Cascaded omega-shaped optical fiber probe, sensor and application thereof

Abstract

The invention relates to the field of biosensing, in particular to a cascaded omega-shaped optical fiber probe, a sensor and application thereof. And cancer cell diagnosis and treatment are integrated fundamentally through a photon-substance synergistic effect. The engineered Omega-topology induces significant modal recoupling effects and controls bend-induced losses, creates local photon hotspots, resulting in extraordinary refractive index sensitivity (962.9 nm / RIU). Therefore, the MCF-7 cells can be quantitatively detected at an ultra-low detection limit (2.1 cells / mL). Meanwhile, the waveguide is converted into a plasma nanometer heater through nanometer texture Au-NBP functionalization. Under the excitation of 808 nm laser, limited light energy is converted into heat energy through non-radioactive relaxation, and local temperature rise of delta T = 111 DEG C is generated in the environment. This spatio-temporal limited high temperature achieves efficient cell ablation (71.7% mortality) by protein denaturation. The deterministic integration of sensing-activation capabilities in a single microfiber device represents a normal form transition to an early cancer closed-loop treatment system.

Description

Technical Field

[0001] This invention relates to the field of biosensing, specifically to cascaded Ω-shaped fiber optic probes, sensors, and their applications. Background Technology

[0002] Fiber optic sensors have demonstrated significant application potential in the detection of cells and bacteria, with their core advantages lying in their ultra-high detection sensitivity, excellent resistance to electromagnetic interference, and support for real-time dynamic monitoring under minimally invasive interventions. However, current research paradigms in fiber optic-based diagnostic and therapeutic technologies are significantly biased towards in-situ analysis, with a noticeable lag in research on the dynamic clearance and monitoring of harmful cells and bacteria. Therefore, existing systems still face challenges: at the structural level, miniaturized flexible probes suitable for vascular implantation have not yet been achieved; regarding the treatment cycle, the kinetic efficiency of photothermal response needs improvement to accelerate the treatment rate; most critically, the physical mechanism of photothermal therapy (PTT) remains unclear, especially at the fiber-cell interface, where it is difficult to determine whether the radiation mode or the evanescent wave plays a dominant role in photothermal conversion, directly limiting the precise control and performance optimization of device treatment efficiency. Summary of the Invention

[0003] To address the challenge of unclear interaction mechanisms between evanescent fields and radiative modes in existing technologies, this paper proposes an M–N–M cascaded Ω-shaped fiber probe and sensor. This structure is based on a triple-coupled photonic mechanism: the M–N–M cascade, through mode mismatch, promotes the redistribution of optical energy and enrichment in the cladding, significantly enhancing the evanescent field energy density; the Ω-shaped bending structure, through bending-induced loss and mode reconstruction, enhances the escape power of radiative modes while exciting more higher-order modes, synergistically expanding the spatial distribution and local intensity of the evanescent field. By adjusting the bending diameter and cascade length, the energy ratio of the evanescent field and the radiative field can be actively adjusted, thereby clarifying the dominant mechanism in photothermal therapy. This overcomes the limitations of ambiguity and insufficient efficacy in traditional fiber optic sensing, providing a quantitatively controllable photonic platform for the dynamic and precise removal of harmful cells and bacteria.

[0004] The specific plan is as follows: A cascaded Ω-shaped fiber probe, wherein the cascaded Ω-shaped fiber probe contains an Ω-shaped M–N–M structure, wherein the MNM structure is composed of coreless fiber (NCF) and multimode fiber (MMF) with the coating removed, wherein the two ends of the coreless fiber are respectively connected to two segments of the multimode fiber, and the surface of the MNM structure contains gold nanoparticles (Au NBPs).

[0005] The introduction of NCF in the cascaded structure leads to mode mismatch at the MMF-NCF interface, significantly increasing the proportion of higher-order modes in subsequent transmission. Its stronger transverse field component effectively enhances the evanescent field intensity on the fiber surface. Meanwhile, the Ω-shaped high-curvature structure disrupts the total internal reflection condition, forcing some of the transmitted light to leak out in the form of radiation, simultaneously enhancing both the evanescent field and the intensity of the radiated field diverging into the environment. The synergistic effect of these two physical mechanisms allows this cascaded structure to significantly enhance sensor performance, dramatically improve the detection sensitivity to changes in environmental refractive index, and enhance the application potential based on the photothermal conversion effect of the probe surface material.

[0006] Furthermore, the coreless optical fiber cladding diameter is 125 μm. Furthermore, the connection is a fusion weld.

[0007] Furthermore, the LSPR absorption peak dominated by the gold nanoparticles is 760 nm–880 nm. Preferably, the LSPR absorption peak dominated by the gold nanoparticles is 810 nm.

[0008] Furthermore, the gold nanoparticles are selected from conical gold nanoparticles or a mixture of conical and spherical gold nanoparticles.

[0009] The conical particles are selected from nanostars, nanorods, and bipyramids; preferably, the conical particles are bipyramids.

[0010] Preferably, the gold nanoparticles are a mixture of conical and spherical gold nanoparticles; more preferably, the average major axis of the mixture is 55 nm.

[0011] This invention chooses conical gold nanoparticles because they exhibit a hotspot effect. When light shines on a conical (or pointed) gold nanostructure, the electromagnetic field near the tip is greatly enhanced, forming a highly concentrated micro-region, known as a "hotspot." Essentially, this utilizes the sharp geometry of the nanoparticles to compress and significantly enhance light energy within a nanoscale space through localized surface plasmon resonance and a lightning rod effect, resulting in more and stronger hotspots. The two tips of a single conical gold nanostructure (such as a nanorod) can form a powerful hotspot. When the tips of two or more conical gold nanoparticles approach each other (forming a nanogap, such as a few nanometers or even sub-nanometers), a coupling effect occurs, exciting a stronger "gap hotspot" than a single-tip hotspot.

