CN109112598B

CN109112598B - Method for preparing self-assembled myrica gold SERS substrate with assistance of iron nano dot matrix

Info

Publication number: CN109112598B
Application number: CN201810984514.3A
Authority: CN
Inventors: 王军; 钟承权; 单雅倩; 宁爱凤
Original assignee: Ningbo University
Current assignee: Ningbo University
Priority date: 2018-08-28
Filing date: 2018-08-28
Publication date: 2020-06-26
Anticipated expiration: 2038-08-28
Also published as: CN109112598A

Abstract

The invention relates to a method for preparing a self-assembled myrica gold SERS substrate with the assistance of an iron nano dot matrix, which comprises the following steps: preparing an AAO template with uniform aperture, growing iron nanorods on the AAO template, and forming a waxberry-shaped gold nano lattice which is orderly arranged after gold plating. Compared with the prior art, the invention has the advantages that: the invention has the characteristics of simple and easy preparation process, high-efficiency and simple synthesis process, no pollution and low cost, and utilizes the waxberry-shaped self-assembled Au nanosphere array structure which is formed on the iron nanorods in the evaporation process and has large area, regular and ordered structure, controllable structure and high sensitivity, and the self-assembled SERS substrate can form a rough surface and a regularly arranged nano array, has high Raman enhancement activity, can be repeatedly utilized, improves the stability of SERS and can be widely applied to trace detection.

Description

Method for preparing self-assembled myrica gold SERS substrate with assistance of iron nano dot matrix

Technical Field

The invention relates to a preparation method of a metal nano array substrate, in particular to a method for preparing a self-assembled myrica gold SERS substrate by using an iron nano dot matrix in an auxiliary manner.

Background

With the progress of scientific technology, ordered noble metal nano arrays are paid more and more attention to with unique performance, and related research results are widely applied in the fields of surface raman enhanced (SERS) substrates, solar cells, micro-nano optoelectronic devices and the like. Among many noble metal materials, gold (Au) is widely used for the preparation and research of metal nanostructure arrays due to its excellent properties. The performance of metal nanostructures mainly depends on Localized Surface Plasmon Resonance (LSPR), and is closely linked with relevant parameters such as the size and the shape of the nanostructures. Therefore, how to realize the efficient preparation of the metal nano-array and the flexible adjustment of the special appearance and size, and effectively reduce the cost is one of the main problems in the research of the metal nano-array.

So far, various micro-nano machining precision methods are proposed to realize the preparation of various metal nano-arrays and the control method of the structure size, wherein the most representative methods are mainly an etching method and a template method, such as photoetching, electron beam etching and the like. Although these various methods have high precision, the processing efficiency is low, the cost is high, and the problems of large-size and large-scale sample preparation are not facilitated, so that the application of the methods in the preparation of micro and nano metal structures and small devices is limited.

Surface Enhanced Raman Scattering (SERS) is one of the widely used examples of metal nanoarrays, and because it can realize rapid detection of trace amounts and ensure the food safety of people, it has been widely used in various subject fields, mainly relating to the development fields of biology, chemistry, analytical chemistry, and detection of organic content. The SERS enhancement effect is explained mainly from both the electromagnetic mechanism of the roughened metal surface of the substrate and the chemical mechanism associated with the adsorbed molecules that produce the effect. Therefore, to improve the enhancement effect of SERS, the nanoperformance of the substrate is improved first. The substrate manufactured by the traditional manufacturing method is not easy to form a uniformly distributed nano lattice, so that the test result is unstable; and the traditional preparation method has the problems of complicated process, high preparation cost and the like, and the development of SERS as a trace detection tool is greatly limited by the problems. Therefore, the preparation of stable and low-cost nano-array micro-nano structures as substrates is an important step for promoting the development of SERS.

Disclosure of Invention

The invention aims to solve the technical problem of the prior art, and provides a method for preparing a self-assembled myrica gold SERS substrate by using an iron nano dot matrix in an auxiliary manner, wherein the method is simple in process, high in production efficiency and low in cost, and the prepared SERS substrate is controllable in structure, good in stability and reusable.

