JP2011058050A - Composite metal nanoparticle and method for producing the same, and multiphoton absorption material or multiphoton absorption reaction auxiliary containing composite metal nanoparticle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple method for producing composite metal nanoparticles having both the feature of anisotropically grown particulates which can tune the resonance wavelength and the feature of neighboring particulates which can produce a stronger surface plasmon enhancement field, and to provide a multiphoton absorption material or a multiphoton absorption reaction auxiliary containing the composite metal nanoparticles. <P>SOLUTION: At least part of a base metal (for example, silver) applied on the surface of nanoparticles having shape anisotropy (for example, gold) is replaced with a noble metal (for example, gold) by the difference of ionization tendency in a solution containing ions of a metal nobler than the base metal (for example, gold) which can produce a plasmon enhancement field, thereby forming composite metal nanoparticles. The multiphoton absorption material or reaction auxiliary containing the composite metal nanoparticles is applied, for example, to a three-dimensional multilayer optical memory, a material for light shaping, and a two-photon fluorescent microscope. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a composite metal nanoparticle that generates a large plasmon enhancement field, and more particularly, a noble metal that covers a surface of a core particle having shape anisotropy and generates a plasmon enhancement field. The present invention relates to a method for producing composite metal nanoparticles substituted with a metal, composite metal nanoparticles obtained thereby, and a multiphoton absorption material or a multiphoton absorption reaction aid containing the composite metal nanoparticles.

  When using the two-photon absorption reaction, which is one of the multiphoton absorption processes, the reaction is caused by absorption proportional to the square of the excitation light intensity, which is a characteristic of the two-photon absorption reaction. It is known that a reaction can be caused only at the focal point. In other words, it is possible to cause a reaction only at an arbitrary desired position inside the substance, and furthermore, it is possible to cause a photoreaction only at a portion where the light intensity is high at the center of the focused spot. Expectations are rising for records that exceed the limits.

  However, the absorption cross section of the multiphoton absorption reaction represented by the two-photon absorption reaction is extremely small, the peak output of a femtosecond laser or the like is remarkably high, and it is essential to perform excitation with an expensive and large pulse laser light source. Have the problem of being. Because of these problems, in order to spread applications that take advantage of the excellent features of multiphoton absorption reaction, the large pulse laser is not required, for example, the reaction is induced by a semiconductor laser. It can be said that development of a highly sensitive multiphoton absorbing material that can be performed is indispensable.

  On the other hand, as a method for enhancing and sensitizing so-called photoreaction, a method using a surface plasmon enhancement field excited on a metal surface is known. For example, a surface plasmon microscope that detects a very small amount of sample with high sensitivity will be described as an example. The surface plasmon enhancement field is generated only in a limited region of several hundred nm or less from the surface on the metal thin film formed on the high refractive index medium. By placing an ultra-thin film sample on the surface of this metal thin film, the same effect as that obtained when the light stronger than the excitation light irradiated by the surface plasmon enhancement field is obtained, and the photoreaction and fluorescence are enhanced. It is known.

  This sensitization arrangement allows high-sensitivity detection, but the spatial distribution of the enhancement field depends on the shape of the metal thin film and the range that can be illuminated with excitation light (the arrangement and shape of the photorefractive index medium carrying the metal thin film). Application) is limited to a specific field (high-sensitivity detection method) using a small amount of sample. For example, it has been proposed to use silver as a metal thin film material having a typical plasmon enhancing effect (see Patent Document 1).

  In the case of using a plasmon enhancement field excited by metal fine particles for a metal thin film, the plasmon excited on the surface of the metal fine particles is a localized plasmon enhancement field having a smaller spread than in the case of Patent Document 1. The spread is limited to the region of 100 nm or less around the metal fine particles. For this reason, the sample adsorbed on the particle surface is used as a microprobe that can be observed with high sensitivity, or metal fine particles are sampled by utilizing the non-propagating light confined in a microscopic area. It is used as a microprobe microscope that obtains an observation image from the relationship between the signal and position obtained by moving in the vicinity.

  In the former case (microprobe), fluorescence from a sample existing on the surface of metal fine particles attached or arranged on the glass surface or the like is enhanced and observed by a localized plasmon enhancement field on the surface of the metal fine particles. In the case of the latter (microprobe microscope), methods such as scanning microparticles on the surface of the sample using the principle of optical tweezers that holds the microparticles by the radiation pressure of light are used. It has been.

  Moreover, in order to select the wavelength used for observation, the method regarding tuning of the resonant wavelength by a spherical core cell structure is disclosed (refer patent document 2). However, since the resonance wavelength is determined by the dimensional ratio of the core and the cell, it is difficult to obtain particles having the same resonance wavelength with good reproducibility by the method of Patent Document 2.

  Furthermore, a method using aggregated nanoparticles has been disclosed for the purpose of making the enhancement effect more remarkable by connecting localized plasmon enhancement fields between a plurality of fine particles (see Patent Document 3). In other words, high-sensitivity observation including multiphoton process is performed by arranging aggregated nanoparticles in the microcavity. However, in the method of Patent Document 3, it is difficult to control the aggregate shape of the aggregated particles, and the influence of the scattering of the aggregate is significant, so that the method is limited to use in a micro region such as in a microcavity. Yes.

On the other hand, there is a gold nanorod as means for generating a surface plasmon enhancement field instead of a fine metal sphere. The gold nanorod is a material that can change the resonance wavelength by changing the aspect ratio and can cover from about 540 nm to the near infrared (about 1100 nm). As an example of a production method, it is disclosed that particles having a uniform resonance wavelength can be obtained by producing metal nanorods by an electrochemical reaction in a solution containing a surfactant (Patent Document). 4).
In addition, a technique is disclosed in which a surface plasmon enhancement field generated by a gold nanorod is used as a sensitization method for a two-photon absorption material by utilizing the property that fine particles having the same resonance wavelength of a gold nanorod can be obtained with good reproducibility ( (See Patent Document 5).

  Further, in order to obtain a surface plasmon enhancement field having a larger enhancement intensity, it is conceivable to use silver nanorods instead of gold. For example, it has been reported that silver nanorods are obtained by microwave heating an aqueous solution of PVP (polyvinylpyrrolidone) and silver nitrate to thermally decompose silver nitrate (see Non-Patent Document 1). However, in Non-Patent Document 1, although fine silver nanorods are obtained, the formation of spherical silver nanoparticles is not suppressed, and silver nanorods having a uniform resonance wavelength have not been obtained.

  Further, it has been reported that silver nanorods are dispersed in a polymer and silver nanorods are precipitated by thermal decomposition after uniaxial stretching (see Non-Patent Document 2). However, in the method of Non-Patent Document 2, silver nanorods are deposited in pores having anisotropy obtained by uniaxial stretching, so that the obtained rods are large and the productivity is low.

  Furthermore, after the growth of the gold nanorods, excess surfactant contained in the growth solution is removed by centrifugation, silver nitrate is added, and the alkali is reduced with sodium hydroxide to reduce the silver on the surface of the gold nanorods. A technique for growing in parallel has been reported (see Non-Patent Document 3). According to the method of Non-Patent Document 3, silver can be anisotropically grown on the surface of the gold nanorod, but a centrifugal separation step is necessary to separate the surfactant, and silver nitrate is alkaline, There are still many problems such as easy precipitation as silver oxide and difficult pH control.

  As a method for obtaining a larger plasmon enhancement field, a method using a larger enhancement field called a hot spot generated between adjacent fine particles is disclosed instead of the enhancement field by a single fine particle described so far. However, the simulation is based on FDTD or only close observation of the fine particles applied on the plane is observed (see Non-Patent Document 4).

  As this improvement, a technique is also disclosed in which the surface of a gold nanorod is coated with a separated silver coating and an enhanced field generated between the silver coatings is used (see Patent Documents 6 and 7). According to the disclosed technique, a gold nanorod, which is a noble metal, is coated with silver, which is a base metal, by chemical reduction. According to this method, the silver coating grows only when silver supersaturation due to reduction occurs, and the surface of the gold nanorod is densely formed to the extent that hot spots are generated. It is difficult to obtain composite particles that generate hot spots with good reproducibility.

