AFM tips: how sharp are they?

From both simple estimates and a 'blind' reconstruction based on cryo-AFM i mages of filamentous actin, we find that the radius of curvature at the ape x of Si3N4 tips can be as small as 1 nm with a conical angle in the range 3 0 similar to 40 degrees, revealing a relatively high aspect ratio that is m uch greater than previously anticipated. Our results show that commercially available cantilevers are often sharp enough for routine high resolution i maging of biological materials, and suggest that factors other than an inhe rent blunt tip are probably responsible for frequent occurrences of poor re solution.