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Oct 27, 2008
Refreshments will be served.
City College of New York, 160 Convent Avenue, Steinman Hall, Rm. 312
phone (212) 650-7232
Professor Nicholas Kotov, from the University of Michigan, speaks on the topic of: Self-Assembled Systems of Nanoparticles: Surprising Analogies with Proteins and New Optical Properties.
Figure 1: (A) Schematics of the system of CdTe NWs and Au NPs with plasmon-exciton interactions. (B) Calculated geometry of self-organized CdTe sheets with hexagonal packing. closely matching the experiment. A B Surface chemistries of nanoparticles and proteins reveal a lot of similarities which can also be traced in chemical and biological behavior starting from processing techniques to cell signaling. In this presentation they will be reviewed and compared. Special attention will be given self-organization phenomena taking place with semiconductor nanocolloids starting with supercrystals from nearly spherical nanoparticles and nanoparticle bioconjugates to 1D and 2D assemblies. Comparison of the processes in solution of CdTe and other nanocolloids reveals a number of surprising similarities with processes in proteins. The conclusion that will be reached that this is the result of fundamental analogy in the scales between proteins and nanoparticles. This conclusion will be substantiated by a variety of experimental and theoretical observations of analogies between biological effects of nanoparticles and proteins. In essence, the talk will show that anisotropic forces arising between nanocrystalline particles drive the self-assembly behavior of these colloidal particles. Interaction anisotropy between CdTe nanoparticles in solution leads to their spontaneous, template-free organization into free-floating sheets. Electrostatic interactions arising from a dipole moment and a small positive charge combined with directional hydrophobic attraction between the nanoparticles are the driving forces for the self-assembly, which we demonstrate by computer simulation. The laws governing this process show conceptual similarities with assembly of proteins. Electronic interactions in nanoparticle assemblies represent one of the fundamental problems of nanotechnology. Excitons and plasmons are the two most typical excited states of nanostructures, which were shown to produce coupled electronic systems. The concept of these interactions between the Au and CdTe nanoparticles and nanowires will be discussed in terms of quantum mechanical coupling of excited states and unusual optical effects. As such, in presence of dynamic component for excitons theory predicts that emission of coupled excitations in nanowires with variable electronic confinement is stronger, shorter, and blue-shifted. These predictions were confirmed with high degree of accuracy in molecular spring assemblies, where one can reversibly change the distance between the exciton and plasmon. The prepared systems were made protein-sensitive by incorporating antibodies in molecular springs. Modulation of exciton-plasmon interactions can serve as wavelength-based biodetection tool, which can resolve difficulties of quantification of luminescence intensity for complex media and optical pathways. Relevant References. Z. Tang, N. A. Kotov, M. Giersig, Science 2002, 297, 237-240. Tang, Z. Zhang, Z.; Wang Y.; Glotzer, S. C. Kotov, N. A., Science, 2006, 314 (5797) 274-278. Sinyagin, A. Belov, A. Tang, Z. Kotov. N. A. J. Phys. Chem. B 2006, 110(14), 7500-7507 J. Lee, A. O. Govorov, N. A. Kotov, Angew. Chem. Intern. Ed. 2005, 44, 7439-7442. J. Lee, A. O. Govorov, J. Dulka, N. A. Kotov, Nano Lett. 2004, 4, 2323-2330. J. Lee, A. O. Govorov, N. A. Kotov, Nature Materials. 2007, 6(4), 291-295.
Refreshments will be served.
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