U.S. patent application number 10/859530 was filed with the patent office on 2004-12-09 for method for fabricating a carbon nanotube array and a biochip using the self-assembly of supramolecules and staining of metal compound.
Invention is credited to Choi, Do Hwan, Jung, Dae Hwan, Jung, Hee Tae, Kwon, Ki Young, Lee, Su Rim.
Application Number | 20040245209 10/859530 |
Document ID | / |
Family ID | 33487906 |
Filed Date | 2004-12-09 |
United States Patent
Application |
20040245209 |
Kind Code |
A1 |
Jung, Hee Tae ; et
al. |
December 9, 2004 |
Method for fabricating a carbon nanotube array and a biochip using
the self-assembly of supramolecules and staining of metal
compound
Abstract
A method for fabricating a carbon nanotube (CNT) nanoarray,
which includes the steps of forming a thin film of supramolecules
on a substrate on which metal catalyst for CNT synthesis is
deposited, inducing the self-assembly of the supramolecules by
annealing to form a regular structure, selectively staining the
formed regular structure with a metal compound, etching the metal
compound-stained thin film to form a nanometer or smaller size
pattern, forming a nanopattern of metal catalyst by using the
nanopattern of supramolecules stained with the formed metal
compounds, and growing carbon nanotubes (CNTs) vertically on the
formed metal catalyst nanopattern. A biochip is readily fabricated
by binding bioreceptor(s) to CNTs of the CNT nanoarray.
Inventors: |
Jung, Hee Tae; (Daejeon,
KR) ; Jung, Dae Hwan; (Daejeon, KR) ; Kwon, Ki
Young; (Gyeongsangbuk-do, KR) ; Lee, Su Rim;
(Gangwon-do, KR) ; Choi, Do Hwan; (Seoul,
KR) |
Correspondence
Address: |
INTELLECTUAL PROPERTY / TECHNOLOGY LAW
PO BOX 14329
RESEARCH TRIANGLE PARK
NC
27709
US
|
Family ID: |
33487906 |
Appl. No.: |
10/859530 |
Filed: |
June 2, 2004 |
Current U.S.
Class: |
216/8 ;
216/58 |
Current CPC
Class: |
C01B 2202/08 20130101;
C01B 32/162 20170801; B82Y 30/00 20130101; B82Y 40/00 20130101 |
Class at
Publication: |
216/008 ;
216/058 |
International
Class: |
C23F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 5, 2003 |
KR |
10-2003-0036530 |
Claims
What we claim is:
1. A method for fabricating carbon nanotubes (CNT) nanoarray, which
comprises the steps of: (a) forming on a substrate a thin film of a
metal catalyst selected from the group consisting of Fe, Ni, Co,
and alloys of said metals; (b) forming a thin film of
supramolecules inducing self-assembly on the thin film of the metal
catalyst; (c) self-assembling the supramolecules by annealing to
form a regular structure; (d) selectively staining the formed
regular structure with a metal compound; (e) removing a portion
which is not stained with the metal compound by etching wherein the
metal compound-stained thin film is used as a mask, thereby forming
nanopattern of a supramolecule stained with the metal compound; (f)
forming nanopattern of the metal catalyst by ion-milling using the
nanopattern of the supramolecule as a mask; and (g) arranging CNTs
vertically on the nanopattern of the metal catalyst
supramolecules.
2. The method of claim 1, wherein the supramolecule is a
disc-shaped dendrimer, fan-shaped supramolecules or cone-shaped
supramolecules.
3. The method of claim 2, wherein the supramolecule is the compound
of the following formula (1): 4
4. The method of claim 1, wherein step (c) includes heating the
supramolecules above their liquid crystal transition temperature
and then cooling slowly.
5. The method of claim 1, wherein the metal compound of the step
(d) comprises ruthenium tetraoxide (RuO.sub.4).
6. The method of claim 1, which additionally comprises a step of
exposing carboxyl functionality by plasma treatment of ends of the
vertically arranged CNTs.
7. A method of fabricating a biochip, comprising attaching to a
CNT, in a CNT nanoarray fabricated according to the method of claim
1, a bioreceptor selected from the group consisting of proteins,
peptides, amino acids, DNA, PNA, enzymatic substrates, ligands,
cofactors, carbohydrates, lipids, oligonucleotides, and RNA.
8. The method of claim 7, wherein the bioreceptor is attached to a
CNT in said nanoarray by applying an electric field.
9. The method of claim 8, wherein a charge of a polarity opposite
to a net charge of the bioreceptor is applied to the CNT.
10. The method of claim 8, wherein the bioreceptor is attached to
the CNT using a binding aid.
11. The method of claim 10, wherein the binding aid comprises a
chemical substance having an aldehyde, amine or imine group
attached to a terminal carbon group.
12. A method for fabricating a biochip, which comprises binding to
a terminal carboxyl functionality of a CNT, in a CNT nanoarray
fabricated by the method of claim 6, a bioreceptor having an amine
group(NH.sub.2).
13. The method of claim 12, which comprises using a coupling agent
and a coupling aid for inducing formation of an amide bond in said
binding.
