Figure presents the TEM image of Fe3O4@PDA, revealing an average seed size of 300 ± 60 nm. Figure displays the TEM image of the mpGNS-3 system synthesized at a 2:2:1 chemical ratio, showing the formation of two distinct types of nanostars-small and large. Given that the core of mpGNS reached approximately 202 nm, we inferred that the smaller nanostars were gold nanostars, likely impurities. To eliminate these impurities, we conducted magnetic separation, which successfully removed the small gold nanostars, as confirmed by the absence of small nanostars in the purified sample. ). To investigate the elemental distribution of the mpGNS-3 nanoparticles, we performed energy-dispersive X-ray (EDX) spectroscopy (Figure ), confirming that Fe is localized at the core, while Au and Ag are distributed on the surface. The elemental line profile of mpGNS-3 further supports this distribution, validating the successful formation of the magneticplasmonic nanostructure. Additionally, the STEM-EDX image of multiple mpGNS-3 nanoparticles demonstrates a highly monodisperse morphology, with Fe confined to the core and Au and Ag coating the surface (Figure ). The absorbance spectra of the nanoparticles reveal that the plasmon peak of mpGNS is red shifted from 544 nm to the 1054 nm range (Figure ). As expected, the formation of sharp branches on the mpGNS increases progressively from mpGNS-1 to mpGNS-3, resulting in stronger LSPR effects. Consequently, the absorbance peak undergoes a red shift, and the peak intensity significantly increases compared to that of the iron oxide nanoparticles.