U.S. patent number 7,217,562 [Application Number 10/414,620] was granted by the patent office on 2007-05-15 for gradient structures interfacing microfluidics and nanofluidics, methods for fabrication and uses thereof.
This patent grant is currently assigned to Princeton University. Invention is credited to Robert H. Austin, Han Cao, Stephen Chou, Jonas O. Tegenfeldt.
United States Patent |
7,217,562 |
Cao , et al. |
May 15, 2007 |
Gradient structures interfacing microfluidics and nanofluidics,
methods for fabrication and uses thereof
Abstract
The present invention relates to a device for interfacing
nanofluidic and microfluidic components suitable for use in
performing high throughput macromolecular analysis. Diffraction
gradient lithography (DGL) is used to form a gradient interface
between a microfluidic area and a nanofluidic area. The gradient
interface area reduces the local entropic barrier to nanochannels
formed in the nanofluidic area. In one embodiment, the gradient
interface area is formed of lateral spatial gradient structures for
narrowing the cross section of a value from the micron to the
nanometer length scale. In another embodiment, the gradient
interface area is formed of a vertical sloped gradient structure.
Additionally, the gradient structure can provide both a lateral and
vertical gradient.
Inventors: |
Cao; Han (Blawenburg, NJ),
Tegenfeldt; Jonas O. (Lund, SE), Chou; Stephen
(Princeton, NJ), Austin; Robert H. (Princeton, NJ) |
Assignee: |
Princeton University
(Princeton, NJ)
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Family
ID: |
29739674 |
Appl.
No.: |
10/414,620 |
Filed: |
April 16, 2003 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20040033515 A1 |
Feb 19, 2004 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60419742 |
Oct 18, 2002 |
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60373409 |
Apr 16, 2002 |
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Current U.S.
Class: |
435/287.2;
422/68.1; 435/288.6; 536/23.1; 435/288.5; 435/288.2; 422/50;
422/504 |
Current CPC
Class: |
B01L
3/502746 (20130101); B81C 1/00119 (20130101); G03F
7/2008 (20130101); B01L 3/502707 (20130101); G01N
21/6486 (20130101); G01N 33/48721 (20130101); B01L
3/502761 (20130101); B82Y 30/00 (20130101); B01L
2400/086 (20130101); B01L 2400/0415 (20130101); B01L
2300/0896 (20130101); B01L 2200/12 (20130101); B01L
3/502715 (20130101); B81C 2201/0159 (20130101); B81B
2201/058 (20130101); B81C 2201/0157 (20130101); B01L
2200/027 (20130101); B01L 2300/0654 (20130101); Y10T
436/143333 (20150115); B01L 2200/0663 (20130101) |
Current International
Class: |
C12M
3/00 (20060101); C12Q 1/68 (20060101); G01N
15/06 (20060101); C07H 21/04 (20060101) |
Field of
Search: |
;435/6,287.1,288.5,288.6
;436/94,805 ;422/50,68.1,99 ;536/23.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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WO 00/09757 |
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Feb 2000 |
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WO |
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WO 01/37958 |
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May 2001 |
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WO |
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WO 02/07199 |
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Jan 2002 |
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WO |
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WO 03/010289 |
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Feb 2003 |
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WO |
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WO 03/079416 |
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Sep 2003 |
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WO |
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WO 03/106693 |
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Dec 2003 |
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WO |
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Primary Examiner: Sisson; Bradley L.
Attorney, Agent or Firm: Woodcock Washburn LLP
Government Interests
DARPA Grant Number MDA972-00-1-0031 supported work that led to
portions of the inventions described herein. Accordingly, the U.S.
Government may have rights in these inventions.
Parent Case Text
This patent application claims the benefit of priority to U.S.
Provisional Patent Application No. 60/373,409, filed on Apr. 16,
2002 and U.S. Provisional Patent Application No. 60/419,742, filed
Oct. 18, 2002.
Claims
What is claimed is:
1. A method for fabricating a fluidic device comprising the steps
of: providing a nanofluidic area on a substrate, the nanofluidic
area capable of communicating fluid therethrough, the nanofluidic
area comprising a plurality of nanofluidic structures capable of
being substantially enclosed between the substrate and a sealing
material surmounting said nanofluidic structures, the plurality of
nanofluidic structures characterized as having a lateral spacing
distance in the range of from about 2 nm to about 200 nm; forming a
microfluidic area on said substrate, the microfluidic area capable
of communicating fluid therethrough, the microfluidic area
comprising a plurality of microfluidic structures capable of being
substantially enclosed between the substrate and the sealing
material, the plurality of microfluidic structures characterized as
having a lateral spacing distance in the range of from about 0.5
microns to about 5 microns; and forming a gradient interface area
between said nanofluidic area and said microfluidic area, said
gradient interface area capable of being in fluid communication
between said nanofluidic area and said microfluidic area, said
gradient interface area comprising a plurality of gradient
structures capable of being substantially enclosed between the
substrate and the sealing material, the plurality of gradient
structures characterized as having a lateral spacing distance
relative to each other, and the gradient interface area
characterized as having a vertical spacing distance relative to the
substrate and the sealing material, wherein the lateral spacing
distance between the gradient structures, or the vertical spacing
distance of the gradient interface area, or both, ranges from about
0.5 microns to about 5 microns adjacent to said microfluidic area
to about 2 nm to about 200 nm adjacent to said nanofluidic area;
wherein said steps of forming said gradient interface area and
forming said microfluidic area are formed simultaneously by the
steps of: coating photoresist over said substrate; providing a
photomask over said photoresist, said photomask patterning said
microfluidic area and said gradient interface area; providing a
blocking mask over said photomask, said blocking mask extending
over a portion of said photomask applied over said nanofluidic
area; and exposing said photomask to light.
