A simple and highly sensitive biosensor based on a fiber-optic coupler is developed. The change of refractive index due to biomolecular interaction on the surface of the coupler can be detected as the change of the transmission power. The sensitivity of the sensor is evaluated to be a noise level equivalent to a refractive index variation of 4×10−6. The binding of streptavidin is detected to be concentration dependent over a range of 0.5–2μg∕ml, by immobilizing biotin on the coupler surface via aminosilan treatment. This sensor allows the construction of a low-cost, portable, and label-free biosensing system.

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We investigated the reduction mechanism of surface oxide on aluminum alloy powders containing magnesium, by x-ray photoelectron spectroscopy using synchrotron radiation (SR-XPS). The reduction is the initial reaction in a new aluminum nitridation method developed by one of the authors. In heating the powders to 823 K, magnesium soluted in the powders moves from the inner region to the surface at temperatures below 573 K, and finally, above 773 K, the magnesium reduces the aluminum oxide of powder surfaces by chemical reaction, which breaks the surface oxide films, and metallic aluminum appears on the topmost surface of the powders. These results suggest that the SR-XPS system is very useful for dynamic chemical reaction analysis of the surface via in situ measurement.

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