CN107014799B - Graphene/silver nanoflower/PMMA sandwich structure flexible SERS substrate and preparation method thereof - Google Patents

Abstract

The invention discloses a graphene/silver nanoflower/PMMA "sandwich" structure flexible SERS substrate and a preparation method thereof, which solve the problem that the rigid substrate of SERS in the prior art is difficult to adapt to various surface topographies and precious metal nanostructures Due to the inability to achieve tight bonding with the substrate and the easy oxidation of noble metal nanostructures, the flexible structure enables the prepared SERS substrate to be attached to the surface of various morphologies for in-situ detection, and the in-situ Raman signal can be detected. detection effect. The specific scheme is: a flexible SERS substrate, including a single-layer graphene, a silver nano-flower layer grown on the surface of the single-layer graphene, and a PMMA film covering the surface of the silver nano-flower layer, so that the silver nano-flower layer is sandwiched between the single-layer graphene and the between PMMA films.

Description

A graphene/silver nanoflower/PMMA "sandwich" structure flexible SERS substrate and its Preparation

technical field

The invention belongs to the field of flexible SERS substrate preparation, in particular to a graphene/silver nanoflower/PMMA "sandwich" structure flexible SERS substrate and a preparation method thereof.

Background technique

Surface-enhanced Raman scattering (SERS) has attracted widespread attention since its inception because it can effectively amplify the inherent Raman signal and achieve ultra-sensitive single-molecule detection, and has been gradually applied to chemical detection, food safety, and environmental monitoring. an area. There are two widely accepted mechanisms of SERS: physical enhancement and chemical enhancement. Physical enhancement is mainly caused by the electric field enhancement caused by surface plasmon resonance, and chemical enhancement is mainly caused by charge exchange between substrates and molecules. Generally speaking, rough noble metal surfaces and noble metal nanostructures are mainly physical enhancements, while noble metal planes, some semiconductors, and new 2D layered materials are mainly chemical enhancements. The SERS substrate that combines the two enhancement principles with each other is a hot research direction.

In recent years, studies have shown that graphene has a chemically enhanced SERS effect, and graphene itself has many advantages: (1) graphene’s good biomolecular affinity makes it useful as a biomolecule enrichment layer; (2) graphene The chemically enhanced SERS effect enables graphene to serve as an additional enhancement layer; (3) the good chemical inertness of graphene enables graphene to serve as a natural protective layer for noble metal nanostructures; (4) the fluorescence quenching property of graphene makes it Can be used as a fluorescence quenching layer. Combining graphene and metal nanostructures to make composite SERS substrates has been a hot research field in recent years, and good results have been achieved. Most of the SERS substrates are rigid substrates. Such rigid material substrates that cannot be bent are difficult to adapt to various surface topographies, and it is even more difficult to perform in-situ trace detection of substances. The noble metal nanostructures (gold, silver, copper, etc.) on the rigid substrate are generally prepared and then transferred to the rigid substrate. However, the process of preparing graphene-metal nanostructure composite SERS substrates by the transfer method is extremely complicated, and the physical composite cannot realize the tight integration of graphene-metal nanostructures, and the traditional noble metal nanostructures are generally nanoparticles. The signal enhancement effect is poor and the detection sensitivity is limited. In addition, the oxidation problem of the used noble metal nanostructures (gold, silver, copper, etc.) is also one of the difficult problems to overcome.

To sum up, the rigid substrates of SERS in the prior art are difficult to adapt to various surface topographies, the noble metal nanostructures cannot be tightly combined with the substrate, and the noble metal nanostructures are easily oxidized. There is currently no effective solution. Program.

SUMMARY OF THE INVENTION

Flexible SERS substrates have many rare advantages, such as: flexible SERS substrates can be attached to the outer surface of objects of different shapes for in-situ detection of Raman signals, and SERS flexible substrates with good light transmittance can be placed on liquid surfaces for non-destructive testing. Raman signal detection. These advantages make flexible SERS substrates highly practical and have great potential for in situ trace detection of real objects.

Although no one has yet used graphene for the preparation of flexible SERS substrates, the flexibility of graphene makes it a material for flexible SERS substrates, so the inventors began to try to use graphene for the preparation of flexible SERS substrates.

