A flexible SERS sensor for sweat marker detection and a preparation method and application thereof

Abstract

The application provides a flexible SERS sensor for sweat marker detection and a preparation method and application thereof.The SERS sensor is a composite structure of a Janus nanofiber membrane and a gold nanoparticle film; the Janus nanofiber membrane is composed of a hydrophilic fiber layer and a hydrophobic fiber layer, and the gold nanoparticle film is closely attached to the surface of the hydrophilic layer of the Janus nanofiber membrane.The SERS sensor has a one-way microfluidic transmission performance, can effectively collect sweat in the hydrophilic layer, and can keep the hydrophobic layer almost dry, thereby enhancing the skin comfort.The preparation method and structure of the SERS sensor are simple, and the SERS sensor has the characteristics of lightness, thinness, softness, stretchability, wearability, high sensitivity, high selectivity, good stability and the like, so that the SERS sensor becomes an excellent SERS sensor material, can measure the pH level and the concentration of lactic acid, uric acid and the like in sweat, and provides real-time data support for health management and disease prevention.

Description

Technical Field

[0001] This invention belongs to the field of biosensor technology, specifically relating to a flexible SERS sensor for detecting sweat biomarkers, its preparation method, and its application. Background Technology

[0002] Hormone testing in bodily fluids plays a vital role in medical diagnosis and treatment. Hormones are chemical messengers produced by the body's endocrine system, crucial for regulating physiological processes such as metabolism, growth and development, and reproductive function. By detecting hormone levels in blood, urine, or other bodily fluids, various diseases can be detected and diagnosed at an early stage, such as thyroid dysfunction, diabetes, and gonadal dysfunction. Furthermore, hormone testing helps doctors assess patients' health conditions, develop personalized treatment plans, and monitor treatment effectiveness.

[0003] Monitoring an individual's health is crucial for assessing physical condition and facilitating early disease detection. In this regard, sweat is a valuable and readily available source of information, containing various molecules reflecting physiological status, including hydrogen ions (H+), lactic acid, glucose, cortisol, and other hormones directly related to acid-base balance, energy metabolism, exercise intensity, stress levels, endocrine function, and chronic diseases such as diabetes. Furthermore, because sweat is a byproduct of skin excretion, samples can be conveniently and non-invasively collected, making it ideal for providing comfortable health monitoring services for athletes or those with chronic conditions. Wearable smart devices have made significant progress in addressing the need for human health monitoring through their real-time data tracking, personalization, and user convenience capabilities. Wearable devices utilizing sweat monitoring represent an effective and advanced method for achieving physiological monitoring.

[0004] Typically, the amount of sweat produced by a single instance is relatively small; therefore, sweat acquisition is a crucial initial step in sweat monitoring. Cotton fabrics are known for their superior sweat-wicking ability, primarily due to the unique porous structure and capillary action of cotton fibers, which endow them with strong hydrophilicity. Upon contact with hydrophilic fibers, sweat is transferred from the skin surface to these fibers under the influence of surface tension and wettability. Furthermore, prolonged contact between the skin and saturated hydrophilic fibers can lead to discomfort and promote bacterial growth due to the need for prolonged sweat monitoring. In addition to small molecule information substances, sweat also contains trace amounts of proteins that can affect the sensing performance of these molecules and contribute to microbial proliferation. Therefore, ideally, wearable devices placed on the skin must effectively acquire sweat while ensuring relatively dry skin and efficient separation of interfering components.

[0005] Current wearable sweat detection methods are mainly divided into optical and electrochemical methods. Electrochemical methods require the design of complex and precise two-electrode or three-electrode systems, which increases the complexity of the entire device and the difficulty of manufacturing.

[0006] Optical sensors are relatively simple to design and manufacture, characterized by low cost and low technological barriers. They typically possess high sensitivity and resolution, enabling the detection of minute changes. For example, in the biomedical field, precise monitoring of biomarker concentration changes can be achieved by analyzing specific wavelengths of reflected or transmitted light in a sample. Furthermore, because light signals can propagate through air, these sensors exhibit excellent performance in remote monitoring applications. With advancements in nanotechnology, novel nanomaterials have been integrated into optical sensing systems, thereby improving their performance and expanding their application range. Surface-enhanced Raman scattering (SERS) is a highly sensitive optical sensing method capable of single-molecule detection; high selectivity is typically achieved through the use of nanostructures and surface modifications. Moreover, due to the inherently weak Raman scattering signals in aquatic environments, SERS technology demonstrates significant advantages in detecting trace markers in water-based systems.

