Programmable Nanomaterials

The ability to synthesize materials by design is one of the greatest outstanding scientific challenges. Advances towards meeting this challenge will lead to discoveries in fields such as plasmonics, photonics, catalysis, and energy sciences.

In the Mirkin group, we employ a novel approach to the realization of materials by design, where nanoparticle “atoms” functionalized with a dense shell of oligonucleotides are assembled via oligonucleotide “bonds” into crystalline superlattices with tunable compositions, symmetries, and lattice parameters. The high degree of control over the assembly characteristics of these oligonucleotide-nanoparticle conjugates, termed “programmable atom equivalents” (PAEs), is enabled by the exceptional molecular recognition, tunability, and predictability of the nucleic acid bonds (Fig. 1). Unlike atomic systems in which the bonding character of an atom is dictated by its atomic composition and configuration of valence electrons, PAEs allow one to independently control the nanoparticle core (tunability in the nanoparticle size, shape, or composition) separately from the oligonucleotide “bonds” (controllable nucleic acid type, sequence, length, flexibility, and strength).

While PAEs provide discrete control over crystal engineering where the location of every nanoparticle is fixed, we discovered that small nanoparticles (~1.5 nm) functionalized with DNA can be mobile within nanoparticle lattices (Fig. 2). Specifically, these small particles, termed electron equivalents (EEs), readily diffuse within stabilize lattices of repulsive PAEs. The diffusion (i.e., delocalization) of EEs introduces the concept of metallicity to colloidal crystal engineering, where metallic, intermetallic, and other complex phases can now be targeted. Ongoing research in the Programmable Nanomaterials subgroup focuses on exploiting the functionalities of the nanoparticle atoms in the crystalline state, tuning the nature of the DNA bonds, and studying the diffusive properties of small nanoparticles functionalized with DNA.

Employing the programmability of the DNA bond to create tunable and responsive nanoparticle superlattices

Biological systems are inherently responsive to external stimuli, enabling a high degree of control over complex processes such as signaling cascades. We are developing several unique approaches for designing oligonucleotide bonds that enable a similar degree of responsiveness and tunability to be incorporated into PAE superlattices. One example of this is the concept of “transmutable nanoparticles,” which include a number of closed ‘hairpin’ DNA strands along the surface of nanoparticles that cannot link with strands on neighboring particles (Fig. 5). The addition of “effector” strands, which are short oligonucleotide sequences that act as switches and can open these hairpins, allows the particles to bond into a particular lattice arrangement. By using different switches and combinations of nanoparticles, we can effectively and dynamically change the bonding character of “transmutable nanoparticles” and drive their crystallization pathway along multiple thermodynamic trajectories.