Development of thermophoretic µ-device for measuring Soret coefficient

Thermophoresis is the mass transport induced by a temperature gradient where the Soret coefficient ST is a measure for the established concentration gradient in a temperature gradient. It has gained a lot of interest in the biotechnology to monitor the binding between proteins and ligands [1]. To obtain quantitative thermophoretic parameters in those complex systems, the existing methods are not suitable as they are limited to binary mixtures or consume large sample amounts in the order of 30-50 mL. Recently, a thermophoretic lab-on-a-chip device with a small sample volume of 10 µL was developed to measure ST using a confocal microscope. With a microwire for heating, large temperature gradients up to ~106 K/m could be achieved [2]. However, a 3D temperature profile around the wire complicated the analysis for determining ST. To overcome the drawback of this chip, we propose a thermophoretic µ-device with a 1D temperature profile. In this instrument a measurement channel with a sample volume of 20 µL lies between a heating and cooling channel. Temperature gradients up to ~104 K/m can be achieved. Using a confocal microscope, the temperature profile is measured by fluorescence lifetime imaging microscopy (FLIM) with Rhodamine B (RhB) and the concentration is determined from the fluorescence intensity. Fluorescent polystyrene particles with a diameter of 25 nm are used for comparing ST to a validated optical method (Thermal Diffusion Forced Rayleigh Scattering (TDFRS)) [3] and the recently developed thermophoretic chip [2]. ST probed by the developed device agrees within the uncertainty with TDFRS and thermophoretic lab-on-a-chip measurements.Literature:[1] D. Niether and S. Wiegand, J. Phys. Condens. Matter 31, 2019, 503003. [2] N. Lee, D. Afanasenkau, P. Rinklin, B. Wolfrum, and S. Wiegand, Lab Chip, Submitted[3] O. Syshchyk, et al., Eur. Phys. J. E, 2016, 39, 12