Figure 1.

Setup for rotational actuation of particles and proteins. (a) Magnetic particles are bound to a glass substrate by means of the Protein G–IgG complex or the IgG–IgG complex. (b) Inside a fluid cell, the particles are actuated by a rotating magnetic field generated by a quadrupole electromagnet with slanted (45°) soft-iron pole tips. (c) The particle orientation is visualized by means of attached small green fluorescent spheres. The bright spot at the center of the particle is an artifact due to the applied bright-field light. The bright spot is exploited to track the particle center.