Flexible SERS (Surface Enhanced Raman Scattering) sensor for sweat marker detection as well as preparation method and application of flexible SERS sensor

Abstract

The invention provides a flexible SERS (Surface Enhanced Raman Scattering) sensor for sweat marker detection as well as a preparation method and application of the flexible SERS sensor. The SERS sensor disclosed by the invention is of 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 tightly attached to the surface of the hydrophilic layer of the Janus nanofiber membrane. The SERS sensor has one-way microfluidic transmission performance, sweat can be effectively collected on the hydrophilic layer, meanwhile, the SERS sensor is kept almost dry on the hydrophobic layer, and the skin comfort is enhanced. The SERS sensor is simple in preparation method and structure, has the characteristics of lightness, thinness, softness, stretchability, wearable performance, high sensitivity, high selectivity, good stability and the like, becomes an excellent SERS sensor material, can measure the pH level in sweat and the concentration of lactic acid, uric acid and the like, and provides real-time data support for health management and disease prevention.

Description

Technical Field

[0001] The present invention belongs to the technical field of biosensors, and particularly relates to a flexible SERS sensor for sweat biomarker detection, a preparation method thereof, and an application thereof. Background Art

[0002] The detection of body fluid hormones is of great significance in medical diagnosis and treatment. Hormones are chemical messengers produced by the human endocrine system and are crucial for regulating physiological processes such as metabolism, growth and development, and reproductive function. By detecting the hormone levels in blood, urine, or other body fluids, various diseases such as thyroid dysfunction, diabetes, and gonadal dysfunction can be detected and diagnosed at an early stage. In addition, hormone detection can also help doctors evaluate the health status of patients, develop personalized treatment plans, and monitor the treatment effects.

[0003] Monitoring an individual's health status is crucial for assessing the physical condition and facilitating early disease detection. In this regard, sweat is a valuable and easily accessible source of information, containing various molecules that reflect physiological conditions, including hydrogen ions (H+), lactate, glucose, cortisol, and other hormones directly related to chronic diseases such as acid-base balance, energy metabolism, exercise intensity, stress level, endocrine function, and diabetes. In addition, since sweat is a byproduct of skin excretion, its sample can be collected conveniently and non-invasively, making it an ideal choice for providing comfortable health monitoring services for athletes or patients with chronic diseases. Wearable smart devices have made significant progress in meeting the needs of human health monitoring through their ability to track real-time data, personalize, and provide user convenience. Wearable devices using sweat monitoring are an effective and advanced method for physiological monitoring.

[0004] Under normal circumstances, the amount of sweat produced by a single instance is relatively small. Therefore, the acquisition of sweat is the key initial step in sweat monitoring. Cotton fabrics are well-known for their excellent sweat absorption ability, mainly due to the unique porous structure of cotton fibers and capillary action, which endow it with strong hydrophilicity. After contacting with hydrophilic fibers, sweat is transferred from the skin surface to these fibers under the influence of surface tension and wettability. In addition, due to the long-term monitoring of sweat, the long-term contact between the skin and saturated hydrophilic fibers may cause discomfort and promote bacterial growth. In addition to small molecule information substances, sweat also contains trace amounts of proteins, which will affect the sensing performance of these molecules and lead to the reproduction of microorganisms. Therefore, ideally, the wearable device placed on the skin must effectively acquire sweat while ensuring the relative dryness of the skin and effectively separating interfering components.

[0005] Current wearable sweat detection methods are mainly divided into optical and electrochemical methods. The electrochemical method requires the design of a complex and precise two-electrode or three-electrode system, which increases the complexity and processing difficulty of the entire device.

[0006] The design and manufacturing process of optical sensors is relatively simple, featuring low cost and low technical barriers. Optical sensors usually have high sensitivity and resolution and can detect subtle changes. For example, in the biomedical field, by analyzing the reflected or transmitted light of a specific wavelength in a sample, precise monitoring of the concentration changes of biomarkers can be achieved. In addition, since optical signals can be transmitted through air, these sensors exhibit excellent performance in remote monitoring applications. With the progress of nanotechnology, new nanomaterials have been integrated into optical sensing systems, thus improving their performance and expanding their application scope. Surface-enhanced Raman scattering (SERS) technology is a highly sensitive optical sensing method capable of single-molecule detection; high selectivity is usually achieved by using nanostructures and surface modification. Moreover, due to the inherently weak Raman scattering signal in the aqueous environment, SERS technology has demonstrated outstanding 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 collect sweat and separate interfering components, with high sensitivity, stability and selectivity, so as to accurately measure the components of human sweat through SERS technology, thereby providing real-time data support for health management and disease prevention. Summary of the Invention

