A lead ion sensor and method based on a liquid crystal whispering-gallery mode resonator

Abstract

This invention discloses a lead-ion sensor and method based on a liquid crystal whispering-gallery mode resonator. The sensor includes a functionalized liquid crystal glass microbubble and a tunable scanning laser, a single-mode fiber, a tapered fiber, and a power meter sequentially connected via a single-mode fiber. The tapered fiber is disposed on one side of the functionalized liquid crystal glass microbubble, which contains interface modifications for capturing single-stranded DNA. The resonant light field signal enters the power meter, which obtains a spectrum. The spectral signal in the liquid crystal whispering-gallery mode spectrum initially exhibits a red shift, followed by a blue shift. The spectral shift is the sum of the red and blue shift values. Lead ion detection is achieved by measuring the spectral shift in the liquid crystal whispering-gallery mode. 2+ High-resolution sensing. Compared with existing technologies, this invention overcomes the defect of small spectral drift in WGM, thereby triggering stronger spectral changes to achieve a lower detection limit, and is integrable.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and particularly to a lead-ion (Pb) sensor based on a liquid crystal whispering-gallery (WGM) mode fiber-coupled optical microresonator. 2+ Sensors and detection methods. Background Technology

[0002] Lead ions (Pb) 2+ Detection methods include atomic absorption spectrometry, inductively coupled plasma mass spectrometry, and inductively coupled plasma atomic emission spectrometry. Although these methods have made significant progress, they still suffer from drawbacks such as cumbersome operation and long processing times. Therefore, there is a need to develop simpler techniques to detect lead ions (Pb). 2+ Rapid detection.

[0003] Whispering gallery mode (WGM) is a surface mode that relies on total internal reflection of the light field at the boundary, enhancing the photo-matter interaction of the surface. WGM resonators exhibit advantages such as high quality factor, strong evanescent field, and small mode volume, resulting in excellent background suppression and high sensitivity. Due to these significant advantages, WGM resonators have attracted considerable attention in recent years and have been extensively studied in the field of heavy metal sensing: WGM cavities are formed or surrounded by heavy metal ions, providing them with strong optical feedback. However, these sensors still primarily focus on changes in the physical parameters (refractive index) of the heavy metal ion solution itself, thus limiting their sensitivity and multidimensional sensing applications. Furthermore, liquid crystals (LCs), as a fast-response, highly sensitive, and low-cost material, have also been developed for forming sensing applications. Small changes at the LC interface and external stimuli can trigger orientation transitions in LC molecules, and these orientation changes (up to 100 μm) can be propagated downwards by the LC molecules at the interface, further enhancing their sensing signal response.

[0004] Therefore, a liquid crystal WGM optical resonator was developed for Pb 2+ The sensing and detection method is a technical problem that urgently needs to be solved in this invention. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing WGM-based DNA hybridization sensors and propose a lead-ion sensor and method based on a liquid crystal whispering-gallery mode resonator. By combining WGM resonator sensing technology with liquid crystal amplification technology, the fabrication of a liquid crystal WGM sensor and its application in the detection of Pb are realized. 2+ The detection.

[0006] This invention is achieved using the following technical solution:

[0007] A lead-ion sensor based on a liquid crystal whispering-gallery mode resonator includes a functionalized liquid crystal glass microbubble and a tunable scanning laser, a single-mode fiber, a tapered fiber, and a power meter sequentially connected via a single-mode fiber. The tapered fiber is disposed on one side of the functionalized liquid crystal glass microbubble, which contains interface modifications for capturing single-stranded DNA. The tunable scanning laser emits laser light, which is transmitted through the single-mode fiber to the tapered fiber, generating an evanescent field. This evanescent field is then coupled and embedded into the functionalized liquid crystal glass microbubble by the tapered fiber. The transmitted laser excites a whispering-gallery mode on the annular surface of the functionalized liquid crystal glass microbubbles. These microbubbles constitute a liquid crystal whispering-gallery mode resonant cavity. The resonant light field coupled from the microbubbles returns to the single-mode fiber via the tapered optical fiber. The resonant light field signal enters the power meter, which is used to obtain the spectrum. The spectral signal in the liquid crystal whispering-gallery mode spectrum initially exhibits a red shift, followed by a blue shift. The spectral shift is the sum of the red and blue shift values. Pb is obtained by measuring the spectral shift of the liquid crystal whispering-gallery mode. 2+ High-resolution sensing.

