JP6375191B2 - Method for producing metal nanoparticle dispersion, solution containing metal cluster, method for producing the same, coating film thereof, and ascorbic acid sensor - Google Patents

Description

  The present invention relates to a method for producing a dispersion of metal nanoparticles, a method for producing a solution containing metal clusters, a luminescent metal cluster, and a coating film and a sensor using the same.

  It is known that when noble metals such as Ag, Au, Pt, Pd, Rh, Ir, Ru, and Os are made minute, any noble metal exhibits a specific optical property due to a quantum effect. Among them, Au has a unique light absorption characteristic called plasmon absorption by forming nanoparticles to a particle size of about 20 nm, and has a characteristic hue such as red, magenta, and bluish violet depending on the size and shape of the particles. It is known to show.

Hereinafter, the background art and its problems will be described using gold (Au) of noble metals as an example.
As a method for producing gold (Au) nanoparticles, a method of reducing gold by applying a reducing agent to a gold salt solution is generally known. Non-Patent Document 1 discloses a method of reducing chloroauric acid with sodium citrate hydrate. Patent Documents 1 and 2 disclose a method for producing a gold nanoparticle dispersion by reducing a gold salt solution with citrate and ascorbate.

  Patent Document 3 discloses that a gold (Au) plate placed in a liquid is irradiated with a pulsed laser to physically remove fine gold from the gold plate with a large energy of the laser, and gold nanoparticles are placed in the liquid. A method for producing dispersed gold nanoparticles is disclosed.

  Non-Patent Document 2 discloses that gold nanoparticles are produced by a so-called submerged plasma method in which plasma is generated by applying a pulse width of 2 μs and a voltage of 2.5 kV to a tungsten electrode in a chloroauric acid solution containing potassium chloride. It has been shown to generate. Further, in Patent Document 4, noble metal nanoparticles are generated by a liquid plasma method in which a voltage is applied between at least one pair of noble metal electrodes in an aqueous solution to generate plasma, and the noble metal is added to oxide particles present in the aqueous solution. A manufacturing method for supporting nanoparticles is disclosed.

  However, in the method of reducing a gold salt solution, there are always counterions other than gold, and since a reducing agent / additive is used, the gold nanoparticle dispersion is used to reduce those counterions and impurities as impurities. It was difficult to remove the components derived from the additives. In addition, the gold salt used as a raw material is much more expensive and less supplied than gold as a noble metal, the supply of gold nanoparticles is not sufficient, and industrial application is difficult to proceed.

  The method of pulsed laser irradiation was a method for producing gold nanoparticles that did not contain impurities other than gold and dispersion solution, which was proposed to solve the problem of the technique for reducing such gold salt solution. Must be an expensive picosecond pulsed laser on the order of picoseconds, and the laser spot must be scanned on the target gold, making large equipment and complex processes unnecessary from an industrial application perspective It was not a method.

In the case of the in-liquid plasma method, it has been suggested that metal nanoparticles may be generated from the electrode metal in a liquid not containing impurities. However, in Patent Document 4, a salt such as potassium chloride is used to obtain a stable plasma. In addition to the liquid, it is described that it is preferable to adjust the electrical conductivity of the aqueous solution between 300 μS / cm and 3000 μS / cm , and plasma generation in a liquid not containing impurities, that is, having low electrical conductivity It did not suggest any technical possibility.
On the other hand, a state in which Au nanoparticles are miniaturized to 1 nm or less and several to several tens of Au atoms are gathered is called an Au cluster, and an example in which strong light emission (fluorescence) is caused by a quantum effect is known.

  As a method for producing Au clusters, a method of reducing Au by applying a reducing agent to an Au salt solution is generally known. Non-Patent Document 3, Non-Patent Document 4, Patent Document 5 and Patent Document 6 are prepared by reducing a chloroauric acid or halogenohaloacid solution containing a polyamidoamine dendrimer as a template with sodium borohydride. The method is shown. The obtained Au clusters have different emission peak wavelengths depending on the number of atoms, the emission peak wavelength of Au8 consisting of 8 gold (Au) atoms is 455 nm (blue), and similarly the emission peak wavelength of A5 is 385 nm (ultraviolet). ), The emission peak wavelength of Au13 is 510 nm (green), the emission peak wavelength of Au23 is 760 nm (red), and the emission peak wavelength of Au31 is 866 nm (near infrared). Patent Document 7 discloses a method for producing Au clusters by causing a phosphine compound to act on a chloroauric acid or a gold halide compound as a stabilizer.

