JP2005171306A - Method of producing metal fine particulate layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce a metal particulate layer having uniform thickness used, e.g., for a sensor with localized plasmon resonance applied. <P>SOLUTION: A substrate 1 composed of porous alumina in which a plurality of micropores 12a are formed by anodization, is used to fill a plurality of metal colloid particles 13 into each micropore 12a in the substrate 12 by coating, and thereafter, the metal colloid particles 13 are heated, thus organic molecules 13b are volatilized, and, further, the metal particulates 13a are dissolved. Subsequently, the temperature is reduced to a room temperature to resolidify the metal, thus metal particulates 16 in which the diameter h in the depth direction of each micropore 12a is uniform are produced. In this way, a uniform metal particulate layer 17 having thickness h is obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a metal fine particle layer, and more particularly to a method for producing a metal fine particle layer having a uniform thickness.

  It is known that metal fine particles such as gold and silver having a size of 200 nm or less absorb light of a specific wavelength due to a localized plasmon resonance phenomenon. The absorption wavelength is known to change depending on the size of the fine particles and the refractive index around the fine particles, and application of this localized plasmon resonance phenomenon to a biosensor is considered.

  For example, as disclosed in Patent Document 1, a fine structure in which metal fine particles are fixed in layers on a surface of a dielectric or semiconductor is used as a sensor unit, and localized plasmon resonance is applied to refract the sample. Sensors that measure rates and the like are known.

  This sensor basically detects the intensity of the measurement light that has passed through (that is, transmitted through or reflected through) the layered metal fine particles, and means for irradiating the fine metal particles of the fine structure with measurement light. And a light detection means.

  In the above-described sensor, when the measurement light is irradiated to the layered metal fine particle portion, localized plasmon resonance occurs at a specific wavelength, thereby significantly increasing scattering and absorption of the measurement light. Therefore, if the intensity of the measurement light that has passed through the layered metal fine particles is detected, it is possible to confirm the occurrence of localized plasmon resonance by observing that the intensity of the detection light rapidly decreases.

  At this time, the wavelength of light at which localized plasmon resonance occurs and the degree of scattering and absorption of measurement light depend on the refractive index of the medium existing around the metal fine particles. That is, as the refractive index increases, the resonance peak wavelength shifts to the longer wavelength side, and the scattering and absorption of measurement light increase. Therefore, with the sample arranged around the layered metal fine particles, the portion of the metal fine particles is irradiated with the measurement light, and then the intensity of the measurement light passing through this portion is detected, so that the refractive index of the sample, The physical properties of the corresponding sample can be measured.

Conventionally, as a fine structure used in a sensor to which this localized plasmon resonance is applied, for example, as shown in Patent Document 1, a metal colloid monolayer film is formed on a surface portion of a substrate. Things are known. In addition, as shown in Non-Patent Documents 1 and 2, there is known that a metal fine particle layer is formed by filling fine particles of anodized porous alumina having a plurality of fine holes formed on one surface with fine metal particles. It has been. Note that such anodized porous alumina itself having a plurality of fine holes is also described in Patent Document 2, Non-Patent Document 3, and the like.
Japanese Unexamined Patent Publication No. 2000-356587 Japanese Patent Laid-Open No. 11-200090 Journal of Applied Physics, 1978, Vol. 49, No. 5, p. 2929 Journal of Applied Physics, 1980, Vol. 51, No. 1, p.754 Hideki Masuda, “Highly Ordered Metal Nanohole Array Based on Anodized Alumina”, Solid State Physics, 1996, Vol. 31, No. 5, p.493

  The absorption wavelength in the sensor using the above-described localized surface plasmon varies depending on the particle size of the metal particles. Therefore, if multiple particles irradiated to incident light at the time of sensing have a non-uniform particle size, absorption occurs at each particle size, resulting in a broad absorption spectrum as a whole, and absorption spectrum shift during sensing There arises a problem that the detection ability of the quantity is lowered, that is, the sensing accuracy is lowered. Therefore, in a sensor using a localized surface plasmon, in order to sharpen the absorption wavelength and perform highly sensitive detection, it is required to make the particle diameter of the metal particles uniform.