  Examples of a method of using composite metal nanoparticles that generate a large plasmon enhancement field include a two-photon absorption material containing the composite metal nanoparticles or a material containing a reaction aid. By using this material, it is possible to reduce the reaction threshold of the two-photon absorption reaction or to cause a reaction at the condensing point. For example, an optical recording material (three-dimensional recording medium), an optical modeling material Application as a two-photon absorption fluorescent material has attracted attention.

  For example, in the field where applications of three-dimensional optical recording media (three-dimensional multilayer optical memory) including composite metal nanoparticles and two-photon absorption materials are expected, recently, networks such as the Internet and high-definition TV have rapidly spread. is doing. In addition, HDTV (High Definition Television) will soon be broadcast, and there is an increasing demand for a large-capacity recording medium for recording image information of 50 GB or more, preferably 100 GB or more inexpensively and easily for consumer use. Furthermore, for business use such as computer backup use and broadcast backup use, an optical recording medium capable of recording large-capacity information of about 1 TB or more at high speed and at low cost is required. Under such circumstances, the conventional two-dimensional optical recording medium such as DVD ± R is about 25 GB at most even if the recording / reproducing wavelength is shortened due to the physical principle, and is sufficiently large enough to meet future demands. It cannot be said that capacity can be expected.

Under the circumstances as described above, a three-dimensional optical recording medium has been attracting attention as an ultimate high-density, high-capacity recording medium. Three-dimensional optical recording media can be recorded in dozens or hundreds of layers in the three-dimensional (film thickness) direction, resulting in tens or hundreds of times the ultra-high density and ultra-high capacity recording of conventional two-dimensional recording media. That is what we are trying to achieve.
In a three-dimensional optical recording medium using a two-photon absorption material, tens or hundreds of times of recording based on the physical principle described above, so-called bit recording is possible, and higher density recording is possible. From this, it can be said that the three-dimensional optical recording medium is an ultimate high-density, high-capacity optical recording medium.

In order to provide a three-dimensional optical recording medium, it is necessary to be able to access and write at an arbitrary place in the three-dimensional (film thickness) direction. As a means for this, a method using a two-photon absorption material and holography (interference) There is a method of using.
For example, as a three-dimensional original optical recording medium using a two-photon absorption material, a method of reading with fluorescence using a fluorescent substance for recording and reproduction (for example, see Patent Documents 8 and 9), absorption or fluorescence using a photochromic compound (For example, refer to Patent Documents 10 and 11) and the like have been proposed.

However, neither of the above-mentioned Patent Documents 8 and 9 describes a specific two-photon absorption material, and even an example of an abstractly presented two-photon absorption compound is a two-photon absorption compound with extremely low two-photon absorption efficiency. Is used.
Further, since the photochromic compounds used in Patent Documents 10 and 11 are reversible materials, there are problems in nondestructive reading, long-term storage stability, S / N ratio of reproduction, and the like, which are practical as optical recording media. It cannot be said that it is a certain method. In particular, in terms of non-destructive readout, long-term storage stability of recording, etc., it is preferable to reproduce by changing the reflectance (refractive index or absorptivity) or emission intensity using an irreversible material. There is no example that specifically discloses the absorbent material.

  In addition, a recording apparatus, a reproducing apparatus, a reading method, and the like that perform three-dimensional recording by refractive index modulation have been proposed, but there is no description of a method using a two-photon absorption three-dimensional optical recording material (for example, a patent) References 12 and 13).

Note that there is a difference in reducing power between the step of reducing the metal salt in the solution and the method of generating a rod-shaped metal nanorod by irradiating the solution obtained by scientifically reducing the metal salt (see, for example, Patent Document 14). A method of generating nano-sized metal fine particles using two large reducing agents (for example, see Patent Document 15) is disclosed. However, a larger surface plasmon enhancement field cannot be expected only with the configuration obtained by such a manufacturing method.
Also disclosed is a multiphoton absorption functional material in which fine particles of a metal that generates a plasmon enhancement field on a metal surface or fine particles that are at least partially coated with the metal are dispersed (see, for example, Patent Document 16). . It is an effective method for generating surface plasmon enhancement fields in bulk materials, but it can sensitize multiphoton absorption materials (eg, two-photon absorption materials) with high sensitivity or multiphoton absorption materials (eg, two-photon absorption materials). It is not enough to promote the reaction of the material).

  The present invention has been made in view of the above prior art, and features of anisotropically grown fine particles capable of tuning the resonance wavelength and features of adjacent fine particles capable of generating a stronger surface plasmon enhancement field (between adjacent fine particles). In addition to providing a composite metal nanoparticle having a large surface plasmon enhancement field due to a hot spot generated in a simple process, it is possible to provide a reproducible and low-cost composite metal nanoparticle with a simple process. A photon absorbing material and a multiphoton absorbing reaction aid are provided.

  As a result of intensive studies, the present inventors have found that the above problems can be solved by the inventions described in the following [1] to [11], and have reached the present invention. Hereinafter, the present invention will be specifically described.

  [1]: The above-mentioned problem is that a metal (noble metal) coated on the surface of a nanoparticle having shape anisotropy is capable of generating a plasmon enhancement field, and is a metal nobler than the base metal ( This is solved by a method for producing composite metal nanoparticles characterized in that a noble metal is substituted by a difference in ionization tendency in a solution containing noble metal ions.

[2]: In the method for producing a composite metal nanoparticle according to [1] above, a nanoparticle dispersion preparation step for forming a dispersion containing nanoparticles having the shape anisotropy;
A base metal-coated nanoparticle production step of coating a base metal on the nanoparticle surface having shape anisotropy in the dispersion;
A noble metal substitution step of substituting at least a part of the base metal coating the surface of the base metal-coated nanoparticles with a noble metal due to a difference in ionization tendency between the base metal and the noble metal in a solution containing the noble metal ions;
It is characterized by including.

  [3]: In the noble metal substitution step of the method for producing composite metal nanoparticles according to [2] above, the solution used in the base metal-coated nanoparticle production step is used as it is, and the solution contains the noble metal ions. It is characterized by performing substitution with a base metal.

  [4]: In the method for producing composite metal nanoparticles according to [2] or [3] above, after the base metal-coated nanoparticle production step, the surface of the base metal is treated with a silane coupling agent, At least a part of the noble metal is substituted.

  [5]: The method for producing composite metal nanoparticles according to any one of [1] to [4], wherein the nanoparticles having shape anisotropy are gold nanorods.

  [6]: In the method for producing composite metal nanoparticles according to any one of [1] to [5], the base metal coated on the surface of the nanoparticle having shape anisotropy is silver, and the base metal The precious metal that replaces at least a part is gold.

  [7] In the method for producing a composite metal nanoparticle according to [5] or [6] above, a nanoparticle dispersion preparation step for forming a dispersion containing nanoparticles having the shape anisotropy, and the dispersion A base metal-coated nanoparticle preparation step of coating a surface of a nanoparticle having shape anisotropy in a liquid with a base metal, and at least part of the base metal coating the surface of the base metal-coated nanoparticle in a solution containing ions of the noble metal A noble metal substitution step of substituting a noble metal due to a difference in ionization tendency of the base metal and the noble metal, and the dispersion in the base metal-coated nanoparticle production step includes gold nanorods, silver nitrate, ascorbic acid and amines, Silver is anisotropically grown on the gold nanorod surface by a reduction reaction of the dispersion.

  [8]: The method for producing a composite metal nanoparticle according to any one of [1] to [7], wherein a surface of the composite metal nanoparticle is covered with an insulating layer.

[9]: The above problem is a composite metal nanoparticle obtained by the production method according to any one of [1] to [8],
A composite characterized in that at least a part of a base metal coated on the surface of a nanoparticle having shape anisotropy is substituted with a metal (noble metal) nobler than the base metal capable of generating a plasmon enhancement field. Solved by metal nanoparticles.

