Cd2+ and temperature dual-parameter optical fiber chemical sensing system in water environment

Abstract

A kind of water environment cadmium ion and temperature double parameter optical fiber chemical sensing system relates to water body environment detection field.In the above system, spontaneous emission light source is near infrared light source;The surface of optical fiber sensing unit is coated with magnetic MOF-cadmium ion imprinted polymer;The light signal generated by spontaneous emission light source enters optical fiber sensing unit, optical spectrometer collects the transmission spectrum signal of optical fiber sensing unit, and the collected spectrum data are output to photoelectric detection module;Photoelectric detection module converts light signal into electrical signal and transmits to demodulation module;Demodulation module gives the cadmium ion concentration and temperature according to input signal using machine learning algorithm.The present application has higher specific recognition ability to cadmium ion, and can effectively separate the coupling influence of cadmium ion concentration and temperature on sensing signal.

Description

Technical Field

[0001] This invention relates to the field of water environment monitoring. Background Technology

[0002] Cadmium, a typical highly toxic heavy metal, usually exists in water as divalent cadmium ions. Unlike most organic pollutants, cadmium ions are difficult to degrade naturally after entering the environment and can accumulate in the human body through the food chain. Studies have shown that after entering the human body, cadmium readily binds to functional groups such as sulfhydryl, hydroxyl, and amino groups in proteins, gradually accumulating in tissues such as the kidneys, liver, and bones, leading to diseases such as kidney damage, osteoporosis, and abnormal bone metabolism. Due to cadmium's long biological half-life in the human body, long-term exposure to low concentrations can also cause serious harm.

[0003] Currently, methods for detecting cadmium ions mainly include atomic absorption spectrometry, atomic emission spectrometry, atomic fluorescence spectrometry, and inductively coupled plasma mass spectrometry. While these methods offer high detection accuracy and low detection limits, they generally suffer from drawbacks such as expensive and bulky instruments, long detection cycles, complex operating procedures, and cumbersome sample pretreatment, making them unsuitable for rapid detection of cadmium ions in complex aquatic environments. This is particularly true in environments such as groundwater surrounding mining areas, tailings leachate, and water bodies affected by industrial emissions, where the complex composition and diverse coexisting ions can easily interfere with the stability of the detection signal, thus placing higher demands on the environmental adaptability, specificity, and stability of the detection technology. Furthermore, sudden water pollution incidents are often characterized by their sudden occurrence, rapid spread, and urgent response, further requiring detection methods with rapid response, trace identification, and online continuous monitoring capabilities.

[0004] Fiber optic sensing technology offers a novel approach for the real-time and rapid detection of cadmium ions due to its advantages such as simple structure, high sensitivity, and fast response speed. However, existing fiber optic sensing technologies have certain drawbacks in cadmium ion detection. For example, while attaching sensitive materials to the surface of sensing fibers provides good cadmium ion response characteristics, it cannot accurately identify interference from other coexisting ions in the environment, leading to significant errors in practical environmental detection (e.g., patent publication number CN115420709B). Alternatively, the regenerability and stability of sensitive materials are poor, making effective integration with fiber optic sensors difficult (e.g., patent publication number CN113694901B). Furthermore, fiber optic sensors detect the measured parameter by tracking only a single signal feature, making it difficult to separate the coupling effects of multiple environmental parameters on the sensor, and thus susceptible to cross-interference from environmental factors such as temperature during actual measurements. Therefore, it is necessary to develop sensitive materials with higher specificity and more advanced sensor demodulation techniques. Summary of the Invention

[0005] The purpose of this invention is to solve or alleviate the above-mentioned problems of the prior art and to provide a fiber optic chemical sensing system for cadmium ions and temperature in an aquatic environment.

[0006] The present invention provides a dual-parameter fiber optic chemical sensing system for cadmium ions and temperature in an aquatic environment, comprising a spontaneous emission light source, a fiber optic sensing unit, a spectrometer, a photoelectric detection module, and a demodulation module. The spontaneous emission light source is a near-infrared light source. The surface of the fiber optic sensing unit is coated with a magnetic MOF-cadmium ion imprinted polymer. The light signal generated by the spontaneous emission light source enters the fiber optic sensing unit. The spectrometer acquires the transmission spectrum signal of the fiber optic sensing unit and outputs the acquired spectral data to the photoelectric detection module. The photoelectric detection module converts the light signal into an electrical signal and transmits the electrical signal to the demodulation module. The demodulation module uses a machine learning algorithm to determine the cadmium ion concentration and temperature based on the input signal.

