DNA attachment to optically trapped beads in microstructures monitored by bead displacement

Reversibly binding silicone cartridges have been developed to form reaction containers in which ‘single molecule chemistry’ can be performed. We use an optical trap to drive 1μm streptavidin-coated beads into a region containing biotinylated DNA until binding of a strand of DNA occurs. A quadrant detector is used in reflective mode to track the lateral position of trapped beads. Relative motion between the bead and the solution causes a viscous drag force which is increased when a single strand of DNA is attached to the bead; DNA-bead attachment is done in minutes with less than a femtomole of DNA. The method allows the study of single molecule digestion.