Continuously tunable surface plasmon resonance sensor

Abstract

The application discloses a kind of continuously tunable surface plasmon resonance sensors, belong to microfluidic sensor field, including liquid metal flow channel in bottom layer and the sample solution flow channel to be measured in upper layer, two layers of flow channel are separated by film;Liquid metal flow channel is Archimedes spiral structure, and the sample solution flow channel to be measured is circular ring structure, and the reconstruction and tuning of sensor are realized by accurate control to liquid metal.The sensor structure of the application has the characteristics of small volume, high sensitivity and tunability.In addition, due to the encapsulability and good biocompatibility of the sensor, the sensor is expected to be implanted in vivo, and the real-time monitoring function thereof is realized by using external excitation.

Description

Technical Field

[0001] This invention relates to the field of microfluidic sensor technology, and in particular to a continuously tunable surface plasmon resonance sensor. Background Technology

[0002] Microwave sensing has been a field of interest for decades. Information such as the amplitude, velocity, and phase of microwave signals (including radiation, scattering, refraction, and reflection) can be used to characterize the physical parameters of the sample under test. Surface plasmon resonance (SPR) is a resonant mode existing in the microwave band, referring to the collective oscillation of conduction electrons at the interface between a metal and a dielectric. It plays a crucial role in plasmonic resonant sensors. SPR sensors have advantages such as high sensitivity, small size, ease of integration, and real-time monitoring capabilities. However, current technological advancements in the manufacturing methods and devices of plasmonic resonant sensors face the following problems or limitations: Traditional plasmonic resonant sensors often use copper as the conductor, which suffers from metal fatigue, high rigidity, and susceptibility to oxidation. Furthermore, traditional sensors of this type are mostly designed with fixed parameters, unable to be dynamically adjusted according to actual needs, thus limiting their application range. Summary of the Invention

[0003] This invention provides a continuously tunable surface plasmon resonance sensor, proposing a miniaturized, highly sensitive, and biocompatible continuously tunable surface plasmon resonance sensor. Through microfluidic technology, precise control of liquid metal can be achieved, thereby improving the accuracy of sensor fabrication and allowing for arbitrary customization of its resonant frequency within a specific resonant range.

[0004] A first aspect of the present invention provides a continuously tunable surface plasmon resonance sensor, comprising: a liquid metal channel located at the bottom layer and a sample solution channel located at the top layer, the two channels being separated by a thin film; the liquid metal channel having an Archimedean spiral structure and the sample solution channel having a ring structure.

[0005] In one embodiment of the present invention, the liquid metal in the liquid metal channel is a eutectic gallium indium alloy.

[0006] In one embodiment of the present invention, the liquid metal channel and the sample solution channel are integrated into a microfluidic chip design, and the excitation source of the continuously tunable surface plasmon resonance sensor is a separate design.

[0007] In one embodiment of the present invention, the performance of the continuously tunable surface plasmon resonance sensor is adjusted by controlling the ratio of liquid metal to sodium hydroxide solution in the liquid metal channel.

[0008] In one embodiment of the present invention, the width of the liquid metal channel is 0.3 mm and the depth is 0.7 mm, the depth of the sample solution channel is 0.3 mm, and the thickness of the film between the two channels is 0.2 mm.

[0009] In one embodiment of the present invention, the liquid metal flow channel follows the Archimedes spiral equations x = 0.11·t·cos(t) and y = 0.11·t·sin(t), where the value of t ranges from 6 to 42.

[0010] The continuously tunable surface plasmon resonance sensor of this invention has the following advantages:

[0011] 1. Microfluidic technology enables precise control of liquid metals, thereby improving the accuracy of sensor manufacturing and allowing for arbitrary customization of the resonant frequency within a specific resonant range;

[0012] 2. By using liquid metal as the sensing material, the sensor performance can still be further optimized by fine-tuning its structure after the sample is added.

[0013] 3. By integrating the resonator and sample solution cavity into a microfluidic chip, the gap between them is minimized, making it easier for the evanescent wave to interact with the sample solution and improving the sensitivity of the sensor.

[0014] 4. The sensor and excitation source (microstrip line) are designed to be separable, allowing the sensor to be implanted in the body for real-time monitoring via external excitation.

[0015] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0016] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0017] Figure 1 This is a schematic diagram of the structure of the continuously tunable surface plasmon resonance sensor of the present invention; wherein, the black part represents sodium hydroxide solution and the white part represents liquid metal.

