True molecular resolution in liquid by frequency-modulation atomic force microscopy

Abstract

The increasing attention directed towards nanobiological science requires high-resolution imaging tools for the liquid environment. We have been successful in recording molecular-resolution images of polydiacetylene in water with the frequency-modulation atomic force microscopy (FM-AFM). With the oscillation amplitude of a force-sensing cantilever reduced to 0.20 nm, we were able to overcome the large frequency noise due to the low Q-factor of cantilever resonance in water. We have obtained vertical and lateral resolutions of 10 pm and 250 pm, respectively. This method enables nondestructive imaging of soft biological samples with a load force on the order of 1 pN.