Nanomechanical imaging of soft samples in liquid using atomic force microscopy

The widely used dynamic mode atomic force microscopy (AFM) suffers severe sensitivity degradation and noise increase when operated in liquid. The large hydrodynamic drag between the oscillating AFM cantilever and the surrounding liquid overwhelms the dissipative tip-sample interaction forces that are employed for nanomechanical imaging. In this article, we show that the recently developed Trolling-Mode AFM based on a nanoneedle probe can resolve nanomechanical properties on soft samples in liquid, enabled by the significantly reduced hydrodynamic drag between the cantilever and the liquid. The performance of the method was demonstrated by mapping mechanical properties of the membrane of living HeLa cells.