Comparison of Newtonian and non-Newtonian fluid dynamics on removal efficiency of non-specifically bound proteins in SAW biosensors

Surface acoustic wave (SAW) devices are finding increasing use in medical diagnostic applications, such as detection of specific proteins in bodily fluids for detection of pathologies. In applications aimed at biological sensing, the sensing medium such as blood exhibits a Non-Newtonian behavior. We have recently shown that SAW induced acoustic streaming which refers to fluid motion induced by high frequency sound waves, is an important phenomenon that can be used for the removal of non-specifically bound (NSB) proteins from the device surface¹. The removal efficiencies of NSB can be significantly different when the device interacts with Non-Newtonian fluids. This work reports on the influence of non-Newtonian fluid dynamics on the acoustic streaming and fluid velocity profiles in SAW devices, using a computational fluid-structure interaction finite element model. A two-port SAW device, based on 100 MHz YZ Lithium Niobate substrate, in contact with a fluid film was modeled using a three-dimensional bi-directionally coupled fluid-structure interaction model. Blood is modeled as a Non-Newtonian fluid whose viscosity is defined using the Carreau model. To elucidate the effect of non-Newtonian dynamics on acoustic streaming, results are compared with Newtonian fluid with viscosity at infinite shear rate. A transient analysis of the fluid flow profiles on the SAW device indicates significant differences between fluid velocity patterns, magnitudes of fluid velocities, and wall shear stresses for Non-Newtonian fluid loading on the device when compared to a Newtonian fluid. Our results indicate that the peak fluid velocities decreased for non-Newtonian fluid loading suggesting a significant viscous dissipation of energy as compared to the case of a Newtonian fluid. The extent of induced shear stresses at the piezoelectric device-fluid interface is almost two orders of magnitude higher for Non-Newtonian fluids. These results have implications in biosensing as wel- as micro-fluidic applications involving Non-Newtonian fluids.