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DNA-based Assembly of Nanoparticle Crystals

Our nanoparticle subgroup has developed a new and versatile DNA-based strategy for organizing nanoparticle superlattices without the use of any base-pairing. Some of our current research directions include:

1. Real-time dynamical self-organization of nanoparticle superlattices
2. Patterning superlattices into nanoscale features with micromolds
3. Assembly of nanoparticle crystals at 1D, 2D and 3D levels

We believe that our DNA-based systems will find a plethora of applications in high-efficiency solar cells, novel nanocatalysis and ultra-sensitive sensors.

Nanopatterning by Controlled Evaporation

We developed a simple approach for patterning highly-ordered arrays of nanoparticles (both 2D and 3D) that uses a soft stamp for to regulate the drying process of microdroplets containing DNA-capped nanoparticles. This technique provides rational control over the local nucleation and growth of the nanoparticle superlattices. Using DNA-capped gold nanoparticles as a model system, we have patterned nanoparticle superlattices over large areas into a number of versatile structures by varying the stamp pattern and applied pressure, including single-particle-width corrals, single particle-thick microdiscs and submicrometre-sized 'supra-crystals'. We believe that this technique is versatile enough to be applied to other types of nanoparticles for plasmonic applications as well as for the patterning of proteins and large macromolecules.

Free-standing Nanoparticle Superlattice Membranes

Free-standing Nanoparticle Superlattice Membranes We have developed the first DNA-based route towards monolayered free-standing nanoparticle superlattices (suspended highly-ordered nanoparticle arrays), which have potential applications as optoelectronic materials that are free from substrate-induced interference. DNA-conjugated gold nanoparticles were utilized in a microhole-confined, drying-mediated self-assembly process. Without using Watson–Crick base-pairing, we produced discrete, free-standing superlattice membranes that were stabilized by physical interactions between the DNA ligands. In addition, both structure (inter-particle spacings) and functional properties (plasmonic and mechanical) can be rationally controlled by adjusting DNA length. Our method opens a simple yet efficient avenue towards the assembly of artificial nanoparticle solids in their ultimate thickness limit—a promising step that may enable the integration of free-standing superlattices into solid-state nanodevices.

Nanoparticle Crystallization Studies

We study how nanoparticles arrange can into highly-ordered crystals, and how attaching DNA to the nanoparticles provides control over the crystallization process. We were able to produce three-dimensional crystals simply by drying a solution containing DNA-capped nanoparticles. The spacing within the 3D crystals could also be controlled by changing the DNA length, but could also adjust dynamically to their environmental conditions. For example, varying the humidity or salt concentrations within the crystals produced reversible shrinkage and expansion. These studies suggest that it may be possible in the future to develop "smart", environmentally-adaptable nanoscale materials based on DNA-nanoparticle assemblies. Studies of the crystal formations were performed using small-angle x-ray scattering spectroscopy at CHESS, which is a technique typically used to investigate the partially ordered materials on the nanoscale and the physical characteristics of large macromolecules.

Relevant Literature

W.L. Cheng, N.Y. Park, M.T. Walter, M.R. Hartman, D. Luo, Nanopatterning self-assembled nanoparticle superlattices by moulding microdroplets, Nature Nanotechnology 3 (2008) 682-690.

W.L. Cheng, M.J. Campolongo, J.J. Cha, S.J. Tan, C.C. Umbach, D.A. Muller, D. Luo, Free-standing nanoparticle superlattice sheets controlled by DNA, Nature Materials 8 (2009) 519-525.

W.L. Cheng, M.J. Campolongo, S.J. Tan, D. Luo, Freestanding ultrathin nano-membranes via self assembly, Nano Today 4 (2009) 482-493.

W.L. Cheng, M.R. Hartman, D.-M. Smilgies, R. Long, M.J. Campolongo, R. Li, K. Sekar, C.-Y. Hui, D. Luo, Probing in real time the soft crystallization of DNA-capped nanoparticles, Angewandte Chemie International Edition 49 (2010) 380-384.

R. Long, C.-Y. Hui, W.L. Cheng, M.J. Campolongo, D. Luo, Size effect on failure of pre-stretched free-standing nanomembranes, Nanoscale Research Letters 5 (2010) 1236-1239.

M.J. Campolongo, S.J. Tan , D-M. Smilgies, M. Zhao , Y. Chen, I. Xhangolli , W.L. Cheng , D. Luo. Crystalline Gibbs monolayers of DNA-capped nanoparticles at the air-liquid interface. ACS Nano. 5, 7978-7985 (2011).