Optical fiber surface noble metal nanoparticle self-assembly device and detection method thereof

Abstract

This application relates to the field of fiber optic sensing technology and provides a device and method for detecting the self-assembly of noble metal nanoparticles on the surface of an optical fiber. The method includes: sending detection light from a broadband light source to a single-mode fiber circulator; transmitting the detection light to a single-mode fiber jumper; switching between a first state and a second state, and receiving reflected light from the single-mode fiber jumper; and determining the self-assembled dense monolayer state of the noble metal nanoparticles at the end of the single-mode fiber jumper based on interference waves. This method for detecting the self-assembled dense monolayer state of noble metal nanoparticles on the surface of an optical fiber uses a single common optical fiber for detection. By observing dynamic interference waves, the self-assembled dense monolayer state of the noble metal nanoparticles is determined, revealing that effectively densely packed monolayer noble metal nanoparticles can achieve a peak state of enhanced electric field under coupled localized surface plasmon resonance mode, and this can be recorded during the period of maximum amplitude of the dynamic interference wave. This method does not have strict requirements on reagent purity and pH environment, greatly reducing the preparation cost and operational complexity of the nanoparticle array. It possesses high uniformity and can be controlled on-site and operated in real time.

Description

Technical Field

[0001] This application relates to the field of fiber optic sensing technology, and in particular to a device for the self-assembly of noble metal nanoparticles on the surface of an optical fiber and a method for detecting such devices. Background Technology

[0002] Highly conductive nanoparticle layers can be used to improve the physical, chemical, optical, or other properties of optical fiber surfaces. Localized surface plasmon resonance typically occurs in highly conductive noble metal nanoparticles. Various methods exist for monolayer coating of highly conductive noble metal nanoparticles onto different types of substrate surfaces. Nanoparticle coatings can form monolayers, multilayers, and ordered or disordered arrays on the substrate. Techniques such as nanoimprint lithography, electron beam lithography, two-photon polymerization, nanosphere lithography, and anodic aluminum oxide templates can be used to coat noble metal nanoparticles onto substrate surfaces; however, these methods require large and expensive equipment such as electron beam lithography machines. Other methods, on the other hand, require specific conditions with strong limitations regarding reagent purity and pH value.

[0003] The above methods have technical problems such as high cost, complex process and strict environmental requirements, making it difficult to achieve large-scale, low-cost and highly uniform nanoparticle array preparation. Summary of the Invention

[0004] The optical fiber surface noble metal nanoparticle self-assembly device and its detection method provided in this application can realize the preparation of large-scale, low-cost, and highly uniform nanoparticle arrays, and can also be controlled on-site and operated in real time.

[0005] The first aspect of this application provides a method for detecting the state of a dense monolayer of self-assembled noble metal nanoparticles on an optical fiber surface, comprising: a broadband light source sending detection light to a single-mode fiber circulator; the single-mode fiber circulator receiving the detection light and transmitting it to a single-mode fiber jumper; wherein the bottom of the single-mode fiber jumper is stripped of its protective sleeve and cladding layer; controlling the single-mode fiber jumper to switch between a first state and a second state; the first state is that the end of the single-mode fiber jumper is located inside the solution, and the second state is that the end of the single-mode fiber jumper is located outside the solution and at a preset height; the single-mode fiber circulator receives... The system receives reflected light from a single-mode fiber optic patch cord; wherein the reflected light is generated by the reflected detection light of the single-mode fiber optic patch cord, and the solution includes noble metal nanoparticles. When the single-mode fiber optic patch cord switches from a first state to a second state, a droplet is present at the end of the single-mode fiber optic patch cord. The end of the single-mode fiber optic patch cord and the droplet form a Fabry-Perot resonant cavity to generate an interference wave. The self-assembled dense monolayer state of the noble metal nanoparticles at the end of the single-mode fiber optic patch cord is determined based on the interference wave in the reflected light; wherein the self-assembled dense monolayer state includes a monolayer saturated state, a monolayer unsaturated state, and a monolayer supersaturated state.

[0006] In some feasible implementations, the self-assembled dense monolayer state of noble metal nanoparticles at the end of a single-mode fiber optic patch cord is determined based on interference waves, including: determining the self-assembled dense monolayer state of noble metal nanoparticles at the end of a single-mode fiber optic patch cord based on the amplitude or trough of the interference wave.

[0007] In some feasible implementations, determining the self-assembled dense monolayer state of noble metal nanoparticles at the end of a single-mode fiber optic patch cord based on interference waves includes: determining that the self-assembled dense monolayer state at the end of the single-mode fiber optic patch cord is a monolayer unsaturated state when the single-mode fiber optic patch cord switches between a first state and a second state a preset number of times and the amplitude of the interference wave increases; determining that the self-assembled dense monolayer state at the end of the single-mode fiber optic patch cord is a monolayer saturated state when the single-mode fiber optic patch cord switches between a first state and a second state a preset number of times and the amplitude of the interference wave remains unchanged; and determining that the self-assembled dense monolayer state at the end of the single-mode fiber optic patch cord is a monolayer oversaturated state when the single-mode fiber optic patch cord switches between a first state and a second state a preset number of times and the amplitude of the interference wave decreases.

[0008] In some feasible implementations, the method for detecting the state of a dense monolayer of noble metal nanoparticles on the fiber surface before the broadband light source sends detection light to the single-mode fiber circulator also includes: stripping the protective sleeve from the single-mode fiber jumper; and modifying the end of the single-mode fiber jumper facing the solution.

[0009] In some feasible implementations, the end of the single-mode fiber optic patch cord facing the solution is modified, including: pretreating the end of the single-mode fiber optic patch cord with a mixed solution of concentrated sulfuric acid and hydrogen peroxide; and modifying the end of the single-mode fiber optic patch cord with 3-aminopropyltriethoxysilane to form a silane layer at the end of the single-mode fiber optic patch cord.

