JP2018035406A - Novel core-shell type nanoparticle and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel nanoparticle that can suppress a temporal change of saturation magnetization and can maintain, therefore, a higher level of the saturation magnetization after temporal change.SOLUTION: A core-shell type nanoparticle contains (a) a core containing Au, and (b) a shell containing at least one selected from the group consisting of Fe, Co, and Ni. In a preferred embodiment, the portion (a) consists of a simple substance of Au, and the portion (b) comprises Fe and Co in a metal state.SELECTED DRAWING: None

Description

  The present invention relates to a novel core-shell type nanoparticle and a method for producing the same.

  Nanoparticles made of magnetic materials are expected to be applied to magnetic separation, magnetic immunodiagnosis, MRI imaging, and the like by utilizing the magnetic signals generated by nanoparticles and the ability to be manipulated by an external magnetic field. On the other hand, metal nanoparticles have physical and chemical properties different from those of bulk metals, and are extremely important substances from the viewpoints of both basic and applied. In particular, among metal nanoparticles, nanoparticles of noble metals such as Au and Ag are interesting substances that exhibit unique optical effects such as localized surface plasmon resonance and surface enhanced Raman scattering.

  In recent years, magnetic-plasmonic hybrid nanoparticles have attracted attention as a promising material capable of simultaneously performing plasmonic imaging and magnetic manipulation. Non-Patent Document 1 has, as magnetic-plasmonic composite nanoparticles, a core composed of Ag, a magnetic shell composed of FeCo, and a shell composed of Ag on the outside thereof (Ag @ FeCo @ Reported on nanoparticles. Non-Patent Document 2 reports the resistance of AgAu @ FeCo @ AgAu type nanoparticles to oxidation compared to Ag @ FeCo @ Ag type nanoparticles.

  On the other hand, as a method for producing metal nanoparticles, a method by reduction of a metal salt is well known. As metal salts, halides, nitrates and the like are mainly used. In the aforementioned non-patent document 2, nanoparticles are synthesized by a production method combining a polyol method and a hot injection method. Here, after heating to a mixed solution of silver nitrate, oleylamine, oleic acid, 1,2-hexadecanediol, and tetraethylene glycol, iron (III) acetylacetonate, cobalt (II) acetylacetonate, oleylamine, and By adding a mixed solution of toluene, and further increasing the temperature, a mixed solution of silver nitrate, oleylamine, and toluene (in the case of synthesizing AgAu @ FeCo @ AgAu type, further containing gold (III) acetate) is added. It has been reported that the desired nanoparticles were obtained.

S. Nishimura et al. , J. et al. Phys. Chem. C 116 (2012) 4511 M.M. Takahashi et al. , 2016 MRS Spring Meeting & Exhibit J. et al. P. 13 (March 28-April 1, 2016)

  An object of the present invention is to provide a novel nanoparticle capable of suppressing a change in saturation magnetization with time, and thus maintaining a higher saturation magnetization after a change with time. is there.

  Recently, the present inventors synthesized Au @ FeCo nanoparticles, a nanoparticle composed of a core composed of Au and a shell composed of an FeCo alloy, by a novel manufacturing method. In the conventional Ag @ FeCo @ Ag nanoparticles, the oxidation of the intermediate shell composed of FeCo is suppressed to some extent by the electron transfer from the Ag core to the FeCo shell. Long-term chemical stability in air may not be sufficient. In this regard, Au @ FeCo nanoparticles have a higher electronegativity than Au, and therefore the degree of electron transfer from the core to the shell is larger, so that the decrease in saturation magnetization over time can be suppressed. Practically, it can be expected to have better oxidation resistance than Ag @ FeCo.

The present invention provides the following.
[1] (a) a core containing Au;
(B) a shell containing at least one selected from the group consisting of Fe, Co, and Ni;
Core-shell type nanoparticles containing
[2] The nanoparticle according to 1, wherein the portion (a) is made of Au.
[3] The nanoparticle according to any one of 1 and 2, wherein the part (b) contains Fe and Co.
[4] The nanoparticle according to any one of 1 to 3, which has magnetism.
[5] The nanoparticle according to any one of 1 to 4, wherein the part (b) includes at least one metal state selected from the group consisting of Fe, Co, and Ni.
[6] The nanoparticle according to any one of 1 to 5, wherein the portion (b) has an oxide containing at least one selected from the group consisting of Fe, Co, and Ni.
[7] A method for producing nanoparticles according to any one of 1 to 6, comprising a step of reducing gold acetate (III) to obtain part (a).
[8] The production method according to 7, wherein gold (III) acetate is reduced in the presence of an Fe salt and a Co salt.

  According to the present invention, a novel core-shell nanoparticle and a method for producing the same are provided.

TEM image of the obtained Au @ FeCo nanoparticles XRD pattern of the obtained Au @ FeCo nanoparticles

  The present invention provides a core-shell nanoparticle having a novel structure that can suppress the change in saturation magnetization with time, and thus can maintain the saturation magnetization after the change with time higher.

