Sensing device based on stretchable metasurface and heavy metal ion sensing method

Abstract

The invention provides a sensing device based on a stretchable metasurface and a heavy metal ion sensing method, and belongs to the technical field of optical sensing. The device comprises a flexible stretchable substrate and an optical metasurface arranged on the flexible stretchable substrate, a periodic nanostructure of the device can spontaneously suck liquid to be measured through the capillary effect, and meanwhile the metasurface period can be changed by stretching the substrate so as to tune the wavelength of an optical formant. The method comprises the following steps: applying strain to tune wavelength, introducing liquid to be measured to spontaneously fill, collecting spectrum and analyzing spectrum characteristics to determine the heavy metal ions. According to the invention, through integration of mechanical tuning and capillary sampling functions, the existing technical problems are solved, multi-dimensional detection based on wavelength selection and spectral line analysis is realized, and the device has the beneficial effects of high selectivity, high sensitivity, portability and capability of realizing multi-ion parallel detection.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical sensing, and in particular to a sensing device based on a stretchable metasurface and a heavy metal ion sensing method. BACKGROUND

[0002] Heavy metal ion (such as mercury, lead, cadmium, etc.) pollution has become a global ecological and health problem, which is widely derived from industrial emissions, agricultural production, food processing and other fields. It has the characteristics of strong toxicity, difficult degradation and easy enrichment, and can enter the human body through soil, water, food chain and other ways, causing a series of serious health risks such as nervous system damage and organ lesions, and causing irreversible damage to the ecological balance.

[0003] Existing heavy metal ion detection technologies can be divided into two categories: one is high-precision laboratory detection technology, such as atomic absorption spectrometry, inductively coupled plasma mass spectrometry, etc. Although this kind of technology can achieve trace level detection accuracy, it relies on large and precise instruments, professional operators and complex sample pretreatment processes, and has high detection cost and long time consumption, which cannot meet the actual needs of on-site rapid screening and real-time monitoring. The other is a field operation type detection technology, represented by traditional colorimetric method, which has certain application in basic detection due to its simple operation and low cost, but has inherent defects such as high detection limit, poor selectivity (easy to be interfered by coexisting ions), and single detection dimension (cannot realize multi-ion parallel detection), which is difficult to meet the precise detection needs of complex matrix samples.

[0004] In recent years, colorimetric sensing technology based on optical micro-nano structure has provided a new direction for breaking through the bottleneck of traditional detection technology due to its unique optical regulation capability. This kind of technology converts ion concentration change into intuitive color signal through the interaction of micro-nano structure and light, and has the advantages of high sensitivity and visualization. However, the existing related research still faces key technical bottlenecks: on the one hand, the wide spectrum coverage ability is insufficient, it is difficult to realize full-band tuning in the visible spectrum range, which limits the feasibility of multi-ion parallel coding detection; on the other hand, the sample demand is large and relies on complex fluid control device, which restricts its application in portable and on-site detection scenarios, and there is no mature solution that can meet the requirements of high sensitivity, wide spectrum coding, multi-ion parallel detection and portable operation at the same time. SUMMARY

[0005] The purpose of the present application is to solve the problems of low sensitivity, poor selectivity, complex operation, dependence on external equipment and difficulty in realizing high-selectivity parallel detection of multiple ions on a single portable device in the existing heavy metal ion detection technology. Specifically, the present application aims to provide a sensing device based on a stretchable metasurface and a heavy metal ion sensing method to realize high-selectivity chemical analysis based on multi-dimensional optical signals.

[0006] To achieve the above object, the application provides a sensing device based on a stretchable metasurface, comprising: a flexible stretchable substrate; an optical metasurface with periodic nanostructures arranged on the flexible stretchable substrate; the periodic nanostructures of the optical metasurface are configured to be able to spontaneously absorb a liquid to be measured into a sensing region of the optical metasurface by capillary effect; wherein the tensile strain of the flexible stretchable substrate can change the period of the optical metasurface, thereby tuning the resonance peak wavelength in the reflection spectrum or transmission spectrum thereof.

[0007] Further, the flexible stretchable substrate is made of a polydimethylsiloxane material and is configured to be able to realize elastic deformation within a preset strain range.

[0008] Further, the optical metasurface is a multilayer dielectric metasurface, comprising a top dielectric layer, an intermediate dielectric layer and a bottom dielectric layer arranged in order from top to bottom, and the top dielectric layer, the intermediate dielectric layer and the bottom dielectric layer constitute a gradient refractive index structure. wherein the three layers of dielectric materials are SiO2, TiO2 and Al2O3 from top to bottom.

