CN114113031A - Three-dimensional SERS substrate and preparation method and application thereof - Google Patents
Three-dimensional SERS substrate and preparation method and application thereof Download PDFInfo
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- G—PHYSICS
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- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/65—Raman scattering
- G01N21/658—Raman scattering enhancement Raman, e.g. surface plasmons
Abstract
The invention relates to a preparation method of a three-dimensional SERS substrate, and the three-dimensional SERS substrate obtained by the method has good uniformity, large specific surface area, simple process and convenient operation. In addition, the method does not relate to ultraviolet lithography, electron beam lithography and the like, and does not need expensive equipment, so the cost is low. Noble metal nano-particles are densely and uniformly distributed on the surface of the three-dimensional SERS substrate, and under the irradiation of exciting light, the electromagnetic coupling among the noble metal nano-particles can generate abundant 3D SERS 'hot points', so that the SERS substrate has high sensitivity, can be integrated into substrates with different materials as a sensitive area for SERS detection, and is used for various molecular detections. In addition, the three-dimensional SERS substrate can realize rapid and complete degradation of molecules to be detected after being irradiated by ultraviolet rays, so that the substrate can be recycled, the problem of disposable use of the traditional SERS substrate is solved, the cost is low, and the three-dimensional SERS substrate is suitable for mass production.
Description
Technical Field
The invention belongs to the technical field of functionalized nano materials, and particularly relates to a three-dimensional SERS substrate and a preparation method and application thereof.
Background
Surface Enhanced Raman Scattering (SERS) has the advantages of being non-destructive, ultra-sensitive, low in sample requirement, unique in "fingerprint", and the like, and has been widely used in many fields such as analytical chemistry, biosensing, food and environmental security, and the like.
Most of the research is currently devoted to develop a composite three-dimensional nanostructure of noble metal/ZnO nanostructures and other nanomaterials as SERS active substrates, including graphene oxide, silicon nanopillars, carbon fibers, etc. However, most of the manufacturing methods at present have complicated manufacturing processes and require the use of expensive equipment, such as focused ion beam etching, ultraviolet lithography, electron beam lithography, and chemical synthesis growth technology (VLS). Other possible methods with lower cost include, for example, Metal Assisted Catalytic Etching (MACE) and nanosphere lithography (NSL), but the three-dimensional SERS substrates produced by these methods have poor uniformity and small specific surface area.
Therefore, there is an urgent need to develop a new method for preparing a three-dimensional SERS substrate, which has the advantages of low cost, simple process, and convenient operation, and can ensure high uniformity and large specific surface area of the substrate.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a preparation method of a three-dimensional SERS substrate, which does not relate to ultraviolet lithography, electron beam lithography and the like, does not need expensive equipment and has low cost. In addition, the method has simple process and convenient operation, and can ensure that the obtained substrate has high uniformity and large specific surface area.
In order to achieve the above object, the present invention provides the following technical solutions.
A method of preparing a three-dimensional SERS substrate, comprising:
providing a substrate;
forming a polymer layer on the upper surface of the substrate, wherein the polymer layer is made of a polymer material which can be bombarded by plasma;
subjecting the polymer layer to plasma bombardment, thereby forming a nano forest structure;
forming a metal oxide film on the surface of the nano forest structure;
forming metal oxide nanorods on the surface of the metal oxide film by a hydrothermal method; and
and forming a noble metal layer on the surface of the metal oxide film and the surface of the metal oxide nanorod to obtain the three-dimensional SERS substrate.
The invention also provides the three-dimensional SERS substrate obtained by the preparation method.
The invention also provides application of the three-dimensional SERS substrate in molecular detection.
The invention also provides a preparation method of the SERS microfluidic chip, which comprises the following steps:
providing a substrate;
forming a polymer layer on the upper surface of the substrate, wherein the polymer layer is made of a polymer material which can be bombarded by plasma;
patterning the polymer layer, so as to remove the edge part of the polymer layer and expose the corresponding upper surface part of the substrate to form a window;
carrying out plasma bombardment on the patterned polymer layer so as to form a nano forest structure;
arranging a shielding plate at the window, so that the shielding plate surrounds the nano forest structure;
forming a metal oxide film on the surface of the nano forest structure;
forming metal oxide nanorods on the surface of the metal oxide film by a hydrothermal method;
forming a noble metal layer on the surface of the metal oxide film and the surface of the metal oxide nanorod;
removing the shielding plate, thereby exposing an upper surface of the substrate; and
bonding a packaging shell with a sample inlet and a sample outlet with the upper surface of the exposed substrate, so that the packaging shell encapsulates the nano forest structure on which the metal oxide nano rods are arranged.
The invention also provides the SERS microfluidic chip obtained by the preparation method.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention provides a preparation method of a three-dimensional SERS substrate, which does not relate to ultraviolet lithography, electron beam lithography and the like, and does not need expensive equipment, so the cost is low. In addition, the method has simple process and convenient operation, and can ensure that the obtained substrate has high uniformity and large specific surface area.
2. Noble metal nano-particles are densely and uniformly distributed on the surface of the three-dimensional SERS substrate prepared by the method, and under the irradiation of exciting light, the electromagnetic coupling among the noble metal nano-particles can generate abundant 3 DSERS' hot points, so that the SERS substrate has high sensitivity, can be integrated into substrates with different materials as a sensitive area for SERS detection, and is used for various molecular detections. The SERS substrate realizes the trace detection of p-aminophenol and adenine, and the minimum detection limit of the SERS substrate reaches 10-9M and 10-7M。
In addition, various molecules attached to the three-dimensional SERS substrate can be degraded quickly and completely after being irradiated by ultraviolet rays, so that the substrate subjected to ultraviolet ray irradiation treatment can be recycled, the problem of disposable use of the traditional SERS substrate is solved, the cost is low, and the three-dimensional SERS substrate is suitable for mass production.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:
fig. 1 shows a cross-sectional view of a substrate provided in example 1.
