CN102590176A - Surface-enhanced Raman scattering probe and preparation method thereof - Google Patents

Abstract

The invention relates to a surface-enhanced Raman scattering probe and a preparation method thereof. The probe is a sandwich structure consisting of core noble metal nanorods, a middle sandwich layer wrapped with Raman signal molecules, and a noble metal shell layer formed by growing on the outer surface. constitute. Its preparation method firstly absorbs or couples Raman signal molecules on the surface of noble metal nanorods, then wraps the Raman signal molecules with silicon dioxide or polydielectric to form a middle sandwich layer, and then grows outside it to form a noble metal shell layer. The present invention designs a surface-enhanced Raman scattering probe with a sandwich structure, fully utilizes the surface plasmon interaction between the gold nanorod and the outer metal shell to generate a strong local electromagnetic field strength, greatly enhances the Raman signal, and overcomes the The shortcomings of the two-dimensional substrate are difficult to repeat, expensive and complex. At the same time, the size of the surface-enhanced Raman scattering signal nanoprobe is less than 200nm, which is beneficial to the application of living biological detection and biological imaging as a biological probe.

Description

A surface-enhanced Raman scattering probe and its preparation method

technical field

The invention relates to the fields of nanomaterials and life analysis chemistry, in particular to a surface-enhanced Raman scattering (SERS) probe and a preparation method thereof.

Background technique

The signal intensity of surface-enhanced Raman spectroscopy is several to ten orders of magnitude higher than that of ordinary Raman spectroscopy, so surface-enhanced Raman scattering signals are used for the detection of extremely low concentrations or even single molecules, and when detecting organic molecules and biomolecules It shows the technical characteristics of being very simple, fast and cheap. Since Nie Shuming (science, 1997, 275, 1102-1106) reported single-molecule surface-enhanced Raman scattering (SERS) detection technology in 1997, especially Mirkin (Science, 2002, 297, 1536-1540) and Since the group of Nie Shuming (Nat.Biotech, 2008, 26, 83-89) reported the SERS detection technology of DNA, RNA and cancer markers in vivo, the research of SERS has received great attention including physics, chemistry and biologists. And it has aroused great research interest.

At present, it is still necessary to thoroughly unravel the mystery of the physical mechanism of SERS. However, it is widely accepted that the enhancement of the local electromagnetic field leads to the enhancement of the molecular Raman signal. Spherical nanoparticles with a non-smooth surface have the best enhancement effect, but irregular nanoparticles with a sharp end tend to lead to a strong Raman enhancement effect. It is further found that the interaction between particles in aggregates composed of two or more nanoparticles Electromagnetic fields can be further enhanced, and these localized spaces of electromagnetic fields are called "hot-spots". Generally speaking, the SERS enhancement factor of a single particle is 106, and the enhancement factor caused by "hot spots" can reach more than ten orders of magnitude. Therefore, people use various methods such as self-assembly and microfabrication to construct nanostructures and Two-dimensional SERS substrates (Nano. Lett. 2006, 6, 2173-2176; Nano. Lett. 2007, 7, 2080-2088). However, these methods have disadvantages such as low reproducibility, complicated operation, and expensive preparation.

Contents of the invention

In view of the above deficiencies, the purpose of the present invention is to propose a surface-enhanced Raman scattering probe and its preparation method to solve the problems of low repeatability of the product manufacturing method, complicated operation, and high preparation cost. The development of chemistry paves the way.

In order to solve the above technical problems, the present invention proposes a surface-enhanced Raman scattering probe, which is characterized in that: the probe is a sandwich structure, and the middle sandwich layer and the center are wrapped by core noble metal nanorods and Raman signal molecules. It consists of a noble metal shell layer grown on the surface of the sandwich layer.

Further, the noble metal nanorods in the core are gold nanorods with an aspect ratio between 2-6 and a surface plasmon absorption region within the wavelength range of 500-2000nm.