14. A biochip fabricated by the method of claim 7, in which a
bioreceptor, selected from the group consisting of proteins,
peptides, amino acids, DNA, PNA, enzymatic substrates, ligands,
cofactors, carbohydrates, lipids, oligonucleotides, and RNA, is
attached to a CNT of said CNT nanoarray.
15. A method of detecting reaction between biomaterials and
bioreceptors, which comprises using the biochip of claim 14 to
effect a bioreceptor/biomaterial reaction.
16. A biochip fabricated by the method of claim 12, in which a
bioreceptor, selected from the group consisting of proteins,
peptides, amino acids, DNA, PNA, enzymatic substrates, ligands,
cofactors, carbohydrates, lipids, oligonucleotides, and RNA, is
bound to a CNT in said CNT nanoarray by an amide bond.
17. A method of detecting reaction between biomaterials and
bioreceptors, which comprises using the biochip of claim 16 to
effect a bioreceptor/biomaterial reaction.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to a method for
fabricating a carbon nanotube (CNT) nanoarray, which comprises the
steps of forming a thin film of supramolecules on a substrate,
inducing the self-assembly of the supramolecules by annealing to
form a regular pattern, selectively staining the formed regular
pattern with a metal compound, etching the metal compound-stained
thin film to form a nanometer or smaller size metal catalyst
pattern, and growing carbon nanotubes (CNTs) vertically on the
formed metal catalyst pattern. The invention also relates to a
method for fabricating a biochip, including attachment of a
bioreceptor to the above fabricated CNT array.
[0003] 2. Background of the Related Art
[0004] Formerly, surface pattern formation has been achieved by
photolithography using a polymeric thin film as photoresist, but
the realization of a nanometer-sized, highly precise pattern by
this method encounters many difficulties, because of limitations in
the wavelength of light capable of being used and the necessity for
provision of an apparatus and technology suitable for such light
wavelength, as well as issues relating to the resolution of the
polymer itself.
[0005] Since the year 1990, there have been attempts to use new
photoresists in photolithography and to increase the resolution of
pattern using light of a shorter wavelength. Furthermore,
patterning techniques of a completely new concept, such as
nanopatterning techniques using soft lithography, started to
appear. Such techniques have advantages in that they allow
inexpensive patterning and continuous operations. However, their
resolution limit is a level of about 100 nm and it is difficult to
expect a further increase in resolution leading to an increase in
integration density.
[0006] Meanwhile, Korean patent No. KR 10/263671B1 discloses a
method for forming nanometer-sized fine patterns using
supramolecules as a patterning material. In this method, the
thickness of fine pattern remaining in a groove is ensured using
one additional buffer layer in order to ensure a margin for
excessive etching, and a spacer is also formed on the buffer layer
in order to reduce the size of the groove. However, the number of
process steps is large, and the pattern size is a level of several
tens of nanometers.
[0007] Korean patent publication No. KR 2002-0089528A discloses a
small-sized, self-assembled structure for forming devices that are
widely used in the microelectronic industry. The self-assembly
method disclosed in this application provides the ability to form
arrays in association with a surface, but it is impossible for the
self-assembly itself to determine the position of a device-forming
material within the boundary along the surface. Thus, in forming a
device within the boundary along the surface, an individual
positioning technique is necessary, and a suitable positioning
technique is used with the self-assembly method, to form a
structure capable of functioning as an individual part in
integrated electronic circuits. The positioning technique permits
one to determine the boundary of a structure by lithography, direct
formation methods or other positioning techniques, so that a
patterned substrate is formed and a device is assembled on the
substrate by self-assembly.
[0008] A self-assembled structure can be combined with a structure
formed by the conventional chemical or physical deposition
technique, and an integrated electronic circuit can comprise
integrated optical parts. The self-assembled structure can be
formed using nanoparticle dispersion in such a manner that the
desired structure is obtained by adjustment according to a material
surface state and temperature and concentration conditions. A
linker, one end of which is bound to the substrate surface and the
other end of which is chemically bound to nanoparticles, is used,
and selective binding using the linker can be used to yield a
self-assembly process of nanoparticles.
[0009] Another selective binding method is to use natural
interaction, such as electrostatic and chemical interaction, to
perform the self-assembly process of nanoparticles, in which the
nanoparticles are deposited in micropores such that they are
positioned within the boundary defined by porous regions. The
micropores can be found in certain materials, such as inorganic
oxides or two-dimensional organic crystals, or suitable micropores
can be formed by, for example, ion milling or chemical etching.
However, this method is disadvantage in that the process is
complex, and a spacing between pattern remains at a level of
several tens to hundreds of nanometers.
[0010] Furthermore, Korean patent publication No. 2003-0023191A
discloses a method for forming a nanometer-sized ultrafine pattern
using a self-assembled monomolecular layer. This method comprises
the steps of forming a layer of aromatic imine molecules with
substituted end groups on a substrate, selectively binding and
cutting the substituent groups of the aromatic imine molecule
layer, and hydrolyzing the resulting aromatic imine molecule layer,
thereby enabling the pattern to be formed in a short time. However,
the pattern size according to this method still remains at a level
of several tens of nanometers.
