CN111208110A - Flexible Raman enhanced substrate and preparation method and application thereof - Google Patents
Flexible Raman enhanced substrate and preparation method and application thereof Download PDFInfo
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Abstract
The invention provides a flexible Raman enhancement substrate and a preparation method and application thereof.A passivation layer formed by self-assembly of alkyl mercaptan molecules is coated on the surface of gold nanoparticles by a liquid/liquid interface self-assembly method, so that the gold nanoparticles have a core-shell structure, and the gold nanoparticles with the core-shell structure are assembled at the interface in a hexagonal closest packing manner to form a super-crystal structure; the invention obtains a flexible Raman enhancement substrate with highly ordered surface, and the enhancement factor of the flexible Raman enhancement substrate can reach 3.5 multiplied by 107The Raman spectrum detection device can almost realize single molecule detection, the relative standard deviation of the Raman spectrum is about 4% during detection, Raman enhancement signals are clean, the reliability and the repeatability are excellent, the quantitative analysis of the Raman spectrum can be realized, the flexible polymer substrate layer can be attached to the surface with any shape to carry out Raman spectrum detection by introducing the flexible polymer substrate layer, meanwhile, back incidence type Raman detection and normal incidence type Raman detection are realized, and the application range of the Raman spectrum is widened.
Description
Technical Field
The invention relates to the field of surface-enhanced Raman spectrum detection, in particular to a flexible Raman-enhanced substrate and a preparation method and application thereof.
Background
The development of the Surface Enhanced Raman Scattering (SERS) technology provides a wide application prospect for the application of Raman spectra, the SERS effect is based on the fact that when a substance to be detected is placed on the surface of a Raman enhanced substrate, the intensity of incident light can be amplified due to the enhancement of a local field caused by metal surface plasmas on the surface of the Raman enhanced substrate, the intensity of the output Raman spectrum of the substance to be detected is greatly increased, and the SERS effect can realize high-sensitivity Raman spectrum detection at a single molecular level.
The surface of the Raman enhancement substrate capable of generating the SERS effect is mostly metal, the commonly used metal comprises gold (Au), silver (Ag), copper (Cu) and the like, the Surface Plasmon Resonance (SPR) of gold is positioned in a visible light region and a near infrared region and has good chemical stability, so the gold is most widely applied in the field of the Raman enhancement substrate, the currently commonly used Raman enhancement substrate is mostly a rough gold surface or a gold nanoparticle (AuNP) surface, for example, CN104089942A discloses a surface enhancement Raman substrate with super-hydrophobic property, the SERS substrate is prepared by cleaning foamed nickel and soaking the foamed nickel in a noble metal salt aqueous solution, then the obtained SERS substrate is modified by long alkyl mercaptan molecules to obtain the surface enhancement Raman substrate with the super-hydrophobic property, and when the obtained surface enhancement Raman substrate is used for detecting polycyclic aromatic hydrocarbon, the detection limit can reach 10-8The mol/L level, however, the signal-to-noise ratio of the detection result is too low to realize quantitative concentration analysis; CN103344624A discloses a method for preparing a surface-enhanced Raman scattering substrate by a solution method, which comprises the steps of preparing alkyl mercaptan modified metal nanoparticles with the diameter of 1-5 nm, dissolving the metal nanoparticles in an organic solvent to prepare metal nanoparticle sol with the concentration of 60-100 mg/mL, coating the obtained sol on a substrate, spin-coating the obtained sol on the substrate at the rotating speed of 1500-3000 r/min for 30-60 s to obtain a metal colloid film, placing the obtained metal colloid film in a muffle furnace, heating to 140-250 ℃ within 5min, keeping the temperature for 5-30 min, and cooling to room temperature to obtain the surface-enhanced Raman scattering substrate, wherein the relative standard deviation of the obtained surface-enhanced Raman scattering substrate is 5-6.8% when Raman detection is carried out, and the enhancement factor is 10%6～107Within the range of (1); however, the above-mentioned surface-enhanced raman scattering substrate obtained in the prior art has the same obvious disadvantages while having a high enhancement factor, for example, direct contact between the molecule to be measured and the enhancement substrate may cause a series of chemical adsorption, metal-to-molecule charge transfer, metal-catalyzed side reactions, etc., resulting in complex signal, white noise, low authenticity, etc. of the surface-enhanced raman spectrumThe defect that the limitation of the traditional surface enhancement technology is a key problem limiting the development of the current surface enhanced Raman spectroscopy detection field by designing and developing a novel Raman enhanced substrate.
