JP5151097B2 - Composite metal nanoparticles, multiphoton absorption reaction materials and reaction products containing composite metal nanoparticles, and multiphoton absorption reaction aids containing composite metal nanoparticles - Google Patents

Description

  The present invention relates to a material having a variable wavelength characteristic that causes a reaction with high sensitivity by a multiphoton absorption reaction using a surface plasmon enhancement field of a metal, and more specifically, a metal microstructure that generates a plasmon enhancement field is deposited. Composite metal nanoparticles, multi-photon absorption reaction materials and composite products containing composite metal nanoparticles and multi-photon absorption materials, and multi-photon absorption reaction assistants containing composite metal nanoparticles and multi-photon absorption reaction accelerators About.

When a two-photon absorption reaction, which is one of the multiphoton absorption processes, is used, 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 occur 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 for processing records exceeding the limits are increasing.

However, the absorption cross section of the multiphoton absorption reaction represented by the two-photon absorption reaction is extremely small, and it is indispensable to carry out excitation with an expensive and large-sized pulsed laser light source such as a femtosecond laser. It has a problem that it is said.
Because of having such problems, in order to spread the application utilizing the excellent characteristics of the 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 it is essential to develop a highly sensitive multiphoton absorbing material.

  On the other hand, as a method for enhancing / sensitizing a photoreaction, a method using a surface plasmon enhancement field excited on a metal surface is known. For example, when a surface plasmon microscope is applied, an extremely thin film (surface plasmon enhancement field is limited to a few hundred nm or less from the surface) disposed on a metal thin film formed on a high refractive index medium. (For example, refer to Patent Document 1).

The above proposal is an example of a surface plasmon microscope that detects a small amount of sample with high sensitivity, and the surface plasmon enhancement field is at most several hundreds from the surface on the metal thin film formed on the high refractive index medium as described above. It occurs only in a limited region below nm. 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 described.
The enhancement field created by the metal thin film has a spatial extent equivalent to the wavelength of light, and is nearly an order of magnitude larger than the localized plasmon enhancement field by fine particles, which will be described later. However, in reality, high-sensitivity detection is possible, but due to the limitation of coupling with excitation light, the special optical arrangement as described above is essential. That is, the area where the sensitization effect can be obtained is limited to the area along the metal thin film and the illuminable range with the excitation light (depending on the arrangement and shape of the photorefractive index medium carrying the metal thin film). The application is limited to the field of high-sensitivity detection using a small amount of sample. Silver is used as a metal thin film material having a typical plasmon enhancing effect.

Further, a technique regarding a measurement method using a surface plasmon enhancement field excited by metal fine particles is known (for example, see Patent Document 2).
The plasmon excited on the surface of the metal fine particle in this technique is a localized plasmon enhancement field having a smaller spread than the technique disclosed in Patent Document 1, and the spread is limited to a region of 100 nm or less around the metal fine particle. Is done. Therefore, (a) the sample adsorbed on the particle surface is used as a microprobe that can be observed with high sensitivity, or (b) the localized plasmon enhancement field is a non-propagating light confined in a microscopic region. Thus, it is used as a microprobe microscope that obtains an observation image from the relationship between the obtained signal and the position by moving metal fine particles in the vicinity of the sample.
In the case of the former (a), fluorescence from a sample present 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 (b), a method such as scanning fine particles on the surface of the sample by the principle of optical tweezers that holds the fine particles by the radiation pressure of light is used. Yes. In addition, the tuning of the resonant wavelength by the spherical core cell structure has been disclosed in order to select the wavelength to be used for observation. However, since the resonant wavelength is determined by the dimensional ratio between the core and the cell, particles having the same resonant wavelength are reproducible. Difficult to get.

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

On the other hand, in recent years, research has been conducted on a technique using gold nanorods as means for generating a surface plasmon enhancement field instead of the metal fine particles as described above. The gold nanorod has a characteristic that the resonance wavelength can be changed by changing the aspect ratio, and is a material capable of covering from about 540 nm to the near infrared (about 1100 nm). As an example of a method of producing metal nanorods related to gold nanorods, a method of producing by a electrochemical reaction in a solution containing a surfactant has been proposed (for example, see Patent Document 4). It is said that particles having a uniform resonance wavelength can be obtained with good reproducibility by this production method.
However, a gold nanorod having a low aspect ratio corresponding to a resonance wavelength of around 540 nm of spherical gold fine particles has a problem that only an enhancement level comparable to that of spherical particles can be obtained. Furthermore, a fine plasmon enhanced field generation source having a large enhancement effect that can be used at 420 to 500 nm has not been obtained with a metal other than gold, and such fine high aspect ratio particles having the same resonance wavelength are not obtained. Is not yet known.

  Such a multiphoton absorbing material including composite metal nanoparticles having a plasmon enhancement field or a material including a reaction aid is provided as a stable dispersion solution and a mixture that can be applied or cast. Since the reaction threshold of the multiphoton absorption reaction at the time of modeling is lowered and the reaction can occur only at the condensing point, it has been attracting attention because various applications that have not been possible before are possible. Application to three-dimensional optical recording media, stereolithography materials, fluorescent microscopes, and the like has attracted particular attention.

  For example, a three-dimensional optical recording medium using a two-photon absorption material is used, and a method of reading with fluorescence using a fluorescent substance for recording and reproduction (see, for example, Patent Documents 5 and 6) or absorption using a photochromic compound A method of reading with fluorescence (see, for example, Patent Documents 7 and 8) has been proposed.

However, none of the above Patent Documents 5 and 6 and Patent Documents 7 and 8 are presented as specific two-photon absorption materials, and the compounds described are also considered from the viewpoint of two-photon absorption efficiency. Even if it is a very small compound.
Further, since the photochromic compounds used in Patent Documents 7 and 8 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 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 absorption rate) or emission intensity using an irreversible material. There were no examples that specifically disclosed 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 (see, for example, Patent Documents 9 and 10). However, these proposals do not describe a method using a two-photon absorption three-dimensional optical recording material.

Another application example is a material for optical modeling. As such a material for optical modeling, for example, a method of forming a bell-shaped convex structure portion by exposing a surface of a polymer film having a photosensitive function to interference exposure with a pulse laser beam without using a mask is proposed. (For example, refer to Patent Document 11).
In the above proposal, there is no description regarding a material for optical modeling that is an object of the present invention, that is, a material for optical modeling that performs a multiphoton absorption reaction using a localized plasmon enhancement field.

Still another application example is application to a fluorescence microscope, for example.
As a scanning optical microscope, for example, there has been proposed a microscope having a configuration capable of expanding the NA of the light collecting element and expanding the number of fields of view while improving the utilization efficiency of illumination light (for example, patents). Reference 12).
The above proposal does not describe a fluorescence microscope that performs multiphoton absorption using the localized plasmon enhancement field of the present invention.

JP 2004-156911 A Special table 2001-513198 gazette Japanese translation of PCT publication No. 2004-530867 Japanese Patent Laying-Open No. 2005-068447 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 2005-134873 A Japanese Patent Laid-Open No. 9-230246

As described above, in the application products using the conventional multi-photon reaction process, a high output is required for the reaction inside the three-dimensional substance, so that the laser irradiation apparatus used is large and expensive. Special ones (eg, femtosecond lasers) are required, limiting their practicality.
As a result of studies conducted by the present inventors to solve this problem, the surface of core particles (for example, rod-shaped core particles) having shape anisotropy having different lengths in the vertical and horizontal directions is irradiated with laser light on the surface. It has been found that the above problems can be solved by using composite metal nanoparticles in which the entire surface of the core particle is coated with a metal film capable of developing an enhancement field.