[0010] In some feasible implementations, the plane at the end of the single-mode fiber patch cord is parallel to the surface of the solution.

[0011] In some feasible implementations, the noble metal nanoparticles include all types of gold or silver nanoparticles; wherein multiple noble metal nanoparticles are the same or different in size, and the surface of the noble metal nanoparticles is covered with an organic layer or not covered with an organic layer.

[0012] The first aspect of this application provides a method for detecting the self-assembled dense monolayer state of noble metal nanoparticles on an optical fiber surface. This method uses a spectrometer to analyze the amplitude and frequency changes of interference waves in reflected light in real time. A single common single-mode optical fiber is used for detection. By observing the dynamic interference wave, the self-assembled dense monolayer state of the noble metal nanoparticles is determined, avoiding nanoparticle aggregation. This reveals that effectively densely packed monolayers of noble metal nanoparticles can achieve peak states with enhanced coupled localized surface plasmon resonance electric fields. Furthermore, the method can record data during the period of maximum amplitude of the dynamic interference wave. During the detection process, the preparation of noble metal nanoparticles is simple, requiring no strong solvents and having no strict requirements on reagent purity, pH environment, or the specific noble metal nanoparticles. This significantly reduces the cost and operational complexity of preparing noble metal nanoparticle arrays, exhibits high uniformity, and allows for on-site control and real-time operation.

[0013] The second aspect of this application provides a device for the self-assembly of noble metal nanoparticles on the surface of an optical fiber, comprising: a broadband light source configured to transmit detection light; a single-mode fiber circulator, the first end of which is connected to the broadband light source and configured to receive the detection light; a single-mode fiber patch cord, one end of which is connected to the second end of the single-mode fiber circulator and configured to receive the detection light and generate reflected light; a standard photometric cuvette disposed opposite to the single-mode fiber patch cord, the cuvette containing a solution of noble metal nanoparticles; a height-adjustable stage, the cuvette being disposed on the stage, the stage being configured to move the cuvette toward or away from the single-mode fiber patch cord, thereby switching the single-mode fiber patch cord between a first state and a second state; and a spectrometer connected to the third end of the single-mode fiber circulator, configured to receive the reflected light and determine the self-assembled dense monolayer state of the noble metal nanoparticles at the end of the single-mode fiber patch cord based on the interference wave in the reflected light.

[0014] In some feasible implementations, the height-adjustable stage is also configured to move the standard photometric cuvette along a first direction to place the single-mode fiber optic patch cord in a first state; the height-adjustable stage is also configured to move the standard photometric cuvette along a second direction to place the single-mode fiber optic patch cord in a second state; the first direction and the second direction are opposite to each other.

[0015] In some feasible implementations, the height-adjustable worktable includes: a first mounting platform; a second mounting platform, disposed opposite to the first mounting platform, configured to hold a standard photometric cuvette; and a drive unit connected between the first and second mounting platforms, configured to drive the second mounting platform to move relative to the first mounting platform.

[0016] The optical fiber surface noble metal nanoparticle self-assembly device provided in the second aspect of this application adopts the optical fiber surface noble metal nanoparticle self-assembly dense monolayer state detection method provided in the first aspect. Its beneficial technical effects can be found in the first aspect, and will not be repeated here. Attached Figure Description

[0017] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of a self-assembly device for noble metal nanoparticles on the surface of an optical fiber, provided in an embodiment of this application. Figure 2 This is a schematic flowchart of a method for detecting the self-assembly of noble metal nanoparticles on the surface of an optical fiber, provided in an embodiment of this application. Figure 3 This is a schematic diagram of a Fabry-Perot resonant cavity provided in an embodiment of this application; Figure 4 This is a schematic diagram of a Fabry-Perot resonant cavity for the nanoparticle covering stage provided in an embodiment of this application; Figure 5 This application provides an embodiment of the optical reflectance spectrum of a single-mode fiber optic patch cord tail measured in air, water, and after being lifted out of the water and forming a droplet; Figure 6 This is a schematic diagram of a Fabry-Perot resonant cavity during the nanoparticle covering process at the end of a single-mode fiber optic patch cord, as provided in an embodiment of this application. Figure 7 This is an embodiment of the present invention, showing normalized spectra measured during the gold nanoparticle coating process and scanning electron microscopy imaging of a single-mode fiber optic patch cord end layer of gold nanoparticles. Figure 8 This is an embodiment of the present invention, showing normalized spectra measured during the silver nanoparticle coating process and scanning electron microscopy imaging of a single-mode fiber optic patch cord end silver nanoparticle monolayer.

[0019] Illustration markings: 1. Broadband light source; 2. Single-mode fiber circulator; 21. First end; 22. Second end; 23. Third end; 3. Single-mode fiber patch cord; 31. Cladding layer; 32. Fiber core; 33. Silane layer; 34. Noble metal nanoparticle layer; 3a. First semi-transparent mirror; 3b. Second mirror; 3c. Third mirror; 3d. Fourth mirror; 4. Standard photometric cuvette; 41. Solution; 42. Noble metal nanoparticles; 5. Height-adjustable stage; 51. First mounting platform; 52. Second mounting platform; 53. Drive unit; 6. Spectrometer. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are all within the protection scope of this application.

[0021] In the following description, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0022] Furthermore, in this application, directional terms such as "upper," "lower," "inner," and "outer" are defined relative to the indicated placement of the components in the accompanying drawings. It should be understood that these directional terms are relative concepts, used for relative description and clarification, and can change accordingly depending on the placement of the components in the accompanying drawings.