[0018] Figure 2 This is a schematic diagram of the excitation source of the present invention. The dark part represents the microstrip line, and the light part represents the dielectric substrate.

[0019] Figure 3 This is a schematic diagram of the structure of the microfluidic chip of the present invention. The light-colored layer is the microfluidic channel, and the dark-colored layer is the substrate or separator of different thicknesses.

[0020] Figure 4 This is a diagram showing the magnetic field intensity distribution along the Z-axis of the sensor of the present invention.

[0021] Figure 5 Transmission (S) corresponding to different numbers of revolutions of the sensor of the present invention 21 ) Spectral diagram, where n represents the number of spiral loops;

[0022] Figure 6 S corresponding to different outer diameters of the sensors of the present invention 21 Spectral diagram, where r represents the outer diameter of the helical ring. Detailed Implementation

[0023] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0024] In recent years, liquid metals have attracted increasing attention due to their unique properties and numerous potential applications. Room-temperature liquid metals have been used to develop reconfigurable antennas, absorbing materials, and metasurfaces for polarization control, bandpass filters, and beam steering. Liquid metals possess the properties of traditional metals, along with a degree of fluidity, allowing them to be deformed and thus improving the performance of these devices. The use of liquid metals in surface plasmon sensors holds promise for achieving novel sensing capabilities that are impossible with solid metals. First, the fluid properties of liquid metals enable reversible sensor responses, meaning sensors can be reused multiple times without significant performance degradation. Second, liquid metals can be used to fabricate complex sensor shapes, enabling the development of high-performance sensors and improved sensitivity. Due to their low toxicity, gallium-based liquid metals have gradually become one of the main focuses of liquid metal research. Metamaterial units / arrays can exhibit sensitive responses to liquids, and metamaterials composed of liquid metals also possess tunable properties. Devices made using liquid metals, aided by microfluidics, exhibit precise and convenient characteristics. The development of a continuously tunable surface plasmon resonance sensor based on liquid metal and microfluidic technology is of great significance for improving the adaptability and performance of sensors. Continuously tunable surface plasmon resonance sensors have broad application prospects in biomedicine, environmental monitoring, and other fields due to their advantages such as high sensitivity, small size, low cost, good biocompatibility, and continuous tunability.

[0025] Specifically, Figure 1 This is a schematic diagram of the structure of a continuously tunable surface plasmon resonance sensor according to an embodiment of the present invention.

[0026] likeFigure 1 As shown, this continuously tunable surface plasmon resonance sensor includes: a liquid metal channel at the bottom layer and a sample solution channel at the top layer, separated by a thin film; the liquid metal channel has an Archimedean spiral structure, and the sample solution channel has a circular ring structure. In the diagram, mark 1 indicates the inlet of the liquid metal channel, mark 2 indicates the outlet of the liquid metal channel, mark 3 indicates the inlet of the sample solution channel, and mark 4 indicates the outlet of the sample solution channel.

[0027] The sensor of the present invention integrates two microfluidic channels. The lower Archimedes spiral channel is used to fill an easily reconfigurable liquid metal, which can be adjusted to change the shape and size of its distribution in the channel. The upper annular channel is used to fill the sample solution to be tested.

[0028] In embodiments of the present invention, the liquid metal in the liquid metal channel is a non-toxic, odorless, low-melting-point, and easily reconfigurable eutectic gallium-indium alloy (EGaIn).

[0029] In embodiments of the present invention, the liquid metal channel and the sample solution channel are integrated into a microfluidic chip design, and the excitation source of the continuously tunable surface plasmon resonance sensor is a separate design.

[0030] In an embodiment of the present invention, the performance of a continuously tunable surface plasmon resonance sensor is adjusted by controlling the ratio of liquid metal to sodium hydroxide solution in the liquid metal flow channel.

[0031] By controlling the injection of different proportions of liquid metal and sodium hydroxide solution into the Archimedes spiral circulation channel, this sensor can be customized with resonant units of different sizes and structures. After adding the sample to be tested into the sample solution channel, injecting sodium hydroxide solution to fine-tune the sensor's structure can further optimize its performance (such as sensitivity and resonant frequency).

[0032] In an embodiment of the present invention, the width of the liquid metal channel is 0.3 mm and the depth is 0.7 mm, the depth of the sample solution channel is 0.3 mm, and the thickness of the film between the two channels is 0.2 mm.