Fig. 2 shows a cross-sectional view of the substrate surface provided in example 1 after a polymer layer has been provided.
Figure 3 shows a cross-sectional view of the surface of the polymer layer provided in example 1 after plasma bombardment to form nano-forest structures.
Fig. 4 shows a cross-sectional view of the nano forest structure of example 1 after a ZnO film is deposited on the surface.
Fig. 5 shows a cross-sectional view of the ZnO nanorod-nanoforest composite structure formed via hydrothermal growth in example 1.
Fig. 6 shows a cross-sectional view after metal nanoparticles are deposited on the surface of the ZnO nanorod-nanoforest composite structure in example 1.
Fig. 7 shows the scanning electron microscope photograph of the nano forest structure in example 1 after a ZnO film is deposited on the surface.
Fig. 8 shows a scanning electron micrograph of the ZnO nanorod-nano forest composite structure after gold nanoparticles are deposited on the surface thereof in example 1.
Fig. 9 shows a cross-sectional view of a nano forest-nano cone composite structure formed after plasma etching in example 2.
Figure 10 shows a cross-sectional view after removal of surface nano-forest structures by wet etching in example 2.
Fig. 11 is a cross-sectional view showing a ZnO film deposited on the surface of the nanocone structure in example 2.
Fig. 12 shows a cross-sectional view of a ZnO nanorod-nanocone composite structure formed via hydrothermal growth in example 2.
Fig. 13 shows a cross-sectional view after metal nanoparticles are deposited on the surface of a ZnO nanorod-nanocone composite structure in example 2.
FIG. 14 shows the SEM image of example 2 after removing the surface nano forest structure by wet etching and depositing a ZnO film on the surface of the nano cone structure.
Fig. 15 shows a scanning electron micrograph of a ZnO nanorod-nanocone composite structure formed through hydrothermal growth in example 2.
Fig. 16 shows a cross-sectional view of uv exposure of the polymer layer in example 3.
Fig. 17 shows a cross-sectional view of the plasma bombardment of the patterned polymer layer surface to form patterned nano-forest structures in example 3.
Fig. 18 shows a cross-sectional view after a ZnO film is deposited on the surface of the patterned nano-forest structure in example 3.
Fig. 19 shows a cross-sectional view of ZnO nanorods formed via hydrothermal growth in example 3 in combination with a ZnO nanorod-nanoforest composite structure.
Fig. 20 shows a cross-sectional view after depositing metal nanoparticles on the surface of ZnO nanorods and ZnO nanorod-nanoforest composite structure in example 3.
Fig. 21 shows a cross-sectional view of the masking plate aligned over the patterned nano-forest structure surface in example 4.
Fig. 22 shows a cross-sectional view of the patterned nano forest structure with the shielding plate after a ZnO film is deposited on the surface of the patterned nano forest structure in example 4.
Fig. 23 shows a cross-sectional view of ZnO nanorods formed via hydrothermal growth in example 4 in combination with a ZnO nanorod-nanoforest composite structure.
Fig. 24 shows a cross-sectional view of example 4 after deposition of metal nanoparticles on the surface of ZnO nanorods with a ZnO nanorod-nanoforest composite structure, followed by removal of a shielding plate.
Fig. 25 shows a cross-sectional view of the PDMS package body of example 4 after punching and aligned bonding with the substrate.
FIG. 26 shows the Raman spectra of the Au/ZnO/nano forest based three-dimensional SERS substrate tested on different concentrations of rhodamine 6G solution in example 5.
Fig. 27 shows the raman spectra of Au/ZnO/nano forest based three-dimensional SERS substrates tested on p-aminophenol solutions of different concentrations in example 5.
FIG. 28 shows the Raman spectra of Au/ZnO/nano forest based three-dimensional SERS substrates tested on different concentrations of adenine solution in example 5.
FIG. 29 shows that the three-dimensional SERS substrate based on Au/ZnO/nano forest in example 5 has a concentration of 10 under the irradiation of ultraviolet light-6And a Raman spectrum diagram for real-time degradation of the M rhodamine 6G solution.
Description of the reference numerals
The device comprises a substrate 1, a polymer layer 2, a nano forest structure 3, a ZnO film 4, a ZnO nanorod 5, a noble metal thin layer 6, a nano cone 7, a mask 8, ultraviolet light 9, a baffle plate 10, a packaging shell 11, a sample inlet 12 and a sample outlet 13.
Detailed Description
Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be understood that the description is illustrative only and is not intended to limit the scope of the present disclosure. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present disclosure.
Various structural schematics according to embodiments of the present disclosure are shown in the figures. The figures are not drawn to scale, wherein certain details are exaggerated and possibly omitted for clarity of presentation. The shapes of various regions, layers, and relative sizes and positional relationships therebetween shown in the drawings are merely exemplary, and deviations may occur in practice due to manufacturing tolerances or technical limitations, and a person skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions, as actually required.
In the context of the present disclosure, when a layer/element is referred to as being "on" another layer/element, it can be directly on the other layer/element or intervening layers/elements may be present. In addition, if a layer/element is "on" another layer/element in one orientation, then that layer/element may be "under" the other layer/element when the orientation is reversed.