  However, in the above-mentioned production method, chloroauric acid and gold halide, which are Au raw materials, are deleterious substances, and the reagent is expensive and the transaction amount is usually as small as 1 g. In addition, since the raw material is a gold salt, a halide ion such as a chloride ion (Cl-) as a counter anion always remains in the reaction system in addition to Au, and cannot be separated and removed from the Au nanoparticles. The problem is that safety and labeling accuracy when applied to biomarkers cannot be sufficiently secured. Further, in the production method using a polyamidoamine dendrimer as a template, the polyamidoamine dendrimer is also not suitable for mass production of Au clusters because the production amount is small and very expensive. In addition, the smallest Au cluster among Au clusters obtained by reducing the gold salt solution of the phosphine compound is Au11 (registered trademark: undecagold) having 11 atoms, but it retains the light emission characteristics. It was not.

  Patent Document 5 and Patent Document 6 also disclose a method for producing a luminescent Au cluster by mixing an aqueous chloroauric acid solution and ascorbic acid. The mixing of ascorbic acid is not a non-luminescent Au cluster. In order to suppress the formation of the above, it should be carried out under a low temperature environment condition of 4 ° C. under light shielding or in a room temperature buffer solution.

Japanese Patent No. 2834400 Japanese Patent No. 2990254 JP 2009-299112 A JP 2014-97476 A U.S. Pat. No. 7,914,588 U.S. Pat. No. 8,536,119 JP2013-255887A

Nature Physical Science, 1973, Volume 20, p241 Grinding, 2008, No51, p30-36 Physical Review Letters, 2004, Vol. 93, No. 7, 077402-1 Abstracts of Annual Meeting of the Physical Society of Japan, 25aPS-63, 2006

An object of the present invention is to solve the above-described problems, and to produce a high-purity metal nanoparticle dispersion liquid containing no dispersant in a short time with simple and versatile equipment, and the above-mentioned The object is to provide a method for producing a solution containing a luminescent metal cluster which is excellent in dispersion stability, storage stability and biocompatibility from a metal nanoparticle dispersion.
Furthermore, an object of the present invention is to provide a thin film that emits light using a solution containing the metal cluster and an ascorbic acid sensor.

As a result of intensive investigations, the inventors completely solved the problems of the prior art, found a high-quality metal nanoparticle dispersion production method with high purity and high dispersion stability, and the metal nanoparticle dispersion liquid. Has been used to find a method for producing a luminescent metal cluster having high dispersion stability and storage stability and an aqueous solution containing the same, and the present invention has been completed.
That is, the present invention comprises the following technical means.

[1] A method for producing a metal nanoparticle dispersion by generating discharge plasma between at least one pair of metal electrodes arranged in a liquid,
(1) The conductivity of the liquid is 20 μS / cm or less,
(2) The metal electrode is made of Ag, Au, Cu, Pt, Pd, Rh, Ir, Ru, Os, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Al, C, Si, Ga , Ge, Se, Y, Zr, Nb, Mo, Tc, In, Sn, Sb, Te, Hf, Ta, W, Re, Tl, Pb, Bi and at least one metal selected from lanthanoids,
(3) The metal nanoparticle dispersion liquid, wherein the plasma is an AC discharge plasma generated by applying a voltage between the metal electrodes so that an AC voltage is 800 V to 20 kV and a short-circuit current is 40 mA or less. [2] The method for producing a metal nanoparticle dispersion according to [1], wherein the liquid is distilled water or pure water.
[3] The method for producing a metal nanoparticle dispersion liquid according to [1] or [2], wherein an interelectrode distance between the metal electrodes is 3 mm from a contact state.
[4] A step of mixing the metal nanoparticle dispersion liquid produced by the method for producing a metal nanoparticle dispersion liquid according to any one of [1] to [3] and ascorbic acid at room temperature. A method for producing a luminescent solution containing metal clusters.

[ 5 ] The method for producing a luminescent solution containing a noble metal cluster according to [ 4 ], wherein the metal nanoparticles are Au or Pt .
[ 6 ] A method for producing a thin film that emits light by irradiation with ultraviolet rays, which is obtained by applying and drying a solution containing the metal cluster according to [ 4 ] or [ 5 ].
[ 7 ] The liquid obtained by mixing the metal nanoparticle dispersion produced by the method for producing a metal nanoparticle dispersion according to any one of [1] to [3] and a specimen containing ascorbic acid is irradiated with ultraviolet rays. A method for detecting and quantifying ascorbic acid , comprising means for detecting luminescence.