[0033] In embodiments of the present invention, the liquid metal flow channel follows the Archimedes spiral equations x = 0.11·t·cos(t) and y = 0.11·t·sin(t), where the value of t ranges from 6 to 42.

[0034] The integrated chip in the experiment can be realized using existing microfluidic technology. Figure 1A schematic diagram of a sensor composed of liquid metal and a microfluidic chip is shown. The liquid metal channel is a helical arm, following Archimedes' equations x = 0.11·t·cos(t) and y = 0.11·t·sin(t), where t ranges from 6 to 42, and the origin is located at the center of the resonator. The channel width is 0.3 mm and the depth is 0.7 mm. The radius of the entire helical channel, measured at the end of the helical arm, is 5.5 mm. Figure 1 Mark 1 indicates the inlet of the liquid metal flow channel, and mark 2 indicates the outlet of the liquid metal flow channel. Mark 3 indicates the inlet of the sample solution flow channel, and mark 4 indicates the outlet of the sample solution flow channel. The sample solution flow channel has a circular annular structure with an outer diameter of 5.9 mm and an inner diameter of 1.3 mm. The sensor is excited by a 50 Ω microstrip line at the bottom. Figure 2 As shown, a semi-circular ring structure with a radius of 5.8 mm is located in the center of the microstrip line to achieve higher excitation efficiency. To ensure compatibility between the resonator and the microstrip circuit, a 15 mm diameter hole is fabricated on the ground plane. The substrate uses F4B dielectric material with a dielectric constant of 2.65 and a thickness of 0.5 mm. The copper layer thickness is 0.018 mm on both the top (microstrip line pattern) and bottom (ground plane) sides. To accommodate sensor structures of different sizes to fit the microstrip line, the relative position of the microfluidic chip on the F4B dielectric substrate can be flexibly adjusted in the experiment. Detailed geometric design is described in... Figure 3 As specified, the liquid metal channel is located at the bottom, and the sample solution channel is located at the top. The parameters are as follows: t1 = 0.6 mm, t2 = 0.3 mm, t3 = 0.2 mm, t4 = 0.7 mm, t5 = 0.2 mm.

[0035] EGaIn was selected as the liquid metal electrode in this experiment. Compared to pure gallium (melting point 29.8℃), the melting point of EGaIn can be finely tuned by adjusting the ratio of gallium to indium, making it liquid at room temperature. Due to its inherent good fluidity, EGaIn exhibits a lower melting point (8℃) and stable conductivity compared to solid electrodes, even under large tensile strains. An Archimedes spiral ring structure forms a microfluidic channel to load EGaIn. To prevent oxidation of the liquid metal, sodium hydroxide solution is injected from the inlet of EGaIn to first purge air. Next, a measured amount of EGaIn is injected into the spiral arm. Finally, sodium hydroxide solution is injected again to reconstruct EGaIn. Therefore, the shape of EGaIn can be customized, demonstrating a high degree of flexibility.

[0036] Evanescent waves play an important role in plasmonic resonant sensors. For example... Figure 4As shown, the magnetic field magnitude distribution along the z-axis of the plasmonic resonant sensor is illustrated. Compared to the weak magnetic field present in the resonant cavity, the magnetic field on both sides of the cavity increases rapidly. Typically, the attenuation length of the evanescent wave refers to the distance at which the power decays to 1 / e of its maximum value. Calculations from the magnetic field distribution diagram show that this distance is approximately 1.6 mm. The evanescent wave is related to the magnetic dipole mode; the narrower the gap between the liquid metal channel and the solution channel, the higher the interaction efficiency between the evanescent wave generated by the sensor and the sample solution.

[0037] The microfluidic chip is made of polycarbonate (PC) and polymethyl methacrylate (PMMA), with a top layer of solution microfluidic channels and a bottom layer of liquid metal channels. The intermediate spacer between the solution and liquid metal channels is only 0.2 mm thick, allowing evanescent fields to pass more easily through the gap. Furthermore, the intermediate substrate separates the test solution from the resonator, preventing contamination of the resonator during sensing. The solution channels are 0.3 mm thick with a capacity of 30 μL, including narrow inlet and outlet channels. An Agilent N5230C vector network analyzer was used to measure S in the experiment. 21 Spectral diagram. To further explore the potential applications of the proposed sensor in environmental monitoring, key sensor performance characteristics, such as quality factor (Q-factor) and resonant intensity, were investigated. The Q-factor is defined as Q = fr / FWHM, where fr is the resonant frequency. The following examples illustrate the invention using two sensors with different reconfigurable modes.

