WO2010027124A1

WO2010027124A1 - Metal nanoparticles of various sizes and shapes having functional groups and method for preparing the same

Info

Publication number: WO2010027124A1
Application number: PCT/KR2008/006851
Authority: WO
Inventors: Bong Hyun Chung; Im Sik Chung; Hyun Joon Song; Dae Ha Seo; Choong Il Yoo
Original assignee: Korea Research Institute Of Bioscience And Biotechnology
Priority date: 2008-09-08
Filing date: 2008-11-20
Publication date: 2010-03-11
Also published as: KR20100029568A; KR101066545B1

Abstract

The present invention relates to metal nanoparticles of various sizes and shapes having functional groups on the surface thereof and a method for preparing the same, and more particularly, to metal nanoparticles coated with a poly(vinylpyrrolidone) copolymer having functional groups and a method for preparing the same. According to the present invention, it is possible to readily prepare metal nanoparticles of regular hexahedral, regular octahedral, spherical shapes and the like, having a particle size of 10 to 500 nm, which comprises functional groups such as hydroxyl group, amine group, carboxyl group and the like on the surface thereof so as to be able to connect various organic molecules to biomolecules, without any post treatment of the metal nanoparticles such as surface treatment, substitution and the like.

Description

Metal Nanoparticles of Various Sizes and Shapes Having Functional Groups and Method for Preparing the Same

TECHNICAL FIELD

The present invention relates to metal nanoparticles of various sizes and shapes having functional groups on the surface thereof and a method for preparing the same, and more particularly, to metal nanoparticles coated with a poly(vinylpyrrolidone) copolymer having functional groups and a method for preparing the same.

BACKGROUND ART

It has been known that properties of metal nanoparticles can be controlled depending on their size, shape, composition, crystallinity and structure, like semiconductor nanoparticles such as quantum dots. Because of such property, the metal nanoparticles can be applied to catalysts, electronics, optics, information storage, chemical and biological sensors and the like, and thus have been actively studied (Xia, Y. et al, Chem. Eur. J., 11 :454-463, 2005).

Generally, the methods for preparing the metal nanoparticles include gas phase synthesis using a high voltage under vacuum condition and liquid phase synthesis using a polymer or single surfactant molecules in an organic solvent. Particularly, the gas phase synthesis has a drawback in that it requires a separate specific apparatus as well as exhibits low productivity and workability whereas the liquid phase synthesis advantages in that it exhibits superior productivity and workability, such that it can be readily carried out with relatively low production cost and can mass-produce the metal nanoparticles. One of the representative liquid phase synthesis to prepare the metal nanoparticles is the polyol synthesis (U.S. Patent No. 4,539,041). This is a method for preparing colloidal particles of late transition metals including noble metals, such as gold (Au), silver(Ag), copper(Cu), platinum (Pt), palladium (Pd), nickel (Ni), cobalt (Co), iridium (Ir), osmium (Os), ruthenium (Ru), iron (Fe) and the like, and an alloy thereof, in which the colloidal particles are prepared via reduction of a metal precursor in a polyol at a high temperature. In order to prevent the aggregation of the colloidal particles, poly(vinylpyrrolidone) is added, whereby the prepared metal nanoparticles are coated with the poly(vinylpyrrolidone). Also, it is known that by using the above-described method, not only the size but also the shape of nanoparticles to be prepared can be controlled in case of gold, silver and platinum, that is, the prepared nanoparticles have various shapes in addition to the sphere shape. Further, the change in properties of the nanoparticles according to changes in shape has been intensively studied (Xia, Y. and Halas, J.H., MRS Bull, 30:338- 343, 2005).

Meanwhile, in order to effectively use the properties of such metal nanoparticles to expand their applicability, it is very important to introduce functional groups, capable of bonding to other organic molecules and biomolecules, on the surface of the nanoparticles. One of the general methods to provide functional groups on the surface of the metal nanoparticles includes the substitution of a single molecule ligand on the surface of the metal nanoparticles prepared by using single surfactant molecules. However, in case of the metal nanoparticles prepared by using a polymer surfactant, it is not easy to provide functional groups by the substitution of a polymer on the surface thereof with a single molecule ligand.

