Composite particles and their manufacturing methods, and sensor elements

Abstract

This invention provides a novel structure that can be used in sensor elements and the like, and is effectively used as an enhancement component for enhancing the luminescence of a light-emitting body. A composite particle is provided, comprising: a core particle; and a metallic particle aggregate layer disposed on at least a portion of the surface of the core particle, the metallic particle aggregate layer comprising a plurality of metallic particles disposed separately from each other.

Description

Technical Field

[0001] This invention relates to a composite particle, a method for manufacturing the same, and a sensor element. Prior Technology

[0002] A technique for enhancing fluorescence by utilizing local plasmaon resonance of metal nanoparticles is known (e.g., Patent Document 1). A study on local plasmaon resonance induced by silver nanoparticles is shown in Non-Patent Document 1. [Existing technical documents] [Patent Literature]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 08-271431 [Non-patent literature]

[0004] [Non-Patent Literature 1] T. Fukuura and M. Kawasaki, "Long Range Enhancement of Molecular Fluorescence by Closely Packed Submicro-scale Ag Islands", e-Journal of Surface Science and Nanotechnology, 2009, 7, 653 Summary of the Invention

[0005] [The problem that the invention aims to solve] One object of the present invention is to provide a novel structure that can be used in sensor elements and the like, and is effectively used as an enhancement component for enhancing the light emission of a light-emitting body. Another object of the present invention is to provide a sensing element including the structure described above.

[0006] [Methods for solving problems] The present invention provides the composite particles shown below, a method for manufacturing the same, and a sensor element. [1] A composite particle comprising: Core particles; and A layer of metallic particle aggregates is disposed on at least a portion of the surface of the core particles. The metal-based particle aggregate layer comprises multiple metal-based particles arranged separately from each other. [2] The composite particles as described in [1], wherein the average particle size of the plurality of metal particles is greater than 5 nm and less than 1600 nm. [3] The composite particles as described in [1] or [2], wherein the plurality of metal particles are configured such that the average distance between them and their adjacent metal particles is greater than 1 nm and less than 150 nm. [4] The composite particle as described in any one of [1] to [3], wherein the standard deviation of the average distance is less than 50 nm. [5] The composite particle as described in any one of [1] to [4], wherein the surface of the core particle comprises a curved surface. [6] The composite particle as described in [5], wherein at least the metal particle aggregate layer is disposed on the curved surface. [7] The composite particles as described in any one of [1] to [4], wherein the core particles have a particle size of 0.3 μm or more but less than 10 μm. [8] The composite particle as described in any one of [1] to [7], wherein the metal-based particle aggregate layer is disposed over the entire surface of the core particle. [9] The composite particle as described in any one of [1] to [8] further comprises a protective layer covering at least the surface of the plurality of metallic particles.

[10] The composite particles as described in [9], wherein the protective layer comprises an insulating material.

[11] The composite particles as described in [9] or

[10] , wherein the thickness of the protective layer is greater than 3 nm and less than 200 nm.

[12] The composite particle as described in any one of [9] to

[11] , wherein the protective layer covers the entire surface of the core particle and the metallic particle.

[13] The composite particles as described in any one of [1] to

[12] are used in a sensor element.

[14] A method for manufacturing composite particles, wherein the composite particles comprise: Core particles; and A layer of metallic particle aggregates is disposed on at least a portion of the surface of the core particles. The composite particle layer comprises multiple metal particles arranged separately from each other, and the method for manufacturing the composite particles includes: The step of growing the metallic particles on the surface of the core particles.

[15] The method for manufacturing composite particles as described in

[14] further includes a heat treatment step after the growth step.

[16] A method for manufacturing composite particles as described in

[14] or

[15] , wherein after the growth step, a step is further included in forming a protective layer that at least covers the surface of the plurality of metallic particles.

[17] A composite particle comprising: Core particles; A metallic material layer is disposed on at least a portion of the surface of the core particle; and A protective layer that covers the surface of the metallic material layer.

[18] The composite particles as described in

[17] , wherein the protective layer comprises an insulating material.

[19] The composite particles as described in

[17] or

[18] , wherein the thickness of the protective layer is greater than 3 nm and less than 200 nm.

[20] A sensing element for detecting a substance to be detected, the sensing element comprising: substrate; Composite particles, disposed on the substrate; and The capturing unit, disposed on the composite particle, has a capturing substance specifically bonded to the substance being detected. The composite particles comprise: Core particles; and A layer of metallic particle aggregates is disposed on at least a portion of the surface of the core particles. The metal-based particle aggregate layer comprises multiple metal-based particles arranged separately from each other.

[21] The sensor element as described in

[20] , wherein the composite particles further comprise a protective layer covering at least the surface of the plurality of metallic particles. The capturing part is disposed on the protective layer.

[0007] [The effects of the invention] A novel structure can be provided that can be used in sensor elements and the like, and effectively serves as an enhancement component for enhancing the light emission of a light-emitting body. Additionally, a sensor element including this structure can be provided. Simple Explanation of the Diagram

[0008] Figure 1 is a plan view schematically illustrating an example of the composite particles of the present invention. Figure 2 is a cross-sectional view schematically illustrating an example of the composite particles of the present invention. Figure 3 is a cross-sectional view schematically illustrating another example of the composite particles of the present invention. Figure 4 is a schematic diagram illustrating an example of the metal particle growth step in the plating process. Figure 5 is a cross-sectional view schematically illustrating another example of the sensor element of the present invention. Figure 6 is an SEM image (11000x scale) of the composite particles (after heat treatment) obtained in Example 1. Figure 7 is an SEM image (10000x scale) of the composite particles containing the protective layer obtained in Example 2. Figure 8 shows an image obtained during the fluorescence intensity measurement of sample 1. Figure 9 shows an image obtained during the fluorescence intensity measurement of sample 2. Figure 10 is a SEM image (6000x scale) of the composite particles obtained in Example 3. Figure 11 is an SEM image (35,000x scale) of the composite particles obtained in Example 3. Figure 12 is a SEM image (20,000x scale) of the composite particles obtained in Example 4. Figure 13 shows an image obtained during the fluorescence intensity measurement of sample 3. Figure 14 shows an image obtained during the fluorescence intensity measurement of sample 4. Figure 15 is a SEM image (7000x scale) of the composite particles containing the protective layer obtained in Example 5. Figure 16 is an SEM image (30,000x scale) of the composite particles containing the protective layer obtained in Example 5. Figure 17 is a STEM cross-sectional image (100,000x scale) of the composite particles containing the protective layer obtained in Example 5. Figure 18 is a SEM image (90,000x scale) of the composite particles obtained in Example 7. Figure 19 is a SEM image (20,000x scale) of the composite particles obtained in Example 8. Figure 20 is a SEM image (30,000x scale) of the laminate containing composite particles obtained in Example 9. Figure 21 is a SEM image (35,000x scale) of the stack containing composite particles obtained in Example 10. Figure 22 is a SEM image (35,000x scale) of the stack containing composite particles obtained in Example 11. Implementation

[0009] <Composite Particles> (1) Summary Figure 1 is a plan view schematically illustrating an example of the composite particle (hereinafter also simply referred to as "composite particle") of the present invention, and Figure 2 is a cross-sectional view schematically illustrating an example of the composite particle. The composite particle 1 includes: a core particle 10; and a metal-based particle aggregate layer disposed on at least a portion of the surface of the core particle 10. The metal-based particle aggregate layer is an aggregation of a plurality of metal-based particles 20 supported on the core particle 10, and is a layer comprising a plurality of metal-based particles 20 disposed separately from each other.

[0010] In the examples shown in Figures 1 and 2, the metal-based particle aggregate layer is disposed on the entire surface of the core particle 10. Since the multiple metal-based particles 20 constituting the metal-based particle aggregate layer are separated from each other, there are regions in the metal-based particle aggregate layer where no metal-based particles 20 are present, and the surface of the core particle 10 is exposed in these regions.

[0011] The metallic particle aggregate layer formed on the core particles is called a plasma structure. A "plasma structure" refers to a structure that exhibits localized plasma resonance. Plasma refers to the compression-sparse waves of free electrons generated by the collective vibration of free electrons within the structure.

[0012] According to composite particles, the intensity of luminescence (e.g., fluorescence) from a luminescent body, such as one used to label a substance being detected, can be enhanced through local plasma resonance. Therefore, composite particles are preferably used as luminescence enhancement components for various sensor elements. By applying composite particles to sensor elements, the sensitivity, quantitative accuracy, and / or reproducibility (stability) of the quantitative results can be improved. A preferred example of a sensor element is a biosensor element.

[0013] Composite particles can exhibit the characteristics described in [a] and [b]. These characteristics are believed to be manifested through the interactions between local plasma particles represented by multiple metallic particles constituting the metallic particle aggregate layer. [a] The range of plasma resonance exhibited by the metal-based particle aggregate layer (the range of luminescence enhancement effect brought about by plasma) is wide, and it can even enhance the luminescence of luminescent bodies in the range of hundreds of nm (e.g. 200 nm) from the surface of the metal-based particle aggregate. [b]Because the metallic particle aggregate layer exhibits strong plasma resonance, a strong luminescence enhancement effect can be obtained.

[0014] Regarding [a], the composite particles can enhance the luminescence of light-emitting bodies positioned at distances of, for example, 10 nm or more from the metal-based particle aggregate layer, further tens of nanometers (e.g., 20 nm, 30 nm, or 40 nm) or more, or even 100 nm or 200 nm or more. Regarding [b], the intensity of the plasma resonance exhibited by the composite particles is not simply the sum of the local plasma resonances exhibited by the individual metal-based particles at a specific wavelength, but rather an intensity exceeding that. In the composite particles, the individual metal-based particles interact to exhibit strong plasma resonances. This strong plasma resonance is considered to be manifested through the interaction between local plasmas of the metal-based particles.

[0015] Generally, when the absorption spectrum of a plasma structure is measured by spectrophotometry, the plasma resonance peak (hereinafter also referred to as the "plasma peak") is observed as the longest wavelength in the ultraviolet-visible region. The intensity of the plasma resonance of the plasma structure can be evaluated based on the absorbance at the maximum wavelength of the plasma peak. There is a tendency for a higher absorbance value to correspond to a stronger plasma resonance.

[0016] The absorption spectrum of the plasma structure can be determined by spectrophotometry. Specifically, the absorption spectrum can be obtained as follows: An incident light in the ultraviolet-visible region is irradiated vertically onto the back side (opposite to the metal particle aggregate) of a glass substrate with a metal particle aggregate deposited on it. The intensity I of the transmitted light in all directions to the metal particle aggregate side is measured using an integrating sphere spectrophotometer. The same incident light is then irradiated vertically onto the side of a substrate of the same thickness and material as the sample being measured, but without the metal particle aggregate deposited on it. The intensity I0 of the transmitted light in all directions from the opposite side of the incident surface is measured using an integrating sphere spectrophotometer. The absorbance, which is the vertical axis of the absorption spectrum, is then expressed by the following formula: Absorbance = -log 10(I / I0) express. Absorption spectra can be measured using a general spectrophotometer.

[0017] In addition, when measuring the maximum wavelength and absorbance of plasma sub-peaks located on the longest wavelength side in the ultraviolet-visible region, an objective lens and spectrophotometer can be used to narrow the measurement field of view for absorption spectroscopy measurement.

[0018] (2) Core particles Core particles are the particles that make up the nucleus of composite particles. There are no particular restrictions on the shape of core particles; they can be shapes with curved surfaces or shapes without curved surfaces. Shapes whose surfaces include curved surfaces can be exemplified by spheres, ellipses of revolution, etc. Shapes whose surfaces do not include curved surfaces can be exemplified by polyhedra, etc. Core particles can also have a portion of their surface that is curved and the remainder that is planar. Core particles can also be amorphous. The core particles are preferably spherical or nearly spherical.

