KR101135157B1 - Porous gold nanofiber and nanorod conjugated porous gold/non-porous solid gold for molecular sensing, and process for preparing the same - Google Patents

Abstract

The present invention relates to a porous gold nanofibers for molecular detection and a solid gold cross nanorod without porous gold / pores, and a method of manufacturing the same. In the porous gold nanostructure for molecular detection according to the present invention, after coating platinum on one surface of the nanoporous membrane template by sputtering, silver / gold-silver metal is sequentially electrochemically inside the nanoporous membrane template. Deposition or electrolytic deposition of silver / gold / gold-silver / gold metal in sequence, and then remove the film with hydrofluoric acid solution, characterized in that prepared by selectively removing silver with nitric acid. In addition, by repeatedly repeating the process of electrochemically depositing gold and gold-silver metal on the nano-porous film on which silver is deposited, a solid gold multi-cross nanorod with no porous gold / pores can be prepared.

Description

Porous gold nanofiber and nanorod conjugated porous gold / non-porous solid gold for molecular sensing, and process for preparing the same}

The present invention relates to a porous gold nanofibers for molecular detection and a solid gold cross nanorod without porous gold / pores, and a method of manufacturing the same.

As the size of particles decreases, the surface area increases as the ratio of atoms constituting the surface increases with the size of the particles, and when the nanometer level reaches nanometers (nm), As the proportion of atoms on the surface increases, they exhibit unique properties that differ from the electrical, magnetic and optical properties seen at the macroscopic level.

Precious metals such as gold and silver are of interest because of their unique optical properties at the metal surface when in the form of nanostructures. In particular, since gold has stability that is harmless to the human body and does not easily react with other substances, studies on the synthesis of gold nanoparticles having a specific shape or size, medical research as a drug carrier, and life such as cosmetics and toothpaste Research into applications has been underway, and various results by these studies have been commercialized.

In general, gold nanostructures are widely used in catalysts, chemical and biosensors, photoelectric devices, optical devices, nano devices, and surface enhanced Raman scattering (SERS), depending on the size and shape of the particles. In addition, gold nanostructures exhibit various optical properties depending on their shape. The spherical gold nanostructure has a strong absorption peak at 500 nm to 600 nm, whereas the absorption peak occurs at 500 nm to 1500 nm in the form of nanowire bars, nanoplates and nano boxes.

The local electromagnetic field of the surface of nanoparticles due to the surface plasmon resonance phenomenon greatly enhances Raman scattering of molecular species adsorbed on the surface together with chemical effects, thereby enabling molecular detection with high sensitivity. In general, single silver nanoparticles exhibit more than 1000 times the molecular sensing ability of single gold nanoparticles. Moreover, a local electromagnetic field is formed in the cavity created when the precious metal nanoparticles are aggregated to form a so-called hot spot. It is noteworthy that when gold particles are aggregated, they exhibit a similar level of molecular detection as silver.

Therefore, if nanostructures are prepared using gold, which is a chemically and biologically stable material, it may be useful for molecular detection.

While the present inventors studied the nanostructure using gold for molecular detection, after coating platinum on one surface of the nanoporous membrane template by sputtering, silver / gold-silver metal was applied inside the nanoporous membrane template. Electrodeposited sequentially or electrochemically depositing silver / gold / gold-silver / gold metals, followed by removal of the membrane with hydrofluoric acid solution and selective removal of silver with nitric acid, followed by porous gold nanofibers and porous gold / pores. A solid gold cross nanorod was prepared without the above, and it was confirmed that the molecular detection ability of the porous gold nanofibers prepared without the porous gold / porous gold / pore was excellent and completed the present invention.

The present invention is to provide a porous gold nanofibers for molecular detection and a solid gold cross nanorod without porous gold / pores, and a method of manufacturing the same.

According to the present invention, after coating platinum on one surface of the nanoporous membrane mold by sputtering, silver and gold-silver metal are sequentially electrochemically deposited inside the nanoporous membrane mold, and then the film is removed by hydrofluoric acid solution and nitric acid. To be prepared by selectively removing the silver, to provide a porous gold nanofiber for molecular detection having a diameter of 30 ~ 80nm.