The technical scheme adopted by the invention for solving the technical problems is as follows: a method for preparing a self-assembled myrica gold SERS substrate with assistance of an iron nano dot matrix is characterized by comprising the following steps:

1) preparing an AAO template with the aperture of 60-80nm by an anodic oxidation method;

2) cleaning the AAO template prepared in the step 1) to remove impurities, and flattening and cleaning the surface;

3) electroless deposition of iron nanorods on an AAO template: preparing a ferrous chloride solution of 0.9-1.2 mol/L, and growing the iron nanorods according to the aperture of the AAO template through electroless deposition; after deposition, putting the mixture into a vacuum drying oven for drying to obtain the iron nanorod arrays which are regularly arranged;

4) and (3) performing evaporation gold plating on the AAO template: and 3) plating gold particles on the AAO template of the iron nanorod array prepared in the step 3) in a vacuum environment by adopting a vacuum coating method to obtain the waxberry-shaped substrate with the Au nanosphere array.

Preferably, the specific preparation process of the AAO template in step 1) is as follows:

a. at least 99.99 percent of high-purity aluminum sheets are placed in a tube furnace, and annealing is carried out for 3-4 hours at the temperature of 450-550 ℃ under the protection of nitrogen so as to remove surface stress;

b. ultrasonically cleaning for 4-6 minutes by using acetone and alcohol, and removing oil stains on the surface;

c. using HClO₄Polishing an aluminum sheet for 1.5-2.5 min under the condition that the current is 0.5-0.7A by using ethanol and polishing solution with the volume ratio of 1: 8-1: 10;

d. oxidizing an aluminum sheet for 3.5-4.5 hours by adopting 0.3-0.5 mol/L oxalic acid solution under the conditions that the voltage is 35-45V and the temperature is 9-11 ℃;

e. d, placing the aluminum sheet oxidized in the step d in a phosphoric acid chromic acid solution, and drying for 5-7 hours at the temperature of 55-65 ℃ to remove an oxidation film;

f. oxidizing an aluminum sheet for 9-11 h by adopting 0.3-0.5 mol/L oxalic acid solution under the condition that the voltage is 35-45V;

g. and (5) drying for later use.

Preferably, the cleaning in the step 2) is performed by using 0.8-1 mol/L dilute sodium hydroxide solution, and then surface impurities are removed to make the surface smooth and clean.

Preferably, in the step 3), before electroless deposition, the AAO template is cut off to remove the peripheral aluminum sheet part, only the intermediate aluminum oxide is left, the prepared ferrous chloride solution is placed into a reaction kettle, the AAO template is placed into a polytetrafluoroethylene mold, the polytetrafluoroethylene mold is wound and sealed by a glue permeation tape, after deposition, the reaction kettle is placed into a vacuum drying oven for drying, the heating rate of the vacuum drying oven is 5-7 ℃/min, the set temperature is 140-160 ℃, and the heat preservation is carried out for 1.5-2.5 h.

Preferably, the specific process of evaporating gold on the AAO template in the step 4) comprises the step of placing the AAO template of the iron nanorod array prepared in the step 3) in an ion vacuum coating instrument, wherein an evaporation source is a high-purity gold target with the purity of at least 99.999 percent, and the vacuum degree is 3-5 × 10^-6Pa, the speed is 0.18-0.22A/S, and evaporation is carried out for 270-330S, so as to obtain the waxberry-shaped Au nanosphere array substrate.

Compared with the prior art, the invention has the advantages that: the invention has the characteristics of simple and easy preparation process, high-efficiency and simple synthesis process, no pollution and low cost, and utilizes the waxberry-shaped self-assembled Au nanosphere array structure which is formed on the iron nanorods in the evaporation process and has large area, regular and ordered structure, controllable structure and high sensitivity, and the self-assembled SERS substrate can form a rough surface and a regularly arranged nano array, has high Raman enhancement activity, can be repeatedly utilized, improves the stability of SERS and can be widely applied to trace detection.

