Vectorially-Coupled Reaction Networks in Low-Dimensional Nanofluidic Structures

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Reactions are the central events of chemistry and controlling their behavior and the locations where they occur is at the heart of chemical measurements and making new chemicals. Ideally, scientists want to design reactions so they occur rapidly, make efficient use of all the chemical participants, employ inexpensive chemicals and environmentally friendly conditions, and produce easily-isolated chemical products. In nature, such as in biological cells, these stringent objectives are achieved by spatially-organized reaction networks. Dr. Paul Bohn's research team at the University of Notre Dame mimics nature by designing and developing networks of reactions whose behavior is controlled by electrical stimulus and whose location is defined by the size of the reaction vessel. In their work with electron-transfer reactions, they carefully build specially-designed structures from nanometer-sized materials, whose nature and placement leads to particular, well-defined, and highly efficient reactions occurring in specific locations. Furthermore, electrical control of the location-specific reactions and movement of nearby liquid allows for shuttling of chemical products from one reaction site to another one downstream, where they are used as the chemical starting materials for another defined reaction process. All the reactions are sped up using enzymes, nature's chemical reaction catalysts. The Bohn team is developing an understanding of how electrical voltages can be applied to control the activity of catalysts. The research efforts are integrated with new education and training programs that cut across disciplinary lines within the University of Notre Dame and combine talents from multiple universities. In the process, these activities address specific NSF goals including development of a diverse, globally competitive science-technology-engineering-mathematics workforce; increased partnerships between academia and industry; and improved economic competitiveness.The principal goal of this project supported by the Chemical Measurement and Imaging Program and partial co-funding from the Molecular Separations, Electrochemical Systems, and Process Systems, Reaction Engineering and Molecular Thermodynamics Programs at NSF is to develop networks of spatially-organized redox reactions which can be controlled by electrical signals to manage transport, dictate reactivity, and isolate products. The overall goal is addressed by developing control over delivery of reactant molecules and particles to a reactive site as well as control over reactivity, within zero- and one-dimensional electrochemical nanostructures. The team also combines these nanostructures to develop full three-dimensional control over cascade reactions to produce vectorially-controlled reaction networks (VCRNs). The first objective is the development of high-precision nanoscale architectures to support VCRNs by simultaneous control over transport and reactivity using both metal-insulator multilayer stack-based nanopores and hierarchically-organized assemblies. The second objective explores ways in which electrochemical potential can be used to control activity of enzymes bound to one of the electrodes. Using horseradish peroxidase, HRP, as a model oxidoreductase enzyme, the intrinsic reactivity of the electrode-bound enzyme is followed using a fluorogenic redox reaction that converts a non-fluorescent reactant into fluorescent product within the ultrahigh sensitivity environment of an electrochemical zero-mode waveguide. These capabilities are being combined and tested using a set of stringent single enzyme kinetics experiments, in which the HRP is moved among the available locations and tested for intrinsic reactivity when coupled to an electrochemical potential control signal. The ultimate goal of this work is to leverage control of single reaction events to create a preparative scale capability for VCRNs. To test this capability, two-enzyme electrochemically-modulated reaction systems are being coupled to individual reactions in a spatially coordinated manner and used to deliver the reaction products to a downstream collection point. This project has impact outside the principal discipline of chemical analysis, especially in the general area of cascade reactions - powerful constructs in chemical synthesis that are used, for example, in enzymatic biofuel cells to capture the full electrochemical reducing power of fuel sources.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.