Lipid-assembled Nanotubes for Analytical Chemistry

Natural and synthetic lipids self-assemble in water to form micelles, fibers, sheets, vesicles, and liposomes, which are important materials for analytical chemistry. Rational design of lipids and optimization of self-assembly conditions enable us to produce nanotubes that have the following unique structural and morphological features: (i) perfect one-dimensional nanochannels, (ii) distinct, functionalizable outer/inner surfaces and membrane walls, and (iii) transformation abilities. The one-dimensional nanochannels act as separation and analytical sites. Separation of peptides, which are differed by only a single amino acid, is achieved during transport of the peptides through the nanochannels with precisely controlled diameters and interactional groups. Polythiophene boronic acids encapsulated in nanochannels have a planer one-dimensional conformation and selectively bind to glucose, while those in bulk solutions have a random coil conformation and favorably bind to fructose. Encapsulation of enzymes in nanochannels allows us to construct bioreactors, which exhibit excellent kinetic parameters, reusability, and recyclability due to enhancement of the thermal/chemical stability of the enzymes by a confinement effect of the nanochannels. Nanotube liquid crystals, based on side-by-side alignment of oligoethyleneglycol-coated nanotubes in water, act as templates for construction of surfactant-free gold nanorods with controllable diameters and tunable localized-surface-plasmon-resonance (LSPR) properties. The LSPR band of the gold nanorods densely functionalized with a thiol derivative bearing 12-crown-4 ether responses to Li ion among alkaline metal ions. Fluorescent-lipid assembled nanotubes cause molecular packing rearrangement as well as morphological transformation, in response to amino acid analytes. Naked-eye detectable fluorescence color changes and hydrogel formation as the result of the amplification of the molecular- and nanometer-scaled changes brought to not only qualitative analysis but also chiral sensing of a specific amino acid among 20 amino acids. Creation of tailor-made nanotubes for analytes will provide a simple, quick, and on-site analysis in biological, medical, and environmental fields.