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Recently introduced DNA nanomolds allow the shape-controlled growth of metallic nanoparticles. Here we demonstrate that this approach can be used to fabricate longer linear metal nanostructures of controlled lengths and patterns. To this end, we establish a set of different interfaces that enable mold interactions with high affinity and specificity. These interfaces enable and control the modular assembly of mold monomers into larger mold superstructure with programmable dimension in which each mold monomer remains uniquely addressable. Preloading the molds with nanoparticle seeds subsequently allows the growth of linear gold nanostructures whose lengths are controlled by the DNA structure. Exploiting the addressability of individual mold monomers furthermore allows achievement of site-specific metallization, that is, to create defined metal patterns. We think that the introduced approach provides a useful basis to fabricate nanomaterials with complex shapes and material composition in a fully programmable and modular fashion.

We introduce a new concept for the solution-based fabrication of conductive gold nanowires using DNA templates. To this end, we employ DNA nanomolds, inside which electroless gold deposition is initiated by site-specific attached seeds. Using programmable interfaces, individual molds self-assemble into micrometer-long mold superstructures. During subsequent internal gold deposition, the mold walls constrain the metal growth, such that highly homogeneous nanowires with 20-30 nm diameters are obtained. Wire contacting using electron-beam lithography and electrical conductance characterization at temperatures between 4.2 K and room temperature demonstrate that metallic conducting wires were produced, although for part of the wires, the conductance is limited by boundaries between gold grains. Using different mold designs, our synthesis scheme will, in the future, allow the fabrication of complex metal structures with programmable shapes.

We present a hybrid single-molecule technique combining magnetic tweezers and Forster resonance energy transfer (FRET) measurements. Through applying external forces to a paramagnetic sphere, we induce conformational changes in DNA nanostructures, which are detected in two output channels simultaneously. First, by tracking a magnetic bead with high spatial and temporal resolution, we observe overall DNA length changes along the force axis. Second, the measured FRET efficiency between two fluorescent probes monitors local conformational changes. The synchronized orthogonal readout in different observation channels will facilitate deciphering the complex mechanisms of biomolecular machines.

The characterization of three-dimensional inhomogeneous illumination fields is a challenge in modern microscopy. Here we use a four-arm DNA junction as a nanomechanical translation stage to move a single fluorescent quantum dot through an exponentially decaying evanescent field. Recording the emission of the quantum dot within the evanescent field as well as under homogeneous illumination allows one to directly obtain the intensity distribution of the excitation field without additional deconvolution. Our method will allow the characterization of a broad range of illumination fields and to study near-field effects between small optical probes.

The application of three-dimensional DNA origami objects as rigid mechanical mediators or force sensing elements requires detailed knowledge about their complex mechanical properties. Using magnetic tweezers, we directly measure the bending and torsional rigidities of four- and six-helix bundles assembled by this technique. Compared to duplex DNA, we find the bending rigidities to be greatly increased while the torsional rigidities are only moderately augmented. We present a mechanical model explicitly including the crossovers between the individual helices in the origami structure that reproduces the experimentally observed behavior. Our results provide an important basis for the future application of 3D DNA origami in nanomechanics.

We introduce a simple experimental system to study dynamics of needle-like nanoobjects in two dimensions (2D) as a function of their surface density close to the isotropic-nematic transition. Using fluorescence correlation spectroscopy, we find that translational and rotational diffusion of rigid DNA origami nanoneedles bound to freestanding lipid membranes is strongly suppressed upon an increase in the surface particle density. Our experimental observations show a good agreement with results of Monte Carlo simulations of Brownian hard needles in 2D.

We introduce a new concept that allows the synthesis of inorganic nanoparticles with programmable shape. Three-dimensional DNA origami nanostructures harboring an internal cavity are used as molds. A small gold nanoparticle within the cavity nucleates solution-based gold deposition leading to mold filling. We demonstrate the fabrication of 40 nm long rodlike gold particles with quadratic cross section and the formation of higher order assemblies of the obtained particles, which is mediated by their DNA shell.

Inside cells, motor proteins perform a variety of complex tasks including the transport of vesicles and the separation of chromosomes. We demonstrate a novel use of such biological machines for the mechanical manipulation of nanostructures in a cell-free environment. Specifically, we show that purified kinesin motors in combination with chemically modified microtubules can transport and stretch individual λ-phage DNA molecules across a surface. This technique, in contrast to existing ones, enables the parallel yet individual manipulation of many molecules and may offer an efficient mechanism for assembling multidimensional DNA structures.