Positioning of extended individual DNA molecules on electrodes by non-uniform AC electric fields

Recent research in the field of nanometre-scale electronics has focused on two fundamental issues: the operating principles of small-scale devices, and schemes that lead to their realization and eventual integration into useful circuits. Experimental studies on molecular to submicrometre quantum dots and on the electrical transport in carbon nanotubes have confirmed theoretical predictions of an increasing role for charging effects as the device size diminishes. Nevertheless, the construction of nanometre-scale circuits from such devices remains problematic, largely owing to the difficulties of achieving inter-element wiring and electrical interfacing to macroscopic electrodes. The use of molecular recognition processes and the self-assembly of molecules into supramolecular structures might help overcome these difficulties. In this context, DNA has the appropriate molecular-recognition and mechanical properties, but poor electrical characteristics prevent its direct use in electrical circuits. Here we describe a two-step procedure that may allow the application of DNA to the construction of functional circuits. In our scheme, hybridization of the DNA molecule with surface-bound oligonucleotides is first used to stretch it between two gold electrodes; the DNA molecule is then used as a template for the vectorial growth of a 12 microm long, 100 nm wide conductive silver wire. The experiment confirms that the recognition capabilities of DNA can be exploited for the targeted attachment of functional wires.

During the AC electrokinetic manipulation of particles in suspension on microelectrode structures, strong frequency-dependent fluid flow is observed. The fluid movement is predominant at frequencies below the reciprocal charge relaxation time, with a reproducible pattern occurring close to and across the electrode surface. This paper reports measurements of the fluid velocity as a function of frequency and position across the electrode. Evidence is presented indicating that the flow occurs due to electroosmotic stress arising from the interaction of the electric field and the electrical double layer on the electrodes. The electrode polarization plays a significant role in controlling the frequency dependence of the flow. Copyright 1999 Academic Press.