Continuous Mesoporous Aluminum Oxide Film with Perpendicularly Oriented Mesopore Channels

Mesoporous aluminum oxide (MAO) films with perpendicularly oriented cylindrical mesopores (pore diameter: ca. 10 nm) were successfully deposited on a glass substrate by a surfactant-templating approach using aluminum nitrate as an aluminum source. The perpendicular orientation of mesopores was confirmed by grazing-incidence small-angle X-ray scattering and neutron reflection experiments. The thickness of the MAO film was around 100 nm, with a surface roughness of less than 6 nm. Since the inner surface of MAO pores was positively charged, negatively charged glucose oxidase molecules could be densely loaded into the cylindrical mesopores without significant loss of enzymatic activity. The present MAO film is potentially useful as an inorganic host material for an enzyme toward the development of a biocatalytic system.

Fabrication and optical sensing properties of mesoporous silica nanorod arrays

A mesoporous silica nanorod (MSNR) array on a gold (Au) film was fabricated and used as an optical waveguide (OWG) sensor. A resolution of the refractive index (RI) as high as 3.6 × 10⁻⁸ RIU was achieved.

Nanoporous waveguide sensor with optimized nanoarchitectures for highly sensitive label-free biosensing

Label-free optical biosensors have attracted much attention, and nanoporous metal-oxide membranes with uniform pore structure and diameter are promising candidates for platforms of label-free optical biosensors. However, development of such sensors with high sensitivity still remains challenging. In this paper, we report on the remarkably enhanced sensitivity of a label-free nanoporous optical waveguide (NPWG) sensor composed of a porous anodic alumina (PAA) waveguiding film and an aluminum cladding film. The enhanced sensitivity was achieved by engineering nanostructures and tuning optical properties of the PAA film. Careful tuning of the porosity, pore density, thickness, and refractive index of the PAA film could significantly improve the sensitivity of the NPWG sensor toward adsorption of bovine serum albumin (BSA) onto the PAA surface, and the optimized sensor responded to the adsorption of BSA with an extraordinarily large red shift (>300 nm) of a waveguide mode due to the large adsorption capacity of the PAA film and the inherently high sensitivity of the waveguide mode. The Fresnel calculations suggested that the potential sensitivity of the NPWG sensor was much higher than that of the conventional surface plasmon resonance (SPR) sensors.