Nano-electrokinetic ion enrichment of highly viscous fluids in micro-nanochannel

The principle of ion concentration polarization (ICP) is the most efficient method for achieving nano-electrokinetic ion enrichment. In this paper, nano-electrokinetic ion enrichment of highly viscosity fluids in micronanochannel was investigated. Based on the Poisson-Nernst--Plank (PNP) equations coupled with the Navier-Stokes equation, ion enrichment and enrichment breakdown, the effects of the width and wall structure of the nanochannel on the ion enrichment were investigated. It is concluded that the ion enrichment is attributed to the balance between the electrophoresis effect provided by the applied voltage and the repulsive force generated by the surface charge. The ion enrichment is divided into three stages: enrichment generation, enrichment promotion and enrichment breakdown. When the applied voltage increases, the ion concentration first increases. When the voltage reaches the peak, it gradually decreases. At the same voltage, both the peak concentration and the peak voltage increase as the width of the nanochannel decreases. The nanochannel of the square wave wall structure has highest peak concentration than the zigzag type, the multi-wave type and the straight line type. This work provides a significant theoretical basis for increasing enrichment ratio and ion concentration in low concentration molecular detection tasks.