Hyperspectral consistency detection method based on SERS (Surface Enhanced Raman Scattering) substrate surface hydrophilic structure

Abstract

The invention relates to the technical field of hyperspectral consistency detection, and discloses a hyperspectral consistency detection method based on an SERS (Surface Enhanced Raman Scattering) substrate surface hydrophilic structure, which comprises the following steps: S1, preparing an SERS substrate with a silver nanoflower structure by adopting a method of combining a lyotropic liquid crystal soft template with electrochemical deposition, and adjusting the deposition voltage to obtain an SERS substrate with a silver nanoflower structure; and three substrates with different morphologies and roughness factors are obtained. By changing the deposition voltage in the preparation process, three substrates with different morphologies and roughness are prepared. The method comprises the steps that firstly, three different SERS substrates are subjected to contact angle measurement through a contact angle measuring instrument, finally, a contact angle result and the surface roughness are fitted, and the result is displayed to conform to a Wenzel theoretical model. And finally, measuring the spectrum consistency by using the R6G solution as a sample to be detected. The smaller the contact angle is, the distribution uniformity of the to-be-detected sample is greatly improved, and the hyperspectral consistency in the quantitative analysis detection process is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of hyperspectral consistency detection, and in particular relates to a hyperspectral consistency detection method based on a hydrophilic structure on a SERS substrate surface. Background Art

[0002] Surface enhanced Raman scattering technology has been widely used in environmental pollution monitoring, food safety testing, pesticide residue analysis and other fields due to its advantages such as high sensitivity, rapid non-destructive detection and molecular specificity. The strength of the Raman spectral signal is not only related to the enhancement factor of the SERS substrate, but also affected by the concentration of the sample to be tested. Therefore, when using SERS technology to perform quantitative detection and analysis of the sample to be tested, it is particularly important to achieve high spectral consistency of the SERS substrate.

[0003] At present, the research on improving spectral consistency focuses on the uniform construction of "hot spots". For example, in 2022, Yan et al. constructed a tunable local surface plasmon resonance (LSPR) Ag@PDMS substrate, and achieved the adjustment of the distribution of "hot spots" by changing the size of the optical cavity unit in the nanocavity array.

[0004] In 2024, Sweedan and others used focused ion beam (FIB) lithography technology to accurately etch a periodic double-line grating nanoscale structure on a single crystal gold wafer, and also achieved a more uniform distribution of "hot spots" to improve the consistency of spectral signals.

[0005] However, in practical applications, the sample to be tested is usually titrated onto the SERS substrate. Due to the interaction between the surface tension of the droplet and the wettability of the substrate surface, the droplet will present a "spherical crown" shape on the substrate surface. As a result, the sample molecules cannot evenly cover the entire substrate surface, and the degree of molecular aggregation varies significantly in different areas. In the center of the droplet, the molecules are more enriched, while at the edge, they are less enriched. Even if the distribution of the "hot spots" is very uniform, there are still large errors in the spectral signals at different positions. This affects the accuracy and repeatability of the results in quantitative detection. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a hyperspectral consistency detection method based on the hydrophilic structure of the SERS substrate surface, which can overcome the above problems or at least partially solve the above problems.

[0007] The present invention is achieved by a high-spectrum consistency detection method based on the hydrophilic structure of the SERS substrate surface, comprising:

[0008] S1. A SERS substrate with a silver nanoflower structure was prepared by using a lyotropic liquid crystal soft template combined with an electrochemical deposition method. The deposition voltage was adjusted to obtain three substrates with different morphologies and roughness factors.

[0009] S2. The contact angles of the three substrates were measured by a contact angle meter, and the results were 70.6°, 38.3°, and 18.2°, respectively. The surface roughness was fitted with the contact angle results, and the results showed that they were consistent with the common Wenzel hydrophilic theory model.

[0010] S3. Spectral consistency measurement was performed using R6G solution as the sample to be tested. The R6G solution was measured on three SERS substrates. After natural drying, the spectral intensity was measured multiple times around and in the middle of the droplet. The spectral consistency was evaluated by the coefficient of variation. This shows that improving the hydrophilicity of the surface of the SERS substrate structure can greatly improve the distribution uniformity of the sample to be tested, thereby achieving high spectral consistency in the quantitative analysis and detection process.

[0011] Preferably, in the present invention, the deposition voltage is adjusted to 5V, 5.5V, and 6V respectively.

