JP6032622B2 - Colloidal gold solution and method for producing the same - Google Patents

Description

  The present invention relates to a stable colloidal gold solution and a method for producing the same.

In recent years, gold nanoparticles have been used in many fields such as catalysts, medicine, sensing, electronics, color materials, paints and the like. In these applications, a gold colloid solution in which gold nanoparticles are stably dispersed in a solvent such as water is often used as a raw material. Most colloidal gold solutions are produced using chloroauric acid (HAuCl ₄ ) as a raw material, and a large amount of chloride ions remain in the solution when gold nanoparticles are obtained by reducing chloroauric acid. Yes.

  Gold nanoparticles have been studied for use as conductive pastes and catalysts. However, if chloride ions remain in the gold colloid solution, it is not preferable because it causes corrosion, catalyst poisoning, and the like. Therefore, a method for desalting treatment has been developed. However, when desalting using, for example, an ion exchange resin, a considerable amount of gold colloid having a negative surface charge is adsorbed in the same manner as chloride ions, so that the concentration of gold nanoparticles in the colloid is significantly reduced. Has been pointed out (see, for example, Patent Document 1).

  In order to avoid the above-mentioned problem of chloride ions, a method of producing a metal colloid from a metal salt that does not contain halide ions such as chloride ions has been proposed (see, for example, Patent Document 2). However, in general precious metal colloid preparation methods including Patent Document 2, the metal salt or metal complex is dissolved in water, and then a protective agent and a reducing agent are added. The use of metal salts or metal complexes is not considered.

  In addition, there is an example in which gold nanoparticles are obtained by adding gold acetate to an alkyldiol solution, adding oleic acid and oleylamine, and heating to 180 ° C. (see, for example, Non-Patent Document 1). However, it is recognized that gold acetate is hardly soluble in water and cannot be used as a raw material for aqueous colloids. Therefore, a colloid using gold acetate as a raw material and water as a solvent has not yet been reported. Under such circumstances, the gold colloid material is rarely used except for chloroauric acid.

JP 2009-120901 A Japanese Patent Laid-Open No. 11-151436

Monodispersed Core-Shell Fe3O4 @ Au Nanoparticles, L. Wan et al. , J .; Phys. Chem. B, 109 (2005) 21593-21601.

  The main object of the present invention is to provide a stable colloidal gold solution using water as a solvent. Another object of the present invention is to provide a method by which such a colloidal gold solution can be easily prepared.

As a result of intensive studies to solve the above problems, the present inventors have found that when ethanol is added to a gold acetate aqueous dispersion, a red colloidal gold solution can be obtained after several minutes at room temperature. The present invention has been completed as a result of further research based on such knowledge. That is, the present invention provides a colloidal gold solution and a method for producing the colloidal gold solution of the following modes.
Item 1. Gold nanoparticles having a particle diameter of 100 nm or less in water and an anion R—COO ⁻ (a) represented by the following general formula (a)
(Wherein R represents a linear or branched alkyl group having 1 to 4 carbon atoms)
A colloidal gold solution.
Item 2. Item 2. The colloidal gold solution according to Item 1, wherein the anion is an acetate ion.
Item 3. Item 3. The colloidal gold solution according to Item 1 or 2, further comprising a protective colloid.
Item 4. Item 4. The colloidal gold solution according to any one of Items 1 to 3, wherein the protective colloid is at least one selected from the group consisting of polyvinylpyrrolidone, polyethylene glycol, polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, and carboxymethylcellulose. .
Item 5. Item 5. The colloidal gold solution according to any one of Items 1 to 4, further comprising a reducing agent comprising an alcohol having a primary hydroxyl group and / or a secondary hydroxyl group.
Item 6. Item 6. The colloidal gold solution according to any one of Items 1 to 5, wherein the concentration of the gold nanoparticles is 0.0001 to 50% by weight.
Item 7. The gold colloid solution in any one of Claims 1-6 which does not contain a chloride ion substantially.
Item 8. A method for producing a colloidal gold solution comprising the following steps:
(I) a step of preparing a dispersion by dispersing gold carboxylate in water; and (ii) by reducing the gold carboxylate by acting a reducing agent in the dispersion obtained in step (i). A step of obtaining a colloidal gold solution.
Item 9. The reduction uses at least one selected from the group consisting of alcohols having primary hydroxyl groups and / or secondary hydroxyl groups, polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, gelatin, starch, dextrin, carboxymethyl cellulose, methyl cellulose, and ethyl cellulose. Item 9. A method for producing a colloidal gold solution according to Item 8.
Item 10. Item 10. The method according to Item 8 or 9, wherein the gold carboxylate is gold acetate.
Item 11. Item 11. The method according to any one of Items 8 to 10, wherein the dispersion contains a protective colloid.
Item 12. Item 12. The method according to any one of Items 8 to 11, wherein the protective colloid is at least one selected from the group consisting of polyvinylpyrrolidone, polyethylene glycol, polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, and carboxymethylcellulose.

