The Macromolecular, Supramolecular, and Nanochemistry Program along with the Chemical Measurement and Imaging Program in the Chemistry Division supports Professor Jeffrey T. Petty at Furman University to control and fine-tune the colors and emissions of nanoscale metal chromophores (color-producing molecules) using DNA strands as scaffolds. This research impacts the burgeoning area of metal-linked DNA constructs that expand the genetic code of DNA for optical sensing and imaging applications. Metals are widely used in society due to their high conductivity, malleability, and reflectivity. As metal particles shrink to nanometer dimensions of 1000 times smaller than the thickness of a human hair, their electrons reorganize and new properties emerge. For example, although bulk silver is highly reflective, clusters of a few-atoms of silver have diverse colors that depend on the cluster size, shape, and charge. Through the combined expertise of Professor Petty at Furman University along with Professors Raquel Lieberman and Robert Dickson at the Georgia Institute of Technology, atomic-resolution structures of nanoscale DNA-silver clusters are measured with X-ray diffraction. The electronic organization of the nanoscale structures are probed over nano- to milli-second time scales with laser-precision. The educational broader impact of the project centers on the mentoring and training of undergraduate students at Furman University, a primarily undergraduate institution, through a comprehensive research experience. Furman undergraduate students spearhead their individual research projects through close collaboration with graduate students and faculty from major research universities such as the Georgia Institute of Technology and the University of Münster.
With this support from the Macromolecular, Supramolecular, and Nanochemistry Program and the Chemical Measurement and Imaging Program, Professor Petty?s team at Furman University develops DNA-silver cluster chromophores using a structure-guided approach. Silver clusters with ~10 atoms are stabilized by DNA strands, and the spectra and photophysics of these adducts are encoded via the DNA nucleobases. To date, DNA-silver cluster chromophores have been empirically developed for specific sensing and imaging applications. A recent atomic-level structure of a DNA-silver cluster complex identifies three structural motifs that show how the silvers and DNA are organized. A DNA dimer with two A2C4 strands traps eight silver atoms that are arranged as in the Big Dipper asterism. A subset of five silver atoms mimics the dipper because they have a trapezoid shape. These are separated by metallic bond distances and are likely the chromophoric core of the green-emitting complex. The three other silver atoms resemble the dipper handle because they disperse between pairs of cytosines and join the DNA strands. These three bonding motifs are selectively modified by borrowing tools from chemistry and biochemistry. The modification tools are for chemically modifying nucleobase heteroatoms, enzymatically excising nucleobases, and synthetically linking DNA strands. The electronic environment of the resulting clusters is comprehensively characterized via steady-state, time-resolved, and chirooptical spectroscopies. DNA-cluster conjugates with distinctive spectra are characterized by mass spectrometry to determine the numbers and distributions of silver atoms within the complex. These species are then screened using a wide range of solution conditions to form crystals and analyzed by X-ray diffraction to establish the relationship between the DNA-silver bonding and silver cluster spectra.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
