Real-Time Imaging of Laser-Induced Nanowelding of Silver Nanoparticles in Solution

Nanowelding of metallic nanoparticles induced by laser illumination is of particular interest because it provides convenient and controlled means for shape-conversion of nanoparticles and fabrication of nanodevices. However, the kinetics of the laser-induced nanoparticle nanowelding remains largely unexplored. Herein, we exploited fluorescence microscopy to directly image the real-time nanowelding kinetics of silver nanoparticles (AgNPs) when illuminated with a continuous wave laser at 405 nm. We observed that the laser illumination induced the AgNPs to form higher-order branched structures or assemblies. More importantly, we quantified the sizes of the laser-induced assemblies and found that the dependence of the average size (A) of the assemblies on the illumination time t followed A ∝ 1 – e–ᵗ/τ. An analytical model based on simple polymerization was developed to predict and understand the measured kinetics. We experimentally verified the model by varying the laser power and the concentration of AgNPs. Furthermore, we improved the model by taking into account the merging of assemblies and predicted that the laser-induced assembling kinetics was diffusion-limited, which was then verified experimentally with AgNPs in 50% glycerol. Lastly, in contrast to the single-phased ohmic nanocontact produced by the laser-induced nanowelding, we found that the formed higher-order structures were separated into different photoluminescent domains and different regions of the same laser-induced assembly showed asynchronous, uncorrelated blinking behaviors. This work is expected to facilitate the development of better nanowelding strategies of metallic nanoparticles for broader applications.