A method for detecting glucose in sweat using a mica-based hydrogel-functionalized metasurface.

Abstract

This invention discloses a method for detecting glucose in sweat using a mica-based hydrogel-functionalized metasurface, comprising the following steps: 1) preparing a mica-based terahertz sensor; 2) modifying the mica-based terahertz sensor with hydrogel to obtain a hydrogel composite terahertz sensor; 3) using a terahertz time-domain spectroscopy (THz-TDS) system to test the terahertz transmission spectrum of the hydrogel composite terahertz sensor in a dry state, using it as a reference spectrum; 4) applying the sweat sample to be tested onto the surface of the hydrogel composite terahertz sensor, collecting the terahertz transmission spectrum in the test state, using it as the test spectrum; comparing the test spectrum with the reference spectrum, calculating the resonant peak frequency shift, and establishing a correlation curve between glucose concentration and the resonant peak frequency shift, thereby detecting glucose concentration. This method has high detection sensitivity and a low detection limit.

Description

Technical Field

[0001] This invention belongs to the field of non-invasive blood glucose detection technology, specifically relating to a method for detecting glucose in sweat from a mica-based hydrogel-functionalized metasurface. Background Technology

[0002] Diabetes mellitus is a common chronic metabolic disease with a continuously rising incidence, making it a significant public health issue worldwide. Accurate monitoring of blood glucose levels is crucial for early screening, disease assessment, and long-term management of diabetes. Current traditional blood glucose testing methods mostly rely on blood sampling and analysis, which are invasive procedures with drawbacks such as inconvenience, poor patient compliance, and difficulty in achieving high-frequency continuous monitoring. Therefore, developing non-invasive, convenient, and highly sensitive glucose testing technologies has significant clinical value for early diagnosis and long-term management.

[0003] Sweat, as an easily obtainable bodily fluid sample, offers advantages such as non-invasive collection, continuous acquisition, and suitability for wearable testing, making it an important target for non-invasive glucose monitoring. However, the glucose concentration in sweat is typically low, making detection difficult using traditional methods. With the rapid development of modern micro-nano technology, metasurfaces have emerged as sensors for the effective detection of glucose in sweat. The paper "Research on Glucose Sensing Based on Polymer / Metal Composite Metamaterials" (Li Shanlei, Sensors & Microsystems, Vol. 43, No. 12, 2024) publicly proposes a terahertz biomolecular sensing enhancement method based on polymer / metal composite metamaterials. The polymer / metal composite metamaterial was fabricated using in-situ rapid femtosecond laser processing. The low dielectric constant of the polymer substrate significantly enhanced the electromagnetic response intensity of the biomolecular-terahertz-surface microstructure, enabling sensitive detection of glucose markers. Experimental results show that the metamaterial device has a high Q value of 4.11, a sensing sensitivity of 4.1 THZ / (mol / L) for glucose solutions in the concentration range of 2–10 mmol / L, and a detection limit of 0.085 mmol / L. However, existing methods for detecting glucose in sweat still suffer from problems such as insufficient sensitivity, low specificity, and limited detection stability. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for detecting glucose in sweat on a mica-based hydrogel functionalized metasurface, which has high detection sensitivity and low detection limit.

[0005] The technical solution provided by this invention is a method for detecting glucose in sweat from a mica-based hydrogel-functionalized metasurface, comprising the following steps:

[0006] 1) Mica pretreatment is performed to obtain a mica substrate with a thickness of 20-50 μm. Photoresist is coated on the surface of the mica substrate, photolithography is performed, and gold is plated to obtain a mica substrate terahertz sensor.

[0007] 2) Acrylamide, 3-acrylamidophenylboronic acid and N,N'-methylenebisacrylamide are the main components, mixed in a mol ratio of (78-79):20:(1-2), and dissolved in PBS buffer to prepare a mixed solution; a redox initiation system is prepared using 10-20 wt% ammonium persulfate aqueous solution and 2-4% v / v tetramethylethylenediamine aqueous solution; the redox initiation system is added to the mixed solution to obtain the hydrosol precursor solution;

[0008] 3) The mica-based terahertz sensor was modified with a hydrogel precursor solution. The modified mica-based terahertz sensor was then placed in PBS buffer for swelling and equilibration to obtain a hydrogel composite terahertz sensor.

[0009] 4) The terahertz transmission spectrum of the hydrogel composite terahertz sensor in a dry state was tested using a terahertz time-domain spectroscopy system (THz-TDS) as a reference spectrum.

[0010] 5) Apply the sweat sample to be tested to the surface of the hydrogel composite terahertz sensor, collect the terahertz transmission spectrum under the test state, and use it as the test spectrum; compare the test spectrum with the reference spectrum, calculate the frequency shift of the resonance peak, and establish the relationship curve between glucose concentration and spectral response characteristics, so as to realize the detection of glucose concentration in sweat.

