Fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocage as well as preparation method and application of fluorescence visualization-photoelectrochemical dual-mode PFOS sensor

Abstract

The invention discloses a fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on a molecular nanocage as well as a preparation method and application thereof, and belongs to the technical field of environmental pollutant detection. Comprising a substrate, a titanium dioxide TiO2 layer and a lead coordination beta-cyclodextrin molecular nanocage MNCs layer which are sequentially arranged from bottom to top, and the titanium dioxide TiO2 layer and the lead coordination beta-cyclodextrin molecular nanocage MNCs layer form a TiO2 / MNCs heterostructure. Electron transfer of a TiO2 / MNCs interface is hindered through host-guest combination of PFOS and MNCs, so that the photocurrent concentration dependency is reduced; meanwhile, the PFOS limits intramolecular movement of the MNCs, inhibits non-radiative decay and enhances fluorescence emission. The sensor disclosed by the invention has the advantages of ultrahigh sensitivity, wide linear range, excellent selectivity and visual fluorescence response capability, and can be applied to dual-mode detection of PFOS in a complex water body.

Description

Technical Field

[0001] This invention relates to the field of environmental pollutant detection technology, specifically to a dual-mode PFOS sensor based on the synergistic effect of molecular nanocages (MNCs) and TiO2 photoelectrodes, and its preparation method. Background Technology

[0002] Persistent organic pollutants (POPs) are known for their environmental persistence, bioaccumulation, and long-range atmospheric transport capabilities, all of which pose a global threat to ecosystems and human health. These substances—including pesticides, industrial compounds, and unintentionally generated byproducts—exhibit strong resistance to degradation and can still produce toxic effects even at extremely low concentrations. Perfluorooctane sulfonate (PFOS), a typical representative of perfluorinated and polyfluoroalkyl substances (PFAS), is receiving increasing regulatory attention due to its widespread detection in aquatic systems and its strong association with health hazards such as bone health, immunotoxicity, and endocrine disruption.

[0003] Despite increasingly stringent regulations, perfluorooctane sulfonate (PFOS) remains widely present in various industrial and consumer products. Traditional detection techniques, such as liquid chromatography-tandem mass spectrometry (LC-MS / MS), while offering excellent sensitivity, rely on expensive instruments and complex sample preparation processes, making real-time on-site monitoring difficult in resource-constrained environments. Portable immunoassays, while simple to operate, often exhibit cross-reactions with structurally similar PFAS substances like perfluorooctanoic acid (PFOA), leading to false positives in complex sample matrices. More importantly, most current sensing platforms fail to meet the new regulations' nanogram / upgrade detection standards, particularly in the presence of high ionic strength samples and other interfering factors, where their detection performance often falls short.

[0004] In recent years, the emerging photoelectrochemical analysis technology has attracted considerable attention because it can be combined with other analytical methods to construct sensing platforms with dual-mode signal output. This technology employs a "photoexcitation-electric detection" mode, offering advantages such as low background noise, high sensitivity, and clear separation of input and output signals. Meanwhile, fluorescence detection technology also generates fluorescence signals by irradiating fluorescent substances with specific excitation light. Therefore, it is possible to combine fluorescence detection technology with photoelectrochemical (PEC) analysis technology to achieve high-precision dual-mode analysis. However, integrating these two methods remains a challenge. Summary of the Invention

[0005] Purpose of the invention: To address the problems of poor selectivity, low sensitivity, and susceptibility to interference from complex matrices in PFOS detection, this invention provides a fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocages, which can achieve both rapid qualitative and precise quantitative detection.

[0006] Technical solution: To achieve the above objectives, the technical solution adopted by this invention is as follows: A fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocages includes a substrate, a titanium dioxide (TiO2) layer, and a lead-coordinated β-cyclodextrin molecular nanocage (MNCs) layer arranged sequentially from bottom to top. The titanium dioxide (TiO2) layer and the lead-coordinated β-cyclodextrin molecular nanocage (MNCs) layer form a TiO2 / MNCs heterostructure.

[0007] Preferably, the substrate is an ITO conductive glass substrate.

