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Circularly polarized light-emitting nanoparticle

外国特許コード F110005529
整理番号 N052-23WO
掲載日 2011年9月7日
出願国 アメリカ合衆国
出願番号 93506609
公報番号 20110038025
公報番号 8390913
出願日 平成21年3月26日(2009.3.26)
公報発行日 平成23年2月17日(2011.2.17)
公報発行日 平成25年3月5日(2013.3.5)
国際出願番号 JP2009056060
国際公開番号 WO2009122994
国際出願日 平成21年3月26日(2009.3.26)
国際公開日 平成21年10月8日(2009.10.8)
優先権データ
  • 特願2008-088945 (2008.3.29) JP
  • 2009JP056060 (2009.3.26) WO
発明の名称 (英語) Circularly polarized light-emitting nanoparticle
発明の概要(英語) Provided is a compound semiconductor nanoparticle that exhibits circularly polarized luminescence characteristics.
CdS prepared inside a core of ferritin, which is a cage-like protein, exhibits a high circularly polarized luminescence (CPL).
A wavelength of the circularly polarized luminescence (CPL) can be controlled by laser irradiation, thereby enabling utilization of the compound semiconductor nanoparticle in the field of bionanotechnology, for example, in creating a WORM (Write-Once Read-Many times) memory.
As the cage-like protein, which is a protein with a cavity formed therein, a protein belonging to the ferritin protein family, such as apoferritin, or a recombinant thereof can be used.
従来技術、競合技術の概要(英語) BACKGROUND ART
Recently in the field of biotechnology, remarkable developments are being made, applications to other fields are being sought, and research on application to semiconductor microfabrication technology (bionanotechnology) is also being pursued.
In the biotechnology field, products (amino acid residues) can be controlled at the molecular level based on a blueprint called "DNA," and all proteins formed from the various amino acid residues have a self-assembling ability that enables forming of "nanoblocks" that are not dispersed in size.
Thus by employing biotechnology, the formation of a product can be controlled at the nanoscale, and in the incorporation of a semiconductor component in the product, application of biotechnology to semiconductor microfabrication technology becomes apparent.
Here, as arts in which biotechnology is applied to semiconductor microfabrication technology, arts of forming a quantum dot using a cage-like protein called ferritin, which is present in living bodies, have been disclosed (refer to Patent Document 1 and Patent Document 2).
As shown in FIG. 1, ferritin has a structure that includes a spherical protein outer shell portion, which has a diameter of 12 nm and is made up of 24 protein monomer, and a core portion 1A, which is a central portion of the outer shell portion, has a diameter of approximately 6 nm, absorbs Fe ions from inside a living body, and holds the ions in the form of an oxide.
Ferritin is called a cage-like protein due to having the protein outer shell portion and the core portion.
Ferritin has an active site that oxidizes the absorbed Fe ions, and the Fe ions are accumulated as the oxide, 5Fe2O3.9H2O.
A protein with which the metal oxide core is removed from the ferritin is called apoferritin, and besides Fe, apoferritin is capable of accumulating microparticles made of various metals, such as nickel (Ni), cobalt (Co), manganese (Mn), etc. TEM images of various metal nanoparticles prepared inside apoferritin are shown in FIG. 2
As described above, ferritin has the structure including the metal oxide in the core portion and the outer shell in which 24 protein monomers are assembled together.
The ferritin has a self-assembling ability and can thus be formed readily as a uniform film, and the outer shell proteins have a characteristic of being readily decomposed and removed by UV ozone heat treatment, etc.
Here, the self-assembling ability of ferritin can be utilized to control an adsorption position of ferritin on a semiconductor substrate, and by selectively removing the outer shell protein of the ferritin, a structure with which the core metal oxide is aligned in a two-dimensional matrix as shown in FIG. 2 can be prepared.
It is also known that, with ferritin, a nanoparticle of a compound semiconductor, formed of two or more types of elements, can be prepared in the core portion (refer to Patent Document 3).
Due to a quantum confinement effect, a nanoparticle of a compound semiconductor expresses physical properties that differ greatly from those of a bulk state.
In particular, such nanoparticles have ideal fluorescence characteristics, such as a high luminance, a high light resistance, a broad excitation spectrum, and a narrow fluorescence spectrum, and are thus attracting attention as next-generation optoelectronic materials.
Meanwhile, since the development of a water-soluble compound semiconductor nanoparticle that uses a hydrophilic coating molecule, active research is being carried out on applications of compound semiconductor nanoparticles to biotechnology, such as bioimaging, immunoassay, etc.
By the art disclosed in Patent Document 3, use of a quantum size effect of a microparticle made of a semiconductor has become possible, and in a case of a compound semiconductor microparticle that emits fluorescence when excited, use in a biological substance labeling method, etc., has become possible.
TEM images of various compound semiconductor nanoparticles prepared inside apoferritin are shown in FIG. 3.
As described above, compound semiconductor nanoparticles are gathering attention as a next-generation optoelectronic material.
However presently, the circumstances are such that the uses of compound semiconductor nanoparticles in the biotechnology field are limited to alternatives to light-emitting organic molecules.
Up to now, the present inventors, with an aim at creating highly luminescent circularly polarized light-emitting molecules, have created helical polymers, aromatic low-molecular-weight molecules, and compound semiconductor nanoparticles that are optically active and light-emitting and have examined circularly polarized luminescence (CPL) characteristics of these substances.
Circularly polarized luminescence (CPL) refers to a difference in emission intensities of right circularly polarized light and left circularly polarized light emitted from an optically active molecule (see FIG. 4).
Although such circularly polarized luminescence (CPL) has been used from before for evaluation of a steric structure of an organic molecule in an excited state, application to polarized light sources for high-luminance liquid crystal displays as well as three-dimensional displays, memory materials, optical communication, and other forms of advanced light information processing are being anticipated recently.
As substances exhibiting circularly polarized luminescence (CPL), bioluminescent substances, light-emitting rare earths, optically active conjugate polymers, etc., are known.
Among compound semiconductors, GaAs has been reported to exhibit circularly polarized luminescence when excited by a circularly polarized laser.
However, there have been no reports so far of circularly polarized luminescence being achieved with a compound semiconductor nanoparticle (see, for example, Non-Patent Document 1).
Although as an attempt to see if a compound semiconductor exhibits circularly polarized luminescence (CPL) has been made in regard to circular dichroism (CD) active CdS synthesized from an optically active thiol compound, this report indicated that the compound semiconductor nanoparticle is CPL inactive (see Non-Patent Document 2).