[0007] Optionally, the machine learning algorithm is a residual neural network, which sequentially includes an initial normalization layer, six convolutional layers, and six fully connected layers, with a residual block set between two adjacent convolutional layers.

[0008] Optionally, an identity shortcut connection is used to fuse the input features of the residual block with the residual mapping.

[0009] Optionally, the magnetic MOF-cadmium ion-imprinted polymer is prepared by the following method: Step A1: Prepare Fe3O4 magnetic nanoparticles; Step A2: Prepare Fe3O4@Cd-MOF composite using the Fe3O4 magnetic nanoparticles; Step A3: Disperse the Fe3O4@Cd-MOF composite in tetrahydrofuran solution and add 1,5-naphthalene diisocyanate to form a pre-assembled system; Step A4: Add a crosslinking agent and an initiator to the pre-assembled system to form a Fe3O4@Cd-MOF-doped polyurea composite material; Step A5: Treat the composite material to obtain the magnetic MOF-cadmium ion-imprinted polymer.

[0010] Optionally, the Fe3O4 magnetic nanoparticles in the magnetic MOF-cadmium ion-imprinted polymer have a mass fraction of 1% to 10%.

[0011] Optionally, the fiber optic sensing unit is prepared by the following method: Step B1: Pre-treating the fiber optic sensing unit etched with a long-period fiber grating to hydroxylate the surface of the fiber optic sensing unit; Step B2: Treating the pre-treated fiber optic sensing unit with an ethanol solution containing a silane coupling agent to obtain a silanized modified fiber optic sensing unit; Step B3: Grinding the magnetic MOF-cadmium ion-imprinted polymer into powder and dispersing it in an ethanol / water mixed solvent to form a suspension; Step B4: Immersing the silanized modified fiber optic sensing unit in the suspension to deposit the magnetic MOF-cadmium ion-imprinted polymer on the surface of the fiber optic sensing unit to obtain a fiber optic sensing unit coated with a sensitive material; Step B5: Curing the sensitive material, washing, and drying the fiber optic sensing unit coated with the sensitive material to obtain a fiber optic sensing unit with a magnetic MOF-cadmium ion-imprinted polymer fixed on its surface.

[0012] Optionally, the silane coupling agent is 3-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, or 3-glycidyl etheroxypropyltrimethoxysilane.

[0013] This invention uses MOF-based cadmium ion imprinted polymer as the sensitive material of the fiber optic sensing unit. The high specific surface area and ordered pore structure of the material provide more ion imprinting recognition sites, making the fiber optic sensing unit extremely sensitive to changes in cadmium ion concentration. At the same time, the designability of MOF (such as material selection and pore parameters) significantly enhances the specific recognition ability of cadmium ions.

[0014] Based on the above advantages, the MOF-cadmium ion imprinted polymer is combined with an optical fiber sensor, which makes full use of the high sensitivity of the optical fiber sensor to changes in surface refractive index. This makes the detection sensitivity, detection limit and response speed of cadmium ions of the present invention significantly better than traditional cadmium ion detection methods.

[0015] By introducing a one-dimensional residual neural network as a demodulation method, and constructing skip connections to enable the network to learn residuals rather than complete mappings, the residual neural network can directly extract feature information from complex environmental spectral data. This effectively separates the coupling effect of cadmium ion concentration and temperature on the sensing signal, avoiding the concentration measurement error caused by temperature drift in traditional methods, thereby significantly improving the measurement accuracy and robustness of the sensor in variable temperature environments. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a dual-parameter fiber optic chemical sensing system for cadmium ions and temperature in an aquatic environment, according to an embodiment of this application.

