Patent Publication Number: US-8969118-B2

Title: Integrated carbon nanotube field effect transistor and nanochannel for sequencing

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 13/690,963, entitled “INTEGRATED CARBON NANOTUBE FIELD TRANSISTOR AND NANOCHANNEL FOR SEQUENCING”, filed on Nov. 30, 2012, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     The present invention relates to nanodevices, and more specifically, to sequencing using an integrated carbon nanotube field effect transistor and nanochannel. 
     Nanopore sequencing is a method for determining the order in which nucleotides occur on a strand of deoxyribonucleic acid (DNA). A nanopore (also referred to a pore, nanochannel, hole, etc.) can be a small hole in the order of several nanometers in internal diameter. The theory behind nanopore sequencing is about what occurs when the nanopore is submerged in a conducting fluid and an electric potential (voltage) is applied across the nanopore. Under these conditions, a slight electric current due to conduction of ions through the nanopore can be measured, and the amount of current is very sensitive to the size and shape of the nanopore. If single bases or strands of DNA pass (or part of the DNA molecule passes) through the nanopore, this can create a change in the magnitude of the current through the nanopore. Other electrical or optical sensors can also be positioned around the nanopore so that DNA bases can be differentiated while the DNA passes through the nanopore. 
     The DNA can be driven through the nanopore by using various methods, so that the DNA might eventually pass through the nanopore. The scale of the nanopore can have the effect that the DNA may be forced through the hole as a long string, one base at a time, like thread through the eye of a needle. Recently, there has been growing interest in applying nanopores as sensors for rapid analysis of biomolecules such as deoxyribonucleic acid (DNA), ribonucleic acid (RNA), protein, etc. Special emphasis has been given to applications of nanopores for DNA sequencing, as this technology holds the promise to reduce the cost of sequencing below $1000/human genome. 
     SUMMARY 
     According to an embodiment, a method for base recognition in an integration of a transistor and a nanochannel is provided. The method includes forcing a target molecule down to a carbon nanotube a single base at a time in the nanochannel. The target molecule is forced to the carbon nanotube by applying a gate voltage to a top electrode of the transistor, by a narrow thickness of the nanochannel, or both by applying the gate voltage to the top electrode of the transistor and by the narrow thickness of the nanochannel. The nanochannel having been patterned over the carbon nanotube exposes an exposed portion of the carbon nanotube at a bottom wall of the carbon nanotube, where the top electrode of the transistor is positioned over the exposed portion of the carbon nanotube through the nanochannel. The exposed portion of the carbon nanotube is smaller than a separating distance between bases on the target molecule, and the exposed portion of the carbon nanotube is configured to only accommodate the single base at a time. The target molecule is stretched by the narrow thickness of the nanochannel and by applying a traverse voltage across a length direction of the nanochannel between a first electrode and a second electrode at opposite ends of the nanochannel in the length direction. The target molecule is frictionally restricted by the narrow thickness of the nanochannel causing the target molecule to stretch as the target molecule restrictedly translocates in the length direction while the traverse voltage is applied. The method includes measuring a transistor current while the single base of the target molecule is forced down to the exposed portion of the carbon nanotube in the nanochannel. The single base affects the transistor current. The method includes determining an identity of the single base according to a change in the transistor current while the single base is forced down to the exposed portion of the carbon nanotube in the nanochannel. 
     According to an embodiment, a system for base recognition of a target molecule is provided. The system includes a transistor having a source electrode, a drain electrode, and a top electrode. The source electrode is electrically connected to the drain electrode by a carbon nanotube. A nanochannel is formed perpendicularly to the carbon nanotube and formed with a longitudinal direction extending away from the source electrode and the drain electrode. The nanochannel is formed of an insulating layer except at a single bottom location of the nanochannel. The single bottom location of the nanochannel is an exposed portion of the carbon nanotube, and the nanochannel is only formed of the carbon nanotube at the single bottom location. A size of the exposed portion of the carbon nanotube at the single bottom location is less than a separation distance between bases of the target molecule. The top electrode is positioned above the nanochannel to vertically line up to the exposed portion of the carbon nanotube at the single bottom location. The top electrode forces the target molecule down to the carbon nanotube a single base at a time in the nanochannel, and the target molecule is forced to the carbon nanotube by applying a gate voltage to the top electrode of the transistor and by a narrow thickness of the nanochannel. A transistor current is measured while the single base of the target molecule is forced down to the carbon nanotube in the nanochannel, so that the single base affects the transistor current. An identity of the single base is determined according to a change in the transistor current while the single base is forced down to the exposed portion of the carbon nanotube in the nanochannel. 
     Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the advantages and the features, refer to the description and to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIGS. 1A through 1E  illustrate cross-sectional views of fabricating an integrated carbon nanotube field effect transistor (CNT-FET) and nanochannel device according to an embodiment, in which: 
         FIG. 1A  is a cross-sectional view of the device with a carbon nanotube; 
         FIG. 1B  is a cross-sectional view of an electrically insulating layer deposited on the surface of the device; 
         FIG. 1C  is a cross-sectional view of a nanochannel or nanotrench formed through the insulating layer exposing the carbon nanotube; 
         FIG. 1D  is a cross-sectional view of another electrically insulating layer deposited on the previous insulating layer to seal the nanochannel; and 
         FIG. 1E  is a cross-sectional view of the device with electrodes deposited. 
         FIG. 2A  is a cross-sectional view of an integrated carbon nanotube field effect transistor and nanochannel system according to an embodiment. 
         FIG. 2B  is a top view the integrated carbon nanotube field effect transistor and nanochannel system according to an embodiment. 
         FIG. 3A  is an abbreviated version of a cross-sectional view of the carbon nanotube field effect transistor and nanochannel system according to an embodiment. 
         FIG. 3B  is an abbreviated version of a top view of the carbon nanotube field effect transistor and nanochannel system according to an embodiment. 
         FIGS. 4A and 4B  together are a flow diagram illustrating a method for base recognition in a transistor and a nanochannel system according to an embodiment. 
         FIG. 5  is a block diagram that illustrates an example of a computer (computer test setup) having capabilities, which may be included in and/or combined with embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the present invention provides techniques to integrate the carbon nanotube field effect transistor (CNT-FET) and nanochannel for DNA/RNA sequencing. Single or double strand DNA/RNA can be pulled through the nanochannel which can confine the motion of DNA/RNA. The CNT-FET can read the nucleotide (i.e., base) information when the DNA/RNA moves over the carbon nanotube inside nanochannel. The DNA/RNA can be pulled down towards the carbon nanotube by a vertical electrical field. The DNA/RNA also can be stretched by the transverse electrical field and/or physical size of the interface between the carbon nanotube and the top sealing insulating film. 
     Currently, different state of the art methods are employed to control the trap, ratchet the long DNA/RNA, and sense single nucleotide information. Those methods may have their own advantages, but have not realized the DNA/RNA sequencing in low cost and short time with high accuracy. The embodiment utilizes the CNT-FET as a sensor to read the nucleotide information when the DNA/RNA is moving over the carbon nanotube. The nanochannel, vertical electrical field, and transverse electrical field can confine the conformation and movement of DNA/RNA in the nanochannel. 
       FIGS. 1A through 1E  illustrate cross-sectional views of fabricating the integrated the carbon nanotube field effect transistor (CNT-FET) and nanochannel device  100  according to an embodiment.  FIGS. 1A through 1E  may be generally referred to as  FIG. 1 .  FIG. 1  illustrates the processes to integrate the CNT-FET and nanochannel for DNA/RNA sequencing so that the bases of a target molecule being tested can be individually pressed to an exposed portion of the carbon nanotube. 
       FIG. 1A  is a cross-sectional view of forming the multilayered device  100 . The device  100  includes a substrate  101  which may be any electrically insulating substrate such as silicon. An electrically insulating film  102  is deposited on the substrate  101 . The electrically insulating film  102  may be a dielectric material such as hafnium oxide. A carbon nanotube  103  is selectively placed on the surface of the electrically insulating film  102 . 
       FIG. 1B  illustrates that an electrically insulating film  104  which may be grown with atomic layer deposition to control the accuracy of thickness. The insulating film may be silicon dioxide, aluminum oxide, etc. The thickness of the electrically insulating film  102  can be a few to tens of nanometers, such as, e.g., 10 nm. The thickness of the electrically insulating film  104  can be, e.g., 3 to 5 nm. 
