VISCOELASTICITY OF LIVING CELLS ALLOWS HIGH-RESOLUTION IMAGING BY TAPPING MODE ATOMIC-FORCE MICROSCOPY

Application of atomic force microscopy (AFM) to biological objects and processes under physiological conditions has been hampered so far by the deformation and destruction of the soft biological materials invok ed. Here we describe a new mode of operation in which the standard V-s haped silicon nitride cantilever is oscillated under liquid and damped by the interaction between AFM tip and sample surface. Because of the viscoelastic behavior of the cellular surface, cells effectively ''ha rden'' under such a tapping motion at high frequencies and become less susceptible to deformation. Images obtained in this way primarily rev eal the surface structure of the cell. It is now possible to study phy siological processes, such as cell growth, with a minimal level of per turbation and high spatial resolution (similar to 20 nm).