Since the existing preparation method of the three-dimensional SERS substrate is complex in process, expensive equipment is required to be used, and the uniformity and specific surface area of the three-dimensional SERS substrate obtained by the existing method are poor, the invention provides a novel method for preparing the three-dimensional SERS substrate, which comprises the following steps.
A method of preparing a three-dimensional SERS substrate, comprising:
first, a substrate is provided.
The substrate of the present invention may be a silicon-based substrate, such as single crystal silicon, polycrystalline silicon, or amorphous silicon; glass, quartz; sapphire; polymethyl methacrylate (PMMA); polytetrafluoroethylene (PTFE) or cross-linked polystyrene. The present invention is not particularly limited to the substrate, and a conventional substrate suitable for a microfabrication process may be used. The shape and size of the substrate in the present invention is also not particularly limited, and may be, for example, a 4-inch, 8-inch, or 12-inch disk.
And then, forming a polymer layer on the upper surface of the substrate, wherein the material of the polymer layer is a polymer material which can be bombarded by plasma.
The material of the polymer layer can be positive photoresist (such as polyimide), negative photoresist, Polydimethylsiloxane (PDMS), or other polymer material that can be bombarded by plasma and has C, H, O as the main element. The polymer layer may have a thickness of 0.2 to 10 μm.
Preferably, when the polymer layer is a positive photoresist (e.g., polyimide) or a negative photoresist, the polymer layer can be patterned prior to plasma bombardment. Preferably, patterning is performed by exposing and developing the polymer layer. The exposure and development may be performed, for example, in an ultraviolet exposure machine. In some embodiments, the exposure and development can be performed in an ultraviolet exposure machine using a mask, wherein the opaque portion of the mask can be shaped as a circle, a square, a triangle, or the like, and the area of the opaque portion can be 1-200 μm2The distance between the opaque portions may be 100 to 1000 μm. The exposure time and exposure dose can be selected according to the thickness of the polymer layer. And patterning the polymer layer to obtain the nano forest structure with controllable appearance. The nano forest with controllable appearance is taken as a promising nano material and can be prepared in a large area without the limitation of a substrate material.
And then, carrying out plasma bombardment on the polymer layer, thereby forming a nano forest structure.
The plasma is a mixture of one or more of oxygen plasma, argon plasma, and nitrogen plasma. The plasma gas source of the present invention may be any plasma capable of bombarding the polymer layer to form a nano forest structure. Preferably, when the polymer layer is a positive photoresist, in order to make the shape of the nano forest structure stronger for the subsequent deposition of the metal oxide film, the plasma gas source used in the present invention is a mixed gas of oxygen plasma and argon plasma. The flow rate of the plasma gas source can be 10-100 sccm, the RF power can be 50-350W, and the pressure in the chamber can be 5-30 mTorr. The formed nano-forest structure comprises a plurality of nano-pillars. The height of the nano-column can be 2-4 μm, and the diameter can be 200-400 nm. The nano-forest structure with high aspect ratio provides a 3D framework allowing a greater number of metal oxide nanorods to grow on its sidewalls.
In one embodiment, the plasma bombardment of the present invention is performed in a plasma cleaning apparatus. Preferably, after forming the nano forest structures and before forming the metal oxide film, the substrate is anisotropically etched with the nano forest structures as a mask to form pyramidal nanostructures. The anisotropic etching may be performed, for example, by a Reactive Ion Etching (RIE) process. The etching gas may be a fluorine-based gas, a chlorine-based gas, or a bromine-based gas, or may be SF6And CHF3Mixed gas of (1), Cl2Mixed gas of HBr and SF6And Cl2Mixed gas of (2), or SF6And C4F8The mixed gas of (1). The pyramidal nanostructures comprise a plurality of nanocones. The diameter of the bottom of the nanocone can be 80-500 nm, the diameter of the tip can be 20-100 nm, and the height can be 0.5-1.5 μm.
Preferably, after forming the pyramidal nanostructures, the nano-forest structures of the surface of the pyramidal nanostructures are removed. For example, the removal may be performed by wet etching, and the solution of the wet etching is buffered oxide etching solution (BOE), i.e., a mixed solution of hydrofluoric acid and ammonium fluoride. The time of wet etching is not particularly limited, as long as the nano forest structure can be completely removed. The silicon-based nano forest structure is prepared by the method, and a photoetching process and a mask with a complex structure are not required to be prepared, so that the processing cost is reduced. In addition, the method can also control the depth-to-width ratio of the nano-cone by controlling the etching time. Preferably, after removing the nano forest structures of the tapered nano structure surface, a metal oxide film may be formed on the tapered nano structure surface. The specific formation method is as follows.
Next, a metal oxide film is formed on the surface of the nano forest structure.
Preferably, the material of the metal oxide film may be ZnO, TiO, or CuO, but may also be other metal oxide semiconductor materials commonly used in the art. Preferably, the metal oxide film may be formed by a conventional thin film deposition process. The thin film deposition process may be, for example, Physical Vapor Deposition (PVD), such as magnetron sputter deposition, Chemical Vapor Deposition (CVD), and Atomic Layer Deposition (ALD). In some embodiments, the metal oxide film is formed by magnetron sputtering deposition, wherein the sputtering power is 100-200W, the sputtering pressure is 1-5 Pa, and the sputtering time is 10-100 min. Preferably, the thickness of the metal oxide film may be 50 to 150 nm. The metal oxide film formed by the magnetron sputtering deposition method has high uniformity, high speed and lower cost.
Then, metal oxide nanorods are formed on the surface of the metal oxide film by a hydrothermal method.
