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Dr. Dickson's group is developing novel single molecule methods for the study of intermolecular interactions in biological and materials systems. By directly imaging anisotropic dipolar single molecule emission and modeling expected emission patterns, we have developed the world's only methods for determining true 3-D single molecule orientations. Since each molecule interacts differently with its surroundings, great diversity is observed in molecular behaviors. For example, single molecules in polymeric matrices exhibit surprising rotational mobilities that are indicative of nanoscale polymer dynamics. Such molecular orientational studies directly probe both biological and materials systems to provide greatly enhanced understandings of their dynamics. Single Molecule Biophysics. Having observed orientation-dependent interactions of fluorescently labeled, single proteins, precise studies of biological mechanisms are performed. Unfortunately, standard fluorescent labels are often unsuitable for long-time single molecule imaging, especially in living systems. Thus, in order to make single molecule methods more accessible, we are developing Au and Ag nanoclusters as a new class of fluorescent labels in biology. These high brightness, robust nanomaterials should enable direct labeling of proteins to image live cells, study protein-protein interactions, and potentially watch individual proteins as they fold to their native conformations. Au and Ag nanoclusters exhibit discrete excitation and emission due to being composed of only a few atoms. Consequently, with size-tunable optical properties and absoprtion comparable to semiconductor quantum dots, but with improved photostability, these nanoclusters offer new opportunities in biological labeling. For example, the extremely small size will be less invasive; noble metals are not toxic; and their discrete energy levels enable energy transfer experiments to be performed—all with weak mercury lamp illumination on the single molecule level. Much brighter and more robust than organic dye molecules, these advanced inorganic nano-materials are being utilized both as optical memory elements and as photo-activated biological labels. Optical Properties of Individual Nanoparticles. We have created and are currently studying the properties of extremely brightly fluorescing photo-activated nanoparticles . Much brighter and more robust than organic dye molecules, these advanced inorganic nano-materials are being utilized both as optical memory elements and as photo-activated biological labels. Single Molecule Electroluminescence. We have created the first electroluminescent single molecules/nanoclusters at room temperature. The discrete energy levels of these 2-20 atom nanoclusters yield molecular emission with color being indicative of nanocluter size. Employing negative differential resistance-like behavior in the EL, we have created single molecule LEDs, single nanocluster logic gates, and even a full adder constructed from only two nanoclusters. We are currently studying the charge injection into different nanoclusters to characterize the interfaces crucial to all nanoscale/molecular electronics and optoelectonics devices.