Hybrid Nanopore for Molecular Sensing Applications

Abstract

Molecular sensing is of great interest from fundamental understanding of a molecule and from biosensing application perspective also. Nanopores are now widely used for molecular sensing and utilize the ionic current for detection. Molecules passing through a nanopore cause a step change in the ionic current; which depends on the length and width of the molecule. Nanopore sensors can be classified as biological and solid-state nanopores. Integration of the solid-state nanopore with a biological one helps overcome many of the limitations like size reproducibility, translocation velocity and analyte specificity. Here we present the development of a hybrid nanopore by integrating a silicon nitride (SiNx) based solid-state nanopore with a beta-barrel porin OmpG. Solid-state nanopore were fabricated on a free standing membrane. 50 nm thick SiNx membranes with a dimension of 50 x 50 µm2 were fabricated using chemical vapor deposition, photo-lithography, reactive ion and chemical etch. Hour-glass shaped nanopores, with a half cone angle of 20°, ranging from 2 nm to 8nm in size were sputtered out on the SiNx membrane using JOEL 2200FS TEM. The pore current was then measured in a specialized cell filled with ionic solution. Bias was applied using Ag/AgCl electrodes interfaced to Axon-patch 200B amplifier. The characterized solid-state nanopores were tested for their sensing ability. The desired molecule was added to cis side of the device; the charged molecule was then electrophoretically pulled through the pore onto the electrode on trans side. Hybrid nanopore has been achieved by inserting OmpG protein onto a 4.1 nm or a 4.7 nm sized solid-state nanopores. The intrinsic gating characteristic of the protein remained observed, demonstrating the proper-functioning of the protein. Molecular translocation through this hybrid nanopore would be observed and the results from this study will be presented.