       FIG. 1C  illustrates a nanochannel  105  (e.g., a nanotrench) formed through the insulating film  104  down to the carbon nanotube  103 . The bottom of the nanochannel  105  is the carbon nanotube  103  (itself) at an isolated location that exposes the carbon nanotube  103  (as discussed further herein). The height of the nanochannel  105  is the thickness of the insulating film  104  deposited on the carbon nanotube  103 . For example, the thickness of the insulating film  104  deposited on the carbon nanotube  103  may be controlled to be 1 to 2 nanometers (nm), such that the depth/height of the nanochannel  105  is correspondingly 1 to 2 nm. The nanochannel  105  may be fabricated by standard semiconductor technology, such as, e.g., e-beam lithography, helium ion microscope, etc. 
       FIG. 1D  illustrates an electrically insulating film  106  deposited on the insulating film  104  to seal the nanochannel  105 . The micro contact printing (as film transfer) may be employed to fabricate the electrically insulating film  106  as understood by one skilled one the art. As one example, the whole piece of electrically insulating film  106  is first formed on other substrates, and then transferred onto the nanochannel  105 . So electrically insulating film  106  is placed on the top the nanochannel  105 , bonding with the insulating film  104  and sealing nanochannel  105 . Accordingly, the electrically insulating film  106  does not fill the inside of the nanochannel  105 . 
     The nanochannel  105  is formed with the carbon nanotube  103  as a bottom portion, the insulating film  104  as the nanochannel  105  sidewalls, and the electrically insulating film  106  as the top of the nanochannel  105 . The length of the nanochannel may be 100 nm to several micrometers in length. In one case, the insulating film  106  may be deposited on the insulating film  104  before the nanochannel  105  is formed. In this case, the nanochannel  105  is opened through the insulating film  104  after the insulating film  106  has been deposited. 
     In  FIG. 1E , electrodes  107  and  108  are respectively deposited on opposite sides of the carbon nanotube  103 . The electrodes  107  and  108  are contacts physically and electrically connected to the carbon nanotube  103 . A top electrode  109  is deposited on the electrically insulating film  106 . The electrodes  107  and  108  may be metal contacts for the carbon nanotube  103 , and the top electrode  109  may be a metal contact (not connected to the carbon nanotube  103 ). The metal contacts of electrodes  107 ,  108 , and  109  may be any metal such as gold, titanium nitride, etc. 
       FIGS. 2A and 2B  illustrate an integrated carbon nanotube field effect transistor and nanochannel system  200  of the device  100  according to an embodiment.  FIGS. 2A and 2B  may generally be referred to as  FIG. 2 . 
       FIG. 2A  is a cross-sectional view of the system  200 . A voltage source  215  is connected to the substrate  101  and connected to the top electrode  109 . The voltage source  215  produces a gate voltage bias for the CNT-FET device  100 . The gate voltage bias of the voltage source  215  generates the vertical electrical field  205  between the substrate  101  and top electrode  109 , which correspondingly generates downward forces  210  that pull the DNA or RNA inside the nanochannel  105  towards the carbon nanotube  103 . The arrows for the vertical electrical field  205  and the downward forces  207  are shown to the left of the figure so as not to obstruct the details, but it is understood that the vertical electrical field  205  and the downward forces  207  are in the device  100 . The ground  216  is connected to the negative side of the voltage source  215  and top electrode  109 . 
       FIG. 2B  is a top view of the system  200 . Inlet  210  and outlet  209  are the locations for an inlet reservoir (with the DNA/RNA molecules as samples to be sequenced) and an outlet reservoir to capture the molecules. The inlet and outlet reservoirs are not shown in  FIG. 2  so at not to obscure the figure but are understood by one skilled in the art. The inlet  210  and outlet  209  represent that the two reservoirs have been lifted from the  FIG. 2B  so that the nanochannel  105  can be viewed. The inlet and outlet reservoirs are respectively sealed at the inlet  210  and outlet  209 . The inlet and outlet reservoirs and the nanochannel  105  are filled with a buffer solution. The buffer solution is an electrically conductive electrolyte solution as understood by one skilled in the art. The DNA/RNA sample can be placed into the buffer solution (e.g., introduced into the inlet reservoir) for sensing. 