[0009] Further, the three layers of dielectric materials adopt a gradient refractive index to realize the antireflection condition at the air / TiO2 and TiO2 / substrate boundaries. and ; n1 represents the refractive index of the top layer SiO2; n2 represents the refractive index of the bottom layer Al2O3; n air : the refractive index of air; n TiO2 : the refractive index of the intermediate spacer layer TiO2; n PDMS : the refractive index of the PDMS substrate.

[0010] Further, the refractive indices of the two kinds of media above and below the three layers of dielectric materials are n and n , respectively, and the thicknesses are λ0 / (4×n1) and λ0 / (4×n2), respectively, wherein

[0011] Further, the optical metasurface is composed of a nanostructure array of a single layer of high refractive index medium, and the nanostructure array is an amorphous silicon nanodisk array.

[0012] Further, the periodic nanostructures are a series of mutually parallel nanometer-long strip-shaped ridge structures, and the stretching direction of the flexible stretchable substrate is perpendicular to the extension direction of the nanometer-long strip-shaped ridge structures.

[0013] To achieve the above object, the application further provides a heavy metal ion sensing method, applied to any one of the above-mentioned sensing devices based on stretchable metasurfaces, comprising: applying a first strain to the flexible stretchable substrate to tune the resonance peak wavelength of the optical metasurface to a first preset wavelength; applying a to-be-detected liquid to the optical metasurface to spontaneously fill the sensing area; collecting a reflection spectrum or a transmission spectrum at the first preset wavelength to obtain a first spectral feature; determining whether the to-be-detected liquid contains a target heavy metal ion or determining the concentration thereof based on the first spectral feature.

[0014] Further, after the step of determining whether the to-be-detected liquid contains a target heavy metal ion or determining the concentration thereof, the method further comprises: applying a second strain to the flexible stretchable substrate to tune the resonance peak wavelength of the optical metasurface to a second preset wavelength, the second preset wavelength being different from the first preset wavelength; collecting a reflection spectrum or a transmission spectrum at the second preset wavelength to obtain a second spectral feature; combining the first spectral feature and the second spectral feature to determine the types or concentrations of two or more heavy metal ions in the to-be-detected liquid.

[0015] Optionally, the first spectral feature and / or the second spectral feature comprises a quality factor or a peak intensity of the resonance peak.

[0016] Compared with the prior art, the application has the following beneficial effects: Firstly, the application realizes high selectivity and multi-ion parallel detection capability. By actively stretching the substrate, the resonance peak can be accurately tuned to the wavelength most sensitive to a specific ion. In combination with the analysis of the characteristic influence of the ion on the spectral line shape (such as the quality factor or intensity), multi-dimensional detection based on wavelength selection and line shape analysis is realized, so that multiple different ions in a mixed solution can be distinguished and detected on a single device through step-by-step tuning, significantly improving the selectivity. Secondly, the application has high sensitivity and portability. The capillary effect between nanostructures is used to realize spontaneous and rapid enrichment of nanoliter-level to-be-detected liquid, without any external fluid control pump, greatly simplifying the device structure and operation process, making the device highly integrated and portable, and improving the detection sensitivity due to sample enrichment. In addition, the application has a wide spectral detection range. The stretchable property of the flexible substrate enables the resonance peak to be continuously tuned within a wide spectral range of hundreds of nanometers, providing a wide coding space for detecting multiple analytes with different spectral response characteristics. Finally, the application has a fast response. The passive capillary sampling process can be completed in a short time, combined with the rapid response mechanism of optical resonance, so that the entire detection process is very fast, meeting the needs of on-site rapid screening. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art 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.

[0018] Figure 1 This is a schematic diagram of the structure of a sensing device provided in an embodiment of this application; Figure 2 The quantitative curves of the reflection spectrum as a function of the strain rate (0-30%) of the PDMS substrate and its color changes are shown. Figure 3 The evolution of the reflection spectrum and color changes of the metasurface structure under strain on a PDMS substrate when different loss-causing and harmful substances are added to the metasurface structure; Figure 4 The effect of Hg2+ concentration on color properties was analyzed; Figure 5 A schematic diagram of a structure for realizing broadband encoded heavy metal ion colorimetric sensing by using capillary action to drive a metasurface, provided in an embodiment of this application; Figure 6 Signaling interaction timing diagram of a multi-ion detection method provided in the embodiments of this application; Figure 7 This is a flowchart illustrating a sensing method provided in an embodiment of this application.

