Ag / ag2o / ag nanosphere array sers substrate, preparation method and application

Abstract

The application belongs to the technical field of Raman spectrum detection, and discloses an Ag / Ag2O / Ag nanosphere array SERS substrate, a preparation method and application. Polystyrene (PS) spheres are self-assembled and arranged in a hexagonal close-packed manner on a silicon wafer, silver is evaporated, exposed to air to naturally oxidize to form an oxide layer, silver is evaporated again to form a uniform three-layer nanosphere array, and an Ag / Ag2O / Ag nanosphere array SERS substrate is obtained. By controlling the deposition thickness of the silver layer and the oxidation time of the bottom silver layer, SERS substrates with different properties can be obtained. The SERS substrate provided by the application can be applied to a detection chip, and experimental results show that when the concentration of R6G is as low as 10 ‑9 M, the SERS substrate can still detect Raman signals, which indicates that it has the potential for trace detection.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of Raman spectrum detection, and particularly relates to an Ag / Ag2O / Ag nanosphere array SERS substrate, a preparation method and application. BACKGROUND

[0002] As a kind of spectroscopic analysis technique, surface enhanced Raman scattering (SERS) has been widely applied in biomedical, clinical diagnosis, environmental sensing application and food safety field, etc. in trace chemical and biological molecule detection at extremely low concentration even single molecule level. The main principle of SERS is local surface plasmon resonance caused by collective oscillation of electrons, which leads to electromagnetic field enhancement of surface nanostructure. Ag, Au, Cu and other noble metals are widely considered as ideal nanostructure materials, among which silver nanostructure becomes the first choice of SERS substrate due to its superior plasmonic effect and low cost compared with other metals. The sensitivity of substrate can be effectively improved by adjusting the shape and gap of nanostructure. The existing technology adopts atomic layer deposition or TEO method to coat nanoparticles to obtain shell structure on the surface of the ball, but such method is expensive and can only be applied to liquid nanoparticles, which is an important factor affecting the effect of SERS substrate. SUMMARY

[0003] Therefore, the application aims to provide an Ag / Ag2O / Ag nanosphere array SERS substrate, a preparation method and application, which has a multi-layer structure, large area, low cost, good uniformity, bending resistance, high detection sensitivity, simple preparation method, controllable thickness, low cost and wide application.

[0004] To solve the above problems, the application provides the following technical solutions.

[0005] An Ag / Ag2O / Ag nanosphere array SERS substrate includes a hard substrate, a polystyrene sphere array in a hexagonal close-packed array structure is self-assembled on the hard substrate, and the polystyrene sphere array has an Ag / Ag2O / Ag layer on the surface away from the hard substrate.

[0006] Further, the material of the hard substrate is one or more of ordinary glass, quartz glass, ceramic, indium tin oxide (ITO), copper, aluminum, iron, steel, alloy, diamond, sapphire, Si, GaAs, polymethyl methacrylate, polycarbonate, polyvinyl chloride, polyethylene, polypropylene, polyvinylidene fluoride and polytetrafluoroethylene. The thickness of the hard substrate is not required.

[0007] Further, the hard substrate is a silicon wafer.

[0008] Further, the diameter of the polystyrene balls is 600-900 nm.

[0009] Further, the diameter of the polystyrene balls is 600 nm. When the diameter is 600 nm, the polystyrene balls are more easily assembled on the hard substrate.

[0010] Further, in the Ag / Ag2O / Ag layer, the thickness of the outer Ag layer is 30-120 nm.

[0011] Further, in the Ag / Ag2O / Ag layer, the thickness of the outer Ag layer is 30 nm, and the Ag2O layer is formed by oxidizing the bottom Ag layer at 25℃ for 24 h.

[0012] The application also provides a preparation method of the Ag / Ag2O / Ag nanosphere array SERS substrate, comprising the following steps:

[0013] S1. Self-assembling on the surface of a hard substrate to form a monolayer of polystyrene ball array in a hexagonal close-packed array structure;

[0014] S2. Depositing an Ag layer on the side surface of the polystyrene ball array away from the hard substrate to obtain a polystyrene ball array with a bottom Ag layer;

[0015] S3. Oxidizing the polystyrene ball array with a bottom Ag layer to form an Ag2O layer with a target thickness on the surface of the bottom Ag layer;

[0016] S4. Depositing an Ag layer on the surface of the Ag2O layer to obtain an Ag / Ag2O / Ag nanosphere array SERS substrate.

