Concentration Effects of a Biopolymer in a Microfluidic Device

This paper builds upon our previous effort exploring the behavior of biological macromolecules subjected to a microfluidic flow; here we focus on concentrated solutions of macromolecules. Epifluorescence microscopy and a fluorescent probe were used to visualize λ-DNA molecules flowing through a silicon-fabricated microfluidic device. The flow path consisted of an inlet reservoir, contracting into a long straight channel, and then expanding into an outlet reservoir. Macromolecules in the flow experienced an elongational flow at the channel contraction along the channel centerline and a shear flow at the channel walls. Previous results on dilute solutions with concentration c = 0.001c* indicated that both types of flow can stretch a macromolecule. Generally, stretching increases with the Deborah number (De) and a prolonged exposure to high De may lead to chain scission. In this study, the concentration of λ-DNA in solution was increased to c = 0.1c*, and all other variables were held constant. Although both flow types stretched λ-DNA molecules, the deformation in the more concentrated solution was less than that in dilute solution. Furthermore, in contrast to dilute solution at the same or slightly higher De, no evidence of molecular degradation was observed as the macromolecules traveled through the channel. These findings are relevent when designing microfluidic systems for conducting biochemical analyses.