Therefore, the present inventors have conducted studies to develop a method for readily preparing metal nanoparticles having functional groups on the surface thereof. As a result, the present inventors have found that the functional groups can be provided on the surface of the metal nanoparticles by adding a poly(vinylpyrrolidone) copolymer containing desired functional groups in the preparation process of the metal nanoparticles via reduction of a metal ion precursor, without carrying out any additional process. On the basis of this founding, the present invention has been completed.

SUMMARY OF INVENTION

It is an object of the present invention to provide metal nanoparticles of various sizes and shapes having functional groups on the surface thereof by coating a poly(vinylpyrrolidone) copolymer having functional groups thereon and a method for preparing the same.

To achieve the above object, the present invention provides a method for preparing metal nanoparticles having functional groups on the surface thereof, which comprises the steps of: (a) mixing a solution of a poly(vinylpyrrolidone) copolymer dissolved in a polyol with a metal ion precursor; (b) heating the mixture solution obtained in the step (a) to reduce the metal ion precursor, thereby forming metal nanoparticles coated with the poly(vinylpyrrolidone) copolymer and having functional groups on the surface thereof; and (c) separating and purifying the metal nanoparticles obtained in the step (b).

The present invention also provides metal nanoparticles of various sizes and shapes having functional groups on the surface thereof, which are prepared by the above method.

Other features and embodiments of the present invention will be more apparent from the following detailed description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 shows metal nanoparticles having functional groups on the surface thereof according to the present invention.

FIG. 2 shows the result of infrared spectroscopy of the spherical gold nanoparticles having hydroxyl groups on the surface thereof according to the present invention ((a): 1 -hour reaction, (b): 5 -hour reaction)

FIG. 3 shows scanning electron microscope photographs of the spherical gold nanoparticles having hydroxyl groups on the surface thereof according to the present invention ((a): gold nanoparticles having a diameter of 35 nm, (b): gold nanoparticles having a diameter of 50 nm, (c): gold nanoparticles having a diameter of 80 nm).

FIG. 4 shows scanning electron microscope photographs of the regular hexahedral gold nanoparticles having hydroxyl groups on the surface thereof according to the present invention.

FIG. 5 shows scanning electron microscope photographs of the regular octahedral gold nanoparticles having hydroxyl groups on the surface thereof according to the present invention.

FIG. 6 shows the result of infrared spectroscopy of the spherical gold nanoparticles having carboxyl groups on the surface thereof according to the present invention.

FIG. 7 shows scanning electron microscope photographs of the spherical gold nanoparticles having carboxyl groups on the surface thereof according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS In one aspect, the present invention relates to a method for preparing metal nanoparticles having functional groups on the surface thereof, which comprises the steps of: (a) mixing a solution of a poly(vinylpyrrolidone) copolymer dissolved in a polyol with a metal ion precursor; (b) heating the mixture solution obtained in the step (a) to reduce the metal ion precursor, thereby forming the metal nanoparticles coated with the poly(vinylpyrrolidone) copolymer and having the functional groups on the surface thereof; and (c) separating and purifying the metal nanoparticles obtained in the step (b).

Since the poly(vinylpyrrolidone) copolymer used in the present invention has various functional groups, it can be used without any additional process in the preparation of the metal nanoparticles to form the functional groups on the surface of the metal nanoparticles.

In the present invention, the heating in the step (b) is preferably performed at a temperature of 100 to 300⁰C . Herein, if the heating in the step (a) is performed at a temperature of lower than 100⁰C , the heating is not performed sufficiently and the reduction does not take place effectively, whereby the nanoparticles are not formed. If the heating is performed at a temperature of higher than 300 °C , the properties of the solution can be changed by the high temperature.

