JP3719665B2 - Recombinant basket protein and noble metal-recombinant basket protein complex - Google Patents

Description

【図面の簡単な説明】
【図１】フェリチンの構造を模式的に示す図である。
【図２】（ａ）−（ｃ）は、本発明の第１の実施形態に係る組み換えアポフェリチンを模式的に示す断面図である。
【図３】基板上に配置された金内包アポフェリチンを模式的に示す図である。
【図４】基板上に配置された金内包アポフェリチンの電子顕微鏡写真を示す図である。
【図５】本発明の第２の実施形態に係るヌクレオチド検出装置を概略的に示す図である。
【図６】本発明の第３の実施形態に係る，金粒子からなるドット体をフローティングゲートとして利用した不揮発性メモリセルの構造を示す断面図である。
【図７】（ａ）−（ｃ）は、本発明の第４の実施形態に係る微小構造体の形成工程を示す断面図である。
【図８】本発明の第５の実施形態に係り、第４の実施形態において形成された微小構造体形を利用した光半導体装置の断面図である。
【図９】本発明により形成された、外表面と保持部の両方に貴金属粒子を保持する金−アポフェリチン複合体を模式的に示す図である。
【符号の説明】
１ 核
２ 外殻
３ チャネル
４ 保持部
７ クロロ金酸イオン（ＡｕＣｌ₄）^-
７’ 金（Ａｕ）原子
１０ ヌクレオチド検出装置
１１ 基板
１２ 金粒子
１３ チオールＤＮＡ
１５ 金内包アポフェリチン
２１ ｐ型Ｓｉ基板
２２ 素子分離酸化膜
２３ ゲート酸化膜
２４ ドット体
２５ シリコン酸化膜
２６ ポリシリコン電極
２７ａ 第１のｎ型拡散層
２７ｂ 第２のｎ型拡散層
２８ 層間絶縁膜
２９ コンタクトホール
３０ タングステンプラグ
３１ａ 第１のアルミニウム配線
３１ｂ 第２のアルミニウム配線
３３ 金粒子
３４ シリコン基板
４１ シリコン基板
４２ 半導体微細柱
４３ 絶縁層
４４ 透明電極
４９ 絶縁分離層
５０ 側方電極
５１ ｐ型ウェル
Ｒｑａ 量子化領域
６１ 第１の金粒子
６２ 第２の金粒子
６３ 外殻[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a noble metal-recombinant apoferritin complex produced using a gene recombination technique, a production method thereof, and a related technique.
[0002]
[Prior art]
In recent years, research on bioelectronics combining biotechnology and electronics has been actively conducted, and some biosensors using proteins such as enzymes have already been put into practical use.
[0003]
As one of the attempts to apply such biotechnology to other fields, apoferritin, a protein having a function of holding a metal compound, incorporates metal or metal compound particles into nanometer order uniform size particles. There is research to try. Research is being conducted to introduce various metals or metal compounds into apoferritin depending on the use of the fine particles.
[0004]
Here, apoferritin will be described. Apoferritin is a protein that exists widely in the living world, and plays a role in regulating the amount of iron, which is an essential trace element in vivo. A complex of iron or an iron compound and apoferritin is called ferritin. If iron is present in the body more than necessary, it is harmful to the living body, so excess iron is stored in the body in the form of ferritin. Ferritin then releases iron ions as needed and returns to apoferritin.
[0005]
FIG. 1 is a schematic diagram showing the structure of ferritin (iron-apoferritin complex). As shown in the figure, ferritin is a globular protein having a molecular weight of about 460,000 in which 24 monomer subunits formed from one polypeptide chain are assembled by non-covalent bonds, and its diameter is about 12 nm. Higher heat stability and higher pH stability than other proteins. At the center of the spherical protein (outer shell 2) is a hollow holding portion 4 having a diameter of about 6 nm, and the outside and the holding portion 4 are connected via a channel 3. For example, when divalent iron ions are taken into ferritin, the iron ions enter from the channel 3 and are oxidized at a place called a ferrooxidase center (iron oxidation active center) in a part of the subunits, and then the holding unit 4. And is concentrated in the negative charge region on the inner surface of the holding portion 4. Then, 3000 to 4000 iron atoms are assembled, and ferrihydrite (5Fe₂O_Three・ 9H₂O 2) held in the holding unit 4 in the form of crystals. In the present specification, fine particles containing metal atoms held in the holding portion are referred to as “nuclei”. Here, the diameter of the nucleus 1 shown in FIG. 1 is substantially equal to the diameter of the holding portion 4 and is about 6 nm.
[0006]
Further, the core 1 is removed by a relatively simple chemical operation, and the particle in which the core 1 is removed and only the outer shell 2 is called apoferritin. Using this apoferritin, an apoferritin-fine particle complex in which a metal other than iron or a metal compound is artificially supported has also been produced.
[0007]
To date, manganese (P. Mackle, 1993, J. Amer. Chem. Soc. 115, 8471-8472; FCMeldrum et al., 1995, J. Inorg. Biochem. 58, 59-68), uranium (JF Hainfeld, 1992, Proc. Natl. Acad. Sci. USA 89, 11064-11068), beryllium (DJPrice, 1983, J. Biol. Chem. 258, 10873-10880), aluminum (J. Fleming, 1987, Proc. Natl. Acad. Sci. USA, 84, 7866-7870), zinc (D. Price and JGJoshi, Proc. Natl. Acad. Sci. USA, 1982, 79, 3116-3119), cobalt (T. Douglas and VTStark, Inorg. Chem., 39, 2000, 1828-1830), introduction of a metal or a metal compound into apoferritin has been reported. The diameter of the core 1 made of these metals or metal compounds is also approximately equal to the diameter of the apoferritin holding portion 4 and is about 6 nm.
[0008]
In nature, the outline of the process in which the nucleus 1 containing an iron atom is formed in ferritin is as follows.
[0009]
On the surface of the channel 3 (see FIG. 1) connecting the outside and inside of the ferritin particle, an amino acid having a negative charge is exposed under the condition of pH 7-8, and Fe having a positive charge.²⁺Ions are taken into the channel 3 by electrostatic interaction. There are 8 channels 3 per apoferritin.
[0010]
Like the inner surface of channel 3, the inner surface of ferritin holding portion 4 is exposed to many glutamic acid residues, which are amino acid residues having a negative charge at pH 7-8, and Fe taken in from channel 3 is exposed.²⁺The ions are oxidized at the ferroxidase center and further guided to the internal holding unit 4. Then, iron ions are concentrated by electrostatic interaction, and ferrihydrite (5Fe₂O_Three・ 9H₂O) Crystal nucleation occurs.
[0011]
Thereafter, iron ions that are sequentially taken in are attached to the nuclei of the crystal to grow nuclei made of iron oxide, and nuclei 1 having a diameter of 6 nm are formed in the holding part 4. The above is the outline of iron ion uptake and nucleation of iron oxide.
[0012]
Next, the operation for introducing iron into apoferritin will be described below.
[0013]
First, HEPES buffer solution, apoferritin solution, ammonium iron sulfate (Fe (NH_Four)₂(SO_Four)₂) Mix each solution in the order of the solution to prepare a ferritin solution. In this ferritin solution, the final concentrations of HEPES buffer are 100 mmol / L (pH 7.0), apoferritin is 0.5 mg / mL, and ammonium iron sulfate is 5 mmol / L. In addition, all operations for preparing ferritin are performed at room temperature, and stirring is performed with a stirrer.
[0014]
Next, in order to complete the uptake reaction of iron ions into the apoferritin and the oxidation reaction of the incorporated iron, the ferritin solution is left as it is overnight. By this operation, iron oxide having a uniform size is introduced into the apoferritin holding portion, and ferritin (a complex of apoferritin and fine particles) is generated.
[0015]
Next, the ferritin solution is put in a container and centrifuged using a centrifuge at 3,000 rpm for 15-30 minutes to remove the precipitate. Subsequently, the supernatant after removing the precipitate is further centrifuged at 10,000 rpm for 30 minutes to precipitate unnecessary aggregates in which ferritin is aggregated, and then removed. At this time, ferritin is present in a dispersed state in the supernatant.
[0016]
Next, the supernatant solvent is replaced by dialysis from a pH 7.0 7.0 mmol / L HEPES buffer solution to a 150 mmol / L NaCl solution to prepare a new ferritin solution. There is no particular need to adjust the pH here.