[0019] Figure reference numerals: 1-Top layer medium; 2-Spacer layer medium; 3-Bottom layer medium; 4-Liquid to be tested; 5-Flexible stretchable substrate; S10-Providing sensing device step; S20-Applying strain and tuning wavelength step; S30-Adding sample and capillary filling step; S40-Acquiring reflectance spectrum step; S50-Analyzing spectral characteristics and determining ion species and concentration step; 601-Control terminal; 602-Sensor terminal; 610-Applying strain 1; 620-Tune to λ1; 630-Acquiring spectrum 1; 640-Analyzing and obtaining Q value 1; 650-Applying strain 2; 660-Tune to λ2; 670-Acquiring spectrum 2; 680-Analyzing and obtaining Q value 2. Detailed Implementation

[0020] To better understand the technical solutions of this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit this application.

[0021] Embodiment 1 The embodiment of the present application provides a heavy metal ion sensing device based on a stretchable metasurface and application thereof, which can realize high-sensitivity quantitative detection of specific heavy metal ions (such as mercury ions).

[0022] Referring to Figure 1 , the figure is a structural schematic diagram of a sensing device provided by the embodiment of the present application. The core structure of the device includes a flexible stretchable substrate 5 and an optical metasurface arranged on the substrate. In the embodiment, the flexible stretchable substrate 5 is preferably made of a polydimethylsiloxane material with good biocompatibility, high elasticity and high optical transparency. The polydimethylsiloxane substrate provides mechanical support for the entire device; it can be understood that the excellent elasticity enables the device to undergo controllable and recoverable tensile deformation under external force, which constitutes the basis for realizing active tuning of optical properties.

[0023] Arranged on the flexible stretchable substrate 5 is an optical metasurface with a periodic nanostructure. In the embodiment, the optical metasurface is designed as a multilayer dielectric structure to realize high-quality factor optical resonance and extremely low background reflection. Specifically, the metasurface includes a top layer dielectric 1, an interval layer dielectric 2 and a bottom layer dielectric 3 from top to bottom. In order to optimize the optical performance, the material selection and thickness of the three layers of dielectrics are carefully designed. As a preferred scheme, the top layer dielectric 1 adopts a silicon dioxide material, the interval layer dielectric 2 adopts a high refractive index titanium dioxide material, and the bottom layer dielectric 3 adopts an aluminum oxide material. The refractive indices of the three materials form a gradient distribution, that is, the refractive index of titanium dioxide is the highest, and the refractive indices of silicon dioxide and aluminum oxide are lower. This gradient refractive index structure can effectively suppress the broadband reflection of the non-resonant waveband, thereby obtaining a high-contrast resonant spectrum.

[0024] In specific implementation, the metasurface structure: composed of multilayer dielectrics, including a top SiO2 layer, a middle TiO2 layer and a bottom Al2O3 layer, adopts a gradient refractive index (GRIN) layer to realize the antireflection condition at the air / TiO2 and TiO2 / substrate boundaries, wherein and The thickness of each layer is optimized to achieve the best reflection performance. The thickness of the top SiO2 layer is λ0 / (4× n 1) (assuming that λ0 is the resonant wavelength), the thickness of the middle TiO2 layer is about 130 nm (determined according to empirical values and optimization simulation), and the thickness of the bottom Al2O3 layer is λ0 / (4× n2) The total thickness is approximately 300 nm. The square width is 175 nm, and the period is 350 nm (adjustable range 200-500 nm). The entire metasurface structure is fabricated on a polydimethylsiloxane (PDMS) substrate, which provides mechanical flexibility and optical transparency.

[0025] In practical implementation, the thickness of the spacer layer 2 (titanium dioxide layer) is designed to be approximately 130 nanometers in terms of specific geometric parameters. The thicknesses of the top layer medium 1 (silicon dioxide layer) and the bottom layer medium 3 (alumina layer) are designed based on the antireflection film principle, and their thicknesses can be approximated as one-quarter of the wavelength of the central working wavelength λ0 in the corresponding medium, i.e., λ0 / (4×n1) and λ0 / (4×n2), where n1 and n2 are the refractive indices of silicon dioxide and alumina, respectively. The total thickness of the entire multilayer dielectric film can be controlled to approximately 300 nanometers.

