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

Abstract

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.

pH effect on the synthesis of different size silver nanoparticles evaluated by DLS and their size-dependent antimicrobial activity

“…In a reducing environment, some syntheses use a surface stabilizer and other are based only on reducing AgNO 3 with sodium borohydride (NaBH 4 ). In the case of routes without using surface stabilizer, smaller nanoparticles are formed, which are less stable over time [10][11][12]. The use of ligands allows obtaining larger nanoparticles; however, they are more stable over time [13][14][15].…”

pH-Driven Reversible Assembly and Disassembly of Colloidal Gold Nanoparticles

“…Low-dimensional plasmonic nanoparticle assemblies with new optical properties have recently attracted considerable attention because of the near-field coupling between adjacent particles (Liu D. et al, 2018 ; Li and Yin, 2019 ; Li et al, 2020a ). The ideal way is the reversible assembly of such plasmonic nanostructures, which could enable dynamic tuning of the surface plasmon coupling by responding the external stimuli, and therefore by taking advantage of the ultrasensitive gap-dependent properties of plasmonic coupling, they have great promises for applications such as colorimetric sensors, bio- and chemical detection, and therapeutics (Bonacchi et al, 2016 ; Pillai et al, 2016 ; Liu L. et al, 2018 ; Zhou et al, 2021 ). Recent studies have demonstrated the reversible assembly by controlling the nanoparticle separation via various methods, for example, by modulating solvent composition to change the ionic strength of the solution, adding moisture, thermo-, photo-, magnetical-, and pH-responsive ligands, or reversible linking molecules (such as DNA) (Liu et al, 2012 ; Liu L. et al, 2019 ; Ding et al, 2016 ; Fan et al, 2016 ; He et al, 2016 , 2019 ; Grzelczak et al, 2019 ; Li et al, 2020b ; Severoni et al, 2020 ).…”

Dynamic Color‐Switching of Plasmonic Nanoparticle Films

“…[19] Recently,w eh ave demonstrated an ew limited-ligandprotection strategy for the synthesis of AgNP assemblies with tunable plasmonic properties. [20] Thepresence of poly(acrylic acid) (PAA) ligand on AgNP surface allows reversible particle assembly and dynamic color change through manipulation of AgNPs surface charges by pH variation in solution. Herein, we introduce an ovel strategy for developing as olid plasmonic color-switching film by coupling the reversible humidity-sensitive salt hydrolysis with the deprotonation/ protonation of surface-capped PA A.…”

“…Recently, we have demonstrated a new limited‐ligand‐protection strategy for the synthesis of AgNP assemblies with tunable plasmonic properties . The presence of poly(acrylic acid) (PAA) ligand on AgNP surface allows reversible particle assembly and dynamic color change through manipulation of AgNPs surface charges by pH variation in solution.…”