[0012] When conical and spherical gold nanoparticles are mixed, a synergistic effect is achieved. First, as mentioned above, conical particles exhibit a hotspot effect, while spherical particles act as hotspot "couplers" and "amplifiers" for these particles. When a spherical particle approaches the tip of a conical particle, a gap hotspot is formed. The electromagnetic field enhancement intensity of this gap is far higher than that generated by a single tip, because the plasma oscillations of the two particles are strongly coupled. Second, from a synthetic perspective, mixed conical and spherical nanoparticles are easier to prepare than simple conical nanoparticles. The introduction of spherical particles can reduce fluctuations in the detection signal and improve measurement reproducibility, because the hotspot no longer depends solely on the extremely small and potentially unevenly distributed region at the tip of the conical particle. The simultaneous addition of conical and spherical gold nanoparticles essentially involves the intelligent combination of a "stable building block" (sphere) and a "powerful enhancement engine" (cone). This strategy maximizes the utilization of the plasma coupling effect, achieving extremely high electromagnetic field enhancement while maintaining structural stability, spectral tunability, and fabrication feasibility.

[0013] The term "localized surface plasmon resonance" refers to the collective oscillation of free electrons in gold nanostructures driven by light (electromagnetic waves). Resonance occurs when the frequency of the light matches the intrinsic frequency of the electron collective oscillation. At this point, the nanostructure efficiently absorbs and scatters light, and the electromagnetic field is strongly localized on and around the surface of the structure.

[0014] The term "lightning rod effect" refers to the high concentration of electron charge density at the tip of a cone or sharp curve, which causes the electromagnetic field to be amplified several times more at the tip than in flat areas.

[0015] Furthermore, the bending radius of the MNM structure is 0.4 mm - 1.4 mm, and the length of the coreless optical fiber is 0.4 cm - 1.2 cm. In some embodiments, the bending radius is selected from 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, and 1.3 mm, and the length of the coreless optical fiber is selected from 0.4 cm, 0.5 cm, 0.6 cm, 0.7 cm, 0.8 cm, 0.9 cm, 1.0 cm, 1.1 cm, and 1.2 cm.

[0016] In some embodiments, the bending radius is selected from 0.4 mm, 0.6 mm, 0.8 mm, 1.1 mm, and 1.3 mm, and the length of the coreless optical fiber is selected from 0.4 cm, 0.6 cm, 0.8 cm, 1.0 cm, and 1.2 cm.

[0017] Preferably, the bending radius is 0.4 mm-1.4 mm, and the length of the coreless optical fiber is 0.4 cm-0.8 cm.

[0018] On the other hand, the present invention discloses a method for preparing the cascaded Ω-shaped optical fiber probe, which is as follows: a coreless optical fiber is fused together in the middle of a multimode optical fiber with the coating removed to form an MNM cascade structure, and then it is bent into an Ω-shaped structure with a specific curvature diameter by a thermoforming process, and then the surface of the Ω-shaped structure is modified with nano-gold.

[0019] Preferably, the preparation method is as follows: (1) Select a 250 μm cladding multimode fiber (MMF) and strip the coating layer using wire strippers; (2) The part with the coating removed is artificially cut into two parts, and coreless fiber (NCF) is fused at the cut position to form an MNM cascade structure; (3) The MNM cascade structure is placed on a butane flame and bent into an Ω-shaped structure with a specific curvature diameter under the action of external force.

[0020] (4) Modify the surface of the Ω-shaped structure with nano-gold.

[0021] Preferably, the length of the coating layer to be peeled off is 0-3 cm, and in some embodiments, the length can be selected as 0 cm, 0.1 cm, 0.2 cm, 0.3 cm, 0.4 cm, 0.5 cm, 0.6 cm, 0.7 cm, 0.8 cm, 0.9 cm, 1.0 cm, 1.1 cm, 1.2 cm, 1.3 cm, 1.4 cm, 1.5 cm, 1.6 cm, 1.7 cm, 1.8 cm, 1.9 cm, 2.0 cm, 2.1 cm, 2.2 cm, 2.3 cm, 2.4 cm, 2.5 cm, 2.6 cm, 2.7 cm, 2.8 cm, 2.9 cm, or 3.0 cm.

[0022] More preferably, the length of the coating layer being peeled off is 2 cm to 3 cm.

[0023] On the other hand, the present invention discloses a cascaded Ω-shaped fiber optic probe biosensor, the biosensor comprising the aforementioned cascaded Ω-shaped fiber optic probe.

[0024] On the other hand, the present invention discloses an experimental apparatus, which includes the cascaded Ω-shaped optical fiber probe or the biosensor.

[0025] Furthermore, the experimental apparatus also includes an output device, a detector, an optical fiber patch cord, and a light source. The light source includes a communication light source and a laser light source. One end of the cascaded Ω-shaped optical fiber probe or the cascaded Ω-shaped optical fiber probe biosensor couples the communication light source and the laser light source to the probe via the optical fiber patch cord. The other end of the cascaded Ω-shaped optical fiber probe or the cascaded Ω-shaped optical fiber probe biosensor is connected to the input end of the detector. The output end of the detector is connected to the output device via the optical fiber patch cord. Preferably, the laser light source is a 760-880 nm laser light source, and more preferably, the laser light source is an 808 nm laser.

[0026] Based on the lasers available on the market, 808 nm is the most suitable. Near-infrared lasers in the 760-880 nm band are also effective.

[0027] The core mechanism by which the sensor achieves ablation relies on the precise size control of Au NBPs, allowing their long-axis-dominated LSPR absorption peak to be precisely matched to 810 nm. This resonates with the 808 nm laser wavelength, exciting a nonradiative relaxation process. This converts incident photon energy into lattice thermal energy through electron-phonon coupling, resulting in a controllable temperature rise at the fiber / cell interface. This design integrates the dual functions of "sensing and ablation": LSPR displacement enables real-time cell detection, while near-infrared resonance-enhanced photothermal effect achieves in-situ cell ablation.