  According to the present invention, a colloidal gold solution that is stable over a long period of time without causing precipitation or the like is provided. More specifically, by using gold carboxylate as a source of gold nanoparticles, the anion represented by the formula (a) is adsorbed on the gold nanoparticle surface without substantially containing chloride ions. This provides a colloidal gold solution that is stably dispersed in water.

  Furthermore, according to the method for producing a colloidal gold solution of the present invention, a stable colloidal gold solution containing no chloride ions can be obtained. Therefore, there is no need for post-treatment to remove chloride ions, and a highly concentrated gold colloid solution can be obtained simply and efficiently. Further, according to the method of the present invention, coarse particles are not produced as a by-product in the production process.

  Conventionally, as a preparation condition of a metal colloid, a solution in which a metal salt is completely dissolved is usually used as a starting point, and few examples of preparing a metal colloid using a hardly soluble metal salt have been reported. In particular, with respect to a colloidal gold solution, there has been no report of obtaining a highly concentrated colloidal gold solution using a hardly soluble metal salt as a raw material. On the other hand, according to the present invention, it is possible to prepare a gold colloid solution having a high concentration with a simple system.

1 is a graph showing a UV-VIS spectrum of a colloidal gold prepared from gold acetate in Example 1. FIG. FIG. 2 is a graph showing a TEM photograph of gold colloid prepared from gold acetate in Example 1 and from which PVP has been removed, and the size distribution of gold particles. 3 is a graph showing the UV-VIS spectrum of colloidal gold prepared from gold acetate in Example 2. FIG. FIG. 4 is a graph showing a TEM photograph of gold colloid prepared from gold acetate in Example 2 and from which PVP has been removed, and the size distribution of gold particles.

1. Colloidal gold solution The colloidal gold solution of the present invention comprises a gold nanoparticle having a particle diameter of 100 nm or less in water and an anion R-COO ⁻ (a) represented by the following general formula (a):
(Wherein R represents a linear or branched alkyl group having 1 to 4 carbon atoms)
It is characterized by including.

  In the present specification, the anion represented by the general formula (a) may be referred to as “carboxylate” and its gold salt may be referred to as “gold carboxylate”.

When halide ions such as chloride ions are contained in the colloidal gold solution, problems such as corrosion and catalyst poisoning occur when used as a conductive paste or catalyst. It is preferable to use a gold compound that does not contain halide ions. In the present invention, it is preferable to use carboxylated gold (that is, gold carboxylate), preferably carboxylated trivalent gold as a source of gold nanoparticles. Specific examples of such a gold compound include Au (CH ₃ COO) ₃ , Au (C ₂ H ₅ COO) ₃ , and Au (HCOO) ₃ . The gold carboxylate may contain a basic salt such as Au (OH) (CH ₃ COO) ₂ , Au (OH) ₂ (CH ₃ COO). As the gold carboxylate, one of these may be used alone, or two or more may be used in combination. Among these gold carboxylates, gold acetate (Au (CH ₃ COO) ₃ ) is preferably used from the viewpoint that it is easily available and has an appropriate solubility in water.

  The average particle diameter of the gold nanoparticles contained in the gold colloid solution of the present invention is 100 nm or less, preferably 50 nm or less, more preferably 2 to 40 nm. Here, an average particle diameter refers to the value calculated | required by number average from the size distribution obtained by observation with a transmission electron microscope (TEM).

The concentration of the gold nanoparticles in the gold colloid solution of the present invention is usually 0.0001 to 50% by weight, preferably 0.001 to 10% by weight, and more preferably 0.01 to 5% by weight. Here, among all the gold used for the preparation, the concentration of gold nanoparticles present in the liquid as nanoparticles exhibiting plasmon absorption is the same in the medium (the same concentration when PVP or the like is added to water) and gold. A calibration curve (straight line) obtained by performing UV-VIS measurement on several kinds of known samples having different concentrations of nanoparticles and plotting the optical density (OD) value at the wavelength (λ _max ) exhibiting the maximum plasmon absorption against the concentration. It can be approximated by

The anion represented by the following general formula (a) contained in the colloidal gold solution of the present invention may exist in a state dissolved in the colloidal gold solution, and is adsorbed on the surface of the gold nanoparticle. May be present.
R-COO ^- (a)
In the formula, R represents hydrogen or a linear or branched alkyl group having 1 to 4, preferably 1 to 2, more preferably 1 carbon atoms. Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, isopropyl, a butyl group, an isobutyl group, a sec-butyl group, and a t-butyl group, and a methyl group is preferable. The anion represented by the general formula (a) is preferably an acetate ion (CH ₃ COO ⁻ ).

  Moreover, the gold colloid solution of the present invention may contain a protective colloid. The protective colloid may be appropriately selected from conventionally known colloids. For example, polyvinyl pyrrolidone (PVP), polyvinyl alcohol, polyethylene glycol, polyacrylic acid, sodium polyacrylate, gelatin, starch, dextrin, carboxymethylcellulose, methylcellulose, Examples thereof include ethyl cellulose and glutathione. Among these, polyvinyl pyrrolidone, polyethylene glycol, polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, and carboxymethyl cellulose are preferable, and polyvinyl pyrrolidone and polyethylene glycol are more preferable. These protective colloids may be used alone or in combination of two or more. These protective colloids may be modified or modified within a range not impairing the effects of the present invention. When a polymer is used as the protective colloid, its molecular weight is not particularly limited as long as the effect of the present invention is exhibited. For example, polyvinylpyrrolidone is specifically PVP K-15 (average molecular weight 1 manufactured by Kishida Chemical). 10,000), K-30 (average molecular weight 40,000), K-90 (average molecular weight 360,000), and the like can be used.

