MSE Special Seminar: Structure Determination and Photophysical Characterization of DNA Stabilized Silver Nanoclusters

Abstract: In the past twenty years, DNA has been used as a scaffold to stabilize atomically monodisperse silver nanoclusters. Thanks to their size below 2 nm, DNA-embedded Ag nanoclusters (DNA-AgNCs) are characterized by discrete energy levels, hence they can absorb and emit visible and near-infrared (NIR) light. The combination of mass spectrometry and single crystal X-ray diffraction of HPLC-purified DNA-AgNCs is a powerful tool to determine the charge and structure of the encapsulated AgNC. Such information is not only relevant to design new DNA-AgNCs with tailored properties, but it is also important for bio-conjugation experiments and essential for electronic structure calculations. Particularly, single crystal X-ray diffraction measurements are paramount to gain insight into the atomic arrangement of the silver atoms, the coordinate bonds to the DNA and the overall DNA conformation. However, every step in the crystallization and structure determination process is neither trivial nor guaranteed to succeed. The structures of two different emitters are presented, along with their photophysical characterization. One structure and seven mutations thereof are related to a NIR emitter formed by 16 Ag atoms encapsulated by two DNA decamers that take on a horse-shoe-like conformation. Thanks to mass spectrometry performed by Gonzàlez-Rosell et al., it was then found that two chloride ligands are also present in the structure, and the overall charge of the nanocluster is 8+. The second structure corresponds to a 4-valence-electron green-emitting DNA-AgNC, which becomes dual emissive when in the crystalline and dried states.

Bio: Cecilia Cerretani is an assistant professor in physical chemistry at the University of Copenhagen, Denmark. Cerretani graduated in chemistry from the University of Florence, Italy, in 2017, and obtained her Ph.D. from the University of Copenhagen, in 2020. She has been working in professor Tom Vosch’s group since her Ph.D. fellowship. Cerretani’s research interests revolve around atomically precise emitters formed by a very limited number of silver atoms and cations stabilized by DNA oligomers. Specifically, she works on the synthesis and spectroscopic characterization, via steady-state and time-resolved fluorescence techniques, of DNA-templated silver nanoclusters (DNA-AgNCs). Part of her research focuses also on the crystallization and structure determination of these emissive species in order to infer the relationship between the photophysical and structural properties. This knowledge can then be used to design DNA-AgNCs for specific applications.