Measuring biomolecular forces

In addition to imaging, the AFM can be used to measure the forces acting between the probe and the substrate. In aqueous environments the AFM is routinely able to measure forces as small as 10-20 pN. For the investigation of biomolecular samples, the small probe-sample contact areas and force-measurement range provided by the AFM make it exquisitely suited for the study of single biomolecular interactions or properties. 

In another related approach, often referred to as single molecule force spectroscopy (SMFS), force measurements have also been used to determine the intramolecular forces within a range of biopolymeric molecules, including proteins, polysaccharides and nucleic acids. In such measurements, a molecule becomes attached to the probe surface during probe-sample contact (typically through physisorption) and then it is 

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Allison DP, Hinterdorfer P, Han WH. Biomolecular force measurements and the atomic force microscope. Current Opinion in Biotechnology. 2002 13(1) 47-51. 

Other less common DNA sensors have been described, such as the use of magnetic microbeads on a solid substrate, to detect and characterize many individual biomolecular interaction events simultaneously using the concept of measuring changes in the intermolecular forces by arrays of microfabri-cated magnetoresistive DNA sensors, as developed by Baselt et al. [18]. 

Like all material things, the structure and behaviour of biological systems are governed by the interplay between thermal motion of molecules and the various interaction forces between them. This chapter reviews the basics of thermodynamic equilibrium at the molecular level, leading to ways in which we can measure the various components of thermodynamic forces in biomolecular systems. 

Willemsen OH, Snel MME, Cambi A, Greve J, Grooth BGD, Figdor CG (2000) Biomolecular interactions measured by atomic force microscopy. Biophys 179 3267-3281... 

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