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

Abstract

Gold−silver alloy nanoparticles are interesting for multiple applications, including heterogeneous catalysis, optical sensing, and antimicrobial properties. The inert element gold acts as a stabilizer for silver to prevent particle corrosion, or conversely, to control the release kinetics of antimicrobial silver ions for long-term efficiency at minimum cytotoxicity. However, little is known about the kinetics of silver ion leaching from bimetallic nanoparticles and how it is correlated with 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 the irreversible silver ion leaching. Single-particle leaching profiles revealed a reduction in silver ion leaching rate due to the alloying with gold as well as two leaching stages, with a large heterogeneity in rate constants. We modeled the initial leaching stage as a shrinking-particle with a rate constant that exponentially depends on the silver content. The second, slower leaching stage is controlled by the electrochemical oxidation potential of the alloy being steadily increased by the change in relative gold content and diffusion of silver atoms through the lattice. Interestingly, individual nanoparticles with similar sizes and compositions exhibited completely different silver ion leaching yields. Most nanoparticles released silver completely, but 25% of them appeared to arrest leaching. Additionally, nanoparticles became slightly porous. Alloy nanoparticles, produced by scalable laser ablation in liquid, together with kinetic studies of silver ion leaching, provide an approach to design the durability or bioactivity of alloy nanoparticles.

Opportunities and Challenges for Alternative Nanoplasmonic Metals: Magnesium and Beyond

“…Furthermore, alloying can enhance other properties such as corrosion and degradation. 55 , 56 Rationally combining elements for stability and plasmonic response may be a way to stabilize the reactive group I metals and instill some of their low losses and high quality resonances into another metal; such promising nanostructures have yet to be reported. Overall, while there is a limited track record of drastic improvements in plasmonic quality due to the fundamental nature of the materials, a new discovery that would dramatically change the quality factor has the potential to propel plasmonics to a new era.…”

“…Further, alloys can stabilize NPs against degradation, as was shown for the decrease of Ag ion leaching in the presence of Au. 56 Recent work has demonstrated steps toward “stainless Mg”; 55 however, much remains to be done to adapt these approaches to the nanoscale.…”

“…Excitingly, not all alloys behave monotonically: some element combinations, such as the nonisovalent alloys of Au and Pd, display sensitive nonmonotonic relationships between the alloying concentration and the dielectric function with the function in some cases exceeding that of either of the constituents. Furthermore, alloying can enhance other properties such as corrosion and degradation. , Rationally combining elements for stability and plasmonic response may be a way to stabilize the reactive group I metals and instill some of their low losses and high quality resonances into another metal; such promising nanostructures have yet to be reported. Overall, while there is a limited track record of drastic improvements in plasmonic quality due to the fundamental nature of the materials, a new discovery that would dramatically change the quality factor has the potential to propel plasmonics to a new era.…”

Conceptual Developments of Aryldiazonium Salts as Modifiers for Gold Colloids and Surfaces

“…The resulting gold–silver alloy nanostructures are highly effective as antibacterial agents. The presence of gold nanoparticles has a major effect on controlling silver ion oxidative leaching and the on-demand release of silver ions for antibacterial function. , …”

Quantifying Chemical Composition and Reaction Kinetics of Individual Colloidally Dispersed Nanoparticles

“…Other elemental analysis techniques like energy-dispersive X-ray spectroscopy (EDS) combined with scanning transmission electron microscopy (STEM) provide valuable elemental mapping of individual nanoparticles . However, EDS/STEM analyses require dried samples and are limited by the number of nanoparticles within a field of view, which restricts sample size . Although gaining traction, in situ electron microscopy analysis of nanoparticle composition remains technically challenging and may expose nanoparticle samples to free radicals, which may complicate the monitoring of chemical reactions at the single nanoparticle level. , …”