  Near-field optics can overcome the diffraction limit by creating strong
optical gradients to enable the trapping of nanoparticles. However, it remains
challenging to achieve efficient stable trapping without heating and thermal
effects. Dielectric structures have been used to address this issue, but they
usually offer weak trap stiffness. In this work, we exploit the Fano resonance
effect in an all-dielectric quadrupole nanostructure to realize a twenty-fold
enhancement of trap stiffness, compared to the off-resonance case. This enables
a high effective trap stiffness of $1.19$ fN/nm for 100 nm diameter polystyrene
nanoparticles with 3.5 mW/$\mu$m$^{2}$ illumination. Furthermore, we
demonstrate the capability of the structure to simultaneously trap two
particles at distinct locations within the nanostructure array.
