Produced via reversible addition-fragmentation chain-transfer (RAFT) polymerization

the monodispersed and narrow molecular weight distribution polymers

poly(tert-butyl methylacrylat) (PtBMA)

were prepared by hydrolysis to poly(methylacrylic acid) (PMAA) with thiol ending groups.The PMAA monolayer protected gold nanoparticles (PMAA-@ -GNPs) were then formed through binding the thiol groups to gold surface while chloroauric acid was reduced to GNPs.Characterized by high-resolution transmission electron microscopy (HRTEM) and UV-Vis spectroscopy

the PMAA-@ -GNPs showed the formation of monodisperse spherical particles with the long-term stability in aqueous solution.The optical properties and the assembly state of the PMMA-@ -GNPs are sensitive to pH.Under acidic conditions (pH 1.5)

because of the protonated form of PMAA undergoing a hydrophobicity change

the polymer chains shrink and wrap around the GNPs surface

which leads to the GNPs assembly and an absorption red shift of the surface plasmon resonance (SPR).However

after adjusting the pH value of the solution to an alkaline environment (pH 9.2)

PMAA-@ -GNPs can be redispersed

resulting in an absorption blue shift of the SPR.And the optical signal of PMAA-@ -GNPs changes little after more cycles of the reversible assembly/dispersion processes.