JPWO2007058173A1 - Metal nanoplate-immobilized substrate and method for producing the same - Google Patents

Abstract

In order to obtain metal nanoparticles that can be suitably applied to sensing devices, optical devices, electronic devices, and the like, the metal nuclides attached to the surface of the substrate are immersed in a solution containing the same kind of metal ions and the reduction proceeds. Provides a metal nanoplate-immobilized substrate comprising metal nanoplates immobilized on the substrate surface.

Description

  The present invention relates to a metal nanoplate-immobilized substrate and a method for producing the same, and an electrochemical element and a battery electrode including the metal nanoplate.

In recent years when nanotechnology has attracted attention, metal nanoparticles having a particle size of several nanometers to several hundred nanometers have specific optical properties, electrical properties, magnetic properties and catalytic action. Application of a metal nanoparticle-immobilized substrate obtained by immobilizing particles to a substrate is expected to be applied to sensing devices, optical devices, electronic devices, and the like.
Here, “metal nanoparticles” usually mean spherical particles of nm size, but in recent years, metal nanoparticles having various shapes have been proposed by changing production conditions. For example, it is possible to produce metal nanoparticles having various shapes such as rod-shaped particles having different aspect ratios (Non-Patent Document 1).

Moreover, although the diameter of the said conventional metal nanoparticle is 10 nm-100 nm, for example, the metal nanostructure which has a very large flat part compared with the said thickness is also reported. The metal nanostructure having such a flat portion has a unique shape such as a polygon depending on the type of metal and the manufacturing conditions, and can also be referred to as a “metal nanoplate”.
Although there are very few research reports on metal nanoplates (for example, Non-Patent Document 2), in Non-Patent Document 1, the anionic phospholipid dimyristol-L-α-phosphatidyl-DL-glycerol is used. It has been reported that hexagonal plate-like metal nanoparticles are formed by using (DMPG) as a metal protective agent.

However, in the said nonpatent literature 1, it is only reported that the metal nanoplate was formed in aqueous solution and the aqueous solution in which the said metal nanoplate was disperse | distributed was obtained. That is, there has been no report on metal nanoplates immobilized on a substrate, and it has not been clear about an efficient production method of metal nanoplates or physical properties of metal nanoplates immobilized.
For example, Patent Document 1 discloses a method for producing nanoplates of “precipitated calcium carbonate particles” used as a filler in the field of papermaking and plastics. Metal nanoplates are materials, physical properties, and production conditions. It differs greatly in terms of use and the like, and the production method cannot be applied to a metal as it is to efficiently produce metal nanoplates immobilized on a substrate.

In addition, the present inventors have found a method for directly immobilizing metal nanoparticles on a substrate without using a cross-linking reagent layer or the like, and have conducted research (see Patent Document 2). An immobilized metal nanoplate was not obtained.
Nikhil R. Jana, Latha Gearheart, Catherine J. Murphy, J. Phys. Chem. B 2001, 105, 4065-4067 D. Ibano, Y. Yokota, T. Tomonaga, Chem. Lett., 32, 574 (2003) JP-T-2004-533396 JP 2005-187915 A

  In view of the prior art as described above, an object of the present invention is to provide a metal nanoplate immobilized on a substrate as a material that can be suitably applied to a sensing device, an optical device, an electronic device, and the like, and a method for manufacturing the same. Is to obtain more easily and reliably.

In order to solve the above problems, the present invention provides:
A method of immobilizing a metal nanoplate on the surface of a substrate,
(1) attaching a metal nuclide on the surface of the substrate;
(2) After the step (1), the step of growing the nuclide,
The manufacturing method of the metal nanoplate fixed base material characterized by these is provided.

In the step (1), the base material is brought into contact with a seed solution containing a metal compound constituting the metal nanoplate, a protective agent, and a first reducing agent, and the metal is provided on at least a part of the surface of the base material. Of nuclide,
In the step (2), it is preferable that the base material to which the nuclide is attached is brought into contact with a growth solution containing the metal compound and a hydrophilic polymer, and the nuclide is grown on the surface.

The metal is preferably at least one of gold, silver, platinum and palladium.
The protective agent preferably contains trisodium citrate.
The first reducing agent preferably contains sodium tetrahydroborate.
The hydrophilic polymer preferably contains at least one of polyvinyl pyrrolidone and polyethylene glycol.

The growth solution preferably further contains a second reducing agent.
The second reducing agent preferably contains ascorbic acid.
Furthermore, the metal is preferably gold.

  This invention provides the metal nanoplate fixed base material containing the metal nanoplate manufactured by the manufacturing method of said metal nanoplate fixed base material.

It is preferable that a (111) plane of the crystal plane of the metal is exposed on at least one plane of the metal nanoplate.
The thickness of the metal nanoplate is preferably 20 to 30 nm.
The metal nanoplate is preferably polygonal having a plurality of acute or obtuse corner portions.
Furthermore, the present invention provides an electrochemical element and a battery electrode including the metal nanoplate-immobilized substrate.

  Here, the “metal nanoplate” in the present invention refers to the first flat portion constituting one surface (front or back) and the other surface (back or front) facing the first surface. It refers to a metal plate (plate-like metal particles) having a second flat portion). Further, when it has a thickness on the order of nm (several nm to several hundred nm, preferably 20 to 30 nm, more preferably 10 to 20 nm, particularly preferably 10 nm or less), and its shape approximates to a circle, for example, about 100 nm It has a diameter of ˜1 μm.

  The “metal nanoplate” may have a substantially uniform thickness or a nonuniform thickness as a whole within the thickness range. A porous part having pores at least in part may be formed. In a more preferred embodiment, the metal nanoplate has a polygonal shape having a plurality of acute or obtuse corner portions on the outer periphery, and an edge portion is formed on a side between the corner portions. .

  In other words, the “metal nanoplate” in the present invention has a configuration in which “metal nanoparticles” are formed by two-dimensional growth based on nuclides. The “nuclide” in the present invention refers to a kind of metal nanoparticles (for example, a particle size of about 4 nm) generated by a reaction between a metal ion and a reducing agent in a seed solution described later. “Metal nanoparticles” have ordinary meaning as a general technical term in the present invention, and are metal fine particles having a size on the order of nm (several nm to several hundred nm). Depending on the particle size, metal nanoparticles have so-called “quantum size effects” such as special catalytic properties, optical properties, electronic properties, and magnetic properties. It is considered to have an “effect”.