  According to the present invention, a high-purity metal nanoparticle dispersion containing no dispersant can be produced in a short time with inexpensive and general-purpose equipment. Furthermore, since the metal nanoparticle dispersion obtained by the present invention does not contain a protective agent, it can be used as an active catalyst. Further, depending on the type of metal such as Au, Ag, Cu, etc., there is plasmon absorption in the visible range, so that it is colored and can be used as a color material for biosensors and a color material for ink, and is useful for industrial applications.

  In addition, according to the present invention, a luminescent metal cluster excellent in dispersion stability, storage stability, and biocompatibility and an aqueous solution containing the same can be produced with inexpensive and general-purpose equipment. Furthermore, the present invention provides a metal cluster that emits light by selectively reacting with metal ascorbic acid (L form of vitamin C is an optical isomer) among organic acids. It is also useful as a mechanism.

The conceptual diagram of the apparatus concerning this invention. The figure of the visible light annihilation spectrum of the gold nanoparticle dispersion liquid produced in Example 1. The electronic absorption spectrum and emission spectrum of the Au cluster aqueous solution produced in Example 6. The emission spectrum of the Au cluster thin film produced in Example 12.

(Manufacturing method of metal nanoparticles not using metal salt)
In the method for producing a metal nanoparticle dispersion according to the present invention, an AC voltage is 800 V or more and 20 kV or less and a short-circuit current is 40 mA or less between at least one pair of metal electrodes arranged in a liquid having an electric conductivity of 20 μS / cm or less. In this way, a metal nanoparticle dispersion is produced by applying AC voltage to generate AC discharge plasma.

  The method for producing the metal nanoparticle dispersion of the present invention includes Ag, Au, Cu, Pt, Pd, Rh, Ir, Ru, Os, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Al. , C, Si, Ga, Ge, Se, Y, Zr, Nb, Mo, Tc, In, Sn, Sb, Te, Hf, Ta, W, Re, Tl, Pb, Bi and at least one of lanthanoids Each metal nanoparticle dispersion liquid can be manufactured using a kind of metal as a raw material.

  Among the above-mentioned metals, the metal nanoparticle dispersion liquid of any one of Ag, Au, Pt, Pd, Rh, Ir, Ru, and Os is difficult to be oxidized based on the redox potential inherent to the metal and is stable. In particular, these noble metals are useful in that they have high catalytic action, and among these, Au or Pt metal nanoparticle dispersions are particularly useful.

The conceptual diagram of the apparatus used for metal nanoparticle dispersion liquid manufacture of this invention is shown in FIG.
The apparatus for producing a metal nanoparticle dispersion boosts, for example, a small voltage (referred to as a primary voltage) such as a transformer (transformer) to a high voltage (referred to as a secondary voltage) in an electrically insulating container (103). It comprises at least one pair of metal electrodes (101) connected to a high voltage generator (106). Since a high voltage of 20 kV at maximum is applied to the electrode, it is necessary to electrically insulate the container, and the metal electrode is installed in the container via an electric insulating material (102). For example, the electrical insulating material (102) has a hole formed in a resin block, and a rod-shaped metal is passed through the hole to ensure electrical insulation. As the insulating material, a resin or a ceramic can be used. In the case of a resin, a resin that does not change even when in contact with a liquid is preferable.

The pair of metal electrodes may be placed in the liquid at a distance of 3 mm between the tips from the contact state. The metal electrode is connected to the high voltage generator (106) by the wiring (107), and the metal electrode and the high voltage generator (106) may be connected in the electrical insulating material (102). Then, as shown in the conceptual diagram of FIG. 1, a part of the metal electrode is insulated by the electric insulating material (102), and the other end of the electrode is installed so as to come out from the liquid into the air and connected outside the container. You may do it. Since the present invention uses an insulating liquid of 20 μS / cm or less, the connection method of FIG. 1 is possible. By applying the connection method of FIG. 1, not only the structure of the apparatus becomes simple, but also replacement / maintenance of the metal electrode from the apparatus main body becomes easy, and the value as equipment increases.