[0007] Therefore, it is of great significance to develop a SERS sensor material that can ensure relatively dry skin, enhance comfort, effectively capture sweat and separate interfering components, and possess high sensitivity, stability and selectivity, so as to accurately measure the composition of human sweat through SERS technology and thus provide real-time data support for health management and disease prevention. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a flexible SERS sensor for sweat marker detection, its fabrication method, and its applications. The SERS sensor of this invention features a simple fabrication method and structure, and is characterized by its thinness, flexibility, stretchability, and wearability, allowing for seamless integration with human skin or clothing and providing excellent comfort. The sensor is a composite structure of a Janus nanofiber membrane and a gold nanoparticle film. The Janus nanofiber membrane consists of hydrophilic and hydrophobic fiber layers and possesses unidirectional microfluidic transport properties, making it suitable for human skin and promoting sweat collection. Sweat can transfer from the hydrophobic layer to the hydrophilic layer, where the hydrophilic layer effectively extracts trace amounts of sweat secreted by the skin, while the hydrophobic layer maintains a dry contact interface, thereby enhancing user comfort during wear and effectively separating interfering components. Furthermore, by tightly bonding a functional self-assembled gold nanoparticle thin film layer to the surface of the hydrophilic layer of a Janus nanofiber membrane, a highly sensitive, selective, and stable SERS sensor material was developed. As a SERS substrate, the concentrations of components such as pH level, lactic acid, and uric acid in sweat were measured by Raman spectroscopy detection and spectral analysis, providing real-time data support for health management and disease prevention.

[0009] The technical solution of the present invention is as follows:

[0010] A flexible SERS sensor for detecting sweat markers is a composite structure of Janus nanofiber membrane and gold nanoparticle film. The Janus nanofiber membrane consists of hydrophilic and hydrophobic fiber layers, and the gold nanoparticle film is tightly adhered to the surface of the hydrophilic fiber layer. The hydrophilic fiber layer is a composite fiber membrane of polyacrylonitrile (PAN) and polyethyleneimine (PEI), and the hydrophobic fiber layer is a polyurethane (PU) fiber membrane.

[0011] According to a preferred embodiment of the present invention, the thickness of the Janus nanofiber membrane is 80-120 μm, and the thickness of the gold nanoparticle film is 10-20 nm.

[0012] According to a preferred embodiment of the present invention, the diameter of the fibers in the hydrophilic fiber layer is 0.31±0.04μm, and the diameter of the fibers in the hydrophobic fiber layer is 1.28±0.27μm.

[0013] The above-mentioned method for preparing a flexible SERS sensor for sweat biomarker detection includes the following steps:

[0014] (1) Polyacrylonitrile and polyethyleneimine are fully dissolved in N,N-dimethylformamide, and bubbles are removed by ultrasonication to obtain spinning solution. Then, hydrophilic fiber layer is obtained by electrospinning.

[0015] (2) Polyurethane was fully dissolved in N,N-dimethylformamide, and bubbles were removed by ultrasonication to obtain a spinning solution; then the spinning solution was deposited onto the hydrophilic fiber layer by electrospinning, and dried to obtain a Janus nanofiber membrane.

[0016] (3) Heat the HAuCl4 aqueous solution to boiling, add sodium citrate aqueous solution, and react to obtain gold nanoparticle aqueous solution; add n-hexane, and let stand to form aqueous solution / n-hexane interface; add ethanol, and the gold nanoparticles migrate to the aqueous solution / n-hexane interface and self-assemble into gold nanoparticle film; use Janus nanofiber membrane as carrier to recover the gold nanoparticle film from the interface, so that the gold nanoparticle film is tightly attached to the surface of the hydrophilic fiber layer of Janus nanofiber membrane, and obtain a flexible SERS sensor for sweat marker detection.

[0017] According to a preferred embodiment of the present invention, in step (1), the mass ratio of polyacrylonitrile to polyethyleneimine is 2-4:1, and the total mass concentration of polyacrylonitrile and polyethyleneimine in the spinning solution is 6-10%.