[0028] On the other hand, the present invention discloses the application of the cascaded Ω-shaped fiber optic probe, the biosensor, and the experimental device in the fields of cancer cell detection and photothermal therapy.

[0029] Definitions: The term "harmful cells" refers to cells such as tumor cells and cancer cells that are detrimental to an organism.

[0030] The term "multimode fiber (MMF)" refers to an optical fiber designed to transmit multiple optical modes (i.e., multiple light paths) simultaneously. The "mode" in "multimode" refers to the electromagnetic field distribution pattern of the light wave. Due to its relatively large core diameter, light incident from a light source can be received at multiple different angles and propagate forward within the core via "total internal reflection" or "refraction," thus forming multiple different propagation paths. The structure of a multimode fiber, from the inside out, includes the core, cladding, and coating. The core is made of high-purity silica glass, doped with impurities (such as germanium) to increase its refractive index, and is the main channel for light transmission. The cladding is also high-purity silica glass, but its refractive index is intentionally designed to be slightly lower than that of the core, using the principle of total internal reflection to confine the light forward within the core. The coating is typically one or more layers of UV-cured acrylate resin or silicone; its main purpose is to protect the fragile glass fiber from damage.

[0031] The term "coreless fiber (NCF)," also known as "hollow-core fiber" or "hollow-core photonic crystal fiber," refers to a type of optical fiber whose core region consists of air (or vacuum). Light waves primarily propagate through the air channel, but this revolutionary fiber confines light propagation within the air through microstructural effects such as photonic bandgap or anti-resonance. It features a structure with periodic microstructure cladding or an anti-resonant glass ring cladding.

[0032] The term "functionalization" refers to the modification of optical fiber surfaces with functional groups through physical and / or chemical means. These "functional groups" are atoms or groups of atoms that determine the chemical properties of organic compounds. They play a crucial role in organic chemical reactions and determine the properties of organic substances. Common functional groups include amino (-NH2), hydroxyl (-OH), carboxyl (-COOH), ether (RO-R'), aldehyde (-CHO), and carbonyl (C=O).

[0033] The terms "subject" and "patient" are used interchangeably and refer to a mammal in need of treatment, such as companion animals (e.g., dogs, cats, etc.), farm animals (e.g., cattle, pigs, horses, sheep, goats, etc.), and laboratory animals (e.g., rats, mice, guinea pigs, etc.). Typically, a subject is a person in need of treatment. In some implementations, the term "subject" refers to a person with a disease requiring treatment.

[0034] The term "cascaded Ω-shaped fiber" includes an MNM cascade structure and a multimode fiber portion with the coating intact. The multimode fiber portion with the coating intact facilitates connection to a light source and detector (or "spectrometer"), while also preventing damage to the MNM cascade structure. The term "cascaded Ω-shaped fiber probe" refers to a "cascaded Ω-shaped fiber" functionalized with gold nanoparticles on an MNM cascade structure; in this case, the MNM cascade structure can be called a "probe." The term "cascaded Ω-shaped fiber probe sensor" refers to a cascaded Ω-shaped fiber probe further modified with aptamers, antigens, antibodies, or other recognition molecules to bind to the detection substance. The recognition molecule corresponds to the detection substance and can bind specifically or non-specifically.

[0035] The term "NCF length" refers to the length of N in MNM.

[0036] The term "fusion splicing" refers to connecting optical fibers using a fiber optic fusion splicer under the action of electrical discharge.

[0037] The term "conical gold nanoparticles" refers to gold nanoparticles that are rhomboid, conical, or similar in shape, with a larger middle and gradually smaller or pointed ends.

[0038] The term "spherical gold nanoparticles" refers to gold nanoparticles that are spherical, ellipsoidal, or near-spherical in shape.

[0039] Beneficial effects: The sensor of this invention can achieve a rapid photothermal response within 1.3 seconds, with a steady-state temperature of 110 ± 2.4°C and a refractive index sensitivity of 962.9 nm / RIU.

[0040] The sensor’s compact size further enhances its advantages for minimally invasive fiber optic diagnostics and treatment.

[0041] The sensing platform couples a broadband light source and laser to the probe via a Y-type fiber optic coupler. The laser excites a photothermal effect on the probe surface; the transmitted light signal is acquired by a spectrometer and analyzed by a computer to detect changes in the external environment. To achieve integrated sensing and ablation functions, the probe surface is functionalized using a self-assembly process. Au NBPs on the probe surface are modified to have an optimized aspect ratio and combined with a T-type aptamer, endowing the sensor with both sensing and cell ablation capabilities. Attached image description: To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of the fabrication process for a cascaded Ω-shaped fiber optic probe.

[0043] Figure 2 For the surface functionalization and characterization of cascaded Ω-shaped optical fibers: (a) SEM morphology of Au NBPs; (b) Absorption spectrum of AuNBPs (Inset: colloidal image and major-to-minor diameter statistics, average major-to-minor diameter 55 nm); (c) and (d) are SEM verification of AuNBP modification on the optical fiber surface; (d) is a local magnification of the image in (c).

[0044] Figure 3 This is a schematic diagram of the experimental setup.

[0045] Figure 4 Co-optimization of dual-parameter performance by bending diameter (NCF length = 0.6 cm). (a) Maximum temperature rise at the sensing interface under different bending diameters; (b) Statistical distribution of local temperature rise; (c) Statistical analysis of the wavelength of the characteristic peak of LSPR (RIS).

[0046] Figure 5 Co-optimization of NCF length on dual-parameter performance (bending diameter = 0.4 mm): (a) maximum temperature rise of the sensing interface under different NCF lengths; (b) statistical distribution of local temperature rise; (c) statistical analysis of LSPR characteristic peak wavelength RIS.

