Polyallylamine assisted synthesis of 3D branched AuNPs with plasmon tunability in the vis-NIR region modification.

This paper describes the synthesis of highly branched gold nanoparticles through a facile seeded growth approach using poly(allylamine hydrochloride) (PAH) as shape inducing agent. The obtained branched Au NPs present highly tunable optical properties in the Vis-NIR region from ca. 560 nm to 1260 nm. We controlled the morphology, and therefore the optical response, of the NPs by either changing the gold salt to seed ratio or fine-tuning the solution pH. We proposed that the formation of size-dependent PAH-AuCl4- aggregates as demonstrated by dynamic light scattering measurements, together with pH-dependent gold salt speciation, might be responsible for the branched morphology. Advanced electron microscopy techniques demonstrated the polycrystalline nature of the NPs and facilitated a better understanding of branched morphology. Additionally, the refractive index sensitivity estimated by the inflexion point of the Localized Surface Plasmon Resonance (LSPR) band can be controlled by tuning the nanoparticle branching. Furthermore, the versatility of the PAH chemistry allowed the easy functionalization of the synthesized NPs.