  The present invention has been made in view of the above, and has a variable wavelength characteristic (near infrared to blue region) that enables sensitization of a multiphoton absorption reaction by light irradiation without requiring a large and expensive laser irradiation light source. In addition to providing a composite metal nanoparticle that can be used as an efficient excitation source, a highly sensitive multiphoton including a composite metal nanoparticle and a multiphoton absorbing material is provided. An object of the present invention is to provide a highly sensitive multiphoton absorption reaction aid containing an absorption reaction material, composite metal nanoparticles, and a multiphoton absorption reaction accelerator. In addition, it can be applied to various application fields (three-dimensional optical recording media, stereolithography materials, fluorescence microscopes, etc.) using the features such as ultra-high density, ultra-precision, and high resolution that are exhibited by using these materials. To do.

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 ( 8 ), and have reached the present invention. Hereinafter, the present invention will be specifically described.

(1): A metal microstructure that expresses a localized plasmon enhancement field by light irradiation is provided on the surface of a core particle having shape anisotropy having different lengths in the vertical and horizontal directions and spaced apart in an island shape. It is the featured composite metal nanoparticles. In this case, the core particle is a gold nanorod, and a buffer layer is provided between the surface of the core particle and a metal microstructure that expresses a plasmon enhancement field by light irradiation, and the light irradiation The composite metal nanoparticles are characterized in that the metal microstructure that expresses the plasmon enhancement field is silver.

  By using core particles having shape anisotropy, nanoparticles with a desired aspect ratio (ratio of length and width) can be used as cores with good reproducibility. The core particle shape and the metal of the metal microstructure Efficiency of surface plasmon enhancement field in the wavelength range from near infrared to blue region by utilizing the kind of metal and the interaction between adjacent metal microstructures provided in the shape of islands It is possible to provide composite metal nanoparticles that can be used as a mechanical excitation source. The composite metal nanoparticles can be used in a wide wavelength range, and provide a near-field generation source with an unprecedented enhancement effect. In addition, since the metal microstructures that generate the enhancement effect are provided in an island shape and are configured from so-called aggregates of ultrafine particles, the degree of freedom in setting the size of the composite metal nanoparticles themselves is increased. As the degree of freedom increases, the manufacturing margin increases and the cost can be reduced.

  Gold nanorods can be selected from a wide range of aspect ratios, and can be obtained as core particles having desired longitudinal and lateral lengths, that is, different shape anisotropies of minor and major axes. The selection of “ultrafine particles” may yield composite nanoparticles that can be enhanced at least up to the blue region, realizing an unprecedented efficient photoreaction process, and high density and high definition. Can be used in various application fields.

  By providing an oxide or nitride buffer layer as described later between the surface of the core particle and the metal microstructure (ultrafine particles), the shape of the composite metal nanoparticles, such as the aspect ratio, changes with time. Is suppressed, and more stable operation is possible even in a reaction under a high-energy laser beam. For this reason, an efficient photoreaction process can be realized under a wider range of reaction conditions, and can be used for a wider range of reaction conditions and various application products.

( 2 ) The composite metal nanoparticle according to (1 ), wherein the metal microstructure that expresses a localized plasmon enhancement field by light irradiation is composed of a plurality of layers.

  The localized plasmon enhancement field generated around the composite metal nanoparticle is a superposition of the localized plasmon enhancement fields generated by the metal microstructures (ultrafine particles). This effect can be obtained, for example, by making the resonance wavelengths of the plurality of layers the same for the purpose of increasing the coupling efficiency for each particle, and obtaining a larger enhancement effect. It is also possible to design as particles having a resonance wavelength of. Therefore, an efficient photoreaction process can be realized under a wider range of reaction conditions, and it can be used for various application products because it can meet various specifications.

( 3 ): A multiphoton absorption reaction material comprising the composite metal nanoparticles according to (1) or (2) and a multiphoton absorption material.

( 4 ): The multiphoton absorption reaction material according to ( 3 ), wherein the multiphoton absorption material is a two-photon absorption material.

( 5 ): The multiphoton absorption reaction material according to (3) or (4) , wherein the multiphoton absorption material is a multiphoton absorption dye.

According to the multiphoton absorption reaction material of ( 3 ) to ( 5 ), a localized plasmon enhanced field generation source capable of corresponding to the near infrared to blue region, that is, a composite metal nanoparticle that is an efficient excitation source, and a multiphoton It contains an absorbing material (for example, diarylethene, photocurable resin, etc.), and can cause a high-density, high-definition reaction at an arbitrary three-dimensional position inside the substance. The threshold value of the reaction is lowered by the large enhancement effect of the composite metal nanoparticles, and an expensive light source such as a femtosecond laser, which has been conventionally required, is not necessary, and the cost of the apparatus used for the reaction can be greatly reduced.
Therefore, by using the multiphoton absorption reaction material of the present invention, application products using various multiphoton reaction processes such as three-dimensional memory and three-dimensional modeling can be realized.

( 6 ): A multiphoton absorption reaction product obtained from the multiphoton absorption reaction material according to any one of ( 3 ) to ( 5 ).

If a multiphoton absorption reaction product is used to produce a multiphoton absorption reaction product, for example, when used as a three-dimensional recording medium, ultrahigh density optical recording (terabyte class) can be realized and used as an optical modeling material. In some cases, it is possible to form an ultra-precision three-dimensional structure.
Furthermore, if a two-photon absorption fluorescent material is used as a multiphoton absorption material and used in a two-photon fluorescence microscope, it is possible to observe with high sensitivity without causing deterioration or adverse effects of the device under test.

( 7 ): A multiphoton absorption reaction aid comprising the composite metal nanoparticles according to (1) or (2) and a multiphoton absorption reaction accelerator.

( 8 ): The multiphoton absorption reaction accelerator according to (7) , wherein the multiphoton absorption reaction accelerator is a two-photon absorption reaction accelerator.

According to the multiphoton absorption reaction auxiliary agent of ( 7 ), ( 8 ), the composite metal nanoparticle as a local plasmon enhanced field generation source capable of corresponding to the blue region from the near infrared, and the multiphoton (two-photon) absorption reaction By containing an accelerator (for example, a polymerization initiator, a photosensitizer, etc.), a highly sensitive reaction is possible as compared with the case of using a conventional multiphoton photon absorption reactant or reaction aid. Naturally, a high-density, high-definition reaction can be caused at an arbitrary three-dimensional position inside the substance. Therefore, application products using various multiphoton reaction processes such as three-dimensional modeling can be realized by using the multiphoton absorption reaction material of the present invention. In addition, the use of a multiphoton absorption reaction aid lowers the reaction threshold, eliminating the need for expensive light sources such as femtosecond lasers that were required in the past, and greatly reducing the cost of equipment used in applied products. Is possible.

According to the composite metal nanoparticles of the present invention, it can be applied as an efficient excitation source of reaction in a wide wavelength range from the near infrared to the blue region, and a localized plasmon enhancement field is generated at an arbitrary position in a three-dimensional space inside the substance. Since it can be used as a source, a photoreaction can be caused only at the center of the focused spot without requiring a large pulse laser.
Further, according to the multiphoton absorption reaction material, the multiphoton absorption reaction product, and the multiphoton absorption reaction aid of the present invention, a high-density, high-definition reaction can be induced at an arbitrary three-dimensional position inside the substance. For example, processing and recording exceeding the diffraction limit such as ultra-high density optical recording and ultra-precision three-dimensional structure can be realized. Furthermore, if a multiphoton absorption material is used for a fluorescence microscope, it is possible to observe with high sensitivity.

