Plasmonic Scattering as an Efficient Tool for a Force-Free Technique to Follow Single DNA Molecules

One of the promising methods for single molecule studies is Tethered Particle Motion (TPM). The technique layout that was developed a decade ago [1], is based on anchoring one end of a DNA molecule (or any other polymer of interest) to a surface, and labeling the opposite end with an optical marker. In solution, the marker moves randomly in a volume that is governed by the restrictions set by the DNA molecule. Tracking and analyzing its position distribution provides an essential tool to follow the dynamics of the DNA conformations [2, 3]. Most of the TPM systems use a CCD camera to detect the projected position of the bead on a two-dimensional plane, and the information on the bead height above the surface is lost. Here we show how TPM can be exploited for three-dimensional particle tracking using Total Internal Reflection (TIR) [4] illumination system. We also report of the deviations between the lateral distribution and the axial distribution.