The principle of the self-assembly of metal nanoparticles is mainly based on the controllability of the shape of the metal nanoparticles and the uniformity of the assembled surface, the highly ordered self-assembly of the nanoparticles can form a uniform Raman-enhanced substrate, which is beneficial to the uniform distribution of molecules to be detected on the surface of the substrate, thereby improving the repeatability and stability of Raman signals.
Therefore, on the basis of the prior art, a person skilled in the art needs to design a gold nanoparticle array formed by self-assembly, so as to prepare a novel raman enhancement substrate, the raman enhancement substrate material needs to have a higher enhancement factor, can prevent a reaction between a molecule to be detected and the enhancement substrate, can realize quantitative raman spectrum detection, and simultaneously needs to have certain flexibility and transparency, and can realize flexible self-support, so as to realize raman spectrum detection on the surface of an insoluble material.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a novel Raman enhancement substrate, the Raman enhancement substrate material needs to have a higher enhancement factor, can prevent the reaction between the molecules to be detected and the enhancement substrate, can realize quantitative Raman spectrum detection, and simultaneously needs to have certain flexibility and transparency, and can realize flexible self-support so as to realize Raman spectrum detection on the surface of an insoluble material.
To achieve the purpose, one of the objects of the present invention is to provide a flexible raman enhancement substrate, which includes a flexible polymer substrate layer and a gold nanoparticle layer having a core-shell structure, which is hexagonal closest packed on the surface of the flexible polymer substrate layer.
The surface of the gold nano particle is coated with a passivation layer formed by self-assembly of alkyl mercaptan molecules, so that the gold nano particle has a core-shell structure.
In the invention, the alkyl mercaptan molecules play a role of skeleton molecules in the self-assembly process, and the surface of the gold nanoparticles is wrapped by the alkyl mercaptan molecules to form a core-shell structure, so that the agglomeration of the gold nanoparticles can be prevented, the dispersion of the gold nanoparticles is facilitated, and the distance between the gold nanoparticles can be regulated.
Under the synergistic action of surface tension, Van der Waals force among nano particles and intermolecular force on the surface of the flexible polymer, the gold nano particles with the core-shell structure can be self-assembled at an interface to form a uniform and ordered hexagonal closest-packed superlattice structure, and the uniform and ordered hexagonal closest-packed superlattice structure is transferred to the surface of the flexible polymer substrate layer, so that a flexible, transparent and self-supporting Raman enhanced substrate can be obtained.
Preferably, the distance between the gold nanoparticles is 2-50 nm, such as 3nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm or 48 nm.
Preferably, more than 90% of the spacing between the gold nanoparticles is 2-10 nm, and the gold nanoparticles with the partial spacing provide almost all Raman enhancement effect.
The particle size of the gold nanoparticles is preferably 8 to 100nm, for example, 9nm, 12nm, 15nm, 18nm, 21nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, or 95nm, and the like, more preferably 25 to 80nm, and most preferably 40 to 50 nm.
Preferably, the layer of gold nanoparticles is, and consists only of, a layer of gold nanoparticles.
Preferably, the surface of the gold nanoparticle is further coated with an internal standard molecule, and the internal standard molecule is a standard molecule with a stable structure and capable of calibrating the position of each peak in a Raman spectrum test.
Preferably, the internal standard molecule is an internal standard molecule containing a sulfydryl, and further preferably any one molecule of 4-mercaptopyridine, 4-mercaptobenzoic acid or 4-mercaptoaniline.
Preferably, the alkyl thiol molecule is a n-alkyl thiol molecule, and more preferably a n-alkyl thiol molecule with 10-24 carbon atoms (for example, carbon atoms of 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, or 23, etc.), and when the n-alkyl thiol molecule with carbon atoms is coated on the surface of the gold nanoparticle, the formed passivation layer is dense, which is beneficial to the formation of a core-shell structure and the dispersion of the gold nanoparticles, and simultaneously, the distance between the gold nanoparticles can be adjusted.
Preferably, the flexible polymer in the flexible polymer substrate is any one or a mixture of at least two of polymethyl methacrylate, polydimethylsiloxane, polyethylene terephthalate or polyvinyl alcohol, and the polymer has high flexibility and good affinity to the gold nanoparticles, so that the gold nanoparticles can be self-assembled to form a hexagonal closest-packed superlattice structure;
preferably, the thickness of the flexible polymer substrate is 1 to 1000 μm, for example, 2 μm, 10 μm, 20 μm, 40 μm, 100 μm, 200 μm, 300 μm, 400 μm, 600 μm, 800 μm, 950 μm, etc., and one skilled in the art can select the thickness of any flexible polymer substrate according to the requirements of light transmittance or mechanical strength. .