[0026] The multilayer dielectric film is patterned into a periodic array of nanostructures using processes such as nanoimprinting or etching. In this embodiment, the nanostructure is a periodically arranged array of square blocks. The side length (width) of each block is approximately 175 nanometers, and the initial period P of the unstretched array is approximately 350 nanometers. This carefully designed structure can support high-quality guided-mode resonance in the visible light band and generate a sharp resonance peak in the reflection spectrum.

[0027] It should be noted that in this embodiment, the periodic nanostructure of the optical metasurface is configured to spontaneously draw the test liquid 4 into the sensing area through capillary action. Specifically, the periodically arranged nanoblocks form tiny gaps and channels with widths and depths at the sub-micrometer level. When a drop of test liquid 4 (e.g., an aqueous solution containing heavy metal ions) comes into contact with the metasurface, significant capillary forces are generated in these micro- and nano-channels due to the strong interaction between the liquid and the hydrophilic metasurface material (e.g., silica) and the surface tension of the liquid. This force is sufficient to overcome the viscous resistance of the liquid itself, driving the liquid to spontaneously and rapidly wet and fill the gaps in the entire nanostructure array without any external pump or power source, forming a uniform liquid film with a thickness of less than 1 micrometer. This allows the analyte in the test liquid 4 to fully contact the sensing interface of the metasurface (mainly the sidewalls and top surface of the nanostructure).

[0028] As another feature of the device in this embodiment, by applying tensile strain to the flexible stretchable substrate 5, the period P of the optical metasurface can be linearly changed, thereby actively and continuously tuning the resonant peak wavelength in its reflection spectrum. When a uniaxial tensile force is applied to the flexible stretchable substrate 5 made of polydimethylsiloxane, the substrate elongates along the stretching direction, and the optical metasurface above it deforms accordingly, causing the period P of the nanocube array to increase in the stretching direction. According to the principle of guided mode resonance or grating coupling, the resonant wavelength is positively correlated with the structural period. Accordingly, as the period increases, the resonant peak in the reflection spectrum shifts to a longer wavelength direction, i.e., a redshift occurs. In this embodiment, by applying a strain of 0% to about 30%, the resonant peak in the unstretched state in the blue-violet region (e.g., about 447 nm) can be continuously tuned to the red region (e.g., about 700 nm), covering the entire visible spectrum. This broadband tuning capability allows the reflected color of the device to draw a broad trajectory on the chromaticity diagram, covering more than 140% of the sRGB color gamut.

[0029] For specific implementation details, please refer to [link / reference]. Figure 2 From three dimensions—structural periodicity, reflection spectrum, and color gamut coverage—the system presents the optical properties of periodic nanosurfaces and their supporting role in colorimetric sensing technology for heavy metal ions. Figure 2 The two-dimensional mapping diagram in (a) intuitively shows that as the metasurface structure period increases from 200 nm to 500 nm, the reflection peak wavelength continuously redshifts from 400 nm to 700 nm, clearly demonstrating the positive correlation between the structure period and the resonance wavelength. Figure 2 (b) The reflectance spectrum curves corresponding to different periods further verify that the reflectance peak can be precisely tuned in the entire visible light band by adjusting the structural period, which provides feasibility for multi-ion color coding detection. Figure 2 (c) The CIE chromaticity diagram shows that the metasurface's color coverage exceeds the sRGB standard and approaches the Adobe RGB wide color gamut, possessing rich color variation capabilities and accurately distinguishing different heavy metal ions through color differences. These characteristics collectively support heavy metal detection technology based on stretchable metasurfaces, which can change the structural period through mechanical stretching to achieve broadband reflection tuning and multi-ion parallel color encoding, laying a key optical foundation for high-sensitivity, portable on-site heavy metal detection.

[0030] See below. Figure 4 This document describes in detail the detection of mercury ions (Hg) using the apparatus described in this embodiment. 2+ The method.

[0031] This image visually illustrates the changes in reflectance spectrum and structural color differences of mercury ions (Hg) from two dimensions. 2+ The effect of concentration on the optical properties of metasurfaces demonstrates their high sensitivity and visualization capabilities in the quantitative detection of heavy metals. The three-dimensional reflectance spectrum on the left: the horizontal axis represents wavelength (400-700nm, visible light range), the vertical axis represents reflectance, and the depth axis represents Hg. 2+ Concentration (0-1000ppm). With Hg 2+ As the concentration increases, the intensity of the reflection peak at a specific wavelength (approximately 650-700 nm) on the metasurface decreases significantly, and the peak shape gradually broadens – this is because Hg… 2+ Interacting with metasurfaces introduces additional optical losses, leading to increased resonant energy dissipation. This pattern of "the higher the concentration, the weaker the reflection peak" provides a spectroscopic basis for quantitative detection.

