  Near-field patterns of light provide a way to optically trap, deliver and
sort single nanoscopic particles in a wide variety of applications in
nanophotonics, microbiology and nanotechnology. Using rigorous electromagnetic
theory, we investigate the forces and trapping performance of near-field
optical tweezers carrying spin and orbital angular momenta. The trapping field
is assumed to be generated by a total internal reflection microscope objective
at a glass-water interface in conditions where most of the transmitted light is
evanescent. We find novel aspects of these tweezers, including the possibility
to rotate and stably trap nanoscopic beads. More importantly, we show that,
under near-field conditions, the contributions of of spin and orbital angular
momenta to the rotation of small particles are almost equivalent, opening the
possibility to cancel each other when they have opposite sign. We show that
these conditions result in optimal optical trapping, giving rise to extremely
effective optical tweezers for nanomanipulation, having both circular symmetry
and relatively weak rotation.
