Abstract:
A technique for embedding a nanotube in a nanopore is provided. A membrane separates a reservoir into a first reservoir part and a second reservoir part, and the nanopore is formed through the membrane for connecting the first and second reservoir parts. An ionic fluid fills the nanopore, the first reservoir part, and the second reservoir part. A first electrode is dipped in the first reservoir part, and a second electrode is dipped in the second reservoir part. Driving the nanotube into the nanopore causes an inner surface of the nanopore to form a covalent bond to an outer surface of the nanotube via an organic coating so that the inner surface of the nanotube will be the new nanopore with a super smooth surface for studying bio-molecules while they translocate through the nanotube.

Description:
BACKGROUND 
     Exemplary embodiments relate to nanodevices, and more specifically, to providing a smooth inner surface for a nanopore by fixing a nanotube inside the nanopore. 
     Recently, there has been growing interest in applying nanopores as sensors for rapid analysis of biomolecules (e.g., polymers) such as deoxyribonucleic acid (DNA), ribonucleic acid (RNA), protein, etc. 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. 
     Nanopore sequencing is a technique for determining the order in which nucleotides occur on a strand of DNA. A nanopore is simply a small hole of the order of several nanometers in internal diameter. The theory behind nanopore sequencing has to do with what occurs when the nanopore is immersed in a conducting fluid and an electric potential (voltage) is applied across it: 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 put around the nanopore so that DNA bases can be differentiated while the DNA passes through the nanopore. 
     BRIEF SUMMARY 
     According to an exemplary embodiment, an apparatus for embedding a nanotube in a nanopore is provided. The apparatus includes a membrane separating a reservoir into a first reservoir part and a second reservoir part, and the nanopore is formed through the membrane for connecting the first and second reservoir parts. An ionic fluid fills the nanopore, the first reservoir part, and the second reservoir part. A first electrode is dipped in the first reservoir part, and a second electrode is dipped in the second reservoir part. A voltage bias is applied to the first and second electrodes to drive the nanotube into the nanopore so that the inner surface of the nanopore forms a covalent bond to an outer surface of the nanotube via an organic coating 
     According to an exemplary embodiment, a system for embedding a nanotube in a nanopore is provided. The system includes an apparatus including a membrane separating a reservoir into a first reservoir part and a second reservoir part, where the nanopore is formed through the membrane for connecting the first and second reservoir parts. An ionic fluid fills the nanopore, the first reservoir part, and the second reservoir part. A first electrode is dipped in the first reservoir part, and a second electrode is dipped in the second reservoir part. Also, the system includes a voltage source configured to drive the nanotube into the nanopore in order to cause an inner surface of the nanopore to form a covalent bond to an outer surface of the nanotube via an organic coating. 
     According to an exemplary embodiment, an apparatus is provided for embedding a nanotube in a nanopore. The apparatus includes a membrane separating a reservoir into a first reservoir part and a second reservoir part, and the nanopore is formed through the membrane for connecting the first and second reservoir parts. An ionic fluid fills the nanopore, the first reservoir part, and the second reservoir part. A first electrode is dipped in the first reservoir part, and a second electrode is dipped in the second reservoir part. The nanotube is driven into the nanopore by a difference in fluidic pressure on two sides of the membrane, which causes an inner surface of the nanopore to form a covalent bond to an outer surface of the nanotube via an organic coating. 
     Additional features are realized through the techniques of the present disclosure. Other systems, methods, apparatus, and/or computer program products according to other embodiments are described in detail herein and are considered a part of the claimed invention. For a better understanding of exemplary embodiments and 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 foregoing and other features of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  depicts a cross-sectional schematic of a nanodevice with a nanopore embedded with a carbon nanotube according to an exemplary embodiment. 
         FIG. 2A  illustrates an approach to embed a carbon nanotube inside a nanopore of a nanodevice according to an exemplary embodiment. 
         FIG. 2B  illustrates the carbon nanotube attached/bonded to the inside of the nanopore according to an exemplary embodiment. 
         FIG. 2C  illustrates the carbon nanotube attached to the inside of the nanopore after processing according to an exemplary embodiment. 
         FIG. 3A  illustrates another approach to embed a carbon nanotube inside a nanopore of a nanodevice according to an exemplary embodiment. 
