We are using an engineered polymer chain to follow the folding and unfolding trajectories of single chains by optical means. Unfolding is triggered either by chemical denaturation or by the use of flow. It provides single molecule unfolding and refolding at no external forces (force-free).
The linear chains are surface-tethered at one edge using Halotag technology (Promega) while at the other end we use exposed Cys which allows us tethering them to 80 nm gold nanobeads. We exploit our standard TPM setup to follow the nanobead diffusion, and find the variations in end-to-end distance due to the perturbations described above. Our setup enables us to perform long observations of the same molecules and hence we can describe the entire unfolding and then refolding trajectory for the same polymer chain at different denaturant concentrations.