High-Q dynamic force microscopy in liquid and its application to living cells

We present a new dynamic force microscopy technique for imaging in liquids in the piconewton regime. The low quality factor (Q) of the cantilever is i ncreased up to three orders of magnitude by the implementation of a positiv e feedback control. The technique also includes a phase-locked loop unit to track the resonance of the cantilever. Experiments and computer simulation s indicate that the tip-sample forces are below 100 pN, about two orders of magnitude lower than in conventional tapping mode atomic force microscopy. Furthermore, the spectroscopic ability is greatly enhanced. Either the pha se shift or the resonant frequency shows a high sensitivity to variations i n either the energy dissipation or conservative interactions between the ti p and the sample, respectively. The potential of this technique is demonstr ated by imaging living cells.