     Electrodes  218  and  219  are electrodes that are connected to a voltage source  211  and ammeter  212 . The electrodes  218  and  219  may be silver/silver chloride, platinum, etc. DNA (as a target molecule  305  shown in  FIG. 3 ) will be pulled through the nanochannel  105  by the electrical field generated by voltage of the voltage source  211 . The ammeter  212  can monitor/measure the ionic current change through the nanochannel  105  when the DNA or RNA is captured and driven inside the nanochannel  105 . The change (e.g., drop) in ionic current when the target molecule is in the nanochannel  105 , lets the operator (or computer  500  in  FIG. 5 ) know that the target molecule is present. 
     The positive side of a voltage source  213  may be connected to electrode  107  (as the source) and the negative side of the voltage source  213  may be connected to the electrode  108  (as the drain), voltage source  213  produces the voltage for the CNT-FET device  100 . Ammeter  214  monitors/measures the source-drain current (i.e., transistor current) through the carbon nanotube  103  (e.g., from electrode  107  to electrode  108 ) in the CNT-FET device  100  which can detect nucleotide information (based on the change in source-drain current (i.e., transistor current)) when the DNA/RNA passes over (and touches) the carbon nanotube  103  inside nanochannel  105 . The negative voltage applied to the top electrode  109  also pushes the negatively charged DNA molecule to the carbon nanotube  103  for base sensing at a specific bottom location of the nanochannel  105  at which the carbon nanotube  103  is exposed. 
     When no target molecule is in the nanochannel  105 , a baseline current curve (e.g., measured by ammeter  214 ) is established by a voltage sweep of the voltage source  213  (e.g., for voltages 1-5) to generate a baseline voltage versus current curve for the transistor. For example, the voltage of voltage source  213  is applied to the electrodes  107  and  108  and the transistor current is measured by ammeter  214 . From a conventional current flow, current flows from voltage source  213 , into electrode  107 , through the carbon nanotube  103  (e.g., through the metallic shell), out through the electrode  108 , into ammeter  214  (for transistor current measurement), and into the negative side of the voltage source  213 . 
     Also, a baseline (nucleotide) current is established for each base such as base A, base G, base C, and base T for a DNA molecule by individually introducing a (previously) known base into the system  200  for testing to obtain the transistor current unique to each base. As one example case, only base A is introduced into the inlet reservoir at inlet  210 . When base A is pulled into the nanochannel  105  by the voltage of voltage source  211  (e.g., the force of the electric field and the force of the negative polarity of the electrode  218  pushing the negatively charged DNA molecule), the base A interacts with (e.g., touches) the carbon nanotube  103  at a specific bottom location  310  (hole/via) of the nanochannel  105  as shown in  FIG. 3B . The charges on the base A (in this example) will cause a transfer of charges to the electrical current carriers flowing on the carbon nanotube  103 . This will cause the electrical current (measured by the ammeter  214 ) on the carbon nanotube  103  to change (e.g., drop or increase) as the base A touches the carbon nanotube  103  at the specific bottom location  310  of the nanochannel  105 . This process individually occurs for base A, G, C, and T to establish a transistor current baseline, and the respective electrical current change (e.g., the magnitude and time duration of the change) is measured and recorded for each of the respective bases A, G, C, and T. The respective transistor current change (e.g., drop in electrical current for a particular time duration) is used to compare against and identify bases on a target molecule that needs to be sequenced. 
     Once the system  200  is flushed (as understood by one skilled in the art), the target molecule  305  to be tested is introduced into the inlet reservoir at the inlet  210 . The voltage of voltage sources  211 ,  213 , and  215  are all turned on (and remain on during testing). By the voltage of voltage source  211  (i.e., electric voltage potential via electrodes  218  and  219  in the respective inlet and outlet reservoirs), the electric field (not shown) and negative polarity (of electrode  218  push) translocates (moves) the target molecule into (and through) the nanochannel  105 . While in the nanochannel  105 , the voltage of voltage source  215  drives/pushes the target molecule (i.e., the backbone) and a single base against (i.e., to touch) the carbon nanotube  103  at the specific bottom location  310 . While this single base is touching the carbon nanotube  103  and while the voltage of voltage source  213  is applied, the electrical current changes (i.e., source drain current of the transistor drops or increases for a time duration) while the single base touches the carbon nanotube  103  through the specific bottom location  310  of the nanochannel  105 . 