[0017] Figure 2 These are transmission spectra of water under different cadmium ion concentrations in embodiments of the present invention;

[0018] Figure 3 This is a sensitivity fitting graph of cadmium ion concentration in an embodiment of the present invention;

[0019] Figure 4 This is a graph showing the selective test results for different ions in an embodiment of the present invention;

[0020] Figure 5 This is a graph showing the repeatability test results for different ions in an embodiment of the present invention;

[0021] Figure 6 This is a graph showing the stability test results of different ions in an embodiment of the present invention;

[0022] Figure 7 This is a fitting graph of cadmium ion concentration sensitivity under different temperature conditions in an embodiment of the present invention;

[0023] Figure 8 This is a graph showing the prediction results of cadmium ion concentration by the demodulation module in an embodiment of the present invention;

[0024] Figure 9 This is a graph showing the prediction results of the demodulation module for the dual parameters of cadmium ion concentration and temperature in an embodiment of the present invention. Detailed Implementation

[0025] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0026] As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context indicates otherwise. It should be further understood that the terms “comprising,” “including,” indicate the presence of the stated feature, operation, element, component, item, kind, and / or group, but do not preclude the presence, occurrence, or addition of one or more other features, operations, elements, components, items, kinds, and / or groups. The terms “or” and “and / or” as used herein are interpreted as inclusive, or mean any one or any combination thereof. Thus, “A, B, or C” or “A, B, and / or C” means “any one of: A; B; C; A and B; A and C; B and C; A, B, and C.” Exceptions to this definition occur only when combinations of elements, functions, or operations are inherently mutually exclusive in some manner.

[0027] To address the above-mentioned problems in the prior art, this invention provides a dual-parameter fiber optic chemical sensing system for cadmium ions and temperature in an aquatic environment, which can achieve accurate measurement of cadmium ion concentration and water temperature in the aquatic environment.

[0028] Figure 1 This is a schematic diagram of a dual-parameter fiber optic chemical sensing system for cadmium ions and temperature in an aquatic environment, according to an embodiment of this application. Figure 1 As shown, the system includes a spontaneous emission light source 1, an optical fiber sensing unit 2, a spectrometer 3, a photodetector 4, and a demodulation module 5.

[0029] The spontaneous emission source 1 is a near-infrared source with a wavelength range of 1520~1620nm. It is used to excite the coupling between the forward-propagating fiber core mode and the forward-propagating cladding mode in the fiber optic sensing unit 2 to form a transmission spectral signal with obvious interference valley characteristics, so as to realize dual-parameter sensing of cadmium ion concentration and temperature in the water environment.

[0030] The input end of the fiber optic sensing unit 2 is connected to the output end of the spontaneous emission light source 1. The surface of the fiber optic sensing unit 2 is coated with a magnetic MOF-cadmium ion imprinted polymer, wherein the mass fraction of Fe3O4 magnetic nanoparticles in the magnetic MOF-cadmium ion imprinted polymer is 1%~10%. This polymer, as a specific sensitive material for cadmium ions, is used to convert changes in the concentration of cadmium ions in the surrounding environment into changes in transmission spectrum signals, thereby achieving specific identification of cadmium ions in the water environment and avoiding interference from other coexisting ions in the water.

[0031] The spectrometer 3 is connected to the output end of the fiber optic sensing unit 2 to collect the transmission spectral signal emitted from the fiber optic sensing unit 2 and output the collected optical signal to the photoelectric detection module 4.

[0032] The photoelectric detection module 4 converts the optical signal from the spectrometer 3 into an electrical signal and transmits the electrical signal to the demodulation module 5.

[0033] The demodulation module 5 is preferably implemented using a computer program. When implemented using a computer program, the demodulation module 5 runs on the computer and is used to integrate and process the received electrical signals. It also uses machine learning algorithms to predict the cadmium ion concentration, temperature, and characteristic wavelength values ​​in the aquatic environment, thereby separating the measurement results of the two variables: cadmium ion concentration and temperature. The measurement results can also be output and displayed via the computer.

[0034] Specifically, the aforementioned machine learning algorithm is a residual neural network model, which sequentially includes an initial normalization layer, six convolutional layers, and six fully connected layers. A residual block is set between two adjacent convolutional layers. The residual block extracts features from the output of the previous convolutional layer. The features extracted by the residual block are fused with the residual mapping of the residual block using an identity shortcut connection, and used as the input of the next convolutional layer.

[0035] The basic structure of a residual neural network is as follows:

[0036]

[0037] Where x is the input of the residual block, y is the output of the residual block, and F(x,{W i}) represents the residual mapping to be learned, and +x represents the identity mapping;

[0038] Residual mapping F(x,{W i The expression for} is:

[0039]

[0040] in, and This is the weight matrix. and The bias term is ReLU(z) = max(0, z), which is the activation function.