[0017] Further, the deposition method is vacuum thermal deposition evaporation.

[0018] Further, the oxidation treatment is placing in a natural environment at 25℃ for 24 h.

[0019] Further, the rate of vacuum thermal deposition evaporation is 0.3 A / s.

[0020] The application also provides the use of the above-mentioned Ag / Ag2O / Ag nanosphere array SERS substrate or the Ag / Ag2O / Ag nanosphere array SERS substrate prepared by the above-mentioned preparation method in a detection chip, and the detection chip is used for detecting the single molecule level and / or the biomolecule level.

[0021] Further, the detection chip is a detection chip for detecting R6G (dye molecules), and the detection limit is 10 -9 M.

[0022] Compared with the prior art, the preparation method provided by the application forms a nanosphere array on the surface of a hard substrate by a self-assembly method, forms an Ag / Ag2O / Ag layer multi-layer structure on the nanosphere array by directly using the method that silver naturally oxidizes to form a medium layer on the surface, the multi-layer material coated on the surface of the nanosphere has additional degrees of freedom in the plasmonic band, can more effectively enhance Raman scattering, and realizes simple and controllable preparation of a multi-layer SERS substrate, large-area preparation, and excellent performance. The preparation method provided by the application can obtain SERS substrates with different performances by regulating the deposition thickness of the silver layer and the oxidation time of the bottom layer of silver. Experimental results show that the performance of the SERS substrate reaches the maximum when the oxidation time is 24 hours, and the SERS signal is 5.2 times stronger than that of a single-layer silver nanosphere array with the same thickness, 50 points on the surface of the sample are randomly selected for Raman signal testing, and an RSD value of 4.67% is obtained, which shows that the substrate has good uniformity. When the R6G concentration is as low as 10 -9 M, the Raman signal can still be detected, which shows that the substrate has potential for trace detection. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0024] Figure 1 is a structural schematic diagram of the Ag / Ag2O / Ag nanosphere array SERS substrate provided by the application;

[0025] Figure 2 is a preparation process schematic diagram of the Ag / Ag2O / Ag nanosphere array SERS substrate provided by the embodiment 1 of the application;

[0026] Figure 3 is a scanning electron microscope (SEM) diagram of the sample obtained in step S1 in the embodiment 1 of the application;

[0027] Figure 4 is a SEM diagram of the sample (single-layer self-assembly to form hexagonal close-packed PS spheres on which silver is evaporated) obtained in step S2 in the embodiment 1 of the application;

[0028] Figure 5SEM images of Ag / Ag2O / Ag nanosphere array SERS substrates obtained in Examples 1-3 of the present application, wherein (a) is the SEM image of the Ag / Ag2O / Ag nanosphere array SERS substrate with a total thickness of 60 nm obtained in Example 1, (b) is the SEM image of the Ag / Ag2O / Ag nanosphere array SERS substrate with a total thickness of 120 nm obtained in Example 2, and (c) is the SEM image of the Ag / Ag2O / Ag nanosphere array SERS substrate with a total thickness of 240 nm obtained in Example 3;

[0029] Figure 6 Raman spectra of 10 -6 Raman spectra of 10

[0030] Figure 7 Figure 4 is a plot of the intensity of the Ag / Ag2O / Ag nanosphere array SERS substrate obtained in Example 4 of the present application versus the oxidation time of the oxidation layer, and the total thickness of the silver film is 120 nm;

[0031] Figure 8 Raman spectra of 50 -6 Raman spectra of 10

[0032] Figure 9 Raman spectra of different concentrations of rhodamine 6G probe molecules measured on the Ag / Ag2O / Ag nanosphere array SERS substrate obtained in Example 1 of the present application. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0034] The present application provides an Ag / Ag2O / Ag nanosphere array SERS substrate, and the structure is as followsFigure 1 As shown, it comprises a hard substrate silicon wafer, a polystyrene sphere array in a hexagonal close-packed array structure is self-assembled on the hard substrate, and the Ag / Ag2O / Ag layer is on the side surface of the polystyrene sphere array away from the hard substrate.