In the present invention, the metal oxide nanorods and the metal oxide film are made of the same material. The hydrothermal method can be carried out in a hydrothermal reaction kettle, and the used raw material solution is a mixed solution of zinc nitrate hexahydrate and hexamethylenetetramine. The temperature of the hydrothermal reaction can be 80-100 ℃, and the reaction time can be 1-5 h. The length of the metal oxide nanorod can be 50-400 nm, and the diameter of the metal oxide nanorod can be 5-100 nm. The metal oxide nanorods not only can provide a scaffold to improve the utilization rate of gaps between adjacent nanorods in a unit area, but also can generate more active sites to load noble metal nanoparticles. The introduction of the metal oxide nanorods greatly improves the SERS performance of the substrate based on a pure nano forest structure, enables the substrate to have better photocatalytic property, can rapidly degrade organic molecules on the surface of the substrate within 15min, enables the organic molecules to be applied to the detection of the organic molecules again, and avoids resource waste caused by disposable use. Meanwhile, compared with the SERS substrate only containing a noble metal layer, a large amount of interface regions between the noble metal nanoparticles and the metal oxide nanorods are provided for charge transfer, and when charge transition energy between the metal oxide-noble metal interface and organic molecules is matched with excitation energy of laser, chemical enhancement occurs, further resulting in greater enhancement of raman signals of the organic molecules.
And finally, forming a noble metal layer on the surface of the metal oxide film and the surface of the metal oxide nanorod to obtain the three-dimensional SERS substrate.
Preferably, the noble metal layer may be formed by a physical vapor deposition method. In some embodiments, the noble metal layer is formed by electron beam evaporation, wherein the pressure in the chamber may be 1 × 10-5～1×10-4Pa, the evaporation rate may be
The evaporation time can be 8-15 min. The material of the noble metal can be Au, Ag or Cu. The thickness of the noble metal layer can be 10-30 nm. Preferably, after the noble metal layer is deposited by electron beam evaporation, the noble metal layer is annealed, wherein the annealing temperature can be 350-450 ℃, and the annealing time can be 2-4 h.
Preferably, after the noble metal layer is formed, the surface of the resulting three-dimensional SERS substrate may be subjected to a hydrophobic treatment. For example, the surface hydrophobic treatment may be performed using a fluorine-based gas or a Hexamethyldisilazane (HMDS) gas. Since the three-dimensional SERS substrate of the invention has a three-dimensional structure, more air pockets exist inside the substrate. The hydrophobic treatment is carried out on the surface of the substrate, so that liquid drops of a sample to be detected can be effectively prevented from entering the air pocket, the liquid drops of the sample to be detected are finally and intensively distributed on the surface of a groove formed by metal oxide nanorods covered by noble metal nano particles, the liquid drops of the sample to be detected are arrayed on the surface of the substrate, and the positioning Raman detection of various biochemical molecules can be realized under an optical microscope. Therefore, the three-dimensional SERS substrate prepared by the method can be used for detecting specific molecular components in pesticides, additives, pigments, foods, fruits and vegetables or biomedical samples and the like.
The invention also provides a preparation method of the SERS microfluidic chip with the three-dimensional structure, which comprises the following steps. Unless otherwise specified, the preparation method involves various raw materials and various parameters which are the same as or similar to the preparation method of the three-dimensional SERS substrate, and the description of the same or similar parts is not repeated below.
First, a substrate is provided.
And then, forming a polymer layer on the upper surface of the substrate, wherein the material of the polymer layer is positive photoresist or negative photoresist.
The positive photoresist may be polyimide.
And patterning the polymer layer, thereby removing the edge part of the polymer layer and exposing the corresponding upper surface part of the substrate to form a window.
In some embodiments, the exposure and development are performed in an ultraviolet exposure machine using a reticle, wherein the opaque portion of the reticle covers a middle portion of the upper surface of the polymer layer, and the opaque portion of the reticle may be shaped as a circle, a square, a triangle, or the like. After exposure and development, the middle part of the polymer layer is remained, and the edge part is completely removed, so that the edge part of the upper surface of the substrate is exposed, and a shielding plate is convenient to arrange subsequently. The present invention is not particularly limited in the width of the edge portion of the polymer layer to be removed, as long as the substrate is allowed to be bonded to the package housing. In this production method, patterning the polymer layer is an indispensable step for ensuring bonding and encapsulation of the substrate and the encapsulation case.
And then, carrying out plasma bombardment on the patterned polymer layer so as to form a nano forest structure.
Then, a shielding plate is arranged at the window, so that the shielding plate surrounds the nano forest structure.
The edge of the substrate is covered by the shielding plate, so that the edge part of the upper surface of the substrate is flat and smooth after the shielding plate is removed, and the substrate is convenient to bond with a packaging shell in a follow-up manner. The shielding plate can be a high-temperature-resistant rigid substrate, and the material of the shielding plate can be Cr-Mo steel plate, iron-based heat-resistant alloy, nickel-based heat-resistant alloy, molybdenum-based heat-resistant alloy, niobium-based heat-resistant alloy or tungsten-based heat-resistant alloy and the like. The shielding plate may have a circular ring structure, a square ring structure, a rectangular ring structure, or the like, and the length (i.e., the outer circumference) of the ring shielding plate may be 1 to 10cm, the width (i.e., the difference between the outer diameter and the inner diameter) of the ring shielding plate may be 1 to 10cm, and the thickness of the ring shielding plate may be 1 to 500 μm.
And then, forming a metal oxide film on the surface of the nano forest structure.
Then, metal oxide nanorods are formed on the surface of the metal oxide film by a hydrothermal method.
Next, a noble metal layer is formed on the surface of the metal oxide film and the surface of the metal oxide nanorods.