  The metal nanoplate is at least one surface, preferably one of the first flat portion (one main surface) and the second flat portion (the other main surface) of the metal nanoplate. One surface is fixed in contact with at least a part of the surface of the substrate. Therefore, “the (111) plane of the crystal plane of the metal is exposed on at least one surface of the metal nanoplate” means that the state of the first flat portion and the second flat portion is: It means that at least a part of the flat portion not in contact with the substrate corresponds to the (111) plane of the crystal plane of the metal.

  In other words, "the (111) plane of the crystal plane of the metal is exposed on at least one surface of the metal nanoplate" means "at least a part of at least one surface of the metal nanoplate. Is composed of (111) planes of the metal crystal planes "or" at least part of at least one plane of the metal nanoplate is (111) of the metal crystal planes " It can be said that it is a state. Of course, the (111) plane may be exposed in both the first flat portion and the second flat portion.

  The metal nanoplate-immobilized base material of the present invention having the above-described configuration has excellent electrical characteristics, and particularly when the metal nanoplate is in contact with a specific compound (substance), electron transfer is performed. The remarkable effect that the electrolytic current is easily increased and the electrolytic current is increased is obtained. Accordingly, the metal nanoplate-immobilized substrate of the present invention can be suitably used for an electrochemical device for detecting the specific compound.

  Moreover, according to the manufacturing method of the metal nanoplate fixed base material of this invention, the said metal nanoplate fixed base material of this invention can be obtained more simply and reliably. That is, according to the present invention, the shape of the metal nanoplate can be controlled, and the metal nanoplate can be stably immobilized on the substrate.

It is a front view of the plate-shaped substrate immersed in the seed solution, and more specifically, is a conceptual diagram showing a state in which nuclides are attached to the surface of the plate-shaped substrate. It is the sectional view on the AA line in FIG. FIG. 1 is a diagram (a cross-sectional view taken along the line AA in FIG. 1) showing a state after the plate-like base material after the nuclide formation step shown in FIGS. 1 and 2 is brought into contact with a growth solution to grow the nuclide. is there. It is an electron micrograph of the surface of an indium tin oxide (ITO) board | substrate after the nuclide formation process in this invention. It is an AFM photograph of the surface (gold | metal nanoplate) of the ITO substrate after the nuclide formation process in this invention. It is an electron micrograph of the substrate surface obtained using the condition (a) (Comparative Example 2) in the examples of the present invention. It is an electron micrograph of the substrate surface obtained using the conditions (Example 2) of (b) in the Example of this invention. It is an electron micrograph of the substrate surface obtained using the condition (Example 1) of (c) in the Example of this invention. It is an electron micrograph of the substrate surface obtained using the conditions (Example 3) of (d) in the Example of this invention. It is an electron micrograph of the substrate surface obtained using the condition (e) (Comparative Example 3) in the examples of the present invention. In the examples of the present invention, the optical absorption spectra of the gold nanoplates obtained using the condition (c) (Example 1) and the gold nanoparticles obtained using the condition (a) (Comparative Example 2) are shown. FIG. The figure which shows the XRD data (2 (theta)) obtained by measuring the gold | metal nanoplate obtained using the conditions (Example 1) of (c) in the Example of this invention using an X-ray diffraction (XRD) apparatus. It is. It is an electron micrograph of the substrate surface obtained using the condition (a) (Comparative Example 4) in the examples of the present invention. In the Example of this invention, it is an electron micrograph of the substrate surface obtained using the conditions (Example 5) of (b). It is an electron micrograph of the substrate surface obtained using the condition (Example 1) of (c) in the Example of this invention. It is an electron micrograph of the substrate surface obtained using the condition (d) (Comparative Example 6) in the examples of the present invention. It is a figure which shows the structure of the apparatus for measuring the electrochemical response used in the Example of this invention. It is a figure which shows the cyclic voltammogram measured with respect to the oxidation reduction reaction system of ferricyan-ferrocyan. It is a figure which shows the cyclic voltammogram measured with respect to the oxidation-reduction reaction system of cytochrome c. It is a figure which shows the cyclic voltammogram measured with respect to the oxidation-reduction reaction system of p-benzoquinone. It is an electron micrograph of the substrate surface obtained in Example 4 of the present invention. It is a figure which shows the XRD data (2 (theta)) obtained by measuring the gold | metal nanoplate obtained in Example 4 of this invention using the X-ray-diffraction (XRD) apparatus. It is a figure which shows the cyclic voltammogram measured with respect to the oxidation reduction reaction system of ferricyan-ferrocyan. It is a figure which shows the cyclic voltammogram measured with respect to the oxidation-reduction reaction system of cytochrome c. It is a figure which shows the cyclic voltammogram measured with respect to the redox reaction system of ascorbic acid. It is the electron micrograph of the substrate surface obtained by changing CTAB density | concentration in the Example of this invention.

1. Metal nanoplate-immobilized substrate First, metal nanoplates immobilized on the substrate surface are included by immersing the metal nuclide attached to the substrate surface in a solution containing the same type of metal ions and proceeding with the reduction. A metal nanoplate fixed base material is demonstrated.

  Various metals can be considered as the metal that forms the metal nanoplate having the above-described configuration. For example, a metal nanoparticle having a particle size of about 4 nm as a nuclide is generated by a reduction reaction in a seed solution described later. From the viewpoint that it can be made, it is preferably at least one of gold, silver, platinum, and palladium.

  Especially, it is excellent in the point which can obtain the metal nanoplate fixed to the base material more reliably by the manufacturing method of the metal nanoplate fixed base material of this invention mentioned later, and an electrical property (for example, electroconductivity). From the viewpoint that the obtained gold (gold) nanoplate-immobilized substrate can be effectively used as an electrochemical element, gold is preferable. In particular, in the case of a gold nanoplate-immobilized substrate, it can be more reliably applied as an element used for self-organization, protein detection, etc. by fixing motor molecules, DNA, etc. using the gold nanoplate as a core. preferable.

  Moreover, in the metal nanoplate fixed base material of this invention, the (111) plane of the crystal plane of the metal which comprises the said metal nanoplate in the said metal nanoplate is exposed. As a typical merit by exposing the (111) plane in this way, for example, using a flat surface at the atomic level, (1) In combination with other atomic level observation methods and spectroscopy, The electron transfer reaction can be analyzed at the molecular level, and (2) the self-assembled monomolecular film (typically a thiol derivative) is modified to be easily applied to a sensor.

