Solid state nanopore membranes have rapidly evolved as a pivotal technology with a myriad of applications including but not limited to label-free single-molecule sensing and identification, ultra-filtration, ion pumps, osmotic power generation, nanowire templates, environmental monitoring, etc. At the same time, they offer intriguing properties for studying many fundamental phenomena at the nanoscale such as ion-current rectification, Debye layer formation, surface charge modulation, biomolecular interactions etc. This presentation will cover the fabrication, characterisation, and application of solid state nanopore membranes with attendees having the opportunity to choose and focus on one specific topic.

The talk will cover two different classes of membrane materials, i.e., polymers and silicon-based materials. Whereas polymer foils can be purchased commercially, silicon-based membranes such as silicon dioxide, silicon nitride and silicon oxynitride were fabricated in-house employing Micro-Electro-Mechanical Systems processing. Nanopores were fabricated by two different methods, the track-etch technology and the controlled breakdown (CBD) technique. For the track-etch technology, the membranes were irradiated with swift heavy ions with energies ranging from 89 MeV to 2200 MeV. When such energetic ions pass through the membrane, they leave long, narrow damaged regions in their wake, called ‘ion tracks’. Ion tracks often exhibit preferential chemical etching over the bulk, which can lead to the formation of pores or channels with high aspect ratio. On the other hand, CBD utilises an electric field to fabricate and enlarge a nanopore with sub-nm precision in a very thin (<30 nm) membrane. Nanopores in polymers were fabricated using track etch technology while both track-etch technology and CBD were used for fabrication of nanopores in silicon-based membranes. 

It is important to understand the structure of the ion tracks not only for their use in nanopore fabrication but also to gain a fundamental understanding of the track formation and recovery processes. Hence, part of the work focuses on characterising the structure of ion tracks in both membrane systems. It will characterise the damage induced by swift heavy ions and discuss how it can be healed by annealing as well as how annealing can be used to change the shape of nanopores. Furthermore, methods for fabrication of bioinspired nanopores as well as conical, double conical and funnel shaped nanopores will be presented. 

Characterization techniques such as small angle X-ray scattering (SAXS), SEM, AFM and ion conductivity measurements were used. New form-factor models for analysing SAXS data were developed and result in novel findings including solving a four-decade old problem about the shape of track-etched nanopores in polycarbonate. Lastly, the biomolecular sensing applications of the nanopores fabricated in ultra-thin membranes (<10 nm thick) will be presented. Results from DNA, RNA and protein sensing will be shown. As more and more proteins are emerging as biomarkers for different diseases, a method to identify and discriminate between similar proteins using machine learning algorithms was developed. The structural characterisation of neuron-specific transfer RNA and impact of C50U substitution (which contributes to neurodegeneration) and its dependence on Mg2+ concentration will also be explored.

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