Nano-sized Optical Fluorescence Labels Developed at Geogia Tech

Georgia Tech researchers Robert Martin Dickson and Jie Zheng have created nano-sized optical fluorescence labels. According to U.S. Patent 7,611,907 granted to Georgia Tech Research Corporation (Atlanta, GA), the compositions are encapsulated noble metal nanoclusters which are capable of fluorescing. The fluorescent labels provide certain advantages over known fluorescent labels, which include the small size, much stronger absorption and emission under weak illumination, facile synthesis and conjugation to proteins, tunable emission color, and the option to genetically program the labels such that proteins can be directly labeled intracellularly.

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.

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, his group is 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.