[0018] According to a preferred embodiment of the present invention, in step (1), the electrospinning conditions are as follows: the voltage is 20kV, the spinning solution propulsion rate is 0.5-2mL / h, the hydrophilic fiber layer is collected on a rotating drum receiver, and the distance between the needle tip and the collecting electrode is 10-20cm.

[0019] According to a preferred embodiment of the present invention, in step (2), the mass concentration of polyurethane in the spinning solution is 20-25%.

[0020] According to a preferred embodiment of the present invention, in step (2), the electrospinning conditions are as follows: the voltage is 18kV, the spinning solution propulsion rate is 0.3-0.8mL / h, the distance between the needle tip and the collector electrode is 10-20cm, and the spinning solution is deposited onto the hydrophilic fiber layer on the surface of the rotating drum receiver.

[0021] According to a preferred embodiment of the present invention, in step (3), the concentration of the HAuCl4 aqueous solution is 0.5-2 mmol / L, the concentration of the sodium citrate aqueous solution is 36-40 mmol / L, and the volume ratio of the HAuCl4 aqueous solution to the sodium citrate aqueous solution is 8-12:1.

[0022] According to a preferred embodiment of the present invention, in step (3), the reaction time is 10-20 min, and the reaction is carried out under boiling conditions.

[0023] According to a preferred embodiment of the present invention, in step (3), the volume ratio of the gold nanoparticle aqueous solution to n-hexane is 2-4:2, and the volume ratio of ethanol to n-hexane is 1:1.

[0024] According to the present invention, the flexible SERS sensor has high SERS enhancement capability and good stability, and can detect Rhodamine 6G (R6G) probe molecules at concentrations as low as 10. -10 At mol / L, the SERS signal intensity of different batches of samples showed high consistency, and the relative deviation of the Raman characteristic peak intensity remained at a low level (<10%).

[0025] The aforementioned application of the flexible SERS sensor for sweat biomarker detection is used to detect the pH and / or biomarkers in sweat.

[0026] According to the present invention, the marker is preferably lactic acid or uric acid.

[0027] According to a preferred embodiment of the present invention, the method for detecting the pH of sweat includes the following steps: immersing a SERS sensor in an aqueous solution of 4-aminobenzoic acid (4-MBA) with a concentration of 0.5-2 mmol / L for 2 hours, then removing, washing, and drying to obtain a modified SERS sensor; then, adding sodium acetate buffer solutions of different pH values ​​dropwise onto the modified SERS sensor, drying, and establishing the COO-pH relationship between pH and 4-MBA using Raman spectroscopy and spectral analysis. - Quantitative relationship between the intensity ratio of Raman characteristic peaks of tensile vibration and aromatic ring vibration; Sweat droplets were added to the hydrophobic surface of a modified SERS sensor, dried, and detected by Raman spectroscopy and spectral analysis, based on the relationship between pH and the COO of 4-MBA. -The relationship between the ratio of the Raman peak intensity of tensile vibration and aromatic ring vibration is used to detect the pH of sweat.

[0028] According to a preferred embodiment of the present invention, the method for detecting lactic acid or uric acid in sweat includes the following steps: adding lactic acid or uric acid solutions of different concentrations to a SERS sensor, drying, and then performing Raman spectroscopy detection and spectral analysis to establish a quantitative relationship between the intensity of the Raman characteristic peaks of lactic acid or uric acid and their concentration; adding sweat to the hydrophobic surface of the SERS sensor, drying, and then performing Raman spectroscopy detection and spectral analysis to detect lactic acid or uric acid in sweat based on the relationship between the intensity of the Raman characteristic peaks of lactic acid or uric acid and their concentration.

[0029] The technical features and beneficial effects of this invention are as follows:

[0030] 1. The sensor of the present invention has a simple preparation method and structure, and is characterized by being thin, soft, stretchable, and wearable. It is comfortable to wear for a long time and reduces interference with daily activities.

[0031] 2. The sensor of this invention is a composite structure of Janus nanofiber membrane and gold nanoparticle film. The Janus nanofiber membrane consists of hydrophilic and hydrophobic fiber layers, and the self-assembled gold nanoparticle film is tightly bonded to the surface of the hydrophilic fiber layer of the Janus nanofiber membrane. The hydrophilic fiber layer is PAN / PEI fiber, and the hydrophobic fiber layer is PU fiber.

