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 H 2 O 2 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 H 2 O 2 media, the soft protein microtubes are self‐propelled by jetting O 2 bubbles from the open‐end terminus. The effects of H 2 O 2 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‐Fe 3 O 4 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 %.