The invention also aims to provide a preparation method of the flexible Raman enhancement substrate, which comprises the following steps:
preparing hydrosol of gold nanoparticles, mixing the hydrosol of the gold nanoparticles with a first organic solvent, adding a second organic solvent solution containing alkyl mercaptan molecules into the mixture, uniformly mixing to obtain a mixed solution, standing until the mixed solution is obviously layered, and obtaining a gold nanoparticle film layer with a core-shell structure at an interface of an organic phase and a water phase;
step (2), coating a flexible polymer solution on a sacrificial layer substrate, drying to obtain a flexible polymer film, removing an organic layer on the gold nanoparticle film layer in the mixed solution in the step (1), obliquely inserting the flexible polymer film into a water layer below the gold nanoparticle film layer, then obliquely lifting, transferring the gold nanoparticles with the core-shell structure to the surface of the flexible polymer film, and after drying, enabling the gold nanoparticles with the core-shell structure to be self-assembled on the surface of the flexible polymer film to form a hexagonal closest-packed structure;
and (3) etching and removing the sacrificial layer substrate of the flexible polymer film with the surface containing the gold nanoparticles in the step (2) by using etching liquid, and cleaning and removing the etching liquid and other soluble substances to obtain the flexible Raman enhancement substrate.
Preferably, the gold nanoparticle hydrosol described in step (1) is obtained by reducing a boiling chloroauric acid solution with sodium citrate and/or ascorbic acid.
Preferably, the first organic solvent in step (1) is a water-miscible organic solvent, and more preferably acetone.
Preferably, the second organic solvent in step (1) is a water-insoluble organic solvent, and further preferably n-hexane.
Preferably, the second organic solvent solution containing alkyl thiol molecules described in step (1) further contains an internal standard molecule.
Preferably, the ratio of the amount of the internal standard molecule to the amount of the alkyl thiol molecule is 1:40 to 60, for example, 1:41, 1:42, 1:43, 1:44, 1:45, 1:46, 1:47, 1:48, 1:49, 1:50, 1:51, 1:52, 1:53, 1:54, 1:55, 1:56, 1:57, 1:58, or 1: 59.
Preferably, the standing time in step (1) is 10-30 min, such as 11min, 12min, 13min, 14min, 15min, 16min, 17min, 18min, 19min, 20min, 21min, 22min, 23min, 24min, 25min, 26min, 27min, 28min or 29 min.
Preferably, the sacrificial layer substrate in the step (2) is an aluminum foil substrate or a copper foil substrate.
Preferably, the drying in step (2) is natural air drying or heating drying at a temperature within 170 ℃.
Preferably, the drying temperature in step (2) is 100-120 deg.C, such as 101 deg.C, 103 deg.C, 105 deg.C, 107 deg.C, 109 deg.C, 111 deg.C, 113 deg.C, 115 deg.C, 117 deg.C or 119 deg.C.
Preferably, the drying time in step (2) is 5-20 min, such as 6min, 7min, 8min, 9min, 10min, 11min, 12min, 13min, 14min, 15min, 16min, 17min, 18min or 19 min.
Preferably, the etching solution in the step (3) is an acidic ferric trichloride solution.
Preferably, the etching time in step (3) is 15-30 min, such as 16min, 17min, 18min, 19min, 20min, 21min, 22min, 23min, 24min, 25min, 26min, 27min, 28min or 29 min.
Preferably, the cleaning in the step (3) is sequentially performed by using deionized water, dilute hydrochloric acid and deionized water.
The invention also aims to provide the application of the flexible enhanced Raman substrate in normal incidence type Raman detection and back incidence type Raman detection;
the normal incidence type Raman detection comprises the steps that a substance to be detected is dissolved, prepared into a sample, coated or adsorbed on one side of a gold nanoparticle layer of the flexible enhanced Raman substrate, and a detection beam directly irradiates the substance to be detected to perform Raman spectrum test;
the back-incident Raman detection comprises the steps of dissolving and sampling a substance to be detected, coating or adsorbing the substance to be detected on one side of a gold nanoparticle layer of the flexible enhanced Raman substrate, enabling a detection light beam to penetrate through the flexible polymer substrate layer to carry out Raman spectrum test, or directly attaching one side of the gold nanoparticle layer to the surface containing the substance to be detected, and enabling the detection light beam to penetrate through the flexible polymer substrate layer to carry out Raman spectrum test.