         FIG. 3B  illustrates the carbon nanotube attached/bonded to the inside of the nanopore according to an exemplary embodiment. 
         FIG. 3C  illustrates the carbon nanotube attached to the inside of the nanopore after processing according to an exemplary embodiment. 
         FIG. 4A  illustrates an additional approach to embed a carbon nanotube inside a nanopore of a nanodevice according to an exemplary embodiment. 
         FIG. 4B  illustrates the carbon nanotube attached/bonded to the inside of the nanopore according to an exemplary embodiment. 
         FIG. 4C  illustrates the carbon nanotube attached to the inside of the nanopore after processing according to an exemplary embodiment. 
         FIG. 5  is a method for embedding a nanotube inside a nanopore according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An issue in DNA sequencing is to control the translocation of the DNA through the nanopore. The surface roughness of the nanopore and the dangling bonds on the surface of the nanopore may present problems for DNA sequencing. After drilling a solid-state nanopore using an electron beam, the pore surface may exhibit nanometer scale corrugations (e.g., folds, wrinkles, groves, etc.). Similar to the scaling behavior of a self-affine rough surface, the smaller a nanopore is the rougher the inner pore surface is. Additionally, nanopores drilled using the same procedure may have different surface roughness, causing each pore to be unique. Thus, experiments that are performed using nanopores with rough surfaces and/or dangling bonds may likely (or may possibly) show inconsistent results because of the unpredictable interactions between DNA and the inner surface of the nanopore. For example, simulations show that the effective electric driving forces on DNA are different if the surface roughness of the same-sized nanopores is different. 
     Exemplary embodiments are configured to attach carbon nanotubes at the inner surface of the nanopore and leverage the smoothness of the inner surface of carbon nanotubes. This approach can eliminate the physical surface roughness as well as the dangling bonds at the inner surface of the nanopore, which are the sources of unpredictable interactions between DNA and the inner surface of the nanopore. Additionally, the chemical inertness of carbon nanotubes will be a potential benefit, such as by protecting the metal electrodes employed at the inner surface of the nanopore. 
     Now turning to the figures,  FIG. 1  depicts a cross-sectional schematic of a nanodevice  100  with a nanopore embedded with a carbon nanotube according to an exemplary embodiment. The nanodevice  100  illustrates a DNA translocation setup. A membrane  150  is made of one or more insulating films  101  with a nanopore  103  formed through the insulating film  101 . A carbon nanotube  102  is embedded at the inner surface of the nanopore  103 . The insulating film  101  of the membrane  150  partitions a reservoir  104  into two reservoir parts, which are reservoir part  105  and reservoir part  106 . The reservoir  104  (including reservoir parts  105  and  106 ) and the nanopore  103  are then filled with ionic buffer/fluid  107  (e.g., such as a conductive fluid). 
     A polymer  108  such as a DNA molecule(s) is loaded into the nanopore  103  by an electrical voltage bias of the voltage source  109 , which is applied across the nanopore  103  via two electrochemical electrodes  110  and  111 . The electrodes  110  and  111  are respectively dipped in the ionic buffer  107  of the reservoir part  105  and the reservoir part  106  in the reservoir  104 . 
     There are various state of the art techniques for sensing DNA bases and controlling the motion of the DNA, and the roughness and the dangling bonds in a regular (state of the art) nanopore may pose a potential problem. However, the smooth inner surface of the nanotube  102  will provide a (very) smooth surface with no dangling bonds for characterization (i.e., nanopore sequencing of the DNA) and movement of the polymer  108 . 