Drawings

FIG. 1 is a schematic diagram of a process for preparing a self-assembled SERS substrate provided by the present invention;

FIG. 2 is a morphology of the AAO template prepared in example 1 of the present invention;

FIG. 3a is an SEM image of the AAO template after growing the iron nanorods in example 1 of the invention;

FIG. 3b is the SEM morphology of the AAO template after the iron nanorods are grown in example 2 of the invention;

FIG. 3c is the SEM morphology of the AAO template after the iron nanorods are grown in example 3 of the invention;

FIG. 4a is a diagram showing the morphology of the Au nanoarray after gold evaporation in example 1 of the present invention;

FIG. 4b is an enlarged view of the Au nanospheres of FIG. 4 a;

FIG. 5a is an EDX diagram of Fe nanoarrays in example 1 of the present invention;

FIG. 5b is EDX diagram of Au nanosphere array of example 1 of the present invention;

FIG. 6 is a Raman data graph of non-vapor-plated and vapor-plated gold in example 1 of the present invention;

FIG. 7 is a graph showing Raman data before and after washing in example 1 of the present invention.

Detailed Description

The invention is described in further detail below with reference to the accompanying examples.

Example 1:

a method for preparing a self-assembled myrica gold SERS substrate with assistance of an iron nano dot matrix comprises the following specific steps:

1) preparing an AAO template with the pore diameter of 60-80 nm:

a. putting 99.99 percent of high-purity aluminum sheets into a tube furnace, and annealing for 4 hours at 500 ℃ under the protection of nitrogen to remove surface stress;

b. ultrasonically cleaning for 5 minutes by using acetone and alcohol, and removing oil stains on the surface;

c. using HClO₄Polishing aluminum sheet with polishing solution of ethanol (volume ratio of 1:9) at current of 0.6A for 2 min;

d. oxidizing an aluminum sheet for 4 hours by adopting 0.4mol/L oxalic acid solution under the conditions that the voltage is 40V and the temperature is 10 ℃;

e. d, placing the aluminum sheet oxidized in the step d in a phosphoric acid chromic acid solution, and drying for 6 hours at 60 ℃ to remove an oxidation film; oxidizing an aluminum sheet for 10 hours by adopting 0.4mol/L oxalic acid solution under the condition that the voltage is 40V;

f. drying for later use; the prepared AAO template is shown in FIG. 2; preparing an AAO template with the aperture of 60-80nm by an anodic oxidation method;

2) cleaning the AAO template obtained in the step 1) by using 0.8-1 mol/L dilute sodium hydroxide solution to remove surface impurities and make the surface smooth and clean;

3) electroless deposition of iron nanorods on an AAO template:

a. cutting off the peripheral aluminum sheet part of the AAO template, and only remaining the middle alumina;

b. preparing 1mol/L ferrous chloride tetrahydrate solution, weighing 35ml, putting the AAO template into a 50ml reaction kettle, putting the AAO template into a polytetrafluoroethylene mold, and winding and sealing the polytetrafluoroethylene mold by using a glue permeation tape;

c. setting the temperature rise rate of the furnace to 6 ℃, setting the temperature per minute to 150 ℃, and keeping the temperature for two hours;

d. naturally cooling, ultrasonically cleaning, and drying for later use;

4) and (3) performing evaporation gold plating on the AAO template:

putting the AAO template of the iron nano rod into an ion vacuum coating instrument, wherein an evaporation source is a high-purity gold target with the purity of 99.999 percent and the vacuum degree is 4 × 10^-6Pa, the rate is 0.2A/S, vapor deposition is carried out for 300S, a substrate with good appearance is obtained, and the appearance of the iron nano array under SEM is shown in figure 3 a; the morphology of the Au nanosphere array under SEM is shown in FIG. 4a and FIG. 4 b.