[0019] The particle size of the core particles is, for example, 0.3 μm or more but less than 10 μm, preferably 0.5 μm or more but less than 8 μm, more preferably 1 μm or more but less than 5 μm, and even more preferably 1 μm or more but less than 3 μm. This invention also relates to a composite particle group, which is a collection of multiple composite particles. In the composite particle group, the particle size of the core particles can refer to the average particle size of the core particle group (a collection of multiple core particles).

[0020] The particle size of the core particles was determined using the following method. A scanning electron microscope (SEM) image containing the core particles was obtained from directly above using a JSM-5500 scanning electron microscope (manufactured by Nippon Electronics Corporation) or an equivalent device. In the SEM image, five tangent diameters were randomly drawn from within the core particle image (each tangent diameter line can pass only through the interior of the core particle image, with one being the longest line drawn that passes only through the interior of the core particle). The average value of these tangent diameters was taken as the particle size. The tangent diameter is defined as the perpendicular line connecting the particle's outline (projected image) to the distance between two parallel lines tangent to the particle's outline (projected image) (Nikkan Kogyo Shimbun, "Particle Measurement Technology," 1994, p. 5).

[0021] Furthermore, the average particle size was measured using the following method. A scanning electron microscope (SEM) of the substrate (glass substrate, etc.) with the core particle cluster attached, viewed from directly above, was acquired using a JSM-5500 or equivalent device manufactured by Nippon Electronics Co., Ltd. In this SEM image, ten core particles were randomly selected, and five tangent diameters were randomly drawn from the image of each core particle (wherein, the straight lines serving as tangent diameters can all pass only through the interior of the core particle image, and one of these is the longest straight line drawn that passes only through the interior of the core particle). These average tangent diameters were then used as the average value (average tangent diameter). The average tangent diameter was obtained for all ten selected core particles. The definition of tangent diameter is the same as described above. The length of 1 / 4 of the average tangent diameter of each core particle was defined as the "edge region length" of each core particle. Furthermore, the range of the "edge region length" from the outline of each core particle in the SEM image towards the inside of the core particle was defined as the "edge region" of each core particle. Furthermore, if any of the ten core particles overlap with the edge regions of other core particles, that core particle is discarded, and core particles are randomly selected again according to the number of insufficient particles. The average tangent diameter is then obtained in the same manner. This process is repeated as needed to obtain the average tangent diameter for the ten core particles that do not overlap with edge regions. The average of the ten obtained average tangent diameters is taken as the average particle size.

[0022] The particle size of the core particles contained in the composite particles can be determined by the following formula. Core particle size = (average particle size of composite particles) - 2 × {(average height of metallic particles) + (thickness of protective layer)} The average particle size of the composite particles can be measured in the same way as that of the core particles. Methods for determining the average height of the metallic particles and the thickness of the protective layer will be described later.

[0023] There are no particular limitations on the material of the core particles, but from the viewpoint of improving the function of the composite particles as light-enhancing components, the core particles are preferably non-conductive, and therefore preferably contain insulating materials. Examples of insulating materials include: inorganic insulating materials such as silicon dioxide, titanium dioxide, alumina, and silicon nitride; and organic insulating materials such as resin materials (e.g., polystyrene, acrylic resins, cellulose nanofibers, paper, nitrocellulose, epoxy resins, etc.). Additionally, semiconductors such as silicon can also be used. When it is desired to obtain composite particles containing spherical or substantially spherical core particles, silicon dioxide is the preferred material for the core particles, as it is industrially easy to manufacture spherical or substantially spherical particles.

[0024] Core particles can contain two or more materials. Core particles can be single-layer or multi-layer structures. For example, core particles can exhibit non-conductivity by having a core containing a metallic material and a shell containing an insulating material. Examples include silicon with an insulating film, or metals (aluminum, copper, chromium, or composites thereof) with an insulating film.

[0025] (3) Metallic particle aggregate layer The metallic particle aggregate layer is disposed on at least a portion of the surface of the core particle, or it may be disposed across the entire surface of the core particle. The multiple metallic particles constituting the metallic particle aggregate layer are separated from each other.

[0026] Metallic particles include materials capable of plasma resonance in the ultraviolet-visible region. The term "material capable of plasma resonance in the ultraviolet-visible region," when referring to nanoparticles or their aggregates, means materials that exhibit plasma peaks in the ultraviolet-visible region during absorbance spectroscopy measurements using spectrophotometry. Examples of metallic materials capable of plasma resonance in the ultraviolet-visible light region include: noble metals such as gold, silver, copper, platinum, and palladium; metals other than noble metals such as aluminum and tantalum; alloys containing metals selected from these noble metals and other metals; and metal compounds (metal oxides or metal salts, etc.) containing metals selected from these noble metals and other metals. Among these, noble metals such as gold, silver, copper, platinum, and palladium are preferred as metallic materials capable of plasma resonance in the ultraviolet-visible light region, and silver is more preferred from the viewpoint of being inexpensive and having low absorption (small imaginary part of the dielectric function at visible light wavelength).

[0027] From the viewpoint of effectively obtaining the effects described in [a] and [b], the average particle size of the plurality of metal-based particles constituting the metal-based particle aggregate layer can be 5 nm or more, preferably 30 nm or more, more preferably 100 nm or more, further preferably 200 nm or more, and further preferably 250 nm or more. From the viewpoint of effectively obtaining the effects described in [a] and [b], the average particle size of the plurality of metal-based particles constituting the metal-based particle aggregate layer is, for example, 1600 nm or less, preferably 800 nm or less, more preferably 550 nm or less, further preferably 450 nm or less, further preferably 400 nm or less, and particularly preferably 350 nm or less. The optimal average particle size of metallic particles is to be appropriately selected based on the type of metallic material constituting the metallic particles.

[0028] The average particle size of the plurality of metallic particles refers to the average particle size of the selected six metallic particles in a top-down SEM image of a substrate (glass substrate, etc.) containing the composite particles. Five tangent diameters are randomly drawn from the image of each metallic particle (wherein, the straight lines serving as tangent diameters can all pass only through the interior of the metallic particle image, with one being the longest straight line that passes only through the interior of the metallic particle). The average value of these tangent diameters (hereinafter also referred to as the "average tangent diameter") is used as the average particle size of each metallic particle. The definition of the tangent diameter is the same as described above.

[0029] To provide a more detailed explanation of the method for determining the average particle size, firstly, the SEM images were measured using a scanning electron microscope (JSM-5500) manufactured by Nippon Electronics Co., Ltd., or an equivalent device. Next, the obtained images were read at 1280 pixels horizontally × 960 pixels vertically using ImageJ, a free image processing software manufactured by the National Institutes of Health. Then, the random number generation function RANDBETWEEN in Excel, a spreadsheet software manufactured by Microsoft, was used to obtain six random numbers from 1 to 1280 (x1, x2, x3, x4, x5, x6) and six random numbers from 1 to 960 (y1, y2, y3, y4, y5, y6). Six sets of random number combinations are obtained from the six random numbers obtained: (x1, y1), (x2, y2), (x3, y3), (x4, y4), (x5, y5), and (x6, y6). The values ​​of the random numbers generated from 1 to 1280 are set as the x-coordinates, and the values ​​of the random numbers generated from 1 to 960 are set as the y-coordinates, resulting in six sets of coordinate points: (x1, y1), (x2, y2), (x3, y3), (x4, y4), (x5, y5), and (x6, y6). Then, the average tangent diameter is obtained for each of the six metallic particle images containing these coordinate points, and the average particle size is obtained as the average of these six tangent diameter averages. At this point, if at least one of the six coordinate points in the six random number combinations is not included in the image of the metal-based particle, or if more than two coordinate points are included in the same metal-based particle, the random number combination is discarded, and the random number is generated again until all six coordinate points are included in different metal-based particle images. Additionally, the "edge region" of the core particle is obtained from the same observation image. Furthermore, if, among the six metal-based particles, there are metal-based particles that overlap with the edge regions of the core particle containing each metal-based particle, the random number combination is discarded, and the random number is generated again until all six coordinate points are included in different metal-based particle images, and there are no metal-based particles that overlap with the edge regions of the core particle containing each metal-based particle. The average tangent diameter is obtained in the same manner as described above. The above operations are repeated as needed to obtain the average tangent diameter for the six metal-based particles that do not overlap with the edge regions of the core particle. The average of the six obtained average tangent diameters is taken as the average particle size.

[0030] Typically, the average particle size of the metallic particles is smaller than the particle size of the core particles that support them. The ratio of the particle size of the core particles to the average particle size of the metallic particles is, for example, 2 or more and 10,000 or less, preferably 4 or more and 5,000 or less, and more preferably 6 or more and 1,000 or less.

[0031] In a layer of metallic particles, multiple metallic particles are arranged such that the average distance (hereinafter also referred to as "average interparticle distance") between them and their adjacent metallic particles is greater than 1 nm and less than 150 nm. By arranging multiple metallic particles with this average interparticle distance, strong plasma resonance can be obtained, and the effect of extending the range of plasma resonance can be improved. From the viewpoint of effectively achieving the effects described in [a] and [b], the average interparticle distance is preferably 1 nm or more and 120 nm or less, more preferably 1 nm or more and 100 nm or less, further preferably 1 nm or more and 80 nm or less, further preferably 1 nm or more and 60 nm or less, and particularly preferably 1 nm or more and 40 nm or less. If the average interparticle distance is less than 1 nm, electron migration based on the Dexter mechanism occurs between particles, which is detrimental to local plasma deactivation.

[0032] The average interparticle distance refers to the average of the interparticle distances of six randomly selected metallic particles in a top-down SEM image of a substrate (such as a glass substrate) containing the composite particles. For each selected metallic particle, the interparticle distance to its neighboring metallic particles is calculated. The interparticle distance to neighboring metallic particles is the average of the distances measured to each of all adjacent metallic particles (the minimum distance between the surfaces of adjacent metallic particles).

[0033] To explain the method for measuring the average interparticle distance in more detail, firstly, the SEM images were measured using a scanning electron microscope (SEM) of JEOL Ltd., or an equivalent device. Next, the obtained images were read using ImageJ, a free image processing software manufactured by the National Institutes of Health (NIH), at a resolution of 1280 pixels horizontally × 960 pixels vertically. Then, the RANDBETWEEN function in Excel, a spreadsheet software manufactured by Microsoft, was used to generate six random numbers from 1 to 1280 (x1 to x6) and six random numbers from 1 to 960 (y1 to y6). From each of these six random numbers, six sets of random number combinations (x1, y1) to (x6, y6) were obtained. The values ​​of random numbers generated from 1 to 1280 are set as the x-coordinate, and the values ​​of random numbers generated from 1 to 960 are set as the y-coordinate, resulting in six sets of coordinate points (x1, y1) to (x6, y6). Then, for each of the six metal-based particle images containing these coordinate points, the inter-particle distance between the metal-based particle and its adjacent metal-based particles is obtained. The average inter-particle distance is then obtained as the average of these six inter-particle distances. If at least one of the six coordinate points in the six sets of random numbers is not included in a metal-based particle image, or if more than two coordinate points are included within the same metal-based particle, the random number combination is discarded, and the random numbers are generated repeatedly until all six coordinate points are included in different metal-based particle images. Additionally, the "edge region" of the core particle is obtained from the same observation image. Furthermore, if any of the six metal-based particles overlap with the edge regions of the core particle containing the other metal-based particles, discard the random number combination and repeat the generation of random numbers until all six coordinate points are contained within different metal-based particle images and no metal-based particles overlap with the edge regions of the core particle containing the other metal-based particles. The inter-particle distances are then obtained in the same manner. This process is repeated as needed to obtain the inter-particle distances for the six metal-based particles that do not overlap with the edge regions of the core particle. The average of the six obtained inter-particle distances is taken as the average inter-particle distance.

[0034] In the metallic particle aggregate layer, the multiple metallic particles are preferably configured such that the standard deviation of the average interparticle distance is less than 50 nm. By configuring the metallic particles in such a way that the standard deviation is within this range, strong plasma resonance can be obtained, and the effect of extending the effective range of plasma resonance can be improved. From the viewpoint of effectively obtaining the effects of [a] and [b], the standard deviation of the average interparticle distance is preferably 40 nm or less, more preferably 30 nm or less, further preferably 25 nm or less, and further preferably 20 nm or less. From the viewpoint of effectively obtaining the effects of [a] and [b], the standard deviation of the average interparticle distance is preferably 0.1 nm or more, more preferably 0.2 nm or more, and further preferably 0.3 nm or more.