The recitation of numerical ranges herein includes not only the above-recited numerical values, but also any numerical values between non-recited numerical ranges, and is not intended to be exhaustive or to limit the invention to the precise numerical values encompassed within the range for brevity and clarity.
Compared with the prior art, the invention has the beneficial effects that:
the surface of the gold nano particle is coated with a passivation layer formed by self-assembly of alkyl mercaptan molecules, so that the gold nano particle has a core-shell structure, and then a gold nano particle layer with the core-shell structure is in a hexagonal closest packing modeThe surface of the flexible polymer substrate layer is uniformly distributed to form a super-crystal structure, so that a flexible Raman enhancement substrate with highly ordered surface can be obtained, and the enhancement factor can reach 3.5 multiplied by 107The Raman spectrum detection device can almost realize single molecule detection, the relative standard deviation of the Raman spectrum is about 4% during detection, Raman enhancement signals are clean, the reliability and the repeatability are excellent, the quantitative analysis of the Raman spectrum can be realized, the flexible polymer substrate layer can be attached to the surface with any shape to carry out Raman spectrum detection by introducing the flexible polymer substrate layer, meanwhile, back incidence type Raman detection and normal incidence type Raman detection are realized, and the application range of the Raman spectrum is widened.
Drawings
Fig. 1 is a TEM photograph of a flexible raman-enhanced substrate 1 obtained in example 1 according to an embodiment of the present invention.
FIG. 2 shows the flexible Raman-enhanced substrates 1-5 obtained in examples 1-5 according to the embodiment of the present invention at a detection concentration of 10-8Raman spectrum of the crystal violet solution at mol/L.
FIG. 3 shows a pair of concentrations of 10 of the flexible Raman-enhanced substrate 1 obtained in example 1 according to an embodiment of the present invention-8Performing normal incidence Raman detection on the crystal violet solution of mol/L, and directly detecting the concentration of 10 by using a Raman spectrometer without using a Raman enhanced substrate-4Raman spectrum obtained from mol/L crystal violet solution.
FIG. 4 shows that the flexible Raman-enhanced substrate 1 obtained in example 1 has a concentration of 10-8And carrying out normal incidence type Raman detection and back incidence type Raman detection on the mol/L crystal violet solution to obtain a Raman spectrum.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments.
In the invention, hydrosols of gold nanoparticles with different particle sizes can be purchased in the market, and can also be prepared by adopting the following method according to the prior art:
hydrosol of gold nanoparticles having an average particle diameter of 15 nm: the reducing mixture (containing 1mL of a 1 wt% solution of trisodium citrate)) Boiling 50mL of chloroauric acid solution (containing 1mL of 1 wt% HAuCl) was added rapidly4Solution and 49mL of deionized water), mixing and stirring vigorously, obtaining gold nanoparticle hydrosol with the average particle size of 15nm after the mixed solution is changed from colorless to blue and then quickly changed to bright red, and storing the gold nanoparticle hydrosol at 5 ℃ after the gold nanoparticle hydrosol is cooled.
Hydrosol of gold nanoparticles having an average particle diameter of 45 nm: 1.5mL of the above gold nanoparticle aqueous sol having an average particle diameter of 15nm was diluted to 20mL as a seed solution, which was put in a three-necked flask, and 10mL of a reducing solution (containing 2mL of 1 wt% HAuCl) was added thereto by a peristaltic pump at a rate of 0.25mL/min under strong stirring4Solution and 10mL solution containing 0.5mL sodium citrate and 0.25mL ascorbic acid), after the injection by the peristaltic pump is finished, stirring and heating the mixed solution to boiling, and continuously refluxing for 30min to obtain the gold nanoparticle hydrosol with the average diameter of 45 nm.
By changing the addition amounts of the seed solutions in the above method to 6mL, 10mL and 4mL, hydrosols of gold nanoparticles having average particle diameters of 25nm, 78nm and 95nm, respectively, can be obtained in this order.