  The metal used for the electrode may have a purity of 99.9% or more and act as at least one pair of counter electrodes, and the shape is not particularly limited. It is easy to arrange in.

  A high voltage generator for generating plasma may use a transformer that generates an alternating voltage (secondary voltage) of a maximum of 20 kV, and may be either an inverter type or a winding type. The primary side voltage source may be either direct current or alternating current, but in Japan, an AC single phase 100V power source, an AC single phase 200V power source or an AC three phase 200V power source which is a general commercial power source can be used. . Naturally, when the present invention is implemented outside of Japan, a power supply suitable for the power supply situation in each country may be used as the primary side voltage. Among the high voltage generators, neon transformers for lighting neon tubes are easy to obtain, and the secondary side voltage is a maximum of 15 kV and the short-circuit current is 20 mA, which is preferable. And when adjusting the secondary side voltage of a transformer, what is necessary is just to adjust a transformer primary side voltage using a voltage regulator or a variable resistor.

  The container filled with the liquid needs to be electrically insulating as well. Preferably, glass or resin can be used.

As the liquid, a liquid having an electric conductivity of 20 μS / cm or less is used.
If the electrical conductivity is higher than this, impurities are present in the liquid, which is not preferable because the purity of the metal nanoparticle dispersion to be produced is lowered. In addition, if the conductivity is high, an electric field is formed from other than the plasma generation site among the electrode metals arranged in the liquid (referred to as a leakage electric field), and the applied voltage is dispersed, resulting in a larger voltage for plasma generation. Energy (high voltage) is required, which is not preferable from the viewpoint of energy consumption.
As the liquid, water (distilled water or pure water) and an organic solvent having a conductivity of 20 μS / cm or less can be used alone or in combination. When the liquid is used, the conductivity due to mixing of impurities should not be greater than 20 μS / cm . The type of the organic solvent is not particularly limited, and examples thereof include alcohols such as methanol, ethanol and isopropyl alcohol, glycols such as ethylene glycol and propylene glycol (diols in chemical classification), acetone, methyl ethyl ketone, and the like. Solvents that are easily miscible with water, such as ketones, celloselves such as ethylene glycol monomethyl ether and propylene glycol monomethyl ether, are preferred.

  In order to produce metal nanoparticles, the equipment is installed as shown in FIG. 1 using the equipment and members described above, and a predetermined voltage is applied. If plasma is not generated even when a voltage is applied, a pair of electrodes may be brought into contact with each other and short-circuited. Plasma discharge starts simultaneously with the short circuit. Due to the large energy of the plasma, metal microparticles, that is, metal nanoparticles, are stripped from the metal electrode. Once plasma is generated, the distance between the electrodes is slightly increased so that plasma generation continues. If the distance between the electrodes is too great, the plasma will disappear. When it disappears, the electrodes may be brought into contact again to cause plasma discharge again. The distance between the electrodes at this time is preferably 3 mm from the contact state, and the control of the distance between the electrodes may be manual or automatic. In manual operation, the electrode is moved while visually observing the state of plasma generation. In automatic operation, the voltage and current between a pair of Au electrodes are monitored using an oscilloscope, for example. Controls the distance between Au electrodes by detecting three values: current value when short circuit (short circuit current), current value when plasma is generated (plasma current), and current value when plasma is not generated (non-plasma current) do it. Specifically, when a non-plasma current is detected, the pair of electrodes are moved in a contact direction until a short-circuit current is detected. When the short-circuit current is detected, the pair of electrodes are moved away from each other until the plasma current is detected. When a non-plasma current is detected in this state, the pair of electrodes are moved in contact with each other until a short-circuit current is detected again. This control may be repeated. The moving speed of the electrode during the control is preferably as fast as possible because the plasma generation time per unit time becomes long, but is not particularly limited, and if an existing mechanical control mechanism such as a motor or vibration is used. Good.

  When plasma is generated continuously, the temperature of the liquid rises, so a heat exchanger for cooling or a cooling thermostatic bath is attached to the outer periphery of the container to suppress the rise in the temperature of the liquid in the apparatus. Nanoparticles can be produced. When a heat exchanger or a cooling thermostat attached to the outside of the container is attached, the container is more preferably made of glass with good heat exchange efficiency.

