The reactivity of single magnesium nanoparticles towards corrosion and galvanic replacement.

Magnesium (Mg) nanoparticles are promising for plasmonic applications due to their wide resonance range, biocompatibility, and low cost. The low reduction potential of Mg leads to high reactivity, a double-edged sword yielding fast corrosion in water but also opportunities for synthetic strategies based on galvanic replacement. This study uses single particle dark field scattering to monitor the real-time dynamics of Mg nanoparticle corrosion and galvanic replacement by Pd, Cu, Pt, and Au. We find that while corrosion starts immediately and proceeds gradually, galvanic replacement typically exhibits a significant induction stage, lasting up to two hours, followed by a rapid reaction phase. Results indicate that the induction stage is likely governed by the hydration and breakdown of the protective, native MgO surface. Consistent with this explanation, the duration of the induction stage decreases with increasing precursor concentration, decreasing pH of the metal precursor, and with the addition of water or NaCl known to accelerate MgO hydration. These mechanistic insights provide a foundation for designing the synthesis of Mg-based bimetallic nanostructures for plasmonic applications, as demonstrated for the Mg-Cu system in this paper.