[0047] Figure 6 Photothermal efficiency and therapeutic efficacy of cascaded Ω-shaped fiber optic sensors. (a) Comparison of heating efficiency between cascaded Ω-shaped fiber optic sensors and plastic-coated fiber optic sensors. (b) Heating efficiency of the Ω-shaped fiber optic sensor as a function of incident laser power (808 nm). (c) Thermal cycling stability during six consecutive heating-cooling cycles. (d) Fitted heating and cooling curves show rapid thermal response. (e) Schematic diagram of the photothermal therapy (PTT) mechanism utilizing localized surface heating. (f) Controlled temperature regulation of the sensor surface at the treatment setpoint (49.7 °C).

[0048] Figure 7 The cell capture performance of the Ω-shaped fiber optic sensor. (a) Schematic diagram of the principle of the Ω-shaped fiber optic sensor capturing MCF-7 cells. (b) Normalized characteristic spectrum of single concentration (2×10⁻⁶). (c) Fitting curve of the center wavelength shift of the characteristic peak in single concentration detection. (d) Normalized characteristic spectrum of concentration gradient (5×10⁻⁶) drop experiment. (e) Dynamic response of the center wavelength shift of the characteristic peak in the concentration gradient drop experiment. (f) Linear relationship between the center wavelength shift of the characteristic peak in the concentration gradient drop experiment and the logarithm of cell concentration. (gj) Fluorescence analysis of the control group (no laser irradiation): (g) Calcium ion-AM staining (green) indicates live cells. (h) Propidium iodide (PI) staining (red) indicates dead cells. (i) Combined image of (g) and (h). (j) Calculation of quantitative cell death rate in the control group. (kn) Fluorescence analysis of the experimental group (after PTT irradiation): (k) Calcium ion-AM staining. (l) PI staining. (m) Combined image of (k) and (l). (n) Quantitative cell death rate after PTT treatment. 4 cells / mL 2 -5×10 4 cells / mL Detailed Implementation

[0049] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application. Reagents not specifically marked with their source in this application are all conventional commercially available products.

[0050] Example 1: Fabrication of a Cascaded Ω-Shaped Fiber Optic Probe 1. The fabrication process of cascaded Ω-shaped optical fibers is as follows: Figure 1 As shown, a coreless fiber is fused together in the middle of a multimode fiber with the coating removed to form an MNM cascade structure, which is then bent into an Ω-shaped structure with a specific curvature diameter through a thermoforming process.

[0051] Specifically as follows: (1) Select 250 μm cladding multimode fiber (MMF) and strip the coating layer using wire strippers; (2) The part with the coating removed is artificially cut into two parts, and coreless fiber (NCF) is fused at the cut position to form an MNM cascade structure; (3) The MNM cascade structure is placed on a butane flame and bent into an Ω-shaped structure with a specific curvature diameter under the action of external force.

[0052] In the cascaded structure, the length of the NCF is 0.4 cm - 1.2 cm, and can be selected from 0.4 cm, 0.5 cm, 0.6 cm, 0.7 cm, 0.8 cm, 0.9 cm, 1.0 cm, 1.1 cm, and 1.2 cm. In this embodiment, the coreless fiber cladding diameter is 125 micrometers, and the fiber type is: Yangtze Optical Fibre and Cable, CL 0-125-0-250.

[0053] The length of the coating layer to be peeled off is 0 cm to 3 cm, and can be selected from 0 cm, 0.1 cm, 0.2 cm, 0.3 cm, 0.4 cm, 0.5 cm, 0.6 cm, 0.7 cm, 0.8 cm, 0.9 cm, 1.0 cm, 1.1 cm, 1.2 cm, 1.3 cm, 1.4 cm, 1.5 cm, 1.6 cm, 1.7 cm, 1.8 cm, 1.9 cm, 2.0 cm, 2.1 cm, 2.2 cm, 2.3 cm, 2.4 cm, 2.5 cm, 2.6 cm, 2.7 cm, 2.8 cm, 2.9 cm, and 3.0 cm.

[0054] In this embodiment, the length of the coating layer to be peeled off is selected as 2.4 cm.

[0055] In this embodiment, the welding is performed using a Japanese Fujikura welding machine in a multi-mode configuration.

[0056] The specific step (2) can be performed as follows: use a fiber optic cleaver to cut the multimode fiber into two parts; fused one end of a coreless fiber at the cut point of one part; after cutting and fusion of the coreless fiber to a specific length, connect the other end of the coreless fiber to the cut point of the other part to form an MNM cascade structure.

[0057] 2. Synthesis of Au NBPs (1) Preparation of seed solution: HAuCl aqueous solution (0.01 M, 0.125 mL) and trisodium citrate solution (0.01 M, 0.25 mL) were added together to 9.625 mL of deionized water, followed by rapid addition of freshly prepared NaBH solution (0.01 M, 0.15 mL) under vigorous stirring. An orange-red gold nanoparticle seed solution was obtained after the reaction. This solution was aged at room temperature for at least 2 hours to ensure complete hydrolysis of unreacted NaBH, ultimately forming a stable pink seed solution. 444 (2) Preparation of growth solution: Take 40 mL of cetyltrimethylammonium bromide (CTAB) solution (0.1 M), and add HAuCl solution (2 mL), AgNO solution (10 mM, 0.4 mL), HCl solution (1.0 M, 0.6 mL), and ascorbic acid (AA, 0.1 M, 0.32 mL) sequentially. After each addition, stir vigorously until the solution is homogeneous. After adding AA, the solution changes from light yellow to colorless as Au is reduced to Au. Then, inject 0.3 mL of the seed solution prepared above into the growth solution. Place the mixture in a 30℃ water bath overnight to allow gold nanobipyramidal structures (Au NBPs) to grow gradually. During the process, the growth solution gradually changes from colorless and transparent to purplish-red, indicating the formation of Au NBPs. The final product is centrifuged (9000 r / min, 15 min), the precipitate is collected and redispersed in deionized water for subsequent use. 43 3++ (3) Ligand exchange method to modify Au NBPs solution Take 8 mL of the synthesized Au NBPs solution and add 0.8 mL of sodium polystyrene sulfonate (PSS) solution (solvent: 5 mM NaCl solution, PSS concentration: 0.01 g / mL). React in a 30°C water bath for 1 hour. After the reaction, centrifuge the mixture at 9000 r / min for 15 minutes, discard the supernatant, and redisperse the resulting precipitate in 8 mL of deionized water. Repeat the above PSS modification and centrifugation washing process once. Disperse the final precipitate in a mixture of 2 mL of deionized water and 6 mL of citrate solution (5 mM), and incubate in a 30°C water bath for 12 hours to achieve the replacement of the surface ligand from CTAB to citrate. Then centrifuge again at 9000 r / min for 15 minutes and remove the supernatant. Finally, disperse the precipitate in a mixture of 1 mL of deionized water and 3 mL of citrate solution to obtain an Au NBPs dispersion stably coated with citrate ions.

