Acoustofluidics 11: Affinity specific extraction and sample decomplexing using continuous flow acoustophoresis

Acoustic standing wave technology combined with ligand complexed microbeads offers a means for affinity specific selection of target analytes from complex samples. When realized in a microfluidic format we can capitalize on laminar flow and acoustic forces that can drive cells or microbeads across fluid interfaces. Given this, we have the ability to perform carrier fluid (suspending medium) exchange operations in continuous flow in microfluidic chips based solely on acoustofluidic properties. A key issue here is to ensure that a minimum of the original carrier fluid follows the cells/particles across the fluid interface. Simple processing protocols can be achieved that may outperform macroscale magnetic bead-based sample extraction or centrifugation steps, which can also be straightforwardly integrated with downstream analytical instrumentation. This tutorial outlines some basic fluidic configurations for acoustophoresis based sample decomplexing and details the different system parameters that will impact the outcome of an acoustophoresis based affinity extraction experiment or a cell medium exchange step. Examples are given of both targeted extraction of microbes and selective elusion of molecular species.