[0011] Meanwhile, dip-pen nanolithography was reported in which the
tip of an atomic force microscope is stained with surfactant
molecules having a chemical affinity for a solid substrate, and
nanofeatures are formed on the substrate, much like the tip of a
pen would write with ink on paper (Piner, R. D. et al., Science,
283:661, 1999). This technique has an advantage in that it is
possible to achieve a high-resolution pattern as small as 5 nm in
special resolutions using an ultra-sharp tip. However, this
technique has a problem in that the pattern must be separately
formed in a serial processing manner, so that a long time is
required to achieve the desired features, thus making it difficult
to directly apply this technique to mass production.
[0012] As described above, although various methods, including
photolithography and etching methods using ultraviolet light and
X-ray, are being introduced, the formation of sub-100 nm patterns
has reached intrinsic limitations. In an attempt to resolve this
issue, bottom-up methods are being widely studied as a substitute
for the existing top-down methods.
[0013] The bottom-up methods are based on the formation of
microstructures by the self-assembly of molecules, and among such
basic technologies, a method of analyzing the microstructure of
supramolecules by a scanning electronic microscope has been
reported (Hudson, S. D. et al., Science, 278:449, 1997) and it has
been reported that the orientation of supramolecules varies
depending on the surface property of a substrate (Jung, H. T. et
al., Macromolecules, 35:3717, 2002). However, these publications
describe only the microstructure analysis of supramolecules and the
orientation of supramolecules, respectively.
[0014] Studies are being conducted on forming sub-100 nm patterns
using block copolymers, e.g., involving the formation of regular
patterns using block copolymers and the formation of dot-shaped
patterns using metal staining (Park, M. et al., Science, 276:1401,
1997). However, the patterns formed by such methods remain at a
level of several tens of nanometers or larger size, since they rely
on the molecular chain of the polymers. Also, the use of the block
copolymers has problems in that the aspect ratio of the pattern
formed is not large, the structure of a thin film is complex, and
it is difficult to give an orientation to the structure of the thin
film.
[0015] Meanwhile, microarray protein chips are of high importance
in current researches on diagnostic proteomics. An early array
technology (U.S. Pat. No. 5,143,854) that utilized a
photolithographic technique for a polypeptide array on the surface
of a substrate has recently generated new interest and is the
subject of ongoing work. In particular, increasing importance is
being attached to development of a microarray-type format in
various immunoassays, including antigen-antibody pairs and
enzyme-liked immunosorbent assays.
[0016] However, it is not easy to make the protein array smaller
than the DNA array or to integrate or arrange the protein array
into a substantial format having increased sensitivity. The lattice
pattern of DNA oligonucleotides can be produced on the surface of a
substrate by photolithography, but in the case of a protein
consisting of several hundreds of amino acids, more highly
integrated lattice patterns with high density (for example, an
antibody can comprise about 1,400 amino acids) are required for the
exact diagnosis of diseases on the substrate surface. It is not
easy to satisfy this requirement.
[0017] Another problem with proteins is that they can easily lose
their three-dimensional structure during manipulation under
denaturing conditions (Bernard, A. et al., Anal. Chem., 73:8,
2001), so that the manipulation of proteins has many
limitations.
[0018] A solution to such problems requires that the proteins be
processed in such manner that they can be arrayed at high
resolution without loss of their three-dimensional structure.
Towards this objective, various approaches, including inkjet
printing, drop-on-demand technology, microcontact printing, and
soft lithography have been proposed. However, arrays formed by such
methods are characterized by spacing dimensions of several tens of
micrometers to several millimeters, and no techniques have been
found that produce highly integrated diagnostic protein nanoarrays
having a high density character, while maintaining the
three-dimensional structure of the protein.
[0019] Because of their properties of excellent structural
rigidity, chemical stability, ability to act as ideal
one-dimensional (ID) "quantum wires" with either semiconducting or
metallic behaviors, a large aspect ratio, and empty interior, CNTs
exhibit a broad range of potential applications as a basic material
of flat panel displays, transistors, energy reservoirs, etc., and
as various sensors with nanosize.
[0020] The CNT synthesis using known methods of CVD synthesis
involves first depositing Fe, Ni, Co or the alloy of these three
metals as a metal catalyst on a substrate, etching the deposited
substrate with water-diluted HF, mounting the sample on a quartz
boat, and then after inserting the quartz boat into the reactor of
a CVD device, additionally etching the metal catalyst film using
NH.sub.3 gas at 750.about.-1050.degree. C. to form fine metal
catalyst particles with nanosize. Since the CNT is synthesized on
the fine metal catalyst particles, forming the fine metal catalyst
particles is an important process in the CVD synthesis method.
However, arranging the metal catalyst in a patterned form with
regular intervals is impossible in such method. Therefore, it is
important to array the metal catalyst for arranging the CNT
vertically at regular intervals.
[0021] As a solution to such problems, the growth of CNT on a
nickel catalyst array fabricated by using e-beam lithography has
been reported (Li, J. et al., Nano Letter, 3:597, 2003). However,
such approach has many limitations in application to large size
substrates and mass-production.
