Cylindrical Silicon On Insulator Solid State Nanopores For Charge Selective Nanoparticle Filtering

Rapid separation of specific biomolecules like virions and other nanoparticles through a solid state nanopore is of vital importance to various biomedical applications and bioanalytical studies. Several factors such as external applied transmembrane voltages, particle size and surface charge density of the nanopore are being investigated to improve the separation efficiency. However, in most cases the transmembrane electric field is not strong enough to pull the particles into the pore. Our goal is to use a voltage bias applied to the substrate of our specific silicon-on-insulator nanopore to significantly increase the nanoparticle translocation rate through the aperture, enhancing the performance of the device as a particle-selective filter. The ability to apply a substrate bias to single silicon-on-insulator cylindrical nanopores via the top silicon layer offers a tremendous advantage over regular silicon nitride nanopores. Moreover, the nanopore process flow is compatible with standard cleanroom facilities allowing a similar high throughput fabrication. The buried oxide layer provides a robust etch stop for the nanopore membrane and the sub-100nm aperture size is precisely controlled by electron beam lithography and thermal oxidation. The applied substrate bias changes the transverse conductance of the nanopore at low electrolyte concentrations (<10-4M HCl) when the Debye length is comparable to the dimensions of the nanopore. The bias depletes or attracts the H+ ions, being theions contributing to the ionic current flow within the nanopore, thereby decreasing or increasing the ionic current. When a positive substrate bias is applied to silicon device layer, it attracts negative charged nanoparticles such as polystyrene beads, which subsequently pass through the pore and repel positively charged particles away from the aperture entrance, acting as a charge-selective filter.