Acoustic-wave-induced analyte separation in narrow fluidic confinements in the presence of interfacial interactions

Abstract

In the present work, we attempt to analyze the influences of acoustic forces, in conjunction with the intrinsic electrokinetic effects as well as the near-wall attractive and repulsive forces, on the transport and size-based separation of charged analytes in a background-pressure-driven flow through a narrow fluidic confinement. By executing a regular perturbation analysis, we establish that the speed of traverse and the extent of spreading (dispersion) of the analyte bands is effectively determined by the ratio of particle to channel heights, channel height relative to the Debye length, and all other significant acoustic and nonacoustic parameters. These factors in tandem may dictate the analyte separation characteristics (quantified by the resolution of separation), in tune with the particular harmonic of the acoustic wave, the strengths of the induced electrical double layer fields, and the van der Waals interaction mechanisms. We quantitatively pinpoint the relationship between the harmonics to be employed and particle sizes to be separated. Our study reveals that there is a critical channel height beyond which the acoustic effects may effectively mask the near-wall interactions and below which the transverse migrative influences induced by the walls may influence the separation characteristics in a rather profound manner. The results implicate an interesting high-efficiency separation regime that can be obtained with a judicious combination of the background flow, energy intensity of the acoustic effects, and induced electrical double layer interactions.