2. The method of claim 1 wherein said gradient interface area
comprises a plurality of gradient structures, and the lateral
spacing distance between said gradient structures is decreased
towards said nanofluidic area.
3. The method of claim 2 wherein said distance between said
gradient structures is reduced to range from about 2 nm to below
about 500 nanometers.
4. The method of claim 2 wherein said distance between said
gradient structures is reduced to range from about 2 nm to below
about 10 nm.
5. The method of claim 2 wherein said distance between said
gradient structures is reduced to about 2 nm.
6. The method of claim 2 wherein said gradient structures range in
vertical elevation from about 2 microns adjacent to said
microfluidic area to a vertical elevation ranging from about 2 nm
to less than about 500 nm adjacent to said nanofluidic area.
7. The method of claim 2 wherein said gradient structures are
branched channels.
8. The method of claim 1 wherein said gradient interface area
decreases in vertical elevation from about 2 microns adjacent to
said microfluidic area to a vertical elevation ranging from about 2
mn to less than about 500 nm adjacent to said nanofluidic area.
9. The method of claim 1 wherein said blocking mask causes light
diffraction along an edge of said blocking mask.
10. The method of claim 9 further comprising the step of: selecting
said edge of blocking mask for controlling said light
diffraction.
11. The method of claim 1 wherein said blocking mask is formed of a
material which is opaque to light.
12. The method of claim 1 wherein said blocking mask is formed of a
metal.
13. The method of claim 1 wherein said blocking mask is formed of
aluminum foil.
14. The method of claim 1 further comprising the step of:
developing said photoresist after said step of placing said
blocking mask over said photomask, wherein said photoresist has a
gradient of undeveloped photoresist along a light diffraction area,
said light diffraction area caused by an edge of said blocking
mask.
15. The method of claim 1 wherein said photomask has a thickness in
a range of about 1 mm to about 10 mm.
16. The method of claim 1 wherein said blocking mask has a
thickness in the range of about 1 mm to about 12 mm.
17. The method of claim 1 wherein said step of providing a blocking
mask over said photomask further comprises the step of: controlling
a distance between said blocking mask and said photomask, wherein
said distance controls an amount light diffraction along an edge of
said blocking mask.
18. The method of claim 1 wherein said nanofluidic structures are
selected from the group consisting of nanopillars, nanopores and
nanochannels.
19. The method of claim 18 wherein said nanofluidic structures
comprise nanochannels, said nanochannels being provided by:
nanoimprint lithography, interference lithography, self-assembled
copolymer pattern transfer, spin coating, electron beam
lithography, focused ion beam milling, photolithography, reactive
ion-etching, wet-etching, plasma-enhanced chemical vapor
deposition, electron beam evaporation, sputter deposition, or any
combination thereof.
20. A fluidic device formed by the method of claim 1.
21. The method of claim 1, wherein the width of the gradient
interface area formed between the nanofluidic area and the
microfluidic area is in the range of from about 2 microns to about
40 microns.
22. The method of claim 1, wherein the width of the gradient
interface area formed between the nanofluidic area and the
microfluidic area is in the range of from about 2 microns to about
20 microns.
23. A method for fabricating a fluidic device comprising the steps
of: providing a nanofluidic area on a substrate, the nanofluidic
area capable of communicating fluid therethrough, the nanofluidic
area comprising a plurality of nanofluidic structures capable of
being substantially enclosed between the substrate and a sealing
material surmounting said nanofluidic structures, the plurality of
nanofluidic structures characterized as having a lateral spacing
distance in the range of from about 2 nm to about 200 nm; forming a
microfluidic area on said substrate, the microfluidic area capable
of communicating fluid therethrough, the microfluidic area
comprising a plurality of microfluidic structures capable of being
substantially enclosed between the substrate and the sealing
material, the plurality of microfluidic structures characterized as
having a lateral spacing distance in the range of from about 0.5
microns to about 5 microns; and forming a gradient interface area
between said nanofluidic area and said microfluidic area, said
gradient interface area capable of being in fluid communication
between said nanofluidic area and said microfluidic area, said
gradient interface area comprising a plurality of gradient
structures capable of being substantially enclosed between the
substrate and the sealing material, the plurality of gradient
structures characterized as having a lateral spacing distance
relative to each other, and the gradient interface area
characterized as having a vertical spacing distance relative to the
substrate and the sealing material, wherein the lateral spacing
distance between the gradient structures, or the vertical spacing
distance of the gradient interface area, or both, ranges from about
0.5 microns to about 5 microns adjacent to said microfluidic area
to about the diameter of a biopolymer; wherein said steps of
forming said gradient interface area and forming said microfluidic
area are formed simultaneously by the steps of: coating photoresist
over said substrate; providing a photomask over said photoresist,
said photomask patterning said microfluidic area and said gradient
interface area; providing a blocking mask over said photomask, said
blocking mask extending over a portion of said photomask applied
over said nanofluidic area; and exposing said photomask to
light.
24. The method of claim 23, wherein the width of the gradient
interface area formed between the nanofluidic area and the
microfluidic area is in the range of from about 2 microns to about
40 microns.
25. The method of claim 23, wherein the width of the gradient
interface area formed between the nanofluidic area and the
microfluidic area is in the range of from about 2 microns to about
20 microns.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to bionanotechnology and in
particular to a method of fabricating a hybrid
microfluidic/nanofluidic device having a gradient structure formed
by a modified photolithography technique at the interface between
microfluidic and nanofluidic portions of the device and uses
thereof.