     There may be many techniques with many different materials that can be utilized to make the nanodevice  100  shown in  FIG. 1 . According to an exemplary embodiment,  FIGS. 2A ,  2 B, and  2 C illustrate one approach to embed a carbon nanotube inside a nanopore of a nanodevice  200  such as a chip.  FIGS. 2A ,  2 B, and  2 C depict a cross-sectional schematic of the nanodevice  200 . In  FIG. 2A , a membrane  250  includes a substrate  201  (e.g., such as silicon), between membrane parts  202  and  203 . The membrane parts  202  and  203  may be made of a material (such as Si 3 N 4  (silicon nitride)) with a high etching selectivity with respect to the substrate  201 . The membrane part  202  may also contain other material layers, such as metal layers, etc., for any desired application. A window  255  is opened into the membrane part  203  using, e.g., reactive ion etching, and the substrate  201  will be etched through to the membrane part  202 ; etching through the window  255  of the membrane part  203  as well as through the substrate  201  will form a free-standing membrane part  260  of the membrane part  202 . In the case of a silicon substrate for the substrate  201 , the etchant could be KOH (potassium hydroxide) or TMAH (tetramethylammonium hydroxide) at 80° C. A nanopore  207  is made/formed through the free-standing membrane part  260  of the membrane part  202 . The membrane  250  (including the free-standing membrane part  260 ) partitions a reservoir  208  into reservoir part  209  and reservoir part  210 . The reservoir  208  (including reservoir parts  209  and  210 ) and the nanopore  207  formed through membrane part  202  are (then) filled with ionic buffer/fluid  211 . The nanopore  207  is a small aperture formed in, e.g., the free-standing membrane part  260  of the membrane part  202 . 
     As shown in  FIG. 2A , the outer surface of a carbon nanotube  204  can be coated with an organic coating  205 . The organic coating  205  is configured to be covalently bonded to the inner surface of the nanopore  207 . The organic coating  205  and/or the carbon nanotube  204  is charged (by tuning the pH of the ionic buffer  211 ), such that the carbon nanotube  204  can be transported/driven into the nanopore  207  by the voltage source  109  applying a voltage bias to electrodes  110  and  111 , and then the carbon nanotube  204  can be covalently bonded to the inner surface of the nanopore  207 , as shown in  FIG. 2B . Alternatively and/or additionally, a fluidic pressure adjustment device  280  can be communicatively connected to the reservoir part  210  via a port  282 , and a fluidic pressure adjustment device  285  can be communicatively connected to the reservoir part  209  via another port  284  in one implementation. To drive the carbon nanotube  204  (which can be charged or uncharged) into the nanopore  207 , the fluidic pressure adjustment device  280  is configured to apply a positive fluidic pressure to the reservoir part  210  and/or the fluidic pressure adjustment device  285  is configured to apply a negative fluidic pressure to the reservoir part  209 . The carbon nanotube  204  is driven into the nanopore  207  by the difference in fluidic pressure on both sides of the membrane  250  caused by fluidic pressure adjustment device  280  and  285 . Also, the carbon nanotube  204  can be driven into the nanopore  207  by the positive fluidic pressure of the fluidic pressure adjustment device  280  alone or by the negative fluidic pressure of the fluidic pressure adjustment device  285  alone. The fluidic pressure adjustment devices  280  and  285  may be pumps or syringes respectively linked via ports  282  and  284  to the reservoir parts  210  and  209  to apply the desired pressure. 
     The ionic buffer  107  and  211  in the reservoirs  104  and  208  can be any salt dissolved in any solvent (water or organic solvent) with any pH depending on the application. One example of the ionic buffer  107  and  211  includes a KCl (potassium chloride) solution in water with a pH range from 6-9 for DNA translocation. Accordingly, the electrodes  110  and  111  can be any electrodes for electrochemical reactions that match the salt and solvent. For example, Ag/AgCl electrodes can be a good match for the KCl solution in water. 
     As discussed further below, the organic coating  205  is a material having chemical properties that cause the organic coating  205  (applied to the carbon nanotube  204 ) to covalently bond to the inner surface material of the nanopore  207 . As a result of the covalent bond, the carbon nanotube  204  is securely attached to the nanopore  207 . 
     Once the carbon nanotube  204  is attached to the inner surface of nanopore  207 , both sides (e.g., top and bottom) of the membrane  250  (including the attached nanotube  204 ) can be processed/etched with O 2  (oxygen) plasma to tailor (e.g., remove) the parts of the carbon nanotube  204  that are extending outside of the nanopore  207 , as shown in  FIG. 2C . In  FIG. 2C , the height of the carbon nanotube  204  (e.g., the top and bottom) is aligned with the height of the membrane part  202  after the O 2  plasma processing. The polymer  108  (shown in  FIG. 1 ) may be driven into the carbon nanotube  204  attached to the nanopore  207  for sequencing by a nanopore sequencer (not shown), and the sequencing occurs in the nanopore  207  (formed by the carbon nanotube  204 ) as understood by one skilled in the art. 