[0035] The standard deviation of the average interparticle distance is defined as follows. In a top-down SEM image of a substrate (glass substrate, etc.) containing composite particles, a metallic particle is randomly selected. For this metallic particle, the interparticle distance with its neighboring metallic particles is calculated. The interparticle distance with its neighboring metallic particles is the average of the distances (minimum distances between surfaces) measured with each of the adjacent metallic particles. In the SEM image, five metallic particles different from the aforementioned one are randomly selected. For these five metallic particles, the interparticle distances with their neighboring metallic particles are calculated in the same manner. The standard deviation of the interparticle distances with their neighboring metallic particles for a total of six metallic particles obtained in this manner is defined as the standard deviation of the average interparticle distance.

[0036] To explain in more detail the method for determining the standard deviation of the average interparticle distance, firstly, the SEM images were measured using a JSM-5500 scanning electron microscope manufactured by NJE Inc. or an equivalent device. Next, the obtained images were read at 1280 pixels horizontally × 960 pixels vertically using ImageJ, a free image processing software manufactured by the National Institutes of Health. Then, the RANDBETWEEN function in Excel, a spreadsheet software manufactured by Microsoft, was used to obtain six random numbers (x1 to x6) from 1 to 1280, and six random numbers (y1 to y6) from 1 to 960. From each of these six random numbers, six sets of random number combinations (x1, y1) to (x6, y6) were obtained. The values ​​of random numbers generated from 1 to 1280 are set as the x-coordinate, and the values ​​of random numbers generated from 1 to 960 are set as the y-coordinate, resulting in six sets of coordinate points (x1, y1) to (x6, y6). Then, for each of the six metal-system particle images containing these coordinate points, the inter-particle distances between the metal-system particle and its adjacent metal-system particles are obtained. The standard deviation of the average inter-particle distance is then obtained as the standard deviation of these six inter-particle distances. If at least one of the six coordinate points in the six sets of random numbers is not included in a metal-system particle image, or if more than two coordinate points are included within the same metal-system particle, the random number combination is discarded, and the random numbers are generated repeatedly until all six coordinate points are included in different metal-system particle images. Additionally, the "edge region" of the core particle is obtained from the same observation image. Furthermore, if any of the six metal-based particles overlap with the edge regions of the core particle containing the other metal-based particles, discard the random number combination and repeat the generation of random numbers until all six coordinate points are contained within different metal-based particle images and no metal-based particles overlap with the edge regions of the core particle containing the other metal-based particles. The inter-particle distances are then obtained in the same manner. This process is repeated as needed to obtain the inter-particle distances for the six metal-based particles that do not overlap with the edge regions of the core particle. The standard deviation of the average inter-particle distance is obtained as the standard deviation of the inter-particle distances of these six particles with respect to their neighboring metal-based particles.

[0037] From the viewpoint of effectively obtaining the effects described in [a] and [b], the average height of the plurality of metal particles constituting the metal particle aggregate layer is preferably 5 nm or more and 500 nm or less, more preferably 10 nm or more and 300 nm or less, further preferably 30 nm or more and 200 nm or less, further preferably 50 nm or more and 150 nm or less, and particularly preferably 55 nm or more and 150 nm or less.

[0038] The average height of the plurality of metallic particles was determined using the following method: A cross-sectional image of the composite particle was acquired using a scanning electron microscope "JSM-5500" manufactured by Nippon Electronics Co., Ltd., or an equivalent device. From the acquired cross-sectional image, ten points were randomly selected on the outer contour surface of the particle containing the core particle and the metallic particle aggregate layer (the composite particle without a protective layer). Then, straight lines were drawn from each of these ten points in the manner that the shortest distance to the outer surface of the core particle was obtained, and the average length of the ten obtained straight lines was taken as the average height of the metallic particle.

[0039] From the viewpoint of effectively obtaining the effects of [a] and [b], the aspect ratio of the multiple metal particles constituting the metal particle aggregate layer is preferably 1 or more and 8 or less, more preferably 1 or more and 7 or less, further preferably 1.5 or more and 7 or less, and further preferably 1.5 or more and 6 or less. The aspect ratio is defined by the ratio of the average particle size to the average height (average particle size / average height). The metallic particles may be spherical, but from the viewpoint of effectively obtaining the effects of [a] and [b], a flat shape with an aspect ratio greater than 1 is preferred.

[0040] From the perspective of highly effective plasma excitation, metallic particles are preferably those with smooth curved surfaces, especially flat shapes with smooth curved surfaces, but the surface may also contain some minor bumps (roughness), in this sense, metallic particles can also be amorphous.

[0041] For a composite particle, the number of metallic particles contained in the metallic particle aggregate layer is typically six or more, preferably 30 or more. By forming a metallic particle aggregate layer containing six or more metallic particles, strong plasma resonance and an extended range of plasma resonance can easily be exhibited through the local plasma-to-plasma interactions of the metallic particles. For a composite particle, the number of metallic particles contained in the metallic particle aggregate layer can be, for example, 50 or more, and further, 1000 or more, or even 10000 or more. From the perspective of easily exhibiting strong plasma resonance and the extension of the plasma resonance range, the number density of metallic particles is preferably seven or more, and more preferably fifteen or more, relative to the surface area of ​​the core particle of 1 μm². Composite particles with a metallic particle aggregate layer disposed on the surface of the core particle, and composite particles with a protective layer (described later) disposed on the surface of the particle, can have surface irregularities or be manufactured with surface irregularities. Composite particles with surface irregularities have a larger surface area. Therefore, when this composite particle is applied to a sensor element, a large amount of the captured substance, and thus the substance to be detected, can be bonded to the surface of the composite particle. This is beneficial for improving the detection sensitivity and detection accuracy of the sensor element.

[0042] From the perspective of easily exhibiting strong plasma resonance and the extended range of plasma resonance, the metallic particle aggregate layer deposited on the surface of the core particle is preferably non-conductive as a layer. From this perspective, it is also preferable that the surface of the core particle on which the metallic particles are disposed is non-conductive. The metallic particles themselves may also be conductive.

[0043] In one embodiment of the composite particle, the core particle includes a curved surface, on which at least a layer of metallic particle aggregates is disposed. In another embodiment of the composite particle, the core particle is spherical or substantially spherical, and the layer of metallic particle aggregates is disposed over the entire surface of the core particle.

[0044] (4) Protective layer As illustrated in the cross-sectional view of another example of a composite particle, namely the composite particle 2 shown in FIG3, the composite particle may further include a protective layer 30. The composite particle 2 includes: a core particle 10, a metal-based particle aggregate layer (an aggregate of multiple metal-based particles 20) disposed on at least a portion of the surface of the core particle 10, and a protective layer 30 covering at least the surface of the multiple metal-based particles 20.

[0045] Forming a protective layer is advantageous in the following respects. [A] When composite particles are used as a luminescence enhancement component to enhance the intensity of luminescence from a luminescent body used to label the substance being tested, if the luminescent body is in direct contact with the metallic particles of the composite particles, extinction may occur due to electron tunneling from the luminescent body to the metallic particles, potentially reducing the enhancement effect. By providing a protective layer on the metallic particles, the luminescent body can be reliably separated from the metallic particles, thus suppressing extinction. [B] can improve the stability (oxidation resistance, etc.) and environmental stability (e.g., light resistance, humidity resistance, heat resistance, etc.) of composite particles (core particles and / or metal particles).

[0046] From the perspective of [A], the protective layer can be formed in such a way that it at least covers the surfaces of the multiple metal particles constituting the metal particle aggregate layer, but it can also be formed in a way that covers the entire surface including the surface of the core particle and the surfaces of the multiple metal particles, as shown in FIG3.

[0047] Regarding the viewpoint in [A], the protective layer is preferably made of a non-conductive material, i.e., an insulating material. Examples of insulating materials include spin-on glass (SOG; for example, those containing organosiloxane materials), inorganic insulating materials such as SiO₂, SiN, TiO₂, Al₂O₃, and Si₃N₄, and organic insulating materials such as resin materials (e.g., polystyrene, acrylic resins, epoxy resins, etc.). The protective layer may include two or more materials. The protective layer may be a single-layer structure or a multi-layer structure.

[0048] There is no particular limitation on the thickness of the protective layer, for example, it is 3 nm or more, preferably 10 nm or more. From the viewpoint that the light emission from the light source is effectively enhanced when composite particles are used as light-enhancing components in a sensor element that captures the detected substance marked by the light-emitting body on the protective layer and analyzes the detected substance, the thickness of the protective layer is, for example, 200 nm or less, preferably 150 nm or less, more preferably 100 nm or less, and even more preferably 80 nm or less, and even more preferably 50 nm or less.

[0049] The thickness of the protective layer was measured using the following method. A cross-sectional image of the composite particles was acquired using a scanning electron microscope (JSM-5500) manufactured by Nippon Electronics Co., Ltd., or an equivalent device. From the acquired cross-sectional image, ten points were randomly selected on the outer contour surface of the particles (composite particles without a protective layer), including the core particle and the metallic particle aggregate layer. These points are on the surface of the metallic particles, i.e., the surface forming the interface with the protective layer. Then, straight lines were drawn from each of these ten points in the manner shortest to the outer surface of the protective layer, and the average length of these ten straight lines was taken as the thickness of the protective layer.

[0050] In a preferred embodiment of the composite particle, a protective layer covers the entire surface of the particle (the composite particle without the protective layer), which includes a core particle and a layer of metallic particles. In this embodiment, the outer surface of the protective layer may have unevenness following the surface irregularities of the composite particle without the protective layer (based on the irregularities of the metallic particles), or it may be smooth without unevenness. Figure 3 shows an example of a protective layer with surface irregularities. When the composite particle is used in a sensor element, from the viewpoint of increasing the amount of detectable substance bonded to the surface of the composite particle, the protective layer preferably has surface irregularities.

[0051] When a protective layer covers the entire surface of a composite particle without a protective layer, the protective layer can be formed with a relatively uniform thickness across the entire surface, or it can be formed with an uneven thickness, such as being locally thicker or thinner. When composite particles are used as light-enhancing components in a sensor element that captures and analyzes a substance marked by a light emitter on a protective layer, from the viewpoint of minimizing the variation in distance from the metallic particle aggregate layer to the light emitter due to the position of the composite particle surface where the substance marked by the light emitter is captured, the protective layer is preferably formed with a uniform or relatively uniform thickness across the entire surface. Furthermore, as shown in Figure 5 (described later), when the composite particles are housed within a recess in a substrate, composite particles with an unevenly thick protective layer may not be able to be housed within the recess, and in such cases, there is a risk of detection defects occurring within the composite particles. On the other hand, if the composite particles with the protective layer are spherical or nearly spherical, then substrates or filters that are microscale-processed and designed to hold or allow the composite particles to pass through can, as intended, hold or allow them to pass through. However, if the thickness of the protective layer is uneven, there is a risk that the composite particles may not behave as intended, leading to undesirable outcomes.

[0052] <Methods for Manufacturing Composite Particles> This invention provides a method for manufacturing composite particles. Referring to Figures 1 and 2, the composite particle includes a core particle 10 and a metal-based particle aggregate layer disposed on at least a portion of the surface of the core particle 10. The metal-based particle aggregate layer is an aggregation of a plurality of metal-based particles 20 supported on the core particle 10, and is a layer comprising a plurality of metal-based particles 20 disposed separately from each other. In the example shown in Figures 1 and 2, the metal-based particle aggregate layer is disposed on the entire surface of the core particle 10. For details regarding the specific structure of the composite particle obtained by the manufacturing method described herein, the core particle, the metal-based particle aggregate layer, and the material of the metal-based particles, please refer to the description in the section on <composite particles>. The method for manufacturing composite particles of the present invention can preferably be used as the method for manufacturing composite particles described in the <Composite Particles> section.