  The fine structure formed by forming a metal colloid monolayer film on the surface portion of the substrate described in Patent Document 1 can be suitably formed as a monolayer film in a state where metal fine particles are isolated from each other without condensing. However, since the particle size variation of the metal colloid is about 10%, it is difficult to make the size uniform.

  On the other hand, the fine pores of anodized porous alumina can make the pore size variation 3% or less, which is smaller than the metal colloid particle size variation 10%, and is suitable for manufacturing a device having a uniform particle size. Yes.

  However, conventionally, when filling fine particles of porous alumina with metal fine particles, the plating method or vapor deposition method is mainly used, but filling each fine hole to a uniform depth in a large area of several cm square or more. It is very difficult to do. That is, it was difficult to obtain a metal fine particle layer having a uniform thickness.

  In view of the above circumstances, an object of the present invention is to provide a method for producing a metal fine particle layer capable of easily producing a metal fine particle layer having a uniform thickness.

In the method for producing a metal fine particle layer of the present invention, the fine particle obtained by coating metal fine particles with organic molecules on each of the plural fine holes of a substrate made of porous alumina having a plurality of fine holes produced by anodization. Packing a plurality of metal colloidal particles having a diameter smaller than the diameter of the pores,
The metal colloidal particles are heated to volatilize the organic molecules, and the metal fine particles in the plurality of metal colloidal particles are dissolved to have the same diameter as the diameter of the micropores at the bottom of each of the micropores. It is characterized by producing fine metal particles.

  As the metal fine particles, gold or silver is particularly preferable.

  The diameter of the micropores is preferably 10 to 200 nm.

  In addition, when the diameter of the micropores is 30 to 200 nm, it is desirable that the diameter of the metal colloid particles is 10 to 30 nm.

  Furthermore, the temperature at which the metal colloid particles are heated is desirably 120 to 600 ° C.

  The “porous alumina having a plurality of fine pores produced by anodic oxidation” is formed as a porous oxide film on the surface of aluminum by anodizing aluminum in an acidic electrolytic solution. This porous alumina is formed with extremely fine pores having a diameter of about several nanometers to several hundred nanometers extending in a direction substantially perpendicular to the surface independently of each other, and the fine pores are arranged at substantially equal intervals. It is characterized by being formed. The diameter, depth, and interval of the fine holes can be set relatively freely by controlling the conditions of anodization (see Non-Patent Document 3).

  According to the method for producing a metal fine particle layer of the present invention, each of a plurality of micropores of a substrate made of porous alumina is filled with metal colloid particles, the metal colloid particles are heated to volatilize the organic molecules, and The metal fine particles in the plurality of metal colloidal particles are dissolved to generate metal fine particles having the same diameter as the diameter of the fine holes at the bottom of each of the fine holes. It is possible to easily produce a metal fine particle layer having a regular arrangement and a uniform thickness composed of a plurality of metal fine particles having a uniform particle size in the depth direction.

  In addition, since the metal colloidal particles are used, there is an effect that the metal fine particles can be dissolved at a heating temperature lower than the original melting point of the metal of about 120 to 600 ° C.

  The metal fine particle layer produced by the method for producing a metal fine particle layer of the present invention has a uniform particle size, and therefore the thickness of the metal fine particle layer is uniform. Therefore, the metal fine particle layer is used for a sensor using a localized plasmon. Thus, the sensor can perform measurement with higher sensitivity than before.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 schematically shows the steps of a method for producing a metal fine particle layer according to an embodiment of the present invention. First, as shown in FIG. 1 (1), an aluminum substrate 11 having a surface of porous alumina 12 (hereinafter referred to as anodized alumina 12) having a plurality of micropores prepared by anodization is prepared. By coating the anodized alumina 12 from one surface side where the fine holes 12a are formed, the metal colloidal particles 13 having a diameter smaller than the diameter d (diameter) of the fine holes 12a are filled into the fine holes 12a. The diameter d of the anodized alumina 12 is, for example, about 10 to 200 nm. The metal colloidal particles 13 are formed by coating the metal fine particles 13a with the organic molecules 13b. When the diameter d of the anodized alumina 12 is about 30 to 200 nm, the average particle size of about 10 to 30 nm can be used. Good. Since the number of filled metal colloidal particles 13 is determined by the diameter and volume of the micropores, the particle size of the metal colloidal particles 13, etc., each micropore 12a is filled with approximately the same amount of metal colloidal particles 13.

