Self-Propelled Soft Protein Microtubes with a Pt Nanoparticle Interior Surface

Human serum albumin (HSA) microtubes with an interior surface composed of Pt nanoparticles (PtNPs) are self-propelled in aqueous H₂ O₂ medium. They can capture cyanine dye and Escherichia coli (E. coli) efficiently. Microtubes were prepared by wet templating synthesis by using a track-etched polycarbonate (PC) membrane with alternate filtrations of aqueous HSA, poly-l-arginine (PLA), and citrate-PtNPs. Subsequent dissolution of the PC template yielded uniform hollow cylinders made of (PLA/HSA)₈ PLA/PtNP stacking layers (1.16±0.02 μm outer diameter, ca. 23 μm length). In aqueous H₂ O₂ media, the soft protein microtubes are self-propelled by jetting O₂ bubbles from the open-end terminus. The effects of H₂ O₂ and surfactant concentrations on the velocity were investigated. The swimming microtube captured cyanine dye in the HSA component of the wall. Addition of an intermediate γ-Fe₃ O₄ layer allowed manipulation of the direction of movement of the tubule by using a magnetic field. Because the exterior surface is positively charged, the bubble-propelled microtubes adsorbed E. coli with high efficiency. The removal ratio of E. coli by a single treatment reached 99 %.