The plasmonic behaviours of gold nanoparticles with different thiol ( n = 6, 10, 12) capping agents

The intense absorbance and scattering of incident light at the surface plasmon resonance wavelength of gold nanoparticles (AuNPs) is of paramount importance in its various and diverse applications. Being governed by their morphologies and surface chemistry, the optical property of AuNPs can be tuned to suit variety of applications by careful and systematic engineering of the particle surface. Among other variables, the nature of the ligands or capping agents employed and their concentrations play vital roles. Three different alkanethiols, namely 1-dodecanethiol (DDT), 1-decanethiol (DT) and 1-hexanethiol (HT) were investigated as capping agents in different concentration of gold/thiol ([Au]/[Thiol]) ratios of 7:1, 5:1, 3:1, 1:1, 1:3 and 1:5. First, the AuNPs with average particle sizes of 2 nm and characterised by 1 H NMR, UV–visible, and TEM. The 1 H NMR confirmed the capping of gold nanoparticles by the thiol. The TEM image confirmed the monodispersity of the nanoparticles with average size distributions of 2.4 nm, and plasmon absorption wavelength peaks at 505 nm was confirmed by the UV. There were variations in the values of the plasmonic peaks with the nature and concentrations of the capping agents.