Material deposition techniques for control of solid state aperture surface properties
The invention provides a method for molecular analysis. In the method, sidewalls are formed extending through a structure between two structure surfaces, to define an aperture. A layer of material is deposited on the aperture sidewalls and the two structure surfaces. The aperture with the deposited material layer is then configured in a liquid solution with a gradient in a chemical potential, between the two structure surfaces defining the aperture, that is sufficient to cause molecular translocation through the aperture.
1. A method for molecular analysis comprising:
forming sidewalls extending through a membrane between two surfaces of the membrane to define an aperture in the membrane;
depositing by an atomic layer deposition technique a layer of material, selected from aluminum oxide and magnesium oxide, on the aperture sidewalls and the two surfaces of the membrane to form a nanopore in the membrane;
configuring the nanopore with the deposited material layer in a liquid ionic solution that is characterized by a solution pH of at least about 8 and that includes nucleic acid polymer molecules to be analyzed;
applying a gradient in electrical potential between the two membrane surfaces defining the nanopore to cause the nucleic acid polymer molecules in the ionic solution to translocate through the nanopore;
providing a nanopore sidewall surface electrical charge state, with the deposited material layer, that is substantially electrically neutral at the ionic solution pH to enable both positively-charged and negatively-charged ions and nucleic acid polymer molecules in the ionic solution to translocate through the nanopore substantially without charge selectivity; and
producing an electrical sensing signal as nucleic acid polymer molecules translocate through the nanopore.
2. The method of claim 1 wherein the membrane comprises a freestanding membrane supported by a substrate.
3. The method of claim 1 wherein the membrane comprises a silicon nitride membrane that is supported by a silicon substrate.
4. The method of claim 1 wherein the sidewalls comprise a continuous sidewall surface defining the aperture.
5. The method of claim 4 wherein the sidewalls define a circular aperture.
6. The method of claim 4 wherein the sidewalls define a rectangular aperture.
7. The method of claim 1 wherein forming the sidewalls comprises etching through the membrane thickness between the two membrane surfaces.
8. The method of claim 7 wherein etching through the membrane thickness comprises ion beam etching of the membrane.
9. The method of claim 8 wherein ion beam etching of the membrane comprises etching with a focused Ga + ion beam.
10. The method of claim 1 wherein the deposited layer of material is characterized as being substantially chemically stable.
11. The method of claim 1 wherein the deposited layer of material is characterized as being substantially thermally stable.
12. The method of claim 1 wherein the deposited layer of material is characterized as being substantially conformal.
13. The method of claim 1 wherein the nanopore with the deposited material layer is characterized by substantially no cation selectivity at the pH of the ionic liquid solution.
14. The method of claim 1 wherein depositing a layer of Al 2 O 3 comprises reaction of Al(CH 3 ) 3 and hydroxyl groups in an atomic layer deposition process.
15. The method of claim 1 wherein depositing a layer of magnesium oxide comprises reaction of a reactive, volatile, thermally stable magnesium compound and hydroxyl groups in an atomic layer deposition process.
16. The method of claim 1 wherein the nanopore with the deposited material layer is characterized by a diameter less than about 100 nm.
17. The method of claim 1 wherein the nanopore with the deposited material layer is characterized by a diameter less than about 50 nm.
18. The method of claim 1 wherein the nanopore with the deposited material layer is characterized by a diameter less than about 20 nm.
19. The method of claim 1 wherein the nanopore with the deposited material layer is characterized by a diameter less than about 10 nm.
20. The method of claim 1 wherein the nanopore with the deposited material layer is characterized by a diameter less than about 5 nm.
21. The method of claim 1 wherein the deposited layer of material is about 1 Å in thickness.
22. The method of claim 1 wherein the material layer deposition is repeated a number of cycles to produce a deposited material thickness of less than 10 nm.
23. The method of claim 22 wherein the material layer deposition is repeated a number of cycles to produce a deposited material thickness of less than 5 nm.
24. The method of claim 1 wherein the nanopore with the deposited material layer is characterized by a diameter that allows passage of a DNA molecule through the nanopore.
25. The method of claim 1 wherein the liquid solution in which the nanopore is configured comprises two solutions, with one solution at each of the two structure surfaces defining the nanopore.
26. The method of claim 25 wherein one of the two solutions is provided with molecules to be caused to translocate through the nanopore.
27. The method of claim 25 wherein an electrical bias is applied between the two solutions to cause molecular translocation through the nanopore.
28. The method of claim 1 wherein the electrical sensing of translocation of molecules through the aperture is characterized by 1/ƒ signal noise that is less than about 10 pA 2 /Hz, where ƒ is signal frequency.
29. The method of claim 1 wherein the deposited material layer provides a nanopore sidewall surface condition that is substantially non-selective to cations over polyanionic DNA and RNA molecules in the ionic solution to be translocated through the nanopore.
30. The method of claim 1 wherein the liquid solution is characterized by a pH of at least about 11.
31. The method of claim 1 wherein the ionic liquid solution comprises KCl.
32. The method of claim 1 wherein the ionic liquid solution comprises Tris-HCl.
33. The method of claim 1 wherein the ionic liquid solution comprises EDTA.
34. The method of claim 1 wherein the molecules in the ionic liquid solution comprise anionic molecules.
35. The method of claim 1 wherein the molecules in the ionic liquid solution comprise polyanionic molecules.
36. The method of claim 1 wherein producing an electrical sensing signal comprises measuring blockage in ionic current through the nanopore as molecules translocate through the nanopore.
37. The method of claim 1 wherein the nanopore sidewall surfaces with the deposited material layer are characterized as substantially insoluble in the ionic liquid solution at the pH of the ionic liquid solution.