Encased cantilevers for low-noise force and mass sensing in liquids

Viscous damping severely limits the performance of resonator based sensing in liquids. We present encased cantilevers that overcome this limitation with a transparent and hydrophobic encasement built around the resonator. Only a few micrometers of the cantilever probe protrude from the encasement and water does not enter the encasement. This maintains high Q-factors and reduces the thermo-mechanical noise levels by over one order of magnitude and reaches minimal detectable forces of 12 fN/·Hz in liquids. These probes expand the frontiers of cantilever based sensing. We discuss their design and fabrication with special focus on squeeze film damping and demonstrate their successful application for quantitative mass sensing of single nanoparticles and gentle Atomic Force Microscopy imaging of soft matter in liquids.