Applying Maxwell stress tensor and 3D FDTD methods, physical properties of nanoparticle trapping by evanescent wave
near the NSOM probe, including trapping size, trapping position and role of other forces versus optical trapping force,
are revealed. From the distribution of trapping force acted on a nanoparticle along three axis directions, it is found that
the nanoparticle tends to be trapped to the aperture edge and center surface of the probe tip. In experiments 120 nm
polystyrene particles are trapped in a multi-circular shape and two circles of polystyrene particles are arranged to
different positions on the substrate. The results indicate that the NSOM probe is able to trap nanoparticles with lower laser intensity than that required by conventional optical manipulator.