Electroosmotic Flow in Microchannel with Black Silicon Nanostructures

Abstract

Although electroosmotic flow (EOF) has been applied to drive fluid flow in microfluidic chips, some of the phenomena associated with it can adversely affect the performance of certain applications such as electrophoresis and ion preconcentration. To minimize the undesirable effects, EOF can be suppressed by polymer coatings or introduction of nanostructures. In this work, we presented a novel technique that employs the Dry Etching, Electroplating and Molding (DEEMO) process along with reactive ion etching (RIE), to fabricate microchannel with black silicon nanostructures (prolate hemispheroid-like structures). The effect of black silicon nanostructures on EOF was examined experimentally by current monitoring method, and numerically by finite element simulations. The experimental results showed that the EOF velocity was reduced by 13 ± 7%, which is reasonably close to the simulation results that predict a reduction of approximately 8%. EOF reduction is caused by the distortion of local electric field at the nanostructured surface. Numerical simulations show that the EOF velocity decreases with increasing nanostructure height or decreasing diameter. This reveals the potential of tuning the etching process parameters to generate nanostructures for better EOF suppression. The outcome of this investigation enhances the fundamental understanding of EOF behavior, with implications on the precise EOF control in devices utilizing nanostructured surfaces for chemical and biological analyses.

Recent Progress of Black Silicon: From Fabrications to Applications

“…( b ) Experimental setup for black silicon nanostructures current monitoring. Adapted from reference [ 109 ], with permission from Royal Society of Chemistry © 2020. ( c ) Using black silicon to achieve surface-assisted laser desorption/ionization mass spectrometry imaging.…”

“…Finally, a mechanism based on the Dember effect explained th nomenon. In 2018, A. Lim et al [109] studied the effect of nanostructured black silicon electroosmotic flow effect, which was used to accurately control the fluid velocity crofluidic chips. The researchers have proposed a new technique that uses dry e electroplating, and molding (DEEMO) processes and RIE to fabricate long-silico silicon microchannels.…”

Editorial for the Special Issue on Micro/Nano-Chip Electrokinetics, Volume II

“…Lu et al [ 11 ] used a molecular dynamics simulation to study the electroosmotic flow in rough nanochannels, with particular attention to the fluid–solid interactions. Lim et al [ 12 ] developed a technique to fabricate microchannels with black silicon nanostructures for a controllable suppression of electroosmotic flow.…”

Electroosmotic Flow Hysteresis for Fluids with Dissimilar pH and Ionic Species

“…In contrast, FASS employs an applied electric field with a constant voltage to stack/accumulate the sample ions at the interface between the low conductivity sample solution and the high conductivity background electrolyte (BGE) [ 16 , 17 ]. Sample dispersion due to the non-uniform EOF velocities adversely affects the resolution and sensitivity of both ITP and FASS; this can be minimized by coating water-soluble polymers [ 18 , 19 ], and constructing nanostructures within a microchannel [ 20 , 21 , 22 ].…”