Magnetic Orientational Linear Dichroism Spectra of Magnetic Nanoparticles as a Probe of the Dispersion State

Applications of magnetic and electromagnetic forces in micro-analytical systems

Novel applications of magnetic fields in analytical chemistry have become a remarkable trend in the last two decades. Various magnetic forces have been employed for the migration, orientation, manipulation, and trapping of microparticles, and new analytical platforms for separating and detecting molecules have been proposed. Magnetic materials such as functional magnetic nanoparticles, magnetic nanocomposites, and specially designed magnetic solids and liquids have also been developed for analytical purposes. Numerous attractive applications of magnetic and electromagnetic forces on magnetic and non-magnetic materials have been studied, but fundamental studies to understand the working principles of magnetic forces have been challenging. These studies will form a new field of magneto-analytical science, which should be developed as an interdisciplinary field. In this review, essential pioneering works and recent attractive developments are presented.

Critical Detection of Agglomeration of Magnetic Nanoparticles by Magnetic Orientational Linear Dichroism

Magnetic orientational linear dichroism (MOLD) spectroscopy was found to be useful for detecting the initiation of the agglomeration process of COOH-modified iron-oxide magnetic nanoparticles (MNPs) in water, which was produced by the addition of a small amount of a cationic surfactant or a metal ion. The critical association of MNPs leading to agglomeration was detected from the increase of the maximum MOLD value as well as from the shift of the maximum wavelength of the MOLD spectrum. The magnetic field dependence of MOLD was analyzed by the Langevin equation, and the apparent association numbers of MNPs in the agglomerates were obtained.