Single-molecule & Biophysics
DNA - Protein interaction method by using metal nano-particles
We develope a single-molecule detection method that is based on tethered particle motion (TPM). In TPM a biopolymer such as DNA or RNA is immobilized onto a glass slide. The other end of the molecule is labeled with a micro- or nano-meter scale bead. The position of the bead in solution is limited within a volume that depends on the length of the biopolymer. A precise determination of this volume allows the prediction of the length of the immobilized biopolymer and possible variations in its length due to interaction with other molecules (e.g. proteins) or due to differences in its environment by changing the pH, salt concentration and so on.
Our method makes use of gold (diameter ~80 nm) and silver nanospheres (~40 nm) in contrast to the polystyrene beads usually applied in TPM. These metallic beads differentially scatter polychromatic light depending on the bead size due to the plasmon-photon interaction. Gold beads are commonly tagged with anti-biotin antibodies and silver beads with anti-fluorescein antibodies. Each double-stranded DNA fragment (~5 kbp) is labeled with a single metallic bead and tethered on a gold substrate via a thiol linkage (gold bead) or via a streptavidin/biotin system (silver beads).
