  Acoustical tweezers based on focused acoustical vortices open some tremendous
perspectives for the in vitro and in vivo remote manipulation of millimetric
down to micrometric objects, with combined selectivity and applied forces out
of reach with any other contactless manipulation technique. Yet, the synthesis
of ultra-high frequency acoustical vortices to manipulate precisely micrometric
objects remains a major challenge. In this paper, the synthesis of a 250 MHz
acoustical vortex is achieved with an active holographic source based on
spiraling interdigitated transducers. It is shown that this ultra-high
frequency vortex enables to trap and position individual particles in a
standard microscopy environment with high spatial selectivity and nanoNewton
forces. This work opens perspectives to explore acoustic force spectroscopy in
some force ranges that were not accessible before.