[0008] A method for implementing a lead-ion sensor based on a liquid crystal whispering-gallery mode resonator includes the following steps:

[0009] S1. Heating the microbubbles to pull out the original commercial fused silica microcapillaries;

[0010] S2. Heat the waist of the capillary obtained by S1, and pressurize and expand the inside of the microcapillary to form microbubbles.

[0011] S3. Single-stranded DNA is captured by immobilizing on the inner surface of the cavity of the microbubble obtained in S2.

[0012] S4. Remove unbound captured single-stranded DNA and fill the empty binding sites in the cavity of the microbubble;

[0013] S5, Pb 2+ After being added to the deoxyribonuclease solution, it was injected into the cavity of the microbubbles obtained in S4, and the unbound deoxyribonuclease was washed away.

[0014] S6. Single-mode optical fiber is used to stretch and heat it with a flame to make a tapered optical fiber. The tapered optical fiber is fixed on a support and the displacement stage is adjusted so that the waist diameter of the tapered optical fiber is on the same side as the microbubble position obtained in S5, and optical field coupling is achieved.

[0015] S7. Inject LC molecules into the microbubbles obtained in S6, and then seal both ends of the microcapillary.

[0016] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0017] 1) As a reference for Pb 2+ The sensitive liquid crystal whispering-gallery mode resonator features small size, low cost, and real-time monitoring. Its integrability holds promise for building microfluidic chips with sensing capabilities.

[0018] 2) This sensor exhibits a triple amplification effect, combining DNA molecule polarization, LC molecule orientation transition, and WGM. Utilizing liquid crystal as a signal amplifier overcomes the limitations of relying solely on Pb. 2+ The slight spectral drift in WGM caused by minute changes in the refractive index of the solution itself triggers a stronger spectral change to achieve a lower detection limit. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a lead ion sensor structure based on a liquid crystal WGM resonant cavity according to the present invention;

[0020] Figure 2 This is a functionalized schematic diagram of the liquid crystal whispering-gallery mode resonator.

[0021] Figure 3 The transmission response spectrum of the lead ion sensor over time, as measured by a power meter, is shown.

[0022] Figure label:

[0023] 1. Tunable scanning laser; 2. Tapered fiber; 3. Functionalized liquid crystal glass microbubble; 4. Power meter; 5. Support; 6. Three-dimensional displacement stage; 7. 8. Single-mode fiber. Detailed Implementation

[0024] The technical solution will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] like Figure 1The diagram shows a schematic of a lead-ion sensor structure based on a liquid crystal whispering-gallery (WGM) resonator according to the present invention. The sensor consists of a tunable scanning laser 1, a tapered optical fiber 2, a functionalized liquid crystal glass microbubble 3, and a power meter 4, all connected via a single-mode optical fiber. The position of the tapered optical fiber 2 is controlled and adjusted by a support 5 and a three-dimensional displacement stage 6. The tunable scanning laser, acting as the system's laser source, emits laser light as the incident light. The incident light entering from the single-mode optical fiber 7 generates an evanescent field via the tapered optical fiber 2, which is then coupled and embedded into the functionalized liquid crystal glass microbubble 3. The light propagates on the annular surface of the functionalized liquid crystal glass microbubble, exciting a whispering-gallery (WGM) mode. Part of the light energy is coupled out of the functionalized liquid crystal glass microbubble 3 and returns to the single-mode optical fiber 8 via the tapered optical fiber 2. The functionalized liquid crystal glass microbubble 3 constitutes a whispering-gallery (WGM) resonator. This invention is a lead-ion sensor based on a liquid crystal whispering-gallery (WGM) resonator. 2+ sensor.