Further, the intermediate sandwich layer is silicon dioxide or polydielectric with a thickness of 1-10 nm, wherein the polydielectric is at least sodium polystyrene sulfonate/polypropylene amine hydrochloride, polyacrylic acid/polypropylene amine One of hydrochloride, sodium polystyrene sulfonate/polydipropylene dimethylamine hydrochloride or polyacrylic acid/polydipropylene dimethylamine hydrochloride.

Further, the Raman signal molecules wrapped in the middle sandwich layer are at least mercaptobenzene, mercaptoanilinium, mercaptopyridine, p-mercaptotoluene, rhodamine dye molecules, fluorescein isothiocyanate, tetramethylrhodamine- One of 6-isothiocyanic acid, 4-mercaptopyridine, 2,3-dichloromercaptobenzene, 2-monochloromercaptobenzene or mercaptonaphthalene.

Further, the noble metal shell layer is a gold metal shell layer or a silver metal shell layer with a continuous and smooth surface and a thickness of 10-50 nm.

The present invention also proposes a preparation method for preparing the above-mentioned surface-enhanced Raman scattering probe, comprising steps:

Ⅰ. Prefabrication of noble metal nanorods with an aspect ratio between 2-6 and a surface plasmon absorption region within the wavelength range of 500-2000nm;

Ⅱ. Reacting the Raman signal molecules with the noble metal nanorods prepared in step I, so that the Raman signal molecules are adsorbed or coupled on the surface of the noble metal nanorods of the probe;

Ⅲ. Forming an intermediate sandwich layer wrapping Raman signal molecules on the surface of the noble metal nanorods prepared in step Ⅱ;

Ⅳ. Add amination solution to the ethanol solution dispersion system, modify the surface of the intermediate sandwich layer of the probe prepared by step Ⅲ with amino functional groups, and prepare a 1-3nm noble metal colloid solution by tetrakishydroxymethyl phosphorus chloride reduction method As a growth seed for the preparation of the precious metal shell;

V. Mixing the probes modified with amino functional groups with the noble metal colloidal solution, so that the surface of the silica middle sandwich layer adsorbs the growth seeds of the noble metal shell layer;

VI. Under the catalysis of the reducing agent, the probe prepared in step V is dispersed in the corresponding noble metal salt solution, and the reduced noble metal atoms grow epitaxially along the crystal lattice of the growth seed to form a continuous and smooth noble metal outer shell.

Further, the step III adopts the hydrolysis method of tetraethyl orthosilicate alkali solution, and forms a silicon dioxide sandwich layer wrapped with Raman signal molecules on the surface of the noble metal nanorods prepared in step II, wherein the tetraethyl orthosilicate The concentration is between 0.1mmol/L-2.0mmol/L, the pH value of the alkaline solution is adjusted by sodium hydroxide to be between 6-14, and the molar ratio of ethyl orthosilicate to noble metal nanorods is 1:200-200:1.

Further, the step III adopts the electrostatic adsorption layer-by-layer self-assembly method to form a polydielectric intermediate sandwich layer wrapping Raman signal molecules on the surface of the noble metal nanorods prepared in step II. For each layer of self-assembly, the noble metal nanorods Dissolve in sodium chloride solution, add any polydielectric component, centrifuge after 30 minutes, repeat the self-assembly several times, and add the same or different polydielectric components for each self-assembly.

Further, the amination solution in step IV is aminopropyltriethoxysilane or aminopropyltrimethoxysilane.

The proposal and implementation of the technical solution of the present invention has outstanding beneficial effects compared with the prior art: by designing a surface-enhanced Raman scattering probe with a sandwich structure, the surface plasmon interaction between the gold nanorod and the outer metal shell can be fully utilized The action produces a strong local electromagnetic field strength, which greatly enhances the Raman signal of the signal molecule. This sandwich structure overcomes the shortcomings of two-dimensional substrates that are difficult to repeat, expensive, and complex. At the same time, the surface enhances the Raman scattering signal nanometer The size of the probe is less than 200 nm, which is beneficial to the application of biological detection and biological imaging as a biological probe.

Description of drawings

Figure 1 is a schematic diagram of the synthetic route for the synthesis of the sandwich structure.

