A silver ink film capable of highly sensitive detection of capsaicin and its preparation and application

Abstract

The present invention discloses a silver ink film capable of highly sensitive detection of capsaicin, a preparation method thereof, and an application thereof in surface-enhanced Raman scattering detection. The preparation method comprises: adding a mixed solution of sodium hydroxide and hydroxylamine hydrochloride to a silver nitrate solution under stirring, and stirring until the reaction is complete to obtain a uniform milky white mixture of silver nanocolloid; centrifuging the silver nanocolloid at a speed of 5000-15000 r / min for 5-30 minutes, discarding the supernatant to obtain concentrated silver nanocolloid; mixing the concentrated silver nanocolloid with ethyl cellulose and α-terpineol, stirring, and ultrasonically treating to obtain a uniform silver ink; in the silver ink, the content of concentrated silver nanocolloid is 25wt%-55wt%, the content of ethyl cellulose is 4wt%-6wt%, and the remainder is α-terpineol; using a sizing machine to spin-coat the silver ink onto a clean polished silicon wafer, and vacuum drying to obtain a silver ink film.

Description

Technical Field

[0001] The present invention relates to the technical field of surface-enhanced Raman scattering (SERS), and in particular to a silver ink film capable of highly sensitively detecting capsaicin, a preparation method thereof, and applications thereof. Background Art

[0002] Raman scattering was first discovered by Indian scientist C.V. Raman in the late 1920s. However, its early applications were hampered by the weakness of the Raman signal and limited detection sensitivity. This situation was not improved until the advent of laser technology in the 1960s, when the use of near-infrared lasers effectively reduced fluorescence interference in the visible light region, thereby overcoming the problem of weak Raman signals. In 1974, Fleischmann, a researcher at the University of Southampton in the UK, while studying the Raman spectra of pyridine molecules on roughened silver surfaces, unexpectedly discovered that the Raman signal of these molecules was abnormally enhanced. This suggested that a mechanism could enhance the Raman signal intensity of the analytes, but the underlying mechanism was not fully investigated. Subsequently, in 1977, scientists such as Van Duyne and Creighton conducted a more systematic analysis of Fleischmann's findings, confirming the key role of the roughened silver surface in enhancing the Raman signal of pyridine molecules. This discovery marked a major breakthrough in the development of Raman spectroscopy. Since then, the phenomenon of significantly enhancing the Raman signal when molecules adsorb on specific metal surfaces has been named surface-enhanced Raman scattering (SERS). Due to its rapid and sensitive nature, SERS technology has become increasingly widely used in food safety testing. It can be used to detect specific compounds, pesticide residues, metal contaminants, pathogens, and more in food, significantly improving detection efficiency.

[0003] Capsaicin, the primary chemical component responsible for the spicy flavor of chili peppers, is characterized by high lipid solubility, stability, and a high boiling point. These properties make it difficult to completely remove, making its presence a key indicator for identifying waste cooking oils. Li et al. applied a diazo coupling reaction to a complex of p-aminothiophenol (4-ATP) and capsaicin. The resulting azo dye served as a SERS probe. They then prepared gold nanorods (Au NRs) using a seed-mediated growth method and used them as SERS substrates. This method achieved a detection limit of 3.24×10 -12 M (Food Analytical Methods, 2022, 15: 3468-3478). Liu et al. used SERS technology to detect and identify illegal edible oils by molecular derivatization of capsaicin, with a detection limit of 10-8 M (ACS Omega 2017, 2, 8401-8406). The above methods are complicated and cannot detect capsaicin efficiently and conveniently. Summary of the Invention

[0004] In response to the above technical problems and the shortcomings in the art, the present invention provides a silver ink film capable of highly sensitive detection of capsaicin, as well as its preparation method and application. The preparation process of the present invention is simple, low-cost, and easy to operate. The obtained film has high detection sensitivity, and the SERS detection limit of capsaicin can be as low as 10 -13 M, which helps to realize the rapid detection of capsaicin and provides ideas for the efficient identification of waste cooking oil.