[0032] 3. The Janus nanofiber membrane in the sensor of this invention has a unidirectional microfluidic transport function. When a droplet comes into contact with the hydrophobic fiber layer, the droplet will gradually penetrate and reach the hydrophilic fiber layer. The capillary force applied by the hydrophilic fiber layer acts as an effective pumping mechanism to continuously draw the droplet from the hydrophobic surface to the hydrophilic layer, so that the droplet eventually reaches the surface of the gold nanoparticle film.

[0033] Therefore, the hydrophobic layer in the sensor maintains close contact with the skin, while the hydrophilic layer primarily collects trace amounts of sweat. Sweat can be unidirectionally transported from the hydrophobic layer to the hydrophilic layer, ultimately reaching the surface of the gold nanoparticle film. This effectively saturates the entire hydrophilic region while maintaining a near-dry state on the hydrophobic side. The Janus nanofiber membrane is woven with numerous pores, giving it specific separation capabilities. During unidirectional transport, macromolecules exhibit slower movement, resulting in limited diffusion distances. Furthermore, due to the osmotic effect, larger molecular impurities (such as proteins) in sweat are effectively retained within the membrane, while smaller chemical molecules can diffuse to SERS hotspots. Thus, the sensor of this invention facilitates sweat collection while ensuring skin dryness, effectively reducing discomfort associated with sweat adhesion, inhibiting microbial growth, and enhancing user comfort, making it an ideal carrier for wearable sensors.

[0034] 4. In the sensor of this invention, gold nanoparticles are closely attached to the hydrophilic layer surface of the Janus nanofiber membrane, which can serve as a SERS substrate. The SERS signal can be enhanced through molecular modification. As a SERS sensor, it can achieve sensitive detection of different markers.

[0035] 5. The SERS sensor of this invention has high sensitivity, selectivity and stability. Through Raman spectroscopy detection and spectral analysis, it can detect the pH of sweat and / or lactic acid or uric acid in sweat, providing real-time data support for health management and disease prevention. Attached Figure Description

[0036] Figure 1 Figures showing the structural characterization and hydrophilic / hydrophobic properties of the Janus nanofiber membrane and sensor.

[0037] Figure 2 This is a diagram showing the unidirectional microfluidic transport behavior of the Janus nanofiber membrane.

[0038] Figure 3 SERS spectra of different concentrations of R6G used as the SERS substrate (a), and statistical distribution and relative deviation of the Raman characteristic peak intensities of R6G from different batches of SERS substrates (b).

[0039] Figure 4 The SERS spectra of 4-MBA at different pH values ​​are obtained by using the sensor as the SERS substrate.

[0040] Figure 5 SERS spectra of lactic acid at different concentrations, with the sensor serving as the SERS substrate.

[0041] Figure 6 SERS spectra of uric acid at different concentrations, with the sensor serving as the SERS substrate. Detailed Implementation

[0042] To better understand the present invention, specific embodiments are described below. Unless otherwise specified, the experimental methods used in the embodiments are conventional methods. Unless otherwise specified, the materials and reagents used in the embodiments are commercially available.

[0043] Example 1

[0044] A method for fabricating a flexible SERS sensor for detecting sweat biomarkers includes the following steps:

[0045] (1) PAN and PEI were dissolved in DMF at a mass ratio of 3:1, with a total mass concentration of 8wt% for PAN and PEI. The mixture was stirred overnight at 70°C with a magnetic stirrer to ensure complete dissolution of the drugs. After stirring, the mixture was sonicated for 5 minutes to remove air bubbles and obtain the spinning solution. Then, electrospinning was performed. The electrospinning machine voltage was 20kV, the spinning solution feed rate was 1mL / h, and the distance from the needle tip to the collector was 15cm. The hydrophilic fiber layer was collected on a rotating drum receiver.

[0046] (2) Dissolve PU in DMF and stir overnight at 70°C using a magnetic stirrer to ensure complete dissolution. After stirring, remove air bubbles from the PU solution by ultrasonication to obtain a PU electrospinning solution with a concentration of 22 wt%. Then, electrospin the PU solution to deposit electrospun fibers onto the prepared hydrophilic fiber layer using electrospinning. After drying, a Janus nanofiber membrane is formed. The electrospinning process parameters are: applied voltage 18 kV, distance from needle tip to collector 15 cm, spinning solution feed rate 0.5 mL / h, and a rotating roller with a hydrophilic fiber layer on its surface obtained in step (1) as the receiver.