[0032] The effect of heavy metal Hg ion concentration on color properties was analyzed, with pre-stretched PDMS enabling metasurface periodic matching of target ion characteristic peaks (such as Hg). 2+ (Corresponding to a 447nm period), capillary-driven automatic filling of the test liquid forms a submicron-level detection layer (filling time <30 seconds). See also... Figure 7 A specific detection method includes the following steps: Step S10, providing a sensing device with the above-described structure. Step S20, presetting the device. Specifically, a first strain is applied to the flexible stretchable substrate 5 to tune the resonance peak wavelength of the optical metasurface to the first preset wavelength. According to preliminary experimental studies, mercury ions have the most significant effect on the optical loss of the metasurface at a specific wavelength. Assuming that the characteristic response wavelength is 447 nm, the operator can apply a precise tensile strain (e.g., about 30%) to the polydimethylsiloxane substrate using a micro-stretching device and monitor the reflection spectrum in real time using a micro-spectrometer until the center wavelength of the resonance peak stabilizes at 447 nm. Step S30, applying the test liquid 4 to the optical metasurface. The operator can use a micropipette to draw nanoliters of the test aqueous solution and gently drop it onto the sensing area of ​​the metasurface. As mentioned above, after the droplet contacts the metasurface, it will spontaneously fill the gaps in the nanostructure within a very short time (e.g., within 30 seconds) driven by capillary force, completing the passive loading process of the sample. Step S40: Acquire and analyze the reflectance spectrum. After the sample loading is complete and stabilized, use a spectrometer to measure the reflectance spectrum near a wavelength of 447 nm to obtain the first spectral characteristics reflecting information about the liquid to be tested. Step S50: Based on the obtained first spectral characteristics, determine whether the target heavy metal ions are present in the liquid to be tested or determine their concentration. Please refer to [link to relevant documentation]. Figure 4When the test liquid is pure water, the metasurface exhibits a sharp, high-intensity reflection peak at 447 nm, demonstrating a high quality factor (Q value). When the test liquid contains mercury ions, these ions undergo chemical or physical adsorption with the metasurface material (especially titanium dioxide or surfaces with specific functionalization modifications). This interaction introduces additional optical losses. Increased optical losses lead to aggravated energy dissipation in the resonant cavity, specifically manifested in the reflection spectrum as a significant decrease in the peak intensity of the resonance peak and a broadening of the peak shape (i.e., an increase in the full width at half maximum), resulting in a significant decrease in the quality factor (Q value), where the Q value can be defined as the ratio of the resonance wavelength to the full width at half maximum. This decrease in peak intensity and Q value becomes more pronounced with increasing mercury ion concentration. By pre-establishing calibration curves for the peak intensity or Q value corresponding to standard solutions of mercury ions at different concentrations, the concentration of mercury ions in an unknown sample can be deduced by measuring the spectral characteristics, achieving quantitative detection. The device in this embodiment achieves a detection limit on the order of parts per million (ppm), and the entire detection process is rapid and portable.

[0033] In practical implementation, the fabrication steps of a heavy metal ion colorimetric sensor include: 1. Material selection and preparation: SiO2, TiO2 and Al2O3 materials with appropriate refractive indices are selected, and the thickness of each layer is precisely controlled by electron beam lithography and plasma etching technology to prepare metasurface structures.

[0034] 2. Photolithography process: Electron beam lithography (EBL, accuracy ±5nm) + reactive ion etching (RIE, SF6 gas) is used. 3. Material deposition: SiO2 / Al2O3 is grown by PECVD, and TiO2 is deposited by ALD (thickness deviation <3%). 4. PDMS substrate preparation: Oxygen plasma activation enhances adhesion, and PDMS substrates are prepared by mold casting to ensure high optical transparency and mechanical flexibility.

[0035] 5. Metasurface-substrate integration: The prepared metasurface structure is transferred onto a PDMS substrate to form a complete colorimetric sensor.

[0036] 6. Capillary effect: Utilizing the hydrophilicity of the metasurface of the medium, the test liquid spontaneously wets into the submicron detection area through the capillary effect, thus completing the enrichment of nanoscale samples.

[0037] In some embodiments, the metasurface structure has a unit cell period of 350 nm, a prism height of 300 nm, and a width of 175 nm. By adjusting the strain of the PDMS substrate, the reflection peak can be continuously tuned from 400 nm to 700 nm, covering 140% of the sRGB color gamut, providing a color coding space for multi-ion parallel detection.

