Dimensionality Effects at the Single Nanocrystal Level, FRET Between Semiconductor Nanorods and Multiple Dye Acceptors

Ido Hadar, Institute of Chemistry and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem, Israel
Uri Banin, Institute of Chemistry and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem, Israel

Colloidal semiconductor nanocrystals are outstanding donors in energy transfer processes due to their unique size and shape dependent optical properties, their exceptional photostability, and chemical processability. In the current research we examine the dimensionality effect in energy transfer between single heterostructure nanocrystals of spherical and rod shape, serving as donors, and multiple organic dye molecules attached to their surface acting as acceptors. Förster resonant energy transfer (FRET) to individual dye molecules attached to a single nanocrystal is identified via step like changes in both acceptor and donor emission, enabling to calculate the efficiency of energy transfer and distance of each acceptor individually. The ability to trace single molecules attached to the surface of a nanocrystal as well as single binding events offers a unique tool to study the surface chemistry of various nanocrystals. Statistical analysis of many single particles allows extracting the geometrical distribution of acceptor dyes on the nanocrystal surface, reflecting its dimensionality. Moreover, the inner geometry of these heterostructures, such as the location of the seed and shell thickness can be studied by analysis of the obtained distance distribution. Additionally, due to their high extinction coefficient, the nanocrystals serve as an optical antenna that enhances the excitation and emission of the dye molecules through the FRET interaction. These measurements enable to gain deeper understanding of the energy transfer process between semiconductor nanocrystals of various geometries and dye molecules, and promote its utilization for extremely sensitive sensing applications at the single molecule level.