In the present invention, the poly(vinylpyrrolidone) copolymer is a compound represented by the following formula I:

Formula I

wherein R is selected from the group consisting of H, CH₃, C₂H₅ and X, X is any one selected from the group consisting of OH, OC(=O)R', C(=O)OH,

CC=O)OR', C(=O)NHR', NH₂ and NHC(=O)OR, R¹ denotes a C1-C20 alkyl or aryl group, m and n are an integral number in the range of from 50 to 10,000 and the ratio of m to n (m:n) is 1 :9 to 99:1.

In the poly(vinylpyrrolidone) copolymer represented by Formula I, the amount of the poly(vinylpyrrolidone) should be at least 10% so as to control the size and shape of the metal nanoparticles to be prepared. Thus, preferably, m:n is 1 :9 to 99: 1.

In the present invention, the poly(vinylpyrrolidone) has a molecular weight of 10,000 to 1,000,000. Herein, if the poly(vinylpyrrolidone) has a molecular weight of less than 10,000, it cannot effectively surround the surface of the nanoparticles. If it has a molecular weight of more than 1,000,000, the viscosity increases excessively and the reaction products become nonuniform, whereby uniform nanoparticles cannot be obtained.

In the present invention, the metal of the metal ion precursor is selected from the group consisting of gold (Au), silver(Ag), copper (Cu), platinum (Pt), palladium

(Pd), nickel (Ni), cobalt (Co), iridium (Ir), osmium (Os), ruthenium (Ru), iron (Fe) and an alloy thereof. Preferably, the metal is selected from gold (Au), silver (Ag), copper (Cu), platinum (Pt) and palladium (Pd). In the present invention, an ion precursor of the metal is used and preferably, a conventional ion precursor commonly used in the art is used.

In the present invention, the polyol is preferably selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, poly(ethylene glycol) having a molecular weight of less than 5,000, propandiol, butandiol, pentandiol, hexandiol, glycerol and a mixture thereof. In the present invention, the solution of the poly(vinylpyrrolidone) copolymer dissolved in a polyol has a concentration of 0.1 to 20% (w/v). If the solution has a concentration of less than 0.1% (w/v), there does not exist a sufficient amount of the polymer to stabilize the surface in the preparation of the metal particles and thus, the particles are very nonuniform and become bigger. If the solution has a concentration of more than 20% (w/v), the polymer solution has a viscosity increased and the reactant becomes nonuniform, whereby uniform metal nanoparticles cannot be prepared.

In the present invention, the metal ion precursor in the step (a) is preferably dissolved in a polyol. The solution of the metal ion precursor dissolved in the polyol has a concentration of 10 to 500 mM. Herein, when the concentration of the metal ion precursor in the solution is less than 10 mM, the metal nanoparticles are not formed. When the concentration of the metal ion precursor is more than 500 mM, the particle size of the prepared particles is excessively increased. Also, as the concentration of the metal ion precursor is increased within the foregoing concentration range, the particle size of the prepared metal nanoparticles is proportionally increased. Thus, the size of the metal nanoparticles can be controlled by using the concentration of the metal ion precursor.

In the present invention, the main factor controlling the size of the metal nanoparticles is the ratio of the poly(vinylpyrrolidone) to the metal ion precursor and the concentration of the solution of the metal ion precursor dissolved in the polyol. As the amount of the poly(vinylpyrrolidone) is increased in the ratio of the poly(vinylpyrrolidone) to the metal ion precursor, the size of the prepared metal nanoparticles is decreased. As the concentration of the solution of the metal ion precursor dissolved in the polyol is decreased, the size of the prepared metal nanoparticles is decreased. For example, when the metal nanoparticles prepared by using a ratio of the metal ion precursor to the poly(vinylpyrrolidone) of 1 :4 are compared to the metal nanoparticles prepared by using a ratio of 1 :2, the metal nanoparticles prepared by using the ratio of 1 :4 have a particle size smaller than that of the metal nanoparticles prepared by using the ratio of 1 :2.

In the present invention, the step (b) is preferably performed for 0.5 to 24 hours. If the step (b) is performed for less than 0.5 hour, functional groups are not formed on the surface of the final metal nanoparticles. If the step (b) is performed for more than 24 hours, there is no benefit from the increase in time.

