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 fluorescing Ag clusters . Having made these water-soluble, the outstanding photostability and brightness of DNA-encapsulated Ag nanocluster emitters offer great promise as materials and biological labels.

SAFIRe. We have developed the concept of optically modulated fluorescence for selective recovery of our emitters from within overwhelming background. This adapts the concept of modulation as used in traditional high resolution absorption spectroscopy to fluorescence imaging, and has allowed discrimination of nanocluster, cyanine dye, and fluorescent protein signals with signal:background improvements exceeding 100-fold. This expands the dimensionality of imaging to include dark state lifetimes, and is performed by modulating long-wavelength transient absorptions of our designed emitters. Such methods do not increase background, but simply shift our signals of interest to a unique detection frequency, enabling its selective recovery without background. Interaction timescales and selective imaging enable a wide variety of protein interactions and locations to be studied.

Directly find my publications on Pubmed Central.

or a more complete list on Google Scholar.