Evanescent light scattering with magnetic colloids

We measure magnetic interactions between paramagnetic colloidal beads and an external magnetic field by using total internal reflection microscopy (TIRM). Our results demonstrate that TIRM can be applied to absorptive paramagnetic probe particles and thus extends the range of interaction types which can be addressed with this method. With our setup, we can detect magnetic forces on single superparamagnetic particle ranging from about 10 to 600 fN.publishe