<Nanoparticles>
The present invention provides a core-shell type nanoparticle comprising the following part (a) and part (b).
(A) Core containing Au (b) Shell containing at least one selected from the group consisting of Fe, Co, and Ni

<Part (a)>
The part (a) in the nanoparticle contains at least gold (Au). This is because Au has a higher electronegativity than Ag (silver), and therefore has a higher degree of electron transfer from the core to the shell, and is considered to have better oxidation resistance than the Ag @ FeCo system. The part (a) is selected from the group consisting of Ag, platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), and osmium (Os), which are noble metals other than Au. Or at least one of the same group 11 elements as Au and Ag, and may contain copper (Cu) having similar properties. Since these materials are inert and stable, the stability of the nanoparticles against oxidation can be enhanced as in the case of Au. In addition, coloring by plasmon absorption has the advantage that the presence of nanoparticles can be detected and the concentration of particles can be quantified by measuring absorbance. In a preferred embodiment, the portion (a) is made of Au or an alloy of Ag and Au, regardless of the material of the portion (b) (Au alone, that is, substantially consisting of Au or substantially consisting of Au). It is preferably composed of an alloy of Ag and Au), more preferably Au alone. This is because it is easy to determine the particle concentration by measuring the absorbance even when the concentration due to plasmon absorption is strong and the concentration is low in the liquid.

<Part (b)>
The part (b) in the nanoparticles is composed of a material containing at least one selected from the group consisting of Fe (iron), Co (cobalt), and Ni (nickel).

In a preferred embodiment, part (b) contains Fe and Co, regardless of the material of part (a). The reason is that when Fe and Co are contained, a high saturation magnetization and a high magnetic permeability are exhibited by forming an FeCo alloy. In general, it is known that the addition of Co to Fe increases saturation magnetization, and in a more preferred embodiment, the portion (b) is composed of an alloy of Fe _30-70 and Co, and in a more preferred embodiment, the portion ( b) is composed of a magnetic material containing an alloy of Fe _40-60 and Co, for example Fe ₅₀ Co ₅₀ .

Part (b) may include at least one metal state selected from the group consisting of Fe, Co, and Ni. If these are included, the saturation magnetization tends to increase, which is preferable. Further, the portion (b) may include an oxide including at least one selected from the group consisting of Fe, Co, and Ni. When it has an oxide, changes in various physical properties such as coloring and magnetism due to oxidation of the nanoparticles over time are reduced, which is preferable in practical use. In particular, if the oxide has magnetism, such as magnetite (Fe ₃ O ₄ ), maghemite (γ-Fe ₂ O ₃ ) CoFe ₂ O ₄ , oxides of ferrites such as NiFe ₂ O ₄ , Even when the magnetism changes, the high saturation magnetization is exhibited, which is particularly preferable in practice. An example of at least one metal state selected from the group consisting of Fe, Co, and Ni is FeCo. Examples of at least one oxide selected from the group consisting of Fe, Co, and Ni include nickel oxides such as NiO and NiO ₂ , cobalt oxides such as CoO, CoO ₂ , CoO ₃ , and Co ₃ O ₄ , FeO, Fe ₂ O ₃ , Fe ₃ O ₄ , Fe ₄ O _{5 and} other iron oxides, Co _x Fe _1-x O, Co _x Fe _2-x O ₄ , Co ₂ FeO _{4 and} other cobalt and iron composite oxidation _{things, Ni x Fe 1-x O} , Ni x Fe 2-x O 4, Ni 2 FeO 4 such composite oxides of nickel and iron, CoNi ₂ O ₄ or the like composite oxide of nickel and cobalt, Co _0.5 Ni _0.5 Fe ₂ O _{4 and} other complex oxides of nickel, cobalt, and iron. Particularly preferred examples are CoFe ₂ O ₄ and Fe ₃ O ₄ . The presence of at least one metal state selected from the group consisting of Fe, Co, and Ni can be confirmed by XPS (X-ray photoelectron spectroscopy) measurement, and consists of Fe, Co, and Ni. The inclusion of an oxide containing at least one selected from the group can be confirmed by XRD (X-ray diffraction) measurement.

The material constituting the part (b) is preferably selected from magnetic materials as appropriate because it can impart magnetism to the nanoparticles. The known magnetic material is selected from, for example, these oxides such as Fe alone, Co alone, Ni alone, magnetite (Fe ₃ O ₄ ), maghemite (γ-Fe ₂ O ₃ ), or Fe, Co, and Ni. And a magnetic material containing two or more elements. Examples of the magnetic material containing two or more elements selected from Fe, Co, and Ni include, for example, FeCo alloys, FeNi alloys, CoNi alloys, FeCoNi alloys, and ferrites such as CoFe ₂ O ₄ and NiFe ₂ O _4. An oxide etc. are mentioned.

  The material constituting the part (b) may further contain other elements. Examples of other elements are nitrogen (N) or carbon (C), or Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo, Ag, Ga, Sc, It may be at least one nonmagnetic metal selected from V, Y, Nb, Pb, Cu, In, Sn, and rare earth elements.

