Faster high-speed atomic force microscopy for imaging of biomolecular processes.

High-speed atomic force microscopy (HS-AFM) has enabled observing protein molecules during their functional activity at rates of 1-12.5 frames per second (fps), depending on the imaging conditions, sample height, and fragility. To meet the increasing demand for the great expansion of observable dynamic molecular processes, faster HS-AFM with less disturbance is imperatively needed. However, even a 50% improvement in the speed performance imposes tremendous challenges, as the optimization of major rate-limiting components for their fast response is nearly matured. This paper proposes an alternative method that can lower the feedback control error and thereby enhance the imaging rate. This method can be implemented in any HS-AFM system by minor modifications of the software and hardware. The resulting faster and less-disturbing imaging capabilities are demonstrated by the imaging of relatively fragile actin filaments and microtubules near the video rate, and of actin polymerization that occurs through weak intermolecular interactions, at ∼8 fps.