Optical trapping of small particles typically requires
the use
of high NA microscope objectives. Photonic metasurfaces are an attractive
alternative to create strongly focused beams for optical trapping
applications in an integrated platform. Here, we report on the design,
fabrication, and characterization of optical metasurfaces with a numerical
aperture up to 1.2 and trapping stiffness greater than 400 pN/μm/W.
We demonstrate that these metasurfaces perform as well as microscope
objectives with the same numerical aperture. We systematically analyze
the impact of the metasurface dimension on the trapping performance
and show efficient trapping with metasurfaces with an area as small
as 0.001 mm2. Finally, we demonstrate the versatility of
the platform by designing metasurfaces able to create multisite optical
tweezers for the trapping of extended objects.