In the present invention, silver nitrate (AgNO₃) may be further added in the step (a) in a molar ratio OfAgNO₃ : the metal ion precursor of 1/1000 : 1/10.

In the present invention, AgNO₃ functions to control the shape of metal nanoparticles to be prepared. For the addition thereof in the step (a), AgNO₃ may be dissolved in the polyol to be added in a solution form or be directly added after measurement of the weight of AgNO_3. Herein, the concentration of AgNO₃ dissolved in the polyol is not particularly limited. However, the ratio of AgNO₃ to the metal ion precursor is very important in order for AgNO₃ to perform the function of controlling the shape of metal nanoparticles to be prepared. Preferably, AgNO₃ is added to the metal ion precursor with a molar ratio of 1/1000 : 1/10. When AgNO₃ is added in an amount out of the foregoing range, it cannot function to control the shape of metal nanoparticles.

Although the theory, on the basis of which AgNO₃ controls the shape of the metal nanoparticles, has not yet been clearly discovered, it is believed that silver determines the direction of the crystal growth. Thus, when silver is added in a small amount, the prepared nanoparticles are a regular octahedral shape having the { 111 } surface. When silver is added in an amount more than that, the prepared nanoparticles are a regular hexahedral shape having the { 100} surface. When silver is added in an amount far more than that, the prepared nanoparticles are a spherical shape having both the { 111 } surface and the { 100} surface. As a concrete example, when Ag/ Au is about 1/50, spherical gold nanoparticles can be obtained. When Ag/Au is about 1/200, regular hexahedral gold nanoparticles can be obtained. When Ag/Au is about 1/600, regular octahedral gold nanoparticles can be obtained.

In the present invention, the separation and purification in the step (c) is performed by dispersing the metal nanoparticles in an organic solvent, followed by precipitation. The organic solvent is preferably selected from the group consisting of alcohols, chloroform, methylene chloride, toluene and a mixture thereof. That is, it is preferred that the separation and purification in the step (c) is performed by repeating at least twice a process comprising dispersing the metal nanoparticles obtained in the step (b) in the above-described organic solvents and centrifuging the dispersion to obtain a precipitate.

In another aspect, the present invention relates to metal nanoparticles of various sizes and shapes having functional groups on the surface thereof, which are prepared according to the above-described method, and more particularly, the present invention relates to metal nanoparticles comprising a poly(vinylpyrrolidone) copolymer layer coated on the surface thereof, in which the poly(vinylpyrrolidone) copolymer layer contains functional groups (FIG. 1).

In the present invention, the functional groups are selected from the group consisting of hydroxyl group, amine group and carboxyl group.

In the present invention, although the type of the poly(vinylpyrrolidone) copolymer used to prepare the metal nanoparticles is different, desired functional groups can be formed on the surface of the metal nanoparticles to be prepared by hydrolysis during the preparation process.

That is, when a poly(vinylpyrrolidone)-poly(vinyl alcohol) type copolymer or poly(vinylpyrrolidone)-poly(vinylacetate) type copolymer is used as the poly(vinylpyrrolidone) copolymer, it is possible to prepare metal nanoparticles having hydroxyl groups (-OH) formed on the surface thereof. When a copolymer selected from the group consisting of a poly(vinylpyrrolidone)-poly(acrylic acid) type copolymer, a poly(vinylpyrrolidone)-poly(acrylate) type copolymer and a poly(vinylpyrrolidone)-poly(acrylamide) type copolymer is used as the poly(vinylpyrrolidone) copolymer, it is possible to prepare metal nanoparticles having carboxyl group (-COOH) formed on the surface thereof. When a poly(vinylpyrrolidone)-poly(vinylamine) type copolymer is used, it is possible to prepare metal nanoparticles having amine group (-NH₂) formed on the surface thereof.

In the present invention, the metal nanoparticles have a particle size of 10 to 500 nm. The metal nanoparticles have a shape selected from the group consisting of a regular hexahedron, a regular octahedron and a sphere. The shape of the metal nanoparticles can be controlled by AgNO₃ which is added during the preparation process.

