Biosensing with Oleosin-Stabilized Liquid Crystal Droplets

Abstract

Liquid crystals (LCs) are rapidly emerging as novel platforms for chemical, physical, and biological sensing. With regards to biosensing, LCs can be used to detect amphiphiles such as lipids, fatty acids, digestive surfactants, and bacterial endotoxins. However, designing LC-based sensors in a manner that preserves their sensitivity and responsiveness to these stimuli, and possibly increasing the biocompatibility, remains challenging. In this work, we investigate the stabilization of LC droplets by oleosins, plant-sourced and highly surface active proteins due to their extended amphipathic helix. We show that purified oleosins, at sub-μM concentrations, readily stabilize nematic LC droplets without switching their alignment, allowing them to detect surfactants at μM concentrations. We give direct evidence of the localization of oleosins at the LC-water interface using fluorescent labelling, and show that the stabilized droplets remain stable over months. Interestingly, chiral LC droplets readily switch in the presence of nanomolar oleosin concentrations, an unexpected behavior that we explain by accounting for the energy barriers required for switching the alignment between the two cases. We thus set forth a two-fold conclusion: oleosin-stablized nematic LC droplets present a biocompatible and sustainable alternative for bioanalyte detection, while chiral LCs can be used as highly sensitive and non-invasive sensors for detecting amphipathic helices in biological systems.