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Magnetic nanoparticles have been attracting much interest as a labeling material in the fields of advanced biological and medical applications such as drug delivery, magnetic resonance imaging, and array-based assaying. In this review, synthesis of iron oxide magnetic nanoparticles via a reverse micelle system and modification of their surface by an organosilane agent are discussed. Furthermore, as a practical biological assay system, the magnetic detection of biomolecular interactions is demonstrated by using the combination of a patterned substrate modified with a self-assembled monolayer and the magnetic nanoparticles.

The purpose of this research is to demonstrate a new design for a cortisol immunosensor for the noninvasive and quantitative analysis of salivary cortisol. We propose a cortisol immunosensor with a fluid control mechanism which has both a vertical flow and a lateral flow. The detected current resulting from a competitive reaction between the sample cortisol and a glucose oxidase (GOD)-labeled cortisol conjugate was found to be inversely related to the concentration of cortisol in the sample solution. A calibration curve using the relative detected current showed an R2 = 0.98 and CV = 14% for a range of standard cortisol solutions corresponding to the concentrations of native salivary cortisol (0.1 – 10 ng/ml). The measurement could be accomplished within 35 minutes and the cortisol immunosensor could be reused. These results show promise for realizing an on-site and easy-to-use biosensor for cortisol. Used for evaluation of human salivary cortisol levels, the cortisol immunosensor measurement corresponded closely with commercially available ELISA method (R2 = 0.92). Our results indicate the promise of the new cortisol immunosensor for noninvasive, point-of care measurement of human salivary cortisol levels.

The spontaneous deposition process of Ni on Si(100) surface in aqueous alkaline solution was investigated by electrochemical measurements and in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR FTIR). The open circuit potential (OCP) profile revealed that the deposition reaction was self-terminated as the potential steeply shifted in the positive direction after a certain immersion time. Auger depth profiles of specimens after the termination of the deposition reaction indicated that the surface was not completely covered by Ni. To clarify the deposition behavior, anodic reaction of Si in an aqueous alkaline solution containing no Ni ions was investigated by in situ ATR FTIR and electrochemical measurements. It was found that the deposition reaction was initiated by the formation of suboxide species of Si at the surface. This suboxide species served as "reductant" for Ni ions. Subsequently, the anodic reactions such as the oxidation of suboxide species and the anisotropic etching to 〈111〉 direction proceeded spontaneously. When 〈111〉 oriented microfacets were formed, the surface was passivated with silicon dioxide. Because of the silicon dioxide insulating properties, the electron generation by Si oxidation is inhibited, and then, the OCP sharply shifted in the positive direction. Apparently, the formation of 〈111〉 oriented microfacets at the surface led to the self-termination of the Ni deposition process. This study shows that the overall deposition reaction of Ni is significantly affected by the anodic reaction of Si, including the oxidation and the anisotropic etching.