  Non-invasive optical manipulation of particles has emerged as a powerful and
versatile tool for biological study and nanotechnology. In particular, trapping
and rotation of cells, cell nuclei and sub-micron particles enables unique
functionality for various applications such as tissue engineering, cancer
research and nanofabrication. We propose and demonstrate a purely optical
approach to rotate and align particles using the interaction of polarized light
with photonic crystal nanostructures to generate enhanced trapping force. With
a weakly focused laser beam we observed efficient trapping and transportation
of polystyrene beads with sizes ranging from 10 um down to 190 nm as well as
cancer cell nuclei. In addition, we demonstrated alignment of non-spherical
particles using a 1-D photonic crystal structure. Bacterial cells were trapped,
rotated and aligned with optical intensity as low as 17 uW/um^2.
Finite-difference time domain (FDTD) simulations of the optical near-field and
far-field above the photonic crystal nanostructure reveal the origins for the
observed results. This approach can be extended to using 2-D photonic crystal
nanostructures for full rotation control.