<Core, shell, double shell>
The nanoparticle of the present invention is a core-shell type, wherein the part (a) is a core and the part (b) is a shell. In a preferred embodiment, the nanoparticles may be of a double shell type having a second shell outside the shell. In the present invention, the term “core shell type” includes a double shell type unless otherwise specified, and the term “shell” includes a second shell (also referred to as “double shell”). In addition, regarding the present invention, when the configuration of the nanoparticles is expressed using “@”, the inner side is shown on the left side and the outer side is shown on the right side unless otherwise specified. For example, “Au @ FeCo @ Ag” is a double-shell type (core-shell-second shell type) nanoparticle, a core made of Au and a shell made of a material containing Fe and Co. And nanoparticles including the outermost shell (double shell) made of Ag.

  The average particle diameter of the core in the nanoparticles of the present invention is not particularly limited, but is, for example, from 1 nm to 500 nm, preferably from 2 nm to 200 nm, and more preferably from 4 nm to 100 nm. Further, in the nanoparticles of the present invention, the outermost shell in the case of not being a double shell type, and the average thickness of the inner shell in the case of a double shell type are not particularly limited, for example, 0.5 nm to 250 nm, It is preferably 1 nm or more and 100 nm or less, and more preferably 2 nm or more and 50 nm or less. Furthermore, in the nanoparticles of the present invention, the average thickness of the outermost shell in the case of the double shell type is not particularly limited, for example, 0.5 nm or more and 20 nm or less, preferably 0.7 nm or more and 10 nm or less, More preferably, it is 1 nm or more and 5 nm or less.

  The average particle diameter of the entire nanoparticle is not particularly limited, but it is 3 nm or more and 1000 nm or less, for example, 5 nm or more and 500 nm or less, regardless of whether it is a double shell type or a double shell type. Is more preferable, and it is more preferably 8 nm or more and 200 nm or less.

  The average particle diameter of the nanoparticle core and the average thickness of the shell can be determined as follows. A nanoparticle sample diluted with an appropriate solvent such as ethanol is dropped on the microgrit and dried to prepare a sample for TEM observation. Thereafter, a sample STEM-HAADF image is taken. At this time, a qualitative analysis of the constituent elements can also be performed using an EDX (Energy Dispersive X-ray spectroscopy) apparatus or the like. The area range of the nanoparticles in the obtained STEM-HAADF image is processed using image analysis software, and the average value is obtained by measuring the core particle diameter (equivalent circular area diameter) and the shell thickness contained in the composite nanoparticle. The average particle diameter of the core and the thickness of the shell are obtained based on the calculated values. Depending on the sample, the core-shell structure may be confirmed from the TEM image. The average particle size of the nanoparticles can be measured as follows. First, a TEM (transmission electron microscope) photograph including a sufficiently large number of nanoparticles in the visual field is prepared. Next, in this TEM photograph, the particle diameters of a plurality of, preferably 300 to 500, nanoparticles are measured. When the shape of the nanoparticles is not a perfect circle, the major axis diameter is measured. The average value of the measured particle diameter is calculated, and this is taken as the average particle diameter of the nanoparticles.

<Magnetic>
The nanoparticles preferably have magnetism. This is because if nanoparticles have ferromagnetism, ferrimagnetism, or superparamagnetism, they can be separated and migrated using magnetism, and the presence of nanoparticles can be detected based on magnetic signals. . More preferably, the nanoparticles have superparamagnetism. This is because in the absence of an external magnetic field, the nanoparticles do not have a magnetic moment, and thus aggregation of the nanoparticles can be suppressed. Whether the nanoparticles have ferromagnetism, ferrimagnetism, or superparamagnetism can be confirmed by measuring the magnetic properties of the nanoparticles with a magnetic property measuring apparatus equipped with a superconducting quantum interference magnetometer (SQUID). .

  The nanoparticles of the present invention having magnetism are suppressed from changing with time in saturation magnetization under practical use conditions. Therefore, even when it changes over time, the nanoparticles can maintain a higher saturation magnetization than the conventional one. Whether or not the change in saturation magnetization over time is suppressed is determined based on the measurement of the magnetization of the particles immediately after the synthesis under practical conditions (for example, an atmosphere at 25 ° C. and a relative humidity of 50%). Based on the value of magnetization measured for nanoparticles after storage for several weeks, the retention rate of saturation magnetization (maintenance rate (%) = (saturation magnetization after storage) / (saturation magnetization immediately after synthesis) × 100) Can be determined by seeking The maintenance rate is preferably 10% or more, more preferably 15% or more, and further preferably 20% or more.

<Atomic composition ratio>
In the present invention, the atomic composition ratio of Au in the nanoparticles represented by the following formula to Fe, Co and Ni, that is, (Au atom concentration in the nanoparticles): (total of Fe, Co and Ni in the nanoparticles) Can be in the range of 1 or more and 99 or less: 99 or less and 1 or more. However, (Au atom concentration in nanoparticles) + (total atom concentration of Fe, Co and Ni in nanoparticles) = 100. The atomic composition ratio is preferably 2 or more and 80 or less: 98 or less and 20 or more, more preferably 3 or more and 60 or less: 97 or less and 40 or more, and further preferably 5 or more and 50 or less: 95 or less and 50 or more.

  The atomic composition ratio can be calculated based on the measured values obtained by dissolving the target nanoparticles in an appropriate acid such as aqua regia and performing a composition analysis using a plasma emission spectrometer.