[0011] In step 1), reducing the thickness of the mica substrate helps to reduce the absorption and disturbance of terahertz waves by the substrate, thereby improving the resonant response; a thickness of 20–50 μm is preferable. An excessively thin substrate increases the difficulty of peeling and processing. A mica substrate thickness of 20 μm is optimal.

[0012] In step 2), acrylamide, 3-acrylamidophenylboronic acid and N,N'-methylenebisacrylamide are mixed in a mol ratio of (78-79):20:(1-2) and dissolved in PBS buffer to prepare a mixed solution.

[0013] Specifically,

[0014] a) Weigh acrylamide, 3-acrylamidophenylboronic acid and N,N'-methylenebisacrylamide in a mol ratio of (78-79):20:(1-2) for later use.

[0015] b) First, prepare PBS buffer, then add the prescribed amounts of acrylamide, 3-acrylamidophenylboronic acid and N,N'-methylenebisacrylamide in sequence, and vacuum process to obtain a mixture.

[0016] Preferably, the molar ratio of acrylamide, 3-acrylamidophenylboronic acid and N,N'-methylenebisacrylamide is 78:20:1.5.

[0017] In step 2), the total weight percentage of acrylamide, 3-acrylamidophenylboronic acid, and N,N'-methylenebisacrylamide in the mixture is 8-12 wt%. Preferably, the total weight percentage of acrylamide, 3-acrylamidophenylboronic acid, and N,N'-methylenebisacrylamide in the mixture is 10 wt%.

[0018] In step 2), a redox initiation system is prepared using a 10–20 wt% ammonium persulfate aqueous solution and a 2–4% v / v tetramethylethylenediamine aqueous solution; adding the redox initiation system to the mixture yields the hydrosol precursor solution; specifically:

[0019] a) Dissolve ammonium persulfate in deionized water to prepare an aqueous solution of ammonium persulfate with a mass concentration of 10-20 wt%;

[0020] b) Dissolve tetramethylethylenediamine in deionized water to prepare an aqueous solution of tetramethylethylenediamine with a volume concentration of 2-4% v / v;

[0021] c) Add ammonium persulfate aqueous solution and tetramethylethylenediamine aqueous solution to the mixture to prepare hydrogel precursor solution.

[0022] Preferably, the amount of ammonium persulfate aqueous solution added is 1% to 2% of the weight of the mixture; the amount of tetramethylethylenediamine aqueous solution added is 1% to 2% of the weight of the mixture.

[0023] Before the hydrogel precursor solution modification in step 3), 3-aminopropyltriethoxysilane (APTES) was coated on the surface of the mica-based terahertz sensor to improve the bonding performance between the mica substrate surface and the hydrogel interface. A molecular bridge was established between the mica substrate and the hydrogel by connecting the silane end to the mica and the amino end to / adsorb the hydrogel, improving wetting, adhesion, and film uniformity. The coating thickness was a monolayer or close to a monolayer. Coating method: A 1.0 v / v% APTES / anhydrous ethanol solution was prepared, uniformly spread on a clean metasurface, allowed to stand at room temperature for 10 min, and then dried at room temperature.

[0024] Step 3) involves modifying the mica-based terahertz sensor with a hydrogel precursor solution, including the following steps:

[0025] a) A polyimide film is used to form a thin film ring around the upper surface of the mica substrate terahertz sensor. The thin film ring and the upper surface of the mica substrate terahertz sensor form a receiving cavity, and a cover glass is added to the receiving cavity for fixation.

[0026] b) Inject the hydrogel precursor solution into the receiving cavity to form a hydrogel layer; the thickness of the hydrogel layer is 20-100 μm.

[0027] c) Remove the film ring and glass slide, and wash the hydrogel layer with deionized water.

[0028] The thickness of the hydrogel is determined by the height of the cavity enclosed by the polyimide film. The thickness of the hydrogel layer is 20-100 μm. A high Q value can be achieved within this range. A high Q value can well reflect the resolution of the sensor. A high Q value can, to some extent, overcome the loss caused by electromagnetic radiation and is manifested as a sharper resonance peak in the spectrum.

[0029] More preferably, the hydrogel layer thickness is 20 μm, at which point the effect is best.

[0030] In step 3), the mica-based terahertz sensor modified with the hydrogel precursor solution is immersed in PBS buffer for 10–15 min. The pH of the PBS buffer is 7.4.

[0031] Steps 4 and 5).

[0032] Δf = f test -f ref ;

[0033] Where f ref f is the resonant frequency corresponding to the reference spectrum. test The resonant frequency corresponding to the test spectrum; Δf is in GHz.

[0034] By establishing a curve relating Δf to glucose concentration (mM), and measuring the frequency shift Δf of a sweat sample with unknown glucose concentration, the glucose concentration can be inferred, thus enabling qualitative and quantitative detection of glucose concentration in sweat.

[0035] After glucose detection, the hydrogel composite terahertz sensor can be immersed in PBS buffer (pH 7.4) for 10–15 minutes. This allows the hydrogel composite terahertz sensor to return to baseline and be used again for detection, thus improving the sensor's reusability.

