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 photo-lithographically defined squares (400 μm × 400 μm), 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 × 400 μm2 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.

Research highlights
► Fabrication of amphiphilic, magnetically guidable micro-platform is demonstrated.
► Magnetic as well as different wettability properties are integrated within porous anodic alumina chips.
► The “micro-rafts” self-aligned at hydrophilic/hydrophobic interfaces and can precisely be guided along such interfaces.