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.

High-Resolution Micropatterned Teflon AF Substrates for Biocompatible Nanofluidic Devices

“…First, the kinetic spreading coefficient β of SPE lipids on Teflon AF is ∼10 times higher compared to SU-8. 15 At the same time, the lipid's diffusion coefficient D on Teflon AF is around 0.8 μm 2 /s compared to 0.3 μm 2 /s on SU-8. 15 This means that on Teflon AF lipid spreading and lipid mixing are greatly accelerated compared to the previously used SU-8 and EPON 1002F.…”

“…15 At the same time, the lipid's diffusion coefficient D on Teflon AF is around 0.8 μm 2 /s compared to 0.3 μm 2 /s on SU-8. 15 This means that on Teflon AF lipid spreading and lipid mixing are greatly accelerated compared to the previously used SU-8 and EPON 1002F. Furthermore, by using patterned Teflon AF, the large problem of autofluorescence from photoresists is overcome, even though very little fluorescence originates from residual S1813 which was used during the fabrication.…”

Did Solid Surfaces Enable the Origin of Life?

“…When a MLV is brought in contact with a high energy substrate in an aqueous surrounding ( Figure 3 A), it spreads isotropically and wets the entire available surface until the accessible lipid material in the reservoir is completely depleted. On glass, the membranes generally spread as a bilayer [ 28 , 29 ] ( Figure 3 B), while on hydrophobic surfaces as a monolayer [ 11 , 12 , 30 ] ( Figure 3 C). The most commonly experimentally investigated form of bio (mimetic) membranes is the bilayer, as the plasma membrane of contemporary cells as well as most of the intracellular membranes are single lipid bilayers.…”

Lipid Self-Spreading on Solid Substrates

“…When the reservoir is completely consumed and the spreading velocity reaches zero, the circumference of a spreading monolayer starts to "evaporate" [68]. Evaporation occurs when the hydrophobic tails of individual lipids lay open and completely adhere to the substrate.…”