  Directed high-speed motion of nanoscale objects in fluids (nano swimmers) can
have a wide range of applications like molecular machinery, nano robotics, drug
delivery, and material assembly. Here, we report ballistic plasmonic Au
nanoparticle (NP) swimmers with unprecedented speeds realized by not only
optical pushing but also pulling forces from a single Gaussian laser beam. Both
the optical pulling and high swimmer speeds are made possible by a unique
NP-laser interaction. The Au NP excited by the laser at the surface plasmon
resonance peak can generate a nanoscale bubble, which can encapsulate the NP
(i.e., supercavitation) to create a virtually frictionless environment for it
to move, like the Leidenfrost effect. While optical forces are mostly positive,
certain NP-bubble configurations can lead to negative optical forces that pull
the NP to swims against the photon stream. The demonstrated ultra-fast,
light-driven NP movement may benefit a wide range of nano- and bio-applications
and provide new insights to the field of negative optical force.
