PhD candidate, Northwestern University


Exploiting bio-inspired self-assembly for the design of responsive materials

Designer materials, synthesized using nanoscale objects, often have unique properties that have never been seen before in nature. With crystals in particular, crystal size has been proven to be a key parameter that dictates material properties. Oligonucleotides can be utilized to precisely arrange nanoparticles in three-dimensions, creating systems where structure-function relationships can be investigated across multiple length scales. With DNA as a programmable bonding element, variations in DNA sequence and length and nanoparticle size and shape can be tuned to systematically change the lattice symmetry and parameters of the resulting crystal for many different particle compositions. Here, we explore how small molecules or solution ionic strength can be used to deliberately change the bond strength of the DNA to mediate nanoparticle crystallization kinetics and the resulting single crystal domain size. Indeed, we can tailor crystal size from 500 nm to 21 µm and post-synthetically modify such single crystals using intercalators to strengthen the connections between the particles that define them. This also allows layers of different particles to be epitaxially grown onto a seed crystal without perturbing its structure. In this way, novel two-component core-shell single crystals with unusual photophysical properties have been realized.


Epitaxy: Programmable Atom Equivalents Versus Atoms

Abstract: The programmability of DNA makes it an attractive structure-directing ligand for the assembly of nanoparticle (NP) superlattices in a manner that mimics many aspects of atomic crystallization. However, the synthesis of multilayer single crystals of defined size remains a challenge. Though previous studies considered lattice mismatch as the major limiting factor for multilayer assembly, thin film growth depends on many interlinked variables. Here, a more comprehensive approach is taken to study fundamental elements, such as the growth temperature and the thermodynamics of interfacial energetics, to achieve epitaxial growth of NP thin films. Both surface morphology and internal thin film structure are examined to provide an understanding of particle attachment and reorganization during growth. Under equilibrium conditions, single crystalline, multilayer thin films can be synthesized over 500 × 500 μm2 areas on lithographically patterned templates, whereas deposition under kinetic conditions leads to the rapid growth of glassy films. Importantly, these superlattices follow the same patterns of crystal growth demonstrated in atomic thin film deposition, allowing these processes to be understood in the context of well-studied atomic epitaxy and enabling a nanoscale model to study fundamental crystallization processes. Through understanding the role of epitaxy as a driving force for NP assembly, we are able to realize 3D architectures of arbitrary domain geometry and size.

Pub.: 05 Dec '16, Pinned: 21 Aug '17