  Next, by putting the aluminum substrate 11 together in a heater such as a baking furnace and heating to 120 to 600 ° C., the organic molecules 13b covering the metal fine particles of the metal colloid particles are volatilized and the metal fine particles 13a are dissolved. Then, it is solidified by lowering to room temperature. As a heating method, FIG. 1B shows an example in which the metal colloidal particles 13 are heated by irradiating the laser beam 15.

  Thereby, as shown in FIG. 1 (3), one metal fine particle 16 having a diameter substantially the same as the diameter of the fine hole 12a is formed from the plurality of metal colloidal particles 13. The thickness h of the metal fine particles 16 is substantially equal in each fine hole 12a, and the metal fine particle layer 17 having the same thickness h is formed.

  More specific examples of the production method of the present invention will be described. The manufacturing process is the same as that shown in FIG. 1, and will be described with reference to FIG.

  Gold colloidal particles 13 (Fine Swear Gold manufactured by Nippon Paint Co., Ltd.) were dropped onto anodized alumina 12 having regularly arranged micropores and applied with a spinner. As a result, the colloidal gold particles 13 were filled into the fine holes 12a.

  At this time, the diameter d of the fine holes 12a was 50 nm, the depth was 70 nm, and the diameter of the gold colloidal fine particles 13 was about 10 nm. At this time, about 125 gold colloidal fine particles 13 were filled in one fine hole 12a on average.

  Thereafter, the aluminum substrate 11 was placed in a heater and heated to about 500 ° C. The gold colloidal fine particles 13 may be dissolved by irradiating the gold colloidal fine particles 13 with a laser. In that case, energy of about 500 ° C. can be given to the colloidal gold fine particles 13, and the laser irradiation conditions are set so that the organic matter can be decomposed and gold can be dissolved.

  The organic molecules 13b of the gold colloidal fine particles 13 were volatilized by heating, and the gold particles 13a were dissolved. Thereafter, one particle 16 was generated from the plurality of colloidal gold particles 13 by lowering the temperature. The diameter of the gold fine particles 16 is substantially the same as the diameter of the micropores, and the thickness (diameter in the micropore depth direction) h is about 50 nm in the depth direction of the gold microparticles generated in each micropore. The diameter varied less than 10%. In this way, a gold fine particle layer 17 having a uniform thickness h could be obtained.

  Next, a method for forming the layered anodized alumina 12 on the aluminum substrate 11 will be described. There are several methods as such a method. Basically, when the aluminum substrate 11 is anodized in an acidic electrolytic solution, an oxide film is formed, and the generated oxide film is dissolved. The method of proceeding simultaneously is applied. According to this method, minute pits (small holes) are randomly generated on the surface of the oxide film formed on the aluminum substrate 11 at the beginning of the anodic oxidation by the dissolving action by the acid. As the anodic oxidation progresses, some of the pits grow preferentially and are arranged at substantially equal intervals. In the portion where the pits are once formed in the oxide film, a higher electric field is applied as compared with other portions, so that dissolution of the portion is further promoted. As a result, the layered anodized alumina 12 is selectively dissolved along with its growth to form the micropores 12a, while the portion that remains undissolved and surrounds the micropores 12a is formed.

  In the anodized alumina 12 obtained as described above, a large number of fine holes 12a are regularly arranged. These micropores 12a extend in a direction substantially perpendicular to the surface of the anodized alumina 12, and are cylindrical spaces having substantially the same cross-sectional shape and closed bottoms.

  Note that Japanese Patent Laid-Open Nos. 2001-9800 and 2001-138300 disclose methods for controlling the formation positions of the fine holes. In these methods, for example, a melting start point is formed at a desired position by irradiating aluminum with a focused ion beam. By performing the anodic oxidation treatment as described above after this treatment, the fine holes 12a can be formed at desired positions. In addition, when the focused ion beam is irradiated, by controlling the conditions such as the irradiation amount, beam diameter, irradiation energy, etc., the shape and composition of the dent at the melting start point can be changed. The diameter of the fine hole 12a can be freely controlled.