  As described above, the composite metal nanoparticles in the present invention have an island-like metal microstructure that expresses a localized plasmon enhancement field by light irradiation on the surface of core particles having shape anisotropy having different lengths in the vertical and horizontal directions. It is characterized by being provided apart from each other.

That is, a localized plasmon enhancement field localized in the very vicinity of the particle is generated around the composite metal nanoparticle of the present invention. The enhancement of the localized plasmon enhancement field is determined not only by the shape of the particle and the type of metal, but also by the interaction with other metal nanoparticles present in the vicinity.
First, the effect of the particle shape and metal species will be described. One known as a nanoparticle having a large enhancement effect is a rod-shaped fine particle. 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 with spherical fine particles, the resonance wavelength shifts to the longer wavelength side as the particle 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.

  The inventors have selected the most suitable material for the surface material generating the localized plasmon enhancement field or the material constituting the surface vicinity and the core material for determining the aspect ratio, and the entire surface of the core material is enhanced by the localized plasmon enhancement. It has been found that a composite nanoparticle coated with a metal that generates a field has a large enhancement effect at a desired wavelength. The composite nanoparticles have a large local plasmon enhancement effect not only when the longitudinal size of the particles is ½ or less of the excitation light wavelength, but also when ½ or more.

Next, the plasmon interaction between adjacent metal microstructures (ultrafine particles) provided on the surface of the core particle in an island-like manner will be described.
When the isolated ultrafine particles that do not overlap in the localized plasmon enhancement field generated on the surface of the ultrafine particles are brought close to each other, energy can be exchanged between them, and the localized plasmon enhancement field is biased. As a result, a region with a higher intensity is generated as compared with the isolated localized plasmon enhancement field. In addition, as described above, the entire localized plasmon enhancement field constituted by a large number of minute localized plasmon enhancement fields that are close enough to exchange energy with each other is as large as the wavelength that excites the localized plasmon. In contrast, unlike the isolated localized plasmon enhancement field, it is possible to sense the phase of the excitation light. Such a close collection of fine localized plasmon enhancement fields spreads to a wavelength as well as the spread of the surface plasmon enhancement field generated on the thin film.
Therefore, in the region where the particle diameter of the composite metal nanoparticles is small, a strong enhancement effect of the localized plasmon enhancement field due to the interaction between the island-shaped metal microstructures (ultrafine particles) constituting the surface is expressed, Compared to composite metal nanoparticles in which the entire surface of the core material is coated with a metal that generates a localized plasmon enhancement field, a greater enhancement effect is exhibited.

In addition, as the composite metal nanoparticles become larger, the ease of coupling with the excitation light of the metal microstructures (ultrafine particles) is maintained, and the entire composite nanoparticles can sense the phase. Thus, a localized plasmon enhancement field having a property close to that of a thin film, that is, a spread of about the wavelength (about 5 to 10 times that of a normal localized plasmon enhancement field) can be obtained.
Therefore, if the large localized plasmon enhancement field of the composite nanoparticle is used, the dispersion concentration required to obtain the enhancement effect can be reduced, the scattering effect is suppressed, and the enhancement by the efficient localized plasmon enhancement field is achieved. The effect is demonstrated.
Even in the case of the composite metal nanoparticles having any of the above-mentioned sizes, the enhancement effect of the localized plasmon enhancement field can contribute to high sensitivity of the two-photon absorption reaction.

  In the present invention, a core particle (having a shape anisotropy with different lengths in the vertical and horizontal directions) capable of selectively obtaining a desired aspect ratio relatively easily is used, and the core particle is crystal-grown. Crystal groWth can be formed as cores of the metal to form metal microstructures (ultrafine particles) in the form of islands, and a wide range of metal high aspect ratio composite metal nanoparticles can be obtained With good reproducibility. The tuning of the absorption wavelength depends on the type of the deposited metal microstructure, the structure of the deposited metal microstructure (the size of individual parts (very fine particles) in the segmented island structure, etc.) and the particle shape. This can be done by changing the ratio.

Here, in order to obtain a divided island-like structure, for example, in the step of obtaining a film-like deposit by covering the entire surface of the core material with metal, an initial island-like structure was formed. It is also possible to use a method of stopping in stages.
Since the external dimension of the metal microstructure is a factor that determines the fundamental resonance wavelength, shape stability is important, and thus shape control is particularly important.
Furthermore, in the present invention, by using a so-called fragmented metal microstructure in which ultrafine particles are provided on the surface of the core particle so as to be spaced apart from each other, a plurality of localized plasmon enhancement fields can be obtained near-field optically. An effect equivalent to the configuration arranged close to each other can be obtained. As a result, a larger enhancement effect can be obtained as compared with the composite metal nanoparticles having a core cell structure in which the entire surface of the core material is uniformly coated with metal.
The shape of each metal microstructure constituting the metal structure is not particularly limited as long as it is arranged in the form of islands on the core particle so as to be close enough to transfer energy, and spherical. Various forms such as particles having anisotropy and cracked film can be used.

In the composite metal nanoparticles, the core particles having shape anisotropy having different short diameters and long diameters are preferably gold nanorods.
In particular, by using gold nanorods that can easily obtain high-aspect-ratio nanoparticles as crystal growth nuclei, it is possible to create metal microstructures (ultrafine particles) spaced apart in islands with a wide range of metals with high reproducibility. Thus, a high aspect ratio nanorod can be obtained.
By changing the selection of the metal species, the shortest wavelength of the localized plasmon resonance wavelength can be changed, and by selecting the aspect ratio, the structure of the metal microstructure that generates the localized plasmon enhancement field, etc., in a wide wavelength range. The light enhancement effect by the localized plasmon enhancement field appears and can be used.

  In the composite metal nanoparticle, a bonding interface is formed between the surface of the core particle having shape anisotropy having different lengths in the vertical and horizontal directions and the metal microstructure that develops the localized plasmon enhancement field by light irradiation. It is preferable to provide a buffer layer for isolation.

  When dissimilar metals are in direct contact with each other, it is an interface that constitutes nanoparticles with a large surface energy state, so the interface profile collapses due to a mechanism such as interdiffusion, and as a result, it adheres to the surface of the core particles. Deviation from the localized plasmon resonance wavelength inherent in the metal microstructure occurs. Under actual operating conditions using laser light, this process is accelerated. Therefore, by providing a buffer layer that isolates the dissimilar metal interface, a localized plasmon resonance wavelength unique to the metal microstructure can be stably obtained. Furthermore, it is also possible to appropriately embed a metal part that generates a localized plasmon enhancement field constituting the metal microstructure in the buffer layer.

  As the material of the buffer layer, it is possible to use oxides, nitrides, and the like, and by using a material having a particularly strong covalent bond, mass transfer due to a solid phase reaction accompanying diffusion or temperature rise is suppressed. A configuration in which a desired aspect ratio is kept more stable under laser light irradiation is also possible.

  Furthermore, in the composite metal nanoparticles, it is preferable that the metal microstructure that expresses a localized plasmon enhancement field by light irradiation is composed of a plurality of layers.