[0041] The training process of the residual neural network is as follows: the transmission spectrum data corresponding to different cadmium ion concentrations at different temperatures are used as input, and the cadmium ion concentration and ambient temperature in the environment are used as output. After randomly shuffling the collected transmission spectrum data, 70%~85% are selected as the training set, and the rest are used as the test set. The training continues until the model converges.

[0042] The demodulation module 5's dual-parameter prediction results for cadmium ion concentration and temperature were obtained through the coefficient of determination (R²). 2 The coefficient of determination (COD) and mean squared error (MSE) are used for evaluation, and the comparison between the predicted values ​​and the true values ​​is displayed. The expressions for COD and MSE are as follows:

[0043]

[0044]

[0045] In the formula For the first The actual value of each sample For residual neural networks to the first The predicted value for each sample, This represents the mean of the actual values. Indicates the number of samples.

[0046] The preparation method of the above-mentioned magnetic MOF-cadmium ion imprinted polymer includes the following steps A1 to A5.

[0047] Step A1: Prepare Fe3O4 magnetic nanoparticles.

[0048] 2.7g and 1.0g Dissolve in 100 mL of deionized water, heat to 80 °C under nitrogen protection, then add 10 mL of 25% ammonia water, stir and react for 30 minutes, and then perform magnetic separation and washing to obtain Fe3O4 nanoparticles. Dry the Fe3O4 nanoparticles in a vacuum environment for later use.

[0049] Step A2: Prepare Fe3O4@Cd-MOF composites using Fe3O4 magnetic nanoparticles.

[0050] Dissolve 6-12 mmol (preferably 9 mmol) of H3L ligand in 4-5 mL (preferably 4.5 mL) of 2.5 mol / L sodium hydroxide aqueous solution, add 0.05-0.2 g (preferably 0.1 g) of Fe3O4 nanoparticles prepared in step A1, and ultrasonically disperse for 30 minutes. Then, add 7-13 mmol (preferably 10 mmol) of [unspecified ingredient] under rapid stirring. Continue stirring for 10-20 seconds (preferably 15 seconds) to obtain a white gel containing Fe3O4. Next, heat the obtained gel at 80°C to dry to constant weight, and then wash it three times each with water and ethanol to obtain the Fe3O4@Cd-MOF complex.

[0051] Step A3: Disperse the Fe3O4@Cd-MOF complex in a tetrahydrofuran solution and add 1,5-naphthalene diisocyanate to form a pre-assembled system.

[0052] The Fe3O4@Cd-MOF complex was dispersed in 20-30 mL (preferably 25 mL) of tetrahydrofuran solution, and 15-18 mmol (preferably 16.5 mmol) of 1,5-diisocyanate naphthalene was added. The mixture was reacted at 30-40 °C (preferably 35 °C) for 3-4 hours (preferably 3.5 hours) to form a pre-assembled system.

[0053] Step A4: Add crosslinking agent and initiator to the pre-assembled system to form Fe3O4@Cd-MOF doped polyurea composite material.

[0054] Crosslinking agent N,N'-methylenebisacrylamide and initiator azobisisobutyronitrile (AIBN) were added to the pre-assembled system. The mixture was heated to 60–80 °C (preferably 70 °C) under nitrogen protection and stirred for 12–24 hours (preferably 18 hours) to form a Fe3O4@Cd-MOF-doped polyurea composite material. The Fe3O4@Cd-MOF-doped polyurea composite material was cooled to room temperature, filtered, and washed three times with ethanol.

[0055] Step A5: The composite material is processed to obtain a magnetic MOF-cadmium ion imprinted polymer.

[0056] The composite material obtained in step A4 was immersed in 20 mL of a NaH2PO4 foaming agent solution of 2.0~3.5 mol / L (preferably 2.8 mol / L) for 10~20 minutes (preferably 15 minutes), then removed and air-dried at room temperature. It was then heated with a microwave at a power of 250~300W (preferably 280 W) for 2~4 minutes (preferably 3 minutes), washed three times with water and ethanol respectively, and dried. Then, 25 mL of dilute hydrochloric acid of 1.5~2.5 mol / L (preferably 2.0 mol / L) was added to the composite material at 25°C, and the mixture was stirred for 40~60 minutes (preferably 50 minutes) to remove cadmium ions. After washing three times again with water and ethanol respectively, the mixture was dried at 80°C to constant weight to obtain the magnetic MOF-cadmium ion imprinted polymer. The mass fraction of Fe3O4 magnetic nanoparticles in the polymer was determined to be approximately 5.2%.

