Jumping mode atomic force microscopy obtains reproducible images of Alzheimer paired helical filaments in liquids

Alzheimer paired helical filaments (PHF) have been investigated with atomic force microscopy (AFM) under physiological conditions. Dynamic mode (DM) and jumping mode (JM) AFM have been employed as imaging techniques. Data obtained in solution have been compared to data obtained in ambient air with DM. In liquids, PHF particles show distortion and irreversible damage when imaged with DM. On the contrary, JM images of PHF particles are reproducible and out of apparent damage. Dimensions of the PHF particles measured with JM, are in agreement with previously reported electron microscopy data. We have found that the forces involved in DM imaging are larger than those involved in JM imaging and hence we believe that this is the main reason of the damage caused by the tip when using DM in solution.