[0008] Another objective of this invention is to provide a method for fabricating a fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocages, comprising the following steps: Step 1: Add β-cyclodextrin and PbCl2 to deionized water, add a mixed reaction solvent of cyclohexanol and triethylamine, place in a reaction vessel to react, cool, filter and wash to obtain a solution of lead-coordinated β-cyclodextrin molecular nanocages (MNCs). Step 2: Drop a TiO2 nanoparticle suspension onto an ITO glass substrate, dry and then anneal to obtain an ITO / TiO2 photoelectrode. Step 3: A solution of lead-coordinated β-cyclodextrin molecular nanocages (MNCs) is dropped onto the surface of an ITO / TiO2 photoelectrode and dried to form a TiO2 / MNCs heterostructure sensor.

[0009] Preferably, in step 1, the molar ratio of β-cyclodextrin to PbCl2 is 1:7-9; and in step 1, the volume ratio of cyclohexanol to triethylamine is 1:0.9-1.1.

[0010] Preferably, the washing process in step 1 uses ethanol and water.

[0011] Preferred: In step 1, the reaction temperature in the reactor is 100 °C-120 °C, and the reaction time is 36-60 hours.

[0012] Preferably, the concentration of the TiO2 nanoparticle suspension in step 2 is 9-11 mg / mL.

[0013] Preferably, the concentration of the lead-coordinated β-cyclodextrin molecular nanocages (MNCs) solution in step 3 is 1.8-2.2 mg / mL.

[0014] Another objective of this invention is to provide an application of a molecular nanocage-based fluorescence visualization-photoelectrochemical dual-mode PFOS sensor in PFOS detection.

[0015] Preferably, the application includes: In PEC mode, the host-guest interaction between PFOS and MNCs hinders electron transfer at the TiO2 interface, resulting in a gradual decrease in photocurrent as the PFOS concentration increases. In fluorescence mode, PFOS restricts intramolecular motion of MNCs and inhibits nonradiative decay channels, resulting in enhanced fluorescence intensity.

[0016] Compared with the prior art, the present invention has the following advantages: 1. This sensor exhibits excellent linear response to PFOS in photoelectrochemical mode, with a detection range of 0.2 nM ~ 2 × 10⁻⁶. 4 The detection limit is 0.16 nM, which is better than most reported detection methods.

[0017] 2. The platform exhibits a significant decrease in photocurrent (quantitative detection) and an increase in fluorescence (visual detection) in the presence of PFOS. The complementary nature of the two signals enhances the accuracy and reliability of the detection, effectively avoiding false positives or false negatives.

[0018] 3. The method for preparing a PFOS dual-mode response sensing platform of the present invention uses readily available raw materials, mild and easily controllable reaction conditions, saves reaction costs, and ensures the yield of the target product.

[0019] 4. The dual-mode PFOS response sensing platform of this invention can be applied to the detection of PFOS in real water samples. These results demonstrate that this sensing platform is a powerful tool for accurate PFOS detection and holds promise for achieving precise detection of perfluorooctane sulfonic acid in complex environments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of a dual-mode PFOS sensor; Figure 2 This is a schematic diagram of the preparation process; Figure 3 This is a diagram showing the optimization of TiO2 incubation concentration screening conditions in this invention; Figure 4 This is a diagram showing the optimization of MNC incubation time screening conditions in this invention; Figure 5 This is a diagram showing the optimization of MNCs incubation concentration screening conditions in this invention; Figure 6 The excitation and emission spectra of the MNCs in this invention; Figure 7 The FTIR spectra of TiO2 and TiO2 / MNCs heterostructures in this invention are shown. Figure 8 The images show the photoelectrochemical (PEC) response diagrams of different modified electrodes in this invention and their corresponding EIS Nyquist plots. Figure 9 This is a graph evaluating the specific detection performance of the sensing platform for PFOS in this invention. Figure 10 This is a graph illustrating the renewability performance evaluation of the sensing platform in this invention. Figure 11 This is an evaluation graph of the PFOS detection performance of the sensing platform in this invention; Figure 12 This is a fluorescence and visualization diagram of the sensing platform in this invention. Detailed Implementation

[0021] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the invention. After reading this invention, any modifications of the invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims. Example

[0022] To address the problems of poor selectivity, low sensitivity, and susceptibility to interference from complex matrices in PFOS detection, this embodiment provides a fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocages, such as... Figure 1 As shown, the structure comprises, from bottom to top, a substrate, a titanium dioxide (TiO2) layer, and a lead-coordinated β-cyclodextrin (MNC) molecular nanocage layer, forming a TiO2 / MNCs heterostructure. The substrate is an ITO glass substrate. By using TiO2 to provide the photoelectrochemical signal and the molecular nanocages to provide the fluorescence signal, fluorescence detection and PEC analysis are combined to obtain a dual-readout sensing platform.