[0058] The results are as follows Figure 2 As shown in a, Figure 2a) shows the SEM morphology of Au NBPs, revealing that the synthesized Au NBPs are a mixture of conical and spherical particles. Figure 2 b statistically analyzed the average major diameter of the colloid, and it can be seen that the average major diameter is 55 nm.

[0059] 3. Fabrication of Cascaded Ω-Shaped Fiber Optic Probes The surface functionalization of the MNM cascade structure (sensing region) was performed using a self-assembly method.

[0060] Specifically as follows: (1) The sensing area was immersed in a piranha solution (the volume ratio of concentrated sulfuric acid to hydrogen peroxide was 3:1) for 30 minutes to achieve surface hydroxyl functionalization; (2) Subsequently, it was placed in a 4% APTES hydrolysis solution (the volume ratio of APTES, ethanol and deionized water was 1:23:1) and reacted for 50 minutes to introduce amino functional groups; (3) The probe was immersed in a solution of Au NBPs coated with citrate, and Au NBPs nanoparticles were modified on its surface by electrostatic adsorption and coordination to prepare a cascaded Ω-shaped fiber probe.

[0061] The results are as follows Figure 2 As shown in Figures b-2d, Figure 2b illustrates the precise matching of the LSPR absorption peak dominated by the long axis of Au NBPs to 810 nm. The core mechanism by which the sensor achieves ablation relies on the precise size control of Au NBPs. The synergistic resonance between the 810 nm and 808 nm laser wavelengths excites a nonradiative relaxation process, converting the incident photon energy into lattice thermal energy through electron-phonon coupling, resulting in a controllable temperature rise at the fiber / cell interface. Figure 2 c and 2d confirm that Au NBPs were successfully applied to the fiber surface.

[0062] Example 2: Construction of the Experimental Apparatus like Figure 3 As shown, the experimental setup includes a light source, a detector, an output device, the cascaded Ω-shaped fiber optic probe, and fiber optic jumpers. One end of the cascaded Ω-shaped fiber optic probe is coupled to a broadband light source (Ocean Optics, HL-2000, 400-1100 nm, 10W) ​​and an 808 nm laser (manufacturer: lasever Inc, model: LSR-PS-Ⅱ) via a Y-fiber coupler. The other end of the cascaded Ω-shaped fiber optic probe is connected to the input end of the spectrometer. The output end of the spectrometer is connected to the output device via fiber optic jumpers to output the results.

[0063] The sensor employs a low-power broadband light source. A high-power laser generates a photothermal effect to heat the probe surface. The transmitted light signal is acquired by a spectrometer and analyzed by a computer to detect changes in the external environment.

[0064] Example 3: Performance Verification of Cascaded Ω-Shaped Fiber Optic Probe The specific steps are as follows: a. Experimental procedure for refractive index gradient detection Sucrose solutions with volume fractions of 0%, 2%, 4%, 6%, 8%, and 10% were prepared, and the refractive index values ​​corresponding to each concentration were determined by referring to a standard refractive index table. The functionalized fiber optic probes were cleaned and dried before use. During the experiment, a broadband light source was first turned on, and the optical signal was transmitted to the probe tip via a Y-type fiber coupler. The probe was sequentially placed in sucrose solutions with different refractive indices, and the refractive index of the surrounding environment was changed in ascending order of concentration to construct a gradient-changing refractive index detection environment. Transmission spectral signals were acquired in real time using a spectrometer, and the data was processed, analyzed, and saved using a computer system.

[0065] b. Photothermal effect experiment operation An 808 nm laser was activated, and the output laser light was transmitted to the functionalized probe tip via a Y-type fiber coupler. Using gold nanobipyramids (Au NBPs) modified on the probe surface, which were controllably synthesized and had an absorption peak at 810 nm, localized surface plasmon resonance was induced under laser excitation, resulting in photothermal conversion and heat generation. Temperature distribution data were acquired in real time using a FLIR infrared thermal imaging system, and the thermal signal was quantitatively processed and analyzed using accompanying software. 1. Study on bending diameter The fiber bending diameter, through modulation of the mode reconstruction effect and bending-induced loss (BIL) in the cascaded structure, is crucial for achieving high-efficiency optical transmission. For example... Figure 4 As shown, this study experimentally analyzes the effect of bending diameter on refractive index sensitivity and excitation temperature in a cascaded Ω-shaped fiber probe. Due to the presence of BIL (Bend-In-Limit), fiber bending disrupts the total internal reflection condition, leading to the conversion of some waveguide light into leakage modes, significantly enhancing the surface radiation field energy. This radiation energy is converted into heat energy by the surface-modified Au NBPs through non-radiative relaxation, causing a local temperature rise at the sensing interface. A smaller bending diameter exacerbates the deviation from the total internal reflection condition, increases the proportion of leakage modes, thereby enhancing the photothermal conversion efficiency and making the local temperature rise effect more significant. Figure 4(a, 4b). On the other hand, the change in bending diameter modulates the number of guided wave modes through the mode reconstruction effect; a smaller diameter excites more higher-order modes, significantly improving the spatial distribution range and energy density of the evanescent field. When the evanescent field couples with the LSPR of AuNBPs, the enhanced field confinement improves the LSPR excitation efficiency, which is reflected in the wavelength variation of the sensor ( Figure 4 c) Improved refractive index sensitivity and intensity. Experiments show that reducing the bending diameter significantly improves temperature rise and wavelength sensitivity, reaching peak performance at 0.4 mm (average temperature rise: 126 ± 1.8°C; wavelength RIS: 933.09 nm / RIU), but significant thermal effects are produced in the range of 1.4 mm-0.4 mm, with temperatures above 50°C, and the sensitivity is very high in all these ranges.