2. Description of the Related Art
Nanotechnology, electronics and biology are combined in the newly
emerging field of bionanotechnology. Nanofabrication of extremely
small fluidic structures, such as channels, can be used in
bionanotechnology for the direct manipulation and analysis of
biomolecules, such as DNA, and proteins at single molecule
resolution. For example, the channels can be used for stretching
genomic DNA and scanning for medically relevant genetic or
epigenetic markers. New insights of understanding the
confinement-mediated entropic behavior of biopolymers in
ultra-small nanoscale fluidics have just started to emerge.
On the nanometer scale, DNA is a stiff molecule. The stiffness of
the molecule is described by a parameter called the persistence
length. Despite the relative stiffness of DNA for sufficiently long
molecules, it tends to form a disordered tangle of compact random
coils in free solution. The conformation of a polymer in free
solution has been referred to as a spherical "blob" by the polymer
dynamics community. The size of the blob depends on the length of
the DNA molecule and the persistence length.
It has been described that in order to uniformly stretch chain-like
long DNA, dimensions of nanofluidic structures should be near, in
the vicinity of or smaller than the persistence length of double
stranded DNA of about 50 nm to about 70 nm. Arrays of up to half
millions of nanochannels fabricated over a 100 mm wafer using
nanoimprinting lithography (NIL) with sealed channels having a
cross section as small as 10 nm by 50 nm to stretch, align and
analyze long genomic DNA in a highly parallel fashion, and the
resulting have been described in Cao H., Wang J., Tegenfeldt P.,
Austin R. H., Chen E., Wei W. and Chou S. Y., Fabrication of 10 nm
Enclosed Nanofluidic Channels (2002) Applied Physics Letters, Vol.
81, No. 1, pp174. It is challenging to efficiently move long DNA
arranged as a blob into the small channels, since it is
energetically unfavorable for long biopolymers to spontaneously
elongate and enter nanochannels directly from the environment due
to the large free energy needed to overcome negative entropy
change, as illustrated in FIGS. 1A 1B. For example, a double
stranded T4 phage DNA molecule with a length of 169 kilobases will
form a Gaussian coil with a radius of gyration
(Rg=(L.rho./6).sup.1/2, where L is the length and .rho. the
persistence length of the DNA), approximately 700 nm in aqueous
buffer solution which is many times the width of the opening of the
nanochannels. Consequently, problems such as DNA clogging at the
junction of nano- and macro-environment have arisen and undermine
the performance of conventional nanofluidic devices.
U.S. Patent Application No. 2002/0160365 describes a method for
separation of long strands of DNA by length by forcing the
molecules to traverse a boundary between a low-force energy region
and a high-force energy region. The high-force energy region is a
diverse pillar region. The low-force energy region is a larger
chamber formed adjacent the high-force energy region.
U.S. Patent Application No. 2002/0072243 describes fabrication
techniques using a pattern of sacrificial and permanent layers to
define the interior geometry of a fluidic device. A pattern for a
fluidic device having microchannels and an array of retarding
obstacles is defined in a resist layer. The pattern is produced
using lithographic techniques. For electron beam lithography and
for deep structures made with photolithography, a hard pattern mask
is required to assist in pattern transfer. An inlet chamber, outlet
chamber, inlet microchannel, outlet chamber and an array of holes
is formed in a sacrificial layer. A ceiling layer is deposited to
cover the sacrificial layer. The ceiling layer enters the holes to
form closely spaced pillars. The sacrificial layer is removed to
form microchannels between the floor and ceiling layers. The
pillars act as a sieve or an artificial gel filter for fluid
flowing through the system. Steps needed in removing the
sacrificial materials, such as heating the substrate up to 200
400.degree. C., limits the use of certain materials. Electron beam
lithography has the flexibility to write different patterns, but
has low throughput and high manufacturing costs.
It is desirable to provide an improved structure interfacing
between microfluidic and nanofluidic components of a device for
reducing the local entropic barrier to nanochannel entry and an
improved method for fabrication thereof.
SUMMARY OF THE INVENTION
The present invention relates to a device for interfacing
nanofluidic and microfluidic components suitable for use in
performing high throughput i.e., macromolecular analysis.
Diffraction gradient lithography (DGL) is used to form a gradient
interface between a microfluidic area and a nanofluidic area. The
gradient interface area reduces the local entropic barrier to
nanochannels formed in the nanofluidic area.
In one embodiment, the gradient interface area is formed of lateral
spatial gradient structures for narrowing the cross section of a
value from the micron to the nanometer length scale. In another
embodiment, the gradient interface area is formed of a vertical
sloped gradient structure. Additionally, the gradient structure can
provide both a lateral and vertical gradient. The gradient
structures can be used to squeeze and funnel biomolecules into a
small nanofluidic area.
In one aspect of the invention, a method for fabricating a fluidic
device by diffraction gradient lithography comprises forming a
nanofluidic area on a substrate, forming a microfluidic area on the
substrate and forming a gradient interface area between the
nanofluidic area and the microfluidic area. The gradient interface
area can be formed by using a blocking mask positioned above a
photo mask and/or photoresist during photolithography. The edge of
the blocking mask provides diffraction to cast a gradient light
intensity on the photoresist. In another embodiment, a system is
provided for fabricating the fluidic device.
In one aspect of the invention, the nanofluidic components comprise
nanoscale fluidic structures. The nanofluidic structures can
include nanopillars, nanopores and nanochannel arrays.
