentration, time response, and specificity detection.

[0041] Cu 2+ Concentration, specificity, and time response were measured. All solutions were adjusted to pH 7.2-7.4 using PBS buffer. The specific steps were as follows: (a)Cu 2+ Concentration detection: The PMPCF-MZI sensor (5) modified with three-dimensional network hydrogel was rinsed multiple times with deionized water and anhydrous ethanol and placed in a flow cell (4). Cu at different concentrations was prepared using PBS buffer solution with a pH of 7.4. 2+ The solutions were prepared at concentrations of 10 pM, 100 pM, 1 nM, 10 nM, 100 nM, 1 uM, and 10 uM. PBS buffer was added to the flow cell (4), and the initial spectrum was recorded using a spectrometer (6). The solution in the flow cell (4) was rinsed with deionized water, and then Cu was added. 2+ The solution was added to the flow cell (4) and allowed to stand for 10 minutes. Then, the interference spectrum was recorded using a spectrometer (6). The optical fiber was then removed and re-coated using the same steps. Different concentrations of Cu were added sequentially. 2+ The solution was prepared by repeating the above steps to obtain Cu solutions of different concentrations. 2+ The interference spectrum of the solution was obtained, and the fitted curve was plotted, as follows: Figure 3 As shown. (b) Time response detection: PBS buffer was added to the flow cell (4), and the initial spectrum was recorded using a spectrometer (6). Subsequently, 10 nM Cu was added to the flow cell (4). 2+ The solution was tested and the spectral response was recorded for 60 minutes using a spectrometer (6). Interference spectra were recorded every minute for the first 10 minutes and every 10 minutes for the next 50 minutes. The time response of the PMPCF-MZI sensor (5) was evaluated by the interference spectral drift. Figure 4 As shown. (c) Specificity detection: 1 nM Cu was prepared using PBS buffer solution with a pH of 7.2-7.4. 2+ Ca 2+ Fe 3+ Hg 2+ K + Mg 2+ Na + and Pb 2+ Test solution. First, the interference spectrum of the PMPCF-MZI sensor (5) in PBS buffer was detected. The optical fiber was rinsed multiple times with deionized water and anhydrous ethanol. The test solution was added to the flow cell and allowed to stand for 10 min. Then, the interference spectrum was recorded using a spectrometer (6). After removing the optical fiber, it was recoated using the same steps. Different test solutions were added sequentially, and the above steps were repeated to evaluate the specificity of the PMPCF-MZI sensor (5) for different ions, such as Figure 5 As shown.

[0042] Example 6: Preparation of a fluorescent detection solution (56) that can specifically bind to copper ions.

[0043] In this embodiment, the preparation and modification of the fluorescent detection solution (56) that can specifically bind to copper ions are as follows: the prepared composite fluorescent probe (52) is added to a PBS buffer with a pH of 7.2-7.4 and fully dispersed to obtain a uniform fluorescent detection solution.

[0044] Example 7: Cu 2+ Fluorescence detection.

[0045] Cu 2+For fluorescence detection, all solutions were adjusted to pH 7.2-7.4 using PBS buffer. The specific steps were as follows: equal volumes of fluorescence detection solution were mixed with copper ion solutions of different concentration gradients, shaken thoroughly, and incubated at room temperature for 5 minutes. The samples were then irradiated with a UV lamp, and fluorescence images of each sample were acquired. When the fluorescence detection solution (56) containing GSH-Au NCs@ZIF-8 reacted fully with copper ions, it was observed as a change in fluorescence intensity under a UV lamp. Qualitative detection of copper ions was achieved by visually observing the presence or absence of brightness or differences in intensity of the fluorescence images. Figure 2 As shown.

[0046] The embodiments described above provide a detailed explanation of the technical solution of the present invention, but the scope of protection of this disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the protection scope of the present invention.

Claims

1.A method for detecting copper ion concentration based on hydrogel coated PMPCF-MZI and fluorescent colorimetric dual sensing, the detection device is composed of a broadband light source (1), a single-mode optical fiber (2), a polarization controller (3), a flow cell (4), a PMPCF-MZI sensor (5), and a spectrum analyzer (6). characterized in that The broadband light source (1) is connected to the left end of the polarization controller (3) through the single-mode optical fiber (2), the polarization controller (3) is connected to the PMPCF-MZI sensor (5), and the right end of the sensor is connected to the spectrum analyzer (6). The PMPCF-MZI sensor (5) is composed of a single-mode optical fiber (51), a PMPCF (54), and a single-mode optical fiber (55) in sequence; the PMPCF has a length of 3 cm, is washed with deionized water and anhydrous ethanol for three times, is fixed in the flow cell (4), and is coated with a three-dimensional network hydrogel (53) prepared from a composite fluorescent probe (52) composed of GSH-stabilized gold nanoclusters embedded in ZIF-8, sodium alginate, and CaCl2, and is baked at 50℃ for 60 minutes to form a film. The broadband light source (1) has a working wavelength range of 1500 nm-1620 nm. The method for detecting copper ion concentration based on hydrogel coated PMPCF-MZI and fluorescent colorimetric dual sensing has the following detection steps: first, fix the PMPCF-MZI sensor (5) in the flow cell (4); then, add a copper ion solution to be detected into the flow cell (4); when the hydrogel (53) on the surface of the PMPCF-MZI (5) adsorbs copper ions, the volume and refractive index of the hydrogel (53) change, which is manifested as a drift of the interference spectrum on the spectrum analyzer (6); by comparing the relationship between different copper ion concentrations and the drift of the interference spectrum, the concentration of copper ions in the water environment is quantitatively detected; the composite fluorescent probe (52) is added to a PBS buffer solution with a stable pH value to prepare a uniform fluorescent detection solution (56); then, an equal volume of the detection solution (56) is mixed with copper ion solutions with different concentration gradients, and after being shaken and mixed, the mixture is incubated at room temperature for 5 minutes; the sample is irradiated with an ultraviolet lamp, and the fluorescence images of the samples are collected; when the fluorescent detection solution (56) containing GSH-Au NCs@ZIF-8 fully reacts with copper ions, the fluorescence intensity changes under the ultraviolet lamp; finally, by visually observing whether there is a difference in brightness or intensity of the fluorescence images, the qualitative detection of copper ions is realized.

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