Aaron Thurber

The Influences of Cell Type and ZnO Nanoparticle Size on Immune Cell Cytotoxicity and Cytokine Induction

Nanotechnology represents a new and enabling platform that promises to provide a range of innovative technologies for biological applications. ZnO nanoparticles of controlled size were synthesized, and their cytotoxicity toward different human immune cells evaluated. A differential cytotoxic response between human immune cell subsets was observed, with lymphocytes being the most resistant and monocytes being the most susceptible to ZnO nanoparticle-induced toxicity. Significant differences were also observed between previously activated memory lymphocytes and naive lymphocytes, indicating a relationship between cell-cycle potential and nanoparticle susceptibility. Mechanisms of toxicity involve the generation of reactive oxygen species, with monocytes displaying the highest levels, and the degree of cytotoxicity dependent on the extent of nanoparticle interactions with cellular membranes. An inverse relationship between nanoparticle size and cytotoxicity, as well as nanoparticle size and reactive oxygen species production was observed. In addition, ZnO nanoparticles induce the production of the proinflammatory cytokines, IFN-γ, TNF-α, and IL-12, at concentrations below those causing appreciable cell death. Collectively, these results underscore the need for careful evaluation of ZnO nanoparticle effects across a spectrum of relevant cell types when considering their use for potential new nanotechnology-based biological applications.

Electrostatic Interactions Affect Nanoparticle-Mediated Toxicity to Gram-Negative Bacterium Pseudomonas aeruginosa PAO1

Nanoscale materials can have cytotoxic effects. Here we present the first combined empirical and theoretical investigation of the influence of electrostatic attraction on nanoparticle cytotoxicity. Modeling electrostatic interactions between cells and 13 nm spheres of zinc oxide nanoparticles provided insight into empirically determined variations of the minimum inhibitory concentrations between four differently charged isogenic strains of Pseudomonas aeruginosa PAO1. We conclude that controlling the electrostatic attraction between nanoparticles and their cellular targets may permit the modulation of nanoparticle cytotoxicity.

Correlation between saturation magnetization, bandgap, and lattice volume of transition metal (M=Cr, Mn, Fe, Co, or Ni) doped Zn1−xMxO nanoparticles

This work reports on transition metal doped ZnO nanoparticles and compares the effects doping with different transition metal ions has on the structural, optical, and magnetic properties. Zn1−xMxO (M=Cr, Mn, Fe, Co, or Ni) nanoparticles were prepared by a chemical process for x=0.02 and 0.05 in powder form. The powders where characterized by x-ray diffraction (XRD), spectrophotometry, and magnetometry. The Zn1−xMxO samples showed a strong correlation between changes in the lattice parameters, bandgap energy, and the ferromagnetic saturation magnetization. Unit cell volume and bandgap, determined from XRD and spectrophotometry respectively, were maximized with Fe doping and decreased as the atomic number of the dopant moved away from Fe. Bandgap was generally lower at x=0.05 than x=0.02 for all dopants. The saturation magnetization reached a maximum of 6.38 memu/g for Zn0.95Fe0.05O.

Magnetic Gas Sensing Using a Dilute Magnetic Semiconductor

The authors report on a magnetic gas sensing methodology to detect hydrogen using the ferromagnetic properties of a nanoscale dilute magnetic semiconductor Sn0.95Fe0.05O2. This work demonstrates the systematic variation of saturation magnetization, coercivity, and remanence of Sn0.95Fe0.05O2 with the hydrogen gas flow rate, thus providing clear experimental evidence of the concept of magnetic gas sensing (using the magnetic property of a material as a gas sensing parameter). Based on the results of using hydrogen as an example for reducing gases, it is believed that any reducing gas capable of changing the oxygen stoichiometry of Sn0.95Fe0.05O2 can be detected using this method. Furthermore, this method presents an alternative gas sensing technology without the use of the electrical contacts.

Structure–magnetic property relationship in transition metal (M=V,Cr,Mn,Fe,Co,Ni) doped SnO2 nanoparticles

This work reports the results of an extensive search for ferromagnetism in SnO2 doped with a wide range of transition metal cations (M=V, Cr, Mn, Fe, Co, and Ni). By varying the dopant concentration in the 0–12% range, signatures of ferromagnetic behavior in varying degrees were observed with most dopants. The room temperature magnetic moments per dopant ion were low in all the systems and Co (0.13μB∕ion), Fe (0.014μB∕ion), and Cr (0.06μB∕ion) showed relatively the strongest ferromagnetic behavior. In these systems, the observed ferromagnetism initially increased reaching a maximum in the 1–12% range and then gradually weakened and eventually disappeared at higher concentration. The limiting dopant concentration xL at which ferromagnetic behavior reaches a maximum varies with dopant type and has a strong relation to structural changes revealed from detailed x-ray diffraction (XRD) analysis. The XRD data indicated that the lattice volume for every Sn1−xMxO2 system decreased with increasing x in the 0⩽xL ra...