According to the present invention, it is possible to prepare metal nanoparticles having various sizes and shapes while having functional groups formed by using a poly(vinylpyrrolidone) copolymer during the preparation process thereof, thus providing a method for preparing metal nanoparticles having various sizes and shapes while having functional groups on the surface thereof in a simple manner, excluding a separate process needed in prior art to attach the functional groups on the metal nanoparticles. Also, it is possible to prepare composites comprising organic, molecules connected with biomolecules, using the metal nanoparticles having functional groups, which is prepared by the above method.

Examples Hereinafter, the present invention will be described in further detail with reference to examples. It is to be understood, however, that these examples are for illustrative purposes only and are not to be construed to limit the scope of the present invention.

Example 1: Preparation of spherical gold nanoparticles having hydroxyl groups on the surface thereof by using pory(vinylpyrrolidone)- poly(vinylacetate)

Spherical gold nanoparticles having hydroxyl groups on the surface thereof were prepared by using poly(vinylpyrrolidone)-poly(vinylacetate) as a poly(vinylpyrrolidone) copolymer, pentandiol as a polyol and HAuCl₄-3H₂O as a metal ion precursor.

0.15 ml Of AgNO₃ solution dissolved in pentandiol (20 mM; Ag/Au = 1/50) was added to 21 ml of pentandiol and heated to a temperature of 260 "C . 3 ml of the HAuCl₄-3H₂O solution (50 mM) and a solution of 0.27 g of poly(vinylpyrrolidone)- poly(vinylacetate) (vinylpyrrolidoneivinylacetate^ 1.3: 1, weight average molecular weight = 50,000, Aldirich agent) dissolved in 6 ml of pentandiol were slowly added thereto and thoroughly mixed at the same temperature for 1 to 5 hours, while stirring. Herein, Ag/Au refers to the molar ratio of Ag to Au. It was confirmed by infrared spectroscopy that after reaction for 1 hour, there remain traces the acetate group (FIG. 2(a)), while after reaction for 5 hours, all acetate groups were hydrolyzed into hydroxyl groups (FIG. 2(b)).

Next, excessive polyol, polymers and by-products were removed by washing with ethanol 5 times to obtain spherical gold nanoparticles having a particle size of 50 nm (FIG. 3(b)). When the pentandiol was used in an amount of 31 ml and 11 ml under the same conditions, the spherical gold nanoparticles had a particle size of 35 nm and 80 nm, respectively (FIG. 3(a) and 3(c)). As shown in Table 1, it was confirmed that when the amount of pentandiol used was decreased, the prepared gold nanoparticles had a particle size increased. From this result, it was suggested that the prepared gold nanoparticles had a particle size inversely proportional to the concentration of poly ol.

Table 1

Comparative Example 1: Preparation of gold nanoparticles by using poly(vinylpyrrolidone)

Metal nanoparticles were prepared as described in the method of Example 1, using poly(vinylpyrrolidone) instead of the poly(vinylpyrrolidone) copolymer. That is, gold nanoparticles were prepared by the same method as described in Example 1, using poly(vinylpyrrolidone) instead of poly(vinylpyrrolidone)-poly(vinylacetate).

As a result, regular octahedral gold nanoparticles having a particle size of 80 nm were obtained. When the poly(vinylpyrrolidone) copolymer was used to prepare the metal nanoparticles, the same results as those obtained by the conventional preparation of the metal nanoparticles using a poly(vinylpyrrolidone) homopolymer was obtained. Therefore, it was suggested that the method for preparing metal nanoparticles by using a poly(vinylpyrrolidone) copolymer according to the present invention can be used as a substitute for the conventional method for preparing metal nanoparticles by using a poly(vinylpyrrolidone) homopolymer.