In another aspect of the invention, a fluidic device is formed of a
gradient interface between a nanofluidic area and a microfluidic
area, at least one sample reservoir in fluid communication with the
microfluidic area, the sample reservoir capable of releasing a
fluid and at least one waste reservoir in fluid communication with
the nanofluidic area, the waste reservoir capable of receiving a
fluid. In another aspect a system for carrying out analysis is
provided including a fluidic device is formed of a gradient
interface between a nanofluidic area and a microfluidic area, at
least one sample reservoir in fluid communication with the
microfluidic area, the sample at least one reservoir capable of
releasing a fluid and at least one waste reservoir in fluid
communication with at least one of the channels the waste reservoir
capable of receiving a fluid, signal acquisition and a data
processor. The signal can be a photon, electrical current/impedance
measurement or change in measurements. The fluidic device can be
used in MEMS and NEMS devices.
In another embodiment, methods for analyzing at least one
macromolecule are provided which, for example, include the steps
of: providing a fluidic device formed of a gradient interface
between a nanofluidic area and a microfluidic area, at least one
sample reservoir in fluid communication with the microfluidic area,
the at least one sample reservoir capable of releasing a fluid and
at least one waste reservoir in fluid communication with the
nanofluidic area, the waste reservoir capable of receiving a fluid,
transporting at least one macromolecule from the microfluidic area
to the nanofluidic area to elongate the at least one macromolecule,
detecting at least one signal transmitted from the at least one
macromolecule and correlating the detected signal to at least one
property of the macromolecule.
Cartridges including a nanofluidic chip in accordance with this
invention are also disclosed herein. Such cartridges are capable of
being inserted into, used with and removed from a system such as
those shown herein. Cartridges useful with analytical systems other
than the systems of the present invention are also comprehended by
this invention.
The invention will be more fully described by reference to the
following drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a schematic diagram of a prior art device including
nanochannels.
FIG. 1B is a graph of entropy change to the nanochannels of the
device of FIG. 1A.
FIG. 2 is a schematic diagram of a device for interfacing
microfluidic and nanofluidic components in accordance with the
teachings of the present invention.
FIG. 3 is a graph of entropy change to the nanochannels of the
device of FIG. 2.
FIGS. 4A 4D diagrammatically illustrate a process incorporating
diffraction gradient lithography (DGL) to fabricate a micropost
array and interface gradient structure.
FIGS. 5A 5B diagrammatically illustrate a process incorporating
diffraction gradient lithography (DGL) to fabricate a sloped
gradient interface area.
FIG. 6A is a schematic diagram of a method for adjusting the
diffraction gradient using thickness.
FIG. 6B is a schematic diagram of a method for adjusting the
diffraction gradient using a variable distance.
FIG. 7 is a schematic diagram of a microfluidic/nanofluidic
chip.
FIG. 8 is a schematic diagram of a system for analyzing
macromolecules using the microfluidic/nanofluidic chip.
FIG. 9A is an optical image during fabrication of the device of the
present invention after photoresist development, in accordance with
FIG. 4B, step 4.
FIG. 9B is a scanning electronic microscope during fabrication of
the device of the present invention after pattern transfer and
photoresist removal, in accordance with FIG. 4C, step 5.
FIG. 10A is a scanning electronic microscope during fabrication of
the device of the present invention after pattern transfer and
photoresist removal using a first etching condition, in accordance
with FIG. 4C, step 5.
FIG. 10B is a scanning electronic microscope during fabrication of
the device of the present invention after pattern transfer and
photoresist removal using a second etching condition, in accordance
with FIG. 4C, step 5.
FIG. 11A is an intensified charge coupled device (CCD) image of
fluorescent long DNA molecules entering the prior art nanofluidic
chip shown in FIG. 1.
FIG. 11B is an intensified charge coupled device (CCD) image of
fluorescent long DNA molecules entering device 10 shown in FIG.
2.
DETAILED DESCRIPTION
Reference will now be made in greater detail to a preferred
embodiment of the invention, an example of which is illustrated in
the accompanying drawings. Wherever possible, the same reference
numerals will be used throughout the drawings and the description
to refer to the same or like parts.
FIG. 2 is a schematic diagram of device 10 for interfacing
microfluidic and nanofluidic components in accordance with the
teachings of the present invention. Gradient interface area 12 is
positioned between microfluidic area 14 and nanofluidic area 16.
Microfluidic area 14 can comprise a plurality of microposts 18
formed on substrate 19. For example, microposts 18 can have a
diameter in the range of about 0.5 to about 5.0 microns and
distance D.sub.1 between microposts 18 can be in the range of about
0.5 to about 5.0 microns. In one embodiment, microposts 18 have a
diameter in the range of about 1.2 to about 1.4 microns and a
distance D.sub.1 between microposts 18 in a range of about 1.5 to
about 2.0 microns.
Nanofluidic area 16 can comprise a plurality of nanochannel arrays
20 including a surface having a plurality of nanochannels 21 in the
material of the surface. By "a plurality of channels" is meant more
than two channels, typically more than 5, and even typically more
than 10, 96, 100, 384, 1,000, 1,536, 10,000, 100,000 and 1,000,000
channels. Nanochannels 21 can be provided as a plurality of
parallel linear channels across substrate 19. Nanochannels 21 can
have a trench width of less than about 150 nanometers, more
typically less than 100 nanometers, and even more typically less
than: 75, 50, 25 and 15 nanometers. In certain embodiments, the
trench width can be about 10 nanometers. In the present invention,
the trench width can be at least 2 nm, and typically at least 5 nm.
Nanochannels 21 can have a trench depth of less than about 200
nanometers.