[0022] Recently, researches have been conducted to detect both
protein-protein and protein-ligand reactions by means of
electrochemical changes of CNT after immobilization of a
biomaterial (Dai, H. et al., ACC. Chem. Res., 35:1035, 2002;
Sotiropoulou, S. et al., Anal. Bioanal. Chem., 375:103, 2003;
Erlanger, B. F. et al., Nano Lett., 1:465, 2001; Azamian, B. R. et
al., JACS, 124:12664, 2002).
[0023] The reasons that CNT attracts public attention as a biochip
material and technique include the following: firstly, CNT needs no
labeling; secondly, CNT has high sensitivity to electric or
electrochemical signal change; and thirdly, CNT is capable of
reacting in an aqueous solution without deterioration of a protein
because it has chemical functional groups. The application of
biological systems to CNT as a well-arranged and new nanomaterial,
will create important fusion technologies in various fields,
including for example disease diagnosis (hereditary diseases),
proteomics and nanobiotechnology.
[0024] Many applications of CNT in the bioengineering field have
recently appeared. Applications of CNT to biochips, for
applications such as glucose biosensors, detection of protein,
detection of a specific DNA sequence, and the like, have been
proposed (Sotiropoulou, S. et al., Anal. Bioanal. Chem., 375:103,
2003; Chen, R. J. et al., Proc. Natl. Acad. Sci. USA, 100:4984,
2003; Cai, H. et al., Anal. Bioanal. Chem., 375:287, 2003). At the
present time, the most universal method for detecting the result of
a reaction in a biochip is to use conventional fluorescent
materials and isotopes (Toriba, A. et al., Biomed. Chromatogr.,
17:126, 2003; Syrzycka, M et al., Anal. Chim. Acta, 484:1, 2003;
Rouse, J. H. et al., Nano Lett., 3:59, 2003). However, as novel
methods to easily and precisely measure an electrical or
electrochemical signal are attempted, there are increased demands
for CNT as a new material.
[0025] The methods of preparing a high density CNT multiplayer,
attaching DNA thereon and detecting complementary DNA, are useful
in genotyping, mutation detection, pathogen identification and the
like. PNA (peptide nucleic acid: DNA mimic) that is
regio-specifically fixed on a single walled CNT and its
complementary binding to probe DNA, have been reported (Williams,
K. A. et al., Nature, 420:761, 2001). Also, the fixing of an
oligonucleotide on a CNT array by a electrochemical method and its
use to detect DNA by guanine oxidation has been reported (Li, J. et
al., Nano Lett., 3:597, 2003). These methods, however, do not apply
CNT to the fabrication and development of biochips.
[0026] Recently, a high capacity biomolecule detection sensor using
CNT has been disclosed (WO 03/016901 Al). This patent publication
describes a multi-channel type biochip produced by arranging a
plurality of CNTs on a substrate using a chemical linker and
attaching various types of receptors. However, this structure has
the substantial disadvantage of relative weakness to environmental
changes.
SUMMARY OF THE INVENTION
[0027] Accordingly, the present inventors have conducted intensive
studies to develop a simpler method for forming a several
nanometer-sized ultrahigh density pattern. The inventors have
discovered that by forming a metal catalyst pattern of several
nanometer or smaller size, utilizing supramolecular self-assembly
and selective metal compound staining techniques, and growing CNT
vertically on the formed pattern, a CNT array can be produced in a
ready and efficient manner.
[0028] The invention provides a method for fabricating a CNT array,
by steps including arranging CNT on a nanopattern of metal catalyst
formed by using supramolecular self-assembly and selective metal
compound staining.
[0029] The invention additionally provides a method for fabricating
a biochip, which includes the attachment of a bioreceptor to a CNT
array fabricated in accordance with the invention.
[0030] Other aspects, features and embodiments of the invention
will be more fully apparent from the ensuing disclosure and
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 schematically shows a self-assembly process of
supramolecules. FIG. 1a shows that disc-shaped dendrimers (1) and
fan-shaped supramolecules (2) are self-assembled into cylindrical
structures (3) which are then arranged into three-dimensional
hexagonal structures (4). FIG. 1b shows that cone-shaped molecules
(5) are self-assembled into spherical structures (6) which are
arranged into a three-dimensional regular structures (7).
[0032] FIG. 2 schematically shows a process for forming a
nanopattern and CNT array for the fabrication of a biochip
according to one aspect of the present invention.
[0033] FIG. 3 is a schematic diagram showing the process of
introducing carboxyl groups and removing the caps on the ends of
the grown CNT.
[0034] FIG. 4 is a transmission electron microscope photograph
showing that supramolecules are self-assembled into hexagonal
pillar-shaped regular structures.
[0035] FIG. 5 is a scanning electron microscope photograph showing
a nanopattern formed according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS
THEREOF
[0036] To achieve the above objects, the present invention provides
a method for fabricating a carbon nanotube (CNT) nanoarray, which
includes the steps of: (a) forming on a substrate a thin film of a
metal catalyst selected from the group consisting of Fe, Ni, Co,
and alloys of such metals; (b) forming a thin film of
supramolecules inducing self-assembly on the thin film of the metal
catalyst; (c) self-assembling the supramolecules by annealing to
form a regular structure; (d) selectively staining the formed
regular structure with a metal compound; (e) removing a portion
which is not stained with the metal compound, by etching, wherein
the metal compound-stained thin film is used as a mask, thereby
forming a nanopattern of supramolecules stained with the metal
compound; (f) forming nanopattern of a metal catalyst by
ion-milling using the nanopattern of the supramolecule as a mask;
and (g) vertically arranging CNTs on the nanopattern of the metal
catalyst supramolecules.
