“…As such, we expect this approach will be a valuable label-free probe for ionic transport in a wide range of physical, chemical, and biological contexts, including product formation and collection in (photo)electrochemical energy conversion, , water splitting, phototriggered ion transport, ion transport in soft matter, aqueous battery function, dissolution dynamics after proper calibration of the refractive index near saturation, microfluidic ion flow, bioelectronic device function, or even label-free electrophysiology dynamics . It could also be readily combined with established strategies to optically detect oxygen and hydrogen evolution, especially since the sensitivity required to see gaseous products is orders of magnitude lesser than what we have demonstrated for solution-phase species, and to potentially probe three-dimensional ion transport in such contexts. , Second, the MSE analysis used here could serve as a general approach to reveal nondiffusive behavior or spatially dependent transport parameters. Specifically, similar to the case for carrier transport probed by spatiotemporal methods, , deviations from diffusive transport manifest as nonlinear MSE curves that would be readily discerned.…”