University of South Carolina, Department of Chemistry and Biochemistry
“INTERFACIAL CHEMISTRY OF SEMICONDUCTOR NANOCRYSTALS”
Colloidal semiconductor nanocrystals – a type of quantum dot (QD) – are well-known as bright, highly photostable inorganic fluorophores that can be well-suited to imaging applications in biology. Additionally, the delocalized electronic states present in nanoscale semiconductors should offer distinctive ways to interact with and report on the biological environment. Such applications require good control of the interfacial chemistry of inorganic nanoparticles: in particular, to guide the formation of core/shell heterostructures to optimize brightness, and to introduce a surface coating that can enable the particles to function properly in the biological environment while limiting hydrodynamic size and avoiding quenching of the QD excited state. Significant progress has been made in identifying specific examples that comprise these features, especially for the case of metal chalcogenide semiconductors, but there remains only a limited understanding of the reaction mechanisms and thermodynamics associated with the elaboration of the surfaces of such particles with inorganic and organic layers. I will describe recent work at USC in which we have investigated the formation of CdS shells on CdSe nanocrystals under alternating layer addition conditions to evaluate the proposed selective ionic layer adhesion and reaction (SILAR) mechanism of shell growth, and ongoing work to directly measure the thermodynamics of ligand exchange reactions as part of a long-term effort to negotiate the trade-offs of binding strength against other properties such as fluorescence in the design of molecular monolayer coatings for biological applications of QDs.
Monday, October 15, 2012 @ 4:00 PM in Burson 115. Refreshments served at 3:45 PM
References for further reading:
1. Andrew B. Greytak, Peter M. Allen, Wenhao Liu, Jing Zhao, Elizabeth R. Young, Zoran Popović, Brian J. Walker, Daniel G. Nocera, and Moungi G. Bawendi. Alternating layer addition approach to CdSe/CdS core/shell quantum dots with near-unity quantum yield and high on-time fractions. Chemical Science, 3 2028 (2012).
2. Wenhao Liu, Andrew B. Greytak, Jungmin Lee, Cliff R. Wong, Jongnam Park, Lisa F. Marshall, Wen Jiang, Peter N. Curtin, Alice Y. Ting, Daniel G. Nocera, Dai Fukumura, Rakesh K. Jain, and Moungi G. Bawendi. Compact biocompatible quantum dots via RAFT-mediated synthesis of imidazole-based random copolymer ligand.. J. Am. Chem. Soc, 132 472 (2010).