presents a schematic representation of the two-step synthesis and purification process of mpGNS. In the first step, Fe3O4 seeds were coated with polydopamine (PDA), which enhances gold deposition and formation of spikes. In the second step, mpGNS was synthesized and purified by adding HAuCl4, AgNO3, and ascorbic acid in a 2:2:1 ratio. To obtain different mpGNS morphologies (mpGNS-1, mpGNS-2, and mpGNS-3), three distinct concentrations of these reagents were used while maintaining the fixed ratio. Notably, this surfactant-free synthesis method results in gold nanostar impurities, which can be effectively removed via magnetic purification. Figure displays 3D models of the mpGNS structure and its various morphologies.