Biophysical Journal 60: 777-785 (1991)
© 1991 the Biophysical Society

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Electrostatic interaction in atomic force microscopy

Max Planck Institut für Biophysik, Kennedyallee 70, 6000 Frankfurt a.M. 70, Germany

ABSTRACT

In atomic force microscopy, the stylus experiences an electrostatic force when imaging in aqueous medium above a charged surface. This force has been calculated numerically with continuum theory for a silicon nitrite or silicon oxide stylus. For comparison, the Van der Waals force was also calculated. In contrast to the Van der Waals attraction, the electrostatic force is repulsive. At a distance of 0.5 nm the electrostatic force is typically 10^-12-10^-10 N and thus comparable in strength to the Van der Waals force. The electrostatic force increases with increasing surface charge density and decreases roughly exponentially with distance. It can be reduced by imaging in high salt concentrations. Below surface potentials of 50 mV, a simple analytical approximation of the electrostatic force is described.

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