Figure 2 shows the UV absorption spectra of gold nanorods with different aspect ratios.

Figure 3 is a TEM image of SiO ₂ wrapped gold nanorods with Raman signal molecules attached.

Figure 4 is the surface-enhanced Raman scattering spectrum of p-mercaptoanilinium caused by the sandwich structure.

Detailed ways

The creators of the present invention have innovatively proposed a new structure of a surface-enhanced Raman scattering probe and a brand-new and easy-to-preparation method for the problems of low repeatability, complicated operation, and expensive preparation of the probe in the prior art. . From its structural characteristics, the probe is a sandwich structure, which is composed of a core of noble metal nanorods, a middle sandwich layer wrapped with Raman signal molecules, and a noble metal shell layer formed on the surface of the center sandwich layer. The core noble metal nanorods are gold nanorods with an aspect ratio between 2-6 and a surface plasmon absorption region between 500-2000nm wavelength range; the middle sandwich layer is silicon dioxide or polydielectric with a thickness of 1-10nm. Man signal molecules are wrapped in it, and the outermost noble metal shell layer is a gold metal shell layer or a silver metal shell layer with a continuous and smooth surface and a thickness of 10-50nm.

As a preferred version, wherein the polydielectric is at least sodium polystyrene sulfonate/polypropylene amine hydrochloride, polyacrylic acid/polypropylene amine hydrochloride, sodium polystyrene sulfonate/polydipropylene dimethylamine One of hydrochloride or polyacrylic acid/polydipropylene dimethylamine hydrochloride. The Raman signal molecules are at least mercaptobenzene, mercaptoanilinium, mercaptopyridine, p-mercaptotoluene, rhodamine dye molecules, fluorescein isothiocyanate, tetramethylrhodamine-6-isothiocyanate, 4-mercaptopyridine, One of 2,3-dichloromercaptobenzene, 2-monochloromercaptobenzene or mercaptonaphthalene.

From the summary of the preparation method of the surface-enhanced Raman scattering probe, it mainly includes the following six steps: 1. Pre-preparing a noble metal with an aspect ratio between 2-6 and a surface plasmon absorption region between 500-2000nm wavelength range Nanorods; Ⅱ. React the Raman signal molecules with the noble metal nanorods prepared in step Ⅰ, so that the Raman signal molecules are adsorbed or coupled on the surface of the noble metal nanorods of the probe; Ⅲ. The noble metal nanorods prepared in step Ⅱ The surface forms an intermediate sandwich layer wrapping Raman signal molecules; IV, adding an amination solution to the ethanol solution dispersion system, and modifying the surface of the intermediate sandwich layer of the probe prepared in step III with amino functional groups, and simultaneously using tetrahydroxymethyl chloride Preparation of 1-3nm noble metal colloidal solution by phosphorous reduction method is used as the growth seed for preparing the noble metal shell layer; V. Mixing the probe modified with amino functional groups with the noble metal colloid solution, so that the surface of the silica intermediate sandwich layer adsorbs the noble metal shell Ⅵ. Under the catalysis of the reducing agent, the probe prepared in step Ⅴ is dispersed in the corresponding noble metal salt solution, and the reduced noble metal atoms grow epitaxially along the crystal lattice of the growth seed, forming a continuous and smooth noble metal shell layer .

In view of the difference in the material of the intermediate sandwich layer, the method of preparing the intermediate sandwich layer in step III is also different. The method of hydrolyzing the tetraethyl orthosilicate alkali solution can be used to form a wrapped Raman signal on the surface of the noble metal nanorods prepared in step II. Molecular silica intermediate sandwich layer, the concentration of ethyl orthosilicate is between 0.1mmol/L-2.0mmol/L, sodium hydroxide adjusts the pH value of the alkaline solution between 6-14, ethyl orthosilicate and precious metal The molar ratio of the nanorods is 1:200-200:1. It is also possible to use the electrostatic adsorption layer-by-layer self-assembly method to form a polydielectric sandwich layer wrapping Raman signal molecules on the surface of the noble metal nanorods prepared in step II. For each layer of self-assembly, the noble metal nanorods are dissolved in sodium chloride Then add any polydielectric component to the solution, and centrifuge after 30 minutes. The self-assembly is repeated several times, and the polydielectric components added in each self-assembly are the same or different.