[0026] The scanning laser 1 emits a laser beam, which is transmitted through the single-mode fiber 7 and into the tapered fiber 2, generating an evanescent field.

[0027] The relative positions of the tapered optical fiber 2 and the functionalized liquid crystal glass microbubble 3 are adjusted until optical field coupling is achieved. Part of the optical signal is coupled out from the functionalized liquid crystal glass microbubble 3 and returns to the single-mode optical fiber 8 through the tapered optical fiber 2, achieving the target Pb. 2+ High-resolution concentration sensing;

[0028] The corresponding optical signal from the single-mode fiber 8 enters the power meter 4, and the target Pb is obtained by measuring the spectral shift of the whispering-gallery mode (WGM). 2+ The results of the concentration test.

[0029] Among them, functionalized liquid crystal glass microbubbles 3 serve as the main sensitive element, used to achieve the binding of captured single-stranded DNA (ssDNA, base sequence (5'-3'): NH2-(CH2)6-TTTTTTGCGTCACTTGATGTATGT), providing a stable and reliable WGM resonant cavity for LC molecules. The ribonucleoside adenosine (rA) in the captured single-stranded DNA is contained in the synthesized DNAzyme (base sequence (5'-3'):

[0030] SH-(CH2)6-ACATCAAGTGACGCACATrAGCATGCATGTTTTTTTTTTCATCTTAGGGGCTGCGGAGTAATGTC) as Pb 2+ The cleavage site. With partial substrate (by Pb) 2+ The release of the cleaved DNAzyme fragments enabled Pb to be released. 2+The cleaved DNAzyme fragments hybridize with ssDNA, altering the interfacial topology. This is due to the high refractive index (n) of the liquid crystal. e =1.69, n o =1.51, n e n o (Representing the refractive indices of the "extraordinary ray" and "ordinary ray" in the liquid crystal birefringence phenomenon, respectively), the light field will pass through the glass cavity (refractive index n = 1.44) and enter the liquid crystal region, where total internal reflection occurs. On the one hand, the DNA hybridization process promotes an increase in the concentration of double-stranded DNA (dsDNA) in the sample to be tested, causing molecular polarization, thereby changing the effective refractive index of the functionalized liquid crystal glass microcavity 3, which is initially manifested as a spectral redshift in the WGM spectrum; on the other hand, due to Pb 2+ The resulting DNA hybridization process triggers a change in liquid crystal orientation (from vertical orientation to planar orientation), and the refractive index followed by the TM mode has a change from n e Turning n o The trend is that the echo-gallery mode (WGM) spectrum exhibits a blue shift. Finally, the total spectral response is calculated as the sum of the red shift and blue shift values ​​and used as a sensing parameter to achieve the final Pb... 2+ High-resolution sensing. The TM mode is a transverse magnetic mode, where the magnetic field is perpendicular to the propagation direction, and the electric field is also perpendicular to the propagation direction.

[0031] The method for fabricating a whispering-gallery mode (WGM) resonator of the present invention includes the following steps:

[0032] Step 1: Use commercially available fused silica microcapillaries with an outer radius of 158 μm and an inner radius of 126 μm to create microbubbles, stretching the original microcapillaries when heated with an oxyhydrogen flame with a diameter on the order of centimeters.

[0033] Step 2: The waist of the microcapillary is heated by an oxyhydrogen flame with a diameter of millimeters. The internal pressure of the microcapillary is increased and expanded by a pressure control device, thereby expanding the waist of the microcapillary to form a microbubble with a diameter of 190μm and an inner wall thickness of about 4μm.