[0053] The method for manufacturing composite particles includes the step of growing multiple metallic particles on the surface of a core particle (metallic particle growth step). Examples of methods for growing metallic particles include sputtering, vapor deposition (vacuum vapor deposition, etc.), and plating.

[0054] (1) Sputtering method As a sputtering method, examples include placing core particles or groups of core particles on a substrate such as a glass substrate, and then performing a sputtering process on the core particles or groups of core particles placed on the substrate. For example, the core particles or groups of core particles can be electrostatically adsorbed onto the substrate, and the substrate can be introduced into a sputtering apparatus for sputtering. Furthermore, even when core particles or core particle groups are electrostatically adsorbed onto a substrate and the substrate is then fed into a sputtering apparatus for sputtering, metal-based particles can still grow on the surface of the core particles in contact with the substrate by performing film formation under conditions described below. This is because sputtering the atoms of the metal-based material at high pressure and low speed significantly reduces (e.g., less than 3 mm) the mean free path of the ejected metal-based material atoms, making it easier for the metal-based material atoms to wrap around the surface of the core particles. In addition, by using fewer core particles for electrostatic adsorption, the core particles can move on the substrate during film formation, thereby making the aforementioned wrapping more likely.

[0055] In sputtering, from the viewpoint of forming a metal-based particle aggregate layer with well-controlled average particle size, average height, average interparticle distance and its standard deviation, it is preferable to grow the metal-based particles at an extremely low rate relative to the heated core particles or core particle groups.

[0056] The growth rate of metallic particles on the core particle surface, measured by the average height growth rate, is preferably less than 1 nm / min, more preferably less than 0.5 nm / min, and even more preferably less than 0.3 nm / min. The average height growth rate mentioned here can also be referred to as the average deposition rate or the average thickness growth rate of the metallic particles, and can be expressed by the following formula: Average height of metallic particles / growth time of metallic particles The definition of "average height of metallic particles" is as described above. The growth time of metallic particles refers to the time from the start to the end of the growth process, specifically the supply time of the metallic material. When the method for growing metallic particles is sputtering, the growth time is called the sputtering time.

[0057] The temperature of the core particles in the metal-based particle growth step also depends on the material of the metal-based particles, preferably above 80°C and below 450°C, more preferably above 100°C and below 400°C, even more preferably above 120°C and below 400°C, and even more preferably 300°C or around (approximately 300°C ± 10°C).

[0058] By adjusting the average height growth rate, core particle temperature, and / or metal-based particle growth time, the average particle size, average height, aspect ratio, average inter-particle distance, and standard deviation of multiple metal-based particles grown on the core particle can be controlled.

[0059] The pressure (pressure within the device chamber) used to grow metallic particles is not particularly limited as long as it is sufficient for growth, and is usually less than atmospheric pressure. There is no particular limitation on the lower limit of the pressure, but it is preferably 0.5 Pa or more, more preferably 2 Pa or more, and even more preferably 10 Pa or more, to facilitate adjusting the average height growth rate within the aforementioned range.

[0060] There are no particular limitations on the sputtering method; direct current argon ion sputtering, which uses an electric field to accelerate argon ions generated by an ion gun or plasma discharge and irradiate the target, can be used. Appropriate adjustments can be made to other conditions in the sputtering method, such as the current value, voltage value, and substrate-target distance, to achieve an average height growth rate of less than 1 nm / min for the growth of metal-based particles. Methods that do not allow core particles to adhere to the substrate and form a film directly can be used, or the core particle powder can be stirred continuously or intermittently during film formation. For example, in sputtering (powder sputtering), vapor deposition (powder vapor deposition), CVD (chemical vapor deposition) (powder CVD), and atomic layer deposition (ALD), methods that involve stirring the core particle powder during film formation, as described above, can also be used.

[0061] From the viewpoint of effectively forming a metal-based particle aggregate layer with the aforementioned preferred average particle size, average height, average interparticle distance, and standard deviation, it is preferable that, in the metal-based particle growth step, not only is the average height growth rate set to less than 1 nm / min, but the average particle size growth rate is also set to less than 5 nm. When the average height growth rate is less than 1 nm / min, the average particle size growth rate is typically less than 5 nm. More preferably, the average particle size growth rate is 1 nm / min or less. The average particle size growth rate is defined by the following formula: Average particle size of metallic particles / growth time of metallic particles The definitions of "average particle size of metallic particles" and "growth time of metallic particles" are as described above.

[0062] In order to obtain a metal-based particle aggregate layer with the aforementioned preferred average particle size, average height, average interparticle distance and standard deviation, it is preferable to appropriately adjust the metal-based particle growth time in the metal-based particle growth step while taking into account the preferred manufacturing conditions.

[0063] (2) Plating method The plating method includes the following steps as the metal-based particle growth steps, which are to reduce the cations by immersing the core particles in a plating solution containing cations of the metal constituting the metal-based particles (hereinafter also referred to as "metal cations"), thereby forming a metal-based particle aggregate layer on the surface of the core particles.

[0064] In the aforementioned step, the reduction of the metal cations is performed while the core particles are immersed in a plating solution containing metal cations that constitute the metal-based particles. This step, for example, as shown in FIG4, can be performed by adding the core particles 10 to a plating solution 60 containing metal cations contained in a tank 50 under stirring. When the core particles 10 are immersed in the plating solution 60 containing metal cations, the metal (0 valence) generated by the reduction of the metal cations begins to deposit on the surface of the core particles 10. As the reaction time progresses, the deposited metal grows into particles, thereby forming an aggregate of metal-based particles (metal-based particle aggregate layer). Preferably, the metal-based particle aggregate layer forms on the entire surface of the core particles 10.

[0065] In one embodiment, the plating solution 60 can be prepared by mixing a metal cation solution containing metal cations and a reducing agent solution containing a reducing agent. The metal cation solution containing metal cations typically contains metal cations and a solvent. The plating solution 60 may also contain two or more metal cations.

[0066] The solvent contained in the metal cation solution is preferably a solvent capable of dissolving the corresponding metal salt contained in the metal cation solution serving as the metal cation source, such as water. The metal cation solution may contain two or more solvents. For example, the solvent may contain an organic solvent that is miscible with water (e.g., alcohols).

[0067] The concentration of metal cations in the plating solution 60 is preferably 0.0008 mol / L or higher, more preferably 0.002 mol / L or higher, even more preferably 0.0035 mol / L or higher, even more preferably 0.006 mol / L or higher, and particularly preferably 0.01 mol / L or higher. If the concentration of metal cations is within the aforementioned range, metal-based particles can grow at a suitable rate, thus easily and controllably forming a metal-based particle aggregate layer with a favorable shape (average particle size, average height, average interparticle distance, and standard deviation). Furthermore, if the concentration of metal cations is within the aforementioned range, sufficient metal-based particles can easily form on the entire surface of each core particle 10. To ensure a suitable growth rate for the metal-based particles, the concentration of metal cations in the plating solution 60 is preferably 0.4 mol / L or lower, more preferably 0.3 mol / L or lower, even more preferably 0.15 mol / L or lower, and even more preferably 0.05 mol / L or lower.

[0068] In the metal-based particle growth step, the ratio of the volume VS [cm³] of the core particle 10 to the volume VL [cm³] of the plating solution 60, VS / VL, is preferably 0.03 or less. This facilitates the formation of a metal-based particle aggregate layer comprising multiple metal-based particles arranged separately on the surface of the core particle 10. If the ratio exceeds 0.03, a continuous metal film is easily formed on the core particle 10, and sometimes it is difficult to form a metal-based particle aggregate layer. From the viewpoint of easily forming a metal-based particle aggregate layer and easily and controllably forming a metal-based particle aggregate layer with a preferred shape, the ratio is more preferably 0.020 or less, more preferably 0.010 or less, more preferably 0.005 or less, particularly preferably 0.003 or less, and most preferably 0.002 or less. Furthermore, considering the mass production of composite particles, the ratio is typically 0.00001 or higher, preferably 0.0001 or higher, more preferably 0.0005 or higher, and even more preferably greater than 0.0005. The volume VS of the core particle 10 can be obtained by dividing the total weight of the particles by the particle density.

[0069] The plating solution 60 preferably includes both a metal cation and a reducing agent capable of reducing the metal cation to a zero-valent metal. If a reducing agent is included, it is preferably present in the plating solution 60 just before the core particle 10 is immersed in it. For example, as described, a plating solution 60 containing both a metal cation and a reducing agent can be prepared by mixing a metal cation solution containing the metal cation and a reducing agent solution containing the reducing agent. The reducing agent solution is a liquid containing a reducing agent and a solvent, preferably a solution in which the reducing agent is dissolved in a solvent. The solvent included in the reducing agent solution is preferably a solvent capable of dissolving the reducing agent, such as water. The reducing agent solution may contain two or more solvents. For example, the solvent may contain an organic solvent that is miscible with water (e.g., an alcohol).

[0070] As a reducing agent, it is preferable to use a reducing agent with low reducing power, and its standard redox potential is preferably -0.5 V or higher, preferably -0.45 V or higher. The standard redox potential mentioned here is the value when the standard hydrogen electrode is set as the cathode at pH 7 and 25°C. If the standard redox potential of the reducing agent used is within the aforementioned range, the metal-based particles can grow at a moderate rate, thus easily forming a metal-based particle aggregate layer. When the standard redox potential is within the aforementioned range, it is also advantageous in that it is easy to controllably form a metal-based particle aggregate layer with a better shape. If the reducing power of the reducing agent is too high, the growth rate of the metal-based particles is too fast, easily resulting in a continuous metal film. Examples of reducing agents with a standard redox potential of -0.5 V or higher include glucose and ascorbic acid. Plating solution 60 may also contain two or more reducing agents.

[0071] The concentration of the reducing agent in the plating solution 60 is preferably 1 mol / L or less, more preferably 0.8 mol / L or less, even more preferably 0.4 mol / L or less, even more preferably 0.3 mol / L or less, and particularly preferably 0.25 mol / L or less. If the concentration of the reducing agent is within the aforementioned range, metal-based particles can grow at a suitable rate, thus easily and controllably forming a metal-based particle aggregate layer with a favorable shape. To ensure a suitable growth rate for the metal-based particles, the concentration of the reducing agent in the plating solution 60 is preferably 0.000001 mol / L or more, more preferably 0.000005 mol / L or more, even more preferably 0.000008 mol / L or more, even more preferably 0.00001 mol / L or more, and particularly preferably 0.0008 mol / L or more.

[0072] The ratio of the concentration of the reducing agent in the plating solution 60 to the saturation concentration of the reducing agent in the plating solution 60, in percentage terms, is preferably 8% or less, more preferably 4% or less, further preferably 2% or less, further preferably 1% or less, and particularly preferably 0.8% or less. If this ratio is within the aforementioned range, metal-based particles can grow at a suitable rate, thus easily and controllably forming a metal-based particle aggregate layer with a favorable shape. To ensure a suitable growth rate for the metal-based particles, the ratio is preferably 0.0005% or more, more preferably 0.001% or more, further preferably 0.003% or more, further preferably 0.005% or more, and particularly preferably 0.01% or more. If the ratio is excessively high, it is difficult to control the shape of the metal-based particle aggregate layer, and a continuous metal film is easily formed. The saturation concentration of the reducing agent in the plating solution 60 is the saturation concentration at which the reducing agent dissolves in the solvent (excluding metal cations) contained in the plating solution 60 at the temperature at which the core particles 10 are immersed in the plating solution 60.

[0073] The plating solution 60 may contain one or more bonding agents that bond with metal cations to form chelates and stabilize the metal cations, as well as other additives. Examples of bonding agents include amine-based bonding agents such as ethylenediamine, ethylenediaminetetraacetic acid, tetrasodium ethylenediaminetetraacetic acid, and triethylenetetramine hexaacetic acid; ammonia; nitrotriacetic acid; sodium thiosulfate; succinate; succinimide; citrate; or iodide salts. From the viewpoint of achieving an appropriate growth rate for the metal particles, amine-based bonding agents or ammonia are preferred, more preferably amine-based bonding agents, and even more preferably ethylenediamine. When the plating solution 60 is prepared by mixing a metal cation solution and a reducing agent solution, the bonding agent may be pre-contained in the metal cation solution.

