Fabrication of Metallised Solid-State Nanopores Using Electrodeposition with Ionic Current Feedback

Abstract

In recent years, solid state nanopores fabricated in thin insulating membranes have been successfully employed as a new tool to detect and characterise the passage of DNA molecules. These nanopores circumvent some of the problems associated with protein channels, and offer the additional advantage of tunable pore size.Although several experiments have clearly demonstrated that modulations of ionic current during translocation of RNA or DNA molecules can be used to discriminate between polynucleotides, a key challenge with nanopores is to find methods to slow down and control the DNA translocation. It has been proposed that the presence of a metallic probe located at the nanopore can potentially enhance the electrostatic interaction between the DNA molecule and nanopore surface and hence reduce translocation times. Moreover, by applying an electric potential to the metallic nanopore it is possible to control the charge and ultimately allow for sorting and sizing of DNA fragments.Here we report a novel method to fabricate these metallic nanopores with apparent diameters below 20 nm using electrochemical deposition and on-line ionic current feedback. Starting from large nanopores (diameter 100-200 nm) milled into gold silicon nitride membranes using a focused ion beam, we electrodeposit platinum onto the gold surface, reducing the effective pore diameter. By monitoring the ion current simultaneously, the electrodeposition process can be terminated at any pre-defined value of the pore conductance in a precisely controlled and reproducible way. Our approach is applicable to single nanopores as well as nanopore arrays, and can easily be extended to metal deposits other than Pt. In order to highlight their potential for single-molecule biosensing applications, we also show electrophoretic translocation of lambda DNA in a proof-of-concept experiment.