To analyze single molecules, including DNA, scientists need to manipulate and transport them through fluidic pathways. Using entropic nanoconfinement, they can pin DNA and other nano-sized species near constrictions in fluidic channels. To drive transport, researchers also exploit plasmons, electron oscillations in metals that resonate when excited by light. Localized heat from light-induced plasmon excitations produces thermal gradients and fluid motion that propel molecules forward. However, combining nanoconfinement with plasmonic transport has been a challenge. Nanoconfinement demands fluid channels that are less than the radius of gyration of the desired molecule—for many DNA molecules, that’s about 0.5 μm—whereas plasmonic flow-based transport requires channel heights greater than 1 μm.
Now Anders Kristensen at the Technical University of Denmark and colleagues have succeeded in joining the two techniques. Their demonstration of directed DNA transport opens the door for light-controlled manipulation of biopolymers in readily available microscope systems. The trick was embedding metallic...