[0066] 2. Study on NCF length The MNM cascade structure induces a mode mismatch at the MMF-NCF interface, causing optical energy to transfer to the cladding, thereby synergistically improving sensor sensitivity and photothermal conversion efficiency.

[0067] like Figure 5 As shown, the NCF length modulates performance through a dual-path mechanism: reducing the NCF length reduces the attenuation of the radiation field enhanced by bending and cascading effects in the sensing region, leading to a sharp increase in photothermal conversion efficiency, with local temperature rise exceeding 140℃. Figure 5 (a, 5b); Simultaneously, shortening the NCF length significantly reduces evanescent field transmission attenuation, enhances the local field confinement of Au NBPs, and simultaneously improves wavelength and intensity sensitivity. However, when NCF < 0.5 cm, the dominant effect of radiation field energy shift leads to evanescent field intensity attenuation, resulting in a decrease in wavelength sensitivity ( Figure 5 c), while the compensation of the intensity signal by the radiation field maintains its upward trend. Optimal balance is achieved at NCF = 0.6 cm: the probe surface temperature rise can reach over 110°C, the wavelength sensitivity reaches 933.09 nm / RIU, and the energy distribution of the radiation field and evanescent field maximizes sensing stability. Given that intensity sensitivity is easily affected by ambient light interference, and the wavelength characteristic peak is located near 808 nm, this interference can be avoided. Subsequent experiments used wavelength shift detection as a reliable method. Experiments show that reducing the NCF length significantly improves temperature rise and wavelength sensitivity, but excessively short lengths cause a decrease in wavelength sensitivity. Peak performance is reached at 0.6 cm (average temperature rise: 110 ± 2.4°C; wavelength RIS: 962.9 nm / RIU), but overall, the thermal effect is good and the sensitivity is very high between 0.4 cm and 0.8 cm.

[0068] 3. Photothermal performance This application's novel cascaded Ω-shaped fiber optic probe integrates multiple design factors and exhibits excellent heating and cooling performance. Figure 7 This sensor employs a cascaded MNM fiber structure, enhancing the proportion of higher-order modes through mode mismatch. The reduced fiber diameter of 250 μm achieves a small bending diameter (0.4–1.4 mm), thereby strengthening the mode recoupling effect and bending-induced loss. Furthermore, Au NBPs were chosen as the primary plasmonic material for photothermal excitation on the fiber surface, exhibiting superior photothermal conversion efficiency compared to Au NRs. The synergistic effect of these design elements results in a significant improvement in local heating performance compared to our group's previous plastic-clad fiber sensor (600 μm multimode fiber), such as… Figure 6 As shown in figure a (0.4 mm bending diameter and 0.6 cm NCF length). The local surface temperature can be controlled by adjusting the power of the 808 nm laser source. Figure 6 b). The sensor also exhibits excellent thermal cycling stability, maintaining consistent heating and cooling characteristics over at least 6 cycles. Figure 6 c). Crucially, it achieves rapid heating, raising the surface temperature to 110°C above ambient temperature in just 1.3 seconds. Figure 6 d). This combination of rapid response, precise temperature control, and stability fully meets the requirements for reliable temperature transfer in photothermal therapy applications.

[0069] Example 4: Application Research of Cascaded Ω-Shaped Fiber Optic Probes The experimental cells or bacteria can be purchased or cultured at home. For culture at home, refer to the cell culture methods in existing literature. This invention does not limit this, as long as they are living cells.

[0070] The selection of aptamers only requires that they be nucleic acid aptamers that target high expression of cell membrane proteins, and that they have high selectivity and high specificity; there are no structural requirements for the aptamers.

[0071] a. Fabrication of cascaded Ω-shaped fiber optic probe biosensors The probe of the above-mentioned cascaded Ω-shaped fiber optic probe was placed in a solution containing a trapping structure and incubated overnight to achieve directional immobilization and assembly of the aptamer on the surface of gold nanoparticles, and finally a cascaded Ω-shaped fiber optic probe biosensor that can be used for cell or bacterial recognition and detection was obtained.

[0072] b. Cell detection experimental procedures Using the experimental setup constructed in Example 2, a dynamic cell capture and quantitative detection experiment was conducted. First, the broadband light source was turned on, and the biosensor from step a was immersed in deionized water. After the output spectral signal stabilized, cell suspension was added in a gradient. For the first 60 minutes of the experiment, the system was kept cell-free as a zero-concentration baseline. Subsequently, cell suspension was added dropwise in batches, increasing the cell concentration in the solution in a stepwise manner. Transmission spectra were continuously acquired for 60 minutes at each concentration gradient to obtain steady-state response signals. Finally, the obtained spectral data were systematically processed and analyzed.

