Immobilizing Biological Molecules on AFM Probes for MRFM and TREC Studies

Ligand molecules for a particular receptor can be attached to the tip of an AFM probe, transforming the probe into a sensitive, chemically selective biosensor for that receptor [Riener et al. 2003]. Molecular recognition force microscopy (MRFM) is a single-molecule AFMbased technique that relies heavily on nanoscale surface chemistry, nanoscale biochemical immobilization chemistry, and bioconjugation chemistry. In MRFM, single-molecule unbinding interactions between AFM probe-bound ligands and substrate-bound receptor pairs are observed and quantified one by one as the AFM cantilever approaches and then is subsequently withdrawn from the surface many times. The nanoNewtonscale molecular unbinding events are generally detected by measuring the optical deflection of the flexible AFM cantilever. These force spectroscopy (FS) experiments can provide valuable information about the structure and dynamics of molecular unbinding events at the single-molecule level [Noy et al. 1997]. In addition to intermolecular interactions, this technique has also been effectively applied to gain an understanding of the intramolecular forces involved in protein folding and polymer elongation [Allison et al.2002].