  The metal nanoplate can take various shapes, but is preferably a polygonal shape (for example, a triangle or a hexagon) having a plurality of acute or obtuse corner portions (vertices) on the outer periphery. Furthermore, it is preferable that the metal nanoplate has an edge portion formed along a substantially linear side between the corner portion. At this time, all the straight portions corresponding to the sides of the metal nanoplate are in a state of being cut off with respect to the substrate surface, and the portion (surface) that is cut up with respect to the surface of the substrate corresponds to the edge portion. May be an acute angle or an obtuse angle with respect to the substrate surface.

  The present inventors infer the reason why the metal nanoplate-immobilized substrate of the present invention exhibits excellent electrochemical characteristics by having such a shape as follows. That is, if the electron transfer only in the flat part of ITO that constitutes the metal and the substrate constituting the metal nanoplate, for example, is considered, the responsiveness of the metal nanoplate-immobilized substrate of the present invention is a metal flat plate. The responsiveness of a flat electrode made of only electrodes or ITO cannot be exceeded. On the other hand, in the metal nanoplate-immobilized substrate of the present invention, there are three-dimensional electron movements due to the presence of nano-ordered parts (that is, the corner part and the edge part). Conceivable. For example, for molecules present in the vicinity of the corner or edge, there is a possibility of electron movement from the ITO plane and electron movement from the corner or edge of the gold plate, which is effective. It is inferred that it may contribute to electron transfer.

  Regarding cytochrome c, which will be described later, for example, electron transfer is not observed in a flat plate electrode made of gold, but this is because cytochrome c is adsorbed and denatured on the electrode surface, and the electron transfer in the entire electrode is inhibited. It is said that there is. On the other hand, for example, in the gold nanoplate-immobilized substrate of the metal nanoplate-immobilized substrate of the present invention, cytochrome c denaturation is suppressed by the three-dimensionalization of the corner portion and the edge portion, and It is considered that the electron transfer between the heme iron part in the cytochrome c and the outside proceeds well due to the three-dimensional structure of the corner part and the edge part.

  Moreover, although various base materials can be used as the base material, it is preferable to use a conductive base material. As a material constituting the conductive base material, a conventionally known material used for an electrochemical element or the like is used. Various materials such as metal oxides such as tin oxide, indium oxide, ITO, ruthenium oxide and titanium oxide, metals such as nickel, platinum, gold, aluminum, iron and copper, semiconductors such as germanium, silicon and gallium arsenide, graphite , Carbon materials such as graphite, expanded graphite, glassy carbon, carbon fiber and diamond.

  The base material can take various shapes. In addition to a sheet shape in view of the shape of a general electrochemical device such as a battery or a sensor, for example, a plate shape, a granular shape, a spherical shape, a lump shape, and a mesh shape are also included. For example, it is possible to use a non-woven fabric made of carbon fiber.

  In addition, there is no limitation in the dimension of the said base material, It can select suitably. For example, those skilled in the art can appropriately adjust according to the dimensions and specifications of the desired metal nanoplate-immobilized substrate and the dimensions and specifications of the electrochemical element produced using the metal nanoplate-immobilized substrate. Is possible.

Among the above-mentioned base materials, a sheet-like ITO base material from the viewpoint of realizing a thin metal nanoplate-fixed base material excellent in conductivity and flexibility and an electrochemical element using the same. Is preferably used. In particular, since ITO is excellent in transparency, it is also suitable for measuring optical characteristics. Such an ITO base material comprises indium dioxide (In ₂ O ₃ ) and tin dioxide (SnO ₂ ) on a glass substrate in a predetermined molar ratio (for example, 95: 5, 90:10, or 80:20). It is obtained by sputtering and forming an ITO film (transparent electrode) having a thickness of about several tens of nanometers.

  The metal nanoplate-immobilized substrate of the present invention having the above-described configuration (especially, obtained by immobilizing a gold nanoplate on an ITO substrate) has excellent electrical characteristics. When contacted with a specific compound, a novel and remarkable effect is obtained that the electrolysis current is likely to occur and the electrolysis current is increased. For example, an increase in the electrolysis current is observed when it comes into contact with ferrocyanide ions (anions) whose electron transfer is reversible, cytochrome c (positive charge on the surface), ascorbate ions (anions), etc., which normally do not easily transfer electrons.

  The reason why such a novel and remarkable effect is obtained is not clear, but in the metal nanoplate-immobilized substrate with the (111) face exposed, the conductivity of the metal nanoplate portion is unmodified (metal nanoplate The so-called integrated nanoelectrode is formed, and the electrolysis current is affected by the three-dimensional diffusion in the supply of the compound in the integrated nanoelectrode. This is considered to be because of the increase (two-dimensional diffusion is given priority in the case of a normal plate electrode, but the current increases in three-dimensional diffusion). In the case of a compound such as cytochrome c, as described above, it is considered that an electron transfer reaction is likely to occur between the nano-ordered portion and the substrate surface in the periphery of the metal nanoplate. It is done.

  As described above, the metal nanoplate-immobilized substrate of the present invention has excellent electrical characteristics, and particularly when the metal nanoplate is in contact with a specific compound, it easily causes electron transfer and has an electrolytic current. The remarkable effect of increasing is obtained. Accordingly, the metal nanoplate-immobilized substrate of the present invention can be suitably used for an electrochemical device for detecting the specific compound.

2. Production method of metal nanoplate-immobilized substrate The metal nanoplate-immobilized substrate of the present invention as described above includes (1) a step of attaching a metal nuclide on the surface of the substrate, and (2) the step (1). ), And a step of growing a nuclide adhering on the surface of the substrate.
More specifically, in the step (1), the substrate is brought into contact with a seed solution containing a metal compound constituting the metal nanoplate, a protective agent, and a first reducing agent, and at least the substrate Attach the metal nuclide to some surface,
In the step (2), the base material to which the nuclide is attached is brought into contact with a growth solution containing the compound and a hydrophilic polymer, and the nuclide is grown on the surface to form a metal nanoplate.

(1) Nuclide formation process (seeding process)
This step is a step of attaching a metal nuclide constituting a metal nanoplate to be immobilized to at least a part of the surface of the substrate. Here, the “nuclide” is an extremely fine metal fine particle (metal nanoparticle) that is a source (seed) on which the metal nanoplate grows.

