We describe fractionation of sub-micron vesicles and particles suspended in high conductivity electrolytes using an electrokinetically biased Deterministic Lateral Displacement (DLD) device. An optimised, asymmetric array of micron-sized pillars and gaps, with an AC electric field applied orthogonal to the fluid flow gives an approximately ten-fold reduction in the intrinsic critical diameter (Dc) of the device. The asymmetry in the device maximises the throughput. Fractionation of populations of 100 nm and 400 nm extruded vesicles is achieved in 690 mS m-1 KCl, and 100 nm, 200 nm and 500 nm polystyrene particles in 105 mS m-1 KCl. The electrokinetically biased DLD may provide solutions for simple and rapid isolation of extracellular vesicles.