  Further, as a method for increasing the density of the micropores 12a in particular, for example, there is a method using oxalic acid. That is, by using oxalic acid as an electrolytic solution for anodization and performing anodization under a constant voltage of about 40 V, the fine holes 12a are regularly arranged and formed at a high density. Since the ordering of the arrangement of the micropores 12a proceeds as the anodizing time elapses, the micropores 12a that are highly ordered and arranged at a high density are formed by anodizing for a long time. Can do.

  As described above, since the diameter, interval, and depth of the fine holes 12a can be controlled relatively freely, the metal fine particles 16 can be formed in any uniform size and can be regularly arranged. As a result, when the metal fine particle layer 17 formed on the anodized alumina 12 is applied to a sensor to be described later, the sensitivity can be increased and the sensitivity can be stabilized.

  Next, an embodiment of a sensor using the metal fine particle layer 17 produced by the method for producing a metal fine particle layer according to the present invention will be described. In the present embodiment, the entire aluminum substrate 11 provided with the anodized alumina 12 having the metal fine particle layer 17 formed thereon as shown in FIG. When used in a sensor, the metal constituting the metal fine particle layer 17 is particularly preferably gold or silver. Since gold has high corrosion resistance, stable sensor characteristics can be obtained when it is used as a sensor, which will be described later, and it is easy to handle the sensor when it is manufactured and used. The sensitivity when the chip is used as a sensor can be further increased.

  FIG. 2 is a side view showing an embodiment of a sensor using the fine structure 10. As shown in the figure, the sensor irradiates the measurement light 23 obliquely toward the fine structure 10 in the container 20 with the fine structure 10 fixed to the bottom and a transparent window 22 formed on the upper surface. The light source 24 includes a white light source 24 and a spectroscopic detector 25 that spectroscopically detects the measurement light 23 reflected by the fine structure 10.

  In the container 20, the fine structure 10 is arranged in a state in which the portion of the anodized alumina 12 filled with the metal fine particles 16 faces upward. In addition, a liquid sample 21 to be measured is supplied into the container 20 so as to be in contact with the anodized alumina 12.

  When the fine structure 10 is irradiated with the measurement light 23 which is white light through the transparent window 22, the measurement light 23 is reflected by the metal fine particles 16 (see FIG. 1), and the reflected measurement light 23 is spectrally detected. The spectrum is detected by the detector 25. In this case, the measurement light 23 passes through the portion of the anodized alumina 12 where the metal fine particles 16 are present, and is reflected upward on the aluminum substrate 11. The measurement light 23 reflected here is also spectrally detected by the spectral detector 25.

The spectral intensity characteristic of the reflected light detected in this way is basically as shown by the solid line in FIG. That is, when the measuring light 23 to the portion of the fine metal particles 16 of the anodized alumina 12 is irradiated, there respect to light of a particular wavelength lambda _LP scattering and absorption of the measuring light by the localized plasmon resonance increases specifically. Therefore, the reflected light intensity is remarkably reduced for the light of this wavelength λ _LP .

The light wavelength (resonance peak wavelength) λ _{LP at which} localized plasmon resonance occurs and the degree of scattering and absorption of the measurement light 23 depend on the refractive index of the liquid sample 21 existing around the metal fine particles 16. That is, as the refractive index increases, the resonance peak wavelength λ _LP shifts to the longer wavelength side, and the scattering and absorption of the measurement light 23 increase. Accordingly, as shown in FIG. 2, the liquid sample 21 is stored in the container 20, and the portion of the anodized alumina 12 is irradiated with the measurement light 23, and the resonance peak wavelength λ _LP at that time is detected, for example. The refractive index of the sample 21 and the physical properties of the liquid sample 21 corresponding to the refractive index can be measured.

  Further, since the metal fine particle layer 17 of the microstructure 10 used in this sensor has high uniformity, the absorption and scattering spectral characteristics of the measurement light 23 change sharply. Accordingly, when this sensor is used, the refractive index of the liquid sample 21 and the physical properties of the liquid sample 21 corresponding to the refractive index can be measured with extremely high accuracy.

  The characteristics shown in FIG. 3 can be obtained in advance based on experience or experiment.