  When the protective colloid is contained in the gold colloid solution of the present invention, the content thereof is not particularly limited as long as it is not more than the solubility in water, but usually 0.1 to 1000 mol, preferably 0. 1-500 mol, More preferably, 0.1-100 mol is mentioned. Here, when the protective colloid is a polymer, it is handled as a molar amount in the monomer unit.

  Water is used as a solvent for the colloidal gold solution of the present invention. Here, the water is not particularly limited, but it is desirable to use water that does not contain impurities such as chloride ions, such as distilled water, ion exchange water, purified water, pure water, and ultrapure water.

  The gold colloid solution of the present invention may contain a reducing agent. The reducing agent can be appropriately selected from conventionally known reducing agents, and examples thereof include alcohols having a primary hydroxyl group such as methanol, ethanol, 1-propanol, and ethylene glycol; 2-propanol, 2-butanol, and the like. Alcohols having secondary hydroxyl groups; alcohols having both primary and secondary hydroxyl groups such as glycerin; aldehydes such as formaldehyde and acetaldehyde; saccharides such as glucose, fructose, glyceraldehyde, lactose, arabinose and maltose; citric acid, citric acid Organic acids such as sodium citrate, potassium citrate, ammonium citrate, tannic acid, ascorbic acid, sodium ascorbate, potassium ascorbate and salts thereof; borohydrides such as sodium borohydride and potassium borohydride Salt; hydrazine, hydrazine hydrochloride, and hydrazine and its inorganic salts such as hydrazine sulfate. These reducing agents may be used alone or in combination of two or more. Among these reducing agents, an alcohol having a primary hydroxyl group and / or a secondary hydroxyl group is preferable, and ethanol, methanol and the like are more preferable. Some protective colloids can be used as a reducing agent. Specific examples of the protective colloid that can also be used as a reducing agent will be described in the step (i) described later.

  When the reducing agent is contained in the colloidal gold solution of the present invention, the content thereof is not particularly limited as long as the effects of the present invention are not impaired, but 1 to 100000 mol, preferably 1 to 50000 mol, relative to 1 mol of gold, More preferably, 1 to 20000 mol is mentioned.

The gold colloid solution of the present invention preferably contains substantially no halide ion (X) which is any of fluoride ion, chloride ion, bromide ion and iodide ion. As a result, even when the colloidal gold solution of the present invention is used as a conductive paste or a catalyst, it is possible to prevent problems such as the occurrence of corrosion due to halide ions and the fact that halide ions become catalyst poisons. In the present invention, the phrase “substantially free of halide ions” means that the amount of halide ions is small relative to the amount of gold in the gold colloid solution. For example, when a colloidal gold solution is prepared using chloroauric acid (HAuCl ₄ ), the molar ratio of halide ion (X) to gold (Au) (X / Au) unless chloride ion removal treatment is performed. Is usually around 4. On the other hand, in the present invention, the molar ratio (X / Au) of halide ion (X) to gold (Au) in the colloidal gold solution is, for example, 0.4 or less, or 0.04 or less, and further 0.004. It can be. Even when a halide ion-containing raw material such as chloroauric acid is used, it is possible to reduce the halide ion concentration by performing a desalting treatment after the gold colloid solution is produced. The solution can be made into a gold colloid solution having a predetermined halide ion concentration or less without performing a desalting treatment.

  The colloidal gold solution of the present invention may contain a conventionally known additive depending on the application. Examples of such additives include colorants, stabilizers, surfactants, dispersants, thickeners, and the like.

  The colloidal gold solution of the present invention can be applied to uses such as conductive inks, conductive pastes, catalysts, sensors, bonding materials, coloring materials, paints, biomarkers and the like.

2. Method for Producing Gold Colloid Solution The present invention provides a method for producing a gold colloid solution, which can easily prepare the gold colloid solution as described above. The method for producing the colloidal gold solution includes the following steps (i) and (ii).

Step (i)
In this step (i), gold carboxylate is dispersed in water to obtain a dispersion. Here, gold carboxylate and water as a solvent are as described in the above “1. Gold colloid solution”.

  When the gold carboxylate is dispersed in this step (i), water containing a protective colloid may be used as a solvent. By adding the protective colloid, the particle size distribution of the gold nanoparticles can be narrowed, and the stability of the resulting gold colloid solution can be improved. Specific protective colloids are as described in “1. Colloidal gold solution” above.