[0008] Aiming at the deficiencies of the existing technology, the present invention provides a flexible SERS sensor for sweat biomarker detection, its preparation method and application. The preparation method and structure of the SERS sensor of the present invention are simple, featuring light, thin, flexible, stretchable, wearable, etc., and can be seamlessly attached to human skin or clothing, with good comfort. The sensor of the present invention is a composite structure of a Janus nanofiber membrane and a gold nanoparticle thin film. The Janus nanofiber membrane is composed of hydrophilic and hydrophobic fiber layers and has unidirectional microfluidic transport performance, suitable for human skin to promote sweat collection; sweat can be transferred from the hydrophobic layer to the hydrophilic layer, and the hydrophilic layer effectively extracts trace sweat secreted by the skin, while the hydrophobic layer can maintain a dry contact interface, thereby enhancing the comfort of the user during wearing and being able to effectively separate interfering components. In addition, a functional self-assembled gold nanoparticle thin film layer is closely attached to the surface of the hydrophilic layer of the Janus nanofiber membrane to develop a SERS sensor material with high sensitivity, selectivity and stability. As a SERS substrate, the concentration of components such as pH level, lactic acid and uric acid in sweat is measured through 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 sweat biomarker detection, which is a composite structure of a Janus nanofiber membrane and a gold nanoparticle thin film; the Janus nanofiber membrane is composed of a hydrophilic and a hydrophobic fiber layer, and the gold nanoparticle thin 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.

[0011] Preferably according to the present invention, the thickness of the Janus nanofiber membrane is 80 - 120 μm, and the thickness of the gold nanoparticle thin film is 10 - 20 nm.

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

[0013] The preparation method of the above-mentioned flexible SERS sensor for sweat biomarker detection includes the steps:

[0014] (1) Dissolve polyacrylonitrile and polyethyleneimine fully in N,N-dimethylformamide, ultrasonically remove bubbles to obtain a spinning solution, and then obtain the hydrophilic fiber layer by electrospinning.

[0015] (2) Dissolve polyurethane fully in N,N-dimethylformamide, ultrasonically remove bubbles to obtain a spinning solution; then deposit the spinning solution onto the hydrophilic fiber layer by electrospinning method and dry to obtain the Janus nanofiber membrane.

[0016] (3) Heat the HAuCl 4 aqueous solution to boiling, add sodium citrate aqueous solution, and obtain an aqueous solution of gold nanoparticles through reaction; add n-hexane, let it stand to form an aqueous solution / n-hexane interface; add ethanol, and the gold nanoparticles migrate to the aqueous solution / n-hexane interface to self-assemble into a gold nanoparticle thin film; use the Janus nanofiber membrane as a carrier to recover the gold nanoparticle thin film from the interface, so that the gold nanoparticle thin film is closely attached to the surface of the hydrophilic fiber layer of the Janus nanofiber membrane, and obtain a flexible SERS sensor for sweat biomarker detection.

[0017] Preferably according to 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] Preferably according to the present invention, in step (1), the electrospinning conditions are as follows: the voltage is 20 kV, the spinning solution feeding rate is 0.5 - 2 mL / h, the hydrophilic fiber layer is collected on a rotating drum receiver, and the distance between the needle tip and the collector is 10 - 20 cm.

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

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

[0021] Preferably according to the present invention, in step (3), HAuCl 4 The concentration of the 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 HAuCl 4 aqueous solution to the sodium citrate aqueous solution is 8-12:1.

[0022] Preferably according to the present invention, in step (3), the reaction time is 10-20 min, and the reaction is carried out under boiling conditions.

[0023] Preferably according to the present invention, in step (3), the volume ratio of the aqueous solution of gold nanoparticles 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 ability and good stability, and can detect the lowest concentration of rhodamine 6G (R6G) probe molecules to 10 -10 mol / L. The SERS signal intensities of different batches of samples show high consistency, and the relative deviation of the Raman characteristic peak intensities remains at a low level (<10%).

