Micrometric periodic assembly of magnetotactic bacteria and magnetic nanoparticles using audio tapes (original) (raw)
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IEEE Transactions on Magnetics, 2000
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 (Fe O ) and functionalized cobalt ferrite (CoFe O ) 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.
Nano Letters, 2004
Controlled assembly of magnetic nanoparticles was demonstrated by manipulating magnetotactic bacteria in a fluid with microelectromagnets. Magnetotactic bacteria synthesize a chain of magnetic nanoparticles inside their bodies. Microelectromagnets, consisting of multiple layers of lithographically patterned conductors, generate versatile magnetic fields on micrometer length scales, allowing sophisticated control of magnetotactic bacteria inside a microfluidic chamber. A single bacterium was stably trapped and its orientation was controlled; multiple groups of bacteria were assembled in a fluid. After positioning the bacteria, their cellular membranes were removed by cell lysis, leaving a chain and a ring of magnetic nanoparticles on a substrate.
Morphological Changes in Magnetotactic Bacteria in Presence of Magnetic Fields
2007
Nanomagnets manufactured by magnetotactic bacteria hold immense promise in magnetically directed drug delivery. In spite of discovery of these bacteria nearly three decades ago, it is not known how the bacteria are able to keep the nanomagnets trapped inside biological membranes (vesicles called magnetosomes). Understanding the physical nature of interactions, which these nanomagnets are capable of, is essential for envisaging any directed drug delivery application. We analyzed the morphology of two magnetic bacterial strains, Magnetospirillum magnetotacticum and Magnetospirillum gryphiswaldense, by defining the features of individual bacteria in two dimensions as length and width (in microns) under different magnetic fields using bar magnets. The control morphologies were taken to be the features of bacteria not under the influence of any magnetic field other than the earth's own. Using analysis of variance (ANOVA), we found statistically significant morphological changes in the M. magnetotacticum under different conditions. In contrast, there were no morphological differences observed for M. gryphiswaldense under any conditions. The width of M. magnetotacticum was found to be significantly higher for the control conditions compared to any magnetic condition. The length of M. magnetotacticum was found to be significantly lower when only south poles of the bar magnets (single or couple) were towards the bacteria. These results reflect a possible difference in packaging of magnetosomes inside two different strains of magnetic bacteria and imply that it may be important to select the right microbial source of nanomagnets (in contrast to using just any strain), trapped inside biological membranes, for potential targeted drug delivery applications, whereby enhanced sensitivity to external magnetic fields would be preferred.
PLoS ONE, 2013
Magnetotactic bacteria possess organelles called magnetosomes that confer a magnetic moment on the cells, resulting in their partial alignment with external magnetic fields. Here we show that analysis of the trajectories of cells exposed to an external magnetic field can be used to measure the average magnetic dipole moment of a cell population in at least five different ways. We apply this analysis to movies of Magnetospirillum magneticum AMB-1 cells, and compare the values of the magnetic moment obtained in this way to that obtained by direct measurements of magnetosome dimension from electron micrographs. We find that methods relying on the viscous relaxation of the cell orientation give results comparable to that obtained by magnetosome measurements, whereas methods relying on statistical mechanics assumptions give systematically lower values of the magnetic moment. Since the observed distribution of magnetic moments in the population is not sufficient to explain this discrepancy, our results suggest that non-thermal random noise is present in the system, implying that a magnetotactic bacterial population should not be considered as similar to a paramagnetic material.
Magnetic Colloids from Magnetotactic Bacteria: Chain Formation and Colloidal Stability
Langmuir, 2002
Single-domain magnetite (Fe3O4) crystals, harvested from magnetotactic bacteria, display on transmission electron micrographs the cluster morphologies (folded chains, flux-closure rings) predicted for magnetic colloids with dominant dipolar attractions. These strong attractions are responsible for the linear magnetite chains inside bacteria but do not affect the colloidal stability of the bacteria, as confirmed by analytic sedimentation experiments. Calculations of the interaction energy between dipole chains show that the magnetic component of the interbacteria interaction is negligible due to screening of dipolar forces: the bacteria sense only the geomagnetic field but not each other's compass.
The Nano-Magnetic Dancing of Bacteria Hand-in-Hand with Oxygen
Brazilian Archives of Biology and Technology
Magnetotactic bacteria are mostly microaerophilic found at the interface between oxic-anoxic zones. We report a magnetotactic bacterial strain isolated from an oil refinery sludge sample that grows aerobically in simple chemical growth medium, 9K. They open a new window of isolation of magnetic nanoparticles through an easy natural living system.
A Study of Magnetic Properties of Magnetotactic Bacteria
Biophysical Journal, 1986
The first direct measurements of magnetic properties of magnetotactic bacteria from natural samples are presented. Measurements were made at 4.2 K, using a Superconducting Quantum Interfering Device (SQUID) magnetometer. From the magnetization results an anisotropy is obtained that is typical of magnetized ferroor ferri-magnetic materials. The average magnetic moment of the bacteria determined from the results is in good agreement with the estimated moment from electron microscopy.
Magnetic-field induced rotation of magnetosome chains in silicified magnetotactic bacteria
Scientific reports, 2018
Understanding the biological processes enabling magnetotactic bacteria to maintain oriented chains of magnetic iron-bearing nanoparticles called magnetosomes is a major challenge. The study aimed to constrain the role of an external applied magnetic field on the alignment of magnetosome chains in Magnetospirillum magneticum AMB-1 magnetotactic bacteria immobilized within a hydrated silica matrix. A deviation of the chain orientation was evidenced, without significant impact on cell viability, which was preserved after the field was turned-off. Transmission electron microscopy showed that the crystallographic orientation of the nanoparticles within the chains were preserved. Off-axis electron holography evidenced that the change in magnetosome orientation was accompanied by a shift from parallel to anti-parallel interactions between individual nanocrystals. The field-induced destructuration of the chain occurs according to two possible mechanisms: (i) each magnetosome responds indivi...
Assessing bacterial magnetotactic behavior by using permanent magnet blocks
Chinese Science Bulletin, 2014
Assessing the movement of magnetotactic bacteria (MTB) under magnetic fields is a key to exploring the function of the magnetotaxis. In this study, a simple method was used to analyze the behavior of MTB, which was based on the accumulation of cells on the walls of a test tube when two permanent magnet blocks were applied on the tube. Experimental results showed a significant difference among the movements of the polar MTB, axial MTB, and ferrofluid. The polar magnetotactic cells aggregated as spots above or below the two magnet blocks besides the aggregated spots underneath the magnet blocks. By contrast, the axial magnetotactic cells aggregated only as two round spots underneath the magnet blocks, and more cells aggregated in the center than all around of the spot. For the ferrofluid, two spots were also formed underneath the magnet blocks, and the aggregated particles formed a ring shape. Magnetic calculation by finite element method was used to analyze the phenomenon, and the findings were reasonably explained by the MTB features and magnetic field theory. A scheme that differentiates polar MTB, axial MTB, and magnetic impurity could be developed, which would be beneficial to fieldworks involving MTB in the future.