(Metal cluster manufacturing method)
The metal nanoparticle dispersion by the production method described above is a metal nanoparticle dispersion made of a high-purity metal that does not contain chemical components other than metals, and is therefore suitable as a raw material for a solution containing the metal cluster of the present invention. The higher the concentration of the raw material metal nanoparticle dispersion, the easier the visual observation of the light emission from the resulting metal cluster. For example, in the case of Au nanoparticle dispersion, gold (Au) plasmon in the dispersion If the linear light transmittance at the peak of the absorption band (450 nm to 600 nm) is 80% or less (optical path length 1 cm), it can be determined that the concentration is sufficient.

  In the method for producing a solution containing a metal cluster of the present invention, first, ascorbic acid is mixed and dissolved in a metal nanoparticle dispersion at room temperature. Ascorbic acid may be either L-form or D-form. At this time, mixing is performed so that the concentration of ascorbic acid is in the range of 0.1 mmol / L to 1000 mmol / L. More preferably, it is in the range of 1 mol / L to 100 mmol / L. After mixing and dissolving, a black floating substance is observed within a few hours. However, when kept at room temperature for several days, the black floating substance disappears and a uniform transparent solution composed of a metal cluster-ascorbic acid complex is obtained. The transparent solution at this time may be colored according to the kind of metal. It is also possible to promote the production of a uniform transparent solution by heating to the boiling point of the solvent. When the obtained transparent solution is irradiated with ultraviolet rays, light emission derived from the metal cluster can be visually confirmed. In the case of an Au cluster solution, there are at least two types of Au clusters, Au8 and Au13, from the emission spectrum. Therefore, the luminescent color appears white to human eyes due to the additive color mixture of blue and green.

(Preparation of luminescent thin film containing metal clusters)
A luminescent thin film containing metal clusters can be obtained by applying and drying the metal cluster solution obtained by the production method described above on a substrate. The material of the base material used at this time is not particularly limited, but paper, glass, metal, ceramics, plastics and the like can be used. Usually, when applying a solution, it is desirable that the substrate surface is hydrophilic. As the treatment for hydrophilizing the substrate surface, known surface treatment methods such as plasma treatment, ultraviolet ozone treatment, acid treatment, and alkali treatment can be applied. Various coating methods such as spin coating, dip coating, and bar coating can be applied as the coating method. The drying treatment after coating may be natural drying at room temperature or heat drying at an arbitrary temperature up to 250 ° C. When the thin film obtained by the above method is irradiated with ultraviolet rays, light emission from the metal cluster can be visually confirmed.

(Ascorbic acid (vitamin C) sensor)
A metal nanoparticle dispersion of the present invention that does not use a metal salt as a raw material is allowed to act on a specimen containing vitamin C (L-ascorbic acid). The specimen to be acted on may be either solid or liquid. In the case of a solid, the sample may be added to the metal nanoparticle dispersion, and in the case of a liquid, the liquid and the metal nanoparticle dispersion may be mixed. However. In the case of a solid, the specimen must be completely dissolved in the dispersion solvent. Although the molecular mechanism details are not clear when applied, metal nanoparticles selectively react with ascorbic acid in organic acids containing carboxyl groups and hydroxy groups to form metal cluster-ascorbic acid complexes. To do. The storage temperature after the action can be heated as long as the specimen does not change in quality, but is preferably 100 ° C. or lower. Since the metal cluster-ascorbic acid complex emits light when irradiated with ultraviolet rays, it can be easily detected. The amount of the metal cluster-ascorbic acid complex produced is determined according to the amount of vitamin C present in the specimen. Since the emission intensity is proportional to the amount of the metal cluster-ascorbic acid complex, if a calibration curve of the emission intensity and the amount of L-ascorbic acid is prepared in advance, the amount of ascorbic acid in the sample can be obtained from the emission intensity. .

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to this.

[Example 1]
A metal plate (Tanaka Kikinzoku Kogyo) with a purity of 99.9%, a thickness of 1 mm, and a 25 mm square was cut to produce two strips of 25 mm length and 1 mm square. A pair of insulated electrodes was produced by punching a hole in a 12.5 mm × 25 mm, 5 mm thick Teflon (registered trademark) block and passing a strip of gold. The gold tips of a pair of insulated electrodes prepared at the center of a glass petri dish (φ70 mm, depth 18 mm) were arranged with a 1 mm gap. Thereafter, 30 ml of distilled water (15 μS / cm Nacalai Tesque) was added, and the gold tip of the insulating electrode was placed in water. After applying 9 kV to the insulating electrode using a neon transformer (Lesship), the insulating electrode was brought into contact with it to generate plasma. Thereafter, plasma generation was continued for 30 minutes while finely adjusting the distance between the electrodes. As a result, distilled water in the petri dish became reddish purple. When the visible light extinction spectrum of the obtained reddish purple liquid was measured using a spectrophotometer, an absorption maximum based on gold plasmon absorption was observed at 522 nm (FIG. 2). Further, when the particle size distribution was measured by a dynamic light scattering method, d50 (particle size at which the cumulative frequency of particle size was 50%) was 30 nm. Table 1 shows the maximum absorption wavelength, d50, and appearance color.