[0005] The specific technical solutions are as follows:

[0006] In a first aspect, the present invention provides a method for preparing a silver ink film capable of highly sensitively detecting capsaicin, comprising the steps of:

[0007] (1) Adding a mixed solution of sodium hydroxide and hydroxylamine hydrochloride to a silver nitrate solution under stirring, and keeping stirring until the reaction is complete to obtain a uniform milky white mixture of silver nanocolloid;

[0008] (2) centrifuging the silver nanocolloid solution at a speed of 5000-15000 r / min (e.g., 10000 r / min, etc.) for 5-30 minutes (e.g., 10 minutes, etc.), discarding the supernatant to obtain concentrated silver nanocolloid;

[0009] (3) mixing the concentrated silver nano-colloid with ethyl cellulose and α-terpineol, stirring, and ultrasonically treating to obtain a uniform silver ink; in the silver ink, the content of the concentrated silver nano-colloid is 25wt%~55wt%, the content of the ethyl cellulose is 4wt%~6wt%, and the rest is the α-terpineol;

[0010] (4) Using a coating machine, the silver ink is spin-coated onto a clean, polished silicon wafer and vacuum-dried to obtain a silver ink film.

[0011] The inventors have found that if ordinary silver powder (nanosilver) is directly mixed with ethyl cellulose and α-terpineol to prepare silver ink, the silver dispersion in the resulting silver ink is very poor. The present invention adopts the hydroxylamine hydrochloride reduction method to prepare silver nanocolloid, and uses the homemade concentrated silver nanocolloid as a precursor to mix with ethyl cellulose and α-terpineol in a specific ratio to prepare silver ink, and further uses a sizing machine to spin coat to form a silver ink film capable of highly sensitive detection of capsaicin. According to the preparation method of the present invention, a silver ink with excellent dispersion uniformity can be formed, and the concentrated silver nanocolloid can be evenly dispersed in the mixed system of ethyl cellulose and α-terpineol, thereby ensuring the preparation of a high-quality silver ink film. The resulting silver ink film has high detection sensitivity, and the SERS detection limit of capsaicin can be as low as 10 -13 M.

[0012] In some embodiments, in step (1), the concentrations of sodium hydroxide and hydroxylamine hydrochloride in the mixed solution can be independently 0.01 to 1 M. Furthermore, in step (1), the concentration of sodium hydroxide in the mixed solution is preferably 0.04 to 0.05 M, and the concentration of hydroxylamine hydrochloride is preferably 0.03 to 0.035 M. The reaction of preparing silver nanocolloid by hydroxylamine hydrochloride reduction method needs to be carried out under alkaline conditions. Sodium hydroxide is used to adjust the pH value of the solution to an appropriate value. Hydroxylamine hydrochloride is used as a reducing agent. Its concentration is related to the Ag particle size and dispersion degree of the final generated silver nanocolloid. At the preferred concentration, the Ag particle size of the generated silver nanocolloid is more uniform and the SERS detection sensitivity is higher.

[0013] In some embodiments, in step (1), the concentration of the silver nitrate solution may be 10 -4 ~10 -2 M. Furthermore, in step (1), the concentration of the silver nitrate solution is preferably 0.0008-0.0020 M, for example, 0.0011 M. The concentration of silver nitrate is related to the Ag particle size and dispersion of the final silver nanocolloid. At the preferred concentration, the Ag particle size in the generated silver nanocolloid is more uniform, the Ag particle distribution is more uniform, and the Ag particles are neither over-dispersed nor over-agglomerated, resulting in higher SERS detection sensitivity.

[0014] In some embodiments, in step (3), the stirring speed may be 600-1200 r / min, for example, 1000 r / min.

[0015] In some embodiments, in step (3), the stirring time may be 10 to 30 minutes.

[0016] In some embodiments, in step (3), the temperature of the ultrasound can be 28-32°C, for example, 30°C.

[0017] In some embodiments, in step (3), the ultrasonication time may be 30 to 35 minutes.

[0018] In step (3) of the present invention, the content of ethyl cellulose in the silver ink is required to be 4wt%~6wt%, such as 4.9wt%, 5wt%, 5.1wt%, etc. The silver ink with the above ethyl cellulose content has high film quality after spin coating, and has a low detection limit of up to 10 when used for capsaicin SERS detection. -13 The inventors have tried silver inks with other ethyl cellulose contents and found that the resulting silver inks either had poor dispersion of the silver nanocolloid, were difficult to form into films, or had low SERS sensitivity and a high SERS detection limit for capsaicin.