[0038] Furthermore, in some embodiments, the metasurface structure, combined with capillary effects, enables the detection of heavy metal ions with only nanoliter samples, significantly improving detection efficiency and sensitivity. Combined with the rapid spectral response mechanism of metasurface resonance modes, detection time can be greatly shortened, meeting the needs of rapid on-site screening.

[0039] Example 2 This embodiment aims to illustrate the broad applicability of the technical solution of this application, and its core concept is not limited to a specific combination of materials and structures. As an optional implementation, this embodiment provides a variant of the sensing device using different materials and structures.

[0040] In this embodiment, the flexible and stretchable substrate 5 is made of transparent polyurethane elastomer. Transparent polyurethane is also a polymer material with excellent elasticity and optical transparency, which can meet the requirements of mechanical tuning.

[0041] Accordingly, the structure of the optical metasurface was also adjusted. Unlike the multilayer dielectric structure in Example 1, the metasurface in this embodiment is composed of a single layer of high-refractive-index dielectric. Specifically, a periodically arranged array of amorphous silicon nanodisks is fabricated on a transparent polyurethane substrate using nanofabrication techniques. Amorphous silicon has a high refractive index in the visible light band, which can support strong Mie resonances. By precisely designing the height and diameter of the nanodisks, they can generate high-quality Mie resonance modes in the target wavelength range, thereby forming clear resonance peaks in the reflection or transmission spectra. At the same time, the spacing between the nanodisks is optimized to ensure that sufficiently strong capillary forces are generated to achieve spontaneous filling of the liquid to be tested.

[0042] The operation of this device is similar to that of Example 1. By applying uniaxial stretching to the transparent polyurethane substrate, the period of the amorphous silicon nanodisc array in the stretching direction can be changed, thereby achieving continuous tuning of its Mie resonance wavelength. After the liquid to be tested is dropped onto the metasurface, the liquid will spontaneously fill the gaps between the nanodiscs due to capillary effect. The analytes (such as heavy metal ions) in the liquid to be tested interact with the surface of the amorphous silicon nanodiscs. This interaction can manifest as an alteration of the local refractive index environment around the nanodiscs, or as the introduction of optical loss as described in Example 1. Both mechanisms will cause measurable changes in the resonance peaks in the reflection spectrum, such as a shift in the position of the resonance peaks, or changes in their quality factor and peak intensity. By monitoring these changes in spectral characteristics, the analytes can also be detected.

[0043] This embodiment demonstrates that the key to realizing the core function of this application lies in the synergistic combination of a flexible, stretchable substrate and a periodic nano-optical structure with capillary effect, rather than being limited to a polydimethylsiloxane substrate or a specific multilayer dielectric metasurface structure. It is understood that other flexible substrate materials capable of providing elasticity, as well as any other nanostructures capable of changing their periodicity and supporting optical resonance (such as nanopillars, nanopores, gratings, etc.), as long as their geometry can generate a capillary effect, fall within the scope of this application.

[0044] Example 3 This embodiment details how to use a single sensing device to detect multiple different heavy metal ions (e.g., mercury ions, Hg) in a mixed solution. 2+ and cadmium ions Cd 2+ Selective parallel detection of wavelength selection and line shape analysis is achieved. This method fully utilizes the active spectral tuning capability of the device presented in this application, realizing a multi-dimensional detection strategy that combines wavelength selection and line shape analysis.

[0045] This embodiment employs the same sensing device structure as in Embodiment 1, namely, a multilayer dielectric metasurface based on a polydimethylsiloxane substrate. The technical principle of this method lies in the wavelength-dependent effect of different types of heavy metal ions on optical loss when interacting with the metasurface. That is, one type of ion may cause the largest decrease in Q value at wavelength λ1, while another type of ion may cause the largest decrease in Q value at a different wavelength λ2. This method utilizes this difference in response.

[0046] Please refer to the following: Figure 3 , Figure 6 , Figure 3 This schematically illustrates the principle of multidimensional detection, namely that different types of lossy substances (representing different ions) will cause different changes in the spectral line shape; Figure 6 The dynamic process of multi-ion detection is intuitively displayed in the form of a signaling interaction timing diagram.