       FIG. 3A  illustrates an abbreviated version of a cross-sectional view of the system  200  with the carbon nanotube field effect transistor (CNT-FET) and nanochannel device  100 . So as not to obscure  FIGS. 3A and 3B  for the reader, certain elements of the system  200  are omitted but it is understood that the omitted elements are part of the figures as discussed herein.  FIG. 3A  illustrates how the voltage applied to the top electrode  109  (e.g., gate electrode) drives the target molecule  305  down, by particularly pressing a single base  350  to the carbon nanotube  103  at the specific bottom location  310  of the nanochannel  105 . The charges (positive or negative) on this particular base  350  interacts the electrical current (charge carriers) flowing on the carbon nanotube  103 , to cause the electrical current to change (drop or increase) when measured by the ammeter  214 . The electrical field  205  is shown pointing up (and to the left side of the figure so as not obstruct the figure). The downward forces  210  (including the negative voltage polarity applied to the top electrode  109 ) are pushing the single base  350  on to (an exposed portion  315  of) carbon nanotube  103 , while the other bases such as bases  351  and  352  do not touch the carbon nanotube  103  in the nanochannel  105  (at the same time that the single base  350  touches the carbon nanotube  103 ). The distance X separating each base of the target molecule  305  (such as DNA or RNA) is greater than “d” half of the diameter of the carbon nanotube  103 . As such, this ensures that only a single base of the target molecule  305  touches and interacts with the carbon nanotube  103  at a time, because any two bases are too far apart. As an example, the distance X between the bases may be 0.7 nm while d (half of the diameter of the carbon nanotube) may be 0.5 nm. 
     Also, the thickness (also referred to as the depth and height) of the nanochannel  105  is narrow compared to the height and size of the bases of the target molecule  305 . This narrow thickness provides two benefits. The narrowed thickness of the nanochannel  105  causes the bases (and backbone of the target molecule  305 ) to frictionally rub the inner surface of the nanochannel  105  as the traverse electric field (of the voltage source  212 ) advances the target molecule  305  through the nanochannel  105 . This friction causes the target molecule  305  to stretch for sequencing/reading. Also, the narrowed thickness of the nanochannel  105  helps to confine the bases of the target molecule  305  so that the bases can touch (exposed portion of) the carbon nanotube  103  at the specific bottom location  310  of the nanochannel  105 . The diameter of single-stranded DNA is about 1 nm. In order to physically stretch the single-stranded DNA  305 , the thickness of the nanochannel  105  should be around 2 nm. The gap is about 1 nm between the carbon nanotube  103  and the top cover  106 . So the single strand DNA can be stretched by the physical size of nanochannel  105  when the single strand DNA  305  is pulled through the nanochannel  105  by the electrical field between two electrodes  218  and  219 . 
     This process of reading the bases of the target molecule  305  occurs for each of the bases, and the change in electrical current (i.e., transistor current flowing over carbon nanotube  103 ) when each individual base touches the carbon nanotube  103  is respectively measured (by ammeter  214 ) and recorded for each base (e.g., by the computer  500 ). Accordingly, the change in electrical current (and time duration) is used to compare against (and match) the baseline change in electrical current for each of the respective bases A, G, C, and T (measured at the onset). For example, the change in electrical current for the known bases previously measured may have shown that the baseline current amplitude of base A dropped to amplitude A at 2 volts, the baseline current amplitude of base G dropped to amplitude G at 2 volts, the baseline current amplitude of base C dropped to amplitude C at 2 volts, and the baseline current amplitude of base T dropped to amplitude T (e.g., at 2 volts applied by the voltage source  213 ). These baseline electrical currents for the known bases are compared against the amplitude measured for the individual (unknown) bases of the target molecule  305  (e.g., at 2 volts applied by the voltage source  213 ). 
