Magnetic nanoparticles have been extensively studied in the past half century and continue to maintain interest because of their potential use in areas ranging from storage of high-density data to biomedical applications. In this work, we present magnetic Fe-, Ni- and Co-system nanoparticles prepared by chemical reduction of corresponding salts under a mild condition using hydrazine hydrate as reducing agent. Phase compositions, morphology and size of the nanoparticles were studied by X-ray diffraction, Field-emission SEM and energy-dispersive spectroscopy analysis. For biomedical applications, the nanoparticles were tested against bacteria E.coli and tests were performed using varying concentrations of Fe-, Ni- and Co-system nanoparticles.