[0038] Example 1:

[0039] This example demonstrates S 21 The relationship between the spectral pattern and the number of helical turns n. When r = 4.5 mm, Figure 5 The sensor's S values ​​are shown when n = 1, 2, 3, and 4. 21 Spectral diagram. In this example, the corresponding sensor resonant frequencies are 0.63 GHz, 0.66 GHz, 0.81 GHz, and 2.16 GHz. With increasing revolutions, the sensor's resonant frequency decreases due to the increased capacitance. When n = 1, the sensor's resonant frequency is significantly higher than when n = 2, 3, and 4. Furthermore, the Q values ​​of the sensor when n = 2, 3, and 4 are 40.1, 41.1, and 41.0, respectively, significantly greater than the Q value of 21.2 when n = 1. Additionally, the resonant intensities when n = 1, 2, 3, and 4 are -9.1 dB, -6.1 dB, -4.4 dB, and -3.7 dB, respectively. This shows that the resonant intensity decreases with increasing n.

[0040] Example 2:

[0041] This example demonstrates S 21The relationship between the spectral lines and the outer diameter r of the spiral ring. When n = 3... Figure 6 The S-values ​​of the sensor are shown when r = 4.5 mm, 3.8 mm, 3.1 mm, and 2.4 mm. 21 Spectral diagram. In this example, the corresponding sensor resonant frequencies are 0.62 GHz, 0.8 GHz, 1.115 GHz, and 1.63 GHz. The resonant frequency gradually decreases with increasing radius. Furthermore, when r = 4.5 mm, 3.8 mm, 3.1 mm, and 2.4 mm, the sensor's Q values ​​are 41.1, 40.2, 34.6, and 23.3, respectively, and the resonant intensities are -4.5 dB, -5.8 dB, -6.6 dB, and -6.9 dB, respectively. This shows that the sensor's Q value increases with increasing r, while the resonant intensity decreases with increasing r.

[0042] The continuously tunable surface plasmon resonance sensor proposed in this invention is realized by integrating a resonator unit and a flow channel for the sample solution into a single microfluidic chip. The resonator unit is fabricated by injecting liquid metal into an Archimedean spiral flow channel. The flow channel for the sample solution is located directly above the resonator unit, and they are separated from each other by a thin film. The liquid metal is a non-toxic, odorless, low-melting-point eutectic gallium-indium alloy (EGaIn), and the sensor's reconstruction and tuning are achieved through precise control of EGaIn. The sensor resonates by being excited by a custom-designed microstrip line placed below it; the sensor and microstrip line are designed to be separable. The sensor structure using this technical solution features small size, high sensitivity, and tunability. Furthermore, due to the sensor's encapsulation and good biocompatibility, it is expected to be implanted in the body, enabling real-time monitoring through external excitation.

[0043] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0044] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "N" means at least two, such as two, three, etc., unless otherwise explicitly specified.

Claims

1. A continuously tunable surface plasmon resonance sensor, characterized in that, include: The liquid metal channel is located at the bottom layer and the sample solution channel is located at the top layer, with the two channels separated by a thin film. The liquid metal channel has an Archimedean spiral structure, and the sample solution channel has a circular ring structure; the liquid metal channel and the sample solution channel are integrated into a microfluidic chip design, and the excitation source of the continuously tunable surface plasmon resonance sensor is a separate design.

2. The continuously tunable surface plasmon resonance sensor according to claim 1, characterized in that, The liquid metal in the liquid metal channel is a eutectic gallium-indium alloy.

3. The continuously tunable surface plasmon resonance sensor according to claim 1, characterized in that, The performance of the continuously tunable surface plasmon resonance sensor can be adjusted by controlling the ratio of liquid metal to sodium hydroxide solution in the liquid metal channel.

4. The continuously tunable surface plasmon resonance sensor according to claim 1, characterized in that, The liquid metal channel has a width of 0.3 mm and a depth of 0.7 mm, the sample solution channel has a depth of 0.3 mm, and the film between the two channels has a thickness of 0.2 mm.

5. The continuously tunable surface plasmon resonance sensor according to claim 1, characterized in that, The liquid metal flow channel follows the Archimedes spiral equation. x = 0.11·t·cos(t) and y = 0.11·t·sin(t) , where t ranges from 6 to 42.

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