  In this seeding process, it is possible to use a phenomenon in which a base material is brought into contact with a metal colloid solution called a seed solution, and nuclides adhere to fine concave portions or convex portions on at least a part of the surface of the base material. The size of the concave portion or the convex portion may be on the order of nm. For example, even on the surface of a macroscopic flat glass substrate or the like, the presence of the concave portion or the convex portion is recognized when observed on the nm order. Therefore, it can be said that almost all the base materials have concave portions or convex portions.

  Here, FIG. 1 is a front view of a plate-like substrate immersed in a seed solution, and more specifically, is a conceptual diagram showing a state in which nuclides are attached to the surface of the plate-like substrate. 2 is a cross-sectional view taken along line AA in FIG. As shown in FIGS. 1 and 2, the nuclide 11 is attached to the surface of the plate-like substrate 10. The term “attachment” here is considered to mean not physical adsorption but physical adsorption by an anchor effect or the like.

  In the seeding step, the seed solution may be brought into contact with a portion of the base material on which the metal nanoplate is to be fixed. A method of immersing the base material in the seed solution, forming a flow path, and forming the base material A method of circulating the seed solution in the flow path in which the liquid crystal is installed, a method of dropping or applying the seed solution on the substrate, and the like can be employed.

Here, the seed solution will be described. The seed solution includes a metal compound constituting the metal nanoplate, a protective agent, and a first reducing agent.
Examples of preferable metals constituting the metal nanoplate include gold, silver, platinum, and palladium as described above. Correspondingly, examples of the metal ion source contained in the seed solution include metal salts such as nitrates and chlorides of gold, silver, platinum or palladium. More specifically, for example, tetrachloroauric acid, silver nitrate or palladium chloride can be used.

  The protective agent contained in the seed solution plays a role of protecting zero-valent metal nanoparticles and aggregates produced by reducing the metal ions. Therefore, as the protective agent, for example, it is conceivable to use various surfactants in addition to trisodium citrate.

Further, as the reducing agent (first reducing agent) contained in the seed solution, various reducing agents can be used as long as the condition that the metal ion can be reduced is satisfied. For example, sodium tetrahydroborate (NaBH ₄ ), citric acid, ascorbic acid and the like. Among these, NaBH ₄ is preferably used from the viewpoint that a compound produced by the reduction reaction (a compound produced by oxidation of the reducing agent itself) hardly affects the subsequent reaction.

The composition of the seed solution can be adjusted as appropriate as long as the nuclide is formed and the metal nanoplate of the present invention is obtained. However, for example, when the seed solution contains a metal salt, trisodium citrate and NaBH ₄ , if the concentration of the metal salt is too high, the seed solution becomes a suspension rather than a colloid, This is not preferable because it may interfere with the nuclide formation process and the subsequent nuclide growth process. Further, the amount of the reducing agent such as NaBH ₄ is preferably an excess amount that can reduce all the metal ions contained in the seed solution.

  In this step, the substrate is brought into contact with a seed solution having the above composition, and the temperature of the seed solution at this time is not particularly limited as long as the nuclide can be formed and adhered, but for example, It should just be room temperature (for example, 20-30 degreeC), Preferably it is 25 degreeC.

  Further, the time for contacting the substrate with the seed solution is not particularly limited as long as the nuclide can be formed and adhered, but it may be, for example, about 30 minutes or more, and the nuclide is more reliably formed. From the viewpoint of adhering to the base material, it is preferably about 2 hours or longer. In addition, after performing this process and before performing the following nuclide formation process, you may wash | clean the said base material with water, being careful not to peel off the said nuclide from a base material.

  In addition, you may heat-process the said base material after a nuclide formation process and before a nuclide growth process. For example, using a constant temperature dryer, the substrate is heated at a temperature of 250 ° C. for 1 hour or longer. By this operation, the citrate ions that protected the surface of the gold nanoparticles in the seed solution can be removed, and it is considered that the bonding centering on the nuclide is strengthened.

(2) Nuclide growth process (growth process)
In this step, the substrate to which the nuclide is attached is brought into contact with a growth solution containing the metal compound and a hydrophilic polymer, and the nuclide is mainly grown two-dimensionally on the surface to form a metal nanoplate. It is a process. That is, the base material to which the nuclide is attached is brought into contact with a growth solution, and the nuclide is grown to a certain size and shape. This nuclide growth step utilizes a metal reduction reaction, and the nuclide is grown crystallographically while maintaining an equilibrium state.

  The method for producing a metal nanoplate-immobilized substrate of the present invention includes the nuclide formation step and the nuclide growth step as in the metal fine particle production method described in Patent Document 2 above. It is completely different. And by this process, metal nanoplate can be directly formed in the base-material surface not through the conventional crosslinking reagent layer.

  Here, FIG. 3 is a diagram showing a state after the nuclide is grown by bringing the plate-like substrate after the nuclide formation step shown in FIGS. 1 and 2 into contact with the growth solution (A in FIG. 1). -A line sectional view). In FIG. 3, a nuclide 12 grown two-dimensionally in the plane direction of the plate-like substrate 10 and a nuclide 13 grown in a spherical shape are shown on the plate-like substrate 10.

  Further, in the growth step, the growth solution may be brought into contact with the portion of the base material to which the nuclide is attached (that is, the portion where the metal nanoplate structure grows), and the substrate is immersed in the growth solution. A method in which a growth solution is circulated through the flow path in which a base is provided by forming a path, a method in which a growth solution is dropped or applied to a region where a nuclide is present on the base, and the like can be employed.

  Here, the growth solution will be described. The growth solution contains the same metal compound and hydrophilic polymer as the seed solution. Moreover, you may contain a reducing agent (2nd reducing agent) so that it may mention later. When the hydrophilic polymer contained in the growth solution is used, when the nuclide is grown on the substrate, the metal constituting the nuclide can be reduced and the metal nanoplate is grown mainly two-dimensionally. Can be formed.

  For example, polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG) can be used as the hydrophilic polymer. The molecular weight of the hydrophilic polymer is not particularly limited as long as the nuclide can be grown to form the metal nanoplate of the present invention. The molecular weight of PVP is, for example, about 55,000. The molecular weight of PEG may be about 200, for example.

