DNA templates silver clusters with magic sizes and colors for multi-cluster fluorescent assemblies*

The natural inclusion of information in DNA, a vital part of life's rich complexity, can also be exploited to create diverse structures with multiple scales of complexity. Now emerging in novel photonic applications, DNA-stabilized silver clusters (Ag$_N$-DNA) are compelling examples of multi-scale DNA-directed assembly: individual fluorescent clusters, each templated by specific DNA base motifs, can then be arranged together in DNA-mediated multi-cluster assemblies with nanoscale precision. We discuss how DNA imbues Ag$_N$-DNA with unique features. Our optical data on pure Ag$_N$-DNA show that DNA base-cationic silver ligands impose rod-like shapes for neutral silver clusters, whose length primarily determines fluorescence color [1]. This shape anisotropy leads to the aspherical Ag$_N$-DNA magic number cluster sizes and ``magic color'' groupings [2]. We exploit DNA's sequence properties to extract multi-base motifs that select certain magic cluster sizes, using machine learning algorithms applied to large data sets [3]. With these base motifs, we design DNA scaffolds to arrange multiple atomically precise Ag$_N$ together in nanoscale proximity. We demonstrate that clusters are stable when held at separations below 10 nm, both in bicolor, dual cluster DNA clamp assemblies [4] and in one-dimensional assemblies of atomically precise clusters arrayed on DNA nanotubes.\\[4pt] [1] D. Schultz \textit{et al.}, Adv. Mater. \textbf{25}, 2797 (2013).\\[0pt] [2] S. M. Copp \textit{et al.}, J. Phys. Chem. Letters. \textbf{5}, 959 (2014).\\[0pt] [3] S. M. Copp \textit{et al.}, Adv. Mater. \textbf{26}, 5839 (2014).\\[0pt] [4] D. Schultz, S. M. Copp \textit{et al.}, ACS Nano \textbf{7}, 9798 (2013).