  Among the protective colloids described above, for example, polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, gelatin, starch, dextrin, carboxymethylcellulose, methylcellulose, ethylcellulose and the like can be used as a reducing agent, and among these, preferred May include polyvinyl pyrrolidone, polyethylene glycol, polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, and carboxymethyl cellulose, and more preferable examples of polyvinyl pyrrolidone and polyvinyl alcohol are obtained because a more stable gold colloid solution can be obtained. Therefore, when these are already added to the dispersion as protective colloids in this step (i), a gold colloid solution can be prepared without adding a separate reducing agent in the following step (ii).

  The amount of the protective colloid added is not particularly limited as long as it is not higher than the solubility in water, but is usually 0.1 to 1000 mol, preferably 0.1 to 500 mol, more preferably 0.1 to 1 mol of gold. ˜100 mol is mentioned.

  In this step (i), the method for dispersing the gold carboxylate in water can be appropriately selected from methods usually used for dispersing powder in water. For example, a magnetic stirrer, a touch mixer And an ultrasonic cleaner. Moreover, you may use combining these apparatuses. Although it does not specifically limit as conditions at the time of disperse | distributing, Specifically, the process (60 second) by an ultrasonic cleaner is illustrated after a touch mixer (240 rpm, 10 second). Such treatment may be repeated a plurality of times (for example, 1 to 20 times, preferably 5 to 10 times).

  For example, when gold acetate is used as the gold carboxylate, the dispersion exhibits a brown color and shows a Tyndall phenomenon, so that it can be confirmed that the dispersion is in a colloidal state.

  The dispersion concentration of the dispersion obtained in this step (i) is not particularly limited as long as it has the dispersion concentration of gold carboxylate necessary to obtain the target colloidal gold solution. From the viewpoint of stability, the amount is usually 0.0001 to 50% by weight, preferably 0.001 to 10% by weight in terms of gold metal.

Gold carboxylate is known to dissolve slightly in water as ions. For example, the solubility of gold acetate is described in Non-Patent Document 2 (GC Bond et al., Chapter 4 Preparation of Supported Gold Catalysts, Catalysts by gold (Series editor, G. J. Hutchings, p. 89), p. 89). Press (2006)) is reported to be 10 ⁻⁵ M or less. Thus, although a limited interpretation of the present invention is not desired, it is expected that when gold carboxylate is dispersed in water, some will dissolve in water and the remainder will be dispersed in water as a colloid.

Step (ii)
In this step (ii), a gold colloid solution is obtained by reducing the gold carboxylate by acting a reducing agent in the dispersion obtained in the step (i).

  In this step (ii), the reduction of the gold carboxylate can be performed by adding a reducing agent to the dispersion obtained in the step (i). The reducing agent is as described in “1. Colloidal gold solution” above, preferably an alcohol having a primary hydroxyl group and / or a secondary hydroxyl group, more preferably ethanol, methanol and the like. The amount of the reducing agent that acts on the dispersion is not particularly limited as long as it has a number of moles equal to or greater than the redox equivalent to the number of moles of gold in the dispersion, but for example, 1 to 100,000 per mole of gold. Mol, preferably 1 to 50000 mol, more preferably 1 to 20000 mol. For example, when the reducing agent is alcohol, the volume ratio is preferably in a range where it can be uniformly dissolved in water, and such volume ratio can be appropriately set based on the number of moles.

  The conditions for causing the reducing agent to act on the dispersion are not particularly limited as long as the gold carboxylate in the dispersion can react with the reducing agent, and stirring or the like may be performed as necessary. Further, the reaction temperature is not particularly limited, and can be appropriately set depending on the type of reducing agent to be used. For example, 1 to 100 ° C, preferably 5 to 40 ° C, more preferably 10 to 30 ° C. Can be mentioned.

  For example, when a relatively strong reducing agent such as ethanol or methanol is used, the reaction proceeds sufficiently in several minutes under room temperature conditions, but when a weak reducing agent such as 2-propanol or polyvinylpyrrolidone which is also a protective colloid is used. Can take days to months at room temperature. Therefore, when a weak reducing agent is used, the reaction rate can be increased by heating the reaction solution to raise the reaction temperature, and gold colloid can be produced in several minutes to several hours. The heating temperature is not particularly limited as long as the colloidal gold can be produced, and examples thereof include 40 to 100 ° C, preferably 60 to 100 ° C, and more preferably 80 to 100 ° C. More specifically, if gold acetate is used in combination with gold acetate, protective colloid, and polyvinylpyrrolidone as the reducing agent, a high concentration of gold can be obtained by heating at 80 to 100 ° C. for 5 to 60 minutes. A colloidal solution can be obtained.

  Moreover, in this process (ii), you may remove an excess protective colloid as needed. The removal method is not particularly limited and may be appropriately selected from conventionally known methods. For example, centrifugal filtration, membrane separation, dialysis, electrodialysis and the like can be performed. Depending on the amount of protective colloid to be removed, these treatments may be performed multiple times. Further, the obtained colloidal gold solution may be subjected to treatments such as pH adjustment, concentration and purification according to a conventionally known method, if necessary.

