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.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a divisional application of U.S. patent application Ser. No. 11/536,178, filed Sep. 28, 2006, now U.S. Pat. No. 8,333,394, which is a divisional application of U.S. patent application Ser. No. 10/414,620, filed on Apr. 16, 2003, now U.S. Pat. No. 7,217,562, which claims the benefit of priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 60/373,409, filed on Apr. 16, 2002 and U.S. Provisional Application No. 60/419,742, filed Oct. 18, 2002, each of which applications are incorporated by reference herein in their entirety. 
     
    
     STATEMENT OF GOVERNMENT SUPPORT 
       [0002]    This invention was made with government support under DARPA Grant Number MDA972-00-1-0031. The government has certain rights in the invention. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    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. 
         [0005]    2. Description of the Related Art 
         [0006]    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. 
         [0007]    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. 
         [0008]    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, pp 174. 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=(Lρ/6) 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. 
         [0009]    U.S. Patent Application Publication 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. 
         [0010]    U.S. Patent Application Publication 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° 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. 
         [0011]    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 
       [0012]    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. 
         [0013]    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. 
         [0014]    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. 
         [0015]    In one aspect of the invention, the nanofluidic components comprise nanoscale fluidic structures. The nanofluidic structures can include nanopillars, nanopores and nanochannel arrays. 
         [0016]    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. 
         [0017]    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. 
         [0018]    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, 
         [0019]    The invention will be more fully described by reference to the following drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1A  is a schematic diagram of a prior art device including nanochannels. 
           [0021]      FIG. 1B  is a graph of entropy change to the nanochannels of the device of  FIG. 1A . 
           [0022]      FIG. 2  is a schematic diagram of a device for interfacing microfluidic and nanofluidic components in accordance with the teachings of the present invention. 
           [0023]      FIG. 3  is a graph of entropy change to the nanochannels of the device of  FIG. 2 . 
           [0024]      FIGS. 4A-4D  diagrammatically illustrate a process incorporating diffraction gradient lithography (DGL) to fabricate a micropost array and interface gradient structure. 
           [0025]      FIGS. 5A-5B  diagrammatically illustrate a process incorporating diffraction gradient lithography (DGL) to fabricate a sloped gradient interface area. 
           [0026]      FIG. 6A  is a schematic diagram of a method for adjusting the diffraction gradient using thickness. 
           [0027]      FIG. 6B  is a schematic diagram of a method for adjusting the diffraction gradient using a variable distance. 
           [0028]      FIG. 7  is a schematic diagram of a microfluidic/nanofluidic chip. 
           [0029]      FIG. 8  is a schematic diagram of a system for analyzing macromolecules using the microfluidic/nanofluidic chip. 
           [0030]      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 . 
           [0031]      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 . 
           [0032]      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 . 
           [0033]      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 . 
           [0034]      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 . 
           [0035]      FIG. 11B  is an intensified charge coupled device (CCD) image of fluorescent long DNA molecules entering device  10  shown in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    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. 
         [0037]      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 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 1  between microposts  18  in a range of about 1.5 to about 2.0 microns. 
         [0038]    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. 
         [0039]    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. 
         [0040]    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. 
         [0041]    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. 
         [0042]    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 (μm) 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 hereby each incorporated in their entirety by reference into this application. 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. 
         [0043]    In an alternate embodiment, nanofluidic area  16  can comprise nanoscale fluidic structures. For example, the nanoscale fluidic structures can comprise nanopillars and nanospheres. 
         [0044]    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 . 
         [0045]    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. 
         [0046]    Gradient structures  23  can provide a gradual elevation of height H 1  from substrate  19 . Nanofluidic area  16  can have a shallower depth DP 1  than depth DP 2  of microfluidic area  14 . Accordingly, gradual elevation of height H 1  from microfluidic area  14  to nanofluidic area  16  provides improved interconnection of microfluidic area  14  with nanofluidic area  16 . 
         [0047]    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 . 
         [0048]    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 . 
         [0049]    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. 
         [0050]    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. 
         [0051]    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 , 
         [0052]    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. 
         [0053]    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 . 
         [0054]    Width W 2  of blocking mask  35  and distance between photomask  34  and blocking mask  35  can be varied to determine the distance D 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 2  in the range of about 1 mm to about 10 mm. W 2  can be formed of one or more additional blocking masks which are fused to blocking mask  35  for increasing Width W 2  of blocking mask  35 . Blocking mask  35  can be coated on photomask  34 . 
         [0055]    In an alternate embodiment, distance D 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 1 , X 2 , Y 1 , Y 2  directions. Aligner  42  can move photomask  34  in the X 1 , X 2 , Y 1 , Y 2  directions. Distance D 3  can be varied upon movement of blocking mask  35  towards and away from photoresist  32 . Distance D 3  determines diffraction to photoresist  32 . For example, a smaller distance D 3  provides a narrower diffraction zone in gradient interface area  12 . 
         [0056]    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 . 
         [0057]    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. 
         [0058]    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. 
         [0059]    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. 
         [0060]    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. 
         [0061]    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. 
         [0062]    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. 
         [0063]    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 . 
         [0064]    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. 
         [0065]    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. 
         [0066]    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). 
         [0067]    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 . 
         [0068]    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. 
         [0069]    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. 
         [0070]    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. 
         [0071]    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. 
         [0072]    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. 
         [0073]    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. 
         [0074]    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. 
         [0075]    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. 
         [0076]    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. 
         [0077]    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. 
         [0078]    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. 
         [0079]    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 
       [0080]    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° 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 2 O 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. 
         [0081]      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 2  and CHF 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. 
         [0082]      FIGS. 10A-10B  illustrate cleaved profile SEM images showing the gradual reduction of the gaps between the microposts, typically from 1.2 μm 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. 
         [0083]    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. 
         [0084]    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.