[0036] Compared with the prior art, this application has the following beneficial effects:

[0037] 1) The base uses mica, which is flexible and non-toxic. It can be applied directly to the skin and can still be used normally after repeated bending.

[0038] 2) Under normal circumstances, the moisture in sweat has a very strong absorption effect on terahertz waves, greatly affecting the signal and resulting in large detection errors. Furthermore, the coffee ring effect occurs after sweat dries, also affecting signal intensity. Complete drying also fails to maintain cell viability, further increasing detection errors. Therefore, sweat cannot be detected using terahertz technology. However, this invention, through improvements to the hydrogel formulation and specific selection of hydrogel thickness, utilizes a highly three-dimensional polymerized network of the hydrogel to circumvent the coffee ring effect, enabling direct and accurate detection of glucose in sweat.

[0039] 3) After calculation, the detection sensitivity of this detection method is 63.124 GHz / mM and the detection limit is 0.0667 mM.

[0040] Instruction manual illustrations

[0041] Figure 1 A terahertz sensor structure based on a mica substrate;

[0042] Figure 2 The effect of different hydrogel thicknesses on transmittance;

[0043] Figure 3 The effect of different mica thicknesses on transmittance;

[0044] Figure 4 This is a schematic diagram of the overall process;

[0045] Figure 5 A schematic diagram of the process of a mica-based terahertz sensor.

[0046] Figure 6 A schematic diagram of the process for a hydrogel composite terahertz sensor;

[0047] Figure 7 The graph shows the changes in terahertz transmission spectra for samples with different glucose concentrations.

[0048] Figure 8 The graph shows the fitting relationship between the frequency shift of the resonance peak and the concentration of low-concentration glucose.

[0049] Figure 9 To restore the baseline image of the hydrogel composite terahertz sensor. Detailed Implementation

[0050] The following specific embodiments further illustrate the present invention, but are not intended to limit the present invention.

[0051] Example 1

[0052] 1. A mica substrate with a thickness of 20 μm is obtained by pre-processing flexible mica. Photoresist is coated on the surface of the mica substrate, photolithography is performed, and gold is plated to obtain a mica substrate terahertz sensor.

[0053] Specifically:

[0054] 1.1 Mica Pretreatment:

[0055] a) Mechanically peeling the flexible mica involves using a scalpel to lift the layered structure at the edge of the mica, combined with ultrasonic vibration to assist in layering, and using adhesive tape to assist in peeling off the surface mica, resulting in fresh, atomically flat mica.

[0056] b) The smooth mica was washed in acetone and anhydrous ethanol in sequence, and then dried to obtain the mica substrate.

[0057] 1.2 Coating and etching of photoresist:

[0058] a) Place the cleaned mica substrate on the spin coater turntable, add an appropriate amount of photoresist using a dropper or pipette, and spin coat the substrate with a uniform thickness and no interference patterns on the surface.

[0059] b) Transfer the spin-coated mica to a hot plate and bake at 100°C for 5 minutes;

[0060] c) Place the designed photomask onto the mask chuck of the ultraviolet lithography machine, and use the ultraviolet lithography machine to expose the mica to form the pattern on the mask;

[0061] 4) Develop the mica substrate in the developer solution, then rinse it in deionized water and dry it.

[0062] 1.3, Gold plating:

[0063] a) Gold deposition is performed by placing a mica substrate with a photoresist pattern into a high-vacuum resistance thermal evaporation coating system;

[0064] b) The mica substrate with deposited metal was removed from the coating system and subjected to ultrasonic treatment in an acetone solution. Then, deionized water was used to remove residual acetone, and the sample was dried by nitrogen purging to obtain the mica-based terahertz sensor. The specific shape of the gold resonator array is shown in [reference needed]. Figure 1 .

[0065] 2. Preparation of hydrogel precursor solution:

[0066] a) Weigh acrylamide, 3-acrylamidophenylboronic acid and N,N'-methylenebisacrylamide at a molar ratio of 78:20:1.5 and set aside.

[0067] b) Prepare PBS buffer by sequentially adding acrylamide, 3-acrylamidophenylboronic acid, and N,N'-methylenebisacrylamide in the above-mentioned proportions, followed by vacuum treatment to obtain a mixture; the total weight of acrylamide, 3-acrylamidophenylboronic acid, and N,N'-methylenebisacrylamide accounts for 10 wt% of the weight of the mixture.

[0068] c) Dissolve ammonium persulfate in deionized water to prepare a 10 wt% ammonium persulfate aqueous solution;

[0069] d) Dissolve tetramethylethylenediamine in deionized water to prepare a 2% v / v tetramethylethylenediamine aqueous solution;

[0070] e) Add 1% by weight of ammonium persulfate aqueous solution and 1% by weight of tetramethylethylenediamine aqueous solution to the mixture, mix well, and the hydrosol precursor solution is obtained.

