We demonstrate on-chip manipulation of individual nanoparticles in suspension with active control of position at the nanometer scale, through the control of the motion of geometrically constrained domain walls (DWs) in magnetic nano-conduits. Magnetic nanoparticles are captured by the stray field of a DW and their transport and release is obtained via precise control over DW nucleation, displacement, and annihilation processes. In comparison with other manipulation techniques, our approach is unique because it combines the true single nano-particle manipulation ability at the nanoscale and the compatibility with lab-on-chip applications. As magnetic nano-particles are widely used for tagging molecules or cells, our method holds great potential for biological applications involving manipulation, transport and sorting of molecules and cells on surfaces. This work opens the way towards the realization of microchip …