The plurality of metal microstructures described herein refers to a product obtained by laminating a surface of core particles having shape anisotropy, by performing a process of creating metal microstructures a plurality of times with different materials interposed therebetween.
An example of a metal microstructure in which different materials are combined is shown below.
For example, a metal structure made of island-like ultrafine particles made of silver is first deposited on the core particle, and then a SiO ₂ layer is formed as a buffer layer, and further separated, and a metal microstructure made of island-like silver is further separated. The case where it forms and forms a body etc. is mentioned.
Here, the buffer layer does not need to have a complete film-like structure on the surface of the core particle, and can be an island shape or a spherical shape, similar to the metal constituting the metal microstructure. The layers may be substantially separated. “Substantially separated” means that each of the islands, spheres, etc. constituting the metal microstructure by solid phase reaction such as diffusion is fused or particle-grown at least beyond the metal microstructure. It means that there is an inhibitory effect.

  In the plurality of metal microstructures, the conditions may be changed as appropriate even if the metal constituting each structure or the divided parts constituting each layer have the same size. When each structure is the same, the absorption wavelength is the same, and the absorption amount per one composite metal nanoparticle is the sum of the absorption amounts for each structure. In addition, the enhancement field that can be formed in the surrounding area has a strength obtained by superimposing both enhancement fields. That is, the property as a scatterer is almost the same, and only the property as the source of the enhanced field is enhanced. Further, the absorption wavelength of each structure may be shifted to a desired wavelength by appropriately changing at least one of the metal species or the size of each divided part. When the absorption wavelength of each structure is shifted, for example, a single particle can exhibit an enhancement effect with respect to light having a plurality of wavelengths corresponding to a plurality of chemical species contributing to the photoreaction.

  As described above, the multiphoton absorption reaction material in the present invention is characterized by comprising composite metal nanoparticles and a multiphoton absorption material.

Such a multiphoton absorption material including a composite metal nanoparticle having a localized plasmon enhancement field is capable of a highly sensitive reaction as compared with the case where a conventional multiphoton photon absorption reaction product is used. Since it can be a stable dispersion solution or mixture that can be cast, etc., it can be used for products applying various multiphoton reaction processes such as 3D modeling and 3D memory.
For example, combining composite metal nanoparticles as a source of localized plasmon enhancement field with multiphoton absorbing dyes and multiphoton absorbing materials such as diarylethene, acrylate-based and epoxy-based photocurable resins (multiphoton absorbing materials) The multiphoton absorption reaction material can cause a high-density, high-definition reaction at an arbitrary position inside the three-dimensional substance. Further, by lowering the reaction threshold, an expensive light source such as a femtosecond laser that has been conventionally required can be eliminated, and the cost can be significantly reduced.
In addition, the multiphoton absorption reaction product in the present invention is obtained by the photoreaction of such a multiphoton absorption reaction material.

  Further, the multiphoton absorption reaction aid in the present invention is characterized by comprising composite metal nanoparticles and a multiphoton absorption reaction accelerator.

According to the multiphoton absorption reaction aid of the present invention, a highly sensitive reaction is possible compared to the case where a conventional multiphoton photon absorption reaction aid is used, and various multiphotons such as three-dimensional modeling and three-dimensional memory are available. It is possible to realize high-density, high-definition products that apply the reaction process.
For example, by combining a composite metal nanoparticle as a localized plasmon enhancement field source and a multiphoton (two-photon) absorption reaction accelerator such as a polymerization initiator or a photosensitizer, an acrylate type or an epoxy type Resins can cause reactions with high sensitivity. In addition, the use of a multiphoton absorption reaction aid reduces the reaction threshold, eliminates the need for expensive light sources (eg, femtosecond lasers) that have been required in the past, and significantly reduces the cost of equipment used in the manufacture of applied products. It becomes possible.

Multi-photon absorption reaction materials (composite metal nanoparticles + multi-photon absorption materials) including composite metal nanoparticles with localized plasmon enhancement fields as described above, or multi-photon absorption reaction aids (composite metal nanoparticles + multi-particles) Photon absorption reaction accelerators) can be processed in various forms including coating and casting. For example, by utilizing characteristics such as a decrease in reaction threshold of multiphoton absorption reaction, Application becomes possible.
As typical application examples, a three-dimensional multilayer optical memory, an optical modeling material, and a two-photon fluorescence microscope will be described below.

[Application to three-dimensional multilayer optical memory]
Recently, networks such as the Internet and high-definition TV are rapidly spreading. In addition, HDTV (High Definition Television) will soon be broadcast, and there is an increasing demand for a large-capacity recording medium for easily and inexpensively recording image information of 50 GB or more, preferably 100 GB or more for consumer use. Furthermore, in 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 on the physical principle, and the recording is large enough to meet future requirements. It cannot be said that capacity can be expected.

Under such circumstances, a three-dimensional optical recording medium has attracted 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 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 that, a method using a two-photon absorption material and holography (interference) There is a method of using.

  In a three-dimensional optical recording medium using a two-photon absorption material, so-called bit recording is possible over tens or hundreds of times based on the physical principle described above, and higher density recording is possible. It can be said to be the ultimate high-density, high-capacity optical recording medium.

  As a three-dimensional optical recording medium using a two-photon absorption material, as described in the background art, a method of reading with fluorescence using a fluorescent substance for recording and reproduction, or a method of reading with absorption or fluorescence using a photochromic compound Although a method and the like have been proposed, it cannot be said that the method is suitable for providing the above three-dimensional optical recording medium.

  As described above, the reaction is caused using the excitation energy obtained by non-resonant two-photon absorption, and as a result, the emission intensity when the laser focus (recording) part and the non-focus (non-recording) part are irradiated with light is determined. If modulation is possible with a method that cannot be rewritten, it is possible to cause emission intensity modulation with extremely high spatial resolution in any place in three-dimensional space, and it can be applied to three-dimensional optical recording media that are considered to be the ultimate high-density recording medium. It becomes possible. Furthermore, since non-destructive readout is possible and the material is an irreversible material, it can be expected to have good storage stability and is practical.

  However, currently available two-photon absorption compounds have a low two-photon absorption capability, so a very high-power laser is required as a light source and a long recording time is required. In particular, for use in a three-dimensional optical recording medium, construction of a two-photon absorption three-dimensional optical recording material capable of performing recording with two-photon absorption with high sensitivity in order to achieve a high transfer rate. Is essential. For that purpose, the difference in the light emission ability of the two-photon absorption optical recording material by some method using the two-photon absorption compound excited state and the two-photon absorption compound excited state that can absorb two photons with high efficiency and generate an excited state. Although a material containing a recording component that can efficiently form a thin film is effective, such a material has hardly been disclosed so far, and it has been desired to construct such a material.

As described above, a recording layer is formed by using the multiphoton absorption reaction material of the present invention composed of composite metal nanoparticles and a multiphoton (two-photon) absorption material as a localized plasmon enhancement field source capable of corresponding to various wavelength ranges, After performing high-density recording (three-dimensional recording) using two-photon absorption by light irradiation, the recording material is irradiated with light to detect the difference in light emission intensity, or the reflectivity due to refractive index change It can be played back by detecting the change in.
That is, if the multiphoton absorption reaction material of the present invention is used, a two-photon absorption three-dimensional optical recording method and a reproducing method using the two-photon absorption three-dimensional optical recording medium with an ultra-high density are provided.

  The multiphoton (two-photon) absorption reaction material of the present invention consisting of composite metal nanoparticles and a multiphoton (two-photon) absorbing material can be made into a dispersion solution dispersed in various solvents as necessary. If used, it can be applied directly onto the substrate using, for example, a spin coater, roll coater or bar coater, or first cast as a film and then laminated to the substrate by conventional methods, Thus, a two-photon absorption optical recording material can be obtained.

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.
The substrate is preferably, but not limited to, 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. .
The substrate may be provided with tracking guide grooves and address information in advance. The solvent used can be removed by evaporation during drying. Heating or reduced pressure may be used for evaporation removal.