       FIG. 3B  illustrates an abbreviated version of the system  200  from a top view. Particularly, top electrode  109  and the top sealing layer (i.e., electrically insulating  106 ) of the nanochannel  105  have been lifted off to show the nanochannel  105 .  FIG. 3B  shows the exposed portion  315  of the carbon nanotube  103  through the bottom location  310  of the nanochannel  105 . This exposed portion  315  of the carbon nanotube  103  touches and interacts with the single base  350  (which represents any individual base) of the target molecule  305  at a time. The exposed portion  315  of the carbon nanotube  103  may be 1 nm (nanometer), which is the diameter d of the carbon nanotube  103 . The width of the exposed portion  315  is the width of the nanochannel  105 . The width of nanochannel  105  can be 1 to 2 nm, which can help to linearize the single-stranded DNA. The 1 nm diameter of the carbon nanotube  103  of the exposed portion  315  only allows one base of the target molecule to touch the exposed portion  315  at any time. 
     In  FIG. 3B , the dashed lines show that the carbon nanotube  103  runs underneath the electrically insulating material/film  104  and that the carbon nanotube  103  electrically connects to the electrodes  107  and  108 . Also, the dashed lines show that the carbon nanotube  103  is not electrically connectable for interaction except at the exposed portion  315 . 
       FIGS. 4A and 4B  are a method  400  for base recognition in an integration of a transistor and a nanochannel system  200  according to an embodiment. Reference can be made to  FIGS. 1-3  and  5 . 
     A target molecule (e.g., the target molecule  305 ) is forced down to (touch) the carbon nanotube  103  a single base at a time in a nanochannel  105  at block  405 . The target molecule  305  is forced to the carbon nanotube  103  by applying a gate voltage (by voltage source  213 ) to the top electrode  109  of the transistor, by a narrow thickness of the nanochannel  105 , or both by applying the gate voltage to the top electrode  109  of the transistor and by the narrow thickness of the nanochannel  105 . 
     At block  410 , the nanochannel  105  has been patterned over the carbon nanotube  103  to expose the exposed portion  315  of the carbon nanotube  103  at a bottom wall of the carbon nanotube  103 , and the top electrode  109  of the transistor is positioned over the exposed portion  315  of the carbon nanotube  103  up through nanochannel  105 . 
     At block  415 , the exposed portion  315  of the carbon nanotube  103  is smaller than a separating distance (e.g., distance X) between bases on the target molecule  305 , and the exposed portion  315  of the carbon nanotube  103  is configured (with a size) to only accommodate a single base (e.g., base  350 ) at a time. 
     The target molecule  305  is stretched by the narrow thickness of the nanochannel  105  and by applying a traverse voltage (by the voltage source  211 ) across a length direction (e.g., from the inlet  210  to the outlet  219 ) of the nanochannel  105  between a first electrode (e.g., electrode  218 ) and a second electrode (e.g., electrode  219 ) at opposite ends of the nanochannel  105  in the length direction at block  420 . 
     At block  425 , the target molecule  305  is frictionally restricted by the narrow thickness (and/or width) of the nanochannel  105  causing the target molecule to stretch as the target molecule  305  restrictedly translocates in the length direction while the traverse voltage is applied. 
     A transistor current (when voltage of voltage source  213  is applied) is measured (by the ammeter  214 ) while the single base of the target molecule  305  is forced down to (touch) the exposed portion  315  of the carbon nanotube  103  in the nanochannel  105 , such that the single base affects the transistor current (e.g., causes the electrical current to drop or increase) at block  430 . 
     At block  435 , an identity (such as base A, G, C, and T) of the single base (e.g., base  350 ) is determined according to a change in the transistor current while the single base is forced down to the exposed portion  315  of the carbon nanotube  103  in the nano channel  105 . 
