Fig. 4.

Nanoindentation of a viral capsid. a Schematics of the experiment. The capsid and AFM cantilever tip are indicated with a realistic relative scale. Mechanical information can be collected, in the form of force versus distance data, during both the indentation and retraction phases of the experiment. b Force versus distance plot obtained on a T7 phage particle (Vörös et al. 2017). Force sawteeth during indentation and retraction point at buckling and unbuckling events, respectively, which result in stepwise, 6-nm reversible structural changes in the capsid. The slope of the indentation trace may be used to calculate the stiffness of the capsid