Example 1
The flexible raman-enhanced substrate 1 is prepared by the following steps:
preparing 10mL of hydrosol of gold nanoparticles (with the average particle size of 45nm), mixing the hydrosol of the gold nanoparticles with 10mL of acetone, adding an n-hexane solution containing 73.5 mu mol of n-dodecyl mercaptan (DDT) and 1.5 mu mol of 4-mercaptopyridine (4-Mpy) into the mixture to obtain a mixed solution, shaking the mixed solution for 1min violently to fully disperse the components in the mixed solution, immediately transferring the mixed solution into a water tank with a baffle, standing for 10-30 min, performing self-assembly on the nanoparticles to obtain a gold nanoparticle film layer with a core-shell structure at an interface of an organic phase and a water phase, and adjusting the position of the baffle according to the film forming area to stably form the gold nanoparticle film layer, wherein the gold nanoparticle film layer is golden when viewed from the side, blue-purple when viewed from the front, and the organic layer and the water layer on the upper side and the lower side are colorless transparent layers;
step (2), coating an aqueous solution of polymethyl methacrylate on a substrate made of aluminum foil in a rotating speed of 2000 r/min, naturally drying to obtain a flexible polymer film with the thickness of about 10 microns, washing the gold nanoparticle film layer obtained in the step (1) twice by using pure n-hexane, removing redundant molecules which are not subjected to self-assembly, removing an organic layer on the gold nanoparticle film layer by using a suction pipe, obliquely inserting the flexible polymer film into a water layer below the gold nanoparticle film layer after the residual organic layer is naturally volatilized, obliquely lifting, transferring the gold nanoparticles with the core-shell structure to the surface of the flexible polymer film, and drying for 10min at 120 ℃ by using a hot plate to enable the gold nanoparticles with the core-shell structure to be self-assembled on the surface of the flexible polymer film to form a hexagonal closest-packed structure;
and (3) etching by using an etching solution acidic ferric trichloride solution for 15-30 min to remove the substrate made of the aluminum foil of the flexible polymer film containing the gold nanoparticles on the surface in the step (2), then sequentially cleaning by using deionized water, dilute hydrochloric acid and deionized water, and removing residual etching solution and other soluble substances to obtain the flexible Raman enhancement substrate 1.
Example 2
The flexible raman-enhanced substrate 2 is prepared by the following steps:
the only difference from example 1 was that the average particle diameter of gold nanoparticles in the gold nanoparticle aqueous sol was 15nm, the amount of DDT added was 98. mu. mol, and the amount of 4-Mpy added was 2. mu. mol.
Example 2a flexible raman-enhanced substrate 2 was obtained.
Example 3
The flexible raman-enhanced substrate 3 is prepared by the steps of:
the only difference from example 1 was that the average particle diameter of gold nanoparticles in the gold nanoparticle aqueous sol was 25nm, the amount of DDT added was 40. mu. mol, and the amount of 4-Mpy added was 1. mu. mol.
Example 3 a flexible raman-enhanced substrate 3 was obtained.
Example 4
The flexible raman-enhanced substrate 4 is prepared by:
the only difference from example 1 was that the average particle diameter of gold nanoparticles in the gold nanoparticle aqueous sol was 78nm, the amount of DDT added was 13. mu. mol, and the amount of 4-Mpy added was 0.3. mu. mol.
Example 4a flexible raman-enhanced substrate 4 was obtained.
Example 5
The flexible raman-enhanced substrate 5 is prepared by:
the only difference from example 1 was that the average particle diameter of gold nanoparticles in the gold nanoparticle aqueous sol was 95nm, the amount of DDT added was 10. mu. mol, and the amount of 4-Mpy added was 0.2. mu. mol.
Example 5 a flexible raman-enhanced substrate 5 was obtained.
Example 6
The flexible raman-enhanced substrate 6 is prepared by:
the only difference from example 1 is that n-dodecylmercaptan in step (1) is replaced with the same molar amount of n-docosylmercaptol.
Example 6 a flexible raman-enhanced substrate 6 was obtained.
Example 7
The flexible raman-enhanced substrate 7 is prepared by the following steps:
the only difference from example 1 is that the 4-mercaptopyridine in step (1) was replaced by the same molar amount of 4-mercaptoaniline.
Example 7 a flexible raman-enhanced substrate 7 was obtained.
Example 8
The flexible raman-enhanced substrate 8 is prepared by:
the only difference from example 1 is that no 4-mercaptopyridine was added in step (1).
Example 8 a flexible raman-enhanced substrate 8 was obtained.
Example 9
The flexible raman-enhanced substrate 9 is prepared by the following steps:
the only difference from example 1 is that the aqueous solution of polymethyl methacrylate in step (2) was replaced with a polydimethylsiloxane solution.
Example 9 a flexible raman-enhanced substrate 9 was obtained.
Comparative example 1
The raman-enhanced substrate obtained in example 1 in CN103344624A was used as comparative example 1.