  As a result of intensive studies by the present inventors, it has been found that the reaction composition such as redox on the surface of the nanoparticles can be promoted when the atomic composition ratio is in the above range. The reason for this is not clear, but due to the difference in Fermi energy and electronegativity between part (a) and part (b), charge separation is promoted and electron donation to the surface material of the nanoparticle occurs, and reactions such as redox This is presumed to promote activity. Further, when the atomic composition ratio is in the above range, when the part (b) is made of a magnetic material, the dispersion of the nanoparticles in the liquid by the action of the part (a) while sufficiently maintaining the magnetism. It is also preferable in that the stability can be maintained and the stability of the nanoparticles against oxidation can be sufficiently enhanced.

  The atomic composition ratio is preferably 2 or more and 80 or less, more preferably 3 or more and 60 or less, and still more preferably 5 or more and 50 or less.

<Nanoparticle production method>
The method for producing the nanoparticles of the present invention is not particularly limited, and various physical methods (vapor phase deposition, laser ablation, etc.), chemical methods (metal salt reduction, sol-gel method, micelle, thermal decomposition), etc. Can be used. One particularly preferable production method is a method using reduction of a metal salt.

(Starting material)
As the metal salt which is a starting material for the nanoparticles in the present invention, various metal salts such as various metal ion salts, metal alkoxides, and organometallic complexes may be used.

Various Au salts (gold compounds) can be used. For example, gold chloride (I
), Gold iodide (I), gold cyanide (I), chlorocarbonyl gold (I), gold cyanide (I)
Potassium, sodium gold (I) cyanide, gold (I) sulfide, gold (III) bromide, gold chloride (I
II), gold iodide (III), gold acetate (III), dimethyl (acetylacetonate) gold (III), chloroauric acid (III) tetrahydrate, chloroauric acid (III) trihydrate, chloride Sodium goldate (III) dihydrate, potassium chloroaurate (III), gold sulfide (III) and the like can be used. In particular, it is preferable to use gold (III) acetate from the viewpoint of productivity because it is easy to obtain the nanoparticles of the present invention. According to studies by the present inventors, it is often difficult to obtain the nanoparticles of the present invention from other Au salts such as gold chloride and chloroauric acid. In the aforementioned Non-Patent Document 2, it is attempted to produce nanoparticles that are AgAu alloy @ FeCo @ AgAu alloy using gold (III) acetate.

  Moreover, a gold colloid can be used as a gold raw material. Although it does not specifically limit as a particle size of a gold colloid, 2 nm or more and 100 nm or less are preferable from a viewpoint of dispersion stability.

  Various Ag salts (silver compounds) can be used. For example, silver sulfate, silver carbonate, silver nitrate, silver acetate, silver iodide, silver perchlorate, silver phosphate, silver benzoate, silver tetrafluoroborate, silver trifluoroacetate, silver hexafluoroacetylacetonate, etc. can be used. it can.

Various types of Fe salts (iron compounds) can be used. For example, iron (II) acetate, iron (III) hydroxide acetate, iron (III) chloride, iron (III) chloride hexahydrate, iron (II) chloride tetrahydrate, iron (II) sulfate, iron sulfate (II) heptahydrate, iron (III) sulfate, iron (II) bromide, iron (II) iodide, iron (III) sulfate nonahydrate, iron (II) sulfate hydrate, iron nitrate (II), iron (III) nitrate, iron (III) nitrate nonahydrate, iron (III) perchlorate, iron (III) pyrophosphate, iron (III) phosphate, iron (II) phosphate 8 water Japanese hydrate, iron (III) phosphate n hydrate, iron (II) citrate, iron (III) citrate hydrate, iron (III) ammonium citrate, iron (II) oxalate, iron oxalate ( II) Hydrate, iron (III) oxalate ammonium trihydrate, potassium hexacyanoferrate (III), hexacyanoiron II) Potassium acid trihydrate, sodium hexacyanoferrate (III) decahydrate, iron (II) fumarate, iron (II) lactate, iron (II) lactate trihydrate, iron (II) gluconate Dihydrate, iron (II) ethoxide, acetylacetone iron (II), acetylacetone iron (III) (iron (III) acetylacetonate), iron (III) trisdipipivalate, carbonyl iron Fe (CO) ₅ , Fe ₃ (CO) ₁₂ , Fe ₂ (CO) ₉ , ammonium iron (II) sulfate hexahydrate, sodium pentacyanonitrosyl iron (III) dihydrate, and the like can be used.