  [10] The above-mentioned problem is solved by a multiphoton absorbing material comprising composite metal nanoparticles obtained by the production method according to any one of [1] to [8].

  [11]: The above-mentioned problem is solved by a multiphoton absorption reaction auxiliary agent comprising composite metal nanoparticles obtained by the production method according to any one of [1] to [8].

According to the present invention, a composite metal nanoparticle having both the characteristics of anisotropically grown fine particles capable of tuning the resonance wavelength and the characteristics of adjacent fine particles capable of generating a stronger surface plasmon enhancement field, in a simple process, It can be provided with good reproducibility and at low cost. That is, it is formed by replacing at least part of the base metal (base metal) film covering the surface of the nanoparticle (core particle) having shape anisotropy with the noble metal (precious metal: generating a plasmon enhancement field). A larger surface plasmon enhancement field generated between the separated particles (between adjacent fine particles: hot spots) can be used.
The plasmon enhancement field of the composite metal nanoparticle of the present invention sensitizes a multiphoton absorbing material (for example, a two-photon absorbing material) with high sensitivity or reacts a multiphoton absorbing material (for example, a two-photon absorbing material). Can be encouraged. In other words, since multiphoton absorption sensitivity (for example, two-photon absorption sensitivity) is higher than in the past, sensitization and reaction can be accelerated at high speed.
In addition, it is not necessary to increase the intensity of light applied to the multiphoton absorbing material, so that deterioration and destruction of the material can be suppressed, and adverse effects on the characteristics of other components in the material can also be suppressed. Since a small and inexpensive laser light source can be used as an excitation light source, it is possible to develop a practical application capable of mass production. Application fields include, for example, application to a three-dimensional multilayer optical memory, application to a material for optical modeling, application to a two-photon fluorescence microscope, and the like.
In the present invention, the dispersion in the base metal-coated nanoparticle production step contains gold nanorods, silver nitrate, ascorbic acid and amines, and silver is anisotropically grown on the gold nanorod surface by a reduction reaction of the dispersion. For example, silver can be selectively grown on a specific crystal plane of the gold nanorod as it is in a gold nanorod growth solution dispersed under a high-concentration surfactant. If at least a part of silver in such a silver-coated nanorod is replaced with a noble metal due to a difference in ionization tendency using a noble metal (for example, gold), a hot spot that generates a larger surface plasmon enhancement field (between adjacent fine particles) ) And can function as a photoreaction enhancement means that can tune the resonance wavelength over a wide wavelength range. If the composite metal nanoparticle and the multiphoton absorption material according to the present invention are used in combination, it is possible to solve various reactions requiring a highly sensitive photoreaction process by an inexpensive means.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system schematic diagram (a) and a schematic cross-sectional view (b) of a recording medium for explaining application of a multiphoton absorption material containing composite metal nanoparticles of the present invention to a three-dimensional recording medium. It is a conceptual diagram which shows the optical modeling system for demonstrating the application to the material for optical modeling of the multiphoton absorption material containing the composite metal nanoparticle (reaction adjuvant) of this invention. It is a conceptual diagram for demonstrating the application to the two-photon excitation laser scanning microscope (two-photon fluorescence microscope) of the multiphoton absorption material containing the composite metal nanoparticle of this invention.

As described above, the method for producing composite metal nanoparticles in the present invention can generate a plasmon enhancement field on at least a part of a base metal (base metal) coated on the surface of nanoparticles having shape anisotropy, In the solution containing ions of a metal (noble metal) that is nobler than the base metal, the noble metal is substituted by a difference in ionization tendency (the present invention [1]).
In addition, at least a part of a base metal (base metal) coated on the surface of the nanoparticle having shape anisotropy includes ions of a metal (noble metal) nobler than the base metal capable of generating a plasmon enhancement field. In the method for producing composite metal nanoparticles that are replaced with noble metals by the difference in ionization tendency in solution,
A nanoparticle dispersion preparing step of forming a dispersion containing nanoparticles having the shape anisotropy;
A base metal-coated nanoparticle production step of coating a base metal on the nanoparticle surface having shape anisotropy in the dispersion;
A noble metal substitution step of substituting at least a part of the base metal that coats the surface of the base metal-coated nanoparticles with a noble metal due to a difference in ionization tendency between the base metal and the noble metal in a solution containing ions of the noble metal. It is a characteristic (the present invention [2]).

  Around the metal nanoparticles, a localized plasmon enhancement field localized near the particle is generated. The enhancement of the localized plasmon enhancement field depends on the particle shape and metal type. For example, rod-shaped fine particles are known as nanoparticles having a large enhancement effect. The wavelength exhibiting the greatest enhancement of the rod-shaped metal fine particles is the resonance wavelength determined by the metal species and the aspect ratio. That is, starting from spherical fine particles, the resonance wavelength shifts to the longer wavelength side as the aspect ratio increases, and the intensity increases as compared with spherical fine particles. Therefore, in order to obtain metal fine particles exhibiting a high enhancement effect at a desired wavelength, it is important to select a material metal and an aspect ratio.

  Conventionally, for this purpose, gold nanorods have been used as a material having a uniform aspect ratio and particle size and high strength. In addition, it is aimed to obtain high-aspect-ratio nanoparticles of a wide range of metals with good reproducibility by performing crystal growth using nanoparticles that can selectively obtain a desired aspect ratio relatively easily. As a result, it has been studied to coat with dissimilar metals (isotropic growth / precipitation). However, the plasmon absorption of the coated metal is dominant only in the region where the film thickness of the coated metal is thick, and the particles are larger in the visible region than the core particles.

  In contrast to coating nanoparticles with dissimilar metals, separating the coated metals in islands provides a greater plasmon enhancement effect with minimal volume (between adjacent particles), and also suppresses visible light scattering sufficiently. The As a method for producing a coated metal having such a structure separated in an island shape, a deposition method has been studied so far, but it is difficult to form a configuration (adjacent fine particle configuration) separated in an island shape in the deposition method, An alternative method was needed. As a result of intensive studies by the present inventors, it has been found that partial substitution of the coated metal using the difference in ionization tendency as described above is more effective in place of the precipitation method.

As described above, according to the manufacturing method of the present invention, it is possible to produce an anisotropically grown fine particle that can tune the resonance wavelength, an optimal process for imparting shape anisotropy, and a stronger surface plasmon enhancement field. It is possible to obtain composite metal nanoparticles that can be used in a wide wavelength range and have a function as a high-intensity near-field generation source. .
According to the production method of the present invention, a wide range of materials can be selected, for example, if the metal coated with nanoparticles having shape anisotropy is silver, gold or platinum can be used as a metal that replaces at least a part of silver. Furthermore, if the surface of the nanoparticle having shape anisotropy is coated with a metal lower than silver, it can be used as a metal that replaces silver in addition to gold and platinum. In addition, a wide range of metal high aspect ratio nanoparticles can be obtained with good reproducibility.
That is, since the composite metal nanoparticles produced by the method of the present invention have a function of a near-field generation source that can be used in a wide wavelength range, a highly sensitive multiphoton absorption material and reaction aid can be obtained by using this. As a result, various applications utilizing the multiphoton process become possible.

Nanoparticles (core particles) having shape anisotropy are not particularly limited as long as they have shape anisotropy, but in order to reduce light scattering loss, they must be smaller than the target wavelength. is important. In addition, the selection of the aspect ratio is important for enhancing the interaction with light. Gold nanorods are known as a material system that is fine and can easily select an aspect ratio.
Gold nanorods are preferably used as the nanoparticles having the shape anisotropy (core particles) in the method for producing composite metal nanoparticles of the present invention (the present invention [5]).
Due to the characteristics of gold nanorods that can easily obtain fine particles with uniform aspect ratio, it is possible to mass-produce a plasmon enhancement field optimized for the excitation wavelength and having a large enhancement intensity at low cost. In addition, by using this enhanced field, it is possible to provide a highly sensitive multiphoton absorption process at low cost.