In addition,

1) the step of coating platinum on one surface of the nanoporous membrane template by sputtering,

2) electrochemically depositing and filling silver into the platinum-coated nanoporous membrane template;

3) electrochemically depositing and filling gold inside the nanoporous membrane template on which silver is deposited;

4) electrochemically depositing and filling a gold-silver alloy in the mold on which the silver / gold metal is deposited;

5) electrochemically depositing and filling gold inside the nanoporous membrane mold on which the silver / gold / gold-silver metal is deposited;

6) removing the film by dipping the nanoporous membrane template on which the silver / gold / gold-silver / gold metal is deposited in a hydrofluoric acid solution, and

7) It provides a method for producing a solid gold cross-linked nano-rod with no porous gold / pores for molecular detection comprising the step of removing the silver by adding nitric acid to the nanostructure from which the membrane is removed.

In addition, the present invention provides a solid gold cross nanorod without the porous gold / pores for molecular detection prepared by the above method.

Hereinafter, the present invention will be described in detail.

The porous gold nanofibers for molecular detection according to the present invention are coated with platinum on one surface of the nanoporous membrane template by sputtering, and then sequentially depositing silver and gold-silver metal in the nanoporous membrane template. After removing the film with hydrofluoric acid solution and selectively removing the silver with nitric acid, it is characterized by having a diameter of 30 ~ 80nm.

In addition, the porous gold / pore-free solid gold cross nanorod of the present invention, after coating platinum on one surface of the nanoporous membrane template by sputtering, silver / gold / gold-silver inside the nanoporous membrane template The gold metal is sequentially electrochemically deposited, and then the film is removed by hydrofluoric acid solution and is selectively prepared by removing silver with nitric acid. The diameter of the porous gold / pore-free solid gold cross nanorods prepared by the above method is 30-500 nm, preferably 30-300 nm.

In addition, the present invention is to produce a solid gold multi-cross nanorods without porous gold / pores by repeatedly repeating the process of electrochemically depositing gold and gold-silver metal on the nano-porous film on which silver is deposited during the process. Can be.

The nanoporous membranes include, but are not limited to, nanoporous alumina membranes, nanoporous titanium dioxide membranes, and the like. In the present invention, nanoporous alumina membranes are preferred. The nanoporous membrane may be prepared or commercially available by anodization.

Conditions for the electrochemical deposition of the silver / gold / gold-silver metal, 10 ~ 1 ~ 5V in a mixed solution consisting of 0.01 ~ 0.1M KAg (CN) ₂ and 0.1 ~ 0.5M Na ₂ CO ₃ in the case of silver Electrochemical deposition is performed for 100 seconds. In the case of gold, electrochemical deposition is performed for 5 to 100 seconds at 1 to 5 V in a mixed solution consisting of 0.01 to 0.05 M KAu (CN) ₂ and 0.1 to 0.5 M Na ₂ CO ₃ . For gold-silver metals, 5 seconds at 1-5 V in a mixed solution consisting of 0.01 to 0.05 M KAu (CN) ₂ , 0.01 to 0.1 M KAg (CN) ₂ , and 0.1 to 0.5 M Na ₂ CO ₃ Electrochemical deposition is performed for 20 minutes.

Cresyl violet acetate (CV) used as a labeling molecule to characterize the surface-enhanced Raman scattering intensity effect of porous gold nanofibers according to the present invention shows the strongest peak at 592 cm ^-1 , and compares the peak intensity It can be seen from the figure that the smaller the diameter of the porous gold nanofibers, the more enhanced the surface enhanced Raman scattering intensity from the labeling molecule. In addition, the porous gold nanofibers of the present invention and the solid gold cross-rods without porous gold / porosity are solid gold nanorods having no surface porosity in the surface enhanced Raman scattering intensity of the porous gold nanorods (p-Au). At least 7 to 8 times higher than Au), the molecular sensing ability is excellent.

Therefore, it is expected that the porous gold nanofibers and the solid gold cross nanorods without porous gold / pores according to the present invention may be widely used in the detection of biochemicals as well as the environmental field.

Hereinafter, preferred embodiments of the present invention will be described in order to facilitate understanding of the present invention. However, the following examples are provided only for the purpose of easier understanding of the present invention, and the present invention is not limited by the examples.