[0074] The process of immersing the core particle 10 in the plating solution 60 to form a metal particle aggregate layer containing multiple metal particles 20 on the core particle 10 can be performed in essentially the same way as electroless plating (chemical plating) using a plating bath. There are no particular limitations on the temperature at which the core particle 10 is immersed in the plating solution 60; for example, it can be 10°C or higher and 100°C or lower, preferably 15°C or higher and 60°C or lower, and more preferably 20°C or higher and 40°C or lower.

[0075] From the viewpoint of easily forming a layer of aggregated metal particles rather than a continuous metal film, and further from the viewpoint of easily and controllably forming a layer of aggregated metal particles with a better shape, it is preferable to keep the growth rate of the metal particles at an appropriate rate. Specifically, in the metal particle growth step, the average height growth rate of the metal particles at a time point 28 minutes after the start of metal deposition on the surface of the core particle 10 is preferably 6 nm / min or less, more preferably 5 nm / min or less, more preferably 4 nm / min or less, and more preferably 3.5 nm / min or less. If the ratio VS / VL is within the aforementioned range, it is easy to control the average height growth rate at a time point 28 minutes after the start of metal deposition within the aforementioned range. Considering the mass production of composite particles, this average height growth rate is typically 1 nm / min or more, preferably 2 nm / min or more.

[0076] Regarding the average height growth rate of the metal-based particles at a time point 28 minutes after the start of metal deposition on the surface of the self-oriented core particle 10, for example, the same metal-based particle growth steps except for ending the reaction within 28 minutes (e.g., filtration separation) can be performed as a preliminary experiment, and the average height obtained in the preliminary experiment can be measured.

[0077] The phrase "starting metal deposition on the surface of core particle 10" refers to the immersion of core particle 10 when the core particle 10 is immersed in a plating solution 60 containing metal cations and a reducing agent to start the metal-based particle growth step, and when the core particle 10 is immersed in a metal cation solution containing metal cations and then a reducing agent (e.g., a reducing agent solution) is added.

[0078] From the perspective of easily forming a layer of aggregated metal particles rather than a continuous metal film, and further from the perspective of easily and controllably forming a layer of aggregated metal particles with a better shape, the metal particle growth steps are preferably to satisfy the following equation (1). 10×10⁻⁷≦X≦600×10⁻⁷(1) If the ratio VS / VL is within the specified range, then the value of X can be easily controlled within the specified range. The value of X is preferably 30 × 10⁻⁷ or higher and 450 × 10⁻⁷ or lower, and more preferably 40 × 10⁻⁷ or higher and 300 × 10⁻⁷ or lower.

[0079] When the core particle 10 is spherical, X is represented by the following formula. [Formula 1] In the formula, a represents the concentration of metal cations in plating solution 60 (mol / L), V represents the volume of plating solution 60 (L), D represents the atomic weight of the metal (0 valence) produced by the reduction of metal cations, B represents the number of core particles 10, C represents the specific gravity of the metal (0 valence) produced by the reduction of metal cations (g / cm 3), and R represents the radius of core particles 10 (cm).

[0080] When the core particle 10 is amorphous, X is represented by the following formula. [Formula 2] In the formula, a, V, D, and C have the same meanings as described above. S represents the total surface area of ​​the core particles 10.

[0081] The number of core particles 10, B, can be calculated from the total weight of the particles, mp, and the density of the particles, Vp, according to the following formula. [Formula 3] In the formula, R represents the same meaning as described above. The radius R (cm) of the core particle 10 is half the average particle size of the core particle 10 as determined above.

[0082] The total surface area S of the core particles 10 can be obtained by measuring the specific surface area using the Brunauer-Emmett-Teller (BET) method and multiplying it by the total weight mp of the particles.

[0083] The term "spherical core particle 10" refers to the fact that, using the same method to acquire SEM images, the tangent diameters of the five core particles used are all ±30% of the average tangent diameter (i.e., above 70% and below 130% of the average particle size of core particle 10). The term "amorphous" refers to a shape that is not spherical.

[0084] By means of plating, a metal-based particle aggregate layer containing multiple metal-based particles 20 can be formed controllably on the surface of the core particle 10. Furthermore, a metal-based particle aggregate layer with a better shape can be formed controllably on the surface of the core particle 10. In addition, by means of plating, a metal-based particle aggregate layer can be easily formed across the entire surface of the core particle 10. Therefore, according to the plating method, the mass production capability of composite particle manufacturing can be improved.

[0085] It is preferable to appropriately control the time of the metal-based particle growth step, that is, the time for the core particle 10 to grow in the plating solution 60. If this time is too long, a metal-based particle aggregate layer containing multiple metal-based particles 20 will not be formed, and a continuous metal film will not be formed. There is a tendency that the longer the time, the larger the average particle size and average height of the metal-based particles, and the smaller the average interparticle distance. The appropriate time for the metal-based particle growth step is preferably determined in advance through preliminary experiments before actually carrying out the metal-based particle growth step.

[0086] (3) Heat treatment steps Alternatively, after the metal-based particle growth step, a heat treatment step can be performed on the core particles carrying the metal-based particles. Through heat treatment, the uniformity of the metal-based particle loading or the distribution of metal-based particles can be achieved, excess metal-based particle material can be evaporated, and the shape of the metal-based particles can be adjusted (increasing particle size and homogenizing height).

[0087] The heat treatment temperature also depends on the material of the metallic particles, preferably above 150°C and below 550°C, more preferably above 200°C and below 500°C, even more preferably above 250°C and below 450°C, even more preferably above 300°C and below 450°C, and most preferably 400°C or around (approximately 400°C ± 10°C).

[0088] (4) Steps for forming a protective layer In the case of manufacturing composite particles that include a protective layer, the step of forming a protective layer is performed after the metal-based particle growth step. The protective layer is formed to at least cover the surfaces of multiple metal-based particles on the surface of the core particle. Regarding the structure, material, etc., of the protective layer, please refer to the description in the <Composite Particles> section.

[0089] One method for forming a protective layer is as follows: A liquid containing a protective layer material is spin-coated onto particles (composite particles without a protective layer) that consist of a core particle and a metal-based particle aggregate layer placed on a substrate. The composite particles without a protective layer can be electrostatically adsorbed onto the substrate.

[0090] Other methods for forming a protective layer include: dry film formation methods such as sputtering (which can be powder sputtering), vapor deposition (which can be powder vapor deposition), and CVD (which can be powder CVD); and wet methods such as dispersing composite particles without a protective layer in a liquid containing a material that forms a protective layer, thereby forming a protective layer on the surface of the composite particles.

[0091] A preferred example of a wet process is the sol-gel method. The sol-gel method involves obtaining the corresponding metal oxide by starting with a solution containing a metal alkoxide or similar raw material, followed by hydrolysis and polymerization reactions. An example of the sol-gel method is the Stober process (the "o" in Stober refers to the vowel "o" (Umlaut). The same applies below). According to this method, tetraethyl orthosilicate is used as a raw material, and the reaction is carried out in an ethanol solvent in the presence of water and ammonia as a catalyst to obtain silicon dioxide (SiO₂). For more information on the Stober process, see W. Stober and A. Fink, *Journal of Colloid and Interface Science*, 26(1), 62-69 (1968).

[0092] The Stobber method allows the formation of a SiO2 layer as a protective layer on composite particles containing a core particle and a metal-based particle aggregate layer. Specifically, the reaction of tetraethyl orthosilicate, etc., as a raw material is carried out in a solution containing a solvent such as an alcohol, water, and ammonia as a catalyst in the presence of the composite particles containing the core particle and the metal-based particle aggregate layer, thereby forming a SiO2 layer on the composite particles.

[0093] The reaction temperature can be appropriately selected, for example, above 0°C and below 100°C, preferably above 10°C and below 60°C. Furthermore, if the reaction solution is ultrasonically treated during the reaction, the coating based on the protective layer tends to become more uniform.

[0094] The thickness of the protective layer depends on the amount of raw material (such as metal alkoxides) relative to the composite particles in the reaction solution, which include the core particles and the metal-based particle aggregate layer. The ratio of the volume of the raw material VG [cm³] to the volume of the composite particles in the reaction solution, VL² [cm³], VG / VL², is, for example, 15 or less, preferably 9 or less, and more preferably 6 or less. This ratio is typically 0.1 or more. There is a tendency to increase the thickness of the protective layer as this ratio increases.

[0095] Raw materials that can be used to form a protective layer containing metal oxides by the sol-gel method are not limited to tetraethyl orthosilicate; for example, methyltrimethoxysilane can also be used.

[0096] <Another implementation method for composite particles> The composite particle of this embodiment includes: a core particle; a metallic material layer disposed on at least a portion of the surface of the core particle; and a protective layer covering the surface of the metallic material layer. Regarding the core particle and the protective layer in the composite particle of this embodiment, the description in the <Composite Particle> section is referenced. Preferably, the metallic material layer covers the entire surface of the core particle. Preferably, the protective layer covers the entire surface of the metallic material layer.

[0097] The metallic material layer included in the composite particles of this embodiment may be, for example, a metallic particle aggregate layer comprising a plurality of metallic particles arranged separately from each other, as described in the "composite particles" section, or it may be a continuous film comprising a metallic material. Examples of metallic materials constituting metallic particles include those described below. Regarding the metallic particle aggregate layer, the description in the "composite particles" section is cited.

[0098] The thickness of the metallic material layer as a continuous film is, for example, 5 nm or more and 500 nm or less, preferably 5 nm or more and 200 nm or less, and even more preferably 5 nm or more and 50 nm or less.

[0099] The thickness of the metallic material layer was measured using the following method. A cross-sectional image of the composite particle was acquired using a scanning electron microscope (JSM-5500) manufactured by Nippon Electronics Co., Ltd., or an equivalent device. Ten points on the outer contour surface of the core particle were randomly selected from the acquired cross-sectional image. Then, straight lines were drawn from each of these ten points in the manner that the shortest distance to the outer surface of the metallic material layer was obtained. The average length of these ten straight lines was taken as the thickness of the metallic material layer.

[0100] Composite particles comprising a metallic material layer as a continuous film can be used, for example, as light-scattering particles. In this case, the composite particles are used in various components requiring light scattering properties.

[0101] According to the composite particles of this embodiment, which include a protective layer on a metallic material layer, the stability (oxidation resistance, etc.) and environmental stability (e.g., light resistance, humidity resistance, heat resistance, etc.) of the composite particles (core particles and / or metallic particles) can be improved.

[0102] <Sensor Components> The sensor element of the present invention (hereinafter also simply referred to as "sensor element") is a sensor element for detecting a substance to be detected, comprising: a substrate; composite particles disposed on the substrate; and a trapping portion disposed on the composite particles, having a trapping substance specifically bonded to the substance to be detected.

[0103] The composite particles included in the sensor element comprise a core particle and a layer of metallic particle aggregates disposed on at least a portion of the surface of the core particle. The metallic particle aggregate layer is a collection of multiple metallic particles carried on the core particle, and is a layer comprising multiple metallic particles disposed separately from each other. The composite particle may further comprise a protective layer at least covering the surface of the multiple metallic particles. The composite particles of the present invention can be used as composite particles. For details regarding the specific structure of the composite particles used in the sensor element, the core particle, the metallic particle aggregate layer, and the material of the metallic particles, please refer to the description in the <Composite Particles> section.

[0104] Figure 5 is a schematic cross-sectional view illustrating an example of a sensor element. The sensor element shown in Figure 5 includes: a substrate 70 having a recess 71 on its surface; the composite particle 2 of the present invention disposed on the substrate 70, and more specifically disposed within the recess 71; and a trapping portion 80 disposed on the composite particle 2, having a trapping substance specifically bonded to the detected substance 90. In the example shown in Figure 5, the trapping portion 80 is disposed on a protective layer of the composite particle 2, but composite particles without a protective layer may also be used, with the trapping portion 80 disposed on the core particle and / or on a metal-based particle aggregate layer.

