Moderate molecular recognitions on ZnO m-plane and their selective capture/release of bio-related phosphoric acids

Novel Separation Media with Metal Oxide Nanostructures for Capillary Electrochromatography

Zinc oxide nanowires (ZnO nanowire, ZnO NWs) are nanostructures that have drawn attention as separation media for efficient biomolecules because of high biological compatibility and low cost. Development of the capillary column (ZnO column) using a ZnO NW to an inner wall has been reported, although there are only a few studies about molecular recognition of a ZnO NW regardless of numerous studies reporting ZnO NWs. In our previous studies, we conducted fundamental research to elucidate molecular recognition of ZnO NW and develop a novel liquid phase separation field. Consequently, we achieved baseline separation of mixed adenosine phosphate analytes using a phosphate buffer in the mobile phase. In this study, to improve the low resistance of ZnO NW toward a solvent, we covered a surface of ZnO NW with titanium oxide (TiO2) thin layers using atomic layer deposition. As a result, the column (TiO2 NW column) showed high affinity toward acidic compounds like the ZnO column, strongly interacting with especially phosphate groups. Resistance of ZnO NW to a weak acidic buffer solution was then dramatically improved. This is because multipoint electrostatic interaction between the phosphate groups and the NW surface occurred. Next, we conducted capillary electrochromatography to examine the possibility for application of separation analysis. The elution order of the phosphorylated compound was successfully controlled by the migration solution containing aqueous acetonitrile with weak acids.

Rational Strategy for Space-Confined Atomic Layer Deposition

Atomic layer deposition (ALD) offers excellent controllability of spatial uniformity, film thickness at the Angstrom level, and film composition even for high-aspect-ratio nanostructured surfaces, which are rarely attainable by other conventional deposition methodologies. Although ALD has been successfully applied to various substrates under open-top circumstances, the applicability of ALD to confined spaces has been limited because of the inherent difficulty of supplying precursors into confined spaces. Here, we propose a rational methodology to apply ALD growths to confined spaces (meter-long microtubes with an aspect ratio of up to 10 000). The ALD system, which can generate differential pressures to confined spaces, was newly developed. By using this ALD system, it is possible to deposit TiO_x layers onto the inner surface of capillary tubes with a length of 1000 mm and an inner diameter of 100 μm with spatial deposition uniformity. Furthermore, we show the superior thermal and chemical robustness of TiO_x-coated capillary microtubes for molecular separations when compared to conventional molecule-coated capillary microtubes. Thus, the present rational strategy of space-confined ALD offers a useful approach to design the chemical and physical properties of the inner surfaces of various confined spaces.