Patent Application
20050112646
The present invention relates to a technology of arranging opposed electrodes in a reaction region for providing sites for an interaction between substances, and applying a predetermined electric field, to thereby perform a control of the high-order structures of the substances, movements of the substances, fixation of the substances, removal of unnecessary substances, etc.
A principal background art relating to the present invention will be described. First, a first background art (related art) is a technology concerning a bioassay integrated substrate so-called DNA chips or DNA microarrays (hereinafter referred to generically “DNA chips”) in which predetermined DNAs are finely arranged by the microarray technique (see, for example, Japanese Patent Laid-open No. Hei 4-505763, and WO98/503841).
The DNA chip technology uses a structure in which a multiplicity of kinds of and a multiplicity of DNA oligo-chains, cDNAs (complementary DNAs) and the like are integrated on a glass substrate or a silicon substrate, and is characterized in that it is possible to perform collective analysis of intermolecular interactions such as hybridization. Therefore, DNA chips have been utilized for analysis of variations in genes, SNPs (single nucleotide polymorphisms) analysis, gene expression frequency analysis, etc. and has come to be utilized widely in drug development, clinical diagnosis, pharmacological genomics, forensic medicine and other fields. Other than the DNA chips, there have also been developed protein chips including proteins on a substrate, biosensor chips for analyzing interactions between various substances, and the like.
A second background art is a technology concerning actions of an electric field on substances present in an electrically charged state in a liquid phase. Specifically, it is known that a nucleotide chain (nucleic acid molecule) is stretched or moved under the action of an electric field in a liquid phase. The principle of this phenomenon is considered as follows. Phosphate ions (negative charges) constituting the skeleton of the nucleotide chain and hydrogen atoms (positive charges) formed by ionization of water present in the surroundings of the phosphate ions are considered to be forming ionic fogs, the polarization vectors (dipoles) generated by the negative charges and the positive charges are as a whole aligned in one direction upon application of a high-frequency high voltage, with the result of extension of the nucleotide chain, and, in addition, when a nonuniform electric field with electric lines of force concentrated on a portion is impressed, the nucleotide chain is moved toward the portion on which the electric lines of force are concentrated (see Seiichi Suzuki, Takeshi Yamanashi, Shin-ichi Tazawa, Osamu Kurosawa and Masao Washizu: “Quantitative analysis on electrostatic orientation of DNA in stationary AC electric field using fluorescence anisotropy”, IEEE Transaction on Industrial Applications, Vol. 34, No. 1, pp.75-83 (1998)). Besides, it is known that when a DNA solution is placed in fine electrodes having a gap of several tens to several hundreds of micrometers and a high-frequency electric field of about 1 MV/m and 1 MHz is applied thereto, dielectric polarization occurs in the DNA present in a random coil form, resulting in that the DNA molecule is stretched in a straight line form in parallel to the electric field. Then, by this electrodynamic effect called “dielectricphoresis”, the polarized DNA is spontaneously drawn to the electrode end, and is fixed in the form of having one end in contact with the electrode edge (see Masao Washizu, “DNA handling conducted while viewing”, Visualized Information, Vol. 20, No. 76 (January, 2000)).
The above-mentioned DNA chip technology is a technology in which a reaction region for providing sites for an interaction between substances in a medium is preliminarily set on a substrate, and a detection nucleotide chain such as a probe DNA is preliminarily fixed in the reaction region, to thereby analyze the hybridization which is an interaction between the detection nucleotide chain and a complementary target nucleotide chain.
In the DNA chip technology, however, there have been the problems that: (1) the fixed detection nucleotide chain shows a high-order structure in which it is entangled or rounded in a random coil form under the action of Brownian motion; (2) an interference (e.g., adhesion or contact) between the fixed detection nucleotide chain and the surrounding surfaces occurs; (3) there is a deviation in the integration density of the detection nucleotide chains on the fixation surface: and (4) non-complementary nucleotide chains and surplus intercalators are present in the vicinity of the fixed detection nucleotide chain.
Hitherto, it has been impossible to solve these problems. At the time of hybridization, therefore, a steric hindrance due to the high-order structured or non-complementary nucleotide chains occurs. Accordingly, the DNA chip technology has had the technical problems that the hybridization efficiency is poor, a long time is taken to achieve the reaction, and pseudo-positivity and pseudo-negativity are generated, with the result of a lowering in detection accuracy.
Accordingly, it is an object of the present invention to provide a detecting unit with which it is possible to freely perform a control of high-order structures of substance, movement of the substances, fixation of the substances, removal of unnecessary substances, etc., and a bioassay substrate provided with the detecting unit.