  Various Co salts (cobalt compounds) can be used. For example, cobalt acetate (II), cobalt acetate (III), cobalt chloride (II), cobalt chloride (II) hexahydrate, ammonium cobalt (II) hexahydrate, cobalt sulfate (II) heptahydrate , Cobalt carbonate, cobalt bromide (II), cobalt bromide (II) hexahydrate, cobalt iodide (II), cobalt carbonate (II), cobalt sulfate (III) nonahydrate, cobalt sulfate (II) Heptahydrate, cobalt (II) ammonium sulfate hexahydrate, cobalt (II) nitrate, cobalt (II) nitrate hexahydrate, cobalt (III) nitrate, cobalt (III) nitrate nonahydrate, nitrous acid Cobalt (III) sodium, cobalt (II) perchlorate, cobalt (III) phosphate, cobalt (II) oxalate dihydrate, cobalt (III) citrate tetrahydrate, oxalic acid Ammonium cobalt (III) trihydrate, cobalt stearate, cobalt oleate, cobalt (II) fumarate, cobalt (II) gluconate dihydrate, cobalt (II) ethoxide, acetylacetone cobalt (II) (cobalt ( II) Acetylacetonate), acetylacetone cobalt (III), acetylacetone cobalt (II) dihydrate, cobalt trisdipivalate (III), ammonium cobalt (II) sulfate hexahydrate, cobalt (II) thiocyanate, hexaamine Cobalt (III) chloride, carbonyl cobalt, cobalt naphthenate, sodium hexanitrocobalt (III), and the like can be used.

  Various Ni salts (nickel compounds) can be used. For example, nickel acetate, nickel chloride, nickel chloride hexahydrate, nickel chloride tetrahydrate, nickel sulfate heptahydrate, nickel ammonium sulfate hexahydrate, nickel carbonate, nickel iodide, nickel bromide, bromide Nickel trihydrate, nickel iodide, nickel sulfate, nickel sulfate hexahydrate, nickel nitrate, nickel nitrate hexahydrate, nickel perchlorate hexahydrate, nickel phosphate, nickel acetate tetrahydrate, cyanide Nickel phosphide monohydrate, nickel oxalate dihydrate, nickel benzoate, nickel citrate hydrate, nickel ammonium oxalate trihydrate, nickel fumarate, nickel gluconate dihydrate, acetylacetonic acid Nickel, nickel acetylacetonate dihydrate, nickel bisdidipivalate, nickel ammonium sulfate hexahydrate, hexa Min nickel chloride, hexane butyl nickel cyclohexane, 2-Echirushikuro hexane nickel, nickel octoate, trifluoromethanesulfonic acid nickel can be used hypophosphite nickel hexahydrate like.

  In production, various components having a reducing action can be used to reduce the metal salt. For example, one or more of 1,2-alkanediols such as ethylene glycol, diethylene glycol, trimethylene glycol, propylene glycol, tetraethylene glycol, and 1,2-hexadecanediol can be used. These polyols exhibit a reducing action when thermally decomposed and oxidized under heating.

  The amount of polyol (total amount when two or more types are used) is preferably 0.1 to 10 in terms of molar ratio to the metal salt.

  In the production, if necessary, a dispersant may be used. As the dispersant, one or more selected from amine, diamine, ethanolamine, alkoxyamine, diamine alcohol, diaminoalkoxy, cyclic amine, alkylthiol, carboxylic acid or polymer dispersant Two or more kinds can be used. Particularly preferred examples are amine-based and carboxylic acid-based. In the amine system, for example, oleylamine, propylamine, dipropylamine, butylamine, dibutylamine, tributylamine, isobutylamine, diisobutylamine, hexylamine, N-methylhexylamine, di-N-octylamine, tri-N-octyl Amine, 2-ethylhexylamine, di (2-ethylhexyl) amine, allylamine, diallylamine, 3-pentylamine, 2-octylamine and the like can be used. In the carboxylic acid system, for example, polycarboxylic acid, polycarboxylic acid ammonium salt, polycarboxylic acid sodium salt, oleic acid, lauric acid, stearic acid, citric acid and the like can be used.

  It is preferable that the addition amount of a dispersing agent (total addition amount when using 2 or more types) is 0.1-10 in the molar ratio with respect to a metal salt.

  In the present invention, as the solvent, water, alcohol, dioxane, tetraethylene glycol and the like as the polar solvent, n-hexane, cyclohexane, octane, decane, dodecane, etc. as the nonpolar solvent, toluene, xylene as the aromatic solvent And dioctyl ether as a high boiling point solvent.

(Production conditions)
In producing the nanoparticles of the present invention, gold acetate is mixed with any one selected from the group consisting of Fe salt, Co salt and Ni salt (hereinafter referred to as “Fe salt etc.”) and reduced by heating. Although the order is not particularly limited, 1) a mixed solution of Fe salt or the like and gold acetate may be heated at room temperature and then heated, or 2) a mixed solution of Fe salt or the like and gold acetate may be prepared and heated at room temperature. Then, gold acetate may be mixed, 3) the gold acetate solution may be preheated and then Fe salt etc. may be mixed, and 4) the gold acetate solution may be preheated and then the Fe salt 5) A mixed solution of Fe salt or the like may be mixed, heated and then mixed with a gold acetate solution, or 6) A mixed solution of Fe salt or the like After preparing and heating, a mixed solution of Fe salt and gold acetate may be mixed. 7) Mixing of Fe salt and gold acetate at room temperature After preparing and heating the solution, a mixed solution of Fe salt or the like and gold acetate may be mixed. 8) After preparing and heating a mixed solution of Fe salt or the like and gold acetate at room temperature, Fe salt or the like 9) After heating the gold acetate solution in advance, Fe salt or the like may be mixed, and gold acetate may be further mixed. 10) A mixed solution of Fe salt or the like is prepared, After heating, the gold acetate solution may be mixed, and Fe salt etc. may be further mixed. 11) A mixed solution of Fe salt etc. and gold acetate is prepared at room temperature, heated, and then mixed with gold acetate, Further, an Fe salt or the like may be mixed. When a mixed solution of Fe salt or the like and gold acetate is prepared at room temperature and then heated, the nanoparticles of the present invention can be obtained with good yield, which is preferable from the viewpoint of productivity. When gold colloid is used in place of gold acetate, the gold colloid can be mixed with Fe salt and the like at various stages and heated as in the case of gold acetate, whereby the nanoparticles of the present invention can be produced. Moreover, other Au salts, like gold acetate, may be able to produce the nanoparticles of the present invention by mixing and heating with an Fe salt or the like at various stages.