[0037] In one embodiment of the present invention, a compound of
the following formula (1) is used as the supramolecules, but it
will be appreciated that any self-assembling supramolecules may
also be used, without limitation. 1
[0038] Examples of the self-assembling supramolecules include
disc-shaped dendrimers (1), fan-shaped supramolecules (2),
stick-chain shaped or cone-shaped molecules (5). An example of the
fan-shaped supramolecules includes a compound of the following
formula (2), an example of the disk-shaped supramolecules includes
a compound of the following formula (3), and an example of the
cone-shaped supramolecules includes a compound of the following
formula (4): 2
[0039] Such supramolecules are formed into a regular structure by
physical secondary binding, such as by van der Waals forces, unlike
polymers in which monomers are covalently bonded. Such
supramolecules are self-assembled by suitable temperature or
concentration, external magnetic field or electric field, etc., to
form certain fine structures. The supramolecules of formula (1)
used in the present invention correspond to the fan-shaped
dendrimers. As shown in FIG. 1a, such fan-shaped dendrimers are
self-assembled into plate-shaped structures (1), which are then
assembled into pillar-shaped structures (3), which are formed into
a three-dimensional hexagonal structure (4). In addition, as shown
in FIG. 1b, the cone-shaped supramolecules (5) are self-assembled
into spheres (6), which are then arranged into a three-dimensional
regular structure (7).
[0040] In the present invention, the thin film in the step (b) is
preferably formed by spin-coating, rubbing, or solution spreading,
which forms a thin film on the water surface, and the annealing in
the above step (c) is preferably performed by heating the
supramolecules above their liquid crystal transition temperature
and then cooling them slowly. Furthermore, the metal compound
staining in the above step (d) is preferably performed by
selectively staining the central portion of the thin film with
ruthenium tetraoxide(RuO.sub.4), and the step (e) is preferably
performed by a reactive ion etching method.
[0041] Thin films in accordance with the invention include films
that have a thickness that does not exceed about 5 mm, which may by
way of example include films having a thickness in a range of from
about 5 nm to about 5 mm, such as films with a thickness of from
about 0.01 .mu.m to about 500 .mu.m.
[0042] In one embodiment of the present invention, the step of
forming CNT on the nanopattern of the substrate can be performed by
any suitable CNT growth method, e.g., any of CNT growth methods
known in the art. In preferred practice, the CNTs are grown
vertically on the substrate by plasma chemical vapor deposition,
thermal chemical vapor deposition, electrophoresis or mechanical
methods (Korean patent publication No. KR 2002-0001260A).
[0043] The present invention in another aspect can additionally
include the step of exposing the carboxyl group by plasma treatment
of the vertically synthesized CNT array end. With such method,
various bioreceptors can be bound chemically after the carboxyl
group exposed on the end of CNT array by plasma treatment.
[0044] In yet another aspect, the present invention provides a
method for fabricating a biochip, in which a bioreceptor selected
from the group consisting of protein, peptide, amino acid, DNA,
PNA, enzymatic substrate, ligand, cofactor, carbohydrate, lipid,
oligonucleotide, and RNA, is attached to the CNT array fabricated
by the above method.
[0045] The step of attaching the bioreceptor to CNTs is performed
in any suitable manner, e.g., by either applying a charge of a
polarity opposite to the net charge of the bioreceptor to CNTs (KR
2003-0014997A), or by using a binding aid. The binding aid
preferably includes a chemical substance having an aldehyde, amine
or imine group attached to a carbon group end.
[0046] In one aspect of the present invention, a method is provided
for fabricating a biochip which includes binding a bioreceptor
having an amine group (NH.sub.2) to the CNT array in which the
carboxyl group is exposed on an upper end, by forming an amide
bond. It is typically preferred to use a coupling agent and a
coupling aid for inducing an amide bond in the broad practice of
the present invention.
[0047] Bioreceptors such as proteins, peptides and amino acids,
possess respective intrinsic isoelectric points, and have a net
charge with a neutral ion, cation or anion according to the ion
intensity or pH of solution. Also, by adjusting the condition of
solution to adjust the electrostatic interaction and hydrophobic
interaction between such bioreceptors and CNTs with a certain
charge, the same or different kinds of bioreceptors can be moved or
arranged on the desired positions of a chip.
[0048] In still another aspect, the present invention provides a
biochip, in which a bioreceptor selected from the group consisting
of proteins, peptides, amino acids, DNAs, PNAs, enzymatic
substrates, ligands, cofactors, carbohydrates, lipids,
oligonucleotides, and RNAs, is attached to the above CNT array.
