Reversible Assembly and Dynamic Plasmonic Tuning of Ag Nanoparticles Enabled by Limited Ligand Protection.

Dynamic manipulation of optical properties through the reversible assembly of plasmonic nanoparticles offers great opportunities for practical applications in many fields. The previous success, however, has been limited to Au nanoparticles. Reversible assembly and plasmonic tuning of Ag nanoparticles (AgNPs) have remained a significant challenge due to difficulty in finding an appropriate surface agent that can effectively stabilize the particle surface and control their interactions. Here, we overcome the challenge by developing a limited-ligand-protection (LLP) strategy for introducing poly(acrylic acid) with precisely controlled coverage to the AgNP surface to not only sufficiently stabilize the nanoparticles but also enable effective control over the surface charge and particle interaction through pH variation. The as-synthesized AgNPs can be reversibly assembled and disassembled and accordingly display broadly tunable coupling of plasmonic properties. Compared to the Au-based system, the success in the reversible assembly of AgNPs represents a significant step toward practical applications such as colorimetric pressure sensing because they offer many advantages, including broader spectral tuning range, higher color contrast, a one-pot process, and low materials and production cost. This work also highlights LLP as a new avenue for controlling the interparticle forces, their reversible assembly, and dynamic coupling of physical properties.