  In order to produce nanoparticles containing Ag, the order of mixing Ag salt and heating and reducing is not particularly limited, but after 1) preparing and heating a mixed solution of gold acetate and Ag salt, a) Fe salt, etc. Or b) a mixed solution of Fe salt or the like and Ag salt, or c) a mixed solution of Fe salt or the like and gold acetate, or d) a mixed solution of Fe salt or the like, gold acetate and Ag salt, or 2 ) Prepare a mixed solution of gold acetate and Ag salt, heat and mix Fe salt etc., then mix a) Gold acetate or b) Ag salt or c) Mixed solution of gold acetate and Ag salt 3) A mixed solution of gold acetate and Ag salt is prepared, heated, mixed with a mixed solution of Fe salt and Ag salt, and then a) gold acetate, or b) Ag salt, or c. ) A mixed solution of gold acetate and Ag salt may be mixed. 4) Mixed solution of gold acetate and Ag salt Is prepared, heated, and mixed with a mixed solution of Fe salt or the like and gold acetate, and then a) gold acetate, or b) Ag salt, or c) a mixed solution of gold acetate and Ag salt may be mixed. 5) After heating the gold acetate solution in advance and mixing the Fe salt and the like, a) Ag salt or b) a mixed solution of gold acetate and Ag salt may be further mixed. 6) Gold acetate After the solution is heated in advance and the Ag salt is mixed, a) Fe salt or the like, or b) a mixed solution of the Fe salt or the like and Ag salt, or c) a mixed solution of the Fe salt or the like and gold acetate, or d) A mixed solution of Fe salt or the like and gold acetate and Ag salt may be mixed. 7) The gold acetate solution is heated in advance, and the mixed solution of Fe salt or the like and gold acetate is mixed, and further a) Ag salt Or b) A mixed solution of gold acetate and Ag salt may be mixed, or 8) the gold acetate solution is heated in advance. After mixing a mixed solution of Fe salt or the like and Ag salt, a) gold acetate, or b) Ag salt, or c) a mixed solution of gold acetate and Ag salt may be mixed, or 9) gold acetate. After the solution is heated in advance, a mixed solution of Fe salt, etc. and gold acetate and Ag salt may be mixed. 10) A mixed solution of Fe salt, etc., gold acetate and Ag salt is heated in advance. Then, a) gold acetate, or b) Ag salt, or c) a mixed solution of gold acetate and Ag salt may be mixed, or 11) a mixed solution such as Fe salt is prepared and heated. After mixing gold acetate, a) Ag salt or b) mixed solution of gold acetate and Ag salt may be further mixed. 12) Mixed solution such as Fe salt is prepared, heated, and then mixed with acetic acid. A mixed solution of gold and Ag salt may be mixed. 13) A mixed solution of Fe salt or the like is prepared, heated, and F After mixing the mixed solution of e salt and gold acetate, a) Ag salt or b) mixed solution of gold acetate and Ag salt may be further mixed. 14) Prepare mixed solution of Fe salt etc. After heating, a mixed solution of Fe salt or the like and gold acetate and Ag salt may be mixed. 15) After preparing and heating a mixed solution of Fe salt or the like and gold acetate at room temperature, a) Ag salt Or b) A mixed solution of gold acetate and Ag salt may be mixed. 16) A mixed solution of Fe salt or the like and gold acetate is prepared at room temperature, heated, then mixed with Ag salt, and further gold acetate. 17) Prepare a mixed solution of Fe salt or the like and gold acetate at room temperature, heat, mix gold acetate, and then mix Ag salt; 18) Ag salt After the solution is heated in advance and mixed with gold acetate, a) Fe salt or the like, or b) Fe salt or the like and Ag salt mixed solution Or c) a mixed solution of Fe salt or the like and gold acetate, or d) a mixed solution of Fe salt or the like, gold acetate and Ag salt, or 19) a mixture of Fe salt or the like, gold acetate and Ag salt at room temperature. After preparing the mixed solution, it may be heated, or 20) after preparing a mixed solution of Fe salt etc. and gold acetate and Ag salt at room temperature and heating, a) gold acetate, or b) Ag salt, or c) A mixed solution of gold acetate and Ag salt, or d) A mixed solution of Fe salt and the like, and gold acetate and Ag salt may be mixed. 21) A mixed solution of the Fe salt and the like, gold acetate and Ag salt at room temperature After preparing and heating, gold acetate may be mixed and Ag salt may be further mixed. 22) A mixed solution of Fe salt, etc., gold acetate and Ag salt is prepared at room temperature, heated, and then Ag is mixed. A salt may be mixed, and further an Ag salt may be mixed. Like gold acetate, the gold colloid can be mixed with an Fe salt or Ag salt at various stages and heated to produce the nanoparticles of the present invention. Moreover, another Au salt, like gold acetate, may be able to produce the nanoparticles of the present invention by mixing and heating with an Fe salt or Ag salt at various stages.