Thereafter, the shielding plate is removed, thereby exposing the upper surface of the substrate.
And finally, bonding a packaging shell with a sample inlet and a sample outlet with the upper surface of the exposed substrate, so that the packaging shell encapsulates the nano forest structure on which the metal oxide nano rods are arranged.
The material of the package housing may be Polydimethylsiloxane (PDMS) or glass. The packaging shell completely encapsulates the nanorod-nano forest composite structure. Preferably, the package housing and the substrate are oxygen plasma bonded. And the structure obtained after bonding is the open SERS detection microfluidic chip.
The SERS microfluidic chip has high detection sensitivity and can be used for biomedical analysis and environmental pollution monitoring. In addition, the SERS microfluidic chip disclosed by the invention can be recycled, is low in cost, avoids the problem that the traditional SERS substrate is used once, and is suitable for mass production.
The invention will be further illustrated with reference to specific embodiments and the accompanying drawings.
Example 1
The embodiment provides a preparation method of a three-dimensional SERS substrate, which mainly comprises the following steps:
(1) a 4 "single crystal silicon wafer was provided as substrate 1, as shown in fig. 1.
(2) A polymer layer 2 with a thickness of 6 μm is spin-coated on the surface of a substrate 1 by a spin coater, as shown in FIG. 2, the material of the polymer layer 2 is a positive polyimide photoresist, and during the spin-coating, the polymer layer is rotated at 750rpm for 8s and then at 2500rpm for 25 s. After spin coating, the substrate 1 was placed on a hot plate at a heating temperature of 120 ℃ for 20min to remove organic matters in the photoresist, thereby increasing the adhesion of the photoresist and curing it.
(3) The surface of the polymer layer 2 is bombarded with plasma in a plasma cleaning device to form nano forest structures 3, as shown in fig. 3. The plasma gas source is mixed gas of oxygen plasma and argon plasma, the radio frequency power is 200W, the pressure in the cavity is 5mTorr, the oxygen flow is 50sccm, the argon flow is 20sccm, the bombardment time of the oxygen plasma is 40min, and the bombardment time of the argon plasma is 80 min. The resulting nanopillars were about 2.8 μm in height and about 280nm in diameter.
(4) A layer of ZnO film 4 with a thickness of 100nm is deposited on the surface of the nano forest structure 3 by a magnetron sputtering method, as shown in fig. 4. Wherein, during sputtering, ZnO ceramic target material with purity superior to 99.99% is adopted, the sputtering power is 150W, the sputtering pressure is 3Pa, and the sputtering time is 60 min. The scanning electron micrograph of the structure obtained in this step is shown in fig. 7.
(5) And (3) growing a compact ZnO nanorod 5 on the surface of the ZnO film 4 by using a hydrothermal growth method. Specifically, zinc nitrate hexahydrate (Zn (NO) was first prepared at a concentration of 50mM each3)2·6H2O) solution and hexamethylenetetramine (C)6H12N4) And (3) solution. And fully and uniformly mixing the two solutions according to the volume ratio of 1:1 to form a precursor solution, and pouring the precursor solution into a polytetrafluoroethylene inner container in the hydrothermal reaction kettle. The substrate sheet with the nano forest structure 3 was placed into the inner container with the front side facing downward and tilted, sealed and placed in an oven at 90 ℃ for 3 hours. After the reaction was completed, the substrate was taken out, repeatedly rinsed 3 times with deionized water, and dried at room temperature. The length of the ZnO nano-rod finally grown is about 350nm, and the diameter is about80nm, as shown in FIG. 5.
(6) Depositing a thin Au layer with a thickness of 20nm on the surface of the ZnO nanorod and the surface of the nano forest structure by electron beam evaporation, as shown in FIG. 6, wherein the pressure in the cavity is 1 × 10-5Pa, evaporation rate of
The evaporation time was 12 min. After annealing for 4 hours at 400 ℃, the metal nano-particles with uniform sizes cover the surfaces of the ZnO nano-rods and the nano forest structure. The scanning electron micrograph of the structure obtained in this step is shown in fig. 8.
Example 2
The embodiment provides a preparation method of a three-dimensional SERS substrate, which comprises the following steps:
(1) a 4 "monocrystalline silicon wafer was provided as substrate 1.
(2) And spin-coating a polymer layer 2 with the thickness of 6 μm on the surface of the substrate 1 by a spin coater, wherein the polymer layer 2 is made of a positive polyimide photoresist, and the spin coater rotates at 750rpm for 8s and then at 2500rpm for 25 s. After spin coating, the substrate 1 was placed on a hot plate at a heating temperature of 120 ℃ for 20min to remove organic matters in the photoresist, thereby increasing the adhesion of the photoresist and curing it.
(3) The surface of the polymer layer 2 is bombarded with plasma in a plasma cleaning device to form nano forest structures 3. Wherein the plasma gas source is oxygen plasma, the radio frequency power is 200W, the pressure in the cavity is 5mTorr, the oxygen flow is 50sccm, and the bombardment time of the oxygen plasma is 40 min. The resulting nanopillars were about 3.5 μm in height and about 100nm in diameter.
(4) The substrate 1 is anisotropically etched by RIE using the nano forest structure 3 as a mask. Wherein the etching gas adopts Cl2And HBr, the gas flow rate is respectively 80 sccm and 40sccm, the chamber pressure is 250mTorr, the radio frequency power is 280W, and the etching time is 200 s. After the etching is finished, a nano forest-nano cone 7 composite structure is formed, as shown in fig. 9. The diameter of the base of the nanocone 7 is about 400nm and the diameter of the tip of the nanocone 7 is about100nm and the height of the nanocones 7 is about 1 μm.