The nanochannels can have sealing material adjacent to the channel
wall material. In this embodiment, the sealing material can reduce
the trench width. Varying the sealing material deposition
parameters can be used to narrow the trench width of the channels.
The deposition parameters can be varied to provide trench widths of
typically less than 100 nanometers. As more material is deposited,
trench widths can be narrowed to less than 75 nanometers, and even
less than: 50 nanometers, 25 nanometers, and 15 nanometers. Trench
widths of about 10 nm can also be provided by the methods of the
present invention. Typically, the resulting trench widths after
deposition will be greater than 2 nm, and more typically greater
than 5 nanometers. Trench depths of less than 175, 150, 125, 100,
75, 50, and 25 nm can also be provided by the methods of the
present invention. Trench depths of about 15 nm can also be
provided. Typically, the trench depths will be at least 5 nm, and
more typically at least 10 nm.
In certain embodiments, the trench depth is typically less than 175
nm, and more typically less than 150 nm, 125 nm, 100 nm, 75 nm, 50
nm and 25 nm. In certain embodiments, the trench depth is about 15
nm. In certain embodiments, the trench depth is at least 2 nm,
typically at least 5 nm, and more typically at least 10 nm. At
least some of the nanochannels 21 can be surmounted by sealing
material to render such channels at least substantially enclosed.
The lengths of the channels of the nanochannel array can have a
wide range.
The lengths of the channels can also be the same or different in
nanochannel array 20. For carrying out macromolecular analysis
using nanochannel array 20 as provided below, it is desirable that
nanochannels 21 are at least about 1 millimeter (mm), 1 micrometer
(.mu.m) or longer. The length of nanochannels 21 is greater than
about 1 millimeter (mm), about 1 centimeter (cm), and even greater
than about 5 cm, about 15 cm, and about 25 cm. Nanochannels 21 can
be fabricated with nanoimprint lithography (NIL), as described in
Z. N. Yu, P. Deshpande, W. Wu, J. Wang and S. Y. Chou, Appl. Phys.
Lett. 77 (7), 927 (2000); S. Y. Chou, P. R. Krauss, and P. J.
Renstrom, Appl. Phys. Lett. 67 (21), 3114 (1995); Stephen Y. Chou,
Peter R. Krauss and Preston J. Renstrom, Science 272, 85 (1996) and
U.S. Pat. No. 5,772,905. Nanochannel 21 can be formed by
nanoimprint lithography, interference lithography, self-assembled
copolymer pattern transfer, spin coating, electron beam
lithography, focused ion beam milling, photolithography, reactive
ion-etching, wet-etching, plasma-enhanced chemical vapor
deposition, electron beam evaporation, sputter deposition, and
combinations thereof. Alternatively, other conventional methods can
be used to form nanochannels.
In an alternate embodiment, nanofluidic area 16 can comprise
nanoscale fluidic structures. For example, the nanoscale fluidic
structures can comprise nanopillars and nanospheres.
Gradient interface area 12 is used to effectively stretch and align
biopolymers 22 before they approach nanofluidic area 16.
Biopolymers 22 can be preliminarily stretched between adjacent
pairs of microposts 18 before entering nanochannels 21. Gradient
interface area 12 reduces the steepness of the entrophy barrier
before biopolymers 22 enter nanofluidic area 16, as shown in FIG.
3.
Referring to FIG. 2, gradient interface area 12 can comprise a
plurality of gradient structures 23 formed on substrate 19.
Distance D.sub.2 between gradient structures 23 is gradually
reduced towards nanofluidic area 16. For example, distance D.sub.2
between gradient structures 23 can be reduced from about 2 microns
to gradually below about 500 nm, about 400 nm, about 200 nm, about
150 nm, about 10 nm, about 5 nm and about 2 nm. In one embodiment,
the distance D.sub.2 between gradient structures 23 is reduced in a
range of about a radius of gyration of biopolymer 22 to
substantially a diameter of biopolymer 22. For example, diameter
D.sub.2 between gradient structures 23 can be reduced in the range
of about 2 nm, a diameter of a DNA module, to about 700 nm, a
radius of gyration of a T4 phage DNA molecule.
Gradient structures 23 can provide a gradual elevation of height
H.sub.1 from substrate 19. Nanofluidic area 16 can have a shallower
depth DP.sub.1 than depth DP.sub.2 of microfluidic area 14.
Accordingly, gradual elevation of height H.sub.1 from microfluidic
area 14 to nanofluidic area 16 provides improved interconnection of
microfluidic area 14 with nanofluidic area 16.
Basic fabrication steps of the present invention using diffraction
gradient lithography are outlined in partial, schematic perspective
views in FIGS. 4A 4C, as including processing steps 1 3. One or
more nanochannels 21 were fabricated on substrate 19 in this
process. Substrate 19 can be a silicon wafer substrate.
Alternatively, any type of material compatible with the
photolithography can be used as a substrate. Substrate 19 was
coated with photoresist 32 after HMDS treatment and baked.
Photomask 34 having a micron size post array can be used to pattern
microfluidic area 14 and gradient interface area 12, in step 1.
In step 2, blocking mask 35 was placed over or coated on photomask
34. Blocking mask 35 extends over portion 36 of photomask 34.
Blocking mask 35 masks portion 38 of nanofluidic area 16 positioned
under portion 36 of photomask 34 to protect nanochannels 21. In
step 3, device 10 was exposed to incident UV light 37. Blocking
mask 35 causes light diffraction along edge 39 of blocking mask
35.
Blocking mask 35 can be formed of any material which is opaque to
exposing light used in optical lithography. For example, blocking
mask 35 can be formed of a metal, such as aluminum foil or an
opaque plastic.
