Elisabeth Gwinn and Deborah Fygenson of the University of California, Santa Barbara are supported by an award from the Macromolecular, Supramolecular and Nanochemistry program for research to build understanding of the spectral properties, solution structures and array potential of fluorescent silver clusters that are stabilized within DNA strands and strand assemblies. Tandem HPLC-mass spectrometry with in-line optical spectroscopy will be used to determine how the optical properties of such Ag:DNAs relate to the number of silver atoms and DNA strands contained in the complexes. Double-stranded DNA strut constructs will be developed to hold individual silver clusters in defined geometries, and to support dual clusters in nanoscale proximity. Measurement of diffusion constants, combined with structural modeling, will probe whether incorporation of the clusters grossly disrupts the designed assemblies. Single molecule microscopy will be used to evaluate polarization signatures of dual silver cluster assemblies held in strut-based constructs and to probe whether silver cluster transition moments are oriented by the underlying DNA assembly. To characterize and enable future exploitation of directional optical interactions of such oriented silver cluster moments, spectral and polarization imaging studies will be carried out on silver cluster arrays formed on DNA nanotubes.
Tiny, light-emitting silver clusters that are held within synthetic DNA strands are beginning to emerge in innovative applications for imaging, molecular logic, and selective sensing. Further development is impeded by the current lack of understanding of the cluster sizes and shapes, and of how they interact with the DNA that keeps them stable. This work will build an understanding of how the color and brightness of Ag:DNAs depends on silver cluster sizes and on the DNA surroundings. The development of strategies to hold multiple clusters in nanoscale proximity on DNA constructs will enable tests of whether the orientation of the clusters is stable enough over time to be exploited in directional interactions of arrayed clusters. Such Ag:DNA constructs may impact technology through future use in signaling chemical, mechanical and electronic events; in new probes of biomolecules, and through fluorescence identification of structural perturbations too subtle to identify with existing microscopies. High-school audiences will be exposed to this multi-disciplinary work through UCSB's School for Scientific Thought, in mini-classes developed and taught by graduate student researchers. The emphasis on undergraduate participation in the research will focus on engaging students who transfer to UCSB from California Community Colleges.