  In addition, the base metal (base metal) film covering the nanoparticle (core particle) having shape anisotropy can be any metal as long as it does not prevent substitution due to the difference in ionization tendency due to the formation of a passive film. Although it can be used, it goes without saying that it is necessary to form a thin film on the gold nanorod and to be a metal that is baser than the noble metal that generates the plasmon enhancement field. An example of such a metal is silver.

In the step of the method for producing composite metal nanoparticles of the present invention, a noble metal (noble metal: for example, a substitute) is added to the dispersion (typically an aqueous solution) containing the base metal-coated nanoparticles obtained in the base metal-coated nanoparticle production step. , Gold) ions (for example, chloroauric acid aqueous solution) are added, and the reaction proceeds under acidity, and the plasmon has a structure in which the noble metal is separated into islands while replacing the base metal (adjacent fine particle configuration). An enhancement field is generated. Base metal-coated nanoparticles in which the core particle surface, which is the previous stage of the composite metal nanoparticles as the final form, is coated with a base metal also has an influence on the controllability of the shape and particle size of the particles by the coating metal. The inventors have found that silver is effective as a coating metal, and that gold is effective as a replacement metal to obtain a desired shape.
That is, in the present invention, it is preferable to use silver as a base metal coated on the surface of the nanoparticle having shape anisotropy (for example, a gold nanorod) and use gold as a noble metal replacing at least a part of the base metal. Yes (present invention [6]).
With such a configuration, in addition to the function and effect of the present invention [1], a large increase in strength can be stably exhibited over a long period of time due to the chemical and physical stability unique to noble metals. Therefore, it is possible to provide a stable and efficient photoreaction process.

  In the base metal-coated nanoparticle preparation step, silver can be anisotropically grown on the gold nanorod surface by a reduction reaction of a dispersion containing gold nanorods, silver nitrate, ascorbic acid and amines (this invention [7] ).

Further, in the noble metal substitution step (substitution step), the solution used in the base metal-coated nanoparticle production step is used as it is (the solution in which the base metal-coated nanoparticles before the growth are grown), and the solution contains the noble metal ions. Thus, substitution with a base metal can be performed (the present invention [3]).
Simplified process by controlling the rate of the substitution reaction based on the difference in ionization tendency between the base metal and the noble metal in the substitution process by the dispersant layer that controls the dispersibility of the base metal-coated nanoparticles. Thus, a hot spot can be generated at a low cost due to the configuration of the adjacent fine particles, and a high-intensity enhancement field can be provided. Therefore, it is possible to provide an efficient photoreaction process for a wider range of reaction conditions and applied products.

In addition, after the base metal-coated nanoparticle production step, the surface of the base metal is treated with a silane coupling agent, and at least a part of the base metal can be replaced with the noble metal (the present invention [4]). .
The dispersant layer covering the base metal-coated nanoparticles before the substitution generally has a composition in which priority is given to characteristics as a growth field of the base metal-coated nanoparticles. By covering the surface of the base metal with a silane coupling agent, the insulation between the fine particles after the noble metal substitution is given, so the distance between the fine particles after the noble metal substitution can be reduced and a larger plasmon enhancement field can be generated. It becomes. In addition, composite metal nanoparticles with substituted metal particles spaced apart at multiple sites can be obtained with good reproducibility by intentionally forming sites with different substitution efficiencies on the surface of the base metal-coated nanoparticles by silane coupling agent treatment. It is done.
In addition, in the silane coupling agent treatment, the coating treatment can be roughened by intentionally diluting the treatment concentration of the silane coupling agent, but even if the entire surface of the base metal is covered with the silane coupling agent, So-called ion mass transfer in the substitution reaction between the base metal and the noble metal is possible, and the composite metal nanoparticles of the present invention are obtained.

Moreover, it is preferable that the surface of the composite metal nanoparticle of this invention is coat | covered with the insulating layer (this invention [8]).
Since the surface of the composite metal nanoparticle is covered with an insulating layer, the composite metal nanoparticle and the multiphoton absorbing material are separated, and the energy absorbed by the multiphoton absorbing material is used for the reaction without being deactivated. Therefore, the reaction system becomes a high yield. That is, by coating the surface of the composite metal nanoparticles with an insulating layer, the reaction efficiency of the multiphoton absorbing material is reduced while the transmission of light energy is maintained (decrease due to quenching due to leakage of excited reaction carriers). It is possible to provide an enhanced field with high sensitivity and high efficiency. For this reason, it is possible to provide an efficient photoreaction process for a wider range of reaction conditions and applied products.

  The insulating layer described here may be, for example, a relatively thin film such as an adsorption film of a silane coupling agent, or a monomolecular film depending on the case, and a metal oxide film or the like functions as an insulating layer. Anything is acceptable. Furthermore, the metal film remaining without being replaced may be oxidized to form an insulating film. However, the insulating film described here does not need to be completely insulated, and is intended to prevent inactivation by absorbing the energy absorbed by the multiphoton absorption material into the composite metal nanoparticles, If it meets this purpose, it is within the scope of the configuration of the present invention.

A composite in which at least a part of the base metal coated on the surface of the nanoparticle having shape anisotropy is replaced with a metal (noble metal) nobler than the base metal capable of generating a plasmon enhancement field by the manufacturing method. Metal nanoparticles are obtained (the present invention [9]).
The composite metal nanoparticles of the present invention have both the characteristics of anisotropically grown fine particles that can tune the resonance wavelength and the characteristics of adjacent fine particles that can generate a stronger surface plasmon enhancement field. If the multi-photon absorption material (for example, two-photon absorption material) is included, the plasmon enhancement field obtained by the composite metal nanoparticles causes a reaction similar to that of a higher intensity excitation light (high sensitivity) In addition, if the multiphoton absorption reaction assistant containing the composite metal nanoparticles is used, the reaction of the multiphoton absorption material (for example, a two-photon absorption material) can be promoted in the same manner. Can be induced with high sensitivity (the present invention [10, 11]).

A multiphoton absorbing material including a composite metal nanoparticle having a plasmon-enhanced field as described above or a material including a reaction aid is provided as a stable dispersion solution and a mixture that can be applied or cast, thereby allowing multiphoton absorption. By lowering the reaction threshold value of the reaction, various unprecedented applications are possible.
The application will be exemplified below, but a two-photon absorption material will be mainly described as a representative example of the multiphoton absorption material.

[Application to three-dimensional multilayer optical memory using two-photon absorption material containing composite metal nanoparticles]
First, application of the multiphoton absorption material (two-photon absorption material) containing the composite metal nanoparticles of the present invention to a three-dimensional recording medium (three-dimensional multilayer optical memory) will be described.

  As described in the background art, a reaction is caused by using excitation energy obtained by non-resonant two-photon absorption, and as a result, light emission when light is irradiated at the laser focus (recording) part and non-focus (non-recording) part. If the intensity can be modulated by a method that cannot be rewritten, the emission intensity can be modulated at an extremely high spatial resolution at any location in the three-dimensional space, leading to a three-dimensional optical recording medium that is considered the ultimate high-density recording medium. Can be applied. Furthermore, non-destructive reading is possible, and since it is an irreversible material, good storage stability can be expected and it is practical.

  However, the currently available two-photon absorption compounds have a low two-photon absorption capability, so that a very high-power laser is required as a light source and a long recording time is required. In particular, for use in three-dimensional optical recording media, construction of a two-photon absorption three-dimensional optical recording material that can perform high-sensitivity, high-luminance recording by two-photon absorption to achieve a fast transfer rate. Is essential. For that purpose, two-photon absorption light (two-photon absorption compound) that can absorb two-photons with high efficiency and generate an excited state, and two-photon absorption light by some method using the excited state of the two-photon absorption compound. A material containing a recording component capable of efficiently forming a difference in light emitting ability of a recording material is promising, but such a material has hardly been disclosed so far, and the construction of such a material has been desired.