In addition, the amination solution in step IV is aminopropyltriethoxysilane or aminopropyltrimethoxysilane.

Two specific examples of the preparation method of the present invention are described in detail below. This embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

Embodiment 1 (the middle sandwich layer is silicon dioxide).

1. Pre-preparation of gold nanorods (reference literature: Chem.Mater.2003, 15.1957): preparation of gold nanorods with an aspect ratio of 2-6 and a maximum ultraviolet absorption in the wavelength range of 500-2000nm.

(1) Preparation of seed solution: Mix 5 mL of 0.5 mmol/L HAuCl ₄ solution with 5 mL of cetyltrimethylammonium bromide (CTAB, 0.2 mol/L) solution and stir magnetically, then add 0.6 mL Freshly prepared NaBH4 (0.01mmol/L) solution was stirred at room temperature for 2 minutes, and it was found that a yellow-brown gold colloid solution was formed, which was used as a seed solution for growing gold nanorods.

(2) Growth of gold nanorods: In a 50mL round bottom flask, add a certain volume of AgNO ₃ (0.1mol/L) solution (the volumes are 0.05mL, 0.08mL, 0.12mL, 0.15mL and 0.18mL, and the AgNO 3 ₃ molar mass determines the aspect ratio of gold nanorods), then add 5mL of CTAB (0.2mol/L) solution and 5mL of HAuCl ₄ (1.0mmol/L) solution, then add 50μL of ascorbic acid (0.10mol/L) Solution, after stirring for 2 minutes, the color of the solution changed from light yellow to a colorless and transparent growth solution, and finally 20 μL of the seed solution for the growth of gold nanorods obtained in step (1) was added, and the color of the solution changed significantly within 10-20 minutes, showing Formation of gold nanorods.

2. Adsorption or coupling of Raman signal molecules on the surface of gold nanorods: The gold nanorod solution prepared in step 1 was centrifuged twice (10000rpm/min, 15min), and the supernatant was removed to remove excess CTAB. The obtained gold nanorods were redispersed in ultrapure water, and a 0.2M solution of Raman signal molecules (such as p-mercaptoanilinium) was added to the aqueous solution of gold nanorods. After magnetic stirring for 3 hours, excess Raman signals were removed by centrifugation. molecular.

3. The surface of gold nanorods is coated with a thin layer of SiO ₂ : disperse the gold nanorods obtained in step 2 in 20mL aqueous solution, adjust the pH of the solution to 10 with 25wt% ammonia water or NaOH, then add 4mL of TEOS (1mM) ethanol solution, magnetically After stirring for 24 h, the SiO ₂ -coated gold nanorods were collected by centrifugation (8000 rpm/min, 30 min), washed three times with water and three times with ethanol, and finally dispersed in 10 mL of ethanol for later use.

4. Amination modification on the surface of SiO ₂ : add 5 mL of nanoparticles prepared in step 3, add 10 mL of absolute ethanol and 1 mL of ammonia water, stir well, then add excess silane coupling agent - aminopropyltriethoxysilane (APTES) or Aminopropyltrimethoxysilane (APTMS) was heated and distilled back for 2 hours, and the product was collected by centrifugation (8000rpm/min), washed three times with deionized water and three times with ethanol to remove excess silylating agent, and then redispersed in 10mL of absolute ethanol.

5. Prepare the seed solution for the growth of the metal shell layer: add 1.0mL of NaOH (0.2M) solution, 1mL of THPC (0.95wt%) aqueous solution and 2.08mL of HAuCl ₄ (24mM) solution in 48mL of ultrapure aqueous solution, in The solution changed from colorless to brown-black within 5 seconds, and the reaction solution was placed in a refrigerator at 4°C in the dark and refrigerated, and kept for more than 2 days for use.

