The combination of their electronic properties and dimensions makes carbon nanotubes ideal building blocks for molecular electronics. However, the advancement of carbon nanotube-based electronics requires assembly strategies that allow their precise localization and interconnection. Using a scheme based on recognition between molecular building blocks, we report the realization of a self-assembled carbon nanotube field-effect transistor operating at room temperature. A DNA scaffold molecule provides the address for precise localization of a semiconducting single-wall carbon nanotube as well as the template for the extended metallic wires contacting it.Individual single-wall carbon nanotubes (SWNT) have been used to realize molecular-scale electronic devices such as singleelectron (1) and field-effect transistors (FET) (2). Several SWNT-based devices have been successfully integrated into logic circuits (3) and transistor arrays (4 ). However, the difficulty in precise localization and interconnection of nanotubes impedes further progress toward larger-scale integrated circuits.Self-assembly based on molecular recognition provides a promising approach for constructing complex architectures from molecular building blocks, such as SWNTs, bypassing the need for precise nanofabrication and mechanical manipulations (5). Biology, with its inherent self-assembly capabilities (6-13), is particularly attractive for this task. Biological recognition has been imparted to carbon nanotubes (14-18), but their self-assembly into functional devices and circuits has not yet been demonstrated. We present a framework for self-assembly of carbon nanotube-based electronics using DNA and homologous genetic recombination. A semiconducting SWNT was localized at a desired address on a DNA scaffold molecule using homologous recombination by the RecA protein from Escherichia coli bacteria (19). DNA metallization, with the RecA doubling as a sequence-specific resist (13), led to the formation of extended conductive wires that electrically contact the SWNT. The conduction through the SWNT was controlled by a voltage applied to the substrate supporting the structure.The SWNT-FET ( Fig. 1) was assembled via a three-strand homologous recombination reaction between a long double-stranded DNA (dsDNA) molecule serving as a scaffold and a short, auxiliary single-stranded DNA (ssDNA) (20). The assembly process was guided by the information encoded in these DNA molecules. The short ssDNA molecule was synthesized so that its sequence is identical to the dsDNA at the designated location of the FET. RecA proteins were first polymerized on the auxiliary ssDNA molecules to form nucleoprotein filaments (Fig. 1, step i), which were then mixed with the scaffold dsDNA molecules. A nucleoprotein filament bound a dsDNA molecule according to the sequence homology between the ssDNA and the designated address on the dsDNA (Fig. 1, step ii). The RecA later helped localize a SWNT at that address and protect the covered DNA segment against metallization (13). Figure ...

Localization of a reducing agent, glutaraldehyde, on DNA molecules directs their metallization into highly conductive wires. DNA can be marked for metallization by aldehyde derivatization while retaining its biological functionality. Patterning the aldehyde derivatization of the DNA molecules in a sequence-specific manner allows to embed the precise metallization pattern into the DNA scaffold without compromising its recognition capabilities or biological functionality. We demonstrate scaffold DNA patterning by hybridization of aldehyde-derivatized and underivatized DNA molecules and by sequence-specific protection against aldehyde derivatization. This approach opens new possibilities in wiring of complex molecular-scale electronic circuits.

Undulatory swimming is a widespread propulsion strategy adopted by many small-scale organisms including various single-cell eukaryotes and nematodes. In this work, we report a comprehensive study of undulatory locomotion of a finite filament using (i) approximate resistive force theory (RFT) assuming a local nature of hydrodynamic interaction between the filament and the surrounding viscous liquid and (ii) particle-based numerical computations taking into account the intra-filament hydrodynamic interaction. Using the ubiquitous model of a propagating sinusoidal waveform, we identify the limit of applicability of the RFT and determine the optimal propulsion gait in terms of (i) swimming distance per period of undulation and (ii) hydrodynamic propulsion efficiency. The occurrence of the optimal swimming gait maximizing hydrodynamic efficiency at finite wavelength in particlebased computations diverges from the prediction of the RFT. To compare the model swimmer powered by sine wave undulations to biological undulatory swimmers, we apply the particle-based approach to study locomotion of the 6

No abstract