[0023] This sensor is constructed from a titanium dioxide (TiO2) photoelectrode and lead-coordinated β-cyclodextrin molecular nanocages (MNCs). Its working principle is as follows: the host-guest binding of PFOS with MNCs hinders electron transfer at the TiO2 / MNCs interface, leading to a decrease in photocurrent concentration dependence; simultaneously, PFOS restricts intramolecular motion of MNCs, suppressing non-radiative decay and enhancing fluorescence emission. This sensor exhibits ultra-high sensitivity (detection limit approximately 0.16 nM), a wide linear range (0.2–20000 nM), excellent selectivity, and visualized fluorescence response capabilities. It can be applied to dual-mode detection of PFOS in complex water bodies, enabling mutual verification of detection results. Example

[0024] This embodiment provides a method for fabricating a fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocages, such as... Figure 2 As shown, it includes the following steps: Step 1: β-cyclodextrin and PbCl2 were added to deionized water at a molar ratio of 1:8. A mixed reaction solvent of cyclohexanol and triethylamine at a volume ratio of 1:10 was added. The mixture was placed in a Teflon-lined reactor and reacted at a reaction temperature of 110 °C for 48 hours. After cooling, the mixture was filtered and washed with ethanol and water to obtain a solution of lead-coordinated β-cyclodextrin molecular nanocages (MNCs). Step 2: After cleaning the ITO glass substrate, 10 μL of TiO2 nanoparticle suspension with a concentration of 10 mg / mL is dropped onto the ITO glass substrate. After drying at room temperature, it is annealed at 300 °C for 30 minutes to obtain the ITO / TiO2 photoelectrode. Step 3: A solution of lead-coordinated β-cyclodextrin molecular nanocages (MNCs) with a concentration of 2 mg / mL is dropped onto the surface of the ITO / TiO2 photoelectrode and dried to form a TiO2 / MNCs heterostructure sensor. Example

[0025] This embodiment provides a method for fabricating a fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocages, such as... Figure 2 As shown, it includes the following steps: Step 1: β-cyclodextrin and PbCl2 were added to deionized water at a molar ratio of 1:7. A mixed reaction solvent of cyclohexanol and triethylamine at a volume ratio of 1:0.9 was added. The mixture was placed in a Teflon-lined reactor and reacted at 100 °C for 60 hours. After cooling, the mixture was filtered and washed with ethanol and water to obtain a solution of lead-coordinated β-cyclodextrin molecular nanocages (MNCs). Step 2: After cleaning the ITO glass substrate, 10 µL of TiO2 nanoparticle suspension with a concentration of 9 mg / mL was dropped onto the ITO glass substrate. After drying at room temperature, it was annealed at 300 °C for 30 minutes to obtain the ITO / TiO2 photoelectrode. Step 3: A solution of lead-coordinated β-cyclodextrin molecular nanocages (MNCs) with a concentration of 1.8 mg / mL is dropped onto the surface of the ITO / TiO2 photoelectrode, and after drying, a TiO2 / MNCs heterostructure sensor is formed. Example