[0023] Highly conductive noble metal nanoparticle layers can be used to improve the physical, chemical, optical, or other properties of optical fiber surfaces. Nanoparticle solutions exhibit strong visible colors due to localized surface plasmon resonance, depending on their size, shape, composition, and surrounding dielectric environment. Under resonant excitation, the localized surface plasmon resonance of noble metal nanoparticles leads to an enhancement of the electric field near their surface, thereby enhancing various light-matter interactions.

[0024] Plasmon resonance mostly occurs in noble metal (gold, silver) nanoparticles. There are various methods for monolayer coating of highly conductive noble metal nanoparticles onto different types of substrate surfaces. Nanoparticle coatings can form monolayers, multilayers, and ordered or disordered arrays on the substrate. Nanoparticles can be coated onto substrate surfaces using techniques such as nanoimprint lithography, electron beam lithography, two-photon polymerization, nanosphere lithography, and anodic aluminum oxide templates. However, these methods require large and expensive equipment such as electron beam lithography machines. Other methods are subject to strict limitations regarding reagent purity and pH values. These methods suffer from high costs, complex processes, and stringent environmental requirements, making it difficult to achieve large-scale, low-cost, and highly uniform nanoparticle array fabrication.

[0025] To address the aforementioned technical problems, this application provides a device and method for detecting the self-assembly of noble metal nanoparticles on the surface of optical fibers. This method for detecting the self-assembled dense monolayer state of noble metal nanoparticles on the surface of optical fibers uses a single common single-mode optical fiber to collect the reflection spectrum and determines the self-assembled dense monolayer state of the nanoparticles by observing dynamic interference waves. It can achieve large-scale, low-cost, and highly uniform noble metal nanoparticle array preparation and can also meet the requirements of on-site control and real-time operation.

[0026] Figure 1 This is a schematic diagram of the structure of a self-assembly device for noble metal nanoparticles on the surface of an optical fiber, provided in an embodiment of this application.

[0027] See Figure 1 As shown, the fiber optic surface noble metal nanoparticle self-assembly device provided in this application embodiment may include a broadband light source 1, a single-mode fiber circulator 2, a single-mode fiber jumper 3, a standard photometric cuvette 4, a height-adjustable stage 5, and a spectrometer 6.

[0028] A broadband light source 1 is used to transmit detection light. The broadband light source 1 outputs a wide-spectrum detection light that can cover the visible to near-infrared band, ensuring a high-sensitivity response to the optical properties of noble metal nanoparticles of different sizes and materials; a single-mode fiber circulator 2 is used to guide the optical path and achieve spatial separation of incident and reflected light.

[0029] Localized surface plasmon resonance (LSPR) refers to the localized surface plasmon resonance effect generated by noble metal nanoparticles in the visible and near-infrared regions (typically 400–2000 nm). When the incident light frequency matches the collective oscillation frequency of free electrons in the noble metal nanoparticles, the free electron group oscillates cooperatively relative to the positive ion lattice, producing strong resonant absorption and scattering, which is LSPR.

[0030] Specifically, the first end 21 of the single-mode fiber circulator 2 is connected to the broadband light source 1, and one end of the single-mode fiber patch cord 3 is connected to the second end 22 of the single-mode fiber circulator 2. The single-mode fiber circulator 2 is used to couple the detection light from the broadband light source 1 into the single-mode fiber patch cord 3.

[0031] In this case, the sheath and cladding layer of the single-mode fiber optic patch cord 3 are stripped off at the end and cut flat with a fiber optic cleaver. The flanged end of the single-mode fiber optic patch cord 3 is connected to the second end 22 of the single-mode fiber optic circulator 2.

[0032] The other end of the single-mode fiber optic patch cord 3 is positioned opposite to the standard photometric cuvette 4, and the plane in which it is located is parallel to the surface of the solution 41.

[0033] In this way, when the end of the single-mode fiber optic patch cord 3 is immersed in the assembly solution 41 in the standard photometric cuvette 4, the end of the single-mode fiber optic patch cord 3 serves as a self-assembly substrate and is directly exposed to the noble metal nanoparticles 42 in the solution 41. Each region on the end of the single-mode fiber optic patch cord 3 can be uniformly contacted with the solution 41, ensuring the interface consistency and repeatability of the noble metal nanoparticles 42 during the end self-assembly process.

[0034] It is important to emphasize that the end of the single-mode fiber optic patch cord 3 should be a completely flat end face structure, and scratches, irregular cut surfaces or other defect structures should be avoided to reduce the interference of end face defects on dynamic interference waves and improve the stability and repeatability of reflection spectrum detection.

[0035] The solution 41 to be assembled contains noble metal nanoparticles 42, which may include gold nanoparticles or silver nanoparticles; wherein multiple noble metal nanoparticles 42 may have the same or different sizes. Gold nanoparticles or silver nanoparticles are noble metal nanoparticles and have excellent localized surface plasmon resonance characteristics.

[0036] The standard photometric cuvette 4 is set on the height-adjustable stage 5. The height-adjustable stage 5 is used to move the standard photometric cuvette 4 toward or away from the single-mode fiber optic patch cord 3, so that the single-mode fiber optic patch cord 3 switches between the first state and the second state.

[0037] Specifically, the height-adjustable stage 5 can be driven by a high-precision stepper motor to achieve precise and controllable displacement. By changing the vertical position of the height-adjustable stage 5, the single-mode fiber optic patch cord 3 can be pulled out of the solution 41. For example, if the height-adjustable stage 5 moves the standard photometric cuvette 4 along the first direction A, the end of the single-mode fiber optic patch cord 3 is completely immersed in the solution 41. At this time, the single-mode fiber optic patch cord 3 is in the first state, and the noble metal nanoparticles 42 are spontaneously adsorbed at the end of the single-mode fiber optic patch cord 3. When the height-adjustable stage 5 moves the standard photometric cuvette 4 along the second direction B, the end of the single-mode fiber optic patch cord 3 leaves the liquid surface and enters the air. At this time, the single-mode fiber optic patch cord 3 enters the second state, and the noble metal nanoparticles in the droplet are adsorbed on the silane layer, thereby locking the monolayer self-assembled morphology. Here, the first direction A and the second direction B can be two opposite sub-directions of the gravity direction of the height-adjustable stage 5.

