Exploring the limits of spatial resolution has been a constant in history of Atomic Force Microscopy imaging. Since its invention in 1986, the AFM has beaten the barrier of resolution continuously thanks to technical developments, miniaturization of tips and implementation of new imaging modes. The double-helix structure of DNA has been always at the horizon of resolution. Today, this milestone has been reached, not only imaging DNA, but also its close relative double-stranded RNA (dsRNA).
dsRNA mediates suppression of specific gene expression, it is the genetic material of a number of viruses, and a key activator of the innate immune response against viral infections. The ever increasing list of roles played by dsRNA in the cell and its potential biotechnological applications has raised over the last decade an interest for the characterization of its mechanical properties and structure, and that includes approaches using Atomic Force Microscopy (AFM) and other single-molecule techniques.
In our group we have pushed the resolution of AFM to visualized the double helix of dsRNA under near-physiological conditions and at enough resolution to resolve the A-form sub-helical pitch periodicity. We have employed different high-sensitive force-detection methods and obtained images with similar spatial resolution. Our work shows that the limiting factors for high-resolution AFM imaging of soft material in liquid conditions are, rather than the imaging mode, the force between tip and sample and the sharpness of the tip appex
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Ares et al. Nanoscale 8,11818-11826 (2016). High resolution atomic force microscopy of double-stranded RNA. LINK