[0105] Figure 5 schematically shows the state in which the labeled (tagged) substance 90 is captured by the capturing unit 80. 91 in Figure 5 indicates a mark bonded to the substance 90. A luminescent body can be listed as an example of such a mark.

[0106] The sensor element detects the substance 90 as follows. The detection can be qualitative or quantitative, such as the identification or quantification of the substance 90. When excitation light is shone onto the labeled substance 90, which is specifically bonded to the composite particle 2, the marker acting as a luminescent body is excited. Then, the metallic particle aggregate layer of the composite particle 2 resonates with the excited luminescent body, exhibiting enhanced plasma luminescence. By detecting the luminescence from the excited luminescent body using a detector, the substance 90 can be detected qualitatively or quantitatively. For example, by measuring the luminescence intensity, the amount of the substance 90 present can be determined qualitatively or quantitatively.

[0107] According to the sensor element including the composite particles of the present invention, the composite particles contain a metal-based particle aggregate layer, thereby exhibiting plasma luminescence enhancement and thus improving detection sensitivity and detection accuracy. For example, it is also possible to arrange the metal particle aggregate layer on the bottom surface of the recess 71 of the substrate 70, and to arrange particles without the metal particle aggregate layer (equivalent to core particles) in the recess 71 instead of composite particles. However, in this case, if the particle size of the particles including the capturing portion on the surface is large (e.g., in the case of micrometers), the labeled detection substance 90 is too separated from the metal particle aggregate layer, and there is a risk that the plasma luminescence enhancement effect cannot be obtained. In contrast, by using composite particles containing a metal-based particle aggregate layer as particles arranged in the recess 71, the distance between the labeled detection substance 90 and the metal particle aggregate layer is shortened, thereby obtaining the plasma luminescence enhancement effect.

[0108] Furthermore, composite particles with a metallic particle aggregate layer disposed on the surface of the core particle, and composite particles with a protective layer disposed on the surface of the particle, can have surface irregularities or be manufactured with surface irregularities. Composite particles with surface irregularities have a larger surface area. Therefore, by using such composite particles as the particles, a large amount of the captured substance, and thus the substance 90 to be detected, can be bonded to the surface of the composite particles. This also helps to improve detection sensitivity and detection accuracy.

[0109] The substance being detected (90) is the substance that is targeted for qualitative or quantitative detection, and is specifically bound to the target substance. There are no particular limitations on the substance being detected (90), and examples include: nucleosides, nucleotides, nucleic acids, proteins, carbohydrates, glycoproteins, lectins, viruses, cells, antibodies, exosomes, etc. Sensor elements whose substance being detected (90) is of biological origin or biologically related are also called biosensor elements.

[0110] Nucleic acids are polymers (nucleotide chains) of phosphate esters of nucleosides formed by glycosidic bonds between purine or pyrimidine bases and sugars. These include oligonucleotides containing deoxyribonucleic acid (DNA), polynucleotides, DNA (full-length or fragments thereof) formed by the polymerization of purine and pyrimidine nucleotides, ribonucleic acid (RNA), and polyamide nucleotide derivatives (peptide nucleic acid, PNA), etc. Furthermore, nucleosides are compounds formed by glycosidic bonds between bases and sugars, nucleotides are compounds formed by phosphate bonds between nucleosides, and both nucleosides and nucleotides are compounds containing bases.

[0111] The term "specific bond" broadly refers to chemical bonds that include non-covalent bonds, covalent bonds, and hydrogen bonds between substances, such as the interactions between protein molecules and the electrostatic interactions between molecules.

[0112] The detection of the captured substance 90 can be performed by pre-labeling the substance 90 with a marker 91, which serves as a luminescent material, and then detecting the luminescence emitted from the marker 91. The marker 91 can also be a marker material specifically bonded to a complex obtained through a specific bond between the captured substance and the substance 90. A luminescent material is a substance that emits light by the injection of excitation energy from excitation light. The luminescence principle of a luminescent material is not limited; examples include fluorescence, phosphorescence, and chemiluminescence. Previously known luminescent materials can be used.

[0113] The capturing substance constituting the capturing section 80 is a substance that functions to capture the target substance 90 by specifically bonding with it. The capturing substance may be, for example, fixed to the surface of the composite particles. The capturing substance may be, for example, a substance having a bonding active group that can specifically bond with the target substance 90. Examples of bonding active groups include carboxyl groups, hydroxyl groups, etc., which can electrostatically interact with the target substance 90. There are no particular limitations on the capturing substance; examples include nucleosides, nucleotides, nucleic acids, proteins, sugars, glycoproteins, etc.

[0114] The substrate 70, which is used as a sensing element, can be made of materials such as silicon, quartz, synthetic quartz, glass, and thermoplastic resin. The composite particles are not necessarily limited to the recesses 71 of the substrate 70, as long as they are arranged in a form that allows them to be fixed or housed on the substrate 70. The substrate 70 may have one or more recesses 71. Examples of substrate 70 include flow cells and microarrays.

[0115] According to the sensor element of the present invention, since it contains composite particles with a wide range of local plasma resonance, the luminescence from the marker 91 can be enhanced even if the distance from the metal-based particle aggregate layer of the composite particles to the marker 91 is a long distance of more than 10 nm. For example, the size of DNA, which can be used as the detected substance 90, can be several nanometers to tens of nanometers, or 5 nm to 15 nm. For example, the size of a virus can be tens to hundreds of nanometers, or 30 nm to 120 nm. In the case of the detected substance 90, the distance between the marker 91 bonded thereto and the metallic particle aggregate layer can be, for example, tens to hundreds of nanometers. Even in this case, the sensor element according to the present invention can enhance the luminescence from the marker 91.

[0116] The distance from the metallic particle aggregate layer to marker 91 can be 15 nm or more, then 25 nm or more, or even more. From the viewpoint of the sensitivity of the sensor element, this distance is preferably 200 nm or less, more preferably 170 nm or less, and even more preferably 150 nm or less.

[0117] The maximum wavelength of the plasma peak in the metallic particle aggregate layer is preferably the same as or close to the emission wavelength of the marked 91. This can more effectively enhance the luminescence enhancement effect brought about by plasma resonance. The maximum wavelength of the plasma peak in the metallic particle aggregate layer can be controlled by adjusting the metal type, average particle size, average height, aspect ratio, average interparticle distance, and / or the standard deviation of the average interparticle distance of the metallic particles constituting it.

[0118] A sensing device including the sensing element of the present invention typically includes, in addition to the sensing element, a light source that emits excitation light for exciting the mark 91, and a detector that detects the emission from the mark 91. The light source and detector may be disposed on different sides or on the same side, with reference to the substrate 70. In one embodiment, the light source is disposed above the substrate 70 (above or to the side of the marked detection substance 90 in FIG. 5), and the detector is disposed below the substrate 70 (back side), that is, disposed on the side opposite to the light source or on the same side as the light source, with reference to the substrate 70. When the detector is disposed below the substrate 70 (back side), the substrate 70 is preferably light-transmitting, and more preferably optically transparent. The light-transmitting substrate 70 preferably has a light transmittance of 80% or more, and more preferably 90% or more, for light to be transmitted therethrough.

[0119] When detecting emission, if there is a risk of excitation light being mixed in, it is preferable to allow the emission light to pass through a wavelength cutoff filter that cuts off the wavelength of the excitation light before it enters the detector.

[0120] Examples of sensing devices include DNA sequencers, DNA microarrays, virus sensors, ion sensors, plate readers (protein wafers, glycan wafers, lectin wafers, etc.), microspectral analyzers, glucose sensors, and other biosensor devices.

[0121] Furthermore, when the composite particles of the present invention are used in a sensor, the composite particles may also be used without being fixed to a substrate. Examples of such use include their application in flow cytometers, or methods of dispersing the composite particles in a liquid medium and bonding the labeled analyte 90 to the dispersed composite particles for analysis. [Example]

[0122] The present invention will be described in more detail below with reference to specific embodiments, but the present invention is not limited to these embodiments.

[0123] <Example 1> (1) Steps for growing metallic particles Silicon dioxide powder (Shin-Etsu Silicone Corporation's "X-52-7042", a group of spherical particles with an average particle size of 4 μm) is electrostatically adsorbed onto a glass substrate. The glass substrate is then guided into a DC magnetron sputtering apparatus with the adsorbed silicon dioxide powder on the glass substrate pointing vertically downwards. Using the DC magnetron sputtering apparatus, under the following conditions, silver particles are grown very slowly on the surface of heated silica powder, forming a metallic particle aggregate layer across the entire surface of the silica powder, thereby obtaining composite particles.

[0124] Gas used: Argon Chamber pressure (sputtering gas pressure): 10 Pa Distance between substrate and target: 100 mm Sputtering power: 4 W Average particle size growth rate of silver particles (average particle size / sputtering time): 0.87 nm / min Average height growth rate of silver particles (=average deposition rate=average height / sputtering time): 0.16 nm / min Heating temperature of silicon dioxide powder: 300℃ Sputtering time: 360 minutes

[0125] (2) Steps for heat treatment The composite particles obtained in step (1) are heat-treated in the atmosphere at 400°C for 1 minute.

[0126] Figure 6 is a SEM image (11000x magnification) of the obtained composite particles (after heat treatment). In this specification, including this SEM image, a JSM-5500 scanning electron microscope manufactured by NJE Inc. was used to acquire the SEM images.

[0127] Based on the SEM image, in the composite particles of Example 1, the average particle size of the silver particles constituting the metal-based particle aggregate layer of the core particles was determined to be 312.4 nm, the average interparticle distance was 30.7 nm, and the standard deviation of the average interparticle distance was 18.6 nm, based on the definition described. Furthermore, based on images taken using an atomic force microscope (AFM) manufactured by Keyence (VN-8010), the average height of the silver particles was determined to be 57.9 nm. Therefore, the aspect ratio (average particle size / average height) of the silver particles was calculated to be 5.4.

[0128] Furthermore, the average particle size (4 μm) of the silicon dioxide powder used as the core particles was determined according to the method for measuring the average particle size of the core particle group.

[0129] <Example 2> The composite particles obtained in Example 1 are electrostatically adsorbed onto a glass substrate. Then, a spin-on-glass (SOG) solution is spin-coated onto the glass substrate with the adsorbed composite particles, and a protective layer is deposited on the composite particles to obtain composite particles containing a protective layer. The SOG solution used is a solution prepared by diluting "OCD T-7 5500T" manufactured by Tokyo Ohka Kogyo Co., Ltd., which is an organic SOG material, with ethanol.

[0130] Figure 7 is a SEM image (10,000x scale) of the obtained composite particles containing the protective layer. Based on this SEM image, it can be confirmed that a protective layer is formed across the entire surface of the composite particles obtained in Example 1. It is confirmed that the protective layer is formed not only on the surface of the silver particles in the metallic particle aggregate layer, but also in the gaps between the silver particles (the exposed core particles).

[0131] <Comparative Example 1> The core particles (silicon dioxide powder) used in Example 1 were used as the particles of Comparative Example 1.

[0132] (Evaluation of the enhancement effect on fluorescence intensity) The composite particles obtained in Example 1 were electrostatically adsorbed onto a glass substrate. Then, a rhodamine B solution was spin-coated onto the glass substrate with the adsorbed composite particles at 2000 rpm for 100 seconds, thereby loading rhodamine B as a fluorescent pigment onto the surface of the composite particles. This was designated as sample 1. The rhodamine B solution used was a 0.15 mM solution prepared by dissolving Rhodamine B (manufactured by Exciton) in ethanol.

[0133] Additionally, using the same method described above, rose red B, a fluorescent pigment, was loaded onto the surface of the particles of Comparative Example 1. This was designated as measurement sample 2.

[0134] For Sample 1 and Sample 2, the fluorescence intensity emitted by Rose Red B (Sample 1) loaded with composite particles and Rose Red B (Sample 2) loaded with silicon dioxide particles was measured using a fluorescence microscope (Olympus FV1000) when irradiated with laser light.