[0017]
Subsequently, the ferritin solution was concentrated to an arbitrary concentration of 1-10 mg / mL, and then CdSO 4 was added to the solution so that the final concentration was 10 mmol / L._Four To agglomerate ferritin.
[0018]
Next, the ferritin solution is centrifuged at 3,000 rpm for 20 minutes to precipitate ferritin aggregates in the solution. The buffer component of the solution is then replaced by dialysis with pH 8.0, 10-50 mmol / L Tris buffer containing 150 mmol / L NaCl.
[0019]
Next, after concentrating the ferritin solution, the ferritin solution is filtered through a gel filtration column to remove the aggregates of ferritin particles and obtain a single ferritin containing iron oxide.
[0020]
The mechanism of iron ion incorporation into ferritin and the preparation method of ferritin encapsulating iron oxide have been described so far, but all other metal ions reported so far are positive ions. Incorporation of these metal ions into apoferritin is thought to proceed by almost the same mechanism as iron ions. Therefore, other metal ions are also introduced into apoferritin basically by the same operation as iron ions.
[0021]
By the way, apoferritin has slightly different sizes of particles that can be held depending on the species from which it is derived. There is also a spherical shell protein that has a structure similar to apoferritin and can hold inorganic fine particles inside. Among these are Listeria ferritin derived from Listeria and Dps protein. There are also proteins that can hold inorganic particles inside, like ferritin, such as the outer protein of viruses such as CCMV, even if they are not spherical.
[0022]
In the present specification, proteins that can hold inorganic fine particles therein, such as the spherical shell protein and virus outer shell protein, are collectively referred to as “cage protein”.
[0023]
  These cage proteins can also hold inorganic particles containing iron.In addition, as related prior literature, Levi, S. et al., Biochem. Journal (1996) 317,467-473 Can mention.
[0024]
[Problems to be solved by the invention]
However, although ferritin holding metal ions such as iron can be prepared by the above-described method, the inner surface of the channel 3 of apoferritin and ferritin is negatively charged as a whole, and thus has the same negative charge. It was difficult to incorporate ions into apoferritin.
[0025]
On the other hand, gold and platinum cannot be ionized alone in an aqueous solution and can only exist as complex ions in an aqueous solution._Four)^-(PtCl_Four)^2-Often used as negative ions. Therefore, it has been difficult for conventional techniques to incorporate noble metal atoms such as gold and platinum into apoferritin.
[0026]
An object of the present invention is to introduce a noble metal atom such as gold into a basket-like protein such as apoferritin by modifying the internal structure of a basket-like protein such as apoferritin, and thus applicable to various microstructures. It is to form noble metal particles.
[0027]
[Means for Solving the Problems]
The recombinant basket-like protein of the present invention is a recombinant basket-like protein produced by a genetic recombination technique, a holding part that can hold noble metal particles inside the recombinant basket-like protein, the holding part, and the recombinant basket And a tunnel-like channel connecting the outside of the protein.
[0028]
Thereby, noble metal particles of uniform size and nanometer order can be formed in the holding part of the recombinant basket-like protein. For example, the noble metal-recombinant basket-like protein complex is arranged on the substrate and the protein part is By performing an operation such as removal, a fine dot body made of a noble metal having excellent chemical stability can be formed on the substrate. This dot body can be used, for example, in a semiconductor manufacturing process.
[0029]
Since the recombinant basket-like protein is apoferritin, it is possible to efficiently produce noble metal particles having a size of nanometer order.
[0030]
Since the noble metal particles are gold or platinum, it is easy to form dot bodies. The produced fine particles can be applied to a single electron transistor or the like.
[0031]
By providing the first neutral amino acid having a molecular size smaller than that of glutamic acid and aspartic acid at the position where the first glutamic acid (Glu) and the first aspartic acid should be present on the inner surface of the channel, It is possible to prevent repulsive force due to electrostatic interaction between a complex ion of a noble metal having a negative charge and a channel. As a result, it becomes possible to incorporate a complex ion of a noble metal into the channel.
[0032]
When the first neutral amino acid is selected from serine, alanine, and glycine, it becomes possible to incorporate a noble metal complex ion into the channel without destroying the three-dimensional structure of the recombinant cage protein.
[0033]
By further providing a basic amino acid or a second neutral amino acid at the position where the second glutamic acid should be present on the inner surface of the holding part, a noble metal complex ion having a negative charge and the holding part It is possible to prevent repulsion due to electrostatic interaction. In particular, when a basic amino acid is provided at the position where the second glutamic acid should exist, a noble metal complex ion is taken in due to the positive charge of the basic amino acid, and as a result, the noble metal complex ion is retained. It is possible to make the part take in a high concentration.
[0034]
When the basic amino acid or the second neutral amino acid is selected from arginine, lysine, and alanine, a complex ion of a noble metal can be incorporated into the holding portion without destroying the three-dimensional structure of the recombinant cage protein. It becomes possible.
[0035]
Since one or more cysteines substituted with amino acids are present on the inner surface of the holding part, the noble metal complex ions incorporated into the holding part can be effectively reduced to deposit noble metal particles. .
[0036]
On the outer surface of the above-mentioned recombinant basket-like protein, a complex ion of a noble metal is reduced on the outer surface of the recombinant basket-like protein by providing a substance having a reducing function smaller than that of the cysteine at the position where cysteine should be present. Can be prevented. As a result, the precipitation of the noble metal particles on the outer surface of the recombinant cage protein is suppressed, and the yield of the noble metal-recombinant cage protein complex that holds the noble metal particles in the holding portion can be increased.
[0037]
The noble metal-recombinant basket-like protein complex of the present invention includes a holding part capable of holding noble metal particles, and a tunnel-like channel connecting the holding part and the outside of the recombinant basket-like protein.
[0038]
Thereby, for example, a fine dot body made of a noble metal can be formed on the substrate by arranging a noble metal-recombinant basket-like protein complex on the substrate and removing the protein portion. This dot body can be used in, for example, a semiconductor manufacturing process.
[0039]
The recombinant cage protein may be apoferritin.
[0040]
Gold or platinum particles may be held on the outer surface.
[0041]
By providing the first neutral amino acid having a molecular size smaller than that of glutamic acid and aspartic acid at the position where the first glutamic acid and first aspartic acid should be present on the inner surface of the channel, a negative charge is obtained. Since repulsive force due to electrostatic interaction can be prevented from occurring between the complex ion of the noble metal and the channel, the noble metal-recombinant cage protein complex is efficiently produced.
[0042]
When the first neutral amino acid is selected from serine, alanine, and glycine, a noble metal-recombinant cage protein complex can be formed without breaking the steric structure.
[0043]
By further providing a basic amino acid or a second neutral amino acid at the position where the second glutamic acid should be present on the inner surface of the holding part, a noble metal complex ion having a negative charge and the holding part Since repulsive force due to electrostatic interaction can be prevented between them, the noble metal-recombinant cage protein complex of the present invention is efficiently produced.
[0044]
When the basic amino acid or the second neutral amino acid is selected from arginine, lysine, and alanine, it becomes possible to hold the noble metal particles without destroying the three-dimensional structure.
[0045]
The noble metal-recombinant basket protein complex of the present invention can be easily formed in a solution containing noble metal ions by the presence of one or more cysteines substituted with amino acids on the inner surface of the holding part. Will be able to.
[0046]
The recombinant DNA of the present invention encodes an amino acid sequence of a recombinant basket-like protein having a holding part capable of holding noble metal particles and a tunnel-like channel connecting the holding part and the outside of the recombinant basket-like protein. .
[0047]
This recombinant DNA enables mass production of recombinant cage proteins using protein engineering techniques.
[0048]
The recombinant cage protein may be apoferritin.
[0049]
The noble metal particles may be gold or platinum.
[0050]
The recombinant protein is provided with a first neutral amino acid having a molecular size smaller than that of glutamic acid and aspartic acid at a position where the first glutamic acid and first aspartic acid should be present on the inner surface of the channel. Can be easily obtained.
[0051]
When the first neutral amino acid is selected from serine, alanine, and glycine, it is possible to obtain a large amount of recombinant basket-like protein for efficiently forming noble metal particles in the holding portion.
