Timothy Gutu

Metabolic Insertion of Nanostructured TiO2 into the Patterned Biosilica of the Diatom Pinnularia sp by a Two-Stage Bioreactor Cultivation Process

Diatoms are single-celled algae that make silica shells or frustules with intricate nanoscale features imbedded within periodic two-dimensional pore arrays. A two-stage photobioreactor cultivation process was used to metabolically insert titanium into the patterned biosilica of the diatom Pinnularia sp. In Stage I, diatom cells were grown up on dissolved silicon until silicon starvation was achieved. In Stage II, soluble titanium and silicon were continuously fed to the silicon-starved cell suspension (approximately 4 x 10(5) cells/mL) for 10 h. The feeding rate of titanium (0.85-7.3 micromol Ti L(-1) h(-1)) was designed to circumvent the precipitation of titanate in the liquid medium, and feeding rate of silicon (48 micromol Si L(-1) h(-1)) was designed to sustain one cell division. The addition of titanium to the culture had no detrimental effects on cell growth and preserved the frustule morphology. Cofeeding of Ti and Si was required for complete intracellular uptake of Ti. The maximum bulk composition of titanium in the frustule biosilica was 2.3 g of Ti/100 g of SiO(2). Intact biosilica frustules were isolated by treatment of diatom cells with SDS/EDTA and then analyzed by TEM and STEM-EDS. Titanium was preferentially deposited as a nanophase lining the base of each frustule pore, with estimated local TiO(2) content of nearly 80 wt %. Thermal annealing in air at 720 degrees C converted the biogenic titanate to anatase TiO(2) with an average crystal size of 32 nm. This is the first reported study of using a living organism to controllably fabricate semiconductor TiO(2) nanostructures by a bottom-up self-assembly process.

ZnO-nanoparticle-coated carbon nanotubes demonstrating enhanced electron field-emission properties

Multiwalled carbon nanotubes (CNTs) were coated, using atomic layer deposition, with a thin layer of ZnO and subsequently annealed. Studies of the morphologies of the ZnO-coated CNTs revealed no significant change in the internal structures (multiwalled graphite sheets) and the diameters of the CNTs, but the ZnO appeared to form bead-shaped single crystalline particles attaching to the surface of the nanotubes. The electron field-emission properties of the ZnO-coated CNTs were dramatically improved over both uncoated CNTs and ZnO nanowires. It is reasoned that numerous ZnO “nanobeads” on the surface of the nanotubes serve as additional emission sites, in addition to the tips of CNTs, and result in the enhancement of electron field emission.

Lanthanide(III)-Doped Magnetite Nanoparticles

Nearly monodisperse lanthanide-doped magnetite nanoparticles were obtained by thermally decomposing a mixture of Fe(acac)(3) and Ln(acac)(3) (acac = acetylacetonate; Ln = Sm, Eu, Gd) in the presence of passivating surfactants. Magnetic studies revealed room-temperature ferromagnetic behaviors of these doped nanoparticles, distinctly different from those of the undoped parent magnetite or the doped nanoparticles prepared by a coprecipitation method.

Self-Assembly of Nanostructured Diatom Microshells into Patterned Arrays Assisted by Polyelectrolyte Multilayer Deposition and Inkjet Printing

Individual shells of the diatom Coscinodiscus were self-assembled into a rectangular array on a glass surface that possessed a polyelectrolyte multilayer patterned through inkjet printing. This patterned thin film possessed hierarchical order with nanostructure provided by the diatom biosilica. The process used two polyelectrolytes with opposite electric potentials to control the surface charge of the substrate. The fine features of the diatom frustules were perfectly preserved as a result of the mild conditions of the deposition process. This technique has the potential to enable large-scale device applications that harness the unique properties of functionalized diatom biosilica.

Peptide-mediated deposition of nanostructured TiO(2) into the periodic structure of diatom biosilica

Diatoms are single-celled algae that make silica shells called frustules that possess periodic structures ordered at the micro- and nanoscale. Nanostructured titanium dioxide (TiO(2)) was deposited onto the frustule biosilica of the diatom Pinnularia sp. Poly-L-lysine (PLL) conformally adsorbed Onto Surface of the frustule biosilica. The condensation of soluble Ti-BALDH to TiO(2) by PLL-adsorbed diatom biosilica deposited 1.32 +/- 0.17 g TiO(2)/g SiO(2) onto the frustule. The periodic pore array of the diatom frustule served as a template for the deposition of the TiO(2) nanoparticles, which completely filled the 200-nm frustule pores and also Coated the frustule Outer Surface. Thermal annealing at 680 degrees C converted the as-deposited TiO(2) to its anatase form with an average nanocrystal size of 19 nm. as verified by x-ray diffraction. electron diffraction, and SEM/TEM. This is the first reported Study of directing the peptide-mediated deposition of TiO(2) into a hierarchical nanostructure using a biologically fabricated template.

