On microchannel acoustophoresis - Experimental considerations and life science applications

Abstract: This thesis presents experimental studies of microchannel acoustophoresis, a technique for manipulation of microscopic objects in suspension by means of acoustic radiation forces induced by ultrasonic standing wave fields. By arranging an acoustic resonance across the width of a microchannel, the path of individual cells or microparticles can be deflected orthogonally to the fluid flow. The propagation of acoustic waves in a microchip is discussed and a theory for the acoustic eigenmodes within the fluid filled channel is presented. With the intention to derive the trajectories of particles, expressions are recapitulated for the acoustic radiation force exerted on a particle in an acoustic field, the induced acoustic streaming in the fluid, and for the microchannel flow velocity profile. The introduced transport phenomena are thereafter used for evaluation of merits and limitations in microchannel acoustophoresis separating systems. In five studies, microchannel acoustophoresis has been adapted for applications in life science. Three of these relate to sample preparation through transfer of cells and microparticles from one suspending fluid to another, for bead based bio-affinity assays, or cell suspension conditioning. A fourth study addresses on-chip elution of surface bound molecules from cells and microparticles. In study five, a system is described for pre-alignment and subsequent separation of cancer cells from blood cells based on their intrinsic acoustic and morphological properties. In study six, a method is presented for measurement of the acoustophoretic velocity field of microparticles. This was done to test the extent to which the resonances in an acoustophoresis microchannel are well described by the current model.

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