In view of the technical problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a flexible SERS substrate with a graphene/silver nanoflower/PMMA "sandwich" structure.

Another object of the present invention is to provide a preparation method of the above-mentioned graphene/silver nanoflower/PMMA "sandwich" structure flexible SERS substrate.

In order to solve the above technical problems, the technical scheme of the present invention is:

A flexible SERS substrate with a graphene/silver nanoflower/PMMA "sandwich" structure, including a single-layer graphene, a silver nanoflower layer grown on the surface of the single-layer graphene, and a PMMA film covering the surface of the silver nanoflower layer, making silver The nanoflower layer is sandwiched between the monolayer graphene and the PMMA film.

Compared with traditional graphene-noble metal nanostructure SERS substrates and rigid SERS substrates, the graphene/silver nanoflowers/PMMA flexible SERS substrates of the present invention have the following advantages: first, the silver nanoflowers are directly grown on the surface of graphene, so that the Silver nanoflowers can be firmly attached to the surface of graphene; secondly, PMMA (polymethyl methacrylate) has a certain strength on the one hand and can be used as a support for flexible SERS substrates; on the other hand, it has good permeability. The optical properties will not affect the enhancement effect of the SERS substrate; thirdly, the silver nanoflowers are firmly fixed between the single-layer graphene and the PMMA film, which not only improves the adhesion of the silver nanoflowers, but also isolates the air. The oxidation of the silver nanoflowers is effectively prevented, thereby improving the lifetime of the SERS substrate. Third, nano-flower-like silver can provide a huge SERS effect, and its signal enhancement effect is much better than that of silver nanoparticles and other structures; Fourth, single-layer graphene has better flexibility, and PMMA has better flexibility. , and has a certain strength, so the prepared SERS substrate is a flexible substrate, and the flexible SERS substrate has wider applicability and can realize in-situ trace detection.

The preparation method of the above graphene/silver nanoflower/PMMA "sandwich" structure flexible SERS substrate includes the following steps: growing a single-layer graphene on a copper foil, and growing a single-layer graphene on the surface of the single-layer graphene by a microcurrent-assisted chemical reduction method. Layer silver nano-flowers, then cover a layer of PMMA film on the silver nano-flower layer, and finally remove the copper foil by etching.

The silver nanoflowers grow directly on the surface of single-layer graphene, which can make the silver nanoflowers firmly adhere to the graphene surface; the silver nanoflowers prepared by the microcurrent-assisted chemical reduction method have a larger specific surface area and stronger Raman The enhanced effect is enhanced, and the generated silver nanoflowers and the monolayer graphene are intercalated, which further improves the bonding strength between the silver nanoflowers and the monolayer graphene.

Further, the single-layer graphene growth method is a CVD (chemical vapor deposition) growth method.

Further, the current size of the microcurrent-assisted chemical reduction method is 50-200 μA/cm ⁻¹ , and the growth time is 10-70 s. Put the copper foil with graphene into the AgNO ₃ solution, the substitution reaction between copper atoms and silver ions will occur to form silver nano-islands. This is the first nucleation and growth process of silver nanocrystals. In order to form a sharp structure The second nucleation and growth process of silver nanocrystals is carried out by the method of micro-current electroplating. At this time, the silver nanoclusters formed by silver atoms are oriented and epigenetic on the surface of silver nanoislands, forming an excellent SERS effect. tip structure.

Further, the current size is 140-180 μA/cm ⁻¹ , and the growth time is 40-60 s.

When the current and growth time are in this range, the prepared silver nanoflowers have stronger Raman signal enhancement effect.

Further, the electrolyte of the microcurrent-assisted chemical reduction method is AgNO ₃ solution, and the concentration of the electrolyte is 1.5-2 g/L.

Further, the method for growing silver nanoflowers by the microcurrent-assisted chemical reduction method specifically includes the following steps: using the graphene/copper foil composite as the negative electrode, using the silver foil as the positive electrode, and the current size is 50-200 μA/cm ^-1 , the AgNO ₃ solution with an auxiliary electrolysis concentration of 1.5-2 g/L and a citric acid mixture of 10-15 g/L are reacted for 10-70 s to obtain a silver nano-flower layer.

