Light-Coupled Chemical Fuel Triggered Dynamic Self-Assembly in Gold Nanoparticles

Abstract

Acquiring precise control over the interparticle interactions is essential for realizing the feat of dynamic self-assembly in nanomaterials. Tuning the ligand surface chemistry is undoubtedly the best way to control the interparticle interactions. The present work demonstrates how a small change in the surface ligand composition on gold nanoparticles (AuNPs) can result in two entirely opposite phenomena in the realms of self-assembly. [-] AuNPs assembled in the presence of a surfactant CTAC to form electrostatic precipitates (thermodynamically equilibrium state). Remarkably, by adding a small amount of positive charge in the NP system, [-/+]4/1 AuNPs could participate in dynamic self-assembly with CTAC (reversible precipitates or kinetically trapped state). The electrostatic force of interaction between the negative charge on the AuNPs and the positive charges on CTAC was responsible for the precipitation. Temporal changes in the interparticle interactions were brought in through a trigger controlled pH change in the system. Change in the pH of the system caused a sea change in the interparticle interactions, leading to the domination of repulsive forces between the [- /+]4/1 AuNPs and CTAC over the previously dominating attractive forces. More interestingly, the present work uses plasmonic heating as the trigger for switching the pH, thereby achieving an unprecedented feat of light-coupled chemical fuel-driven dynamic self-assembly in AuNPs. Utilizing plasmonic heat, an inherent property of AuNPs, to produce a triggered switching between a precipitated self assembled state and a dispersed state provides new avenues to explore dynamic self assembly. The present work also aims to solve the persisting problem of waste accumulation by adopting novel approaches for waste removal through recrystallization. We believe that by using mix-charged AuNPs, we could demonstrate how even a tiny change in the surface chemistry can entirely change the thermodynamics of nanoparticle self-assembly