[0026] This embodiment provides a method for fabricating a fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocages, such as... Figure 2 As shown, it includes the following steps: Step 1: Add β-cyclodextrin and PbCl2 to deionized water at a molar ratio of 1:9, and add a mixed reaction solvent of cyclohexanol and triethylamine at a volume ratio of 1:1.1. The total volume of the reaction system should not exceed 20 mL. Place the reaction in a Teflon-lined reactor at a reaction temperature of 120 °C for 36 hours. After cooling, filter and wash with ethanol and water to obtain a solution of lead-coordinated β-cyclodextrin molecular nanocages (MNCs). Step 2: After cleaning the ITO glass substrate, 10 µL of TiO2 nanoparticle suspension with a concentration of 11 mg / mL is dropped onto the ITO glass substrate. After drying at room temperature, it is annealed at 300 °C for 30 minutes to obtain the ITO / TiO2 photoelectrode. Step 3: A solution of lead-coordinated β-cyclodextrin molecular nanocages (MNCs) with a concentration of 2.2 mg / mL is dropped onto the surface of the ITO / TiO2 photoelectrode, and after drying, a TiO2 / MNCs heterostructure sensor is formed. Example

[0027] This embodiment provides a method for fabricating a fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocages, such as... Figure 2 As shown, it includes the following steps: Step 1: β-Cyclodextrin (0.0227 g, 0.02 mmol) and PbCl2 (0.0445 g, 0.16 mmol) were added to 6 mL of ultrapure water and stirred until homogeneous. Then, a mixed solvent consisting of 3 mL cyclohexanol and 3 mL triethylamine was slowly added dropwise. The mixture was transferred to a 20 mL Teflon-lined autoclave and reacted at 110 °C for 48 hours. After naturally cooling to room temperature, the resulting precipitate was washed with ethanol and deionized water and dried under vacuum at 60 °C to obtain lead-coordinated β-cyclodextrin molecular nanocages (MNCs). Step 2: The ITO conductive glass (20 mm × 10 mm) was ultrasonically treated with acetone, ethanol, and deionized water for 15 min each, and then air-dried. 10 µL of TiO2 nano-suspension (10 mg / mL) was dropped onto the cleaned ITO surface, and after air drying, it was annealed at 300°C for 30 min to obtain a uniform and dense TiO2 film (titanium dioxide TiO2 layer). Step 3: A solution of lead-coordinated β-cyclodextrin molecular nanocages (MNCs) with a concentration of 2 mg / mL is dropped onto the surface of a TiO2 film and allowed to stand and air dry to form a TiO2 / MNCs heterostructure sensor.

[0028] like Figure 3As shown, when using the ITO / TiO2 system in PBS buffer, the photocurrent increases with increasing TiO2 concentration, reaching a maximum at 10 mg / mL. However, further increases in TiO2 concentration lead to a decrease in photocurrent response, as excess TiO2 hinders the electron transfer rate. Therefore, 10 mg / mL was chosen as the optimal TiO2 concentration.

[0029] like Figure 4 As shown, the photocurrent gradually decreases with increasing incubation time, which can be attributed to the inherent poor conductivity of MNCs. When the incubation time reaches 30 minutes, the MNCs are firmly fixed on the TiO2 surface, and further extending the incubation time has little effect on the photocurrent response. Therefore, 30 minutes is selected as the optimal incubation time for modifying MNCs onto the TiO2 surface for PFOS sensing.

[0030] like Figure 5 As shown, the photocurrent intensity gradually decreases with increasing MNC concentration, which can also be attributed to the poor conductivity of MNCs. When the MNC concentration reaches 2 mg / mL, the nanocages can be uniformly and firmly fixed on the TiO2 surface. Therefore, 2 mg / mL was selected as the optimal MNC concentration for PFOS detection.

[0031] like Figure 6 As shown, under ultraviolet light excitation, MNCs exhibit a weak emission peak at 535 nm. Furthermore, monitoring the emission peak at 535 nm reveals a sharp excitation peak at 297 nm in the corresponding excitation spectrum.

[0032] like Figure 7 As shown, the 1000–500 cm⁻¹ region represents the fingerprint region of TiO₂, where the prominent peaks can be attributed to the stretching vibrations of the Ti-O bond. A significant absorption band in the 3200–3600 cm⁻¹ range is attributed to the OH stretching vibration. Compared to pure TiO₂, the intensity of the TiO₂ / MNCs heterostructure in this region is enhanced due to the formation of abundant hydrogen bonds. Furthermore, the TiO₂ / MNCs samples exhibit unique absorption peaks in the 1200–900 cm⁻¹ range, corresponding to the COC stretching vibration and CH bending vibration. These features further confirm the formation of the TiO₂ / MNCs heterostructure, where the COC absorption band is a characteristic peak of MNCs.

