Electrostatic Focusing of Unlabeled DNA into Nanoscale Pores using a Salt Gradient

Solid-state nanopores are sensors capable of analyzing individual unlabelled DNA molecules in solution. While the critical information obtained from nanopores (e.g., DNA sequence) is the signal collected during DNA translocation, the throughput of the method is determined by the rate at which molecules arrive and thread into the pores. Here we study the process of DNA capture into nanofabricated silicon nitride pores of molecular dimensions. For fixed analyte concentrations we find an increase in capture rate as the DNA length increases from 800 to 8,000 basepairs, a length-independent capture rate for longer molecules, and increasing capture rates when ionic gradients are established across the pore. In addition, we show that application of a 20-fold salt gradient enables detection of picomolar DNA concentrations at high throughput. The salt gradients enhance the electric field, focusing more molecules into the pore, thereby advancing the possibility of analyzing unamplified DNA samples using nanopores.