[0034] Step 3: To promote the original vertical alignment of LC molecules, the microcavities were treated with 0.5% (v / v) Dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (DMOAP) solution for 10 minutes at room temperature, followed by rinsing with deionized water for 1 minute. Then, the inner surface of the microcavities was modified with an aqueous solution containing 1% (v / v) Triethoxysilylbutyraldehyde (TEA) and 0.5% DMOAP at 55°C for 1 hour to help fix the captured single-stranded DNA, and the microcavities were rinsed again with deionized water.

[0035] Step 4: To immobilize the captured single-stranded DNA (ssDNA) on the surface within the microbubble cavity, the ssDNA was dissolved in a 20 mM Tris-HCl buffer solution at pH 7.4, which contained 100 mM MgCl2 and 10 mM NaBH3CN. After incubation at 37°C for 2 hours, unbound captured single-stranded DNA was removed using a 2×SSC buffer solution containing 0.1% (v / v) SDS as solute / water as solution. Subsequently, 100 mM 6-mercaptohexane was injected into the microbubble cavity to fill the blank binding sites.

[0036] Step 5: Add Pb 2+ After adding to 100 nM DNAzyme solution, it was injected into ssDNA-functionalized microcavities and incubated for 1 hour. Unbound DNAzyme was washed with 2×SSC buffer containing 0.1% (v / v) SDS.

[0037] Step 6: Use single-mode fiber to fabricate tapered fiber 2 with a waist diameter of 1-2 μm using flame heating and stretching technology. Fix the fabricated tapered fiber 2 on the support 5 and adjust the displacement stage 7 so that the waist diameter of the tapered fiber is close to the position of the microbubble obtained in step 5 and achieve optical field coupling.

[0038] Step 7: Inject LC molecules into the microcavity at a rate of 0.7 μL / min. After the LC molecules reach the microcavity, seal both ends of the microcapillary with UV adhesive to maintain air pressure balance and reduce the influence of LC flow on the spectrum. The fabrication of the liquid crystal WGM optical resonator is now complete. Record the spectral changes of the liquid crystal WGM optical resonator after 10 seconds and continue for 15 minutes.

[0039] As an application example, this invention was used to measure the concentration of lead ion solutions. The ambient temperature was maintained at 26°C, and PBS buffer was used as the solvent to obtain a Pb solution with a concentration of 100 nM. 2+ Solution. According to... Figure 1 The diagram illustrates the optical path construction for a lead-ion sensor based on a liquid crystal whispering-gallery mode resonator. The whispering-gallery mode resonator 3 undergoes chemical functionalization according to steps 3-5, and the transmission response spectrum output by the power meter 4 is measured. Figure 3 The image shows the transmission response of the lead ion sensor as a function of reaction time, as measured by a power meter. The measured transmission response spectrum shows that with increasing reaction time, the transmission response initially exhibits a red shift within 0.5 min, followed by a blue shift. Regarding Pb... 2+ In the detection of solution concentration, the total transmission response can be calculated as the redshift response plus the blueshift response.

[0040] The above description is merely an embodiment of this application and is not intended to limit the scope of protection sought by this invention. For those skilled in the art, any modifications, changes, equivalent substitutions, or variations made without departing from the spirit and principles of this invention fall within the scope of the technical content and protection disclosed in this invention.

