We demonstrate a single-step ultrasonic in situ complexation of salicylic acid during the growth of Fe3O4-reduced graphene oxide nanoparticles (∼10 nm) to improve the antioxidant and antiproliferative effects of pristine drug molecules. These nanoparticles have a precisely defined electronic molecular structure with salicylic acid ligands specifically complexed to Fe­(III)/Fe­(II) sites, four orders of magnitude larger electric surface potential, and enzymatic activity modulated by ascorbic acid molecules. The diminishing efficiency of hydroxyl radicals by Fe3O4-rGO-SA nanoparticles is tenfold higher than that by pristine salicylic acid in the electro-Fenton process. The H+ production of these nanoparticles can be switched by the interaction with ascorbic acid ligands and cause the redox deactivation of iron or enhanced antioxidation, where rGO plays an important role in enhanced charge transfer catalysis. Fe3O4-rGO-SA nanoparticles are nontoxic to erythrocytes, i.e., human peripheral blood mononuclear cells, but surpassingly inhibit the growth of three cancer cell lines, HeLa, HepG2, and HT29, with respect to pristine salicylic acid molecules.