[0052]
A homogeneous amino acid for efficiently forming noble metal particles in the holding part by further comprising a basic amino acid or a second neutral amino acid at a position where the second glutamic acid should be present on the inner surface of the holding part. It becomes possible to obtain a large amount of a recombinant cage protein.
[0053]
When the basic amino acid or the second neutral amino acid is selected from arginine, lysine, and alanine, a recombinant cage protein capable of efficiently retaining precious metal particles can be easily prepared.
[0054]
The presence of one or more cysteines substituted with amino acids on the inner surface of the holding part makes it possible to easily produce a recombinant basket protein that can hold the precious metal particles more efficiently.
[0055]
In the method for producing a recombinant basket-like protein of the present invention, the first glutamic acid and the first aspartic acid located on the inner surface of the channel are replaced with a first neutral amino acid having a molecular size smaller than that of glutamic acid and aspartic acid. Step (a) is included.
[0056]
By this method, a recombinant cage protein capable of efficiently incorporating noble metal particles into the channel can be easily produced.
[0057]
The recombinant cage protein may be apoferritin.
[0058]
In the step (a), the first neutral amino acid is selected from serine, alanine, and glycine, so that the three-dimensional structure of the recombinant basket-like protein is not broken and a complex ion of a noble metal is incorporated into the channel. A recombinant basket-like protein can be prepared.
[0059]
Noble metal particles are further formed in the holding part by further including the step (b) of replacing the second glutamic acid present on the inner surface of the holding part inside the recombinant basket-like protein with a basic amino acid or a second neutral amino acid. Can be easily produced.
[0060]
In the step (b), the basic amino acid or the second neutral amino acid is selected from arginine, lysine, and alanine, so that the three-dimensional structure of the recombinant basket-like protein does not collapse, and the noble metal complex A recombinant cage protein capable of incorporating ions into the holding part can be produced.
[0061]
The step further includes the step (c) of substituting one or more amino acids located on the inner surface of the holding part with cysteine, thereby effectively reducing the noble metal complex ions taken into the holding part to precipitate noble metal particles. Recombinant basket-like protein can be produced. When the noble metal complex ion is reduced, the molecular size is reduced, so that the uptake of the noble metal complex ion into the holding portion is promoted.
[0062]
By further including the step (d) of replacing one or more cysteines located on the outer surface of the recombinant basket-like protein with a substance having a smaller reducing function than the cysteine, the reduction of the noble metal complex ion on the outer surface is achieved. Recombinant cage protein can be made.
[0063]
The method for producing a noble metal-recombinant cage protein complex of the present invention comprises a step of forming a noble metal-recombinant cage protein complex by mixing a noble metal complex ion solution and a recombinant cage protein solution (a). When,
A step (b) of purifying the noble metal-recombinant cage protein complex by passing the solution containing the noble metal-recombinant cage protein complex prepared in the step (a) through a gel filtration column;
Is included.
[0064]
By this method, the recombinant basket-like protein holding the noble metal on the outer surface, the recombinant basket-like protein encapsulating the noble metal, and the side reaction product are fractionated from each other by size. A protein-like complex can be selected.
[0065]
Since the noble metal in the step (a) is gold or platinum, as described above, for example, a dot body made of gold or platinum used in a manufacturing process of a semiconductor device or the like can be formed. In addition, the dot reduction process that has been necessary in the past is not necessary.
[0066]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
A first embodiment of the present invention will be described below.
[0067]
-Production of recombinant (recombinant) apoferritin-
The inventors considered that the following two main obstacles in introducing gold (Au) atoms into apoferritin.
[0068]
One is chloroaurate ion (AuCl_Four)^-Is an electrostatic interaction between apoferritin and apoferritin. The negatively charged amino acids such as glutamic acid and aspartic acid are exposed on the inner surface of the channel 3 and the inner surface of the holding part 4 of ferritin (apoferritin-iron complex) shown in FIG. Negative ion (AuCl_Four)^-Uptake into apoferritin is inhibited by electrostatic interactions with these negatively charged amino acids.
[0069]
The other is (AuCl_Four)^-Is larger than iron ions. Therefore, if the size of the channel 3 of apoferritin is not increased, (AuCl_Four)^-Is physically difficult to capture in channel 3.
[0070]
In order to solve these problems, the inventors modified apoferritin as follows using a gene recombination technique. Hereinafter, the term “recombinant apoferritin” in the present specification refers to apoferritin into which a mutation has been introduced by a gene recombination technique. Moreover, when showing the site | part of an amino acid residue in this specification, unless otherwise indicated, the site | part in the apoferritin derived from the horse liver which does not contain a mutation is meant. Further, since apoferritin is composed of 24 monomer subunits, the term “amino acid sequence of apoferritin” in this specification means the amino acid sequence of the monomer subunit.
[0071]
The gene sequence encoding apoferritin derived from horse liver and the amino acid sequence of apoferritin are known, and the three-dimensional structure has also been elucidated. The apoferritin monomer is composed of 175 amino acid residues, of which the 128th aspartic acid (Asp) and the 131st glutamic acid (Glu) are both located on the inner surface of channel 3 and the 58th , 61st and 64th glutamic acids are both located on the inner surface of the holding part 4. In addition, the 1st to 8th amino acid residues of apoferritin are deleted by processing in vivo.
[0072]
Next, the electrostatic interaction in apoferritin will be described.
[0073]
As described above, in the neutral solution, aspartic acid and glutamic acid having a negative charge are arranged on the inner surface of the apoferritin holding portion 4 and the channel 3, the potential of the entire inner surface of the apoferritin Vin is lower than the external potential Vout of apoferritin. That is, the internal / external potential difference ΔV of apoferritin defined by ΔV = Vin−Vout is ΔV <0 (mV).
[0074]
Where (AuCl_Four)^-Has a negative charge, so (AuCl) inside apoferritin_Four)^-Concentration is Cin, (AuCl in solution)_Four)^-When the concentration is Cout, it is known that the relationship between Cin, Cout, and ΔV is expressed by the following equation (1).
[0075]
Cout / Cin = e^-Δ^{V / kT}                              (1)
In equation (1), e is a natural logarithm, k is a Boltzmann constant, and T is an absolute temperature. From this equation, by increasing ΔV, when the temperature is constant, (AuCl in the interior of apoferritin_Four)^-It can be seen that the concentration can be increased exponentially. For example, when ΔV is a positive value, Cout / Cin is about 80 when ΔV is quadrupled.
[0076]
On the other hand, (AuCl on the inner surface of apoferritin_Four)^-→ The reduction reaction of Au is accelerated if the concentration inside apoferritin increases.
[0077]
In consideration of the above conditions, the inventors of the present application require that Cin is at least three times Cout in order to efficiently generate gold particles in the apoferritin holding portion 4 in the solution. The conclusion was reached. At room temperature, ΔV that satisfies this condition is about 25 (mV) or more. In particular, in order to generate gold particles in the holding part 4 at a sufficient speed, it was considered that ΔV is preferably about 100 (mV) or more.
[0078]
Here, ΔV is obtained by summing the charges of bases existing on the inner surface of apoferritin in consideration of the position. For example, in the apoferritin monomer, it is estimated that ΔV in apoferritin is about 200 (mV) by replacing three glutamic acids located in the holding unit 4 with lysine (Lys). This is considered to be a potential difference sufficient to generate gold particles in the apoferritin holding portion 4.
[0079]
The inventors of the present application produced recombinant apoferritin capable of holding the following gold particles based on the above calculation.
[0080]
FIGS. 2A to 2C are diagrams schematically showing the structure of recombinant apoferritin prepared based on the above-described findings.
[0081]
First, in FIG. 2 (a), in the apoferritin derived from horse liver (hereinafter abbreviated as apoferritin), both amino acids of the 128th aspartic acid and the 131st glutamic acid are changed to serine (Ser). It is a replacement. Here, even if aspartic acid or glutamic acid is substituted with serine, the three-dimensional structure of apoferritin can be maintained. In addition, the 1st to 8th amino acids of apoferritin protrude on the outer surface of apoferritin and are deleted because there is a possibility of hindering the production of higher order structures such as two-dimensional crystallization. This recombinant apoferritin is hereinafter referred to as fer-8-ser.
