Alex Punnoose

Selective Toxicity of Zinc Oxide Nanoparticles to Prokaryotic and Eukaryotic Systems

We report on the toxicity of ZnO nanoparticles (NPs) to gram-negative and gram-positive bacterial systems, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), and primary human immune cells. ZnO NP (~13 nm) showed complete inhibition of E. coli growth at concentrations 3.4 mM, whereas growth of S. aureus was completely inhibited for 1 mM. Parallel experiments using flow cytometry based assays clearly demonstrated that growth inhibitory properties of ZnO NP were accompanied by a corresponding loss of cell viability. Identical ZnO NP had minimal effects on primary human T cell viability at concentrations toxic to both gram-negative and gram-positive bacteria. Collectively, these experiments demonstrate selectivity in the toxic nature of ZnO NP to different bacterial systems and human T lymphocytes. Developing selective toxicity to biological systems and controlling it by NP design could lead to biomedical and antibacterial applications.

Preferential killing of cancer cells and activated human t cells using zno nanoparticles

Nanoparticles are increasingly being recognized for their potential utility in biological applications including nanomedicine. Here we examine the response of normal human cells to ZnO nanoparticles under different signaling environments and compare it to the response of cancerous cells. ZnO nanoparticles exhibit a strong preferential ability to kill cancerous T cells ( approximately 28-35x) compared to normal cells. Interestingly, the activation state of the cell contributes toward nanoparticle toxicity, as resting T cells display a relative resistance while cells stimulated through the T cell receptor and CD28 costimulatory pathway show greater toxicity in direct relation to the level of activation. Mechanisms of toxicity appear to involve the generation of reactive oxygen species, with cancerous T cells producing higher inducible levels than normal T cells. In addition, nanoparticles were found to induce apoptosis and the inhibition of reactive oxygen species was found to be protective against nanoparticle induced cell death. The novel findings of cell selective toxicity, towards potential disease causing cells, indicate a potential utility of ZnO nanoparticles in the treatment of cancer and/or autoimmunity.

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.

Semiconducting and ferromagnetic behavior of sputtered Co-doped TiO2 thin films above room temperature

We have investigated Co-doped TiO2 thin films grown by reactive co-sputtering. X-ray diffraction showed a single phase polycrystalline rutile structure, without any segregation of Co into particulates within the instrumental resolution limit. The atomic content of Co ranged from 1% to 12%. The temperature dependence of resistivity showed an extrinsic semiconducting behavior. From optical absorption measurements, the band gap Eg≈3.25±0.05 eV was found, independent of the Co concentration, and in agreement with a literature value. Room temperature M-H loops showed a ferromagnetic behavior for Co content higher than 3%. The magnetic moment per Co atom was estimated to be about 0.94 μB, suggesting a low spin configuration of Co ions. The temperature dependence of remanent magnetization revealed a Curie temperature higher than 400 K for Co content of 12%.

Room-temperature ferromagnetism in chemically synthesized Sn1−xCoxO2 powders

Room-temperature ferromagnetism is observed in chemically synthesized powder samples of Sn1−xCoxO2 with x=0.005 and 0.01. Magnetic hysteresis loops are observed at 300K with coercivity Hc∼630Oe, saturation magnetization Ms∼0.133μB∕Co ion, and about 31% remanence. Analyses of the magnetization data of paramagnetic samples with x=0.01 and 0.03, measured as a function of temperature (3–330K) and magnetic field (up to 65kOe), indicate the presence of Co+2 ions with spin S=3∕2. Magnetic data obtained from samples prepared at different temperatures indicate that the observed ferromagnetism for x⩽0.01 might have been triggered by changes in the oxygen stoichiometry.

Conversion of methanol to olefins over cobalt-, manganese- and nickel-incorporated SAPO-34 molecular sieves

Silicoaluminophosphate (SAPO)-34 molecular sieves modified with transition metals Co, Mn, and Ni were investigated for their activity, selectivity, and lifetime in the methanol to olefins (MTO) reaction and compared with that of unmodified SAPO-34. The electronic state and location of the metal ions in these materials were determined by magnetic measurements (temperature and magnetic field variations of magnetization). These magnetic studies show that for MnSAPO-34 and CoSAPO-34 metal ions are incorporated into the SAPO framework with concentrations ≃0.12 and 0.17 wt.%, respectively. Nickel modified SAPO-34 samples were prepared by two different procedures. For Ni-SAPO-34 prepared by one procedure (Method I), the magnetic studies show the presence of nanoparticles (Ni or NiO) outside the SAPO framework. For NiSAPO-34 prepared by a second procedure (Method II), these studies show that the nickel ions are incorporated into the SAPO framework. Although the total C2–C4 olefins activity on these materials was comparable to that of unmodified SAPO-34, significant variations in the deactivation behavior were observed among various metal-modified catalysts. MnSAPO-34 was found to be the best catalyst based on catalyst lifetime. In the case of Ni-SAPO-34 (Method I), unusually high amounts of methane were observed in the products due to the presence of nanoparticles outside the SAPO framework.

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.

On the room temperature ferromagnetism in Co-doped TiO2 films

We report detailed studies of magnetization (M) as a function of magnetic field H (up to 50 kOe) and temperature T (5–380 K) in x% Co/TiO2 (rutile) films for x=1, 4, 6, 10, and 12. These films, prepared by sputtering, show room temperature ferromagnetism (RTFM). Measurements of M vs T at H=50 Oe reported here in zero-field-cooled (ZFC) and field-cooled (FC) cases show M peaking at Tp≃30 K for 1% Co to Tp≃125 K for 12% Co doped films whereas bifurcation of the FC and ZFC data is observed near 300 K. For T<Tp, the coercivity Hc rises sharply. These observations and the electron magnetic resonance data suggest that the observed RTFM is at least partly due to magnetic nanoparticles, most likely of Co, that are undetected in standard X-ray diffraction (XRD) for lightly doped samples. XRD studies show that a fraction of Co does substitute for Ti in CoxTi1−xO2. However, because of interference from Co nanoparticles, the RTFM of CoxTi1−xO2 in these samples could not be established.

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.

Hysteresis anomalies and exchange bias in 6.6 nm CuO nanoparticles

In the 6.6 nm particles of CuO with Neel temperature TN≃40 K, hysteresis loops are observed up to 330 K. With decrease in temperature, the coercivity Hc increases slowly up to TN below which rapid increases in Hc and exchange bias He are observed. At 5 K, the ratio He/Hc≃2, decreasing to zero as T→TN. At 10 K, the variation of He, Hc, and the ratio He/Hc with the cooling field show behavior similar to that of the weak ferromagnetic moment resulting from the uncompensated surface spins.