Furthermore, a protective layer (intermediate layer) for blocking oxygen and preventing interlayer crosstalk may be formed on the two-photon absorption optical recording material.
The protective layer (intermediate layer) is made of a plastic film or plate such as polyolefin such as polypropylene or polyethylene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyethylene terephthalate or cellophane film, and is attached electrostatically using an extruder. It may be provided by laminating or by applying a polymer solution. Alternatively, a glass plate may be bonded.
Further, an adhesive or a liquid substance may be present between the protective layer and the two-photon absorption optical recording material (recording layer) and / or between the base material and the recording layer in order to improve the airtightness. Further, the protective layer (intermediate layer) between the photosensitive films may be provided with tracking guide grooves and address information in advance.

  By focusing on an arbitrary layer of the above-described three-dimensional multilayer optical recording medium and performing recording and reproduction, it functions as the three-dimensional recording medium of the present invention. 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.

Hereinafter, preferred embodiments (specific examples) of a three-dimensional multilayer optical memory according to the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments, and three-dimensional recording (in a plane and a film thickness direction). Any other structure may be used as long as it can be recorded).
FIG. 1 is a schematic diagram showing a recording / reproducing system configuration (a) and a configuration section (b) of a recording medium of a three-dimensional multilayer optical memory according to the present invention.

An outline of a recording method according to the system configuration of FIG.
The recording light 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 by the square effect is not performed. That is, selective recording is possible.

  Next, as a reproducing method, the light from the reproducing laser light source 2 (not as high power as the recording light but also a semiconductor laser can be used) is focused into the three-dimensional recording medium 6. 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.

The configuration of the recording medium shown in FIG. A recording layer using a multiphoton absorption reaction material comprising the composite metal nanoparticles of the present invention and a multiphoton absorption material on a flat support (substrate 11), and an intermediate layer (protective layer) 15 for preventing crosstalk are provided. 50 layers are alternately stacked, and each layer is formed by, for example, a spin coating method.
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 to 5 μm. With this structure, the disk size is the same as that of currently popular CD / DVD, and the terabyte class is used. Can be realized. Further, a substrate 12 (protective layer) similar to the substrate 11 or a reflective film made of a high reflectance material is provided by a data reproduction method (transmission / or reflection type).

In the above, a single beam is used at the time of recording, and in this case, ultrashort pulsed light of femtosecond order can be used. Further, at the time of reproduction, it is possible to use light having a wavelength different from that of the beam used for data recording, or light of the same wavelength with 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 similarly formed 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]
Hereinafter, embodiments of the optical modeling material according to the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments.
In FIG. 2, the schematic block diagram of the apparatus used when carrying out optical modeling using the multiphoton absorption reaction material containing the composite metal nanoparticle of this invention and a multiphoton absorption material is shown. Hereinafter, the two-photon stereolithography will be described.

After passing light from the near-infrared pulsed laser light source 21 through the mirror scanner 25, it is collected in a multiphoton absorption reaction material (photocurable resin liquid) 29 containing composite metal nanoparticles and a multiphoton absorption material using a lens. A laser spot is scanned and two-photon absorption is induced to cure the resin only in the vicinity of the focal point to form an arbitrary three-dimensional structure (two-photon micro-stereolithography method). The details of the photocurable resin will be described later.
In FIG. 2, reference numeral 23 denotes a shutter for temporally controlling transmitted light, 24 denotes an ND filter, 27 denotes a lens as an optical means, 28 denotes a computer, and 20 denotes an optically shaped object.

  That is, the pulsed laser beam is condensed by 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.

  In this way, by condensing the pulsed laser light with the lens and inducing two-photon absorption, it is possible to limit the light absorption to the vicinity of the condensing point and harden the resin in a pinpoint manner. Since the condensing point can be freely moved in the photocurable resin liquid by the Z stage 26 and the galvanometer mirror, a desired three-dimensional workpiece can be freely formed in the photocurable resin liquid.

The features of the two-photon stereolithography include the following items.
(A) 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.
(B) Ultra-high speed modeling: When two-photon absorption is used, the photocurable resin is not cured 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.
(C) 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 SIH, when the beam is condensed deeply, the light intensity at the condensing point is reduced by light absorption, and the internal curing becomes difficult. In the present invention, these problems can be solved reliably. .
(D) High yield: In the conventional method, there is a problem that the modeled object is damaged or deformed due to the viscosity or surface tension of the resin, but in this method, the problem is solved because modeling is performed inside the resin.
(E) 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.

The photocurable resin for two-photon stereolithography refers to a multiphoton absorption reaction material including composite metal nanoparticles and a multiphoton absorption material. As the multiphoton absorption material, a two-photon polymerization reaction is performed by irradiating light. A resin having a characteristic of causing a change from a liquid to a solid is used.
The main components are a resin component composed of an oligomer and a reactive diluent and a photopolymerization initiator (including a photosensitizer if necessary). When a photopolymerization initiator or a photosensitizing material is included, these reaction accelerators may be multiphoton absorption reaction accelerators (in this case, the resin may not necessarily be a multiphoton absorption material), A so-called composite metal nanoparticle and a multiphoton absorption reaction accelerator function as a multiphoton absorption reaction aid.
The oligomer is a polymer having a degree of polymerization of about 2 to 20, and those having a large number of reactive groups at the ends are preferably used, and a reactive diluent is added to adjust the viscosity, curability and the like. May be.

  When the photocurable resin containing the composite metal nanoparticles is irradiated with light, the polymerization initiator or photosensitizer absorbs two photons, and reactive species are generated directly from the polymerization initiator or via the photosensitizer. Then, it reacts with the reactive group of the oligomer or reactive diluent to initiate the polymerization. Thereafter, a chain polymerization reaction takes place between them to form a three-dimensional cross-link, and in a short time, a solid resin having a three-dimensional network structure is formed.

  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 the layered three-dimensional modeling, (1) good reactivity, (2) small deposition shrinkage during curing, (3) excellent mechanical properties after curing, etc. are important. .

  The above characteristics are equally important in the method of the present invention. Therefore, a resin developed for layered three-dimensional modeling and having a two-photon absorption characteristic can also be used as a photocurable resin for two-photon optical modeling in the present invention. As specific examples, acrylate-based and epoxy-based photocurable resins are often used, and urethane acrylate-based photocurable resins are particularly preferable.

  For example, as a technique related to optical modeling, it is known that interference exposure is performed on the surface of a photosensitive polymer film without using a mask (for example, JP-A-2005-134873). In the case of stereolithography, it is important to use pulsed laser light in a wavelength region that allows the photosensitive polymer film to exhibit a photosensitive function.

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 site that exhibits the photosensitive function in the photosensitive polymer.
In particular, even if 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 utilizing a multiphoton absorption process upon irradiation with the pulsed laser light, The photosensitive polymer film can exhibit a photosensitive function.

  Specifically, when the pulsed laser light emitted from the light source is condensed and irradiated with the condensed pulsed laser light, multiphoton absorption (for example, two-photon absorption, three-photon absorption, four-photon absorption, Photosensitive polymer film, even if 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. Is substantially irradiated with a pulsed laser beam in a wavelength region that causes the photosensitive polymer film to exhibit a photosensitive function.

  As described above, the pulsed laser beam for the interference exposure may be substantially a pulsed laser beam in a wavelength region that causes 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 of the present invention is used as a photosensitizing material, dispersed in an ultraviolet curable resin or the like, and a photosensitive material solid is used, and the two-photon absorption ability of the photosensitive material solid is used to focus spots (or It is possible to obtain an ultra-precise three-dimensional structure using the characteristic that only the areas to be strengthened are cured.

