"Janus" particles are asymmetric colloids with the ability to self-propel in an ionic solution when submitted to an AC electric field. Modifying the amplitude and frequency of the electric field results in a change of their individual motion (average velocity, type of motion,...) and of their mutual interactions. In this seminar, I will show how we can take advantage of it to target these swimmers to a specified location or induce a phase-transition of the suspension.