Preparation method and application of gold nanoparticle polymer film

Abstract

The invention provides a novel method. Self-assembly of gold nanoparticles (Au NPs) on an oil-water interface is promoted through a supramolecular cross-linked polymer network. According to the technology, the large-area gold nanoparticle polymer film is effectively produced and is suitable for surface enhanced Raman scattering (SERS) sensing application. Compared with a gold nanoparticle membrane prepared by a traditional method, the polymer network cross-linked gold nanoparticle membrane shows remarkably improved mechanical strength, is not easy to break, and can be attached to the surface of an aquatic product for in vivo detection. And due to excellent SERS performance, low cost and high flexibility and stability, the material becomes a promising candidate material for detecting toxic residues in a solution or food in real time.

Description

Technical Field

[0001] The invention relates to a method for preparing a gold nanoparticle polymer film and a study on the detection of trace antibiotics by the method, and belongs to the field of preparation and application of nanocomposite materials. Technical Background

[0002] Antibiotics are widely used in aquaculture, modern medicine, and food additives, especially in animal husbandry and aquaculture. By using them as veterinary drugs or adding them to drinking water or feed for livestock, poultry, fish, shrimp, etc., they can not only effectively prevent and treat various diseases caused by bacterial infections, but also promote animal growth and improve feed utilization. Due to their superior broad-spectrum antibacterial activity and low cost, antibiotics are used in large quantities and frequently, and even abused. Although this frequent and large-scale use of antibiotics has brought immediate results, it has also caused serious concerns in public health. Therefore, detecting trace amounts of antibiotics to prevent human ingestion has become an important area of ​​research for many researchers.

[0003] Currently, the commonly used methods for detecting antibiotics are liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS). With the development of new materials, some more sensitive and advanced detection technologies have begun to be used, such as spectroscopy and electrochemical methods. Spectroscopy is widely used, including but not limited to ultraviolet-visible spectroscopy (UV-Vis), infrared spectroscopy (IR), Raman spectroscopy, etc. Although spectroscopy is not as selective as chromatography and mass spectrometry for complex samples, it is still a fast, simple and low-cost analysis method. The principle of surface-enhanced Raman scattering relies on a specific nanostructured surface, usually a precious metal such as gold or silver, which can produce local surface plasmon resonance, greatly enhancing the electromagnetic field intensity near the metal surface. When a molecule is in this enhanced electromagnetic field, its Raman scattering signal can be increased to 10 under normal conditions. 4 to 10 6 times, achieving the surface enhancement effect. The enhancement effect of SERS scattering signals is not only due to the local enhancement of the electromagnetic field by metal nanostructures, but also includes the chemical enhancement effect caused by the interaction between metals and molecules. The superposition of these two effects enables SERS technology to detect extremely low concentrations or even single molecules. Therefore, surface enhanced Raman spectroscopy, as a technology for rapid and accurate detection and determination of chemical and biochemical substances, has aroused widespread research interest in many fields.

[0004] SERS-active substrates obtained by self-assembly at liquid-liquid interfaces have simplified and rapid preparation processes and are expected to be advantageous in practical applications. The noble metal nanoparticles are densely arranged in these substrates, forming many "hot spots" that can effectively capture sample molecules into these enhanced areas. Although two-dimensional densely arranged noble metal nanoparticle films are excellent SERS substrates, this method still has some inherent limitations. Traditionally prepared gold nanoparticle (Au NPs) films at oil-water interfaces are often unstable due to weak physical interactions, resulting in fragmentation and difficulty in transfer. Therefore, it is crucial to improve the stability of these metal nanoparticle films. Summary of the invention

[0005] Based on the above background, the present invention provides a more efficient, economical and convenient flexible substrate, which enables gold nanoparticles to self-assemble at the water / oil interface to form a stable nanofilm and exhibits a good SERS enhancement effect. The present invention proposes an innovative method to promote the self-assembly of gold nanoparticles at the oil-water interface through a supramolecular cross-linked polymer network, thereby efficiently generating a large area of ​​gold nanoparticle polymer film. Compared with gold nanoparticle films prepared by traditional methods, the mechanical strength of these polymer network cross-linked gold nanoparticle films is significantly improved, so that the film is not easy to break, can exist as an independent film, and can be attached to the surface of aquatic products for in vivo detection. The gold nanoparticle polymer film composite material SERS substrate prepared by the present invention can be used for the detection of a variety of antibiotics, and the material has a significant Raman signal enhancement effect, with a detection limit as low as 10 -11 , indicating that the prepared nanocomposite film has an efficient SERS effect.

