Fluorescence-Encoded Infrared Spectroscopy for Single-Molecule Chemical Dynamics

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With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) Program in the Division of Chemistry, Professor Andrei Tokmakoff and his research group at the University of Chicago are developing new techniques to study the time-dependent behavior of individual molecules in solution. These methods reveal the motions and interactions of molecules during the course of chemical reactions in a manner that has been previously inaccessible. Single molecule (SM) methods have had enormous impact describing molecular processes that occur on surfaces and in biological processes, but their application to problems in solution-phase chemistry remains a persistent challenge. This project attempts to overcome earlier limitations by using a new high-sensitivity detection strategy, fluorescence-encoded infrared spectroscopy (FEIR), with the goal of using vibrational spectroscopy to track how chemical bonds and molecular contacts evolve in time for single molecules in solution. Students working on this project receive training in a cross-disciplinary setting that provides experience on an array of topics including instrument development, optics and spectroscopy, and chemical dynamics. This training in the Tokmakoff group prepares students for leadership roles in scientific research at academic and national labs, or in high-tech companies.The research supported by this grant builds on recent work by Prof. Tokmakoff and his team demonstrating the single-molecule sensitivity of the FEIR approach using photon correlation spectroscopy (CS). The team is now expanding the capabilities of the FEIR technique using new types of chromophores to target a variety of chemical applications. For example, the research team is developing IR vibrational contrast mechanisms for FEIR-CS that use vibrational frequency shifts as reporters of the chemical dynamics for applications such as site-specific bimolecular binding, protonation and deprotonation reactions, and ion transport through electrolytes. Additionally, the team is working to extend FEIR measurements to measure the dynamic information content of single-molecule photon streams that describe bond-specific histories of individual diffusing and reacting molecules. These research efforts are guided by the overarching goal of building a broadly applicable tool to study chemical dynamics and molecular transport processes in liquids, solutions, and other soft materials. The broader impacts of the project also include the development and dissemination of open-access educational resources.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.