Patent Application
20070264154
Aspects included in the present invention will be described below in detail.
(Configuration of Chemical Sensor Element)
A chemical sensor element according to the present invention includes a substrate, metal-containing particles and dielectric particles, and these two kinds of particles are disposed on the substrate. The metal-containing particles are preferably disposed on the substrate in a uniform density.
The chemical sensor element can determine the properties of a liquid specimen by using a localized surface Plasmon resonance method. The properties of the liquid specimen are determined by measuring the refractive index around the metal-containing particles fixed to the chemical sensor element. Therefore, if a sensor element, wherein a substance with particular affinity for a specific substance (target substance) (target-capturing substance) is fixed to the metal-containing particles, is used, the specific substance (target substance) contained in a liquid specimen is held on the surfaces of the metal-containing particles, causing the refractive index of the surfaces of the metal-containing particles to change. In other words, the chemical sensor element according to the present invention can be favorably used for the detection of a specific substance (target substance) contained in a liquid specimen.
The diameter of a metal-containing particle can be selected within a range where localized surface Plasmon resonance is caused, and metal-containing particles can be dispersed in the dispersion. The diameter is preferably not less than 1 nm and not more than 1000 nm.
The examples of metals contained in the metal-containing particles include gold, silver, copper, aluminum, and an alloy having two or more such metals. The metal-containing particles can contain one or more of these metals. Particles having these metals cause localized surface Plasmon resonance. Other than these metals, the metal-containing particles can also contain inorganic materials, such as silica, or organic materials, such as polystyrene.
The diameter of a dielectric particle can be selected within a range where dielectric particles can be dispersed in the dispersion. The diameter is preferably not less than 1 nm and not more than 1000 nm.
The materials utilized in the dielectric particles can be selected from any nonconductive materials, such as silica, polystyrene, PMMA (polymethyl methacrylate).
The diameter of a metal-containing particle can be different from the diameter of a dielectric particle. Specifically, the diameter of a dielectric particle can be larger than the diameter of a metal-containing particle as shown in
The diameter of a dielectric particle can also be smaller than the diameter of a metal-containing particle as shown in
When use in a chemical sensor element is considered, the diameters of metal-containing particles and dielectric particles are preferably not less than 1 nm. Furthermore, for easily dispersing the metal-containing particles and the dielectric particles, their diameters are preferably not more than 1000 nm.
As the material for the substrate, optically transparent glass, quartz, or plastics, such as polycarbonate and polystyrene, can be used. Specifically, the materials that enable the detection using a localized Plasmon resonance method can be used.
As an optically transparent substrate, it is preferable that the absorbance at the wavelength used in measurement is not more than 30%.
The surface of the substrate can be modified by a functional group so as to elevate affinity for metal-containing particles, or to form covalent bonds with chemically modified functional groups on the surfaces of metal-containing particles and dielectric particles. The examples of functional groups to modify the surface of the substrate include amino, thiol and carboxyl groups.
When a chemical sensor element according to the present invention is used for the detection of a target substance, a chemical sensor element having a target-capturing substance with differential affinity for a target substance, and a configuration wherein the target-capturing substance is fixed on the surfaces of metal-containing particles can be favorably used.
(Method for Fabricating Chemical Sensor Element)
A method for a fabricating chemical sensor element of the above-described configuration will be described.
A method for a fabricating chemical sensor element according to the present invention includes preparing a dispersion by dispersing metal-containing particles and dielectric particles, fixing the metal-containing particles and the dielectric particles on the substrate by allowing the dispersion to contact the substrate, and isolating the metal-containing particles and the dielectric particles fixed on the substrate from the dispersion.
As a dispersion medium for dispersing metal-containing particles and dielectric particles, water can be favorably used. An organic solvent, such as DMF (dimethyl formamide) can also be used as a dispersion medium.
Both the two kinds of particles in the dispersion must be uniformly dispersed. In order to disperse metal-containing particles in the dispersion, the diameter of a metal-containing particle is preferably not less than 1 nm and not more than 1000 nm. In order to disperse dielectric particles in the dispersion, the diameter of a dielectric particle is preferably not less than 1 nm and not more than 1000 nm. In order to disperse the two kinds of particles in the dispersion, a surface active agent or the like can be added in the dispersion, or pH can be adjusted. An example of the surface active agents is Tween 20. When the surfaces of metal-containing particles include gold, citric acid can be favorably used as a component to accelerate dispersing.
In the dispersion before disposing metal-containing particles on the substrate, the metal-containing particles should be in a dispersed state.
The disposing density of the metal-containing particles on the substrate can be adjusted by the concentration of the metal-containing particles or the dielectric particles in the dispersion. The disposing density of the metal-containing particles on the substrate when the particles are disposed on the substrate can be lowered, for example, by lowering the concentration of the metal-containing particles, by elevating the concentration of the dielectric particles, or by lowering the concentration of the metal-containing particles and elevating the concentration of the dielectric particles in the dispersion. Alternatively, the disposing density of the metal-containing particles on the substrate when the particles are disposed on the substrate can be elevated by elevating the concentration of the metal-containing particles, by lowering the concentration of the dielectric particles, or by elevating the concentration of the metal-containing particles and lowering the concentration of the dielectric particles in the dispersion. Thereby, the disposing density of the metal-containing particles on the substrate can be controlled from the case when the disposing density is high as shown in
The isolation of the metal-containing particles and the dielectric particles fixed on the substrate from the substrate means to break the contact between the dispersion and the substrate by operations, such as the removal of the substrate from the dispersion and the removal of the dispersion from the container to make the dispersion contact the substrate.
