Nanowires as AFM cantilevers: A detection scheme to gently image and interact with soft materials in fluids

Performing AFM on soft materials in fluids (e.g., living cells) is challenging due to their easy deformation by the tip. The thermal force-noise of the cantilever is the principal limitation to reducing sample deformation and minimizing a cantilever's cross- section reduces its noise significantly. However, the minimum size of the cantilever is currently limited by a conventional deflection detection scheme, which requires a large surface area for laser specular reflection. Here we develop an optical technique to use nanowires as cantilevers, and show that we achieve a force noise in water that is orders of magnitude gentler than conventional AFM. This is a significant milestone towards non-invasive scanning probe imaging of biological processes on the surfaces of vesicles and cell membranes.