  As described above, in the method for producing a gold colloid solution of the present invention, gold carboxylate can be dispersed in water containing a protective colloid as required, and then a reducing agent can be allowed to act. The protective colloid and the reducing agent may be added to water as a solvent to form an aqueous solution, and gold carboxylate may be added thereto to prepare a gold colloid solution. Even when such a method is employed, the same materials and conditions as described above can be employed.

  In the production of the colloidal gold solution of the present invention, preferred combinations of the materials include, for example, gold acetate as the gold carboxylate, polyvinylpyrrolidone and / or polyvinyl alcohol as the protective colloid, and methanol and / or ethanol as the reducing agent. By adopting such a combination, a highly concentrated and stable gold colloid solution can be easily obtained.

  Although it is not desired to interpret the present invention in a limited manner, the reason why a high concentration of gold colloid can be obtained in the present invention can be considered as follows, for example. Since gold carboxylate such as gold acetate is hardly soluble in water, the gold ion concentration in water is considered to be kept at a dilute concentration suitable for gold colloid formation. And, when gold ions are reduced to metallic gold by a reducing agent, it is considered that gold carboxylate can be dissolved again in a trace amount of water. Thus, it is considered that a gold colloid is formed little by little by repeating a minute dissolution and reduction of gold carboxylate, and as a result, a high concentration of gold colloid can be obtained.

  Hereinafter, although an example and a comparative example are given and the present invention is explained still in detail, the present invention is not limited to these.

Example 1
50 mg of polyvinylpyrrolidone (PVP K15, manufactured by Kishida Chemical Co., Ltd.) was dissolved in 10 mL of a 1: 1 solution of ethanol and water. 5 mg of brown powder of gold acetate [Au (CH ₃ COO) ₃ , manufactured by Alfa Aesar, purity 99.99% described in the manufacturer's analysis certificate] was added, touch mixer (IKA, Vortex Genius 3) and ultrasonic cleaner (Used by ASONE, US-2R). As the dispersion treatment, the standard condition is that the touch mixer treatment (10 seconds at 2400 rpm) and the ultrasonic cleaner treatment (60 seconds) are alternately repeated 5 to 7 times, but the number of repetitions depends on the remaining state of precipitation. Was increased or decreased as appropriate. By such a treatment, the undissolved precipitate in the solution is almost eliminated, but a Tyndall phenomenon is observed when the light of the LED light is applied from the side of the container, so that it is not a true aqueous solution but a brown colloidal dispersion. It was confirmed.

  When this dispersion was allowed to stand at room temperature (about 24 ° C.), the liquid color began to turn red in about 10 minutes. After standing overnight, a red gold colloid solution (preparation concentration 1.3 mmol-Au / L) was obtained. The colloidal solution was diluted to 1/10 concentration with water, put into a quartz cell having an optical path length of 1 cm, and UV-VIS spectrum was measured with a spectrophotometer (Shimadzu Corporation, UV-1800). The results are shown in FIG.

In FIG. 1, the horizontal axis represents the wavelength, and the vertical axis represents the value displayed as absorbance in the spectrophotometer. In the colloidal gold solution, the absorbance includes the influence of scattering and reflection in addition to absorption, and is expressed here as optical density. A peak based on surface plasmon absorption was clearly observed in the measured spectrum, and the wavelength (λ _max ) was 527 nm.

It is generally known that the smaller the particle diameter of gold nanoparticles, the smaller the peak wavelength of plasmon absorption. For example, Non-Patent Document 3 (Toshikatsu Kobayashi, Chapter 21 Rich Gold Nanoparticle Paste as Coloring Material, Gold Nanotechnology (supervised by Masami Haruta) pp.273-282 CMC Publishing Co., Ltd. (2009)) The correspondence between the volume average particle diameter (D _Au ) and the plasmon absorption wavelength (λ _max ) is shown. If the gold colloid dispersion medium is the same, both the values of D _Au and λ _max have a linear relationship, and it is possible in principle to determine D _Au from the measured value of λ _max .

Although in this embodiment a dispersion medium for colloidal gold is water, the dielectric constant of the dispersion medium by mixing the reducing agent and protective colloid PVP such as ethanol or the like is changed, _max even λ a D _Au is the same fluctuate. In addition, in the range where D _Au is 50 nm or less, the larger the D _Au is, the stronger the plasmon absorption is. Therefore, when the particle size distribution is wide, it is strongly influenced by large particles, and D _Au and λ are compared with the monodispersed case. The relation of _max shifts. For this reason, it is difficult to accurately determine D _Au from λ _max when the composition of the dispersion medium is different from one another as in this example and the size distribution of the gold nanoparticles is not monodispersed.

Therefore, the relationship between the D _Au value obtained from the TEM measurement of Example 1 and Example 2 described later and λ _max is added to the data point sequence shown in FIG. 8 of Non-Patent Document 3, and a regression line is obtained by the least square method. It was. As a result, the correlation coefficient is 0.96, which is close to 1, so that it can be said that the state of the gold colloid of the present invention is similar to that of the gold colloid shown in FIG. When the range of D _Au corresponding to the range of λ _max (524 to 562 nm) measured in Example 1 and Examples 2 to 33 described later is obtained from the obtained linear equation, it becomes 12 to 37 nm, and in this example It was estimated that a gold colloid having an average particle size of about 10 to 40 nm was obtained.