     Oxygen plasma etching is a form of plasma processing used to fabricate integrated circuits. As understood by one skilled in the art, it involves a high-speed stream of glow discharge (plasma) of an appropriate gas mixture being shot (in pulses) at a sample, such as at the membrane  250 . Although plasma etching is described, it is contemplated that other types of etching may be utilized as understood by one skilled in the art. 
       FIGS. 3A ,  3 B, and  3 C illustrate another approach to embed a carbon nanotube inside a nanopore according to an exemplary embodiment.  FIGS. 3A ,  3 B, and  3 C depict a cross-sectional schematic of the nanodevice  300 . 
     In  FIGS. 3A ,  3 B, and  3 C, the inner surface of the nanopore  207  is coated with the organic coating  215 , which can bond to the carbon nanotube  204 . The description for  FIGS. 3A ,  3 B, and  3 C are the same as for  FIGS. 2A ,  2 B, and  2 C, except that the carbon nanotube  204  is initially uncoated because the coating is applied to the inner surface of the nanopore  207 , instead of on the carbon nanotube  204  (itself). The organic coating  215  in  FIGS. 3A ,  3 B, and  3 C may be the same material as the organic coating  205  in  FIGS. 2A ,  2 B, and  2 C in one implementation, and may be different materials in another implementation. 
     In  FIG. 3A , the membrane  250  includes the substrate  201 , between membrane parts  202  and  203 , and window  255  is opened/etched into the membrane part  203  through the substrate  201  to the membrane part  202  to form the free-standing membrane part  260  of the membrane part  202 , as discussed above. The nanopore  207  is made/formed through the free-standing membrane part  260 . The membrane  250  (including the free-standing membrane part  260 ) partitions a reservoir  208  into reservoir part  209  and reservoir part  210 . The reservoir  208  (including reservoir parts  209  and  210 ) and the nanopore  207  formed through membrane part  202  are then filled with ionic buffer/fluid  211  as discussed above. 
     Unlike  FIG. 2A , the outer surface of the carbon nanotube  204  is not coated with the organic coating  205  in  FIG. 3A . Instead, the inner surface of the nanopore  207  is coated with the organic coating  215 . The organic coating  215  is configured to covalently bond to the outer surface of the uncoated carbon nanotube  204 . If the carbon nanotube  204  is charged (by tuning the pH of the ionic buffer  211  filling the reservoir  208 ), the carbon nanotube  204  can be transported into the nanopore  207  by a voltage bias applied to electrodes  110  and  110  via the voltage source  109 . Also, the carbon nanotube  204  can be driven into the nanopore  207  by the difference in fluidic pressure on both sides of the membrane  250  applied by positive and negative pressures of the fluidic pressure adjustment devices  280  and  285 . Once the carbon nanotube  204  is driven into the nanopore  207 , the carbon nanotube  204  can be covalently bonded to the inner surface of the nanopore  207  via the organic coating  215 , as shown in  FIG. 3B . The organic coating  215  is a material having chemical properties that cause the organic coating  215  (applied to the nanopore  207 ) to covalently bond to the outer surface material of the uncoated carbon nanotube  204 . As a result of this covalent bond, the carbon nanotube  204  is securely attached to the nanopore  207 . 
     Once the carbon nanotube  204  is attached to the inner surface of nanopore  207 , both sides of the membrane  250  (including the attached nanotube  204 ) can be processed with O 2  plasma to tailor (e.g., remove) the extending parts of the carbon nanotube  204  that extend outside of the nanopore  207 , as shown in  FIG. 3C . In  FIG. 3C , the height of the carbon nanotube  204  is aligned to the height of the membrane part  202  after O 2  plasma processing. The polymer  108  (shown in  FIG. 1 ) may be driven into the carbon nanotube  204  attached to the nanopore  207  for sequencing as understood by one skilled in the art. 
       FIGS. 4A ,  4 B, and  4 C illustrate an additional approach to embed a carbon nanotube inside a nanopore according to an exemplary embodiment.  FIGS. 4A ,  4 B, and  4 C depict a cross-sectional schematic of the nanodevice  400  which illustrates a combination of the approaches discussed in  FIGS. 2A ,  2 B,  2 C,  3 A,  3 B, and  3 C. 