[Example 2]
A reddish purple liquid was obtained in the same manner as in Example 1 except that the applied voltage was 5 kV. Table 1 shows the maximum wavelength, d50, and appearance color of the obtained reddish purple liquid.

Example 3
A reddish purple liquid was obtained in the same manner as in Example 1 except that the applied voltage was 1 kV. Table 1 shows the maximum wavelength, d50, and appearance color of the obtained reddish purple liquid.

Example 4
A black transparent liquid was obtained in the same manner as in Example 1 except that Pt wire (outer diameter 0.5 mm, length 50 mm) was used instead of the strip-shaped gold. The appearance color of d50 is shown in Table 1. Since Pt has no clear plasmon absorption, no peak shape was observed in the visible light extinction spectrum.

Example 5
A brown transparent liquid was obtained in the same manner as in Example 1 except that Cu wire (outer diameter 1.5 mm, length 50 mm) was used instead of the strip-shaped gold. The appearance color of d50 is shown in Table 1.

[Comparative Example 1]
A blue-violet liquid was obtained in the same manner as in Example 1 except that the applied voltage was 730V. Table 1 shows the maximum wavelength, d50, and appearance color of the obtained blue-violet liquid.

[Comparative Example 2]
The same procedure as in Example 1 was performed except that a 0.01% by weight sodium chloride aqueous solution (210 μS / cm 2 ) was used in place of distilled water. Recognized, no discharge plasma was generated, and a colored liquid based on gold nanoparticles could not be obtained.

Example 6
The concentration of L-ascorbic acid is 52 mmol / L in an aqueous dispersion of Au nanoparticles having an absorption peak based on plasmon absorption of 522 nm Au produced by an underwater discharge plasma method and having a linear light transmittance (optical path length of 1 cm) of 47%. Added as follows. After dissolving L-ascorbic acid, it was kept at room temperature for 1 week to obtain a pale yellow transparent solution. When this solution was irradiated with an ultraviolet LED (365 nm, about 38 mW / cm 2), white light emission was observed. When an emission spectrum (excitation wavelength: 366 nm) was measured, maximum peaks were observed at 442 nm and 467 nm, and a shoulder peak was observed near 560 nm. Table 2 summarizes the appearance color, peak wavelength of the emission spectrum, emission intensity at the maximum peak, and emission color of the solutions obtained. FIG. 3 shows an electron absorption spectrum and an emission spectrum.

Example 7
A pale yellow transparent solution was prepared in the same manner as in Example 6 except that an Au nanoparticle aqueous dispersion having a linear light transmittance (optical path length of 1 cm) of 77% based on plasmon absorption of 545 nm Au was used. Obtained. Table 2 shows the appearance color, peak wavelength of the emission spectrum, and emission color of the solutions obtained.

Example 8
The procedure was the same as in Example 6 except that a Pt nanoparticle aqueous dispersion having a linear light transmittance of 600 nm (optical path length 1 cm) of 43% (in the case of Pt, plasmon absorption is not recognized) was used. A clear green solution was obtained. Table 2 shows the appearance color, peak wavelength of the emission spectrum, and emission color of the solutions obtained.

Example 9
A colorless transparent solution was obtained in the same manner as in Example 6 except that a Cu nanoparticle aqueous dispersion having a linear light transmittance of 600 nm (optical path length: 1 cm) was 66% was used. Table 2 shows the appearance color, peak wavelength of the emission spectrum, and emission color of the solutions obtained.

Example 10
Using L-ascorbic acid in the same manner as in Example 6 except that a mixture of L-ascorbic acid 15 mmol / L, citric acid monohydrate 15 mmol / L, and L-tartaric acid 15 mmol / L was used. A pale yellow transparent solution containing suspended matter was obtained. Table 2 summarizes the appearance color, peak wavelength of emission spectrum, peak intensity, and emission color of the solutions obtained.