[0082]
Here, the negatively charged aspartic acid and glutamic acid present on the inner surface of the channel 3 are replaced by serine having no charge, thereby eliminating the electrostatic repulsive force and having the negative charge (AuCl_Four)^-(7 in FIG. 2A) is easily taken into the channel 3. In addition, since serine residues are smaller in size than both aspartic acid residues and glutamic acid residues, they enter the channel (AuCl_Four)^-There are fewer physical obstacles when importing.
[0083]
Next, FIG. 2 (b) shows recombinant apoferritin in which the 58th, 61st, and 64th glutamic acids in the amino acid sequence of fer-8-Ser are substituted with arginine (Arg), respectively. This recombinant apoferritin is hereinafter referred to as fer-8-Ser-Arg.
[0084]
Here, the 58th, 61st, and 64th glutamic acid present on the inner surface of the holding part 4 for apoferritin was replaced with arginine having a positive charge, which was incorporated into the channel 3 (AuCl_Four)^-Can be induced to the apoferritin holding portion 4. At this time, even if glutamic acid is substituted with arginine, the three-dimensional structure of apoferritin is retained. Here, it was guided to the holding part 4 (AuCl_Four)^-7 is sequentially reduced to gold (Au) atoms 7 '. In addition, as amino acids to replace the 58th, 61st, and 64th glutamic acids, any amino acids may be used as long as they do not have a negative charge. It may be.
[0085]
Next, shown in FIG. 2 (c) is recombinant apoferritin in which both 54th glutamic acid and 65th arginine in the amino acid sequence of fer-8-Ser-Arg are substituted with cysteine. Hereinafter, this recombinant apoferritin is referred to as fer-8-Ser-Arg-Cys.
[0086]
Here, the 54th glutamic acid and the 65th arginine of the amino acid sequence of fer-8-Ser-Arg are present on the inner surface of the apoferritin holding part 4, so that these amino acids are converted into cysteine having a reducing action. (AuCl incorporated into the holding unit 4 by substitution)_Four)^-7 can be reduced to deposit gold fine particles in the holding part 4. Thereby, the nucleus 1 made of gold can be formed in the holding portion 4 by an operation described later.
[0087]
For the production of the above-mentioned recombinant apoferritin, a known genetic recombination technique and protein expression method are used as described below.
[0088]
First, an appropriate restriction enzyme was prepared from a plasmid Takeda99224 (see S. Takeda et al. Biochim. Biophys. Acta., 1174, 218-220, 1993) prepared by Takeda et al. A DNA fragment encoding the amino acid sequence of apoferritin is cut out.
[0089]
Next, this DNA fragment is inserted into pMK-2, which is a vector plasmid for protein expression, to produce a plasmid for apoferritin expression.
[0090]
Subsequently, PCR (polymerase chain reaction) is carried out using this apoferritin expression plasmid as a template and a single-stranded DNA fragment incorporating the desired mutation as a primer. The target position of the DNA encoding the amino acid of apoferritin A desired mutation is introduced in a site-specific manner. In this way, a plasmid containing a DNA fragment of the mutant apoferritin gene from which the DNA encoding the 1st to 8th amino acids of apoferritin is deleted is prepared. This apoferritin gene DNA fragment may be excised and incorporated into another vector plasmid if necessary.
[0091]
Subsequently, the prepared plasmid was introduced into commercially available Escherichia coli (one of E. coli, Nova Blue), transformed, and then transformed into 37 ° C. using a jar fermenter (mass culture apparatus). Cultivate in large quantities. Since transformed E. coli is resistant to ampicillin, it can be selected by distinguishing it from untransformed E. coli using this as an index.
[0092]
In this Escherichia coli, recombinant apoferritin DNA incorporated into a plasmid is expressed, and apoferritin from which amino acid residues 1 to 8 are deleted (hereinafter referred to as fer-8) is produced in large quantities. . fer-8 is extracted and purified from E. coli cells by the procedure described below.
[0093]
Next, in order to prepare fer-8-Ser, using the plasmid containing the DNA encoding the amino acid sequence of fer-8 obtained in the previous operation as a template, the 128th aspartic acid of apoferritin and PCR is performed using as a primer a single-stranded DNA fragment encoding an amino acid sequence in which both amino acids of the 131st glutamic acid are replaced with serine.
[0094]
Next, a plasmid in which DNA encoding the amino acid sequence of fer-8-Ser is inserted is prepared by the same operation as that for fer-8, and this is introduced into E. coli (Nova Blue) and transformed. After mass transforming the transformed E. coli, fer-8-Ser is extracted and purified from the E. coli cells by the procedure described below.
[0095]
Hereinafter, by the same procedure, a plasmid inserted with DNA encoding the amino acid sequence of fer-8-Ser-Arg and fer-8-Ser-Arg were obtained, and then the amino acid sequence of fer-8-Ser-Arg-Cys A plasmid and fer-8-Ser-Arg-Cys into which DNA encoding the DNA is inserted are obtained.
[0096]
The procedure for extracting and purifying mutant apoferritin in the above-described operation is as follows.
[0097]
First, the culture solution of Escherichia coli after culturing is transferred to a centrifuge tube and set in a centrifuge, and centrifuged at 4 ° C., 10,000 rpm for 25 minutes to precipitate E. coli cells. .
[0098]
Next, after collecting the precipitated cells, the cells are crushed in the liquid using an ultrasonic crusher to elute apoferritin into the liquid. Next, the crushed cells are transferred to a centrifuge tube and set in a centrifuge, and centrifuged at 4 ° C., 10,000 rpm / 25 minutes for 25 minutes. Precipitate.
[0099]
Next, the supernatant (supernatant) is collected from the centrifuge tube, heat-treated at 60 ° C. for 15 minutes, transferred to a centrifuge tube, and centrifuged at 4 ° C., 10,000 rpm / 25 minutes. . By this operation, unnecessary protein is denatured and precipitated at the bottom of the tube.
[0100]
Subsequently, after collecting the supernatant from the centrifuge tube, column chromatography using Q-sepharose HP (gel filtration column) is performed at 4 ° C., and the apoferritin fraction contained in the supernatant is collected. This apoferritin fraction is further purified by flowing through Sephacryl S-300 (gel filtration column) at 25 ° C. and performing column chromatography. By this operation, impurities are removed and purified recombinant apoferritin is obtained.
[0101]
In the present invention, once DNA encoding modified apoferritin is obtained, this DNA can be amplified by a known technique. Therefore, when mass-producing recombinant apoferritin, it is not necessary to repeat the process of gene recombination.
[0102]
-Production of apoferritin holding gold particles-
First, recombinant apoferritin solution and KAuCl_FourSolution (or HAuCl_Four) And each final concentration is 0.5 mg / mL recombinant apoferritin, KAuCl_FourAfter preparing a solution so that 3 mmol / L and pH is 7-9, the solution is allowed to stand at room temperature for 24 hours or longer to allow gold particles to be taken into apoferritin to form a gold-apoferritin complex. Here, as the buffer, 100 mM phosphoric acid is preferably used at pH 7-8, and 100 mM Tris-Hcl is preferably used at pH 8-9.
[0103]
At this time, NaBH_FourIs added to the solution to a concentration of 1 mM or less, alcohol such as ethanol is added to a concentration of 10% or less (v / v), or irradiation with light or ultraviolet light is performed. (AuCl_Four)^-It is also possible to shorten the reaction time by accelerating the reduction reaction. However, NaBH_FourWhen the concentration of the solution exceeds 1 mM, or when the ethanol concentration exceeds 10% (v / v), (AuCl_Four)^-May be reduced before being taken into the apoferritin, and gold particles may be deposited on the outer surface of the apoferritin. The size of the gold particles deposited on the outer surface of the apoferritin varies greatly compared to the size of the gold particles formed by the apoferritin holding portion 4.
[0104]
In addition, inside the apoferritin, the surface of the deposited gold particle itself (AuCl_Four)^-It catalyzes the reduction reaction (autocatalysis). Thus, until the apoferritin holding part 4 is filled (AuCl_Four)^-The reduction reaction continues.
[0105]
In addition, the pH of the solution is 7-9 here when the pH of the solution is 6 or less (AuCl_Four)^-Reduction is very difficult to occur. Conversely, when the pH is 10 or more, (AuCl_Four)^-This is because the progress of the reduction of the metal cannot be controlled.