According to an aspect of the present invention, there is provided a unit for detecting an interaction between substances including:
According to another aspect of the present invention, there is provided a bioassay substrate which includes an interaction detecting unit having:
According to still another aspect of the present invention, there is provided a method of manufacturing an interaction detecting unit including the steps of:
According to the present invention, the high-order structure of a detection nucleotide such as DNA probe or a target nucleotide chain can be put from a random coil form into a stretched state under the action of an electric field applied, so that it is possible to obviate steric hindrances at the time of the interaction such as hybridization. By the action of the electric field, it is possible to align and fix the detection substance on the electrode surfaces, and to enhance the concentrations of the detection substance and the target substances on the surfaces. By these effects, the efficiency and accuracy of the interaction are enhanced, so that the operation time can be shortened, and, since the generation of pseudo-positivity or pseudo-negativity is restrained, the detection accuracy can be enhanced.
The present invention promises a high efficiency of the interaction such as hybridization at the detecting unit, so that it is possible to largely shorten the time required for the interaction. Besides, since it is possible to form an environment promising an easy progress of the interaction with high accuracy, it is possible to suppress the generation of pseudo-positivity or pseudo-negativity. Therefore, the present invention can be utilized for a bioassay substrate such as DNA chip which has such characteristics that the efficiency of the assay operation for interaction detection is excellent and that the detection accuracy is high.
While preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.
The above and other objects, features and advantages of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings, in which:
First, principal technical terms used in the present invention will be defined. The term “interaction” used in the present invention widely means chemical bondings inclusive of non-covalent bonding, covalent bonding, and hydrogen bonding and dissociation between substances, and includes hybridization which is a complementary bonding between nucleic acids (nucleotide chains), for example.
Next, the term “opposed electrodes” means at least one pair of electrodes which are arranged oppositely to each other.
The term “nucleotide chain” means a polymer of a phosphoric acid ester of a nucleoside in which a purine or pyrimidine base and a sugar are bonded by glycoside bonding, and widely includes oligonucleotides inclusive of probe DNAs, polynucleotides, DNAs (whole length or sections thereof) formed by polymerization of purine nucleotide with pyrimidine nucleotide, cDNAs (c probe DNAs) obtained by reverse transcription, RNAs, polyamide nucleotide derivatives (PNAs), etc.
The term “hybridization” means a complementary chain (double chain) forming reaction between nucleotide chains having complementary base sequence structures. The term “mishybridization” means the complementary chain forming reaction which is not normal.
The term “reaction region” means a region which can provide reaction sites for hybridization or other interactions, and examples thereof include a reaction site in the shape of a well capable of preserving or holding a medium such as a liquid phase and a gel. The interaction conducted in the reaction region is not narrowly limited, provided that the interaction conforms to the object or effects of the present invention. Examples of the interaction include not only an interaction between a single-chain nucleic acids, i.e., hybridization but also an interaction between peptide (or protein) and a desired double-chain nucleic acid formed from a detection nucleic acid, an enzyme response reaction and other intermolecular interactions. Where the double-chain nucleic acid is used, for example, the bonding between a receptor molecule of a hormone receptor or the like which is a transcription factor and a response sequence DNA portion, and the like can be analyzed.
The term “detection substance” is a substance which is preliminarily added into the reaction region and which is present in a free state in the region, or a substance which is present in the state of being fixed to a predetermined surface portion of the reaction region. The detection substance is a substance for capturing and detecting a substance showing a specific interaction with the substance, and includes detection nucleotide chains such as DNA probes.
The term “target substance” means a substance which serves as a target of an interaction with the detection substance, and examples thereof include a nucleotide chain having a base sequence complementary to the DNA probe.
The term “steric hindrance” means a phenomenon in which due to the presence of a bulky substituent group in the vicinity of a reaction center or the like in a molecule, the posture of a reaction molecule, or the steric structure (high-order structure), the access of molecules of the medium species becomes difficult and, as a result, it becomes difficult for the desired reaction (hybridization, in the present patent application) to take place.
The term “dielectricphoresis” is a phenomenon in which molecules are driven toward the higher electric field side in a field where the electric field is anisotropic. Further, where an AC voltage is applied, the polarity of polarization is reversed attendant on the reversion of the polarity of the applied voltage, so that the driving effect can be obtained in the same manner as in the case of DC (see “Micromachines and Material Technology (published by CMC Publishing Co., Ltd.)” complied under the supervision of Teru Hayashi, pp.37-46, Chapter 5, Cell and DNA manipulation).
The term “bioassay substrate” means an information integration substrate used for the purpose of biochemical or molecular biological analysis, and includes the so-called DNA chip.
Now, a preferred embodiment of the present invention will be described below referring to the accompanying drawings. First,
Symbol 1a in
The detecting unit la and other detecting units 1b (
The opposed electrodes E1, E2 can be formed of a metal such as gold and aluminum or of a conductor other than metal; for example, they can be formed of a transparent conductor such as ITO (Indium Tin Oxide). Incidentally, the opposed electrodes E1, E2 are connected to a power source V1 shown, by turning ON a switch S1.