The flexible Raman enhancement substrates 1-9 obtained in examples 1-9 of the invention and the Raman enhancement substrate obtained in comparative example 1 were tested and characterized by the following test methods.
(1) Topography testing
The surface topography of the raman-enhanced substrate obtained in each example and the comparative example was measured by a Transmission Electron Microscope (TEM) model Tecnai G220S-TWIN, manufactured by FEI corporation, usa, with the following test parameters: acceleration voltage: 200 KV; a filament: a lanthanum hexaboride filament; lattice resolution: 0.14 nm; dot resolution: 0.24 nm; minimum beam spot size: 1.5 nm.
(2) Enhanced performance testing
A Renisshaw inVia plus type Raman spectrometer manufactured by Renisshaw corporation, UK was used at a concentration of 10- 8Taking a mol/L crystal violet solution as a substance to be detected, respectively carrying out normal incidence type Raman detection and back incidence type Raman detection on the substance by using the flexible enhanced Raman substrates 1-9 obtained by the invention, wherein the testing parameters of a Raman spectrometer are as follows: laser energy: 2 mW; and (3) accumulating time: 10 s; lens magnification: 50 times.
Then, the concentration is 10-4And (3) taking the mol/L crystal violet solution as a substance to be tested, directly testing the Raman spectrum of the crystal violet solution without using the flexible Raman enhancement substrate obtained by the invention, and taking the Raman spectrum as a contrast.
The normal incidence type Raman detection is to dissolve and sample a substance to be detected, coat or adsorb the substance to be detected on one side of the gold nanoparticle layer of the flexible enhanced Raman substrate, and the detection light beam directly irradiates the substance to be detected to carry out Raman spectrum test.
The back-incident Raman detection is to dissolve and sample a substance to be detected, coat or adsorb the substance to be detected on one side of the gold nanoparticle layer of the flexible enhanced Raman substrate, and perform Raman spectrum test by the detection light beam through the flexible polymer substrate layer, or directly attach one side of the gold nanoparticle layer to the surface containing the substance to be detected, and perform Raman spectrum test by the detection light beam through the flexible polymer substrate layer.
(3) Uniformity test
Randomly scanning any position of the flexible enhanced Raman substrate 1-5 obtained by the invention by adopting a Raman spectrometer and test parameters used in the enhanced performance test, wherein the test mode is normal incidence type Raman detection, and detecting that 4-Mpy molecules in the obtained Raman spectrum are 1090cm-1The Relative Standard Deviation (RSD) of the characteristic peak area at (a) characterizes the uniformity of the substrate.
Then, respectively immersing the flexible enhanced Raman substrates 1-5 obtained by the invention into the solution with the concentration of 2 multiplied by 10-91h in mol/L Malachite Green (MG) solution, then washing with ultrapure water, drying at room temperature for 30min, randomly scanning 18 points within optional 20 mu m range in the flexible Raman enhancement substrate 1-5 with adsorbed MG molecules obtained by using the Raman spectrometer, and enabling the MG molecules to be located at 1177cm at each point-1The characteristic peak at (A) is compared with the peak area of 4-Mpy (I)R) For signal determination, the test mode is normal incidence Raman detection, as IRThe relative standard deviation of (a) characterizes the adsorption uniformity of the substrate to the molecule to be detected.
The above test results will be described by taking examples 1 to 5 of the present invention and comparative example 1 as examples.
Fig. 1 is a TEM photograph of a flexible raman enhanced substrate 1 obtained in example 1 of the present invention, from which it is apparent that in the flexible raman enhanced substrate obtained in the present invention, gold nanoparticles having a core-shell structure form a hexagonal closest-packed superlattice structure on the surface of a flexible polymer substrate layer, there is only one layer of gold nanoparticles on the surface of the flexible polymer substrate layer, a passivation layer is formed on the surface by self-assembly of alkyl thiol molecules, the thickness of the shell layer is less than 2nm, and the distance between two adjacent gold nanoparticles is only about 2 nm.
From the morphology test, it can be known that the surface of the flexible raman-enhanced substrate obtained in other embodiments of the present invention also has a superlattice structure same as or similar to that of the flexible raman-enhanced substrate 1, and in the flexible raman-enhanced substrates 2 to 5 obtained in embodiments 2 to 5, the average particle diameters of the gold nanoparticles having the core-shell structure are 15nm, 25nm, 78nm and 95nm, respectively, the thickness of the shell layer is less than 2nm, and the distance between two adjacent gold nanoparticles is about 2 to 10nm, which indicates that the structure of the surface of the flexible raman-enhanced substrate obtained in the present invention is very regular and is very suitable for being used as a raman-enhanced substrate.
