| AVS 56th International Symposium & Exhibition | |
| Applied Surface Science | Wednesday Sessions |
| Session AS+NS-WeM |
| Session: | Nanoparticle and Nanoscale Surface Chemistry II |
| Presenter: | G. Zorn, University of Washington |
| Authors: | G. Zorn, University of Washington S.R. Dave, University of Washington T. Weidner, University of Washington X. Gao, University of Washington D.G. Castner, University of Washington |
| Correspondent: | Click to Email |
Semiconductor nanocrystals (Quantum Dots, (QDs)) have started to play a pivotal role in molecular labeling, cancer diagnostics and tumor imaging due to their quantum mechanical and electronic characteristics. These characteristics give them unique optical properties such as size-tunable emission profiles, broad excitation spectra, long fluorescence lifetimes, large Stokes shifts and high quantum yields. The most common QD type is a CdSe/ZnS core - shell structure surrounded by hydrophobic ligands1; but for biological applications, QDs have to be transferred into aqueous solutions and require specific techniques for the conjugation of small peptides or antibodies onto their surfaces. In this context, a promising and widely used approach is, to encapsulate the nanocrystals with an amphiphilic polymer1,2. Still, there are only few reports regarding characterization of absorbed polymer and theoretical analyses are typically based on simple geometric models.
This work is focused on characterizing the amount of the amphiphilic Poly(maleic anhydride-alt-1-tetradecene) (PMAT, Mw~9000) adsorbed onto a TOPO-coated CdSe/ZnS QD, as well as analyzing the polymer structure and the TOPO – PMAT interaction. An insight into the elemental composition of the nanocrystals before and after PMAT encapsulation is provided along with the orientation of the surrounding organic components. EDAX, XPS and ToF-SIMS suggest the QDs are comprised of non-stoichiometric Cd-enriched QDs with a ~0.5 monolayer ZnS shell. SFG C-H stretching of the CdSe/ZnS nanocrystals before PMAT encapsulation shows that there is a significant degree of orientational order in the TOPO film. Moreover, after PMAT encapsulation SFG C-H stretching indicates a certain degree of order in the PMAT polymer layer. Finally, from XPS analysis the number of PMAT molecules per QD is estimated to be ~7 to 1.
Reference:
1. Smith, A. M.; Dave, S.; Nie, S.; True, L.; Gao, X., Expert Rev. Molec. Diagnos. 2006, 6, 231-244.
2. Rhyner, M. N.; Smith, A. M.; Gao, X.; Mao, H.; Yang, L.; Nie, S., Nanomedicine 2006, 1, 209-217.