[0038] Furthermore, during the aforementioned droplet shrinkage and solidification process, in addition to surface tension, the movement of noble metal nanoparticles also occurs simultaneously. Specifically, while the droplet is still wet, as the solvent continues to evaporate, evaporation-induced convection occurs within the droplet. This convection can move from the central region to the edge region, thereby driving the suspended noble metal nanoparticles to migrate towards the vicinity of the gas-liquid interface. Specifically, charged noble metal nanoparticles are affected by Brownian motion in the liquid, diffusing within a local area and adjusting their relative positions. The combined effect of evaporation-induced convection and Brownian thermal diffusion enables the noble metal nanoparticles to migrate, diffuse, and rearrange within the droplet. The noble metal nanoparticles are adsorbed onto the silane layer through electrostatic interactions between negatively charged gold or silver nanoparticles and positively charged amino groups in the silane molecular layer, ultimately completing the adsorption and immobilization process. The next step is supersaturation.

[0039] The single-mode fiber circulator 2 receives the detection light and transmits the reflected light back to the third end 23. The spectrometer 6 is connected to the third end 23 of the single-mode fiber circulator 2 to receive the reflected light and determine the self-assembled dense monolayer state of the noble metal nanoparticles 42 at the end of the single-mode fiber jumper 3 based on the interference wave in the reflected light.

[0040] When measuring the reflected light signal of the single-mode fiber optic patch cord 3, the patch cord 3 is immersed in solution 41 and then lifted out. A droplet is generated at the end of the patch cord 3, which can be regarded as a cavity. The end face of the cut end of the patch cord 3 and the interfacial liquid air act as a semi-transparent mirror. Therefore, the droplet and the end face of the cut end of the patch cord 3 form a Fabry-Perot resonant cavity. Dynamic interference waves can then be observed at the end of the patch cord 3 using a spectrometer 6. The amplitude and frequency of the dynamic interference waves depend on the geometric parameters of the layer structure between the mirrors, the refractive index and viscosity of solution 41, and the optical properties, geometry, and interparticle distance of the noble metal nanoparticles adsorbed on the end of the patch cord 3. Within a certain coverage time of the noble metal nanoparticles 42, the amplitude of the dynamic interference waves can be observed to increase significantly due to the coupling mode of localized plasmon resonance in the noble metal nanoparticle layer. Scanning electron microscopy images show that this increase in the amplitude of the dynamic interference wave corresponds to the formation of a dense noble metal nanoparticle monolayer at the end of the single-mode fiber optic patch cord 3. This makes dynamic interference wave technology an important means of controlling the preparation of such noble metal nanoparticle monolayers on silica surfaces. In this application, 41 drops of noble metal nanoparticle colloidal solution at the end of the single-mode fiber optic patch cord 3 are used as a Fabry-Perot resonant cavity, allowing for real-time estimation of the parameters of the prepared noble metal nanoparticle monolayer.

[0041] See also Figure 1 As shown, in a specific implementation, the height-adjustable workbench 5 may include: a first mounting platform 51 and a second mounting platform 52.

[0042] The first installation platform 51 is used to provide vertical lifting support for the second installation platform 52. The first installation platform 51 can be placed on a test bench or table.

[0043] The second mounting platform 52 is positioned opposite to the first mounting platform 51. The second mounting platform 52 provides a mounting platform for the standard photometric cuvette 4, which is placed on the surface of the second mounting platform 52 away from the first mounting platform 51.

[0044] One end of the drive unit 53 is connected to the first mounting platform 51, and the other end is connected to the second mounting platform 52. The drive unit 53 is used to drive the second mounting platform 52 to move up and down in the vertical direction relative to the first mounting platform 51, thereby precisely adjusting the distance between the end of the standard photometric cuvette 4 and the single-mode fiber optic patch cord 3.

[0045] Among them, the driving component 53 can be a precision stepper motor, with precise and controllable displacement, ensuring the formation of a stable Fabry-Perot cavity, thereby stabilizing the interference wave and effectively guaranteeing the detection accuracy.

[0046] Figure 2 This is a flowchart illustrating a method for detecting the state of a dense monolayer of noble metal nanoparticles self-assembled on the surface of an optical fiber, as provided in an embodiment of this application.

[0047] See Figure 2 As shown in the embodiments of this application, the method for detecting the state of self-assembled dense monolayer of noble metal nanoparticles on the optical fiber surface may include steps S1 to S5.

[0048] Step S1: Broadband light source 1 sends detection light to single-mode fiber optic circulator 2.

[0049] In this step, the broadband light source 1 can emit a continuous spectrum in the 1440nm to 1650nm band, covering a large communication band, with a spectral width of 210nm. This provides sufficient bandwidth support for the subsequent extraction of parameters from the interference wave, ensuring that the state changes of the 42-layer self-assembled dense monolayer of noble metal nanoparticles are highly sensitive to the interference wave response.

[0050] Step S2: The single-mode fiber circulator 2 receives the detection light and transmits the detection light to the single-mode fiber patch cord 3; wherein, the bottom of the single-mode fiber patch cord 3 is stripped of its protective sleeve and cladding layer 31.

[0051] In this step, the single-mode fiber circulator 2 directionally couples the detection light emitted by the broadband light source 1 to the single-mode fiber jumper 3, while isolating the reflected echo to avoid interference.

[0052] Step S3: Control the single-mode fiber optic patch cord 3 to switch between a first state and a second state. The single-mode fiber optic patch cord 3 switches between a first state and a second state. In the first state, the end of the single-mode fiber optic patch cord 3 is located inside the solution 41. In the second state, the end of the single-mode fiber optic patch cord 3 is located outside the solution 41 and at a preset height.

