Soft-interfaced liquid crystal microfluidics can probe the rigidity of lipid vesicles

Liquid crystal (LC)-aqueous interfaces were shown to respond to the phospholipid interactions via optically observable ordering transitions; however, past attempts lack the quantification of the transport and fusion kinetics of the vesicles at the interfaces. Herein, we investigated the response of flowing LC-aqueous interfaces upon fusion of the vesicles formed by pure 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), or egg sphingomyelin or their mixtures with guest molecules. Using stabilized LC-aqueous interfaces in transparent microfluidic chips that allow spatiotemporal quantification using fluorescence, confocal, and polarized light microscopy, we demonstrated that flowing LC interfaces provide a rapid response to lipid adsorption, where their spatiotemporal interfacial distribution differs depending on the mechanical properties of their vesicles. We show that cholesterol-dissolved lipid complexes result in distinct LC-response kinetics, mainly associated to the changes in their rigidities. Considering the critical role of the mechanical properties of cell membranes in proper cellular function, this study is significant as it offers a continuous and rapid early diagnosis platform for detecting minor mechanical alterations in lipid bilayers, which may lead to cell dysfunction that contributes to critical diseases.