[0025] The above application of the flexible SERS sensor for detecting sweat markers is applied to detect the pH of sweat or / and markers in sweat.

[0026] Preferably according to the present invention, the marker is lactic acid or uric acid.

[0027] Preferably according to the present invention, the method for detecting the pH of sweat includes the steps of: soaking the SERS sensor in a 4-aminobenzoic acid (4-MBA) aqueous solution with a concentration of 0.5-2 mmol / L respectively, taking it out after 2 h, washing and drying to obtain a modified SERS sensor; then dropping sodium acetate buffer solutions with different pH values on the modified SERS sensor respectively, drying, and establishing a quantitative relationship between pH and the ratio of the Raman characteristic peak intensities of the stretching vibration of COO - and the aromatic ring vibration of 4-MBA through Raman spectroscopy detection and spectral analysis; dropping sweat on the hydrophobic surface of the modified SERS sensor, drying, and through Raman spectroscopy detection and spectral analysis, according to the COO of pH and 4-MBA- The detection of sweat pH is realized by the relationship between the stretching vibration and the Raman peak intensity ratio of the aromatic ring vibration.

[0028] Preferably according to the present invention, the detection method of lactic acid or uric acid in sweat includes the steps of: respectively dropping different concentrations of lactic acid or uric acid solutions on the SERS sensor, drying, performing Raman spectroscopy detection and spectral analysis, and establishing a quantitative relationship between the Raman characteristic peak intensity of lactic acid or uric acid and the concentration; dropping sweat on the hydrophobic surface of the SERS sensor, drying, performing Raman spectroscopy detection and spectral analysis, and realizing the detection of lactic acid or uric acid in sweat according to the relationship between the Raman characteristic peak intensity of lactic acid or uric acid and the concentration.

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

[0030] 1. The preparation method and structure of the sensor of the present invention are simple, and it has the characteristics of being thin, light, soft, stretchable, wearable, etc., with good skin comfort, convenient for long-term wearing, and reducing interference with daily activities.

[0031] 2. The sensor of the present invention is a composite structure of a Janus nanofiber membrane and a gold nanoparticle thin film. The Janus nanofiber membrane is composed of a hydrophilic and a hydrophobic fiber layer, and the self-assembled gold nanoparticle thin film is closely attached 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 the present invention has a unidirectional microfluidic transport function. When a liquid droplet contacts the hydrophobic fiber layer, the liquid droplet will gradually penetrate and reach the hydrophilic fiber layer; the capillary force exerted by the hydrophilic fiber layer serves as an effective pumping mechanism to continuously suck the liquid droplet from the hydrophobic surface to the hydrophilic layer, so that the liquid droplet finally reaches the surface of the gold nanoparticle thin film.

[0033] Therefore, the hydrophobic layer in the sensor remains in close contact with the skin, and the hydrophilic layer is mainly used to collect trace amounts of sweat; sweat can be unidirectionally transported from the hydrophobic layer to the hydrophilic layer and finally reach the surface of the gold nanoparticle thin film; effectively saturating the entire hydrophilic region while remaining nearly dry on the hydrophobic side. The Janus nanofiber membrane is woven into many voids, endowing it with a specific separation function. In the unidirectional transport, macromolecules show slower movement, resulting in a limited diffusion distance, and due to the osmotic effect, larger molecular impurities (such as proteins) in sweat are effectively retained in the membrane, while smaller chemical molecules can diffuse to the SERS hot spot region. Therefore, the above makes the sensor of the present invention convenient for collecting sweat, ensuring skin dryness, effectively reducing discomfort related to sweat adhesion, inhibiting microbial proliferation, enhancing user comfort, and thus making it the best carrier for wearable sensors.

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

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

[0036] Figure 1 It is a test diagram of the structural characterization and hydrophilic-hydrophobic properties of the Janus nanofiber membrane and the sensor.

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

[0038] Figure 3 It is the SERS spectrum of different concentrations of R6G of the sensor as an SERS substrate (a), and the statistical distribution and relative deviation diagram of the Raman characteristic peak intensity of R6G of different batches of SERS substrates (b).

[0039] Figure 4 It is the SERS spectrum of 4-MBA at different pH values of the sensor as an SERS substrate.

