Protein Microgel-Stabilized Pickering Liquid Crystal Emulsions Undergo Analyte-Triggered Configurational Transition

Herein, we report a novel approach that involves Pickering stabilization of micometer-sized liquid crystal (LC) droplets with biocompatible soft materials such as whey protein microgel (WPM) to facilitate the analysis of analyte-induced configurational transition of the LC droplets. The WPM particles were able to irreversibly adsorb at the LC-water interface and the resulting WPM-stabilized LC droplets possessed a remarkable stability against coalescence over time. Although the LC droplets were successfully protected by a continuous network of WPM layer, the LC-water interface was still accessible for small molecules such as sodium dodecyl sulphate (SDS) that could diffuse through the meshes of the adsorbed WPM network or through the interfacial pores and induce a LC response. This approach was exploited to investigate the dynamic range of the WPM-stabilized LC droplets response to SDS. Nevertheless, the presence of unadsorbed WPM in aqueous medium reduced the access of SDS molecules to the LC droplets, thus suppressing the configuration transition. An improved LC response to SDS with a lower detection limit was achieved after washing off the unadsorbed WPM. Interestingly, the LC exhibited a detection limit as low as ~0.85 mM for SDS within the initial WPM concentration ranging from 0.005 to 0.1 wt %. Further, we demonstrate that the dose-response behaviour was strongly influenced by the number of droplets exposed to the aqueous analytes as well as the type of surfactants such as anionic SDS, cationic dodecyltrimethylammonium bromide (DTAB) and non-ionic tetra(ethylene glycol)monododecyl ether (C12E4). Thus, our results address key issues associated with the quantification of aqueous analytes and provide a promising colloidal platform towards the development of new classes of biocompatible LC droplet-based optical sensors.