Oxidatively Weathered Quantum Dots: Transformations and Toxicity (NSEC, DMR 0425880)

1. CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 0.25 O O O O O O O O O O O n n n n n n n n n n n 0.20 100 O O O O O O O O O O O 10 mM Acetate Buffer, pH 4.1 MHQ-Fenton 80 S S S Absorbance (a.u.) S S S S S S S S 0.15 Percent of total 60 0.10 40 0.05 20 0 450 500 550 600 Zinc Cadmium Wavelength (nm) C=O OH OH P=O OH PEG350-QD PEG5000-QD Weathered PEG350-QD Weathered PEG5000-QD CdCl2 UV-visible absorbance data suggest dissolution of PEG5000-QDs Gloeophyllum trabeum Courtesy of Prof. K. E. Hammel H2O Acetate Buffer H2O2 H2O2 + Fe MHQ-driven Fenton’s reaction Intensity pH 4, dark Absorbance [Fe+2]:[methoxyhydroquinone (MHQ)]:[H2O2] = 20:20:200 µM [nanoparticles] = 2 nM to 2 µM Wavelength (nm) Raman Shift (cm-1) Oxidatively Weathered Quantum Dots: Transformations and Toxicity (NSEC, DMR 0425880) Joel A. Pedersen, Paige N. Wiecinski, Kevin M. Metz, Tisha C. King Heiden, Andrew N. Mangham, Warren Heideman, Richard E. Peterson, Robert J. Hamers As production and use of nanomaterials increases, introduction of engineered nanoparticles into the environment becomes inevitable. As nanoparticles enter the environment they have the potential to be transformed through environmental redox processes. We developed an in vitro catalytic model mimicking the extracellular chemistry of lignolytic fungi and examined the oxidative stability of poly(ethylene glycol)(PEG)-thiol coated CdSecore/ZnSshell and poly(maleic anhydride-alt-octadecane) (PMAO)/PEG wrapped CdSe quantum dots (QDs). PEGylated QDs were readily broken down under assay conditions. Polymer-wrapping appeared to increase CdSe QD stability against oxidative degradation. We next examined the degree to which oxidative weathering altered to toxicity PEGylated QDs to zebrafish embryos. Oxidatively degraded QDs were more toxic than as-synthesized QDs, and both were more toxic than equivalent amounts of CdCl2. Co-exposure of zebrafish embryos to Cd2+ and selenium nanoparticles recapitulated toxicity observed upon exposure to weathered CdSecore/ZnSshell QDs. Simulated oxidative environmental conditions: Methoxyhydroquinone-driven Fenton’s reaction Stability of polymer-wrapped CdSe QDs under oxidative conditions Toxicity of weathered PEGylated CdSecore/ZnSshell QDs Embryonic zebrafish model Effect of ligand head group on oxidative stability • Zebrafish embryos exposed beginning at 4-6 hours post-fertilization (hpf) • Assays conducted in a 96-well plate format (1 embryo/well). • Dosing solutions renewed and embryos/larvae scored for toxicity and mortality daily for 5 days. Acetate buffer MHQ-Fenton’s reaction • Slight blue shift of first exciton peak following exposure to MHQ-driven Fenton’s reaction • Magnitude of shift depends on ligand head group • Stability under oxidative conditions decreases from thiols > carboxylic acid > phosphonic acid > amine • Polymer-wrapped CdSe QDs had higher stability under oxidative conditions than did PEGylated CdSecore/ZnSshell QDs NH2 Dose-response relationships for weathered and as-synthesized QDs SH PEGylated CdSecore/ZnSshell QD PMAO/PEG-CdSe QD Weathered PEGylated QDs show higher lethaliity (i.e., lower LC50) than as-synthesized QDs. Both are more toxic than an equivalent amount of CdCl2 Representative micrographs of QD exposed zebrafish (120 hpf) Transformations of polymer-wrapped CdSe QDs with polydecanoic Acid (PDA) head group Endpoints of toxicity are similar for as-syntheized and weathered QDs. Endpoints include altered axial curvatures (aac), pericardial edema (pe), ocular edema (oe), tail malformations (tm), and yolk sac malformations (ysm) Transformations of PEGylated QDs by MHQ-Fenton’s reaction UV-visible spectra of PMAO/PEG-PDA-CdSe QDs following exposure to MHQ-Fenton’s reaction • Exposure to H2O2 causes blue shift of 1st exciton peak • No additional effect observed with Fenton’s reaction Synthesis of Se Nanoparticles (SeNPs): Influence of Se-containing aggregates on toxicity SEM image of SeNPs Raman spectra of SeNPs • Metals analysis indicates dissolution of ZnS shell and release of Cd from core Raman spectra of PDA-CdSe QD following exposure to MHQ-Fenton’s reaction IR spectra of PMAO/PEG-PDA-CdSe QDs Synthesis produces elemental SeNPs ~100-200 nm in diameter Dose-response relationships for SeNPs Evidence of polymer degradation during MHQ-Fenton’s exposure Oxidation of Se2- to Se0 following exposure to MHQ-Fenton’s reaction TEM, electron diffraction and EDX indicate the formation of amorphous Se-containing aggregates SeNP co-exposures with CdCl2 recapitulated toxic endpoints of weathered QD exposures King Heiden et al., Environ. Sci. Technol. 2009 (43) 1605-1611; Wiecinski et al., in prep Metz et al. Environ. Sci. Technol. 2009 (43) 1598-1604 Mangham et al., in prep