[0049] According to the present invention, a protein-specific
receptor that binds selectively to a target protein involved in
diseases can be selectively attached to the CNT nanoarray on one
chip by applying an electric field. Also, a bioreceptor that can
interact with various target proteins involved in various diseases
can be attached selectively to CNTs by applying electric fields of
different polarities from each other to the CNTs. Accordingly, it
is possible to diagnose a variety of diseases on one chip in one
step at large amounts in a rapid manner.
[0050] As used herein, the term "bio-nanoarray" is defined to
include biochips and biosensors, in which a bioreceptor that binds
to or reacts with a biomaterial is attached to a nanopattern.
[0051] The present invention is described in greater detail
hereinafter.
[0052] In the general practice of the present invention, a thin
film is formed on a substrate, of Fe, Ni, Co, or an alloy thereof,
as a metal catalyst for growing CNT vertically on a substrate by a
suitable technique such as thermal deposition, e-beam deposition,
sputter, etc. The formed metal catalyst thin film is formed into a
metal catalyst array by use of a nanopattern of supramolecules, as
described herein (FIG. 2).
[0053] According to a preferred embodiment of the present
invention, supramolecules are first dissolved in a tetrahydrofuran
(THF) solvent at a 1-wt % concentration, and the resulting solution
is applied on a substrate to form a thin film of supramolecules. In
forming the thin film of supramolecules, spin-coating, rubbing, or
solution spreading that forms a thin film on the water surface is
preferably used. In this embodiment, a silicon wafer having the
metal catalyst (Fe, Ni, Co, or an alloy thereof) deposited thereon,
is used as the substrate, and the modification of the substrate
surface is not carried out (FIG. 2a).
[0054] Thereafter, the supramolecules are heated above their liquid
crystal phase transition temperature such that they are
self-assembled. Since the supramolecules used in the present
invention have a liquid crystal phase transition temperature of
about 230.degree. C., they are heated to 240.degree. C. and then
cooled slowly. Thus, the supramolecules are self-assembled into
pillar-shaped microstructures (FIG. 2b).
[0055] The self-assembly process of supramolecules by annealing
according to a preferred embodiment of the present invention will
now be described.
[0056] The properties of supramolecules can be modified by
annealing, and starting materials suitable for annealing include
supramolecules produced by pyrolysis. Also, the supramolecules used
as the starting materials can undergo at least one preheating step
under different conditions. The additional treatment in annealing
the supramolecules formed by laser pyrolysis improves their
crystallinity and removes contaminants such as atomic carbon, and
possibly can change their stoichiometry by combining additional
oxygen, or atoms from gaseous or nongaseous compounds. The
supramolecules are preferably heated in an oven so as to provide
uniform heating. The treatment conditions are generally mild so
that a significant amount of sintered particles are not caused.
Thus, the heating temperature is preferably lower than the melting
point of both the starting material and the product. If the thermal
treatment involves a change in composition, the size and shape of
the molecules can be changed even at mild heating temperatures.
[0057] Self-assembled structures are formed on the surface of
material/substrate or within the surface. The self-assembled
structures are positioned within boundaries in the form of
positioned islands, and each of the structures can serve as an
element of circuits or devices having a plurality of elements.
Particularly, each of the structures may be an element of
integrated electronic circuits, and examples of this element
include electrical parts, optical devices and photonic
crystals.
[0058] In order to form a structure within a predetermined
boundary, a process of defining the boundary of the structure and a
separate self-assembly process are required for the formation of
the self-assembled structure. The process of defining the boundary
of the structure utilizes an external force in defining the
structure boundary. It is generally impossible to define the
structure boundary by the self-assembly process itself. When a
composition/material is bound, its self-assembly is based on the
natural sensing function of the composition/material, which causes
natural ordering in the resulting structure. Generally, although
the positioning process can be conducted before or after the
self-assembly process, the nature of treatment steps can also
indicate certain orders. The net effect results in a self-assembled
structure having a region within the boundary, which is covered
with nanoparticles, and also a region outside the boundary, which
is not covered with the nanoparticles. The process of defining the
boundary is linked to the self-assembly process, by either
activating the self-assembly process in the boundary or
inactivating the region outside the boundary. Generally, to carry
out the activating process or the inactivating process, the
application of an external force is necessary.
[0059] The fact that supramolecules are self-assembled into a
regular structure on a substrate can be confirmed by a transmission
electron microscope. A sample was fabricated under the same
conditions as described in the present invention, and a photograph
of the sample taken by the transmission electron microscope is
shown in FIG. 4. The photograph in FIG. 4 suggests that the
supramolecules are self-assembled into hexagonal pillar-shaped
regular structures.
[0060] The step of staining the regular structures of
self-assembled supramolacules with a metal compound according to a
preferred embodiment of the present invention will now be
described.
[0061] First, RuO.sub.4 solution and a substrate coated with a thin
film of supramolecules are maintained in a glass container with the
solution not being in direct contact with the substrate. In this
process, while RuO.sub.4 vapor in the RuO.sub.4 solution is
diffused into a gas phase, the supramolecular thin film on the
substrate is stained with the Ru metal. The stained RuO.sub.4 vapor
chemically selectively reacts with certain portions of the thin
film.
[0062] Although RuO.sub.4 is used in the present invention, osmium
tetraoxide (OsO.sub.4) or other metal compounds capable of
selectively staining the structures formed by supramolecules may
also be used in the present invention.