[0071] 3. Dissolve 3-aminopropyltriethoxysilane (APTES) in anhydrous ethanol to prepare a 1.0 v / v% APTES / anhydrous ethanol solution. Take 50 μL of the solution and spread it evenly on a clean supersurface. Let it stand at room temperature for 10 min and then dry at room temperature.

[0072] 4. The mica-based terahertz sensor was modified using a hydrogel precursor solution, specifically as follows:

[0073] a) A polyimide film is used to form a thin film ring around the upper surface of the mica substrate terahertz sensor. The thin film ring and the upper surface of the mica substrate terahertz sensor constitute a receiving cavity. The height of the receiving cavity is limited to 20 μm. A cover glass is added to the receiving cavity and fixed with a dovetail clip.

[0074] b) Inject the hydrogel precursor solution into the cavity to form a hydrogel layer with a thickness of 20 μm;

[0075] c) Remove the film ring, glass slide, and dovetail clip, and wash the hydrogel layer with deionized water to remove unreacted components;

[0076] d) The hydrogel-modified sensor was then immersed in PBS buffer (pH 7.4) for 10 min to allow for swelling equilibrium. The sensor was then removed and excess liquid on the surface was removed to obtain the hydrogel composite terahertz sensor.

[0077] 5. Using a terahertz time-domain spectroscopy system (THz-TDS), the terahertz transmission spectrum of the hydrogel composite terahertz sensor in a dry state was tested as a reference spectrum.

[0078] 6. Apply the sweat sample to be tested to the surface of the hydrogel composite terahertz sensor, collect the terahertz transmission spectrum under the test state, and use it as the test spectrum; compare the test spectrum with the reference spectrum, calculate the frequency shift of the resonance peak, and establish the relationship curve between glucose concentration and spectral response characteristics, so as to realize the detection of glucose concentration in sweat.

[0079] 7. After completing the glucose detection, the hydrogel composite terahertz sensor can be immersed in PBS buffer (pH 7.4) for 10 minutes to make the hydrogel composite terahertz sensor reusable.

[0080] Example 2

[0081] Example 2 is identical to Example 1 in all steps, except that the thickness of the hydrogel layer in step 4) is 50 μm.

[0082] Example 3

[0083] Example 3 is identical to Example 1 in all steps except that the thickness of the hydrogel layer in step 4) is 100 μm.

[0084] Compare with Example 1

[0085] The steps in Comparative Example 1 and Example 1 are the same, except that the thickness of the hydrogel layer in step 4) is 200 μm.

[0086] Experimental Example 1

[0087] The hydrogel composite terahertz sensors prepared in Examples 1-3 and Comparative Example 1 were subjected to transmittance testing. The test results are shown in [Figure 1]. Figure 2 It is evident that a depth of 20 μm is superior to other curves, and the depth can be used to calculate the Q-value: the quality factor Q can effectively reflect the sensor's resolution. A high Q-value can, to some extent, overcome the losses caused by electromagnetic radiation, resulting in a sharper resonance peak in the spectrum.

[0088] Experiment Example 2

[0089] The hydrogel composite terahertz sensor prepared in Example 1 was used to detect glucose concentration in sweat.

[0090] 1) The terahertz transmission spectrum of the hydrogel composite terahertz sensor in a dry state was tested using a terahertz time-domain spectroscopy system (THz-TDS) as a reference spectrum.

[0091] 2) Apply the sweat sample to be tested to the surface of the hydrogel composite terahertz sensor and collect the terahertz transmission spectrum under the test state as the test spectrum; compare the test spectrum with the reference spectrum and calculate the frequency shift of the resonance peak as the main characteristic parameter; in order to reduce measurement error, the same sample can be measured repeatedly and the average value can be taken.

[0092] 3) Collect terahertz spectral data for different sweat samples, and extract the resonant peak frequency shift as the main spectral response characteristic parameter, see [link to relevant documentation]. Figure 7 ; Construct the mapping relationship between glucose concentration and terahertz spectral response characteristics, see Figure 8 .

[0093] The resonant peak frequency shift is defined as: Δf = f test -f ref The unit is GHz;

[0094] Where f ref f is the resonant frequency corresponding to the reference spectrum. test The resonant frequency corresponding to the test spectrum is used. To avoid the influence of the frequency shift direction on the response intensity characterization, the absolute value of the frequency shift, |Δf|, is used as the sensing response parameter in subsequent analysis, with units of GHz.

[0095] S: Sensitivity, measured in GHz / mM;

[0096] C: Glucose concentration, in mM.

