Surface resistance to nonspecific protein adsorption is currently a subject of great interest and is critical to the performance of biosensors, implanted biomaterials, and drug carriers. Despite extensive research in protein adsorption, there is still a lack of a nano-and molecular-level understanding of the nonfouling mechanism. Combined experimental and simulation studies in this work will target this important problem.
Intellectual Merit: From recent simulation and experimental studies completed by the PI's group, it appears that there is a correlation between the nonfouling properties of oligo (ethylene glycol) (OEG) self-assembled monolayers (SAMs) and the hydration/flexibility of OEG chains. Furthermore, the PI's group demonstrated for the first time that SAMs terminated with phosphorylcholine (PC) or oligo (PC) groups strongly resist nonspecific protein adsorption. While hydrophilic and neutral OEG groups form a hydration layer via hydrogen bonds, zwitterionic groups (e.g., PC) form a hydration layer via electrostatic interactions. Zwitterions are capable of binding significant amounts of water molecules and therefore are potentially excellent candidates for nonfouling materials. In order to provide a complete and solid understanding of the nonfouling mechanism at the molecular level, OEG and PC SAMs are two excellent model systems since they are well-controlled and interact with water via different mechanisms. Thus, this work focuses on (a) study the structural and dynamic behavior of bound water molecules, force-versus-distance curves, and free energy changes for protein interactions with OEG (or PC) SAMs using molecular simulations techniques, (b) probe the structure of bound water molecules around OEG (or PC) chains from infrared-visible sum frequency generation (SFG) and to determine the enthalpy, free energy, and entropy changes for protein adsorption from isothermal titration calorimetry (ITC) and surface Plasmon resonance (SPR) sensor, and (c) investigate the unique properties of smart, nonfouling, and biocompatible zwitterionic carboxybetaine materials and their responsiveness to changes in ionic strength, pH, and temperature.
Broader Impact: The success of this nano-related work will advance our fundamental understanding of the nonfouling mechanism at the molecular level, provide new criteria for evaluating nonfouling materials, and assist the design of new smart, nonfouling, and biocompatible materials. It will have significant impact on various applications, including biosensors, biomaterials, tissue engineering, drug delivery, bioseparation, and marine coatings. While nonfouling surfaces are critical for these technologies, a fundamental understanding of the nonfouling mechanism is a driving force for discoveries of new antifouling materials and coatings. Graduate and undergraduate students will be involved in this project, particularly those from underrepresented groups. Undergraduate researchers will be recruited through well-established outreach programs at local research centers, in which the PI has been actively involved. The PI will develop a new course on Biomolecular Interfaces The new concept of molecular product design as demonstrated in the proposed work will be the main theme of the course. In addition, the knowledge will be disseminated through other courses, such as Frontiers in Nanotechnology and Computational Simulation and Modeling of Materials".