  That is, by using a highly sensitive two-photon absorption material containing the composite metal nanoparticles of the present invention, after recording using the two-photon absorption, the recording material is irradiated with light and the emission intensity is increased. It is possible to reproduce by detecting a difference or detecting a change in reflectance due to a change in refractive index. That is, by using a highly sensitive two-photon absorption material containing the composite metal nanoparticles of the present invention, a two-photon absorption optical recording / reproducing method and a two-photon absorption optical recording material capable of such recording / reproduction are provided. be able to. Furthermore, it is possible to provide a two-photon absorption three-dimensional optical recording material, a two-photon absorption three-dimensional optical recording method and a reproducing method using them.

  The highly sensitive two-photon absorption material containing the composite metal nanoparticles of the present invention can be applied directly on a substrate by using a spin coater, roll coater, bar coater, or the like, or can be cast as a film and then used in a normal method. Can be laminated on a substrate, and a two-photon absorption optical recording material can be obtained by these molding methods.

As used herein, “substrate” means any natural or synthetic support, preferably one that can exist in the form of a flexible or rigid film, sheet or plate.
Preferred substrates include polyethylene terephthalate, resin-primed polyethylene terephthalate, polyethylene terephthalate treated with flame or electrostatic discharge, cellulose acetate, polycarbonate, polymethyl methacrylate, polyester, polyvinyl alcohol, glass and the like. Further, the substrate may be provided with tracking guide grooves and address information in advance.
The solvent used for coating in the molding method can be removed by evaporation at the time of drying. Heating or reduced pressure may be used for evaporation removal.

  Further, a protective layer (intermediate layer) for blocking oxygen and preventing interlayer crosstalk may be formed on the two-photon absorption optical recording material. Protective layer (intermediate layer) is made of electrostatic adhesion or extrusion of plastic film or plate such as polyolefin such as polypropylene and polyethylene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyethylene terephthalate or cellophane film. They may be bonded together by lamination or the like used, or the polymer solution may be applied.

Further, a glass plate may be bonded. Further, an adhesive or a liquid substance may be present between the protective layer and the photosensitive film and / or between the base material and the photosensitive film in order to improve airtightness. Further, the protective layer (intermediate layer) between the photosensitive films may be provided with tracking guide grooves and address information in advance.
By configuring the two-photon absorption optical recording material as described above as a multilayer, a three-dimensional recording medium (three-dimensional multilayer optical recording medium) is provided.

  By focusing on an arbitrary layer of the above-described three-dimensional multilayer optical recording medium (an arbitrary layer of the two-photon absorption optical recording material) and performing recording / reproducing, it functions as a three-dimensional recording medium. Further, even if the layers are not separated by a protective layer (intermediate layer), three-dimensional recording in the depth direction is possible from the two-photon absorption dye characteristics.

Specific examples of preferred embodiments of the three-dimensional multilayer optical recording medium (three-dimensional multilayer optical memory) are shown below, but the present invention is not limited to these embodiments, and three-dimensional recording (recording in the plane and film thickness direction) is performed. Any other structure may be used as long as the structure is possible.
A schematic diagram of a recording / reproducing system of a three-dimensional multilayer optical memory is shown in FIG. 1A, and a schematic sectional view of a recording medium is shown in FIG.

  The outline of the recording method will be described with reference to FIG. 1B, which is a schematic system diagram of FIG. 1A and a schematic sectional view of the recording medium. The recording laser beam 13 from the recording laser light source 1 (for example, a high-power pulse laser light source) is focused into the three-dimensional recording medium 6 by the objective lens 5. At the focus point, recording is performed by two-photon absorption. However, at positions other than the focus point, as described above, the light irradiation power is low, and recording is not performed due to the square effect. That is, selective recording is possible.

  Next, as a reproduction method, light from the reproduction laser light source 2 (not as high power as recording light but also a semiconductor laser can be used) is focused in a three-dimensional medium. Signal light is generated from each layer. By detecting the signal light with a point detector composed of a pinhole 3 and a detector 4, signals from a specific layer can be selectively selected using the principle of a confocal microscope. To detect. With the above configuration, the three-dimensional recording / reproducing functions.

  In the three-dimensional recording medium 6 of FIG. 1B, a two-photon absorption light material (a highly sensitive two-photon absorption material containing the composite metal nanoparticles of the present invention is applied to a substrate A (7) which is a flat support. Recording layer 9 using (containing) and an intermediate layer (protective layer) 12 for preventing crosstalk are alternately laminated by 50 layers, and each layer is formed by spin coating. The thickness of the recording layer is preferably 0.01 to 0.5 μm, and the thickness of the intermediate layer is preferably 0.1 μm to 5 μm. With this structure, the disk size is the same as that of currently popular CD / DVD, and the terabyte class Can be realized. Furthermore, a reflection layer (8) made of the same substrate B as the substrate A (7) or a high reflectance material is formed by a data reproduction method (transmission / or reflection type). In FIG. 1, reference numeral 10 denotes a recording bit, and reference numeral 11 denotes a multilayer disk.

A single beam is used at the time of recording in the three-dimensional multilayer optical memory, and in this case, ultrashort pulse light on the order of femtoseconds can be used. At the time of reproduction, it is also possible to use a light having a wavelength different from that of the beam used for data recording or the same wavelength with a low output. Recording and playback can be performed in either bit units or page units, and parallel recording / playback using a surface light source, a two-dimensional detector, or the like is effective in increasing the transfer rate.
Note that a three-dimensional multilayer optical memory formed in the same manner according to the present invention may have a card shape, a plate shape, a tape shape, a drum shape, or the like.

[Application to stereolithography materials using two-photon absorption materials containing composite metal nanoparticles]
Next, application of the multiphoton absorption material (two-photon absorption material) containing the composite metal nanoparticles (reaction aid) of the present invention to a material for optical modeling will be described.

The optical modeling using the material for optical modeling will be described with reference to an apparatus (optical modeling system) for the two-photon optical modeling method shown in the conceptual diagram of FIG.
In the apparatus shown in FIG. 2, the light from the light source 1 of the near-infrared pulsed laser beam having transparency with respect to the photocurable resin liquid 9 passes through the mirror scanner 5, and then the photocurable resin liquid is used using a lens. 9 is focused, scanned with a laser spot, and induced two-photon absorption to cure the resin only near the focal point to form an arbitrary three-dimensional structure. That is, the optical modeling is performed by the two-photon optical modeling method (two-photon micro optical modeling method).

  Here, the photocurable resin liquid 9 is a high-sensitivity light for two-photon photofabrication that includes the composite metal nanoparticles (reaction aid) of the present invention and a two-photon absorption material (such as a polymerization initiator or a photosensitizer). It is a curable resin. The photocurable resin for two-photon stereolithography is a resin that undergoes a two-photon polymerization reaction when irradiated with light and changes from a liquid to a solid, as will be described later.

  Specifically, the pulsed laser beam is condensed with a lens, and a region with high photon density is formed in the vicinity of the focal point. At this time, since the total number of photons passing through each cross section of the beam is constant, when the beam is scanned two-dimensionally within the focal plane, the total light intensity in each cross section is constant. However, since the probability of occurrence of two-photon absorption is proportional to the square of the light intensity, a region where the generation of two-photon absorption is high is formed only near the condensing point where the light intensity is high.

Thus, by condensing the pulsed laser light with the lens and inducing two-photon absorption, it is possible to limit the light absorption near the condensing point and to cure the resin in a pinpoint manner. The focusing point can be freely moved in the photocurable resin liquid by the Z stage 6 and the galvanometer mirror, so that the desired three-dimensional workpiece (optical modeling object 10) can be freely formed in the photocurable resin liquid. can do.
In FIG. 2, reference numeral 3 denotes a shutter for temporally controlling the amount of transmitted light, reference numeral 4 denotes an ND filter, reference numeral 7 denotes a lens as a condensing means, and reference numeral 8 denotes a computer.