Example 2:

1) preparing an AAO template with the pore diameter of 60-80 nm:

a. putting 99.99 percent of high-purity aluminum sheets into a tube furnace, and annealing for 4 hours at 450 ℃ under the protection of nitrogen to remove surface stress;

b. ultrasonically cleaning for 6 minutes by using acetone and alcohol to remove surface oil stains;

c. using HClO₄Polishing aluminum sheet with polishing solution of ethanol (volume ratio of 1:8) at current of 0.5A for 2.5 min;

d. oxidizing an aluminum sheet for 3.5 hours by using 0.5mol/L oxalic acid solution under the conditions that the voltage is 45V and the temperature is 11 ℃;

e. d, placing the aluminum sheet oxidized in the step d in a phosphoric acid chromic acid solution, and drying for 5 hours at 65 ℃ to remove an oxidation film;

f. oxidizing an aluminum sheet for 11 hours by adopting 0.5mol/L oxalic acid solution under the condition that the voltage is 45V;

g. drying for later use; preparing an AAO template with the aperture of 60-80nm by an anodic oxidation method;

3) electroless deposition of iron nanorods on an AAO template:

b. preparing 0.9mol/L ferrous chloride tetrahydrate solution, weighing 35ml, putting the obtained solution into a 50ml reaction kettle, putting an AAO template into a polytetrafluoroethylene mold, and winding and sealing the polytetrafluoroethylene mold by using a glue permeation tape;

c. setting the heating rate of the furnace to be 7 ℃/min, setting the temperature to be 160 ℃, and keeping the temperature for 1.5 hours;

d. naturally cooling, ultrasonically cleaning, and drying for later use;

4) and (3) performing evaporation gold plating on the AAO template:

putting the AAO template of the iron nano rod into an ion vacuum coating instrument, wherein an evaporation source is a high-purity gold target with the purity of 99.999 percent and the vacuum degree is 5 × 10^-6Pa, the rate of 0.22A/S, vapor deposition for 270S to obtain a substrate with good morphology, and the morphology of the iron nano array under SEM is shown in FIG. 3 b.

Example 3:

1) preparing an AAO template with the pore diameter of 60-80 nm:

a. putting 99.99 percent of high-purity aluminum sheets into a tube furnace, and annealing for 3 hours at 550 ℃ under the protection of nitrogen to remove surface stress;

b. ultrasonically cleaning for 4 minutes by using acetone and alcohol, and removing oil stains on the surface;

c. using HClO₄Polishing aluminum sheet with polishing solution of ethanol (volume ratio of 1:10) at current of 0.7A for 1.5 min;

d. oxidizing an aluminum sheet for 4.5 hours by using 0.3mol/L oxalic acid solution under the conditions that the voltage is 50V and the temperature is 9 ℃;

e. d, placing the aluminum sheet oxidized in the step d in a phosphoric acid chromic acid solution, and drying for 7 hours at 55 ℃ to remove an oxide film;

f. oxidizing an aluminum sheet for 9 hours by adopting 0.3mol/L oxalic acid solution under the condition that the voltage is 50V;

g, drying for later use; preparing an AAO template with the aperture of 60-80nm by an anodic oxidation method;

3) electroless deposition of iron nanorods on an AAO template:

b. preparing 1.2mol/L ferrous chloride tetrahydrate solution, weighing 35ml, putting the obtained solution into a 50ml reaction kettle, putting an AAO template into a polytetrafluoroethylene mold, and winding and sealing the polytetrafluoroethylene mold by using a glue permeation tape;

c. setting the heating rate of the furnace to be 5 ℃/min, setting the temperature to be 140 ℃, and preserving the heat for 2.5 hours;

d. naturally cooling, ultrasonically cleaning, and drying for later use;

4) and (3) performing evaporation gold plating on the AAO template:

putting the AAO template of the iron nano rod into an ion vacuum coating instrument, wherein an evaporation source is a high-purity gold target with the purity of 99.999 percent and the vacuum degree is 3 × 10^-6Pa, the rate of 0.18A/S, vapor deposition for 330S, and the shape of the substrate iron nano array with good shape under SEM is shown in FIG. 3 c.

