(a) Magnetism engineering of magnetic nanoparticles for effective force generation. By tuning the size, composition, and shape of magnetic nanoparticles, a higher saturation magnetization (Ms), which is a critical factor for force generation, can be achieved. (b) Magnetoplasmonic nanoparticles (MPNs). (i) A MPN is comprised of a magnetic core and a plasmonic shell that serve as the force-generating and imaging components, respectively. (ii) Silica core size (dc)-dependent plasmonic absorption shift. ts indicates thickness of gold shells. TEM images (top) of 50 nm MPNs with 20 nm (left), 25 nm (middle) and 30 nm (right) silica cores and their corresponding scattering images (bottom). (iii) Absorption spectra of 50 nm MPNs with 20 nm, 25 nm and 30 nm silica cores. Reproduced with permission from ref 20, copyright 2017 Nature Publishing Group.