The features of the two-photon stereolithography include the following items.
(1) Processing resolution exceeding the diffraction limit: Processing resolution exceeding the diffraction limit of light can be realized by the non-linearity of the two-photon absorption with respect to the light intensity.
(2) Ultra-high speed modeling: When two-photon absorption is used, the photo-curing resin does not cure in principle in a region other than the focal point. For this reason, the light intensity to be irradiated can be increased, and the beam scanning speed can be increased. For this reason, modeling speed can be improved about 10 times.
(3) Three-dimensional processing: The photocurable resin is transparent to near-infrared light that induces two-photon absorption. Therefore, even when the focused light is condensed deeply into the resin, internal curing is possible. In the conventional method (SIH), when the beam is condensed deeply, the light intensity at the condensing point is reduced by light absorption, and the internal hardening becomes difficult. In the present invention, these problems are surely solved. be able to.
(4) High yield: In the conventional method, there is a problem that the molded object is damaged or deformed due to the viscosity or surface tension of the resin. However, in this method, the problem is solved because the modeling is performed inside the resin.
(5) Application to mass production: By using ultra-high-speed modeling, it is possible to manufacture a large number of parts or movable mechanisms continuously in a short time.

  As described above, the photocurable resin for two-photon photofabrication is a highly sensitive two-photon absorption material containing the composite metal nanoparticles of the present invention, causing a two-photon polymerization reaction by irradiating light, A resin that changes from liquid to solid. The main components are a resin component consisting of an oligomer and a reactive diluent and a photopolymerization initiator (including a photosensitizing material as required). An oligomer is a polymer having a degree of polymerization of about 2 to 20, and has a large number of reactive groups at its ends. Furthermore, a reactive diluent is added to adjust viscosity, curability and the like.

  When light is irradiated, a plasmon-enhanced field is generated on the surface of the composite metal nanoparticle, and the polymerization initiator or photosensitizing material absorbs the irradiation light enhanced by this plasmon-enhanced field directly from the polymerization initiator. Alternatively, reactive species are generated through the photosensitizing material and react with the reactive group of the oligomer or reactive diluent to initiate polymerization. Thereafter, a chain polymerization reaction occurs between them to form a three-dimensional cross-link, and the solid resin is changed to a solid resin having a three-dimensional network structure in a short time.

  Photocurable resins are used in fields such as photocurable inks, photoadhesives, and layered three-dimensional modeling, and resins having various characteristics have been developed. In particular, in layered three-dimensional modeling, it is important that (a) the reactivity is good, (b) the deposition shrinkage during curing is small, (c) the mechanical properties after curing are excellent, etc. .

  These characteristics are equally important in this method. Therefore, resins developed for layered three-dimensional modeling that have two-photon absorption characteristics are also used as photocurable resins for two-photon photomolding in this method. Can be used. As specific examples, acrylate-based and epoxy-based photocurable resins are often used, and urethane acrylate-based photocurable resins are particularly preferable.

  As a technique related to the optical shaping in the present invention, for example, a technique in which pulsed laser light is subjected to interference exposure without using a mask on the surface of the photosensitive polymer film containing the composite metal nanoparticles of the present invention can be applied. The pulse laser beam in this case is a pulse laser beam in a wavelength region that exhibits a photosensitive function through the plasmon enhancement field effect of the composite metal nanoparticles in the photosensitive polymer film and the excitation action thereby. is important.

Therefore, the wavelength region of the pulsed laser light can be appropriately selected according to the type of the photosensitive polymer or the type of group or part that exhibits the photosensitive function in the photosensitive polymer. In particular, even when the wavelength of the pulsed laser light emitted from the light source is not in a wavelength region that causes the photosensitive polymer film to exhibit a photosensitive function, by using a multiphoton absorption process upon irradiation with the pulsed laser light, The photosensitive polymer film can exhibit a photosensitive function.
An example of a technique for performing interference exposure on the surface of the photosensitive polymer film without using a mask with a pulsed laser beam is an example described in JP-A-2005-134873.

  Specifically, when the pulsed laser light emitted from the light source is condensed and irradiated with the condensed pulsed laser light, multiphoton absorption (eg, two-photon absorption, three-photon absorption, four-photon absorption, Absorption, five-photon absorption, etc.), and the wavelength of the pulsed laser light emitted from the light source does not reach the photosensitive polymer film even if it is not in the wavelength region where the photosensitive polymer film exhibits the photosensitive function. Was irradiated with a pulsed laser beam in a wavelength region that substantially exerted a photosensitive function on the photosensitive polymer film through the plasmon enhanced field effect of the composite metal nanoparticles in the polymer film and the excitation action thereby It will be.

  As described above, the pulsed laser beam for interference exposure may be substantially a pulsed laser beam having a wavelength region that allows the photosensitive polymer film to exhibit the photosensitive function, and the wavelength is appropriately selected depending on the irradiation conditions. can do. For example, the high-efficiency two-photon absorption material containing the composite metal nanoparticles of the present invention is used as a photosensitizer, dispersed in an ultraviolet curable resin or the like to form a photosensitive solid, and the two-photon absorption ability of the photosensitive solid is used. Thus, it is possible to obtain an ultra-precise three-dimensional structure using the property that only the focal spot is cured.

  Examples of the two-photon absorption material in the present invention include a two-photon absorption polymerization initiator and a two-photon absorption photosensitizing material as described above. By containing composite metal nanoparticles, a conventional two-photon absorption material (two Compared to photon absorption polymerization initiators or two-photon absorption photosensitizers), the two-photon absorption sensitivity is high, so high-speed modeling is possible, and a compact and inexpensive laser light source can be used as an excitation light source, resulting in mass production. Deployment to possible practical applications becomes possible.

[Application to two-photon fluorescence microscope using two-photon absorption material containing composite metal nanoparticles]
Next, application of the two-photon absorption material containing the composite metal nanoparticles of the present invention to a two-photon fluorescence microscope will be described.

  A two-photon excitation laser scanning microscope (two-photon fluorescence microscope) is an image obtained by condensing and scanning a near-infrared pulse laser on a specimen surface and detecting fluorescence generated by excitation by two-photon absorption there. It is a microscope to obtain The basic diagram of the two-photon excitation laser scanning microscope (two-photon fluorescence microscope) is shown in the conceptual diagram of FIG.

  The two-photon fluorescence microscope shown in FIG. 3 includes a laser light source 1 that emits sub-picosecond monochromatic coherent light pulses in the near-infrared region, a light beam conversion optical system 2 that changes a light beam from the laser light source to a desired size, and a light beam conversion optics. A scanning optical system 3 for condensing and scanning the light beam converted by the system on the image plane of the objective lens, an objective lens system 4 for projecting the collected converted light beam on the sample surface 5, and a photodetector 7. I have.

  The two-photon absorption fluorescent material (the composite metal nanoparticle in the sample) is collected in the sample by focusing the pulse laser beam through the dichroic mirror 6 and the light beam conversion optical system and the objective lens system and focusing on the sample surface. The two-photon absorption material contained) causes two-photon absorption to generate induced fluorescence. The sample surface is scanned with a laser beam, the fluorescence intensity at each location is detected by a photodetection device such as the photodetector 7, and a three-dimensional fluorescence image is plotted by a computer based on the obtained positional information. Is obtained. As the scanning mechanism, for example, a laser beam may be scanned using a movable mirror such as a galvanometer mirror, or a sample including a two-photon absorption material placed on a stage may be moved.

  With such a configuration, it is possible to obtain high resolution in the optical axis direction by utilizing the nonlinear effect of two-photon absorption itself. In addition, if a confocal pinhole plate is used, higher resolution (both in-plane and in the optical axis direction) can be obtained.

  Fluorescent dyes for two-photon fluorescence microscopes are used by staining a specimen with the fluorescent dye or by dispersing the fluorescent dye in the specimen, and are used not only for industrial applications but also for three-dimensional image micro-imaging of biological cells. Therefore, a compound having a high two-photon absorption cross section is desired.

