Surface charge regulation mediates anomalous ion transport in silica nanochannels

A hybrid microfluidic-nanofluidic device was evaluated for the transport of a variety of ions with the purpose of enhancing the understanding of surface charge regulation for electrokinetic transport within silica nanochannels. A bank of three nanochannels at 16 nm depth connected two microfluidic channels that acted as fluid and electrolyte reservoirs for the experimental and modeling studies reported in this work. Surface charge regulation was noted to be dependent on the size of the hydrated cation, the type of anion, and the electrolyte concentration for the negatively charged silica nanochannels, with anomalous transport being observed. The results reported here provide new insight into the impact of surface charge regulation as a function of ion type and electrolyte concentration within nanochannels and subsequently raise the possibility of tuning electrolyte solution composition to manipulate surface charge and subsequent electroosmotic flow within nanochannels.