[0097] a) Experimental results show that as glucose concentration increases, the frequency shift of the resonance peak gradually increases and eventually stabilizes. This phenomenon indicates that the effective recognition sites in the phenylboronic acid hydrogel are gradually occupied by glucose molecules, and the swelling degree of the hydrogel gradually reaches saturation. Therefore, the frequency shift response exhibits typical saturation growth characteristics. The mapping relationship between the frequency shift and glucose concentration is established using the Hill equation:

[0098]

[0099] The results show that the established Hill model can accurately describe the change law of frequency shift response gradually approaching saturation during the increase of glucose concentration. It can be used to establish a continuous mapping relationship between frequency shift and glucose concentration, and can also be used to establish a glucose concentration inversion model.

[0100] For samples with unknown concentrations, the terahertz transmission spectrum is first acquired and the resonant peak frequency is extracted; then the corresponding frequency shift |Δf| is calculated; and the frequency shift is substituted into the Hill fitting model mentioned above, and the corresponding glucose concentration C is obtained through numerical solution, thereby realizing the quantitative detection of glucose concentration.

[0101] That is: Sample to be tested → Terahertz spectral acquisition → Extraction of resonant frequency → Calculation of frequency shift Δf → Hill model inversion → Output of glucose concentration.

[0102] b) Because the frequency shift response exhibits a non-linear saturation relationship with glucose concentration, the response capability varies across different concentration ranges. Therefore, average sensitivity is used to evaluate the sensor's detection performance within a specified concentration range. Average sensitivity is defined as:

[0103]

[0104] Where |Δf2||Δf1| represent the frequency shifts at glucose concentrations C2 and C1, respectively. Based on the experimentally measured characteristic frequency changes, the average sensitivity S = 91.818 GHz / mM in the extremely low concentration range of 0–0.5 mM; and the average sensitivity S = 63.124 GHz / mM in the low concentration range of 0–2 mM. These results indicate that the sensor has a high response capability in the low-concentration glucose detection range and can meet the requirements for sweat glucose detection.

[0105] The limit of detection (LOD) is further used to evaluate the sensor's minimum detection capability, and its calculation formula is as follows:

[0106]

[0107] Where: σ represents the standard deviation of the detection signal corresponding to the blank sample, i.e., the 0 mM glucose sample, in GHz.

[0108] S represents the sensor sensitivity, measured in GHz / mM;

[0109] 3: Usually, a signal-to-noise ratio of 3 is used.

[0110] σ = 1.404 GHz;

[0111] Considering that the concentration range of 0–2 mM covers the main application range of sweat glucose detection, the detection limit is calculated using the average sensitivity within this concentration range. The calculated result is:

[0112] LOD=3×1.404 / 63.124=0.0667 mM.

[0113] The results show that the phenylboronic acid hydrogel-functionalized mica-based terahertz metasurface sensor proposed in this invention has high sensitivity and low detection limit, enabling rapid, label-free, and quantitative detection of glucose concentration. Furthermore, the glucose concentration of unknown samples can be directly calculated through the established concentration inversion model.

[0114] 4) After completing the detection, the hydrogel composite terahertz sensor can be immersed in PBS buffer (pH 7.4) for 10 min to restore it to its baseline state before being used for detection again, thereby improving the reusability of the sensor. See [link to relevant documentation]. Figure 9 .

[0115] Example 4

[0116] 1. A mica substrate with a thickness of 50 μm is obtained by pre-processing flexible mica. Photoresist is coated on the surface of the mica substrate, photolithography is performed, and gold is plated to obtain a mica substrate terahertz sensor. The specific mica substrate pre-processing, photoresist coating, etching, and gold plating are the same as in Example 1.

[0117] 2. Preparation of hydrogel precursor solution:

[0118] a) Weigh acrylamide, 3-acrylamidophenylboronic acid and N,N'-methylenebisacrylamide at a mol ratio of 78:20:1 and set aside.

[0119] b) Prepare PBS buffer by sequentially adding the prescribed amounts of acrylamide, 3-acrylamidophenylboronic acid, and N,N'-methylenebisacrylamide, followed by vacuum treatment to obtain a mixture; the total weight of acrylamide, 3-acrylamidophenylboronic acid, and N,N'-methylenebisacrylamide accounts for 8 wt% of the weight of the mixture.

[0120] c) Dissolve ammonium persulfate in deionized water to prepare a 20 wt% ammonium persulfate aqueous solution;

[0121] d) Dissolve tetramethylethylenediamine in deionized water to prepare a 4% v / v tetramethylethylenediamine aqueous solution;

[0122] e) Add 2% by weight of ammonium persulfate aqueous solution and 2% by weight of tetramethylethylenediamine aqueous solution to the mixture, mix well, and the hydrosol precursor solution is obtained.

[0123] 3. Dissolve 3-aminopropyltriethoxysilane (APTES) in anhydrous ethanol to prepare a 1.0 v / v% APTES / anhydrous ethanol solution. Take 50 μL of the solution and spread it evenly on a clean supersurface. Let it stand at room temperature for 10 min and then dry at room temperature.

