Chemical reactions are most often understood from measurements made in bulk solution, where characteristic length scales are large, interfaces occupy a small fraction of the total volume, and transport can often be separated conceptually from intrinsic reaction kinetics. But what happens when chemical systems become sufficiently small that diffusion lengths shrink, surface-area-to-volume ratios increase dramatically, and interfaces become a dominant component of the reaction environment?
Jeffrey E. Dick,
Purdue University
This talk will describe our group’s development of electrochemical measurements to interrogate the coupling among reaction kinetics, mass transport, confinement, and interfacial phenomena in these systems. We begin with aqueous microdroplets, where electrochemical measurements reveal dramatic acceleration of enzymatic turnover as droplet size decreases. By systematically varying characteristic length scale and interfacial environment, we showed that this behavior reflects an increasing contribution from interfacial chemistry and that the gas|liquid interface accelerates enzymatic reactions more strongly than the liquid|liquid interface.
These observations motivated us to deliberately increase surface-area-to-volume ratio using new geometries, such as soap microfilms and floating oil nano films. Microdroplet physical properties also change. Our measurements reveal that adsorbed microdroplets undergo intense nanoscale motion. The same reaction-transport framework extends naturally to living systems. Spheroid tumor models are heterogeneous three-dimensional reaction-diffusion environments characterized by restricted molecular transport, steep spatial gradients, and chemically distinct microenvironments.
I will describe our development of electrochemiluminescence microscopy to visualize reactive chemistry within living spheroids and quantify chemical behavior inaccessible to bulk measurements. Such measurement have also lead to the discovery of diffusional depth profiling, where electrochemiluminescence is used to access three-dimensional geometric information. This new imaging strategy deliberately takes advantage of bimolecular reactions and molecular diffusion as a spatial ruler to recover information away from an electrified interface. Together, these studies demonstrate that as chemical systems become smaller, more heterogeneous, and increasingly multiphase, reaction kinetics and mass transport become inseparable from geometry and interfacial effects and that electrochemical measurements provide a powerful means of revealing new physicochemical phenomena.
Jeffrey E. Dick is the Richard B. Wetherill Professor of Chemistry at Purdue University. He received his B.S. in Chemistry from Ball State University in 2013 and his Ph.D. from the University of Texas at Austin in 2017 under the guidance of Prof. Allen J. Bard. In 2018, he began his independent career at the University of North Carolina at Chapel Hill before joining Purdue in 2022. His research group develops electrochemical measurement tools to probe reactivity in complex, multiphase, and confined environments.