The study of molecular interactions by AFM force spectroscopy

Recent progress in atomic force microscopy (AFM) technology has allowed the measurement of inter- and intramolecular forces at the level of individual molecules. The mechanical manipulation of single polymer chains immobilize d on solid substrates has become possible in solution, as they are spanned and stretched between the tip of an AFM cantilever and the substrate surfac e. This investigation of polymer chains far from their maximum entropy conf igurations has stimulated the refinement of existing polymer theories. From the measured force-distance curves quantitative information can be obtaine d on the elasticity of single macromolecules in solution, on conformational transitions along the chains, about the mechanical stability of chemical b onds and on secondary structures, as well as on the desorption of individua l polymer molecules from solid substrates. Recent applications of AFM singl e molecule force spectroscopy reach from the study of dynamic processes in complex biological systems and intermolecular forces in colloidal systems t o the investigation of new functional materials capable of performing energ y transductions on the level of individual macromolecules. In this article, we present a detailed description of the experimental procedure, followed by an overview of the development, the success and the current challenges o f this technique during the past five years, in which it has rapidly evolve d from the first proof of principle to a highly active field of research.