[0053] In this step, the first and second states of the single-mode fiber optic patch cord 3 can be precisely controlled by adjusting the displacement and speed of the height-adjustable stage 5 along the first and second directions to achieve controllable adsorption and locking of the noble metal nanoparticles 42 at the end of the single-mode fiber optic patch cord 3. By setting a preset height, the end of the single-mode fiber optic patch cord 3 is prevented from being too close to the surface of the solution 41, which could cause liquid surface disturbance or capillary effect interference with the self-assembly process of the nanoparticles; at the same time, the preset height should not be too high to ensure that the switching process between the first and second states of the single-mode fiber optic patch cord 3 is precise, simple, and controllable.

[0054] Figure 3 This is a schematic diagram of a Fabry-Perot resonant cavity provided in an embodiment of this application.

[0055] See Figure 3 As shown, after the end of the single-mode fiber patch cord 3 moves from inside the solution 41 to outside the solution 41, the amplitude and frequency of the wave change over a period of time; therefore, this interference wave is a dynamic interference wave. The change in the reflected light signal is related to the interference in the droplet, which is formed at the end of the single-mode fiber patch cord 3 due to the surface tension of the liquid. The characteristics of the interference wave depend on the optical and geometric parameters of the noble metal nanoparticles on the fiber surface, the interparticle spacing, and the refractive index of the environment.

[0056] See also Figure 3 As shown, after the Fabry-Perot resonator is formed, a semi-transparent mirror is formed inside the liquid. Specifically, a first semi-transparent mirror 3a is formed between the end of the single-mode fiber patch cord 3 and the silane layer droplet; a second mirror 3b is formed between the droplet and the air; a third mirror 3c is formed between the silane layer and the noble metal nanoparticle layer; and a fourth mirror 3d is formed between the noble metal nanoparticle layer and the liquid. Due to the instability of the interfacial liquid-gas system, the second mirror 3b is movable. The lifetime of the Fabry-Perot resonator and the generated interference wave depends on the duration of the droplet's presence, which is related to various factors such as liquid viscosity, ambient temperature, and the presence or absence of vibration. Due to the evaporation of the droplet, the Fabry-Perot resonator is not permanent; its lifetime depends on the lifetime of the droplet. Therefore, it can be reused by repeatedly immersing and pulling the single-mode fiber patch cord 3.

[0057] The appearance of the noble metal nanoparticle layer in the droplet changes the optical parameters and geometry of the Fabry-Perot resonator, and the amplitude and frequency of the dynamic interference wave also change accordingly. This makes the system very sensitive to the presence of the noble metal nanoparticle layer 34 at the end of the single-mode fiber jumper 3.

[0058] To prevent the noble metal nanoparticles 42 from accumulating at the end of the single-mode fiber optic patch cord 3 during this step, the end of the single-mode fiber optic patch cord 3 needs to be treated. Thus, before step S1 is executed, the end of the single-mode fiber optic patch cord 3 can be treated via steps S01 and S02.

[0059] Step S01: Remove the protective sleeve from the single-mode fiber optic patch cord 3.

[0060] In this step, the protective sleeve and the covering layer 31 are peeled off to expose the end face of the fiber core 32.

[0061] Step S02: Modify the end of the single-mode fiber optic patch cord 3 facing the solution 41.

[0062] In this step, the stripped portion of the single-mode fiber optic patch cord 3 can be pretreated with a freshly prepared 3:1 concentrated sulfuric acid / hydrogen peroxide solution ("piranha" solution) to thoroughly remove organic residues and improve the hydrophilicity of the end face. The treatment time should not be too long to avoid damaging the fiber core 32; conversely, the pretreatment time should not be too short to ensure sufficient surface activation. After pretreatment, the cord can be rinsed multiple times with deionized ultrapure water and dried in a nitrogen atmosphere to ensure the end face is clean and uncontaminated, providing a foundation for the uniform adsorption of noble metal nanoparticles 42. The pre-modification treatment time can be controlled between 30 and 60 seconds to balance surface activation efficiency and fiber core 32 integrity. Within 30-60 seconds after mixing, the temperature of the freshly prepared "piranha" solution approaches its boiling point.

[0063] Next, 3-aminopropyltriethoxysilane (APTS) is used to modify the end of the single-mode fiber optic patch cord 3 to form a silane layer 33 at the end of the single-mode fiber optic patch cord 3.

[0064] In this step, anhydrous ethanol or toluene can be used as the reaction solvent. The ethanol system offers mild reaction conditions, is miscible with water, and favors the hydrolysis of 3-aminopropyltriethoxysilane. The volume concentration of APS can be 0.5% to 10%.

[0065] Of course, the above parameters can be adjusted adaptively based on the reaction conditions. For example, heating at 120°C for 30 minutes.

[0066] Figure 4 This is a schematic diagram of the structure of a droplet formed at the end of a single-mode fiber optic patch cord provided in an embodiment of this application.

[0067] See Figure 4 As shown, after pretreatment and modification, the end of the single-mode fiber optic patch cord 3 comes into contact with solution 41 and is then pulled out of solution 41. Due to the surface tension energy modulation effect, a micron-sized hemispherical droplet can be stably formed, and a dual-part reflector structure is formed at the end of the single-mode fiber optic patch cord 3 in the first stage. Specifically, a first semi-transparent reflector 3a is formed between the end of the single-mode fiber optic patch cord 3 and the silane layer, and a second reflector 3b is formed between the droplet and the air. In the second stage, when the self-assembly process of the noble metal nanoparticle layer begins, a third reflector 3c is formed between the silane and the noble metal nanoparticle layer, and a fourth reflector 3d is formed between the noble metal nanoparticle layer and the liquid, together constituting a four-stage reflector system. This fourth-stage dynamic reflector system significantly improves the accuracy of optical path difference control and the stability of interference wave signals, and can capture nanoscale thickness changes with high sensitivity; the droplet curvature radius responds to environmental disturbances in real time, and combined with the modulation effect of the local refractive index of the noble metal nanoparticle layer 34, a dynamically coupled optical resonant cavity is formed, which greatly improves the resolution of surface adsorption events.

