Spatial Resolution in Micrometric Periodic Assemblies of Magnetotactic Bacteria and Magnetic Nanoparticles

We developed a simple method for obtaining micro arrays of magnetic nanoparticles using audio tapes. We present spatial micro-arrangements of magnetotactic bacteria (Magnetospirillum gryphiswaldense), magnetite (Fe₃O₄) and functionalized cobalt ferrite (CoFe₂O₄) nanoparticles. Computer generated square audio waves of different frequencies (100 Hz-10 kHz) were recorded leading to magnetic patterns of different micrometer spatial wavelengths. Drops of aqueous suspensions were deposited on the tapes to control particle density, and bacteria and particles were trapped at locations where magnetic energy is minimized, as observed using conventional optical microscopy after the dispersium medium was evaporated. We discuss the spatial limits of the magnetic nanoparticles and the bacteria assemblies, concluding that cell walls of bacteria inhibit agglomeration and optimize spatial organization.