(5) Removing the nano forest structure 3 by wet etching, wherein the time of the wet etching is 60s, and the solution of the wet etching is buffer oxide etching solution (BOE) which mainly comprises HF aqueous solution (with the concentration of 49%) and NH in a volume ratio of 1:64F aqueous solution (concentration is 40%) and mixing. The resulting structure of this step is shown in fig. 10.
(6) A ZnO film with a thickness of 100nm was deposited on the surface of the nanocone 7 by magnetron sputtering, as shown in fig. 11. Wherein, during sputtering, ZnO ceramic target material with purity superior to 99.99% is adopted, the sputtering power is 100W, the sputtering pressure is 5Pa, and the sputtering time is 20 min. The scanning electron micrograph of the structure obtained in this step is shown in fig. 14.
(7) And (3) growing a compact ZnO nanorod 5 on the surface of the ZnO film by using a hydrothermal growth method. Specifically, zinc nitrate hexahydrate (Zn (NO) was first prepared at a concentration of 50mM each3)2·6H2O) solution and hexamethylenetetramine (C)6H12N4) And (3) solution. And fully and uniformly mixing the two solutions according to the volume ratio of 1:1 to form a precursor solution, and pouring the precursor solution into a polytetrafluoroethylene inner container in the hydrothermal reaction kettle. The substrate sheet with the nanopyramids 7 was placed face down into the inner container, sealed and placed in an oven at 90 ℃ for 3 hours. After the reaction was completed, the substrate was taken out, repeatedly rinsed 3 times with deionized water, and dried at room temperature. The length of the ZnO nano-rod finally grown is about 350nm, and the diameter is about 80 nm. The scanning electron micrograph of the structure obtained in this step is shown in fig. 15.
(8) Depositing a thin Au layer with a thickness of 20nm on the surfaces of the ZnO nanorods and the nanocones by using an electron beam evaporation technique, as shown in FIG. 13, wherein the pressure in the chamber is 1X 10-5Pa, evaporation rate of
The evaporation time was 12 min. After annealing for 4 hours at 400 ℃, the metal nano-particles with uniform sizes cover the surfaces of the ZnO nano-rods and the surfaces of the nano-cone structures.
Example 3
The embodiment provides a preparation method of a three-dimensional SERS substrate, which comprises the following steps:
(1) a 4 "monocrystalline silicon wafer was provided as substrate 1.
(2) And spin-coating a polymer layer 2 with the thickness of 6 μm on the surface of the substrate 1 by a spin coater, wherein the polymer layer 2 is made of a positive polyimide photoresist, and the spin coater rotates at 750rpm for 8s and then at 2500rpm for 25 s. After spin coating, the substrate 1 was placed on a hot plate at a heating temperature of 120 ℃ for 20min to remove organic matters in the photoresist, thereby increasing the adhesion of the photoresist and curing it.
(3) The polymer layer 2 was exposed and developed by an ultraviolet exposure machine, as shown in FIG. 16, in which the opaque portions of the reticle 8 were set in the shape of a long strip, each opaque portion having an area of 100 μm2And the pitch of the opaque parts is 300 μm. The exposure dose is 250mJ/cm during exposure2The exposure time was 30 s. After exposure, the whole structure is placed in 2.38% tetramethylammonium hydroxide (TMAH) solution for cyclic development, the development time is 15s each time, and the cycle times are 4-6. Washing with deionized water for several times, placing in a vacuum constant temperature drying oven at 150 deg.C, standing for 20min, and hardening.
(4) Bombarding the surface of the patterned polymer layer 2 by using plasma in plasma cleaning equipment to form a nano forest structure 3, as shown in fig. 17, wherein a plasma gas source is a mixed gas of oxygen plasma and argon plasma, the radio frequency power is 200W, the pressure in a cavity is 5mTorr, the oxygen flow is 50sccm, the argon flow is 20sccm, the oxygen plasma bombardment time is 40min, and the argon plasma bombardment time is 80 min. The resulting nanopillars were about 2.8 μm in height and about 280nm in diameter.
(5) A layer of ZnO film 4 with a thickness of 100nm was deposited on the surface of the nano forest structure 3 by magnetron sputtering, as shown in fig. 18. Wherein, during sputtering, ZnO ceramic target material with purity superior to 99.99% is adopted, the sputtering power is 200W, the sputtering pressure is 1Pa, and the sputtering time is 80 min.
(6) By hydrothermal growth method inAnd a compact ZnO nanorod 5 grows on the surface of the ZnO film 4. Specifically, zinc nitrate hexahydrate (Zn (NO) was first prepared at a concentration of 50mM each3)2·6H2O) solution and hexamethylenetetramine (C)6H12N4) And (3) solution. And fully and uniformly mixing the two solutions according to the volume ratio of 1:1 to form a precursor solution, and pouring the precursor solution into a polytetrafluoroethylene inner container in the hydrothermal reaction kettle. The substrate sheet with the nano forest structure 3 was placed into the inner container with the front side facing downward and tilted, sealed and placed in an oven at 90 ℃ for 3 hours. After the reaction was completed, the substrate was taken out, repeatedly rinsed 3 times with deionized water, and dried at room temperature. The ZnO nano-rod finally grown is about 350nm in length and about 80nm in diameter, as shown in FIG. 19.
(7) Depositing a thin Au layer with a thickness of 20nm on the surface of the ZnO nanorod and the surface of the nano forest structure by electron beam evaporation, as shown in FIG. 20, wherein the pressure in the cavity is 1 × 10-5Pa, evaporation rate of
The evaporation time was 12 min. After annealing for 4 hours at 400 ℃, the metal nano-particles with uniform sizes cover the surfaces of the ZnO nano-rods and the nano forest structure.