[0068] Step S4: The single-mode fiber circulator receives the reflected light from the single-mode fiber optic patch cord; wherein, the reflected light is formed by the reflected detection light from the single-mode fiber optic patch cord 3, the solution 41 includes noble metal nanoparticles 42, and when the single-mode fiber optic patch cord 3 switches from the first state to the second state, there is a droplet at the end of the single-mode fiber optic patch cord 3, and the end of the single-mode fiber optic patch cord 3 and the droplet form a Fabry-Perot resonant cavity with a fourth-order reflector to generate an interference wave.

[0069] In this step, when the single-mode fiber optic patch cord 3 switches from the first state to the second state, the reflected light from the single-mode fiber optic patch cord 3 is received, and the situation of the noble metal nanoparticles 42 can be analyzed based on the interference wave in the reflected light.

[0070] Step S5: Determine the self-assembled dense monolayer state of the noble metal nanoparticles 42 at the end of the single-mode fiber jumper 3 based on the interference wave in the reflected light; wherein, the self-assembled dense monolayer state includes the monolayer saturated state, the monolayer unsaturated state, and the monolayer oversaturated state.

[0071] In this step, the self-assembly density of noble metal nanoparticles 42 can be determined by the amplitude or trough of the interference wave, thereby obtaining the self-assembled dense monolayer state of noble metal nanoparticles 42.

[0072] Specifically, the amplitude is positively correlated with the self-assembled dense monolayer state. In other words, the greater the density of the self-assembled dense monolayer of the noble metal nanoparticle monolayer 42, the stronger the amplitude of the interference wave due to the coupling mode of local surface plasmon resonance. This indicates that the noble metal nanoparticle layer is more compact and more ordered, and the noble metal nanoparticle 42 is more likely to be in a monolayer saturation state.

[0073] The change in the trough can be used as an auxiliary judgment parameter. When the noble metal nanoparticle layer forms an effective dense monolayer and satisfies the matching condition of coupled local surface plasmon resonance mode, the plasmon resonance can capture part of the light energy and enhance the interference wave, which is manifested as an increase in the amplitude of the interference wave and a significant decrease in the trough. When the amplitude reaches its maximum and the frequency tends to stabilize, it can be determined that the noble metal nanoparticles 42 are approaching or have reached a monolayer saturation state. If the amplitude decreases and is accompanied by abnormal changes in the spectral shape, it indicates that the nanoparticles 42 may have aggregated, stacked, or locally detached, thus tending to a monolayer supersaturation state.

[0074] In one specific implementation, step S5 may include steps S51 to S53.

[0075] Step S51: Based on the fact that the single-mode fiber optic patch cord 3 switches between the first state and the second state a preset number of times and the amplitude of the interference wave increases, the self-assembled dense single-layer state at the end of the single-mode fiber optic patch cord 3 is determined to be a single-layer unsaturated state.

[0076] Step S52: Based on the fact that the single-mode fiber optic patch cord 3 switches between the first state and the second state a preset number of times and the amplitude of the interference wave remains unchanged, the self-assembled dense single-layer state at the end of the single-mode fiber optic patch cord 3 is determined to be a single-layer saturated state.

[0077] Step S53: Based on the fact that the single-mode fiber optic patch cord 3 switches between the first state and the second state a preset number of times and the amplitude of the interference wave decreases, the self-assembled dense single-layer state at the end of the single-mode fiber optic patch cord 3 is determined to be a single-layer oversaturated state.

[0078] The preset number of times can be set according to actual experimental needs, such as 3 or 5 times. By switching between the two states and the preset number of times, the adsorption and fixation process of noble metal nanoparticles 42 on the end of the single-mode fiber optic patch cord 3 is simulated. When the amplitude continues to increase after switching the preset number of times, it indicates that new noble metal nanoparticles 42 can be successfully adsorbed onto the end surface of the single-mode fiber optic patch cord 3 with each switch, and the maximum adsorption amount has not yet been reached, so it is judged as a single-layer unsaturated state; if the amplitude remains stable after switching the preset number of times, it indicates that the sites on the fiber end surface that can be used for the self-assembly of noble metal nanoparticles have been basically occupied, and further state switching cannot significantly increase the adsorption amount of nanoparticles, at which point it is in a single-layer saturated state; when the amplitude decreases, it may be due to excessive state switching causing the adsorbed nanoparticle layer to agglomerate, stack, or partially detach, resulting in a reduction in the number of noble metal nanoparticles 42 that effectively participate in interference, so it is judged as a single-layer oversaturated state.

[0079] Furthermore, in the first stage, where only the silane layer and droplet are formed—that is, in the Fabry-Perot resonant structure composed of two reflective interfaces—the frequency of the dynamic interference wave mainly depends on the viscosity, optical parameters, and geometric parameters of the silane and liquid layers, and gradually increases with the evaporation of the liquid in the droplet. When noble metal nanoparticles begin to appear at the fiber end face and form the second-stage four-reflective interface structure, the frequency of the dynamic interference wave is also related to the saturation degree and geometric morphology of the noble metal nanoparticle layer; when the noble metal nanoparticle layer completes saturated assembly, the frequency of the dynamic interference wave tends to stabilize.

[0080] Therefore, the maximum amplitude, trough variation, and frequency stability of the dynamic interference wave can be combined to comprehensively determine whether the noble metal nanoparticle layer has formed an effective dense monolayer.

