Bio-Templated Ultra-Sensitive Magneto-Plasmonic Photocatalytic Particles Integrated into Soft Robotics

Plasmonic photocatalysts that combine magnetic maneuverability with visible-light activity offer a promising avenue for autonomous water purification. However, integrating these functionalities into a scalable, reusable architecture remains challenging. Here, we report a mucin-mediated green synthesis of a gold/maghemite heterostructured nanoparticle system. X-ray diffraction confirmed the formation of spinel γ-Fe2O3 and face-centered-cubic Au, with crystallite sizes of 4.6 ± 0.8 and 25.7 ± 4.3 nm, respectively. STEM-EDS revealed Au-rich nanoparticles distributed on the γ-Fe2O3-mucin scaffold, while XPS confirmed metallic Au0 and Fe3+ characteristic of maghemite. Valence-band analysis indicated the formation of a Schottky-type Au/γ-Fe2O3 junction. The resulting millimeter-scale beads exhibited a soft magnetic response with a saturation magnetization of approximately 10.8 emu g-1, enabling magnetic steering and recovery. While dispersed nanoparticles achieved ∼90% pollutant degradation, the beads maintained ∼75% efficiency within 80 min under visible-light irradiation and exhibited enhanced stability across multiple cycles. After three photocatalytic cycles, the beads retained approximately 65% degradation efficiency, compared with approximately 53% for the dispersed catalyst. Finally, we demonstrate magnetically guided swarms of these beads for active remediation using only natural light. This work establishes a versatile platform for magnetically addressable, bio-templated soft robots capable of sustainable, reusable water treatment.