Porous anodic alumina: Amphiphilic and magnetically guidable micro-rafts

The present work illustrates the fabrication of wettability-sensitive, magnetically guidable micro-chips ("rafts") based on anodic porous alumina. First, porous anodic alumina is grown with in photolithographically defined squares (400 mu m x 400 mu m), then magnetic nanoparticles are embedded in the porous structure by sucking a ferro-fluid into the nanopores with the help of a permanent magnet. After pore-sealing, the top surface of the alumina patterns is grafted with a self assembled monolayer of octadecylsilane (ODS). This makes the top surface super-hydrophobic while the bottom layer (i.e. barrier layer exposed after selective removal) remains hydrophilic. The resulting 400 x 400 mu m(2) micro-rafts can be easily guided magnetically along amphiphilic interfaces. The principles outlined in this work may provide a basis for manyfold applications for example, in payload delivery or -harvesting devices. (C) 2011 Elsevier B.V. All rights reserved.