[0019] In step (3), the content of the concentrated silver nanoparticles in the silver ink is preferably 35 wt% to 46 wt%, such as 45 wt%. The silver ink under the preferred conditions has a higher film quality after spin coating, and the detection limit for capsaicin SERS detection is lower, which can reach 10 -13 M.

[0020] In some embodiments, in step (4), the parameters of the spin coating of the silver ink by the coater include: 500-5000 r / min for 1-10 min. Furthermore, in step (4), the parameters of the spin coating of the silver ink by the coater preferably include: first 500-600 r / min for 30-35 s, then 900-1100 r / min (e.g., 1000 r / min) for 60-70 s. Under the preferred conditions, the silver ink has higher film quality and better uniformity after spin coating, and the detection limit for capsaicin SERS detection is lower, which can reach 10 -13 M.

[0021] In some embodiments, in step (4), the vacuum drying temperature may be 40-50°C, for example, 45°C.

[0022] In some embodiments, in step (4), the vacuum drying time may be 12 to 36 hours.

[0023] In order to further improve the SERS detection performance of the silver ink film for capsaicin and reduce the detection limit, in some preferred embodiments, the preparation method described in the first aspect further includes the steps of:

[0024] (5) The silver ink film obtained in step (4) is sequentially subjected to acid washing and water washing, and then vacuum drying.

[0025] In step (5), acid washing can remove impurities such as oxides on the surface of the silver ink film, thereby improving the detection sensitivity of the silver ink film and reducing the SERS detection limit of capsaicin.

[0026] In some embodiments, in step (5), the acid used for pickling may include at least one of hydrochloric acid, nitric acid, sulfuric acid, etc.

[0027] In some embodiments, in step (5), the acid concentration used in the pickling may be 0.1-5 M, for example, 0.5 M.

[0028] In some embodiments, in step (5), the pickling time may be 1 to 3 minutes.

[0029] In some embodiments, in step (5), the liquid on the surface of the silver ink film may be blown dry before vacuum drying.

[0030] In some embodiments, in step (5), the vacuum drying temperature may be 30-35°C.

[0031] In some embodiments, in step (5), the vacuum drying time may be 1 to 2 hours.

[0032] In a second aspect, the present invention provides a silver ink film prepared by the preparation method described in the first aspect.

[0033] In a third aspect, the present invention provides the use of the silver ink film described in the second aspect in surface enhanced Raman scattering detection. Furthermore, the Raman probe molecule in the surface enhanced Raman scattering detection is a capsaicin molecule. The silver ink film of the present invention is particularly suitable for SERS detection of capsaicin, and the SERS detection limit of capsaicin can be as low as 10 -13 M.

[0034] In a fourth aspect, the present invention provides a method for surface-enhanced Raman scattering detection using the silver ink film described in the second aspect, comprising the steps of:

[0035] (a) Preparation of Raman probe molecule solutions with different concentrations;

[0036] (b) immersing the silver ink film in a Raman probe molecule solution to allow the Raman probe molecules to adsorb on the silver ink film, then removing the silver ink film and drying it to obtain a silver ink film adsorbed with the Raman probe molecules;

[0037] (c) A silver ink film adsorbed with Raman probe molecules is placed on a laser confocal Raman microscope platform. The laser light source is selected, and the laser power, exposure time, and number of integration times are adjusted to obtain surface-enhanced Raman scattering signal data with the highest signal-to-noise ratio.

[0038] In some embodiments, in step (a), the Raman probe molecule may be a capsaicin molecule.

[0039] In some embodiments, in step (b), the silver ink film may be immersed in the Raman probe molecule solution for 1 to 5 hours, such as 3 hours.

[0040] In some embodiments, in step (c), the wavelength of the laser light source may be 532 nm.

[0041] In some embodiments, in step (c), the laser power may be 0.1-10 mW.

[0042] In some embodiments, in step (c), the test exposure time may be 1 to 15 s, such as 3 s.

[0043] In some embodiments, in step (c), the number of integrations may be 1 to 50 times, such as 3 times.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] 1. The preparation method of the silver ink film of the present invention is simple. The SERS substrate prepared by the preparation method is used to detect capsaicin solution. The detection is simple and the minimum detection limit can reach 10 -13 M.