FIG. 2 shows that the detection concentration of the flexible Raman-enhanced substrates 1-5 obtained in embodiments 1-5 of the present invention is 10-8In the raman spectrum of the crystal violet solution of mol/L, it is obvious that in example 1, when the average particle size of the gold nanoparticles in the flexible raman-enhanced substrate is about 45nm, the raman enhancement effect of the flexible raman-enhanced substrate is strongest.
The enhancement factor is an important parameter for quantitatively evaluating the sensitivity of the substrate and a premise for carrying out quantitative SERS analysis, the enhancement factor refers to a substrate enhancement factor (SSEF), and for the flexible Raman enhancement substrate obtained by the invention, the calculation formula of the substrate enhancement factor (SSEF) can be expressed as follows:
SSEF＝(ISERS/Nsurf)/(IRS/Nvol)。
wherein, ISERSAnd IRSRespectively the integral area, N, of the characteristic peak of the molecule to be detected adsorbed on the substrate and the molecule to be detected in the solutionsurfAnd NvolThe number of active molecules to be detected on the substrate and the number of molecules to be detected irradiated by the laser in the solution are respectively.
According to the Raman spectrogram, the substrate enhancement factors of the flexible Raman enhanced substrates 1-5 obtained in the embodiments 1-5 of the invention are respectively 3.5 × 10 by calculation7、9.0×106、2.2×107、1.5×107And 3X 106All the advantages are better than other prior arts (such as the Raman enhanced substrate obtained in the comparison example 1), which is closely related to the surface high order of the flexible Raman enhanced substrate obtained in the invention.
FIG. 3 shows a pair of flexible Raman-enhanced substrates 1 obtained by using the method of example 1 of the present invention at a concentration of 10-8Performing normal incidence Raman detection on the crystal violet solution at mol/L without using a Raman enhancement substrateThen the concentration is detected to be 10 by using a Raman spectrometer-4The comparison of the Raman spectrum obtained by the mol/L crystal violet solution and the Raman spectrum shows that compared with the direct Raman detection of the solution, the flexible Raman enhancement substrate obtained by the invention has a strong enhancement effect on molecules to be detected, and almost realizes single molecule detection.
FIG. 4 shows that the flexible Raman-enhanced substrate 1 obtained in example 1 of the present invention has a concentration of 10-8The Raman spectra obtained by performing normal incidence type Raman detection and back incidence type Raman detection on the mol/L crystal violet solution are found through comparison, the Raman spectra obtained by the two detection modes have good consistency, both the two incidence modes can obtain real Raman signals, and clear Raman characteristic peaks of an internal standard molecule and a molecule to be detected can be simultaneously obtained in a spectrogram, so that the flexible Raman enhanced substrate obtained by the invention has good flexibility and light transmittance, and the back incidence type detection method can realize the Raman spectrum detection on the surface of an insoluble or irregular object.
From the uniformity test, it can be known that the substrate uniformity and the uniformity of adsorption to molecules to be detected of the flexible raman-enhanced substrates 1 to 5 obtained in embodiments 1 to 5 of the present invention are both excellent, and the Relative Standard Deviation (RSD) thereof is about 4% and 6.5%, respectively, which indicates that the flexible raman-enhanced substrate prepared by the preparation method of the present invention has high repeatability and reliability, and can be used for raman quantitative analysis.
In summary, the invention coats the surface of the gold nanoparticles with the passivation layer formed by self-assembly of alkyl mercaptan molecules to make the gold nanoparticles have the core-shell structure, and then uniformly distributes the gold nanoparticle layer with the core-shell structure on the surface of the flexible polymer substrate layer in the hexagonal closest packing manner to form the super-crystal structure, so that the flexible raman enhancement substrate with highly ordered surface can be obtained, and the enhancement factor can reach 3.5 × 107The Raman spectrum detection device can almost realize single molecule detection, the relative standard deviation of the Raman spectrum is about 4% during detection, Raman enhanced signals are clean, the Raman spectrum detection device has excellent reliability and repeatability, quantitative analysis of the Raman spectrum can be realized, and the flexible polymer substrate layer can be attached to the surface with any shape to carry out Raman light by being introducedSpectrum detection, back incidence type Raman detection and normal incidence type Raman detection are simultaneously realized, and the application range of Raman spectrum is widened.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The flexible Raman enhancement substrate is characterized by comprising a flexible polymer substrate layer and a gold nanoparticle layer which is hexagonal closest packed on the surface of the flexible polymer substrate layer and has a core-shell structure;
the surface of the gold nano particle is coated with a passivation layer formed by self-assembly of alkyl mercaptan molecules, so that the gold nano particle has a core-shell structure.