[0047] In specific implementation, combined with Figure 3 , Figure 3 The evolution of the reflectance spectrum and color changes of the metasurface structure under PDMS substrate strain when different destructive substances are added are shown. The performance of the metasurface structure in multi-ion colorimetric detection is further analyzed, including the tuning of the reflectance spectrum and changes in structural color. Different heavy metal ions (such as Hg) are also considered. 2+ Pb 2+ Cd 2+This introduces differentiated optical losses, corresponding to peak differences in the imaginary part of the metasurface's dielectric constant, resulting in unique optical responses within specific wavelength ranges. Based on this, the tensile strain of the PDMS substrate can continuously tune the metasurface period, thereby altering the reflection peak wavelength and assigning "exclusive wavelength codes" to different ions across the entire visible light region of 400-700 nm. This avoids spectral overlap and enables parallel multi-ion identification—for example, detecting Hg. 2+ Pre-stretching PDMS can tune the corresponding metasurface reflection peak to the blue-violet band, Pb 2+ Corresponding to the green light band, Cd 2+ In the red light band, the characteristic evolution of the reflectance spectrum induced by each ion exhibits no cross-interference. Furthermore, changes in the reflectance spectrum directly translate into visually perceptible differences in structural color, such as Hg. 2+ Darken the blue-purple hue, Pb 2+ Reduce the brightness of green tones and Cd 2+ This results in a shift in red hues, supporting rapid initial screening with the naked eye. Combined with quantitative analysis of reflectance peak position, peak intensity, and Q value using a spectrometer, it also enables precise concentration determination at the ppm level. In summary, metasurfaces, with their "ion specificity due to optical loss + broad-spectrum tuning of PDMS strain + visual encoding of structural colors," offer high selectivity, a wide detection range, and high compatibility in multi-ion colorimetric detection, providing an innovative solution for the simultaneous screening of multiple metal ions in environmental water bodies and food matrices, combining rapid initial screening with precise quantification.

[0048] The specific detection method steps are as follows: First, a sensing device as described in Example 1 is provided, and a mixed test solution containing unknown concentrations of mercury ions and cadmium ions is dropped onto the metasurface, allowing it to spontaneously fill the entire sensing area through capillary effect. Unlike single-ion detection, this process only requires the sample to be loaded once.

[0049] Next, we enter the multi-step detection and analysis stage, which corresponds to... Figure 6 The interactive process is shown. Step 1: Detect the first type of ion (e.g., mercury ions). This process corresponds to... Figure 6The first stage involves the control terminal 601 sending a command to the sensor terminal 602 to apply a first strain 610. The magnitude of this strain is precisely controlled so that the optical metasurface resonance peak of the sensor terminal 602 is tuned to the characteristic response wavelength λ1 of mercury ions (e.g., 447 nm), as shown in step 620. Subsequently, the control terminal 601 sends a spectrum acquisition command 630, and the sensor terminal 602 (or its associated spectrometer) acquires the reflectance spectrum data at this moment and returns it. The control terminal 601 analyzes the received spectral data and calculates the quality factor Q1, as shown in step 640. Since wavelength λ1 is preferred for mercury ions, the change in Q1 primarily reflects the concentration information of mercury ions, while the influence of cadmium ions at this wavelength is relatively small. The second step involves detecting a second ion (e.g., cadmium ions). This process corresponds to... Figure 6 The second stage involves maintaining the sample and device states. Control terminal 601 sends a command to sensor terminal 602 to apply a second strain 650, different from the first strain. This strain is typically larger than the first strain, aiming to further redshift the resonance peak to the characteristic response wavelength λ2 (e.g., 550 nm) of cadmium ions, as shown in step 660. After tuning stabilization, control terminal 601 sends another spectral acquisition command 670 and receives the returned second set of spectral data. Control terminal 601 analyzes this data and calculates the quality factor Q2 at wavelength λ2, as shown in step 680. Similarly, changes in Q2 primarily reflect the concentration information of cadmium ions. The third step involves data processing and concentration determination. After acquiring data in two dimensions (Q1 and Q2), the concentrations of both ions can be simultaneously determined using a pre-established mathematical model. For example, a system of two linear equations can be established: ΔQ1=k 11 [Hg 2+ ]+k 12 [Cd 2+ ]ΔQ2=k 21 [Hg 2+ ]+k 22 [Cd 2+ ] Where ΔQ1 and ΔQ2 are the measured changes in Q value relative to the pure water reference value, [Hg 2+ ] and [Cd 2+ [ ] represents the concentrations of the two ions to be determined. The coefficients kᵢⱼ are elements of the sensitivity matrix, representing the contribution of the j-th ion to the change in Q value at wavelength λᵢ. These coefficients can be pre-calibrated by measuring a series of standard samples with known concentrations. Since at the characteristic wavelength, the diagonal elements are much larger than the off-diagonal elements (i.e., k ≠ ... 11 >>k 12 And k 22 >>k 21 The system of equations is well-state and can be solved stably, thus simultaneously obtaining [Hg]2+ ] and [Cd 2+ The accurate concentration of ions can be determined. In more complex systems, machine learning algorithms such as principal component analysis, partial least squares regression, or neural networks can be used to process multidimensional spectral data, enabling parallel detection of a wider range of ions.