Further, the optical density at λ _max can be used as an index of colloidal gold concentration. The optical path length of the quartz cell used for the measurement is L (cm), the dilution ratio of the solution is F (for example, F = 10 when measured by diluting to 1/10 concentration), and the optical density value at λ _max at that time is Y The maximum converted optical density value (that is, OD _max ) immediately after preparation calculated by the following formula (1) was 6.8 (see Table 1 below).
OD _max = Y × F / L Formula (1)

  Centrifugal filtration was performed to remove PVP from the colloidal gold dispersion (40 days after preparation). Using a centrifugal filter unit (Amicon Ultra-15, manufactured by Millipore) with a molecular weight cut off of 50,000, the colloidal gold dispersion that does not pass through the filter is concentrated to a deep red color after passing through the filter. As a result, a colorless and transparent filtrate was obtained. The operation of adding water to the concentrated dispersion to return to 10 mL and performing centrifugal filtration again was repeated three times. In order to determine the presence or absence of PVP remaining in the filtrate, Non-Patent Document 4 (Binding of Evans Blue On Poly (N-Vinyl-2-Pyrrolidone), M. Marthamuthu and E. Subrariannian, Polymer 12 Bull207 14 (1985)), Evans Blue (EB) solution was added dropwise to measure UV-VIS absorption.

Since the first filtrate showed 639 nm absorption based on the PVP-EB complex, the third filtrate showed no absorption at 639 nm and only 609 nm absorption based on free EB. It was confirmed that PVP could be removed by three centrifugal filtration operations. As a result of adding Evans Blue to a part of the obtained colloidal gold dispersion and measuring UV-VIS absorption, it was confirmed that no PVP remained in the water, which is a dispersion medium of colloidal gold, because there was no absorption at 639 nm. did it. Λ _max in UV-VIS absorption of the colloidal gold solution after removing the PVP (part where Evans Blue was not added) was 529 nm.

  The gold colloid solution after the PVP removal operation was dropped onto a microgrid and dried, and observed with a transmission electron microscope (TEM). A TEM photograph is shown in FIG. It is a gold nanoparticle mixture of various crystal structures (regular icosahedron structure Ih, pentagonal decahedron structure Dh, face-centered cubic lattice structure Fcc), and its particle diameter is observed from about 5 nm to over 20 nm. It was done. The number average particle diameter determined from the size distribution of FIG. 2 was 11.5 nm.

Thereafter, the colloidal gold solution was stored at room temperature, but no precipitate was observed even after 7 months, and the colloidal solution was stable. It was considered that acetate ions and / or a small amount of residual PVP were adsorbed on the gold nanoparticle surface to form a stable gold colloid solution. Table 1 below summarizes the values of λ _max and OD _max immediately after preparation and after 7 months from the removal of PVP.

  Table 1 shows that the particle size and concentration fluctuate when PVP is removed, but there is no significant change during the subsequent 7 months, indicating that the colloid is stable.

Comparative Example 1
Chloroauric acid (HAuCl ₄₎ prepared by weighing crystals of chloroauric acid tetrahydrate (Kishida Kagaku) instead of gold acetate in an electronic balance and dissolving it in a predetermined amount of water as the gold carboxylate of the gold colloid material. A solution was prepared in the same manner as in Example 1 except that 0.13 mL of 0.1 mol / L aqueous solution of) was used. The liquid color at the time of preparation was yellow (liquid color of a normal aqueous solution of chloroauric acid), and the Tyndall phenomenon was not observed, and chloroauric acid was completely dissolved and became a true solution. As in Example 1, it was allowed to stand overnight at room temperature. However, no color change occurred and the solution remained yellow and no colloidal gold was produced.

Example 2
6 g of polyvinylpyrrolidone (PVP K15) was dissolved in 20 mL of water, and 2 mL thereof was taken in a glass screw tube bottle. When 20 mg of gold acetate powder was added and dispersed under the same conditions as in Example 1 using a touch mixer and an ultrasonic cleaner, a brown dispersion liquid was obtained. When a stirrer was inserted, the lid with Teflon-coated packing was closed, and the solution was boiled while stirring on a hot plate stirrer, a red colloidal solution (Au 26.7 mmol / L) was obtained in a few minutes. FIG. 3 shows the UV-VIS spectrum (absorption peak 530 nm) of the colloidal solution diluted to 1/100. The gold particle diameter determined by (Equation 1) was 18.1 nm.

After 40 days from the preparation, 10 mL of water was added to 2 mL of colloidal solution, diluted to 12 mL, and then subjected to centrifugal filtration 6 times under the same conditions as in Example 1 to remove PVP, and water added after the 6th filtration. The colloidal gold solution having the same concentration as that in the preparation was obtained by adjusting the amount. Λ _max in UV-VIS absorption of the colloidal gold solution after removing the PVP (part where Evans Blue was not added) was 524 nm. The values of λ _max and OD _max obtained by the same method as in Example 1 immediately after preparation, after removal of PVP and after 7 months have passed are shown in Table 2 below.