  In producing the nanoparticles of the present invention, when mixing gold acetate or other Au salt with Fe salt or the like, it is preferable to mix them using a solution dissolved in the aforementioned solvent. The same applies when the Ag salt is mixed. Any solution of Ag salt such as Au salt, Fe salt and the like may be mixed after further adding the compound having a reducing action such as polyol as described above or a dispersant such as amine.

  In a typical synthesis, a mixed solution of polyol (for example, tetraethylene glycol and 1,2-hexadecanediol), oleylamine, oleic acid, Fe salt, Co salt, and gold (III) acetate is prepared and used. The production conditions are not limited to this. For example, the solution is heated with stirring under an argon atmosphere, and kept at 80 to 120 ° C. for several minutes to several tens of minutes, whereby gold (III) acetate Can be reduced in the presence of Fe and Co salts to form the core. The temperature of the reaction mixture is then raised to 250-330 ° C. to form a shell and held for several minutes to tens of minutes. Thereafter, heating is stopped and the system is cooled over time.

  The reaction solution after cooling is diluted with acetone, and centrifuged with a centrifugal acceleration at a centrifugal acceleration capable of precipitating nanoparticles. After centrifugation, discard the supernatant, add hexane to the precipitated nanoparticles, disperse with ultrasound, dilute again with acetone, centrifuge, discard the supernatant, and vacuum dry the resulting precipitate, Au @ FeCo nanoparticles are obtained. The nanoparticles thus obtained have metallic Au, Fe, and Co due to the reducing action of 1,2-hexadecanediol and tetraethylene glycol. The obtained dry particles can be redispersed in an appropriate dispersion medium such as water by modifying with a dispersant or the like that improves water dispersibility.

  The average size and size distribution of the resulting nanoparticles can be determined by TEM. Also, the chemical composition of the nanoparticles can be analyzed using ICP-OES, EDS and XPS. The effect of aging on the magnetic properties of the nanoparticles can be analyzed using a SQUID magnetometer.

  The concentration of the obtained nanoparticles (the number of particles / mL, or μg / mL, etc. can be used as a unit) is the optical density (OD, degree of absorption expressed in logarithm) of the liquid containing the nanoparticles. ) Or the peak of absorbance linearly correlates with the concentration of nanoparticles in the liquid, and can be calculated using coefficients determined in advance for each size particle.

<Uses of nanoparticles>
The nanoparticles of the present invention can be used for various applications. The nanoparticle of the present invention can be a magnetic-plasmonic composite nanoparticle, and in particular in the life science field, it can be applied to separation and purification of substances, examination of diseases, diagnosis, imaging, thermotherapy, drug delivery, etc. I can expect.

  EXAMPLES The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited to these examples.

[X-ray diffraction (XRD) measurement]
The nanoparticles were vacuum-dried, and an X-ray diffraction (XRD) measurement was performed using an X-ray diffraction apparatus MiniFlex600 manufactured by Rigaku Corporation and an X-ray source using CuKα. The measurement range was 2θ = 20 ° to 90 °. For assignment of the obtained peak to the crystal phase, the data of PDF card number 00-004-0784 as the Au phase, the data of PDF card number 00-049-1567 as the Co ₅₀ Fe ₅₀ phase, and CoFe ₂ data PDF card number 00-022-1086 as O ₄ phase, Fe ₃ as O ₄ phase using data of PDF card number 00-019-0629 (powder diffraction database PDF-2, Publisher: Ltd. Light stone).

[Transmission electron microscope (TEM) observation]
The sample was diluted with hexane, dropped on the microgrit and dried to obtain a sample for TEM observation, and TEM observation was performed with a transmission electron microscope H-7650 manufactured by Hitachi High-Technologies Corporation.

[Magnetic measurement]
The nanoparticles immediately after synthesis are vacuum-dried and measured with a magnetic property measuring device MPMS manufactured by Quantum Design, Inc. at a temperature of 300 K in a magnetic field range of -50 to 50 (kOe). Described in the column immediately after. The nanoparticles after measurement were held for 21 days in an atmosphere of 25 ° C. and 50% relative humidity, and then magnetization was measured at a temperature of 300 K in a magnetic field of −50 to 50 (kOe). It described in the column after the day.

Further, the maintenance ratio of the saturation magnetization for 21 days was obtained by the following formula and described in the column of the maintenance ratio after 21 days in Table 1.
Maintenance ratio (%) = (saturation magnetization after 21 days) / (saturation magnetization immediately after synthesis) × 100

[Example]
Synthesis of Au @ FeCo nanoparticles:
Using a 50 mL three-necked flask, 0.0706 g of iron (III) acetylacetonate (Fe (acac) ₃ ), 0.0514 g of cobalt (II) acetylacetonate (Co (acac) ₂ ), 0 A mixed solution of 0.187 g of gold (III) acetate, 0.129 g of 1,2-hexadecanediol, 2.15 mL of oleylamine, 1.28 mL of oleic acid and 5 mL of tetraethylene glycol was replaced with an argon atmosphere and stirred. And heated at 100 ° C. for 10 minutes.

