In an embodiment, the present disclosure pertains to a method of making magnetic nanoparticles through the utilization of a microfluidic reactor. In some embodiments, the microfluidic reactor includes a first inlet, a second inlet, and an outlet. In some embodiments, the method includes applying a magnetic nanoparticle precursor solution into the first inlet of the microfluidic reactor through a first flow rate and applying a reducing agent into the second inlet of the microfluidic reactor through a second flow rate. In some embodiments, the magnetic nanoparticles are produced in the microfluidic reactor and collected from the outlet of the microfluidic reactor. In an additional embodiment, the present disclosure pertains to a composition including a plurality of magnetic nanoparticles. In a further embodiment, the present disclosure pertains to a microfluidic reactor.