[0040] Figure 5 It is the SERS spectrum of different concentrations of lactic acid of the sensor as an SERS substrate.

[0041] Figure 6 It is the SERS spectrum of different concentrations of uric acid of the sensor as an SERS substrate. DETAILED DESCRIPTION OF THE INVENTION

[0042] To better understand the present invention, the following specific examples are used for further illustration. The experimental methods used in the examples are all conventional methods unless otherwise specified. The materials, reagents, etc. used in the examples can be obtained from commercial sources unless otherwise specified.

[0043] Example 1

[0044] A preparation method of a flexible SERS sensor for sweat marker detection includes the steps:

[0045] (1) Dissolve PAN and PEI in DMF at a mass ratio of 3:1, with the total mass concentration of PAN and PEI being 8 wt%. Stir overnight at 70 °C with a magnetic stirrer to fully dissolve the drugs. After stirring, ultrasonicate for 5 minutes to remove bubbles to obtain the spinning solution. Then, perform electrospinning. The voltage of the electrospinning machine is 20 kV, the advancing rate of the spinning solution is 1 mL / h, and the distance from the needle tip to the collector is 15 cm. Collect the hydrophilic fiber layer on a rotating drum receiver.

[0046] (2) Dissolve PU in DMF and stir overnight at 70 °C with a magnetic stirrer to fully dissolve the drugs. After stirring, ultrasonicate to remove bubbles in the PU solution to obtain a PU electrospinning solution with a concentration of 22 wt%. Then, electrospin the PU solution onto the prepared hydrophilic fiber layer by electrospinning method. After drying, a Janus nanofiber membrane is formed. The electrospinning process parameters are: applied voltage 18 kV, distance from the needle tip to the collector 15 cm, advancing rate of the spinning solution 0.5 mL / h, and use the rotating drum with the hydrophilic fiber layer obtained in step (1) as the receiver.

[0047] (3) Dissolve 19.7 mg of HAuCl 4 in 50 mL of deionized water to obtain an aqueous solution of HAuCl 4 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 for 15 minutes under boiling conditions to obtain gold nanoparticles.

[0048] (4) Transfer 9 mL of the newly prepared gold nanoparticles to a petri dish, then add 6 mL of hexane, and let it stand to obtain a clear gold nanoparticle aqueous solution / hexane interface. Subsequently, gradually add 6 mL of ethanol to the above solution. As ethanol is added, the gold nanoparticles migrate to the water / hexane interface and self-assemble into a gold nanoparticle thin film. Use the Janus nanofiber membrane as a carrier to recover the obtained gold nanoparticle thin film from the interface, and make the gold nanoparticle thin film closely adhere to the surface of the hydrophilic layer of the Janus nanofiber membrane to obtain a flexible sensor for sweat biomarker detection.

[0049] The sensor obtained in this example is a composite structure of a Janus nanofiber membrane and a gold nanoparticle thin film: as Figure 1 a is the Janus nanofiber membrane, showing relatively uniform appearance on both sides, with only slight color change, and can be bent arbitrarily, having flexible characteristics. Figure 1 b The scanning electron microscope (SEM) image shows that the interface between the hydrophilic and hydrophobic layers is continuous, while maintaining relative independence, with a thickness of about 100 μm. The SEM images of the hydrophobic and hydrophilic layers of the Janus nanofiber membrane are respectively as Figure 1As shown in c and d, the hydrophilic PEI / PAN fibers are thinner in diameter, being 0.31 ± 0.04 μm, while the hydrophobic PU fibers are significantly thicker, approximately 1.28 ± 0.27 μm. As Figure 1 shown in e and 1f, the contact angle is a major indicator of the wetting characteristics of a material. The contact angle of the PU layer reaches 124.8°, indicating superhydrophobicity; while when a water droplet interacts with the surface of the PEI / PAN layer, immediate wetting behavior is exhibited, and the measured contact angle is 20.5°, indicating superhydrophilicity. The specific surface area of the Janus nanofiber membrane prepared in this example is 15.4 m 2 / g, containing micropores with diameters between 3 - 30 nm. The presence of these micropores enables the Janus nanofiber membrane to effectively promote the separation of components in sweat. Figure 1 g and Figure 1 h are SEM images of the hydrophilic PAN / PEI fiber surface before and after loading with a gold nanoparticle thin film, showing that the gold nanoparticles are densely distributed on the surface of the hydrophilic fibers. Meanwhile, the energy dispersive spectrum (EDS) map shows that the gold nanoparticles are uniformly distributed on each fiber, forming a gold nanoparticle thin film ( Figure 1 i).