Example 2; Preparation of regular hexahedral gold nanoparticles having hydroxyl groups on the surface thereof by using poly(vinylpyrrolidone)- poly(vinylacetate) Spherical gold nanoparticles having hydroxyl groups on the surface thereof were prepared by using poly(vinylpyrrolidone)-poly(vinylacetate) as a poly(vinylpyrrolidone) copolymer, pentandiol as a polyol and HAuCl₄-3H₂O as a metal ion precursor.

0.15 ml Of AgNO₃ solution dissolved in pentandiol (20 mM; Ag/Au = 1/200) was added to 21 ml of pentandiol and heated to a temperature of 260 °C . 3 ml of the HAuCl₄-3H₂O solution (50 mM) and a solution of 0.27 g of poly(vinylpyrrolidone)- poly(vinylacetate) (vinylpyrrolidone:vinylacetate= 1.3: 1, weight average molecular weight = 50,000, Aldirich agent) dissolved in 6 ml of pentandiol were slowly added thereto and thoroughly mixed at the same temperature for 5 hours, while stirring. Next, excessive polyol, polymers and by-products were removed by washing with ethanol 5 times to obtain regular hexahedral gold nanoparticles having a particle size of 80 nm (FIG. 4).

Example 3: Preparation of regular octahedral gold nanoparticles having hydroxyl groups on the surface thereof by using poly(vinylpyrrolidone)- poly(vinylacetate)

0.15 ml Of AgNO₃ solution dissolved in pentandiol (20 mM; Ag/Au = 1/600) was added to 21 ml of pentandiol and heated to a temperature of 260 °C . 3 ml of the HAuCl₄-3H₂O solution (50 mM) and a solution of 0.27 g of poly(vinylpyrrolidone)- poly(vinylacetate) (vinylpyrrolidone:vinylacetate= 1.3: 1, weight average molecular weight = 50,000, Aldirich agent) dissolved in 6 ml of pentandiol were slowly added thereto and thoroughly mixed at the same temperature for 5 hours, while stirring. Next, excessive polyol, polymers and by-products were removed by washing with ethanol 5 times to obtain regular octahedral gold nanoparticles having a particle size of 80 nm (FIG. 5).

Example 4: Preparation of spherical gold nanoparticles having carboxyl groups on the surface thereof by using polγ(vinylpyrrolidone)-polv(acrylic acid)

Spherical gold nanoparticles having carboxyl groups on the surface thereof were prepared by using poly (vinylpyrrolidone)-poly (aery lie acid) as a poly(vinylpyrrolidone) copolymer, pentandiol as a polyol and HAuCl₄-3H₂O as a metal ion precursor.

0.15 ml Of AgNO₃ solution dissolved in pentandiol (20 niM; Ag/ Au = 1/50) was added to 21 ml of pentandiol and heated to a temperature of 260 ^°C . 3 ml of the

HAuCl₄-3H₂O solution (50 mM) and a solution of 0.28 g of poly(vinylpyrrolidone)- poly(acrylic acid) (vinylpyrrolidone:acrylic acid=5: l) dissolved in 6 ml of pentandiol were slowly added thereto and thoroughly mixed at the same temperature for 1 hour, while stirring. Herein, the presence of carboxylic acid was confirmed by infrared spectroscopy (FIG. 6). Then, excessive polyol, polymers and by-products were removed by washing with ethanol to obtain spherical gold nanoparticles having a particle size of 20 to 40 nm (FIG. 7).

INDUSTRIAL APPLICABILITY

As described above in detail, according to the present invention, it is possible to readily prepare metal nanoparticles of regular hexahedral, regular octahedral, spherical and the like having a particle size of 10 to 500 nm, which comprises functional groups such as hydroxyl group, amine group, carboxyl group and the like on the surface thereof so as to be able to connect various organic molecules to bio-molecules, without any post treatment of the metal nanoparticles such as surface treatment, substitution and the like.

Although the present invention has been described in detail with reference to the specific features, it will be apparent to those skilled in the art that this description is only for a preferred embodiment and does not limit the scope of the present invention. Thus, the substantial scope of the present invention will be defined by the appended claims and equivalents thereof.