[0012] In the preferred embodiment of the present invention, the coefficients of variation are 17.6%, 12.4% and 4.5% respectively.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] The present invention prepares three substrates with different morphologies and roughness by changing the deposition voltage during the preparation process. Secondly, the contact angle of three different SERS substrates is measured by a contact angle meter. Finally, the contact angle results are fitted with the surface roughness, and the results show that they are consistent with the Wenzel theoretical model. Finally, the R6G solution is used as the sample to be tested for spectral consistency measurement. It shows that the smaller the contact angle, the more uniform the distribution of the sample to be tested is greatly improved, and high spectral consistency is achieved in the quantitative analysis and detection process. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The embodiment of the present invention provides a model diagram of the sample under test presented on the surface of the SERS substrate;

[0016] Figure 2 The embodiments of the present invention provide SERS substrate images at different deposition voltages;

[0017] Figure 3 The embodiment of the present invention provides a SEM characterization image of a SERS substrate;

[0018] Figure 4 A schematic diagram of AFM characterization of a SERS substrate provided by an embodiment of the present invention;

[0019] Figure 5 The embodiment of the present invention provides a table of substrate roughness Ra and roughness factor at different deposition voltages;

[0020] Figure 6 The embodiment of the present invention provides a fitting curve of deposition voltage and roughness factor;

[0021] Figure 7 The embodiment of the present invention provides a fitting curve of the contact angle cosine value and the roughness factor;

[0022] Figure 8 The embodiment of the present invention provides a spectrum measurement position point of the droplet to be measured and an R6G spectrum diagram at the middle position of the droplet to be measured;

[0023] Fig. 9 The embodiment of the present invention provides the substrate at different contact angles at various positions at 613 cm -1 The average spectral intensity measured at ;

[0024] Fig.10 The embodiment of the present invention provides a fitting curve between the coefficient of variation and the contact angle. DETAILED DESCRIPTION

[0025] In order to further understand the content, features and effects of the present invention, the following embodiments are given as examples and described in detail with reference to the accompanying drawings.

[0026] The structure of the present invention is described in detail below in conjunction with the accompanying drawings.

[0027] like Figures 1 to 10 As shown, the hyperspectral consistency detection method based on the hydrophilic structure of the SERS substrate surface provided by the embodiment of the present invention includes: S1, using a lyotropic liquid crystal soft template combined with an electrochemical deposition method to prepare a SERS substrate with a silver nanoflower structure, adjusting the deposition voltage, and obtaining three substrates with different morphologies and roughness factors;

[0028] SERS substrate preparation and morphology characterization

[0029] In the experiment, the preparation of SERS substrate adopts the method of lyotropic liquid crystal soft template combined with electrochemical deposition. First, by adjusting the ratio of oil phase, water phase and surfactant, the lyotropic liquid crystal is made into a stable anti-hexagonal phase. The silver ions in the solution are confined in the cavity of the phase. Then, under the action of the electric field, the silver nanoflower structure is gradually grown and deposited on the cathode plate. The specific preparation method and materials can be referred to previous literature. Since there is a certain competitive relationship between the growth rate and deposition rate of the silver flower structure, the force of the electric field will destroy the balance between the two, resulting in the silver flower structure finally grown on the cathode plate having different morphology and density, which is related to the deposition time. Therefore, we prepare the substrate by adjusting the deposition voltage during the electro-deposition process. The deposition voltage was set to 5V, 5.5V, and 6V respectively, and the other preparation parameters were kept consistent. Finally, SERS substrates with different morphologies were prepared on the ITO cathode plate. Preliminary observation shows that the color of the substrate is relatively consistent and the uniformity is good;

[0030] The morphology of the SERS substrates prepared under different preparation conditions was characterized. First, the thermal field emission scanning electron microscope (SEM) was used to scan the substrates prepared above. The results showed that different silver nanoflower structures can be grown on the SERS substrate by adjusting the deposition voltage. The structure and morphology of the petals will change differently depending on the deposition voltage;

[0031] Secondly, the atomic force microscope (AFM) was used to observe the morphology of the SERS substrate and calculate and characterize the roughness factor, and the scanning diameter range was set to 20 μm;

[0032] Finally, the relationship between different deposition voltages and roughness factors was explored, and the deposition voltage and roughness factor were curve fitted. The results showed that the linear fitting effect was the best, R 2 98%, indicating that there is a good linear relationship between the three deposition voltages selected in the experiment and the roughness factor

[0033] S2. The contact angles of the three substrates were measured by a contact angle meter, and the results were 70.6°, 38.3°, and 18.2°, respectively. The surface roughness was fitted with the contact angle results, and the results showed that they were consistent with the common Wenzel hydrophilic theory model.

