A Simple Method for the Quick Detection and Effective Removal of Trace Amounts of Pd²⁺ and Pt²⁺ Ions

We report a plasmonic platform based on Au nanospheres for the rapid detection and removal of trace Pd²⁺ and Pt²⁺ ions from aqueous systems. Upon exposure to Pd²⁺, Pt²⁺, or a mixture of them in the presence of a reductant, surface deposition occurs on the Au nanospheres, leading to pronounced damping of localized surface plasmon resonance that can be monitored by using ultraviolet-visible spectroscopy. By tuning the amount of Au nanospheres, the optical response can be optimized to achieve sensitive detection over a broad concentration range. Structural analyses reveal that the deposited Pd atoms are incorporated into the near-surface region of the nanospheres through interdiffusion, forming an alloyed layer rather than a sharp core-shell boundary. Because the plasmonic response is directly coupled to material uptake, this system enables simultaneous optical detection and removal of platinum-group metals (specifically, Pd²⁺ and Pt²⁺ in this work) from the solution.