     Further, the method includes that when the target molecule is negatively charged the gate voltage applied by the voltage source  215  is negative. When the target molecule is positively charged the gate voltage the voltage source  215  is positive. Particularly, the gate voltage of the top electrode (and to the body of the substrate  101 ) generates a downward force  207  through the nanochannel  105  above the exposed portion  315 , and the downward force  207  presses the target molecule down to touch (only) the exposed portion  315  of the carbon nanotube (while other bases do not touch the exposed portion  315 ). When the single base is over the carbon nanotube  103 , the downward force  207  presses the single base to touch the exposed portion  315  of the carbon nanotube  103  to sense the identity of the single base. 
     The target molecule  305  is deoxyribonucleic acid or ribonucleic acid. The nanochannel  105  is formed of an insulating material  104  except at the exposed portion  315  of the carbon nanotube  103 . Wherein the nanochannel  105  has a thickness (or depth) that is less than a thickness of the insulating material  104  because the insulating material  104  is deposited on both the carbon nanotube  103  and the insulating material  102  layer underneath carbon nanotube. 
     The thickness (depth) of the nanochannel  105  is (substantially) between 1 to 2 nanometers when the target molecule  305  is a singe strand polynucleotide in order for the target molecule  305  to be stretched as it bumps/slides against the walls of the nanochannel  105 . The thickness of the nanochannel  105  is (substantially) between 2 to 4 nanometers when the target molecule  305  is a double strand polynucleotide in order for the target molecule to be stretched. 
     Also, the thickness of the nanochannel  105  is determined by the diameter of the target molecule to be sequenced in order for the target molecule to be frictionally restricted when translocating through the nanochannel  105 . 
     The traverse voltage (applied by the voltage source  211 ) is substantially between 0 to 5 volts. The gate voltage (applied by the voltage source  215 ) is substantially between −10 to 0 volts when the target molecule  305  is negatively charged. The gate voltage (applied by the voltage source  215 ) is substantially between 0 to +10 volts when the target molecule is positively charged. 
     A coating molecule is applied to the carbon nanotube  103  (e.g., at least at the exposed portion  315 ) to increase sensitivity of the transistor to accept charges from the single base  350  being pressed to the exposed portion  315 . The coating molecule increases a selectivity of bases of the target molecules which may cause certain bases to attach to the exposed portion  315 . As one example, the coating molecule can be 11-mercaptoundecanol, which can be switched based on the polarity by the external voltage (of the voltage source  213 ). The coating molecule can help to trap and sense the single base when the voltage is positive. 
     The transistor comprises a source electrode (e.g., electrode  107 ) and a drain electrode (e.g., electrode  108 ) connected by the carbon nanotube  103 , and wherein the transistor current flows from the source electrode to the drain electrode through the carbon nanotube  103 . 
       FIG. 5  illustrates an example of a computer  500  (e.g., as part of the computer test setup for testing and analysis) which may implement, control, and/or regulate the respective voltages of the voltage sources, respective measurements of the ammeters, and display screens for displaying various current amplitude (amplitude versus dwell (duration) time graphs for the applied voltage) as discussed herein. The computer  500  also stores the respective electrical current amplitudes of each base tested and measured to be compared against the baselines current amplitudes of different bases. 
     Various methods, procedures, modules, flow diagrams, tools, applications, circuits, elements, and techniques discussed herein may also incorporate and/or utilize the capabilities of the computer  500 . Moreover, capabilities of the computer  500  may be utilized to implement features of exemplary embodiments discussed herein. One or more of the capabilities of the computer  500  may be utilized to implement, to connect to, and/or to support any element discussed herein (as understood by one skilled in the art) in  FIGS. 1-4 . For example, the computer  500  which may be any type of computing device and/or test equipment (including ammeters, voltage sources, current meters, connectors, etc.). Input/output device  570  (having proper software and hardware) of computer  500  may include and/or be coupled to the nanodevices and structures discussed herein via cables, plugs, wires, electrodes, patch clamps, etc. Also, the communication interface of the input/output devices  570  comprises hardware and software for communicating with, operatively connecting to, reading, and/or controlling voltage sources, ammeters, and current traces (e.g., magnitude and time duration of current), etc., as discussed herein. The user interfaces of the input/output device  570  may include, e.g., a track ball, mouse, pointing device, keyboard, touch screen, etc., for interacting with the computer  500 , such as inputting information, making selections, independently controlling different voltages sources, and/or displaying, viewing and recording current traces for each base, molecule, biomolecules, etc. 