(8) The surface of the structure shown in fig. 20 was subjected to hydrophobic treatment. Specifically, the structure shown in fig. 20 was left to stand in an HMDS gas atmosphere at 80 ℃ for 10 min.
Example 4
The embodiment provides a preparation method of a three-dimensional SERS microfluidic chip, which comprises the following steps:
(1) a 4 "monocrystalline silicon wafer was provided as substrate 1.
(2) A polymer layer 2 with the thickness of 6 microns is spin-coated on the surface of a substrate 1 through a spin coater, the material of the polymer layer 2 is positive polyimide photoresist, and during spin coating, the polymer layer is firstly rotated at 750rpm for 8s and then rotated at 2500rpm for 25 s. After spin coating, the substrate 1 was placed on a hot plate at a heating temperature of 120 ℃ for 20min to remove organic matters in the photoresist, thereby increasing the adhesion of the photoresist and curing it.
(3) Exposing and developing the polymer layer 2 by using an ultraviolet exposure machine, wherein the opaque part of the mask is in a strip shape and has an area of 200cm2. The exposure dose is 150mJ/cm during exposure2The exposure time was 45 s. After exposure, the whole structure is placed in 2.38% tetramethylammonium hydroxide (TMAH) solution for cyclic development, the development time is 15s each time, and the cycle times are 4-6. Washing with deionized water for several times, placing in a vacuum constant temperature drying oven at 150 deg.C, standing for 60min, and hardening.
(4) And bombarding the surface of the patterned polymer layer 2 by using plasma in plasma cleaning equipment to form a nano forest structure 3, wherein a plasma gas source is mixed gas of oxygen plasma and argon plasma, the radio frequency power is 200W, the pressure in the cavity is 5mTorr, the oxygen flow is 50sccm, the argon flow is 20sccm, the oxygen plasma bombardment time is 40min, and the argon plasma bombardment time is 80 min. The resulting nanopillars were about 2.8 μm in height and about 280nm in diameter.
(5) And (4) arranging a shielding plate 10 at the edge part of the upper surface of the substrate in the structure obtained in the step (4) so that the shielding plate 10 surrounds the nano forest structure 3, wherein the structure is shown in a figure 21.
(6) And depositing a ZnO film with the thickness of 100nm on the surface of the patterned nano forest structure 3 and the upper surface of the baffle plate 10 by a magnetron sputtering method, as shown in FIG. 22. Wherein, during sputtering, ZnO ceramic target material with purity superior to 99.99% is adopted, the sputtering power is 200W, the sputtering pressure is 2Pa, and the sputtering time is 40 min.
(7) And (3) growing a compact ZnO nanorod 5 on the ZnO film 4 by using a hydrothermal growth method. Specifically, zinc nitrate hexahydrate (Zn (NO) was first prepared at a concentration of 50mM each3)2·6H2O) solution and hexamethylenetetramine (C)6H12N4) And (3) solution. And fully and uniformly mixing the two solutions according to the volume ratio of 1:1 to form a precursor solution, and pouring the precursor solution into a polytetrafluoroethylene inner container in the hydrothermal reaction kettle. Placing the substrate sheet with the nano forest structure 3 into the inner container with the front surface facing downwards and incliningSealed and placed in an oven at 90 ℃ for 3 hours. After the reaction was completed, the substrate was taken out, repeatedly rinsed 3 times with deionized water, and dried at room temperature. The ZnO nano-rod finally grown has the length of about 350nm and the diameter of about 80nm, as shown in FIG. 23.
(8) Depositing a 20nm thick Au thin layer on the surfaces of the ZnO nano-rods and the nano forest structure by using an electron beam evaporation technology, wherein the pressure in a cavity is 1 multiplied by 10-5Pa, evaporation rate of
The evaporation time was 12 min. After annealing for 4 hours at 400 ℃, the metal nano-particles with uniform sizes cover the surfaces of the ZnO nano-rods and the nano forest structure. Next, the mask 10 is removed to expose a flat and smooth substrate surface for subsequent bonding with the PDMS encapsulation package, as shown in fig. 24.
(9) And carrying out oxygen plasma bonding on the PDMS package shell 11 with the sample inlet and the sample outlet and the upper surface of the substrate 1, thereby obtaining the SERS microfluidic chip, as shown in FIG. 25. The encapsulating shell 11 completely encapsulates the nanorod-nanoforest composite structure.
Example 5: detection sensitivity and recyclable performance for detecting three-dimensional SERS substrate
The three-dimensional SERS substrate used in this example was the three-dimensional SERS substrate prepared in example 1.
(1) Determining minimum detection limit of three-dimensional SERS substrate to rhodamine 6G
First, the concentrations were set to 10 respectively-6M、10-7M、10-8M、10-9M and 10-10M rhodamine 6G (as a probe molecule) liquid drops are respectively dropped on the surface of the three-dimensional SERS substrate, and the volume of the liquid drops is 4 mu L. Transferring the rhodamine 6G liquid drop to a Raman test platform for SERS signal test after the rhodamine 6G liquid drop is evaporated at room temperature, wherein the model of the used microscopic confocal laser Raman spectrometer is inVia-Reflex, the wavelength is 632.8nm, and finally the lowest detection limit of the three-dimensional SERS substrate to the rhodamine 6G is determined to be 10-10M, as shown in FIG. 26.
