Radiofrequency Stimuli Applied to Suspensions Containing Biogenic Magnetite Nanocrystals: Absorbed Energy Conversion Simona Miclaus 1 , Paul Bechet 4 Department of Technical Sciences “Nicolae Balcescu” Land Forces Academy Sibiu, Romania George Mihai 2 LICETER Laboratory ANCOM Prejmer, Romania Cristina Moisescu 3 , Ioan I. Ardelean 5 Department of Microbiology Institute of Biology Bucharest, Romanian Academy, Bucharest, Romania Simona Oancea 7 , Mihaela Racuciu 8 “Lucian Blaga” University Sibiu, Romania Lucian Barbu Tudoran 6 , Teodora Maria Radu 9 National Institute for R&D of Isotopic and Molecular Technologies Cluj-Napoca, Romania x Abstract—Water-based suspensions of magnetotactic bacteria (MTB) containing magnetite (Fe3O4) nanocrystals in the form of magnetosomes (MS) chained inside the bacteria cells have been exposed to radiofrequency fields with the aim of observing how the electromagnetic energy is converted and expressed as thermal or non-thermal effects. A wide frequency band was tested, (0.1-2.9) GHz, by applying continuous wave stimuli. Significant field strength components were provided and characterized, by using a GTEM cell and adequate expo- dosimetric instruments. The heating rates of the suspensions were measured. Because the recorded values were very low, non- thermal expression of energetic conversion was further investigated by scanning-transmission electron microscopy methods, by various spectroscopic means and by electrical conductivity determinations. Clear non-thermal effects were revealed, which need further research. Keywords—magnetosomes; magnetotactic bacteria; electromagnetic energy; thermal and non-thermal. I. INTRODUCTION Iron oxide nanoparticles of magnetite and maghemite (oxidized form) smaller than 100 nm have a unique superparamagnetic behavior, allowing their remote manipulation by non-static magnetic fields. In the last years they received significant attention in many applications - from which the biomedical ones (i.e. magnetic hyperthermia, magnetic resonance imaging), are maybe the most prominent [1], [2], because these particles are biocompatible and non- toxic and ensure great medical support. The highest quality magnetite nanoparticles are the biogenic ones, and they are produced naturally by magnetotactic bacteria (MTB) in the form of magnetosomes (MS), which are organelles containing endogenous magnetite crystals surrounded by lipid-bilayer membranes and arranged in chains inside the bacteria cells [3], [4]. Synthetic magnetite nanoparticles were mostly investigated for some years, but in the frequency bands of a few hundreds of kHz – especially for hyperthermic interests, while biogenic magnetite crystals are still scarcely analyzed for their response in varied applications, and in particular in larger radiofrequency (RF) ranges [5], [6]. Present work focused on the quantification of the responses of water-based suspensions of MTB containing MS to electromagnetic field (EMF) exposure in the frequency range 100 MHz-2.9 GHz by assessing: a) the heat transformation of the RF energy in this range; b) by modifications highlighted in electronic microscopy images of bacterial cells and MS chains; c) by changes in the transmittance of visible up to infrared radiations after the RF exposure of the suspension; d) by the variation of the static electrical conductivity. II. MATERIALS AND METHODS Magnetospirillum gryphiswaldense (strain DSM 6361) [7], [8], was cultured in specific laboratory conditions as described previously in [9]. After they reached stationary growth phase the cells were harvested by centrifugation and fixed in 1% formalin saline solution (0.9% NaCl) forming the suspension for the experiments. Bacterial concentration (cells/ml) was determined spectrophotometrically using the calibration curve of optical density at 565 nm, versus direct cell counts.