     In  FIGS. 4A ,  4 B, and  4 C, the inner surface of the nanopore  207  is coated with an organic coating  206 , while the outer surface of the carbon nanotube  204  is coated with the organic coating  205 . The organic coating  205  is chemically configured to covalently bond to the organic coating  206 . Additionally, the organic coating  205  is chemically configured to bond to the carbon nanotube  204 , and the organic coating  206  is chemically configured to bond to the inner surface of the nanopore  207 . The organic coating  205  is different from the organic coating  206  in one implementation. In another implementation, the organic coating  205  can be the same material as the organic coating  206 . 
     When the organic coating  205  and/or carbon nanotube  204  is charged (by tuning the pH of the ionic buffer), the carbon nanotube  204  can be transported into the nanopore  207  by a voltage bias applied to electrodes  110  and  110  via the voltage source  109 . Also, the carbon nanotube  204  can be driven into the nanopore  207  by the difference in fluidic pressure on both sides of the membrane  250  applied by the positive and negative pressures of the fluidic pressure adjustment devices  280  and  285 . Once the carbon nanotube  204  coated in the organic coating  205  is driven into the nanopore  207  coated in the organic coating  206 , the carbon nanotube  204  can be covalently bonded to the inner surface of the nanopore  207  via the organic coatings  205   206 , as shown in  FIG. 4B . The organic coating  205  is a material having chemical properties that cause the organic coating  205  (applied to the carbon nanotube  204 ) to covalently bond to the outer surface material of the carbon nanotube  204  and to the organic coating  206 . Similarly, the organic coating  206  is a material having chemical properties that cause the organic coating  206  (applied to the nanopore  207 ) to covalently bond to the outer surface material of the carbon nanotube  204  and to the organic coating  205 . As a result of the covalent bonding, the carbon nanotube  204  is securely attached to the nanopore  207 . 
     As mentioned above, once the carbon nanotube  204  is attached to the inner surface of nanopore  207 , both sides of the membrane  250  (including the attached nanotube  204 ) can be processed with O 2  plasma to tailor (e.g., remove) the extending parts of the carbon nanotube  204  that extend outside of the nanopore  207 , as shown in  FIG. 4C . In  FIG. 4C , the height of the carbon nanotube  204  is aligned to the height of the membrane part  202  after O 2  plasma processing. In one implementation, the height of the carbon nanotube  204  may be slightly less than, more than, or about the same as the height of the membrane part  202  (forming the nanopore  207 ) based on the desired precision of the O 2  plasma processing. The polymer  108  (shown in  FIG. 1 ) may be driven into the carbon nanotube  204  attached to the nanopore  207  for sequencing as understood by one skilled in the art. 
     Although exemplary embodiments described above may be directed to carbon nanotubes, it should be appreciated that the disclosure is not restricted to nanopores with carbon nanotubes. Rather, exemplary embodiments may be applicable for attaching other types of nanotubes to the inside surface of nanopores utilizing the techniques as discussed herein. Additionally, exemplary embodiments are not limited to embedding nanotubes into nanopores, and nanotubes may be embedded into other structures such as vias, nanochannels, etc., as understood by one skilled in the art. 
       FIG. 5  illustrates a method  500  for embedding a nanotube in a nanopore in accordance with an exemplary embodiment. Reference can be made to  FIGS. 1 ,  2 A,  2 B,  2 C,  3 A,  3 B,  3 C,  4 A,  4 B, and  4 C. 
     A reservoir (e.g., reservoir  104 ,  208 ) is configured to include a membrane (e.g., membrane  150 ,  250 ) separating the reservoir into a first reservoir part (e.g., reservoir part  105 ,  210 ) and a second reservoir part (e.g., reservoir part  106 ,  209 ) in which the nanopore (e.g., nanopore  103 ,  207 ) is formed through the membrane for connecting the first and second reservoir parts at block  505 . 
     The nanopore, the first reservoir part, and the second reservoir part are filled with an ionic fluid (e.g., ionic fluid  107 ,  211 ) at block  510 . A first electrode (e.g., electrode  110 ) is dipped in the first reservoir part at block  515 , and a second electrode (e.g., electrode  111 ) is dipped in the second reservoir part at block  520 . 
