Threading DNA through a nanopore

Nanoscale pores are showing increasing promise as tools for DNA analysis, including size determination, folding studies, and base sequencing (see Physics Today, November 2012, page 29). When threading a sewing needle, some people pass the end of the thread through the eye, while other people fold the thread first and then pass the fold through. Similarly, when a nanopore’s electrophoretic forces capture a DNA molecule, the 2-nm-diameter DNA can be pulled through from one of its ends or, if the pore is wide enough, can form a fold somewhere along its length and be pulled through from there. Derek Stein and colleagues at Brown University now offer a statistical study of the fold locations in DNA passing through a voltage-biased 8-nm-diameter nanopore fabricated in silicon nitride. From the observed variations in the electrical current across the pore, the team could readily discern the positions of folds in transiting...