[0035] The application further provides a preparation method of the Ag / Ag2O / Ag nanosphere array SERS substrate, and a process diagram of the preparation method is as shown in Figure 2 As shown, it comprises the following steps:

[0036] S1. Forming a monolayer of polystyrene sphere array in a hexagonal close-packed array structure on the surface of the hard substrate by self-assembly; preferably, the material of the hard substrate can be selected from one or more of common glass, quartz glass, ceramic, indium tin oxide (ITO), copper, aluminum, iron, steel, alloy, diamond, sapphire, Si, GaAs, polymethyl methacrylate, polycarbonate, polyvinyl chloride, polyethylene, polypropylene, polyvinylidene fluoride, and polytetrafluoroethylene; and the thickness of the hard substrate is not required in the application; more preferably, the hard substrate is a silicon wafer with smooth surface.

[0037] S2. Depositing an Ag layer on the side surface of the polystyrene sphere array away from the hard substrate to obtain a polystyrene sphere array with an underlying Ag layer; preferably, the deposition method is vacuum thermal deposition evaporation; more preferably, the rate of the vacuum thermal deposition evaporation is 0.3 A / s.

[0038] S3. Oxidizing the polystyrene sphere array with the underlying Ag layer to form an Ag2O layer with a target thickness on the surface of the underlying Ag layer; preferably, the oxidation method is placing in a natural environment at 25℃ for 24h.

[0039] S4. Depositing an Ag layer on the surface of the Ag2O layer to obtain an Ag / Ag2O / Ag nanosphere array SERS substrate.

[0040] Material preparation: cut the silicon wafer into 0.5cm×0.5cm square silicon wafers; prepare a large glass culture dish, glass sheets, polystyrene (PS) sphere suspension, several glass sheets, and anhydrous ethanol; and perform hydrophilic treatment on the glass sheets and the cut silicon wafers.

[0041] Experimental Example 1

[0042] S1. Forming a monolayer of polystyrene sphere array in a hexagonal close-packed array structure on the surface of the hard substrate by self-assembly;

[0043] S11. Fill the large culture dish with ultrapure water to 2 / 3, and cut and insert the glass sheets into the water surface at an angle of about 45 degrees;

[0044] S12. Mix the PS ball suspension with a mass fraction of 2.5% with anhydrous ethanol at a ratio of 4:1, and put it into an ultrasonic cleaner for 30 minutes to mix thoroughly. At the same time, prepare a 20 mM sodium dodecyl sulfate (SDS) solution;

[0045] S13. Use a needle tube with a maximum range of 20 μl to suck the mixed solution of PS ball suspension and anhydrous ethanol into about 5 μl;

[0046] S14. Aim the needle of the needle tube at a position 2 cm away from the junction of the glass sheet and the liquid surface, and inject it onto the glass sheet at an extremely slow speed, so that the mixed solution flows slowly from the glass sheet to the liquid surface;

[0047] S15. Wait for the colored film formed at the liquid surface to stop injecting, and stand for 30 minutes;

[0048] S16. If the film at the liquid surface is relatively loose, a drop of SDS solution needs to be added to make it close, and if a large area of colored film has been formed, it is not necessary;

[0049] S17. Use tweezers to hold the small silicon sheet after hydrophilic treatment and stretch it into the liquid surface without PS balls from the liquid surface, close to the PS ball film, and randomly tilt the small silicon sheet upward, so that the PS balls at the liquid surface can be transferred to the silicon sheet. The SEM image of the hexagonal close-packed PS balls transferred to the silicon sheet is as follows Figure 3 .

[0050] S2. Deposit an Ag layer on the surface of the polystyrene ball array away from the hard substrate to obtain a polystyrene ball array with an Ag layer at the bottom; the SEM image is as follows Figure 4 .

[0051] S21. Open the vacuum box, and place the prepared sample on the metal plate and about 30 cm above the evaporation source;

[0052] S22. Close the vacuum box, start the mechanical pump, and open the pre-evacuation valve;

[0053] S23. After the vacuum degree reaches 1 Pa, open the electromagnetic valve and start the

[0054] S24. After the rotation speed reaches 3000 r, close the pre-evacuation valve and open the plug-in valve;

[0055] S25. After the vacuum degree reaches 8 × 10 -4 Pa, open the current, and control the evaporation rate at 0.3 A / s;

[0056] S26. After the Ag layer reaches a deposition thickness of 30 nm, close the evaporation according to the specified order, and take out the sample;

[0057] S3. The polystyrene sphere array with the bottom Ag layer prepared in step S2 is subjected to oxidation treatment to form an Ag2O layer with a target thickness on the surface of the bottom Ag layer;

[0058] Specifically, the sample treated in step S3 is placed in a natural dust-free environment at 25 degrees Celsius for 24 hours.