[0073] c. Photothermal therapy experimental verification The biosensor from step a was immersed in the cell suspension for 30 minutes to complete the cell capture process. Subsequently, an 808 nm near-infrared laser (power density: 1.5 W / cm²) was introduced through an optical fiber and continuously irradiated for 10 minutes. The photothermal effect excited by the local surface plasmon resonance of the gold nanostructure was utilized to achieve efficient killing of the captured cells. 2 d. Fluorescence detection to verify cell killing efficiency To quantitatively evaluate the photothermal killing efficiency, a dual-fluorescence staining experiment was performed using Calcein-AM (which marks live cells in green) and propidium iodide (PI, which marks dead cells in red). The control group consisted of cell suspensions untreated by laser irradiation, while the experimental group consisted of the same volume of cell suspensions treated with laser irradiation (i.e., the control group had no laser irradiation in step c, but everything else was the same as the experimental group). The Calcein-AM / PI staining working solution was prepared under light-protected conditions: Calcein-AM, PI, and detection buffer were thoroughly mixed and stored in the dark for later use. Under light-protected conditions, the above staining working solution was added to both groups of cell samples, gently resuspended and mixed, then transferred to cell culture dishes and evenly spread. The samples were incubated in the dark for 30 minutes. Subsequently, images were captured under a fluorescence confocal microscope, and the number of live and dead cells in the fluorescence images was counted using image analysis software to calculate the cell-killing efficiency of photothermal therapy.

[0074] In addition, in order to achieve specific capture of specific cells, specific aptamers need to be attached to the probe surface of the Ω-shaped fiber optic probe.

[0075] The above experimental methods are applicable to the capture and killing of cells and bacteria. The collection, capture and killing times can be adjusted appropriately depending on the target being captured or killed. Since the embodiments in this application cannot exhaustively list the effects, only a few representative cancer cells and bacteria are selected for verification.

[0076] 1. Highly efficient capture and killing of MCF-7 breast cancer cells Tumor metastasis is a leading cause of approximately 90% of cancer-related deaths, and circulating tumor cells (CTCs) are a key step in the metastatic process. Eliminating CTCs can directly block the metastatic chain, significantly reducing the probability of recurrence, and is an important strategy in cancer treatment. Therefore, developing technologies capable of real-time monitoring and effective elimination of CTCs is crucial for improving cancer prognosis; optically based implantable sensors, with their high sensitivity, excellent biocompatibility, and minimally invasive characteristics, provide a promising platform for achieving this goal. Current implantable CTC clearance strategies mainly fall into two categories: First, passive capture devices, such as functionalized magnetic vascular stents (biomimetic adhesion) or mucopolysaccharide-modified silk fibers (steric hindrance-enhanced capture), but these only achieve CTC enrichment, with subsequent analysis relying on in vitro experiments; second, active therapeutic devices, including phototherapy systems combining hybrid cell membrane-modified magnetic particles and microfluidic chips (PTT / PDT in situ inactivation) and nanofiber electrode catheters (antibody-targeted capture + irreversible electroporation killing), but these are disconnected from treatment, and passive capture devices lack in situ analysis capabilities, cannot provide real-time treatment guidance, and have significant toxic side effects. This embodiment uses the unique MNM cascade structure Ω fiber probe of this application for detection, which can raise the surface temperature to 110°C above ambient temperature within 1.3 seconds, achieving a detection limit of 2.1 cells / mL and a cell mortality rate of 79.4 ± 4.9%.

[0077] The cells used in this embodiment are autotrophic, as detailed below: Cell Culture Remove the culture flask containing confluent adherent MCF-7 cells from the CO2 incubator. Discard any discolored culture medium. Gently wash three times with PBS buffer to remove residual culture medium, discarding the wash solution. Add 1 mL of trypsin solution for digestion, observing under a microscope until the cells become rounded, the gaps between them increase, and they are about to detach. After removing the trypsin solution, add 2 mL of PBS buffer and gently pipette until all adherent cells have completely detached. Collect the cell suspension in a centrifuge tube and centrifuge at 1000 r / min for 3 minutes, discarding the supernatant. Resuspend the pellet in PBS to prepare an MCF-7 cell suspension, and store at 2–8℃ for subsequent experiments. In this embodiment, an aptamer that specifically binds to MCF-7 cells was selected, as follows: Synthesis of T-type aptamers in high-salt, low-pH environments (1) Assembly of T-type aptamer structure: 50 μL of MUC1 aptamer (as shown in SEQ ID NO: 1) and AS1411 aptamer DNA (as shown in SEQ ID NO: 2) (with PBS as solvent) were mixed in an equimolar ratio and hybridized by programmed temperature annealing to prepare T-type aptamer structure.

[0078] (2) The aptamer solution was mixed with 1 M NaCl solution (the solvent was an aqueous solution containing 1 wt% trisodium citrate) at a volume ratio of 7:3 to form a T-type aptamer composite solution under high ionic strength and low pH environment for subsequent experiments.

[0079] Cells and aptamers are prerequisites for biosensor applications. Once preparation is complete, other operations are the same as the methods described in abcd of this embodiment. The specific procedures for MCF-7 are as follows. Table 1 below only lists the parts of abcd that are not mentioned for MCF-7: Table 1 Performance Experiments of Cascaded Ω-Shaped Fiber Optic Probe Biosensor

