2.8 N/m. Figure 2a is taken with a Nanosensors- PPP-NCH cantilever with nominal force constant of 40 N/m. This last type of cantilevers was also used to image viruses in buffer solution (fig. S1. Figs. 4, 5 and 6 were also measured with Olympus OMCL- RC800PSA (we have also obtained true atomic resolution on mica using this type of cantilever see text S1 and fig. S1 and S2). Simulations The simulations were carried out using VEDA [31] [32]. More details on simulation can be found in Text S1 and fig. S3. Surface preparation Virus particle adsorption is highly efficient on hydrophobic surfaces. In order to adsorb the virus particles two different hydrophobic surfaces were used: silanized glass surfaces (figs. 2, 3 and 4) and HOPG/figs. 5 and 6). The glass surfaces were by sonicating for 5 minutes in a solution of KOH pellets dissolved in distilled water and ethanol (water:ethanol ratio was around 1:9). A special holder was used to properly expose the substrates to the cleaning product. The KOH solution was then removed and the glass surfaces were washed and sonicated again with distilled water for 5 minutes. This process was repeated up to three times. After this, the glass surfaces were dried in a furnace at 100uC. Once the cleaning is done, the substrate holder was left in a closed glass box with a layer of Hexamethyldisilazane [33] that covers the bottom, this ensures that the holder is properly cleaned for further uses. Finally, the glass surfaces were exposed to silane vapor silanes overnight. This process increases the hydrophobicity of the glass increasing the sticking probability of the virus particles to surface. Before the virus particles were adsorbed we checked the surface state by scanning a few substrates with AFM; clean silanized glass surface, suitable for AFM scanning, should be flat, (we measure a roughness smaller than 1 nm) with a few randomly distributed holes of nanometer size. The HOPG surface where prepared by simply mechanical exfoliation with adhesive tape. This exposed a fresh surface on where a drop of virus solution is deposited. References 1. Flint JS, Enquist LW, Racaniello V, Shalka AM (2004) Principles of virology, ASM Press, Washington D.C. 2. Purohit PK, Kondev J, Phillips R (2003) Mechanics of DNA packaging in viruses. P NATL ACAD SCI USA 100: 3173–3178. 3. Cordova A, Deserno M, Gelbart WM, Ben-Shaul A (2003) Osmotic shock and the strength of viral capsids. Biophys J 85: 70–74. 4. Carrasco C, Douas M, Miranda R, Castellanos M, Serena PA, et al. (2009) The capillarity of nanometric water menisci confined inside closed-geometry viral cages. P NATL ACAD SCI USA 106: 5475–5480. 5. Pugno NM (2008) Flexible nanovectors. Journal of Physics-Condensed Matter 20. 6. Fischlechner M, Donath E (2007) Viruses as building blocks for materials and devices. Angewandte Chemie-International Edition 46: 3184–3193. 7. 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Calabri L, Pugno N, Rota A, Marchetto D, Valeri S (2007) Nanoindentation shape effect: experiments, simulations and modelling. Journal of Physics- Condensed Matter 19. Imaging Viruses in Physiological Conditions Production of virus particles Purified MVM particles were obtained as described in [10]. w29 virions were produced as previously described [34,35] with modifications. Briefly, the B. subtilis strain 110NA (sup2) was infected with wild-type w29. The purification of the phage particles was performed using a one-step cesium chloride gradient standard technique (0.75 g/ml cesium chloride in TMS buffer at pH 7.8). The band corresponding to phage particles was extracted and dialyzed against TMS buffer. Supporting Information Text S1 A discussion of technical details of the manuscript can be found in the supplementary information text. (DOCX) Figure S1 w29 topographies obtained with high stiffness cantilevers (nominal stiffness 40 N/m). 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