Magnetic iron oxide nanoparticles (NPs) have intrinsic advantages over other NPs for various biomedical applications. These advantages include visualization under Magnetic Resonance Imaging (MRI), heating with Radiofrequency (RF), and movement in a magnetic field. There are now numerous efforts to expand the applications of these particles for non-invasive drug and adjuvant delivery, cellular imaging and in vitro cell sorting and purification. In the present study, we describe methods to (i) assess and quantify NP cell association (ii) facilitate NP heat destruction of cells after association with RF and laser. First, we show that (i) the cell association of iron oxide NPs is dependent on the surface coating (surfactant greater than dextran), time, cell-type and extracellular NP concentrations (saturation with concentration and time). Furthermore, the association fits a simple enzyme Michealis-Menten model. Second, (ii) improved heat destruction of cells can be achieved after laser irradiation compared to traditional RF treatment for similar NP associations. These results and assays show promise for cell sorting and purification applications.