Revisiting atomic force microscopy force spectroscopy sensitivity for single molecule studies

Recently, the rapid advances in quantitative biology and polymer science have led to the atomic force microscope AFM being extensively employed for single-molecule force spectroscopy. Deflection sensitivity, a critical factor in single molecule force spectroscopy, is changed due to the change in bending shape of AFM cantilever when a single molecule is attached to the AFM cantilever tip. We quantitatively study this variation in the deflection sensitivity by modeling the single molecule as an AFM tip coupled spring. We further propose correction factors for the deflection sensitivity in various cases of single molecule studies. Since many single biomolecule studies are conducted in aqueous environment, we outline and include the complications induced by the refractive index discontinuity at the air-glass-liquid medium interfaces, laser spot size, and spot location on the cantilever. Finally we present correction factor charts for easy calculation of correction factors for a wide variety of stiffness of single molecules. © 2008 American Institute of Physics. DOI: 10.1063/1.3037206