  From Table 2, as in Example 1, the particle size and concentration varied during PVP removal, but there was no significant change during the subsequent 7 months, indicating that the colloid is stable.

  A TEM photograph of the gold colloid after the PVP removal operation is shown in FIG. FIG. 4 shows that, similarly to Example 1, the present Example 2 is also a mixture of gold nanoparticles having various structures. The particle size distribution was slightly better than in the case of Example 1. The average particle diameter (arithmetic average value usually shown by TEM) obtained from the size distribution of FIG. 4 was 9.8 nm.

Comparative Example 2
Instead of using 20 mg of gold acetate powder in Example 2, 0.1 mol / L aqueous solution of chloroauric acid (HAuCl ₄ ) prepared from chloroauric acid tetrahydrate (Kishida Kagaku) according to the same method as in Comparative Example 1 A solution was prepared in the same manner as in Example 2 except that 0.5 mL was used. Upon boiling to reflux, coarse gold particles precipitated and no gold colloid was produced.

Examples 3-6
25 mg of polyvinylpyrrolidone (PVP K15) was dissolved in 2.5 mL of water in the test tube. Gold acetate powder (5 mg) was added, and the mixture was dispersed under the same conditions as in Example 1 using a touch mixer (IKA Corp., Vortex Genius 3) and an ultrasonic washer (Aiwa Medical Industries, AU-25C). To this, 2.5 mL of the reducing agent shown in Table 3 was added and stirred (Example 3: ethanol, Example 4: methanol, Example 5: ethylene glycol, Example 6: 2-propanol). When covered and allowed to stand at room temperature, Examples 3-5 produced red gold colloids. In Example 6, no change was observed after standing at room temperature for 1 day, but when heated to 100 ° C. in boiling water with the lid on, colloidal gold was immediately formed. After colloid formation, the mixture was allowed to stand at room temperature for 2 days, and UV-VIS measurement was performed. Based on the measured value of λ _max , the OD _max value was calculated based on the formula (1). These values are shown in Table 3 below.

Comparative Example 3
T-Butanol 2.5mL was used as a reducing agent, and other operation was performed like Example 3-6. At room temperature, no change was observed even after 1 day. Furthermore, although it heated in boiling water for 2 hours, the brown precipitate fell, the supernatant became transparent and the gold colloid was not produced | generated. The results are also shown in Table 3 below.

  From Table 3, when alcohol having a primary hydroxyl group or a secondary hydroxyl group is used as the reducing agent (Examples 3 to 6), gold colloid can be generated by reducing gold acetate, but only the tertiary hydroxyl group can be produced. It has been shown that no reduction occurs with t-butanol having.

Examples 7 to 16 <Amount of gold acetate and dispersant>
The amount of polyvinylpyrrolidone (PVP K15) shown in Table 4 was dissolved in 2.5 mL of water in the test tube. The amount of gold acetate powder shown in Table 4 was added to the obtained aqueous solution, and Example 1 was used using a touch mixer (IKA Corp., Vortex Genius 3) and an ultrasonic washer (Aiwa Medical Industries, AU-25C). Dispersion was performed under the same conditions. When 2.5 mL of ethanol was added thereto, the lid was covered and allowed to stand at room temperature, colloidal gold was produced. After standing for 1 day, the UV-VIS spectrum was measured. The values of λ _max and OD _max obtained by the same method as in Example 1 are shown in Table 4 below. In Table 4 below, the Au concentration is the Au concentration by weight in the colloidal solution calculated from the amount of gold acetate used in the preparation. PVP / Au is a molar ratio calculated by the monomer unit (molecular weight 111) of PVP.

Although the conventional precious metal colloid prepared there is an example of changing a large noble metal particle size by the addition of PVP (eg, JP 2005-281817), changing significantly the amount of PVP to gold acetate of lambda _max It is considered that the change is not large, and therefore there is no significant change in the gold nanoparticle diameter. Although colloidal gold is produced regardless of whether or not PVP is added, in Examples 8 to 12 where PVP is added, the OD value is 1.4 times the same even with the same amount of gold acetate compared to Example 7 where PVP is not added. Greater values were obtained. In Examples 13 to 16, as a result of changing the amount of gold acetate, an OD _max value almost linearly related to the concentration of gold nanoparticles was obtained up to a concentration of gold nanoparticles of 0.55% by weight. In Example 16, the value was about 50% of the OD _max value expected from the extrapolation of the straight line.

Examples 17 to 24 <Influence of protective colloid during ethanol reduction>
25 mg of the various dispersants shown in Table 5 were dissolved in 2.5 mL of water in the test tube. 5 mg of gold acetate powder was added, and the mixture was dispersed under the same conditions as in Example 1 using a touch mixer (IKA Corp., Vortex Genius 3) and an ultrasonic washer (Aiwa Medical Industries, AU-25C). To this, 2.5 mL of ethanol was added. The colloidal gold was formed when the lid was left standing at room temperature. The UV-VIS spectrum after standing for 1 day was measured. Based on the measured value of λ _max , the OD _max value was calculated based on the formula (1). These values are shown in Table 5.