[0006] In order to achieve the above technical objectives, the technical solution of the present invention includes:

[0007] (1) The end of polyethylene glycol monomethoxy ether PEG-OH is modified with a reaction site that can initiate an atom transfer radical reaction (ATRP) by chemical reaction, serving as an initiator PEG-X;

[0008] (2) preparing two block copolymers by atom transfer radical reaction of the initiator synthesized above;

[0009] (3) Gold nanoparticles (AuNPs) prepared by citrate reduction method;

[0010] (4) Mixing the polymer dissolved in the organic phase with the polymer dissolved in the gold colloid solution, adding an inducing agent, and letting it stand for a while to obtain a gold nanoparticle-polymer composite film at the water / oil interface. Transferring the obtained gold nanoparticle-polymer film to a mica sheet or a quartz sheet, washing it with deionized water several times, and drying it at room temperature;

[0011] (5) The oil phase was mixed with gold nanoparticles dissolved in the water phase, and an inducer was added and shaken for a while to obtain a pure gold nanoparticle film at the water / oil interface for comparison with the composite film;

[0012] (6) The gold nanoparticle polymer film prepared by the above method was used as a SERS substrate to detect antibiotics.

[0013] Further, the structural formula of the macromolecular initiator is:

[0014]

[0015] X is Br or Cl

[0016] Furthermore, in step (2), the block copolymer is polyethylene glycol-polyacrylic acid (PEG-b-PAA) or polyethylene glycol-poly (4-vinylpyridine).

[0017] Furthermore, in step (2), the temperature and time of the atom transfer radical polymerization are related to the type of polymer monomer. When the monomer is 4VP, the polymerization reaction temperature is 50 o C, when the monomer is tBA, the polymerization temperature is 70 o C. By adjusting the reaction time, polymers with different molecular weights can be obtained.

[0018] Furthermore, in step (3): the AuNPs prepared by the citrate reduction method are 60 nm and are well suspended in the aqueous phase.

[0019] Furthermore, in step (4), PEG-P4VP is dissolved in an organic phase, which is chloroform, dichloromethane, toluene or n-hexane, wherein chloroform is preferred in the present invention. PEG-PAA is dissolved in a gold nanoparticle colloid solution.

[0020] Furthermore, in step (4), the contact angle between the citrate-reduced gold nanoparticles and the organic water interface is made close to 90° by adding an inducer to change the surface charge of the nanoparticles, so that the gold nanoparticles are stably arranged at the interface between the two phases. The inducer is methanol or ethanol, preferably ethanol.

[0021] Furthermore, in step (5): the organic phase includes but is not limited to dichloromethane, chloroform, and n-hexane, preferably chloroform.

[0022] Further, in step (6): in order to quantify the SERS performance of the prepared substrate, we use antibiotics as probe molecules. First, the SERS substrate loaded on the mica sheet is immersed in an antibiotic solution. After being rinsed several times with deionized water at room temperature, it is dried and then Raman detection is performed. The present invention preferably uses antibiotics sulfamethoxazole and ciprofloxacin. Among them, sulfamethoxazole is soluble in water and ciprofloxacin is soluble in methanol.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The present invention develops a one-dimensional inorganic-organic hybrid nanostructure composed of block polymers and gold nanoparticles. Through the Au-N coordination between the pyridine group of PEG-b-P4VP and AuNPs, AuNPs are stabilized to form many active sites suitable for SERS sensing applications. The introduction of poly(ethylene glycol)-block-poly(acrylic acid) PEG-b-PAA further enhances the stability of the material due to the hydrogen bonding interaction between PEG-b-PAA and PEG-b-P4VP. In addition, PEG, as an amphiphilic polymer, enables the two block polymers to interact easily at the water / oil interface.