[0050] Example 2

[0051] To clarify the unidirectional microfluidic transport performance of fluids on the Janus membrane, a physical model was established by dropping a drop of dyed water (≈100 μL, containing 1 wt% rhodamine 6G) onto the hydrophilic and hydrophobic layers of the Janus membrane prepared by the method of Example 1. As Figure 2 shown in a, when the droplet contacts the hydrophobic PU layer, the droplet gradually penetrates and reaches the hydrophilic PEI / PAN layer. The capillary force exerted by the hydrophilic layer acts as an effective pumping mechanism, continuously sucking the liquid from the hydrophobic surface to the hydrophilic surface. Once this path is established, the diffusion rate of the droplet will increase significantly until it completely penetrates and reaches the hydrophilic layer. Moreover, the diffusion area on the hydrophobic layer is much smaller than that on the hydrophilic layer, thus keeping the hydrophobic layer relatively dry.

[0052] Conversely, as Figure 2 shown in b, when the droplet first contacts the hydrophilic PEI / PAN layer of the Janus membrane, the droplet rapidly diffuses across this surface. Meanwhile, due to the superhydrophobic property of the PU layer, the trace of the droplet diffusing towards the adjacent hydrophobic PU layer is very small, and the hydrophilic layer is completely wetted. This long - term contact between the membrane and the skin may cause the skin surface to continuously retain moisture, potentially promoting microbial growth.

[0053] Therefore, by contacting its hydrophobic surface with the skin, the Janus membrane promotes unidirectional liquid transport to the hydrophilic layer while remaining relatively dry, effectively promoting sweat collection, reducing the discomfort associated with sweat adhesion, and inhibiting microbial proliferation, thus making it an optimal carrier for wearable sensors.

[0054] Example 3

[0055] Test on the SERS enhancement ability and stability of the flexible SERS sensor prepared by the method of Example 1:

[0056] The composite structure of the Janus nanofiber membrane and the gold nanoparticle thin film is used as the SERS substrate of the sensor, and rhodamine 6G (R6G) is used as the probe molecule. Aqueous solutions of R6G with different concentrations (10 -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 mol / L) are dropped onto the sensor, and the Raman spectrometer is used for testing at a wavelength of 633 nm. As Figure 3 a is the SERS spectrum obtained from the test, showing that the sensor has excellent SERS enhancement ability and can detect R6G with a minimum detection limit of 10 -10 mol / L, indicating that the SERS sensor has high sensitivity. The SERS hot spots formed by uniform gold nanoparticles significantly enhance the Raman signals of the analyte molecules adsorbed in these regions. Figure 3 b shows the SERS signal intensities of 10 -6 mol / L aqueous R6G solution using different batches of sensor samples as the SERS substrate, showing high consistency. The relative deviation of the Raman characteristic peak intensities remains at a low level (<10%), indicating that the SERS sensor has good reproducibility and stability.

[0057] Application Example 1

[0058] Sweat pH Detection

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

[0060] The sensor prepared by the method of Example 1 is immersed in an aqueous solution of 4-aminobenzoic acid (4-MBA) with a concentration of 1 mmol / L. After soaking for 2 h, it is washed and dried to obtain a modified SERS sensor. 4-MBA is modified on the surface of gold nanoparticles, and the thiol group of gold binds to 4-MBA to expose the carboxyl group; the degree of interaction between the carboxyl group and protons in the solution depends on the pH value, resulting in COO at 1410 - 1430 cm -1 - ​Fluctuations in the intensity of the stretching vibration characteristic Raman peak. 1078 - 1082 cm -1 It is an inherent characteristic peak related to the vibration of the aromatic ring and can be used as an internal standard for calibrating the Raman spectrum. Sodium acetate buffer solutions with pH values of 4, 4.5, 4.8, 5.3, 5.8, and 6.3 were respectively dropped onto the hydrophobic surface of the SERS sensor prepared by the method of Example 1, dried, and detected with a Raman spectrometer at a wavelength of 633 nm.

