  Red blood cells possess unique biomechanical ability to squeeze through
capillaries smaller than their size to enable gas and ion exchange. A key
signature of their active biomechanics is the out-of-equilibrium fluctuation of
the plasma membrane, also known as flickering motion. This active flickering is
driven by motor proteins that connect the forces between the spectrin skeleton
and the lipid bilayer. However, studying flickering motions in living red blood
cells is challenging without altering their physical properties. Here, we
implemented a holographic optical tweezer that sculpted a laser beam to create
a force field distributed directly along the membrane equatorial contour. We
show heterogeneous membrane flickering activity driven by membrane kickers in
free-standing cells. Then we inhibited the active kickers by optical forces
under minimal invasion, thus benchmarking the active motion against thermal
fluctuations. Our work paves the way for optical control of biophysical forces,
providing touchless strategies for mechanotransduction in living cells.