Claims

THE CLAIMS

What is Claimed is:

L A method for preparing metal nanoparticles having functional groups on the surface thereof, which comprises the steps of:

(a) mixing a solution of a poly(vinylpyrrolidone) copolymer dissolved in a polyol with a metal ion precursor;

(b) heating the mixture solution obtained in the step (a) to reduce the metal ion precursor, thereby forming metal nanoparticles coated with the poly(vinylpyrrolidone) copolymer and having functional groups on the surface thereof; and

(c) separating and purifying the metal nanoparticles obtained in the step (b).

2. The method for preparing metal nanoparticles having functional groups on the surface thereof according to claim 1, wherein the metal ion precursor in the step (a) is dissolved in a polyol.

3. The method for preparing metal nanoparticles having functional groups on the surface thereof according to claim I₅ wherein the heating in the step (b) is performed at a temperature of 100 to 300 °C .

4. The method for preparing metal nanoparticles having functional groups on the surface thereof according to claim 1 , wherein the poly(viny lpyrrolidone) copolymer is a compound represented by the following Formula I:

Formula I

wherein R is selected from the group consisting of H, CH₃, C₂H₅ and X, X is selected from the group consisting of OH, OC(O)R¹, C(=0)0H, C(O)OR¹, C(O)NHR¹, NH₂ and NHC(O)OR¹, R' denotes a Cl - C20 alkyl or aryl group, m and n are an integral number in the range of from 50 to 10,000 and the ratio of m to n (m:n) is 1 :9 to 99: 1.

5. The method for preparing metal nanoparticles having functional groups on the surface thereof according to claim 4, wherein the poly(vinylpyrrolidone) has a molecular weight of 10,000 to 1,000,000.

6. The method for preparing metal nanoparticles having functional groups on the surface according to claim 1, wherein the metal of the metal ion precursor is selected from the group consisting of gold (Au), silver(Ag), copper (Cu), platinum (Pt), palladium (Pd), nickel (Ni), cobalt (Co), iridium (Ir), osmium (Os), ruthenium (Ru), iron (Fe) and an alloy thereof.

7. The method for preparing metal nanoparticles having functional groups on the surface thereof according to claim 1 , wherein the polyol is selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, poly(ethylene glycol) having a molecular weight of less than 5,000, propandiol, butandiol, pentandiol, hexandiol, glycerol and a mixture thereof.

8. The method for preparing metal nanoparticles having functional groups on the surface thereof according to claim 1, wherein the solution of the poly(vinylpyrrolidone) copolymer dissolved in a polyol has a concentration of 0.1 to 20% (w/v).

9. The method for preparing metal nanoparticles having functional groups on the surface thereof according to claim 2, wherein the solution of the metal ion precursor dissolved in a polyol has a concentration of 10 to 500 mM.

10. The method for preparing metal nanoparticles having functional groups on the surface thereof according to claim 1, wherein the step (a) is performed by additionally adding silver nitrate (AgNO₃).

11. The method for preparing metal nanoparticles having functional groups on the surface thereof according to claim 10, wherein AgNO₃ is added in a molar ratio of AgNO₃ : the metal ion precursor of 1/1000 : 1/10.

12. The method for preparing metal nanoparticles having functional groups on the surface thereof according to claim 1 , wherein the separation and purification in the step (c) is performed by dispersing the metal nanoparticles in an organic solvent, followed by precipitation.

13. The method for preparing metal nanoparticles having functional groups on the surface thereof according to claim 1, wherein the organic solvent is selected from the group consisting of alcohols, chloroform, methylene chloride, toluene and a mixture thereof.

14. A metal nanoparticle which are prepared by the method of claim 1 or claim 4, and has functional group(s) on the surface thereof.

15. The metal nanoparticle according to claim 14, wherein the functional group(s) are selected from the group consisting of hydroxyl group, amine group and carboxyl group.

16. The metal nanoparticle according to claim 14, which has a particle size of 10 to 500 nm.

17. The metal nanoparticle according to claim 14, which has a shape selected from the group consisting of a regular hexahedron, a regular octahedron and a sphere.