Isotopic signature and nano-texture of cesium-rich micro-particles: Release of uranium and fission products from the Fukushima Daiichi Nuclear Power Plant.

Highly radioactive cesium-rich microparticles (CsMPs) released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) provide nano-scale chemical fingerprints of the 2011 tragedy. U, Cs, Ba, Rb, K, and Ca isotopic ratios were determined on three CsMPs (3.79-780 Bq) collected within ~10 km from the FDNPP to determine the CsMPs' origin and mechanism of formation. Apart from crystalline Fe-pollucite, CsFeSi2O6 · nH2O, CsMPs are comprised mainly of Zn-Fe-oxide nanoparticles in a SiO2 glass matrix (up to ~30 wt% of Cs and ~1 wt% of U mainly associated with Zn-Fe-oxide). The 235U/238U values in two CsMPs: 0.030 (±0.005) and 0.029 (±0.003), are consistent with that of enriched nuclear fuel. The values are higher than the average burnup estimated by the ORIGEN code and lower than non-irradiated fuel, suggesting non-uniform volatilization of U from melted fuels with different levels of burnup, followed by sorption onto Zn-Fe-oxides. The nano-scale texture and isotopic analyses provide a partial record of the chemical reactions that occurred in the fuel during meltdown. Also, the CsMPs were an important medium of transport for the released radionuclides in a respirable form.

Biomarkerless targeting and photothermal cancer cell killing by surface-electrically-charged superparamagnetic Fe3O4 composite nanoparticles.

A major challenge in cancer therapy is localized targeting of cancer cells for maximum therapeutic effectiveness. However, due to cancer heterogeneities, the biomarkers are either not readily available or specific for effective targeting of cancer cells. The key, therefore, is to develop a new targeting strategy that does not rely on biomarkers. A general hallmark of cancer cells is the much increased level of glycolysis. The loss of highly mobile lactate from the cytoplasm inevitably removes labile inorganic cations to form lactate salts and acids as part of the lactate cycle, creating a net of negative surface charges. This net of negative charges on cancer cell surfaces biophysically distinguishes themselves from normal cells. In this study, cancer cells are targeted by using positively-charged, fluorescent, superparamagnetic Fe3O4-composite nanoparticles. The positively-charged Fe3O4 composite nanoparticles bind predominantly to cancer cells due to their negatively-charged surfaces. Upon electrical-charge-mediated Fe3O4 nanoparticle binding onto cancer cells, irradiation by using an 808 nm laser is subsequently applied to induce photothermal hyperthermia that kills the cancer cells directly. The negatively-charged composite nanoparticles are found, however, not to target and bind the cancer cells due to the electrostatic repulsive force between them. This unique strategy paves a new path for effective targeting and direct cancer cell killing without relying on any biomarkers and anticancer drugs.

In-vitro depth-dependent hyperthermia of human mammary gland adenocarcinoma.

Nanoparticle mediated photothermal ablation of cancerous tissue shows promising results and applicability as a highly efficacious treatment method. As a majority of the photothermal work has been conducted with minimal attenuation of the laser before reaching the nanoparticles within surface seeded tumors in-vivo or through buffered media in-vitro, it is important to understand the effects of greater laser attenuation on photothermal efficacy mediated by changes in the scattering and absorption of the laser. Photothermal efficacy using a near infrared (NIR) 785nm laser irradiating polystyrene (PS) stabilized magnetite (Fe3O4) nanoparticles (PS-Fe3O4) is examined on MDA-MB-231 human mammary gland adenocarcinoma in-vitro. Agarose gel columns of various heights were created to simulate soft tissue and subsequently used for NIR laser attenuation. Polystyrene was found to significantly improve magnetite nanoparticle stability in serum containing media and modified Hank's Balanced Salt Solution and was able to induce significant hyperthermic ablation at mass concentrations which also did not elicit significant innate toxicity. Furthermore it was found that the polystyrene coating significantly reduced innate toxicity over 48h compared to uncoated magnetite. Agar gel layers provided similar optical attenuation in the NIR region to skin and prostate.

Photothermal effects and toxicity of Fe3O4 nanoparticles via near infrared laser irradiation for cancer therapy.