PRIOR ART DOCUMENTS
[Patent Document 1] JP99-45990A
[Patent Document 2] JP2003-086715A
[Patent Document 2] WO2007/032241
[Non-Patent Document 1] J. Am. Chem. Soc., 128, 9030 (2006).
[Non-Patent Document 2] Chem. Commun., M. P. Moloney, et al., 2007, page 3900.

特許請求の範囲(英語) [claim1]
1. A circularly polarized light-emitting nanoparticle comprising a compound semiconductor nanoparticle encapsulated in a protein cage, further characterized in that a circularly polarized luminescence wavelength is controlled by laser irradiation of the nanoparticle.
[claim2]
2. The circularly polarized light-emitting nanoparticle according to claim 1, wherein the protein is apoferritin.
[claim3]
3. The circularly polarized light-emitting nanoparticle according to claim 1, wherein the compound semiconductor is a II-VI compound semiconductor.
[claim4]
4. The circularly polarized light-emitting nanoparticle according to claim 3, wherein the II-VI compound semiconductor is CdS or ZnS.
[claim5]
5. A quantum dot memory, wherein circularly polarized light-emitting nanoparticles according to claim 1 are disposed two-dimensionally inside an insulating film layer.
[claim6]
6. A WORM type single quantum dot memory comprising circularly polarized light-emitting nanoparticles according to claim 1.
[claim7]
7. A security paint material comprising circularly polarized light-emitting nanoparticles according to claim 1.
[claim8]
8. A circularly polarized light-emitting nanoparticle comprising a compound semiconductor nanoparticle that is surface-modified by a protein, further characterized in that a circularly polarized luminescence wavelength is controlled by laser irradiation of the nanoparticle.
[claim9]
9. The circularly polarized light-emitting nanoparticle according to claim 8, wherein the compound semiconductor is a II-VI compound semiconductor or a III-V compound semiconductor.
[claim10]
10. A wavelength control method comprising obtaining a compound semiconductor nanoparticle encapsulated in a protein cage, and controlling a circularly polarized luminescence wavelength by laser irradiation of the circularly polarized light-emitting nanoparticle.
[claim11]
11. The wavelength control method according to claim 10, wherein the circularly polarized luminescence wavelength is shifted to a longer wavelength by the laser irradiation.
[claim12]
12. The wavelength control method according to claim 10, wherein an emission wavelength is shifted to a shorter wavelength by the laser irradiation.
  • 発明者/出願人(英語)
  • NAITOU MASANOBU
  • IWAHORI KENJI
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
  • NARA INSTITUTE OF SCIENCE AND TECHNOLOGY
国際特許分類(IPC)
米国特許分類/主・副
  • 359/241
  • 359/301
  • 359/321
参考情報 (研究プロジェクト等) CREST Creation of Novel Nano-material/System Synthesized by Self-organization for Medical Use AREA
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