[0061] As Figure 4 shown, the SERS spectra of the sensor in the pH range of 4.0 - 6.5 were obtained, showing that the sensor has excellent SERS enhancement ability for 4 - MBA, and thus the pH value can be detected in situ by SERS. It can be found that there is a good linear quantitative relationship between the pH value and the signal intensity ratio of 1422 / 1081 (I 1422 / 1081 ). Sweat was dropped onto the hydrophobic surface of the modified SERS sensor, dried, detected by Raman spectroscopy and spectral analysis, and the pH of the sweat can be detected according to the linear correlation relationship, indicating that the method of the present invention can effectively detect the pH of sweat.

[0062] Application Example 2

[0063] Detection of lactic acid in sweat

[0064] Clinically, lactic acid determination is often used to detect diseases such as abnormal liver function, anemia, and severe infections, and can also be used to evaluate the severity of tissue hypoxia in the body, as well as cardiopulmonary function and muscle function. The sensor prepared by the method of Example 1 was used for label - free detection of lactic acid. The detection method is as follows:

[0065] 2 μL of lactic acid aqueous solutions with concentrations of 1 mmol / L, 5 mmol / L, 10 mmol / L, 15 mmol / L, 20 mmol / L, and 25 mmol / L were respectively dropped onto the hydrophobic surface of the sensor prepared by the method of Example 1, and detected with a Raman spectrometer at a wavelength of 633 nm. The SERS spectra of lactic acid with Raman characteristic peaks at 852 cm -1 , 1048 cm -1 , 1080 cm -1 , 1455 cm -1 were obtained, showing excellent SERS enhancement ability for lactic acid, and there is a significant correlation between the peak intensity and the concentration level ( Figure 5 ). The molecule diffuses through the Janus membrane and aggregates around the nanoparticles, where the self - assembled high - density electromagnetic field hotspots significantly enhance its SERS signal. At 852 cm -1Taking the Raman characteristic peak (C-C stretching vibration peak) as an example, it shows that there is a good linear relationship between the Raman peak intensity and the lactic acid concentration. Drop sweat on the hydrophobic surface of the SERS sensor, dry it, detect it by Raman spectroscopy and spectral analysis, and the lactic acid concentration in the sweat can be detected according to the linear correlation relationship, indicating that the method of the present invention can effectively detect lactic acid in sweat.

[0066] Application Example 3

[0067] Detection of Uric Acid in Sweat

[0068] Higher or lower levels of uric acid in the human body may indicate some health problems, such as diseases like simple hyperuricemia, gout, nephritis, liver necrosis, and hepatolenticular degeneration. The sensor prepared by the method of Example 1 is used to detect uric acid in sweat. The detection method is as follows:

[0069] Uric acid solutions with concentration values of 1 μmol / L, 5 μmol / L, 10 μmol / L, 15 μmol / L, 20 μmol / L, and 25 μmol / L (the solvent used is 0.01 mol / L NaOH aqueous solution) are respectively dropped on the hydrophobic surface of the sensor prepared by the method of Example 1, and the Raman spectrometer is used for detection at a wavelength of 633 nm. The SERS spectrum is as Figure 6 shown, showing the Raman characteristic peaks of uric acid at 469 cm -1 , 624 cm -1 , 1140 cm -1 and the significant correlation between the peak intensity and the concentration level. And there is a good linear relationship between the Raman characteristic peak intensity at 624 cm -1 and the uric acid concentration. Drop sweat on the hydrophobic surface of the SERS sensor, dry it, detect it by Raman spectroscopy and spectral analysis, and according to the linear correlation relationship, the uric acid concentration in the sweat can be detected, indicating that the method of the present invention can effectively detect uric acid in sweat.

[0070] The above are only the embodiments of the present invention and are not used to limit the present invention. Those skilled in the art can make various modifications or supplements to the described specific embodiments or take similar ways to substitute, but will not deviate from the spirit of this application or exceed the scope defined by the appended claims.

Claims

1. A flexible SERS sensor for sweat marker detection, characterized in that: The flexible 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 and a hydrophobic fiber layer. The gold nanoparticle film is tightly 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 sweat marker detection according to claim 1, characterized in that: The thickness of the Janus nanofiber film is 80-120 μm, and the thickness of the gold nanoparticle film is 10-20 nm.