[0106]
Then, apoferritin that does not retain side reaction products and gold particles is removed by the same procedure as the purification of iron-containing ferritin, and the resulting solution is fractionated by gel column chromatography to include gold particles. Collect apoferritin as a solution. At this time, apoferritin in which gold particles are formed on the outer surface instead of the holding portion 4 or a small amount of apoferritin in which gold particles are formed on both the holding portion 4 and the outer surface, respectively. can get.
[0107]
When fer-8-Ser or fer-8-Ser-Arg is used as a recombinant apoferritin in a reaction to incorporate gold particles into apoferritin, the gold particles are external as in the case of apoferritin containing gold particles inside. Apoferritin formed on the surface is also generated. This is presumably because the reaction rate of gold deposition on the outer surface of apoferritin is faster than the reaction in which gold particles are formed in the apoferritin holding part 4.
[0108]
On the other hand, by using fer-8-Ser-Arg-Cys as recombinant apoferritin, the yield of apoferritin including gold particles is greatly improved. This is due to the reduction action of cysteine (Cys) introduced into the holding part 4 (AuCl in the holding part 4 of apoferritin._Four)^-This is because the reduction reaction is accelerated. The diameter of the gold particles contained in apoferritin is uniform at about 6 nm. That is, by using the recombinant apoferritin fer-8-Ser-Arg-Cys prepared in this embodiment, gold particles having a uniform size of nanometer order can be efficiently formed. Fine gold particles have applications and advantages not found in other metals, such as application to DNA sensors described later.
[0109]
In this embodiment, the apoferritin used was derived from the liver of the horse, but the apoferritin derived from other organs or apoferritin derived from other organisms, that is, composed of a multimer of monomer subunits, has a holding part inside. It is also possible to use proteins equipped with Since apoferritin derived from other organisms, such as Listeria ferritin derived from Listeria monocytogenes, also has the same three-dimensional structure as that derived from horses, recombinant apoferritin can be obtained by the same operation. Since the diameter of the core of the metal-apoferritin complex varies slightly depending on the species, this allows variation in the diameter of the gold particles.
[0110]
In addition to this, if it is a cage protein that can hold a metal or the like inside, it is possible to hold gold particles by changing the charge inside the channel and inside as in the present embodiment.
[0111]
In addition, in the case of other ferritin family proteins such as Dps protein comprising 12 monomer subunits and having a holding part for holding an inorganic substance inside, noble metal particles are held using the same genetic recombination technology as apoferritin. It is possible.
[0112]
In this embodiment, serine was substituted for both the 128th aspartic acid and the 131st glutamic acid present on the inner surface of channel 3 of apoferritin, but instead of serine, a neutral amino acid having a smaller molecular weight was used. Some glycine or alanine may be substituted.
[0113]
Moreover, in this embodiment, fer-8-Ser-Arg was mentioned as the recombinant apoferritin, but the amino acids substituting the 58th, 61st, and 64th glutamic acids of the amino acid sequence of apoferritin are lysine, alanine, and the like. Any basic, nonpolar or neutral amino acid having no negative charge may be used. Recombinant apoferritin obtained by replacing each of the 58th, 61st, and 64th glutamic acids in the amino acid sequence with lysine is hereinafter referred to as fer-8-Ser-Lys.
[0114]
Recombinant apoferritin obtained by substituting the 58th, 61st, and 64th glutamic acids of the amino acid sequence with alanine is denoted as fer-8-Ser-Ala.
[0115]
Recombinant apoferritin in which both 54th glutamic acid and 65th arginine of fer-8-Ser-Lys are substituted with cysteine is expressed as fer-8-Ser-Lys-Cys. In addition, recombinant apoferritin in which both 54th glutamic acid and 65th arginine of fer-8-Ser-Ala are replaced with cysteine is expressed as fer-8-Ser-Ala-Cys.
[0116]
Among these, the DNA sequence encoding the amino acid sequence of fer-8-Ser-Lys-Cys is described in SEQ ID NO: 1, and the amino acid sequence of fer-8-Ser-Lys-Cys is described in SEQ ID NO: 2, respectively. The amino acid sequence of SEQ ID NO: 2 starts from the 9th tyrosine.
[0117]
In the fer-8-Ser-Lys-Cys prepared in this embodiment, the 58, 61, and 64th (50th, 53, and 56th in SEQ ID NO: 2) Lys DNA sequences are both “aag”. ", But instead of this, it may be" aaa "which codes Lys. The Ser of 128th, 131st (120th, 123rd in SEQ ID NO: 2) and Cys of 54th, 65th (46th, 57th in SEQ ID NO: 2) should be DNA sequences encoding these amino acids. It may be different from the sequence shown in SEQ ID NO: 1. The same applies to other recombinant apoferritins.
[0118]
In addition, the 127th cysteine of recombinant apoferritin such as fer-8-Ser-Arg-Cys, fer-8-Ser-Lys-Cys and fer-8-Ser-Ala-Cys prepared in this embodiment is apo The cysteine is located on the outer surface of ferritin, and this cysteine is presumed to deposit gold particles on the outer surface of apoferritin. Therefore, by making the 127th cysteine of fer-8-Ser-Arg-Cys, fer-8-Ser-Lys-Cys and fer-8-Ser-Ala-Cys into a substance having a reducing function smaller than that of the cysteine It is considered that the precipitation of gold particles on the outer surface of apoferritin is suppressed, and the yield of apoferritin containing gold particles can be further improved. As this method, the 127th cysteine may be substituted with an amino acid such as alanine, or may be reacted with a chemical substance that reacts with a cysteine residue to suppress the reducing function.
[0119]
In this embodiment, a gold-apoferritin complex was prepared._Four)^-Instead of introducing chloroplatinic acid (PtCl_Four)^2-Can be produced into recombinant apoferritin to produce apoferritin retaining platinum particles. However, (PtCl_Four)^2-Is easily reduced in a pH 7-9 solution and platinum is precipitated in the solution, so the pH of the solution needs to be lower than 7. At this time, as the buffer solution, 100 mM acetic acid is used when the pH is around 4, and 100 mM β-alanine is used when the pH is around 3.
[0120]
The industrial use example of the recombinant apoferritin holding the noble metal particles produced in this embodiment will be described in the following embodiment.
[0121]
(Second Embodiment)
First, the configuration of the nucleotide detector in the present embodiment will be described. FIG. 5 is a cross-sectional view showing the structure of the nucleotide detector of this embodiment.
[0122]
As shown in the figure, the nucleotide detector 10 of the present embodiment is a DNA sensor. As shown in FIG. 5, the substrate 11 and the surface of the substrate 11 have a high density and high precision (adjacent particles and It consists of nanometer-size (diameter of about 6 nm) gold particles 12 arranged at an interval of about 12 nm, and single-stranded DNA (thiol DNA) 13 having a sulfur atom at the end. It is a combination.
[0123]
Next, a method for producing the nucleotide detector 10 of the present embodiment will be described. In order to produce the nucleotide detector 10 of this embodiment, it is necessary to arrange and fix the gold particles 12 having a diameter of about 6 nm on the surface of the substrate 11 in a two-dimensional manner with high density and high accuracy.
[0124]
First, recombinant apoferritin (fer-8-Ser-Arg-Cys and gold particle complex; hereinafter referred to as gold-encapsulated apoferritin 15) holding the gold particles 12 of the first embodiment is used as a method described later. By disposing on the surface of the substrate 11.
[0125]
FIG. 3 is a diagram schematically illustrating the gold-encapsulated apoferritin 15 disposed on the substrate 11, and FIG. 4 is a diagram illustrating an electron micrograph of the gold-encapsulated apoferritin 15 disposed on the substrate 11. .
[0126]
When photographing in FIG. 4, gold glucose having a size not taken up by apoferritin was used for staining. Here, the gold glucose staining is used because the dye enters the apoferritin and the presence of the gold particles cannot be confirmed when the dye is stained with a normal dye.
[0127]
By this operation, as shown in FIG. 3 or FIG. 4, a film of gold-encapsulated apoferritin 15 arranged with high density and high accuracy is formed on the substrate 11. FIG. 4 shows that the outer diameter of apoferritin at this time is about 12 nm.
[0128]
Subsequently, the outer shell 2 made of protein in the gold-encapsulated apoferritin 15 is removed to leave only the gold particles 12. Next, the thiol DNA 13 is bonded to the gold particles 12. The DNA used here is a single-stranded DNA.