Further, the etching solution used for etching and removing the copper foil is FeCl ₃ solution, the concentration of the etching solution is 0.5-1M, and the etching reaction temperature is 10-20°C.

A biosensor, comprising the above graphene/silver nanoflower/PMMA "sandwich" structure flexible SERS substrate.

Application of the above graphene/silver nanoflower/PMMA "sandwich" structure flexible SERS substrate in in-situ trace detection of substances.

The beneficial technical effects of the present invention are:

(1) The silver nanoflowers are directly grown on the graphene surface, so that the silver nanoflowers can be firmly attached to the graphene surface;

(2) PMMA, as a support for flexible SERS substrates, has good light transmittance;

(3) Nano flower-like silver can provide a huge SERS effect, and its signal enhancement effect is much better than that of silver nanoparticles and other structures;

(4) The silver nanoflowers are firmly fixed between the graphene and the PMMA film in a "sandwich" structure, which can effectively prevent the oxidation of silver and greatly enhance the life of the substrate.

(5) The flexible structure enables the prepared SERS substrate to be attached to the surface of various morphologies for in-situ detection, and perform in-situ detection of Raman signals.

Description of drawings

The accompanying drawings that form a part of the present application are used to provide further understanding of the present application, and the schematic embodiments and descriptions of the present application are used to explain the present application and do not constitute improper limitations on the present application.

Fig. 1 is the scanning electron microscope image of preparing precursor base copper foil/graphene/silver nanoflower in Example 1;

2 is a scanning electron microscope image of graphene/silver nanoflowers/PMMA prepared in Example 1.

In Fig. 3, (a) is the detection schematic diagram of the graphene/silver nanoflower/PMMA flexible SERS substrate prepared in Example 1; (b) is the graphene/silver nanoflower ^/ PMMA flexible SERS substrate pair 10- Raman enhancement of Rhodamine 6G (R6G) at ¹² M concentration.

Detailed ways

It should be noted that the following detailed description is exemplary and intended to provide further explanation of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It should be noted that the terminology used herein is for the purpose of describing specific embodiments only, and is not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural as well, furthermore, it is to be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates that There are features, steps, operations, devices, components and/or combinations thereof.

Terminology Explanation Section:

A flexible substrate refers to a substrate with low flexural rigidity, which can be bent arbitrarily with the deformation of the surface of the attached object; the rigid substrate has a large flexural rigidity and cannot be arbitrarily bent with the deformation of the surface of the attached object.

Copper foil is made of copper plus a certain proportion of other metals. Generally, there are 90 foil and 88 foil, that is, the copper content is 90% and 88%. The copper foil herein can be any one of these two copper foils, and the copper foil used in the specific embodiment is a copper foil with a copper content of 90%, which is purchased from United Copper Foil (Huizhou) Co., Ltd.

Example 1

1. Using high-purity copper foil as a catalyst, single ^- layer graphene is grown by CVD technology, the carbon source is methane, and the growth substrate is copper foil.

2. A layer of silver nanoflowers is grown on the surface of graphene by a microcurrent-assisted chemical reduction method, specifically: using graphene/copper foil as the negative electrode, using the silver foil as the positive electrode, the current size is 150 μA/cm ^-1 , the electrolyte is AgNO ₃ solution with a concentration of 2g/L and a mixture of citric acid with a concentration of 10g/L, and the reaction time is 50s.

3. Use FeCl ₃ solution with a concentration of 1M as an etching solution to remove the copper foil substrate in an environment of 20°C.