2. The flexible Raman-enhanced substrate of claim 1, wherein the spacing between the gold nanoparticles is 2-50 nm;
preferably, more than 90% of the distance between the gold nano particles is 2-10 nm;
preferably, the particle size of the gold nanoparticles is 8-100 nm, more preferably 25-80 nm, and most preferably 40-50 nm;
preferably, the gold nanoparticle layer consists of only one layer of gold nanoparticles.
3. The flexible raman-enhanced substrate according to claim 1 or 2, wherein said gold nanoparticle surface is further coated with an internal standard molecule;
preferably, the internal standard molecule is an internal standard molecule containing a sulfydryl, and further preferably any one molecule of 4-mercaptopyridine, 4-mercaptobenzoic acid or 4-mercaptoaniline.
4. A flexible Raman-enhanced substrate according to any one of claims 1 to 3, wherein said alkanethiol molecules are n-alkanethiol molecules, and more preferably any one of n-alkanethiol molecules having 10 to 24 carbon atoms.
5. The flexible Raman-enhanced substrate according to any one of claims 1 to 4, wherein the flexible polymer in the flexible polymer substrate is any one or a mixture of at least two of polymethyl methacrylate, polydimethylsiloxane, polyethylene terephthalate or polyvinyl alcohol;
preferably, the thickness of the flexible polymer substrate is 1-1000 μm.
6. A method for preparing a flexible Raman-enhanced substrate according to any one of claims 1 to 5, wherein the method comprises the following steps:
preparing hydrosol of gold nanoparticles, mixing the hydrosol of the gold nanoparticles with a first organic solvent, adding a second organic solvent solution containing alkyl mercaptan molecules into the mixture, uniformly mixing to obtain a mixed solution, standing until the mixed solution is obviously layered, and obtaining a gold nanoparticle film layer with a core-shell structure at an interface of an organic phase and a water phase;
step (2), coating a flexible polymer solution on a sacrificial layer substrate, drying to obtain a flexible polymer film, removing an organic layer on the gold nanoparticle film layer in the mixed solution in the step (1), obliquely inserting the flexible polymer film into a water layer below the gold nanoparticle film layer, then obliquely lifting, transferring the gold nanoparticles with the core-shell structure to the surface of the flexible polymer film, and after drying, enabling the gold nanoparticles with the core-shell structure to be self-assembled on the surface of the flexible polymer film to form a hexagonal closest-packed structure;
and (3) etching and removing the sacrificial layer substrate of the flexible polymer film with the surface containing the gold nanoparticles in the step (2) by using etching liquid, and cleaning and removing the etching liquid and other soluble substances to obtain the flexible Raman enhancement substrate.
7. The preparation method according to claim 6, wherein the gold nanoparticle hydrosol in step (1) is obtained by reducing a boiling chloroauric acid solution with sodium citrate and/or ascorbic acid;
preferably, the first organic solvent in step (1) is a water-miscible organic solvent, and more preferably acetone;
preferably, the second organic solvent in step (1) is a water-insoluble organic solvent, and further preferably n-hexane;
preferably, the second organic solvent solution containing alkyl thiol molecules in step (1) further contains an internal standard molecule;
preferably, the mass ratio of the internal standard molecules to the alkyl mercaptan molecules is 1: 40-60;
preferably, the standing time in the step (1) is 10-30 min.
8. The production method according to claim 6 or 7, wherein the sacrificial layer substrate in the step (2) is an aluminum foil substrate or a copper foil substrate;
preferably, the drying in the step (2) is natural air drying or heating drying at the temperature within 170 ℃;
preferably, the drying temperature in the step (2) is 100-120 ℃;
preferably, the drying time in the step (2) is 5-20 min.
9. The preparation method according to any one of claims 6 to 8, wherein the etching solution in the step (3) is an acidic ferric trichloride solution;
preferably, the etching time in the step (3) is 15-30 min;
preferably, the cleaning in the step (3) is sequentially performed by using deionized water, dilute hydrochloric acid and deionized water.
10. Use of the flexible enhanced Raman substrate according to any one of claims 1 to 5 in normal incidence Raman detection and back incidence Raman detection.
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