Magneto-optical tweezers built around an inverted microscope

We present a simple experimental setup of magneto-optical tweezers built around an inverted microscope. Two pairs of coils placed around the focal point of the objective generate a planarrotating magnetic field that is perpendicular to the stretching direction. This configuration allows us to control the rotary movement of a paramagnetic bead trapped in the optical tweezers. The mechanical design is universal and can be simply adapted to any inverted microscope and objective. The mechanical configuration permits the use of a rather large experimental cell and the simple assembly and disassembly of the magnetic attachment.