Application Note #130 Common Approaches to Tip Functionalization for AFM-Based Molecular Recognition Measurements

technique, atomic force microscopy (AFM) is also uniquely well suited to measuring force interactions at the piconewton and nanonewton scale. This capability has been widely used to measure the nanomechanical properties of materials ranging from polymers to living cells and even to characterize single molecules. These measurements are normally made using common, unmodified AFM probes. However, another type of measurement is made possible by the chemical functionalization of AFM probes. This enables the interaction between two specific molecules to be investigated. Most commonly, these molecules are biomolecules and the interactions measured are specific binding interactions, for instance between an antibody and an antigen. Such interactions are critical to life and it’s known that many diseases have their cause at the molecular level, sometimes resulting in a malfunctioning of molecular recognition and directly impacting cell behavior. Thus, understanding the specific molecular forces between individual receptors and ligands can be of great relevance in biomedical research.1-10 AFM force measurements can be used to estimate the specific unbinding forces between such molecules with piconewton accuracy by attaching one of the molecules (referred to as the ligand) to the AFM tip and probing corresponding receptors on surfaces of interest. This technical note reviews common approaches to functionalizing AFM tips for this type of research. Principles of molecular recognition measurements