[0033] PEC measurements of the sensing platform were performed using a platinum column counter electrode and an Ag / AgCl reference electrode in phosphate buffered saline (PBS, 10 mM, pH 7.4) containing 0.1 M ascorbic acid (AA). The PEC response of the treated photoanode was recorded on a CHI660E electrochemical workstation. Subsequently, under optimized experimental conditions, the PEC responses of ITO / TiO2 / MNCs were recorded from 0.2 nM to 2 × 10⁻⁶ mM. 4 Photocurrent in response to PFOS at different concentrations per nanomolar per liter. A UVGO 78UY ultraviolet lamp (405 nm LED) was used as the excitation source (998 mW).

[0034] like Figure 8 As shown in (A), the bare ITO electrode exhibits the lowest electrochemical signal response, while the ITO / TiO2 electrode shows the highest photocurrent response among the three electrodes. However, the photocurrent response decreases after modification with MNCs. Figure 8 (B) shows that with sequential modification of TiO2 and MNCs, the electron transfer resistance ( R The value of et (i.e., the semicircular portion) first increases and then decreases. This trend is highly consistent with the equivalent circuit element parameters obtained by fitting using ZSimpWin software.

[0035] In addition, we evaluated the PFOS specificity of the sensing platform and the reproducibility of the sensing platform. Figure 9 (10). The responses of PFOS to other structurally similar hydrocarbon analogs (a, blank; b, CTAB (hexadecyltrimethylammonium bromide); c, SDS (sodium dodecyl sulfate); d, SDBS (sodium dodecylbenzene sulfonate); e, sodium 1-octane sulfonate) were compared. Although these interfering compounds slightly suppressed the photoelectrochemical (PEC) response, the signal intensity difference between the PFOS-containing group and the blank control group was minimal. These results confirm that the sensing platform has a strong specific binding capacity for PFOS even in the presence of competing species in complex environments. By testing the photocurrent response of six different electrodes after regeneration, all six electrodes were able to recover at least 87% of their original signal level before binding with PFOS, indicating that the proposed sensing platform has excellent reusability. Example

[0036] This embodiment provides an application of a fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocages in PFOS detection, including: In PEC mode, the host-guest interaction between PFOS and MNCs hinders electron transfer at the TiO2 interface, resulting in a gradual decrease in photocurrent as the PFOS concentration increases. In fluorescence mode, PFOS restricts intramolecular motion of MNCs and inhibits nonradiative decay channels, resulting in enhanced fluorescence intensity.

[0037] To evaluate the performance of this sensing platform, we performed photoelectrochemical tests using PFOS solutions of varying concentrations. When bound to PFOS, the electron transfer resistance of the TiO2 / MNCs electrode increased, and the photocurrent intensity gradually decreased with increasing PFOS concentration. Figure 11 As shown in Figure 11(A), PFOS concentrations (0.2 nM, 2 nM, 20 nM, 200 nM, 2000 nM, 20000 nM) exhibit a significant negative correlation with photocurrent signal intensity. Figure 11(B) further shows that the PEC response value (ΔI) is related to the logarithm (lg) of PFOS concentration. c The relationship is linear, and the fitted equation is Δ. I = -1.0767 lg c -0.9250 ( R ² = 0.9914). The calculated detection limit is 0.16 nM (S / N = 3).

[0038] As shown in Figure 12(A), the fluorescence intensity of the sensing platform gradually increases with increasing PFOS concentration after the addition of different concentrations of PFOS, providing experimental support for the qualitative detection of PFOS through visualization. Figure 12 As shown in (B), fluorescence imaging visually demonstrates the sensing platform's response to PFOS. No fluorescence was observed in the unmodified TiO2 electrode under UV light. After MNC modification, strong green fluorescence was clearly visible to the naked eye, attributed to the inherent luminescent properties of MNCs and their enhanced interfacial interaction with TiO2. In the presence of PFOS, the host-guest binding between PFOS and MNCs restricts intramolecular motion within the nanocage structure, effectively suppressing non-radiative decay, thus leading to enhanced fluorescence emission. The fluorescence intensity exhibits a concentration-dependent increasing trend with increasing PFOS concentration. Notably, even at PFOS concentrations as low as 0.2 nM, significant fluorescence enhancement was directly observed, demonstrating the platform's excellent sensitivity and visual detection capability. The consistent fluorescence enhancement trend further confirms the sensing platform's ability to detect PFOS. Example

[0039] This embodiment provides an application of a molecular nanocage-based fluorescence visualization-photoelectrochemical dual-mode PFOS sensor in the detection of PFOS in real water samples.