[0124] 4. The mica-based terahertz sensor was modified using a hydrogel precursor solution, specifically as follows:

[0125] a) A polyimide film is used to form a thin film ring around the upper surface of the mica substrate terahertz sensor. The thin film ring and the upper surface of the mica substrate terahertz sensor constitute a receiving cavity. The height of the receiving cavity is limited to 100μm. A cover glass is added to the receiving cavity and fixed with a dovetail clip.

[0126] b) Inject the hydrogel precursor liquid into the cavity to form a hydrogel layer with a thickness of 100 μm.

[0127] c) Remove the film ring, glass slide and dovetail clip, and wash the hydrogel layer with deionized water to remove unreacted components;

[0128] d) The hydrogel-modified thickness sensor was then immersed in PBS buffer (pH 7.4) for 15 minutes to allow for swelling equilibrium. The sensor was then removed and excess liquid on the surface was removed to obtain the hydrogel composite terahertz sensor.

[0129] 5. Using a terahertz time-domain spectroscopy system (THz-TDS), the terahertz transmission spectrum of the hydrogel composite terahertz sensor under equilibrium state was tested and used as a reference spectrum.

[0130] 6. Apply the sweat sample to be tested to the surface of the hydrogel composite terahertz sensor, collect the terahertz transmission spectrum under the test state, and use it as the test spectrum; compare the test spectrum with the reference spectrum, calculate the frequency shift of the resonance peak, and establish the relationship curve between glucose concentration and spectral response characteristics, so as to realize the detection of glucose concentration in sweat.

[0131] 7. After completing the glucose detection, the hydrogel composite terahertz sensor can be immersed in PBS buffer (pH 7.4) for 15 minutes to make the hydrogel composite terahertz sensor reusable.

[0132] Example 5

[0133] 1. A mica substrate with a thickness of 30 μm is obtained by pre-processing flexible mica. Photoresist is coated on the surface of the mica substrate, photolithography is performed, and gold is plated to obtain a mica substrate terahertz sensor. The specific mica pre-processing, photoresist coating, etching, and gold plating are the same as in Example 1.

[0134] 2. Preparation of hydrogel precursor solution:

[0135] a) Weigh acrylamide, 3-acrylamidophenylboronic acid and N,N'-methylenebisacrylamide at a mol ratio of 79:20:2 and set aside.

[0136] b) Prepare PBS buffer (pH 7.4), add acrylamide, 3-acrylamidophenylboronic acid and N,N'-methylenebisacrylamide in the prescribed amounts sequentially, and vacuum process to obtain a mixture; the total weight of acrylamide, 3-acrylamidophenylboronic acid and N,N'-methylenebisacrylamide accounts for 12 wt% of the weight of the mixture.

[0137] c) Dissolve ammonium persulfate in deionized water to prepare a 10 wt% ammonium persulfate aqueous solution;

[0138] d) Dissolve tetramethylethylenediamine in deionized water to prepare a 4% v / v tetramethylethylenediamine aqueous solution;

[0139] e) Add 1% by weight of ammonium persulfate aqueous solution and 2% by weight of tetramethylethylenediamine aqueous solution to the mixture, mix well, and the hydrosol precursor solution is obtained.

[0140] 3. Dissolve 3-aminopropyltriethoxysilane (APTES) in anhydrous ethanol to prepare a 1.0 v / v% APTES / anhydrous ethanol solution. Take 50 μL of the solution and spread it evenly on a clean supersurface. Let it stand at room temperature for 10 min and then dry at room temperature.

[0141] 4. The mica-based terahertz sensor was modified using a hydrogel precursor solution, specifically as follows:

[0142] a) A polyimide film is used to form a thin film ring around the upper surface of the mica substrate terahertz sensor. The thin film ring and the upper surface of the mica substrate terahertz sensor constitute a receiving cavity. The height of the receiving cavity is limited to 50 μm, and a cover glass is added to the receiving cavity for fixation.

[0143] b) The hydrogel precursor solution is injected into the cavity for modification to form a hydrogel layer with a thickness of 50 μm;

[0144] c) Remove the film ring, glass slide, and dovetail clip, and wash the hydrogel layer with deionized water to remove unreacted components;

[0145] d) The hydrogel-modified sensor was then immersed in PBS buffer (pH 7.4) for 12 min to allow for swelling equilibrium. The sensor was then removed and excess liquid on the surface was aspirated to obtain the hydrogel composite terahertz sensor.

[0146] 5. Using a terahertz time-domain spectroscopy system (THz-TDS), the terahertz transmission spectrum of the hydrogel composite terahertz sensor in a dry state was tested as a reference spectrum.

[0147] 6. Apply the sweat sample to be tested to the surface of the hydrogel composite terahertz sensor, collect the terahertz transmission spectrum under the test state, and use it as the test spectrum; compare the test spectrum with the reference spectrum, calculate the frequency shift of the resonance peak, and establish the relationship curve between glucose concentration and spectral response characteristics, so as to realize the detection of glucose concentration in sweat.