From Table 5, it was shown that the λ _{max of the} gold colloid obtained varies depending on the type of protective colloid. More specifically, when PVP K-30 (Example 18) or PVPK-90 (Example 19) having a large molecular weight is used as compared to PVP K-15 (Example 17), λ _max becomes relatively small. The formation of gold colloid with small particle size was suggested. Further, when sodium polyacrylate or polyacrylic acid (Examples 21 and 22 respectively) was used, λ _max was increased, suggesting the formation of a gold colloid with a large particle size. Furthermore, when polyethylene glycol, polyvinyl alcohol, or carboxymethyl cellulose (Examples 20, 23, and 24, respectively) was used, λ _{max of the} same level as that of PVP K-15 (Example 17) was shown, and the same level of particles The generation of colloidal gold colloid was suggested, but the OD _max value was lower compared to PVP K-15, indicating a slight decrease in the concentration of gold nanoparticles.

Examples 25-33 <Reduction with various protective colloids>
A predetermined amount of the dispersant shown in Table 6 was added to 5 mL or 2 mL of water in the test tube and dissolved. A predetermined amount of gold acetate powder was added, and the mixture was dispersed under the same conditions as in Example 1 using a touch mixer (IKA Corp., Vortex Genius 3) and an ultrasonic cleaner (Aiwa Medical Industry, AU-25C). Colloidal gold was formed while capping and heating in boiling water for 2 hours. Thereafter, the UV-VIS spectrum was measured after standing at room temperature for 1 day (however, in Examples 30 to 33, after 3 days, Example 26 was left unheated at room temperature for 5 days). Based on the measured value of λ _max , the OD _max value was calculated based on the formula (1). These values are shown in Table 6 below.

Table 6 shows that a gold colloid can be produced when PVP, PEG, PVA or CMC is used as a protective colloid without adding ethanol. When Examples 26 and 27 were compared, a colloid with a large OD _max value was obtained in a short time by heating, whereas a long period of time was required for colloid formation at room temperature and the OD _max value was small. Further, when the amount of gold acetate was increased, it was possible to produce a colloid having an OD _max value exceeding 100 (Examples 29 and 32). When PVP or PVA was used as the protective colloid, stable colloidal gold was obtained even after standing for 3 days (Examples 25 to 30 and 32).

(Summary)
From the above results, it was shown that a stable colloidal gold solution can be obtained according to the present invention. Furthermore, according to the present invention, it was possible to prepare a solution having a much higher concentration than conventional colloidal gold solutions. In addition, it was shown that by using gold carboxylate as a source of gold nanoparticles, a colloidal gold solution applicable to a wide range of applications can be easily prepared without worrying about residual chloride ions. It was.

Claims (11)

Gold nanoparticles having a particle diameter of 100 nm or less in water and an anion R—COO ⁻ (a) represented by the following general formula (a)
(Wherein R represents a linear or branched alkyl group having 1 to 4 carbon atoms)
A colloidal gold solution comprising:
The gold nanoparticle content is 0.01 to 5% by weight,
The gold colloid solution, wherein the molar ratio of chloride ions to gold (chloride ions / gold) in the gold colloid solution is 0.04 or less .   The colloidal gold solution according to claim 1, wherein the anion is acetate ion.   The gold colloid solution according to claim 1 or 2, further comprising a protective colloid. The colloidal gold solution according to claim 3 , wherein the protective colloid is at least one selected from the group consisting of polyvinylpyrrolidone, polyethylene glycol, polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, and carboxymethylcellulose.   Furthermore, the gold colloid solution in any one of Claims 1-4 containing the reducing agent which consists of alcohol which has a primary hydroxyl group and / or a secondary hydroxyl group. The gold colloid solution according to any one of claims 1 to 5 , wherein a molar ratio of chloride ions to gold (chloride ions / gold) in the gold colloid solution is 0.004 or less. A method for producing a colloidal gold solution comprising the following steps:
(I) A step of preparing a dispersion by dispersing gold carboxylate in water , wherein the gold carboxylate is an anion R—COO ⁻ represented by the general formula (a) (wherein R is carbon number 1) And (ii) in the dispersion obtained in the step (i), the gold carboxylate is reduced by acting a reducing agent. Thereby obtaining a gold colloid solution having a molar ratio of chloride ions to gold (chloride ions / gold) of 0.4 or less. The reduction uses at least one selected from the group consisting of alcohols having primary hydroxyl groups and / or secondary hydroxyl groups, polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, gelatin, starch, dextrin, carboxymethyl cellulose, methyl cellulose, and ethyl cellulose. The method for producing a colloidal gold solution according to claim 7 , wherein 9. A method according to claim 7 or 8 , wherein the gold carboxylate is gold acetate. The method according to claim 7 , wherein the dispersion contains a protective colloid. The method according to claim 10 , wherein the protective colloid is at least one selected from the group consisting of polyvinylpyrrolidone, polyethylene glycol, polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, and carboxymethylcellulose.