Biogenic nanosized iron oxides obtained from cultivation of iron bacteria from the genus Leptothrix.

A detailed investigation of nanostructured iron oxides/(oxy)hydroxides gathered after cultivation of bacteria from the genus Leptothrix as iron (II) oxidizers is presented. A specific type of medium is selected for the cultivation of the bacteria. Results for sediment powder and bio-film on glass substrate samples from the same media are discussed. XRD, Raman spectroscopy, SEM, and TEM images and PPMS measurements are used to prove the exact composition of the biogenic products and to interpret the oxidation process. Analysis of the data collected shows that around 80 % of the iron (II) from the growth medium has been transformed into iron (III) in the form of different (oxy)hydroxides, with the rest found to be in a mixed 2,5 valence in magnetite. Our investigation shows that the bio-film sample has a phase content different from that of the powdered biomass and that lepidocrocite (γ-FeOOH) is the predominant and the initial biogenic phase in both samples. Magnetite nanoparticles are a secondary product in the bio-film, part of which possesses a defective quasi-maghemite surface layer. In the powdered biomass, the oxidation steps are not fully completed. The initial products are non-stoichiometric and due to the mixed ferric and ferrous ions present, they develop into: (i) lepidocrocite (γ-FeOOH) as a basic sediment, (ii) magnetite (Fe3O4) and (iii) goethite (α-FeOOH) in small quantities. The average size of all iron-bearing particles is found to be below 30 nm. The magnetic measurements performed show a superparamagnetic behavior of the material at room temperature.

Investigation of iron-containing products from natural and laboratory cultivated Sphaerotilus-Leptothrix bacteria.

Bacterial biomass collected from sheath-forming bacteria of the genera Sphaerotilus and Leptothrix was collected from a high-mountain natural stream water source. The elemental constitution and oxide phases of the products after selective cultivation of the bacteria on two different elective media using neutron activation analysis (NAA), electron microscopy (SEM, TEM), and X-ray diffraction (XRD) were studied. A high enrichment level of iron was revealed by the NAA technique in cultivated isolates as compared to the reference sample from nature. Three types of iron oxide compounds were established after cultivation in Adler's medium: lepidocrocite (γ-FeOOH), magnetite (Fe3O4), and goethite (α-FeOOH). The cultivation in the Isolation medium yielded a single phase, that of goethite, excluding one sample with a distinguishable amount of lepidocrocite. XRD and EM investigations show that the biogenic oxides are nanosized. Our study exemplifies the possibilities of the biotechnology approach for obtaining, under artificial conditions, large quantities of iron-containing by-products that could be of further used in appropriate nano- and biotechnologies.

Retrieving true images through fine grid steps for enhancing the resolution beyond the classical limits: theory and simulations.

We developed the theory of, and tested by extended simulations, a novel method for retrieving true images in a grid step much finer than both the acquisition and the optical microscope limits. We believe that the method is promising in view of avoiding the limitations on the resolution improvement in direct imaging mode systems. Two basic concepts are involved: (i) random (up to 3D) relative displacements of objects with respect to the receiving matrix and (ii) the use of a reference object firmly fixed to small signal objects for avoiding the displacement measurements. The retrieved images are created by rearranging a set of true images acquired with a lower resolution equal to the matrix pixel size. We demonstrate the good quality of the retrieved images and the possibility to visualize and detect small (convolved) objects not observed into the captured images. The method provides good opportunities for effective applications of different inverse algorithms for improving the resolution requiring, as a rule, more precisely sampled images, but at arbitrary relations between the pixel size and the optical diffraction limit. We further demonstrated the application of some deconvolution procedures for extracting highly resolved images in the object and image planes in the presence of noise. The possibility to resolve small objects beyond the two classical limits is shown by means of simulations. The estimates for the method's limiting resolution, combined with proper deconvolution processing, show that resolution in the lower nano-dimension scale (below 10 nm) could be achieved. The requirements to the implementation of the novel method are commented as well.