A cost-effective biodegradable droplet-based 3D-printed device for synthesis of superparamagnetic iron oxide (magnetite, Fe3O4) and metallic (silver, Ag and gold, Au) nanoparticles is demonstrated. The device was successful in confining the reagents in droplets and allowing a sequential flow of droplets to obtain uniform shape and size of both magnetic and metallic nanoparticles, an important characteristic for biomedical and sensing applications. Translating a conventional macroscale glassware-based to a fluidic-based synthesis involved a simple optimization in flow rates of dispersed (aqueous solutions of reagents) and continuous (oil) phases to fine tune the shape and size of magnetic and metallic nanomaterials. TEM confirmed the Fe3O4 and Ag/Au nanoparticles to possess nanoplate and sphere-shaped morphology, respectively. Further, utilization of gravitational force allowed a hassle-free controlled synthesis of nanoparticles, without any clogging of channel walls. Graphical abstract