The performance test procedure is as follows:

1) raman enhancement tests were performed with different concentrations of R6G:

a. rhodamine R6G was formulated into solutions of different concentrations (10)^-4，10^-6，10^-8，10^-10And 10^-12mol/L)；

b. Soaking the gold-plated substrate in rhodamine R6G with different concentrations for 4h in a dark place respectively;

c. selecting a 50X mirror and laser with the wavelength of 532nm to perform Raman test;

2) cleaning the tested substrate, and performing a Raman test again:

a. soaking the substrate in acetone, ultrasonically cleaning for 5min, and then washing with deionized water;

b. soaking the substrate in absolute ethyl alcohol, and continuing ultrasonic cleaning for 5 min; naturally drying after completion for later use;

c. the cleaned substrate is placed on a substrate 10^-4Soaking the mixture in a mol/L rhodamine R6G solution for 4 hours in a dark place;

d. and selecting a 50X mirror and laser with the wavelength of 532nm to perform Raman test.

The raman test results of example 1 are shown in fig. 6 and 7, and the raman test results of examples 2 and 3 are similar to example 1.

As can be seen from FIGS. 1 to 7:

fig. 1 is a 3D schematic diagram of a preparation process of the SERS substrate, in which an AAO template grows iron nanorods in holes through electroless deposition, and then a uniform self-assembled Au nanosphere array is formed on the surface of the iron nanoarray by a vacuum coating method.

As shown in FIG. 2, the AAO template of the two-step anodic oxidation forms a large number of ordered hole arrays, the edge of the upper surface of each hole is provided with 6 protrusions to form 6 vertexes of a hexagon, the holes are uniformly distributed in six angular holes, and in addition, as can be seen from FIG. 2, the size of the hole diameter is 60-80 nm.

In addition, the time length of oxidation, the concentration and type of the oxidizing solution, and the voltage of oxidation can affect the pore size. Therefore, it is necessary to select an appropriate concentration and voltage according to the requirements of the pore size. As shown in FIG. 3, after electroless deposition, an aligned nanorod array is formed on the AAO template, and FIGS. 3a, b and c are electron micrographs of nanorods obtained after changing the oxidation voltage reaction temperature in examples 1, 2 and 3, respectively, and it is obvious that the diameter of the nanorods changes with the voltage and the oxidation time. Therefore, nanorods having different diameters can be obtained by changing the size of the nanopore of the AAO template, and thus the spacing between the nanorods is also changed. EDX analysis of Fe nanoarrays is shown in FIG. 5a, which indicates the presence of Fe element in addition to Al and O, indicating that the composition of the nanorods is Fe, the Al and O peaks belong to aluminum foil and the Cl element comes fromFeCl₂During the deposition process, Fe²⁺The ions gain electrons and are reduced to Fe on the Al surface, and then, over time, nanorods form, a process that can be considered a galvanic reaction, where Al is oxidized to Al³⁺And Fe²⁺Is reduced to Fe.

As shown in fig. 4a, after the AAO template with the grown nanorods is subjected to gold evaporation, an Au nanosphere array with uniform size is formed; in fig. 4b, the Au nanospheres are covered with nanospheres with smaller sizes on the surface, and the whole nanospheres are waxberry-shaped, so that a rough surface is formed; the diameter of the nanosphere is around 100 nm. EDX analysis of Au nanoarrays as shown in fig. 5b, the Al and O peaks belong to aluminum foil, and Au indicates that the nanoarray is composed of gold.