[0046] 2. Compared with other methods, the raw materials used in the preparation process of the silver ink film of the present invention are easily available and low in cost, and the preparation method is simple and convenient. The obtained film substrate has high roughness and a strong SERS signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 The silver ink film with a concentrated silver nano-colloid content of 25 wt% is provided in the specific embodiment to the silver ink film with a concentration of 10 -11 SERS spectrum of capsaicin solution of M.

[0048] Figure 2 The silver ink film with a concentrated silver nano-colloid content of 35 wt% provided in the specific embodiment is subjected to a reaction with a concentration of 10 -13 SERS spectrum of capsaicin solution of M.

[0049] Figure 3 The silver ink film with a concentrated silver nano-colloid content of 45 wt% is provided in the specific embodiment to the silver ink film with a concentration of 10 -13 SERS spectrum of capsaicin solution of M. DETAILED DESCRIPTION

[0050] The present invention will be further described below with reference to the accompanying drawings and specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0051] In the following examples, the operating methods without specifying specific conditions are generally carried out under conventional conditions or conditions recommended by the manufacturer.

[0052] The method for preparing a silver ink film comprises the following steps:

[0053] 1) Evenly mix 4.5 mL of 0.1 mol / L sodium hydroxide solution and 5 mL of 0.06 mol / L hydroxylamine hydrochloride solution. Quickly pour the resulting mixture into 90 mL of vigorously stirred 0.0011 mol / L silver nitrate solution. Stir for 10 minutes until the reaction is complete, obtaining a uniform milky white mixture of silver nanocolloids.

[0054] 2) Centrifuge at 10,000 rpm for 10 minutes, discard the supernatant to obtain the concentrated silver nanogel, and store in the dark at room temperature until use.

[0055] 3) Take three portions of concentrated silver nanogel (0.3 g each) and place them into three 1.5 mL centrifuge tubes, numbering them 1, 2, and 3 respectively;

[0056] 0.060 g of ethyl cellulose and 0.840 g of α-terpineol were added to centrifuge tube No. 1. The resulting mixture contained 25 wt% of concentrated silver nanogel and 5 wt% of ethyl cellulose.

[0057] 0.043 g of ethyl cellulose and 0.514 g of α-terpineol were added to centrifuge tube No. 2. The resulting mixture contained 35 wt% of concentrated silver nanogel and 5 wt% of ethyl cellulose.

[0058] 0.033 g of ethyl cellulose and 0.333 g of α-terpineol were added to centrifuge tube No. 3. In the resulting mixture, the concentrated silver nanocolloid content was 45 wt % and the added amount of ethyl cellulose was 5 wt %.

[0059] 4) Thoroughly magnetically stir and ultrasonically treat centrifuge tubes 1, 2, and 3: First, magnetically stir at 1000 r / min for 30 min, then ultrasonically treat at 30°C for 30 min to ensure complete mixing of the silver ink.

[0060] 5) Use a spin coater to spin-coat the three evenly mixed silver inks onto a clean, polished silicon wafer of 0.5 cm × 0.5 cm. The specific parameters are: first spin coating at 500 r / min for 30 s, then spin coating at 1000 r / min for 1 min, to obtain three silicon wafers coated with silver ink.

[0061] 6) The three silver ink-coated silicon wafers were placed in a drying oven and vacuum-dried at 45°C for 12 h to obtain three types of silver ink films.

[0062] 7) The three silver ink films obtained in step 6) were pickled with 0.5 M hydrochloric acid for 1 min, and then the residual solution on the surface was washed with deionized water.

[0063] 8) Use an ear bulb to dry the liquid on the surface of the three silver ink films obtained in step 7), and then place them in a drying oven and vacuum dry them at 30°C for 1 hour to obtain three silver ink films capable of highly sensitive detection of capsaicin.

[0064] The application of the three prepared silver ink films capable of highly sensitive capsaicin detection in surface-enhanced Raman scattering detection includes the following steps:

[0065] a) Capsaicin molecules were prepared at concentrations of 10 -5 ~10 -15 The solution of M.