Example 11
Using L-ascorbic acid in the same manner as in Example 6 except that a mixture of L-ascorbic acid 30 mmol / L, citric acid monohydrate 15 mmol / L, and L-tartaric acid 15 mmol / L was used. A pale yellow transparent solution containing suspended matter was obtained. Table 2 shows the appearance color, peak wavelength of the emission spectrum, and emission color of the solutions obtained.

Example 12
0.1 mL of the pale yellow transparent liquid obtained in Example 6 was dropped on a slide glass and naturally dried to obtain a colorless transparent thin film. When this thin film was irradiated with an ultraviolet LED (365 nm, about 38 mW / cm 2), light green emission was observed. The emission spectrum at this time is shown in FIG.

[Comparative Example 3]
When L-ascorbic acid was used except that citric acid monohydrate 52 mmol / L was used, a colorless transparent liquid containing a black precipitate was obtained. Even if the obtained liquid was irradiated with ultraviolet rays, no luminescence was observed.

[Comparative Example 4]
When L-ascorbic acid was used except that L-tartaric acid 52 mmol / L was used, a colorless transparent liquid containing a black precipitate was obtained. Even if the obtained liquid was irradiated with ultraviolet rays, no luminescence was observed.

  The metal nanoparticle dispersion of the present invention can produce a metal nanoparticle dispersion with good dispersion stability in a short time with simple equipment despite the fact that it does not contain additives such as a dispersant. For example, the utility value as a coloring material for in-vitro diagnostics used in the medical and healthcare fields is enormous. Moreover, a metal oxide nanoparticle dispersion and a metal hydroxide nanoparticle dispersion can be obtained from these metal nanoparticle dispersions, and the industrial spillover range is extremely wide.

  Furthermore, the present invention can produce a light-emitting metal cluster dispersion having good dispersion stability and a thin film containing the metal cluster in a short time with inexpensive equipment, and is industrially used, particularly in the medical and healthcare fields. The value is enormous. Furthermore, according to the present invention, vitamin C can be sensed and applied to the food and medical fields, and the catalytic function possessed by the metal cluster itself can be used, and the industrial spillover range is extremely wide. It is.

DESCRIPTION OF SYMBOLS 101 Gold electrode 102 Electrical insulation material 103 Electrical insulation container 104 Liquid with electrical conductivity of 20 μS / cm or less 105 Distance between electrodes (0 to 3 mm)
106 High-voltage generator 107 Wiring

Claims (7)

A method for producing a metal nanoparticle dispersion by generating discharge plasma between at least one pair of metal electrodes disposed in a liquid,
(1) The conductivity of the liquid is 20 μS / cm or less,
(2) The metal electrode is made of Ag, Au, Cu, Pt, Pd, Rh, Ir, Ru, Os, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Al, C, Si, Ga , Ge, Se, Y, Zr, Nb, Mo, Tc, In, Sn, Sb, Te, Hf, Ta, W, Re, Tl, Pb, Bi and at least one metal selected from lanthanoids,
(3) The metal nanoparticle dispersion liquid, wherein the plasma is an AC discharge plasma generated by applying a voltage between the metal electrodes so that an AC voltage is 800 V to 20 kV and a short-circuit current is 40 mA or less. Manufacturing method The method for producing a metal nanoparticle dispersion according to claim 1, wherein the liquid is distilled water or pure water. The method for producing a metal nanoparticle dispersion liquid according to claim 1 or 2, wherein the distance between the metal electrodes is 3 mm from the contact state. A metal cluster comprising: a step of mixing a metal nanoparticle dispersion produced by the method for producing a metal nanoparticle dispersion according to claim 1 and ascorbic acid at room temperature. A method for producing a luminescent solution. The method for producing a luminescent solution according to claim 4 , wherein the metal nanoparticles are Au or Pt . Method of manufacturing a thin film that emits applying a solution containing a metal-cluster of claim 4 or claim 5, by ultraviolet irradiation, characterized in that it is obtained by drying. A means for detecting luminescence by irradiating a liquid obtained by mixing a metal nanoparticle dispersion produced by the method for producing a metal nanoparticle dispersion according to any one of claims 1 to 3 with a specimen containing ascorbic acid. A method for detecting and quantifying ascorbic acid , comprising:

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