6. Seeds of the metal shell layer adsorbed on the surface of SiO ₂ : take a certain amount of nanoparticles synthesized in step 4 and add them to the excess colloidal gold seed solution prepared in step 5, stir gently overnight, and filter with a filter membrane with a pore size of 200 nm ( Or perform centrifugation at a centrifugal speed of 4000rpm/min for 30min) to obtain seeds grown on the surface of SiO ₂ adsorbed on metal shells, and disperse them in ultrapure water.

7. Growth of metal shell layer: (1) Add 25mg of K ₂ CO ₃ and 1.5mL of HAuCl ₄ (24mM) or 0.5mL of AgNO ₃ (0.1M) solution to 100mL of ultrapure water, and place the solution in 4 ℃ refrigerated in a dark form, and stored for more than 2 days.

(2) Take 5 mL of the solution obtained in step 6 and add it to 20 mL of the solution in step 7 (1). After gentle stirring, quickly add 100 μl of formaldehyde (37%) aqueous solution, and continue stirring until the color of the solution turns blue, showing metal nanoshells Formation.

Embodiment 2 (the middle sandwich layer is polydielectric).

The same steps as in Example 1 will not be repeated here, but the differences are described in detail as follows: Step 3', after completing Step 2 of Example 1, dissolve the gold nanorods treated in Step 2 in 1.0 mM NaCl solution , add sodium styrene sulfonate (PSS) dissolved in NaCl (1.0mM) stock solution (10mg/ml), centrifuge after 30 minutes, and then disperse in 1.0mM NaCl solution, add polyacrylamine salt dissolved in NaCl (1.0mM) stock solution (10mg/ml) of PAH (PAH) was also centrifuged after 30 minutes, and repeated several times to form a sandwich layer of the polymer.

4'. Mix the gold nanorod particles synthesized in step 3' with the gold seed solution synthesized in step 5 of Example 1, and make the gold seed nanoparticles adsorb on the surface of the polyelectrolyte polymer layer through physical electrostatic interaction.

5'. Disperse the nanomaterials treated in step 4' in the corresponding metal salt (HAuCl ₄ and/or AgNO ₃ ) solution. During the reduction of formaldehyde, the metal ions are reduced to atoms, and the reduced atoms are formed on the polymer surface The gold particles are grown by epitaxial growth to form a continuous and smooth metal shell, and Au/polymer/Au(Ag) nanoprobes with a sandwich structure are obtained.

The innovations of the present invention are: (1) the Raman signal molecules are located between the core of the gold nanorod and the metal shell, and the electromagnetic field enhanced localization is constructed in the single-particle system through the surface plasmon interaction between the gold nanorod and the metal of the shell. domain "hot-spots", to achieve the purpose of generating "hot spots" in two-dimensional ordered substrates, and at the same time achieve the purpose of enhancing the Raman scattering signal of signal molecules; (2) the surface-enhanced Raman scattering of this sandwich structure The signal nano-probe has strong repeatability, simple operation, low price and high sensitivity surface-enhanced Raman scattering signal, and a nano-Raman probe with superior optical characteristics.

The multiple embodiments described above are intended to facilitate the understanding of the technical features of the present invention. To enable those skilled in the art to clearly grasp the innovative essence of the technical solutions of the present invention, it is not intended to provide limited implementations only in terms of functions or product performance. Therefore, in addition to the above-mentioned embodiments, the present invention can also have other multiple implementations. All technical solutions formed by equivalent replacement or equivalent transformation fall within the scope of protection required by the present invention.

Claims (9)

1. surface-enhanced Raman scattering probe, it is characterized in that: said probe is a sandwich structure, the noble metal outer shell that is formed by middle sandwich of layers and the center sandwich of layers superficial growth wherein of the noble metal nano rod of core, Raman signal molecule parcel constitutes.

2. a kind of surface-enhanced Raman scattering probe as claimed in claim 1 is characterized in that: the noble metal nano of said core rod for length-diameter ratio between 2-6, surface plasma absorption region gold nanorods between the 500-2000nm wavelength coverage.

