Characterizing the sizes and interactions of macromolecules under native conditions is a challenging problem in many areas of molecular sciences, which fundamentally arises from the polydisperse nature of biomolecular mixtures. Here, we describe a microfluidic platform for diffusional sizing based on monitoring micron-scale mass transport simultaneously in space and time. We show that the global analysis of such combined space-time data enables the hydrodynamic radii of individual species within mixtures to be determined directly by deconvoluting average signals into the contributions from the individual species. We demonstrate that the ability to perform rapid noninvasive sizing allows this method to be used to characterize interactions between biomolecules under native conditions. We illustrate the potential of the technique by implementing a single-step quantitative immunoassay that operates on a time scale of seconds and detects specific interactions between biomolecules within complex mixtures.
Keywords: diffusion; immunoassay; interactions; polydispersity; proteins; size distribution.