Flow control of thermotropic lipid monolayers

Abstract

There is an increasing interest in using liquid crystalline media as mobile phases in two-dimensional nanofluidic systems. Their small-scale, reduced dimensionality, and plentiful opportunities for functionalisation render such phases advantageous. However, flow control has been difficult to achieve, as the wetting processes which drive area expansion are not dynamically controllable. Here, we report on temperature-controlled monolayer spreading of 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine (DEPE) on the hydrophobic substrates SU-8, and Teflon AF (amorphous fluoropolymer). The gel/liquid phase transition of DEPE at T_c ∼ 38 °C is exploited to toggle spreading of a molecular lipid film on SU-8. We observed that on Teflon AF, DEPE monolayer spreading occurs even below T_c, and exhibits strongly accelerated spreading above the phase transition temperature. Our results demonstrate that switching DEPE monolayer spreading on and off, or, alternatively, switching between fast and slow area expansion, is a feasible approach towards establishing control over lipid film flow in two-dimensional fluidic systems. We also present a chip-based device integrating a patterned surface for 2D-microfluidics and on-chip heating.