Pressure-Induced Enlargement and Ionic Current Rectification in Symmetric Nanopores

Nanopores in solid state membranes are a tool able to probe nanofluidic phenomena or can act as a single molecular sensor. They also have diverse applications in filtration, desalination, or osmotic power generation. Many of these applications involve chemical, or hydrostatic pressure differences which act on both the supporting membrane, and the ion transport through the pore. By using pressure differences between the sides of the membrane and an alternating current approach to probe ion transport, we investigate two distinct physical phenomena: the elastic deformation of the membrane through the measurement of strain at the nanopore, and the growth of ionic current rectification with pressure due to pore entrance effects. These measurements are a significant step toward the understanding of the role of elastic membrane deformation or fluid flow on linear and nonlinear transport properties of nanopores.

Fabrication of solid-state Nanopores for DNA analysis

Maïté Volatier

One of revolutionary technologies to sequence single molecules, such as DNA, is using nanopore devices. A single-channel with nanometer-scale aperture allows an extremely rapid electric analysis of such single molecules. The objective of this work is to fabricate nanopores into robust, solid-state membranes to achieve better performances. The technological challenge is in the small required dimension of the nanopore, around 50-100 nm in diameter and depth. To reach this objective, we used two different techniques: the ion track technique and a microfabrication method associated with Focused Ion Beam (FIB). A literature review has been done on the ion track technique. Threshold values of the ion track formation have been found for different insulator materials (polymers, SiO2, SiN). We did experiments with the linear accelerator UNILAC (Universal Linear Accelerator) at the GSI (Darmstadt, Germany) where we irradiated our samples with heavy gold ions (11.4 MeV/nucleon). On very thin membranes, we expect that a direct perforation would occur, and we chose SiN membranes and SU-8 thin films as samples. However, the experiment of ion bombardment was not possible to be done early enough, thus TEM analysis have not been done yet. If the direct perforation by ion bombardment is not possible, a chemical etching step would be necessary. About the microfabrication method associated with Focused Ion Beam (FIB) perforation, we did experiments at the Center of Micro Nano Technology (CMI) in EPFL. First trial with FIB was done on SiN membranes. In order to obtain required aperture size, reduction of membrane thickness before perforation by FIB was attempted, but this process was difficult to be achieved because of charging. To overcome this dimension limitation we chose a silicon membrane. With silicon membranes, oxidation would be performed after perforation by FIB, since channel opening will be reduced by SiO2 growth. Moreover, this oxide layer allows a functionalisation of the inner surface of the nanopore by silane chemistry. That should improve the resolution of DNA analysis. Though the aperture size reduction by oxidation has not been done yet, refining and perforation by FIB will be done according to this idea. We should reach ca. 100 nm-aperture size. Even if validation measurements are not easy, our specifications should be reached with the oxidation. More experiments and analysis have to be performed for further improvement.

2004

Fundamental Applications of Nanopores: Controlled DNA Translocations to Nanofluidics

Sebastian James Davis

Nanopores are nanometer sized openings that are the connection between two electrolyte filled reservoirs. The measurement of the ion transport flowing through such a pore allows to probe physically or biologically interesting phenomena. These range from the passage of biological molecules, to the modulation of current due to multiple physical effects when the nanopore undergoes mechanical strain or pressure induced flow. Many types of nanopores exist: biological protein pores engineered to be able to sequence DNA, glass nanocapillaries easily interfaced with optical tools, or silicon nitride membrane pores which are a standard tool of recent nanotechnology. This thesis is split into two parts. The first focuses on the use of glass nanocapillaries which allow the facile combination of nanopore experiments with optical tweezers. Optical tweezers are a well established single molecule tool that allow precise force measurement on biologically relevant scales. They are used here for the control of DNA passing through the nanopore. Their ability to measure small scale forces allows the detailed investigation of DNA binding proteins, and attempts to measure the force of DNA passage through biological pores. Extensions of these experiments to the elastic behaviour of DNA during its passage through a nanopore reveal the effects of flow generated by the charged surface of nanopores themselves. This motivates attempts to control such flows as well as the second part of the thesis. The second part of the thesis focuses on nanofluidics, the role of fluid flow and ion transport at the nanoscale. Using a setup combining pressure with nanopores it is possible to probe, via precise measurements of the conduction of the nanopore, the wetting state of the pore. Contamination phenomena are shown to be abundant with such small systems and a description of their effects on standard measurements such as direct current current-voltage curves is given. Following this, pressure is applied to perfectly filled pores and, thanks to a new alternating current detection method, is shown to be able to discern the effect of pressure induced strain at the pore as well as the coupling of hydraulic flow with electrical properties of the pore. Finally, extensions beyond aqueous solvents are explored in both nanocapillaries and silicon nitride pores. For this, room-temperature ionic liquids are used. These liquids are known from previous studies to behave differently at surfaces and in nano-confinement. The nanopore system both with and without added pressure is shown to be a good tool for investigating such phenomena.

EPFL2020

Fabrication of solid-state Nanopores for DNA analysis

Maïté Volatier

2004

Fundamental Applications of Nanopores: Controlled DNA Translocations to Nanofluidics

Sebastian James Davis

EPFL2020