Force Spectroscopy

Single molecule sequencing

A Dunlop, S Hanna & MJ Miles

Collaboratos: E Hasan & J Wattoom (Chemistry) & AN Round (UEA)

An atomic force microscope can be used to carry out force spectroscopy experiments. Force spectroscopy is a dynamic analytical technique that allows the study of mechanical properties of polymer samples and individual chemical bonds. The aim of my project is to be able to determine sequence information about individual polymer chains. It is thought that this could be achieved by performing force spectroscopy experiments on Rotaxane systems. The proposed experimental technique is illustrated figure 1. The resulting force curves will give information about the interactions between the ring and the polymer chain, from which it is hoped the sequence information can be obtained.

Figure 1. Schematic of a nano-lasso operated by force spectroscopy.

Our initial demonstration of the proposed technique is made with a series of polymers based on PEO and the rotaxanes they form with alpha-cyclodextrin (A-CD). Aromatic derivatives were chosen to function as stoppers along the PEO axle as it is known that specific host-guest interactions form between such derivatives and cyclodextrin rings. Figure 2 shows, in detail, the proposed experiment along with an experimental result.

Figure 2. (a) Simulated force spectrum, indicating the process occurring at the AFM probe at each stage as follows: (1) the functionalised AFM probe binds to the tether chain attached to the cyclodextrin molecule; (2) the CD slides along the polymer axle until it reaches a stopper. Stopped from sliding, the polymer behaves as an entropic spring until (3) the CD slides over the stopper. The process repeats (4) - (6) until the CD dethreads over the terminal stopper (7). (b) Force curve obtained experimentally.