Nanopore electrode, nanopore membrane, methods of preparation and surface modification, and use thereof
Provided are fabrication, characterization and application of a nanodisk electrode, a nanopore electrode and a nanopore membrane. These three nanostructures share common fabrication steps. In one embodiment, the fabrication of a disk electrode involves sealing a sharpened internal signal transduction element (“ISTE”) into a substrate, followed by polishing of the substrate until a nanometer-sized disk of the ISTE is exposed. The fabrication of a nanopore electrode is accomplished by etching the nanodisk electrode to create a pore in the substrate, with the remaining ISTE comprising the pore base. Complete removal of the ISTE yields a nanopore membrane, in which a conical shaped pore is embedded in a thin membrane of the substrate.
1. A method of preparing a conical nanopore membrane, comprising:
sealing a conical tip of an internal signal transduction element in a substrate;
polishing the substrate in order to expose the conical tip of the internal signal transduction element;
monitoring an extent of the polishing using a tester;
stopping the polishing when the tester signifies that a disk of a desired radius is exposed, thus producing a nanodisk electrode; and
removing the internal signal transduction element from the substrate, after the nanodisk electrode is created, thus producing a nanopore membrane having a thickness, with a first, exterior, side and a second, interior, side, with the first side being opposite the second side, and having a nanopore extending through the membrane, thus forming a channel connecting the first side to the second side of the membrane, wherein the nanopore has a first opening that opens to the first side of the membrane, a second opening that opens to the second side of the membrane, and a depth.
2. The method according to claim 1 , further comprising modifying the surface properties of at least one of; the first side of the membrane; the second side of the membrane; and the channel connecting the first side to the second side of the membrane to change at least one of an electrical charge density, hydrophobicity and hydrophilicity property thereof.
3. The method according to claim 1 , further comprising etching the exposed disk of the internal signal transduction element before removing the internal signal transduction element from the substrate.
4. The method according to claim 1 , wherein the internal signal transduction element is selected from the group consisting of platinum, tungsten and gold.
5. The method according to claim 1 , wherein the substrate is glass or quartz.
6. The method according to claim 5 , wherein the substrate is a glass or quartz capillary that is sealed to produce a bottom wall.
7. The method according to claim 6 , wherein the internal signal transduction element is sealed in the bottom wall of the capillary.
8. The method according to claim 1 , further comprising heating the substrate to soften the substrate in order to seal the conical tip of the internal signal transduction element in the substrate.
9. The method according to claim 1 , wherein the monitoring step comprises:
measuring intermittently an electrical resistance between an extended part of the internal signal transduction element and a polishing means; and
analyzing the electrical resistance as a function of the thickness of the substrate or above the tip of the internal signal transduction element or as a function of the size of the exposed disk of the internal signal transduction element.
10. The method according to claim 9 , wherein the electrical resistance is analyzed by finite element analysis to estimate the size of the exposed disk of the internal signal transduction element.
11. The method according to claim 9 , wherein the monitoring step further comprises:
examining intermittently the nanodisk electrode during polishing to determine the thickness of the substrate around a sealed area of the conical tip.
12. The method according to claim 1 , wherein the tester is a high-input impedance metal-oxide semiconductor field effect transistor (MOSFET)-based circuit tester.
13. The method according to claim 1 , comprising:
after the disk of the desired radius is exposed, the first side of the membrane is modified with a first entity; and
after the nanopore membrane is created, the channel connecting the first side to the second side of the membrane is modified with a second entity.
14. The method according to claim 13 , wherein the first entity is a reactive silane with an inert terminus, and the second entity is a silane that comprises a first functional group able to react with the substrate and a second functional group able to react with a sensor element able to selectively bind a target analyte.
15. The method according to claim 14 , wherein the first entity is Cl(Me) 2 Si(CH 2 ) 3 CN, and the second entity is EtO(Me) 2 Si(CH 2 ) 3 NH 2 .
16. The method according to claim 1 , further comprising: after the nanopore membrane is produced, the first side of the membrane is modified with a first entity and the channel connecting the first side to the second side of the membrane is modified with a second entity.
17. The method according to claim 16 , wherein the first entity and the second entity are the same.
18. The method according to claim 1 , wherein the first opening of the nanopore has a radius ranging from about 2 nm to about 500 nm, or larger.