[0025] (3) Compared with gold nanoparticle films prepared by traditional methods, the mechanical strength of these polymer network cross-linked gold nanoparticle films is significantly improved. Therefore, the films are not easy to break, can exist as independent films, and can be easily transferred to various solid substrates, including filter paper, copper grids, silicon wafers, tin foil, and aquatic product biological surfaces, which improves their flexibility.

[0026] (4) The gold nanoparticle polymer of the present invention is used as a SERS substrate for the detection of a variety of antibiotics. The Raman enhancement effect of the composite material is obvious, and the detection limit is as low as 10 -11 , indicating that the prepared nanocomposite film has a high efficiency SERS effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Figure 2. The formation process of the gold nanoparticle polymer film.

[0028] Figure 2 are characterization images of gold nanoparticle polymer films, where a is the transmission electron microscopy characterization image of the gold nanoparticle polymer film obtained under (6), and b is the average particle size of 60 nm gold nanoparticles in the gold nanoparticle polymer film obtained under (6).

[0029] Figure 3 This is a comparison chart of gold nanoparticle polymer composite film and pure gold particle film.

[0030] Figure 4 Surface enhanced Raman spectra of the prepared gold nanoparticle-polymer composite film after loading different concentrations of 4-MBA probe molecules.

[0031] Figure 5 Surface enhanced Raman spectra of the prepared gold nanoparticle-polymer composite films loaded with water antibiotic ciprofloxacin.

[0032] Figure 6 Surface enhanced Raman spectra of the prepared gold nanoparticle polymer composite film loaded with water antibiotic sulfamethoxazole DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with specific embodiments:

[0034] Example 1

[0035] A method for preparing a gold nanoparticle polymer composite film SERS substrate and its application in antibiotic detection, comprising the following steps:

[0036] (1) Synthesis of initiator (PEG-Br)

[0037] In an ice-water bath, 10.0 g of polyethylene glycol monomethyl ether with a molecular weight of 5000 was dissolved in 150 ml of toluene. Then, 4 mL of triethylamine was slowly added dropwise. During the addition, 3.5 mL of 2-bromoisobutyryl bromide was added simultaneously. After the reaction was carried out for two hours, the mixture was removed from the ice-water bath and heated to 60°C. o C, and the reaction was continued at this temperature for three days. After the reaction was completed, the mixture was filtered through filter paper and the filtrate was separated. A rotary evaporator was used at 50 o Toluene was evaporated at 400 °C to obtain a dark brown viscous liquid. The liquid was dissolved in 100 mL of dichloromethane, and then a saturated sodium bicarbonate solution was added and shaken vigorously. The lower organic phase was collected, and the aqueous phase was extracted three times with dichloromethane. The combined organic solution was added to dry anhydrous sodium sulfate for concentration. The oily substance was dissolved in dichloromethane, and ether was used as a precipitant and washed and precipitated three times to finally obtain bromide PEG-Br.

[0038] (2) PEG 114 -PtBA 670 Synthesis

[0039] The prepared bromide (800 mg), CuBr (35 mg), pentamethyldiethylenetriamine PMDETA (85 mg), tert-butyl acrylate (10 mL) and solvent 1,4-dioxane (10 mL) were added to a 100 mL reaction tube. After three cycles of cooling and thawing for degassing, the reaction tube was transferred and heated at 80 o The mixture was heated at 400 °C for 5 hours and then cooled to room temperature. Dichloromethane was used as an eluent, and a mixed solution of methanol and water (volume ratio of 1:2) was used as a precipitant. The precipitate was dissolved and dissolved three times, and the product was finally obtained by freeze drying.

[0040] (3) PEG 114 -PAA 670 Synthesis

[0041] The compound was obtained by hydrolyzing the prepared PEG-PtBA with trifluoroacetic acid (3 mL) in dichloromethane for 24 h, and then using dichloromethane as an eluent and n-hexane as a precipitant.

[0042] (4) PEG 114 -P4VP 104 Synthesis

[0043] The prepared bromide (800 mg), CuBr (35 mg), tris(2-dimethylaminoethyl)amine Me6TREN (85 mg), 4-vinylpyridine (10 mL) and solvent N,N-dimethylformamide (10 mL) were added to a 100 mL reaction tube. After three cycles of cooling and thawing for degassing, the reaction tube was transferred and heated at 50 o The reaction was heated at 400 °C for 3 h and then cooled to room temperature. Dichloromethane was used as the eluent and n-hexane was used as the precipitant. The precipitate was dissolved and dissolved three times, and the product was finally obtained by freeze drying.