[0063] According to a preferred embodiment of the present
invention, as the substrate coated with the supramolecular thin
film is subjected to the metal compound staining process and then
an etching process, a portion of the supramolecular thin film on
the substrate is removed so that nanopatterned devices are
ultimately obtained. In this etching process, any method which is
conventionally used in a semiconductor device fabrication process
may be used, without limitation (FIG. 2c). For example, the etching
process can be performed by using an etching solution, such as a
KCN-KOH mixture solution or an HF aqueous solution, or by reactive
ion etching (RIE).
[0064] In the embodiment, a nanopattern of metal catalyst is
finally formed on a substrate, when ion-milling is performed using
the nanopattern stained with the formed metal compound as a mask,
to form an array of Fe, Co, Ni or an alloy thereof, for use as a
catalyst for CNT synthesis on a substrate. (FIG. 2d)
[0065] CNT can be synthesized by known methods in the art. In one
such method, C.sub.2H.sub.2, CH.sub.4, C.sub.2H.sub.4,
C.sub.2H.sub.6, or CO gas is used as a reacting gas, and plasma
chemical vapor deposition, thermal chemical vapor deposition, etc.
is used to grow CNT vertically. If CNT is formed by metal catalyst
nanopattern, CNT having very small diameter can be formed because
the diameter of one pattern is below 10 nm.
[0066] The present invention also includes the process of
introducing carboxyl groups to the vertically grown CNT ends for
binding biomaterials by treating the CNT ends with plasma to open
the end caps of the CNT (FIG. 3).
[0067] The CNT nanoarray formed according to an illustrative
preferred embodiment of the present invention as described above
can be used as important surface substrates in forming a desired
array by reacting various bioreceptors with the CNT nanoarray, in
order to produce biochips of high integration density and small
size.
[0068] Generally, the biochips are fabricated by linking
biomolecules directly to a substrate or linking the biomolecules to
the substrate by means of linker molecules. For example, when
bioreceptors (e.g., DNAs, antibodies or enzymes) must be attached
to the CNT in order to produce DNA chips, protein chips or protein
sensors, the desired bioarray can be fabricated by reacting
carboxyl groups introduced to the CNT ends with amine groups of the
above biomaterial and binding those to the CNT ends with by amide
bonds.
[0069] A method for fabricating DNA chips as bionanoarray articles
according to the present invention, includes the step of attaching
a previously prepared probe to the surface of a solid substrate by
a spotting method. In this case, an amine group-bound probe is
dissolved in 1.times. to 7.times., preferably 2.times. to 5.times.,
and more preferably 3.times. SSC buffer solution (0.45 M NaCl, 15
mM C.sub.6H.sub.5Na.sub.3O.sub.7, pH 7.0), and then spotted to a
CNT end having an exposed carboxyl group by a microarrayer. Then,
the probe is bound to the CNT end by the reaction between aldehyde
and amine. Here, the concentration of the probe is more than 10
pmol/.mu.l, preferably more than 50 pmol/.mu.l, and more preferably
more than 100 pmol/.mu.l. Also, the amine group bound to the probe
is reacted with the carboxyl group introduced to the CNT end at a
humidity of 70-90%, and preferably 80%, for 4-8 hours, preferably
5-7 hours, and most preferably about 6 hours, so that the probe is
bound to the CNT end. An amide coupling agent and EDC/NHS as an aid
can be suitably used in the method.
EXAMPLES
[0070] The present invention will hereinafter be described in
further detail by examples. It will however be obvious to a person
skilled in the art that these examples can be modified into various
different forms and the present invention is not limited to or by
the examples, such examples being presented to further illustrate
the broad scope of the present invention.
Example 1
Synthesis of Supramolecules
[0071] The supramolecules of formula (1) used in the present
invention were synthesized by a process as shown in reaction scheme
(1) below. The result of scanning electron microscopic analysis on
such supramolecules confirmed that the supramolecules are regular
cylindrical structures of nanometer- or smaller size (FIG. 4).
3
Example 2
Modification of Substrate Surface
[0072] The above metal catalyst was deposited on a silicon wafer by
using thermal deposition, e-beam deposition, sputter, etc. to form
a thin film of Fe, Ni, Co, or an alloy thereof, as a metal catalyst
for synthesizing CNT (FIG. 2a).
Example 3
Formation of Thin Film of Supramolecules
[0073] The supramolecules synthesized in Example 1 were dissolved
in a tetrahydrofuran (THF) solvent. The solution was spin-coated on
the silicon wafer of Example 2 to form a thin film (FIG. 2a). In
this Example, the spin-coating was performed at 2,000-3,000 rpm for
10-30 second. During this spin-coating, the thickness of the thin
film can be suitably changed.
Example 4
Annealing
[0074] The thin film of supramolecules was heated to 240.degree. C.
and then cooled slowly, to form regular microstructures (FIG. 3b).