[0057] The method for fabricating an optical fiber sensing unit (i.e., sensing optical fiber) includes the following steps B1 to B5.

[0058] Step B1: Pre-process the fiber optic sensing unit with long-period fiber gratings to hydroxylate the surface of the fiber optic sensing unit.

[0059] The fiber optic sensing unit, engraved with a long-period fiber grating, is sequentially ultrasonically cleaned in acetone, ethanol, and deionized water for 10–15 minutes each (preferably 12 minutes) to remove grease and impurities from the fiber surface. The cleaned fiber optic sensing unit is then immersed in a 1.0–2.0 mol / L (preferably 1.5 mol / L) NaOH solution for 30–60 minutes (preferably 45 minutes) to hydroxylate the fiber surface. After removal, the fiber optic sensing unit is rinsed with deionized water until neutral and then dried with nitrogen gas for later use.

[0060] Step B2: The pretreated fiber optic sensing unit is treated with an ethanol solution containing a silane coupling agent to obtain a silanized fiber optic sensing unit.

[0061] The pretreated fiber optic sensing unit is immersed in an ethanol solution containing 5%–10% (preferably 8%) 3-aminopropyltriethoxysilane (ethanol to deionized water volume ratio of 8:1) and reacted at room temperature for 1–2 hours (preferably 1.5 hours) to graft amino functional groups onto the fiber surface, thus completing the silanization modification of the fiber optic sensing unit. After the reaction, the fiber optic sensing unit is removed, washed with ethanol to remove unreacted silane coupling agent, and then dried in a 60°C oven for 1.5 hours.

[0062] Step B3: Grind the magnetic MOF-cadmium ion-imprinted polymer into powder and disperse it in an ethanol / water mixed solvent to form a suspension.

[0063] The cadmium ion-imprinted polymer of the magnetic MOF obtained in step A5 is ground into a fine powder and dispersed in an ethanol / water mixed solvent at a mass-volume ratio of 2-5 mg / mL (preferably 3.5 mg / mL), wherein the volume ratio of ethanol to water is 1:3-1:5 (preferably 1:4). The mixture is ultrasonically dispersed in the mixed solvent for 20-30 minutes (preferably 25 minutes) to form a uniform magnetic imprinted polymer suspension.

[0064] Step B4: Immerse the silanized fiber optic sensing unit in a suspension to deposit the magnetic MOF-cadmium ion-imprinted polymer on the surface of the fiber optic sensing unit, thus obtaining the fiber optic sensing unit coated with the sensitive material.

[0065] The silanized modified fiber optic sensing unit obtained in step B2 is immersed in the suspension obtained in step B3 for 20-30 minutes (preferably 25 minutes), and an external magnetic field is applied next to the fiber optic sensing unit to promote the uniform deposition of magnetic sensitive material (magnetic MOF-cadmium ion imprinted polymerization) on the surface of the fiber optic sensing unit.

[0066] Step B5: After coating the fiber optic sensing unit with the sensitive material, the sensitive material is cured, washed, and dried to obtain a fiber optic sensing unit with a magnetic MOF-cadmium ion imprinted polymer fixed on its surface.

[0067] The fiber optic sensing unit obtained in step B4 is placed in a vacuum drying oven at 60-75°C (preferably 68°C) for 2-4 hours (preferably 3 hours) to cure it, allowing the magnetic MOF-cadmium ion-imprinted polymer to be firmly fixed to the fiber surface through amino bonds. The cured fiber optic sensing unit is then washed with deionized water to remove any loosely attached polymer particles, and then air-dried at room temperature to obtain the fiber optic sensing unit with the magnetic MOF-cadmium ion-imprinted polymer fixed on its surface.

[0068] In this embodiment of the application, the MOF-cadmium ion-imprinted polymer is fixed on the surface of the optical fiber sensing unit 2 in a functionalized manner, thereby stabilizing the surface structure of the optical fiber sensing unit 2.