  Although the reason why the metal nanoplate can be more reliably formed when the above hydrophilic polymer is used is not clear, the present inventors consider as follows. That is, PVP has a nitrogen atom part having a positive charge and an oxygen atom part having a negative charge, and PEG has an oxygen atom part having a negative charge. Therefore, a metal ion having a positive charge is coordinated to an oxygen atom part having a negative charge, and at least a part of the surface of the base material inhibits crystal growth of the nuclide in a substantially normal direction of the surface. Crystal growth of the nuclide in the surface direction of the surface is promoted. And it is thought that the structure growth of the metal nanoplate is realized by such an action.

  Even in a growth solution containing the above components, the above-mentioned nuclide can be grown to form the metal nanoplate in the present invention. That is, it is considered that the hydrophilic polymer protects metal atoms and has a reducing ability for metal ions. Therefore, in the nuclide growth step of the present invention, it is not necessary to use a reducing agent or a surfactant. However, from the viewpoint of more reliably forming a larger metal nanoplate, the growth solution is also a reducing agent (second A reducing agent) or a surfactant. When such a growth solution is used, it is considered that both (111) face protection by PVP and gentle reduction growth of nanostructures by ascorbic acid and CTAB can be effectively realized.

As the second reducing agent, various reducing agents may be used as long as the condition that metal nanoplates can be formed by helping the two-dimensional growth of the nuclide while reducing the metal ions is satisfied. Examples thereof include sodium tetrahydroborate (NaBH ₄ ), citric acid and ascorbic acid. Among these, CTAB and ascorbic acid are preferably used because the reduction reaction can be continued for a long time in combination with CTAB and can proceed slowly. Moreover, if conditions, such as a density | concentration, are adjusted suitably, the 2nd reducing agent which may be included in a growth solution may differ from the said 1st reducing agent used for a seed solution, or may be the same.

  The composition of the growth solution can be appropriately adjusted within the range in which the nuclide is grown and the metal nanoplate of the present invention is obtained. However, for example, when the growth solution contains a metal salt and polyvinylpyrrolidone, if the concentration of the metal salt is too high, it becomes difficult to control the reduction and precipitation of the metal in the growth solution, which hinders the nuclide growth process. This is not preferable because of fear. The amount of the hydrophilic polymer may be, for example, 0.3 to 1.0 mmol / liter.

  The amount of the second reducing agent such as CTAB and ascorbic acid may be an amount sufficient for the amount of the metal compound. The amount of CTAB may be, for example, 30 to 50 mmol / liter, and the amount of ascorbic acid may be, for example, 0.4 to 0.6 mmol / liter.

  In this step, the substrate is brought into contact with a growth solution having the above composition. The temperature of the growth solution is not particularly limited as long as the nuclide can be grown. For example, it may be 20-30 degreeC), Preferably it is 25 degreeC.

  The time for contacting the substrate with the growth solution is not particularly limited as long as the nuclide can be grown to form the metal nanoplate of the present invention. For example, the time is about 10 hours or more, preferably about It may be 18 hours or more, and from the viewpoint of more reliably growing the nuclide to form the metal nanoplate of the present invention, it is preferably about 24 hours or more.

  In addition, after the nuclide growth step, washing, heating, drying, and the like of the substrate can be performed by a conventional method. For example, a constant temperature dryer may be used and the substrate may be dried by heating at a temperature of 100 ° C. for about 1 hour. By this operation, moisture remaining on the surface of the obtained metal nanoplate-immobilized substrate can be more reliably removed.

3. Electrochemical Element The metal nanoplate-immobilized substrate of the present embodiment can be suitably used as a sensor for detecting a redox substance such as a biological substance. If the metal nanoplate-immobilized substrate is used as a working electrode, it has excellent current response, and is therefore effective in detecting redox substances such as biological substances that generate a minute redox current by an electron transfer reaction.

Here, as the redox substance, an iron cyano complex containing ferrocyanide ions ([Fe (CN) ₆ ] ⁴⁻ ), cytochrome c (cytochrome c), and benzoquinone (one of typical redox substances) p-benzoquione) and the like. Note that cytochrome c is a kind of protein that conducts electron transfer related to the respiratory chain, and is easily used for redox current, so it is often used to measure the redox current response in the field of electrochemistry. It is what In addition, it is preferable to use a phosphate buffer solution (PBS) together with the redox substance, so that the pH value hardly changes and protein denaturation can be prevented.

    As mentioned above, although typical embodiment of this invention was described, this invention is not limited only to these. Therefore, although the metal nanoplate fixed base material of this invention and its manufacturing method are demonstrated in detail below with an Example below, this invention is not limited to these Examples.

Example 1
(1) Nuclide formation step 20 ml of an aqueous solution containing 2.5 × 10 ⁻⁴ mol / liter tetrachloroauric acid (HAuCl ₄ ) and 2.5 × 10 ⁻⁴ mol / liter trisodium citrate; A seed solution was prepared by mixing 5 ml of an aqueous solution containing 1 mol / liter of sodium tetrahydroborate (NaBH ₄ ) in a beaker. More specifically, a tetrachloroauric acid aqueous solution and a trisodium citrate aqueous solution were mixed at room temperature, and the ice-cooled sodium tetrahydroborate aqueous solution was added to the resulting mixture.

In the obtained seed solution, trivalent gold ions (Au ³⁺ ) formed a gold colloid with sodium tetrahydroborate as a reducing agent and were dispersed. When the size of the gold colloid was measured with a transmission electron microscope (TEM), the diameter was about 4 nm.

Next, indium dioxide (In ₂ O ₃ ) and tin dioxide (SnO ₂ ) are sputtered onto a glass substrate at a molar ratio of 95: 5, and an ITO substrate having an ITO film (transparent electrode) having a thickness of about several tens of nm Got. Moreover, the said ITO board | substrate was ultrasonically cleaned in order using acetone and a pure water.

  The ITO substrate was immersed in the seed solution (about 25 ° C.) for about 2 hours, and nuclides were physically adsorbed on the ITO film of the ITO substrate. When the surface of the ITO substrate immediately after immersion was observed with an electron microscope, as shown in FIG. 1, a large number of nuclides (gold colloid) of about 4 nm were physically adsorbed on the fine irregularities on the surface. Was confirmed.

