Flat gold nanostructures on inert substrates like glass or graphite were illuminated by single intensive laser pulses with fluences above the gold melting threshold. The liquid structures produced in this way are far from their equilibrium shape, and a dewetting process sets in. On a time scale of a few nanoseconds, the liquid contracted toward a sphere. During this contraction, the center of mass moved upward, which could lead to detachment of droplets from the surface due to inertia. The resulting velocities were on the order of 10 meters per second for droplets with radii in the range of 100 nanometers.When small droplets impinge on a surface, varying degrees of deposition can be observed, ranging from sticking to rebounding. Sticking is essential for ink-jet printing and in agricultural agents that function by sticking to leaves; rebounding is desirable in cases such as selfcleaning surfaces (1, 2).The physics of impacting droplets has been well studied (3-5), and various types of (macroscopic) droplet sources have been developed (6). The impact-rebound process can be described energetically as the transformation of the impinging drop_s kinetic energy (KE) into surface deformation energy, followed by the inverse process, which detaches the drop (7).We examined whether it is possible to begin with deformed droplets on a surface and observe only the transformation from surface deformation energy to KE, as indicated by droplets jumping off the surface. For this purpose, we used droplets in the submicrometer range, which are much smaller than those typically used in impact studies. Such droplets can readily be obtained in an energetically unfavorable pancakelike shape with a large surface-to-volume ratio by preparing nanostructures in the solid state (e.g., by evaporation) on a substrate that in equilibrium is not wetted by the deposited material. Upon melting the nanostructures with a short laser pulse, dewetting sets in, and under appropriate conditions, detachment of the resulting droplets can be observed.The gold nanostructures we used here were fabricated by colloidal lithography, in which a monolayer of monodisperse spherical particles (with diameters of 1.5 to 3 mm) serves as a deposition mask (8, 9) to produce flat gold triangles with side lengths between 400 and 800 nm (Fig. 1A). The thickness of the evaporated films ranged between 50 and 160 nm. After removal of the colloid mask, these triangular gold structures were irradiated with a frequencydoubled Neodymium Doped Yttrium Aluminum Garnet (Nd:YAG)-laser (wavelength l 0 532 nm, full-width at half maximum of 10 ns). Because the absorption length of the laser radiation is smaller than the thickness of the nanostructure, we have to consider the temperature distribution inside of the nanostructure. An estimate for the thermal diffusion lengths on the time scale of the laser pulse yields 1600 nm for solid gold and 900 nm for molten gold, which is well above the thickness of the structures used here (10). Thus, we can assume that the temperature stays almos...

The fabrication of autonomously moving molecular structures is one of the central challenges in the field of DNA nanodevices.[1] Some of the concepts introduced recently to achieve this goal rely on the sequence-dependent catalytic action of DNA-modifying enzymes such as restriction endonucleases or nicking enzymes [2] while others use the catalytic power of DNA itself by incorporating DNA enzyme sequences into DNA devices.[3] Both approaches have also been used to realize autonomous molecular computers.[4] Another strategy is based on controlled inhibition of DNA hybridization by formation of secondary structure and its acceleration by catalytic DNA strands.[5] These concepts were developed for the autonomous operation of DNA devices fueled by DNA hybridization. A different approach was recently taken by our research group [6] and we could show that the pH-sensitive conformational transition of a cytosinerich DNA strand between a random conformation and the socalled "i motif" could be driven by the oscillating proton concentration generated by a chemical oscillator. In such a system, the temporal succession of the states of the DNA devices is determined by a nonlinear dynamical system rather than by an external operator. We report here how this system can be significantly improved by attaching the DNA conformational switches to a solid substrate. This attachment allows us to operate the chemical oscillator in a continuous flow stirred tank reactor (CSTR) into which a glass chip supporting the DNA devices is placed. In principle, the surface-bound DNA structures can undergo an infinite number of autonomous conformational switching events in this configuration.We showed recently how proton-fueled DNA devices can be driven by an oscillating chemical reaction [6] by using a variant of the Landolt reaction to periodically change the pH value in a continuously fed reactor. To retain the DNA switches within the reaction solution, a reactor without an outlet had to be used. In such a configuration, one cannot reach a steady state since the continuous influx of reaction solution means the average concentrations of the reactants vary. As a result, this dynamic chemical system is driven out of its oscillatory region, thus causing the oscillations to die away after a few periods.To overcome this limitation in the present work we operated the oscillator in a CSTR with two inlets and one outlet. In principle, an infinite number of homogeneous pH oscillations can be generated by using a continuous filling combined with the simultaneous removal of waste materials. However, the DNA devices had to be attached to a solid substrate to prevent loss of the DNA through the reactors outlet. For these experiments, we used thiol-modified, fluorescently labeled DNA switches bound to an ultrathin transparent gold layer on a glass substrate. This allowed a firm covalent attachment of the DNA to the surface while at the same time energy transfer between the fluorophores and the gold layer [7] could be used to characterize the conformational...