[0081] The method for detecting the self-assembled dense monolayer state of noble metal nanoparticles on the surface of optical fibers provided in this application uses a spectrometer 6 to analyze the amplitude and frequency changes of interference waves in the reflected light in real time. A single common optical fiber is used for detection. By observing the dynamic interference waves, the self-assembled dense monolayer state of the noble metal nanoparticles 42 is determined, avoiding nanoparticle aggregation. This reveals the effective dense stacking of the monolayer noble metal nanoparticles 42, which can achieve coupling of local surface plasmon resonance modes and their electric field enhancement. During the detection process, the preparation of the noble metal nanoparticles 42 is simple, requiring no strong solvents and having no strict requirements on reagent purity and pH environment. Multiple noble metal nanoparticles 42 can be of the same or different sizes, greatly reducing preparation costs and operational complexity, enabling large-scale preparation, and allowing for on-site control and real-time operation.

[0082] Figure 5 This application provides an embodiment of the optical reflection spectrum of a single-mode fiber optic patch cord tail measured in air, water, and after being lifted out of the water and forming a droplet.

[0083] See Figure 5 As shown, the horizontal axis represents Wavelength, measured in nanometers (nm), covering the range of 1400nm-1700nm, which falls within the near-infrared light range. The vertical axis represents Intensity, au (relative light intensity).

[0084] In the overall intensity comparison, the reflected light from the end of the single-mode fiber optic patch cord 3 is strongest in air, moderate when water droplets are attached, and weakest when completely submerged in water. Therefore, the water environment state (air / water immersion / droplets) of the end of the single-mode fiber optic patch cord 3 can be accurately distinguished by the spectrum.

[0085] Figure 6 This is a schematic diagram of a Fabry-Perot resonant cavity during the noble metal nanoparticle covering process at the end of a single-mode fiber optic patch cord, as provided in an embodiment of this application; wherein, Figure 6 In (a), it is shown that the end of the single-mode fiber optic patch cord 3 with silane layer 33 is in contact with the solution 41 of noble metal nanoparticles 42. Figure 6 (b) represents the process of lifting the single-mode fiber optic patch cord 3 from the liquid and starting to adsorb noble metal nanoparticles 42; Figure 6 (c) indicates repeated switching between the first and second states, observing the increase in dynamic interference wave amplitude caused by the coupling mode of local surface plasmon resonance. At this time, a densely packed monolayer of noble metal nanoparticles 34 is formed at the end of the single-mode fiber jumper 3. Figure 6 In the middle (d), it indicates that the switching between the first state and the second state is repeated. It is observed that the amplitude of the dynamic interference wave decreases. At this time, noble metal nanoparticles are generated at the end of the single-mode fiber jumper 3, and the noble metal nanoparticles 42 are oversaturated.

[0086] See Figure 6 As shown, no similar amplitude amplification of the dynamic interference wave was observed for the sparse noble metal nanoparticle layer 34 and the supersaturated capping layer. The observable phenomenon of localized surface plasmon resonance is due to the generation of coupled localized surface plasmon resonance modes in the noble metal nanoparticle layer 34. In both cases, the sparse noble metal nanoparticles and the nanoparticle aggregate layer cannot be excited by coupled localized surface plasmon resonance modes, and therefore do not produce an increase in the amplitude of the interference wave.

[0087] Figure 7 This is an embodiment of the present invention, showing normalized spectra measured during the gold nanoparticle coating process and scanning electron microscopy imaging of a single-mode fiber optic patch cord end layer of gold nanoparticles. Figure 8 This is an embodiment of the present invention, showing normalized spectra measured during the silver nanoparticle coating process and scanning electron microscopy imaging of a single-mode fiber optic patch cord end silver nanoparticle monolayer.

[0088] Combination Figure 7 and Figure 8 As shown, Figure 7 The horizontal axis represents Wavelength (in nanometers, nm), and the vertical axis represents Intensity (aunom, normalized relative intensity). Figure 8The horizontal axis represents Wavelength (nm), and the vertical axis represents Intensity (dB, logarithmic relative intensity). When highly conductive noble metal nanoparticles 42 are present at the end of the single-mode fiber jumper 3, and the coupling localized surface plasmon resonance mode matching condition is met, the amplitude of the interference wave increases. Plasmon resonance oscillations capture some light energy and enhance the interference wave, which manifests as an increase in amplitude and a significant decrease in the trough. By comparing the dynamic interference wave amplitude values ​​of the end of the single-mode fiber jumper 3 after immersion in the nanoparticle colloidal solution 41 for different times, the occurrence time of the coupling localized surface plasmon resonance mode of the gold and silver noble metal nanoparticle layer 34 can be easily found. Scanning electron microscopy imaging of the obtained noble metal nanoparticle layer 34 shows that the short-term generation of the observed coupling localized surface plasmon resonance mode, i.e., the maximum dynamic interference wave amplitude, corresponds to the formation of an effective dense monolayer of nanoparticles.

[0089] It should be noted that, upon considering the specification and practicing the application disclosed herein, those skilled in the art will readily conceive of other embodiments of this application. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

[0090] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The true scope is indicated by this application.