[0047] (3) Dissolve 19.7 mg of HAuCl4 in 50 mL of deionized water to obtain an aqueous solution of HAuCl4 with a concentration of 1 mmol / L, and heat to boiling. Quickly add 5 mL of an aqueous solution of sodium citrate with a concentration of 38.8 mmol / L, and react at boiling for 15 minutes to obtain gold nanoparticles.

[0048] (4) 9 mL of freshly prepared gold nanoparticles were transferred to a petri dish, and then 6 mL of hexane was added. The mixture was allowed to stand to obtain a clear gold nanoparticle-water / hexane interface. Subsequently, 6 mL of ethanol was gradually added to the above solution. With the addition of ethanol, the gold nanoparticles migrated to the water / hexane interface and self-assembled into a gold nanoparticle film. The obtained gold nanoparticle film was recovered from the interface using a Janus nanofiber membrane as a carrier, allowing the gold nanoparticle film to adhere tightly to the hydrophilic layer surface of the Janus nanofiber membrane, thus obtaining a flexible sensor for sweat marker detection.

[0049] The sensor obtained in this embodiment is a composite structure of Janus nanofiber membrane and gold nanoparticle thin film: as shown Figure 1 a is a Janus nanofiber membrane, which shows a relatively uniform appearance on both sides with only slight color changes, and can be bent at will, exhibiting flexible characteristics. Figure 1 b-scanning electron microscopy (SEM) images show that the interface between the hydrophilic and hydrophobic layers is continuous while maintaining relative independence, with a thickness of approximately 100 μm. SEM images of the hydrophobic and hydrophilic layers of the Janus nanofiber membrane are shown below. Figure 1As shown in c and d, the hydrophilic PEI / PAN fibers have a finer diameter of 0.31 ± 0.04 μm, while the hydrophobic PU fibers have a significantly larger diameter of approximately 1.28 ± 0.27 μm. Figure 1 As shown in e and 1f, the contact angle is the main indicator of the material's wetting properties. The PU layer has a contact angle of 124.8°, indicating superhydrophobicity; while when water droplets interact with the PEI / PAN layer surface, they exhibit immediate wetting behavior, with a measured contact angle of 20.5°, indicating superhydrophilicity. The Janus nanofiber membrane prepared in this embodiment has a specific surface area of ​​15.4 m². 2 / g, containing micropores with diameters between 3-30 nm. The presence of these micropores enables Janus nanofiber membranes to effectively promote the separation of components in sweat. Figure 1 g and Figure 1 h shows SEM images of the hydrophilic PAN / PEI fiber surface before and after loading a gold nanoparticle film, revealing a dense distribution of gold nanoparticles on the fiber surface. Simultaneously, energy dispersive spectroscopy (EDS) images show that the gold nanoparticles are uniformly distributed on each fiber, forming a gold nanoparticle film. Figure 1 i).

[0050] Example 2

[0051] To elucidate the unidirectional microfluidic transport properties of fluids on the Janus membrane, a drop of stained water (≈100 μL, containing 1 wt% Rhodamine 6G) was added to the hydrophilic / hydrophobic layer of the Janus membrane prepared by the method in Example 1 to establish a physical model. Figure 2 As shown in Figure a, when a droplet contacts the hydrophobic PU layer, it gradually penetrates and reaches the hydrophilic PEI / PAN layer. The capillary force exerted by the hydrophilic layer acts as an effective pumping mechanism, continuously drawing liquid from the hydrophobic surface to the hydrophilic surface. Once this path is established, the droplet's diffusion rate increases significantly until it completely penetrates and reaches the hydrophilic layer. Furthermore, the diffusion area of ​​the hydrophobic layer is much smaller than that of the hydrophilic layer, thus keeping the hydrophobic layer relatively dry.

[0052] On the contrary, such as Figure 2 As shown in b, when a droplet first contacts the hydrophilic PEI / PAN layer of the Janus membrane, the droplet rapidly diffuses across the surface. Simultaneously, due to the superhydrophobic properties of the PU layer, the droplet leaves very little trace of diffusion into the adjacent hydrophobic PU layer, resulting in complete wetting of the hydrophilic layer. This prolonged contact between the membrane and the skin may lead to sustained moisture retention on the skin surface, potentially promoting microbial growth.