(2) Nuclide growth step In a beaker, an aqueous solution containing 0.5 ml of an aqueous solution containing 0.01 mol / liter of tetrachloroauric acid and an aqueous solution containing 0.001 mol / liter of polyvinylpyrrolidone (PVP: molecular weight of about 55,000). 5 ml and 10 ml of water were mixed to prepare a growth solution. More specifically, a tetrachloroauric acid aqueous solution and a PVP aqueous solution were mixed at room temperature, and water was added to the resulting mixture. At this time, the PVP concentration in the growth solution was 0.33 mmol / liter (0.33 mM).

The substrate that had undergone the nuclide formation step was immersed in the growth solution and allowed to stand at 28 ° C. for 24 hours. Thereby, the nuclide was grown to form a gold nanoplate, and a gold nanoplate-immobilized substrate as a metal nanoplate-immobilized substrate of the present invention was obtained.
The surface of the ITO substrate after the nuclide formation step was observed with a scanning electron microscope (SEM) and an atomic force microscope (AFM). The obtained electron micrograph and AFM photograph are shown in FIGS. 4 and 5, respectively. As shown in FIG. 4, the gold nuclide having a diameter of about 4 nm after the nuclide formation step grows two-dimensionally and has a thickness of about 15 nm to about 25 nm and a diameter (between the farthest vertices). Length) A gold nanoplate having a hexagonal shape of about 800 nm to about 1 μm was formed. As a result of reducing trivalent gold ions (Au ³⁺ ) in tetrachloroauric acid while being protected by PVP, it was considered that the nuclide grew two-dimensionally.

<< Comparative Example 1 >>
The same operation as in Example 1 was performed except that the nuclide formation step was not performed. However, no gold nanoplate was formed.

<< Comparative Examples 2-3 and Examples 2-3 >>
The same operation as in Example 1 was performed except that the PVP concentration in the growth solution was changed to the values shown below. For comparison, Example 1 was also performed again.
(A) 3.3 mmol / liter (Comparative Example 2)
(B) 1.7 mmol / liter (Example 2)
(C) 0.33 mmol / liter (Example 1)
(D) 0.17 mmol / liter (Example 3)
(E) 0.03 mmol / liter (Comparative Example 3)

[Evaluation Test 1: Electron Micrograph]
The surface of the ITO substrate after the nuclide formation step was observed with a scanning electron microscope (SEM). Electron micrographs of gold nanoplates or metal nanoparticles obtained using the above conditions (a) to (e) are shown in FIGS.
In the case of FIG. 6 where the PVP concentration is the highest, only almost spherical gold nanoparticles are generated. This is considered to be because the protective ability of PVP is high due to the high concentration and the reduction proceeds faster. In the case of FIG. 10 where the PVP concentration is the lowest, only spherical gold nanoparticles are produced, but the production amount is extremely small. This is considered to be because the reduction rate is low because the PVP concentration is too low. In the case of FIGS. 7 to 9, the gold nanoplate having a plurality of sharp or obtuse edge portions is more reliably generated. However, in the case of FIGS. 7 and 9, the production efficiency of the gold nanoplate is low and the production amount is small. The most gold nanoplates were generated in the case of FIG.
From these results, in order to produce gold nanoplates more reliably, the PVP concentration is within a certain range (for example, 0.03 mmol / liter to 3.3 mmol / liter, preferably 0.17 mmol / liter to 0.17). It can be seen that it is important to adjust to mmol / liter, particularly preferably 0.33 mmol / liter to 1.7 mmol / liter.

[Evaluation Test 2: Light Absorption Spectrum]
Moreover, the light absorption spectrum of the gold nanoplate (Example 1) obtained using the condition (c) and the gold nanoparticle (Comparative Example 2) obtained using the condition (a) was measured. The results are shown in FIG. 11 (a and b in FIG. 11 respectively). That is, in FIG. 11, the light absorption spectrum of the gold nanoplate-immobilized substrate (Example 1) is indicated by reference symbol a (sample a), and the light absorption spectrum of the gold nanoparticle-immobilized substrate (Comparative Example 2) is indicated by reference symbol b ( Sample b).
Both show that gold nanoparticles are formed on the ITO substrate, but sample a (gold nanoplate of Example 1) is compared with sample b (gold nanoparticles of Comparative Example 2). The light absorption is large overall. This is presumably because in the case of sample a, the plate-like metal covered the surface of the ITO substrate, the light was scattered, and the overall absorption shifted.

[Evaluation test 3: X-ray diffraction intensity]
Furthermore, the gold nanoplate (Example 1) obtained using the condition (c) was measured using an X-ray diffraction (XRD) apparatus, and the obtained XRD data (2θ) is shown in FIG. .
From this result, it was found that since the generated gold nanoplate has a strong peak intensity derived from the Au (111) plane, the crystal structure of the gold nanoplate is mainly exposed to the (111) plane.

[Evaluation Test 4: Electrical Characteristics]
The electrochemical responsiveness of the metal nanoplate of the said Example was measured using the apparatus shown in FIG. Specifically, measurement was performed using a working electrode composed of the following metal nanoplate-immobilized substrate. However, the surface of the ITO substrate (ITO side, gold nanoplate or gold nanoparticle side) is covered with a non-conductive coating (filament tape 898 manufactured by Sumitomo 3M Ltd.), and the non-conductive coating has a diameter of 2 mm. A hole was formed, and the obtained opening was used as a working electrode.

(I) bare ITO substrate The ITO substrate used in Example 1 and not subjected to the nuclide formation step and the nuclide growth step.
(Ii) sphere Au-CATB
An ITO substrate in which a nuclide formation step is performed in the same manner as in Example 1, and a nuclide growth step is performed using a growth solution containing CTAB, a reducing agent (ascorbic acid) and a surfactant (CTAB) to immobilize gold nanoparticles.
(Iii) sphere Au-PVP
An nuclide formation step was performed in the same manner as in Example 1, an nuclide growth step was performed using a growth solution with a PVP concentration of 3.3 mmol / liter, and an ITO substrate on which gold nanoparticles were immobilized (Comparative Example 2).
(Iv) Au plate
An ITO substrate on which a gold nanoplate was immobilized (Example 1) obtained in Example 1 (when using a growth solution with a PVP concentration of 0.33 mmol / L).

