Safer by design, transparent, UV-absorbing ZnO nanorods with minimal genotoxicity Georgios A. Sotiriou, Christa Watson, Kim M. Murdaugh, Alison Elder 1 and Philip Demokritou Center for Nanotechnology and Nanotoxicology, Department of Environmental Health, School of Public Health, Harvard University, 665 Huntington Avenue, 02115 Boston, MA 1 University of Rochester Medical Center, 601 Elmwood Ave, 14642 Rochester, NY 13 November 2013 slide 1
ZnO nanoparticles Inorganic semiconductor [1,2] Band-gap E g = 3.3 ev (white color) UV-absorbing Transparent in visible wavelength [3] Applications Cosmetics Sunscreens Filler in polymers Exposure to humans: inevitable [1] Janotti, Van de Walle, Rep. Prog. Phys. 72, 126501 (2009). [2] King, Liang, Carney, Hakim, Li, Weimer, Adv. Funct. Mater. 18, 607 (2008). [3] Hikov, Rittermeier, Luedeman, Herrmann, Muhler, Fischer, J. Mater. Chem. 18, 3325 (2008). 13 November 2013 slide 2
comet structure induced from 4hr exposure of zi Toxicological implications Many in-vitro tox studies linked ZnO NPs to cytotoxicity [1] Primary cytox mechanism: Zn 2+ ion release Direct nanoparticle contact/ ROS generation DNA damage. C.) Positive control cells treated w Traditional comet assay of TK-6 cells treated wi CometChip quantitative assessments. [1] ZnO NPs exhibit high DNA damage potential [2] Doses below cytotoxic level [2] [1] George, Xia, Rallo, Zhao, Ji, Lin, Wang, Zhang, France, Schoenfeld, Damoiseaux, Liu, Lin, Bradley, Cohen, Nel, ACS Nano 5, 1805 (2011). [2] Watson, Ge, Cohen, Pyrgiotakis, Engelward, Demokritou, in revision (2013). 13 November 2013 slide 3
Safer by Design approaches for ENMs The likely success or failure of NT industry depends on nano-ehs matters. While nano-ehs research is progressing, research on safer by design approaches is lacking behind Elements of a Safer by design approach: Reduce Toxicological footprint Maintain functional properties of ENMs Scalability 13 November 2013 slide 4
Safer-by-design approaches for ZnO NPs Altering the tox profile Zn 2+ ion release Direct nanoparticle contact increasing Fe-content at% [1] Example: Fe-doping of ZnO [1] Decreases Zn 2+ ion release Lower cytotoxicity [1] Pitfall: Fe-doping changes the optoelectronic properties [2] Color changes from white to brown undesired for many applications Safer by design approach Engineer safer ZnO nanoparticles while maintaining their optoelectronic properties Scalability of method for industry [2] 0 % 10 % [1] George, Pokhrel, Xia, Gilbert, Ji, Schowalter, Rosenauer, Damoisaeux, Bradley, Madler, Nel, ACS Nano 4, 15 (2010). [2] Aydin, El-sadek, Zheng, Yahia, Yakuphanoglu, Optic Laser Technol. 48, 447 (2013). 13 November 2013 slide 5
A Safer Formulation Concept for flame generated ENMs Scalability? Develop a concept to coat in flight flame generated ENMs with a nanothin layer of SiO2 Features: Scalability, no chemical by products and impurities, high volume production (1) Gass et al.,sus. Chem & Eng., 2013, (2) Xia et al., ACS Nano 2011, 5, 1223 1235 (3) Napierska et al., Particle and Fibre Toxicology 2010, 7,39 (4) Teleki et al., Chem. Mater. 2009, 21, 2094 2100 13 November 2013 (5) Sotiriou et al., Adv. Funct. Mater. 2010, 20, 4250 4257 slide 6
Strategy: In flight SiO 2 coating on ZnO nanoparticles Particle collection SiO 2 -coating SiO 2 coating formation [1,2] Si-precursor vapor injection Core nanoparticle synthesis [1] Teleki, Heine, Krumeich, Akhtar Pratsinis, Langmuir 24, 12553 (2008). [2] Gass, Cohen, Pyrgiotakis, Sotiriou, Pratsinis, Demokritou, ACS Sustainable Chem. Eng. 1, 843 (2013). 13 November 2013 slide 7
Crystallinity Highly crystalline core Identical XRD patterns SiO 2 shell does not influence core crystallinity [1] No free SiO 2 [2,3] [1] Teleki, Heine, Krumeich, Akhtar Pratsinis, Langmuir 24, 12553 (2008). [2] Sotiriou, Schneider, Pratsinis, J. Phys. Chem. C 116, 4493 (2012). [3] Gass, Cohen, Pyrgiotakis, Sotiriou, Pratsinis, Demokritou, ACS Sustainable Chem. Eng. 1, 843 (2013). 13 November 2013 slide 8
Hermetic nature of SiO2 coating X-ray photoelectron spectroscopy (XPS) Photocatalytic activity (MB degradation under UV, l = 254 nm) Si 2s Si 2s Zn 3s Zn 3p coat ing efficiency = 95% Zn-related XPS peaks diminish High coating efficiency Inelastic mean free path of Zn free electrons may penetrate through SiO 2 Pure ZnO is a photocatalyst Degrade organic dyes under UV light Coated ZnO show no MB degradation Hermetic coating 13 November 2013 slide 9
Optoelectronic properties? UV-vis transmission of aqueous suspensions (100 mg/ml) Diffuse-reflectance UV-vis (powder form) E g SiO 2 -coated ZnO nanorods are more transparent Both uncoated and SiO 2 -coated block UV (< 400 nm) Identical optoelectronic properties E g = 3.3 ev In agreement with XRD No sensory changes May be used in cosmetics Sotiriou et al., in submission, 2013. 13 November 2013 slide 10
Genotoxicity - DNA damage TK-6 human lymphoblastoid cells Nano Cometchip assay [1,2] MTT cytotoxicity assay **p-value < 0.01, ***p-value < 0.001 Uncoated ZnO nanorods induce DNA damage SiO 2 -coated ZnO nanorods show a protective DNA damage effect No significant cytotoxicity is observed for all doses [1] DNA damage may be present at no- or low-cytotoxicity doses 1 Watson et al, in review, 2013, 2 Sotiriou et al., in submission, 2013. 13 November 2013 slide 11
Conclusions Synthesis of hermetically SiO 2 -coated ZnO nanorods inflight Hermetic SiO 2 coating No photocatalytic activity SiO 2 presence does not influence the core crystallinity Maintain the desired visible transparency and UV absorption SiO 2 -coated ZnO nanorods exhibit reduced DNA damage 13 November 2013 slide 12
NSF (#1235806) NIEHS (ES-0000002) SNSF (#145392) Acknowledgements 13 November 2013 slide 13
APPENDIX 13 November 2013 slide 14
Zeta-potential 13 November 2013 slide 15
TGA Dm = 0.9 wt% 13 November 2013 slide 16