A magnified image of the nanoparticle distribution on the silica surface is clearly shown in Figures . Few layers of nanoparticles of size ranging between 11-13 nm can be seen firmly resting on the surfaces of the silica helices (Figure ). A careful investigation using high-resolution transmission electron microscopy (HR-TEM) could even detect the presence of isolated crystalline nanoparticles impregnated on the silica surface, characterized by welldefined atomic planes corresponding to Fe3O4 (Figure ). The mechanism of bonding of SPIONs to the silica surface is somewhat interesting, and may be attributed to the formation of stable Fe-O-Si(OH)3 bonds as described elsewhere . The Scanning transmission electron microscope (STEM) mode of imaging has been implemented to quantitatively evaluate the elemental composition of the helices. The STEM image of a typical SPIONs-NR depicting the presence of silicon (Si: Blue) and iron (Fe: Red) is shown in Figure . The relative concentration of silicon and iron expressed in % wt., is understood by the mass fraction, expressed as, Si:Fe ~ 60:40. The duration of hold time (microwave time) and the quantity of nanoparticles used for the microwave coating are the two primary factors which decides the nanoparticle thickness on the silica helices (for details see Supporting Information). The number of nanoparticle stacks adhering to the silica surface can easily be tuned by altering the microwave heating time and the concentration of the precursor nanoparticle dispersion. This is quite unique in a way as one can accordingly control the nanoparticle concentration, or in other words, the magnetic moment of these helices simply by manipulating these two parameters.