Development and Processing Temperature Dependence of Ferromagnetism in Zn0.98Co0.02O

We report the development of room-temperature ferromagnetism (FM), with coercivity Hc=2000Oe and saturation magnetization Ms∼0.01emu∕g, in chemically synthesized powders of Zn0.98Co0.02O processed at 150 °C, and paramagnetism with antiferromagnetic interactions between the Co2+ spins (S=3∕2) in samples processed at higher temperatures 200⩽TP⩽900°C. X-ray diffraction data show a decrease in the lattice parameters a and c with TP, indicating a progressive incorporation of 0.58A sized tetrahedral Co2+ at the substitutional sites of 0.60 A sized Zn2+. Diffuse reflectance spectra show three well defined absorption edges at 660, 615, and 568 nm due to the d‐d crystal field transitions A24(F)→E2(G),A24(F)→T14(P), and A24(F)→T12(G) of high spin (S=3∕2)Co2+ in a tetrahedral crystal field, whose intensities increase with processing temperature. X-ray photoelectron spectroscopy shows that the doped Co2+ ions in the 150 °C processed samples are located mostly on the surface of the particles and they disperse into the...

Size, surface structure, and doping effects on ferromagnetism in SnO2

The effects of crystallite size, surface structure, and dopants on the magnetic properties of semiconducting oxides are highly controversial. In this work, Fe:SnO2 nanoparticles were prepared by four wet-chemical methods, with Fe concentration varying from 0% to 20%. Analysis confirmed pure single-phase cassiterite with a crystallite size of 2.6 ± 0.1 nm that decreased with increasing. Fe% doped substitutionally as Fe3+. Pure SnO2 showed highly reproducible weak magnetization that varied significantly with synthesis method. Interestingly, doping SnO2 with Fe < 2.5% produced enhanced magnetic moments in all syntheses; the maximum of 1.6 × 10−4 µB/Fe ion at 0.1% Fe doping was much larger than the 2.6 × 10−6 µB/Fe ion of pure Fe oxide nanoparticles synthesized under similar conditions. At Fe ≥ 2.5%, the magnetic moment was significantly reduced. This work shows that (1) pure SnO2 can produce an intrinsic ferromagnetic behavior that varies with differences in surface structure, (2) very low Fe doping results ...

A variable temperature Fe3+ electron paramagnetic resonance study of Sn1−xFexO2 (0.00⩽x⩽0.05)

X-band (∼9.5GHz) electron paramagnetic resonance (EPR) studies of Fe3+ ions in Sn1−xFexO2 powders with 0.00⩽x⩽0.05 at various temperatures (5–300K) are reported. These samples are interesting to investigate as Fe doping (⩽5%) produces ferromagnetism in SnO2 [A. Punnooose et al., Phys. Rev. B 72, 054402 (2005)], making it a promising ferromagnetic semiconductor at room temperature. The EPR spectrum at 5K can be simulated reasonably well as the overlap of spectra due to seven magnetically inequivalent Fe3+ ions: four low-spin (S=1∕2) and three high-spin (S=5∕2) ions, characterized by different spin-Hamiltonian parameters, overlapped by three broad ferromagnetic resonance spectra. The three high-spin ions, situated substitutionally in the interior of nanodomains, are characterized by smaller zero-field splitting (ZFS) parameters D and E, so that all their energy levels are populated at 5K. On the other hand, the four low-spin ions are situated interstitially at the surfaces of nanodomains. They are character...

Highly Shape-Selective Synthesis, Silica Coating, Self-Assembly, and Magnetic Hydrogen Sensing of Hematite Nanoparticles

The open forced hydrolysis method and controllable silica growth based on bound water to polyvinylpyrrolidone molecules have been developed for the highly shape (including rhombohedra, semispheres, and rods) selective synthesis, self-assembly, and uniform silica coating (in the unprecedented range of 5-200 nm) of hematite nanoparticles. The open system realizes the direct short-range self-assembly of hematite semispheres in their growth process. The bound water method has been extended to coat gold nanoparticles with tunable silica shell and directly assemble the cores into one-dimensional, dimer, and trimer nanostructures during the coating process. The silica coating increases the particle stability and monodispersity even as hematite is modified into ferromagnetic Fe(3)O(4). The hematite@silica core-shell spheres are assembled into long-range ordered structures with considerable photonic bandgap for the first time due to their high monodispersity. By exploiting the hematite antiferromagnetism caused by the superexchange interaction via intervening oxygen ions that are sensitive to hydrogen, a novel hydrogen sensing based on magnetization variations is achieved in the hematite assemblies. Weakening the antiferromagnetism by reducing the hematite size and/or covering the hematite surface by silica coating suppresses the sensitivity to hydrogen, showing that the antiferromagnetic spin variations on the hematite surface are responsible for the gas sensing.

Improving the selective cancer killing ability of ZnO nanoparticles using Fe doping

Abstract This work reports a new method to improve our recent demonstration of zinc oxide (ZnO) nanoparticles (NPs) selectively killing certain human cancer cells, achieved by incorporating Fe ions into the NPs. Thoroughly characterized cationic ZnO NPs (∼6 nm) doped with Fe ions (Zn1-x Fe x O, x = 0–0.15) were used in this work, applied at a concentration of 24 μg/ml. Cytotoxicity studies using flow cytometry on Jurkat leukemic cancer cells show cell viability drops from about 43% for undoped ZnO NPs to 15% for ZnO NPs doped with 7.5% Fe. However, the trend reverses and cell viability increases with higher Fe concentrations. The non-immortalized human T cells are markedly more resistant to Fe-doped ZnO NPs than cancerous T cells, confirming that Fe-doped samples still maintain selective toxicity to cancer cells. Pure iron oxide samples displayed no appreciable toxicity. Reactive oxygen species generated with NP introduction to cells increased with increasing Fe up to 7.5% and decreased for >7.5% doping.