[0044] (5) Preparation of gold nanoparticles

[0045] Gold nanoparticles were prepared by the common sodium citrate reduction method. Sodium citrate was used as a reducing agent to react with chloroauric acid. During the experiment, the particle size of the gold nanoparticles was controlled by adjusting the ratio between chloroauric acid and trisodium citrate. For 50 nm AuNPs, we can take the following steps: First, add 1.2 mL of 24.88 mM HAuCl4 aqueous solution to 99 mL of deionized water. Next, stir and heat to boiling in an oil bath at 900 r / min, inject 0.65 mL of 1% sodium citrate solution into the solution, continue heating for 30 min, stop stirring, and cool to room temperature. The liquid slowly turns light gray, then dark gray, and finally purple mud color, indicating that AuNPs of this particle size have been successfully synthesized.

[0046] (6) Preparation of AuNPs polymer films

[0047] First, a certain amount of PEG 114 -P4VP 104 Dissolve in 10 mL of chloroform, and dissolve another amount of PEG-PAA in 20 mL of AuNPs colloid solution. 114 -P4VP 104 Add the chloroform solution to a 50 mL beaker as the lower oil phase. Carefully add the PEG 114 -PAA 670The AuNPs colloidal solution was added dropwise to the surface of the chloroform solution as the upper aqueous phase. Then, 10 mL of ethanol was gradually added to the AuNPs colloidal solution. The addition of ethanol will reduce the surface charge of the gold nanoparticles, prompting them to self-assemble at the water / oil interface, making it easier to form a tightly packed monolayer structure. With the addition of ethanol, AuNPs will tend to precipitate at the phase interface. After standing for a period of time, the aqueous phase and the oil phase became clear and transparent, and a layer of AuNPs polymer film was formed at the water / oil interface. The upper aqueous phase was taken out, and the AuNPs polymer film was extracted using a quartz sheet as a carrier and dried.

Claims

1. A method for preparing a gold nanoparticle polymer film, characterized in that: The specific steps include: (1) The end of polyethylene glycol monomethoxy ether PEG-OH is modified with a reaction site for initiating atom transfer radical reaction ATRP through chemical reaction to serve as initiator PEG-X; (2) using the synthesized initiator above to prepare two block copolymers, namely polyethylene glycol-polyacrylic acid PEG-b-PAA and polyethylene glycol-poly(4-vinylpyridine) PEG-b-P4VP, through an atom transfer radical reaction; (3) Preparing a gold colloidal solution containing gold nanoparticles AuNPs by citrate reduction method; (4) A polymer (PEG-b-P4VP) solution dissolved in an organic phase and a polymer (PEG-b-PAA) solution dissolved in a gold colloid solution are mixed to obtain a water / oil two-phase stratified solution. An inducer is then added to the upper aqueous phase. After standing for a while, a gold nanoparticle-polymer composite film is obtained at the water / oil two-phase interface.

2. The method for preparing a gold nanoparticle polymer film according to claim 1, characterized in that: The structural formula of the macromolecular initiator PEG-X is: X is Br or Cl.

3. The method for preparing a gold nanoparticle polymer film according to claim 1, characterized in that: The polymers are polyethylene glycol-polyacrylic acid (PEG-b-PAA) and polyethylene glycol-poly 4-vinylpyridine (PEG-b-P4VP).

4. The method for preparing a gold nanoparticle polymer film according to claim 1, characterized in that: The solvent of the organic phase is chloroform or dichloromethane.

5. The method for preparing a gold nanoparticle polymer film according to claim 1, characterized in that: The inducing agent is methanol or ethanol.

6. A method for detecting antibiotics using the gold nanoparticle polymer film as a SERS substrate according to any one of claims 1 to 5, characterized in that: The obtained gold nanoparticle polymer film is transferred to a mica sheet or a quartz sheet, washed with deionized water for several times, and dried at room temperature; the gold nanoparticle polymer film is used as a SERS substrate to detect antibiotics.

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