[0135] The conditions for measuring fluorescence intensity are as follows. Laser excitation wavelength: 559 nm Detection conditions: Cy5 Objective lens: 40x

[0136] In the fluorescence image obtained by measuring sample 1, five composite particles that are not in contact with other composite particles are randomly selected, and the average value of their "INT" values ​​is calculated. The value obtained by subtracting the background value from the average value is set as fluorescence intensity 1. Similarly, the fluorescence intensity obtained by measuring sample 2 is set as fluorescence intensity 2. Composite particles that are not in contact with other composite particles (sample 1) and silica particles that are not in contact with other silica particles (sample 2) are selected because, especially when silica particles, which are transparent particles, are in contact with each other, the fluorescence intensity becomes uneven due to mutual retroreflection of excitation light or emission light within the particles.

[0137] The background value was determined as follows. For an untreated glass substrate (the same glass substrate used in test sample 1 and test sample 2), an image was obtained by measuring the fluorescence intensity under the same conditions. Five points were randomly selected from the image, and the average value of their "INT" values ​​was calculated. This average value was then set as the background value.

[0138] Fluorescence intensity 1 is approximately 5.1 times that of fluorescence intensity 2. Figure 8 shows an image obtained from the fluorescence intensity measurement of sample 1, and Figure 9 shows an image obtained from the fluorescence intensity measurement of sample 2.

[0139] <Example 3> Add 0.25 mL of 0.05 mol / L potassium hydroxide (KOH) aqueous solution to 50 mL of 0.047 mol / L silver nitrate (AgNO3) aqueous solution and stir. The solution changes from colorless and transparent to brown upon addition of potassium hydroxide. Then, while stirring, add 50 μL each of 3.5 mol / L ethylenediamine (NH2CH2CH2NH2) aqueous solution to the solution until it becomes colorless and transparent. Designate the resulting solution as silver ion solution A.

[0140] 16.6 mL of a 0.06 mol / L glucose aqueous solution was mixed with 8.4 mL of methanol to obtain reducing agent solution B. Silver ion solution A was added to the tank, followed by 200 mg of silicon dioxide powder (Fine Sphere SK-30 manufactured by Nippon Electric Glass Co., Ltd., a group of spherical particles with an average particle size of 3 μm) as core particles. Then, after adding reducing agent solution B to the tank, the liquid in the tank was immediately stirred to immerse the core particles in the plating solution containing silver ion solution A and reducing agent solution B, initiating the growth of silver-containing metallic particles on the surface of the core particles. The preparation of the plating solution and the immersion of the core particles in the plating solution were carried out at 25°C. Stirring was maintained at 25°C. Twenty-eight minutes after the start of impregnation, the core particles (composite particles) with the metal particle aggregate layer are filtered and separated. The filtered material is then washed with a 1:1 volume ratio mixture of acetone and ultrapure water. The supernatant is removed by centrifugation and then dried at 80°C to obtain composite particles.

[0141] <Example 4> The concentration of the reducing agent and the ratio (percentage) of the reducing agent concentration to the saturation concentration were changed to the values ​​shown in Table 1. Otherwise, the metal-based particle growth steps were performed in the same manner as in Example 3 to obtain composite particles.

[0142] <Comparative Example 2> The core particles (silicon dioxide powder) used in Example 3 were the same as those in Comparative Example 2. Furthermore, the average particle size (3 μm) of the silicon dioxide powder used as the substrate was determined according to the method for measuring the average particle size of the particle group.

[0143] Regarding Examples 3 and 4, Table 1 shows the concentration of silver ions in the plating solution, the type of reducing agent, the concentration of the reducing agent, the ratio of the reducing agent concentration to the saturation concentration (percentage), the immersion time of the core particles in the plating solution, the ratio of the core particle volume VS [cm 3] to the plating solution volume VL [cm 3] VS / VL, and the average height growth rate of the metal-based particles at the time point 28 minutes after the start of metal deposition. In Examples 3 and 4, where silicon dioxide powder, which is spherical, is used as the core particle, the value of X calculated according to the formula is 121 × 10⁻⁷.

[0144] Figures 10 and 11 are SEM images of the composite particles obtained in Example 3 (Figure 10: 6000x scale, Figure 11: 35000x scale), and Figure 12 is an SEM image of the composite particles obtained in Example 4 (20000x scale).

[0145] Based on the SEM images, the average particle size and average interparticle distance of the silver particles constituting the metal-based particle aggregate layer of the core particles were determined according to the definition described above. Additionally, the average height of the silver particles was determined according to the definition described above based on the scanning transmission electron microscope (STEM) cross-sectional image (100,000x magnification). A Helios G4 UX scanning transmission electron microscope manufactured by FEI Corporation was used to acquire the SEM cross-sectional image. The aspect ratio of the silver particles was calculated based on the obtained average particle size and average height. The results are shown in Table 1. Furthermore, regarding the composite particles of Example 4, although SEM images were acquired (Fig. 12), the average particle size and average interparticle distance were not determined. As shown in Fig. 12, the metal-based particle aggregate layer of the composite particles of Example 4 contains multiple metal-based particles arranged separately, but compared to the composite particles of Example 3, there are a large number of portions where the metal-based particles are bonded together to form a continuous film.

[0146] [Table 1] Example 3 4 Metal-based particle growth steps Plating solution silver ion concentration mol / L 0.031 0.031 Types of reducing agents - glucose glucose concentration of reducing agent mol / L 0.0133 0.0421 concentration of reducing agent The ratio relative to the saturation concentration % 0.50 1.59 Immersion time of core particles in plating solution minute 28 28 VS / VL - 0.0012 0.0121 Average height growth rate nm / min 3.2 4.1 Physical properties of metallic particle aggregate layers Average particle size nm 304.6 - average height nm 89.7 114.0 Aspect Ratio - 3.40 - Average interparticle distance nm 36.0 -

[0147] (Evaluation of the enhancement effect on fluorescence intensity) After spin-coating a glass substrate with a glass spin-coating (SOG) solution at 3000 rpm, the composite particles obtained in Example 3 were placed on the SOG coating. The SOG coating was then dried at 200°C to fix the composite particles. The SOG solution used was "OCD T-7 5500T" manufactured by Tokyo Ohka Kogyo Co., Ltd., an organic SOG material.

[0148] Next, the Rhodamine B solution was spin-coated onto the surface of the composite particles at 2000 rpm for 100 seconds, thereby loading Rhodamine B as a fluorescent pigment onto the surface of the composite particles. This was designated as sample 3. The Rhodamine B solution used was a 0.15 mM solution prepared by dissolving Rhodamine B manufactured by Exciton in ethanol.

[0149] Additionally, using the same method described above, rose red B, a fluorescent pigment, was loaded onto the surface of the particles of Comparative Example 2. This was designated as measurement sample 4.

[0150] For samples 3 and 4, the fluorescence intensity emitted by rose red B loaded with composite particles (sample 3) and rose red B loaded with silicon dioxide particles (sample 4) under laser irradiation was measured using a fluorescence microscope (Olympus FV1000). The fluorescence intensity was measured under the same conditions as described above.

[0151] In the fluorescence image obtained by measuring sample 3, ten composite particles that are not in contact with other composite particles are randomly selected, and the average value of their "INT" values ​​is calculated. The value obtained by subtracting the background value from the average value is set as fluorescence intensity 3. Similarly, the fluorescence intensity obtained by measuring sample 4 is set as fluorescence intensity 4. Composite particles that are not in contact with other composite particles (sample 3) and silica particles that are not in contact with other silica particles (sample 4) are selected because, especially when silica particles, which are transparent particles, are in contact with each other, the fluorescence intensity becomes uneven due to mutual regressive reflection of excitation light or emission light within the particles.

[0152] The background value was determined as follows. For an untreated glass substrate (the same glass substrate used in test samples 3 and 4), fluorescence intensity was measured under the same conditions to obtain an image. Ten points were randomly selected from the image, and the average value of their "INT" values ​​was calculated. This average value was then set as the background value.

[0153] Fluorescence intensity 3 is 19.7 times that of fluorescence intensity 4. Figure 13 is an image obtained from the fluorescence intensity measurement of sample 3, and Figure 14 is an image obtained from the fluorescence intensity measurement of sample 4.

[0154] <Example 5> A solution was prepared by dissolving 1188 μL of a 25% by mass ammonia (NH3) aqueous solution in 5000 μL of ethanol. The solution was heated to 50°C, and at this temperature, 24.8 mg of the composite particles obtained in Example 3 and 32.4 μL of tetraethyl orthosilicate were added with stirring to prepare a reaction solution. The reaction solution was ultrasonically treated while continuously stirred at 50°C for 4 hours. The supernatant was removed using a centrifuge, followed by washing with water and drying at 80°C to obtain composite particles with a protective layer containing SiO2 formed on the metal-based particle aggregate layer. The ratio of the volume of tetraethyl orthosilicate (VG) [cm3] to the volume of the composite particles containing the core particles and the metal-based particle aggregate layer (VL2) [cm3] in the reaction solution (VG / VL2) was 2.87.

[0155] Figures 15 and 16 are SEM images of the obtained composite particles containing the protective layer (Figure 15: 7000x scale, Figure 16: 30000x scale). Based on these SEM images, it can be confirmed that a protective layer is formed across the entire surface of the composite particles obtained in Example 3. It is confirmed that the protective layer is formed not only on the surface of the silver particles in the metallic particle aggregate layer, but also in the gaps between the silver particles (the exposed core particles). Furthermore, it is confirmed that the surface of the protective layer follows the unevenness of the metallic particle aggregate layer.

[0156] Figure 17 is a STEM cross-sectional image (100,000x magnification) of the composite particles containing the protective layer. The STEM cross-sectional image was acquired using a Helios G4 UX scanning transmission electron microscope manufactured by FEI Corporation. Based on this image, a roughly uniform protective layer with a thickness of approximately 60 nm to 70 nm was confirmed to have formed.

[0157] <Example 6> Add 0.75 mL of 0.05 mol / L potassium hydroxide (KOH) aqueous solution to 150 mL of 0.047 mol / L silver nitrate (AgNO3) aqueous solution and stir. The solution changes from colorless and transparent to brown upon addition of potassium hydroxide. Then, while stirring, add 50 μL each of 3.5 mol / L ethylenediamine (NH2CH2CH2NH2) aqueous solution to the solution until it becomes colorless and transparent. Designate the resulting solution as silver ion solution A.

[0158] 50 mL of a 0.04 mol / L glucose aqueous solution was mixed with 25 mL of methanol to obtain reducing agent solution B. Silver ion solution A was added to the tank, followed by 240 mg of silicon dioxide powder (spherical particles with an average particle size of 1.1 μm manufactured by Nichibukai Chemical Co., Ltd.) as core particles. Then, after adding reducing agent solution B to the tank, the liquid was immediately stirred to immerse the core particles in the plating solution containing silver ion solution A and reducing agent solution B, initiating the growth of silver-containing metallic particles on the surface of the core particles. The preparation of the plating solution and the immersion of the core particles in the plating solution were carried out at 25°C. Stirring was maintained continuously at 25°C. Twenty-eight minutes after the start of impregnation, the core particles (composite particles) with the metal particle aggregate layer are filtered and separated. The filtered material is then washed with a 1:1 volume ratio mixture of acetone and ultrapure water. The supernatant is removed by centrifugation and then dried at 80°C to obtain composite particles.

[0159] <Example 7> Add 5 mL of 0.05 mol / L potassium hydroxide (KOH) aqueous solution to 666.7 mL of 0.0024 mol / L silver nitrate (AgNO3) aqueous solution and stir. The solution changes from colorless and transparent to brown upon addition of potassium hydroxide. Then, while stirring, add 50 μL each of 3.5 mol / L ethylenediamine (NH2CH2CH2NH2) aqueous solution to the solution until it becomes colorless and transparent. Designate the resulting solution as silver ion solution A.