[0050] This embodiment separates the information of different ions in the spectral dimension by performing stepwise, multi-wavelength dynamic spectral measurements on a single device and a single sample, which greatly improves the selectivity of detection and solves the problem that traditional sensors have difficulty distinguishing ions with similar chemical properties. This fully demonstrates the inventiveness and beneficial effects of the solution proposed in this application.

[0051] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A sensing device based on a stretchable metasurface, characterized in that, include: A flexible, stretchable substrate; An optical metasurface with a periodic nanostructure disposed on the flexible stretchable substrate; The periodic nanostructure of the optical metasurface is configured to spontaneously draw the liquid to be tested into the sensing region of the optical metasurface through capillary effect. The tensile strain of the flexible stretchable substrate can change the period of the optical metasurface, thereby tuning the resonant peak wavelength in its reflection or transmission spectrum.

2. The sensing device according to claim 1, characterized in that, The flexible stretchable substrate is made of polydimethylsiloxane material and is configured to achieve elastic deformation within a preset strain range.

3. The sensing device according to claim 1, characterized in that, The optical metasurface is a multilayer dielectric metasurface, comprising a top dielectric layer, a spacer dielectric layer, and a bottom dielectric layer arranged sequentially from top to bottom, and the top dielectric layer, spacer dielectric layer, and bottom dielectric layer constitute a gradient refractive index structure; The three dielectric materials, from top to bottom, are SiO2, TiO2, and Al2O3.

4. The sensing device according to claim 3, characterized in that, The three-layer dielectric uses a gradient refractive index to achieve anti-reflection conditions at the air / TiO2 and TiO2 / substrate boundaries; and n1 represents the refractive index of the top layer SiO2; n2 represents the refractive index of the bottom layer Al2O3; n air The refractive index of air; n TiO2 : The refractive index of the intermediate spacer layer TiO2; n PDMS : The refractive index of the PDMS substrate.

5. The sensing device according to claim 4, characterized in that, The refractive indices of the upper and lower media in the three-layered medium are respectively and . The thicknesses are λ0 / (4×n1) and λ0 / (4×n2), respectively. The characteristic wavelength is determined by the midpoint of the visible light band.

6. The sensing device according to claim 1, characterized in that, The optical metasurface is composed of a nanostructure array made of a single layer of high refractive index medium, and the nanostructure array is an amorphous silicon nanodisk array.

7. The sensing device according to claim 1, characterized in that, The periodic nanostructure is a series of parallel nanorib-shaped ridges, and the stretching direction of the flexible stretchable substrate is perpendicular to the extension direction of the nanorib-shaped ridges.

8. A method for sensing heavy metal ions, applied to a sensing device based on a stretchable metasurface as described in any one of claims 1-7, characterized in that, Includes the following steps: Step 1: Apply a first strain to the flexible stretchable substrate to tune the resonance peak wavelength of the optical metasurface to a first preset wavelength; Step 2: Apply the liquid to be tested onto the optical metasurface, allowing it to spontaneously fill the sensing area; Step 3: Collect the reflection or transmission spectrum at the first preset wavelength to obtain the first spectral characteristics; Step 4: Based on the first spectral characteristics, determine whether the target heavy metal ions are present in the liquid to be tested or determine their concentration.

9. The method according to claim 8, characterized in that, Following step four, the following is also included: Step 5: Apply a second strain to the flexible stretchable substrate to tune the resonance peak wavelength of the optical metasurface to a second preset wavelength, the second preset wavelength being different from the first preset wavelength; Step 6: Collect the reflection or transmission spectrum at the second preset wavelength to obtain the second spectral characteristics; Step 7: Combining the first spectral feature and the second spectral feature, determine the types or concentrations of two or more heavy metal ions in the liquid to be tested.

10. The method according to claim 8 or 9, characterized in that, The first spectral feature and / or the second spectral feature includes the quality factor or peak intensity of the resonance peak.

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