     At block  525 , the nanotube is driven into the nanopore to cause an inner surface of the nanopore (e.g., nanopore  103 ,  207 ) to form a covalent bond to an outer surface of the nanotube (e.g., nanotube  102 ,  204 ) via an organic coating (e.g., organic coating  205 ,  206 ,  215 ), in response to a voltage bias being applied (e.g., by the voltage source  109 ) to the first and second electrodes (e.g., electrodes  110  and  111 ). Also, the carbon nanotube  204  can be driven into the nanopore  207  by the difference in fluidic pressure on both sides of the membrane  250  applied by the positive and negative pressures of the fluidic pressure adjustment devices  280  and  285 . 
     The inner surface of the nanopore  207  may be coated with the organic coating (e.g., organic coating  215  in  FIG. 3A  or organic coating  206  in  FIG. 4A ) to form the covalent bond to the outer surface of the nanotube  204 . Also, the outer surface of the nanotube  204  may be coated with the organic coating  205  to form the covalent bond to the inner surface of the nanopore  207 . 
     In one case, both the inner surface of the nanopore  207  and the outer surface of the nanotube  204  are coated with the organic coating (e.g., the organic coatings  205  and  206  may be the same material in  FIGS. 4A ,  4 B, and  4 C), such that the organic coating on the inner surface of the nanopore  207  and the organic coating on the outer surface of the nanotube  204  cause the covalent bond in response to the voltage source  109  driving the nanotube  204  into the nanopore  207 . 
     In another case, the inner surface of the nanopore  207  is coated with the organic coating and the outer surface of the nanotube is coated with another organic coating (e.g., the organic coatings  205  and  206  may be different materials in  FIGS. 4A ,  4 B, and  4 C), such that the organic coating on the inner surface of the nanopore and the other organic coating on the outer surface of the nanotube cause the covalent bond in response to the voltage source  109  driving the nanotube into the nanopore. 
     The covalent bond via the organic coating causes the nanotube  102 ,  204  to be physically attached to the nanopore  103 ,  207  formed in the membrane  150 ,  250 , and both sides (e.g., top and bottom) of the membrane  150 ,  250  are processed such that a height of the nanotube corresponds to a height of a layer (e.g., membrane part  202 ) of the membrane  250  as shown in  FIGS. 2C ,  3 C, and  4 C. 
     For explanatory purposes, various examples of the organic coatings  205 ,  206 , and  215  are discussed below. It is understood that the chemical molecules of the organic coatings  205 ,  206 , and  215  discussed below are not meant to be limited. 
     The organic coating  205  can be prepared by reaction of aryldiazonium salts with the carbon nanotube  204 . In this reaction, the diazonium salts are reduced by electron transfer from the carbon nanotube  204  to diazonium salts and results in the expulsion of one molecule of nitrogen and formation of a carbon-carbon bond between aryl compound and the carbon nanotube  204 . This is a widely used reaction for functionalization of carbon nanotubes with a variety of aryl compounds mainly because of the simplicity of the reaction and the wide range of arydiazonium salts available through their corresponding arylamines. The reaction of aryldiazonium salts with the carbon nanotube  204  takes place either in aqueous solution or an organic solvent like dichloroethane, chloroform, toluene, dimethylformamide, etc. The reaction of aryldiazonium salts with the carbon nanotube  204  is very fast (e.g., completed within a few minutes) and takes place at room temperature. The preferred, but not required, diazonium salts are those with an additional functionality which can form strong bonds with metal oxides or nitrides inside the nanopore  207 . The additional functionality (to form strong bonds with metal oxides or nitrides inside the nanopore  207 ) can be chosen from carboxylic acids (—CO 2 H), hydroxamic acids (—CONHOH), or phosphonic acids (—PO 3 H 2 ). 
     In  FIGS. 3A ,  3 B, and  3 C, the organic coating  215  is a bifunctional compound/molecule in which one functionality is a diazonium salt and the other functionality can be chosen from hydroxamic acid or phosphonic acid. When the nanopore  207  with inside walls of metal oxide or metal nitride is immersed in a solution of this bifunctional compound/molecule, the inner surface of the nanopore  207  is coated with the self-assembled monolayer of this bifunctional compound/molecule through hydroxamic acid or phosphonic acid functionality and exposes the diazonium functional group; the diazonium functional group can react with the uncoated carbon nanotube  204  (as shown in  FIGS. 3B and 3C ) to form a covalent bond, therefore immobilizing the carbon nanotube  204  inside the nanopore  207 . 