The supramolecules used in the present invention are self-assembled
at 240.degree. C., which can vary according to the kinds of
supramolecules used. At this temperature, the supramolecules have a
sufficient mobility for their self-assembly, and self-assembled
into the most stable structures. In the case of the supramolecules
used in the present invention, three-dimensional structures in
which cylinders are arranged into a hexagonal shape are the most
stable structures. FIG. 4 is a transmission electron microscope
photograph showing that supramolecules are self-assembled into
hexagonal pillar-shaped regular structures.
Example 5
Staining with Ruthenium Tetraoxide (RuO.sub.4)
[0075] Since the supramolecules can be stained with RuO.sub.4
selectively at their central portions, the supramolecules were
exposed to RuO.sub.4 vapor for several minutes, to stain chemically
their central portions with a RuO.sub.4 metal compound (FIG.
2c).
[0076] When the supramolecules was exposed to RuO.sub.4, the
RuO.sub.4 metal compound was diffused into air so that the
supramolecular thin film was stained with the RuO.sub.4 metal
compound. The RuO.sub.4 metal compound chemically reacts with
certain reactive groups (e.g., ether bonds, alcohols, benzene
rings, and amines), and the supramolecules are stained with the
RuO.sub.4 metal compound at their portions corresponding to the
central portions of the supramolecular cylinders.
[0077] The staining metal compound may be replaced with other metal
compounds depending on the kinds of supramolecules employed in
specific applications. For example, osmium tetroxide (OsO.sub.4)
chemically reacts with reactive groups such as carbon double bonds,
alcohols, ether bonds, amines, etc.
Example 6
Etching
[0078] Thereafter, the metal compound-stained thin film of
supramolecules was subjected to an etching process, so that
dot-shaped structures remained at the central portions of the
supramolecular cylinders due to the difference in etch rate between
the staining metal compound and the supramolecules (FIG. 2c). FIG.
5 is a scanning electron microscope photograph showing the
configuration of such dot-shaped structures. In this example, the
etching was carried out using CF.sub.4 gas for about 100 seconds.
This etching time cannot be considered to be common in all cases,
since it varies depending on the apparatus employed. Thus, a test
step for setting etching conditions was required.
Example 7
Method of Forming Nanopattern on Substrate
[0079] The metal catalyst thin film was etched using the
nanopattern of supramolecules stained with the metal compounds
obtained by Examples 1-6, as a mask, thereby forming nanopattern of
metal catalyst. In the present invention, the metal catalyst thin
film for CNT synthesis was formed between the substrate and the
supramolecular thin film and the formed dot-shaped nanopattern
serves as a mask in a subsequent etching step (FIG. 2c).
[0080] The lower portions of the film, on which the dot pattern
stained with RuO.sub.4 metal compounds was formed, were not etched,
while the intermediate thin film layer whose surface was exposed,
was etched, so that the pattern formed by the supramolecules was
transferred to the intermediate thin film layer. This varies
depending on a material used as the intermediate thin film layer.
If the intermediate thin film layer is a metal catalyst thin film
layer for CNT synthesis, it can be etched by ion milling, and
etching conditions are in accordance with the properties of each
thin film layer (FIG. 2d).
Example 8
Fabrication of CNT Array
[0081] Reacting gas such as C.sub.2H.sub.2, CH.sub.4,
C.sub.2H.sub.4, C.sub.2H.sub.6, CO etc. was supplied into a chamber
and power having high frequency was applied to both electrodes to
cause a glow electric discharge, thereby vertically synthesizing
and growing CNT on the metal catalyst nanoarray formed in example
7. The synthesized CNT formed a CNT array on the substrate by the
regular arrangement of fixed metal catalyst (FIG. 2e).
[0082] Moreover, the vertically grown CNT can be treated with
plasma by a method similar to the described in the prior art
(Huang, S. et al., J. Phys. Chem. B, 106:3543, 2002), and carboxyl
groups can be introduced to the CNT by removing the caps of the end
portions. Then, various bioreceptors can be chemically bound to the
CNT.
Example 9
Fabrication of Biochip by Attaching Biomaterial or Bioreceptor to
the CNT Array
[0083] For attaching bioreceptors to the CNT array fabricated
according to example 8, the method of binding by applying a change
of polarity opposite to the net charge of the bioreceptor to the
CNT (KR 2003-0014997A) or using a binding aid can be used (FIG.
2f). The preferred binding aid is a chemical substance having an
aldehyde, amine or imine group attached to a carbon group end.
[0084] Furthermore, a biochip can be fabricated by binding a
bioreceptor having an amine group (NH.sub.2) by means of an amide
bond to the end of the CNT array having an exposed carboxyl group
formed in example 8. For this method, it is preferred that
EDC(1-ethyl-3-(3-dimethylamini-propyl) carbodiimide hydrochloride)
is used as a coupling agent and NHS(N-hydroxysuccinimide),
NHSS(N-hydroxysulfosuccinimide) is used as a coupling aid.
[0085] As described above, the present invention provides a method
for fabricating a CNT array, which involves forming a catalyst
pattern for CNT synthesis using a pillar shaped nanopattern which
is formed by using the supramolecular self-assembly and the
selective metal compound staining as a mask, and arranging CNT on
the pattern. In addition, the present invention provides a method
for fabricating a biochip by attaching a biomaterial or a
biomaterial binding bioreceptor to the CNT nanoarray.
* * * * *