The opposed electrodes E1, E2 are each formed in the shape of being projected toward the reaction region 2, and include projected electrode portions e1, e2 in a needle-like or rod-like form which are opposed to each other.
Of the opposed electrodes E1, E2, each surface on the side for fronting the reaction region 2 is covered with an insulation layer (not shown). The insulation layer plays the role of preventing an electrochemical reaction due to an ionic solution which may be preserved in the reaction region 2. The insulation layer can be formed of such a material as SiO2, SiN, SiOC, SiOF, SiC, TiO2, etc.
Incidentally, though not shown in the figure, the projected electrode portions e1 constituting the electrode E11 and the projected electrode portions e2 constituting the electrode E21 may not necessarily be arrayed at the regular interval, and the interval can be appropriately selected. Besides, there can be adopted a configuration in which the number of the projected electrode portions on one side is greater than the number of the projected electrode portions on the other side, or a configuration in which the number density per unit length of the projected electrode portions on one side is higher than the number density per unit length of the projected electrode portions on the other side. It is considered that the electric lines of force are concentrated more on the side of the projected electrode portions with a higher number density.
Next,
The reaction region 2 can be observed as a recessed portion opened to the upper side, as shown in
Now, referring to
First, an aqueous solution containing a DNA probe D1 as a representative example of the detection substance D is dropped in a predetermined quantity from a nozzle (see
By the application of the electric field, the DNA probe D1 in the librated state denoted by symbol D1 in
Incidentally, in the case where the surface of the projected electrode portion e1 is surface treated with streptoavidin, the system is suitable for fixation of the terminal end of the viotinated DNA probe. Alternatively, in the case where the surface of the projected electrode portion e1 is surface treated with a thiol (SH) group, the system is suitable for fixing the DNA probe, modified with the thiol group at the terminal end thereof, by a disulfide bond (—S—S-bond).
After the fixation of the DNA probe D1 by the above-mentioned method is finished, the assembly is washed with a predetermined buffer solution (e.g., phosphate buffered saline), whereby surplus DNA probes and the DNA probes non-specifically adsorbed on the surface of the projected electrode portion e1 can be removed from the reaction region 2.
Subsequently, a solution containing a target DNA as a representative example of the target substance T shown in
Upon the application of the electric field, the target DNA denoted by symbol T1 in
Next, the switch S1 is turned OFF (see
Generally, the target DNA denoted by symbol T (T1) is longer than the DNA probe D2; therefore, the target DNAs may interfere with each other in the narrow reaction region 2 to bring about a steric hindrance, which hampers the hybridization, or they may adhere to wall surfaces of the reaction region 2 in the vicinity of the fixation surface. Thus, the progress of the hybridization may often be inhibited.
In the present invention, on the other hand, the projected electrode portions e1 and e2 forming a nonuniform electric field have electrode edges present at positions far from the surrounding wall surfaces, and the projected electrode portions can be spaced from each other (see
Incidentally, as shown in the modified embodiment in
Next, based on FIGS. 9 to 12, one example of the method of manufacturing the detecting unit according to the present invention will be described. The detecting unit will be described by taking an embodiment denoted by symbol 1b as a representative example. Taking as an example the case where a substrate 3 is made of a glass, predetermined electrode layers E, E are formed on the glass substrate 3 by use of gold (see
Next, as shown in
Thereafter, by use of an HF solution or the like, the lower side of projected electrode portions is wet etched, to form projected electrode portions E11, E21. Incidentally, since gold is not damaged by the HF solution, a projected electrode structure as shown in
Incidentally, the etching of the glass-made substrate 3 may be carried out at a stroke by soft etching using the HF solution, without adopting the above-mentioned dry etching technique. In the fabrication of the detecting unit according to the present invention, however, it is desirable to jointly use the dry etching and the soft etching, for enhancing controllability of the electrode shape. Besides, in the case of covering the thus formed projected electrode portions with an insulation layer, it is desirable to form a film of SiO2 or the like by CVD, for example.
By preliminarily arranging the detecting units denoted by symbols 1a to 1d above-mentioned in a predetermined array on the substrate, a bioassay substrate such as DNA chip can be provided with which interactions such as hybridization can be made to proceed in a short time and collective analysis can be performed.
Incidentally, the detection of the interaction proceeding at any detecting unit 1a or the like provided on the substrate 5 can be carried out by use of a known optical detection means by which a fluorescent substance preliminarily marked onto the detection substance D fixed to the electrode surface or a fluorescent intercalator inserted and bonded to a substance (double chain nucleic acid) showing an interaction is irradiated with fluorescence exciting rays at a predetermined wavelength and the fluorescence is detected. Alternatively, a method may be adopted in which the light-emitting image of the detecting unit 1a and the like is picked up, and the quantity of light obtained from the image is quantitatively analyzed and detected.
The present invention is not limited to the details of the above described preferred embodiments. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-343955 | Oct 2003 | JP | national |
