(Plenary) High Efficiency Coupling of Chemical Sensing to Chemical Treatment in Low-Dimensional Nanofluidic Structures

We are interested in the design and construction of nanostructured architectures that couple molecular transport (analyte/reagent delivery), chemical sensing (optical or electrochemical) and subsequent chemical processing withinin the same physical construct.  The ultimate goal of these experiments is to produce chemical reagents in situ and consume them directly at a proximal reaction site, all within the confined geometry of a low-dimensional nanostructure, so that chemical transformations may be realized with optimal efficiency.  To realize this goal we are developing sensing strategies that efficiently match electron transfer and spectroscopic probing to low-dimensional, i.e. zero- and one-dimensional nanostructures. In one example, we are studying the tight coupling of electrokinetic nanofluidics to electron transport for high efficiency in situ reagent generation.  Solvent electrolysis at an upstream can be used to generate H₂ or O₂ for downstream catalytic reduction or oxidation reactions.  Chronocoulomtery is performed simultaneously with fluorescence imaging in order to follow the reagent generation quantitatively, then model proton-coupled electron transfer reactions can be used down stream to follow the spatial distribution of reagent through the co-generated OH^- or H⁺.  Because transport and electron transfer are intimately coupled, high efficiency conversions are achieved. The extremely small Peclet numbers characteristic of nanofluidic flow mean that the efficiency of electrochemical treatment is improved to near 100% efficiency in nanofluidic architectures compared to diffusion-limited efficiencies of 5-10% in microfluidic structures.