[0160] 222.2 mL of a 0.006 mol / L glucose aqueous solution was mixed with 111.1 mL of methanol to obtain reducing agent solution B. Silver ion solution A was added to the tank, followed by 46.7 mg of silicon dioxide powder (spherical particles with an average particle size of 0.55 μm manufactured by Nichibukai Chemical Co., Ltd.) as core particles. After adding reducing agent solution B to the tank, the liquid was immediately stirred to immerse the core particles in the plating solution containing silver ion solution A and reducing agent solution B, initiating the growth of silver-containing metallic particles on the surface of the core particles. The preparation of the plating solution and the immersion of the core particles in the plating solution were carried out at 25°C. Stirring was maintained continuously at 25°C. Twenty-eight minutes after the start of impregnation, the core particles (composite particles) with the metal particle aggregate layer are filtered and separated. The filtered material is then washed with a 1:1 volume ratio mixture of acetone and ultrapure water. The supernatant is removed by centrifugation and then dried at 80°C to obtain composite particles.

[0161] <Example 8> Add 0.25 mL of 0.05 mol / L potassium hydroxide (KOH) aqueous solution to 50 mL of 0.047 mol / L silver nitrate (AgNO3) aqueous solution and stir. The solution changes from colorless and transparent to brown upon addition of potassium hydroxide. Then, while stirring, add 50 μL each of 3.5 mol / L ethylenediamine (NH2CH2CH2NH2) aqueous solution to the solution until it becomes colorless and transparent. Designate the resulting solution as silver ion solution A.

[0162] 16.6 mL of a 0.06 mol / L glucose aqueous solution was mixed with 8.4 mL of methanol to obtain reducing agent solution B. Silver ion solution A was added to the tank, followed by 362 mg of alumina powder (Advanced Alumina AA-3 manufactured by Sumitomo Chemical Co., Ltd., with an average particle size of 3 μm amorphous particles) as core particles. After adding reducing agent solution B to the tank, the liquid was immediately stirred to immerse the core particles in the plating solution containing silver ion solution A and reducing agent solution B, initiating the growth of silver-containing metallic particles on the surface of the core particles. The preparation of the plating solution and the immersion of the core particles in the plating solution were carried out at 25°C. Stirring was maintained at 25°C. Twenty-eight minutes after the start of impregnation, the core particles (composite particles) with the metal particle aggregate layer are filtered and separated. The filtered material is then washed with a 1:1 volume ratio mixture of acetone and ultrapure water. The supernatant is removed by centrifugation and then dried at 80°C to obtain composite particles.

[0163] <Example 9> A solution was prepared by dissolving 1188 μL of a 25% by mass ammonia (NH3) aqueous solution in 5000 μL of ethanol. The solution was heated to 50°C, and at this temperature, 24.8 mg of the composite particles obtained in Example 3 and 5.0 μL of tetraethyl orthosilicate were added with stirring to prepare a reaction solution. The reaction solution was ultrasonically treated while continuously stirred at 50°C for 4 hours. The supernatant was removed using a centrifuge, and the mixture was then washed with water and dried at 80°C to obtain composite particles with a protective layer containing SiO2 formed on the metal-based particle aggregate layer. The ratio of the volume of tetraethyl orthosilicate (VG) [cm3] to the volume of the composite particles containing the core particles and the metal-based particle aggregate layer (VL2) [cm3] in the reaction solution (VG / VL2) was 0.443.

[0164] STEM cross-sectional images were obtained in the same manner as in Example 5. Based on these images, a protective layer with a thickness of approximately 20 nm was confirmed to have been formed in a substantially uniform manner.

[0165] <Example 10> A solution was prepared by dissolving 1188 μL of a 25% by mass ammonia (NH3) aqueous solution in 5000 μL of ethanol. The solution was heated to 50°C, and at this temperature, 24.8 mg of the composite particles obtained in Example 3 and 15.0 μL of tetraethyl orthosilicate were added with stirring to prepare a reaction solution. The reaction solution was ultrasonically treated while continuously stirred at 50°C for 4 hours. The supernatant was removed using a centrifuge, and the mixture was then washed with water and dried at 80°C to obtain composite particles with a protective layer containing SiO2 formed on the metal-based particle aggregate layer. The ratio of the volume of tetraethyl orthosilicate (VG) [cm3] to the volume of the composite particles containing the core particles and the metal-based particle aggregate layer (VL2) [cm3] in the reaction solution (VG / VL2) was 1.33.

[0166] STEM cross-sectional images were obtained in the same manner as in Example 5. Based on these images, a protective layer with a thickness of approximately 85 nm was confirmed to have been formed in a substantially uniform manner.

[0167] <Example 11> A solution was prepared by dissolving 1188 μL of a 25% by mass ammonia (NH3) aqueous solution in 5000 μL of ethanol. The solution was heated to 50°C, and at this temperature, 24.8 mg of the composite particles obtained in Example 3 and 32.4 μL of tetraethyl orthosilicate were added with stirring to prepare a reaction solution. The reaction solution was ultrasonically treated while continuously stirred at 50°C for 4 hours. The supernatant was removed using a centrifuge, followed by washing with water and drying at 80°C to obtain composite particles with a protective layer containing SiO2 formed on the metal-based particle aggregate layer. The ratio of the volume of tetraethyl orthosilicate (VG) [cm3] to the volume of the composite particles containing the core particles and the metal-based particle aggregate layer (VL2) [cm3] in the reaction solution (VG / VL2) was 2.87.

[0168] STEM cross-sectional images were obtained in the same manner as in Example 5. Based on these images, it was confirmed that a protective layer with a thickness of approximately 110 nm was formed in a substantially uniform manner.

[0169] For Examples 6 to 8, Table 2 shows the concentration of silver ions in the plating solution, the type of reducing agent, the concentration of the reducing agent, the ratio of the concentration of the reducing agent to the saturation concentration (percentage), the immersion time of the core particles in the plating solution, the ratio of the volume of the core particles VS [cm 3] to the volume of the plating solution VL [cm 3] VS / VL, and the average height growth rate of the metal particles at the time point 28 minutes after the start of metal deposition. The values ​​of X for the core particles used in Examples 6 to 8, calculated according to the formula, are 101 × 10⁻⁷ for Example 6, 41 × 10⁻⁷ for Example 7, and 110 × 10⁻⁷ for Example 8.

[0170] Figures 18-22 are SEM images of the composite particles obtained in Examples 7-11, respectively. Based on the SEM images, the average particle size and average interparticle distance of the silver particles constituting the metallic particle aggregate layer coating the core particle were determined according to the aforementioned definition. Furthermore, the average height of the silver particles, based on the aforementioned definition, was determined based on the STEM cross-sectional images (100,000x magnification). A Helios G4 UX scanning transmission electron microscope manufactured by FEI Corporation was used to acquire the STEM cross-sectional images. The aspect ratio of the silver particles was calculated based on the obtained average particle size and average height. The results are shown in Table 2.

[0171] [Table 2] Example 6 7 8 Metal-based particle growth steps Plating solution silver ion concentration mol / L 0.031 0.0016 0.031 Types of reducing agents - glucose glucose glucose concentration of reducing agent mol / L 0.0089 0.00133 0.0133 concentration of reducing agent The ratio relative to the saturation concentration % 0.34 0.05 0.50 Immersion time of core particles in plating solution minute 28 28 28 VS / VL - 0.0005 0.00002 0.0012 Average height growth rate nm / min 2.5 3.9 3.0 Physical properties of metallic particle aggregate layers Average particle size nm 235.4 321.4 187.5 average height nm 71.3 110.6 83.0 Aspect Ratio - 3.30 2.91 2.26 Average interparticle distance nm 39.0 15.4 35.0

[0172] (Evaluation of the enhancement effect on fluorescence intensity) Using the same method as for the composite particles obtained in Example 3, the enhancement effect on fluorescence intensity of the composite particles of Examples 6, 8, 9, and 11 was evaluated. The results showed that the fluorescence intensity 3 of the composite particles of Examples 6, 8, 9, and 11 was 4.5 times, 1.3 times, 18 times, and 4.6 times that of the fluorescence intensity 4, respectively. The fluorescence intensity 4, as in the evaluation of the composite particles obtained in Example 3, is the fluorescence intensity emitted by the sample 4, which is formed by loading rose red B, a fluorescent pigment, onto the surface of the particles used as core particles in each example.

[0173] 1, 2: Composite particles 10: Core Particles 20: Metallic particles 30: Protective layer 50: slot 60: Plating solution 70:Substrate 71: Depression 80:Capture Department 90: Detected substance 91: Mark

Claims

1. A composite particle comprising: a core particle; and a metal-based particle aggregate layer disposed on at least a portion of the surface of the core particle, the metal-based particle aggregate layer comprising a plurality of metal-based particles disposed separately from each other, the core particle having a particle size of 0.5 μm or more, and the plurality of metal-based particles having a flat shape with an aspect ratio of more than 1.

2. The composite particles as claimed in claim 1, wherein the average particle size of the plurality of metal-based particles is 5 nm or more and 1600 nm or less.

3. The composite particle as claimed in claim 1, wherein the plurality of metallic particles are configured such that the average distance between them and their adjacent metallic particles is greater than 1 nm and less than 150 nm.

4. The composite particles as claimed in claim 3, wherein the standard deviation of the average distance is less than 50 nm.

5. The composite particle as claimed in claim 1, wherein the surface of the core particle comprises a curved surface.

6. The composite particle as claimed in claim 5, wherein the metallic particle aggregate layer is disposed at least on the curved surface.

7. The composite particles as described in any one of claims 1 to 6, wherein the core particles have a particle size of 0.5 μm or more but less than 10 μm.

8. The composite particle as claimed in any one of claims 1 to 6, wherein the metal-based particle aggregate layer is disposed over the entire surface of the core particle.

9. The composite particle as described in any one of claims 1 to 6 further comprises a protective layer covering at least the surface of the plurality of metallic particles.

10. The composite particles as claimed in claim 9, wherein the protective layer comprises an insulating material.

11. The composite particles as claimed in claim 9, wherein the thickness of the protective layer is 3 nm or more and 200 nm or less.

12. The composite particles as claimed in claim 9, wherein the protective layer covers the entire surface of the core particles and the metallic particles.

13. The composite particles as described in any one of claims 1 to 6, used in a sensor element.

14. A method for manufacturing composite particles, the composite particles comprising: a core particle; and a metallic particle aggregate layer disposed on at least a portion of the surface of the core particle, the metallic particle aggregate layer comprising a plurality of metallic particles disposed separately from each other, the method for manufacturing composite particles comprising: The step of growing the metal-based particles on the surface of the core particles, wherein the core particles have a particle size of 0.5 μm or more, and the plurality of metal-based particles have a flat shape with an aspect ratio of more than 1.

15. The method for manufacturing composite particles as claimed in claim 14, wherein after the growth step, a heat treatment step is further included.

16. A method for manufacturing composite particles as claimed in claim 14 or claim 15, wherein after the growth step, the method further includes a step of forming a protective layer covering at least the surface of the plurality of metallic particles.

17. A composite particle comprising: a core particle; a metallic material layer disposed on at least a portion of the surface of the core particle; and a protective layer covering the surface of the metallic material layer.

18. The composite particles as claimed in claim 17, wherein the protective layer comprises an insulating material.

19. The composite particles as claimed in claim 17 or claim 18, wherein the thickness of the protective layer is 3 nm or more and 200 nm or less.

20. A sensor element for detecting a substance to be detected, the sensor element comprising: a substrate; composite particles disposed on the substrate; and a trapping portion disposed on the composite particles, having a trapping substance specifically bonded to the substance to be detected, the composite particles comprising: a core particle; and a metal-based particle aggregate layer disposed on at least a portion of the surface of the core particle, the metal-based particle aggregate layer comprising a plurality of metal-based particles disposed separately from each other, the core particle having a particle size of 0.5 μm or more, and the plurality of metal-based particles having a flat shape with an aspect ratio of more than 1.

21. The sensor element of claim 20, wherein the composite particles further comprise a protective layer covering at least the surface of the plurality of metallic particles, and the capturing portion is disposed on the protective layer.

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