  We report a simple and versatile waterborne synthesis of magnetic nanowires
following the innovative concept of electrostatic "desalting transition".
Highly persistent superparamagnetic nanowires are generated from the controlled
assembly of oppositely charged nanoparticles and commercially available
polyelectrolytes. The wires have diameters around 200 nm and lengths comprised
between 1 {\mu}m and 1/2 mm, with either positive or negative charges on their
surface. Beyond, we show that this soft-chemistry assembly approach is a
general phenomenon independent of the feature of the macromolecular building
blocks, opening significant perspectives for the design of multifunctional
materials.
