By use of electrified co-jetting,[1] magnetite (Fe3O4) nanocrystals were selectively incorporated in one of the two compartments constituting the biphasic nanocolloids. Well dispersed magnetite nanocrystals were synthesized in a presence of stabilizing poly(acrylic acid) (PAA) in distilled water[2] and the suspension was used as one of jetting solutions after extra components such as poly(acryl amide-co-acrylic acid) (PAAm-co-AA) and the model biomolecular dyes were added. The other side jetting solution was composed of same polymers omitting the magnetite nanocrystals. After the biphasic nanocolloids were synthesized by the co-jetting, they are thermally treated at elevated temperature to allow the reaction between the carboxylic acid groups in PAA and amide groups in PAAm to form imide groups.[3] The nanocollids were effectively crosslinked by this thermal imidization reaction, so they maintained their architecture for expended period of time in aqueous environment. The biphasic nature of the nanocolloids was characterized by transmission electron microscopy (TEM). In a major population of the nanocolloids, it was confirmed that the magnetite nanocrystals with 5 to 10 nm diameter were selectively incorporated in only one side of the nanocolloids with about 200 nm diameter. The confocal laser scanning microscopy (CLSM) was employed to examine the movements of the nanocolloids that contain two different fluorescently tagged biomolecules in each side of the colloids. Under the influence of external magnetic field, the biphasic colloids could be controlled not only in translational movement but also in orientation of their internal anisotropy. These biphasic nanocolloids with anisotropic incorporation of magnetic nanocrystals cast a huge potential on the applications like magnetically controlled biomedical imaging or targeted drug delivery.

References [1] K. H. Roh, D. C. Martin, and J. Lahann, Biphasic Janus particles with nanoscale anisotropy, Nat. Mater. 4, 759-763 (2005). [2] S. Si, A. Kotal, T. K. Mandal, S. Giri, H. Nakamura, and T. Kohara, Size-controlled synthesis of magnetite nanoparticles in the presence of polyelectrolytes, Chem. Mater. 16, 3489-3496 (2004). [3] K. H. Roh and J. Lahann, Water-stable Biphasic Nanocolloids with Potential Use as Anisotropic Imaging Probes, in preparation for publication (2006).