     Generally, in terms of hardware architecture, the computer  500  may include one or more processors  510 , computer readable storage memory  520 , and one or more input and/or output (I/O) devices  570  that are communicatively coupled via a local interface (not shown). The local interface can be, for example but not limited to, one or more buses or other wired or wireless connections, as is known in the art. The local interface may have additional elements, such as controllers, buffers (caches), drivers, repeaters, and receivers, to enable communications. Further, the local interface may include address, control, and/or data connections to enable appropriate communications among the aforementioned components. 
     The processor  510  is a hardware device for executing software that can be stored in the memory  520 . The processor  510  can be virtually any custom made or commercially available processor, a central processing unit (CPU), a data signal processor (DSP), or an auxiliary processor among several processors associated with the computer  500 , and the processor  510  may be a semiconductor based microprocessor (in the form of a microchip) or a macroprocessor. 
     The computer readable memory  520  can include any one or combination of volatile memory elements (e.g., random access memory (RAM), such as dynamic random access memory (DRAM), static random access memory (SRAM), etc.) and nonvolatile memory elements (e.g., ROM, erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), programmable read only memory (PROM), tape, compact disc read only memory (CD-ROM), disk, diskette, cartridge, cassette or the like, etc.). Moreover, the memory  520  may incorporate electronic, magnetic, optical, and/or other types of storage media. Note that the memory  520  can have a distributed architecture, where various components are situated remote from one another, but can be accessed by the processor  510 . 
     The software in the computer readable memory  520  may include one or more separate programs, each of which comprises an ordered listing of executable instructions for implementing logical functions. The software in the memory  520  includes a suitable operating system (O/S)  550 , compiler  540 , source code  530 , and one or more applications  560  of the exemplary embodiments. As illustrated, the application  560  comprises numerous functional components for implementing the features, processes, methods, functions, and operations of the exemplary embodiments. 
     The operating system  550  may control the execution of other computer programs, and provides scheduling, input-output control, file and data management, memory management, and communication control and related services. 
     The application  560  may be a source program, executable program (object code), script, or any other entity comprising a set of instructions to be performed. When a source program, then the program is usually translated via a compiler (such as the compiler  540 ), assembler, interpreter, or the like, which may or may not be included within the memory  520 , so as to operate properly in connection with the O/S  550 . Furthermore, the application  560  can be written as (a) an object oriented programming language, which has classes of data and methods, or (b) a procedure programming language, which has routines, subroutines, and/or functions. 
     The I/O devices  570  may include input devices (or peripherals) such as, for example but not limited to, a mouse, keyboard, scanner, microphone, camera, etc. Furthermore, the I/O devices  570  may also include output devices (or peripherals), for example but not limited to, a printer, display, etc. Finally, the I/O devices  570  may further include devices that communicate both inputs and outputs, for instance but not limited to, a NIC or modulator/demodulator (for accessing remote devices, other files, devices, systems, or a network), a radio frequency (RF) or other transceiver, a telephonic interface, a bridge, a router, etc. The I/O devices  570  also include components for communicating over various networks, such as the Internet or an intranet. The I/O devices  570  may be connected to and/or communicate with the processor  510  utilizing Bluetooth connections and cables (via, e.g., Universal Serial Bus (USB) ports, serial ports, parallel ports, FireWire, HDMI (High-Definition Multimedia Interface), etc.). 
     In exemplary embodiments, where the application  560  is implemented in hardware, the application  560  can be implemented with any one or a combination of the following technologies, which are each well known in the art: a discrete logic circuit(s) having logic gates for implementing logic functions upon data signals, an application specific integrated circuit (ASIC) having appropriate combinational logic gates, a programmable gate array(s) (PGA), a field programmable gate array (FPGA), etc. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one more other features, integers, steps, operations, element components, and/or groups thereof. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated 
     The flow diagrams depicted herein are just one example. There may be many variations to this diagram or the steps (or operations) described therein without departing from the spirit of the invention. For instance, the steps may be performed in a differing order or steps may be added, deleted or modified. All of these variations are considered a part of the claimed invention. 
     While the preferred embodiment to the invention had been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.