[0148] 7. After glucose detection, the hydrogel composite terahertz sensor can be soaked in PBS buffer (pH 7.4) for 13 minutes to make the hydrogel composite terahertz sensor reusable.

[0149] Example 6

[0150] 1. A mica substrate with a thickness of 20 μm is obtained by pre-processing flexible mica. Photoresist is coated on the surface of the mica substrate, photolithography is performed, and gold is plated to obtain a mica substrate terahertz sensor. The specific mica substrate pre-processing, photoresist coating, etching, and gold plating are the same as in Example 1.

[0151] 2. Preparation of hydrogel precursor solution:

[0152] a) Weigh acrylamide, 3-acrylamidophenylboronic acid and N,N'-methylenebisacrylamide at a mol ratio of 79:20:1 and set aside.

[0153] b) Prepare PBS buffer by sequentially adding the prescribed amounts of acrylamide, 3-acrylamidophenylboronic acid, and N,N'-methylenebisacrylamide, followed by vacuum treatment to obtain a mixture; the total weight of acrylamide, 3-acrylamidophenylboronic acid, and N,N'-methylenebisacrylamide to the mixture is 11 wt%.

[0154] c) Dissolve ammonium persulfate in deionized water to prepare a 15 wt% ammonium persulfate aqueous solution;

[0155] d) Dissolve tetramethylethylenediamine in deionized water to prepare a 3% v / v tetramethylethylenediamine aqueous solution;

[0156] e) Add 1.5% by weight of ammonium persulfate aqueous solution and 1.5% by weight of tetramethylethylenediamine aqueous solution to the mixture, mix well, and the hydrosol precursor solution is obtained.

[0157] 3. Dissolve 3-aminopropyltriethoxysilane (APTES) in anhydrous ethanol to prepare a 1.0 v / v% APTES / anhydrous ethanol solution. Take 50 μL of the solution and spread it evenly on a clean supersurface. Let it stand at room temperature for 10 min and then dry at room temperature.

[0158] 4. The mica-based terahertz sensor was modified using a hydrogel precursor solution, specifically as follows:

[0159] a) A polyimide film is used to form a thin film ring around the upper surface of the mica substrate terahertz sensor. The thin film ring and the upper surface of the mica substrate terahertz sensor constitute a receiving cavity with a height of 20 μm. A cover glass is added to the receiving cavity for fixation.

[0160] b) Inject the hydrogel precursor solution into the cavity to form a hydrogel layer with a thickness of 20 μm;

[0161] c) Remove the film ring, glass slide, and dovetail clip, and wash the hydrogel layer with deionized water to remove unreacted components;

[0162] d) The hydrogel-modified sensor was then immersed in PBS buffer (pH 7.4) for 15 min to allow for swelling equilibrium. The sensor was then removed and excess liquid on the surface was aspirated to obtain the hydrogel composite terahertz sensor.

[0163] 5. Using a terahertz time-domain spectroscopy system (THz-TDS), the terahertz transmission spectrum of the hydrogel composite terahertz sensor in a dry state was tested as a reference spectrum.

[0164] 6. Apply the sweat sample to be tested to the surface of the hydrogel composite terahertz sensor, collect the terahertz transmission spectrum under the test state, and use it as the test spectrum; compare the test spectrum with the reference spectrum, calculate the frequency shift of the resonance peak, and establish the relationship curve between glucose concentration and spectral response characteristics, so as to realize the detection of glucose concentration in sweat.

[0165] 7. After completing the glucose detection, the hydrogel composite terahertz sensor can be immersed in PBS buffer (pH 7.4) for 10 minutes to make the hydrogel composite terahertz sensor reusable.

[0166] Compare with Example 2

[0167] A mica substrate with a thickness of 10 μm was obtained by pre-processing flexible mica. Photoresist was coated on the surface of the mica substrate, photolithography was performed, and gold was plated to obtain a mica substrate terahertz sensor. The specific mica substrate pre-processing, photoresist coating, etching, and gold plating were the same as in Example 1.

[0168] Compare with Example 3

[0169] Flexible mica was pretreated to obtain a mica substrate with a thickness of 100 μm. Photoresist was coated on the surface of the mica substrate, photolithography was performed, and gold was plated to obtain a mica substrate terahertz sensor. The specific mica substrate pretreatment, photoresist coating, etching, and gold plating were the same as in Example 1.

[0170] Experimental Example 3

[0171] Transmittance testing was performed on the mica-based terahertz sensors prepared in Examples 1 and 4, and Comparative Examples 2 and 3. The test results are shown in [Figure 1]. Figure 3 It can be seen that the sensor is very sensitive to changes in mica thickness. A 10μm mica substrate is too thin and fragile, which is not conducive to its use, while a 100μm substrate is too thick, which will affect the resonance peak effect and result in large errors. A 20μm substrate produces the best results.