Example 1  : Fabrication of Porous Gold Nanofibers

The aluminum plate was immersed in 0.3 M oxalic acid solution and subjected to a 40V voltage to perform anodization. After the anodization step was performed once more, the pore size of the alumina membrane was adjusted using phosphoric acid to prepare a nanoporous alumina membrane (diameter: (A) 45 nm, (B) 57 nm, (C) 78 nm). The prepared nano-porous alumina membrane and a large pore size commercial alumina membrane (Anodisc, Whatman, diameter: (D) 220nm) were used as a template.

Platinum (Pt) was coated on one surface of the prepared nanoporous alumina film to a thickness of about 50 nm by using a sputtering method. For metal deposition, the platinum coated nanoporous alumina membrane was used as the working electrode. The platinum-coated nanoporous alumina membrane was immersed in 20 ml of a mixed solution of 0.05 M KAg (CN) ₂ (potassium dicyanoargentate) and 0.25 M Na ₂ CO ₃ (sodium carbonate) and electrochemically at 2.7 V for 30 seconds. Deposition was performed to introduce silver into the platinum coated nanoporous alumina film. The silver-porous nanoporous alumina film was then immersed in 20 ml of a mixed solution of 0.02 M KAu (CN) ₂ , 0.05 M KAg (CN) ₂ , 0.25 M Na ₂ CO ₃ , and at 2.7 V for 10 minutes. Electrochemical deposition was performed to introduce a gold-silver alloy inside the nanoporous alumina film. The nano-porous alumina membrane in which silver / gold-silver metals were deposited inside the pores was immersed in 10 wt% hydrofluoric acid (HF) solution for 1 hour to remove the alumina membrane, and then treated with concentrated nitric acid (HNO ₃ ) for 30 minutes. Was removed to obtain a black suspension of porous gold nanofibers. The black suspension of the obtained porous gold nanofibers was centrifuged, sonicated and washed with deionized water to obtain porous gold nanofibers.

Imaging and elemental analysis of the prepared gold nanofibers were measured using an FE-SEM (field emission scanning electron microscope, Hitachi, SU-70) equipped with an energy dispersive x-ray spectroscopy (EDX) operating at 10 kV.

The manufacturing process of the porous gold nanofibers of the present invention is shown in FIG. 1, and scanning electron microscopy images of porous gold nanofibers of various diameters of the present invention [(A) 43 nm, (B) 55 nm, (C) 74 nm , (D) 219 nm] and a representative EDX spectrum of (B) 55 nm diameter on a Si wafer are shown in FIG. 2.

As shown in FIG. 2, porous gold nanofibers [A] 43 nm, (B) 55 nm, (C) 74 nm, and (D) 219 nm of various diameters of the present invention have a pore size of about 10 nm. It was confirmed that the porous structure had a fine skeleton dimension of about 12 nm and consisted of pure gold atoms. In addition, it was confirmed by elemental analysis that the ratio of the gold-silver alloy of the porous gold-silver alloy nanofibers of the present invention was composed of gold (Au) atoms and silver (Ag) atoms having an average atomic composition of Au ₂₄ Ag ₇₆ .

Example 2  Fabrication of Porous Gold / Porosity-Free Solid Gold Cross Nanorods

An aluminum plate was immersed in 0.3M oxalic acid solution and subjected to 40V voltage to perform anodization. After performing the anodization step once more, the nanoporous alumina membrane was prepared to have a 70 nm diameter by adjusting the pore size of the alumina membrane using phosphoric acid. Using the prepared nano-porous alumina membrane as a template, a gold / gold-silver alloy was introduced in a two electrode system by using a gold solution and a gold-silver alloy solution alternately with each other.

