Fig. 5.

Assembly of a single ds-DNA chain between two colloids. A polystyrene (PS) bead modified with anti-DIG antibodies is trapped with the optical tweezers (a) and fixed by a micropipette due to capillary forces (b). In the next step, a PS bead on which ds-DNA is immobilized via Biotin–Streptavidin linkers is captured with the optical tweezers and brought in the immediate neighborhood of the colloid held by the micropipette (c). Binding between the Digoxigenin labeled end of a DNA strand with an antidigoxigenin antibody on the surface of the bead held by the micropipette is observed as a sudden decrease of the Brownian fluctuations of the bead in the optical trap (d). By measuring the force extension dependence, it is ensured that just one ds-DNA strand is fixed between the beads