Single-Particle Hyperspectral Imaging Reveals Kinetics of Silver Ion Leaching from Alloy Nanoparticles

Abstract

Gold-silver alloy nanoparticles are have attracted attention for multiple applications, including heterogeneous catalysis, optical sensing, and antimicrobial properties. The inert element gold can act as a stabilizer for silver to prevent particle corrosion to slow down silver ion leaching and increase the durability of plasmonic alloy nanoparticles in sensing or catalytic applications. On the other hand, intentional release of antimicrobial silver ions has been used to fight infections caused by bacteria. Understanding silver ion leaching from gold-silver alloy nanoparticles is a therefore prerequisite to designing alloy nanoparticles with either unintended or intended corrosion. However, little is known about the mechanism and kinetics of silver ion leaching from bimetallic gold-silver nanoparticles and how it is correlated with particle size and silver content, especially not on a single-particle level. To characterize the kinetics of silver ion release from gold-silver alloy nanoparticles, we employed a combination of electron microscopy and single-particle hyperspectral imaging with an acquisition speed fast enough to capture silver ion leaching for a statistically relevant number of individual nanoparticles. Our studies confirmed a reduction in corrosion rate due to the alloying with as little as 10-20 mole% gold. Single-particle leaching profiles revealed two leaching stages, with a large heterogeneity in rate constants. We modelled the initial leaching stage with a shrinking-particle model with a rate constant that exponentially depends on the silver mole fraction. The second, slower leaching stage is controlled by diffusion of silver atoms through a passivating gold rich lattice, and a change in electrochemical potential of the nanoparticle. Individual nanoparticles with similar sizes and compositions exhibited completely different dealloying yields. Most nanoparticles released silver completely, but 25% of them appeared to arrest corrosion. Calculations of average size together with SEM revealed that nanoparticles became slightly porous. Our findings suggest that alloy nanoparticles, produced by scalable laser ablation in liquid, together with kinetic studies of silver ion leaching, provide an approach to selectively design the durability or anti-microbial bioactivity of alloy nanoparticles. Figure 1