[0053] Therefore, by bringing its hydrophobic side into contact with the skin, the Janus membrane can facilitate unidirectional liquid transport to the hydrophilic layer while remaining relatively dry, effectively promoting sweat collection, reducing discomfort associated with sweat adhesion, and inhibiting microbial proliferation, thus making it the best carrier for wearable sensors.

[0054] Example 3

[0055] SERS enhancement capability and stability testing of the flexible SERS sensor prepared by the method in Example 1:

[0056] A composite structure of Janus nanofiber membrane and gold nanoparticle film was used as the substrate for the sensor SERS, with Rhodamine 6G (R6G) as the probe molecule. Different concentrations (10) were used to detect the presence of different gold nanoparticle films. -2 mol / L, 10 -3 mol / L, 10 -4 mol / L, 10 -5 mol / L, 10 -6 mol / L, 10 - 7 mol / L, 10 -8 A mol / L aqueous solution of R6G was added dropwise to the sensor, and Raman spectroscopy was performed at a wavelength of 633 nm. Figure 3 a shows the tested SERS spectrum, demonstrating that the sensor exhibits excellent SERS enhancement capabilities and can detect R6G down to a detection limit of 10. -10 The concentration of mol / L indicates that the SERS sensor has high sensitivity, and the SERS hotspots formed by uniform gold nanoparticles significantly enhance the Raman signal of adsorbed analyte molecules in these regions. Figure 3 b represents 10 different batches of sensor samples used as SERS substrates. -6 The SERS signal intensity of the mol / L 6G aqueous solution showed high consistency, and the relative deviation of the Raman characteristic peak intensity remained at a low level (<10%), indicating that the SERS sensor has good reproducibility and stability.

[0057] Application Example 1

[0058] Sweat pH testing

[0059] The pH value of sweat refers to the acidity or alkalinity of human sweat and is one of the important indicators for judging the acid-base balance, metabolic function, and disease diagnosis in the human body. The sensor prepared by the method in Example 1 was used to detect the pH of sweat. The detection method is as follows:

[0060] The sensor prepared by the method in Example 1 was immersed in a 1 mmol / L aqueous solution of 4-aminobenzoic acid (4-MBA) for 2 hours, followed by washing and drying to obtain the modified SERS sensor. 4-MBA was modified onto the surface of gold nanoparticles, and the thiol groups of gold and 4-MBA exposed carboxyl groups. The degree of interaction between the carboxyl groups and protons in solution depends on the pH value, resulting in a specific pH range of 1410-1430 cm⁻¹. -1 COO -Fluctuations in Raman peak intensity characteristic of tensile vibration. 1078-1082 cm⁻¹ -1 These are inherent characteristic peaks related to aromatic ring vibrations and can be used as internal standards for calibrating Raman spectra. Sodium acetate buffer solutions with pH values ​​of 4, 4.5, 4.8, 5.3, 5.8, and 6.3 were respectively added dropwise to the hydrophobic surface of the SERS sensor prepared by the method in Example 1, dried, and detected by Raman spectrometer at a wavelength of 633 nm.

[0061] like Figure 4 As shown, the SERS spectra of the sensor in the pH range of 4.0-6.5 were obtained, demonstrating that the sensor has excellent SERS enhancement capability for 4-MBA, thus enabling in-situ pH detection using SERS. It can be observed that the signal intensity ratio of pH value to 1422 / 1081 (I...) 1422 / 1081 A good linear quantitative relationship was observed between the two. Sweat was dropped onto the hydrophobic surface of the modified SERS sensor, dried, and then detected by Raman spectroscopy and spectral analysis. Based on the linear correlation, the pH of the sweat could be detected, indicating that the method of this invention can effectively detect the pH of sweat.