[0129]
In this embodiment, a known method can be used to place and fix the gold-encapsulated apoferritin 15 on the surface of the substrate 11 in a two-dimensional manner with high density and high accuracy.
[0130]
For example, a transfer method (Adv. Biophys., Vol. 34, p99-107, (1997)) developed by Yoshimura et al. Described below can be used.
[0131]
In this method, first, a liquid in which gold-encapsulated apoferritin 15 is dispersed is injected into a sucrose solution having a concentration of 2% using a syringe. Then, the liquid floats toward the liquid surface of the sucrose solution.
[0132]
Next, the liquid that first reaches the gas-liquid interface forms an amorphous film made of denatured apoferritin, and the liquid that reaches later adheres under the amorphous film.
[0133]
Next, a two-dimensional crystal of gold-encapsulated apoferritin 15 is formed under the amorphous film. Next, if a substrate 11 (a silicon wafer, a carbon grid, a glass substrate, or the like) is placed on a film composed of an amorphous film and a two-dimensional crystal of gold-encapsulated apoferritin 15, the film composed of this gold-encapsulated apoferritin 15 Is transferred to the surface of the substrate 11.
[0134]
By this method, as shown in FIG. 3, the gold-encapsulated apoferritin 15 can be disposed on the substrate 11 with high density and high accuracy.
[0135]
At this time, by treating the surface of the substrate 11 to be hydrophobic, the film can be transferred onto the surface of the substrate 11 more easily.
[0136]
Next, the outer shell 2 made of protein is removed. Since protein molecules are generally vulnerable to heat, the outer shell 2 can be removed by the heat treatment described below.
[0137]
For example, when left in an inert gas such as nitrogen at 400 to 500 ° C. for about 1 hour, the outer shell 2 and the amorphous film made of protein are burned out, and the gold particles 12 are two-dimensionally formed on the substrate 11. In the form of dots that are regularly arranged with high density and high accuracy.
[0138]
As described above, the gold particles 12 held in the gold-encapsulated apoferritin 15 can appear two-dimensionally on the substrate 11 and can be arranged with high density and high accuracy.
[0139]
Next, formation of the nucleotide detection apparatus 10 of this embodiment is demonstrated below.
[0140]
The nucleotide detector 10 of this embodiment is a device in which thiol DNA 13 is bonded to gold particles 12 arranged on a substrate 11 as described above.
[0141]
The bonding method of the gold particles 12 and the thiol DNA 13 may be as follows: the substrate 11 on which the gold particles 12 are disposed and the aqueous solution of the thiol DNA 13 are brought into contact with each other and left for a predetermined time. This is because sulfur easily reacts with gold, so that a conjugated bond is easily formed with the gold particle 12 at the end of the thiol DNA 13 or thiol RNA.
[0142]
Specifically, when the thiol DNA 13 in the aqueous solution and the gold particles 12 on the substrate 11 come into contact with each other, the sulfur atom S of the thiol DNA 13 and the gold particles 12 are covalently bonded in a one-to-one relationship, and the thiol DNA 13 has an extremely high density. -It is arranged on the substrate 11 with high accuracy. Since the gold particles 12 on the substrate 11 are two-dimensionally arranged with high density and high accuracy, the thiol DNA 13 bonded to the gold particles 12 is also two-dimensionally arranged with high density and high accuracy, and the size of the particles Accordingly, the nucleotide detector 10 in which the number of particles per unit area is uniformly arranged is obtained.
[0143]
In this step, nucleotides such as thiol RNA and PCR primers with thiolated ends may be used instead of thiol DNA 13.
[0144]
In the above step, the concentration of the thiol DNA 13 in the aqueous solution may theoretically be equal to the number of the gold particles 12 on the substrate 11 and the number of the thiol DNA 13. However, in practice, it is preferable that the number of thiol DNAs 13 is larger than the number of gold particles 12. Therefore, in the present embodiment, an aqueous solution of thiol DNA 13 having a high concentration is used so that thiol DNA 13 having a molecular number larger than that of gold-encapsulated apoferritin 15 contained in a dispersed state in the liquid is included.
[0145]
In addition, as the temperature of the aqueous solution of thiol DNA 13 is higher, the bond between the sulfur atom S of the thiol DNA 13 and the gold particles 12 is promoted. However, if the temperature is too high, handling of the aqueous solution of thiol DNA 13 becomes difficult, for example, convection becomes intense. Moreover, since it is disadvantageous from the viewpoint of energy consumption, it is generally preferable to carry out by heating an aqueous solution of thiol DNA 13 to about 20 to 60 ° C.
[0146]
As described above, the nucleotide detector 10 of the present embodiment that can easily detect DNA or RNA to be detected is obtained.
[0147]
Next, a DNA detection method when the nucleotide detector 10 is a DNA sensor will be described.
[0148]
First, a solution containing a DNA group to be detected (a group to be detected) is prepared, and the group to be detected is preliminarily treated with a fluorescent label.
[0149]
The solution of the DNA group to be detected labeled with fluorescence is left in contact with the nucleotide detector 10 on which the thiol DNA 13 is placed.
[0150]
When DNA that hybridizes with the thiol DNA 13 of the nucleotide detection device 10 is present in the detected DNA group after a certain period of time, the thiol DNA 13 of the nucleotide detection device 10 and the DNA in the detected DNA group are: Constructs a double helix and completes a stable bond.
[0151]
Next, if the nucleotide detection device 10 is washed with a solution that does not contain a fluorescent substance such as water, the DNA that has not bound to the thiol DNA 13 of the nucleotide detection device 10 in the detected DNA group and the nucleotide detection device 10 The remaining trace amount of fluorescent material is removed.
[0152]
Thereafter, the surface of the nucleotide detector 10 is irradiated with a light source such as a laser to observe fluorescence. At this time, if a DNA having a sequence that hybridizes with the thiol DNA 13 of the nucleotide detector 10 is present in the group of DNAs to be detected, it emits fluorescence.
[0153]
As described above, whether or not DNA having a predetermined sequence is present in the detected DNA group can be detected based on whether or not fluorescence is emitted.
[0154]
In particular, in the nucleotide detection device 10 of the present embodiment, the thiol DNAs 13 are uniformly arranged over the entire substrate with high density and high accuracy. For this reason, it can be used as a high-performance DNA sensor having high fluorescence intensity, high accuracy and uniformity, and a very high SN ratio. Therefore, when the nucleotide detector 10 of this embodiment is used as a DNA sensor, it can be determined that DNA having a predetermined sequence exists in the detected DNA group if a fluorescence intensity higher than a predetermined value is obtained. That is, there is almost no possibility of erroneous determination of the presence or absence of DNA having a predetermined sequence.
[0155]
Furthermore, in the nucleotide detection apparatus 10 of the present embodiment, the thiol DNA 13 is arranged with high density and high precision uniformly over the entire substrate, and the fluorescence intensity after hybridization of DNA having a predetermined sequence is: There is almost no difference between substrates. Therefore, it is not necessary to change the threshold value of the fluorescence intensity for each substrate in order to determine the presence or absence of hybridized DNA, and it is possible to greatly reduce the trouble of adjusting the fluorescence detector. Demonstrate.
[0156]
In the present embodiment, the case where the nucleotide detection device 10 is a DNA sensor has been described. However, the nucleotide detection device 10 may be an RNA sensor by using an RNA group instead of a DNA group to be detected. it can.
[0157]
Conventionally, a nucleotide detector such as a DNA chip is disposable, but in the nucleotide detector 10 of the present embodiment, the substrate and DNA (or RNA) are firmly fixed via sulfur atoms and gold particles. Therefore, this fixation can be maintained even at a temperature of 100 ° C. Accordingly, the hybridized DNA can be repeatedly used by dissociating it from the thiol DNA and washing it away.
[0158]
Further, instead of the gold-encapsulated apoferritin 15 used in this embodiment, a gold-apoferritin complex obtained by growing gold particles on the outer surface obtained in the first embodiment may be used. Although the gold particles grown on the outer surface of apoferritin are not uniform in size, the gold particles can be arranged on the substrate with high density and high accuracy in the same manner as the gold particles 12 used in this embodiment. . In the first embodiment, when fer-8-Ser-Arg is used, fer-8-Ser-Arg in which gold particles are grown on the outer surface in a very high yield can be obtained, so that gold-encapsulated apoferritin 15 The manufacturing cost of the nucleotide detector 10 can be reduced as compared with the case of using.
