Supplementary Materials for

Insulating behavior of l-DNA on the micron scale

Y. Zhang, R. H. Austin, J. Kraeft, E. C. Cox, and N. P. Ong

End-anchored l-DNA in flowing buffer solution ( Download QuickTime Player )

The l-DNA molecules, with thiol-modified dTTP incorporated into both ends, are specifically attached onto Au electrodes by Au-S bonding.  When an alternating flow of the buffer solution is applied perpendicular to the anchored molecules, the molecules are observed to flex back and forth.  This demonstrates that the attachment is specific to the thiol-modified ends of the DNA and Au electrodes.

The gold electrodes (light vertical stripes in all clips) were laid down on a quartz substrate using standard photolithography techniques. The electrodes are about 4 mm wide and are spaced by either 4 mm or 8 mm.  The l-DNA molecules were stained by a fluoresecent intercalating dye TOTO1 and excited by an Ar ion laser.  Fluorescence images were collected by a CCD camera.

• Video Clip 1 (swift01.mov, 961KB)

A l-DNA molecule bridges the space between two electrodes and flexes with the flow.  DNA molecules with only one end attached are observed to elongate in the flow.

• Video Clip 2 (swift02.mov, 1.6MB)

In Clip 2 a l-DNA molecule with both ends anchored to the same electrode (second from left) is observed to flex with the flow (the flow direction is indicated by unattached molecules).  Elongation of molecules with only one end attached may also be seen (first electrode from left).  The large bright spot on the top left corresponds to non-specific adhesion of DNA coils.

• Video Clip 3 (swift03.mov, 681KB)

Clip 3 shows several DNA molecules bridging the gap between different electrodes.  Flexing of the molecules with the flow may be observed.  Bright spots on the electrodes correspond to non-specific adhesion of DNA coils.

• Figure 1

In a buffer flow (right to left), Molecule a is anchored onto Au at both ends, and bows slightly. Molecules b and c extend in the flow with their right end anchored to an electrode. The fact that molecules b and c extend to the same length indicates that the binding is specific to the ends. The image is an average of 20 frames.

3/28/02, zyx@Princeton.EDU