Mapping Viscoelastic Properties Using Helical Magnetic Nanopropellers.

Artificial micro/nanomachines have been envisioned and demonstrated as potential candidates for targeted drug or gene delivery, cell manipulation, environmental and biological sensing and in lab on chip applications. Here, we have used helical nanomachines to measure the local rheological properties of a viscoelastic media. The position of the helical nanomachine/ nanopropeller was controlled precisely using magnetic fields with simultaneous measurements of the mechanical properties of a complex and heterogeneous fluidic environment. We demonstrated that the motion of the helical nanopropeller is extremely sensitive to fluid elasticity and the speed of propulsion of the nanopropeller can be used as a measure of the local elastic relaxation time. Taken together, we report a promising new technique of mapping the rheological properties by helical nanopropellers with very high spatial and temporal resolutions, with performance superior to existing techniques of passive or active microrheology.