[0159]
(Third embodiment)
In this embodiment, a non-volatile memory cell including a dot body formed using the gold-encapsulated apoferritin produced in the first embodiment as a floating gate will be described. The nonvolatile memory cell and the manufacturing method thereof according to this embodiment are those described in Japanese Patent Application Laid-Open No. 11-233752.
[0160]
FIG. 6 is a cross-sectional view showing the structure of a nonvolatile memory cell using a dot body as a floating gate. As shown in the figure, on a p-type Si substrate 21, a polysilicon electrode 26 functioning as a control gate and a dot body 24 configured by gold fine particles having a particle diameter of about 6 nm and functioning as a floating gate electrode. And a gate oxide film 23 functioning as a tunnel insulating film interposed between the p-type Si substrate 21 and the floating gate, and an inter-electrode insulation between the control gate and the floating gate for transmitting the voltage of the control gate to the floating gate A silicon oxide film 25 functioning as a film is provided. In the p-type Si substrate 21, first and second n-type diffusion layers 27a and 27b functioning as a source or a drain are formed, and the first and second n-type diffusion layers in the p-type Si substrate 21 are formed. The region between 27a and 27b functions as a channel. Further, an element isolation oxide film 22 formed using a selective oxidation method or the like is formed between the illustrated memory cell and the adjacent memory cell for electrical isolation. The first and second n-type diffusion layers 27a and 27b are connected to the first and second aluminum wirings 31a and 31b through the tungsten plug 30, respectively. Although not shown in FIG. 6, the polysilicon electrode 26 and the p-type Si substrate 21 are also connected to the aluminum wiring, and the voltage of each part of the memory cell is controlled by using the aluminum wiring or the like. Yes.
[0161]
This memory cell is easily formed as follows.
[0162]
First, an element isolation oxide film 22 surrounding the active region is formed by the LOCOS method, and then a gate oxide film 23 is formed on the substrate. Thereafter, the dot body 24 is formed on the entire substrate by using the gold-encapsulated apoferritin produced in the first embodiment. At this time, by using apoferritin encapsulating gold particles, it is possible to omit the step of reducing the dot body, which was necessary when using apoferritin encapsulating a conventional metal oxide.
[0163]
Next, a silicon oxide film and a polysilicon film filling the dot body 24 are deposited on the substrate by CVD.
[0164]
Next, the silicon oxide film and the polysilicon film are patterned to form a silicon oxide film 25 that serves as an interelectrode insulating film and a polysilicon electrode 26 that serves as a control gate electrode. Thereafter, impurity ions are implanted using the photoresist mask and the polysilicon electrode 26 as a mask to form first and second n-type diffusion layers 27a and 27b.
[0165]
Thereafter, the interlayer insulating film 28 is formed, the contact hole 29 is opened in the interlayer insulating film 28, the tungsten plug 30 is formed by burying tungsten in the contact hole 29, and the first and second methods. Aluminum wirings 31a and 31b are formed.
[0166]
The memory cell of this embodiment includes a MOS transistor (memory transistor) including a polysilicon electrode 26 that functions as a control gate and first and second n-type diffusion layers 27a and 27b that function as a source or drain, and a floating gate. This is a non-volatile memory cell utilizing the fact that the threshold voltage of the memory transistor changes according to the amount of charge stored in the dot body 24 functioning as This nonvolatile memory cell can obtain a function as a memory for storing binary values. However, by controlling not only the presence / absence of charges stored in the dot body 24 but also the amount of stored charges, a multi-value of three or more values can be obtained. A memory can also be realized.
[0167]
When erasing data, FN (Fowler-Nordheim) current or direct tunneling current through the oxide film is used.
[0168]
For data writing, FN current, direct tunneling current, or channel hot electron (CHE) injection through an oxide film is used.
[0169]
According to the nonvolatile memory cell of this embodiment, since the floating gate is composed of gold fine particles having a particle diameter that is small enough to function as a quantum dot, the amount of accumulated charge is small. Therefore, the amount of current during writing and erasing can be reduced, and a low power consumption nonvolatile memory cell can be configured.
[0170]
In the nonvolatile memory cell of this embodiment, the floating gate is
Since the size of the gold fine particles is uniform, the characteristics at the time of charge injection and extraction are uniform among the gold fine particles, and control can be easily performed in these operations.
[0171]
Further, the dot bodies 24 may be formed continuously in contact with each other, that is, in a state of forming a film as a whole, or may be formed dispersively apart from each other. In this embodiment, since apoferritin containing gold fine particles is used, such a fine dot pattern is formed by a method such as arranging apoferritin after applying hydrophobic treatment to a desired portion of the substrate. It can be formed easily.
[0172]
In this embodiment, gold is used as the constituent material of the dot body, but platinum may be used instead. By using the platinum-encapsulated apoferritin produced in the first embodiment instead of the gold-encapsulated apoferritin, a dot body made of platinum having a diameter of about 6 nm can be formed. In this case as well, there is an advantage that a reduction process of the dot body is unnecessary as in the case of using gold-encapsulated apoferritin.
[0173]
(Fourth embodiment)
As this embodiment, a method of using gold encapsulated apoferritin according to the first embodiment to arrange gold particles on a substrate and using the gold particles as an etching mask will be described.
[0174]
7A to 7C are cross-sectional views illustrating a method for forming a microstructure using gold particles as a mask.
[0175]
First, in the step shown in FIG. 7 (a), after the gold-encapsulated apoferritin is placed on the silicon substrate 34 at a desired position by the same method as in the second embodiment, the heat treatment is performed to form the protein. Remove the outer shell. As a result, gold particles 33 having a diameter of about 6 nm remain on the substrate 34.
[0176]
Here, the use of apoferritin encapsulating gold eliminates the reduction step performed when metal oxide-encapsulated apoferritin is used.
[0177]
Subsequently, in the step shown in FIG.₆ The silicon substrate 34 is selectively etched by performing ion reactive etching (RIE) on the silicon substrate 34 for 5 minutes using a gas. This is because the gold particles 33 are less likely to be etched than the silicon substrate 34.
[0178]
Next, in the step shown in FIG. 7C, when the etching further proceeds, the gold particles 33 are finally removed, and the silicon substrate 34 having a desired pattern remains. According to the method of the present embodiment, a uniform fine columnar pattern (hereinafter, “fine columnar pattern” is referred to as “fine column”) having an upper surface diameter of about 6 nm can be accurately formed on the substrate. That is, the method of the present embodiment enables formation of a fine structure having a uniform size and a fine size (that is, precise processing of the fine structure), which has been difficult in the past.
[0179]
The microstructure formed by the method of the present embodiment can be used for, for example, a light emitting element using a quantum effect described later.
[0180]
In this embodiment, gold particles are used as an etching mask, but platinum particles can be used instead. For this purpose, in the step (a), the platinum-encapsulated apoferritin of the first embodiment may be used instead of the gold-encapsulated apoferritin.
[0181]
Depending on the situation, a reduction step may be unnecessary even if ferritin encapsulating Fe and apoferritin encapsulating Ni, Co, etc. are used, but by using the noble metal encapsulating apoferritin of this embodiment, Even under circumstances, the reduction process can be omitted.
[0182]
In the step (a) of this embodiment, heat treatment was used to remove the outer shell of gold-encapsulated apoferritin, but instead of this, ozone decomposition or chemical decomposition with cyanogen bromide (CNBr) may be used. Good.
[0183]
(Fifth embodiment)
As a fifth embodiment, a method of manufacturing an optical semiconductor device described in Japanese Patent Application Laid-Open No. 08-083940 reported by Eriguchi et al. Using fine columns formed by the processing method of the fourth embodiment. This will be described below.
[0184]
FIG. 8 is a cross-sectional view of an optical semiconductor device using a semiconductor fine column having a top surface diameter of 6 nm formed according to the fourth embodiment.
[0185]
First, in the fourth embodiment, a substrate in which a p-type well 51 is formed in part of n-type silicon and an n-type well is formed on the p-type well 51 is used. This substrate is processed by the method of the fourth embodiment, and semiconductor fine columns 42 made of n-type silicon are formed at a high density.
[0186]
Next, after the side surfaces of the semiconductor micro pillars 42 are covered with an insulating layer 43 made of a silicon oxide film by a thermal oxidation method, the gaps between the semiconductor micro pillars 42 are filled with the insulating layer 43 and the tip surfaces thereof are flattened.
