Transcript Slide 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: Stability of polymer-wrapped CdSe QDs under oxidative conditions Toxicity of weathered PEGylated CdSecore/ZnSshell QDs Methoxyhydroquinone-driven Fenton’s reaction Embryonic zebrafish model Effect of ligand head group on oxidative stability • Zebrafish embryos exposed beginning at 4-6 hours postfertilization (hpf) Acetate buffer • Assays conducted in a 96-well plate format (1 embryo/well). MHQ-Fenton’s reaction C=O • Slight blue shift of first exciton peak following exposure to MHQdriven Fenton’s reaction NH2 OH • Dosing solutions renewed and embryos/larvae scored for toxicity and mortality daily for 5 days. • Magnitude of shift depends on ligand head group Gloeophyllum trabeum Courtesy of Prof. K. E. Hammel pH 4, dark [Fe+2]:[methoxyhydroquinone (MHQ)]:[H2O2] = 20:20:200 µM [nanoparticles] = 2 nM to 2 µM PEGylated CdSecore/ZnSshell QD • Stability under oxidative conditions decreases from thiols > carboxylic acid > phosphonic acid > amine Dose-response relationships for weathered and as-synthesized QDs PMAO/PEG-CdSe QD 120-hpf LC50 µM Cd equivalents no. QD · 100µL-1 PEG350-QD --- --- PEG5000-QD 42 (24-75) 15 × 1012 Weathered PEG350-QD 40 (30- 50) 14 × 1012 14 (9-21) 5 × 10 12 Weathered PEG5000-QD CdCl2 OH SH P=O 410 (270-560) OH • Polymer-wrapped CdSe QDs had higher stability under oxidative conditions than did PEGylated CdSecore/ZnSshell QDs --- 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) 10 mM Acetate Buffer, pH 4.1 MHQFenton 0.20 0.15 0.10 0.05 Endpoints include altered axial curvatures (aac), pericardial edema (pe), ocular edema (oe), tail malformations (tm), and yolk sac malformations (ysm) UV-visible spectra of PMAO/PEG-PDA-CdSe QDs following exposure to MHQ-Fenton’s reaction H2 O Acetate Buffer H2 O 2 H2O2 + Fe 100 Absorbance 0.25 Percent of total Absorbance (a.u.) Transformations of PEGylated QDs by MHQFenton’s reaction Endpoints of toxicity are similar for as-syntheized and weathered QDs. Transformations of polymer-wrapped CdSe QDs with polydecanoic Acid (PDA) head group 80 60 Synthesis of Se Nanoparticles (SeNPs): Influence of Se-containing aggregates on toxicity 40 SEM image of SeNPs 20 MHQ-driven Fenton’s reaction Raman spectra of SeNPs • Exposure to H2O2 causes blue shift of 1st exciton peak • No additional effect observed with Fenton’s reaction 0 450 500 550 Zinc 600 Cadmium Wavelength (nm) Metals analysis indicates dissolution of ZnS shell and release of Cd from core Synthesis produces elemental SeNPs ~100-200 nm in diameter Dose-response relationships for SeNPs Raman spectra of PDA-CdSe QD following IR spectra of PMAO/PEG-PDA-CdSe QDs exposure to MHQ-Fenton’s reaction Intensity UV-visible absorbance data suggest dissolution of PEG5000-QDs Wavelength (nm) Raman Shift (cm-1) TEM, electron diffraction and EDX indicate the formation of amorphous Se-containing aggregates Metz et al. Environ. Sci. Technol. 2009 (43) 1598-1604 Oxidation of Se2- to Se0 following exposure to MHQ-Fenton’s reaction Evidence of polymer degradation during MHQ-Fenton’s exposure 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 Mangham et al., in prep