  Trapping nanoscopic objects to observe their dynamic behaviour for extended
periods of time is an ongoing quest. Particularly, sub-100nm transparent
objects are hard to catch and most techniques rely on immobilisation or
transient diffusion through a confocal laser focus. We present an Anti-Brownian
ELectrokinetic trap (pioneered by A. E. Cohen and W. E. Moerner) to hold
nanoparticles and individual FoF1-ATP synthase proteins in solution. We are
interested in the conformational dynamics of this membrane-bound rotary motor
protein that we monitor using single-molecule FRET. The ABELtrap is an active
feedback system cancelling the nano-object's Brownian motion by applying an
electric field. We show how the induced electrokinetic forces confine the
motion of nanoparticles and proteoliposomes to the centre of the trap.