As described above, when the composite metal nanoparticles of the present invention and a multiphoton absorption reaction accelerator (two-photon absorption polymerization initiator or two-photon absorption photosensitizer) are combined, a multiphoton absorption reaction assistant (two-photon absorption reaction) Auxiliary agent).
Compared to conventional two-photon absorption materials (two-photon absorption polymerization initiators or two-photon absorption photosensitizers), two-photon absorption sensitivity is high, enabling high-speed modeling, and a compact and inexpensive laser as an excitation light source Since a light source can be used, it is possible to develop practical applications that can be mass-produced.

[Application to two-photon fluorescence microscope]
The 2 (multi) photon excitation laser scanning microscope (two photon fluorescence microscope) is a fluorescence generated by being excited by 2 (multi) photon absorption in a near-infrared pulse laser focused on a specimen surface and scanned. It is a microscope which acquires an image by detecting.
Hereinafter, embodiments of the two-photon fluorescence microscope of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments.
In FIG. 3, the schematic of the basic composition of the two-photon excitation laser scanning microscope (two-photon fluorescence microscope) in this invention is shown.

  A two-photon excitation laser scanning microscope 30 shown in FIG. 3 includes a laser light source 31 that emits sub-picosecond monochromatic coherent light pulses in the near-infrared region, and a light beam conversion optical system 32 that changes a light beam from the laser light source to a desired size. A scanning optical system 33 for condensing and scanning the light beam converted by the light beam conversion optical system on the image plane of the objective lens, an objective lens system 34 for projecting the collected converted light beam on the sample surface 35, and light A detector 37 is provided.

  That is, the two-photon absorption fluorescent material (composite metal nanoparticles) in the specimen is collected by focusing the pulsed laser beam through the dichroic mirror 36 at the time of observation through the beam conversion optical system and the objective lens system and focusing on the specimen surface. The fluorescence induced based on the two-photon absorption. That is, a system using a two-photon absorption fluorescent material (for example, a fluorescent dye for a two-photon fluorescence microscope) is used as the multiphoton absorption material of the multiphoton absorption reaction material in the present invention.

Next, the specimen surface is scanned with a laser beam, and the fluorescence intensity at each location is plotted with a computer (not shown) based on position information obtained by detecting the fluorescence with a photodetector such as the photodetector 37. Thus, a three-dimensional fluorescent image is obtained. As a laser beam scanning mechanism, for example, scanning may be performed using a movable mirror such as a galvano mirror, or a specimen containing 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 or dispersing specimens, and can be used not only for industrial applications but also for three-dimensional image microimaging of biological cells, etc. A compound having an absorption cross section is desired.

The multiphoton absorption material (two-photon absorption fluorescent material) containing the composite metal nanoparticles of the present invention can be used as a multiphoton absorption reaction material (two-photon absorption fluorescence reaction material) for a two-photon excitation laser scanning microscope.
If this is used, since it has a larger two-photon absorption cross-sectional area than a conventional two-photon absorption fluorescent material, it exhibits a high two-photon absorption characteristic at a low concentration. Therefore, according to the present invention, not only a highly sensitive two-photon absorption fluorescent reaction material can be obtained, but also it is not necessary to increase the intensity of light applied to the material to be observed, and the deterioration and destruction of the material to be observed are suppressed. And adverse effects on the properties of other components in the material to be observed can be reduced.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, each Example is an example of a structure of this invention, and this invention is not limited to the Example shown below. .

Example 1
In the following procedure, a gold nanorod dispersion, formation of a buffer layer (SiO ₂ ) film, a composite nanoparticle dispersion having a gold nanorod as a core, and a composite nanoparticle / dye mixed dispersion were sequentially prepared.

[Preparation of gold nanorod dispersion]
This will be explained step by step from the creation of gold nanorods using the photoreduction method.
As a raw material solution, 70 ml of a CTAB (cetyltrimethylammonium bromide) aqueous solution (0.18 mol / l), 0.36 ml of cyclohexane, 1 ml of acetone, and 1.5 ml of an aqueous silver nitrate solution (0.01 mol / l) were added and stirred with a magnetic stirrer. Furthermore, after adding 2 ml of chloroauric acid solution (0.024 mol / l), 0.4 ml of ascorbic acid aqueous solution (0.1 mol / l) was added, and it was confirmed 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). By this step, gold nanorods were formed, and a stable dispersion of the gold nanorods was obtained. As a result of observation by a transmission electron microscope, it was confirmed that the gold nanorods in the dispersion had an average particle shape of 50 nm long axis and 12 nm short axis.
In the production of the gold nanorods, the synthesis by the photoreduction method has been shown, but it goes without saying that gold nanorods obtained by various synthesis methods such as electrolysis and growth from seed particles can also be used. By changing the growth conditions, it is possible to easily obtain gold nanorods having different aspect ratios.

[Formation of buffer layer (SiO ₂ ) film]
Next, 10 ml of an acetone solution (1 vol%) of (3-aminopropyl) ethyldiethoxysilane is added to 5 ml of the gold nanorod dispersion obtained above, followed by heat treatment at 80 ° C. for 2 hours, and the surface of the gold nanorod is SiO 2. _Two films were formed. By this step, gold nanorods with a SiO ₂ film were formed.
Further, 5 ml of cyclohexane was added and stirred to obtain a cyclohexane dispersion of gold nanorods with SiO ₂ coating. Here, it goes without saying that the selection of the oily solvent can be appropriately selected, and the dispersion method of the fine particles includes various surfactants including the compound having a thiol group, the kind of the oily solvent, and the dispersion characteristics. It is possible to adopt in consideration.

[Preparation of composite nanoparticle dispersion with gold nanorods as the core]
Next, 0.01 ml of an acetone solution of silver nitrate (0.01 mol / l) was added to 5 ml of the cyclohexane dispersion obtained above, and 0.005 ml while stirring the acetone solution of ascorbic acid (0.01 mol / l). Each was divided into two, 0.01 ml as a total amount was added and reduced by chemical reduction.
The metallic silver produced by the reduction was deposited in the form of islands on the SiO ₂ film on the surface of the gold nanorods dispersed in the solution to form silver microstructures that were separated from each other. Here, the reduction rate can be controlled by the addition amount of silver nitrate, the liquid temperature, and the addition amount of the reducing agent, and the microstructure of the metal microstructure can be controlled by appropriately selecting and combining these conditions. Is possible.
Through the above steps, a composite nanoparticle dispersion having gold nanorods as a core was obtained.

[Preparation of mixed dispersion of composite nanoparticles and dyes]
Furthermore, 0.5 ml of an acetone saturated solution of a two-photon fluorescent dye represented by the following structural formula (I) is injected and stirred into 2 ml of a composite nanoparticle dispersion having the gold nanorods as a core, and the composite nanoparticles and A mixed dispersion of the dye was obtained.

(Example 2)
Using the photoreduction method in the same manner as in Example 1, a silver nanostructure was obtained in the same manner as in Example 1, except that a gold nanorod dispersion having an average particle shape of 100 nm in major axis and 25 nm in minor axis was obtained. Was formed into an island shape, and a mixed dispersion of the composite nanoparticle and the two-photon fluorescent dye represented by the structural formula (I) was prepared.

(Example 3)
A silver microstructure was obtained by the same process as in Example 1 except that a gold nanorod dispersion having an average particle shape of 200 nm in major axis and 50 nm in minor axis was obtained using the photoreduction method in the same manner as in Example 1. Was formed into an island shape, and a mixed dispersion of the composite nanoparticle and the two-photon fluorescent dye represented by the structural formula (I) was prepared.