Claims

1. A method for detecting the state of a dense monolayer of noble metal nanoparticles self-assembled on an optical fiber surface, characterized in that, include: A broadband light source sends detection light to a single-mode fiber optic circulator. The single-mode fiber circulator receives the detection light and transmits the detection light to the single-mode fiber patch cord; wherein, the bottom of the single-mode fiber patch cord has its protective sleeve and cladding stripped off. The single-mode fiber optic patch cord is controlled to switch between a first state and a second state; the first state is that the end of the single-mode fiber optic patch cord is located inside the solution, and the second state is that the end of the single-mode fiber optic patch cord is located outside the solution and at a preset height position. The single-mode fiber circulator receives the reflected light from the single-mode fiber patch cord; wherein the reflected light is formed by the detection light reflected by the single-mode fiber patch cord, the solution includes noble metal nanoparticles, and when the single-mode fiber patch cord switches from the first state to the second state, a droplet is present at the end of the single-mode fiber patch cord, and the end of the single-mode fiber patch cord and the droplet form a Fabry-Perot resonant cavity to generate interference waves; The self-assembled dense monolayer state of the noble metal nanoparticles at the end of the single-mode fiber jumper is determined based on the interference wave in the reflected light; wherein, the self-assembled dense monolayer state includes a monolayer saturated state, a monolayer unsaturated state, and a monolayer supersaturated state.

2. The method for detecting the state of self-assembled dense monolayer of noble metal nanoparticles on optical fiber surface according to claim 1, characterized in that, Determining the self-assembled dense monolayer state of the noble metal nanoparticles at the end of the single-mode fiber jumper based on the interference wave includes: The self-assembled dense monolayer state of the noble metal nanoparticles at the end of the single-mode fiber jumper is determined based on the amplitude or trough of the interference wave.

3. The method for detecting the state of self-assembled dense monolayer of noble metal nanoparticles on optical fiber surface according to claim 2, characterized in that, Determining the self-assembled dense monolayer state of the noble metal nanoparticles at the end of the single-mode fiber jumper based on the interference wave includes: Based on the fact that the single-mode fiber optic patch cord switches between the first state and the second state a preset number of times, and the amplitude of the interference wave increases, the self-assembled dense single-layer state at the end of the single-mode fiber optic patch cord is determined to be a single-layer unsaturated state. Based on the fact that the single-mode fiber optic patch cord switches between the first state and the second state a preset number of times, and the amplitude of the interference wave remains unchanged, the self-assembled dense single-layer state at the end of the single-mode fiber optic patch cord is determined to be a single-layer saturated state. Based on the fact that the single-mode fiber optic patch cord switches between the first state and the second state a preset number of times, and the amplitude of the interference wave decreases, the self-assembled dense single-layer state at the end of the single-mode fiber optic patch cord is determined to be a single-layer oversaturated state.

4. The method for detecting the state of self-assembled dense monolayer of noble metal nanoparticles on optical fiber surface according to claim 1, characterized in that, Before the broadband light source sends detection light to the single-mode fiber circulator, the method for detecting the state of the dense monolayer self-assembled by noble metal nanoparticles on the fiber surface further includes: Remove the protective sleeve from the single-mode fiber optic patch cord. The end of the single-mode fiber optic patch cord facing the solution is modified.

5. The method for detecting the state of self-assembled dense monolayer of noble metal nanoparticles on optical fiber surface according to claim 1, characterized in that, The single-mode fiber optic patch cord is modified at the end facing the solution, including: The ends of the single-mode fiber optic patch cord were pretreated with a mixed solution of concentrated sulfuric acid and hydrogen peroxide. The end of the single-mode fiber optic patch cord is modified with 3-aminopropyltriethoxysilane to form a silane layer at the end of the single-mode fiber optic patch cord.

6. The method for detecting the state of self-assembled dense monolayer of noble metal nanoparticles on optical fiber surface according to claim 1, characterized in that, The plane at the end of the single-mode fiber optic patch cord is parallel to the surface of the solution.

7. The method for detecting the state of self-assembled dense monolayer of noble metal nanoparticles on the surface of optical fibers according to any one of claims 1-6, characterized in that, The precious metal nanoparticles include all types of gold nanoparticles or silver nanoparticles. Among them, the noble metal nanoparticles may be the same or different in size, and the surface of the noble metal nanoparticles may be covered with an organic layer or not.

8. A device for self-assembly of noble metal nanoparticles on the surface of an optical fiber, characterized in that, The optical fiber surface noble metal nanoparticle self-assembly dense monolayer state detection method according to any one of claims 1-7, wherein the optical fiber surface noble metal nanoparticle self-assembly device comprises: A broadband light source is configured to transmit detection light; A single-mode fiber circulator, wherein the first end of the single-mode fiber circulator is connected to the broadband light source and is configured to receive the detection light; A single-mode fiber optic patch cord, one end of which is connected to the second end of the single-mode fiber circulator, is configured to receive the detection light and generate reflected light; A standard photometric cuvette is positioned opposite the single-mode fiber optic patch cord, and the standard photometric cuvette contains a solution containing noble metal nanoparticles. A height-adjustable worktable is provided, wherein the standard photometric cuvette is disposed on the height-adjustable worktable, and the height-adjustable worktable is configured to move the standard photometric cuvette toward or away from the single-mode fiber optic patch cord, so that the single-mode fiber optic patch cord switches between a first state and a second state. A spectrometer, connected to the third end of the single-mode fiber circulator, is configured to receive the reflected light and determine the self-assembled dense monolayer state of the noble metal nanoparticles at the end of the single-mode fiber jumper based on the interference wave in the reflected light.

9. The optical fiber surface noble metal nanoparticle self-assembly device according to claim 8, characterized in that, The height-adjustable worktable is also configured to move the standard photometric cuvette along a first direction so that the single-mode fiber optic patch cord is in the first state. The height-adjustable worktable is also configured to move the standard photometric cuvette along a second direction so that the single-mode fiber optic patch cord is in the second state; the first direction and the second direction are opposite to each other.

10. The optical fiber surface noble metal nanoparticle self-assembly device according to claim 9, characterized in that, The height-adjustable worktable includes: First installation platform; The second mounting platform, which is set opposite to the first mounting platform, is configured to hold the standard photometric cuvette; A drive unit is connected between the first mounting platform and the second mounting platform, and the drive unit is configured to drive the second mounting platform to move relative to the first mounting platform.

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