[0066] b) The three silver ink films prepared in steps 1) to 8) above were immersed in the capsaicin molecule solutions of different concentrations prepared in step a) for 3 h, and then taken out and dried.

[0067] c) Three silver ink films adsorbed with capsaicin molecules were placed on a confocal laser Raman microscope. A laser light source with a wavelength of 532 nm was selected, and the laser power was adjusted to 0.1 mW. The exposure time was 3 s, and the number of integrations was 3. Surface-enhanced Raman scattering signals were measured at 10 different positions.

[0068] Figure 1 The lowest concentration of capsaicin (10 -11 M) and the test data graph with the highest signal-to-noise ratio, Figure 2 The lowest concentration of capsaicin (10 -13 M) and the test data graph with the highest signal-to-noise ratio, Figure 3 The lowest concentration of capsaicin (10 -13 M) and the test data graph with the highest signal-to-noise ratio.

[0069] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for preparing a silver ink film capable of highly sensitive detection of capsaicin, characterized in that: Including steps: (1) Adding a mixed solution of sodium hydroxide and hydroxylamine hydrochloride to a silver nitrate solution under stirring, and keeping stirring until the reaction is complete to obtain a uniform milky white mixture of silver nanocolloid; (2) centrifuging the silver nanocolloid solution at a speed of 5000-15000 r / min for 5-30 minutes, discarding the supernatant to obtain concentrated silver nanocolloid; (3) mixing the concentrated silver nano-colloid with ethyl cellulose and α-terpineol, stirring, and ultrasonically treating to obtain a uniform silver ink; in the silver ink, the content of the concentrated silver nano-colloid is 25wt%~55wt%, the content of the ethyl cellulose is 4wt%~6wt%, and the rest is the α-terpineol; (4) Using a coating machine, the silver ink is spin-coated onto a clean, polished silicon wafer and vacuum-dried to obtain a silver ink film.

2. The preparation method according to claim 1, characterized in that In step (1): In the mixed solution, the concentrations of sodium hydroxide and hydroxylamine hydrochloride are independently 0.01 to 1 M; The concentration of the silver nitrate solution is 10 -4 ~10 -2 M.

3. The preparation method according to claim 1, characterized in that In step (4): The parameters for spin coating silver ink on the spin coater include: 500-5000 r / min for 1-10 min; The vacuum drying temperature is 40-50°C; The vacuum drying time is 12 to 36 hours.

4. The preparation method according to claim 1, characterized in that The preparation method further comprises the steps of: (5) The silver ink film obtained in step (4) is sequentially subjected to acid washing and water washing, and then vacuum drying.

5. The preparation method according to claim 4, characterized in that In step (5): The acid used for pickling includes at least one of hydrochloric acid, nitric acid and sulfuric acid; The acid concentration used in the pickling is 0.1~5 M; The pickling time is 1 to 3 minutes; Blow dry the liquid on the surface of the silver ink film before vacuum drying; The vacuum drying temperature is 30-35° C., and the vacuum drying time is 1-2 h.

6. The silver ink film prepared according to the preparation method according to any one of claims 1 to 5.

7. Use of the silver ink film according to claim 6 in surface enhanced Raman scattering detection.

8. The use according to claim 7, characterized in that The Raman probe molecule in the surface enhanced Raman scattering detection is a capsaicin molecule.

9. A method for surface enhanced Raman scattering detection using the silver ink film according to claim 6, characterized in that: Including steps: (a) Preparation of Raman probe molecule solutions with different concentrations; (b) immersing the silver ink film in a Raman probe molecule solution to allow the Raman probe molecules to adsorb on the silver ink film, then removing the silver ink film and drying it to obtain a silver ink film adsorbed with the Raman probe molecules; (c) A silver ink film adsorbed with Raman probe molecules is placed on a laser confocal Raman microscope platform. The laser light source is selected, and the laser power, exposure time, and number of integration times are adjusted to obtain surface-enhanced Raman scattering signal data with the highest signal-to-noise ratio.

10. The method according to claim 9, characterized in that In step (a), the Raman probe molecule is a capsaicin molecule; In step (c), the wavelength of the laser light source is 532 nm, the laser power is 0.1-10 mW, the test exposure time is 1-15 s, and the number of integration times is 1-50 times.

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