[0062] Application Example 2

[0063] Detection of lactic acid in sweat

[0064] Clinically, lactate measurement is commonly used to detect abnormal liver function, anemia, severe infections, and other diseases. It can also be used to assess the severity of tissue hypoxia, as well as cardiopulmonary and muscle function. A label-free detection of lactate was performed using the sensor prepared according to the method in Example 1. The detection method is as follows:

[0065] Two μL of aqueous lactic acid solutions at concentrations of 1 mmol / L, 5 mmol / L, 10 mmol / L, 15 mmol / L, 20 mmol / L, and 25 mmol / L were respectively added dropwise to the hydrophobic surface of the sensor prepared in Example 1. Raman spectroscopy was performed at a wavelength of 633 nm, and the Raman characteristic peak was observed at 852 cm⁻¹. -1 1048cm -1 1080cm -1 1455cm -1 The SERS spectrum of lactic acid showed excellent SERS enhancement ability, with a significant correlation between peak intensity and concentration level. Figure 5 The molecule diffuses through the Janus film and aggregates around the nanoparticles, where self-assembled high-density electromagnetic field hotspots significantly enhance its SERS signal. (At 852 cm⁻¹) -1Taking the Raman characteristic peak (CC tensile vibration peak) as an example, it shows a good linear relationship between the Raman peak intensity and lactic acid concentration. Sweat was dropped onto the hydrophobic surface of the SERS sensor, dried, and then detected by Raman spectroscopy and spectral analysis. Based on the linear correlation, the lactic acid concentration in the sweat could be detected, indicating that the method of this invention can effectively detect lactic acid in sweat.

[0066] Application Example 3

[0067] Detection of uric acid in sweat

[0068] High or low uric acid levels in the human body may indicate several health problems, such as simple hyperuricemia, gout, nephritis, liver necrosis, and Wilson's disease. A sensor prepared using the method in Example 1 was used to detect uric acid in sweat. The detection method is as follows:

[0069] Uric acid solutions with concentrations of 1 μmol / L, 5 μmol / L, 10 μmol / L, 15 μmol / L, 20 μmol / L, and 25 μmol / L (using a 0.01 mol / L NaOH aqueous solution as the solvent) were respectively added dropwise to the hydrophobic surface of the sensor prepared in Example 1, and Raman spectroscopy was used for detection at a wavelength of 633 nm. The SERS spectra are shown below. Figure 6 As shown, it displays 469cm. -1 624cm -1 1140cm -1 The Raman characteristic peaks of uric acid and the significant correlation between peak intensity and concentration level were observed. (624 cm⁻¹) -1 The Raman characteristic peak intensity exhibits a good linear relationship with uric acid concentration. Sweat droplets are added to the hydrophobic surface of the SERS sensor, dried, and then detected by Raman spectroscopy and spectral analysis. Based on the linear correlation, the uric acid concentration in the sweat can be detected, indicating that the method of this invention can effectively detect uric acid in sweat.

[0070] The above are merely embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or take similar alternatives, but without departing from the spirit of this application or exceeding the scope defined by the appended claims.

Claims

1. A flexible SERS sensor for detecting sweat markers, characterized in that, The flexible SERS sensor is a composite structure of Janus nanofiber membrane and gold nanoparticle film. The Janus nanofiber membrane consists of hydrophilic and hydrophobic fiber layers, and the gold nanoparticle film is closely attached to the surface of the hydrophilic fiber layer. The hydrophilic fiber layer is a composite fiber membrane of polyacrylonitrile (PAN) and polyethyleneimine (PEI), and the hydrophobic fiber layer is a polyurethane (PU) fiber membrane.

2. The flexible SERS sensor for detecting sweat markers according to claim 1, characterized in that, Janus nanofiber membranes have a thickness of 80-120 μm, while gold nanoparticle films have a thickness of 10-20 nm.

3. The flexible SERS sensor for detecting sweat markers according to claim 1, characterized in that, The diameter of the fibers in the hydrophilic fiber layer is 0.31±0.04μm, and the diameter of the fibers in the hydrophobic fiber layer is 1.28±0.27μm.