Example 4
In the same manner as in Example 1, using the photoreduction method, a silver nanostructure was obtained in the same manner as in Example 1 except that a gold nanorod dispersion having an average particle shape of 400 nm in major axis and 80 nm in minor axis was obtained. Was formed into an island shape, and a mixed dispersion of the composite nanoparticle and the two-photon fluorescent dye represented by the structural formula (I) was prepared.

(Example 5)
In the same manner as in Example 1, using the photoreduction method, a silver nanostructure was obtained by the same process as in Example 1, except that a gold nanorod dispersion having an average particle shape of 600 nm in major axis and 100 nm in minor axis was obtained. Was formed into an island shape, and a mixed dispersion of the composite nanoparticle and the two-photon fluorescent dye represented by the structural formula (I) was prepared.

(Example 6)
In the same manner as in Example 1, using the photoreduction method, a silver nanostructure was obtained in the same manner as in Example 1 except that a gold nanorod dispersion having an average particle shape of a major axis of 800 nm and a minor axis of 100 nm was obtained. Was formed into an island shape, and a mixed dispersion of the composite nanoparticle and the two-photon fluorescent dye represented by the structural formula (I) was prepared.

(Example 7)
Using the photoreduction method in the same manner as in Example 1, a silver nanostructure was obtained by the same process as in Example 1, except that a gold nanorod dispersion having an average particle shape of 1600 nm in major axis and 150 nm in minor axis was obtained. Was formed into an island shape, and a mixed dispersion of the composite nanoparticle and the two-photon fluorescent dye represented by the structural formula (I) was prepared.

(Example 8)
First, the same steps as in Example 1 ([preparation of gold nanorod dispersion], [formation of buffer layer (SiO ₂ ) film], [preparation of composite nanoparticle dispersion having gold nanorods as a core]) An island-like silver microstructure was formed on a SiO ₂ film on the surface of a gold nanorod having a major particle size of 50 nm major axis and 12 nm minor axis. A dispersion (cyclohexane solution) containing composite nanoparticles was obtained.

Next, 1 ml of an acetone solution (5 vol%) of (3-aminopropyl) ethyldiethoxysilane is added to the above cyclohexane solution of the composite nanoparticles, and heat treatment is performed at 80 ° C. for 2 hours to form two layers on the surface of the composite nanoparticles. An SiO ₂ film of the eye was formed.

0.01 ml of an acetone solution of silver nitrate (0.01 mol / l) is added to the dispersion solution of the composite nanoparticles on which the second-layer SiO ₂ film is formed, and further an acetone solution of ascorbic acid (0.01 mol / l) is added. While stirring, 0.005 ml was divided into 2 portions, 0.01 ml ml was added as a total amount, and silver was reduced by chemical reduction. The metallic silver produced by the reduction was deposited in the form of islands on the second layer SiO ₂ film of the composite metal nanoparticles on the surface of the ultrafine particles dispersed in the solution.
Through the steps as described above, a cyclohexane dispersion solution of composite metal nanoparticles having a metal microstructure having a structure in which two layers of island-shaped silver separated by a SiO ₂ film as a buffer layer was obtained was obtained. .
Furthermore, the cyclohexane dispersion solution of the composite metal nanoparticles is mixed with a solution containing the two-photon fluorescent dye represented by the structural formula (I) in the same manner as in Example 1, and the composite metal nanoparticles and the two-photon fluorescent dye are mixed. A mixed dispersion was prepared.

Example 9
In the following procedure, a gold nanorod dispersion, a composite nanoparticle dispersion using gold nanorods as a core, and a composite nanoparticle / dye mixed dispersion were sequentially prepared.

As a raw material solution, 70 ml of a CTAB (cetyltrimethylammonium bromide) aqueous solution (0.18 mol / l), 0.36 ml of cyclohexane, 1 ml of acetone, and 1.5 ml of an aqueous silver nitrate solution (0.01 mol / l) were added and stirred with a magnetic stirrer. Furthermore, after adding 2 ml of chloroauric acid solution (0.024 mol / l), 0.4 ml of ascorbic acid aqueous solution (0.1 mol / l) was added, and it was confirmed 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). By this step, gold nanorods were formed, and a stable dispersion of the gold nanorods was obtained. As a result of observation by a transmission electron microscope, it was confirmed that the gold nanorods in the dispersion had an average particle shape of 50 nm long axis and 12 nm short axis.

  To 5 ml of this dispersion, 10 ml of an acetone solution (1 vol%) of dodecanethiol as a surfactant was added and stirred, and further 5 ml of cyclohexane was added and stirred and allowed to stand. Gold nanorods were stably dispersed in cyclohexane.

  Furthermore, 0.01 ml of an aqueous solution of silver nitrate (0.01 mol / l) was added to 5 ml of a cyclohexane dispersion of gold nanorods stably dispersed with dodecanethiol as a surfactant, and further an acetone solution of ascorbic acid (0. (01 mol / l) was divided into two portions of 0.005 ml while stirring, and 0.01 ml was added as a total amount, followed by reduction by chemical reduction. The metallic silver produced by the reduction was deposited in the form of islands (metal microstructures) on the surface of the gold nanorods dispersed in the solution. Through the above steps, a composite nanoparticle dispersion having gold nanorods as a core was obtained.

  Further, 0.5 ml of an acetone saturated solution of a two-photon fluorescent dye represented by the following structural formula (I) is injected and stirred into 2 ml of a composite nanoparticle dispersion having a gold nanorod as a core, and the composite nanoparticle and the dye are mixed. A mixed dispersion was obtained.

(Comparative Example 1)
A two-photon fluorescent dye solution was prepared by mixing 2 ml of cyclohexane with 0.5 ml of a saturated acetone solution of a two-photon fluorescent dye represented by the following structural formula (I). This solution corresponds to a solution obtained by removing the composite nanoparticles from the mixed dispersion of composite nanoparticles and dyes shown in Examples 1 to 9.

(Comparative Example 2)
By the same process as in Example 1, a SiO ₂ film was formed on the surface of the gold nanorod having an average particle shape having a major axis of 50 nm and a minor axis of 12 nm.
0.05 ml of an acetone solution (0.01 mol / l) of silver nitrate is added to 5 ml of a cyclohexane dispersion of the obtained gold nanorods with SiO ₂ coating, and further, while stirring an acetone solution (0.01 mol / l) of ascorbic acid. 0.005 ml each was divided into 10 times, 0.05 ml was added as a total amount, and reduction was carried out by chemical reduction. The metallic silver produced by the reduction is deposited (film-like) so as to cover the entire SiO ₂ film surface of the gold nanorods dispersed in the solution, and the composite metal nanoparticles having a structure in which the silver film is laminated on the so-called buffer layer are formed. Obtained.

  Further, 0.5 ml of an acetone saturated solution of the two-photon fluorescent dye represented by the structural formula (I) is injected and stirred into 2 ml of the composite nanoparticle dispersion having the gold nanorod as a core, and the composite nanoparticle and the dye are mixed. A mixed dispersion was obtained.

(Comparative Example 3)
By the same steps as in Example 9, 5 ml of a cyclohexane dispersion of gold nanorods having an average particle shape of 50 nm major axis and 12 nm minor axis, which was stably dispersed with dodecanethiol as a surfactant, was prepared. A two-photon fluorescent dye solution was prepared by mixing the gold nanorod cyclohexane dispersion with the two-photon fluorescent dye represented by the structural formula (I).

