Abstract

Single Molecule Spectroelectrochemistry of Redox Enzymes and Reactive Oxygen Species in Nano-Optofluidic Structures

Paul Bohn, Arthur J. Schmitt Professor of Chemical and Biomolecular Engineering and Professor of Chemistry and Biochemistry, University of Notre Dame

The next stage in the evolution of lab-on-a-chip devices will likely exploit the numerous unique physical properties that occur in nanoscale structures. New physical phenomena occur when the size of a structure is comparable to physical scaling lengths - e.g. the Debye length in ionic solutions, or the optical screening length in metal nanopores - and these unique physical effects may be usefully exploited to achieve improved control over chemi¬cal manipulations, such as (bio)chemical sensing or processing. In particular, we are interested in the effects that accrue from confining reactants and products to the small volumes characteristic of 0-D and 1-D nanostructures. Zero-dimensional architectures are also being studied in two formats: (1) arrays of nanoconfined recessed ring-disk electrodes in which redox cycling can be carried out at very high efficiency; and (2) electrochemically-active zero-mode waveguides (ZMWs), in which strongly confined optical fields can be coupled to single molecule electron transfer in order to study the dynamics of single enzyme molecules and single redox-active organic chromophores. Now it is possible to combine these formats and use the great power of single molecule probing, coupled to the amplification possibilities in the nanopore-RRDE configuration. Nanoscale separation in nanopore double-ring electrode arrays allows ultra-efficient coupling of counterpoised electron transfer processes between the bottom and upper ring electrodes in an zeptoliter-volume nanopore, while the the Au working electrodes function as optical cladding layers in a ZMW geometry. Initial studies focus on oxidoreductase enzymes, especially flavoenzymes and exploit the fluorescence dynamics of the isoalloxazine chromophore, which exhibits large changes in emission quantum efficiency with redox state.  Thus, the combination of nanofluidics and nanophotonics constitutes a particularly powerful platform to interrogate and use redox enzymes.