[0059] S4. An Ag layer is deposited on the surface of the Ag2O layer to obtain an Ag / Ag2O / Ag nanosphere array SERS substrate.

[0060] S41. The vacuum box is opened, the prepared sample is attached to the metal plate and placed about 30 cm above the evaporation source;

[0061] S42. The vacuum box is closed, the mechanical pump is started, and the pre-evacuation valve is opened;

[0062] S43. After the vacuum degree reaches 1 Pa, the electromagnetic valve is opened, and the

[0063] S44. After the rotation speed reaches 3000r, the pre-evacuation valve is closed, and the plug-in valve is opened;

[0064] S45. After the vacuum degree reaches 8x10 -4 , the current is turned on, and the evaporation rate is controlled at 0.3 A / s;

[0065] S46. After the Ag layer reaches a deposition thickness of 30 nm (total thickness of 60 nm), the evaporation is closed in the specified order, and the sample, i.e., the Ag / Ag2O / Ag nanosphere array SERS substrate, is taken out. Its SEM image is as shown in Figure 5 (a).

[0066] Example 2

[0067] The other steps are the same as in Example 1, the deposition thickness in step S26 is changed to 60 nm, and the deposition thickness in step S46 is changed to 60 nm. That is, the Ag / Ag2O / Ag nanosphere array SERS substrate obtained has a bottom Ag layer and an outer Ag layer with a thickness of 60 nm. The total thickness is 120 nm. Its SEM image is as shown in Figure 5 (b).

[0068] Example 3

[0069] The other steps are the same as in Example 1, the deposition thickness in step S26 is changed to 120 nm, and the deposition thickness in step S46 is changed to 120 nm. That is, the Ag / Ag2O / Ag nanosphere array SERS substrate obtained has a bottom Ag layer and an outer Ag layer with a thickness of 120 nm. The total thickness is 240 nm. Its SEM image is as shown in Figure 5 (c).

[0070] Example 4

[0071] Other steps are the same as Example 1, and the natural oxidation waiting time of step S3 is changed to 8h, 16h, 32h, 40h, 48h, 56h respectively.

[0072] Comparative Example 1

[0073] A polystyrene ball array (single layer) with only a 60nm-thick Ag layer deposited thereon.

[0074] Comparative Example 2

[0075] A polystyrene ball array (single layer) with only a 120nm-thick Ag layer deposited thereon.

[0076] Comparative Example 3

[0077] A polystyrene ball array (single layer) with only a 240nm-thick Ag layer deposited thereon.

[0078] Test Example 1

[0079] The samples in Examples 1-3 and Comparative Examples 1-3 are all dripped with 20μl of 10 -6 M R6G probe molecules, and after drying, the Raman signal is measured using a Raman spectrometer with a laser wavelength of 785nm and a power of 10mW. The measurement results are shown in Figure 6 , wherein (a) is the measurement result of the sample with a thickness of 60nm obtained from Example 1 (three layers) and Comparative Example 1 (one layer), (b) is the measurement result of the sample with a thickness of 120nm obtained from Example 2 (three layers) and Comparative Example 2 (one layer), and (c) is the measurement result of the sample with a thickness of 240nm obtained from Example 3 (three layers) and Comparative Example 3 (one layer); Figure 6 It can be seen that the intensity of the three layers is stronger than that of the single layer with the same thickness, and the intensity is best when the total thickness is 120nm.

[0080] Test Example 2

[0081] The samples in Examples 1 and 4 are all dripped with 20μl of 10 -6 M R6G probe molecules, and after drying, the Raman signal is measured using a Raman spectrometer with a laser wavelength of 785nm and a power of 10mW. The horizontal axis represents the oxidation time, and the vertical axis represents the intensity at the highest peak (621cm -1 ) of the Raman signal. The chart shown in Figure 7 can be drawn, and it can be seen from Figure 7 that when the oxidation time reaches 24h, the Raman signal of the sample is the strongest.