As a photon fluorescence microscope, the example described in Unexamined-Japanese-Patent No. 9-230246 is mentioned, for example.
The scanning fluorescence microscope in this case includes a laser irradiation optical system that emits collimated light expanded to a desired size, and a substrate on which a plurality of condensing elements are formed. A beam splitter that transmits the long wavelength and reflects the short wavelength is disposed between the objective lens system and the substrate on which the light condensing element is formed, and is arranged so as to coincide with the image position of the objective lens system. The fluorescent light is generated by multiphoton absorption on the specimen surface. With such a configuration, it is possible to obtain high resolution in the optical axis direction by utilizing the nonlinear effect of multiphoton absorption itself. In addition, if a confocal pinhole plate is used, higher resolution (both in-plane and in the optical axis direction) can be obtained. Such a two-photon optical element uses, as the optical element, a solid material dispersed in a material having a high two-photon absorption ability, a thin film, or a photocurable resin of the present invention, just like the above-described light control element. Is possible.

  The two-photon absorption material in the present invention can be used as a two-photon absorption fluorescent material for a two-photon excitation laser scanning microscope. Compared to conventional two-photon absorption fluorescent materials, it has a large two-photon absorption cross-sectional area, so that it exhibits high two-photon absorption characteristics at a low concentration. Therefore, according to the present invention, not only a highly sensitive two-photon absorption material can be obtained, but there is no need to increase the intensity of light applied to the material, and deterioration and destruction of the material can be suppressed. The adverse effect on the properties of other components can also be reduced.

  EXAMPLES Hereinafter, although an Example is given and this invention is further demonstrated, each Example is an example of a structure of this invention, and this invention is not limited to these Examples.

Example 1
First, gold nanorods were prepared by the following photoreduction method, and then the surface was coated with silver to prepare base metal-coated nanoparticles. Then, the silver which coat | covers the surface of a base metal coating nanoparticle was partially substituted with gold | metal | money using the difference in ionization tendency, and the composite metal nanoparticle of this invention was created.

[Preparation of gold nanorod dispersion: nanoparticle dispersion preparation process]
As a raw material solution, CTAB (cetyltrimethylammonium bromide) aqueous solution 0.18 (mol / l) 70 ml, cyclohexane 0.36 ml, acetone 1 ml, silver nitrate aqueous solution 0.01 (mol / l) 1.5 ml were added and stirred with a magnetic stirrer. . Furthermore, after adding 2 ml of 0.024 (mol / l) chloroauric acid solution, 0.4 ml of 0.1 (mol / l) aqueous ascorbic acid solution was added to confirm that the color of the chloroauric acid solution disappeared. .

  Next, the liquid for mixing was transferred to a petri dish having a diameter of 100 mm, and ultraviolet rays of 254 nm were irradiated for about 20 minutes with a low-pressure mercury lamp (manufactured by ASONE, SUV-16). This process completed a stable dispersion of gold nanorods. As a result of observation with a transmission electron microscope, the average particle shape of the obtained gold nanorods was 50 nm in major axis and 12 nm in minor axis, and it was confirmed that the particles had shape anisotropy.

  In this example, gold nanorods synthesized by a photoreduction method are shown, but it goes without saying that gold nanorods produced by various synthesis methods such as electrolysis and growth from seed particles can be used. Also, by changing the growth conditions, it is possible to easily obtain gold nanorods having different particle shapes, for example, aspect ratios.

[Preparation of the base metal-coated nanoparticle 1 in which the surface of the gold nanorod is coated with silver: base metal-coated nanoparticle preparation process]
To 6 ml of the completed gold nanorod dispersion, 10 μl of silver nitrate aqueous solution 0.05 (mol / l) and 20 μl of polyethyleneimine (average molecular weight 600) were added and stirred. About 2 hours later, a change in absorbance (spectral shift) of the gold nanorod dispersion was observed, confirming that the gold nanorod surface was coated with silver.
In this example, ascorbic acid was used as a reducing agent at the gold nanorod synthesis stage, and the reaction proceeded without additional charging. Moreover, instead of amines, amines present as impurities of materials having amino groups were used.

[Preparation of composite metal nanoparticle 1 (replace at least a part of silver covering the surface of base metal-coated nanoparticle 1 with gold capable of generating a plasmon enhancement field): noble metal substitution step]
7 ml of an aqueous chloroauric acid solution 0.05 (mol / l) was added to 5 ml of the silver-coated base metal-coated nanoparticle 1 dispersion prepared above and stirred. After about 3 hours, the spectral shift was observed again, confirming that some of the silver was partially substituted with gold.

[Evaluation]
The following evaluation solution (dispersion) is prepared by mixing the composite metal nanoparticles 1 in which a part of silver covering the surface of the base metal-coated nanoparticles 1 created above is partially substituted with gold and the two-photon fluorescent dye. Photon fluorescence measurement was performed.
<Preparation of evaluation solution>
To 2 ml of the composite metal nanoparticle 1 dispersion, 1 vol% 4 ml of an acetone solution of dodecanethiol as a surfactant was added and stirred, and further 4 ml of cyclohexane was added and left standing. The composite metal nanoparticles 1 were stably dispersed in cyclohexane. This and a two-photon fluorescent dye represented by the following structural formula (1) were mixed to prepare an evaluation solution.

<Two-photon fluorescence measurement>
A mixed dispersion of the composite metal nanoparticles 1 and the two-photon fluorescent dye was put into an optical cell having an optical path length of 1 mm to obtain a measurement sample.
An infrared femtosecond laser, Spectra Physics MaiTai (wavelength 780 nm) was used as the two-photon excitation light source, and the condensing points were connected to the mixed solution with a condensing lens having a focal length of 100 mm, and fluorescence of two-photon excitation was measured. .

As a result of measuring the evaluation solution, when the excitation light intensity was doubled, a square effect in which the fluorescence intensity was quadrupled was observed, and it was confirmed to be two-photon absorption fluorescence.
Regarding the evaluation solution in which the composite metal nanoparticle 1 and the two-photon fluorescent dye are mixed, the enhancement of two-photon fluorescence is shown in Table 1 below (the excitation light intensity is an average output of 80 mW).
The evaluation of the enhancement is based on the comparison with the two-photon fluorescent dye solution shown in Comparative Example 1 described later. The meanings of the symbols in the evaluation are as follows.
◎: Especially markedly enhanced ○: Significantly enhanced △: Enhanced one ▲: Enhancement was observed but strength was low

(Example 2)
First, gold nanorods were prepared by the chemical reduction method shown below, and then the surface was coated with silver to prepare base metal-coated nanoparticles. Then, the silver which coat | covers the surface of a base metal coating nanoparticle was partially substituted with gold | metal | money using the difference in ionization tendency, and the composite metal nanoparticle of this invention was created.

[Preparation of gold nanorod dispersion: nanoparticle dispersion preparation process]
As a raw material solution, CTAB (cetyltrimethylammonium bromide) aqueous solution 0.18 (mol / l) 70 ml, cyclohexane 0.36 ml, acetone 1 ml, silver nitrate aqueous solution 0.01 (mol / l) 1.5 ml were added and stirred with a magnetic stirrer. . Furthermore, after adding 2 ml of 0.024 (mol / l) chloroauric acid solution, 0.4 ml of 0.01 (mol / l) sodium borohydride aqueous solution and 0.02 ml of triethylamine were added, and stirring was stopped. And left for 48 hours to complete a gold nanorod dispersion.
As a result of observation by a transmission electron microscope, the average particle shape of the obtained gold nanorods was confirmed to be particles having a major axis of 110 nm and a minor axis of 25 nm, and having shape anisotropy.

[Preparation of base metal-coated nanoparticles 2 with silver coated on the surface of gold nanorods: Base metal-coated nanoparticle preparation process]
To 6 ml of the finished gold nanorod dispersion, 0.05 μl of silver nitrate aqueous solution, 20 μl of butylamine, and 20 μl of ascorbic acid aqueous solution 0.1 (mol / l) were added and stirred. About 2 hours later, a change in absorbance (spectrum shift) of the gold nanorod dispersion was observed, and it was confirmed that silver was grown and coated on the gold nanorod surface.

[Preparation of composite metal nanoparticles 2 (at least a part of silver covering the surface of the base metal-coated nanoparticles 2 is replaced by gold capable of generating a plasmon enhancement field): noble metal replacement step]
To 5 ml of the completed silver-coated composite metal nanorod dispersion, 7 ml of 0.05 (mol / l) chloroauric acid aqueous solution was added and stirred. After about 3 hours, the spectral shift was observed again, confirming that a part of silver was partially substituted with gold.