The substrate isolated from the dispersion is properly cleaned and dried.
The method for fabricating the chemical sensor element according to the present invention can further include fixing metal-containing particles and dielectric particles on the substrate by the above-described fabricating method, and removing the dielectric particles fixed on the substrate. As the method for removing the dielectric particles, plasma ashing can be favorably used, but the method is not limited to plasma ashing. The examples of the materials for dielectric particles that can be decomposed by plasma ashing include organic materials, such as polystyrene.
The method for fixing a target-capturing substance to metal-containing particles can be any method as long as the capturing capacity of the target-capturing substance is impaired. For example, when the target-capturing substance has a functional group with a high affinity for metals, such as thiol, disulfide and amino groups, the target-capturing substance can be directly fixed. Alternately, the target-capturing substance can be fixed via a coupling agent. For example, when the surface of a metal-containing particle is gold, and the target-capturing substance has a functional group with affinity for amino groups, aminoethanethiol, which has an amino group and a thiol group on both ends, can be used.
The present invention will be further specifically described below referring to examples. However, the present invention is not limited only to the following examples.
Amino-group-modified polystyrene (manufactured by Sumitomo Bakelite Co., Ltd.) is used as a substrate; fine gold particles having a diameter of 100 nm (manufactured by BBI) are used as metal-containing particles; and carboxyl-group-modified polystyrene beads having a diameter of 100 nm (manufactured by Techno Chemical Corp.) are used as dielectric particles.
A dispersion of fine gold particles (5.6×109 particles/ml) and polystyrene beads (5.6×109 beads/ml) dispersed in pure water is prepared. A substrate is immersed in the dispersion and allowed to stand for 24 hours to dispose the fine particles on the substrate. After disposing, the substrate is cleaned with pure water, and dried by blowing nitrogen. The product is used as a chemical sensor element. A chemical sensor element can also be fabricated when the concentration of fine gold particles are changed within a range between 5.6×108 particles/ml and 5.6×108 particles/ml, and the concentration of polystyrene beads are changed within a range between 5.6×108 particles/ml and 5.6×109 particles/ml.
Amino-group-modified quartz glass (manufactured by Shin-Etsu Chemical Co., Ltd.) is used as a substrate; fine gold particles having a diameter of 100 nm (manufactured by BBI) are used as metal-containing particles; and carboxyl-group-modified polystyrene beads having a diameter of 100 nm (manufactured by Techno Chemical Corp.) are used as dielectric particles.
A dispersion of fine gold particles (5.6×109 particles/ml) and polystyrene beads (5.6×109 beads/ml) is prepared with pure water. A substrate is immersed in the dispersion and allowed to stand for 24 hours to dispose the particles on the substrate. After disposing, the substrate is cleaned with pure water, and dried by blowing nitrogen. After drying, the polystyrene beads are removed by plasma ashing. The product is used as a chemical sensor element (
Amino-group-modified polystyrene (manufactured by Sumitomo Bakelite Co., Ltd.) is used as a substrate; and fine gold particles having a diameter of 100 nm (manufactured by BBI) are used as metal-containing particles.
A dispersion of fine gold particles (5.6×109 particles/ml) is prepared with pure water. A substrate is immersed in the dispersion and allowed to stand for 24 hours to dispose the fine particles on the substrate. After disposing, the substrate is cleaned with pure water, and dried by blowing nitrogen. In this case, the aggregation of fine gold particles with each other occurred in about a half the number of chemical sensor elements. The detection sensitivity of the chemical sensor element wherein fine gold particles are aggregated is significantly lowered. The aggregation of fine gold particles can be checked by visually observed change in color, and observation using an optical microscope or SEM.
Using chemical sensor elements fabricated in Example 1, Example 2 and Comparative Example 1, target substances present in liquid specimens can be detected as follows:
A method for fixing anti-AFP (α-fetoprotein) antibodies on the surface of gold, which are target-capturing substances used in Example 3, to impart capturing capacity to the surfaces of fine gold particles will be described. The element is immersed in an ethanol solution of 11-mercaptoundecanoic acid, which has a thiol group with a high affinity for gold, which is a material of metal-containing particles in the Example 3 to modify the surface of the above-described structure. Thereby, carboxyl groups are exposed on the surface of the structure. In this state, elements are similarly immersed in an aqueous solution of N-hydroxysulfosuccinimide (manufactured by Dojindo Laboratories) and an aqueous solution of 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (manufactured by Dojindo Laboratories). Thereby, succinimide groups are exposed on the surface of the structure. Furthermore, by bonding streptavidine, the surface of gold is modified by streptavidine. To the streptavidine, boitinated anti-AFP antibodies are fixed.
The AFP concentration in a specimen can be specifically measured by the following operations:
(1) Bring the specimen containing AFP, which is a target substance, into contact with the chemical sensor element to capture the AFP on fine gold particles;
(2) Remove the specimen, and clean the fine gold particles using a phosphoric acid buffer solution; and
(3) Finally, bring the phosphoric acid buffer solution into contact with the fine gold particles, and measure the absorption spectra of the fine gold particles.
When the absorption spectra before reaction are compared with the absorption spectra after reaction, as an example shown in
Although the AFP concentration can be obtained by chemical sensor elements of Examples 1 and 2, the AFP concentration cannot be obtained by chemical sensor elements of Comparative Example 3 wherein fine gold particles are aggregated.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2006-134095, filed May 12, 2006, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-134095 | May 2006 | JP | national |
