Attaching Biological Entities to AFM Cantilevers for Molecular Recognition Studies

W. Travis Johnson, PhD
MRS Fall 2007

Atomic force microscopy (AFM) is an important tool for high resolution studies in biophysics. A strong suit of AFM is its ability to measure ligand-receptor interactions at the picoN scale. Using AFM, scientists can probe and quantify these interactions in their native, liquid environments at physiological pH or perform dynamic experiments in situ by removing or adding ions, solutes, and reagents to the sample environment. Bioconjugation chemistry and surface chemistry are crucial because a selective ligand must be immobilized on the tip of a cantilever so that the AFM can resolve the mechanical force that is required to separate the ligand and its target. The resulting data can be used to calculate forces of unbinding, derive rate constants, and infer structural information about the binding pocket. Biomolecular recognition experiments with AFM can be greatly enhanced through the use of relatively short (~8-10 nm), heterobifunctional, elastic, polyethylene glycol (PEG) linker to immobilize ligands. Selective bifunctional linkers are used in order to permit their sequential immobilization and bioconjugation, while minimizing undesirable polymerizations or self-conjugation.

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