Self-assembled NEMS for pN force detection

Hand brushing of a 3 wt% aqueous solution of polyethylene oxide over a micropillar array, produces a bead-on-a-string (BOS) NEMS structure through a process of capillary-driven self-assembly. The structure is unique in that the highly entangled polymer chains lead to the formation of a nanofiber, 50 - 200 nm diameter, that supports a 10 - 25 micron bead at its midpoint. These structures form even with the inclusion in the polymeric solution of magnetic iron oxide nanoparticles and nanorods below a critical length. The measured force-displacement response (to air streams and magnetic fields) is on the order of 10 picoNewton per micron (pN/μm); i.e., 10 pN, the limiting sensitivity of commercial atomic force microscopes, would be readily detectable under optical microscopes.