Rene Wirtz

Selective dielectrophoretic manipulation of surface-immobilized DNA molecules

The fabrication of nanoscale molecular devices is becoming increasingly important and research into their fabrication has intensified over the last few years. In particular, the attachment of molecular objects onto various surfaces has attracted considerable attention. Here, we report a multistep surface immobilization procedure, which allows the specific and controlled attachment of very long DNA molecules onto gold electrodes. Further, we report the effect of dielectrophoresis on these surface-bound DNA molecules with respect to amplitude and frequency, and we show that selected surface-immobilized DNA molecules can be manipulated by dielectrophoresis. Finally, we investigated the use of dielectrophoresis in conjunction with the multistep surface immobilization of fluorescently labelled, surface-bound λ-DNA in a basic data-storage device.

Influence of alternating current electrokinetic forces and torque on the elongation of immobilized DNA

The authors investigate the elongation and orientation of different-sized deoxyribose nucleic acid (DNA) molecules, tethered onto gold electrodes via a terminal thiol, under the influence of high frequency ac electric fields. The DNA molecules are elongated from a random coil into an extended conformation and orientated along the electric field lines as a result of the forces acting on the molecules during the application of the ac electric fields. Elongation was observed in the frequency range 100 kHz-1 MHz, with field strengths of 0.06-1.0 MV/m. Maximum elongation for all DNA fragments tested, irrespective of size, was found for frequencies between 200 and 300 kHz. The torque acting on the induced dipole in the DNA molecules, complemented by a directional bias force, opposite in direction to the dielectrophoretic force, provides the main contribution to the elongation process. The length of elongation is limited to either half the distance between opposing electrodes or to the contour length of the DNA, whichever is shorter. Further, the authors show that the normalized length of the elongated DNA molecules is independent of the contour length of the DNA

High-sensitivity colorimetric detection of DNA hybridization on a gold surface with high spatial resolution

We present a colorimetric detection method which is able to detect biotinylated oligonucleotides hybridized to thiolated complementary strands bound to a gold surface. Unlike previous colorimetric detection methods, this technique has the advantage of providing spatial information which is of higher resolution than that of an optical microscope, and can also be used on a gold surface. Bulk concentrations down to 10(-9) M of biotinylated oligonucleotides were detectable representing fewer than 7000 molecules of hybridized DNA on a microarray-sized spot (empty set approximate to 35 mum). This technique has potential for DNA detection in molecular electronics and molecular assembly applications, where a high-resolution detection on metal surfaces is required.