Specifically, platinum (Pt) was coated on one surface of the commercial alumina film with a thickness of about 50 nm by using a sputtering method. For metal deposition, the platinum coated nanoporous alumina membrane was used as the working electrode. The platinum-coated nanoporous alumina membrane was immersed in 20 ml of a mixed solution consisting of 0.05 M KAg (CN) ₂ and 0.25 M Na ₂ CO ₃ and subjected to electrochemical deposition at 2.7 V for 30 seconds to coat platinum. Silver was introduced into the nanoporous alumina membrane. The nanoporous alumina film on which silver was deposited was then immersed in 20 ml of a mixed solution of 0.02 M KAu (CN) ₂ and 0.25 M Na ₂ CO ₃ , followed by electrochemical deposition at 2.7 V for 10 to 30 seconds. Gold was introduced into the porous alumina membrane. The silver and gold deposited nanoporous alumina membrane was then immersed in 20 ml of a mixed solution of 0.02 M KAu (CN) ₂ , 0.05 M KAg (CN) ₂ , 0.25 M Na ₂ CO ₃ , and at 2.7 V. Electrochemical deposition was performed for 10 seconds to introduce a gold-silver alloy inside the nanoporous alumina film. The silver / gold / gold-silver metal-deposited nanoporous alumina film was then immersed in 20 ml of a mixed solution of 0.02 M KAu (CN) ₂ and 0.25 M Na ₂ CO ₃ , and 30-100 seconds at 2.7 V. Electrochemical deposition was performed to introduce gold into the nanoporous alumina film. The porous nano-porous alumina film having silver / gold / gold-silver / gold metal deposited inside the pores was immersed in 10 wt% hydrofluoric acid (HF) solution for 1 hour to remove the alumina film, followed by concentrated nitric acid (HNO ₃ ) for 30 minutes. Treatment was performed to remove silver to prepare a solid gold crossover nanorod without porous gold / pores.

In addition, a plurality of processes of repeatedly depositing gold and gold-silver alloys electrochemically on the nanoporous alumina film on which silver was deposited were repeated to prepare a porous gold / porous solid gold multi-cross nanorod.

The manufacturing process of the porous gold / pore-free solid gold cross nanorod of the present invention is shown in Figure 1, the porous gold / pore-free solid gold cross nanorod (A) of the present invention and the porous gold / pore-free solid gold Scanning electron microscope images of multiple cross nanorods (B) are shown in FIG. 3.

As shown in FIG. 3, the porous gold / pore-free solid gold cross nanorod (A) and the porous gold / pore-free solid gold multi-cross nanorod (B) alternate between the porous gold and the solid gold without the pore. It was confirmed that it is bound. In addition, the diameter of the porous gold / pore-free solid gold cross nanorod (A) of the present invention and the porous gold / pore-free solid gold multi-cross nanorod (B) was about 70nm, the pore size of about 10nm It was confirmed that it was a porous structure having a ligament dimension of about 12 nm.

Comparative Example 1  : Preparation of Porous Solid Gold Nanofibers

An aluminum plate was immersed in 0.3M oxalic acid solution and subjected to 40V voltage to perform anodization. After performing the anodization step once more, a nanoporous alumina membrane was prepared by controlling the pore size of the alumina membrane using phosphoric acid. The prepared nano-porous alumina membrane was used as a template.

Platinum (Pt) was thinly coated on one surface of the prepared nanoporous alumina membrane using a sputtering method. The platinum-coated nanoporous alumina membrane was immersed in 20 ml of a mixed solution consisting of 0.02 M KAu (CN) ₂ and 0.25 M Na ₂ CO ₃ and subjected to electrochemical deposition at 2.7 V for 10 minutes to obtain a pore-free solid. Gold nanofibers were prepared.

The prepared pore-free solid gold nanofibers had an average diameter of about 53 nm and exhibited a smooth solid surface without pores.

Experimental Example 1  : Evaluation of Molecular Sensing Ability of Porous Gold Nanofibers

In order to confirm the molecular sensing ability of the porous gold nanofibers of the present invention, surface-enhanced Raman-scattering (SERS) was measured by a self-made micro-Raman microscope.

All measurements were performed using a He-Ne laser with a 633 nm wavelength, and the excitation power (excitation laser poser) was adjusted to 5 mW. SERS spectra were measured for 100 seconds at each sample location and were obtained from particles at various locations. The SERS intensity was derived from an aqueous solution comprising a cresyl violet acetate labeled molecule (within a concentration range of 10 ⁻⁶ to 10 ⁻⁹ mol dm ⁻³ (M) prepared by sequential dilution in HPLC grade ethanol) and gold nanomaterials. Measured. Sample solution was sandwiched between two glass slides and then SERS was measured to avoid solvent evaporation.

Surface-enhanced Raman scattering spectrum (A) of labeling molecule (CV) at concentrations of 10 ⁻⁷ mol dm ⁻³ (M) for porous gold nanofibers of various diameters of the present invention, and porous gold nanofibers at 592 cm ⁻¹ The surface enhanced Raman scattering intensity function (B) with diameter is shown in FIG. 4.

