The development of simple, portable, and low-cost biosensing platforms is of great interest in the clinical diagnosis of disease. Here, we report liquid crystal (LC) droplet-embedded chitosan (CHI) hydrogel films formed by the Ag(+) ion-triggered fast gelation of the CHI/surfactant complex-stabilized LC emulsion which is cast on substrates. The small sheets cut from the LC droplet-embedded hydrogel films combine the advantages of both hydrogels and LC droplets, offering a portable and label-free sensing platform for the real-time detection of bile acids in a small amount of solution. We find that the response time and detection limit of LC droplet-embedded hydrogel sheets for bile acids depend on their chemical structures.
Liquid-crystal droplets are of great interest because of their large surface areas, rich phases, and tunable optical properties. The director configuration of liquid-crystal droplets provides a unique optical sign to detect the events occurring at the droplet surface. In this article, we report the alternating bipolar/radial configuration transitions of 4-n-pentyl-4'-cyanobiphenyl (5CB) droplets triggered by the layer-by-layer coating of negatively charged poly(styrenesulfonate sodium (PSS) and positively charged poly(diallyldimethylammonium chloride) (PDADMAC) on the droplet surface. The alternating configuration transitions are due to the interactions of the 5CB with polar versus nonpolar PDADMAC/PSS multilayer coatings. Furthermore, we find that the coating of PDADMAC/PSS multilayers makes the director configuration of the 5CB in the droplets sensitive to environmental salt concentrations.
J-aggregates are an attractive supramolecular structure with interesting excitation properties found in the light-harvesting antenna of green sulfur bacteria. To structurally mimic the light-harvesting antenna, we synthesize J-aggregate nanotubes with a sharp and intense absorption band (J-band) by the coassembly of lithocholic acid (LCA) and 3,3'-dipropylthiadicarbocyanine iodide (DiSC3(5)) in aqueous solution. We show that the J-aggregate nanotubes can be used as a supramolecular probe for the sensitive and selective detection of dopamine (DA) in phosphate buffered saline (PBS) solution with the detection limit of ∼0.4 nM by simply observing the intensity change of the J-band due to the efficient photoinduced electron transfer from the J-aggregate nanotubes to the adsorbed DA.
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