  The following two-photon fluorescence measurements 1 to 3 were measured using the dispersions prepared in Examples 1 to 9 and Comparative Examples 1 to 3.

<Two-photon fluorescence measurement 1>
A mixed dispersion of silver-coated composite nanoparticles and a two-photon fluorescent dye was placed in an optical cell having an optical path length of 1 mm to prepare a measurement sample. An infrared femtosecond laser, Spectra Physics Co., Ltd., MaiTai (wavelength 780 nm) is used as the two-photon excitation light source, and the two-photon excitation fluorescence is measured with a condensing lens having a focal length of 100 mm and connected to the mixed solution. did.
Regarding the mixed dispersions of the silver-coated composite nanoparticles of Examples 1 to 7 and the two-photon fluorescent dye, the enhancement of two-photon fluorescence is shown in Table 1 below (the excitation light intensity is an average output of 80 mW). Note that Comparative Example 1, which is a relative comparison, is not described in Table 1.
The meanings of the symbols in the evaluation are as follows.
A: Remarkable enhancement effect was observed.
○: The effect of enhancing was recognized.
(Triangle | delta): What showed the fluorescence intensity comparable as the reference | standard solution.

  As can be seen from Table 1, each of the two-photon fluorescent dye solutions of Examples 1 to 7 has a strong fluorescence enhancement as compared with Comparative Example 1 (two-photon dye solution not containing composite nanoparticles). A significant enhancement effect was observed.

<Two-photon fluorescence measurement 2>
Using the same measurement system as the two-photon fluorescence measurement 1, the average output of the excitation light source was set to 400 mW, and the two-photon fluorescence light amount was measured. Samples (dispersions) used for the measurement are Example 1, Example 9, and Comparative Example 1.
Each of the three samples was put in a cell having an optical path length of 1 mm, and the sample in the cell was set so as to be the focal position of the excitation light source, and excitation light was continuously irradiated. Table 2 below shows the results obtained by comparing the amount of fluorescent light immediately after the start of irradiation and the amount of fluorescent light after 30 minutes of continuous irradiation of the same point with each sample in comparison with Comparative Example 1. Note that Comparative Example 1, which is a relative comparison, is not described in Table 2.
The meanings of the symbols in the evaluation are as follows.
A: Remarkable enhancement effect was observed.
○: The effect of enhancing was recognized.

As can be seen from the results in Table 2, both the two-photon fluorescent dye solutions of Example 1 and Example 9 showed a good fluorescence enhancement effect at the start of excitation light irradiation. Even in the fluorescence intensity 20 minutes after the irradiation, in the case of Example 1 in which the island-shaped metal microstructure was provided on the SiO ₂ buffer layer, the enhancement effect was not reduced. On the other hand, in Example 9 in which the island-like metal microstructure was provided directly on the gold nanorod without forming the SiO ₂ buffer layer, the enhancement effect was slightly weaker than that at the start of irradiation, but the enhancement effect was recognized. From this result, it was confirmed that the change with time (reduction) of the two-photon fluorescence enhancement effect generated by the excitation light can be prevented by forming the metal microstructure on the buffer layer.

<Two-photon fluorescence measurement 3>
Using the same measurement system as in the two-photon fluorescence measurement 1, under the same measurement conditions, the two-photon fluorescence intensity of the mixed dispersions of Examples 1 and 8 and Comparative Examples 2 and 3 was observed, and the fluorescence intensity was relatively evaluated. The results are shown in Table 3 below.
The meanings of the symbols in the evaluation are as follows.
A: The one with the strongest fluorescence intensity.
○: Next, the fluorescence intensity was strong.
●: The next weakest fluorescent light in the comparison.
(Triangle | delta): The thing with the weakest fluorescence intensity compared.

As can be seen from the results in Table 3, compared with Comparative Example 2 including composite metal nanoparticles in which the entire SiO ₂ buffer layer surface of the gold nanorods was uniformly coated with a silver film, and Comparative Example 3 consisting only of gold nanorods. In the case of Example 1 and Example 8, large enhancement was shown.
Furthermore, from comparison between Example 1 and Example 8, composite metal nanoparticles (Example 8) in which two layers of island-shaped silver are laminated on the gold nanorod surface via a SiO ₂ buffer layer show the greatest enhancement effect. It was. From this result, it was recognized that the enhancement effect by the further plasmon enhancement field is exhibited by providing a plurality of metal microstructures.

  From the evaluation results in Tables 1 to 3 above, composite metal nanoparticles capable of forming a photoreaction enhancement / sensitization field in the wavelength region from the near infrared to the blue region are provided, and the composite metal nanoparticles And multiphoton absorption reaction materials, or multiphoton absorption reaction aids, it is possible to cause a reaction at any three-dimensional position inside the substance while lowering the reaction threshold. It is possible to realize application to various uses satisfying requirements such as a medium, a material for three-dimensional stereolithography, and a multiphoton fluorescence microscope, such as many ultra high density, ultra high definition, and high resolution.

1 is a schematic diagram showing a recording / reproducing system configuration (a) and a configuration section (b) of a recording medium of a three-dimensional multilayer optical memory according to the present invention. It is a schematic block diagram of the apparatus used when carrying out the optical modeling using the multiphoton absorption reaction material containing the composite metal nanoparticle of this invention and a multiphoton absorption material. It is the schematic which shows the basic composition of the two-photon excitation laser scanning microscope (two-photon fluorescence microscope) in this invention.

Explanation of symbols

L laser light 1 laser light source for recording 2 laser light source for reproduction 3 pinhole 4 detector 5 objective lens 6 three-dimensional recording medium 11 substrate 12 substrate (or reflective film)
13 Recording Bit 14 Recording Layer 15 Intermediate Layer (Protective Layer)
20 Stereolithography 21 Near-infrared pulse laser light source (light source)
23 shutter 24 ND filter 25 mirror scanner 26 Z stage 27 lens 28 computer 29 photocurable resin liquid 30 two-photon excitation laser scanning microscope 31 laser light source 32 light beam conversion optical system 33 scanning optical system 34 objective lens system 35 sample surface 36 dichroic mirror 37 photodetectors

Claims (8)

On the surface of the core particle length and width direction have different shape anisotropy, set apart metal microstructure expressing plasmon enhanced field by irradiation with light in an island shape,
The core particles having shape anisotropy having different lengths in the vertical and horizontal directions are gold nanorods,
A buffer layer is provided for isolating the bonding interface between the surface of the core particle having shape anisotropy having different lengths in the vertical and horizontal directions and the metal microstructure that expresses the plasmon enhancement field by light irradiation,
A composite metal nanoparticle, wherein the metal microstructure that exhibits a plasmon enhancement field by light irradiation is silver . 2. The composite metal nanoparticle according to claim 1, wherein the metal microstructure exhibiting a plasmon enhancement field by light irradiation is composed of a plurality of layers. A multiphoton absorption reaction material comprising the composite metal nanoparticles according to claim 1 or 2 and a multiphoton absorption material. The multiphoton absorption reaction material according to claim 3 , wherein the multiphoton absorption material is a two-photon absorption material. The multiphoton absorption reaction material according to claim 3 or 4 , wherein the multiphoton absorption material is a multiphoton absorption dye. A multiphoton absorption reaction product obtained from the multiphoton absorption reaction material according to any one of claims 3 to 5 . A multiphoton absorption reaction auxiliary agent comprising the composite metal nanoparticles according to claim 1 or 2 and a multiphoton absorption reaction accelerator. The multiphoton absorption reaction accelerator according to claim 7 , wherein the multiphoton absorption reaction accelerator is a two-photon absorption reaction accelerator.

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