More specifically, as shown in FIG. 17, a three-electrode cyclic voltammetry measuring device including a potentiostat 32, a counter electrode 33, a reference electrode 34, and a working electrode 35 was produced. The beaker 30 was filled with a phosphate buffer solution (pH = 7.4) 31 containing a redox substance (reduced form), and one end of the counter electrode 33, the reference electrode 34, and the working electrode 35 was immersed in the phosphate buffer solution 31. As the redox substance, an iron cyano complex containing ferrocyanide ions ([Fe (CN) ₆ ] ⁴⁻ ), cytochrome c, and benzoquinone, which are one kind of typical redox substances (reduced forms), were used.

  By applying a voltage to the working electrode 35, an oxidation-reduction reaction was caused on the surfaces of the counter electrode 33, the reference electrode 34, and the working electrode 35. The applied potential at this time was determined based on the potential of the reference electrode 34 (for example, when the potentiostat 32 applied a potential of 10 mV to the working electrode 35, the actual potential applied to the working electrode 35 was 10 mV. In addition, this is the sum of the potential of the reference electrode 34 itself). In this way, the electron transfer reaction on the surface of the working electrode 35 was measured by increasing the voltage at regular intervals with the potential of the reference electrode 34 as a reference and measuring the redox current I flowing through the working electrode 35. .

  More specifically, a silver / silver chloride electrode is used as the reference electrode 34, the potentiostat 32 is scanned every second with reference to the potential of the reference electrode 34, and the potential E (mV) of the working electrode 35 with respect to the reference electrode 34. ) And the amount of reduction current (μA) flowing through the working electrode 35. In addition, a sample obtained by dissolving 1 mmol / liter of ferrocyanide in a 0.1 mol / liter phosphate buffer solution (FIG. 18), or 0.1 mol of 0.05 mmol / liter of cytochrome c. Measurement was performed at a scan rate of 10 mV / s using a sample (FIG. 19) obtained by dissolving in a / l phosphate buffer solution.

18 to 20 show cyclic voltammograms measured by the apparatus shown in FIG. FIG. 18 shows a cyclic voltammogram measured for the ferricyan-ferrocyan redox reaction system, and FIG. 19 shows a cyclic voltammogram measured for the cytochrome c redox reaction system. FIG. 20 shows a cyclic voltammogram measured for the redox reaction system of p-benzoquinone.
18 to 20, the vertical axis indicates the amount of current, the positive value indicates the oxidation current, and the negative value indicates the reduction current. The horizontal axis represents voltage, a positive value represents an oxidation potential, and a negative value represents a reduction potential.

From the results shown in FIGS. 18 and 19, it can be seen that when the gold nanoplate of the present invention is used (above (iv)), the redox current is increased. This is presumably because a fine gold plate is present on the surface of the ITO substrate and the (111) plane is exposed to the outside, so that an electron transfer reaction is likely to occur.
In the reaction system of FIG. 18 (ferricyan-ferrocyan system), the current value of (iv) is increased by about 1.3 times (comparison of peak values) compared to the cases of (i) and (ii). is doing. In the reaction system of FIG. 19 (cytochrome c), the current value of (iv) is further increased as compared with the cases of (i) and (ii). In addition, in the case of (i) and (ii), almost no current response can be observed, whereas in the case of (iv), an increase in current appears remarkably.

In general, the amount of current is proportional to the concentration. However, the concentration of ferricyan-ferrocyan in FIG. 18 is 1 mmol / liter, whereas the concentration of cytochrome c in FIG. 19 is 0.05 mmol / liter (1/20). Nevertheless, the maximum value of the current amount is 15 μA (FIG. 19) with respect to 6 μA (FIG. 18), and it can be seen that the gold nanoplate of the present invention responds extremely sensitively to cytochrome c.
Although not shown, when a gold electrode was used as the working electrode 35, no oxidation-reduction current was observed as in the case (i).
Further, from the result shown in FIG. 20, in the case of p-benzoquinone as well as in the case of cytochrome c, the increase in current appears remarkably in the case of (iv).

  From the above results, it can be seen that the gold nanoplate-immobilized substrate that is the metal nanoplate-immobilized substrate of the present invention promotes the electron transfer reaction of ferricyan-ferrocyan, cytochrome c, and p-benzoquinone. Therefore, if this property is utilized, an electrochemical element (sensor) that reacts with a specific substance with extremely high sensitivity can be realized.

<< Comparative Examples 4-6 >>
The same operation as in Example 1 was performed except that the molecular weight of PVP in the growth solution was changed to the following values. For comparison, Example 1 was also performed again.
(A) 10,000 (Comparative Example 4)
(B) 29,000 (Example 5)
(C) 55,000 (Example 1)
(D) 1,3,000,000 (Comparative Example 6)

[Evaluation test]
Gold nanoplates or gold nanoparticles were observed with a scanning electron microscope (SEM) on the surface of the ITO substrate after the nuclide formation step. Electron micrographs of gold nanoplates or metal nanoparticles obtained using the above conditions (a) to (d) are shown in FIGS.
From these results, it can be seen that the molecular weight of PVP is preferably about 55,000 in order to produce gold nanoplates more reliably.

Example 4
After the nuclide formation step, the ITO substrate having the nuclide is heated at 250 ° C. for 1 hour or more using a constant temperature dryer, and in the nuclide growth step, growth containing tetrachloroauric acid, PVP, cetyltrimethylammonium bromide (CTAB) and ascorbic acid is performed. The gold nanoplate-immobilized substrate of the present invention was produced in the same manner as in Example 1 except that the substrate was immersed in the solution for 18 hours and the substrate was heated and dried at 100 ° C. for 1 hour after the nuclide growth step. .
In order to prepare a growth solution, first, a mixed solution containing the following components was prepared.
0.01 mol / liter tetrachloroauric acid aqueous solution 0.5 ml 1.0 mmol / liter PVP aqueous solution 10 ml 0.1 mol / liter CTAB aqueous solution 8.0 ml water 2.0 ml A 0.1 mol / liter ascorbic acid aqueous solution was added to 0.1 ml to prepare a growth solution.

[Evaluation Test 1: Electron Micrograph]
Gold nanoplates or gold nanoparticles were observed with a scanning electron microscope (SEM) on the surface of the ITO substrate after the nuclide formation step. The obtained electron micrograph is shown in FIG. From FIG. 22, it can be seen that gold nanoplates are generated more reliably and the amount of generation thereof is large.

