Interactions between DNA and adsorbed poly(l-lysine) (PLL) on liquid crystal (LC) droplets were investigated using polarizing optical microcopy and epi-fluorescence microscopy. Earlier, we demonstrated that adsorption of PLL to the LC/aqueous interface resulted in homeotropic orientation of the LC and thus exhibited a radial configuration of the LC confined within the droplets. Subsequent adsorption of DNA (single-stranded DNA/double-stranded DNA) at PLL-coated LC droplets was found to trigger an LC reorientation within the droplets, leading to preradial/bipolar configuration of those droplets. To our surprise, subsequent exposure of complementary ssDNA to ssDNA/adsorbed PLL-modified LC droplets did not cause the LC reorientation. This is likely due to the formation of polyplexes (DNA–PLL complex) as confirmed by fluorescence microscopy and atomic force microscopy. In addition, dsDNA-adsorbed PLL droplets have been found to be effectively useful to displace (controlled release) propidium iodide (a model drug) encapsulated within dsDNA over time. These observations suggest the potential for a label-free droplet-based LC detection system that can respond to DNA and may provide a simple method to develop DNA-based drug nanocarriers.

Exploring intermolecular interactions in the presence of biomolecules that dictate director configurations of liquid crystals (LCs) enables new techniques for optically probing complex biological phenomena and realizing new classes of sensors and actuators. However, the design of a new approach by probing direct protein-LC interactions (in aqueous media) that can mimic chemico-biological interactions at the cellular level remains elusive. Here, we present a simple method to produce biocompatible LC droplets through poly(l-lysine) (PLL)-LC interactions in situ for reporting the presence of cells and monitoring the real-time interaction of cells with their environments that are mediated by topological defects in those droplets. In addition, responsive PLL droplets have been found to be useful as a template for reporting Annexin V-phosphatidylserine interactions, providing a simple measure of the harmful effect on cell health.

The synthesis, optical properties and thermal behaviour of three novel non-conventional 3,4,9,10-tetrasubstituted perylene-based discotic oligomers are reported for the first time consisting of a perylene core attached to which are four 4-cyanobiphenyl, triphenylene and cholesteryl units via flexible alkyl spacers. All the oligomers self-assemble into a mesophase and exhibit excellent fluorescence emission properties making them suitable for various opto-electronic applications.

The interaction of proteins with endotoxins has divergent effects on lipopolysaccharide (LPS)-induced responses, which serve as a basis for many clinical and therapeutic applications. It is, therefore, important to understand these interactions from both theoretical and practical points of view. This paper advances the design of liquid crystal (LC)-based stimuli-responsive soft materials for quantitative measurements of LPS-protein binding events through interfacial ordering transition. Micrometer-thick films of LCs undergo easily visualized ordering transitions in response to proteins at LPS-aqueous interfaces of the LCs. The optical response of the LC changes from dark to bright after aqueous solutions of hemoglobin (Hb), bovine serum albumin (BSA), and lysozyme proteins (LZM) are in contact with a LPS-laden aqueous-LC interface. The effects of interactions of different proteins with LPS are also observed to cause the response of the LC to vary significantly from one to another; this indicates that manipulation of the protein-LPS binding affinity can provide the basis for a general, facile method to tune the LPS-induced responses of the LCs to interfacial phenomena. By measuring the optical retardation of the 4'-pentyl-4-cyanobiphenyl (5CB) LC, the binding affinity of the proteins (Hb, BSA, and LZM) towards LPS that leads to different orientational behavior at the aqueous interfaces of the LCs can be determined. The interaction of proteins with the LPS-laden monolayer is highest for LPS-Hb, followed by LPS-BSA, and least for LPS-LZM; this is in correlation with their increasing order of binding constants (LPS-Hb>LPS-BSA>LPS-LZM). The results presented herein pave the way for quantitative and multiplexed measurements of LPS-protein binding events and reveal the potential of the LC system to be used as quantitative LC-based, stimuli-responsive soft materials.

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