  Then, after heating to 290 degreeC and hold | maintaining for 15 minutes, heating was stopped and it cooled naturally to room temperature.

  The reaction solution was equally divided into two 50 mL centrifuge tubes (1), and then heacetone was added to each so that the total amount became 45 mL. And it centrifuged for 5 minutes with the centrifugal acceleration 3760 (xg) at 20 degreeC with the centrifuge. After centrifugation, discard the supernatant, add 400 μL of hexane to each centrifuge tube (1), disperse the precipitated particles with ultrasound, and then add new centrifuge tubes (2) to 2 centrifuge tubes ( From 1), 200 μL of the particle dispersion was dispensed. Acetone was added to these four centrifuge tubes (2) until the total volume became 45 mL, and the mixture was centrifuged at 20 ° C. with a centrifugal acceleration of 3760 (× g) for 5 minutes. Finally, the supernatant was discarded, and the resulting precipitate was vacuum-dried to obtain Au @ FeCo nanoparticles.

The TEM image and XRD pattern of the obtained nanoparticles are shown in FIG. 1 and FIG. From these results, the obtained nanoparticles have a clear core-shell structure, and in addition to the Au phase and the Fe ₅₀ Co ₅₀ phase as the crystal structure, CoFe ₂ O ₄ and Fe ₃ O as the oxide phase It was found to have a phase attributed to ₄ .

  Table 1 shows the saturation magnetization immediately after synthesis, the saturation magnetization after holding for 21 days, and the maintenance factor.

[Comparative example]
Synthesis of Ag @ FeCo @ Ag nanoparticles:
Using a 50 mL three-necked flask, a mixed solution of 0.0170 g AgNO ₃ , 0.258 g 1,2-hexadecanediol, 2.68 g oleylamine, 2.26 g oleic acid, 10 mL tetraethylene glycol was added. After substituting with an argon atmosphere, the mixture was heated with stirring and maintained at 100 ° C. for 10 minutes.

Then heated to 170 ° C., 0.0514 g of cobalt (II) acetylacetonate (Co (acac) ₂ ), 0.0706 g of iron (III) acetylacetonate (Fe (acac) ₃ ), 2 mL A mixed solution consisting of oleylamine and 2 mL of toluene was slowly added.

Subsequently, the temperature was further raised to 250 ° C., and a mixed solution consisting of 0.0170 g of AgNO ₃ , 1 mL of oleylamine and 1 mL of toluene was quickly added. After the addition, the temperature was lowered to 230 ° C. over 10 minutes, and then the heating was stopped and the mixture was naturally cooled to room temperature.

  The reaction solution was equally divided into two 50 mL centrifuge tubes (1), and then heacetone was added to each so that the total amount became 45 mL. And it centrifuged for 5 minutes with the centrifugal acceleration 3760 (xg) with the centrifuge. After centrifugation, discard the supernatant, add 400 μL of hexane to each centrifuge tube (1), disperse the precipitated particles with ultrasound, and then add new centrifuge tubes (2) to 2 centrifuge tubes ( From 1), 200 μL of the particle dispersion was dispensed. Acetone was added to these four centrifuge tubes (2) until the total amount became 45 mL, and the mixture was centrifuged for 5 minutes at a centrifugal acceleration of 3760 (× g) using a centrifuge. Finally, the supernatant was discarded, and the resulting precipitate was vacuum-dried to obtain Ag @ FeCo @ Ag nanoparticles.

  Table 1 shows the saturation magnetization immediately after the synthesis of Ag @ FeCo @ Ag nanoparticles, the saturation magnetization after holding for 21 days, and the maintenance ratio.

  According to the present invention, the novel core-shell nanoparticle can be a magnetic-plasmonic composite nanoparticle, particularly in the field of life science, separation / purification of substances, examination of diseases, diagnosis, imaging, thermotherapy, Application to drug delivery etc. can be expected.

Claims (8)

(A) a core containing Au;
(B) a shell containing at least one selected from the group consisting of Fe, Co, and Ni;
Core-shell type nanoparticles containing The nanoparticle according to claim 1, wherein the part (a) is made of Au. The nanoparticle according to any one of claims 1 or 2, wherein the portion (b) comprises Fe and Co. The nanoparticle according to any one of claims 1 to 3, which has magnetism. The nanoparticle according to any one of claims 1 to 4, wherein the part (b) comprises at least one metal state selected from the group consisting of Fe, Co and Ni. The nanoparticle according to any one of claims 1 to 5, wherein the part (b) has an oxide comprising at least one selected from the group consisting of Fe, Co, and Ni. The method for producing nanoparticles according to any one of claims 1 to 6, comprising a step of reducing gold (III) acetate to obtain a part (a). The production method according to claim 7, wherein gold (III) acetate is reduced in the presence of an Fe salt and a Co salt.