  Externally controlled motion of micro and nanomotors in a fluid environment
constitutes a promising tool in biosensing, targeted delivery and environmental
remediation. In particular, recent experiments have demonstrated that fuel-free
propulsion can be achieved through the application of external magnetic fields
on magnetic helically shaped structures. The magnetic interaction between
helices and the rotating field induces a torque that rotates and propels them
via the coupled rotational-translational motion. Recent works have shown that
there exist certain optimal geometries of helical shapes for propulsion.
However, experiments show that controlled motion remains a challenge at the
nanoscale due to Brownian motion that interferes with the deterministic motion
and makes it difficult to achieve controlled steering. In the present work we
employ quantitatively accurate simulation methodology to design a setup for
which magnetic nanohelices of 30 nm in radius, with and without cargo, can be
accurately propelled and steered in the presence of thermal fluctuations. In
particular, we demonstrate fast transport of such nanomotors and devise
protocols in manipulating external fields to achieve directionally controlled
steering at biologically relevant temperatures.