[Evaluation]
An evaluation solution (dispersion) in which the composite metal nanoparticle 2 in which a part of silver covering the surface of the base metal-coated nanoparticle 2 created above is partially substituted with gold and the two-photon fluorescent dye is mixed is prepared and carried out. Evaluation was carried out in the same manner as the two-photon fluorescence measurement in Example 1. The enhancement of two-photon fluorescence is shown in Table 1 below.

(Comparative Example 1)
The gold nanorods prepared in Example 2 (obtained as a gold nanorod dispersion) were used as the nanoparticles of Comparative Example 1 (gold nanorods without a coating treatment or the like).
[Evaluation]
An evaluation solution (dispersion) in which the dispersion containing the nanoparticles of Comparative Example 1 (gold nanorod dispersion) and the two-photon fluorescent dye are mixed is prepared and evaluated in the same manner as the two-photon fluorescence measurement of Example 1. It was. The enhancement of two-photon fluorescence is shown in Table 1 below.

(Comparative Example 2)
The base metal-coated nanoparticles 2 (obtained as a silver-coated gold nanorod dispersion) prepared in Example 2 were used as the nanoparticles of Comparative Example 2.
[Evaluation]
An evaluation solution (dispersion) in which the dispersion containing the nanoparticles of Comparative Example 2 (silver-coated gold nanorod dispersion) and the two-photon fluorescent dye are mixed is prepared and evaluated in the same manner as the two-photon fluorescence measurement of Example 1. Went. The enhancement of two-photon fluorescence is shown in Table 1 below.

(Example 3)
To 3 ml of the dispersion containing composite metal nanoparticles 2 prepared in Example 2, 5 vol% of 3-aminopropylethyldiethoxysilane in acetone and 0.5 ml were added and heat-treated at 80 ° C. for 2 hours to coat with anisotropic silver A SiO ₂ film was formed on the gold nanorod surface (composite metal nanoparticles 3 coated with an insulating layer).

[Evaluation]
An evaluation solution (dispersion) in which the composite metal nanoparticles 3 coated with the insulating layer prepared above and the two-photon fluorescent dye were mixed was prepared and evaluated in the same manner as the two-photon fluorescence measurement of Example 1. . The enhancement of two-photon fluorescence is shown in Table 1 below.

  As shown in Table 1, a composite metal nanoparticle [base metal-coated nanoparticle (silver-coated nanoparticle) having the structure of the present invention was prepared by comparing two-photon excitation fluorescence light amount using a gold nanorod having substantially the same resonance wavelength. Nanoparticles in which at least a part of the base metal (silver) is partially substituted with noble metal (gold)] have confirmed a large plasmon enhancing effect. In addition, it was confirmed that a further increase in strength was exhibited by providing an insulating layer on the surface of the composite metal nanoparticles.

  According to the present invention, using a stronger surface plasmon enhancement field of a composite metal nanoparticle partially substituted with a noble metal that generates a plasmon enhancement field, the multiphoton absorption material can be sensitized with high sensitivity. The reaction of the multiphoton absorbing material can be promoted, and can be applied to various application fields, for example, application to a three-dimensional multilayer optical memory, application to an optical modeling material, application to a two-photon fluorescence microscope. Moreover, there is an advantage that a small and inexpensive laser light source can be used.

(Reference in FIG. 1)
DESCRIPTION OF SYMBOLS 1 Recording laser light source 2 Reproducing laser light source 3 Pinhole 4 Detector 5 Objective lens 6 Three-dimensional recording medium 7 Substrate A
8 Substrate B or reflective layer 9 Recording layer 10 Recording bit 11 Multilayer disc 12 Intermediate layer (protective layer)
13 Recording laser beam (reference numeral in FIG. 2)
DESCRIPTION OF SYMBOLS 1 Light source of near-infrared pulsed laser light having transparency with respect to light curable resin 3 Shutter for temporally controlling excess light amount 4 ND filter 5 Mirror scanner 6 Z stage 7 Lens as light collecting means 8 Computer 9 Light curing Resin liquid 10 Stereolithography (reference numeral in FIG. 3)
DESCRIPTION OF SYMBOLS 1 Laser light source 2 Light beam conversion optical system 3 Scanning optical system 4 Objective lens system 5 Sample surface 6 Dichroic mirror 7 Photodetector

JP 2004-156911 A Special table 2001-513198 gazette JP-T-2004-530869 Japanese Patent Laying-Open No. 2005-068447 JP 2006-330683 A JP 2008-055570 A JP 2008-058209 A JP-T-2001-524245 Special table 2000-512061 gazette Special table 2001-522119 gazette Special table 2001-508221 gazette JP-A-6-28672 JP-A-6-118306 JP-A-2005-97718 JP 2006-169544 A JP 2008-130102 A

The 2nd Annual Meeting of the Nano Society, 2P037 Proceedings of polymer science nanocomposite subcommittee meeting 5 (1), PP5-8 Langmuir, 2008, 24, 3465-3470. Molecular Science, Vol. 1 A0006 (2007)

Claims (11)

  In a solution containing ions of a metal (noble metal) nobler than the base metal capable of generating a plasmon enhancement field at least part of the base metal (base metal) coated on the surface of the nanoparticle having shape anisotropy A method for producing composite metal nanoparticles, characterized by substituting a noble metal with a difference in ionization tendency. A nanoparticle dispersion preparing step of forming a dispersion containing nanoparticles having the shape anisotropy;
A base metal-coated nanoparticle production step of coating a base metal on the nanoparticle surface having shape anisotropy in the dispersion;
A noble metal substitution step of substituting at least a part of the base metal coating the surface of the base metal-coated nanoparticles with a noble metal due to a difference in ionization tendency between the base metal and the noble metal in a solution containing the noble metal ions;
The method for producing composite metal nanoparticles according to claim 1, comprising:   3. The composite metal according to claim 2, wherein, in the noble metal substitution step, the solution used in the base metal-coated nanoparticle production step is used as it is, and the solution contains the noble metal ion to perform substitution with the base metal. A method for producing nanoparticles.   4. The composite according to claim 2, wherein after the base metal-coated nanoparticle production step, the surface of the base metal is treated with a silane coupling agent, and then at least a part of the base metal is replaced with the noble metal. A method for producing metal nanoparticles.   The method for producing composite metal nanoparticles according to claim 1, wherein the nanoparticles having shape anisotropy are gold nanorods.   6. The base metal coated on the surface of the nanoparticle having shape anisotropy is silver, and the noble metal that replaces at least a part of the base metal is gold. A method for producing composite metal nanoparticles. A nanoparticle dispersion preparing step of forming a dispersion containing nanoparticles having the shape anisotropy;
A base metal-coated nanoparticle production step of coating a base metal on the nanoparticle surface having shape anisotropy in the dispersion;
A noble metal substitution step of substituting at least a part of the base metal that coats the surface of the base metal-coated nanoparticles with a noble metal due to a difference in ionization tendency of the base metal and the noble metal in a solution containing ions of the noble metal, and
The dispersion liquid in the base metal-coated nanoparticle production step includes gold nanorods, silver nitrate, ascorbic acid and amines, and silver is anisotropically grown on the gold nanorod surface by a reduction reaction of the dispersion liquid. The manufacturing method of the composite metal nanoparticle of Claim 5 or 6.   8. The method for producing composite metal nanoparticles according to claim 1, wherein a surface of the composite metal nanoparticles is covered with an insulating layer. A composite metal nanoparticle obtained by the production method according to any one of claims 1 to 8,
A composite characterized in that at least a part of a base metal coated on the surface of a nanoparticle having shape anisotropy is substituted with a metal (noble metal) nobler than the base metal capable of generating a plasmon enhancement field. Metal nanoparticles.   A multiphoton absorption material comprising composite metal nanoparticles obtained by the production method according to claim 1.   A multiphoton absorption reaction aid comprising composite metal nanoparticles obtained by the production method according to claim 1.

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