     In  FIGS. 4A ,  4 B, and  4 C, both the carbon nanotube  204  and nanopore  207  are coated with organic monolayers (i.e., organic coatings  205  and  206  respectively). In the case of the carbon nanotube  204 , the organic coating  205  is achieved by reaction of the carbon nanotube  204  with bifunctional diazonium salts which have either alcohol or amine groups, and the organic coating  206  inside the nanopore  207  is a bifunctional molecule having a functional group which forms a bond inside the nanopore  207  wall (e.g., hydroxamic acid or phosphonic acid) and the second exposed functionality which forms a covalent bond through condensation with exposed functionality of the carbon nanotube  204  (e.g. carboxylic acid). For example, the nanopore  207  can be coated with 4-carboxybenzylphosphonic acid by immersion of the nanopore  207  in a dilute (1-5 mmolar) solution of the latter in water or alcohol. After rinsing with the same solvent, the inside of the nanopore  207  (the wall or portion of the nanopore wall must be of metal oxide or nitride) is coated with a self assembled monolayer of 4-carboxybenzylphosphonic acid in a way that phosphonic acid forms covalent bonds with metal oxide or nitride and exposes the carboxylic acid functionality. In the second step, the functionalized carbon nanotube  204  having an alcohol or amine functionality is pulled inside the nanopore  207  and with the aid of a dehydrating agent (which must be present in the salt solution) the two functionalities of carboxylic acid and alcohol (or amine) undergo dehydration to form carboxylic ester (or carboxamide) resulting in immobilization of carbon nanotube  204 . An example of the dehydrating agent (which is also water soluble and can be used in this environment) is N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride. In  FIGS. 4B and 4C , after the organic coating  205  and  206  react with each other to form an ester or amide, the joined coatings are designated as  270 . 
     For the reaction (corresponding to  FIGS. 2A ,  2 B, and  2 C) when the nanopore  207  is uncoated and the carbon nanotube  204  is coated (with organic coating  205  as discussed above), the organic coating  205  is achieved by the reaction of a bifunctional aryldiazonium salt. For example, 4-aminobenzylphosphonic acid is treated with nitrosonium tetrafluoroborate to form corresponding diazonium salt. A solution of this diazonium salt is added to an aqueous dispersion of carbon nanotubes containing small (0.1-1%) amount of surfactant (e.g., sodium dodecylsulfate or sodium cholate). After stirring at room temperature for 30 minutes, the carbon nanotube  204  is functionalized with benzylphsophonic acid. An aqueous solution of the functionalized carbon nanotube  204  obtained above containing 0.1% anionic surfactant is pulled into nanopore  207  (as shown in  FIGS. 2A ,  2 B,  2 C) where the phosphonic acid functionality reacts with the surface of metal oxide (or nitride) inside the nanopore  207  to form a covalent bond. 
     For the reaction (corresponding to  FIGS. 3A ,  3 B, and  3 C) when the nanopore  207  is coated (with organic coating  215 ) and the carbon nanotube  204  is uncoated, the inside of the nanopore  207  is coated (organic coating  215 ) with bifunctional arylamine, e.g., 4-aminophenylhydroxamic acid by immersion of the nanopore  207  in a dilute (1-5 mmolar) solution of the amine in ethanol. After sometime (e.g., 1-24 hours, preferably 1-2 hours) the substrate (forming the nanopore  207 ) is removed and rinsed with ethanol. This step results in self assembly of 4-aminophenylhydroxamic acid on the inside wall of nanopore  207  by formation of covalent bonds through hydroxamic acid functionality with metal oxide (or nitride) of the nanopore  207  and exposing arylamine functionality. Next, the coated nanopore  207  is treated with a dilute solution of nitrosonium ion (e.g., a solution of nitrosonium tetrafluoroborate or dilute solution of sodium nitrite in dilute hydrochloric acid) resulting in transformation of the amine group to diazonium salt. In the last step, the uncoated carbon nanotube  204  in salt solution is pulled into the coated nanopore  207  which will react with diazonium functionality of the self assembled monolayer and form carbon-carbon bond to immobilize the carbon nanotube  204  inside the nanopore  207 . 
     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 ore 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 exemplary embodiments of the invention have 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.