The scanning electron microscope image of the prepared precursor substrate copper foil/graphene/silver nanoflowers is shown in Figure 1. It can be seen from this figure that the diameter of the silver nanoflowers is 80-120nm, the nanoflower spacing is 50-150nm, and the branches The length is 40 to 60 nm. The scanning electron microscope image of the prepared graphene/silver nanoflowers/PMMA is shown in Figure 2. It can be seen from this figure that the bottom of the silver nanoflowers is in the shape of flakes, with a diameter of 80-120 nm and a flake spacing of 50-150 nm. Schematic diagram of the preparation of graphene/silver nanoflowers/PMMA flexible SERS substrate for Raman enhancement of 10 ^-12 M rhodamine 6G (R6G), as shown in (a) in Figure 3, where 1 is the silica substrate, 2 is the R6G molecular layer, 3 is the silver nanoflower, 4 is the PMMA film, 5 is the graphene, and the R6G molecular layer 2 is located between the silica substrate 1 and the flexible SERS substrate. The laser is projected above, and the obtained enhanced Raman scattering signal is detected. The Raman enhancement effect of graphene/silver nanoflowers/PMMA flexible SERS substrate on 10 ^-12 M concentration of rhodamine 6G (R6G) is shown in (b). It can be seen from the figure that for R6G concentrations as low as 10 ^{- 12} M, the detection effect of the flexible SERS substrate is still very good, the Raman characteristic peaks are clearly visible, 1578cm ^-1 is the Raman peak of graphene, and the strongest Raman peak of R6G is located at 614cm ^-1 with an intensity of 2300 counts.

Example 2

1. Using high-purity copper foil as a catalyst, single ^- layer graphene is grown by CVD technology, the carbon source is methane, and the growth substrate is copper foil.

2. A layer of silver nanoflowers is grown on the surface of graphene by a microcurrent-assisted chemical reduction method, specifically: using graphene/copper foil as the negative electrode, using silver foil as the positive electrode, the current size is 200μA/cm ^-1 , the electrolyte is AgNO ₃ solution with a concentration of 1.5g/L and a mixture of citric acid with a concentration of 15g/L, and the reaction time was 55s.

_3. Use FeCl3 solution with a concentration of 0.5M as the etching solution to remove the copper foil substrate in the environment of 10 °C.

Example 3

1. Using high-purity copper foil as a catalyst, single ^- layer graphene is grown by CVD technology, the carbon source is methane, and the growth substrate is copper foil.

2. A layer of silver nanoflowers is grown on the surface of graphene by a microcurrent-assisted chemical reduction method, specifically: using graphene/copper foil as the negative electrode, using silver foil as the positive electrode, the current size is 50 μA/cm ^-1 , the electrolyte is AgNO ₃ solution with a concentration of 1.5g/L and a citric acid mixture of 10g/L, and the reaction time was 60s.

3. Use FeCl ₃ solution with a concentration of 0.8M as the etching solution to remove the copper foil substrate in the environment of 20 ℃.

The above descriptions are only preferred embodiments of the present application, and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the protection scope of this application.

Claims (5)

1. a kind of Graphene/silver nano flower/PMMA " sandwich " structure flexible SERS substrate, it is characterized in that: comprise monolayer graphene, grow in the silver nano flower layer of monolayer graphene surface and be covered on silver nano flower layer surface The PMMA film made of silver nanoflowers is sandwiched between the single-layer graphene and the PMMA film; The preparation method of the graphene/silver nanoflower/PMMA "sandwich" structure flexible SERS substrate consists of the following steps: growing a single-layer graphene on a copper foil, and using a microcurrent-assisted chemical reduction method on the surface of the single-layer graphene A layer of silver nano-flowers is grown, then a layer of PMMA film is covered on the silver nano-flower layer, and finally the copper foil is removed by etching; The microcurrent-assisted chemical reduction method for growing silver nanoflowers specifically includes the following steps: using the graphene/copper foil composite as the negative electrode, using the silver foil as the positive electrode, the current size is 50-200 μA/cm, and the auxiliary electrolyte is the concentration 1.5～2g/L AgNO ₃ solution and 10～15g/L citric acid mixed solution, react for 10～70s to obtain silver nano-flower layer; The copper foil is removed by etching, the etching solution is FeCl3 solution, the concentration _of the etching solution is 0.5-1M, and the corrosion reaction temperature is 10-20°C. 2. SERS substrate according to claim 1, is characterized in that: the growth method of monolayer graphene is chemical vapor deposition growth method. 3 . The SERS substrate according to claim 1 , wherein the current size is 140-180 μA/cm, and the growth time is 40-60 s. 4 . 4. A biosensor, characterized in that it comprises a flexible SERS substrate with a graphene/silver nanoflower/PMMA "sandwich" structure as described in any one of claims 1-3. 5. Application of the graphene/silver nanoflower/PMMA "sandwich" flexible SERS substrate described in any one of claims 1-3 in in-situ trace detection of substances.

Images