A study of the growth curves of C. xerosis and E. coli Bacteria in Mediums Containing Cobalt Ferrite Nanoparticles. Marjorie Flores, Nanell Colón, Omayra Rivera, Nicole Villalba, Yahira Baez, David Quispitupa, Javier Avalos, Oscar Perales * . Department of Science and Technology, Universidad Metropolitana, San Juan, PR 00928-1150. * Department of General Engineering-Materials Science and Engineering, University of Puerto Rico, Mayaguez, P.R, Puerto Rico. ABSTRACT Previous publications 1 demonstrated the sensibility of the bacteria, when these were reproduced in mediums that contain nanoparticles of luminescent silicon. The mentioned effect takes place in the development of a bacteriological sensor. The present investigation is centered on the study of the growth curves of E. coli and C. xerosis, but now in the presence of nanosize particles of Cobalt Ferrite (CoFe 2 O 4 ) which were produced by the co-precipitation method in a watery phase. These nanoparticles present ferromagnetism characteristics (coercivity at room temperature among 600-5000 Oe for a size around 15-40nm). The experiment results evidence that the adaptation period of the bacteria, in contact with a stable suspension of nanoparticles of Ferrite, shows a growth curve of above the one obtained in absence of the nanoparticles (standard curve). The probable interaction of the electric polarity that these possess should be involved with the observed phenomena. INTRODUCTION Non invasive techniques like NMR are frequently used for taking images of human body parts. This is an example of the interaction of the magnetic field and the different bacteria that are in the human body, such as the E. coli, found in the intestinal region. The nanoparticles of Cobalt Ferrite allow a closer view of the interaction between the electric polarity of the bacteria and the external magnetic field from the Cobalt Ferrite; the results will show in the growth curves of the bacteria. There is an increasing interest in magnetic ferrite nanoparticles because of their broad applications in several technological fields including permanent magnets, magnetic fluids, magnetic drug delivery, microwave devices, and high-density information storage. Though Fe 2 O 3 and Co-doped magnetite are already being used in recording media, renewed interest is being shown in cobalt ferrite (CoFe 2 O 4 ), which is considered a potential candidate for high- density recording. This is because of its magnetic properties such as strong anisotropy and hence high coercivity at room temperature and moderate saturation magnetization, along with good mechanical hardness and chemical stability. Routes, the production of cobalt ferrite particles with the desirable size and magnetic properties, are still a challenge. Cobalt ferrite, CoFe 2 O 4 , is a spinel structure magnetic material which exhibita strong anisotropy and hence high coercivity, as well as moderate saturation magnetization at room- temperature. Applications for this material include permanent magnets, magnetic fluids, Mat. Res. Soc. Symp. Proc. Vol. 820 © 2004 Materials Research Society O8.17.1