Plasmonic–Magnetic Au/Ni/Au Triple-Layered Nanopetals for Viscosity Measurement by Fourier Transform Surface Plasmon Resonance

We developed colloidally stable magnetically responsive Au/Ni/Au nanopetals (NPTs) via electrochemical deposition using anodized aluminum oxide templates. These multiblock structures combine plasmonic activity with remote magnetic control in solution. Under a rotating magnetic field, their mechanical motion generates modulated plasmonic signals, analyzed by Fourier transform surface plasmon resonance (FTSPR). Rotation dynamics, synchronous or asynchronous, depend on the balance between magnetic and viscous torques, and above a critical driving frequency, the FTSPR signal disappears due to perturbed motion. Using glycerol–water mixtures, we established a correlation between FTSPR response and viscosity, enabling sensitive, wide-range detection.