[0034] Characterization of hydrophilicity of SERS substrate surface

[0035] To characterize the hydrophilicity of different SERS substrates, we used a water drop contact angle meter to measure the water drop contact angle of the prepared substrates. The results showed that the comprehensive contact angles of the three SERS substrates prepared under different deposition voltages were 70.6°, 38.3°, and 18.2°, respectively.

[0036] In order to verify whether the relationship between the contact angle change law and the roughness factor conforms to the Wenzel model, the cosine value of the measured contact angle is combined with the roughness factor, and the angle cosine values ​​are 0.33, 0.79 and 0.95 respectively. The results show that the linear fitting has the best effect, R 2 The value is 0.96. This shows that as the roughness factor increases, the corresponding cosine value of the contact angle also increases linearly, which is consistent with the Wenzel model theory. Therefore, by changing the contact angle of the droplet on the SERS substrate, the droplet to be tested can be more evenly distributed, improving the consistency of spectral detection;

[0037] S3. Spectral consistency measurement was performed using R6G solution as the sample to be tested. The R6G solution was measured on three SERS substrates. After natural drying, the spectral intensity was measured multiple times around and in the middle of the droplet. The spectral consistency was evaluated by the coefficient of variation. This shows that improving the hydrophilicity of the surface of the SERS substrate structure can greatly improve the distribution uniformity of the sample to be tested, thereby achieving high spectral consistency in the quantitative analysis and detection process.

[0038] Through the above substrate regulation methods, we prepared SERS substrates with different contact angles. Furthermore, we evaluated the influence of the distribution of the samples under different contact angles on the spectral consistency of the SERS substrate.

[0039] With a concentration of 10 -6 mol / l R6G solution was used as the sample to be tested, and 3μl of the same volume of R6G solution was titrated on the surface of the SERS substrate prepared above. After it was naturally air-dried, the Raman spectra at different positions were measured. In order to avoid experimental errors caused by manually dripping the R6G solution, the R6G solution was loaded into the burette of the water drop contact angle meter, and then the R6G solution was titrated onto the SERS substrate through the contact angle meter. After it was naturally air-dried, the spectrum was measured at the same position from the edge of the droplet. In order to improve the accuracy of the spectral data, firstly, five positions including the top, bottom, left, right and middle of the droplet were used as spectral detection positions. Secondly, 5 spectral measurements were performed at each position, and then the intensity average of the characteristic peak was taken for evaluation;

[0040] Finally, we selected a 5X objective lens for spectral measurement, adjusted the integration time to 10s, and set the laser power to 1mw. At this time, the laser spot size was 40μm. According to the literature, the larger the spot size, the smaller the influence of the substrate structure on the spectral consistency. This is the Raman spectrum measured at the middle position of the measured droplet of the SERS substrate prepared at a deposition voltage of 5V;

[0041] The results show that the Raman shift is 613cm -1The characteristic peak spectral intensity at 613cm is strong and consistent. -1 The spectral consistency test was performed by the characteristic peak intensity at 613 cm-1 at the substrates with contact angles of 70.6°, 38.3°, and 18.2°, respectively. -1 The average value of the spectral intensity measured at the contact angle is 70.6°. The results show that when the contact angle is 70.6°, the measured R6G spectral intensity is stronger than that at contact angles of 38.3° and 18.2°. There are two reasons for the analysis. First, when the contact angle is large, the contact area between the R6G droplet and the SERS substrate is small, and the molecular distribution is relatively concentrated. Second, the SERS substrate has the most complete silver nanoflower structure and the largest number of "hot spots", and the enhancement effect of the SERS substrate is relatively stronger. But at the same time, in comparison, when the contact angle is large, there are also large differences in the spectral intensity measured at different positions of the droplet to be tested. This shows that the consistency of the spectrum is poor, and large error results may be produced during quantitative analysis and detection.

[0042] (a), (b), and (c) are the contact angles of 70.6°, 38.3°, and 18.2° at 613 cm -1 The average spectral intensity measured at .

[0043] In order to evaluate the consistency of the spectrum at the middle position and the spectrum at the surrounding positions on the SERS substrate, the average spectrum measured at the surrounding positions was first averaged again, and the final average spectral intensity was compared with the spectral intensity measured at the middle position, and the two sets of spectral data were processed and analyzed using the coefficient of variation. The calculation method is the ratio of the standard deviation (σ) of the Raman spectral intensity to the average value (μ) multiplied by 100%.