[0069] The performance of the dual-parameter fiber optic chemical sensing system for cadmium ions and temperature in an aquatic environment, as described in this application, will be tested below.

[0070] I. Detection Limit and Sensitivity Test

[0071] A cadmium ion solution with a concentration range of 1–100 nM was prepared (specific concentration points were 1 nM, 2 nM, 4 nM, 5 nM, 6 nM, 8 nM, 10 nM, 50 nM, and 100 nM). The solution temperature was controlled at 30°C and the pH at 7. First, the fiber optic sensing unit 2 was immersed in deionized water to determine the spectral baseline. Then, the fiber optic sensing unit 2 was sequentially immersed in cadmium ion solutions of different concentrations for measurement. The stabilization time for each concentration was 5 minutes. The measurement results are as follows: Figure 2 As shown, a significant redshift occurs in the transmission spectrum with increasing cadmium ion concentration. The cadmium ion concentration sensitivity of fiber optic sensing unit 2 is as follows: Figure 3 As shown, within the concentration range of 1–10 nM, the spectral shift exhibits a good linear relationship with the solution concentration, with a sensitivity of 0.246 nm / nM and a linear fit R0. 2 The limit of concentration (LOC) is 0.9974, and the detection limit is as low as 0.489 nM. The sensor still exhibits a significant spectral response in the high concentration range of 50–100 nM.

[0072] II. Selective Testing

[0073] A 10 nM cadmium ion solution was prepared, along with lead, lithium, chromium, and copper ion solutions of the same concentration as interfering ions. The sensor's wavelength response to cadmium ions was tested. Then, the lead, lithium, chromium, and copper ion solutions were mixed with the cadmium ion solution to obtain a mixed solution, and the sensor's wavelength response to the mixed ions was tested. The test results are as follows: Figure 4 As shown, the sensor exhibits the strongest wavelength response to cadmium ions (2.42 nm), while the responses to other interfering ions are all below 0.35 nm, indicating that the sensor of this invention has excellent specific recognition capability for cadmium ions.

[0074] III. Repeatability Testing

[0075] Under the same conditions, cadmium ion solutions with concentrations ranging from 1 to 100 nM were subjected to five cycles of testing. The results are as follows: Figure 5 As shown, the wavelength response error fluctuations at all concentration points are within ±0.03nm, proving that the sensor has good repeatability and reversibility.

[0076] IV. Stability Testing

[0077] Spectra were measured continuously for 30 minutes at each concentration point within the range of 1–100 nM, with the spectra recorded every 3 minutes. The results are as follows: Figure 6 As shown, the wavelength shift at each concentration point is within the error range with no significant fluctuations, proving that the sensor has good detection stability.

[0078] V. Dual-parameter determination of temperature and cadmium ion concentration

[0079] The system described in this application is used to determine the concentration of cadmium ions in an aquatic environment at different temperatures. Cadmium ion standard solutions of different concentrations were prepared, and experiments were conducted within a temperature range of 30–60°C. The cadmium ion concentration sensitivity of the fiber optic sensing unit 2 is as follows: Figure 7 As shown, the transmission spectrum drift is very sensitive to changes in cadmium ion concentration and temperature within the temperature range of 30~60℃, especially within the temperature range of 30~50℃.

[0080] VI. Dual-parameter demodulation based on residual neural networks

[0081] Concentration determination experiments were repeated under different temperature conditions (30℃ to 60℃) to obtain transmission spectral data corresponding to different temperatures and cadmium ion concentrations, constructing a database containing water environment temperature, cadmium ion concentration, and transmission spectra. A residual neural network was constructed; the 1201 wavelength sampling points were randomly shuffled, with 80% selected as the training set and 20% as the test set, and trained until the residual neural network model converged. The demodulation results are shown below. Figure 8 As shown, the trained model performs excellently on the test set. For single cadmium ion concentration prediction, the coefficient of determination R0 is [value missing]. 2 The value is 0.9983, and the mean square error (MSE) is 0.0093. For simultaneous prediction of cadmium ion concentration and temperature as dual parameters, the demodulation results are as follows: Figure 9 As shown, the model's prediction R for concentration 2 The value is 0.9981, and the MSE is 0.0095; the temperature prediction R... 2 The values ​​of 0.9983 and MSE of 0.0094 indicate that the residual neural network used in this invention can effectively separate the coupling effects of temperature and concentration on the sensing signal, and achieve high-precision synchronous demodulation of the two parameters.