Referring to FIG. 4B, in step 4, device 10 was developed using
conventional techniques. Light diffraction caused by edge 39 of
blocking mask 35 generates a gradient in dissolution rate of
photoresist 32 by the developer. During development, exposed
photoresist 32 was completely removed at portion 41 which is not
blocked by blocking mask 35, exposing the substrate surface
underneath. At portion 42, photoresist 32 has a gradient of
undeveloped photoresist along the light diffraction area. The
thickness of the gradient of undeveloped photoresist corresponds to
exposure to diffracted light. At portion 43, blocking mask 35
completely blocks exposure of photoresist 32 to light.
Referring to FIG. 4C, in step 5, photoresist 32 was used as an
etching mask during a reactive ion etching (RIE) process and
gradient patterns in photoresist 32 were transferred into substrate
19.
A light intensity profile on photomask 34 is shown in FIG. 4D. The
light intensity profile shows reduced light intensity along edge 39
of blocking mask 35. The gradient profile can be controlled by the
type of photoresist, development conditions and etching conditions.
For example, a low contrast resist can provide a gradual gradient
profile. Edge 39 of blocking mask 35 can be varied to adjust the
gradient profile. For example, edge 39 can be angled or patterned
to adjust the gradient profile.
In one embodiment, gradient interface area 12 is formed as a
gradual slope from microfluidic area 14 to nanofluidic area 16, as
shown in FIGS. 5A 5B. In this embodiment, one or more nanochannels
were fabricated in substrate 19. Substrate 19 was coated with
photoresist 32 after HMDS treatment and baked, in step 1. In step
2, blocking mask 35 was placed over photoresist 32. Blocking mask
35 extends over portion 36 of photomask 34. Blocking mask 35 masks
portion 38 of nanofluidic area 16 to protect nanochannels 21. In
step 3, device 10 was exposed to incident UV light 37. Blocking
mask 35 causes light diffraction along edge 39 of blocking mask 35.
In step 4, device 10 was developed using conventional techniques.
Photoresist 32 was used as an etching mask during a reactive ion
etching (RIE) process and gradient patterns in photoresist 32 were
transferred into substrate 19. During development, the diminishing
light intensity casted on photoresist 32 forms a gradient vertical
slope in gradient interface area 12 which is transferred into
substrate 16.
Width W.sub.2 of blocking mask 35 and distance between photomask 34
and blocking mask 35 can be varied to determine the distance
D.sub.3 of blocking mask 35 to photoresist 32, as shown in FIGS. 6A
6B. For example, blocking mask 35 can have a varying width W.sub.2
in the range of about 1 mm to about 10 mm. W.sub.2 can be formed of
one or more additional blocking masks which are fused to blocking
mask 35 for increasing Width W.sub.2 of blocking mask 35. Blocking
mask 35 can be coated on photomask 34.
In an alternate embodiment, distance D.sub.3 of blocking mask 35 to
photoresist 32 can be adjusted by adjusting the distance between
blocking mask 35 and photomask 34. Blocking mask 35 can be
positioned over photomask 34 using blocking mask holder 40.
Photomask 34 can be positioned over photoresist 32 using aligner
42. Blocking mask holder 40 can move blocking mask in X.sub.1,
X.sub.2, Y.sub.1, Y.sub.2 directions. Aligner 42 can move photomask
34 in the X.sub.1, X.sub.2, Y.sub.1, Y.sub.2 directions. Distance
D.sub.3 can be varied upon movement of blocking mask 35 towards and
away from photoresist 32. Distance D.sub.3 determines diffraction
to photoresist 32. For example, a smaller distance D.sub.3 provides
a narrower diffraction zone in gradient interface area 12.
In another aspect of the invention, there is provided a
microfluidic/nanofluidic chip that includes the gradient interface
area for interfacing microfluidic and nanofluidic components.
Referring to FIG. 7, microfluidic/nanofluidic chip 100 has
microfluidic area 14, substrate 19, nanofluidic area 16, gradient
interface area 12 and reservoirs 102 for handling samples and
reservoirs 104 for receiving samples and sample collection. Tunnels
103 formed in substrate 19 can be used for connecting reservoirs
102 and 104 respectively to microfluidic area 14 and nanofluidic
area 16.
Nanofluidic area 16 can comprise nanofluidic channels 21 as
described above. Alternatively, nanofluidic area 16 and gradient
interface area 12 can comprise branched channels 106. Branched
channels 106 can be split into smaller and smaller branches range
from about 5.0 microns to about 2 nanometers to provide decreasing
lateral gradient distances between channels providing a lateral
gradient. Branched channels 106 can include a gradual elevation in
height formed using diffraction gradient lithography, as described
above.
The reservoirs are in fluid communication with at least one of the
channels, so that the sample reservoirs are capable of releasing a
fluid into the channels, and the waste reservoirs are capable of
receiving a fluid from the channels. Typically the fluids contain
macromolecules for analysis.
In certain embodiments of the present invention, the
microfluidic/nanofluidic chip contains at least one sample
reservoir formed in the surface of the substrate. Reservoirs can be
defined using photolithography and subsequently pattern transferred
to the substrate using Reactive Ion etching (RIE), chemical etching
or FIB milling directly to create reservoirs in fluid communication
with nanofluidic area 16 or nanochannels 21. In this embodiment, at
least one waste reservoir in fluid communication with at least one
of the channels. Typically, the microfluidic/nanofluidic chip
contains at least 1 sample reservoir. Alternatively, a variety of
other embodiments include various numbers of reservoirs.
