Electroless Fabrication of Cu/Pt Janus Micromotors Driven by Halogen–Copper Redox Reaction

Abstract

Spherical Cu/Pt Janus micromotors were fabricated by electroless copper plating onto sulfonated polystyrene microspheres (∼1 µm diameter) followed by hemispherical platinum sputtering. The electroless plating step provided Cu deposition over the particle surface, and subsequent directional Pt sputtering yielded a hemispherical Pt localization, generating a Cu–Pt bimetallic interface with spatially defined redox asymmetry. In aqueous iodine solution, the Cu/Pt Janus particles showed active displacement without bubble formation. At iodine concentrations of 0.1 and 0.2 mM I₂, representative apparent velocities of ∼2.6 and ∼5.5 µm s⁻¹, respectively, were obtained from particle tracking, whereas no active displacement beyond Brownian-like motion was observed in the absence of iodine. The concentration-dependent motion behavior is consistent with a redox-driven asymmetric reaction field at the Cu/Pt interface, although a definitive propulsion mechanism is not conclusively established here. The present fabrication approach offers batch scalability and material versatility for the development of halogen-driven Janus micromotors as a proof-of-concept platform.