[0082] VII. Applications of Different Silane Coupling Agents

[0083] In the functionalization process of the fiber optic sensing unit, the silane coupling agent 3-aminopropyltriethoxysilane in step B2 was replaced with 3-mercaptopropyltrimethoxysilane, while the other steps remained unchanged. The changes in the sensitivity and detection limit of the sensing system to cadmium ion concentration in the water environment were tested. The tests showed that after silanization modification with 3-mercaptopropyltrimethoxysilane, the MOF-cadmium ion imprinted polymer could also be firmly fixed on the fiber surface. The resulting sensor had a sensitivity of 0.241 nm / nM and a detection limit of 0.51 nM to cadmium ions, comparable to the effect of using 3-aminopropyltriethoxysilane, proving that this alternative solution is also feasible.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A dual-parameter fiber optic chemical sensing system for cadmium ions and temperature in an aquatic environment, characterized in that, It includes a spontaneous emission light source, fiber optic sensing unit, spectrometer, photoelectric detection module, and demodulation module; The spontaneous emission light source is a near-infrared light source; the surface of the fiber optic sensing unit is coated with a magnetic MOF-cadmium ion imprinted polymer. The light signal generated by the spontaneous emission light source enters the fiber optic sensing unit, the spectrometer collects the transmission spectrum signal of the fiber optic sensing unit, and outputs the collected spectral data to the photoelectric detection module. The photoelectric detection module converts the optical signal into an electrical signal and transmits the electrical signal to the demodulation module; The demodulation module uses a machine learning algorithm to provide cadmium ion concentration and temperature based on the input signal.

2. The system as described in claim 1, characterized in that, The machine learning algorithm is a residual neural network, which includes an initial normalization layer, six convolutional layers and six fully connected layers, with a residual block set between two adjacent convolutional layers.

3. The system as described in claim 2, characterized in that, The input features of the residual block and the residual mapping are fused using an identity shortcut connection.

4. The system as described in claim 1, characterized in that, The magnetic MOF-cadmium ion-imprinted polymer was prepared by the following method: Step A1: Preparation of Fe3O4 magnetic nanoparticles; Step A2: Prepare Fe3O4@Cd-MOF composites using the Fe3O4 magnetic nanoparticles; Step A3: Disperse the Fe3O4@Cd-MOF complex in a tetrahydrofuran solution and add 1,5-naphthalene diisocyanate to form a pre-assembled system; Step A4: Add a crosslinking agent and an initiator to the pre-assembled system to form a Fe3O4@Cd-MOF doped polyurea composite material; Step A5: Process the composite material to obtain the magnetic MOF-cadmium ion imprinted polymer.

5. The system as described in claim 4, characterized in that, The Fe3O4 magnetic nanoparticles in the magnetic MOF-cadmium ion-imprinted polymer have a mass fraction of 1% to 10%.

6. The system as described in claim 1, characterized in that, The fiber optic sensing unit is fabricated using the following method: Step B1: Pre-process the fiber optic sensing unit with a long-period fiber grating to make the surface of the fiber optic sensing unit hydroxylated. Step B2: The pretreated fiber optic sensing unit is treated with an ethanol solution containing a silane coupling agent to obtain a silanized modified fiber optic sensing unit. Step B3: Grind the magnetic MOF-cadmium ion-imprinted polymer into powder and disperse it in an ethanol / water mixed solvent to form a suspension; Step B4: Immerse the silanized modified fiber optic sensing unit in the suspension to deposit the magnetic MOF-cadmium ion imprinted polymer on the surface of the fiber optic sensing unit, thereby obtaining the fiber optic sensing unit coated with the sensitive material. Step B5: After coating the fiber optic sensing unit with the sensitive material, the sensitive material is cured, washed, and dried to obtain a fiber optic sensing unit with a magnetic MOF-cadmium ion imprinted polymer fixed on its surface.

7. The system as described in claim 6, characterized in that, The silane coupling agent is 3-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, or 3-glycidyl etheroxypropyltrimethoxysilane.

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