In the concentration range of 10 ^-6 to 10 ^-9 mol dm ^-3 (M) for porous gold nanofibers (p-Au) and pore-free solid gold nanofibers (s-Au) having a 55 nm diameter of the present invention Surface enhanced Raman scattering spectra of the labeling molecule (CV) are shown in FIG. 5.

As shown in FIG. 4, cresyl violet acetate used as a labeling molecule to characterize the surface enhanced Raman scattering intensity effect of the porous gold nanofibers (p-Au) of the present invention showed a strong peak at 592 cm ⁻¹ . From the peak intensity comparison, it was confirmed that the smaller the diameter of the porous gold nanofibers (p-Au), the more enhanced the surface enhanced Raman scattering intensity from the labeling molecule was.

In addition, as shown in Figure 5, the surface-enhanced Raman scattering intensity from the porous gold nanofibers (p-Au) of the present invention is at least 7 times more than in the case of solid gold nanofibers (s-Au) without nanopores It was confirmed to appear high.

Experimental Example 2  : Evaluation of Relative Molecular Sensing Ability of Porous Gold / Porosity-free Solid Gold Cross Nanorods

Surface-enhanced Raman scattering intensity was measured to determine the relative molecular sensing ability of surface-enhanced Raman scattering intensity (SERS) activity of porous gold nanofibers (p-Au) compared to solid gold nanofibers (s-Au) without nanopores. Two-dimensional (2D) Raman scattering imaging studies were performed using a commercially available Raman microscope system (JASCO, NRS-3100).

Scanning electron microscopy images, optical images and surface enhanced Raman scattering spectra of the solid gold crossover nanorods without porous gold / pore of the present invention are shown in FIG. 6 ((A) scanning electron microscopy images, (B) porous gold and pores) Magnified image of (A), (C) optical image, (D) two-dimensional (2D) Raman scattering image, (E) Raman spectrum of solid gold nanorod without nano pores, (F) Raman spectrum of porous gold nanorods].

As shown in FIG. 6, in the Raman scattering image of the porous gold / pore-free solid gold cross nanorod of the present invention, the surface enhancement Raman scattering intensity of the porous gold nanorod (p-Au) is a solid gold nanorod without nanoporosity. It was confirmed that it appeared about 8 times higher than (s-Au). Accordingly, it can be seen that the porous gold / pore-free solid gold cross nanorod of the present invention has excellent molecular sensing ability.

The cresyl violet acetate used as a labeling molecule to characterize the surface enhanced Raman scattering intensity effect of the porous gold nanofibers according to the present invention shows a strong peak at 592 cm ^-1 , and the diameter of the porous gold nanofibers It can be seen that the smaller the enhancement of surface enhanced Raman scattering intensity from the labeling molecule. In addition, the porous gold nanofibers of the present invention and the solid gold cross-rods without porous gold / porosity are solid gold nanorods having no surface porosity in the surface enhanced Raman scattering intensity of the porous gold nanorods (p-Au). At least 7 ~ 8 times higher than Au), the molecular sensing ability is excellent. Therefore, it is expected that the porous gold nanofibers and the solid gold cross nanorods without porous gold / pores according to the present invention may be widely used in the detection of biochemicals as well as the environmental field.

1 is a schematic view showing the manufacturing process of the porous gold nanofibers of the present invention or the solid gold cross nanorods without porous gold / pores [(A) platinum coating, (B) silver deposition, (F, H) gold Deposition, (C, G) gold-silver alloy deposition, (D, I) nanoporous template film removal, and (E, J) silver removal].

2 is a scanning electron microscope image of various diameters of porous gold nanofibers of the present invention ((A) 43 nm, (B) 55 nm, (C) 74 nm, (D) 219 nm) and (B) on a Si wafer. ) Is a diagram showing a representative EDX spectrum of 55 nm diameter.

3 is a scanning electron microscope image of a porous gold / pore-free solid gold cross nanorod (A) and a porous gold / pore-free solid gold multi-cross nanorod (B) of the present invention.

FIG. 4 shows the surface enhanced Raman scattering spectrum (A) of the labeling molecule (CV) at a concentration of 10 ⁻⁷ mol dm ⁻³ (M) for porous gold nanofibers of various diameters of the present invention, and porous gold at 592 cm ⁻¹ . Figure showing the surface enhanced Raman scattering intensity function (B) according to the diameter of the nanofibers.