Claims

1. A method for fabricating a lead-ion sensor based on a liquid crystal whispering-gallery mode resonator, characterized in that, The sensor comprises a functionalized liquid crystal glass microbubble and a tunable scanning laser, a single-mode fiber, a tapered fiber, and a power meter sequentially connected via a single-mode fiber. The tapered fiber is disposed on one side of the functionalized liquid crystal glass microbubble, which contains interface modifications for capturing single-stranded DNA. The tunable scanning laser emits laser light, which travels through the single-mode fiber to the tapered fiber, generating an evanescent field. This evanescent field is then coupled and embedded into the functionalized liquid crystal glass microbubble by the tapered fiber. Continuing laser transmission further enhances the functionality of the microbubble. The annular surface of the liquid crystal glass microbubble excites a whispering-gallery mode. The functionalized liquid crystal glass microbubble constitutes a liquid crystal whispering-gallery mode resonant cavity. The resonant light field coupled from the functionalized liquid crystal glass microbubble returns to the single-mode fiber through the tapered optical fiber. The resonant light field signal enters the power meter, which is used to obtain the spectrum. The spectral signal in the liquid crystal whispering-gallery mode spectrum initially exhibits a red shift, followed by a blue shift. The spectral shift is the sum of the red shift and the blue shift. Pb is obtained by measuring the spectral shift of the liquid crystal whispering-gallery mode. 2+ High-resolution sensing, wherein the method includes the following steps: Step 1: Use commercially available fused silica microcapillaries to create microbubbles, stretching the original microcapillaries by heating them with an oxyhydrogen flame with a diameter on the order of centimeters. Step 2: The waist of the microcapillary is heated by an oxyhydrogen flame, and the inside of the microcapillary is pressurized and expanded by a pressure control device, thereby expanding the waist of the microcapillary and forming microbubbles. Step 3: Treat the microbubbles with a 0.5% DMOAP solution at room temperature and wash with deionized water; then, modify the inner surface of the microbubbles with an aqueous solution containing 1% TEA and 0.5% DMOAP at 55°C to help fix and capture single-stranded DNA, and rinse the microbubbles again with deionized water. Step 4: Immobilize the captured single-stranded DNA on the surface within the microbubble cavity: Dissolve the captured single-stranded DNA in a 20 mM Tris-HCl buffer solution at pH 7.4, which contains 100 mM MgCl2 and 10 mM NaBH3CN, and incubate. Then, remove unbound captured single-stranded DNA using a 2×SSC buffer solution containing 0.1% SDS solution. Subsequently, inject 6-mercaptohexane into the microbubbles to fill the blank binding sites. The base sequence of the captured single-stranded DNA, from the 5' end to the 3' end, is NH2-(CH2)6-TTTTTTGCGTCACTTGATGTATGT. Step 5: Add Pb 2+ After being added to the DNAzyme solution, it was injected into microvesicles that capture single-stranded DNA functionalization and incubated. Unbound DNAzyme was washed with 2×SSC buffer containing 0.1% SDS. The DNAzyme sequence, from the 5' end to the 3' end, is arranged as SH-(CH2)6-ACATCAAGTGACGCACATrAGCATGCATGTTTTTTTTTTCATCTTAGGGGCTGCGGAGTAATGTC. Step 6: Use single-mode fiber to fabricate tapered fiber with waist diameter using flame heating and stretching technology. Fix the fabricated tapered fiber on the support and adjust the displacement stage so that the waist diameter of the tapered fiber is close to the position of the microbubble obtained in step 5 and achieve optical field coupling. Step 7: Inject liquid crystal molecules into microbubbles. After the liquid crystal molecules reach the microbubbles, seal both ends of the microcapillary.

2. The method as described in claim 1, characterized in that, The position of the tapered optical fiber is controlled and adjusted by a support and a three-dimensional displacement stage.

3. The method as described in claim 1, characterized in that, The microbubbles have a diameter of 190 μm and an inner wall thickness of approximately 4 μm.

4. The method as described in claim 1, characterized in that, The Tris-HCl buffer solution has a pH of 7.4 and a molar concentration of 20 mM.

5. The method as described in claim 1, characterized in that, The molar concentration of the 6-mercaptohexane is 100 mM.

6. The method as described in claim 1, characterized in that, The molar concentration of the DNAzyme solution is 100 nM.

7. The method as described in claim 1, characterized in that, The waist diameter of the tapered optical fiber is 1~2µm.

8. The method as described in claim 1, characterized in that, The liquid crystal molecules were injected at a rate of 0.7 μL / min.

9. The method as described in claim 1, characterized in that, In step 4, the incubation is carried out at 37°C.

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