(705g) Molecular Assemblies of Nanoparticles: Surprising Analogy with Proteins and New Optical Properties

Physical properties of nanoparticles and nanowires are currently well understood. The next frontier is conceptualization of larger structures, such as nanoscale assemblies. This talk will discuss the two paradigms in this field: (1) spontaneous assemblies of nanoparticles and (2) quantum mechanical interactions of metallic and semiconductor building blocks in nanoscale assemblies. 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. We found that nanoparticles show conceptual similarities with assembly of proteins. This supposition was recently confirmed by assembly of nanoparticles into spiral systems similar to those found in many biological systems.

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.