The photothermal effect of magnetite (Fe3O4) nanoparticles was characterized by photonic absorption in the near-infrared (NIR) region. Upon laser irradiation at 785 nm, the Fe3O4 nanoparticles generate localized hyperthermia in tumorous lesions, which is an effective strategy for cancer therapy; however, uncoated magnetite possesses an innate toxicity which can lead to drawbacks in the clinical setting. To reduce innate toxicity, a poly(acrylic acid) (PAA) coating on the nanoparticles was investigated in order to determine the alterations to stability and the degree of toxicity in an attempt to create a higher utility vector. It was found that the PAA coating significantly reduced the innate toxicity of the uncoated magnetite. Furthermore, the efficacy of PAA-coated magnetite nanoparticles (PAA-Fe3O4) was investigated for treating MDA-MB-231 (human mammary gland adenocarcinoma) cultures in viable concentration ranges (0.1-0.5mg/ml). An appropriate PAA-Fe3O4 concentration range was then established for inducing significant cell death by hyperthermic ablation, but not through innate toxicity.

Amorphization of nanocrystalline monoclinic ZrO2 by swift heavy ion irradiation.

Bulk ZrO(2) polymorphs generally have an extremely high amorphization tolerance upon low energy ion and swift heavy ion irradiation in which ballistic interaction and ionization radiation dominate the ion-solid interaction, respectively. However, under very high-energy irradiation by 1.33 GeV U-238, nanocrystalline (40-50 nm) monoclinic ZrO(2) can be amorphized. A computational simulation based on a thermal spike model reveals that the strong ionizing radiation from swift heavy ions with a very high electronic energy loss of 52.2 keV nm(-1) can induce transient zones with temperatures well above the ZrO(2) melting point. The extreme electronic energy loss, coupled with the high energy state of the nanostructured materials and a high thermal confinement due to the less effective heat transport within the transient hot zone, may eventually be responsible for the ionizing radiation-induced amorphization without transforming to the tetragonal polymorph. The amorphization of nanocrystalline zirconia was also confirmed by 1.69 GeV Au ion irradiation with the electronic energy loss of 40 keV nm(-1). These results suggest that highly radiation tolerant materials in bulk forms, such as ZrO(2), may be radiation sensitive with the reduced length scale down to the nano-metered regime upon irradiation above a threshold value of electronic energy loss.

Adsorbed U(VI) surface species on muscovite identified by laser fluorescence spectroscopy and transmission electron microscopy.

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) were applied to investigate the species of uranyl(VI) adsorbed onto muscovite platelets and muscovite suspensions (grain size: 63-200 microm). TRLFS provided evidence for the presence of two adsorbed uranium(VI) surface species on edge-surfaces of muscovite. The two species showed different positions of the fluorescence emission bands and different fluorescence lifetimes indicating a different coordination environment for the two species. HAADF-STEM revealed that nanoclusters of an amorphous uranium phase were attached to the edge-surfaces of muscovite powder during batch sorption experiments. These U-nanoclusters were not observed on {00/} cleavage planes of the muscovite. The surface species with the shorter fluorescence lifetimes are interpreted as truly adsorbed bidentate surface complexes, in which the U(VI) binds to aluminol groups of edge-surfaces. The surface species with the longer fluorescence lifetimes are interpreted to be an amorphous U(VI) condensate or nanosized clusters of polynuclear uranyl(VI) surface species with a particle diameter of 1 to 2 nm. Depending on the size of these clusters the fluorescence lifetimes vary; i.e., the larger the nanosized clusters, the longer is the fluorescence lifetime.

Uraninite and fullerene in atmospheric particulates.

Particulates emitted from coal-burning power plants typically contain very small amounts of uranium (<10 ppm). Because of the extremely low concentrations, the form of the uranium has been unknown. Using a variety of advanced electron microscopy techniques, we have identified for the first time nanocrystals of uraninite, UO2+x, encapsulated in carbonaceous matter (< or = 50 nm) similar to fullerene. We have also identified, for the first time, closely associated fullerenes, C60. The "carbon-caged" nanocrystals of uraninite are protected from the immediate oxidation that would lead to increased mobility of uranium in the environment. Still, the presence of uranium in the very fine fraction of atmospheric particulates provides another pathway for radiation exposure.