[0040] Table 1. Feasibility verification of a dual-mode PFOS sensor using the standard addition method. The feasibility of this dual-mode sensing platform was validated using the standard addition method in water samples from Xuanwu Lake (Nanjing, China). Samples were pretreated with a 0.20 μm filter to remove suspended particles before detection. PFOS at concentrations of 0.20 nM, 20.0 nM, and 2000.0 nM (as shown in Table 1) was then added to the water sample matrix. Recovery rates ranged from 100.24% to 105.00%, with relative standard deviations (RSDs) consistently below 9.52%.

[0041] Table 2. Using LC-MS method To further verify the precision and reliability of the PEC platform, high-performance liquid chromatography-mass spectrometry (LC-MS) was used as the benchmark method for comparative verification. As shown in Table 2, the calculated t-test values ​​(1.00-1.27) were all below the critical threshold of ±2.306, confirming that there was no statistically significant difference between the PEC detection results and the LC-MS measurements. These experimental results fully demonstrate the applicability of this dual-mode sensing platform for reliable PFOS detection in complex real-world water samples.

[0042] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocages, characterized in that, The structure comprises, from bottom to top, a substrate, a titanium dioxide (TiO2) layer, and a lead-coordinated β-cyclodextrin (MNC) molecular nanocage layer, wherein the titanium dioxide (TiO2) layer and the lead-coordinated β-cyclodextrin (MNC) molecular nanocage layer form a TiO2 / MNCs heterostructure.

2. The fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocages according to claim 1, characterized in that: The substrate is an ITO conductive glass substrate.

3. A method for fabricating a fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocages as described in claim 1, characterized in that, Includes the following steps: Step 1: Add β-cyclodextrin and PbCl2 to deionized water, add a mixed reaction solvent of cyclohexanol and triethylamine, place in a reaction vessel to react, cool, filter and wash to obtain a solution of lead-coordinated β-cyclodextrin molecular nanocages (MNCs). Step 2: Drop a TiO2 nanoparticle suspension onto an ITO glass substrate, dry and then anneal to obtain an ITO / TiO2 photoelectrode. Step 3: A solution of lead-coordinated β-cyclodextrin molecular nanocages (MNCs) is dropped onto the surface of the ITO / TiO2 photoelectrode to form a TiO2 / MNCs heterostructure sensor through hydrogen bonding interactions between the materials.

4. The fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocages according to claim 3, characterized in that: In step 1, β-cyclodextrin and PbCl2 are mixed at a molar ratio of 1:7-9; cyclohexanol and triethylamine are mixed at a volume ratio of 1:0.9-1.

1.

5. The fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocages according to claim 4, characterized in that: In step 1, ethanol and water are used for washing.

6. The fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocages according to claim 5, characterized in that: In step 1, the reaction temperature in the reactor is 100 °C-120 °C, and the reaction time is 36-60 hours.

7. The fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocages according to claim 6, characterized in that: In step 2, the concentration of the TiO2 nanoparticle suspension is 9-11 mg / mL.

8. The fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocages according to claim 7, characterized in that: The concentration of the lead-coordinated β-cyclodextrin molecular nanocages (MNCs) solution in step 3 is 1.8-2.2 mg / mL.

9. The application of the fluorescence visualization-photoelectrochemical dual-mode PFOS sensor based on molecular nanocages as described in claim 1 in PFOS detection.

10. The application according to claim 9, characterized in that, include: In PEC mode, the host-guest interaction between PFOS and MNCs hinders electron transfer at the TiO2 interface, resulting in a gradual decrease in photocurrent as the PFOS concentration increases. In fluorescence mode, PFOS restricts intramolecular motion of MNCs and inhibits nonradiative decay channels, resulting in enhanced fluorescence intensity.

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