DoD Multidisciplinary University Research Initiative
Richard A. Kiehl, Principal Investigator

Goal. The goal of this MURI is to exploit DNA, protein, and peptide strategies, together with chemical synthetic techniques, to create metallic nanoparticle arrays for systematic study of quantum many-body physics in normal metal and magnetic nanoparticle systems. This study will provide a foundation for the development of a reliable biological route to precision assembly of quantum electronic systems that can operate at room temperature.

Overview. The creation of new structures can open the door to new phenomena. We propose to exploit biology to create structures for systematically exploring many-body physics in arrays of nanoparticles (NPs). We will seek to observe and analyze the spectrum of novel behaviors possessed by these nanoscale systems.

Examples of many-body physics involving nanoparticle collective degrees of freedom are already well known. Coulomb blockade physics in which electrons tunnel between nanoparticles changing nanoparticle total electron numbers is one important example. The moment orientation of magnetic nanoparticles has also received attention in recent years. In the past, interest has often focused on regimes in which these degrees of freedom can be treated classically. Our focus will be on the quantum behavior of collective degrees of freedom, especially in interacting NP systems. We believe that this frontier can be revealed by biological assembly, and that it has greater potential in the search for fundamentally new science.

Until now, systematic study of such systems has not been possible because of the inability to fabricate the needed nanostructures with the required precision, control, and quality. The requirements for precision are extreme, not only in NP size but in position. Moreover, for systematic studies, these dimensions must be tailored with the same precision. The structures must also be of high quality in terms of materials and structural uniformity. For systematic study, the components should be also interchangeable with negligible change in the surrounding structure.

Biological assembly potentially offers the fabrication technology needed to explore many-body physics in quantum electronic arrays. DNA scaffolding has been shown to be a promising approach for assembly NP arrays in the several nanometer size regime. DNA offers a way to construct 2D and 3D scaffolding with a precision approaching the 0.34-nm nucleotide separation, together with a capability for tailoring the scaffolding geometry at these dimensions. Because of the cooperative nature of the self-assembly process and the structure's crystalline form, the achievable quality of DNA scaffolding is potentially high. Attachment of NP to the scaffolding by Watson-Crick base pairing or other biochemical approaches provides an “additive” fabrication process, thereby allowing dissimilar components to be assembled in close proximity.

The 3D structure of proteins offers a biological scaffolding that is particularly attractive for organizing more complex modular subcomponents. Protein-assembled NP dimers or trimers could provide a quantum-mechanical subsystem, which could then be assembled into periodic arrangements on DNA scaffolding to allow subcomponent interaction. The specific affinity of peptides to inorganic surfaces offers a means for binding NPs with certain compositions and orientations into the scaffolding.

Biological assembly has another important advantage over other strategies. It is well suited to exploiting versatile techniques for chemical synthesis of metallic particles with organic shells developed in recent years. These techniques allow the synthesis of monodisperse metallic NP that are stabilized and monofunctionalized for precision binding to biological scaffolding. They also allow precise control of chemical bonding between metallic core and organic shells, which is critical for controlling electron transport in these structures.

Huang (UCLA, MSE) brings expertise in identifying biomolecules that possess highly specific affinity to inorganic materials. She will exploit phage display techniques and develop protocols for identifying short peptides sequences that will specifically bind to core/shell NP in the 2-8 nm range in this study.

Kent (NYU, Physics) brings expertise experimental studies of magnetic nanostructures, including quantum tunneling of magnetization, spin transport and spin momentum transfer. He will use techniques including sensitive microwave spectroscopy and magnetometry methods to probe magnetic interaction in NP arrays.

Kiehl (U of MN, ECE) brings expertise in top-down nanofabrication processing and bottom-up DNA self-assembly of NP arrays and in electrical characterization of nanoscale structures. His group will perform studies of electronic transport in nanocontacted structures and will use proximal nanoprobe techniques (C-AFM, NSOM) for spatially characterizing transport.

MacDonald (U of TX, Physics) brings broad experience in the theory of many-electron physics of correlated electronic states in metals and on theories of nanomagnetism and spntronics. His group will develop models for quantum many-body effects of NP and their interactions in arrays and determine methods for probing and analyzing these effects experimentally.

Murray (IBM T. J. Watson; U. Penn, Chemistry) brings expertise in the synthesis, characterization and integration of magnetic nanocrystals. Close coordination with the Nuckolls team will allow optimization of core inorganic and surface organic and organometallic chemistry for the magnetic NP components in this study.

Nuckolls (Columbia U, Chemistry) brings expertise in how reaction chemistry can be used in the design of nanostructed objects and devices. He will apply his knowledge of how to interface metals and molecules to simultaneously connect and assemble particles in nanoscaffoldings derived from either DNA or proteins.

Seeman ( New York University , Chemistry) founded DNA nanotechnology in 1982. He has built target objects, lattices and nanomechanical devices from branched DNA motifs. He will use his expertise to organize nanoparticles and proteins on DNA lattices, both in 2D and in 3D.

Wang (UCLA) brings in the expertise in the use of microwave techniques and magneto-transport to study many-body effect of magnetic dot arrays as well as the techniques for fabricating test structures. He will investigate transport properties of magnetic NP arrays for studying exchange interaction and carrier-carrier interaction.

Yeates (UCLA, Chemistry and Biochemistry) brings expertise in protein assembly, structure, and design, particularly in proteins that self-assemble into oligomeric and higher order supramolecular structures. He will exploit protein-based strategies for assembling NP dimer and trimer subcomponents for these studies.