For use in macromolecular analysis, microfluidic/nanofluidic chip
100 can provide at least a portion of nanofluidic area 16 capable
of being imaged with a two-dimensional detector. Imaging of the
nanofluidic area 16 is provided by presenting the nanochannels and
any sealing material to suitable apparatus for the collection of
emitted signals, such as optical elements for the collection of
light from the nanochannels. In this embodiment, the
microfluidic/nanofluidic chip is capable of transporting a
plurality of elongated macromolecules from a sample reservoir,
across macrofluidic area and across the nanofluidic area.
In certain embodiments of the present invention, the
microfluidic/nanofluidic chip contains an apparatus for
transporting macromolecules from the sample reservoirs, through the
macrofluidic area, nanofluidic area, and into the waste reservoirs.
A suitable apparatus includes at least one pair of electrodes
capable of applying an electric field across at least some of the
channels in at least one direction. Electrode metal contacts can be
integrated using standard integrated circuit fabrication technology
to be in contact with at least one sample and at least one
collection/waste reservoir to establish directional electric field.
Alternating current (AC), direct current (DC), or both types of
fields can be applied. The electrodes can be made of almost any
metal, and are typically thin Al/Au metal layers deposited on
defined line paths. Typically at least one end of one electrode is
in contact with buffer solution in the reservoir.
In certain embodiments of the present invention, the
microfluidic/nanofluidic chip contains at least two pair of
electrodes, each providing an electric field in different
directions. With at least two sets of independent electrodes, field
contacts can be used to independently modulate the direction and
amplitudes of the electric fields to move macromolecules at desired
speed or directions.
In another aspect of the present invention, system 200 is used for
carrying out macromolecular analysis, as shown in FIG. 8. System
200 includes a microfluidic/nanofluidic chip 100 as described
herein, and an apparatus for detecting at least one signal
transmitted from one or more fluids in nanochannels 21 of the
microfluidic/nanofluidic chip 100.
In various embodiments of the present invention, the system further
includes at least one of the following: a transporting apparatus to
transport a fluid through at least microfluidic area 14 and
nanochannels 21; a sample loading apparatus for loading at least
one fluid to sample reservoirs in microfluidic/nanofluidic chip
100; image or signal detectors and a data processor.
Microfluidic/nanofluidic chip 100 used in system 200 is typically
disposable, individually packaged, and having a sample loading
capacity of 1 50,000 individual fluid samples.
Microfluidic/nanofluidic chip 100 typically has sample loading
openings and a reservoir, or sample loading openings and plates
connected with a sealing mechanism, such as an O-ring. Electrodes
202 are connected to electric potential generator 204 and
microfluidic/nanofluidic chip 100. Electrodes 202 and electric
potential generator 204 can be connected with metal contacts.
Suitable metal contacts can be external contact patches that can be
connected to an external scanning/imaging/electric-field tuner.
In one embodiment of the present invention, system 200 includes an
apparatus to excite the macromolecules inside the channels and
detect and collect the resulting signals. Laser beam 206 is focused
using a focusing lens 208 to a spot on nanofluidic area 16. The
generated light signal from the macromolecules inside the
nanofluidic area or nanochannels (not shown) is collected by
focusing/collection lens 209, and is reflected off a dichroic
mirror/band pass filter 210 into optical path 212, which is fed
into CCD (charge coupled device) camera 213. Alternatively,
exciting light source could be passed through a dichroic
mirror/band pass filter box 210 and focusing/collecting scheme from
the top of the chip. Various optical components and devices can
also be used in the system to detect optical signals, such as
digital cameras, PMTs (photomultiplier tubes), and APDs (Avalanche
photodiodes).
System 200 can include data processor 214. Data processor 214 can
be used to process the signals from CCD 213 to project the digital
image of nanofluidic area 16 on display 215. Data processor 214 can
also analyze the digital image to provide characterization
information, such as macromolecular size statistics, histograms,
karyotypes, mapping, diagnostics information and display the
information in suitable form for data readout 216.
Microfluidic/nanofluidic chip 100 can be encased in a suitable
housing, such as plastic, to provide a convenient and
commercially-ready cartridge or cassette. Typically the nanofluidic
cartridges will have suitable features on or in the housing for
inserting, guiding, and aligning the sample loading device with the
reservoirs. Insertion slots, tracks, or both can be provided in the
plastic case.
Macromolecular fluid samples that can be analyzed by the system
includes fluids from a mammal (e.g., DNA, cells, blood, Serum,
biopsy tissues), synthetic macromolecules such as polymers, and
materials found in nature (e.g., materials derived from plants,
animals, and other life forms). Such fluid samples can be managed,
loaded, and injected using automated or manual sample loading
apparatus of the present invention.
In another aspect of the present invention, there is provided a
method of analyzing at least one macromolecule. In this invention,
the analysis includes the steps of providing a
microfluidic/nanofluidic chip 100 according to the present
invention, providing the at least one sample reservoir with at
least one fluid, the fluid comprising at least one macromolecule;
transporting the at least one macromolecule from a macrofluidic
area through a gradient interface area into the at least one
channel to elongate said at least one macromolecule; detecting at
least one signal transmitted from the at least one elongated
macromolecule; and correlating the detected signal to at least one
property of the at least one macromolecule.
In one embodiment of the present invention, the method of analyzing
a macromolecule includes wetting the channels using capillary
action with a buffer solution or a buffer solution containing
macromolecules. Macromolecules such as polymers and DNA can be
introduced into nanochannel arrays by electric field, capillary
action, differential surface tension by temperature or chemical
gradient or differential pressure such as vacuum.
Various macromolecules can be analyzed using the present method.
