We demonstrate a single-step facile approach for the synthesis of glycine (amino acid) passivated Fe3O4 magnetic nanoparticles (GMNPs) using soft chemical route. The surface passivation of Fe3O4 nanopartides with glycine molecules was evident from infrared spectroscopy, thermal and elemental analyses, and light scattering measurements. These nanoparticles show better colloidal stability, good magnetization, excellent self-heating capacity under external AC magnetic field and cytocompatibility with cell lines. Further, the active functional groups (-NH2) present on the surface of Fe3O4 nanoparticles can be accessible for routine conjugation of biomolecules/biolabelling through well-developed bioconjugation chemistry. Specifically, a new colloidal glycine passivated biocompatible Fe3O4 nanoparticles with excellent specific absorption rate (SAR) have been fabricated, which can be used as an effective heating source for hyperthermia treatment of cancer (thermal therapy). (C) 2011 Elsevier Inc. All rights reserved.