[Evaluation test 2: X-ray diffraction intensity]
Furthermore, the gold nanoplate (Example 4) obtained using the above conditions was measured using an X-ray diffraction (XRD) apparatus, and the obtained XRD data (2θ) is shown in FIG.
From this result, it is understood that the generated gold nanoplate has a strong peak intensity derived from the Au (111) plane, and no peaks derived from the (200) plane and the (220) plane are observed. This is thought to be because the coverage of the ITO substrate with the gold nanoplates has increased considerably, and the proportion of the (111) plane on the gold nanoplate surface has become relatively large.

[Evaluation Test 3: Electrical Characteristics]
Using the apparatus shown in FIG. 17, the electrochemical responsiveness of the metal nanoplate of the above example was measured in the same manner as in Example 1. Specifically, measurement was performed using a working electrode composed of the following metal nanoplate-immobilized substrate.
(A) Metal gold electrode (b) bare ITO substrate The ITO substrate used in Example 1, which has not undergone the nuclide formation step and the nuclide growth step.
(C) sphere Au-CATB
An ITO substrate in which a nuclide formation step is performed in the same manner as in Example 1, and a nuclide growth step is performed using a growth solution containing CTAB, a reducing agent (ascorbic acid) and a surfactant (CTAB) to immobilize gold nanoparticles.
(D) Au plate
The ITO substrate obtained by fixing the gold nanoplate obtained in Example 4.

More specifically, measurement was performed for potassium ferrocyanide (K ₄ [Fe (CN) ₆ ]), cytochrome c, and ascorbic acid using a three-electrode cyclic portammetry measuring apparatus shown in FIG. The results are shown in FIGS.
As a sample, a 0.1 mol / L phosphate buffer solution (pH = 7) containing 1 mmol / L ferrocyan ion (FIG. 23), 0.05 mmol / L cytochrome c at 20 mmol / L. Sample obtained by dissolving in phosphate buffer solution (pH = 7) (FIG. 24), or sample obtained by dissolving 1 mmol / liter ascorbic acid in 0.1 mol / liter phosphate buffer solution Using (pH = 7) (FIG. 25), the measurement was performed at a scan rate of 20 mV / s.

From the results shown in FIG. 23 to FIG. 25, it can be seen that when the gold nanoplate of the present invention is used (the above (d)), the redox current is increased. This is presumably because a fine gold plate is present on the surface of the ITO substrate and the (111) plane is exposed to the outside, so that an electron transfer reaction is likely to occur.
From the above results, it can be seen that the gold nanoplate-immobilized substrate as the metal nanoplate-immobilized substrate of the present invention promotes the electron transfer reaction of potassium ferrocyanide, cytochrome c and ascorbic acid. Therefore, if this property is utilized, an electrochemical element (sensor) that reacts with a specific substance with extremely high sensitivity can be realized.

<< Comparative Example 7 and Examples 5-7 >>
The same operation as in Example 4 was performed except that the CTAB concentration was changed to 0.01 mol / liter, 0.03 mol / liter, 0.04 mol / liter or 0.05 mol / liter. An electron micrograph of the obtained substrate is shown in FIG. 26 correspond to the following conditions.
A: CTAB concentration 0.01 mol / liter (Comparative Example 7)
B: CTAB concentration 0.03 mol / liter (Example 5)
C: CTAB concentration 0.04 mol / liter (Example 6)
D: CTAB concentration 0.05 mol / liter (Example 7)
From these results, it can be seen that gold nanoplates are more reliably generated when the CTAB concentration is 0.03 mol / liter or more.

  The metal nanoplate-immobilized substrate of the present invention is an electrochemical detector element (electrochemical element) or electrode for detecting a redox substance containing a specific biological substance, an electrode, or a biological battery (electrolysis containing a biological substance). It can be considered to be applied to a battery for taking out an electric current from a liquid.

Claims (16)

A method of immobilizing a metal nanoplate on the surface of a substrate,
(1) attaching a metal nuclide on the surface of the substrate;
(2) After the step (1), the step of growing the nuclide,
A method for producing a metal nanoplate-immobilized substrate characterized by the following. In the step (1), the base material is brought into contact with a seed solution containing a metal compound constituting the metal nanoplate, a protective agent, and a first reducing agent, and the metal is provided on at least a part of the surface of the base material. Of nuclide,
Contacting the substrate to which the nuclide is attached in the step (2) with a growth solution containing the metal compound and a hydrophilic polymer, and growing the nuclide on the surface of the substrate;
The manufacturing method of the metal nanoplate fixed base material of Claim 1 characterized by these. The metal is at least one of gold, silver, platinum and palladium;
The manufacturing method of the metal nanoplate fixed base material of Claim 1 or 2 characterized by these. The protective agent comprises trisodium citrate;
The manufacturing method of the metal nanoplate fixed base material of Claim 2 characterized by these. The first reducing agent comprises sodium tetrahydroborate;
The manufacturing method of the metal nanoplate fixed base material of Claim 2 characterized by these. The hydrophilic polymer comprises at least one of polyvinylpyrrolidone and polyethylene glycol;
The manufacturing method of the metal nanoplate fixed base material of Claim 2 characterized by these. The growth solution further comprises a second reducing agent;
The manufacturing method of the metal nanoplate fixed base material of Claim 2 characterized by these. The second reducing agent comprises ascorbic acid;
The manufacturing method of the metal nanoplate fixed base material of Claim 7 characterized by these. The metal is gold;
The manufacturing method of the metal nanoplate fixed base material of Claim 3 characterized by these.   The metal nanoplate fixed base material containing the metal nanoplate manufactured by the manufacturing method of the metal nanoplate fixed base material in any one of Claims 1-9. The (111) plane of the crystal plane of the metal is exposed on at least one plane of the metal nanoplate;
The metal nanoplate fixed base material of Claim 10 characterized by these. The metal nanoplate has a thickness of 20 to 30 nm,
The metal nanoplate fixed base material of Claim 10 or 11 characterized by these. The metal is at least one of gold, silver, platinum and palladium;
The metal nanoplate fixed base material in any one of Claims 10-12 characterized by these. The metal nanoplate is a polygonal shape having a plurality of acute or obtuse corner portions;
The metal nanoplate fixed base material in any one of Claims 10-13 characterized by these. Including the metal nanoplate-immobilized substrate according to any one of claims 10 to 14,
An electrochemical element characterized by the above. Including the metal nanoplate-immobilized substrate according to any one of claims 10 to 14,
A battery electrode characterized by the above.