[0082] Test Example 3

[0083] The sample in Example 1 is dripped with 20μl of 10 -6The R6G probe molecules of M were dried, and then the Raman signals were measured by using a Raman spectrometer with a laser wavelength of 785 nm and a power of 10 mW. The signals were measured at 50 different points on the sample, and the RSD graph as shown in Figure 8 was drawn, which reflected the uniformity of the sample.

[0084] Test Example 4

[0085] The sample obtained in Example 1 was dripped with 20 μl of different concentrations of R6G probe molecules, and then dried. The Raman signals were measured by using a Raman spectrometer with a laser wavelength of 785 nm and a power of 10 mW. The measurement results of Test Example 1 are shown in Figure 9 . Figure 9 It is shown that the minimum detection limit can reach 10 -9 M.

[0086] The above examples are only used to illustrate the technical solutions of the present application, and not to limit it. Although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some technical features can be replaced by equivalents. Such modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An Ag / Ag2O / Ag nanosphere array SERS substrate, characterized in that, The Ag / Ag2O / Ag nanosphere array SERS substrate comprises a hard substrate, and a polystyrene sphere array in a hexagonal close-packed array structure is self-assembled on the hard substrate, and the Ag / Ag2O / Ag layer is arranged on the side surface of the polystyrene sphere array away from the hard substrate. The Ag / Ag2O / Ag nanosphere array SERS substrate is prepared by a preparation method comprising the following steps: S1. Forming a monolayer of a polystyrene sphere array in a hexagonal close-packed array structure on the surface of a hard substrate by self-assembly; S2. Depositing an Ag layer on the side surface of the polystyrene sphere array away from the hard substrate to obtain a polystyrene sphere array with a bottom Ag layer; S3. Oxidizing the polystyrene sphere array with a bottom Ag layer to form an Ag2O layer on the surface of the bottom Ag layer; S4. Depositing an Ag layer on the surface of the Ag2O layer to obtain an Ag / Ag2O / Ag nanosphere array SERS substrate; The deposition is vacuum thermal deposition evaporation. 2.The Ag / Ag 2 O / Ag nanosphere array SERS substrate according to claim 1, characterized in that, The hard substrate is a silicon wafer. 3.The Ag / Ag 2 O / Ag nanosphere array SERS substrate of claim 1, wherein, The diameter of the polystyrene sphere is 600 nm. 4.The Ag / Ag 2 O / Ag nanosphere array SERS substrate of claim 1, wherein, In the Ag / Ag2O / Ag layer, the Ag2O layer is formed by oxidizing the bottom Ag layer at 25°C for 24 hours.

5. The Ag / Ag20 / Ag nanospheres array SERS substrate according to claim 1, wherein, In the Ag / Ag2O / Ag layer, the thickness of the outer Ag layer is 30-120 nm.

6. A method for preparing an Ag / Ag2O / Ag nanosphere array SERS substrate, characterized in that, The preparation method comprises the following steps: S1. Forming a monolayer of a polystyrene sphere array in a hexagonal close-packed array structure on the surface of a hard substrate by self-assembly; S2. Depositing an Ag layer on the side surface of the polystyrene sphere array away from the hard substrate to obtain a polystyrene sphere array with a bottom Ag layer; S3. Oxidizing the polystyrene sphere array with a bottom Ag layer to form an Ag2O layer on the surface of the bottom Ag layer; S4. Depositing an Ag layer on the surface of the Ag2O layer to obtain an Ag / Ag2O / Ag nanosphere array SERS substrate; The deposition is vacuum thermal deposition evaporation.

7. The preparation method according to claim 6, characterized in that, The oxidation treatment is placing in a natural environment at 25°C for 24 hours.

8. The preparation method according to claim 7, characterized in that, The rate of vacuum thermal deposition is 0.3 A / s.

9. The Ag / Ag2O / Ag nanosphere array SERS substrate of any one of claims 1-5 or the Ag / Ag2O / Ag nanosphere array SERS substrate prepared by the preparation method of any one of claims 6-8 is applied in a detection chip for detecting a single molecule level and / or a biomolecule level.

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