Here, in the above embodiment, the measurement light 23, which is reflected white light, is spectrally detected to detect the resonance peak wavelength λ _LP , but monochromatic light is used as the measurement light, and the resonance peak wavelength λ _LP is used. The refractive index, physical properties, and the like of the liquid sample 21 can be measured even by detecting a change in light intensity due to a shift in light, a scattering of the measurement light 23, and a change in absorption.

  Further, a case where a metal fine particle layer is used for a biosensor will be described. A schematic configuration diagram of the biosensor is shown in FIG.

  The biosensor shown in FIG. 4 differs from that shown in FIG. 2 only in that, for example, an antibody 31 is attached to the surface of the metal fine particle 16 of the microstructure 10 as shown in FIG. Other configurations are basically the same. In this biosensor, a specimen solution 32 to be measured is supplied into the container 20 so as to be in contact with the anodized alumina 12 of the microstructure 10. At this time, if the sample solution 32 contains a specific antigen 33 that specifically binds to the antibody 31, the antigen 33 binds to the antibody 31 of the microstructure 10 as shown in FIG.

When the antigen 33 is bound to the antibody 31 in this way, the refractive index of the peripheral portion of the fine metal particle 16 of the fine structure 10 is changed, so that the absorption and scattering spectral characteristics of the measurement light 23 detected by the spectroscopic detector 25 are changed. For example, this change is that the resonance peak wavelength was λ _LP 1 as shown by the broken line in FIG. 6 before the binding of the antibody 31 and the antigen 33, but after the binding, the resonance peak wavelength was as shown by the solid line in the same figure. It appears as a shift of the resonance peak wavelength as changing to λ _LP 2. Therefore, by detecting a change in the resonance peak wavelength with the spectroscopic detector 25, it is possible to check whether or not the antibody 31 and the antigen 33 are bound, that is, whether or not the antigen 33 is present in the sample solution 32.

  Also in the present embodiment, since the metal fine particle layer having a uniform thickness is used, the absorption and scattering spectral characteristics of the measurement light 23 change sufficiently sharply, and the slight binding between the antibody 31 and the antigen 33. Can be detected with high accuracy.

  The metal fine particle layer 17 produced by the production method of the present invention is not only used for the above-mentioned sensor, but also has a uniform layer thickness, and the absorption wavelength can be easily controlled by changing the size of the fine particles. Therefore, it can also be used as a filter that absorbs a specific wavelength.

Schematic explaining the method for producing a metal fine particle layer Schematic side view showing a sensor using a metal fine particle layer produced according to an embodiment of the present invention. Graph showing spectral intensity characteristics of measurement light detected by the sensor of FIG. The schematic side view which shows another sensor using the metal fine particle layer produced by embodiment of this invention Schematic side view showing the state of the microstructure of FIG. 4 during sample analysis FIG. 4 is a graph illustrating changes in spectral intensity characteristics of measurement light detected by the sensor of FIG.

Explanation of symbols

10 Microstructure
11 Aluminum substrate
12 Anodized alumina
12a Fine pores in anodized alumina
13 Metal colloidal particles
13a Metal fine particles
13b Organic molecules
16 Metal fine particles
17 Metal fine particle layer
20 containers
21 Liquid sample
22 Transparent window
23 Measuring light
24 White light source
25 Spectral detector
31 antibodies
32 Sample solution
33 antigen

Claims (5)

Metal colloidal particles having a diameter smaller than the diameter of the fine pores formed by coating organic fine particles on each of the fine pores of the substrate made of porous alumina having a plurality of fine pores produced by anodization A plurality of
The metal colloidal particles are heated to volatilize the organic molecules, and the metal fine particles in the plurality of metal colloidal particles are dissolved to have the same diameter as the diameter of the micropores at the bottom of each of the micropores. A method for producing a metal fine particle layer, characterized by producing metal fine particles.   The method for producing a metal fine particle layer according to claim 1, wherein the metal fine particles are gold or silver.   The method for producing a metal fine particle layer according to claim 1 or 2, wherein the diameter of the micropore is 10 to 200 nm. The diameter of the micropore is 30 to 200 nm,
The method for producing a metal fine particle layer according to claim 3, wherein the diameter of the metal colloid particles is 10 to 30 nm.   The method for producing a metal fine particle layer according to any one of claims 1 to 4, wherein the heating temperature is 120 to 600 ° C.

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