[0187]
Further, the insulating layer on the surface of the tip of the flattened semiconductor fine pillar 42 is removed from the insulating layer 43, and the transparent electrode 44 is formed thereon.
[0188]
Note that the side of the quantization region Rqa on the silicon substrate 41 is partitioned from other regions by a pre-formed insulating isolation layer 49. A side electrode 50 penetrating the insulating separation layer 49 is also formed in advance, and is connected to the silicon substrate 41 that functions as a lower electrode with respect to the transparent electrode 44 that is the upper electrode of each semiconductor fine column 42.
[0189]
Thereby, an optical semiconductor device is formed, and when a forward voltage is applied between the transparent electrode 44 and the side electrode 50, electroluminescence occurs at room temperature. Further, by changing the carrier injection voltage, electroluminescence of visible light corresponding to each emission of red, blue and yellow occurs.
[0190]
According to the present embodiment, it is possible to realize an optical semiconductor device having high luminous efficiency that has been difficult to implement until now.
[0191]
(Other embodiments)
In the production process of the gold-apoferritin complex of the first embodiment, a small amount of gold-apoferritin complex holding gold particles on both the outer surface and the holding part is obtained.
[0192]
FIG. 9 is a view showing a gold-apoferritin complex holding gold particles on both the outer surface and the holding part. In the figure, the diameter of the first gold particles 61 held in the holding portion is about 6 nm, and the size of the second gold particles 62 formed on the outer surface of apoferritin varies, but at least The size is larger than the first gold particles 61 encapsulated in apoferritin. The first gold particles 61 held in the holding part are surrounded by an outer shell 63 of apoferritin.
[0193]
This gold-apoferritin complex is arranged in a film shape on a silicon substrate or the like so that the second gold particles 62 are on the top.
[0194]
This substrate can be further processed to produce a double-dot type nonvolatile memory cell having the first gold particles 61 and the second gold particles 62 as floating gates. This non-volatile memory cell is characterized by a long data retention time. This is because particles with different sizes are different in the ease of charge entry and release, so that the input information is discharged. This is because it can be held by the gold particles that are difficult to do. Here, by using the gold-apoferritin complex, a nonvolatile memory cell having a long retention time can be easily formed.
[0195]
Further, by using apoferritin, nanometer-sized gold particles can be used as a floating gate, so that a memory cell can be miniaturized.
[0196]
Further, in the present embodiment, only the gold-apoferritin complex was used, but by using a complex of another metal and apoferritin in combination with the gold-apoferritin complex, dots having different levels were used. A non-volatile memory that can be manufactured and has a long holding time can be easily manufactured.
[0197]
In this embodiment, apoferritin that holds platinum on the outer surface and the holding portion may be used instead of apoferritin that holds gold on the outer surface and the holding portion, and this and gold are held. Apoferritin may be used in combination.
[0198]
【The invention's effect】
According to the recombinant apoferritin and the production method thereof, the noble metal-recombinant apoferritin complex and the production method thereof of the present invention, a noble metal atom is introduced into apoferritin by modifying the internal structure using a gene recombination technique. As a result, it becomes possible to form noble metal particles applicable to various microstructures. Moreover, said recombinant apoferritin can be obtained efficiently by using the Escherichia coli and the recombinant gene of the present invention.
[0199]
[Sequence Listing]

[Brief description of the drawings]
FIG. 1 is a diagram schematically showing the structure of ferritin.
FIGS. 2A to 2C are cross-sectional views schematically showing recombinant apoferritin according to the first embodiment of the present invention.
FIG. 3 is a view schematically showing gold-encapsulated apoferritin disposed on a substrate.
FIG. 4 is an electron micrograph of gold-encapsulated apoferritin placed on a substrate.
FIG. 5 is a diagram schematically showing a nucleotide detection apparatus according to a second embodiment of the present invention.
FIG. 6 is a cross-sectional view showing the structure of a nonvolatile memory cell using a dot body made of gold particles as a floating gate according to a third embodiment of the present invention.
FIGS. 7A to 7C are cross-sectional views showing the steps of forming a microstructure according to the fourth embodiment of the present invention. FIGS.
FIG. 8 is a cross-sectional view of an optical semiconductor device using a microstructure formed in the fourth embodiment according to the fifth embodiment of the present invention.
FIG. 9 is a view schematically showing a gold-apoferritin complex formed by the present invention and holding precious metal particles on both the outer surface and the holding part.
[Explanation of symbols]
1 nucleus
2 outer shell
3 channels
4 Holding part
7 Chloroauric acid ion (AuCl_Four)^-
7 'gold (Au) atom
10 Nucleotide detector
11 Substrate
12 Gold particles
13 Thiol DNA
15 Gold Apoferritin
21 p-type Si substrate
22 Device isolation oxide film
23 Gate oxide film
24 dot body
25 Silicon oxide film
26 Polysilicon electrode
27a First n-type diffusion layer
27b Second n-type diffusion layer
28 Interlayer insulation film
29 Contact hole
30 Tungsten plug
31a First aluminum wiring
31b Second aluminum wiring
33 gold particles
34 Silicon substrate
41 Silicon substrate
42 Semiconductor micro-pillars
43 Insulating layer
44 Transparent electrode
49 Insulation separation layer
50 Side electrode
51 p-type well
Rqa quantization region
61 First gold particles
62 second gold particles
63 Outer shell

Claims (11)

A recombinant basket-like protein produced by genetic recombination technology,
A holding part inside the above-mentioned recombinant basket-like protein and capable of holding precious metal particles;
A tunnel-like channel connecting the holding part and the outside of the recombinant basket-like protein,
The recombinant cage protein is apoferritin,
A first neutral amino acid having a molecular size smaller than that of glutamic acid and aspartic acid is provided at a position where the first glutamic acid (Glu) and the first aspartic acid (Asp) should be present on the inner surface of the channel. ,
A recombinant basket-like protein further comprising a basic amino acid or a second neutral amino acid at a position where the second glutamic acid should be present on the inner surface of the holding part . The recombinant basket-like protein according to claim 1 ,
A recombinant basket-like protein, wherein the noble metal particles are gold or platinum. The recombinant basket-like protein according to claim 1 ,
A recombinant cage protein, wherein the first neutral amino acid is selected from serine (Ser), alanine (Ala), and glycine (Gly). The recombinant basket-like protein according to claim 1 ,
A recombinant cage protein, wherein the basic amino acid or the second neutral amino acid is selected from arginine (Arg), lysine (Lys), and alanine (Ala). The recombinant basket-like protein according to claim 1,
One or more cysteine (Cys) substituted with an amino acid exists in the inner surface of the said holding | maintenance part, The recombinant basket-like protein characterized by the above-mentioned. The recombinant basket-like protein according to claim 1,
A recombinant cage protein characterized in that a substance having a reducing function smaller than that of cysteine is provided on the outer surface of the recombinant cage protein at a position where cysteine should be present. A noble metal-recombinant cage protein complex composed of noble metal particles and a recombinant cage protein,
The recombinant cage protein comprises a holding part capable of holding noble metal particles, and a tunnel-like channel connecting the holding part and the outside of the recombinant basket protein,
The recombinant cage protein is apoferritin,
A first neutral amino acid having a molecular size smaller than that of glutamic acid and aspartic acid at a position where the first glutamic acid and first aspartic acid should be present on the inner surface of the channel;
A noble metal-recombinant cage protein complex further comprising a basic amino acid or a second neutral amino acid at a position where the second glutamic acid should be present on the inner surface of the holding part . The noble metal-recombinant cage protein complex according to claim 7 ,
A noble metal-recombinant cage protein complex characterized by holding gold or platinum particles on the outer surface. The noble metal-recombinant cage protein complex according to claim 7 ,
A noble metal-recombinant cage protein complex, wherein the first neutral amino acid is selected from serine, alanine, and glycine. The noble metal-recombinant cage protein complex according to claim 7 ,
The noble metal-recombinant cage protein complex, wherein the basic amino acid or the second neutral amino acid is selected from arginine, lysine and alanine. The noble metal-recombinant cage protein complex according to claim 7 ,
A noble metal-recombinant cage protein complex characterized in that one or more cysteines substituted with amino acids are present on the inner surface of the holding part.

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