As shown in fig. 6, rhodamine (rhodamine 6G, R6G) with different concentrations was selected as a probe to perform surface raman enhancement test on the uniformly arranged Au nano-lattice. When a sample is measured, a laser micro-Raman spectrometer and a 50X long-distance objective lens are adopted, the integration time is 1s, the integration times is 3, and the excitation wavelength is 532 nm. FIG. 6 is a Raman spectrum of rhodamine (R6G ) at different concentrations on an Au nano-lattice substrate, wherein R6G is used as a probe molecule, the spectrum curve at different concentrations is (a)10^-4mol/L；(b)10^-6mol/L；(c)10^-8mol/L；(d)10^-10mol/L；(e)10^-12mol/L. As can be seen from FIG. 6, when the concentration of rhodamine (R6G ) was gradually increased, the diffraction peaks of the Raman spectrum were enhanced to 599, 763, 1173, 1298 and 1351, 1498, 1637cm^-1The diffraction peak at (A) represents the characteristic peak of R6G, and the concentration of rhodamine (rhodamine 6G, R6G) is 10^-4The mol/L enhancing effect is most obvious; the concentration of rhodamine (rhodamine 6G, R6G) is 10^-12At mol/L, at 599, 763, 1173, 1298 and 1351, 1498, 1637cm^-1There was still a weak peak. As can be seen in the upper left hand diagram of FIG. 6, at 1637cm^-1The diffraction peak at (a) increases with increasing concentration of R6G. Combined with SEM image analysis, the number of gold nanospheres on the substrate is large, and a large number of nanospheres with smaller sizes exist on the surface of the substrate, so that more nanogaps and Raman enhanced 'hot spots' are formed "It is also more aligned than the common nanospheres, so the coupling enhancement is also enhanced, and the substrate can detect 10^-12Rhodamine (rhodamine 6G, R6G), the enhancement effect reaches 10¹²More than twice.

As shown in fig. 7, the raman signal with Au nano-lattice showed a diffraction peak, and R6G (curve a) was detected. In addition, SERS signals (curve b) are obtained in the same area through the cleaned Au nano-lattice, and tests show that the Au nano-lattice can be repeatedly used. The AAO template without R6G and without Au nano-lattice (curve d) has no diffraction peak. This cleaning process involved sonication in acetone for 60 seconds, soaking in alcohol, and rinsing in deionized water, followed by drying in ambient air. The Au nano-lattice after washing has a weak diffraction peak, which should be solved by repeating the washing for many times (curve c).

In conclusion, the invention has the characteristics of simple preparation process, high efficiency of the synthetic process, no pollution and low cost: on one hand, the method has simple process, does not need complicated processing steps (such as complex processing processes of oxygen ion etching, ion beam etching, atomic evaporation, sol-gel method and the like), and also saves high-cost instruments; on the other hand, the myrica Au nano array can be formed by self-assembly, and the micro-nano structure does not need to be additionally regulated, so that a great amount of time and energy are saved. When the waxberry Au nanosphere array structure with large area, regular and ordered structure, controllable structure and high sensitivity is used as the SERS substrate, a rough surface and an orderly-arranged array can be formed, so that the waxberry Au nanosphere array structure has high Raman enhancement activity, can be repeatedly utilized, has good stability and can be widely applied to trace detection.

Claims

1. A method for preparing a self-assembled myrica gold SERS substrate with assistance of an iron nano dot matrix is characterized by comprising the following steps:

2. The method of claim 1, wherein: the specific preparation process of the AAO template in the step 1) is as follows:

g. and (5) drying for later use.

3. The method of claim 1, wherein: and 2) cleaning by using 0.8-1 mol/L dilute sodium hydroxide solution, and then removing surface impurities to make the surface smooth and clean.

4. The method of claim 1, wherein: and 3) cutting off the peripheral aluminum sheet part of the AAO template before electroless deposition, only remaining intermediate aluminum oxide, putting the prepared ferrous chloride solution into a reaction kettle, putting the AAO template into a polytetrafluoroethylene mold, winding and sealing the polytetrafluoroethylene mold by using a glue-permeable tape, drying in a vacuum drying oven after deposition, wherein the heating rate of the vacuum drying oven is 5-7 ℃/min, the set temperature is 140-160 ℃, and keeping the temperature for 1.5-2.5 h.

5. The method according to claim 1, wherein the step 4) of vapor plating gold on the AAO template comprises the specific steps of placing the AAO template of the iron nanorod array prepared in the step 3) in an ion vacuum coating apparatus, wherein an evaporation source is a high-purity gold target with a purity of at least 99.999% and a vacuum degree of 3-5 × 10^-6Pa, the speed is 0.18-0.22A/S, and evaporation is carried out for 270-330S, so as to obtain the waxberry-shaped Au nanosphere array substrate.