3. a kind of surface-enhanced Raman scattering probe as claimed in claim 1; It is characterized in that: sandwich of layers is the silicon dioxide of thickness 1-10nm or gathers dielectric in the middle of said, and the wherein said dielectric that gathers is at least a kind of in diallyl dimethyl amine hydrochloride or the poly propenoic acid diallyl dimethyl amine hydrochloride of kayexalate/polypropylene-base amine hydrochlorate, poly propenoic acid propenyl amine hydrochlorate, kayexalate/gather.

4. a kind of surface-enhanced Raman scattering probe as claimed in claim 1; It is characterized in that: the said Raman signal molecule in the middle of being wrapped in the sandwich of layers is at least sulfydryl benzene, sulfydryl puratized agricultural spray, mercaptopyridine, to sulfydryl toluene, Luo Dan name dye molecule, fluorescein isothiocynate, tetramethyl rhodamine-6-isothiocyanic acid, 4-mercaptopyridine, 2, a kind of in 3-dichloro sulfydryl benzene, 2-one chlorine sulfydryl benzene or the mercaptonaphthalene.

5. a kind of surface-enhanced Raman scattering probe as claimed in claim 1 is characterized in that: said noble metal outer shell is surperficial continuously smooth and thickness metal shell or the silver metal shell between 10-50nm.

6. the preparation method of a surface-enhanced Raman scattering probe is characterized in that comprising step:

I, pre-prepared length-diameter ratio are between 2-6, the surface plasma absorption region noble metal nano rod between the 500-2000nm wavelength coverage;

II, with the noble metal nano rod reaction that Raman signal molecule and step I make, make the Raman signal molecular adsorption or be coupled at the noble metal nano rod surface of probe;

III, the noble metal nano rod surface that makes in the step II form the middle sandwich of layers of parcel Raman signal molecule;

IV, in the ethanolic solution disperse system, add amination solution; The middle sandwich laminar surface of probe to the step III makes is modified the amino functional group, prepares the growth seed of the precious metal colloid solution of 1-3nm as preparation noble metal outer shell with the THPC reducing process simultaneously;

V, the probe that will be modified with the amino functional group mix with precious metal colloid solution, make the growth seed of sandwich laminar surface absorption noble metal outer shell in the middle of the silicon dioxide;

VI, under reductive agent catalysis, the probe that the step V makes is scattered in the corresponding precious metal salt solution, the precious metal atom that is reduced forms smooth noble metal outer shell continuously along the lattice epitaxial growth of growth seed.

7. the preparation method of a kind of surface-enhanced Raman scattering probe as claimed in claim 6; It is characterized in that: said step III adopts the method for ethyl orthosilicate aqueous slkali hydrolysis; Form the middle sandwich of layers of silicon dioxide of parcel Raman signal molecule on the noble metal nano rod surface that the step II makes; Wherein the concentration of ethyl orthosilicate is between 0.1mmol/L～2.0mmol/L; NaOH is regulated aqueous slkali pH value between 6～14, and ethyl orthosilicate is 1:200～200:1 with the mole dosage ratio of noble metal nano rod.

8. the preparation method of a kind of surface-enhanced Raman scattering probe as claimed in claim 6; It is characterized in that: said step III adopts Electrostatic Absorption self-assembly method layer by layer; The noble metal nano rod surface that makes in the step II forms the sandwich of layers in the middle of the dielectric of gathering of parcel Raman signal molecule, for each layer self assembly, the noble metal nano rod is dissolved in sodium chloride solution; Add any again and gather dielectric composition; Carry out centrifugal treating after 30 minutes, said self assembly is carried out for several times repeatedly, and each time self assembly is added, and to gather dielectric composition identical or different.

9. the preparation method of a kind of surface-enhanced Raman scattering probe as claimed in claim 6, it is characterized in that: amination solution is aminopropyl triethoxysilane or aminopropyl trimethoxysilane in the said step IV.

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