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Force Measurements

- a major tool for nanotechnology

- two methods have been used with proteins:

        A. SFA = surface force apparatus

        B. AFM = atomic force microscope

SFA =  surface force apparatus

measures the forces between two macroscopic, curved surfaces, where radius is R=1-2 cm as a function of their separation D within +1A by optical interferometry

absolute force sensitivity of SFA is lower than of AFM, but forces forces scale with surface dimensions, so for relatively large  contact areas, accurate force profiles can be measured 

only method that can measure force F, absolute surface separation D and local geometry of the surfaces

method of choice for accurate force/distance profiles between surfaces

AFM = atomic force microscope

measures the relative cantilever displacement (delta Dc) within +1A, but the absolute separation D between the surfaces cannot be determined

the soft cantilever allows one to make very sensitive measurements of single molecule interactions between the small probe tip and the surface

method of choice for measuring weak, short-range forces such as single bond strengths or molecular force extension profiles for which one doesn't need to know the absolute distance D and the local geometry is not critical

© 2002 Judith Klein-Seetharaman, University of Pittsburgh. This website was created December 12, 2002 and updated December 12, 2002. For questions or comments please contact Judith Klein-Seetharaman at jks33@pitt.edu.