Studies of single molecules in their natural form

Single molecule studies make possible the characterization of molecular processes and the identification of biophysical sub-populations that are not accessible through ensemble studies. We describe tethered particle motion, a method that allows one to study single molecules in their natural form without having to apply any external forces. The method combines darkfield microscopy with a metal nanobead. It permits the study of the biophysical properties of the tethered particles, as well as protein-DNA interactions. The method is not suitable for in vivo studies, and we therefore describe two other methods that are appropriate for live-cell imaging.