[0172] Experiment Example 4

[0173] The hydrogel composite terahertz sensor prepared in Example 1 was coated with a 0 mM glucose solution, and its transmission spectrum was measured as a baseline. After cleaning and drying, 20 μL of a 0.5 mM glucose solution was added to the sensor surface. After the reaction was complete, the water was absorbed, and the sensor was then immersed in PBS buffer for 10 min before its transmission spectrum was measured. The same method was used to test 1 mM, 2 mM, 5 mM, and 10 mM glucose solutions sequentially, followed by PBS washing, and then terahertz transmission spectrum detection was performed. The results are shown in [Figure 1]. Figure 9 After multiple uses, the frequency shift of the sensor did not change, indicating that the sensor can recover its detection level after being soaked in PBS buffer and has good repeatability.

Claims

1. A method for detecting glucose in sweat from a mica-based hydrogel-functionalized metasurface, characterized in that: Includes the following steps: 1) Mica pretreatment is performed to obtain a mica substrate with a thickness of 20-50 μm. Photoresist is coated on the surface of the mica substrate, photolithography is performed, and gold is plated to obtain a mica substrate terahertz sensor. 2) Acrylamide, 3-acrylamidophenylboronic acid and N,N'-methylenebisacrylamide are the main components, mixed in a mol ratio of (78-79):20:(1-2), dissolved in PBS buffer to prepare a mixed solution; 10-20 wt% ammonium persulfate aqueous solution and 2-4% v / v tetramethylethylenediamine aqueous solution are used as the redox initiation system, and the redox initiation system is added to the mixed solution to obtain the hydrosol precursor solution; 3) The mica-based terahertz sensor was modified with a hydrogel precursor solution. The modified mica-based terahertz sensor was then placed in PBS buffer for swelling and equilibration to obtain a hydrogel composite terahertz sensor. 4) The terahertz transmission spectrum of the hydrogel composite terahertz sensor in a dry state was tested using a terahertz time-domain spectroscopy system (THz-TDS) as a reference spectrum. 5) Apply the sweat sample to be tested to the surface of the hydrogel composite terahertz sensor and collect the terahertz transmission spectrum under the test state as the test spectrum; By comparing the test spectrum with the reference spectrum, calculating the frequency shift of the resonance peak, and establishing the relationship curve between glucose concentration and spectral response characteristics, the glucose concentration in sweat can be detected.

2. The method for detecting glucose in sweat using a mica-based hydrogel-functionalized metasurface according to claim 1, characterized in that: In step 1), the mica substrate thickness is 20 μm.

3. The method for detecting glucose in sweat using a mica-based hydrogel-functionalized metasurface according to claim 1, characterized in that: In step 2), the molar ratio of acrylamide, 3-acrylamidophenylboronic acid and N,N'-methylenebisacrylamide is 78:20:1.

5.

4. The method for detecting glucose in sweat using a mica-based hydrogel-functionalized metasurface according to claim 1, characterized in that: In step 2), the total weight of acrylamide, 3-acrylamidophenylboronic acid and N,N'-methylenebisacrylamide accounts for 8 to 12 wt% of the weight of the mixture.

5. The method for detecting glucose in sweat from a mica-based hydrogel-functionalized metasurface according to claim 1, characterized in that: In step 2), the total weight of acrylamide, 3-acrylamidophenylboronic acid and N,N'-methylenebisacrylamide accounts for 10 wt% of the weight of the mixture.

6. The method for detecting glucose in sweat using a mica-based hydrogel-functionalized metasurface according to claim 1, characterized in that: In step 2), the amount of ammonium persulfate aqueous solution added is 1% to 2% of the weight of the mixture; the amount of tetramethylethylenediamine aqueous solution added is 1% to 2% of the weight of the mixture.

7. The method for detecting glucose in sweat using a mica-based hydrogel-functionalized metasurface according to claim 1, characterized in that: Prior to the hydrogel modification in step 3), 3-aminopropyltriethoxysilane was coated onto the mica-based terahertz sensor surface.

8. The method for detecting glucose in sweat using a mica-based hydrogel-functionalized metasurface according to claim 1, characterized in that: Step 3) involves modifying the mica-based terahertz sensor with a hydrogel precursor solution, including the following steps: a) A polyimide film is used to form a thin film ring around the upper surface of the mica substrate terahertz sensor. The thin film ring and the upper surface of the mica substrate terahertz sensor form a receiving cavity, and a cover glass is added to the receiving cavity for fixation. b) Inject the hydrogel precursor solution into the receiving cavity to form a hydrogel layer; the thickness of the hydrogel layer is 20-100 μm. c) Remove the film ring and glass slide, and rinse the hydrogel layer with deionized water.

9. The method for detecting glucose in sweat using a mica-based hydrogel-functionalized metasurface according to claim 8, characterized in that: The thickness of the hydrogel layer is 20 μm.

10. The method for detecting glucose in sweat from a mica-based hydrogel-functionalized metasurface according to claim 1, characterized in that: After glucose detection, the hydrogel composite terahertz sensor can be immersed in PBS buffer for 10–15 min.

Images