Understanding molecular surface/interface structures of polymers and proteins is important for many applications and processes, such as biomaterial design, anti-biofouling control, bio-adhesion, modern micro- and nano-electronic devices, nano-imprinting, and blood coagulation. We are investigating such molecular level interfacial structures of polymers and proteins by using state-of-the-art techniques including sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM), supplemented by other techniques, such as Fourier transform infrared spectroscopy (FTIR), FTIR-attenuated total reflection (FTIR-ATR) spectroscopy, contact angle goniometry, Raman scattering, and fluorescence spectroscopy. Research in our group is highly interdisciplinary and includes many aspects of modern science such as analytical chemistry, physical chemistry, materials chemistry, surface science, laser techniques, nonlinear optics, molecular spectroscopy, microscopy, and nano-technology.
Substantial progress has been made to achieve understanding of molecular level structures of bulk proteins, due to improvements of modern analytical techniques, such as X-ray diffraction and nuclear magnetic resonance (NMR) spectroscopy. However elucidation of molecular structures of proteins at interfaces is still a difficult task. In our group, detailed molecular structures of interfacial proteins at various interfaces in situ are being investigated using SFG, AFM and other techniques. For example, interfacial structural changes of factor XII after adsorption onto a surface is being studied to understand the molecular mechanism of blood coagulation initiation on foreign surfaces. Interactions between mussel adhesive proteins and various polymer surfaces are being examined to help design effective fouling control/release coatings for vessels and equipment in the marine environment. Interfacial structures of various model proteins and their isotope labeled analogues are being investigated to validate SFG as a powerful technique to elucidate molecular structures of interfacial proteins. Structures of membrane proteins are also under study. At the same time, responses of biomedical polymer surfaces to water and various biological molecules are being explored, which provides important information for the deign of biomaterials with improved biocompatibility. In addition, surface structures of polymer coatings of biosensors have been elucidated.
In our group, we are also using SFG, AFM and other supplemental techniques to study buried interfaces involving polymer materials at the molecular level. For example, interfaces between various polymers and surfactants, self-assembled monolayers, as well as adhesion promoters have been investigated. Understanding the fundamentals of such interfacial structures is vital in many important applications including adhesion, coatings, nano-imprinting, surfactants, lithography, and liquid crystal displays. In addition, molecular details and kinetics of nano-diffusion have been elucidated in our group.
Research in our group also involves the application of SFG and AFM to study nano-materials. We are studying interfacial structures of poly (lactic acid) nano-fibrous tissue templates and their interactions with the human body. We hope that we can develop these nano-materials into next-generation scaffolds for tissue regeneration.
Xiaoyun Chen, Haizhong Tang, Mark A. Even, Jie Wang, Gregory Tew, Zhan Chen, "Observing a Molecular Knife at Work", J. Am. Chem. Soc., 128, 2711-2714 (2006). Highlighted in Nature, February 2006
Jie Wang, Xiaoyun Chen, Matthew L. Clarke, Zhan Chen, "Detection of Chiral SFG Vibrational Spectra of Proteins and Peptides at Interfaces", Proc. Natl. Acad. Sci. USA, 102, 4978-4983 (2005)
Chunyan Chen, Jie Wang, Cheryl L. Loch, Dongchan Ahn, Zhan Chen, "Demonstrating the Feasibility of Monitoring the Molecular-Level Structures of Moving Polymer/Silane Interfaces During Silane Diffusion Using SFG", J. Am. Chem. Soc., 126, 1174-1179 (2004)
Jie Wang, Mark A. Even, Xiaoyun Chen, Alvin H. Schmaier, J. Herbert Waite, Zhan Chen, "Detection of Amide I Signals of Interfacial Proteins in situ Using SFG", J. Am. Chem. Soc., 125, 9914-9915 (2003)
Jie Wang, Sarah M. Buck, Mark A. Even, Zhan Chen, "Molecular Responses of Proteins at Different Interfacial Environments Detected by Sum Frequency Generation Vibrational Spectroscopy", J. Am. Chem. Soc., 124, 13302-13305 (2002)
Jie Wang, Zoltan Paszti, Mark A. Even, Zhan Chen, "Measuring Polymer Surface Ordering Differences in Air and in Water by Sum Frequency Generation (SFG) Vibrational Spectroscopy", J. Am. Chem. Soc., 124, 7016-7023 (2002)