It is well known that charged analytes in the presence of nonuniform electric fields accumulate at locations where the relevant driving forces balance, and a wide range of ionic stacking and focusing methods are commonly employed to preconcentrate charged molecules for the purpose of amplifying low signal levels in biosensing applications. In particular, nanofluidic channels with spatially varying conductivity distributions have been shown to provide increased preconcentration of charged analytes due to the existence of a finite electric double layer (EDL), in which electrostatic attraction/repulsion from protonated/deprotonated surface groups produce nonuniform transverse ion distributions. In this work, we show that one can achieve greater levels of sample accumulation by using field-effect control via wall-embedded gate electrodes to tailor the surface potential heterogeneity in a nanochannel with overlapped EDLs. In addition to accomodating for previously demonstrated stacking and focusing mechanisms, we find that the coupling between two-dimensional ion distributions and the axial electric field under overlapped EDL conditions can generate an ion concentration polarization (CP) interface in the middle of the channel. Under an applied electric field, this CP interface can be used to rapidly concentrate sample ions between two stationary regions of different surface potential and charge density [1].
References:
[1] Eden, A., McCallum, C., Storey, B.D., Pennathur, S., Meinhart, C.D. (2017). Analyte preconcentration in nanofluidic channels with nonuniform zeta potential. Physical Review Fluids, 2, 124203.