[0044]

[0045] The results show that the coefficients of variation of the three SERS substrates are 17.6%, 12.4% and 4.5% respectively. The coefficient of variation and contact angle are fitted by curves, and the linear fitting effect is the best. 2 The coefficient of variation is 0.93, indicating that there is a linear relationship between the coefficient of variation and the contact angle. The smaller the contact angle, the smaller the coefficient of variation and the better the spectral consistency.

[0046] Preferably, in the present invention, the deposition voltage is adjusted to 5V, 5.5V, and 6V respectively.

[0047] In the preferred embodiment of the present invention, the coefficients of variation are 17.6%, 12.4% and 4.5% respectively.

[0048] Structural model of hydrophilic surface of SERS substrate

[0049] The contact angle is an important parameter used to measure the wettability of a structure surface. At present, the common models that use the contact angle to characterize the surface are the Wenzel model and the Cassie model. The Wenzel model is applicable to the case where the droplet is in complete contact with the substrate surface, that is, there is no air gap between the solid and the liquid. The Cassie model is applicable to the case where the droplet is not in complete contact with the substrate surface, that is, there is an air gap between the two.

[0050] According to Wenzel's theoretical model,

[0051] cosθ=rcosθ0 (2)

[0052] Among them, θ is the measured contact angle, which is the angle formed by the actual contact between the droplet, the substrate surface and the air. θ0 is the intrinsic contact angle, which refers to the contact angle of the droplet when the contact surface is absolutely smooth. r is the roughness factor. That is, the ratio of the actual and projected solid surface areas (r=1 for smooth surface and r>1 for rough surface). According to the theoretical model, on a hydrophilic surface (θ<90°), the cosine value of the actual contact angle and the roughness factor show a positive correlation. Therefore, this paper proposes a simple method to improve the high-spectral consistency of the SERS substrate. Without modifying the substrate surface, the preparation parameters that affect the growth of the substrate structure are directly and appropriately adjusted to change the morphology of the substrate, thereby affecting the roughness factor of the substrate surface, and finally achieving precise control of the contact angle of the sample to be tested. Taking the SERS substrate with a silver nanoflower structure prepared by the liquid crystal soft template method as an example, its structural growth morphology is affected by the voltage and deposition time during the electrodeposition process. Therefore, by changing the deposition voltage or time, the prepared SERS substrate can have different degrees of "hydrophilicity". When the sample is titrated onto the SERS substrate, different contact angles are formed on the substrate surface, and ultimately different concentration distributions are formed. When the contact angle is small, the sample can be naturally and evenly spread on the substrate surface, and the sample molecules are evenly distributed on the substrate surface, thus achieving high spectral consistency in the quantitative analysis and detection process.

[0053] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0054] The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this patent will not depart from the scope of the technical solution of the present invention.

Claims

1. A method for detecting the consistency of a high spectrum of hydrophilic structures on the surface of a SERS substrate, characterized in that: include, S1. The SERS substrate was prepared by using a lyotropic liquid crystal soft template combined with electrochemical deposition. The deposition voltage was adjusted to obtain three substrates with different morphologies and roughness factors. S2. The contact angles of the three substrates were measured by a contact angle meter; the surface roughness was fitted with the contact angle results, and the results showed that they were consistent with the common Wenzel hydrophilic theory model; S3, using R6G solution as the sample to be tested to measure the spectral consistency, the R6G solution was measured on three SERS substrates, and after natural drying, the spectral intensity was measured multiple times around and in the middle of the droplet; and the spectral consistency was evaluated by the coefficient of variation; It is shown that improving the hydrophilicity of the surface of the SERS substrate structure can improve the distribution uniformity of the sample to be tested, thereby achieving high spectral consistency during quantitative analysis and detection.

2. The method for detecting the consistency of a high spectrum based on the hydrophilic structure of a SERS substrate surface as claimed in claim 1, characterized in that: The deposition voltage was adjusted to 5V, 5.5V, and 6V respectively.

3. The method for detecting the consistency of a high spectrum based on the hydrophilic structure of a SERS substrate surface according to claim 1, characterized in that: The coefficients of variation were 17.6%, 12.4% and 4.5%, respectively.

4. The method for detecting the consistency of a high spectrum based on the hydrophilic structure of a SERS substrate surface according to claim 1, characterized in that: The contact angles of the three substrates were measured and the results were 70.6°, 38.3°, and 18.2°, respectively.

5. The method for detecting the consistency of a high spectrum based on the hydrophilic structure of a SERS substrate surface according to claim 1, characterized in that: The SERS substrate has a silver nanoflower structure.

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