Microscale diffusiophoresis of proteins

Abstract Living systems are characterised by their spatially highly inhomogeneous nature which is susceptible to modify fundamentally the behaviour of biomolecular species, including the proteins that underpin biological functionality in cells. Spatial gradients in chemical potential are known to lead to strong transport effects for colloidal particles, but their effect on molecular scale species such as proteins has remained largely unexplored. Here we demonstrate with microfluidic measurements that individual proteins can undergo strong diffusiophoretic motion in salt gradients in a manner which is sufficient to overcome diffusion and lead to dramatic changes in their spatial organisation on the scale of a cell. Moreover, we demonstrate that this phenomenon can be used to control the motion of proteins in microfluidics devices. These results open up a path towards a physical understanding of the role of gradients in living systems in the spatial organisation of macromolecules and highlight novel routes towards protein sorting applications on device.