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• Stan Shihyao Chou

Stan Shihyao Chou

Materials Science and Engineering
Northwestern University
Room: B560, Silverman Hall
Chemistry of Life Processes Institute
2170 Campus Drive
Evanston IL, 60208-3113
Phone:(847) 491-5809 (L)
Facsimile:(847) 467-6573
Email: s-chou@northwestern.edu

Educational Background

Research Objectives and Approach

• Magnetic nanostructure synthesis and functionalization
• Biotemplated assembly of magnetic nanostructures
• SPM and cryo-EM characterization of organic-magnetic nanostructures

Research Objectives

• A water droplet's natural curved surface highlights the role of curvature in nature, a symbol of energy minimization. In a similar fashion, under different energetic considerations, a supermolecule can be curved based on circumstance. To encourage curvature in self-assembled supermolecules, we postulate that curved surfaces, in combination with differing stiffness and charge, can be used as self-assembly templates. To that end, taking nanoparticles with decreasing radius functionalized using combinations of synthesized charged and neutral ligands, we wish to create self assembled DNA-tile surfaces that conform to the substrate. In the case of infinite radius of curvature, substrate of varying material stiffness and charge can be used as template. In this exercise, we wish to empirically understand, and characterize how self-asssembly of DNA tiles can be influenced by external charged surfaces, their stiffness and material make-up.

• Complementary to the first study, suppose the scenario in which DNA tiles contain exposed and unpaired bases, we postulate the differing DNA bases can be utilized as templates for fabricating metal clusters. In this study, we wish to first understand metal ion affinities towards binding pockets on unmodified nucleic bases. Commercially available modifications that facilitate specific metal sequestering will also be pursued. Penultimately, the goal of this exercise is to reduce the sequestered metal ions to produce subnanometer atomic clusters. Ideally, the nucleic bases (A, T, G, C) would demonstrate sufficient metal ion discrimination to allow inexpensive molecular patterning based on DNA sequence. Identification of successful metal nanocluster patterning can be done through each's characteristic properties, such as fluorescence (Ag, Au) and magnetism (Fe, Mn, Co).

• Connected to the two previous efforts are the physical measurements of empirical products. Physical characterization and extended understanding the influence of the environment, including buffer composition and time, can be completed using dry/fluid AFM with complementing cryogenic TEM. It is expected that sample preparation techniques will have to be amended based on altered empirical products. Practical challenges exist abound in the process of developing sample preparation protocols that can produce repeatable results. In cross correlating the three techniques, we wish to elucidate characteristic differences that results due to alteration of analytical techniques. Furthermore, in cryo-TEM techniques, we wish to take advantage of electron transparent substrates used during assembly process to provide natural contrast and enhancements. Elasticity mapping of surface functionalized substrates may be possible through picoforce techniques on newer generation DI AFMS. In characterizing metallic binding to nucleic acid pockets, ITC and CD spectrometry will be used.

Publications

• Kashid, R. V., Late, D. J., Chou, S. S., Huang, Y. K., De, M., Joag, D. S., More, M. A., & Dravid, V. P. (2013). Enhanced Field-Emission Behavior of Layered MoS₂ Sheets. Small (Feb 21)
• Chou, S. S., Kaehr, B., Kim, J., Foley, B. M., De, M., Hopkins, P. E., Huang, J., Brinker, C. J., & Dravid, V. P. (2013). Chemically Exfoliated MoS₂ as Near-Infrared Photothermal Agents. Angewandte Chemie-International Edition, 52(15), 4160-4164
• Chou, S. S., De, M., Kim, J., Byun, S., Dykstra, C., Yu, J., Huang, J. X., & Dravid, V. P. (2013). Ligand Conjugation of Chemically Exfoliated MoS₂. Journal of the American Chemical Society, 135(12), 4584-4587
• Chou, S. S., De, M., Luo, J. Y., Rotello, V. M., Huang, J. X., & Dravid, V. P. (2012). Nanoscale Graphene Oxide (nGO) as Artificial Receptors: Implications for Biomolecular Interactions and Sensing. Journal of the American Chemical Society, 134(40), 16725-16733
• De, M., Chou, S. S., Joshi, H. M., & Dravid, V. P. (2011). Hybrid magnetic nanostructures (MNS) for magnetic resonance imaging applications. Advanced Drug Delivery Reviews, 63(14-15), 1282-1299
• De, M., Chou, S. S., & Dravid, V. P. (2011). Graphene Oxide as an Enzyme Inhibitor: Modulation of Activity of alpha-Chymotrypsin. Journal of the American Chemical Society, 133(44), 17524-17527
• Chou, S. S., De, M., Joshi, H. M., Richter, F., & Dravid, V. P. (2011). Ultrastabilzation of magnetic nanostructure with multi-functionality: Cellular interactions. Abstracts of Papers of the American Chemical Society, 241
• Tark, S. H., Srivastava, A., Chou, S., Shekhawat, G., & Dravid, V. P. (2009). Nanomechanoelectronic signal transduction scheme with metal-oxide-semiconductor field-effect transistor-embedded microcantilevers. Applied Physics Letters, 94(10)
• Chou, S. S., Kim, Y. Y., Srivastava, A., Murphy, B., Balogun, O., Tark, S. H., Shekhawat, G., & Dravid, V. P. (2009). Microcantilever array with embedded metal oxide semiconductor field effect transistor actuators for deflection control, deflection sensing, and high frequency oscillation. Applied Physics Letters, 94(22)

Stan with Professor Dravid and fellow graduate, Aiming Yan, in June, 2013.