Fabrication of carbon nanotube-based nanodevices using a combination technique of focused ion beam and plasma-enhanced chemical vapor deposition

This study focuses on the fabrication of two nanodevice prototypes which utilized vertical and horizontal carbon nanotubes used the focused ion beam to localize the catalysts, followed by plasma-enhanced chemical vapor deposition. First, metal-gated carbon nanotube field emitter arrays were fabricated on multilayer substrates containing an imbedded catalyst layer. Second, horizontally aligned single-walled carbon nanotubes were grown on a transmission electron microscopy grid. This allows the carbon nanotubes to be directly analyzed in a transmission electron microscope. It is expected that the methodology introduced here will open up opportunities for the direct fabrication of carbon nanotube based nanodevices.

Electron microscopy and optical characterization of cadmium sulphide nanocrystals deposited on the patterned surface of diatom biosilica

Intricately patterned biosilica obtained from the shell of unicellular algae called diatoms serve as novel templates for fabrication of optoelectronic nanostructures. In this study, the surface of diatom frustules that possessed hierarchical architecture ordered at the micro and nanoscale was coated with a nanostructured polycrystalline cadmium sulphide (CdS) thin film using a chemical bath deposition technique. The CdS thin film was composed of spherical nanoparticles with a diameter of about 75 nm. The CdS nanoparticle thin film imparted new photoluminescent properties to the intricately patterned diatom nanostructure. The imparted photoluminescent properties were dependent on the CdS coverage onto the frustules surface. The intrinsic photoluminescent properties of the frustules were strongly quenched by the deposited CdS. The origin of PL spectra was discussed on the basis of the band theory and native defects.

Biogenic silica based Zn2SiO4:Mn2+ and Y2SiO5:Eu3+ phosphor layers patterned by inkjet printing process

We demonstrate herein the fabrication of patterned layers of Zn2SiO4:Mn2+ and Y2SiO5:Eu3+ phosphor materials based on nanostructured diatom biosilicavia the inkjet printing process.

Nanofabrication of Green Luminescent Zn2SiO4 : Mn Using Biogenic Silica

Chemical solution depostion of nanocrystalline Zn2SiO4:Mn on the biogenic silica frustule derived from the cultured marine diatom (Pinnularia sp.) is reported. Our deposition process uses rather simple chemistry that consists of only metal halides and water. Two types of nanostructures can be generated, depending upon the level of the initial chemical deposition coverage. The nanostructured Zn2SiO4:Mn exhibited bright green photoluminescence. The intricate micro and nanostructures of the frustule were preserved after the chemical solution deposition and postannealing processes. (c) 2007 The Electrochemical Society.

Thermal annealing activates amplified photoluminescence of germanium metabolically doped in diatom biosilica

There is significant interest in the fabrication of germanium (Ge) doped silica for optoelectronic device applications. In this study, highly photoluminescent Ge centers, metabolically doped into diatom biosilica, are activated by thermal annealing in air. Diatoms are single celled photosynthetic algae that make silica shells called frustules. These frustules possess intricate features and patterns on the nano- and micro-scale. A two-stage photobioreactor cultivation strategy is used to biologically fabricate diatom biosilica doped with Ge, ranging from 0.24 to 0.96 weight percent Ge. X-Ray photoelectron spectroscopy (XPS) and electron diffraction show that a mixture of amorphous germanium dioxide (GeO2) and germanium oxide (GeO) is doped into the frustule structure. Annealing in air thermally converts the amorphous GeO2 to GeO, commensurate with an enhancement in the photoluminescence. Thermal gravimetric analysis (TGA) and photoluminescence of annealed biosilica with and without Ge confirm that the photoluminescence originates from GeO photoluminescent centers, and not from the inherent photoluminescence of the biosilica. This is the first study to thermally activate and characterize highly photoluminescent Ge centers metabolically doped into diatom biosilica.