(2) Determination of minimum detection limit of three-dimensional SERS substrate on p-aminophenol molecules
First, the concentrations were set to 10 respectively-5M、10-6M、10-7M、10-8M and 10-9M p-aminophenol drops are respectively dropped on the surface of the three-dimensional SERS substrate, and the volume of the drops is 4 mu L. At room temperature, after the p-aminophenol liquid drops are evaporated, transferring the p-aminophenol liquid drops to a Raman test platform for SERS signal test, wherein the model of the used microscopic confocal laser Raman spectrometer is inVia-Reflex, the wavelength is 632.8nm, and finally the lowest detection limit of the three-dimensional SERS substrate to the p-aminophenol is determined to be 10-9M, as shown in FIG. 27.
(3) Determination of minimum detection limit of three-dimensional SERS substrate for adenine biomolecule
First, the concentrations were set to 10 respectively-3M、10-4M、10-5M、10-6M and 10-7And respectively dripping the adenine liquid drops of M on the surface of the three-dimensional SERS substrate, wherein the volume of the liquid drops is 4 mu L. At room temperature, after the adenine liquid drops are evaporated, transferring the adenine liquid drops to a Raman test platform for SERS signal test, wherein the model of the used microscopic confocal laser Raman spectrometer is inVia-Reflex, the wavelength is 632.8nm, and finally the lowest detection limit of the three-dimensional SERS substrate to adenine biomolecules is determined to be 10-7M, as shown in FIG. 28.
(4) Recyclable performance for detecting three-dimensional SERS substrate
By detecting the concentration of the three-dimensional SERS substrate pair to be 10-6The photocatalytic degradation capability of M rhodamine 6G determines the recyclability of the substrate. The method comprises the following specific steps. To a concentration of 10-6M rhodamine 6G liquid drops on the surface of the three-dimensional SERS substrate. After the rhodamine 6G droplets evaporated at room temperature, the substrate was subjected to ultraviolet irradiation for different times (0, 3, 6, 9, 12, 15min) using a 500W high-pressure mercury lamp. And then, transferring the SERS signal to a Raman test platform to test the SERS signal, wherein the model of the used microscopic confocal laser Raman spectrometer is inVia-Reflex, and the wavelength is 632.8 nm. As shown in fig. 29, as the ultraviolet irradiation time period increases, the intensity of the corresponding characteristic peak of rhodamine 6G gradually decreases. When ultravioletAfter the line irradiation is carried out for 15 minutes, no obvious Raman signal can be detected on the surface of the substrate, which shows that all rhodamine 6G molecules are degraded, and the degradation rate reaches 100%. After the rhodamine 6G molecules are all degraded, the substrate can be repeatedly used for molecular detection. Therefore, the three-dimensional SERS substrate has recyclable performance.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.
Claims (10)
1. A method for preparing a three-dimensional SERS substrate is characterized by comprising the following steps:
providing a substrate;
forming a polymer layer on the upper surface of the substrate, wherein the polymer layer is made of a polymer material which can be bombarded by plasma;
subjecting the polymer layer to plasma bombardment, thereby forming a nano forest structure;
forming a metal oxide film on the surface of the nano forest structure;
forming metal oxide nanorods on the surface of the metal oxide film by a hydrothermal method; and
and forming a noble metal layer on the surface of the metal oxide film and the surface of the metal oxide nanorod to obtain the three-dimensional SERS substrate.
2. The method according to claim 1, wherein the polymer layer is made of a positive photoresist or a negative photoresist; patterning the polymer layer prior to the plasma bombardment.
3. The production method according to claim 1 or 2, characterized by further comprising:
after forming the nano forest structure and before forming the metal oxide film, anisotropically etching the substrate with the nano forest structure as a mask to form a pyramidal nano structure.
4. The method of manufacturing according to claim 3, further comprising: and removing the nano forest structure on the surface of the conical nano structure, and forming a metal oxide film on the surface of the conical nano structure.
5. The production method according to claim 1 or 2, characterized by further comprising: after the noble metal layer is formed, the surface of the obtained three-dimensional SERS substrate is subjected to hydrophobic treatment.
6. The production method according to claim 1, wherein the polymer layer is a positive photoresist, a negative photoresist, or polydimethylsiloxane;
the metal oxide film and the metal oxide nanorod are made of ZnO, TiO, CuO or other metal oxide semiconductor materials; the metal oxide film and the metal oxide nanorod are made of the same material;
the noble metal is made of Au, Ag or Cu.
7. A three-dimensional SERS substrate obtained by the production method according to any one of claims 1 to 6.
8. Use of the three-dimensional SERS substrate of claim 7 in molecular detection.
9. A preparation method of the SERS microfluidic chip is characterized by comprising the following steps:
providing a substrate;
forming a polymer layer on the upper surface of the substrate, wherein the polymer layer is made of a positive photoresist or a negative photoresist;
patterning the polymer layer, so as to remove the edge part of the polymer layer and expose the corresponding upper surface part of the substrate to form a window;
carrying out plasma bombardment on the patterned polymer layer so as to form a nano forest structure;
arranging a shielding plate at the window, so that the shielding plate surrounds the nano forest structure;
forming a metal oxide film on the surface of the nano forest structure;
forming metal oxide nanorods on the surface of the metal oxide film by a hydrothermal method;
forming a noble metal layer on the surface of the metal oxide film and the surface of the metal oxide nanorod;
removing the shielding plate, thereby exposing an upper surface of the substrate; and
bonding a packaging shell with a sample inlet and a sample outlet with the upper surface of the exposed substrate, so that the packaging shell encapsulates the nano forest structure on which the metal oxide nano rods are arranged.
10. The SERS microfluidic chip obtained by the preparation method according to claim 9.
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