Materials Research Lecture

Intrinsic ability of nanoparticles (NPs) to self-organize can be seen virtually everywhere around us. Some manifestations of this ability are apparent, for instance, stacking and gelation of clay nanosheets. Other manifestations are less obvious. They include, however, such a common biological process as biomineralization of bones and teeth. Although omnipresent, the mechanisms of these processes are not well understood and include many surprises. A step toward clarification of these mechanisms can be achieved by juxtaposition of selforganization processes known for biological species and NPs. Key results of biomimetic and theoretical analysis based on consideration of electrostatic and dispersion interactions of such processes will be presented.

Two general classes of assemblies will be considered. Self-organized structures known as "terminal" cannot grow beyond a certain size. The second class of assemblies known as "extended" may continuously grow along specific directions. The distinction between these two cases will be made based on the balance of attractive and repulsive interactions between NPs using simplified phase diagrams. The fundamental problems associated with quantitative description of forces between NPs will be elaborated.

Practical relevance of terminal assemblies from biological species and surfactants (fatty acids, lipids, proteins, etc) is based on their simplicity, versatility, and multifunctionality. Self-limited supraparticle assemblies from NPs obtained by balancing electrostatic repulsion with van der Waals attraction, embody the same advantages very well. In addition, they also retain special optical, electrical, and catalytic properties of inorganic nanomaterials. Self-limited supraparticles can be made from a variety of charged NPs as well as from their combinations with biomolecules. Low molecular weight molecules can be easily incorporated into them as well. Terminal assemblies were also made using self-limited biological interactions typical for oligonucleotide strands. Chiral assemblies with geometry of "open scissors" were made from gold nanorods using this approach. They demonstrated exceptionally low detection limits for detection (LOD) of DNA and proteins when circular dichroism spectroscopy is used for an analytical tool. Surprisingly, LODs in chiroplasmonic method are lower than other colorimetric, SERS, or fluorescent techniques based on NPs.

The bench-to-product transition for extended assembles is enabled by their ability to produce electrically conductive submicro-, micro-, and macroscale structures. Oriented attachment processes typical for water-soluble NP makes possible epitaxial lattice-to-lattice connectivity for solution processable electronic devices. If time permits, unusually highly conductive materials made by layer-by-layer assembly of Au NPs and device prototypes from NPs of semiconductors will be demonstrated.

Relevant References.

1. Z. Tang, N. A. Kotov, M. Giersig, Science, 2002, 297, 237-240.

2. Z. Tang,. Z. Zhang,; Y. Wang; S. C. Glotzer, Kotov, N. A., Science, 2006, 314 (5797) 274-278.

3. J. Lee, A. O. Govorov, N. A. Kotov, Nature Materials. 2007, 6(4), 291-295.

4. S. Srivastava, A. Santos, K. Critchley, K.-S. Kim, P. Podsiadlo, K. Sun, J. Lee, C. Xu, G. D. Lilly, S. C.

Glotzer, and N. A. Kotov, Science, 2010, 327, 1355-1359.

5. M. Yang, K. Sun, N. A. Kotov, J. Am. Chem. Soc., 2010, 132 (6), pp 1860–187.

6. Y. Zhou, M. Yang, K. Sun, Z. Tang and N. A. Kotov, J. Am. Chem. Soc., 2010, 132 (17), 6006–6013

7. N. A. Kotov, Inorganic Nanoparticles as Protein Mimics, Science, 2010, 330 (6001), 188-189.

8. S. I.Yoo, N.A. Kotov, Angewandte Chemie, 2011, 50(22), 5110–5115.

9. Y. Xia et al, Nature Nanotechnology, 2011, 6, 580-587.

10. W. Yan, et al, J. Am. Chem. Soc. 2012, J. Am. Chem. Soc. 134 (36), 15114–15121

11. L. Xu, et al Chem. Soc. Rev., 2013, 42, 3114-3126.

12. Y. Kim, J. Zhu, et al Stretchable nanoparticle conductors with self-organized conductive pathways; Nature,

2013, 500, 59-64.

13. J.-Y. Kim. N. A. Kotov Charge Transport Dilemma of Solution-Processed Nanomaterials, Chem. Mater.,

2014, 26 (1), pp 134–152.

14. J. I. Park et al, Terminal Supraparticle Assemblies from Similarly Charged Protein Molecules and

Nanoparticles Nature Comm, 2014, in press

More about the Speaker: Prof. Nicholas A. Kotov is Joseph and Florence Cejka Professor of Engineering at University of Michigan.  He graduated from Moscow State University where he was working on working on biomimetic interfaces for solar energy conversion.  The focus of his current research projects is self-organization of nanoparticles into complex biomimetic systems – chains, sheets, helices and others.   Such assemblies enable integration with microscale technologies and energy-conservative production of biosensing, energy conversion, electronic devices, catalysts, and protective coatings. His ongoing research projects also include advanced composites made by the layer-by-layer (LBL) assembly that represent another example of biomimetic nanoscale materials.  Mechanical properties of LBL multilayers from nanoparticle of clay and other materials replicating those of nacre as the unique natural composite material were at the onset of his studies in this area.  Prof. Kotov receives multiple university, national, and international awards. He was elected as Fellow of Royal Society of Chemistry in 2012 and MRS Fellow in 2014.  He serves as an Associate Editor for ACS Nano and as a member of Advisory Boards of several nanotechnology and materials journals.