4. A method for preparing a flexible SERS sensor for sweat biomarker detection as described in any one of claims 1-3, comprising the steps of: (1) Polyacrylonitrile and polyethyleneimine are fully dissolved in N,N-dimethylformamide, and bubbles are removed by ultrasonication to obtain a spinning solution; then a hydrophilic fiber layer is obtained by electrospinning. (2) Polyurethane was fully dissolved in N,N-dimethylformamide, and bubbles were removed by ultrasonication to obtain a spinning solution; then the spinning solution was deposited onto the hydrophilic fiber layer by electrospinning and dried to obtain a Janus nanofiber membrane. (3) Heat the HAuCl4 aqueous solution to boiling, add sodium citrate aqueous solution, and react to obtain gold nanoparticle aqueous solution; add n-hexane, and let stand to form aqueous solution / n-hexane interface; add ethanol, and the gold nanoparticles migrate to the aqueous solution / n-hexane interface and self-assemble into gold nanoparticle film; use Janus nanofiber membrane as carrier to recover the gold nanoparticle film from the interface, so that the gold nanoparticle film is tightly attached to the surface of the hydrophilic fiber layer of Janus nanofiber membrane, and obtain a flexible SERS sensor for sweat marker detection.

5. The method for preparing a flexible SERS sensor for sweat marker detection according to claim 4, characterized in that, Step (1) includes one or more of the following conditions: i. The mass ratio of polyacrylonitrile to polyethyleneimine is 2-4:1, and the total mass concentration of polyacrylonitrile and polyethyleneimine in the spinning solution is 6-10%. ii. The electrospinning conditions are as follows: the voltage is 20kV, the spinning solution feed rate is 0.5-2mL / h, the hydrophilic fiber layer is collected on a rotating drum receiver, and the distance between the needle tip and the collecting electrode is 10-20cm.

6. The method for preparing a flexible SERS sensor for detecting sweat biomarkers according to claim 4, characterized in that, Step (2) includes one or more of the following conditions: i. The mass concentration of polyurethane in the spinning solution is 20-25%; ii. The electrospinning conditions are as follows: the voltage is 18kV, the spinning solution feed rate is 0.3-0.8mL / h, the distance between the needle tip and the collector is 10-20cm, and the spinning solution is deposited onto the hydrophilic fiber layer on the surface of the rotating drum receiver.

7. The method for preparing a flexible SERS sensor for sweat marker detection according to claim 4, characterized in that, Step (3) includes one or more of the following conditions: i. The concentration of HAuCl4 aqueous solution is 0.5-2 mmol / L, and the concentration of sodium citrate aqueous solution is 36-40 mmol / L; the volume ratio of HAuCl4 aqueous solution to sodium citrate aqueous solution is 8-12:1; ii. The reaction time is 10-20 min, and the reaction is carried out under boiling conditions; iii. The volume ratio of gold nanoparticle aqueous solution to n-hexane is 2-4:2; the volume ratio of ethanol to n-hexane is 1:

1.

8. The application of the flexible SERS sensor for sweat marker detection as described in any one of claims 1-3, characterized in that, It is used to detect the pH of sweat and / or markers in sweat; said markers are lactic acid or uric acid.

9. The application according to claim 8, characterized in that, The method for detecting the pH of sweat includes: immersing the SERS sensor in an aqueous solution of 0.5-2 mmol / L 4-aminobenzoic acid (4-MBA) for 2 hours, then removing, washing, and drying to obtain the modified SERS sensor; then, adding sodium acetate buffer solutions of different pH values ​​dropwise onto the modified SERS sensor, drying, and establishing the COO-pH relationship between pH and 4-MBA using Raman spectroscopy and spectral analysis. - Quantitative relationship between the intensity ratio of Raman characteristic peaks of tensile vibration and aromatic ring vibration; Sweat droplets were added to the hydrophobic surface of a modified SERS sensor, dried, and detected by Raman spectroscopy and spectral analysis, based on the relationship between pH and the COO of 4-MBA. - The pH of sweat can be detected by measuring the ratio of the Raman characteristic peak intensities of tensile vibration and aromatic ring vibration.

10. The application according to claim 8, characterized in that, The method for detecting lactic acid or uric acid in sweat includes the following steps: adding lactic acid or uric acid solutions of different concentrations to a SERS sensor, drying, detecting by Raman spectroscopy and spectral analysis, and establishing a quantitative relationship between the intensity of the Raman characteristic peaks of lactic acid or uric acid and their concentration. Sweat droplets are placed on the hydrophobic surface of the SERS sensor, dried, and then detected by Raman spectroscopy and spectral analysis. The detection of lactic acid or uric acid in sweat is achieved based on the relationship between the intensity of the Raman characteristic peaks of lactic acid or uric acid and their concentration.

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