(586d) Simultaneous Measurement of Thermophoretic and Brownian Particle Motion Using Multiple Particle Tracking Microrheology

Modern at-home diagnostic tests can be reliable for initial diagnoses. To confirm these results, more sensitive hospital laboratory tests are typically used. In diagnosis of viral infections, the biological sample undergoes several time- and resource-intensive processing steps before viral particles are detected. In areas with limited access to laboratories, quick-acting and sensitive diagnostic methods are vital for monitoring health. We aim to develop a resource-efficient particle separation technique to help create sensitive single-step diagnostic tests that quantify the viral load by separating and concentrating viral particles from a biological sample. To drive separation of micron-sized charged colloidal particles from a bulk solution in a small sample, we will use thermophoresis, directional motion of particles due to a near surface ion flux in response to a temperature gradient. To capture this motion, we use 2D multiple particle tracking microrheology (MPT), a passive microrheological technique that quantifies Brownian particle motion and relates it to material rheological properties. Using MPT to measure particle motion while a 1D thermal gradient is applied to the sample enables simultaneous measurements of local temperature-dependent fluid viscosity and thermophoretic particle movement. Measuring local rheological properties is crucial for optimizing rheology-dependent thermophoretic separation in complex biological fluids with variable properties. To verify this technique’s accuracy in simultaneously measuring viscosity and particle velocity, we analyze Brownian and thermophoretic motion of particles in Newtonian solutions with varying glycerol concentrations. Viscosities from the measured Brownian component are consistent with tabulated viscosities for glycerol solutions, suggesting the reliability of this method. Experimental thermophoretic diffusion and velocity values are within range of current theoretical estimates, confirming particles are translating due to thermophoresis. While current theories on what drives thermophoresis in complex fluids are not yet experimentally confirmed, this novel technique allows us to characterize thermophoresis in fluids with variable properties. By quantifying how temperature-dependent material properties, such as viscosity, affect the extent of thermophoretic particle diffusion, we can optimize thermophoresis-based separation in complex fluids and advance the design of more robust bioseparations techniques.