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

4. A method for preparing a flexible SERS sensor for sweat marker detection according to any one of claims 1 to 3, comprising the steps of: (1) fully dissolving polyacrylonitrile and polyethyleneimine in N,N-dimethylformamide, removing bubbles by ultrasonication, and obtaining a spinning solution; and then obtaining a hydrophilic fiber layer by electrospinning; (2) fully dissolving the polyurethane in N,N-dimethylformamide, removing bubbles by ultrasound, and obtaining a spinning solution; then depositing the spinning solution onto the hydrophilic fiber layer by electrospinning, and drying to obtain a Janus nanofiber membrane; (3) The HAuCl4 aqueous solution is heated to boiling, and the sodium citrate aqueous solution is added to obtain a gold nanoparticle aqueous solution through reaction; n-hexane is added and allowed to stand to form an aqueous solution / n-hexane interface; ethanol is added, and the gold nanoparticles migrate to the aqueous solution / n-hexane interface and self-assemble into a gold nanoparticle film; the Janus nanofiber membrane is used as a 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 the Janus nanofiber membrane, thereby obtaining 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: In step (1), one or more of the following conditions are included: 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 were as follows: voltage was 20 kV, spinning solution advancement rate was 0.5-2 mL / h, the hydrophilic fiber layer was collected on a rotating drum receiver, and the distance between the needle tip and the collector was 10-20 cm.

6. The method for preparing a flexible SERS sensor for sweat marker detection according to claim 4, characterized in that: In step (2), one or more of the following conditions are included: i. The mass concentration of polyurethane in the spinning solution is 20-25%; ii. The electrospinning conditions are as follows: the voltage is 18 kV, the spinning solution advancing rate is 0.3-0.8 mL / h, the distance between the needle tip and the collector is 10-20 cm, and the spinning solution is deposited on 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: In step (3), one or more of the following conditions are included: i. The concentration of the HAuCl4 aqueous solution is 0.5-2 mmol / L, and the concentration of the sodium citrate aqueous solution is 36-40 mmol / L; the volume ratio of the HAuCl4 aqueous solution to the sodium citrate aqueous solution is 8-12:1; ii. The reaction time is 10-20 minutes, and the reaction is carried out under boiling conditions; iii. The volume ratio of the gold nanoparticle aqueous solution to n-hexane is 2-4:2; the volume ratio of ethanol to n-hexane is 1:

1.

8. The use of a flexible SERS sensor for sweat marker detection according to any one of claims 1 to 3, characterized in that: It is used to detect the pH of sweat and / or a marker in sweat; the marker is lactic acid or uric acid.

9. The use according to claim 8, characterized in that: The pH detection method of sweat includes: immersing the SERS sensor in a 4-aminobenzoic acid (4-MBA) aqueous solution with a concentration of 0.5-2 mmol / L, taking it out after 2 hours, washing and drying it to obtain a modified SERS sensor; then dripping sodium acetate buffer solutions with different pH values ​​on the modified SERS sensor, drying it, and establishing the relationship between pH and 4-MBA COO by Raman spectroscopy detection and spectral analysis. - The quantitative relationship between the ratio of the Raman characteristic peak intensities of stretching vibration and aromatic ring vibration was obtained. Sweat was dropped onto the hydrophobic surface of the modified SERS sensor and dried. Raman spectroscopy and spectral analysis were performed to determine the relative humidity of the COO of 4-MBA. - The pH value of sweat can be detected by the ratio of the Raman characteristic peak intensities of stretching vibration and aromatic ring vibration.

10. The use according to claim 8, characterized in that: The method for detecting lactic acid or uric acid in sweat comprises the steps of: dropping lactic acid or uric acid solutions of different concentrations onto a SERS sensor, drying, and establishing a quantitative relationship between the intensity of the lactic acid or uric acid Raman characteristic peak and the concentration through Raman spectrum detection and spectrum analysis; Sweat is dropped onto the hydrophobic surface of the SERS sensor, dried, and subjected to Raman spectroscopy and spectral analysis. Lactic acid or uric acid in sweat can be detected based on the relationship between the intensity of the Raman characteristic peak of lactic acid or uric acid and its concentration.

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