Holding Single Molecules with Temperature Gradients

Frank Cichos

Molecular Nanophotonics Group, Universit├Ąt Leipzig

Holding single molecules in liquids is still a challenge as Brownian motion fueled by thermal energy is randomizing molecular position quickly and common forces to counteract this erratic motion commonly scale with the volume. The benefits of holding and manipulating a single molecule are however huge as this would allow for long time observations of molecular conformation detecting rare events, molecular reactions and true bi-molecular interactions. Here we report on a method which employs the fuel of Brownian motion – thermal energy – to confine Brownian motion of single molecules in liquid. By generating time-dependent feedback controlled inhomogeneous temperature fields with a laser heated gold structure, we create thermophoretic drive fields which allow the confinement of single molecules in solution. The feedback control and the inhomogeneous character of the temperature field even allow for a trapping a well controlled number of multiple molecules. We expect that this simple method and an extension to large arrays of traps will pave the way for controlled molecular interactions studies.