[0080] The results are as follows: (1) Cell detection: Highly efficient capture of adenocarcinoma cells MCF-7 ( Figure 7 T-type aptamers were immobilized on the surface of Au NBPs under high-salt / low-pH conditions, and cells were captured by their specific binding to the MCF-7 surface antigen. Figure 7 a). In the single-concentration validation experiment (2×10), the normalization analysis of the spectral characteristic peaks showed signal saturation, and the goodness of fit of the center wavelength shift curve reached R, confirming that the novel fiber optic sensor has the ability to capture MCF-7 cells. Figure 7 b, 7c). Dynamic capture quantification experiments involved gradient addition of MCF-7 cell suspension (1×10⁻⁶) to deionized water. No wavelength drift was observed in the first 60 minutes (zero cell concentration); subsequent additions showed red shift and reached saturation within 60 minutes of each subsequent batch addition. Figure 7 d, 7e). Within a concentration range of 5 × 10⁻⁶, the wavelength redshift was linearly related to the logarithm of cell concentration (R), with a detection limit of 2.1 cells / mL. Figure 7 f). This cascaded Ω-shaped sensor tracks the cell capture process in real time by monitoring spectral shift (Δλ), demonstrating its ultra-high sensitivity in capture and quantitative detection. 4 cells / mL 2 =0.99 5 cells / mL 2 -5×10 4 cells / mL 2 =0.99 (2) Photothermal capacity Leveraging the superior photothermal capabilities of a novel cascaded Ω-shaped fiber optic sensor, we further validated its efficacy in targeted cell elimination, utilizing localized photothermal effects to kill captured MCF-7 breast cancer cells. Figure 7e). The functionalized sensor probe was immersed in MCF-7 cells (2 × 10⁻⁶). 4 A 30-minute capture cycle was performed in a solution containing (cells / mL). Subsequently, an 808 nm near-infrared laser (power density: 1.5 W / cm²) was transmitted via fiber optic cable for 10 minutes. This excitation triggered intense localized heating via surface-bound Au NBPs, generating a temperature of 49.7 ± 0.8 °C within the irradiated region. Figure 7 This result was confirmed by thermal imaging. This temperature significantly exceeded the typical heat tolerance threshold (42 °C) for tumor cells.

[0081] (3) Fluorescence detection To quantitatively assess cell-killing efficiency, a dual-fluorescence staining experiment was performed using Calcein-AM (to stain live cells green) and propidium iodide (PI, to stain dead cells red). Confocal laser scanning microscopy (CLSM) images showed a clear contrast: the experimental group (after laser irradiation, ...) Figure 7 The irradiated cell (kn) exhibited a broad red fluorescent region, indicating extensive cell death, while the control group (unirradiated) showed a similar pattern. Figure 7 The cells (gj) primarily exhibited green fluorescence, indicating viable cells. Quantitative analysis of the fluorescence area ratio determined that the cell death rate in the irradiated group was 79.4 ± 4.9%, significantly higher than the 7.7 ± 1.7% in the control group.

[0082] These results clearly demonstrate that this cascaded Ω-shaped fiber optic sensor platform can not only capture target MCF-7 cells but also effectively kill them through precisely controlled photothermal ablation. Fluorescence contrast provides a direct, quantifiable, and visually compelling method for assessing treatment outcomes, highlighting the sensor's potential to integrate cancer cell capture and localized photothermal therapy in a minimally invasive setting.

[0083] While specific embodiments have been described above with reference to disclosed examples and embodiments, such embodiments are merely illustrative and do not limit the scope of the invention. Changes and modifications can be made by those skilled in the art without departing from the broader aspects of the invention as defined in the appended claims.

[0084] All publications, patents, and patent documents are incorporated herein by reference as if they were individually incorporated herein by reference. This should not be construed as limiting any aspects inconsistent with this disclosure. The invention has been described with reference to various specific and preferred embodiments and techniques. However, it should be understood that many variations and modifications can be made while remaining within the spirit and scope of the invention.

Claims

1. A cascaded Ω-shaped fiber optic probe, characterized in that, The cascaded Ω-shaped fiber probe contains an Ω-shaped M–N–M structure. The MNM structure is composed of a coreless fiber and a multimode fiber with the coating removed. The two ends of the coreless fiber are respectively connected to two segments of the multimode fiber. The surface of the MNM structure contains gold nanoparticles.

2. The cascaded Ω-shaped fiber optic probe as described in claim 1, characterized in that, The connection is a fusion weld.

3. The cascaded Ω-shaped fiber optic probe as described in claim 1, characterized in that, The LSPR absorption peak dominated by the gold nanoparticles is 760-880 nm; preferably, the LSPR absorption peak dominated by the gold nanoparticles is 810 nm.

4. The cascaded Ω-shaped fiber optic probe as described in claim 3, characterized in that, The gold nanoparticles are selected from conical gold nanoparticles, spherical gold nanoparticles, or a mixture of both.

5. The cascaded Ω-shaped fiber optic probe as described in any one of claims 1-4, characterized in that, The bending radius of the MNM structure is 0.4 mm - 1.4 mm, and the length of the coreless optical fiber is 0.4 cm - 1.2 cm. Preferably, the length of the coreless optical fiber is 0.4 cm - 0.8 cm.

6. The method for fabricating the cascaded Ω-shaped fiber optic probe as described in any one of claims 1-4, characterized in that, Specifically, a coreless fiber is fused together in the middle of a multimode fiber with the coating removed to form an MNM cascade structure. Then, it is bent into an Ω-shaped structure with a specific curvature diameter through a thermoforming process. Subsequently, nano-gold is modified on the surface of the Ω-shaped structure.

7. A cascaded Ω-shaped fiber optic probe biosensor as described in claim 1, characterized in that, The biosensor includes the cascaded Ω-shaped optical fiber probe as described in any one of claims 1-5.

8. An experimental apparatus, characterized in that, The experimental setup includes the cascaded Ω-shaped fiber optic probe as described in any one of claims 1-5 or the biosensor as described in claim 7.

9. The experimental apparatus as described in claim 8, characterized in that, It also includes an output device, a detector, an optical fiber patch cord, and a light source. The light source includes a communication light source and a laser light source. One end of the cascaded Ω-shaped optical fiber probe or the cascaded Ω-shaped optical fiber probe biosensor couples the communication light source and the laser light source to the probe through the optical fiber patch cord. The other end of the cascaded Ω-shaped optical fiber probe or the cascaded Ω-shaped optical fiber probe biosensor is connected to the input end of the detector. The output end of the detector is connected to the output device through the optical fiber patch cord. Preferably, the laser light source is an 808nm laser.

10. The application of the cascaded Ω-shaped fiber optic probe according to any one of claims 1-5, the biosensor according to claim 7, and the experimental device according to any one of claims 8-9 in the fields of cancer cell detection and photothermal therapy.

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