For analyzing DNA typical process conditions include providing
dilute solutions of DNA which are stained at a ratio of 4:1 to 10:1
base pair/dye with a suitable dye. Suitable dye stains include
TOTO-1, BOBO-1, BOBO-3 (Molecular Probes, Eugene, Oreg.). Solutions
of stained DNA can be further diluted and treated with an
anti-oxidant and an anti-sticking agent.
In one embodiment of the present invention, the method of analyzing
a macromolecule includes the sizing of one DNA macromolecule. One
DNA macromolecule can be extracted from a single cell or spore,
such as anthrax, and suitably transported (e.g., in a polymerized
gel plugs) to avoid breakage.
The length of a single DNA can be detected/reported and intensity
profile can be plotted. In various embodiments of the present
invention, the method of analyzing a macromolecule includes
correlating the detected signal to at least one of the following
properties: length, conformation, and chemical composition. Various
macromolecules that can be analyzed this way include, biopolymers
such as a protein, a polypeptide, and a nucleic acid such as RNA or
DNA or PNA. For DNA nucleic acids, the detected signals can be
correlated to the base pair sequence of said DNA.
The typical concentration of the macromolecules in the fluid will
be one macromolecule, or about at least attogram per ml, more
typically at least one femtogram per ml, more typically at least
one picogram per ml, and even more typically at least one nanogram
per ml. Concentrations will typically be less than about 5
micrograms per milliliter and more typically less than about 0.5
micrograms per milliliter.
In one embodiment of the present invention, the method of analyzing
a macromolecule measures the length of macromolecules having an
elongated length of greater than 150 nanometers, and typically
greater than about 500 nanometers, about 1 micron, about 10
microns, about 100 microns, about 1 mm, about 1 cm, and about 10 cm
long.
DNA having greater than 10 base pairs can also be analyzed using
the present methods. Typically, the number of base pairs measured
can be greater than 100 base pairs, greater than 1,000 base pairs,
greater than 10,000 base pairs, greater than 100,000 base pairs and
greater than 1,000,000 base pairs. DNA having more than 1 million,
10 million, and even 100 million basepairs can be analyzed with the
present methods.
In one embodiment of the present invention, the methods can be used
to analyze one or more of the following: restriction fragment
length polymorphism, a chromosome, and single nucleotide
polymorphism.
The invention can be further illustrated by the following examples
thereof, although it will be understood that these examples are
included merely for purposes of illustration and are not intended
to limit the scope of the invention unless otherwise specifically
indicated. All percentages, ratios, and parts herein, in the
Specification, Examples, and claims, are by weight and are
approximations unless otherwise stated.
EXAMPLES
Large arrays of nanochannels were first fabricated on an entire Si
substrate chip using nanoimprinting lithography, described in S. Y.
Chou, P. R. Krauss, and P. J. Renstrom, Appl. Phys. Lett. 67 (21),
3114 (1995); Stephen Y. Chou, Peter R. Krauss and Preston J.
Renstrom, Science 272, 85 (1996) and U.S. Pat. No. 5,772,905. This
chip was spin coated with positive tone photoresist (AZ5214-E)
using standard protocol at 4000 rpm for 1 min after HMDS treatment
and baked at 110.degree. C. for 2 min. A Karl Suss MA-6 contact
aligner and a uniform micron feature size hexagon array photomask
were used to pattern the microfluidic area. A blocking mask of a
piece of aluminum foil was placed on top of the photomask. The
distance between the blocking mask and the photoresist surface was
about 3 mm. The chip was exposed at 400 nm UV light in hard contact
mode for 35 seconds and developed with a standard procedure (AZ312
MIF:H.sub.2O 1:1). The photoresist was used as an etching mask
during a subsequent reactive ion etching (RIE) process and the
gradient patterns in the photoresist were transferred into the
underlying Si substrate.
FIG. 9A shows a top view optical image of the actual gradient chip
after photoresist development. The gaps between posts were then
etched into the chip using a combination of O.sub.2 and CHF.sub.3
plasma followed by removal of the resist using acetone. FIG. 9B
shows a scanning electronic microscope (SEM) image of the
interfacing zone with gradient lateral spacing between microposts
after pattern transfer and photoresist removal. The area directly
under the blocking mask with the prefabricated nanochannels is
protected from RIE by the masking photoresist.
FIGS. 10A 10B illustrate cleaved profile SEM images showing the
gradual reduction of the gaps between the microposts, typically
from 1.2 .mu.m gradually to below 400 nm, and the gradual elevation
of the substrate of the fluidic chip to interconnect to the
shallower nanofluidic channels. The gradient profile shown in FIGS.
10A and 10B is slight differently controlled by the choice of
photoresist, development and etching conditions.
Fluorescently stained long DNA molecules were introduced into prior
art nanofluidic chips shown in FIG. 1 and device 10 shown in FIG.
2. In FIG. 11A, DNA entered from the right side of the image, and
approached and stalled at the edge of the prior art nanofluidic
chip, causing fouling of the chip. In FIG. 11B, lambda phage DNA
molecules or genomic BAC DNA were partially uncoiled when they
entered the gradient area, and slowed down at the edge of the
nanochannels due to "uphill" entrophy. Larger DNA molecules moved
into the nanochannels continuously and remained stretched, with
significantly improved efficiency. Moving DNA molecules can be seen
in the left part of the image as long white streaks after image
integration.
It is to be understood that the above-described embodiments are
illustrative of only a few of the many possible specific
embodiments which can represent applications of the principles of
the invention. Numerous and varied other arrangements can be
readily devised in accordance with these principles by those
skilled in the art without departing from the spirit and scope of
the invention.
* * * * *
References