FIG. 5 shows 10 ⁻⁶ to 10 ⁻⁹ mol dm ⁻³ (M) of porous gold nanofibers (p-Au) and pore-free solid gold nanofibers (s-Au) with 55 nm diameter of the present invention. Figure shows the surface enhanced Raman scattering spectrum of the labeling molecule (CV) in the concentration range.

FIG. 6 shows scanning electron microscopy images, optical images and surface enhanced Raman scattering spectra of solid gold crossover nanorods without porous gold / pore of the invention [(A) Scanning electron microscopy image, (B) Porous gold (A) magnified image of (A), (C) optical image, (D) two-dimensional (2D) Raman scattering image, (E) Raman spectrum of solid gold nanorod without nanopores , And (F) Raman spectra of porous gold nanorods].

Claims (11)

Platinum was coated on one surface of the nanoporous membrane template by sputtering. Then, silver and gold-silver metal were sequentially electrochemically deposited inside the nanoporous membrane template, and then the film was removed with hydrofluoric acid solution. Prepared by removing selectively, porous gold nanofibers for molecular detection having a diameter of 30 ~ 80nm. The porous gold nanofiber of claim 1, wherein the nanoporous membrane is a nanoporous alumina membrane or a nanoporous titanium dioxide membrane. The method of claim 1, wherein the electrochemical deposition of silver is performed for 10 to 100 seconds at 1 ~ 5V in a mixed solution consisting of 0.01 ~ 0.1M KAg (CN) ₂ and 0.1 ~ 0.5M Na ₂ CO ₃ Porous gold nanofibers for molecular detection. The method of claim 1, wherein the electrochemical deposition of the gold-silver metal is a mixture consisting of 0.01 ~ 0.05M KAu (CN) ₂ , 0.01 ~ 0.1M KAg (CN) ₂ , 0.1 ~ 0.5M Na ₂ CO ₃ Porous gold nanofibers for molecular detection, characterized in that performed for 5 seconds to 20 minutes at 1 ~ 5V in solution. 1) coating platinum on one surface of the nanoporous membrane template by sputtering, 2) electrochemically depositing and filling silver into the platinum-coated nanoporous membrane template; 3) electrochemically depositing and filling gold inside the nanoporous membrane template on which silver is deposited; 4) electrochemically depositing and filling a gold-silver alloy in the mold on which the silver / gold metal is deposited; 5) electrochemically depositing and filling gold inside the nanoporous membrane mold on which the silver / gold / gold-silver metal is deposited; 6) removing the film by dipping the nanoporous membrane template on which the silver / gold / gold-silver / gold metal is deposited in a hydrofluoric acid solution, and 7) The method of manufacturing a solid gold cross-linked nano-rod without a gold / pore for molecular detection, comprising the step of removing the silver by adding nitric acid to the nanostructure from which the membrane was removed. The method of claim 5, wherein the nanoporous membrane is a nanoporous alumina membrane or a nanoporous titanium dioxide membrane. 6. The method of claim 5, wherein the electrochemical deposition of silver in the step 2) is 10 ~ 100 seconds at 1 ~ 5V in a mixed solution consisting of 0.01 ~ 0.1M KAg (CN) ₂ and 0.1 ~ 0.5M Na ₂ CO ₃ Method for producing a solid gold cross-linked nano-rod without molecular gold, pores for molecular detection. The method of claim 5, wherein the electrochemical deposition of gold in steps 3) and 5) is carried out at 1 ~ 5V in a mixed solution consisting of 0.01 ~ 0.05M KAu (CN) ₂ and 0.1 ~ 0.5M Na ₂ CO ₃ Method for producing a solid gold cross-linked nano-rod without a porous gold / pores, characterized in that performed for 5 to 100 seconds. The method of claim 5, wherein the electrochemical deposition of the gold-silver metal in step 4) is 0.01 ~ 0.05M KAu (CN) ₂ , 0.01 ~ 0.1M KAg (CN) ₂ , 0.1 ~ 0.5M Na ₂ CO Method for producing a solid gold cross-linked nano-rod without a porous gold / pores for molecular detection, characterized in that carried out for 5 seconds to 20 minutes at 1 ~ 5V in a mixed solution consisting of _three . 6. The method of claim 5, wherein the steps 3) and 4) are repeated. 5. A porous gold / pore-free solid gold cross nanorod manufactured by the method of any one of claims 5 to 10 and having a diameter of 30 to 500 nm.

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