Oxidatively Weathered Quantum Dots: Transformations and Toxicity (NSEC, DMR ) Joel A. Pedersen, Paige N. Wiecinski, Kevin M. Metz, Tisha C. King Heiden, Andrew N. Mangham, Warren Heideman, Richard E. Peterson, Robert J. Hamers Toxicity of weathered PEGylated CdSe core /ZnS shell QDs Embryonic zebrafish model Simulated oxidative environmental conditions: Methoxyhydroquinone-driven Fenton’s reaction 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 CdSe core /ZnS shell 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 CdCl 2. Co-exposure of zebrafish embryos to Cd 2+ and selenium nanoparticles recapitulated toxicity observed upon exposure to weathered CdSe core /ZnS shell QDs. [Fe +2 ]:[methoxyhydroquinone (MHQ)]:[H 2 O 2 ] = 20:20:200 µM pH 4, dark [nanoparticles] = 2 nM to 2 µM Synthesis of Se Nanoparticles (SeNPs): Influence of Se-containing aggregates on toxicity Synthesis produces elemental SeNPs ~ nm in diameter Dose-response relationships for SeNPs Gloeophyllum trabeum Courtesy of Prof. K. E. Hammel Dose-response relationships for weathered and as-synthesized QDs Representative micrographs of QD exposed zebrafish (120 hpf) 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) PEG 350 -QD Weathered PEG 350 -QD Weathered PEG QD PEG QD CdCl 2 Weathered PEGylated QDs show higher lethaliity (i.e., lower LC 50 ) than as-synthesized QDs. Both are more toxic than an equivalent amount of CdCl 2 SEM image of SeNPs Raman spectra of SeNPs SeNP co-exposures with CdCl 2 recapitulated toxic endpoints of weathered QD exposures Transformations of PEGylated QDs by MHQ- Fenton’s reaction Absorbance (a.u.) Wavelength (nm) 10 mM Acetate Buffer, pH 4.1 MHQ- Fenton UV-visible absorbance data suggest dissolution of PEG QDs Metals analysis indicates dissolution of ZnS shell and release of Cd from core Zinc Cadmium Percent of total TEM, electron diffraction and EDX indicate the formation of amorphous Se-containing aggregates 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. Stability of polymer-wrapped CdSe QDs under oxidative conditions Acetate buffer MHQ-Fenton’s reaction P=O OH NH 2 SH C=O OH Effect of ligand head group on oxidative stability Metz et al. Environ. Sci. Technol (43) King Heiden et al., Environ. Sci. Technol (43) ; Wiecinski et al., in prep Mangham et al., in prep 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 CdSe core /ZnS shell QDs Transformations of polymer-wrapped CdSe QDs with polydecanoic Acid (PDA) head group Acetate Buffer H2OH2O H2O2H2O2 MHQ-driven Fenton’s reaction H 2 O 2 + Fe Wavelength (nm) Absorbance UV-visible spectra of PMAO/PEG-PDA-CdSe QDs following exposure to MHQ-Fenton’s reaction Exposure to H 2 O 2 causes blue shift of 1 st exciton peak No additional effect observed with Fenton’s reaction Raman spectra of PDA-CdSe QD following exposure to MHQ-Fenton’s reaction Raman Shift (cm -1 ) Intensity Oxidation of Se 2- to Se 0 following exposure to MHQ-Fenton’s reaction IR spectra of PMAO/PEG-PDA-CdSe QDs Evidence of polymer degradation during MHQ-Fenton’s exposure S O O CH 3 n S O O n S O O n S O O n S O O n S O O n S O O n S O O n S O O n S O O n S O O n PEGylated CdSe core /ZnS shell QD PMAO/PEG-CdSe QD