  The ability to control the location of nanoscale objects in liquids is
essential for fundamental and applied research from nanofluidics to molecular
biology. To overcome their random Brownian motion, the electrostatic fluidic
trap creates local minima in potential energy by shaping electrostatic
interactions with a tailored wall topography. However, this strategy is
inherently static -- once fabricated the potential wells cannot be modulated.
Here, we propose and experimentally demonstrate that such a trap can be
controlled through a buried gate electrode.We measure changes in the average
escape times of nanoparticles from the traps to quantify the induced
modulations of $0.7k_\rm{B}T$ in potential energy and 50 mV in surface
potential. Finally, we summarize the mechanism in a parameter-free predictive
model, including surface chemistry and electrostatic fringing, that reproduces
the experimental results. Our findings open a route towards real-time
controllable nanoparticle traps.
